Ezetimibe improves hepatic steatosis in relation to autophagy in obese and diabetic rats

AIM: To investigate whether ezetimibe ameliorates hepatic steatosis and induces autophagy in a rat model of obesity and type 2 diabetes. METHODS: Male age-matched lean control LETO and obese and diabetic OLETF rats were administered either PBS or ezetimibe(10 mg/kg per day) via stomach gavage for 20 wk. Changes in weight gain and energy intake were regularly monitored. Blood and liver tissue were harvested after overnight fasting at the end of study. Histological assessment was performed in liver tissue. The concentrations of glucose, insulin, triglycerides(TG), free fatty acids(FFA), and total cholesterol(TC) in blood and TG, FFA, and TG in livertissue were measured. m RNA and protein abundance involved in autophagy was analyzed in the liver. To investigate the effect of ezetimibe on autophagy and reduction in hepatic fat accumulation, human Huh7 hepatocytes were incubated with ezetimibe(10 μmol/L) together with or without palmitic acid(PA, 0.5 mmol/L, 24 h). Transmission electron microscopy(TEM) was employed to demonstrate effect of ezetimibe on autophagy formation. Autophagic flux was measured with bafilomycin A1, an inhibitor of autophagy and following immunoblotting for autophagy-related protein expression.RESULTS: In the OLETF rats that received ezetimibe(10 mg/kg per day), liver weight were significantly decreased by 20% compared to OLETF control rats without changes in food intake and body weight(P 0.05). Lipid parameters including TG, FFA, and TC in liver tissue of ezetimibe-administrated OLETF rats were dramatically decreased at least by 30% compared to OLETF controls(P 0.01). The serum glucose, insulin, HOMA-IR, and lipid profiles were also improved by ezetimibe(P 0.05). In addition, autophagy-related m RNA expression including ATG5, ATG6, and ATG7 and the protein level of microtubule-associated protein light chain 3(LC3) were significantly increased in the liver in rats that received ezetimibe(P 0.05). Likewise, for hepatocytes cultured in vitro, ezetimibe treatment significantly decreased PA-induced fat accumulation and increased PA-reduced m RNA and protein expression involved in autophagy(P 0.05). Ezetimibe-increased autophagosomes was observed in TEM analysis. Immunoblotting analysis of autophagy formation with an inhibitor of autophagy demonstrated that ezetimibe-increased autophagy resulted from increased autophagic flux. CONCLUSION: The present study demonstrates that ezetimibe-mediated improvement in hepatic steatosis might involve the induction of autophagy.     

Exenatide improves hepatic steatosis by enhancing lipid use in adipose tissue in nondiabetic rats

AIM:To investigate the metabolic changes in skeletal muscle and/or adipose tissue in glucagon-like peptide-1-induced improvement of nonalcoholic fatty liver disease(NAFLD).METHODS:Male Wistar rats were fed either a control diet(control group)or a high-fat diet(HFD).After 4wk,the HFD-fed rats were subdivided into two groups;one group was injected with exenatide[HFD-Ex(+)group]and the other with saline[HFD-Ex(-)group]every day for 12 wk.The control group received saline and were fed a control diet.Changes in weight gain,energy intake,and oxygen consumption were analyzed.Glucose tolerance tests were performed after 8 wk of treatment.Histological assessments were performed in liver and adipose tissue.RNA expression levels of lipid metabolism related genes were evaluated in liver,skeletal muscle,and adipose tissue.RESULTS:Exenatide attenuated weight gain[HFDEx(-)vs HFD-Ex(+)]and reduced energy intake,which was accompanied by an increase in oxygen consumption and a decrease in the respiratory exchange ratio[HFD-Ex(-)vs HFD-Ex(+)].However,exenatide did not affect glucose tolerance.Exenatide reduced lipid content in the liver and adipose tissue.Exenatide did not affect the expression of lipid metabolism-related genes in the liver or skeletal muscle.In adipose tissue,exenatide significantly upregulated lipolytic genes,including hormone-sensitive lipase,carnitine palmitoyltransferase-1,long-chain acyl-CoA dehydrogenase,and acyl-CoA oxidase 1[HFD-Ex(-)vs HFD-Ex(+)].Exenatide also upregulated catalase and superoxide dismutase 2[HFD-Ex(-)vs HFD-Ex(+)].CONCLUSION:In addition to reducing appetite,enhanced lipid use by exenatide in adipose tissue may reduce hepatic lipid content in NAFLD,most likely by decreasing lipid influx into the liver.     

