Enhanced Insulin Secretion Research Articles

Insights into the molecular mechanism of positive cooperativity between partial agonist MK-8666 and full allosteric agonist AP8 of hGPR40 by Gaussian accelerated molecular dynamics (GaMD) simulations

Activation of human free fatty acid receptor 1 (FFAR1, also called hGPR40) enhances insulin secretion in a glucose-dependent manner. Hence, the development of selective agonist targeting hGPR40 has been proposed as a therapeutic strategy of type 2 diabetes mellitus. Some agonists targeting hGPR40 were reported. The radioligand-binding studies and the crystal structures reveal that there are multiple sites on GPR40, and there exists positive binding cooperativity between the partial agonist MK-8666 and full allosteric agonist (AgoPAM) AP8. In this work, we carried out long-time Gaussian accelerated molecular dynamics (GaMD) simulations on hGPR40 to shed light on the mechanism of the cooperativity between the two agonists at different sites. Our results reveal that the induced-fit conformational coupling is bidirectional between the two sites. The movements and rotations of TM3, TM4, TM5 and TM6 due to their inherent flexibility are crucial in coupling the conformational changes of the two agonists binding sites. These helices adopt similar conformational states upon alternative ligand or both ligands binding. The Leu1384.57, Leu1865.42 and Leu1905.46 play roles in coordinating the rearrangements of residues in the two pockets, which makes the movements of residues in the two sites like gear movements. These results provide detailed information at the atomic level about the conformational coupling between different sites of GPR40, and also provide the structural information for further design of new agonists of GPR40. In addition, these results suggest that it is necessary by considering the effect of other site bound in structure-based ligands discovery.

CDK2 limits the highly energetic secretory program of mature β cells by restricting PEP cycle-dependent KATP channel closure

SUMMARYHallmarks of mature β cells are restricted proliferation and a highly energetic secretory state. Paradoxically, cyclin-dependent kinase 2 (CDK2) is synthesized throughout adulthood, its cytosolic localization raising the likelihood of cell cycle-independent functions. In the absence of any changes in β cell mass, maturity, or proliferation, genetic deletion of Cdk2 in adult β cells enhanced insulin secretion from isolated islets and improved glucose tolerance in vivo. At the single β cell level, CDK2 restricts insulin secretion by increasing KATP conductance, raising the set point for membrane depolarization in response to activation of the phosphoenolpyruvate (PEP) cycle with mitochondrial fuels. In parallel with reduced β cell recruitment, CDK2 restricts oxidative glucose metabolism while promoting glucose-dependent amplification of insulin secretion. This study provides evidence of essential, non-canonical functions of CDK2 in the secretory pathways of quiescent β cells.

Analysis on the mechanism of enhancing insulin secretion by TRPM2 channel in a pancreatic <i>β</i>-cell

Analysis on the mechanism of enhancing insulin secretion by TRPM2 channel in a pancreatic <i>β</i>-cell

SIRT2 ablation inhibits glucose-stimulated insulin secretion through decreasing glycolytic flux.

Rationale: Sirtuins are NAD+-dependent protein deacylases known to have protective effects against age-related diseases such as diabetes, cancer, and neurodegenerative disease. SIRT2 is the only primarily cytoplasmic isoform and its overall role in glucose homeostasis remains uncertain.Methods: SIRT2-knockout (KO) rats were constructed to evaluate the role of SIRT2 in glucose homeostasis. The effect of SIRT2 on β-cell function was detected by investigating the morphology, insulin secretion, and metabolomic state of islets. The deacetylation and stabilization of GKRP in β-cells by SIRT2 were determined by western blot, adenoviral infection, and immunoprecipitation.Results: SIRT2-KO rats exhibited impaired glucose tolerance and glucose-stimulated insulin secretion (GSIS), without change in insulin sensitivity. SIRT2 deficiency or inhibition by AGK2 decreased GSIS in isolated rat islets, with lowered oxygen consumption rate. Adenovirus-mediated overexpression of SIRT2 enhanced insulin secretion from rat islets. Metabolomics analysis revealed a decrease in metabolites of glycolysis and tricarboxylic acid cycle in SIRT2-KO islets compared with control islets. Our study further demonstrated that glucokinase regulatory protein (GKRP), an endogenous inhibitor of glucokinase (GCK), was expressed in rat islets. SIRT2 overexpression deacetylated GKRP in INS-1 β-cells. SIRT2 knockout or inhibition elevated GKRP protein stability in islet β-cells, leading to an increase in the interaction of GKRP and GCK. On the contrary, SIRT2 inhibition promoted the protein degradation of ALDOA, a glycolytic enzyme.Conclusions: SIRT2 ablation inhibits GSIS through blocking GKRP protein degradation and promoting ALDOA protein degradation, resulting in a decrease in glycolytic flux.

