Skeletal muscle oxidative capacity in rats fed high-fat diet.

OBJECTIVE: To investigate whether young rats respond to high-fat feeding through changes in energy efficiency and fuel partitioning at the level of skeletal muscle, to avoid obesity development. In addition, to establish whether the two mitochondrial subpopulations, which exist in skeletal muscle, ie subsarcolemmal and intermyofibrillar, are differently affected by high-fat feeding. DESIGN: Weaning rats were fed a low-fat or a high-fat diet for 15 days. MEASUREMENTS: Energy balance and lipid partitioning in the whole animal. State 3 and state 4 oxygen consumption rates in whole skeletal muscle homogenate. State 3 and state 4 oxygen consumption rates, membrane potential and uncoupling effect of palmitate in subsarcolemmal and intermyofibrillar mitochondria from skeletal muscle. RESULTS: Rats fed a high-fat diet showed an increased whole body lipid utilization. Skeletal muscle NAD-linked and lipid oxidative capacity significantly increased at the whole-tissue level, due to an increase in lipid oxidative capacity in subsarcolemmal and intermyofibrillar mitochondria and in NAD-linked activity only in intermyofibrillar ones. In addition, rats fed a high-fat diet showed an increase in the uncoupling effect of palmitate in both the mitochondrial populations. CONCLUSIONS: In young rats fed a high-fat diet, skeletal muscle contributes to enhanced whole body lipid oxidation through an increased mitochondrial capacity to use lipids as metabolic fuels, associated with a decrease in energy coupling.     

Statin modulates insulin signaling and insulin resistance in liver and muscle of rats fed a high-fat diet

Recent studies have shown that statins might have relevant effects on insulin resistance in animal models and in humans. However, the molecular mechanisms that account for this improvement in insulin sensitivity are not well established. The aim of the present study was to investigate the effect of a statin on insulin sensitivity and insulin signaling in liver and muscle of rats fed on a high-fat diet (HFD) for 4 weeks, treated or not with lovastatin during the last week. Our data show that treatment with lovastatin results in a marked improvement in insulin sensitivity characterized by an increase in glucose disappearance rate during the insulin tolerance test. This increase in insulin sensitivity was associated with an increase in insulin-induced insulin receptor (IR) tyrosine phosphorylation and, in parallel, a decrease in IR serine phosphorylation and association with PTP1B. Our data also show that lovastatin treatment was associated with an increase in insulin-stimulated insulin receptor substrate (IRS) 1/phosphatidylinositol 3-kinase/Akt pathway in the liver and muscle of HFD-fed rats in parallel with a decrease in the inflammatory pathway (c-jun N-terminal kinase and I kappa beta kinase (IKKbeta)/inhibitor of kappaB/nuclear factor kappaB) related to insulin resistance. In summary, statin treatment improves insulin sensitivity in HFD-fed rats by reversing the decrease in the insulin-stimulated IRS-1/phosphatidylinositol 3-kinase/Akt pathway in liver and muscle. The effect of statins on insulin action is further supported by our findings that HFD rats treated with statin show a reduction in IRS-1 serine phosphorylation, I kappa kinase (IKK)/inhibitor of kappaB/nuclear factor kappaB pathway, and c-jun N-terminal kinase activity, associated with an improvement in insulin action. Overall, these results provide important new insight into the mechanism of statin action in insulin sensitivity.     

