AMPK作为治疗2型糖尿病新靶点的研究进展

2型糖尿病以葡萄糖和脂类的异常代谢为特征,部分归因于周缘组织的胰岛素抵抗。腺苷酸活化蛋白激酶(AMPK)是一种异源三聚体蛋白,由α、β和γ3个亚单位组成。AMPK在调节肌体能量代谢的平衡方面起总开关作用。在肌肉和肝脏中,AMPK的活化增强了葡萄糖的摄取、脂肪酸氧化作用和胰岛素敏感性,并且减少了葡萄糖、胆固醇和甘油三酯的产生。有研究表明,治疗2型糖尿病的一线药物二甲双胍和罗格列酮对机体代谢的影响部分通过AMPK途径。因此,AMPK及其信号通路有望成为治疗肥胖和2型糖尿病的新药理学靶点。     

Friendly, and not so friendly, roles of Rac1 in islet β-cell function: lessons learnt from pharmacological and molecular biological approaches

Glucose-stimulated insulin secretion [GSIS] involves a sequence of metabolic events leading to small G-protein [e.g., Rac1]-mediated cytoskeletal remodeling to promote granule mobilization toward the plasma membrane for fusion and release of insulin. Existing evidence supports a positive modulatory role for Rac1 in GSIS. Specific regulatory factors of Rac1 function, including the guanine nucleotide exchange factors [e.g., Tiam1] have also been identified and studied in the islet. Inhibition of Tiam1/Rac1 signaling axis attenuates GSIS suggesting its pivotal role in insulin secretion. In addition to its positive [i.e., friendly] roles in GSIS, Rac1 also plays “non-friendly” role[s] in the islet function. For example, it up-regulates the intracellular reactive oxygen species [ROS] levels via activation of phagocyte-like NADPH oxidase [Nox]. Despite the emerging evidence that a tonic increase in intracellular ROS is necessary for GSIS, experimental evidence also suggests that chronic exposure of β-cells to high glucose, palmitate or cytokines results in the onset of oxidative stress leading to reduction in mitochondrial membrane potential, cytosolic accumulation of cytochrome C and activation of caspase-3 leading to β-cell apoptosis. Pharmacological and molecular biological inhibition of Rac1 activation affords partial protection against Nox-induced oxidative stress and mitochondrial dysfunction induced by elevated glucose, lipids or cytokines. Herein, we overview the existing evidence to suggest positive as well as negative modulatory roles of Rac1 in islet function. Potential avenues for future research including development of inhibitors to halt the Rac1–Nox activation and generation of oxidative stress leading to the metabolic dysfunction of the β-cell are discussed.     

糖尿病患者血尿酸与胰岛素抵抗的相关性

目的探讨糖尿病患者血尿酸(UA)与胰岛素抵抗的关系。方法测定141例2型糖尿病患者空腹胰岛素(FINS)、空腹血糖(FBG)、血UA、甘油三酯(TG)。采用稳态模式(HOMA)评价胰岛素抵抗,并根据胰岛素抵抗指数(HOMA-IR)中位数(2．294),将糖尿病患者分为胰岛素敏感组和胰岛素抵抗组,比较血UA、TG水平的变化。结果胰岛素抵抗组与胰岛素敏感组比较,血UA水平无显著性差异(t=0．056, P＞0．05):糖尿病合并高尿酸血症组与正常血UA组间HOMA-IR无显著性差异(t=0．320,P＞0．05)。相关分析结果,血UA与HOMA-IR无相关性(r=0．0237,P＞0．05),TG与HOMA-IR呈明显正相关(r=0．1931,P＜0．05)。结论糖尿病患者血UA与胰岛素抵抗似无明显相关性。     

Reactive oxygen species and insulin resistance: the good, the bad and the ugly

Reactive oxygen species (ROS) contribute to the progression of various human diseases, including type 2 diabetes mellitus (T2DM). ROS can suppress the insulin response and contribute to the development of insulin resistance, a key pathological feature of T2DM. Paradoxically, ROS generated by NADP(H) oxidases at the plasma membrane and endomembranes might also be required for normal intracellular signaling. Growth factors, cytokines and hormones such as insulin promote the generation of ROS for the coordinated inactivation of protein tyrosine phosphatases and the promotion of tyrosine phosphorylation-dependent signaling. A recent study has established the potential of H(2)O(2) to enhance insulin sensitivity in vivo and attenuate the development of insulin resistance. Thus, ROS have the capacity to both promote and attenuate the insulin response. Here I review evidence indicating that ROS promote insulin sensitivity versus insulin resistance and discuss the potential complications associated with the widespread use of antioxidants.     

