Ezetimibe decreases SREBP-1c expression in liver and reverses hepatic insulin resistance in mice fed a high-fat diet

Ezetimibe inhibits intestinal cholesterol absorption, thereby reducing serum cholesterol. Recent studies suggest that ezetimibe affects liver steatosis and insulin resistance. We investigated the impact of ezetimibe on insulin sensitivity and glucose metabolism in C57BL/6 mice. We analyzed 4 mouse groups fed the following diets: normal chow (4% fat) for 12 weeks, normal chow for 10 weeks followed by normal chow plus ezetimibe for 2 weeks, high-fat chow (32% fat) for 12 weeks, and high-fat chow for 10 weeks followed by high-fat chow plus ezetimibe for 2 weeks. In the normal chow + ezetimibe group, ezetimibe had no impact on body weight, fat mass, lipid metabolism, liver steatosis, glucose tolerance, or insulin sensitivity. In the high-fat chow + ezetimibe group, ezetimibe had no impact on body weight or fat mass but significantly decreased serum low-density lipoprotein cholesterol, triglyceride, and glutamate pyruvate transaminase levels; liver weight; hepatic triglyceride content; and hepatic cholesterol content and increased the hepatic total bile acid content. In association with increases in IRS-2 and Akt phosphorylation, ezetimibe ameliorated hepatic insulin resistance in the high-fat chow + ezetimibe group, but had no effect on insulin sensitivity in primary cultured hepatocytes. A DNA microarray and Taqman polymerase chain reaction revealed that ezetimibe up-regulated hepatic SREBP2 and SHP expression and down-regulated hepatic SREBP-1c expression. SHP silencing mainly in the liver worsened insulin resistance, and ezetimibe protected against insulin resistance induced by down-regulation of SHP. Ezetimibe down-regulated SREBP-1c in the liver and reversed hepatic insulin resistance in mice fed a high-fat diet.     

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.     

Sustained activation of the mammalian target of rapamycin nutrient sensing pathway is associated with hepatic insulin resistance, but not with steatosis, in mice

Aims/hypothesis Activation of nutrient sensing through mammalian target of rapamycin (mTOR) has been linked to the pathogenesis of insulin resistance. We examined activation of mTOR-signalling in relation to insulin resistance and hepatic steatosis in mice.Materials and methods Chronic hepatic steatosis and hepatic insulin resistance were induced by high-fat feeding of male C57BL/6Jico mice for 6 weeks. In addition, acute hepatic steatosis in the absence of insulin resistance was induced by pharmacological blockade of β-oxidation using tetradecylglycidic acid (TDGA). mTOR signalling was examined in liver homogenates.Results High-fat feeding caused obesity (p<0.001), hepatic steatosis (p<0.05) and hepatic insulin resistance (p<0.05). The phosphorylation of mTOR and its downstream targets p70S6 kinase and S6 ribosomal protein was two-fold higher in mice on a high-fat diet than in mice fed standard chow (all p<0.05) and associated with enhanced rates of protein synthesis. Acute induction of hepatic steatosis with TDGA had no effect on mTOR activity. The increased activity of the mTOR pathway in livers from mice on a high-fat diet could not be ascribed to diet-induced alterations in known modulators of mTOR activity such as circulating plasma leucine levels, phosphorylation of protein kinase B and AMP-activated protein kinase, and changes in mitochondrial function.Conclusions/interpretation High-fat diet induces increase of the mTOR nutrient sensing pathway in association with hepatic insulin resistance, but not with hepatic lipid accumulation as such.     