利拉鲁肽对高脂饲养大鼠骨骼肌脂质沉积及骨骼肌超微结构的影响

目的研究胰高血糖素样肽1类似物利拉鲁肽对高脂喂养胰岛素抵抗(IR)大鼠骨骼肌脂质沉积及骨骼肌细胞超微结构的影响。方法雄性Wistar大鼠54只,随机普通饲养16只、高脂饲养38只,饲养8周后,各取5只大鼠判定大鼠IR状态,造模成功后,将高脂饲养大鼠分为高脂组、干预组1[利拉鲁肽100μg/(kg·d)]、干预组2[利拉鲁肽200μg/(kg·d)],每组11只,另11只普通饲养为对照组。药物干预2周后,检测骨骼肌内甘油三酯(mTG)、长链脂肪酰辅酶A(LCACoA),透射电镜观察大鼠骨骼肌细胞超微结构改变。结果与对照组比较,高脂组mTG、LCACoA含量升高[(19.58±1.63)μmol/g vs(9.99±0.90)μmol/g;(6.70±0.18)nmol/g vs(2.51±0.18)nmol/g,P0.01];与高脂组比较,干预组1LCACoA含量下降[(6.10±0.37)nmol/g vs(6.70±0.18)nmol/g,P0.05],干预组2mTG、LCACoA含量明显下降[(13.57±0.66)nmol/g vs(19.58±1.63)nmol/g,(4.73±0.31)nmol/g vs(6.70±0.18)nmol/g,P0.01]。干预组1和干预组2较高脂组和对照组脂滴减少、线粒体肿胀减轻。结论利拉鲁肽可呈浓度依赖性减少高脂喂养大鼠mTG和LCACoA含量,可能是减轻IR的原因之一。     

The effect of exercise training on glucose tolerance and skeletal muscle triacylglycerol content in rats fed with a high-fat diet

The aim of the present study was to evaluate the effect of exercise training on glucose tolerance and glycogen and triacylglycerol (TG) content in different types of skeletal muscles and in the liver of rats fed with a high-fat diet. From 8 to 11 weeks of age male Wistar rats were fed with isocaloric standard (control) or high-fat diet (HFD--59% calories as fat) and were additionally assigned to a sedentary or trained group (4 weeks of training on a treadmill). An intravenous glucose tolerance test (IVGTT) with the determination of basal and post load insulin was performed before the final tissue sampling. HFD rats developed marked hyperinsulinemia. Exercise training improved glucose tolerance and insulin response in the control group only (AUC for glucose in control sedentary vs control trained, p<0.05; AUC for insulin: control sedentary vs control trained, p<0.005). Liver glycogen was significantly lower in the HFD group (p<0.05 vs control sedentary) and did not increase after exercise training. Muscle and liver TG content was markedly higher in the HFD group in comparison to control (p<0.0001 in all cases). Exercise training increased TG content in the control group in all examined tissues except white gastrocnemius (p<0.001 in all cases compared to sedentary controls), and did not affect tissue TG in the HFD group. After exercise training there was still markedly higher tissue TG content in the HFD group vs control (p<0.0001 in all cases). We conclude that beneficial metabolic effects of training are impaired in high-fat fed rats and that training does not completely reverse metabolic disturbances in this group of animals.     

Enhanced skeletal muscle and liver protein synthesis with structured lipid in enterally fed burned rats

We assessed the effects of total enteral nutrition with long-chain triacylglycerides (LCT), medium-chain triacylglycerides (MCT), or two structured lipids, modified dairy fat (MDF) and modified MCT (Captex 810B, Capital City Products, Columbus, OH), on protein and energy metabolism in hypermetabolic burned rats (25% to 30% body surface area). Male Sprague-Dawley rats (200 +/- 10 g) were continuously gastrostomy-fed isovolemic diets that provided 50 kcal/d, 2 g amino acids/d and 40% nonprotein calories as lipid for three days. Changes in body weight, nitrogen balance, serum albumin, indirect calorimetry, whole body leucine kinetics, and rectus muscle and liver protein kinetics were determined. Whole body leucine kinetics and tissue fractional protein synthetic rates (FSR, percent per day) were estimated using a four-hour constant intravenous infusion of L-[1-14C]leucine on day 3. The group of rats enterally fed MDF lost less body weight than the other groups (P less than or equal to .05). MDF and Captex 810B produced a positive and significantly greater (P less than or equal to .05) daily and cumulative nitrogen balance than either LCT or MCT. Oxygen consumption (P less than or equal to .05) and total energy expenditure (P less than or equal to .05) were elevated approximately 22% with MDF as compared with LCT or MCT. Rectus muscle FSR and absolute rate of protein synthesis were increased 19% with MDF (P less than or equal to .05) as compared with LCT or MCT.(ABSTRACT TRUNCATED AT 250 WORDS)     