Bergenin protects pancreatic beta cells against cytokine-induced apoptosis in INS-1E cells

Beta cell apoptosis induced by proinflammatory cytokines is one of the hallmarks of diabetes. Small molecules which can inhibit the cytokine-induced apoptosis could lead to new drug candidates that can be used in combination with existing therapeutic interventions against diabetes. The current study evaluated several effects of bergenin, an isocoumarin derivative, in beta cells in the presence of cytokines. These included (i) increase in beta cell viability (by measuring cellular ATP levels) (ii) suppression of beta cell apoptosis (by measuring caspase activity), (iii) improvement in beta cell function (by measuring glucose-stimulated insulin secretion), and (iv) improvement of beta cells mitochondrial physiological functions. The experiments were carried out using rat beta INS-1E cell line in the presence or absence of bergenin and a cocktail of proinflammatory cytokines (interleukin-1beta, tumor necrosis factor-alpha, and interferon- gamma) for 48 hr. Bergenin significantly inhibited beta cell apoptosis, as inferred from the reduction in the caspase-3 activity (IC50 = 7.29 ± 2.45 μM), and concurrently increased cellular ATP Levels (EC50 = 1.97 ± 0.47 μM). Bergenin also significantly enhanced insulin secretion (EC50 = 6.73 ± 2.15 μM) in INS-1E cells, presumably because of the decreased nitric oxide production (IC50 = 6.82 ± 2.83 μM). Bergenin restored mitochondrial membrane potential (EC50 = 2.27 ± 0.83 μM), decreased ROS production (IC50 = 14.63 ± 3.18 μM), and improved mitochondrial dehydrogenase activity (EC50 = 1.39 ± 0.62 μM). This study shows for the first time that bergenin protected beta cells from cytokine-induced apoptosis and restored insulin secretory function by virtue of its anti-inflammatory, antioxidant and anti-apoptotic properties. To sum up, the above mentioned data highlight bergenin as a promising anti-apoptotic agent in the context of diabetes.

Inhibitory evaluation of Curculigo latifolia on α-glucosidase, DPP (IV) and in vitro studies in antidiabetic with molecular docking relevance to type 2 diabetes mellitus

The inhibition of α-glucosidase and DPP enzymes capable of effectively reducing blood glucose level in the management of type 2 diabetes. The purpose of the present study is to evaluate the inhibitory potential of α-glucosidase and DPP (IV) activity including with the 2-NBDG uptake assay and insulin secretion activities through in vitro studies. The selected of active compounds obtained from the screening of compounds by LC-MS were docked with the targeted enzyme that involved in the mechanism of T2DM. From the results, root extracts displayed a better promising outcome in α-glucosidase (IC50 2.72 ± 0.32) as compared with the fruit extracts (IC50 3.87 ± 0.32). Besides, root extracts also displayed a better activity in the inhibition of DPP (IV), enhance insulin secretion and glucose uptake activity. Molecular docking results revealing that phlorizin binds strongly with α-glucosidase, DPP (IV) and Insulin receptor (IR) enzymes with achieving the lowest binding energy value. The present work suggests several of the compounds have the potential that contribute towards inhibiting α-glucosidase and DPP (IV) and thus effective in lowering post-prandial hyperglycaemia.

