Berberine acutely inhibits insulin secretion from beta-cells through 3',5'-cyclic adenosine 5'-monophosphate signaling pathway

Berberine, a hypoglycemic agent, has recently been shown to activate AMP-activated protein kinase (AMPK) contributing to its beneficial metabolic effects in peripheral tissues. However, whether berberine exerts a regulatory effect on beta-cells via AMPK or other signaling pathways and counteracts glucolipotoxicity remains uncertain. In the present study, the impact of berberine on beta-cell function was investigated in vivo and in vitro. In high-fat-fed rats, berberine treatment for 6 wk significantly decreased plasma glucose and insulin levels before and after an oral glucose challenge along with the reduction of body weight and improvement of blood lipid profile. In accordance with the in vivo results, berberine acutely decreased glucose-stimulated insulin secretion (GSIS) and palmitate-potentiated insulin secretion in MIN6 cells and rat islets. However, pretreated with berberine for 24 h augmented the response of MIN6 cells and rat islets to glucose and attenuated the glucolipotoxicity. Berberine acutely increased AMPK activity in MIN6 cells. However, compound C, an AMPK inhibitor, completely reversed troglitazone-suppressed GSIS, not berberine-suppressed GSIS. Otherwise, berberine decreased cAMP-raising agent-potentiated insulin secretion in MIN6 cells and rat islets. These results suggest that the activation of AMPK is required for troglitazone-suppressed GSIS, whereas cAMP signaling pathway contributes, at least in part, to the regulatory effect of berberine on insulin secretion.     

Identification of 9-cis-retinoic acid as a pancreas-specific autacoid that attenuates glucose-stimulated insulin secretion

The all-trans-retinoic acid (atRA) isomer, 9-cis-retinoic acid (9cRA), activates retinoic acid receptors (RARs) and retinoid X receptors (RXRs) in vitro. RARs control multiple genes, whereas RXRs serve as partners for RARs and other nuclear receptors that regulate metabolism. Physiological function has not been determined for 9cRA, because it has not been detected in serum or multiple tissues with analytically validated assays. Here, we identify 9cRA in mouse pancreas by liquid chromatography/tandem mass spectrometry (LC/MS/MS), and show that 9cRA decreases with feeding and after glucose dosing and varies inversely with serum insulin. 9cRA reduces glucose-stimulated insulin secretion (GSIS) in mouse islets and in the rat β-cell line 832/13 within 15 min by reducing glucose transporter type 2 (Glut2) and glucokinase (GK) activities. 9cRA also reduces Pdx-1 and HNF4α mRNA expression, ～8- and 80-fold, respectively: defects in Pdx-1 or HNF4α cause maturity onset diabetes of the young (MODY4 and 1, respectively), as does a defective GK gene (MODY2). Pancreas β-cells generate 9cRA, and mouse models of reduced β-cell number, heterozygous Akita mice, and streptozotocin-treated mice have reduced 9cRA. 9cRA is abnormally high in glucose-intolerant mice, which have β-cell hypertropy, including mice with diet-induced obesity (DIO) and ob/ob and db/db mice. These data establish 9cRA as a pancreas-specific autacoid with multiple mechanisms of action and provide unique insight into GSIS.     

Stevioside counteracts the glyburide-induced desensitization of the pancreatic beta-cell function in mice: studies in vitro

