Crucial roles of Nox2-derived oxidative stress in deteriorating the function of insulin receptors and endothelium in dietary obesity of middle-aged mice

Background and Purpose

Systemic oxidative stress associated with dietary calorie overload plays an important role in the deterioration of vascular function in middle-aged patients suffering from obesity and insulin resistance. However, effective therapy is still lacking.

Experimental Approach

In this study, we used a mouse model of middle-aged obesity to investigate the therapeutic potential of pharmaceutical inhibition (apocynin, 5 mM supplied in the drinking water) or knockout of Nox2, an enzyme generating reactive oxygen species (ROS), in high-fat diet (HFD)–induced obesity, oxidative stress, insulin resistance and endothelial dysfunction. Littermates of C57BL/6J wild-type (WT) and Nox2 knockout (KO) mice (7 months old) were fed with a HFD (45% kcal fat) or normal chow diet (NCD, 12% kcal fat) for 16 weeks and used at 11 months of age.

Key Results

Compared to NCD WT mice, HFD WT mice developed obesity, insulin resistance, dyslipidaemia and hypertension. Aortic vessels from these mice showed significantly increased Nox2 expression and ROS production, accompanied by significantly increased ERK1/2 activation, reduced insulin receptor expression, decreased Akt and eNOS phosphorylation and impaired endothelium-dependent vessel relaxation to acetylcholine. All these HFD-induced abnormalities (except the hyperinsulinaemia) were absent in apocynin-treated WT or Nox2 KO mice given the same HFD.

Conclusions and Implications

In conclusion, Nox2-derived ROS played a key role in damaging insulin receptor and endothelial function in dietary obesity after middle-age. Targeting Nox2 could represent a valuable therapeutic strategy in the metabolic syndrome.     

Anthelmintics nitazoxanide protects against experimental hyperlipidemia and hepatic steatosis in hamsters and mice

Lipid metabolism disorders contribute to hyperlipidemia and hepatic steatosis. It is ideal to develop drugs simultaneous improving both hyperlipidemia and hepatic steatosis. Nitazoxanide is an FDA-approved oral antiprotozoal drug with excellent pharmacokinetic and safety profile. We found that nitazoxanide and its metabolite tizoxanide induced mild mitochondrial uncoupling and subsequently activated AMPK in HepG2 cells. Gavage administration of nitazoxanide inhibited high-fat diet (HFD)-induced increases of liver weight, blood and liver lipids, and ameliorated HFD-induced renal lipid accumulation in hamsters. Nitazoxanide significantly improved HFD-induced histopathologic changes of hamster livers. In the hamsters with pre-existing hyperlipidemia and hepatic steatosis, nitazoxanide also showed therapeutic effect. Gavage administration of nitazoxanide improved HFD-induced hepatic steatosis in C57BL/6J mice and western diet (WD)-induced hepatic steatosis in Apoe^–/– mice. The present study suggests that repurposing nitazoxanide as a drug for hyperlipidemia and hepatic steatosis treatment is promising.     

