Enhanced Lipid Oxidation and Maintenance of Muscle Insulin Sensitivity Despite Glucose Intolerance in a Diet-Induced Obesity Mouse Model

Background

Diet-induced obesity is a rising health concern which can lead to the development of glucose intolerance and muscle insulin resistance and, ultimately, type II diabetes mellitus. This research investigates the associations between glucose intolerance or muscle insulin resistance and tissue specific changes during the progression of diet-induced obesity.

Methodology

C57BL/6J mice were fed a normal or high-fat diet (HFD; 60% kcal fat) for 3 or 8 weeks. Disease progression was monitored by measurements of body/tissue mass changes, glucose and insulin tolerance tests, and ex vivo glucose uptake in intact muscles. Lipid metabolism was analyzed using metabolic chambers and ex vivo palmitate assays in intact muscles. Skeletal muscle, liver and adipose tissues were analyzed for changes in inflammatory gene expression. Plasma was analyzed for insulin levels and inflammatory proteins. Histological techniques were used on muscle and liver cryosections to assess metabolic and morphological changes.

Principal Findings/Conclusions

A rapid shift in whole body metabolism towards lipids was observed with HFD. Following 3 weeks of HFD, elevated total lipid oxidation and an oxidative fiber type shift had occurred in the skeletal muscle, which we propose was responsible for delaying intramyocellular lipid accumulation and maintaining muscle’s insulin sensitivity. Glucose intolerance was present after three weeks of HFD and was associated with an enlarged adipose tissue depot, adipose tissue inflammation and excess hepatic lipids, but not hepatic inflammation. Furthermore, HFD did not significantly increase systemic or muscle inflammation after 3 or 8 weeks of HFD suggesting that early diet-induced obesity does not cause inflammation throughout the whole body. Overall these findings indicate skeletal muscle did not contribute to the development of HFD-induced impairments in whole-body glucose tolerance following 3 weeks of HFD.     

A high-fat diet catalyzes progression to hyperglycemia in mice with selective impairment of insulin action in Glut4-expressing tissues

Insulin resistance impairs postprandial glucose uptake through glucose transporter type 4 (GLUT4) and is the primary defect preceding type 2 diabetes. We previously generated an insulin-resistant mouse model with human GLUT4 promoter-driven insulin receptor knockout (GIRKO) in the muscle, adipose, and neuronal subpopulations. However, the rate of diabetes in GIRKO mice remained low prior to 6 months of age on normal chow diet (NCD), suggesting that additional factors/mechanisms are responsible for adverse metabolic effects driving the ultimate progression of overt diabetes. In this study, we characterized the metabolic phenotypes of the adult GIRKO mice acutely switched to high-fat diet (HFD) feeding in order to identify additional metabolic challenges required for disease progression. Distinct from other diet-induced obesity (DIO) and genetic models (e.g., db/db mice), GIRKO mice remained leaner on HFD feeding, but developed other cardinal features of insulin resistance syndrome. GIRKO mice rapidly developed hyperglycemia despite compensatory increases in β-cell mass and hyperinsulinemia. Furthermore, GIRKO mice also had impaired oral glucose tolerance and a limited glucose-lowering benefit from exendin-4, suggesting that the blunted incretin effect contributed to hyperglycemia. Secondly, GIRKO mice manifested severe dyslipidemia while on HFD due to elevated hepatic lipid secretion, serum triglyceride concentration, and lipid droplet accumulation in hepatocytes. Thirdly, GIRKO mice on HFD had increased inflammatory cues in the gut, which were associated with the HFD-induced microbiome alterations and increased serum lipopolysaccharide (LPS). In conclusion, our studies identified important gene/diet interactions contributing to diabetes progression, which might be leveraged to develop more efficacious therapies.     

Liraglutide modulates gut microbiota and reduces NAFLD in obese mice

Metabolic disorders such as insulin resistance and diabetes are associated with obesity and nonalcoholic fatty liver disease (NAFLD). The aggressive form of a fatty liver disease may progress to cirrhosis and hepatocellular carcinoma. Furthermore, recent studies demonstrated that there is a dysbiosis in the gut microbiota associated with early stages of metabolic disease. Therefore, the identification and repurposing of drugs already used to treat insulin resistance may be an excellent option for other disorders. We evaluated the effect of liraglutide on obesity, NAFLD and gut microbiota modulation in two different animal models of obesity: the ob/ob mice and the high-fat diet (HFD)-fed mice. Liraglutide treatment induced significant weight loss in both obesity models, showed improvements in glycemic parameters and reduced inflammatory cell infiltration in the cecum and the liver. In ob/ob mice, the liraglutide treatment was able to reduce the accumulation of liver fat by 78% and reversed steatosis in the HFD mice. The gut microbiota analysis showed that liraglutide changed the overall composition as well as the relative abundance of weight-relevant phylotypes such as a reduction of Proteobacteria and an increase of Akkermansia muciniphila in the treated HFD group. We show that liraglutide can lead to weight loss and gut microbiota modulations, and is associated with an improvement of NAFLD. Furthermore, by generating a profile of the intestinal microbiota, we compiled a list of potential bacterial targets that may modulate metabolism and induce a metabolic profile that is considered normal or clinically controlled.     