The sulfonylurea glyburide (GB) is one of the most frequently used drugs in diabetes treatment. Long-term pretreatment with GB causes elevated basal insulin secretion (BIS) and decreased glucose-stimulated insulin secretion (GSIS). These characteristics may play an important role for the development of hypoglycemia and secondary failure. Stevioside (SVS), a substance extracted from leaves of Stevia rebaudiana Bertoni, enhances GSIS but not BIS. The aim of the present study was to clarify whether 24-hour exposure of isolated mouse islets to GB causes dose-dependent decrease in the GSIS and whether it is possible to counteract this desensitization by SVS. We also tested the impact of the incretin glucagon-like peptide-1 (GLP-1) on the GB-induced desensitization. After 24-hour preincubation with GB in combination with SVS or GLP-1, we measured the basal and glucose-stimulated insulin responses and the total islet insulin content. We also determined the fold change in gene expression of pancreatic and duodenal homeobox 1 and glucose transporter isoform 2. After 24-hour preincubation in 11.1 mmol/L glucose, GB (10(-11)-10(-3) mol/L) caused a dose-dependent decrease in GSIS (16.7 mmol/L glucose) (P < .001). GB (10(-7) mol/L) pretreatment elevated BIS, but neither SVS (10(-7) mol/L) nor GLP-1 (10(-7) mol/L) could reverse this. Interestingly, the GB-induced desensitization of GSIS was counteracted by both SVS (P < .05) and GLP-1 (P < .05). SVS reversed the decrease in insulin content caused by GB pretreatment (P < .05). GB pretreatment did not change gene expression of pancreatic and duodenal homeobox 1 nor glucose transporter isoform 2, whereas SVS significantly up-regulated the expression of both genes by more than 2-fold (P < .05). Our results showed that SVS in combination with GB did not reverse GB-induced increase in BIS, whereas both SVS and GLP-1 counteracted GB-induced desensitization of GSIS. SVS is able to counteract the desensitizing effects of GB and may be a putative new drug candidate for the treatment of type 2 diabetes mellitus.     

Upregulation of β-cell genes and improved function in rodent islets following chronic glucokinase activation

Glucokinase (GK) plays a critical role in controlling blood glucose; GK activators have been shown to stimulate insulin secretion acutely both in vitro and in vivo. Sustained stimulation of insulin secretion could potentially lead to β-cell exhaustion; this study examines the effect of chronic GK activation on β-cells. Gene expression and insulin secretion were measured in rodent islets treated in vitro with GKA71 for 72 h. Key β-cell gene expression was measured in rat, mouse and global GK heterozygous knockout mouse islets (gk(del/wt)). Insulin secretion, after chronic exposure to GKA71, was measured in perifused rat islets. GKA71 acutely increased insulin secretion in rat islets in a glucose-dependent manner. Chronic culture of mouse islets with GKA71 in 5 mmol/l glucose significantly increased the expression of insulin, IAPP, GLUT2, PDX1 and PC1 and decreased the expression of C/EBPβ compared with 5 mmol/l glucose alone. Similar increases were shown for insulin, GLUT2, IAPP and PC1 in chronically treated rat islets. Insulin mRNA was also increased in GKA71-treated gk(del/wt) islets. No changes in GK mRNA were observed. Glucose-stimulated insulin secretion was improved in perifused rat islets following chronic treatment with GKA71. This was associated with a greater insulin content and GK protein level. Chronic treatment of rodent islets with GKA71 showed an upregulation of key β-cell genes including insulin and an increase in insulin content and GK protein compared with glucose alone.     

Exendin‐4 ameliorates diabetic symptoms through activation of glucokinase

Background: Glucagon‐like peptide‐1 (GLP‐1) and its stable analogue exendin‐4 maintain glucose homeostasis by modulating insulin secretion from pancreatic β‐cells and controlling hepatic glucose output. Glucokinase (GK), by catalysing the first step in glycolysis, plays an important role in glucose‐stimulated insulin secretion and hepatic glucose metabolism. In the present study, we investigated the effects of exendin‐4 on GK in high fat‐fed and alloxan‐treated diabetic mice. Methods: The effects of alloxan (5, 10 and 20 μmol/L) on insulin release from isolated murine islets, as well as glycogen synthesis by isolated murine hepatocytes, were assessed. The effects of exendin‐4 (10 nmol/kg, twice daily for 4 weeks) were assessed in high fat‐fed, alloxan (50 mg/kg, i.v.)‐treated C57 mice. Glucokinase activity was assessed in the same model. Results: Pretreatment with exendin‐4 attenuated alloxan‐induced decreases in insulin release and glycogen synthesis in islets and hepatocytes. The alloxan‐induced decrease in the GK activity in islets and hepatocytes was also ameliorated by exendin‐4 treatment. Pretreatment with the GLP‐1 receptor antagonist exendin‐9 (100 nmol/L) blocked the effects of exendin‐4 on the liver and pancreas. Treatment of high‐fat fed, alloxan‐treated diabetic mice with exendin‐4 (10 nmol/L, i.p.) reduced the severity of diabetic symptoms. Specifically, exendin‐4 treatment reduced serum glucose by 50% and %HbA1c by 24% compared with control and significantly decreased HOMA‐IR by 39% and increased HOMA‐β by 150%. In addition, exendin‐4 treatment significantly reduced body weight by 6.8% and serum triglycerides by 35%. Conclusions: The results indicate that glucose‐stimulated insulin release and glycogen synthesis are decreased by alloxan due to reduced GK activity. These findings provide further insight into the mechanism by which exendin‐4 regulates glucose homeostasis.     