小鼠代谢综合征模型的特征及西布曲明的治疗作用研究

目的研究高脂饲料诱导C57BL/6 J小鼠形成代谢综合征(MS)模型的特点,以及盐酸西布曲明对MS小鼠的治疗作用。方法用含10%猪油、2%胆固醇及0.4%胆酸钠的高脂饲料喂养9 wk♂C57BL/6 J小鼠18.5 wk,然后用西布曲明8 mg.kg-1灌胃10 d。实验终点时测定体重、腹腔内脏脂肪及肝脏湿重和肝游离脂肪酸(FFA)含量;取血分离血清测定血脂、血糖和血清胰岛素水平,并计算胰岛素抵抗指数;肝组织进行HE染色和油红O染色,光镜下观察脂肪病变程度。结果模型组小鼠脂肪重量及系数、肝脏重量均明显升高,肝组织切片光镜下可见明显的脂肪病变;血总胆固醇(TC)、高密度脂蛋白胆固醇(HDL-C)及低密度脂蛋白胆固醇(LDL-C)水平均升高,且以LDL-C升高最为明显;高胆固醇喂养使模型小鼠血甘油三酯(TG)水平降低。西布曲明可改善MS小鼠的中心性肥胖、高血糖、高胰岛素血症和胰岛素抵抗,并进一步降低MS小鼠的血TG水平;但是,西布曲明可增加肝FFA含量,对MS小鼠的肝脏湿重及肝脂肪病变无改善作用。结论高脂饲料长期喂养C57小鼠可成功建立类似人类MS表现的动物模型;西布曲明可改善MS小鼠的中心性肥胖、糖脂代谢异常、增加机体对胰岛素的敏感性,对MS有一定的治疗作用。     

Ablation of Akt2 and AMPKα2 rescues high fat diet-induced obesity and hepatic steatosis through Parkin-mediated mitophagy

Given the opposing effects of Akt and AMP-activated protein kinase (AMPK) on metabolic homeostasis, this study examined the effects of deletion of Akt2 and AMPKα2 on fat diet-induced hepatic steatosis. Akt2–Ampkα2 double knockout (DKO) mice were placed on high fat diet for 5 months. Glucose metabolism, energy homeostasis, cardiac function, lipid accumulation, and hepatic steatosis were examined. DKO mice were lean without anthropometric defects. High fat intake led to adiposity and decreased respiratory exchange ratio (RER) in wild-type (WT) mice, which were ablated in DKO but not Akt2^−/− and Ampkα2^−/− mice. High fat intake increased blood and hepatic triglycerides and cholesterol, promoted hepatic steatosis and injury in WT mice. These effects were eliminated in DKO but not Akt2^−/− and Ampkα2^−/− mice. Fat diet promoted fat accumulation, and enlarged adipocyte size, the effect was negated in DKO mice. Fat intake elevated fatty acid synthase (FAS), carbohydrate-responsive element-binding protein (CHREBP), sterol regulatory element-binding protein 1 (SREBP1), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), peroxisome proliferator-activated receptor-α (PPARα), PPARγ, stearoyl-CoA desaturase 1 (SCD-1), phosphoenolpyruvate carboxykinase (PEPCK), glucose 6-phosphatase (G6Pase), and diglyceride O-acyltransferase 1 (DGAT1), the effect was absent in DKO but not Akt2^−/− and Ampkα2^−/− mice. Fat diet dampened mitophagy, promoted inflammation and phosphorylation of forkhead box protein O1 (FoxO1) and AMPKα1 (Ser⁴⁸⁵), the effects were eradicated by DKO. Deletion of Parkin effectively nullified DKO-induced metabolic benefits against high fat intake. Liver samples from obese humans displayed lowered microtubule-associated proteins 1A/1B light chain 3B (LC3B), Pink1, Parkin, as well as enhanced phosphorylation of Akt, AMPK (Ser⁴⁸⁵), and FoxO1, which were consolidated by RNA sequencing (RNAseq) and mass spectrometry analyses from rodent and human livers. These data suggest that concurrent deletion of Akt2 and AMPKα2 offers resilience to fat diet-induced obesity and hepatic steatosis, possibly through preservation of Parkin-mediated mitophagy and lipid metabolism.KEY WORDS: Akt2, AMPK, Parkin, High fat intake, Obesity, Steatosis, Mitophagy, FoxO1     

Ablation of Akt2 and AMPKα2 rescues high fat diet-induced obesity and hepatic steatosis through Parkin-mediated mitophagy