Mitochondrial dysfunction due to long-chain Acyl-CoA dehydrogenase deficiency causes hepatic steatosis and hepatic insulin resistance

Alterations in mitochondrial function have been implicated in the pathogenesis of insulin resistance and type 2 diabetes. However, it is unclear whether the reduced mitochondrial function is a primary or acquired defect in this process. To determine whether primary defects in mitochondrial beta-oxidation can cause insulin resistance, we studied mice with a deficiency of long-chain acyl-CoA dehydrogenase (LCAD), a key enzyme in mitochondrial fatty acid oxidation. Here, we show that LCAD knockout mice develop hepatic steatosis, which is associated with hepatic insulin resistance, as reflected by reduced insulin suppression of hepatic glucose production during a hyperinsulinemic-euglycemic clamp. The defects in insulin action were associated with an approximately 40% reduction in insulin-stimulated insulin receptor substrate-2-associated phosphatidylinositol 3-kinase activity and an approximately 50% decrease in Akt2 activation. These changes were associated with increased PKCepsilon activity and an aberrant 4-fold increase in diacylglycerol content after insulin stimulation. The increase in diacylglycerol concentration was found to be caused by de novo synthesis of diacylglycerol from medium-chain acyl-CoA after insulin stimulation. These data demonstrate that primary defects in mitochondrial fatty acid oxidation capacity can lead to diacylglycerol accumulation, PKCepsilon activation, and hepatic insulin resistance.     

Melatonin improves insulin resistance and hepatic steatosis through attenuation of alpha‐2‐HS‐glycoprotein

Melatonin plays an important role in regulating circadian rhythms. It also acts as a potent antioxidant and regulates glucose and lipid metabolism, although the exact action mechanism is not clear. The α2‐HS‐glycoprotein gene (AHSG) and its protein, fetuin‐A (FETUA), are one of the hepatokines and are known to be associated with insulin resistance and type 2 diabetes. The aim of this study was to determine whether melatonin improves hepatic insulin resistance and hepatic steatosis in a FETUA‐dependent manner. In HepG2 cells treated with 300 μmol/L of palmitic acid, phosphorylated AKT expression decreased, and FETUA expression increased, but this effect was inhibited by treatment with 10 μmol/L of melatonin. However, melatonin did not improve insulin resistance in FETUA‐overexpressing cells, indicating that improvement in insulin resistance by melatonin was dependent on downregulation of FETUA. Moreover, melatonin decreased palmitic acid‐induced ER stress markers, CHOP, Bip, ATF‐6, XBP‐1, ATF‐4, and PERK. In addition, in the high‐fat diet (HFD) mice, oral treatment with 100 mg/kg/day melatonin for 10 weeks reduced body weight gain to one‐third of that of the HFD group and hepatic steatosis. Insulin sensitivity and glucose intolerance improved with the upregulation of muscle p‐AKT protein expression. FETUA expression and ER stress markers in the liver and serum of HFD mice were decreased by melatonin treatment. In conclusion, melatonin can improve hepatic insulin resistance and hepatic steatosis through reduction in ER stress and the resultant AHSG expression.     

