Asiatic acid improves insulin secretion of β cells in type 2 diabetes through TNF- α/Mfn2 pathway / 浙江大学学报·医学版

OBJECTIVES@#To investigate the effects and molecular mechanisms of asiatic acid on β-cell function in type 2 diabetes mellitus (T2DM).@*METHODS@#The T2DM model was established by high fat diet and streptozotocin injection in ICR mice, and the effects of asiatic acid on glucose regulation were investigated in model mice. The islets were isolated from palmitic acid-treated diabetic mice. ELISA was used to detect the glucose-stimulated insulin secretion, tumor necrosis factor (TNF)-α and interleukin (IL)-6. ATP assay was applied to measure ATP production, and Western blotting was used to detect protein expression of mature β cell marker urocortin (Ucn) 3 and mitofusin (Mfn) 2. The regulatory effects of asiatic acid on glucose-stimulated insulin secretion (GSIS) and Ucn3 expression were also investigated after siRNA interference with Mfn2 or treatment with TNF-α.@*RESULTS@#Asiatic acid with the dose of 25 mg·kg－1·d－1 had the best glycemic control in T2DM mice and improved the homeostasis model assessment β index. Asiatic acid increased the expression of Mfn2 and Ucn3 protein and improved the GSIS function of diabetic β cells in vitro and in vivo (both P<0.05). Moreover, it improved the ATP production of islets of T2DM mice in vitro (P<0.05). Interfering Mfn2 with siRNA blocked the up-regulation of Ucn3 and GSIS induced by asiatic acid. Asiatic acid inhibited islet TNF-α content and increased Mfn2 and Ucn3 protein expression inhibited by TNF-α.@*CONCLUSIONS@#Asiatic acid improves β cell insulin secretion function in T2DM mice by maintaining the β cell maturity, which may be related to the TNF-α/Mfn2 pathway.

DTBNP and DTDP increase glucose-stimulated insulin secretion in INS-1 cell / 实用医学杂志

Objective To investigate the role of sulfydral redox agent in the modulation of insulin secretion and the potential mechanism. Methods Insulin secretion was evaluated in INS-1 cells after treatment with different concentrations of glucose and sulfydral redox agents by a standard insulin radio immunoassay. Results Glucose concentration-dependently potentiates insulin secretion was observed in INS-1 cells. DTBNP and DTDP could not only significantly increase glucose-stimulated insulin secretion (GSIS), but also increase insulin secretion in nifedipine-pretreated cells, which could be abrogated by DTT. Importantly, pharmacological ablation of L-type calcium channels by nifedipine and/or ablation of K ATP channelby diazoxide both could potentiate glucose-induced insulin secretory. Conclusions Sulfydral redox agent could regulates GSIS. DTBNP and DTDP may increase insulin secretion via regulating the activities of KATP, L-type CaV channel and IP3 receptor.

Hexane Extract of Orthosiphon stamineus Induces Insulin Expression and Prevents Glucotoxicity in INS-1 Cells

BACKGROUND: Hyperglycemia, a characteristic feature of diabetes, induces glucotoxicity in pancreatic beta-cells, resulting in further impairment of insulin secretion and worsening glycemic control. Thus, preservation of insulin secretory capacity is essential for the management of type 2 diabetes. In this study, we evaluated the ability of an Orthosiphon stamineus (OS) extract to prevent glucotoxicity in insulin-producing cells. METHODS: We measured insulin mRNA expression and glucose-stimulated insulin secretion (GSIS) in OS-treated INS-1 cells after exposure to a high glucose (HG; 30 mM) concentration. RESULTS: The hexane extract of OS elevated mRNA expression of insulin as well as pancreatic and duodenal homeobox-1 of INS-1 cells in a dose-dependent manner. The hexane OS extract also increased the levels of phosphorylated phosphatidylinositol 3-kinase (PI3K) in a concentration-dependent manner. Additionally, Akt phosphorylation was elevated by treatment with 100 and 200 micromol of the hexane OS extract. Three days of HG exposure suppressed insulin mRNA expression and GSIS; these expressions were restored by treatment with the hexane OS extract. HG elevated peroxide levels in the INS-1 cells. These levels were unaffected by OS treatment under both normal and hyperglycemic conditions. CONCLUSION: Our results suggested that the hexane extract of OS elevates insulin mRNA expression and prevents glucotoxicity induced by a 3-day treatment with HG. This was associated with the activation of PI-3K and Akt.

