非诺贝特对高脂饮食诱导胰岛素抵抗大鼠血浆脂联素和内脂素的影响

胰岛素抵抗（insulin resistances，IR）是肥胖和2型糖尿病的重要病理生理特征。非诺贝特是过氧化物酶体增殖物激活受体-α激动剂，具有抗炎、改善胰岛素抵抗和调节脂肪因子分泌的作用”.本研究观察非诺贝特对高脂饮食诱导胰岛素抵抗大鼠的糖代谢、脂联素和内脂素的影响，探讨非诺贝特改善胰岛素抵抗的可能机制。     

棕榈酸通过抑制IRS-1表达诱导大鼠骨骼肌细胞胰岛素抵抗

摘 要 目的：建立L6细胞胰岛素抵抗模型,筛选出最佳诱导条件,并探讨其作用机制。 方法: 用MTT法确定棕榈酸、胰岛素对L6细胞增殖的影响;用葡萄糖检测试剂盒检测葡萄糖含量,确定不同浓度的棕榈酸、胰岛素对L6细胞葡萄糖消耗的影响;通过Western Blot法检测IRS-1、PI3K、P-AKT、AKT、GLUT4的蛋白表达。结果: 0.4 mmol·L^-1棕榈酸诱导12 h、5×10^-7 mol·L^-1胰岛素诱导24 h以上,对L6细胞生长无影响且出现明显胰岛素抵抗,移除刺激后24 h内能够抑制胰岛素刺激状态下的糖转运;棕榈酸降低了IRS-1、PI3K、P-AKT、GLUT4在L6细胞上的表达。结论:高浓度棕榈酸能够通过抑制IRS-1等靶蛋白表达诱导L6细胞产生胰岛素抵抗。     

JNK在棕榈酸造成骨骼肌细胞胰岛素抵抗中的作用

目的:探讨棕榈酸造成L6GLUT4myc骨骼肌细胞胰岛素抵抗的机制中,c-Jun N-末端激酶(JNK)的作用。方法:第一部分将细胞分两组,分别用0.3 mmol／L的棕榈酸盐或用溶剂牛血清白蛋白（BSA）孵育16 h;第二部分在如上处理的后30 min加入JNK的抑制剂,用或不用胰岛素刺激后,检测细胞膜上GLUT4myc的含量以及蛋白激酶B(Akt)、JNK和胰岛素受体底物1（IRS1）的磷酸化。结果：与溶剂组相比,棕榈酸组中胰岛素刺激的GLUT4myc转位和Akt的磷酸化降低(P<0.05);JNK和IRS1Ser307的磷酸化水平则没有变化。结论：棕榈酸导致L6骨骼肌细胞胰岛素抵抗的机制可能不涉及JNK或JNK的作用很小。     

非诺贝特对高脂喂养的糖尿病大鼠骨骼肌UCP3基因表达的影响

目的观察长期高脂喂养对糖尿病(DM)大鼠骨骼肌解偶联蛋白3(UCP3)基因表达的影响以及非诺贝特治疗后其表达的变化。方法Wistar大鼠随机分为正常饮食对照组(NC)、DM正常饮食组(DN),DM高脂饮食组(DH)和DM高脂饮食非诺贝特治疗组(DHF)。10wk后留取空腹血浆测定血糖(FPG)、甘油三酯(TG)、游离脂肪酸(FFA)和胰岛素,同时测定骨骼肌细胞内TG和FFA,RT-PCR法测定骨骼肌UCP3 mRNA表达。结果与NC组和DN组相比,DH组大鼠血浆和肌肉内FFA和TG均明显升高,骨骼肌UCP3基因表达明显增加(P<0.01),胰岛素抵抗指数(HOMA2-IR)明显升高(P<0.01)。给予非诺贝特后可以明显改善上述异常(P<0.01),同时观察到骨骼肌内UCP3基因表达较DH组明显增加(P<0.01)。结论高脂喂养可增加糖尿病大鼠血浆脂质水平,引起肌肉组织内脂质沉积,导致胰岛素抵抗(IR)。非诺贝特有降低血浆脂肪酸水平和肌肉内脂质沉积,改善胰岛素敏感性的作用,其作用可能与增强UCP3基因表达有关。     