Effects of resveratrol and other polyphenols in hepatic steatosis

Non-alcoholic fatty liver disease covers a wide spectrum of liver pathologies which range from simple steatosis to non-alcoholic steatohepatitis. Polyphenols are members of a very large family of plant-derived compounds that can have beneficial effects on human health, and thus their study has become an increasingly important area of human nutrition research. The aim of the present review is to compile published data concerning the effects of both isolated polyphenols as well as polyphenol extracts, on hepatocyte and liver fat accumulation under different steatosis-inducing conditions. The results reported clearly show that this group of biomolecules is able to reduce fat accumulation, but further studies are needed to establish the optimal dose and treatment period length. With regard to the potential mechanisms of action, there is a good consensus. The anti-lipidogenic effect of polyphenols is mainly due to reduced fatty acid and triacylglycerol synthesis, increased in fatty acid oxidation, and reduced of oxidative stress and inflammation. As a general conclusion, it can be stated that polyphenols are biomolecules which produce hepatoprotective effects. To date, these beneficial effects have been demonstrated in cultured cells and animal models. Thus, studies performed in humans are needed before these molecules can be considered as truly useful tools in the prevention of liver steatosis.     

丹栀逍遥散对非酒精性脂肪性肝病大鼠LKB1/AMPK/ACC通路及肝脂肪变性的影响

目的:探讨丹栀逍遥散对非酒精性脂肪性肝病(NAFLD)大鼠肝脏激酶B1(LKB1)/腺苷酸活化蛋白激酶(AMPK)/乙酰辅酶A羧化酶(ACC)通路及肝脂肪变性的影响。方法:SD雄性大鼠随机分为空白组、模型组、水飞蓟宾组(26.25 mg·kg^-1)、丹栀逍遥散高、中、低剂量组(38.0、19.0、9.5 g·kg^-1),每组13只。采用高脂饲料连续喂养8周复制非酒精性脂肪肝(NAFLD)大鼠模型。模型复制成功后水飞蓟宾组和丹栀逍遥散各剂量组大鼠开始灌胃给予相应的药物,连续给药4周,给药结束后进行取材和相关指标的检测。给药期间,观察各组大鼠的精神状况、毛色、饮食、活动等一般状态,记录给药前后大鼠体重变化;取大鼠肝、肾、脾脏并称重,计算脏器指数;生化法检测肝组织中丙氨酸氨基转移酶(ALT)、天门冬氨酸氨基转移酶(AST)、甘油三脂(TG)、总胆固醇(TC)、游离脂肪酸(NEFA)含量;苏木精-伊红染色(HE)观察各组大鼠肝组织病理变化;Western blot检测肝组织中LKB1、AMPKα1、AMPKα2、ACC及其磷酸化水平。结果:与空白组相比,模型组大鼠毛色发黄暗淡,精神萎靡;体重增量、肝脏指数、肝组织中ALT、AST、TG、TC、NEFA水平均显著升高(P<0.05),肝细胞排列紊乱,胞界不清晰,较多的脂肪空泡;肝细胞中LKB1、p-LKB1、AMPKα1、p-AMPKα1、AMPKα2、p-AMPKα2、p-ACC蛋白表达水平明显降低,ACC蛋白表达升高(P<0.05);与模型组相比,水飞蓟宾组和丹栀逍遥散高、中剂量组大鼠一般状态有不同程度的改善,体重增量、肝脏指数、肝组织中ALT、AST、TG、TC、NEFA水平均显著降低(P<0.05),病理损伤程度减轻;肝细胞中LKB1、p-LKB1、AMPKα1、p-AMPKα1、AMPKα2、p-AMPKα2、p-ACC蛋白表达水平明显升高,ACC蛋白表达降低(P<0.05)。结论:丹栀逍遥散可能通过LKB1/AMPK/ACC信号通路,降低脂肪的合成,改善肝功能,减轻NAFLD模型大鼠肝脂肪变性。     