TLQP-21 changes in response to a glucose load

BackgroundThe TLQP-21 peptide potentiates glucose-stimulated insulin secretion, hence we investigated its endogenous response to glucose. MethodsFasted mice received intraperitoneal glucose (3 g/kg), or saline (controls), and were sacrificed 30 and 120 min later (4 groups, n = 6/group). We investigated TLQP-21 in pancreas and plasma using immunohistochemistry, enzyme-linked immunosorbent assay (ELISA) and high performance liquid chromatography (HPLC), as well as TLQP-21 receptors (gC1q-R and C3a-R1) expression in pancreas by immunohistochemistry. ResultsIn pancreas, TLQP-immunoreactivity (TLQP-ir.) was shown in insulin-, glucagon- and somatostatin-containing cells. Upon glucose, TLQP-ir. decreased at 30 min (∼40 % vs. controls), while returning to basal values at 120 min. In all groups, C3a-R1 was localized in ∼50 % of TLQP labelled islet cells (mostly central), while gC1q-R was detected in ∼25 % of TLQP cells (mainly peripheral). HPLC fractions of control pancreas extracts, assessed by ELISA, confirmed the presence of a TLQP-21 compatible-form (∼2.5 kDa MW). In plasma, TLQP-ir. increased at 30 min (∼30 %), with highest concentrations at 120 min (both: p<0.05 vs. controls), while HPLC fractions showed an increase in the TLQP-21 compatible form. ConclusionsUpon hyperglycaemia, TLQP-21 would be released from islets, to enhance insulin secretion but we cannot exclude an autocrine activity which may regulate insulin storage/secretion.

P35 El INGAP-PP estimula cambios a nivel transcripcional tanto en células endocrinas como no endocrinas del islote

Introducción: el INGAP-PP, un pentadecapéptido derivado del INGAP (Islet Neogenesis Associated Protein), potencia la secreción de insulina frente al estímulo de glucosa, aumenta la masa de células ß insulares y las protege de la acción citotóxica de la estreptozotocina. Estas evidencias nos permiten proponerlo como un posible recurso terapéutico para la prediabetes y diabetes tipo 2.Objetivos: estudiar los mecanismos, a nivel transcriptómico, que condicionan los efectos del INGAP-PP destacando la contribución de distintos tipos celulares en su rol terapéutico.Materiales y métodos: se aislaron islotes de rata Wistar macho normales y se cultivaron 4 días en ausencia o presencia de INGAP-PP y glucosa 11 mM. Luego de comprobar el efecto potenciador del INGAP-PP sobre la secreción de insulina inducida por glucosa 16,7 mM, se extrajo ARN de los islotes de ambos grupos y se realizó una secuenciación masiva (RNA-seq).

O4 Efecto del INGAP-PP sobre la expresión de genes involucrados en la remodelación de la matriz extracelular y la angiogénesis determinados por un análisis transcriptómico de islotes de ratas

Introducción: el INGAP-PP es un péptido derivado de INGAP que, en animales normales y con diabetes, aumenta la masa celular ß, la capacidad angiogénica insular y potencia la secreción de insulina estimulada por glucosa (SIEG) y otros secretagogos. Esto le adjudica un potencial terapéutico que actuaría específicamente en la patogenia celular de la diabetes. Conocer su posible efecto sobre los cambios globales en los perfiles de expresión génica insular facilitaría la comprensión de su mecanismo de acción.Objetivos: conocer, a través de un estudio transcriptómico, el efecto del INGAP-PP sobre la expresión génica de las células insulares y la posible regulación de distintas vías de señalización implicadas.Materiales y métodos: islotes aislados (colagenasa) de rata Wistar normales fueron cultivados 4 días en medio RPMI en ausencia (C) o presencia de INGAP-PP 50 µg/ml (I) y glucosa 11 mM. A su término se utilizaron 100 islotes de cada grupo para estudiar la SIEG en presencia de glucosa 3,3 mMó 16,6 mM (RIA). Del resto de los islotes se extrajo ARN total, una alícuota fue sometida a secuenciación masiva de ARN (RNA-seq) y otra fue retrotranscripta a ADNc para utilizarlo como molde en qPCR de marcadores de desarrollo, regeneración y angiogénesis.

Antidiabetic compounds 8a, 8b, 8k, and 9h enhance insulin secretion: activity and mechanism.