Obesity Potentiates AOM-Induced Colon Cancer

Obesity and diet affect the incidence and severity of various types of cancer, including colon cancer. It is not known whether obesity, independent of diet, is a risk factor for colon adenocarcinoma. We used azoxymethane (AOM) to induce colon cancer in mature genetically obese male Zucker rats (fa/fa) on low-fat crude diet (LFC, 10% fat) and their lean counterparts (Fa/fa and Fa/fa) on high-fat crude diet (HFC, 40% fat) for three months. At death visible tumors, histopathology, and colonic aberrant crypt (AC) formation were studied by blinded investigators. At death the obese animals were heavier (719 ± 19 g; mean ± sem) than lean animals regardless of diet or genotype (Fa/fa-LFC:451 ± 6 g; Fa/fa-HFC:441 ± 10 g; Fa/Fa-HFC:412 ± 9 g; P < 0.001 vs fa/fa by ANOVA). All AOM-treated rats developed AC, compared to none of the saline-injected controls. Macroscopic adenocarcinoma developed in 8/9 obese rats on LFC (P < 0.001), compared to none in lean rats regardless of diet. Obese rats had significantly more AC (876 ± 116) than any of the lean rats (Fa/fa-LFC:550 ± 99; Fa/fa-HFC:325 ± 37; Fa/Fa-HFC:360 ± 36; P < 0.05 vs fa/fa). We conclude that obesity more than exposure to high-fat diet was associated with colon carcinogenesis in these rats.     

Serum insulin and lipogenesis in the suckling ‘fatty’ fa/fa rat

Summary Preobese fatty fa/fa rats identified by their decreased rectal temperature were either given access to high carbohydrate chow or maintained on a suckling only diet till 20 days of age. Serum insulin, hepatic and adipose tissue fatty acid synthesis and lipogenic enzyme activities were low in suckling preobese fa/fa. In animals with access to chow diet, hepatic lipogenesis was unaltered, serum insulin rose to similar levels in lean and preobese fa/fa (lean 62±5; preobese 69±4 U/ml), but adipose tissue lipogenesis was increased to higher levels in the preobese than lean rats (lean 0.56±0.12; preobese 1.80±0.22 mol. tissue^-1. h^-1). The activities of glucose-6-phosphate dehydrogenase, acetyl coenzyme A carboxylase and fatty acid synthetase were increased in adipose tissue of preobese fa/fa rats. Neither streptozotocin treatment nor pretreatment with Triton WR 1339 abolished the difference in adipose tissue lipogenesis between lean and preobese fa/fa rats. Preobese fa/fa rats showed an enhanced insulin secretory response to a glucose load.     

Olmesartan prevents cardiovascular injury and hepatic steatosis in obesity and diabetes, accompanied by apoptosis signal regulating kinase-1 inhibition

Dietary obesity is associated with type 2 diabetes and cardiovascular diseases, although the underlying mechanism is unknown. This study was undertaken to elucidate the role of angiotensin II and apoptosis signal regulating kinase-1 (ASK1) in obesity/diabetes-associated cardiovascular complications and hepatic steatosis. Mice fed a high-fat diet were treated with olmesartan, an angiotensin II type 1 receptor blocker, to elucidate the role of angiotensin II in diabetic mice. Treatment of mice fed a high-fat diet with olmesartan markedly suppressed cardiac inflammation and fibrosis, as well as vascular endothelial dysfunction and remodeling, induced by obesity/diabetes. Moreover, olmesartan suppressed the disruption of the vascular endothelial NO synthase dimer in diabetic mice. Olmesartan also significantly prevented hepatic steatosis and fibrosis in diabetic mice. These beneficial effects of olmesartan on diabetic mice were associated with the attenuation of ASK1 activation in these mice. ASK1-deficient mice and wild-type mice were compared, regarding the effects of a high-fat diet. A comparison between ASK1-deficient and wild-type mice showed that ASK1 deficiency attenuated cardiac inflammation and fibrosis, as well as vascular endothelial dysfunction and remodeling induced by obesity/diabetes. The amelioration of vascular endothelial impairment by ASK1 deficiency was attributed to the prevention of endothelial NO synthase dimer disruption. ASK1 deficiency also significantly lessened hepatic steatosis in diabetic mice. In conclusion, our work provided the evidence that ASK1 is significantly activated in diet-induced diabetic mice and contributes to cardiovascular diseases and hepatic steatosis in diabetic mice. Moreover, the beneficial effects of angiotensin II inhibition on dietary diabetic mice seem to be mediated by the inhibition of ASK1 activation.     

