Islet Cell Viability Research Articles

Hybrid Congregation of Islet Single Cells and Curcumin-Loaded Polymeric Microspheres as an Interventional Strategy to Overcome Apoptosis Associated with Pancreatic Islets Transplantation

Hypoxic or near-anoxic conditions that occur in the core of transplanted islets induce necrosis and apoptosis during the early stages after transplantation, primarily due to loss of vascularization during the isolation process. Moreover, secretion of various cytokines from pancreatic islets is detrimental to the viability of islet cells in vitro. In this study, we aimed to protect pancreatic islet cells against apoptosis by establishing a method for in situ delivery of curcumin to the pancreatic islets. Self-assembled heterospheroids composed of pancreatic islet cells and curcumin-loaded polymeric microspheres were prepared by the three-dimensional cell culture technique. Release of curcumin in the microenvironment of pancreatic islets promoted survival of the islets. In hypoxic culture conditions, which mimic the in vivo conditions after transplantation, viability of the islets was significantly improved, as indicated by a decreased expression of pro-apoptotic protein and an increased expression of anti-apoptotic protein. Additionally, oxidative stress-induced cell death was suppressed. Thus, unlike co-transplantation of pancreatic islets and free microspheres, which provided a wide distribution of microspheres throughout the transplanted area, the heterospheroid transplantation resulted in colocalization of pancreatic islet cells and microspheres, thereby exerting beneficial effects on the cells.

Viability and functional recovery of pancreatic islet cells co-cultured with liver, salivary glands and intestine cells

This study aimed to examine the co-culturing of the rat islets with liver, salivary glands and intestine primary cells in vitro and in vivo models of islet injury. Viability of pancreatic islet cells co-cultured was determined using trypan blue. Glucose level was measured in vivo condition by glucose oxidase method. Insulin levels were also determined in vivo and in vitro conditions by ELISA method. The in vitro results of this study showed that pancreatic islet cells co-cultured with liver, salivary glands and intestine cells caused a significant rise in insulin level. These effects displayed the following hierarchy: liver > salivary glands > intestine. On day 28, the insulin level of rats exposed to alloxan decreased compared with the rats that received non-treated islet transplantation. However, the insulin level of rats exposed to alloxan that received co-cultured islets with liver cells, salivary gland cells and intestine cells increased when we compared with the rats that received non-treated islet transplantation. Islet-transplanted diabetic rats showed the preserved ability to regulate blood glucose levels throughout the study period, suggesting prolongation of islet graft survival. We investigate the possibility that the epithelial lining of the tissues provide viability and functional recovery of the injured pancreatic islet cells.

Perfluoroalkyl substances and beta cell deficient diabetes

AimsPerfluoroalkyl substances (PFAS) are synthetic hydrocarbons shown to preserve pancreatic islet cell viability and reduce islet cell hypoxia and apoptosis. We investigated the relationship of serum PFAS with diabetes, and whether this varied by diabetes type. Methods6,460 individuals with and 60,439 without diabetes from the C8 Health Project, were categorized into three groups: type 1 (n=820), type 2 (n=4,291), or uncategorized diabetes (n=1,349, missing data on diabetes type or diabetes based on blood sugar at study entry). Four PFAS were investigated: perfluorohexane sulfonate (PFHxS), perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and perfluorononaoic acid (PFNA). ResultsPFAS levels were significantly lower in those with diabetes, and lowest in those with type 1 diabetes. In age and sex adjusted analyses, ORs (CI) for type 1, type 2, and uncategorized diabetes compared to no diabetes were 0.59 (0.54–0.64), 0.74 (0.71–0.77), 0.84 (0.78–0.90), respectively for PFHxS; 0.69 (0.65–0.74), 0.87 (0.89–0.91), 0.92 (0.88–0.97), respectively for PFOA; 0.65 (0.61–0.70), 0.86 (0.82–0.90), 0.93 (0.86–1.03), respectively for PFOS; and 0.65 (0.57–0.74), 0.94 (0.88–1.00), 0.95 (0.85–1.06), respectively for PFNA. Further adjustment for eGFR and other covariates did not eliminate these inverse associations. ConclusionsPFAS levels were negatively associated with diabetes. This inverse relationship was strongest for type 1 diabetes, suggesting the relationship with serum PFAS may vary with the severity of islet cell deficiency.

