Curcumin inhibits glucose production in isolated mice hepatocytes

Curcumin is a compound derived from the spice turmeric, and is a potent anti-oxidant, anti-carcinogenic, and anti-hepatotoxic agent. We have investigated the acute effects of curcumin on hepatic glucose production. Gluconeogenesis and glycogenolysis in isolated hepatocytes, and gluconeogenetic enzyme activity after 120 min exposure to curcumin were measured. Hepatic gluconeogenesis from 1 mM pyruvate was inhibited in a concentration-dependent manner, with a maximal decrease of 45% at the concentration of 25 microM. After 120 min exposure to 25 microM curcumin, hepatic gluconeogenesis from 2mM dihydroxyacetone phosphate and hepatic glycogenolysis were inhibited by 35% and 20%, respectively. Insulin also inhibited hepatic gluconeogenesis from 1mM pyruvate and inhibited hepatic glycogenolysis in a concentration-dependent manner. Curcumin (25 microM) showed an additive inhibitory effect with insulin on both hepatic gluconeogenesis and glycogenolysis, indicating that curcumin inhibits hepatic glucose production in an insulin-independent manner. After 120 min exposure to 25 microM curcumin, hepatic glucose-6-phosphatase (G6Pase) activity and phosphoenolpyruvate carboxykinase (PEPCK) activity both were inhibited by 30%, but fructose-1,6-bisphosphatase (FBPase) was not reduced. After 120 min exposure to 25 microM curcumin, phosphorylation of AMP kinase alpha-Thr(172) was increased. Thus, the anti-diabetic effects of curcumin are partly due to a reduction in hepatic glucose production caused by activation of AMP kinase and inhibition of G6Pase activity and PEPCK activity.     

Irisin对2型糖尿病小鼠血糖的影响及机制

目的:研究Irisin对2型糖尿病(type 2 diabetes mellitus,T2DM)小鼠血糖的影响及机制。方法:采用喂养高脂饮食结合腹腔注射小剂量的链脲佐菌素(STZ)建立T2DM小鼠模型。Western blot检测Irisin经腹腔注射后的血浆水平。血糖仪检测T2DM小鼠经腹腔注射Irisin后30、60、90、120、150、180和210 min的血糖水平。Western blot检测注射Irisin后肝脏组织中葡萄糖-6-磷酸酶(G6pase)和磷酸烯醇式丙酮酸羧化酶(PEPCK)的表达。结果:1与正常饮食(ND)组相比,高脂饮食(HD)组小鼠在第6周时血糖糖水平明显增加(P0.05),且葡萄糖耐量降低,说明T2DM小鼠造模成功。2与对照(Control)组相比,Control+Irisin组血浆中的Irisin蛋白水平明显升高(P0.05)。3与T2DM+Vehicle(生理盐水)组相比,T2DM+Irisin组血糖于30 min时开始降低,60 min时出现显著差异(P0.05),到120 min时下降到最低点,以后逐渐升高。4与Control组相比,T2DM组G6pase和PEPCK的水平升高(P0.05),经外源给予Irisin后,G6pase和PEPCK的水平下降(P0.01)。结论:Irisin对T2DM小鼠具有降低血糖的作用,这可能与降低T2DM小鼠肝脏糖异生有关。     

Comparison between starvation and consumption of a high protein diet: plasma insulin and glucagon and hepatic activities of gluconeogenic enzymes during the first 24 hours