Ameliorative effects of lutein on non-alcoholic fatty liver disease in rats

AIM: To investigate the therapeutic effects of lutein against non-alcoholic fatty liver disease(NAFLD) and the related underlying mechanism.METHODS: After 9 d of acclimation to a constant temperature-controlled room(20 ℃-22 ℃) under 12h light/dark cycles,male Sprague-Darley rats were randomly divided into two groups and fed a standard commercial diet(n = 8) or a high-fat diet(HFD)(n = 32) for 10 d.Animals receiving HFD were then randomly divided into 4 groups and administered with 0,12.5,25,or 50 mg/kg(body weight) per day of lutein for the next 45 d.At the end of the experiment,the perinephric and abdominal adipose tissues of the rats were isolated and weighed.Additionally,serum and liver lipid metabolic condition parameters were measured,and liver function and insulin resistance state indexes were assessed.Liver samples were collected and stained with hematoxylin eosin and Oil Red O,and the expression of the key factors related to insulin signaling and lipid metabolism in the liver were detected using Western blot and real-time polymerase chain reaction analyses.RESULTS: Our data showed that after being fed a high-fat diet for 10 d,the rats showed a significant gain in body weight,energy efficiency,and serum total cholesterol(TC) and triglyceride(TG) levels.Lutein supplementation induced fat loss in rats fed a highfat diet,without influencing body weight or energy efficiency,and decreased serum TC and hepatic TC and TG levels.Moreover,lutein supplementation decreased hepatic levels of lipid accumulation and glutamic pyruvic transaminase content,and also improved insulin sensitivity.Lutein administration also increased the expression of key factors in hepatic insulin signaling,such as insulin receptor substrate-2,phosphatidylinositol 3-kinase,and glucose transporter-2 at the gene and protein levels.Furthermore,high-dose lutein increased the expression of peroxisome proliferators activated receptor-α and sirtuin 1,which are associated with lipid metabolism and insulin signaling.CONCLUSION: These results demonstrate that lutein has positive effects on NAFLD via the modulation of hepatic lipid accumulation and insulin resistance.     

Genetic depletion of Soat2 diminishes hepatic steatosis via genes regulating de novo lipogenesis and by GLUT2 protein in female mice

Depletion of the cholesterol esterifying enzyme acyl-Coenzyme A: cholesterol acyltransferase 2 (ACAT2, encoded by Soat2) protects mice from atherosclerosis, diet-induced hypercholesterolemia, and hepatic steatosis when fed high-cholesterol diet. The glucose transporter 2 (GLUT2) represents the main gate of glucose uptake by the liver. Lipid synthesis from glucose (de novo lipogenesis; DNL) plays a pivotal role in the development of hepatic steatosis. Inhibition of DNL is a successful approach to reverse hepatic steatosis, as shown by different studies in mice and humans. Here we aimed to investigate whether depletion of Soat2 per se can reduce hepatic steatosis, also in the presence of very low levels of cholesterol in the diet, and the underlying mechanisms. Female Soat2?/? and wild type mice were either fed high-fat or high-carbohydrate diet and both contained <0.05% (w/w) cholesterol. Analysis in serum, liver, muscles and adipose tissues were performed. We found Soat2?/? mice fed high-fat, low-cholesterol diet to have less hepatic steatosis, decreased expression of genes involved in DNL and lower hepatic GLUT2. Similar findings were found in Soat2-/- mice fed high-carbohydrate, low-cholesterol diet.ConclusionDepletion of Soat2 reduces hepatic steatosis independently of the presence of high levels of cholesterol in the diet. Our study provides a link between hepatic cholesterol esterification, DNL, and GLUT2.     

Influence of diet composition on obesity, hyperlipemia and liver steatosis in Zucker fa/fa rats pair-fed with Zucker Fa/- rats

The effect of a four-week experiment on ten fa/fa Zucker rats (aged seven weeks at the beginning) fed on a lipid-rich diet (HL: 31 per cent w/w lipids, 45.6 per cent starch) was compared to that of a control diet (C: 10 per cent lipids, 66 per cent starch) on control Fa/- rats using a special pair-feeding apparatus that made it possible to obtain an identical intake rhythm. Energy level of the intake was significantly higher for the HL diet than for the C diet. At the end of the experiment, fa/fa rats remained obese and hyperlipemic, and still showed liver steatosis. With equal energy levels ingested, the obesity of fa/fa rats was comparable for both diets; hypertriglyceridemia and hypercholesterolemia were identical for both diets. When compared to the C diet, the HL diet modified neither their obesity nor their hyperlipemia. Obese rat liver on the HL diet showed lower levels for triacylglycerols, cholesterol, GGT, ALT, LDH and aldolase activities, while hepatic glycerol kinase and AST activities were higher than and comparable to, respectively, the C diet. Thus the HL diet led to a decreased liver steatosis for fa/fa rats as compared to the C diet.     