Effect of ursodeoxycholic acid on hepatic steatosis in rats

Ursodeoxycholic acid (UDCA) has been shown to have hepatoprotective effects in various liver diseases. This drug has also been found to be effective in patients with nonalcoholic steatohepatitis, improving hepatic steatosis (HS) significantly. The aim of this study was to evaluate whether UDCA has an effect on both preventing and regressing HS in rats. To induce fatty liver, a choline-deficient diet (CDD) was used. For the rats assigned to receive UDCA, a 1.5% UDCA solution was administered at a dose of 25 mg/kg/day using an oral feeding tube. Assesment of HS was based on the quantification of percentage of hepatocytes containing lipid vacuoles. Forty-three male Wistar rats were randomly divided into two protocols. In protocol I, 7 rats were fed a standard diet (SD) plus UDCA for 30 days (control group). In protocol II, 19 rats were fed CDD and 17 rats were fed CDD plus UDCA for 30 days. At the end of this period, after performing liver biopsies, either SD or SD plus UDCA was started in both CDD-fed rats and CDD plus UDCA-fed rats for 30 days in a random order without the knowledge of the degrees of steatosis developed. At the end of this period, liver biopsies were repeated in order to evaluate whether UDCA has an effect on the regression of HS. In protocol I, there were no specific findings on the histological examination of the livers at 30 days. In protocol II, the percentage of HS in CDD plus UDCA-fed rats was significantly lower than CDD-fed rats at the end of the same period (percentage of steatosis, mean ± sd: 12.2 ± 29.6 to 23.2 ± 34.1 respectively, P = 0.0201); after starting either SD or SD plus UDCA, steatosis was almost completely regressed at 30 days in all rats that developed that steatogenic changes. UDCA seems to prevent HS in rats; addition of UDCA to SD does not cause a further contribution in regressing HS.     

高脂饮食诱导幼龄大鼠肝脂肪性变和胰岛素抵抗的发生及二甲双胍的干预作用

目的 通过高脂饮食诱导幼龄大鼠建立非酒精性脂肪性肝病（NAFLD）伴胰岛素抵抗模型,探讨NAFLD幼鼠胰岛素抵抗的发生机制及二甲双胍的干预疗效.方法 将60只3周龄刚离乳雄性SD大鼠按随机数字表法分为3组：对照组、高脂组及二甲双胍组（高脂＋二甲双胍）,每组各20只.对照组予普通饮食,高脂组和二甲双胍组给予高脂饮食5周,同时对照组和高脂组给予生理盐水灌胃,二甲双胍组给予二甲双胍混悬液灌胃（0.25 g·kg-1·d-1）.第5周末从各组大鼠中随机选取12只进行正常血糖-高胰岛素钳夹试验,评价胰岛素敏感性;另8只大鼠处死并取新鲜肝组织进行肝组织病理形态和脂质沉积观察,其中随机取6只通过实时荧光定量PCR分析肝组织中固醇调节元件结合蛋白-1（SREBP-1）、胰岛素受体（IR）、胰岛素样生长因子-1（IGF-1）mRNA的表达.组织学分级差异比较采用秩和检验进行分析.其他指标采用单因素ANOVA分析,两两比较采用LSD法.结果 实验5周后：（1）体重：对照组[（316±17）g]、高脂组[（202±21）g]、二甲双胍组[（171±19）g],3组间两两比较差异有统计学意义（P＜0.01）.（2）病理结果：高脂组大鼠肝脏符合典型的NAFLD病理特征.（3）葡萄糖输注率高脂组、对照组、二甲双胍组分别为（6.51±1.52）、（11.57±1.97）、（13.08±2.33）mg·kg-1·min-1.（4）与对照组相比,高脂组肝组织SREBP-1 mRNA表达较高[0.85±0.10比1.67±0.28,P＜0.05],IR mRNA[（1.16±0.22）比（0.56±0.22）,P＜0.01]、IGF-1 mRNA[（0.87±0.14）比（0.26±0.14）,P＜0.01]表达较低;高脂组与二甲双胍组肝组织SREBP-1 mRNA、IR mRNA、IGF-1 mRNA比较差异无统计学意义（P＞0.05）.结论 高脂饲养5周可建立幼龄SD大鼠NAFLD并发胰岛素抵抗模型,二甲双胍预防可提高机体胰岛素敏感性,其减少NAFLD幼鼠体重的作用与幼鼠体重是否超标可能无关.     