Nutrient responsive nesfatin-1 regulates energy balance and induces glucose-stimulated insulin secretion in rats

Nesfatin-1 is a recently discovered anorexigen, and we first reported nesfatin-like immunoreactivity in the pancreatic β-cells. The aim of this study was to characterize the effects of nesfatin-1 on whole-body energy homeostasis, insulin secretion, and glycemia. The in vivo effects of continuous peripheral delivery of nesfatin-1 using osmotic minipumps on food intake and substrate partitioning were examined in ad libitum-fed male Fischer 344 rats. The effects of nesfatin-1 on glucose-stimulated insulin secretion (GSIS) were examined in isolated pancreatic islets. L6 skeletal muscle cells and isolated rat adipocytes were used to assess the effects of nesfatin-1 on basal and insulin-mediated glucose uptake as well as on major steps of insulin signaling in these cells. Nesfatin-1 reduced cumulative food intake and increased spontaneous physical activity, whole-body fat oxidation, and carnitine palmitoyltransferase I mRNA expression in brown adipose tissue but did not affect uncoupling protein 1 mRNA in the brown adipose tissue. Nesfatin-1 significantly enhanced GSIS in vivo during an oral glucose tolerance test and improved insulin sensitivity. Although insulin-stimulated glucose uptake in L6 muscle cells was inhibited by nesfatin-1 pretreatment, basal and insulin-induced glucose uptake in adipocytes from nesfatin-1-treated rats was significantly increased. In agreement with our in vivo results, nesfatin-1 enhanced GSIS from isolated pancreatic islets at both normal (5.6 mM) and high (16.7 mM), but not at low (2 mM), glucose concentrations. Furthermore, nesfatin-1/nucleobindin 2 release from rat pancreatic islets was stimulated by glucose. Collectively, our data indicate that glucose-responsive nesfatin-1 regulates insulin secretion, glucose homeostasis, and whole-body energy balance in rats.     

Overexpression of mitochondrial FAD-linked glycerol-3-phosphate dehydrogenase does not correct glucose-stimulated insulin secretion from diabetic GK rat pancreatic islets

Summary Glucose-stimulated insulin secretion is impaired in GK (Goto-Kakizaki) rats, perhaps because of abnormalities in glucose metabolism in pancreatic islet beta cells. The glycerol phosphate shuttle plays a major role in glucose metabolism by reoxidizing cytosolic NADH generated by glycolysis. In the pancreatic islets of GK rats, the activity of mitochondrial FAD-linked glycerol-3-phosphate dehydrogenase (mGPDH), the key enzyme of the glycerol phosphate shuttle, is decreased and this abnormality may be responsible, at least in part, for impaired glucose-stimulated insulin secretion. To investigate this possibility, we overexpressed mGPDH in islets isolated from GK rats via recombinant adenovirus-mediated gene transduction, and examined glucose-stimulated insulin secretion. In islets isolated from diabetic GK rats at 8 to 10 weeks of age, glucose-stimulated insulin secretion was severely impaired, and mGPDH activity was decreased to 79 % of that in non-diabetic Wistar rats. When mGPDH was overexpressed in islets from GK rats, enzyme activity and protein content increased 2- and 6-fold, respectively. Basal (3 mmol/l glucose) and glucose-stimulated (20 mmol/l) insulin secretion from the Adex1CAlacZ-infected GK rat islets were, respectively, 4.4 ± 0.7 and 8.1 ± 0.7 ng · islet⁻¹· 30 min⁻¹, and those from mGPDH-overexpressed GK rat islets 4.7 ± 0.3 and 9.1 ± 0.8 ng · islet⁻¹· 30 min⁻¹, in contrast to those from the Adex1CAlacZ-infected non-diabetic Wistar rat islets (4.7 ± 1.6 and 47.6 ± 11.9 ng · islet⁻¹· 30 min⁻¹). Thus, glucose-stimulated insulin secretion is severely impaired in GK rats even in the stage when mGPDH activity is modestly decreased, and at this stage, overexpression of mGPDH cannot restore glucose-stimulated insulin secretion. We conclude that decreased mGPDH activity in GK rat islets is not the defect primarily responsible for impaired glucose-stimulated insulin secretion. [Diabetologia (1998) 41: 649–653] Received: 20 October 1997 and in revised form: 22 December 1997     