阻断肾素-血管紧张素系统对长期高脂喂养大鼠肝脂肪变性的影响

目的 观察长期高脂喂养诱导胰岛素抵抗状态大鼠肝脏脂肪变性与肝内血管紧张素原(AGT)、解偶联蛋白2(UCP-2)和转化生长因子β1(TGFβ1)表达的关系,并通过阻断肾素-血管紧张素系统(RAS)观察是否改善肝脂肪变性,探讨其作用机制.方法 40只大鼠分正常对照组、高脂组、血管紧张素转换酶抑制剂(ACEI)干预高脂组、血管紧张素Ⅱ受体阻滞剂(ARB)干预高脂组.正常血糖高胰岛素钳夹试验评价胰岛素敏感性,免疫组化和RT-PCR检测肝脏内AGT、UCP-2和TGFβ1蛋白及mRNA的表达,并检测血清脂质水平和肝内脂肪含量.结果 正常对照组、高脂组、ACEI干预高脂组、ARB干预高脂组稳态第2小时葡萄糖输注率分别为(11.22±1.45)、(6.22±1.02)、(8.08±1.13)、(8.16±1.26)mg·kg-1·min-1.高脂组血清学指标和肝内脂肪含量均高于正常对照组(P＜0.05),ACEI干预高脂组、ARB干预高脂组与高脂组比较,肝内脂肪含量降低(P＜0.01),脂肪变和纤维化减轻,肝内UCP-2和TGFβ1表达减少(P＜0.05).结论 阻断RAS可改善胰岛素抵抗,并可能通过下调肝内UCP-2和TGFβ1的表达,对长期高脂喂养大鼠肝脏有保护作用.     

Effect of adrenalectomy on the development of a pancreatic islet lesion in fa/fa rats

Summary Adrenalectomy prevents development of obesity and hyperinsulinaemia in obese (fa/fa) Zucker rats, thereby implicating the hypothalamopituitary-adrenal axis in the pathogenesis of obesity. In this study glucose-induced insulin secretion and glucokinase activity were investigated in isolated islets from adrenalectomized and control obese and lean female rats. Islets from control fa/fa rats were more sensitive to glucose with a half-maximal effective concentration (EC₅₀) of 6.1±2.0 mmol · l^–1 compared with 10.6±2.7 mmol · l^–1 for adrenalectomized fa/fa rat islets. Adrenalectomy did not alter the islet sensitivity to glucose in the lean rats (EC₅₀ of 9.4±1.5 mmol · l^–1 and 9.3±2.0 mmol · l^–1 for adrenalectomized and control lean rats respectively). Mannoheptulose did not inhibit insulin secretion from control obese rats; however at concentrations of 1.0 mmol · l^–1 or more it significantly inhibited glucose-induced insulin secretion in adrenalectomized obese and lean, and control lean rat islets (p<0.05). In adrenalectomized fa/fa islets the glucokinase K_m was increased twofold compared with the control fa/fa rats (9.5±1.5 mmol · l^–1 vs 5.0±1.5 mmol · l^–1, respectively), but there was no significant change in glucokinase K_m in the lean rat islets after adrenalectomy. Mannoheptulose (10 mmol · l^–1) caused a significant reduction in glucose phosphorylation in disrupted islets of adrenalectomized fa/fa and lean, and of control lean rats, but not of control fa/fa rats. These data demonstrate that development of abnormal regulation of glycolysis in pancreatic islet beta cells of fa/ fa rats, as indicated by the insulin response to mannoheptulose and glucokinase activity, is dependent on an intact hypothalamo-pituitary-adrenal axis.Abbreviations ADX Adrenalectomy/adrenalectomized - CRH corticotrophin releasing hormone - DMEM Dulbecco's modified Eagle's medium - EC₅₀ half-maximal effective concentration - HPA hypothalamo-pituitary-adrenal - MH mannoheptulose - Hepes 4-(2-hydroxyethyl)-1-piperazineethane sulphonic acid     