Liver steatosis,but not fibrosis,is associated with insulin resistance in nonalcoholic fatty liver disease

Background To address the hypothesis that liver steatosis causes systemic insulin resistance, we sought to determine the liver histological feature that most strongly contributes to insulin resistance in patients with nonalcoholic fatty liver disease (NAFLD). Methods Liver biopsy specimens were obtained from 131 patients with clinically suspected NAFLD. The stage, grade of nonalcoholic steatohepatitis (NASH), and level of steatosis were scored and analyzed in relation to the homeostasis model assessment of insulin resistance (HOMA-IR) and the metabolic clearance rate (MCR), measured using the glucose clamp method. Results In the univariate analysis, the degree of hepatic steatosis (r = 0.458, P < 0.001), stage (r = 0.360, P < 0.001), and grade (r = 0.349, P < 0.01) of NASH were significantly correlated with the HOMA-IR. Multiple regression analysis adjusting for age, sex, body mass index, and each histological score showed that steatosis was significantly and independently associated with HOMA-IR (coefficient = 1.42, P < 0.001), but not with the stage (coefficient = 0.33, P = 0.307) or grade (coefficient = 0.67, P = 0.134) of NASH. Similar independent relationships were observed between steatosis and MCR, but the relationship was weaker (coefficient = −0.98, P = 0.076). Conclusions Steatosis of the liver, but not the stage or the grade of NASH, is associated with insulin resistance in patients with NAFLD.     

Ursodeoxycholic acid improves insulin sensitivity and hepatic steatosis by inducing the excretion of hepatic lipids in high-fat diet-fed KK-Ay mice

Type 2 diabetes mellitus is frequently accompanied by fatty liver/nonalcoholic fatty liver disease. Hence, accumulation of lipids in the liver is considered to be one of the risk factors for insulin resistance and metabolic syndrome. Ursodeoxycholic acid (UDCA) is widely used for the treatment of liver dysfunction. We investigated the therapeutic effects of UDCA on type 2 diabetes mellitus exacerbating hepatic steatosis and the underlying mechanisms of its action using KK-A(y) mice fed a high-fat diet. KK-A(y) mice were prefed a high-fat diet; and 50, 150, and 450 mg/kg of UDCA was orally administered for 2 or 3 weeks. Administration of UDCA decreased fasting hyperglycemia and hyperinsulinemia. Hyperinsulinemic-euglycemic clamp analyses showed that UDCA improved hepatic (but not peripheral) insulin resistance. Hepatic triglyceride and cholesterol contents were significantly reduced by treatment with UDCA, although the genes involved in the synthesis of fatty acids and cholesterol, including fatty acid synthase and 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, were upregulated. Fecal levels of bile acids, neutral sterols, fatty acids, and phospholipids were significantly increased by UDCA treatment. The gene expression levels and protein phosphorylation levels of endoplasmic reticulum stress markers were not changed by UDCA treatment. These results indicate that UDCA ameliorates hyperglycemia and hyperinsulinemia by improving hepatic insulin resistance and steatosis in high-fat diet-fed KK-A(y) mice. Reduction of hepatic lipids might be due to their excretion in feces, followed by enhanced utilization of glucose for the synthesis of fatty acids and cholesterol. Ursodeoxycholic acid should be effective for the treatment of type 2 diabetes mellitus accompanying hepatic steatosis.     