Given the opposing effects of Akt and AMP-activated protein kinase (AMPK) on metabolic homeostasis, this study examined the effects of deletion of Akt2 and AMPKα2 on fat diet-induced hepatic steatosis. Akt2–Ampkα2 double knockout (DKO) mice were placed on high fat diet for 5 months. Glucose metabolism, energy homeostasis, cardiac function, lipid accumulation, and hepatic steatosis were examined. DKO mice were lean without anthropometric defects. High fat intake led to adiposity and decreased respiratory exchange ratio (RER) in wild-type (WT) mice, which were ablated in DKO but not Akt2^−/− and Ampkα2^−/− mice. High fat intake increased blood and hepatic triglycerides and cholesterol, promoted hepatic steatosis and injury in WT mice. These effects were eliminated in DKO but not Akt2^−/− and Ampkα2^−/− mice. Fat diet promoted fat accumulation, and enlarged adipocyte size, the effect was negated in DKO mice. Fat intake elevated fatty acid synthase (FAS), carbohydrate-responsive element-binding protein (CHREBP), sterol regulatory element-binding protein 1 (SREBP1), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), peroxisome proliferator-activated receptor-α (PPARα), PPARγ, stearoyl-CoA desaturase 1 (SCD-1), phosphoenolpyruvate carboxykinase (PEPCK), glucose 6-phosphatase (G6Pase), and diglyceride O-acyltransferase 1 (DGAT1), the effect was absent in DKO but not Akt2^−/− and Ampkα2^−/− mice. Fat diet dampened mitophagy, promoted inflammation and phosphorylation of forkhead box protein O1 (FoxO1) and AMPKα1 (Ser⁴⁸⁵), the effects were eradicated by DKO. Deletion of Parkin effectively nullified DKO-induced metabolic benefits against high fat intake. Liver samples from obese humans displayed lowered microtubule-associated proteins 1A/1B light chain 3B (LC3B), Pink1, Parkin, as well as enhanced phosphorylation of Akt, AMPK (Ser⁴⁸⁵), and FoxO1, which were consolidated by RNA sequencing (RNAseq) and mass spectrometry analyses from rodent and human livers. These data suggest that concurrent deletion of Akt2 and AMPKα2 offers resilience to fat diet-induced obesity and hepatic steatosis, possibly through preservation of Parkin-mediated mitophagy and lipid metabolism.     

Pepsin-digested chicken-liver hydrolysate attenuates hepatosteatosis by relieving hepatic and peripheral insulin resistance in long-term high-fat dietary habit

This study aims to clarify the effects of chicken liver hydrolysates (CLHs) on long-term high-fat diet (HFD)-induced insulin resistance (IR) and hepatosteatosis in mice. In vitro, the 400 μM oleic acid (OA)-added medium successfully stimulated the cellular steatosis on FL83B cells, and the cellular steatosis was attenuated ( p < 0.05) by supplementing with CLHs (4 mg/L). In vivo, the effects of CLHs on IR and hepatosteatosis development were tested in 20-week HFD-fed mice. HFD-induced increases in final body weight, but body weight gains of mice were decreased ( p < 0.05) by supplementing CLHs. Elevated ( p < 0.05) serum aspartate aminotransferase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), free fatty acids (FFAs), triglyceride (TG), total cholesterol (TC), and fasted glucose values in HFD-fed mice decreased ( p < 0.05) by supplementing CLHs. Both results of hepatic steatosis and fibrotic scores also indicated the retardation ( p < 0.05) of the hepatosteatosis in cotreated groups. Moreover, the CLH supplementation sustained ( p < 0.05) hepatic and peripheral insulin signal sensitivity in HFD-fed mice. CLH supplementation could ameliorate hepatic lipid deposition, hepatic/peripheral IR in a long-term high-fat dietary habit, and also improve the universal glucose homeostasis by upregulating hepatic and peripheral insulin sensitivities.     