Effects of ursodeoxycholic acid and／or low-calorie diet on steatohepatitis in rats with obesity and hyperlipidemia

AIM: To evaluate the effects of ursodeoxycholic acid (UDCA) and/or low-calorie diet (LCD) on a rat model of nonalcoholic steatohepatitis (NASH). METHODS: Fifty-five Sprague-Dawley rats were divided into five groups. The control group (n = 9) was fed with standard rat diet for 12 wk, NASH group (n = 10) was fed with high-fat diet consisted of normal diet, 10% lard oil and 2% cholesterol for 12 wk, UDCA group (n = 10) was fed with high-fat diet supplemented with UDCA at a dose of 25 mg/(kg · d) in drinking water for 12 wk, LCD group (n = 10) was fed with high-fat diet for 10 wk and then LCD for 2 wk, and UDCA+LCD group (n = 15) was fed with high-fat diet for 10 wk, followed by LCD+UDCA for 2 wk. At the end of the experiment, body weight, serum biochemical index, and hepatopathologic changes were examined. RESULTS: Compared with the control group, rats in the NASH group had significantly increased body weight, liver weight, and serum lipid and aminotransferase levels. All rats in the NASH group developed steatohepatitis, as determined by their liver histology. Compared with the NASH group, there were no significant changes in body weight, liver weight, blood biochemical index, the degree of hepatic steatosis, and histological activity index (HAI) score in the UDCA group; however, body and liver weights were significantly decreased, and the degree of steatosis was markedly improved in rats of both the LCD group and the UDCA+LCD group, but significant improvement with regard to serum lipid variables and hepatic inflammatory changes were seen only in rats of the UDCA+LCD group, and not in the LCD group. CONCLUSION: LCD might play a role in the treatment of obesity and hepatic steatosis in rats, but it exerts no significant effect on both serum lipid disorders and hepatic inflammatory changes. UDCA may enhance the therapeutic effects of LCD on steatohepatitis accompanied by obesity and hyperlipidemia. However, UDCA alone is not effective in the prevention of steatohepatitis induced by high-fat diet.     

Long-term and rapid regulation of ob mRNA levels in adipose tissue from normal (Sprague Dawley rats) and obese [db/db mice,fa/fa rats) rodents

Summary Increased levels of mRNA transcribed from the ob gene in adipose tissue of obese/hyperinsulinaemic Zucker (fa/fa) rats were detectable as early as 3 weeks after birth and continued to rise there after in parallel with body weight and serum insulin. mRNA levels of two other fat-specific genes (ARL4, FST44) were unaltered. In C57BL/KsJ db/db mice, ob mRNA levels also increased in parallel with body weight and serum insulin, and remained elevated in older animals when insulin levels decreased. In heterozygous control animals (db/ + ; fa/Fa), mRNA levels were comparable with those in the homozygous controls. In normal Sprague Dawley rats, the ob mRNA increased continuously, but more slowly than in Zucker rats, in parallel with body weight and insulin levels, and reached 15 times higher levels in the heaviest rats (400 g) studied. In Sprague Dawley rats made diabetic by an injection of streptozotocin, ob mRNA levels were reduced by approximately 50 % after 24 h. A 24-h fasting period reduced the ob mRNA by 50 % in lean Sprague Dawley and Fa/Fa, but not in obese Zucker fa/fa rats, although insulin levels were reduced in both groups. These data indicate that ob mRNA levels increase in both normal and obese rodents in parallel with age, body weight and serum insulin, reflecting an early (Zucker rats, db-mice) or slowly developing (Sprague Dawley rats) resistance to leptin and insulin. This increase does not appear to be mediated by the recently described rapid regulation of ob mRNA by insulin, but seems to be due to a different, long-term control mechanism which signals the size of the fat depots. [Diabetologia (1996) 39: 758–765] Received: 27 October 1995 and in revised form: 5 December 1995     

Characterization of High-Fat,Diet-Induced,Non-alcoholic Steatohepatitis with Fibrosis in Rats