黄连素对血管平滑肌细胞增殖、大鼠颈动脉球囊损伤模型及PTEN基因表达的影响

目的:探讨黄连素对血管平滑肌细胞(VSMC)增殖、大鼠颈动脉球囊损伤后动脉新生内膜形成及损伤后再狭窄的影响,及其影响是否通过改变PTEN(第10q23染色体的抑癌基因)的表达来实现。方法:MTT法检测黄连素对主动脉VSMC增殖的影响,实时定量RT-PCR及Western blot法测定黄连素对VSMC PTEN在转录及蛋白水平表达的影响。建立颈动脉球囊损伤模型,观察黄连素对新生内膜形成及再狭窄的影响及血管组织表达PTEN的变化。结果:黄连素抑制大鼠主动脉VSMC的增殖,改善损伤血管新生内膜形成及再狭窄;上调PTEN表达,且与浓度呈正相关,200μmol/L黄连素干预VSMC效果最佳;球囊损伤模型再狭窄的预防经过术前、术后各2周的黄连素处理,较单纯术后黄连素处理效果更佳。结论:黄连素可能通过上调PTEN表达来抑制VSMC增殖与球囊损伤模型内膜的增生及损伤后再狭窄。     

Carbachol restores insulin release in diabetic GK rat islets by mechanisms largely involving hydrolysis of diacylglycerol and direct interaction with the exocytotic machinery

In several models of insulin resistance, cholinergically induced insulin secretion is augmented. We studied here whether this also is present in the spontaneously diabetic GK (Goto-Kakizaki) rat pancreas. Using carbachol (50 micromol/L), enhanced insulin release was elicited in perfused pancreas under normal or depolarized conditions in GK compared with control rats at 3.3 mmol/L glucose (p < 0.03). Carbachol fully normalized insulin secretion in GK rats at 16.7 mmol/L glucose through an effect abolished by atropine. Similarly, direct stimulation of protein kinase C (PKC) with the DAG-permeable compound 1-oleoyl-2-acetyl-sn-glycerol (OAG, 300 micromol/L) induced more pronounced insulin release in GK islets than in control islets. The diacylglycerol (DAG) lipase inhibitor RHC-80267 (35 micromol/L) significantly reduced carbachol effects in control and GK islets, but had no effect on OAG-induced insulin release. The enhanced insulinotropic effects of carbachol in GK islets was not accompanied by increased cyclic adenosine monophosphate (cAMP) or arachidonic acid (AA) formation in GK when compared with control islets. In conclusion, cholinergic stimulation induced enhanced insulin release in diabetic GK islets. This is largely mediated through mechanisms involving hydrolysis of DAG to AA and interaction with exocytotic steps of insulin release.     