A Systematic Review of Oxidative Stress and Safety of Antioxidants in Diabetes: Focus on Islets and Their Defense

A growing body of evidence suggests that hyperglycemia-induced oxidative stress plays an important role in diabetic complications, especially beta-cell dysfunction and failure. Under physiological conditions, reactive oxygen species serve as second messengers that facilitate signal transduction and gene expression in pancreatic beta-cells. However, under pathological conditions, an imbalance in redox homeostasis leads to aberrant tissue damage and beta-cell death due to a lack of antioxidant defense systems. Taking into account the vulnerability of islets to oxidative damage, induction of endogenous antioxidant enzymes or exogenous antioxidant administration has been proposed as a way to protect beta-cells against diabetic insults. Here, we consider recent insights into how the redox response becomes deregulated under diabetic conditions, as well as the therapeutic benefits of antioxidants, which may provide clues for developing strategies aimed at the treatment or prevention of diabetes associated with beta-cell failure.

Fuel-Stimulated Insulin Secretion Depends upon Mitochondria Activation and the Integration of Mitochondrial and Cytosolic Substrate Cycles

The pancreatic islet beta-cell is uniquely specialized to couple its metabolism and rates of insulin secretion with the levels of circulating nutrient fuels, with the mitochondrial playing a central regulatory role in this process. In the beta-cell, mitochondrial activation generates an integrated signal reflecting rates of oxidativephosphorylation, Kreb's cycle flux, and anaplerosis that ultimately determines the rate of insulin exocytosis. Mitochondrial activation can be regulated by proton leak and mediated by UCP2, and by alkalinization to utilize the pH gradient to drive substrate and ion transport. Converging lines of evidence support the hypothesis that substrate cycles driven by rates of Kreb's cycle flux and by anaplerosis play an integral role in coupling responsive changes in mitochondrial metabolism with insulin secretion. The components and mechanisms that account for the integrated signal of ATP production, substrate cycling, the regulation of cellular redox state, and the production of other secondary signaling intermediates are operative in both rodent and human islet beta-cells.

Effect of 11β-hydroxysteroid dehydrogenase type 1 gene silencing on glucose stimulated insulin secretion of pancreatic β cell line NIT-1 / 基础医学与临床

Objective To investigate the effect of small interference RNA (siRNA) targeting at 11β-hydroxysteroid dehydrogenase type 1 on the glucose-stimulated insulin secretion (GSIS) in pancreatic β cell line NIT-1 cell.Methods siRNA plasmid vectors specifically targeting at 11β-HSD1 gene were constructed,named as olig886,oligo866 and scrabble control for oligo886,then tansfected into NIT-1 cells.The expression of 11β-HSD1 was detected by RT-PCR and Western blot.O1igo886 vector was transfected into the NIT-1 cells in 25 mmol/L glucose concentrations medium.The insulin secretion level was measured in GSIS test.Results After treatment with 11β-HSD1 siRNA,the mRNA level of 11β-HSD1 in NIT-1 cell was decreased by 78.1%±2.9% and 51.7% ±2.7% inolig886 and oligo866 group respectively.The protein of 11β-HSD1 were decreased by 82.2% ±2.1% and 56.5%±2.0 % respectively.After transfected by olig 8 8 6 vector,the insulin secretion increased in NIT -1 cell.Conclusion 11β-HSD1 gene silencing may improve GSIS in NIT-1 cell 11β-HSD1 regulate local glucocorticoid metabolism in pan-creatic islet and affect the function of insulin secretion.