Plasma insulin, glucagon, glucose, free fatty acids and glycerol, hepatic cyclic AMP and glycogen, and liver phosphoenolpyruvate carboxykinase (PEPCK), fructose 1,6-bisphosphatase (FBPase), glucose 6-phosphatase (G6Pase) and alanine amino transferase (AAT) activities were examined in adult rats during the first 24 h of either starvation or consumption of a high protein, carbohydrate-free (HP) diet. Under both nutritional conditions, plasma insulin fell within 12 h and remained constant thereafter. Glucagon increased 12 h after the start of the experiment and peaked between 18-24 h. The insulin: glucagon ratio was lower during the last 12 h of the experiment. In both experimental groups, liver cyclic AMP increased progressively and peaked between 15-24 h, but it increase was higher on HP diet than on starvation. Whereas plasma glucose remained low on starvation for 24 h, it returned to normal on consumption of the HP diet. In both groups, liver glycogen fell within 12 h and remained low until the end of experiment. FBPase, G6Pase and AAT did not change on starvation, while they increased toward the end of 1 d HP consumption. During starvation or consumption of the HP diet, PEPCK increased progressively and peaked between 15-24 h, but the increase was greater with the HP diet than with starvation. These findings suggest that in the first 24 hours, the adaptative response of hepatic gluconeogenesis is higher with a HP diet than upon starvation.     

Effects of resistin expression on glucose metabolism and hepatic insulin resistance

In order to observe the effect of increased serum resistin on glucose metabolism, insulin sensitivity, and hepatic insulin resistance (IR), mice were intravenously injected with recombinant adenovirus carrying the resistin gene (Adv-resistin-EGFP). Changes in hepatic glucose metabolism were observed using the Periodic Acid-Schiff method. Hepatic AMP-activated protein kinase (AMPK) activation was assessed by Western blot analysis, and glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) mRNA expression was determined using real-time RT-PCR. Although no effect on fasting blood glucose was detected, increased fasting insulin levels, decreased glucose tolerance and insulin sensitivity, and reduced hepatic glycogen levels and AMPK activation were seen in the Adv-resistin-EGFP mice. Finally, elevated G6Pase and PEPCK mRNA expression levels were detected upon overexpression of resistin. Resistin may inhibit hepatic AMPK activity, which results in elevated expression of gluconeogenic enzymes thereby affecting glucose metabolism and leading to decreased glycogen storage that contributes to the development of hepatic IR.     

Direct regulation of glucose and not insulin on hepatic hexose-6-phosphate dehydrogenase and 11β-hydroxysteroid dehydrogenase type 1

Abnormal hepatic gluconeogenesis contributes significantly to both fasting and non-fasting hyperglycemia of patients with type 2 diabetes. 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) regulates the key hepatic gluconeogenic enzymes including phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) through the amplification of glucocorticoid receptor (GR) - mediated tissue glucocorticoid action, and is crucially dependent on hexose-6-phosphate dehydrogenase (H6PDH) - generating NADPH system. Here, we observed that compared with fasting state, H6PDH and 11β-HSD1 expression in livers were all increased under non-fasting state in both normal and diabetic rats, and the non-fasting diabetic group was the highest among the four experimental groups. Moreover, incubation of primary hepatocytes with increasing glucose caused dose-dependent increases in H6PDH, 11β-HSD1, GR, PEPCK and G6Pase expression. Also, glucose-6-phosphate (G6P) had a positive regulation on H6PDH and 11β-HSD1 in hepatocytes. In addition, primary hepatocytes treated with different doses of insulin in high glucose induced alteration of H6PDH and 11β-HSD1 while in low glucose there was no significant effect. These findings suggest that glucose instead of insulin directly regulates H6PDH and 11β-HSD1 and suppression of the two enzymes could be considered as an effective target for the treatment of type 2 diabetes.     

Increased hepatic peroxisome proliferator-activated receptor-gamma coactivator-1 gene expression in a rat model of intrauterine growth retardation and subsequent insulin resistance

Uteroplacental insufficiency and subsequent intrauterine growth retardation (IUGR) increase the risk of type 2 diabetes in humans and rats. Unsuppressed endogenous hepatic glucose production is a common component of the insulin resistance associated with type 2 diabetes. Peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC-1) mediates hepatic glucose production by controlling mRNA levels of glucose-6-phosphatase (G-6-Pase), phosphoenolpyruvate carboxykinase (PEPCK), and fructose-1,6-bisphosphatase (FBPase). We therefore hypothesized that gene expression of PGC-1 would be increased in juvenile IUGR rat livers, and this increase would directly correlate with hepatic mRNA levels of PEPCK, G-6-Pase, and FBPase, but not glucokinase. We found that IUGR hepatic PGC-1 protein levels were increased to 230 +/- 32% and 310 +/- 47% of control values at d 0 and d 21 of life, respectively. Similarly, IUGR hepatic PGC-1 mRNA levels were significantly elevated at both ages. Concurrent with the increased PGC-1 gene expression, IUGR hepatic mRNA levels of G-6-Pase, PEPCK, and FBPase were also significantly increased, whereas glucokinase mRNA levels were significantly decreased. These data suggest that increased PGC-1 expression and subsequent hepatic glucose production contribute to the insulin resistance observed in the IUGR juvenile rat.     