GDF11在棕榈酸诱导骨骼肌细胞胰岛素抵抗中的作用研究

目的探讨GDF11对棕榈酸诱导骨骼肌细胞胰岛素抵抗的影响。方法用棕榈酸构建骨骼肌细胞胰岛素抵抗模型,分为对照组、GDF11干预组、棕榈酸干预组和GDF11联合棕榈酸干预组。CCK-8检测细胞活力,2NBDG检测细胞葡萄糖摄取。实时荧光定量PCR检测肌管标志基因(desmin、myogenin),胰岛素介导葡萄糖摄取相关基因(GLUT-4、IRS-1)及PGC-1α的表达。Western blot检测PGC-1α蛋白水平的表达。结果不同浓度GDF11对骨骼肌细胞活力无明显影响。与对照组相比,棕榈酸干预组葡萄糖摄取及GLUT-4、IRS-1、PGC-1α的表达明显降低(P<0.05)。与棕榈酸干预组相比,GDF11联合棕榈酸干预组葡萄糖摄取及GLUT-4、IRS-1、PGC-1α的表达无明显变化。结论棕榈酸可成功诱导骨骼肌细胞胰岛素抵抗,而GDF11对骨骼肌细胞胰岛素抵抗没有明显改善作用。     

内质网应激信号通路在高脂诱导的心肌细胞损伤中的作用

目的探讨内质网应激信号通路在高脂诱导的心肌细胞损伤中的作用。方法棕榈酸(0.1~0.4 mmol·L~(-1))刺激心肌细胞(0~48 h),CCK-8法评估细胞生长状态,免疫印迹法评估细胞内内质网应激信号通路相关蛋白表达水平及细胞凋亡蛋白表达水平。结果棕榈酸(0.1~0.4 mmol·L~(-1))刺激H9C2心肌细胞24 h,0.2、0.4 mmol·L~(-1)组细胞增殖率均出现明显下降。棕榈酸(0.2 mmol·L~(-1))刺激H9C2心肌细胞时,24、48 h组细胞增殖率均出现明显下降。棕榈酸(0.2 mmol·L~(-1))刺激24 h,GRP78、CHOP、PERKphos、IRE1phos、ATF6等内质网应激相关蛋白及Bax蛋白表达均明显增高(P<0.05),而Bcl-2表达出现明显降低(P<0.05)。预处理内质网应激抑制剂普伐他汀(pravastatin,10mol·L~(-1))的棕榈酸(0.2 mmol·L~(-1))组与不加pravastatin的棕榈酸(0.2 mmol·L~(-1))组相比,Bcl-2及Bax的表达均恢复至正常水平。结论内质网应激信号通路对高脂引起的心肌损伤的发病及治疗均起到重要作用。     

非诺贝特致横纹肌溶解及心肌损害1例

横纹肌溶解是指骨骼肌的分解，许多药物可能引起横纹肌溶解，轻者表现为肌肉疼痛和乏力，重者出现横纹肌溶解症，国内报道不多，而由微粒化非诺贝特所致的横纹肌溶解，尤其同时伴有心肌损害，发生心律失常的则未见报道，现将我院遇到的1例报道如下。     

高脂大鼠非酒精性脂肪肝与胰岛素抵抗的关系

目的 :研究高脂大鼠胰岛素抵抗与脂肪肝的关系。方法 :采用高脂饮食复制大鼠胰岛素抵抗动物模型 ,检测血糖、血清胰岛素、血清甘油三酯和血清游离脂肪酸及肝脏甘油三酯 (TG)含量 ,并做病理切片 ,测定肝脂变面积。结果 :胰岛素抵抗模型组大鼠血糖、血清胰岛素、血清甘油三酯和游离脂肪酸含量、肝脏 TG含量均高于正常对照组。结论 :胰岛素抵抗与脂肪肝的发生密切相关 ,高胰岛素血症、胰岛素抵抗是脂肪肝形成的危险因素。     