Effect of troglitazone on insulin secretion in pancreatic β-cells and its mechanism / 中华内分泌代谢杂志

The effect of troglitazone on glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells and its mechanism were investigated.10 μmol/L troglitazone had no effect on basal insulin secretion,but significantly decreased GSIS and stimulated AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) phosphorylations (all P<0.01).These reactions were completely reversed by AMPK inhibitor compound C,suggesting that the troglitazone acutely inhibits insulin secretion via stimulating AMPK activity in beta cells.

Effect of survivin gene-transfection on cytokine-induced apoptosis in NIT-1 cells / 中华内分泌代谢杂志

Overexpression of survivin may partly protect the NIT-1 cells(mouse insulin-secreting cells) from cytokine-induced apoptosis.In addition, NIT-1 cells transfected with survivin had an slightly improved response of insulin secretion to glucose stimulation.

The primary study on expression and function of PLC? in INS-1 cell lines / 重庆医科大学学报

Objective:To investigate the expression of PLC?in INS-1,and the role of PLC?in glucose-stimulated insulin secretion(GSIS).Methods:(1)The six primers of PLC isoforms were designed.The template of INS-1's RNA was collected,RT-PCR was used to analyse the expression of PLC isoforms.(2)The glucose concentration were set at: 10,20,40,80,100 mmol/L,and stimulated INS-1 respectively.The content of insulin in INS-1's supernatant liquid was detected.The time groups were set as: 20,40,60,80,120 min.The content of insulin in INS-1's supernatant liquid was detected.(3)After the stimulus of glucose,RT-PCR and Western Blot were used to detect the expression of PLC?.Results:(1) PLC?,PLC?,PLC?,PLC?,PLC?were expressed in INS-1.(2) Exposure of INS-1 to 40mM glucose for 60 min,the content of insulin secretion reached the maximum and RT-PCR and Western Blot detected that the expression of PLC?was raised.Conclusion:(1)PLC?was expressed in INS-1.(2)Under the stimulation of glucose,the PLC?'s expression was augmented,so PLC? was probably participated in the signal transduction pathway of GSIS in INS-1.

Study on islet function of SD rats in second and third trimesters of pregnancy / 上海第二医科大学学报

Objective To investigate the glucose tolerance and ability of insulin secretion in SD rats in second and third trimesters of pregnancy. Methods SD rats with pregnancy of 15 d were selected as experimental group(n=6),and another 6 rats of the same batch without pregnancy were served as controls(n=6).Intraperitoneal glucose tolerance trials(IPGTT) were conducted in these two groups.Rat islets were isolated after in situ collagenase digestion through pancreatic duct perfusion,islet morphology was observed by inverted phase contrast microscope,and insulin secretion was determined by radioimmunoassay. Results It was revealed by IPGTT that the levels of glucose at 30,60,90 and 120 min were significantly lower in experimental group than those in control group(P

In vitro study of insulin secretion from mouse pancreatic islets-siriraj experiences.

Pancreatic islet isolation and culture technique are tools for direct investigation of the effects of substances on insulin secretion. Glucose is a well known insulin stimulating substance from the pancreatic islet. This study aims to demonstrate the first success (in Thailand) in islet isolation with intact insulin secretion from a mouse pancreas using collagenase P enzyme and histopaque separation. Isolated islets were cultured in RPMI 1640 for 24 hours before undergoing a glucose stimulation test. Glucose at five different concentrations (2.8, 5.6, 10, 15 and 20 mM glucose was higher than with 2.8mM basal glucose concentration. Insulin secretion increased about 1.7 to 3.5 fold from a basal level of 2.8 mM glucose without any difference in insulin content at any glucose concentrations used. To our knowledge, these data demonstrate the first success in mouse pancreatic islet isolation and culture in Thailand. This technique can be used as a tool for further investigation of the in vitro effects of substances such as plants or new drugs on insulin secretion.