Oleanolic acid supplement attenuates liquid fructose-induced adipose tissue insulin resistance through the insulin receptor substrate-1/phosphatidylinositol 3-kinase/Akt signaling pathway in rats

Oleanolic acid, a triterpenoid contained in more than 1620 plants including various fruits and foodstuffs, has numerous metabolic effects, such as hepatoprotection. However, its underlying mechanisms remain poorly understood. Adipose tissue insulin resistance (Adipo-IR) may contribute to the development and progress of metabolic abnormalities through release of excessive free fatty acids from adipose tissue. This study investigated the effect of oleanolic acid on Adipo-IR. The results showed that supplement with oleanolic acid (25 mg/kg, once daily, by oral gavage) over 10 weeks attenuated liquid fructose-induced increase in plasma insulin concentration and the homeostasis model assessment of insulin resistance (HOMA-IR) index in rats. Simultaneously, oleanolic acid reversed the increase in the Adipo-IR index and plasma non-esterified fatty acid concentrations during the oral glucose tolerance test assessment. In white adipose tissue, oleanolic acid enhanced mRNA expression of the genes encoding insulin receptor, insulin receptor substrate (IRS)-1 and phosphatidylinositol 3-kinase. At the protein level, oleanolic acid upregulated total IRS-1 expression, suppressed the increased phosphorylated IRS-1 at serine-307, and restored the increased phosphorylated IRS-1 to total IRS-1 ratio. In contrast, phosphorylated Akt to total Akt ratio was increased. Furthermore, oleanolic acid reversed fructose-induced decrease in phosphorylated-Akt/Akt protein to plasma insulin concentration ratio. However, oleanolic acid did not affect IRS-2 mRNA expression. Therefore, these results suggest that oleanolic acid supplement ameliorates fructose-induced Adipo-IR in rats via the IRS-1/phosphatidylinositol 3-kinase/Akt pathway. Our findings may provide new insights into the mechanisms of metabolic actions of oleanolic acid.     

Peripheral insulin-sensitizer drug metformin ameliorates neuronal insulin resistance and Alzheimer's-like changes

Alzheimer’s disease (AD) is the most common neurodegenerative disease worldwide. Pharmacological treatments presently available can slow down the progression of symptoms but can not cure the disease. Currently there is widening recognition that AD is closely associated with impaired insulin signaling and glucose metabolism in brain, suggesting it to be a brain-specific form of diabetes and so also termed as “type 3 diabetes”. Hence investigating the role of pharmacological agents that could ameliorate neuronal insulin resistance merit attention in AD therapeutics, however the therapeutics for pathophysiological condition like neuronal insulin resistance itself is largely unknown. In the present study we have determined the effect of metformin on neuronal insulin resistance and AD-associated characteristics in an in vitro model of “type 3 diabetes” by differentiating neuronal cell line Neuro-2a under prolonged presence of insulin. We observed that prolonged hyperinsulinemic conditions in addition to generating insulin resistance also led to development of hallmark AD-associated neuropathological changes. Treatment with metformin sensitized the impaired insulin actions and also prevented appearance of molecular and pathological characteristics observed in AD. The results thus demonstrate possible therapeutic efficacy of peripheral insulin-sensitizer drug metformin in AD by its ability to sensitize neuronal insulin resistance. These findings also provide direct evidences linking hyperinsulinemia and AD and suggest a unique opportunity for prevention and treatment of “type 3 diabetes”.     