增龄对高脂喂养大鼠胰岛素抵抗和骨骼肌内脂肪的影响

目的探讨增龄对高脂喂养大鼠胰岛素抵抗(IR)和骨骼肌内脂肪影响的可能机制。方法将雄性Wistar4～5月龄大鼠16只和22～24月龄大鼠16只分别随机分为青年对照组和老年对照组,青年高脂组和老年高脂组(高脂饲料喂养),每组8只。8周后,行葡萄糖耐量试验,测定0、30、60和120min的血糖和葡萄糖曲线下面积(AUC);采用正葡萄糖-高胰岛素钳夹试验的葡萄糖输注率(GIR)评价IR。结果与老年对照组和青年对照组比较,老年高脂组和青年高脂组GIR降低,骨骼肌TG及长链酯酰辅酶A(LCACoA)明显升高,差异有统计学意义(P<0.05,P<0.01);与老年对照组比较,老年高脂组大鼠各时间点血糖及AUC比较,差异均有统计学意义(P<0.05,P<0.01)。GIR与胰岛素、骨骼肌TG及LCACoA呈负相关。结论老年和高脂喂养大鼠骨骼肌TG和LCACoA含量增加,可能是老年容易发生IR的原因之一。     

Infliximab reverses steatosis and improves insulin signal transduction in liver of rats fed a high-fat diet

Non-alcoholic fatty liver disease, induced by nutritional factors, is one of the leading causes of hepatic dysfunction in the modern world. The activation of proinflammatory signaling in the liver, which is induced by systemic and locally produced cytokines, and the development of hepatic insulin resistance are two important factors associated with the progression from steatosis to steatohepatitis, a pre-cirrhotic condition. The objective of the present study was to evaluate the effect of inhibition of tumour necrosis factor (TNF)-alpha , using the monoclonal antibody infliximab, on the expression of cytokines, induction of steatosis and fibrosis, and insulin signal transduction in the liver of Wistar rats fed a high-fat diet. Ten days of treatment with infliximab significantly reduced the expression of the proinflammatory markers, TNF-alpha , IL-6, IL-1beta , and SOCS-3, in the liver of rats fed a high-fat diet. This was accompanied by reduced fat deposition and fibrosis and by improved insulin signal transduction through insulin receptor (IR)/IR substrate/Akt/FOXO1 and JAK2/STAT3 pathways. In conclusion, short-term inhibition of TNF-alpha with infliximab reduces inflammation and steatosis/fibrosis, while improving insulin signal transduction in an animal model treated with a high-fat diet.     

Oleate metabolism and endogenous triacylglycerol hydrolysis in isolated hepatocytes from rats fed a high-fat diet

In isolated hepatocytes of fat-fed rats, as compared to control fed animals, the cellular uptake of [1-14C] oleate and its oxidation to CO2 were similar but the incorporation of the label into water-soluble products (mainly ketone bodies) was increased by 36.6% whereas its esterification to triacylglycerols and phospholipids decreased by 36%. While endogenous ketogenesis was slightly but not significantly increased, ketone body synthesis from both 2 mM octanoate and 0.7 mM oleate was stimulated two fold. Thus, in the fatfed rats the oxidative pathway is clearly activated whereas long chain fatty acids are preferentially channelled into the oxidation pathway at the expense of esterification. Yet, hepatocyte triacylglycerol content was 3-fold higher after fat-feeding. In this regard, lysosomal triacylglycerol lipase (EC 3.1.1.3) activity, in homogenates of hepatocytes was decreased by 32% (p less than 0.01). This findings suggest a lower breakdown of endogenous triacylglycerols, which, taken together with decreased secretion of VLDL lipoprotein triacylglycerol (Kalopissis et al. Biochem. J. 198: 373, 1981) and an in vivo increased fatty acid influx to the liver may contribute to the accumulation of lipids in the livers of fat-fed rats.     