曲格列酮对胰岛β细胞胰岛素分泌的影响及机制研究

研究曲格列酮对胰岛β细胞(MIN6细胞株)胰岛素分泌的影响,并探讨其机制.10μmol/L曲格列酮短期抑制大鼠胰岛和MIN6细胞的葡萄糖刺激的胰岛素分泌(GSIS,P<0.01),增加AMP活化的蛋白激酶(AMPK)、乙酰辅酶A羧化酶(ACC)的磷酸化水平(均P<0.01),而AMPK抑制剂复合物C可使其AMPK、ACC的磷酸化水平以及胰岛素分泌完全恢复.     

cAMP-mediated signaling normalizes glucose-stimulated insulin secretion in uncoupling protein-2 overexpressing beta-cells

We investigated whether an increase in cAMP could normalize glucose-stimulated insulin secretion (GSIS) in uncoupling protein-2 (UCP2) overexpressing (ucp2-OE) beta-cells. Indices of beta-cell (beta-TC-6f7 cells and rodent islets) function were measured after induction of ucp2, in the presence or absence of cAMP-stimulating agents, analogs, or inhibitors. Islets of ob/ob mice had improved glucose-responsiveness in the presence of forskolin. Rat islets overexpressing ucp2 had significantly lower GSIS than controls. Acutely, the protein kinase A (PKA) and epac pathway stimulant forskolin normalized insulin secretion in ucp2-OE rat islets and beta-TC-6f7 beta-cells, an effect blocked by specific PKA inhibitors but not mimicked by epac agonists. However, there was no effect of ucp2-OE on cAMP concentrations or PKA activity. In ucp2-OE islets, forskolin inhibited ATP-dependent potassium (K(ATP)) channel currents and (86)Rb(+) efflux, indicative of K(ATP) block. Likewise, forskolin application increased intracellular Ca(2+), which could account for its stimulatory effects on insulin secretion. Chronic exposure to forskolin increased ucp2 mRNA and exaggerated basal secretion but not GSIS. In mice deficient in UCP2, there was no augmentation of either cAMP content or cAMP-dependent insulin secretion. Thus, elevating cellular cAMP can reverse the deficiency in GSIS invoked by ucp2-OE, at least partly through PKA-mediated effects on the K(ATP) channel.     

他汀类调脂药对大鼠胰岛胰岛素分泌的影响及机制研究

目的 观察不同他汀类药物对大鼠胰岛葡萄糖刺激的胰岛素分泌(GSIS)的抑制作用及机制.方法 新鲜分离或经24 h培养的胰岛均匀分为对照组、阿托伐他汀组、氟伐他汀组和普伐他汀组,对照组给予Kreb-Ringer碳酸氢盐缓冲液,他汀类药物组分别给予100μmol/L阿托伐他汀、氟伐他汀和普伐他汀,水浴30 min或过夜培养24 h.各组经2.8、5.5、11.1、16.7、25.0 mmol/L葡萄糖刺激后,37℃水浴法测定胰岛GSIS变化,生物化学发光法测定三磷酸腺苷(ATP)含量.结果 100μmol/L阿托伐他汀水浴30 min后,在16.7 mmol/L葡萄糖刺激下,与相应对照组比较,ATP含量[(9.54±1.64)pmol/胰岛比(12.33±1.89)pmol/胰岛]及胰岛素分泌(1.60±0.21比2.39±0.30)均下降(P＜0.05);100 μmol/L氟伐他汀过夜培养24 h后,在16.7 mmol/L葡萄糖刺激下,与相应对照组比较,ATP含量[(10.24±2.01)pmol/胰岛比(12.31±2.16)pmol/胰岛]及胰岛素分泌(3.12±0.32比4.17±0.37)也均下降(P＜0.05).结论 阿托伐他汀、氟伐他汀通过抑制胰岛ATP的生成而抑制GSIS,抑制程度与其脂溶性强弱有关.