Coffee consumption and type 2 diabetes — An extensive review

Coffee is a complex mixture of potentially active chemicals. It contains significant amounts of phenolic polymers, chlorogenic acid and also caffeine. Agricultural factors, roasting, blending, and brewing determine coffee’s chemical composition. Recent epidemiological studies suggest that habitual coffee consumption may help to prevent some chronic diseases including type 2 diabetes. Despite reports from the clinical trials of the effect of caffeine on decreasing insulin sensitivity, long-term prospective studies revealed that coffee may improve fasting glucose, glucose tolerance and insulin sensitivity as well. In the most recent publication habitual coffee drinkers have a lower total and cardiovascular mortality rate among diabetic subjects.     

Prenatal origins of obesity and their complications: Gestational diabetes, maternal overweight and the paradoxical effects of fetal growth restriction and macrosomia

Pregestational (PGDM) and gestational (GDM) diabetes may be associated with a variety of fetal effects including increased rate of spontaneous abortions, intrauterine fetal death, congenital anomalies, neurodevelopmental problems and increased risk of perinatal complications. Additional problems of concern are fetal growth disturbances causing increased or decreased birth weight. Optimal control of maternal blood glucose is known to reduce these changes. Among the long lasting effects of these phenomena are a high rate of overweight and obesity at childhood and a high tendency to develop the “metabolic syndrome” characterized by hypertension, cardio-vascular complications and type 2 diabetes. Similarly, maternal overweight and obesity during pregnancy or excessive weight gain are also associated with increased obesity and complications in the offspring. Although there are different causes for fetal growth restriction (FGR) or for fetal excessive growth (macrosomis), paradoxically both are associated with the “metabolic syndrome” and its long term consequences.The exact mechanism(s) underlying these long term effects on growth are not fully elucidated, but they involve insulin resistance, fetal hyperleptinemia, hypothalamic changes and most probably epigenetic changes. Preventive measures to avoid the metabolic syndrome and its complications seem to be a tight dietary control and physical activity in the children born to obese or diabetic mothers or who had antenatal growth disturbances for other known or unknown reasons.     

葡萄糖负荷试验在急性冠脉综合征中的作用

目的研究葡萄糖负荷试验在急性冠脉综合征（ACS）中的作用。方法入选124例ACS患者,男性69例,女性55例,病情平稳后行75g葡萄糖负荷试验（OGTT）和胰岛素释放试验,根据负荷后2h血糖值分为血糖正常组、糖调节异常组、糖尿病组,分析糖负荷后2h血糖值和胰岛素抵抗的作用。结果（1）急性冠脉综合征患者中新诊断糖尿病患病率为16．9％,糖调节受损患病率为22．58％,总的糖代谢异常患病率为39．51％。（2）糖调节异常组和糖尿病组空腹胰岛素水平升高,与血糖正常组比较存在胰岛素抵抗（P〈0．01）。结论仅仅依靠检测空腹血糖,将漏诊ACS中的部分葡萄糖代谢异常患者;对ACS患者进行葡萄糖负荷试验是必要的;葡萄糖代谢异常者存在不同程度的胰岛素抵抗。     

胰高血糖素样肽-1对胰岛素抵抗3T3-L1脂肪细胞脂肪酸代谢的作用及机制

目的研究胰高血糖素样肽-1(GLP 1)对胰岛素抵抗3T3 L1脂肪细胞脂肪酸代谢的作用及机制。方法采用高糖高胰岛素造成胰岛素抵抗3T3 L1脂肪细胞模型,通过ELISA及Western blot等方法观察GLP 1对此模型脂肪酸代谢的影响及机制。结果 ELISA结果显示,GLP 1对胰岛素抵抗3T3 L1脂肪细胞中游离脂肪酸(FFA)的含量影响与胰岛素相关:在有胰岛素(100 nmol.L-1)存在时,GLP 1可增加上清液中FFA含量;而无胰岛素存在时,GLP 1可减少上清液中FFA含量。GLP 1升高细胞中脂肪酸合成酶(FAS)表达量的作用也必须依赖胰岛素的存在。Western blot结果显示在有胰岛素存在时,GLP 1可促进蛋白激酶B(PKB)磷酸化;而无胰岛素存在时则无此作用。PKB磷酸化的抑制剂LY294002或Wortmannin可阻断胰岛素存在时GLP 1对PKB磷酸化的促进作用及对上清液FFA含量的升高作用。另外,在有(无)胰岛素存在时,GLP 1均可降低激素敏感性脂肪酶(HSL)的蛋白表达量。结论 GLP 1可增强胰岛素抵抗3T3 L1脂肪细胞对胰岛素的敏感性并降低HSL的含量;胰岛素可影响GLP 1对胰岛素抵抗3T3 L1脂肪细胞脂肪酸代谢的调节作用。     