饮食干预对胰岛素抵抗大鼠肝脏组织蛋白激酶B表达的影响

目的在高脂饮食诱导胰岛素抵抗的基础上,观察饮食干预调整对胰岛素抵抗大鼠肝脏蛋白激酶B蛋白（protein kinase B,PKB）表达的影响。方法选取雄性Wistar大鼠30只,分为正常对照组10只,给予低脂饲料;模型组20只,给予高脂饲料。模型组大鼠给予高脂喂养5周后,分为2组：高脂喂养组10只,继续高脂饮食;低脂喂养组10只,给予低脂饮食。干预6周后,蛋白印迹法检测大鼠肝脏组织中胰岛素刺激PKB的蛋白表达含量。结果 （1）5周后,高脂喂养组空腹血糖、胰岛素、三酰甘油、胆固醇及胰岛素抵抗指数（homeostasismodel assessment-insulin resistance index,HOMA-IR）明显升高,胰岛素敏感指数（insulin resistance index,ISI）显著下降,差异有统计学意义（P〈0.01）,出现了胰岛素抵抗,造模成功。（2）低脂饮食干预6周后,与高脂饮食组比较,低脂喂养组大鼠的空腹血糖、三酰甘油、胆固醇及HOMA-IR下降,ISI升高,差异有统计学意义（P〈0.05）。（3）高脂喂养组大鼠肝脏组织中PKB的表达水平明显低于对照组,减少了23.5%,两组PKB表达比较,差异有统计学意义（7.34±0.19 vs.8.97±0.20,t=9.335,P〈0.001）;低脂饮食干预6周后,低脂喂养组PKB蛋白较高脂喂养组增加4.9%,两组比较,差异有统计学意义（7.70±0.18 vs.7.34±0.19,t=10.102,P〈0.001）。结论长期高脂饮食可诱导出胰岛素抵抗,低脂干预后纠正糖脂代谢紊乱,改善胰岛素抵抗,可能与增加肝脏组织中PKB蛋白表达有关。     

二甲双胍降低大鼠肝脏胆固醇和甘油三酯含量的机制探讨

目的 观察二甲双胍对长期高饱和脂肪酸饲养大鼠肝脏腺苷酸活化蛋白激酶α(AMPKα)和PPARα表达和活性的影响,探讨二甲双胍降低肝脏胆固(TC)和甘油三酯(TG)含量的可能机制.方法 Wistar雄性大鼠30只,随机等分为:对照组(C组)、高脂组(HF组)和高脂加二甲双胍组(Met组,高脂喂养4个月,第5个月加用二甲双胍胃1个月),喂养共5个月,测定血清、肝脏组织中的TC和TG含量;分别应用实时PCR、Western印迹检测肝脏AMPKα 和PPARα 的基因转录、蛋白表达和活性水平;PPARα 转录因子DNA结合活性测定用ELISA法.结果 与C组比较,HF组大鼠肝脏AMPKα2和PPAα mRNA表达水平显著降低(均P＜0.05);AMPKα 蛋白表达及活性显著降低(均P＜0.05),PPARα蛋白表达及DNA结合活性分别降低 48.6%、21.6%(均P＞0.05); 肝脏TC、TG含量(均P＜0.05)和血TC、TG水平(均P＜0.01)均显著增高.与HF组比较,Met组肝脏AMPKα2 mRNA和蛋白表达及活性显著增高(均P＜0.05),PPARα蛋白表达增高56.5%(P＞0.05),其DNA结合活性显著增高(P＜0.05);肝脏TC、TG含量血TC、TG水平均显著降低(均P＜0.05).结论 二甲双胍降低长期高脂饲养所致的大鼠肝脏、血中TC、TG水平的增高,可能与其激活肝细胞AMPKα及PPARα有关.     

Nateglinide prevents fatty liver through up-regulation of lipid oxidation pathway in Goto-Kakizaki rats on a high-fat diet