非诺贝特对高甘油三酯血症患者胰岛素敏感性和血管内皮功能的影响

目的 观察非诺贝特对高血脂症患者代谢参数、胰岛素敏感性和血管内皮功能的影响。方法 原发高甘油三酯血症患者60例，每天予非诺贝特0．2g治疗，共12周。治疗前后分别测定甘油三酯（TG）、总胆固醇（TC）、高密度脂蛋白（HDL-C）、低密度脂蛋白（LDL-C）、游离脂肪酸（FFA）、空腹血糖和胰岛素、尿酸（UA）以及血流介导的血管舒张（FMD）。结果 ①非诺贝特可显著降低TG、TC、FFA和UA，升高HDL-C（所有P〈0．01）；②非诺贝特改善胰岛素的敏感性，使胰岛素抵抗减轻6％（P〈0．05）；③非诺贝特可明显改善血流介导的血管扩张（FMD）（P〈0．01）。结论 非诺贝特不但具有调节血脂作用．还具有胰岛素增敏作用和改善内皮功能作用。胰岛素敏感性的增加与HDL水平的升高、FFA水平的降低以及内皮功能的改善有关。     

Role of insulin in the pathogenesis of free fatty acid-induced insulin resistance in skeletal muscle

Insulin resistance is a pathophysiological link of obesity to type 2 diabetes. The initial cause of insulin resistance is critical for prevention and treatment of type 2 diabetes. Lipotoxicity is a well-known concept in the explanation of initiation of insulin resistance. Although there are several prevailing hypotheses about the cellular/molecular mechanisms of lipotoxicity, such as inflammation, oxidative stress, hyperinsulinemia, and ER stress, the relative importance of these hypothesized events remains to be determined. The role of hyperinsulinemia is relatively under documented in the literature for the initiation of insulin resistance. In this review, an interaction of fatty acid and beta-cells, and a synergy between free fatty acids (FFAs) and insulin are emphasized for the role of hyperinsulinemia. This article presents the evidence about FFA-induced insulin secretion in vitro and in vivo, recent advances in the molecular mechanism of FFA action in beta-cells, a role of GPR40 in the development of insulin resistance, and the negative feedback loop of the insulin receptor signal pathway. The negative feedback loop is discussed in detail with a focus on IRS-1 serine kinases. This article provides a substantial support for the role of insulin in the early stages of FFA-associated insulin resistance. The hypothesis of insulin's role in lipotoxicity is referred to as the "insulin hypothesis" in this review. According to this hypothesis, prevention of increased beta-cell response to glucose may be a potential approach for early intervention of metabolic syndrome.     

Sodium butyrate epigenetically modulates high-fat diet-induced skeletal muscle mitochondrial adaptation,obesity and insulin resistance through nucleosome positioning

Background and Purpose

Sodium butyrate (NaB), an epigenetic modifier, is effective in promoting insulin sensitivity. The specific genomic loci and mechanisms underlying epigenetically induced obesity and insulin resistance and the targets of NaB are not fully understood.

Experimental Approach

The anti-diabetic and anti-obesity effects of NaB treatment were measured by comparing phenotypes and physiologies of C57BL/6J mice fed a low-fat diet (LF), high-fat diet (HF) or high-fat diet plus NaB (HF + NaB) for 10 weeks. We determined a possible mechanism of NaB action through induction of beneficial skeletal muscle mitochondrial adaptations and applied microccocal nuclease digestion with sequencing (MNase-seq) to assess whole genome differences in nucleosome occupancy or positioning and to identify associated epigenetic targets of NaB.

Key Results

NaB prevented HF diet-induced increases in body weight and adiposity without altering food intake or energy expenditure, improved insulin sensitivity as measured by glucose and insulin tolerance tests, and decreased respiratory exchange ratio. In skeletal muscle, NaB increased the percentage of type 1 fibres, improved acylcarnitine profiles as measured by metabolomics and produced a chromatin structure, determined by MNase-seq, similar to that seen in LF. Targeted analysis of representative nuclear-encoded mitochondrial genes showed specific repositioning of the −1 nucleosome in association with altered gene expression.