An ideal animal model is necessary for a clear understanding of the etiology, pathogenesis, and mechanisms of human non-alcoholic steatohepatitis (NASH) and for facilitating the design of effective therapy for this condition. We aimed to establish a rat model of NASH with fibrosis by using a high-fat diet (HFD). Male Sprague–Dawley (SD) rats were fed a HFD consisting of 88 g normal diet, 10 g lard oil, and 2 g cholesterol. Control rats were fed normal diet. Rats were killed at 4, 8, 12, 16, 24, 36, and 48 weeks after HFD exposure. Body weight, liver weight, and epididymal fat weight were measured. Serum levels of fasting glucose, triglyceride, cholesterol, alanine aminotransferase (ALT), free fatty acids (FFA), insulin, and tumor necrosis factor-alpha (TNF-α) were determined. Hepatic histology was examined by H&E stain. Hepatic fibrosis was assessed by VG stain and immunohistochemical staining for transforming growth factor beta 1 (TGF-β1), and alpha-smooth-muscle actin (α-SMA). The liver weight and liver index increased from week 4, when hepatic steatosis was also observed. By week 8, the body weight and epididymal fat weight started increasing, which was associated with increased serum levels of FFA, cholesterol, and TNF-α, as well as development of simple fatty liver. The serum ALT level increased from week 12. Steatohepatitis occurred from weeks 12 through 48. Apparent hepatic perisinosodial fibrosis did not occur until week 24, and progressed from week 36 to 48 with insulin resistance. Therefore, this novel model may be potentially useful in NASH study.     

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.     

Branched-chain amino acids alleviate hepatic steatosis and liver injury in choline-deficient high-fat diet induced NASH mice

BackgroundFor successful treatment for nonalcoholic steatohepatitis (NASH), it may be important to treat the individual causative factors. At present, however, there is no established treatment for this disease. Branched-chain amino acids (BCAAs) have been used to treat patients with decompensated cirrhosis.AimIn order to elucidate the mechanisms responsible for the effects of BCAAs on hepatic steatosis and disease progression, we investigated the effects of BCAA supplementation in mice fed a choline-deficient high-fat diet (CDHF), which induces NASH.MethodsMale mice were divided into four groups that received (1) choline-sufficient high fat (HF) diet (HF-control), (2) HF plus 2% BCAA in drinking water (HF-BCAA), (3) CDHF diet (CDHF-control), or (4) CDHF-BCAA for 8 weeks. We monitored liver injury, hepatic steatosis and cholesterol, gene expression related to lipid metabolism, and hepatic fat accumulation.ResultsSerum alanine aminotransferase (ALT) levels and hepatic triglyceride (TG) were significantly elevated in CDHF-control relative to HF-control. Liver histopathology revealed severe steatosis, inflammation, and pericellular fibrosis in CDHF-control, confirming the NASH findings. Serum ALT levels and hepatic TG and lipid droplet areas were significantly lower in CDHF-BCAA than in CDHF-control. Gene expression and protein level of fatty acid synthase (FAS), which catalyzes the final step in fatty acid biosynthesis, was significantly decreased in CDHF-BCAA than in CDHF-control (P < 0.05). Moreover, hepatic total and free cholesterol of CDHF-BCAA was significantly lower than those of CDHF-control.ConclusionsBCAA can alleviate hepatic steatosis and liver injury associated with NASH by suppressing FAS gene expression and protein levels.     

Hepatic and very low-density lipoprotein fatty acids in obese offspring of overfed dams