Anti-toll-like receptor 2 antibody ameliorates hepatic injury,inflammation, fibrosis and steatosis in obesity-related metabolic disorder rats via regulating MAPK and NF-κB pathways

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide, which includes a spectrum of histological liver changes. Non-alcoholic steatohepatitis (NASH) is considered to be the progressive subtype of NAFLD, which is characterized by lobular inflammation and cellular ballooning on the basis of steatosis. There is a critical need to develop novel and effective therapeutic approaches for NAFLD/NASH. The activation of toll-like receptor 2 (TLR2) signaling pathway plays a key role in high-fat-related inflammation, triggering the occurrence and development of NASH. Herein, the anti-TLR2 monoclonal antibody (TLR2 mAb) was prepared and investigated for its ability to ameliorate the inflammatory response in vivo and in vitro. The anti-inflammatory role of TLR2 mAb in vitro was examined in NR8383 macrophage cells and THP-1 derived macrophage cells. For confirmation in vivo, three groups of SD rats were treated for 20 weeks: rats in the control were fed with a standard diet; rates in the IgG and TLR2 mAb groups were fed with a high-fat diet and with IgG or TLR2 mAb, respectively. Liver tissue and serum were collected for further analysis. Results showed that after 4-week treatment with TLR2 mAb, metabolic parameters in rats were improved markedly (body weight, fasting blood glucose level, liver steatosis, inflammatory response and fibrosis). Moreover, western blotting demonstrated that the TLR2 mAb blocked MAPKs and NF-κB activation, and inhibited the expression of inflammatory factors in rat liver tissue. These effects suggested that TLR2 mAb could improve HFD-induced hepatic injury, inflammation, fibrosis and steatosis by suppressing inflammatory response and regulating the hepatic MAPKs and NF-κB signaling pathways. This suggests that TLR2 may be a novel therapeutic target for metabolic diseases especially NASH.     

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.     

Targeting macrophagic 17β-HSD7 by fenretinide for the treatment of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease(NAFLD)is the most common chronic liver disease worldwide and macrophage polarization plays an important role in its pathogenesis. However, which molecule regulates macrophage polarization in NAFLD remains unclear. Herein, we showed NAFLD mice exhibited increased 17β-hydroxysteroid dehydrogenase type 7(17β-HSD7)expression in hepatic macrophages concomitantly with elevated M1 polarization. Single-cell RNA sequencing on hepatic non-parenchymal cells isolated from wi...     

N-acetylcysteine Protects Mice from High Fat Diet-induced Metabolic Disorders

Purpose

To study the effects of N-acetylcysteine (NAC, C₅H₉NO₃S) on diet-induced obesity and obesity-related metabolic disorders.

Methods

Six-week-old male C57BL/6 mice fed a chow or high-fat diet (HFD) were treated with NAC (2 g/L) in drinking water for 11 weeks. Its influences on body weight and food intake were manually measured, and influence on body composition were analyzed by magnetic residence imaging. Glucose meter and ELISA were used to determine serum glucose and insulin levels, as well as lipid content in the liver. The effects of NAC treatment on mRNA levels of genes involved in inflammation, thermogenesis, and lipid metabolism in various tissues were determined by real time PCR.

Results

NAC supplementation inhibited the increase of fat mass and the development of obesity when mice were fed an HFD. NAC treatment significantly lowered HFD-induced macrophage infiltration, and enhanced adiponectin gene expression, resulting in reduced hyperglycemia and hyperinsulinemia, and improvement of insulin resistance. NAC oral administration suppressed hepatic lipid accumulation, as evidenced by lower levels of triglyceride and cholesterol in the liver. The beneficial effects are associated with a decrease of hepatic Pparγ and its target gene expression, and an increase in the expression of genes responsible for lipid oxidation and activation of farnesoid X receptor. Furthermore, NAC treatment also stimulates expression of thermogenic genes.

Conclusion

These results provide direct proof of the protective potential of NAC against HFD-induced obesity and obesity-associated metabolic disorders.