Exenatide对肥胖大鼠肝脏糖异生基因表达的观察

目的 探讨Exenatide对肥胖大鼠肝脏糖异生基因表达的作用。方法将雄性SD大鼠随机分为高脂饮食（HF）组、高脂用药（HF＋Exe）组与正常对照（Nc）组。测定各组肝脏叉头蛋白转录因子O1（FoxO1）、磷酸烯醇式丙酮酸羧化酸（PEPCK）、葡萄糖-6-磷酸酶（G6Pase）mRNA,以及Fox01蛋白水平。结果HF组Fins、TG、FFA升高,Fox01、PEPCK、G6PasemRNA表达上调,Fox01蛋白水平增加（P〈0．05）;Exenatide用药8周后,HF＋Exe组Fins、TG、TC、FFA降低,Fox01、PEPCK、G6PasemRNA表达下调,FoxO1蛋白水平降低（P〈0．05）。结论Exenatide具有改善肥胖大鼠糖脂代谢的作用,其机制可能为抑制肝脏糖异生基因的表达。     

Relationship between hepatic/visceral fat and hepatic insulin resistance in nondiabetic and type 2 diabetic subjects

BACKGROUND AND AIMS: Abdominal fat accumulation (visceral/hepatic) has been associated with hepatic insulin resistance (IR) in obesity and type 2 diabetes (T2DM). We examined the relationship between visceral/hepatic fat accumulation and hepatic IR/accelerated gluconeogenesis (GNG). METHODS: In 14 normal glucose tolerant (NGT) (body mass index [BMI] = 25 +/- 1 kg/m(2)) and 43 T2DM (24 nonobese, BMI = 26 +/- 1; 19 obese, BMI = 32 +/- 1 kg/m(2)) subjects, we measured endogenous (hepatic) glucose production (3-(3)H-glucose) and GNG ((2)H(2)O) in the basal state and during 240 pmol/m(2)/min euglycemic-hyperinsulinemic clamp, and liver (LF) subcutaneous (SAT)/visceral (VAT) fat content by magnetic resonance spectroscopy/magnetic resonance imaging. RESULTS: LF was increased in lean T2DM compared with lean NGT (18% +/- 3% vs 9% +/- 2%, P < .03), but was similar in lean T2DM and obese T2DM (18% +/- 3% vs 22% +/- 3%; P = NS). Both VAT and SAT increased progressively from lean NGT to lean T2DM to obese T2DM. T2DM had increased basal endogenous glucose production (EGP) (NGT, 15.1 +/- 0.5; lean T2DM, 16.3 +/- 0.4; obese T2DM, 17.2 +/- 0.6 micromol/min/kg(ffm); P = .02) and basal GNG flux (NGT, 8.6 +/- 0.4; lean T2DM, 9.6 +/- 0.4; obese T2DM, 11.1 +/- 0.6 micromol/min/kg(ffm); P = .02). Basal hepatic IR index (EGP x fasting plasma insulin) was increased in T2DM (NGT, 816 +/- 54; lean T2DM, 1252 +/- 164; obese T2DM, 1810 +/- 210; P = .007). In T2DM, after accounting for age, sex, and BMI, both LF and VAT, but not SAT, were correlated significantly (P < .05) with basal hepatic IR and residual EGP during insulin clamp. Basal percentage of GNG and GNG flux were correlated positively with VAT (P < .05), but not with LF. LF, but not VAT, was correlated with fasting insulin, insulin-stimulated glucose disposal, and impaired FFA suppression by insulin (all P < .05). CONCLUSIONS: Abdominal adiposity significantly affects both lipid (FFA) and glucose metabolism. Excess VAT primarily increases GNG flux. Both VAT and LF are associated with hepatic IR.     