Conclusions and Implications

NaB treatment may be an effective pharmacological approach for type 2 diabetes and obesity by inducing −1 nucleosome repositioning within nuclear-encoded mitochondrial genes, causing skeletal muscle mitochondrial adaptations that result in more complete β-oxidation and a lean, insulin sensitive phenotype.     

Nutrient-induced insulin resistance in human skeletal muscle

Nutrient excess is associated with reduced insulin sensitivity (insulin resistance) and plays a central role in the pathogenesis of type 2 diabetes. Recently, free fatty acids as well as amino acids were shown to induce insulin resistance by decreasing glucose transport/phosphorylation with subsequent impairment of glycogen synthesis in human skeletal muscle. These results do not support the traditional concept of direct substrate competition with glucose for mitochondrial oxidation but indicate that the cellular mechanisms of such lipotoxicity and "proteotoxicity" might primarily affect the insulin signaling cascade. The signaling pathways involved in nutrient dependent modulation of insulin action include protein kinase C isoforms and IkappaB kinase. Therefore, pharmacological modulation of these enzymes might represent a promising target for future treatment of insulin resistance. Finally, hyperglycemia which occurs late in the insulin resistance syndrome further augments insulin resistance by mechanisms summarized as glucose toxicity. Chronic hyperglycemia might lead to inhibition of lipid oxidation and thereby to accumulation of intracellular lipid metabolites. Therefore, glucotoxicity might be in part indirectly caused by lipotoxicity (glucolipotoxicity). In conclusion, different nutrients affect common metabolic pathways and thereby induce insulin resistance in humans.     

Crocetin improves the insulin resistance induced by high-fat diet in rats

BACKGROUND AND PURPOSE: The amelioration of insulin resistance by treatment with crocetin is closely related to the hypolipidaemic effect. The present study is designed to clarify the insulin-sensitizing mechanism of crocetin by elucidating the mechanism of regulation of lipid metabolism by crocetin. EXPERIMENTAL APPROACH: Rats given a high-fat diet were treated with crocetin for 6 weeks before hyperinsulinaemic-euglycaemic clamp. 14C-palmitate was used as tracer to track the fate of non-esterified fatty acids or as substrate to measure beta-oxidation rate. Triglyceride clearance in plasma and lipoprotein lipase activity in tissues were tested. Content of lipids in plasma and tissues was determined. Real-time PCR was used to assay the level of mRNA from genes involved in non-esterified fatty acid and triglyceride uptake and oxidation. KEY RESULTS: Crocetin prevented high-fat-diet induced insulin resistance (increased clamp glucose infusion rate), raised hepatic non-esterified fatty acid uptake and oxidation, accelerated triglyceride clearance in plasma, enhanced lipoprotein lipase activity in liver, and reduced the accumulation of detrimental lipids (DAG and long-chain acyl CoA) in liver and muscle. Genes involved in hepatic lipid metabolism which are regulated by peroxisome proliferator-activated receptor-alpha, were modulated to accelerate lipid uptake and oxidation. CONCLUSIONS AND IMPLICATIONS: Through regulating genes involved in lipid metabolism, crocetin accelerated hepatic uptake and oxidation of non-esterified fatty acid and triglyceride, and reduced lipid availability to muscle, thus decreasing lipid accumulation in muscle and liver, and consequently improving sensitivity to insulin.     

Malonyl CoA, long chain fatty acyl CoA and insulin resistance in skeletal muscle

Malonyl CoA is an inhibitor of carnitine palmitoyl transferase 1 (CPT1), the enzyme that regulates the transfer of long chain fatty acyl CoA into mitochondria. By virtue of this effect, it is thought to play a key role in regulating fatty acid oxidation. Thus, when the supply of glucose to muscle is increased, malonyl CoA levels increase in keeping with a decreased need for fatty acid oxidation, and fatty acids are preferentially esterified to form diaglycerol and triglycerides. In contrast, during exercise, when the need for fatty acid oxidation is increased, malonyl CoA levels fall. Changes in glucose supply regulate malonyl CoA by modulating the concentration of cytosolic citrate, an allosteric activator of acetyl CoA carboxylase (ACC), the rate-limiting enzyme for malonyl CoA formation and a precursor of its substrate cytosolic acetyl CoA. Conversely, exercise lowers the concentration of malonyl CoA, by activating an AMP-activated protein kinase, which phosphorylates and inhibits ACC. A number of reports have linked sustained increases in the concentration of malonyl CoA in muscle to insulin resistance. In this paper, we review these reports, as well as the notion that changes in malonyl CoA contribute to the increases in long chain fatty acyl CoA, (LCFA CoA), diacylglycerol and triglyceride content and changes in protein kinase C activity and distribution observed in insulin-resistant muscle. We also review the implications of the malonyl CoA/LCFA CoA hypothesis to two other proposed mechanisms for insulin resistance, the glucose-fatty acid cycle and the hexosamine theory.     