This study primarily investigated the effects of hypoglycemic compounds (Imeglimin derivatives) on insulin secretion in type 2 diabetes mellitus (T2DM), and further explored the possible mechanism underlying these effects. Firstly, Metformin was used as the initiating compound to synthesize three sets of derivatives which contained Imeglimin structure core. At the cellular level, we screened compounds with better effect on the activity of insulin receptor tyrosine protein kinase (IFcTPK) after the islet β cells were treated with the compounds of different concentrations. The insulin secretion was assessed using radioimmunoassay and the cytotoxicity to islet β cells was evaluated by means of MTT assay following treatment with the compounds. The Ca2+-related mechanism by which these compounds promote insulin secretion was elucidated with whole cell recordings from current-clamp mode. Totally, 48 synthesized compounds were generated, wherein 10 compounds could increase the activity of IFcTPK in HIT-T15 cells better among these compounds. The modified Imeglimin, especially in the structure of hydrophilic hydroxyl or piperidine rings, could improve the activity of the compound to promote insulin secretion. Furthermore, the compounds 8a, 8b, 8k, and 9h revealed high insulin secretion-promoting activity. These compounds enhanced insulin secretion in islet β cells by repressing the ATP-sensitive K(+) and voltage-gated K+ pathway. Our findings indicate that the hypoglycemic compounds 8a, 8b, 8k, and 9h confer better promotive effect on insulin secretion, which provides a reference for the development of drugs with better hypoglycemic activity.

Protein restriction during late gestation in beef cow: effects on growth and meat quality of progeny

The objective of this study was determine whether the amount of protein provided to cows during late gestation would affect postnatal growth and lead to changes on glucose regulation, carcass characteristics and meat quality of steer progeny. At 121 d prepartum, 68 multiparous Angus cows were blocked by BW and expected calving date and randomly assigned to low protein level (LP, 6% CP) or high protein level (HP, 12% CP) and were allotted in 12 pens per treatment. After calving, cows were managed together on improved pastures until weaning. Calves were weighed and body measurements were recorded at birth. Blood samples were taken at birth and each 30 d until weaning at 180 d of age. Male calves were maintained as a group after weaning on native range until 23 month of age when individual steers were fed a finishing diet during 84 d before slaughter. Twenty days before the end of the finishing phase, steers were subjected to an intravenous glucose tolerance test. Body weight at birth tended to be great (P = 0.06) and body mass index was greater (P = 0.04) on HP than LP progeny. Maternal dietary protein concentration had no influence on offspring body weight and growth rate during lactation, rearing or finishing phases (P &gt; 0.10). Rib fat thickness of steers was not affected (P = 0.38) by maternal nutrition treatments, however, LM area was greater in HP steers than LP steers at entrance into the feedlot (P = 0.01) and end of finishing phase (P = 0.04). Glucose concentrations was greater (P &lt; 0.001) on LP calves than HP calves from birth to weaning without any change in insulin concentrations (P &gt; 0.10). Insulin-like growth factor concentrations was lower on LP calves at birth (P &lt; 0.05). During the glucose tolerance test at 24 month of age, glucose concentration after intravenous administration decreased faster (P = 0.002) in LP compared to HP steers. Peak of serum insulin concentration was greater (P = 0.04) and serum insulin concentration tended to decrease (P = 0.08) more rapidly in LP compared to HP steers. Hot carcass weight was similar between treatments (P = 0.69), however dressing percentage was increased in HP relative to LP steers (P = 0.01). Tenderness of Longissimus muscle was increased in HP compared to LP steers (P &lt; 0.001). No treatment differences in troponin-t degradation (P = 0.77) and collagen content (P = 0.58) were observed. Muscle fiber diameter was similar in LP and HP steers (P = 0.20), suggesting that increase of LM area in HP steers could be due to muscle hyperplasia. These data demonstrate that low protein during late gestation in bovine dams may affect fetal growth. Low level of protein compromised glucose regulation in early life and alter glucose regulation, enhancing insulin secretion in steer progeny at 24 month of age. The results indicated that level of protein during mid to late gestation does not affect offspring growth but has impacts on carcass composition and meat quality of steer progeny.

Diet-induced obesity enhances postprandial glucagon-like peptide-1 secretion in Wistar rats, but not in diabetic Goto-Kakizaki rats.