Abstract：

Objective To evaluate the inhibitory effect of statins on glucose-stimulated insulin secretion (GSIS) of pancreatic islet in rat and to explore its mechanisms. Methods According to the average volume, freshly isolated or 24-hour cultured pancreatic islets were randomly divided into control group( incubated with Kreb-Ringer bicarbonate buffer), the atorvastatin group( incubated with 100 μ mol/L atorvastatin), the fluvastatin group (incubated with 100 μ mol/L fluvastatin)and the pravastatin group (incubated with 100 μ mol/L pravastatin). Stimulated by 2. 8,5. 5,11.1,16. 7 mmol/L and 25.0 mmol/L glucose respectively, the effect of 100 μ mol/L statins on ATP content and GSIS was compared in the four groups. GSIS was performed by the 37℃ bath incubation method and ATP content was measured by chemiluminescence method. Results Incubated with 100 μ mol/L atorvastatin for 30 minutes, in the presence of 16. 7 mmol/L glucose, the ATP content [(9. 54 ± 1. 64) pmol/islet vs ( 12. 33 ± 1.89) pmol/islet] and GSIS (1.60 ± 0. 21 vs 2. 39 ± 0. 30) were significantly reduced in comparison with the control group (P＜0. 05). Cultured with 100 μmol/L fluvastatin for 24 hours, the ATP content [( 10. 24 ±2.01 )pmol/islet vs (12. 31 ±2. 16) pmol/islet] and GSIS (3. 12 ± 0. 32 vs 4. 17 ±0. 37 ) were all significantly decreased at the higher glucose concentration of 16. 7 mmol/L ( P ＜ 0. 05). Conclusion Atorvastatin and fluvastatin may inhibit GSIS by decreasing ATP content in pancreatic islet and the inhibitory effect is related to the strength of its lipophilicity.     

Chronic effects of different non-esterified fatty acids on pancreatic islets of rats

Aims: The aim of this study was to examine the chronic effects of different non-esterified fatty acids (NEFA) on insulin secretion by pancreatic islets of normal Wistar rats in vitro. Methods: Pancreatic islets were isolated from normal Wistar rats, and were incubated with 0.2, 0.4, or 0.8 mmol/L palmitate (C16:0), stearate (C18:0), oleate (C18:1), or linoleate (C18:2) for 24 h, then the insulin secretion and pyruvate dehydrogenase (PHD) activity were examined. Results: Neither islet insulin content nor islet DNA content differed among islets incubated with each kind of NEFA. Compared with control, linoleate significantly inhibited glucose-stimulated insulin secretion (GSIS) and PDH activity at each concentration (p<0.05), while others inhibited GSIS and PDH activity significantly only at 0.4 and 0.8 mmol/L (p<0.05). There was no significant difference in GSIS and PDH activity among islets pretreated by palmitate, stearate, and oleate at the same concentration (p>0.05). However, linoleate decreased GSIS more than others at the same concentration (p<0.05), while linoleate (0.4 or 0.8 mmol/L) inhibited PDH activity more than others at the same concentration (p<0.05). Conclusions: Elevation of palmitate, stearate, oleate or linoleate decreases the β-cell secretory response to glucose, through inhibiting PDH activity. Linoleate exerts more negative effect on GSIS than other NEFA.     

辛伐他汀抑制大鼠胰岛β细胞胰岛素分泌的机制研究

目的 观察辛伐他汀对大鼠胰岛β细胞葡萄糖刺激的胰岛素分泌(GSIS)的抑制作用及其机制.方法 8周龄健康雄性Wistar大鼠60只,体重250～300 g,饲养1周内分批处死.采用胆管注射胶原酶法提取大鼠胰岛,将新鲜分离或经24 h培养的大鼠胰岛按体积大小分为对照组(胰岛数=60)和辛伐他汀组(胰岛数=60),对照组给予Kreb-Ringer碳酸氢盐缓冲液,辛伐他汀组以100μmol/L辛伐他汀水浴30 min或过夜培养24 h.两组经2.8、5.5、11.1、16.7、25.0 mmol/L葡萄糖刺激后,采用37 ℃水浴法观测胰岛β细胞GSIS变化,选用生物化学发光法测定腺苷三磷酸(ATP)含量.两组间数据比较采用t检验.结果 100 μmol/L辛伐他汀水浴30 min后,在25.0 mmol/L葡萄糖刺激下,胰岛β细胞ATP含量较相应对照组明显下降[(9.2±1.6)vs(12.1±1.9)pmol/胰岛,t=2.97,P＜0.05],GSIS较相应对照组明显减少(2.31±0.38 vs 3.19±0.41,t=3.154,P＜0.05).100μmol/L辛伐他汀过夜培养24 h后,在11.1 mmol/L葡萄糖刺激下,胰岛β细胞ATP含量较相应对照组明显降低[(9.2±1.4)vs(11.9±2.0)pmol/胰岛,t=2.514,P＜0.05];在2.8 mmol/L葡萄糖刺激下,胰岛素分泌即已明显受到抑制(0.28±0.03 vs 0.47±0.05,t=2.460,P＜0.05).辛伐他汀浓度超过30 μmol/L时,可剂量依赖性地抑制GSIS(2.49±0.21 vs 3.17±0.23,t=2.445,P＜0.05).结论 高浓度辛伐他汀可能通过抑制胰岛β细胞ATP生成而抑制GSIS.     