Role of hepatic AMPK activation in glucose metabolism and dexamethasone-induced regulation of AMPK expression

To elucidate the role of AMPK in hepatic glucose metabolism, dominant negative (DN), constitutively active (CA) forms of the AMPKalpha1 subunit and control vector LacZ were overexpressed by means of adenovirus-mediated gene transfer. Five days after virus injection, hepatic AMPK activity was five-fold higher in CA mice than in DN mice. DN mice were apparently glucose intolerant with a higher fasting plasma glucose level (DN 82.3+/-0.7mg/dl, CA 42.5+/-4.8mg/dl and LacZ 54.3+/-2.4mg/dl). PEPCK, a gluconeogenic key enzyme, mRNA was increased 131.54% and 48.92% in DN mice compared to that of CA and LacZ, respectively. Thus, hepatic AMPK activation plays a role in the suppression of gluconeogenesis and this might be the cause of decreased fasting plasma glucose level in CA mice. We also investigated the effects of dexamethasone on hepatic AMPK expression and activity in rat liver, mice liver, as well as primary cultured hepatocytes. Subcutaneously injecting mice with dexamethasone (1mg/day) for 5 days significantly upregulated hepatic AMPKalpha1 and alpha2 expressions. Similarly, the treatment of primary cultured rat hepatocytes with dexamethasone (1microM) increased expression of the AMPKalpha1 subunit, AICAR-induced AMPK phosphorylation and kinase activity. Although increased AMPK expression cannot be attributed to dexamethasone-induced glucose intolerance, taken together our results raise the possibility that AMPK control liver glucose output and its expression in liver might be modulated by various hormones and growth factors.     

Dehydroepiandrosterone suppresses elevated hepatic glucose-6-phosphatase mRNA level in C57BL/KsJ-db/db mice: comparison with troglitazone

Dehydroepiandrosterone (DHEA) is known to improve hyperglycemia of diabetic C57BL/KsJ-db/db mice that are obese and insulin resistant. In a previous study, we reported that DHEA as well as troglitazone suppresses the elevated hepatic gluconeogenic enzymes, glucose-6-phosphatase (G6Pase) and fructose-1,6-bisphosphatase (FBPase) activities in C57BL/KsJ-db/db mice. In the present study, we evaluated the changes in mRNA of G6Pase and FBPase in db/db mice. Despite hyperinsulinemia, the G6Pase mRNA level of db/db mice was elevated as compared to their heterozygote littermate db/+m mice. In contrast, the FBPase mRNA level was not elevated in db/db mice. Administration of DHEA for two weeks significantly decreased the blood glucose level and the elevated G6Pase mRNA level in db/db mice. No significant changes were seen in the FBPase mRNA level after the administration of DHEA. Administration of troglitazone also decreased the blood glucose and G6Pase mRNA level in db/db mice although no changes were seen in the FBPase mRNA level. These results suggest that the elevation of G6Pase mRNA is important in elucidating the cause of insulin resistance, and that the G6Pase gene is at least one target for the hypoglycemic effects of DHEA as an insulin sensitizing agent in db/db mice.     

Effects of maternal dietary manipulation during different periods of pregnancy on hepatic glucogenic capacity in fetal and pregnant rats near term