Upregulation of fatty acyl-CoA thioesterases in the heart and skeletal muscle of rats fed a high-fat diet

In rodent models of diet-induced obesity, prolonged high-fat feeding increases the cellular uptake of fatty acids and causes lipotoxicity in the heart and skeletal muscle, where substrate overload to beta-oxidation generates mitochondrial stress. We examined the hypothesis that, because of its catalytic properties, acyl-CoA thioesterase (ACOT) would counteract these detrimental situations by modulating intracellular acyl-CoA levels. Rats were fed a low- or high-fat diet for up to 20 weeks, and the expressions of ACOT isoforms and fatty acid beta-oxidation enzymes were analyzed by western blotting. The expressions of ACOT1, ACOT2 and ACOT7 proteins in the heart and soleus muscle were significantly increased, by 2.0-7.6-fold, in rats fed the high-fat diet as compared with the low-fat diet group. These effects were accompanied by increases in carnitine palmitoyltransferase and acyl-CoA oxidase expression. However, ACOT was not induced in the extensor digitorum longus muscle or the liver. Subcellular fractionation of heart and soleus muscle homogenates confirmed expression of both the cytosolic and mitochondrial ACOT isoforms. These results underscore the functional relationship between ACOT and fatty acid oxidation, and suggest adaptive upregulation of ACOT to protect against fatty acid oversupply in the heart and skeletal muscle.     

游离脂肪酸与骨骼肌胰岛素抵抗的研究进展

胰岛素抵抗与肥胖、2型糖尿病、高血压、脂代谢紊乱、异常血凝及纤溶等代谢综合征的发生和发展密切相关。虽然胰岛素抵抗发生机制尚不完全清楚,但大量研究表明游离脂肪酸在机体胰岛素抵抗,特别是骨骼肌胰岛素抵抗方面发挥重要作用。本文就游离脂肪酸引起骨骼肌胰岛素抵抗的作用及其机制进行综述,以期为胰岛素抵抗的改善及治疗带来新的手段。     

Adrenal function and the action of propranolol in surgical stress-mediated insulin resistance of glucose utilization by peripheral tissues in vivo. Inhibition of glucose accumulation in skeletal muscle

The effect of acute adrenalectomy and the action of propranolol on insulin-stimulated glucose utilization was investigated in an in vivo model of peripheral tissues of the rabbit after evisceration and nephrectomy. The lactate/pyruvate ratios in muscle and blood and the content of energy-rich phosphate compounds in muscle were not altered during the experiments. The results obtained in animals with and without intact adrenals were compared. The insulin-mediated glucose utilization was inhibited by 34% in animals with intact adrenals. In the semimembranosus muscle of adrenalectomized rabbits the parameters of glucose metabolism corresponded to those in the 'resting state'. In the muscle of animals with intact adrenals the content of glycogen was decreased and that of glycolytic intermediates was elevated; free glucose was accumulated in the muscle cell. Alterations of the glucose content in skeletal muscle were inversely correlated with the glucose utilization of peripheral tissues. DL-Propranolol (0.05 mg/kg) administered before surgery i.v. to rabbits with intact adrenals not only prevented glycogenolysis and accumulation of glycolytic intermediates but also the stress-mediated glucose accumulation in skeletal muscle. Propranolol abolished the insulin resistance of glucose utilization of peripheral tissues mediated by the adrenals after surgical preparation of the rabbits.