二甲双胍对高脂饲养大鼠肝脏脂肪变的干预作用

目的:探讨胰岛素抵抗在非酒精性脂肪性肝发病中的作用及机制,观察二甲双胍对高脂饲养大鼠肝脏脂肪变的干预效果.方法:21只(?) Wistar大鼠分为3组,每组7只,普通饮食组(SD),高脂饮食组(HF),二甲双胍组(HF- Met)在高脂饮食的同时给予二甲双胍,共8wk.8 wk末处死大鼠,称量附睾脂肪,计算肝指数,生化方法测定ALT、AST、TG、TC、FFA、SOD和MDA.放免法测定空腹胰岛素,逆转录聚合酶链反应(RT-PCR)和ELISA法检测肝脏TNF-αmRNA和蛋白的表达,用葡萄糖输注率(GIR)来评价胰岛素敏感性,并观察肝组织病理变化.结果:与HF相比,HF-Met肝细胞脂肪变和小叶炎症明显减轻,肝指数、胰岛素、AST、ALT、TG、FFA显著下降(3.25±0.26 vs 4.29±0.12,33.37±8.34 vs 46.73±5.24,17.29±5.34 vs 43.48±6.21,4.10±2.47 vs 12.05±4.05,P<0.01;106.0±31.04 vs 141.37±24.87,48.31±16.11 vs 88.34±21.94,P<0.05)TNF-α的表达也显著下降,GIR增加(7.58±1.05 vs 6.31±1.28,P<0.05).结论:二甲双胍干预能明显改善高脂饲养大鼠的胰岛素抵抗,降低肝脏TG、FFA和TNF-α的表达,减轻肝脏脂肪变的程度,提示胰岛素增敏治疗可能是NAFLD防治的一种积极策略.     

Risk factors for hepatic steatosis in adults with cystic fibrosis: Similarities to non-alcoholic fatty liver disease

AIM To investigate the clinical, biochemical and imaging characteristics of adult cystic fibrosis(CF) patients with hepatic steatosis as compared to normal CF controls.METHODS We performed a retrospective review of adult CF patients in an academic outpatient setting during 2016. Baseline characteristics, genetic mutation analysis as well as laboratory values were collected. Abdominal imaging(ultrasound, computed tomography, magnetic resonance) was used to determine presence of hepatic steatosis. We compare patients with hepatic steatosis to normal controls.RESULTS Data was collected on 114 patients meeting inclusion criteria. Seventeen patients(14.9%) were found to have hepatic steatosis on imaging. Being overweight(BMI 25)(P = 0.019) and having a higher pp FEV1(75 vs 53, P = 0.037) were significantly associated with hepatic steatosis. Patients with hepatic steatosis had a significantly higher median alanine aminotransferase level(27 vs 19, P = 0.048). None of the hepatic steatosis patients had frank CF liver disease, cirrhosis or portal hypertension. We found no significant association with pancreatic insufficiency or CF related diabetes.CONCLUSION Hepatic steatosis appears to be a clinically and phenotypically distinct entity from CF liver disease. The lack of association with malnourishment and the significant association with higher BMI and higher pp FEV1 demonstrate similarities with non-alcoholic fatty liver disease. Long term prospective studies are needed to ascertain whether CF hepatic steatosis progresses to fibrosis and cirrhosis.     

Association of chronic hepatitis B virus infection with insulin resistance and hepatic steatosis

Background and Aim: Chronic viral infections such as human immunodeficiency virus and hepatitis C virus (HCV) may decrease tissue response to insulin, thereby causing insulin resistance. In addition, insulin resistance is associated with hepatic steatosis. However, whether these phenomena hold true for chronic hepatitis B virus (HBV) infection remains largely unknown. The present study therefore aimed to investigate the association of chronic HBV infection with insulin resistance and hepatic steatosis. Methods: A total of 507 subjects (243 men and 264 women; mean age 46.56 years) less than 60 years‐old attending a health examination center were enrolled in the study. All the subjects were negative for antibodies against HCV and consumed less than 140 g alcohol/week. Demographic, anthropometric, clinical, and laboratory data were obtained from each subject. Insulin resistance index was determined using homeostasis model assessment (HOMA‐IR). Hepatic steatosis was identified by ultrasound examination. Results: Of the 507 subjects, 50 (9.9%) were positive for hepatitis B surface antigen (HBsAg) and designated HBV carriers. All variables were comparable between HBV carriers and non‐HBV carriers, except that HBV carriers had significantly higher serum alanine aminotransferase and aspartate aminotransferase levels (P < 0.05). By multivariate linear regression, HBV carriers were not associated with insulin resistance. In addition, multivariate regression analyses showed that HBV carriers were not associated with the presence of ultrasonographic fatty liver. Conclusions: Chronic HBV infection seems not to be associated with insulin resistance or hepatic steatosis in HBV carriers.