     

Fenretinide ameliorates insulin resistance and fatty liver in obese mice

Fenretinide (FEN), a ligand of retinol binding protein 4 (RBP4), has been suggested as a measure to reduce insulin resistance and its associated disorders such as obesity, and fatty liver by reducing serum RBP4. We investigated whether there is another possible mechanism by which fenretinide reduces insulin resistance and fatty liver in genetically obese (ob/ob) mice. Male obese mice fed a high-fat diet (45% of calories from fat) were divided into two groups (n=13 each). One (FEN) received fenretinide (20 mg/kg body weight, intraperitoneally) and the other (O) received vehicle three times weekly for 24 d. C57BL/6J mice fed a normal-fat diet (16% of calories from fat) were used as a control (C; n=13). No changes in fat weight and serum leptin level could be observed in FEN mice. Lower plasma RBP4 was observed in FEN mice compared with O mice. Fenretinide improved whole-body insulin sensitivity based on glucose and insulin tolerance tests and the homeostasis model assessment of insulin resistance. Fenretinide decreased the plasma lipid (triglyceride, cholesterol, and free-fatty acid) levels, hepatic TG level, and histological steatosis score. The mechanism by which fenretinide prevents fatty liver may be explained by an increased plasma adiponectin level, increased activation of hepatic AMP-activated protein kinase, and the expression of peroxisome proliferator-activated protein-α and peroxisomal acyl-CoA oxidase, which promote fat oxidation. FEN alleviated insulin resistance and fatty liver in obese mice and thus may act as an anti-lipidemic and anti-diabetic drug.     

EGb761, an extract of Ginkgo biloba leaves,reduces insulin resistance in a high-fat-fed mouse model

EGb761, a standardized and well-defined product extract of Ginkgo biloba leaves, has beneficial effects on the treatment of multiple diseases, including diabetes and dyslipidemia. However, it is still unclear whether EGb761 can increase insulin sensitivity. The objectives of the present study are to evaluate the effects of EGb761 on insulin sensitivity in an obese and insulin-resistant mouse model, established through chronic feeding of C57BL/6J mice with a high-fat diet (HFD), and to explore potential mechanisms. Mice fed with HFD for 18 weeks (starting from 4 weeks of age) developed obesity, dyslipidemia (as indicated by biochemical measurements of blood glucose, triglyceride (TG), total cholesterol (TC), and free fatty acids (FFA)), and insulin resistance (as determined by the oral glucose tolerance test (OGTT) and the homeostasis model assessment of insulin resistance (HOMA-IR) index), compared to control mice fed with a standard laboratory chow. Oral treatment of the HFD-fed mice with EGb761, at low (100 mg/kg), medium (200 mg/kg), or high (400 mg/kg) doses, via oral gavage (once daily) for 8 weeks (starting from 26 weeks of age) dose-dependently enhanced glucose tolerance in OGTT, and decreased both the insulin levels (by 29%, 55%, and 70%, respectively), and the HOMA-IR index values (by 50%, 69%, and 80%, respectively). EGb761 treatment also ameliorated HFD-induced obesity, dyslipidemia, and liver injury, as indicated by decreases in body weight (by 4%, 11%, and 16%, respectively), blood TC levels (by 23%, 32%, and 37%, respectively), blood TG levels (by 17%, 23%, and 33%, respectively), blood FAA levels (by 35%, 38%, and 46%, respectively), and liver index (liver weight/body weight) values (by 12.8%, 25%, and 28%, respectively) in the low, medium, and high EGb761 dose groups, respectively. In further mechanism studies, EGb761 was found to protect hepatic insulin receptor β and insulin receptor substrate 1 from HFD-induced degradation, and to keep the AMP-activated protein kinase, which plays a crucial role in reducing lipotoxicity, from HFD-induced inactivation. We conclude that EGb761 can effectively reduce HFD-induced insulin resistance and ameliorate other symptoms of the metabolic syndrome.     