Glucagon-like peptide-1 (GLP-1) is postprandially secreted from enteroendocrine L-cells and enhances insulin secretion. Currently, it is still controversial whether postprandial GLP-1 responses are altered in obesity and diabetes. To address the issue and to find out possible factors related, we compared postprandial GLP-1 responses in normal rats and in diabetic rats chronically fed an obesogenic diet. Male Wistar rats and diabetic Goto-Kakizaki (GK) rats were fed either a control diet or a high-fat/high-sucrose (HFS, 30 % fat and 40 % sucrose) diet for 26 weeks. Meal tolerance tests were performed for monitoring postprandial responses after a liquid diet administration (62·76 kJ/kg body weight) every 4 or 8 weeks. Postprandial glucose, GLP-1 and insulin responses in Wistar rats fed the HFS diet (WH) were higher than Wistar rats fed the control diet (WC). Although GK rats fed the HFS diet (GH) had higher glycaemic responses than GK rats fed the control diet (GC), these groups had similar postprandial GLP-1 and insulin responses throughout the study. Jejunal and ileal GLP-1 contents were increased by the HFS diet only in Wistar rats. Furthermore, mRNA expression levels of fatty acid receptors (Ffar1) in the jejunum were mildly (P = 0·053) increased by the HFS diet in Wistar rats, but not in GK rats. These results demonstrate that postprandial GLP-1 responses are enhanced under an obesogenic status in normal rats, but not in diabetic rats. Failure of adaptive enhancement of GLP-1 response in GK rats could be partly responsible for the development of glucose intolerance.

Multi-Tissue Acceleration of the Mitochondrial Phosphoenolpyruvate Cycle Improves Whole-Body Metabolic Health

The mitochondrial GTP (mtGTP)-dependent phosphoenolpyruvate (PEP) cycle couples mitochondrial PEPCK (PCK2) to pyruvate kinase (PK) in the liver and pancreatic islets to regulate glucose homeostasis. Here, small molecule PK activators accelerated the PEP cycle to improve islet function, as well as metabolic homeostasis, in preclinical rodent models of diabetes. In contrast, treatment with a PK activator did not improve insulin secretion in pck2-/- mice. Unlike other clinical secretagogues, PK activation enhanced insulin secretion but also had higher insulin content and markers of differentiation. In addition to improving insulin secretion, acute PK activation short-circuited gluconeogenesis to reduce endogenous glucose production while accelerating red blood cell glucose turnover. Four-week delivery of a PK activator invivo remodeled PK phosphorylation, reduced liver fat, and improved hepatic and peripheral insulin sensitivity in HFD-fed rats. These data provide a preclinical rationale for PK activation to accelerate the PEP cycle to improve metabolic homeostasis and insulin sensitivity.

Anti-diabetic activity of diphenhydramine in diabetic rats

The purpose of this project is to study the anti-diabetic effect of on a diabetic rat model. A total of Twenty male Sprague rats were used and it randomly distributed into four groups which are Group I: , Group II: negative control, Group III: and Group IV: and . In diabetic model were induced with via injection at the dosage of 65mg/kg. and FBG (Fasting Blood Glucose) level of diabetic rats were assessed every three days. Blood was collected via cardiac puncture at day 21 after the induction of treatment. Insulin level of the rats was assessed with the Mercodia Rat Insulin ELISA kit. FBG level of group I (12.16 ±3.96, p&amp;lt;0.05) and group IV (11.34 ±3.67, p&amp;lt;0.05) were significantly decreased. Meanwhile, the for all rats did not show any significant increase. However, the insulin level was escalated in group IV (0.74+0.25, p&amp;lt;0.05) significantly. The present study shows that the and the combination of and lowered blood glucose level and enhanced insulin secretion.

Tirzepatide is an imbalanced and biased dual GIP and GLP-1 receptor agonist.

Tirzepatide (LY3298176) is a dual GIP and GLP-1 receptor agonist under development for the treatment of type 2 diabetes mellitus (T2DM), obesity, and nonalcoholic steatohepatitis. Early phase trials in T2DM indicate that tirzepatide improves clinical outcomes beyond those achieved by a selective GLP-1 receptor agonist. Therefore, we hypothesized that the integrated potency and signaling properties of tirzepatide provide a unique pharmacological profile tailored for improving broad metabolic control. Here, we establish methodology for calculating occupancy of each receptor for clinically efficacious doses of the drug. This analysis reveals a greater degree of engagement of tirzepatide for the GIP receptor than the GLP-1 receptor, corroborating an imbalanced mechanism of action. Pharmacologically, signaling studies demonstrate that tirzepatide mimics the actions of native GIP at the GIP receptor but shows bias at the GLP-1 receptor to favor cAMP generation over β-arrestin recruitment, coincident with a weaker ability to drive GLP-1 receptor internalization compared with GLP-1. Experiments in primary islets reveal β-arrestin1 limits the insulin response to GLP-1, but not GIP or tirzepatide, suggesting that the biased agonism of tirzepatide enhances insulin secretion. Imbalance toward GIP receptor, combined with distinct signaling properties at the GLP-1 receptor, together may account for the promising efficacy of this investigational agent.