Increased bile acids in enterohepatic circulation by short-term calorie restriction in male mice

Previous studies showed glucose and insulin signaling can regulate bile acid (BA) metabolism during fasting or feeding. However, limited knowledge is available on the effect of calorie restriction (CR), a well-known anti-aging intervention, on BA homeostasis. To address this, the present study utilized a “dose–response” model of CR, where male C57BL/6 mice were fed 0, 15, 30, or 40% CR diets for one month, followed by BA profiling in various compartments of the enterohepatic circulation by UPLC-MS/MS technique. This study showed that 40% CR increased the BA pool size (162%) as well as total BAs in serum, gallbladder, and small intestinal contents. In addition, CR “dose-dependently” increased the concentrations of tauro-cholic acid (TCA) and many secondary BAs (produced by intestinal bacteria) in serum, such as tauro-deoxycholic acid (TDCA), DCA, lithocholic acid, ω-muricholic acid (ωMCA), and hyodeoxycholic acid. Notably, 40% CR increased TDCA by over 1000% (serum, liver, and gallbladder). Interestingly, 40% CR increased the proportion of 12α-hydroxylated BAs (CA and DCA), which correlated with improved glucose tolerance and lipid parameters. The CR-induced increase in BAs correlated with increased expression of BA-synthetic (Cyp7a1) and conjugating enzymes (BAL), and the ileal BA-binding protein (Ibabp). These results suggest that CR increases BAs in male mice possibly through orchestrated increases in BA synthesis and conjugation in liver as well as intracellular transport in ileum.     

Role of human pregnane X receptor in high fat diet-induced obesity in pre-menopausal female mice

Obesity is a complex metabolic disorder that is more prevalent among women. Until now, the only relevant rodent models of diet-induced obesity were via the use of ovariectomized (“postmenopausal”) females. However, recent reports suggest that the xenobiotic nuclear receptor pregnane X receptor (PXR) may contribute to obesity. Therefore, we compared the roles of mouse and human PXRs in diet-induced obesity between wild type (WT) and PXR-humanized (hPXR) transgenic female mice fed either control or high-fat diets (HFD) for 16 weeks. HFD-fed hPXR mice gained weight more rapidly than controls, exhibited hyperinsulinemia, and impaired glucose tolerance. Fundamental differences were observed between control-fed hPXR and WT females: hPXR mice possessed reduced estrogen receptor α (ERα) but enhanced uncoupling protein 1 (UCP1) protein expression in white adipose tissue (WAT); increased protein expression of the hepatic cytochrome P450 3A11 (CYP3A11) and key gluconeogenic enzymes phosphoenolpyruvate carboxykinase and glucose 6-phosphatase, and increased total cholesterol. Interestingly, HFD ingestion induced both UCP1 and glucokinase protein expression in WT mice, but inhibited these enzymes in hPXR females. Unlike WT mice, CYP3A11 protein, serum 17β-estradiol levels, and WAT ERα expression were unaffected by HFD in hPXR females. Together, these studies indicate that the hPXR gene promotes obesity and metabolic syndrome by dysregulating lipid and glucose homeostasis while inhibiting UCP1 expression. Furthermore, our studies indicate that the human PXR suppresses the protective role of estrogen in metabolic disorders. Finally, these data identify PXR-humanized mice as a promising in vivo research model for studying obesity and diabetes in women.     