Red Ginseng Administration Before Islet Isolation Attenuates Apoptosis and Improves Islet Function and Transplant Outcome in a Syngeneic Mouse Marginal Islet Mass Model

BackgroundTransplantation of isolated islets is a promising treatment for diabetes. Red ginseng (RG) is steamed ginseng and has been reported to enhance insulin secretion–stimulating and anti-apoptotic activities in pancreatic β-cells. In this study, we examined the hypothesis that pre-operative RG treatment enhances islet cell function and anti-apoptosis and investigated whether RG improves islet engraftment by transplant of a marginal mass of syngeneic islets pretreated with RG in diabetic mice. MethodsBalb/c mice were randomly divided into 2 groups, and 1 group was administered RG (400 mg/kg/day orally) for 7 days before islet isolation. In vitro islet viability and function were assessed. After cytokine treatment, cell viability, function, and apoptosis of islet cells were analyzed. Furthermore, we studied the effects of RG in a syngeneic islet graft model. A marginal mass of syngeneic mouse islets was transplanted into diabetic hosts. ResultsIslet pretreatment with RG showed 1.4-fold higher glucose-induced insulin secretion than did control islets. RG pretreatment upregulated B-cell lymphoma 2 (Bcl-2) expression and downregulated Bcl-associated X protein (BAX), caspase-3, and inducible nitric oxide synthase (iNOS) expression. Glucose-induced insulin release, NO, and apoptosis were significantly improved in RG-pretreated islets compared with cytokine-treated islets. RG-pretreated mice exhibited improved marginal mass islet graft survival compared with controls. ConclusionsThese results suggest that pre-operative RG administration enhanced islet function before transplantation and attenuated cytokine-induced damage associated with apoptosis. These studies indicate that inhibition of apoptosis by RG significantly improved islet cell and graft function after isolation and transplantation, respectively.

The Effects of Cord Blood Serum on Survival of Rat Pancreatic Islets during In vitro Culturing

Background: Transplantation of islets of Langerhans can improve glycometabolic control in type 1 diabetic patients; however, recipients usually require islets from 1-3 donor pancreas. Current isolation techniques generally recover <50% of the islets from a given pancreas. This study aimed to determine the effect of cord blood serum (CBS) on isolated pancreatic islet cells in vitro. Methods: Rat pancreatic islets were isolated via collagenase digestion, and then cultured with and without the presence of 50 μl, 100 μl, and 150 μl of CBS. Next, islet cell viability was determined using a fluorescein diacetate and propidium iodide mixture via fluorescence microscopy. Additionally, islet function was evaluated based on insulin secretion. Results: Treatment of primary cultures of rat pancreatic islets with CBS resulted in augmented β-cell viability. It was observed that the viability rate increased as the concentration of CBS increased and that viability was higher in the 150 μl of CBS group than in the control group. CBS was observed to preserve β-cell glucose responsiveness and insulin secretion under basal (3.3 mmoll-1) and stimulated (16.7 mmoll-1) glucose conditions. Moreover, a significant increase in insulin secretion was observed following treatment with 50 μl of CBS. Conclusions: The present findings show that cord blood serum treatment of freshly isolated rat islets had a positive effect on islet survival by increasing their viability. We think these findings suggest that CBS might be a suitable factor for optimizing and stimulating recovery, and subsequent function of islets during in vitro culturing, indicating that CBS might play an important role in the biophysiological function of pancreatic islets.

Completion pancreatectomy and islet cell autotransplantation as salvage therapy for patients failing previous operative interventions for chronic pancreatitis