Background and aim: Low birth weight is associated with an increased incidence of adult glucose intolerance, type 2 diabetes and cardiovascular disease in humans. In pregnant rats, dietary calorie or protein deprivation results in growth retarded pups, which become glucose intolerant adults with abnormal hepatic glucose metabolism and gluconeogenic enzyme activities. However, whether these abnormalities are present before birth remain unknown.Methods and results: This study examined the effects of manipulating dietary protein and carbohydrate intake during rat pregnancy on the fetal and maternal hepatic activities of the gluconeogenic enzymes, glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK). Wistar rats were fed ad libitum with either standard chow throughout pregnancy (25% protein, 57% carbohydrate, n = 6) or an isocaloric, low protein, high carbohydrate diet (LPHC, 8% protein, 81% carbohydrate) for different periods of pregnancy (early, 0–10 days, n = 6; late, 10–20 days, n = 7; throughout, 0–20 days, n = 6) before tissue collection at day 20. The LPHC diet had no effect on fetal or placental weights, or on fetal hepatic activities of G6Pase and PEPCK in the early LPHC group. In contrast, fetuses of dams fed the LPHC diet in late or throughout pregnancy had lower body and placental weights, and higher hepatic G6Pase and PEPCK activities than controls. Maternal hepatic G6Pase activity was elevated in all LPHC groups, while maternal PEPCK activity was only increased significantly in the late LPHC group.Conclusions: Feeding a LPHC diet, particularly during late pregnancy, therefore, up-regulates fetal and maternal hepatic glucogenic capacity.     

Transgenic mice overexpressing phosphoenolpyruvate carboxykinase develop non-insulin-dependent diabetes mellitus.

An increase in hepatic gluconeogenesis is believed to be an important factor responsible for the fasting hyperglycemia detected in patients with non-insulin-dependent diabetes mellitus (NIDDM). Phosphoenolpyruvate carboxykinase (GTP) (PEPCK; EC 4.1.1.32) is a regulatory enzyme of gluconeogenesis. To study the role of the expression of PEPCK gene in the development of NIDDM, we have produced lines of transgenic mice expressing a PEPCK minigene under control of its own promoter. Transgenic mice were hyperglycemic and had higher serum insulin concentrations. In addition, alterations in liver glycogen content and muscle glucose transporter GLUT-4 gene expression were detected. The overexpression of the PEPCK gene led to an increase in glucose production from pyruvate in hepatocytes in primary culture. When intraperitoneal glucose tolerance tests were performed, blood glucose levels were higher than those detected in normal mice. This animal model shows that primary alterations in the rate of liver glucose production may induce insulin resistance and NIDDM.     

肝脏胰岛素抵抗与肝糖输出调控基因表达的关系

目的观察高脂饮食饲养造成的肝脏胰岛素抵抗与肝糖输出有关的调控基因表达的关系。方法将8周龄雄性SD大鼠随机分为2组:正常饲养组(10例)和高脂饮食饲养组(10例)。饲养期间动态观察体重和空腹血糖变化趋势。饲养至28周实验终点时取空腹血测胰岛素和甘油三酯。采用肝脏对3H-2- 脱氧葡萄糖的摄取能力测定各组的肝脏胰岛素敏感性,用蒽酮法测定肝糖原含量,并用逆转录聚合酶链反应法分析糖异生和糖原合成关键酶肝脏磷酸烯丙醇羧激酶、葡萄糖-6-磷酸酶、糖原合成酶和PPAR γ协同刺激因子1 α的mRNA表达的变化。结果高脂饮食饲养大鼠出现明显腹型肥胖。血浆甘油三酯水平升高。饲养18周开始,高脂饮食组空腹血糖增加[正常饲养组(4．77±0．63)mmol／L,高脂饮食组[(5．45± 0.87)mmol／L,P<0．05],此差异持续到28周;肝脏3H-2-脱氧葡萄糖摄取率高脂饮食组较正常饲养组下降42．0％,肝糖原含量增加92．4％(P<0．01)l磷酸烯丙醇羧激酶mRNA增加41．5％,协同刺激因子1α mRNA增加30．8％(P<0．05)。结论长期高脂饮食诱导肝脏协同刺激因子1α和肝脏磷酸烯丙醇羧激酶基因表达,糖异生增加,同时肝糖分解不能相应受到抑制,导致肝糖输出增加及空腹血糖升高。     

Chronic suppression of insulin by diazoxide alters the activities of key enzymes regulating hepatic gluconeogenesis in Zucker rats