游离脂肪酸对胰岛素瘤细胞系βTc6细胞葡萄糖激酶和葡萄糖转运蛋白2表达及胰岛素分泌功能的影响

目的 探讨游离脂肪酸（FFA）对小鼠胰岛素瘤细胞系βTc6细胞葡萄糖激酶（GK）和葡萄糖转运蛋白2（GLUT2）的表达及相应的胰岛素分泌功能变化的影响.方法用不同浓度FFA（0.25、0.50、1.00 mmol/L）干预βTc6细胞24 h,应用逆转录（RT）-PCR法和Western Blot法检测GK和GLUT2表达情况,并观察细胞形态及葡萄糖刺激的胰岛素分泌功能（GSIS）的变化.应用单因素方差分析进行统计学分析.结果 （1）经过0.25 mmol/L FFA 作用24 h后,未见细胞形态学及GSIS 明显变化,细胞内GK和GLUT2 mRNA及其蛋白的表达水平与空白对照组（GK对照组0.80±0.12,GLUT2对照组0.72±0.11）比较亦未发生明显改变（均P〉0.05）;（2）0.50～1.00 mmol/L FFA 作用24 h之后,βTc6细胞内可见脂滴积聚,细胞团有崩解的趋势,随着浓度的增大,上述现象愈加明显.细胞GK（GKFFA0.500.32±0.05,GKFFA1.000.24±0.03）和GLUT2 （GLUT2FFA0.500.28±0.04,GLUT2FFA1.000.21±0.03）mRNA表达逐渐减低（均P〈0.05）,相应的蛋白表达水平亦逐步降低,胰岛素分泌也逐渐减少（均P〈0.05）.结论 低浓度FFA对胰岛β细胞生存和GK、GLUT2表达以及GSIS没有明显影响,但较高浓度的FFA将损害β细胞,并抑制GK和GLUT2表达以及GSIS.     

Insulin secretion is stimulated by ethanol extract of Anemarrhena asphodeloides in isolated islet of healthy Wistar and diabetic Goto-Kakizaki Rats.

BACKGROUND: The hypoglycemic effect of extract of Anemarrhena asphodeloides has been accounted for by the substance mangiferin which increases insulin sensitivity. The present study aimed to investigate whether an ethanol extract of Anemarrhena asphodeloides would stimulate insulin secretion and if so, further elucidate the mechanism behind this effect. METHODS: Isolated pancreatic islets of normal Wistar rats and spontaneously diabetic Goto-Kakizaki (GK) rats were batch incubated or perifused to study effect of Anemarrhena asphodeloides extract (TH2) on insulin release. RESULTS: At 3.3 mM glucose, 2, 4, and 8 mg/ml TH2 increased the insulin release of Wistar rat islets 2.5-, 4.1-, and 5.7-fold, respectively (p < 0.05) and of GK rat islets 1.7-, 3.0-, and 6.3-fold, respectively (p < 0.01). Similarly at 16.7 mM glucose, 2, 4 and 8 mg/ml TH2 increased insulin release of Wistar rat islets 1.5-, 2.2-, and 3.8-fold, respectively (p < 0.05) and of GK rat 2.5-, 4.2-, and 11.9-fold, respectively (p < 0.01). In perifusions of islets, TH2 also increased insulin secretion that returned to basal levels when TH2 was omitted from the perifusate. Mangiferin had no effect on insulin secretion of islets. In islets depolarized by 30 mM KCl and B-cell K-ATP channels kept open by 0.25 mM diazoxide, TH2 (8 mg/ml) further enhanced insulin secretion at 3.3 but not at 16.7 mM glucose. Pertussis toxin suppressed the insulin stimulating effect of 2 and 8 mg/ml TH2 by 35 % and 47 % (p < 0.05 and p < 0.001, respectively). CONCLUSIONS: Ethanol extract of the roots of Anemarrhena asphodeloides contains a substance, TH2, that stimulates insulin secretion both at 3.3 and 16.7 mM glucose in islets of normal Wistar and diabetic GK rats. The mechanism behind TH2-stimulated insulin secretion involves an effect on the exocytotic machinery of the B-cell, mediated via pertussis toxin-sensitive Gi- (or Ge-) proteins.     