Traditional decompressive and/or pancreatic resection procedures have been the cornerstone of operative therapy for refractory abdominal pain secondary to chronic pancreatitis. Management of patients that fail these traditional interventions represents a clinical dilemma. Salvage therapy with completion pancreatectomy and islet cell autotransplantation (CPIAT) is an emerging treatment option for this patient population; however, outcomes after this procedure have not been well-studied. All patients undergoing CPIAT after previous decompressive and/or pancreatic resection for the treatment of chronic pancreatitis at our institution were identified for inclusion in this single-center observational study. Study end points included islet yield, narcotic requirements, glycemic control, and quality of life (QOL). QOL was assessed using the Short Form (SF)-36 health questionnaire. Sixty-four patients underwent CPIAT as salvage therapy. The median age at time of CPIAT was 38 years (interquartile range [IQR], 14.7-65.4). The most common etiology of chronic pancreatitis was idiopathic pancreatitis (66%; n = 42) followed by genetically linked pancreatitis (9%; n = 6) and alcoholic pancreatitis (8%; n = 5). All of these patients had previously undergone prior limited pancreatic resection or decompressive procedure. The majority of patients (50%; n = 32) underwent prior pancreaticoduodenectomy, whereas the remainder had undergone distal pancreatectomy (17%; n = 11), Frey (13%; n = 8), Puestow (13%; n = 8), or Berne (8%; n = 5) procedures. Median time from initial surgical intervention to CPIAT was 28.1 months (IQR, 13.6-43.0). All of these patients underwent a successful CPIAT. Mean operative time was 502.2 minutes with average hospital duration of stay of 13 days. Islet cell isolation was feasible despite previous procedures with a mean islet yield of 331,304 islet cell equivalents, which totaled an islet cell autotransplantation of 4,737 ± 492 IEQ/kg body weight. Median patient follow-up was 21.2 months (IQR, 7.9-36.8). Before CPIAT, all patients required a mean of 120.8 morphine equivalent milligrams per day (MEQ/d), which improved to 48.5 MEQ (P < .001 compared with preoperative requirements) at most recent follow-up. Of these patients, 44% (n = 28) achieved narcotic independence. All patients were able to achieve stable glycemic control with a mean insulin requirement of 16 units per day. Of these patients, 20% (n = 13) were insulin independent after CPIAT. Mean postoperative glycosylated hemoglobin was 7.8% (range, 4.6-12.5). Islet cell viability was confirmed with endocrine testing and mean C-peptide levels 6 months after CPIAT were 0.91 ng/mL (range, 0.1-3.0). The SF-36 QOL survey administered postoperatively demonstrated improvement in all tested modules. This study is the first to examine the results of salvage therapy with CPIAT for patients with refractory chronic pancreatitis. Patients undergoing CPIAT achieved improved postoperative narcotic requirements, stable glycemic control, and improved QOL.

Collagen esterification enhances the function and survival of pancreatic β cells in 2D and 3D culture systems

Collagen, one of the most important components of the extracellular matrix (ECM), may play a role in the survival of pancreatic islet cells. In addition, chemical modifications that change the collagen charge profile to a net positive charge by esterification have been shown to increase the adhesion and proliferation of various cell types. The purpose of this study was to characterize and compare the effects of native collagen (NC) and esterified collagen (EC) on β cell function and survival. After isolation by the collagenase digestion technique, rat islets were cultured with NC and EC in 2 dimensional (2D) and 3 dimensional (3D) environments for a long-term duration in vitro. The cells were assessed for islet adhesion, morphology, viability, glucose-induced insulin secretion, and mRNA expression of glucose metabolism-related genes, and visualized by scanning electron microscopy (SEM). Islet cells attached tightly in the NC group, but islet cell viability was similar in both the NC and EC groups. Glucose-stimulated insulin secretion was higher in the EC group than in the NC group in both 2D and 3D culture. Furthermore, the mRNA expression levels of glucokinase in the EC group were higher than those in the NC group and were associated with glucose metabolism and insulin secretion. Finally, SEM observation confirmed that islets had more intact component cells on EC sponges than on NC sponges. These results indicate that modification of collagen may offer opportunities to improve function and viability of islet cells.

Glucose plus metformin compared with glucose alone on β-cell function in mouse pancreatic islets.