OBJECTIVES: Chronic attenuation of hyperinsulinemia by diazoxide (DZ), an inhibitor of glucose-mediated insulin secretion, improved insulin sensitivity and glucose tolerance and caused down-regulation of lipid metabolizing enzymes in adipose tissue and decreased the rate of weight gain in mildly hyperglycemic obese Zucker rats. Since the liver plays a central role in glucose homeostasis, we studied the effect of chronic insulin suppression on key insulin-sensitive enzymes regulating hepatic gluconeogenesis. METHODS: DZ (150 mg/kg per day) or vehicle (control) was administered to 7-week-old female obese and lean Zucker rats for a period of 4 weeks. RESULTS: DZ-treated animals showed lower fasting plasma insulin levels (P<0.001) than their controls. Plasma glucose levels were lower in DZ obese rats than in controls (P<0.001), without a significant change in DZ lean animals. DZ had no effect on glucose transporter 2 protein expression in either strain. DZ treatment resulted in lower hepatic glucokinase (P<0.001) and glucose-6-phosphatase (P<0.0001) and phosphoenolpyruvate carboxykinase (PEPCK) activities only in obese rats compared with controls (P<0.001). However, DZ-treated lean rats demonstrated higher PEPCK activity than controls (P<0.002). DZ-treated animals demonstrated enhanced hepatic glucose-6-phosphate content (P<0.01), glycogen synthase activity (P<0.0001) and glycogen content (P<0.02) compared with their controls despite increased hepatic glycogen phosphorylase a activity in these animals (P<0.02). CONCLUSIONS: Chronic suppression of hyperinsulinemia in obese Zucker rats by DZ decreased the activities of key enzymes regulating hepatic gluconeogenesis, implying that attenuation of the hyperinsulinemic state by DZ may be therapeutically beneficial.     

Hepatic glucose metabolism in humans--its role in health and disease

The liver is mainly responsible for maintaining normal concentrations of blood glucose by its ability to store glucose as glycogen and to produce glucose from glycogen breakdown or gluconeogenic precursors. During the last decade, new techniques have made it possible to gain further insight into the turnover of hepatic glucose and glycogen in humans. Hepatic glycogen varies from approximately 200 to approximately 450 mM between overnight fasted and postprandial conditions. Patients with type-1 diabetes (T1DM), type 2 diabetes (T2DM) or partial agenesis of the pancreas exhibit increased endogenous glucose production and synthesize only 25-45% of hepatic glycogen compared with non-diabetic humans. This defect can be partly restored in T1DM by combined long- and short-term optimized treatment with insulin. In T2DM, increased gluconeogenesis was identified as the main cause of elevated glucose production and fasting hyperglycaemia. These patients also exhibit augmented intracellular lipid accumulation which could hint at a link between deranged glucose and lipid metabolism in insulin-resistant states.     

抵抗素与肝脏胰岛素抵抗的关系

抵抗素是一种脂肪细胞因子,研究发现高抵抗素水平可诱导肝脏胰岛素抵抗发生,其机制可能是抑制腺苷酸活化蛋白激酶(AMPK)磷酸化,上调糖异生关键酶PEPCK和G6Pase的表达促进糖异生,从而使肝糖输出增多。肝脏是胰岛素作用的重要靶点,也是机体代谢的关键器官。肝脏胰岛素抵抗时,糖脂代谢紊乱加重机体胰岛素抵抗,促进2型糖尿病的发生。AMPK是物质代谢的关键激酶,通过磷酸化作用调节糖脂代谢相关酶的活性以及调节机体的能量平衡。抵抗素通过AMPK调节肝糖代谢这一观点为探讨抵抗素在胰岛素抵抗中的作用提供了新的思路。     

核糖体蛋白S6激酶1基因沉默对小鼠肝脏胰岛素抵抗的影响

目的 探讨核糖体蛋白S6激酶1基因沉默对db/db小鼠肝脏胰岛素抵抗的影响及机制.方法 采用随机数字表法将24只9周龄健康雄性db/db小鼠(体质量44.5～48.2 g)随机分至对照组(n1=12)和实验组(n=12),实验组小鼠尾静脉注射核糖体蛋白S6激酶1短发夹RNA重组基因腺病毒,对照组尾静脉注射含U6启动子空...