Nrf2 deficiency improves glucose tolerance in mice fed a high-fat diet

Nrf2, a master regulator of intracellular redox homeostasis, is indicated to participate in fatty acid metabolism in liver. However, its role in diet-induced obesity remains controversial. In the current study, genetically engineered Nrf2-null, wild-type (WT), and Nrf2-activated, Keap1-knockdown (K1-KD) mice were fed either a control or a high-fat Western diet (HFD) for 12 weeks. The results indicate that the absence or enhancement of Nrf2 activity did not prevent diet-induced obesity, had limited effects on lipid metabolism, but affected blood glucose homeostasis. Whereas the Nrf2-null mice were resistant to HFD-induced glucose intolerance, the Nrf2-activated K1-KD mice exhibited prolonged elevation of circulating glucose during a glucose tolerance test even on the control diet. Feeding a HFD did not activate the Nrf2 signaling pathway in mouse livers. Fibroblast growth factor 21 (Fgf21) is a liver-derived anti-diabetic hormone that exerts glucose- and lipid-lowering effects. Fgf21 mRNA and protein were both elevated in livers of Nrf2-null mice, and Fgf21 protein was lower in K1-KD mice than WT mice. The inverse correlation between Nrf2 activity and hepatic expression of Fgf21 might explain the improved glucose tolerance in Nrf2-null mice. Furthermore, a more oxidative cellular environment in Nrf2-null mice could affect insulin signaling in liver. For example, mRNA of insulin-like growth factor binding protein 1, a gene repressed by insulin in hepatocytes, was markedly elevated in livers of Nrf2-null mice. In conclusion, genetic alteration of Nrf2 does not prevent diet-induced obesity in mice, but deficiency of Nrf2 improves glucose homeostasis, possibly through its effects on Fgf21 and/or insulin signaling.     

ROS signaling, oxidative stress and Nrf2 in pancreatic beta-cell function

This review focuses on the emerging evidence that reactive oxygen species (ROS) derived from glucose metabolism, such as H₂O₂, act as metabolic signaling molecules for glucose-stimulated insulin secretion (GSIS) in pancreatic beta-cells. Particular emphasis is placed on the potential inhibitory role of endogenous antioxidants, which rise in response to oxidative stress, in glucose-triggered ROS and GSIS. We propose that cellular adaptive response to oxidative stress challenge, such as nuclear factor E2-related factor 2 (Nrf2)-mediated antioxidant induction, plays paradoxical roles in pancreatic beta-cell function. On the one hand, induction of antioxidant enzymes protects beta-cells from oxidative damage and possible cell death, thus minimizing oxidative damage-related impairment of insulin secretion. On the other hand, the induction of antioxidant enzymes by Nrf2 activation blunts glucose-triggered ROS signaling, thus resulting in reduced GSIS. These two premises are potentially relevant to impairment of beta-cells occurring in the late and early stage of Type 2 diabetes, respectively. In addition, we summarized our recent findings that persistent oxidative stress due to absence of uncoupling protein 2 activates cellular adaptive response which is associated with impaired pancreatic beta-cell function.     

罗格列酮对2型糖尿病患者血清抵抗素的影响

目的研究罗格列酮（ROS）对2型糖尿病患者血清抵抗素（resistin）水平的影响。方法选择初诊2型糖尿病患者56例,随机分为治疗组36例,对照组20例,两组均给予一般治疗,治疗组另外给予口服罗格列酮（ROS）4mg,每日1次,总疗程12周,测定指标包括一般项目、血糖和血清胰岛素及抵抗素,以胰岛素抵抗（HOMA）模型评价组织胰岛素敏感性。结果ROS治疗12周后,患者空腹血糖、血清胰岛素水平、胰岛素抵抗指数（HOMA-IR）及血清抵抗素水平均明显降低（P〈0．05）,与对照组比较有明显改善（P〈0．05）。结论ROS能显著降低2型糖尿病患者胰岛素抵抗程度,改善糖代谢,可能与改善人血清抵抗素水平有关。     