Dyslipidemia and fatty liver are important components of the metabolic syndrome and are the factors most commonly associated with the development of nonalcoholic fatty liver disease. Delayed and excessive insulin secretion in response to food intake is a key element in the onset of these risk factors. Nateglinide (NAT) is known to restore early-phase insulin secretion. We assessed the effect of NAT on postprandial hypertriglyceridemia and fatty liver in type 2 diabetic Goto-Kakizaki (GK) rats. The GK rats fed a high-fat diet containing 30% beef tallow twice a day were administered either the vehicle alone or NAT (50 mg/kg) before each meal for 12 weeks. Delayed insulin secretion and an increase of total insulin release were caused by feeding 30% beef tallow to the rats. This diet also induced postprandial hypertriglyceridemia and increased the hepatic triglyceride content. Treatment with NAT restored early-phase insulin secretion without any increase of total insulin release and also reduced postprandial hypertriglyceridemia and the hepatic triglyceride content. There was up-regulation of the hepatic expression of peroxisome proliferators-activated receptor alpha and its downstream enzymes after 12 weeks of NAT treatment, as well as normalization of the plasma total ketone body level. Furthermore, NAT also up-regulated hepatic expression of the adiponectin receptor AdipoR2, although there was no effect on the plasma adiponectin level. These findings indicate that long-term treatment with NAT prevented the development of fatty liver through the up-regulation of hepatic lipid oxidation pathways. Restoration of early-phase insulin secretion and suppression of recurrent postprandial hypertriglyceridemia might be involved in these effects of NAT. The present results may support the use of NAT to prevent the onset and progression of the metabolic syndrome and chronic liver disease.     

Helianthus tuberosus(Jerusalem artichoke) tubers improve glucose tolerance and hepatic lipid profile in rats fed a high-fat diet

Objective:To analyze the effects of feeding Helianthus tuberosus(HT) tubers on glucose tolerance and lipid profile in rats fed a high-fat diet(HFD). Methods:A normal HFD or HFD including 10 w/w% HT tubers(HFD + HT) was fed to F334/Jcl rats. After 10 weeks,organ weights,glucose tolerance,and lipid profile were analyzed. Results:The body weight,liver weight,and epidermal fat content in the HFD group were higher than those of the normal group,and similar to those of the HFD + HT group. The oral glucose tolerance test at 10 weeks revealed that the blood glucose level 30 minutes after beginning the test in the HFD + HT group was significantly lower than that in the HFD group. Liver triglyceride and total cholesterol levels in the HFD + HT group were significantly lower than those in the HFD group. Fecal triglyceride and total cholesterol levels in the HFD + HT group were higher than those in the HFD group. Histological analyses revealed that fat and glycogen accumulation increased in the HFD group,but decreased in the HFD + HT group. Conclusions:These results indicate that HT tubers have anti-fatty liver effects based on improvements in glucose tolerance and the hepatic lipid profile.     

白藜芦醇对高脂饮食大鼠骨骼肌不同线粒体亚群氧化、抗氧化水平和胰岛素敏感性的影响

目的 观察白藜芦醇对高脂饮食大鼠骨骼肌不同线粒体亚群氧化、抗氧化水平及胰岛素敏感性的影响.方法 8周龄雄性SD大鼠分为普通饮食组(NC组)、高脂饮食组(HF组)及白藜芦醇干预高脂饮食组(HFR组);干预8周后检测各组大鼠骨骼肌肌膜下(SS)及肌纤维间(IMF)线粒体氧化应激及抗氧化水平,并观察各组大鼠整体及骨骼肌胰岛素敏感性的变化.结果 与NC组相比,HF组大鼠胰岛素敏感性明显下降(P＜0.05),SS及IMF线粒体活性氧簇(ROS)和丙二醛的水平明显增加,SS线粒体抗氧化酶活性均下降,而IMF线粒体抗氧化酶活性均增高(均P＜0.05).与HF组相比,HFR组胰岛素敏感性明显改善,SS及IMF线粒体的抗氧化酶活性均明显增高,ROS和丙二醛的含量明显下降到NC组水平(均P＜0.05).结论 白藜芦醇对高脂饮食大鼠骨骼肌不同线粒体亚群氧化应激水平均有明显的改善作用,并且显著增加其胰岛素敏感性.     