Increased adiposity on normal diet, but decreased susceptibility to diet-induced obesity in mu-opioid receptor-deficient mice

The mu-opioid receptor encoded by the Oprm1 gene plays a crucial role in the mediation of food reward and drug-induced positive reinforcement, but its genetic deletion has been shown to provide food intake-independent, partial protection from diet-induced obesity. We hypothesized that mu-opioid receptor-deficient mice would show an even greater, intake-dependent, resistance to high-fat diet-induced obesity if the diet comprises a sweet component. We generated an F2 population by crossing the heterozygous offspring of homozygous female Oprm1(-/-) mice (on a mixed C57BL/6 and BALB/c genetic background) with male inbred C57BL/6 mice. Groups of genotyped wild-type (WT) and homozygous mutant (KO) males and females were fed either control chow or a high caloric palatable diet consisting of sweet, liquid chocolate-flavored Ensure together with a solid high-fat diet. Food intake, body weight, and body composition was measured over a period of 16 weeks. Unexpectedly, male, and to a lesser extent female, KO mice fed chow for the entire period showed progressively increased body weight and adiposity while eating significantly more chow. In contrast, when exposed to the sweet plus high-fat diet, male, and to a lesser extent female, KO mice gained significantly less body weight and fat mass compared to WT mice when using chow fed counterparts for reference values. Male KO mice consumed 33% less of the sweet liquid diet but increased intake of high-fat pellets, so that total calorie intake was not different from WT animals. These results demonstrate a dissociation of the role of mu-opioid receptors in the control of adiposity for different diets and sex. On a bland diet, normal receptor function appears to confer a slightly catabolic predisposition, but on a highly palatable diet, it confers an anabolic metabolic profile, favoring fat accretion. Because of the complexity of mu-opioid gene regulation and tissue distribution, more selective and targeted approaches will be necessary to fully understand the underlying mechanisms.     

Review article: the treatment of non-alcoholic steatohepatitis with thiazolidinediones

It is generally accepted that non-alcoholic fatty liver disease will be the most frequent liver disease in the near future and that the management of patients with non-alcoholic fatty liver disease will be a challenge for hepatologists in the next decades. Non-alcoholic fatty liver disease is considered the hepatic manifestation of the metabolic syndrome, in which insulin resistance plays a crucial role. Although steatosis will often not progress to severe liver disease, in some patients, it results in cirrhosis and even hepatocellular carcinoma. Therefore, it is important to identify those patients at risk for developing fibrosis. Age, diabetes, obesity and hypertriglyceridaemia are independent risk factors for fibrosis in patients with elevated serum alanine aminotransferase levels and steatosis on ultrasound. The presence of multiple metabolic disorders increases the risk. Apart from diet, exercise and correction of underlying metabolic abnormalities, no specific treatment is available at the moment. Theoretically, thiazolidinediones are an attractive way to treat non-alcoholic fatty liver disease, because they improve insulin resistance. Some preliminary studies with thiazolidinediones were encouraging, as steatosis, inflammation and fibrosis improved in a substantial number of patients. Although no serious side effects occurred in the pilot studies, we should look vigilantly for hepatotoxicity, as the first generation thiazolidinediones proved to be toxic for the liver.     

Exposure to an environmentally relevant mixture of organochlorine compounds and polychlorinated biphenyls Promotes hepatic steatosis in male Ob/Ob mice