Metformin is currently the first drug of choice for treatment of type II diabetes. The primary function of metformin is to decrease hepatic glucose production mainly by inhibiting gluconeogenesis. The aim of the present study was to investigate the effects of glucose alone (control groups) and glucose and metformin (treatment groups) on pancreatic islets functions. Pancreatic islets were isolated by collagenase digestion and incubated for 24 or 48 h in RPMI-1640 containing 5 mmol/l glucose (control groups 1 and 2, respectively) or 24 h with 25 mmol/l glucose (control group 3) and 15 µmol/l metformin (treatment groups 1, 2 and 3, corresponding to the control groups, respectively). Subsequently, the rate of insulin output from islets, pancreatic and duodenal homeobox 1 (Pdx-1) and insulin genes expression and islet viability were assayed. The rate of insulin secretion in a 5 mmol/l glucose concentration in the 48 h treatment group increased significantly compared with that of the 24 h treatment group (P<0.05). An increase of the glucose concentration (25 mmol/l) caused insulin secretion to increase compared with that of 5 mmol/l glucose. Pdx-1 gene expression in treatment group 2 significantly decreased compared with the control group 2 (P<0.05). The the Pdx-1 gene expression in treatment group 2 decreased compared with that of the treatment group 1. The expression of the insulin gene in treatment group 1 increased compared with control group 1, and in treatment group 2, there was a 2-fold increase in insulin gene expression compared with control group 2. The insulin gene expression in treatment group 2 increased compared with treatment group 1. The percentage of islet cell viability was increased in treatment group 3 by ~40% compared with the islet cells of treatment groups 1 and 2 (P<0/05). These data indicate that glucose and metformin have direct effects on β-cell function.

Nerve Growth Factor Improves Survival and Function of Transplanted Islets Via TrkA-mediated β Cell Proliferation and Revascularization.

Nerve growth factor (NGF), which plays important roles in promoting growth and differentiation of nerve cells, has recently been reported as a regulator in pancreatic β cells in terms of insulin releasing function. In this study, we examined whether NGF stimulation would promote islet graft survival and function in islet transplantation. We found that supplementation of cultured islets with NGF improved the viability of islet cells and induced the production of insulin, vascular endothelial growth factor, and cellular proliferative markers. Because a specific inhibitor of TrkA, K252a, blocked all these effects, we propose that the TrkA receptor is the mediator of NGF stimulation. After transplantation to the kidney subcapsule and liver of syngenic diabetic mice, a higher rate of normoglycemic achievement, increased serum insulin, and improved glucose tolerance were observed in the mice transplanted with NGF-pretreated islet grafts. Histological analysis revealed higher expression of insulin and vascular endothelial growth factor, an increase in proliferative β cells, and revascularization in NGF-pretreated islet grafts without activation of any inflammatory cells. The NGF treatment can therefore serve as a new and promising therapeutic tool for improving islet graft viability and function in islet transplantation.

5,7-Dihydroxy-3,4,6-Trimethoxyflavone Attenuates Ischemic Damage and Apoptosis in Mouse Islets

BackgroundThe transplantation of isolated pancreatic islets is a promising treatment for diabetes. 5,7-dihydroxy-3,4,6-trimethoxyflavone (Eupatilin), a pharmacologically active flavone derived from the Artemisia plant species, has been reported to have antioxidant and anti-inflammatory activities. This study examines the hypothesis that preoperative eupatilin treatment can attenuate ischemic damage and apoptosis before islet transplantation. MethodsIslets isolated from Balb/c mice were randomly divided into 2 groups, and cultured in medium supplemented with or without eupatilin. In vitro islet viability and function were assessed. After treatment with a cytokine cocktail consisting of tumor necrosis factor (TNF)-α, interferon (INF)-γ, and interleukin (IL)-1β, islet cell viability, function, and apoptotic status were determined. The glutathione (GSH) and nitrous oxide (NO) levels were also measured. Proteins related to apoptosis were analyzed using Western blotting. ResultsThere was no difference in cell viability between the 2 groups. Islets cultured in the medium supplemented with eupatilin showed 1.4-fold higher glucose-induced insulin secretion than the islets cultured in the medium without eupatilin. After treatment with a cytokine cocktail, glucose-induced insulin release and the total insulin content of the islets were significantly improved in eupatilin-pretreated islets compared with islets not treated with eupatilin. Apoptosis was significantly decreased, and GSH levels were elevated in the eupatilin-pretreated group. Cytokine-only treated islets produced significantly higher levels of NO, iNOS, and caspase-3 than islets pretreated with eupatilin before cytokine treatment. ConclusionsThese results suggest that preoperative eupatilin administration enhances islet function before transplantation and attenuates the cytokine-induced damage associated with NO production and apoptosis.