Retinoid X receptor gamma-deficient mice have increased skeletal muscle lipoprotein lipase activity and less weight gain when fed a high-fat diet

Retinoids, derivatives of vitamin A, induce hypertriglyceridemia through decreased clearance of very low-density lipoprotein by a lipoprotein lipase (LPL)-dependent pathway. The retinoid X receptor (RXR) gamma isotype, which is highly expressed in skeletal muscle, may be important in mediating the effects of retinoids on skeletal muscle metabolism and triglyceride (TG) clearance. RXRgamma-deficient (-/-) mice had lower fasting plasma TG levels compared with wild-type littermates (33.1 +/- 2.0 vs. 51.7 +/- 6.3 mg/dl, respectively; P < 0.05). Skeletal muscle LPL activity was higher in RXRgamma mice (18.7 +/- 2.2 vs. 13.3 +/- 1.3 nmol free fatty acids/min.g; P = 0.03), but LPL activity was not different in adipose and cardiac tissue, suggesting a specific effect of RXRgamma in skeletal muscle. In addition, when exposed to a 14-wk high-fat diet, RXRgamma -/- mice had less weight gain, which was entirely due to lower fat mass (11.9 +/- 1.8 vs. 14.4 +/- 1.1 g; P = 0.01), and leptin levels were also lower in the RXRgamma -/- mice (17.6 +/- 5.0 vs. 30.9 +/- 6.4 ng/ml; P = 0.03). These data suggest that RXRgamma -/- mice are resistant to gain in fat mass in response to high-fat feeding. This occurs, at least in part, through up-regulation of LPL activity in skeletal muscle. An understanding of the mechanisms governing the role of RXR in TG disposal and metabolism may lead to the rational design of RXR-selective agonists and antagonists that may be useful in common disorders such as dyslipidemia and obesity.     

水飞蓟宾磷脂复合物对高脂饮食大鼠脂肪肝和动脉硬化的影响

目的探讨水飞蓟宾磷脂复合物（水林佳）对高脂饮食大鼠脂肪肝和动脉硬化造模形成的影响。方法22只SD大鼠随机分为3组,对照组（n=6）普通饮食饲养,模型组（n=8）和干预组（n=8）以高脂饮食＋维生素D＋丙基硫氧嘧啶造模,干预组同时在饮水中加用水林佳（225mg·kg^-1·d^-1）,各组大鼠均于实验第16周末处死,常规检测血液生化指标,并观察肝脏和主动脉壁病理改变。结果模型组出现明显的肝脏脂肪变、炎症和坏死,主动脉壁中膜轻度增厚,部分内皮下可见钙化斑,而水林佳干预组肝脏脂肪变和炎症程度较模型组明显改善（P〈0．05）,且伴血清转氨酶水平显著下降（P〈0．01）。然而,水林佳干预组血糖、血脂及主动脉粥样硬化病变情况较模型组无明显改变。结论水林佳能减轻高脂饮食脂肪肝大鼠脂肪性肝炎程度,但无改善糖脂紊乱和动脉硬化作用。     

高脂饮食性非酒精性脂肪性肝病大鼠肝脏PPAR-γ表达增强

目的　探讨过氧化物酶体增值物活化受体γ(PPAR-γ)及其亚型在高脂饮食所致非酒精性脂肪性肝病(NAFLD)大鼠肝脏的表达及其意义。方法　模型组SD大鼠给予高脂肪高胆固醇饮食饲养 ,分批于实验第 8、12、2 6、2 4周处死 ,同期设普通饮食饲养大鼠作对照。免疫组织化学和RT-PCR分别检测大鼠肝脏PPAR-γ的表达。结果　模型组大鼠第 8周呈现单纯性脂肪肝 ,第 12～ 2 4周从脂肪性肝炎进展为脂肪性肝炎伴肝纤维化。免疫组织化学和RT PCR显示 ,随着造模时间延长 ,肝脏PPAR-γ的表达逐渐增强。模型组肝脏PPAR-γ1mRNA表达于第 2 4周达到高峰 (与对照组相比升高 3 .5倍 ,P <0 .0 1) ,PPAR-γ2 mRNA表达于造模第 16周时达高峰 (较对照组升高 5 .8倍 ,P <0 .0 1)。相关分析显示 ,仅PPAR-γ2 mRNA与肝脂变程度之间关系密切 (r =0 .89,P <0 .0 5 )。结论　持续 2 4周的高脂饮食可以成功复制大鼠NAFLD模型 ,模型大鼠肝脏PPAR-γ表达增强 ,NAFLD大鼠肝细胞可能部分具有脂肪细胞的特征 ,即脂肪变的肝细胞发生成脂性改变