超敏C反应蛋白细胞间黏附分子-1与妊娠糖尿病患者胰岛素抵抗的关系研究

目的研究炎症因子超敏C反应蛋白(hs-CRP)、可溶性细胞间黏附分子-1(sICAM-1)与妊娠糖尿病(GDM)患者胰岛素抵抗的关系,探讨GDM的发病机制。方法比较72例GDM(GDM组)、66例妊娠期糖耐量减低组(GIGT)和64例口服葡萄糖耐量试验(OGTT)正常的孕妇(NGT组)的血清hs-CRP、sICAM-1、血糖(FBG)及空腹胰岛素(FINS)水平,计算稳态模型胰岛素抵抗指数(HOMA-IR)。结果 GDM组血清HOMA-IR、FBG、FINS、hs-CRP、sICAM-1、OGTT时体质量增加值(GWG)均高于GIGT组(P<0.01),且GIGT组高于NGT组(P<0.01)。多元线性逐步回归分析显示HOMA-IR受hs-CRP、sICAM-1影响。结论 GDM患者血清hs-CRP、sICAM-1水平显著升高,加重了胰岛素抵抗。     

Improvement of insulin resistance by removal of systemic hydrogen peroxide by PEGylated catalase in obese mice

Insulin resistance, a condition in which insulin action is impaired, is one of the characteristic features of type 2 diabetes. Excessive amounts of reactive oxygen species (ROS) interfere with the insulin signaling pathway, which leads to the progression of insulin resistance. To examine whether removal of systemic hydrogen peroxide is effective in improving insulin resistance, polyethylene glycol-conjugated catalase (PEG-catalase), a derivative with a long circulation half-life, was repeatedly injected into leptin-deficient ob/ob or high fat diet-induced obese mice for 16 or 10 consecutive weeks, respectively. Although ob/ob mice gradually gained weight with time irrespective of the treatment, repeated intraperitoneal injections of PEG-catalase significantly reduced glucose levels in the fed state. Glucose and insulin tolerance tests also showed PEG-catalase significantly improved glucose tolerance and insulin sensitivity in ob/ob mice, respectively. Similar but less marked results were obtained in the diet-induced obese mice. Treatment of 3T3-L1 adipocytes with glucose oxidase (GO) increased lipid hydroperoxide formation and reduced insulin-stimulated Akt phosphorylation. Addition of catalase or PEG-catalase significantly inhibited the GO-induced changes in adipocytes. These findings indicate that systemic removal of hydrogen peroxide by PEG-catalase activates the insulin signaling pathway and improves insulin resistance in obese mice.     

Effect of the urotensin-II receptor antagonist palosuran on secretion of and sensitivity to insulin in patients with Type 2 diabetes mellitus

AIMS

To investigate the effects of palosuran, a nonpeptidic, potent and selective antagonist of the urotensin-II receptor, on insulin and glucose regulation in 20 diet-treated patients with Type 2 diabetes mellitus in a double-blind, placebo-controlled, randomized, crossover, proof-of-concept study.

METHODS

After 4 weeks'' oral treatment with 125 mg palosuran or placebo b.i.d., effects on insulin secretion and sensitivity and blood glucose levels were assessed by means of a hyperglycaemic glucose clamp, meal tolerance test, homeostasis model assessment-insulin resistance score, and daily self-monitoring of blood glucose. Plasma concentrations of palosuran were determined for 12 h on the last day of intake.

RESULTS

Palosuran did not affect second-phase insulin response (primary end-point) during the hyperglycaemic glucose clamp in comparison with placebo [paired difference of −1.8 µU ml⁻¹, 95% confidence interval (CI) −7.8, 4.2]. Likewise, no effects of palosuran were detected on the first-phase insulin response, or on insulin secretion and blood glucose levels during the meal tolerance test or on homeostasis model assessment-insulin resistance score. No clinically significant effects on daily blood glucose profiles were observed during the study. Geometric mean C_max and AUC_τ (95% CI) and median t_max (range) in this patient population were 180 ng ml⁻¹ (125, 260), 581 ng·h ml⁻¹ (422, 800) and 3.0 h (0.67, 4.3), respectively.

CONCLUSIONS

The results of this study indicate that antagonism of the urotensin-II system does not influence insulin secretion or sensitivity or daily blood glucose levels in diet-treated patients with Type 2 diabetes.