Viability and Functional Assessment of Murine Pancreatic Islets After Transportation Between Korea and Japan

BackgroundOrgan donor scarcity remains a restricting factor for pancreatic islet transplantation. To date, limited information is available on the impact of long-distance transportation on transplantable pancreatic islets. The objective of this study was to assess the effects of transportation on the viability and function of murine pancreatic islet cells. MethodsThe isolated murine pancreatic islets were transported from Japan to Korea with the use of commercial modes of transportation: subway and commercial airplane. After transportation, the islets were assessed by performing a viability assay and by evaluating the islets' insulin secretion in response to glucose stimulation. A comparative study was performed for evaluating the insulin secretory responses of transported and control islets (not transported). ResultsThere was no evidence of contamination in the transported pancreatic islets. No significant differences were observed in the viability and functionality of the transported and control islet cells. ConclusionsThese findings show the feasibility of pancreatic islet transportation from Japan to Korea. Our data could be used not only for the inter-Asian but also for global advancement of animal and human islet transportation methods and transplantation research.

WS6 induces both alpha and beta cell proliferation without affecting differentiation or viability.

Agents that stimulate human pancreatic beta cell proliferation are needed to improve diabetes mellitus treatment. Recently, a small molecule, WS6, was observed to stimulate human beta cell proliferation. However, little is known about its other effects on human islets. To better understand the role of WS6 as a possible beta cell regenerative therapy, we carried out in-depth phenotypic analysis of WS6-treated human islets, exploring its effects on non-beta cell proliferation, beta cell differentiation, and islet cell viability. WS6 not only stimulated beta cell proliferation in cultured human islets (in agreement with previous reports), but also human alpha cell proliferation, indicating that WS6 is not a beta cell-specific mitogen. WS6 did not change the proportion of insulin-positive beta cells or the expression of beta cell-specific transcription factors, suggesting that WS6 does not alter beta cell differentiation, and WS6 had no effect on human islet cell apoptosis or viability. In conclusion, WS6 stimulates proliferation of both human beta and alpha cells while maintaining cellular viability and the beta cell differentiated phenotype. These findings expand the literature on WS6 and support the suggestion that WS6 may help increase human islet mass needed for successful treatment of diabetes.

Influence of adenosine on preservation of porcine pancreas in islet transplantation.

Ischemia time during transplantation has greatly restricted the quality and utilization of grafts. To improve the quality of islet transplantation, adenosine was added into the University of Wisconsin (UW) pancreas perfusate to assess its effect on islet yield and function in porcine pancreas. Ten pancreata from donation after cardiac death pigs were obtained and randomly divided into two groups: control group (N = 5) with UW perfusion solution, and experimental group (N = 5) with adenosine-enriched UW perfusion solution. The yield and purity of the islet cells were counted after they were collected, purified, and stained with dithizone. Acridine orange/propidium iodide staining was applied to determine islet cell viability. Islet function was assessed by glucose stimulated insulin secretion assays, and released insulin was quantified by enzyme-linked immunosorbent assay. The metabolic substrates of the pancreas were analyzed by trace dialysis technology. We found that the addition of adenosine in UW perfusion solution significantly increased the yield, purity and viability of islet cells, as well as enhanced their insulin release. In addition, the levels of metabolic substrates, pyruvate and lactate, were significantly reduced. The addition of adenosine could effectively increase islet cell viability during mechanical perfusions, which may improve islet transplantation. This perfusion protocol may be clinically feasible, and should be considered in the clinical setting.

The effect of time and temperature on viability and performance of Langerhans islets separated from Balb/c mouse after death.

Background:Tissue transplantation plays a pivotal role in the treatment of diseases. Pancreatic beta cell transplantation is the best way to obtain normal blood glucose in patients with diabetes type 1. However, it is not clear how long endocrine pancreas cells can be used for transplantation after the donor's death. The present study was conducted to analyze the performance and viability of pancreatic islet cells after death.Materials and Methods:Pancreas was separated from Balb/c mice at different times (0, 1, 4, 6, 12, and 24 h after death) at temperatures of 4°C and 23°C, and was cultured in Roswell_Park_Memorial_Institute (RPMI) 1640. Insulin shock, MTT assay, aldehyde fuchsin staining, dithizone staining, and florescence microscopy methods were applied to analyze the performance of beta cells, cell viability, islets’ diagnosis, islet cells’ diagnosis, and viable and necrotic cells diagnosis, respectively.Results:Islets of Langerhans and beta cells were diagnosed. By increasing the temperature and time, the viability and performance of beta cells decreased significantly (P < 0.05).Conclusion:The best condition for keeping the islets of Langerhans in terms of viability and performance is 4 h after death at temperature of 4°C.