Hepatic steatosis is recognized as an independent risk factor for the development of cardiovascular disease. While obesity and type 2 diabetes are well‐established risk factors in the development of hepatic steatosis, recent studies have revealed exposure to mixtures of persistent organic pollutants (POPs), which are environmental contaminants in various fatty foods, can promote steatosis. Thus, the present study was designed to determine if exposure to a defined mixture of prevalent polychlorinated biphenyls (PCBs) and organochlorine (OC) pesticides or their metabolites promote hepatic steatosis in a genetically induced model of type 2 diabetes, the leptin‐deficient ob/ob mouse. Male C57BL/6J wild type (WT) or ob/ob mice were administered an environmentally relevant mixture of PCBs and OCs for 7 weeks via oral gavage. Exposure to POPs did not significantly alter fasting serum glucose or insulin levels. However, POPs exposure significantly increased hepatic triglyceride content in ob/ob animals, while decreasing serum triglyceride levels. This POPs‐mediated increase in hepatic triglyceride content did not appear to be associated with significantly increased inflammation in either the liver or adipose. Exposure to POPs significantly induced the expression of cytochrome P450 3a11 in WT animals, yet the expression of this cytochrome was significantly downregulated in ob/ob animals regardless of POPs exposure. Taken together, the present data indicate exposure to an environmentally relevant mixture of both PCBs and OC pesticides in ob/ob mice promotes hepatic steatosis while decreasing hypertriglyceridemia, which demonstrates exposure to a defined mixture of POPs alters systemic lipid metabolism in a genetically induced model of obesity and type 2 diabetes. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1399–1411, 2017.     

Effects of the Combination of Evogliptin and Leucine on Insulin Resistance and Hepatic Steatosis in High-Fat Diet-Fed Mice

In this study, we aimed to investigate the effects of 8 weeks of treatment with a combination of evogliptin and leucine, a branched-chain amino acid, in mice with high-fat diet (HFD)-induced diabetes. Treatment with evogliptin alone or in combination with leucine reduced the body weight of the mice, compared to the case for those from the HFD control group. Long-term treatment with evogliptin alone or in combination with leucine resulted in a significant reduction in glucose intolerance; however, leucine alone did not affect postprandial glucose control, compared to the case for the mice from the HFD control group. Furthermore, the combination of evogliptin and leucine prevented HFD-induced insulin resistance, which was associated with improved homeostasis model assessment for insulin resistance, accompanied by markedly reduced liver fat deposition, hepatic triglyceride content, and plasma alanine aminotransferase levels. The combination of evogliptin and leucine increased the gene expression levels of hepatic peroxisome proliferator-activated receptor alpha, whereas those of the sterol regulatory element-binding protein 1 and stearoyl-CoA desaturase 1 were not altered, compared to the case in the HFD-fed mice (p<0.05). Thus, our results suggest that the combination of evogliptin and leucine may be beneficial for treating patients with type 2 diabetes and hepatic steatosis; however, further studies are needed to delineate the molecular mechanisms underlying the action of this combination.     

Silymarin improved diet-induced liver damage and insulin resistance by decreasing inflammation in mice

Context: Silymarin is the main flavonoid extracted from milk thistle, which has been used to treat liver diseases.

Objective: The in vivo effect of silymarin on HFD-induced insulin resistance and fatty liver in mice was studied.

Materials and methods: Male C57BL/6 mice were fed with high-fat diet (HFD) to induce obesity and insulin resistance and treated with 30, 60?mg/kg silymarin for 18 days. Food intake, body weight and the content/histology of epididymal fat and liver tissue were examined; the content of lipids, AST, ALT and inflammatory cytokines in serum were estimated.

Results: Administration of silymarin caused bodyweight loss in diet induced obesity (DIO) mice (HFD group: 47.7?g, 60?mg/kg group: 43.0?g) while the food intake remain unchanged. Silymarin (60?mg/kg) significantly reduced the epididymal fat mass (from 1.75?g to 1.12?g). Elevated plasma lipids (TC 6.1?mM, TG 1.3?mM, LDL 1.2?mM) in DIO mice were all suppressed by silymarin (TC 4.5?mM, TG 0.89?mM, LDL 0.9?mM), as well as insulin (5.1?ng/ml in HFD group to 2.0?ng/ml (60?mg/kg silymarin). Examination of cytokine levels (TNF-α, IL-1β and IL-6) in each group proved that silymarin treatment significantly decreased inflammation in DIO mice. Finally, silymarin effectively protected liver from HFD-induced injury as evidenced by decreasing histological damage and reducing ALT and AST levels, as follows: ALT; 47.4?U/L in HFD group to 28.4?U/L (60?mg/kg silymarin); AST; 150.1?U/L in HFD group to 88.1?U/L (60?mg/kg silymarin) in serum.