Glucose and insulin regulate glycosylphosphatidylinositol-specific phospholipase D expression in islet [beta ] cells

Insulin resistance is associated with a compensatory islet hyperactivity to sustain adequate insulin biosynthesis and secretion to maintain near euglycemia. Both glucose and insulin are involved in regulating proteins required for insulin synthesis and secretion within the islet and islet hypertrophy. We have determined that glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) is present within the secretory granules of islet beta cells. To determine if GPI-PLD is regulated in islet beta cells, we examined the effect of glucose and insulin on GPI-PLD expression in rat islets and murine insulinoma cell lines. Glucose (16.7 mmol/L) increased cellular GPI-PLD activity and mRNA levels 2- to 7-fold in isolated rat islets and betaTC3 and betaTC6-F7 cells. Insulin (10(-7) mol/L) also increased GPI-PLD mRNA levels in rat islets and betaTC6-F7 cells 2- to 4-fold commensurate with an increase in GPI-PLD biosynthesis. To determine if islet GPI-PLD expression is increased in vivo under conditions of islet hyperactivity, we compared GPI-PLD mRNA levels in islets and liver from ob/ob mice and their lean littermates. Islet GPI-PLD mRNA was increased 5-fold while liver mRNA and serum GPI-PLD levels were reduced 30% in ob/ob mice compared with lean littermate controls. These results suggest that glucose and insulin regulate GPI-PLD mRNA levels in isolated islets and beta-cell lines. These regulators may also account for the increased expression of GPI-PLD mRNA in islets from ob/ob mice, a model of insulin resistance and islet hyperactivity.     

小檗碱对大鼠心室肌细胞短暂外向钾电流的影响

目的研究小檗碱对大鼠心室肌细胞膜短暂外向钾电流(Ito)的影响,探讨小檗碱在离子通道水平的药理作用机制。方法用急性酶解法分离大鼠心室肌细胞,应用膜片钳全细胞记录技术,观察不同浓度的小檗碱对Ito的影响。结果小檗碱(1,3,10,30,100,300μmol/L)可浓度依赖性地降低Ito,半数抑制浓度(IC50)为40.21μmol/L,30μmol/L小檗碱可使Ito电流-电压曲线下移,但不改变曲线形状。小檗碱使Ito失活曲线向负电位方向变化,半数失活电压减小;对激活曲线无明显影响,未改变Ito激活特性。结论小檗碱可浓度依赖性地阻滞大鼠心室肌细胞的Ito。     

β细胞素对体外培养大鼠胰岛的影响

研究β细胞素(BTC)对体外培养大鼠胰岛的作用。BTC无促胰岛急性分泌作用,但对长期培养大鼠胰岛的葡萄糖刺激的胰岛素分泌(GSIS)具有一定保护效力;实时PCR及免疫荧光检测胰高血糖素、胰岛素、PDX-1、葡萄糖转运子2的表达未随培养时间延长而丰度下降,BTC可能不是通过调节上述基因的表达来维护胰岛GSIS功能的。