The combined effects of developmental programming and high-fat feeding at weaning on fatty acid metabolism of the offspring are not well known. In the present study, we aim at characterizing the influence of maternal and offspring's own diets on liver and very low-density lipoprotein (VLDL) lipids; fatty acid profiles of VLDL and liver phospholipids, triglycerides, and cholesteryl esters; and hepatic enzyme activities. Twenty obese male rats born to cafeteria diet–fed dams and 20 control rats born to control diet–fed dams were selected. At weaning, 10 rats of each group were fed control or cafeteria diet. Obese rats had a significant increase in serum glucose, insulin, leptin, VLDL apolipoprotein B100 and lipid levels, and hepatic fatty acid synthase and a reduction in acyl–coenzyme A oxidase and dehydrogenase activities compared with control pups at day 21 and day 90. Hepatic steatosis was apparent only at day 90. The proportions of saturated fatty acids and monounsaturated fatty acids and the oleic to stearic acid ratio were significantly increased, whereas polyunsaturated fatty acids and the arachidonic to linoleic acid ratio were decreased, in liver and VLDL lipids of obese pups compared with controls. The cafeteria diet at weaning induced more severe abnormalities in obese rats. In conclusion, maternal cafeteria diet induced a permanent reduction in hepatic β-oxidation and an increase in hepatic lipogenesis that caused liver steatosis and VLDL and fatty acid alterations in adult offspring. These preexisting alterations in offspring were worsened under a high-fat diet from weaning to adulthood. Nutritional recommendations in obesity must then target maternal and postnatal nutrition, especially fatty acid composition.     

Granulocyte-colony stimulating factor prevents the development of hepatic steatosis in rats

Background and aims. Previously, we reported that granulocyte-colony stimulating factor (G-CSF) improves hepatic steatosis in experimental animals. It may also have preventive effects on the development of hepatic steatosis. Therefore, we investigated the preventive effects of G-CSF by using a high-fat diet (HFD) rat model. Materials and methods. Twelve rats were fed HFD and 6 rats were fed control diet from 10 weeks of age. Once little steatosis was confirmed in the liver (after 10 weeks of feeding the HFD; at 20 weeks of age), HFD rats were randomly divided into two groups and treated with either G-CSF (100 Mg kg^-1 day^-1 for 5 consecutive days every other week; HFD/G-CSF rats) or saline (HFD/saline rats) for 10 weeks at 20 weeks of age. All rats were sacrificed at 30 weeks of age. Histology was examined by hematoxylin and eosin (H-E) and Oil Red O staining, and the expression levels of genes of associated with lipogenesis and β-oxidation enzymes were determined by qRT-PCR.Results. Histological examinations revealed that HFD/G-CSF rats had significantly lower lipid accumulation in their hepatocytes than did HFD/saline rats (p < 0.05). HFD/G-CSF rats also showed lower expression levels of genes associated with lipogenesis and higher expression levels of genes associated with β-oxidation than HFD/saline rats (p < 0.05). Conclusion. In conclusion, we found that G-CSF prevented development of hepatic steatosis in an HFD rat model. The preventive effect may be associated with the regulation of gene expression involved in hepatic lipogenesis and β-oxidation.     

Melatonin reduces hepatic mitochondrial dysfunction in diabetic obese rats

Hepatic mitochondrial dysfunction is thought to play a role in the development of liver steatosis and insulin resistance, which are both common characteristics of obesity and type 2 diabetes mellitus (T2DM). It was hypothesized that the antioxidant properties of melatonin could potentially improve the impaired functions of hepatic mitochondria in diabetic obese animals. Male Zucker diabetic fatty (ZDF) rats and lean littermates (ZL) were given either melatonin (10 mg/kg BW/day) orally for 6 wk (M‐ZDF and M‐ZL) or vehicle as control groups (C‐ZDF and C‐ZL). Hepatic function was evaluated by measurement of serum alanine transaminase and aspartate transaminase levels, liver histopathology and electron microscopy, and hepatic mitochondrial functions. Several impaired functions of hepatic mitochondria were observed in C‐ZDF in comparison with C‐ZL rats. Melatonin treatment to ZDF rats decreases serum levels of ALT (P < 0.001), alleviates liver steatosis and vacuolation, and also mitigates diabetic‐induced mitochondrial abnormalities, glycogen, and lipid accumulation. Melatonin improves mitochondrial dysfunction in M‐ZDF rats by increasing activities of mitochondrial citrate synthase (P < 0.001) and complex IV of electron transfer chain (P < 0.05) and enhances state 3 respiration (P < 0.001), respiratory control index (RCR) (P < 0.01), and phosphorylation coefficient (ADP/O ratio) (P < 0.05). Also melatonin augments ATP production (P < 0.05) and diminishes uncoupling protein 2 levels (P < 0.001). These results demonstrate that chronic oral melatonin reduces liver steatosis and mitochondria dysfunction in ZDF rats. Therefore, it may be beneficial in the treatment of diabesity.