Discussion and conclusion: Our results suggested that silymarin-induced alleviation of inflammatory response could be a mechanism responsible for its benefits against liver damage and insulin resistance.     

Hepatic effects of a methionine-choline-deficient diet in hepatocyte RXRalpha-null mice

Retinoid X receptor-alpha (RXRalpha) is an obligate partner for several nuclear hormone receptors that regulate important physiological processes in the liver. In this study the impact of hepatocyte RXRalpha deficiency on methionine and choline deficient (MCD) diet-induced steatosis, oxidative stress, inflammation, and hepatic transporters gene expression were examined. The mRNA of sterol regulatory element-binding protein (SREBP)-regulated genes, important for lipid synthesis, were not altered in wild type (WT) mice, but were increased 2.0- to 5.4-fold in hepatocyte RXRalpha-null (H-RXRalpha-null) mice fed a MCD diet for 14 days. Furthermore, hepatic mRNAs and proteins essential for fatty acid beta-oxidation were not altered in WT mice, but were decreased in the MCD diet-fed H-RXRalpha-null mice, resulting in increased hepatic free fatty acid levels. Cyp2e1 enzyme activity and lipid peroxide levels were induced only in MCD-fed WT mice. In contrast, hepatic mRNA levels of pro-inflammatory factors were increased only in H-RXRalpha-null mice fed the MCD diet. Hepatic uptake transporters Oatp1a1 and Oatp1b2 mRNA levels were decreased in WT mice fed the MCD diet, whereas the efflux transporter Mrp4 was increased. However, in the H-RXRalpha-null mice, the MCD diet only moderately decreased Oatp1a1 and induced both Oatp1a4 and Mrp4 gene expression. Whereas the MCD diet increased serum bile acid levels and alkaline phosphatase activity in both WT and H-RXRalpha-null mice, serum ALT levels were induced (2.9-fold) only in the H-RXRalpha-null mice. In conclusion, these data suggest a critical role for RXRalpha in hepatic fatty acid homeostasis and protection against MCD-induced hepatocyte injury.     

Exendin-4 Improves Nonalcoholic Fatty Liver Disease by Regulating Glucose Transporter 4 Expression in ob/ob Mice

Exendin-4 (Ex-4), a glucagon-like peptide-1 receptor (GLP-1R) agonist, has been known to reverse hepatic steatosis in ob/ob mice. Although many studies have evaluated molecular targets of Ex-4, its mechanism of action on hepatic steatosis and fibrosis has not fully been determined. In the liver, glucose transporter 4 (GLUT4) is mainly expressed in hepatocytes, endothelial cells and hepatic stellate cells (HSCs). In the present study, the effects of Ex-4 on GLUT4 expression were determined in the liver of ob/ob mice. Ob/ob mice were treated with Ex-4 for 10 weeks. Serum metabolic parameters, hepatic triglyceride levels, and liver tissues were evaluated for hepatic steatosis. The weights of the whole body and liver in ob/ob mice were reduced by long-term Ex-4 treatment. Serum metabolic parameters, hepatic steatosis, and hepatic fibrosis in ob/ob mice were reduced by Ex-4. Particularly, Ex-4 improved hepatic steatosis by enhancing GLUT4 via GLP-1R activation in ob/ob mice. Ex-4 treatment also inhibited hepatic fibrosis by decreasing expression of connective tissue growth factor in HSCs of ob/ob mice. Our data suggest that GLP-1 agonists exert a protective effect on hepatic steatosis and fibrosis in obesity and type 2 diabetes.