A narrative review of current trends in liraglutide: insights into the unmet needs in management of type 2 diabetes and obesity.

Liraglutide is a long-acting human glucagon-like peptide-1 (GLP-1) analogue and an effective treatment for patients with metabolic diseases including type 2 diabetes mellitus (T2DM) and obesity. This review focuses on the mechanism of action of liraglutide as a well-known glucagon-like peptide-1 receptor agonist (GLP-1 RA) in patients with T2DM and obesity. The lower and the higher doses of GLP-1 RAs are used for glycaemic control in T2DM and in obesity respectively. GLP-1 RAs such as liraglutide enhance insulin secretion and inhibit glucagon release via the stimulation of glucagon-like peptide-1 receptors (GLP-1Rs). Liraglutide decreases hemoglobin A1c (HbA1c) in type 2 diabetes (T2D) patients when prescribes as monotherapy or in combination with one or more antidiabetic drugs. Usually, it is well tolerated with minor hypoglycemia in combination therapy. Liraglutide reduces cardiovascular events and related risk factors including improvement of lipid profile and control of blood pressure. Accordingly, it can be cost-effective and may be a budget neutral medication option by considering its protective effect on the cardiovascular system in long-term use in the health care plan. In the near future, by pharmacogenomics approach, prediction of the highest patient's response with the lowest adverse drug reactions and also rationality of drug development will be possible. Liraglutide can be used as a desirable medicine for glycemic control and obesity. It shows extensive evidence based benefits in diabetes complications. In this narrative review, we have summarized and evaluated studies related to the role of liraglutide in clinical practice.

Bioactive Phytochemicals Isolated from Akebia quinata Enhances Glucose-Stimulated Insulin Secretion by Inducing PDX-1.

Chocolate vine (Akebia quinata) is consumed as a fruit and is also used in traditional medicine. In order to identify the bioactive components of A. quinata, a phytosterol glucoside stigmasterol-3-O-β-d-glucoside (1), three triterpenoids maslinic acid (2), scutellaric acid (3), and hederagenin (4), and three triterpenoidal saponins akebia saponin PA (5), hederacoside C (6), and hederacolchiside F (7) were isolated from a 70% EtOH extract of the fruits of A. quinata (AKQU). The chemical structures of isolates 1–7 were determined by analyzing the 1D and 2D nuclear magnetic resonance (NMR) spectroscopic data. Here, we evaluated the effects of AKQU and compounds 1–7 on insulin secretion using the INS-1 rat pancreatic β-cell line. Glucose-stimulated insulin secretion (GSIS) was evaluated in INS-1 cells using the GSIS assay. The expression levels of the proteins related to pancreatic β-cell function were detected by Western blotting. Among the isolates, stigmasterol-3-O-β-d-glucoside (1) exhibited strong GSIS activity and triggered the overexpression of pancreas/duodenum homeobox protein-1 (PDX-1), which is implicated in the regulation of pancreatic β-cell survival and function. Moreover, isolate 1 markedly induced the expression of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), insulin receptor substrate-2 (IRS-2), phosphoinositide 3-kinase (PI3K), and Akt, which regulate the transcription of PDX-1. The results of our experimental studies indicated that stigmasterol-3-O-β-d-glucoside (1) isolated from the fruits of A. quinata can potentially enhance insulin secretion, and might alleviate the reduction in GSIS during the development of T2DM.

Histone deacetylase 3-selective inhibitor RGFP966 ameliorates impaired glucose tolerance through β-cell protection

The potential therapeutic effect of histone deacetylase 3 (HDAC3) pharmacologic inhibition on diabetes has been focused recently. RGFP966, as a highly-selective HDAC3 inhibitor, its possible roles and underlying mechanism in the treatment of diabetes needs to be clarified. In this study, low-dose streptozotocin (STZ)-induced pre-diabetic mice were used to test the regulatory ability of RGFP966 in blood glucose and insulin. We isolated the islets both from normal C57BL/6 J mice and KKAy mice with spontaneous type 2 diabetes to determine the potency of RGFP966 on glucose-stimulated insulin secretion. NIT-1 pancreatic β-cells induced by sodium palmitate (PA) were applied to identify the protective effects of RGFP966 against β-cell apoptosis. The results showed that administration of RGFP966 in the pre-diabetic mice not only significantly reduced hyperglycemia, promoted phase I insulin secretion, improved morphology of islets, but also increased glucose infusion rate (GIR) during hyperglycemic clamp test. When treated in vitro, RGFP966 enhanced insulin secretion and synthesis in islets of normal C57BL/6J mice and diabetic KKAy mice. In addition, it partially attenuated PA-induced apoptosis in NIT-1 cells. Therefore, our research suggests that RGFP966, probably through selective inhibition of HDAC3, might serve as a novel potential preventive and therapeutic candidate for diabetes.