Islet Cell Sparing Effects of Bee-Venom in Rat Pancreas.

Purpose: Bee venom (BV) contains biologically active components that cause anti-inflammatuar and anti-oxidative effects in various inflammatory diseases. Therefore, we have investigated its effects on rat islet cell viability and function and its relation with oxidative stress. However, bee venom effects on pancreatic islet cell function and islet cell viability are not known. Methods: Islet cells were isolated from 2-3 month old Sprague Dawley male rats (Diskapi Training and Research Hospital, Pancreatic Islet Cell Research Center). BV were extracted from Bombous Terresteris. Rat islets were incubated for 48 hours without BV (control group) and with BV (2.5 mcg/ml, 5 mcg/ml, 7 mcg/ml). Also, all of the groups were incubated in 5.6 mM glucose and 16.7 mM glucose to stimulate glucotoxicity. Insulin levels were determined by ELISA and stimulation index (SI) were calculated. Islet cell viability were examined with mixture of fluorodeoxiacetate and propidium iyodid by using a fluorescence microscope. Malondialdehyde and protein carbonyl (PC) levels were determined spectrophometrically to detect BV effect. Results: Islet cell viability were found statistically higher in the group treated with 2.5 mcg/ml BV according to control and other groups (p<0.05). SI were statistically higher in BV treated groups compared with control group cultured for 48 hours or not (p<0.05). We investigated levels of malondialdehyde and PC in all groups, however, there were no significant difference between groups (p>0.05). Conclusion: These results indicate a benefit of bee venom for islet cell viability and function, but has no effect on oxidative parameters of malondialdehyde and PC levels according to this study. These positive effects might occur by antiinflammatuar action of BV or antioxidant effect by other oxidative pathways.

A Preconditioning Regimen with a PKCε Activator Improves Islet Graft Function in a Mouse Transplant Model

Transplantation of islets isolated from deceased donor pancreata is an attractive method of β-cell replacement therapy for patients with type 1 diabetes (T1D). However, the loss of islet cell viability and function during the peritransplant period is a limiting factor to long-term islet engraftment. Activation of the isoenzyme PKCɛ may improve islet survival and function. The current study assesses the effects of PKCɛ activation on islet graft function in a syngeneic streptozotocin-induced diabetic mouse model. Islets were isolated from wild-type BALB/c mice preconditioned with either a PKCɛ activator (ψɛRACK) or a TAT carrier control peptide. Islets were further treated with the same agents during isolation, purification, and incubation prior to transplantation. Two hundred seventy-five islet equivalents were transplanted under the kidney capsule of streptozotocin-induced diabetic BALB/c mice. Islet function was assessed by measurement of blood glucose levels every 3 days for 42 days after transplant and through an intraperitoneal glucose tolerance test (IPGTT). The time for return to euglycemia in mice transplanted with islets treated with ψɛRACK was improved at 14 ± 6 days versus 21 ± 6 days with TAT-treated islets. The IPGTT showed a 50% reduction in the area under the curve associated with an improved insulin response in mice transplanted with ψɛRACK-treated islets compared to TAT-treated islets. A preconditioning regimen using PKCɛ agonist before pancreatic recovery and during islet isolation improves islet graft function and resistance to high glucose stress after transplantation.

The Administration of Recombinant Thyrotrophic Hormone (rTSH) to Culture Medium Improves Islet Cell Viability in Rats.

The Administration of Recombinant Thyrotrophic Hormone (rTSH) to Culture Medium Improves Islet Cell Viability in Rats.

Enhanced MIN-6 beta cell survival and function on a nitric oxide-releasing peptide amphiphile nanomatrix.