Inhibition of miR-153, an IL-1β-responsive miRNA, prevents beta cell failure and inflammation-associated diabetes

ObjectiveSystemic levels of up-regulated IL-1β and IL-1 receptors promote the pathogenesis of inflammation-associated diabetes. IL-1 receptor antagonist (IL-Ra) has shown slightly elevated beta cell function in patients with type 2 diabetes without significant improvement of hyperglycaemia. We investigated whether miR-153, an IL-1β responsive miRNA, could mimic IL-1β effects and whether its interruption would improve blood glucose control then offer an assistant curative approach to inflammation-associated diabetes. Materials/methodsAntago-miR-153 and Ago-miR-153 were injected into the abdominal aorta of leptin receptor-mutant db/db mice and C57BL/6 J mice, respectively. Blood glucose levels, glucose tolerance tests, insulin tolerance tests and insulin levels were regularly checked. Proteomic profiling combined with unbiased bioinformatics analysis, as well as experimental techniques, were utilized to identify target genes of miR-153. Anti-miR-153 and plasmid-based recovery assays were also performed using primary mouse islets and beta cell lines. ResultsThe miR-153 expression level was increased in IL-1β–treated beta cells and primary islets from the diabetic rodents. Pancreas overexpression of miR-153 caused glucose intolerance in C57BL/6 J mice but no alterations in body weight or insulin sensitivity. The inhibition of miR-153 temporarily reduced hyperglycaemia of db/db mice due to enhanced insulin secretion. Antago-miR-153 treatment ameliorated glucose intolerance in db/db mice during our observation period but did not improve insulin sensitivity. Mechanistically, miR-153 targeted three members of SNAREs to disturb insulin granule docking, thereby decreasing basal insulin secretion. Overexpression of anti-miR-153 or SNARE rescued the IL-1β–induced basal insulin secretion defect. Furthermore, miR-153 targeted beta cell–specific transcriptional factors and survival molecules to inhibit insulin biosynthesis and cell viability. ConclusionsThe IL-1β-responsive miR-153 targets SNAREs, beta cell specific TFs and other key factors to eventually causes beta cell failure. Inhibiting miR-153 with Antago-miR-153 prevents hyperglycaemia in db/db mice, indicating that miR-153 may be a promising therapeutic target for the treatment of inflammation-associated diabetes.

Eugenol Improves Insulin Secretion and Content of Pancreatic Islets from Male Mouse.

Glucose homeostasis is required for control of insulin secretion. Phenolic compounds improved glucose-stimulated insulin secretion (GSIS). Eugenol is a phenolic compound that may increase GSIS. So, it was decided to investigate the effect of eugenol on the insulin secretion and content of pancreatic islets from the male mice. In this experimental study, 3-month-old NMRI mice (20–25 g) were prepared. The pancreatic islets of Langerhans were isolated using the collagenase digestion method and divided into 12 groups: glucose 2.8, 5.6, and 16.7 mM, glucose 2.8 mM + eugenol 50, 100, and 200 µM, glucose 5.6 mM + eugenol 50, 100, and 200 µM, and glucose 16.7 mM + eugenol 50, 100, and 200 µM. The islet's insulin secretion and content were measured after 1 hour and 24 hours incubation at 37°C, respectively, by the ELISA assays method and related commercial kit. Present results showed that all doses of eugenol increased islet's insulin secretion and content in the medium containing glucose concentrations 2.8, 5.6, and 16.7 mM (P < 0.05). In conclusion, eugenol as a phenolic compound increased insulin secretion and content of pancreatic islets. The moderate dose of this compound enhanced insulin secretion during hypo- and hyperglycemic conditions, as well as a high dose of eugenol, increased insulin content. Finally, present research suggested that the administration of eugenol 100 µM was suitable for the early stage of T2DM as well as eugenol 200 µM for the advanced stage of this disease.