Innovative biomaterial strategies are required to improve islet cell retention, viability, and functionality, and thereby obtain clinically successful outcomes from pancreatic islet cell transplantation. To address this need, we have developed a peptide amphiphile-based nanomatrix that incorporates multifunctional bioactive cues and sustained release of nitric oxide. The goal of this study was to evaluate the effect of this peptide amphiphile nanomatrix on the viability and functionality of MIN-6 islet cells. Additionally, this study provides insight into the role of nitric oxide in islet cell biology, given that conventional nitric oxide donors are unable to release nitric oxide in a controlled, sustained manner, leading to ambiguous results. It was hypothesized that controlled nitric oxide release in synergy with multifunctional bioactive cues would promote islet cell viability and functionality. Nitric oxide-releasing peptide amphiphile nanomatrices within the range of 16.25 μmol to 130 μmol were used to analyze MIN-6 cell behavior. Both 32.5 μmol and 65 μmol peptide amphiphiles showed improved MIN-6 functionality in response to glucose over a 7-day time period, and the elevated functionality was correlated with both PDX-1 and insulin gene expression. Our results demonstrate that nitric oxide has a beneficial effect on MIN-6 cells in a concentration-dependent manner.

Elevated levels of branched‐chain amino acids have little effect on pancreatic islet cells, but l‐arginine impairs function through activation of the endoplasmic reticulum stress response

Recent metabolic profiling studies have identified a correlation between branched-chain amino acid levels, insulin resistance associated with prediabetes and susceptibility to type2 diabetes. Glucose and lipids in chronic excess have been reported to induce toxic effects in pancreatic β-cells, but the effect of elevated amino acid concentrations on primary islet cell function has not been investigated to date. The aim of this study was to investigate the effect of chronic exposure to various amino acids on islet cell function in vitro. Isolated rat islets were incubated over periods of 48h with a range of concentrations of individual amino acids (0.1μm to 10mm). After 48h, islets were assessed for glucose-dependent insulin secretion capacity, proliferation or islet cell apoptosis. We report that elevated levels of branched-chain amino acids have little effect on pancreatic islet cell function or viability; however, increased levels of the amino acid l-arginine were found to be β-cell toxic, causing a dose-dependent decrease in insulin secretion accompanied by a decrease in islet cell proliferation and an increase in islet cell apoptosis. These effects were not due to l-arginine-dependent increases in production of nitric oxide but arose through elicitation of the islet cell endoplasmic reticulum stress response. This novel finding indicates, for the first time, that the l-arginine concentration in vitro may impact negatively on islet cell function, thus indicating further complexity in relationship to in vivo susceptibility of β-cells to nutrient-induced dysfunction.

TGF-β Superfamily Member Nodal Stimulates Human β-Cell Proliferation While Maintaining Cellular Viability

In an effort to expand human islets and enhance allogeneic islet transplant for the treatment of type 1 diabetes, identifying signaling pathways that stimulate human β-cell proliferation is paramount. TGF-β superfamily members, in particular activin-A, are likely involved in islet development and may contribute to β-cell proliferation. Nodal, another TGF-β member, is present in both embryonic and adult rodent islets. Nodal, along with its coreceptor, Cripto, are pro-proliferative factors in certain cell types. Although Nodal stimulates apoptosis of rat insulinoma cells (INS-1), Nodal and Cripto signaling have not been studied in the context of human islets. The current study investigated the effects of Nodal and Cripto on human β-cell proliferation, differentiation, and viability. In the human pancreas and isolated human islets, we observed Nodal mRNA and protein expression, with protein expression observed in β and α-cells. Cripto expression was absent from human islets. Furthermore, in cultured human islets, exogenous Nodal stimulated modest β-cell proliferation and inhibited α-cell proliferation with no effect on cellular viability, apoptosis, or differentiation. Nodal stimulated the phosphorylation of mothers against decapentaplegic (SMAD)-2, with no effect on AKT or MAPK signaling, suggesting phosphorylated SMAD signaling was involved in β-cell proliferation. Cripto had no effect on human islet cell proliferation, differentiation, or viability. In conclusion, Nodal stimulates human β-cell proliferation while maintaining cellular viability. Nodal signaling warrants further exploration to better understand and enhance human β-cell proliferative capacity.