Sex hormones regulate metainflammation in diet-induced obesity in mice

Men have a statistically higher risk of metabolic and cardiovascular disease than premenopausal women, but the mechanisms mediating these differences are elusive. Chronic inflammation during obesity contributes to disease risk and is significantly more robust in males. Prior work demonstrated that compared with obese males, obese females have reduced proinflammatory adipose tissue macrophages (ATMs). Given the paucity of data on how sex hormones contribute to macrophage responses in obesity, we sought to understand the role of sex hormones in promoting obesity-induced myeloid inflammation. We used gonadectomy, estrogen receptor–deficient alpha chimeras, and androgen-insensitive mice to model sex hormone deficiency. These models were evaluated in diet-induced obesity conditions (high-fat diet [HFD]) and in vitro myeloid assays. We found that ovariectomy increased weight gain and adiposity. Ovariectomized females had increased ATMs and bone marrow myeloid colonies compared with sham-gonadectomized females. In addition, castrated males exposed to HFD had improved glucose tolerance, insulin sensitivity, and adiposity with fewer Ly6c^hi monocytes and bone marrow myeloid colonies compared with sham-gonadectomized males, although local adipose inflammation was enhanced. Similar findings were observed in androgen-insensitive mice; however, these mice had fewer CD11c⁺ ATMs, implying a developmental role for androgens in myelopoiesis and adipose inflammation. We concluded that gonadectomy results in convergence of metabolic and inflammatory responses to HFD between the sexes, and that myeloid estrogen receptor alpha contributes minimally to diet-induced inflammatory responses, whereas loss of androgen-receptor signaling improves metabolic and inflammatory outcomes. These studies demonstrate that sex hormones play a critical role in sex differences in obesity, metabolic dysfunction, and myeloid inflammation.     

Human milk derived peptide AOPDM1 attenuates obesity by restricting adipogenic differentiation through MAPK signalling

BackgroundEmerging evidence revealed peptides within breast milk may be an abundant source of potential candidates for metabolism regulation. Our previous work identified numerous peptides existed in breast milk, but its function has not been validated. Thus, our study aims to screen for novel peptides that have the potential to antagonize obesity and diabetes.MethodsA function screen was designed to identify the candidate peptide and then the peptide effect was validated by assessing lipid storage. Afterwards, the in vivo study was performed in two obese models: high-fat diet (HFD)-induced obese mice and obese ob/ob mice. For mechanism study, a RNA-seq analysis was conducted to explore the pathway that account for the biological function of peptide.ResultsBy performing a small scale screening, a peptide (AVPVQALLLNQ) termed AOPDM1 (anti-obesity peptide derived from breast milk 1) was identified to reduce lipid storage in adipocytes. Further study showed AOPDM1 suppressed adipocyte differentiation by sustaining ERK activity at later stage of differentiation which down-regulated PPARγ expression. In vivo, AOPDM1 effectively reduced fat mass and improved glucose metabolism in high-fat diet (HFD)-induced obese mice and obese ob/ob mice.ConclusionsWe identified a novel peptide AOPDM1 derived from breast milk could restrict adipocyte differentiation and ameliorate obesity through regulating MAPK pathway.General significanceOur findings may provide a potential candidate for the discovery of therapeutic drugs for obesity and type 2 diabetes.     

PPARα信号通路激活抵抗高脂和Leptin缺失诱导的肥胖和脂肪肝

脂肪酰基辅酶A氧化酶1(acyl-coenzyme A oxidase 1,Acox1)缺失可通过内源性配体激活过氧化物酶体增殖物激活受体α(peroxisome proliferator-activated receptor-α,PPARα)及其调控的信号通路,从而减轻肥胖基因leptin突变型(ob/ob)小鼠的肥胖和脂肪肝症状,但提高了其肝癌发生率.为进一步研究PPARα信号通路在高脂日粮和leptin缺失诱导的脂肪肝形成过程中的作用,本研究以野生型、Acox1-/-、ob/ob和Acox1Δob/ob小鼠为模型,用正常日粮或60%高脂日粮饲喂10个月.结果显示,正常日粮或高脂日粮饲喂情况下,Acox1-/-和Acox1Δob/ob小鼠的体重、白色脂肪细胞体积、棕色脂肪组织含量及肝脏脂肪含量均分别显著低于WT和ob/ob小鼠.溴化脱氧尿嘧啶核苷(Brdurd)及烯酰辅酶A水合酶(L-PBE)免疫组化染色结果显示Acox1-/-和Acox1Δob/ob小鼠肝脏内肝细胞增殖及L-PBE活性、肝脏重量及其占体重的百分比均显著高于WT和ob/ob小鼠.正常日粮饲喂的WT、Acox1-/-、ob/ob和Acox1Δob/ob小鼠肝癌发生率分别为0%、100%、0%和4%,高脂日粮饲喂后,其肝癌发生率分别为0%、100%、2.9%和100%.Q-PCR结果显示Acox1-/-和Acox1Δob/ob小鼠肝脏内L-PBE、Cyp4a3、Akr1b10、ap2等基因的表达水平显著高于WT和ob/ob小鼠.综上所述,PPARα信号通路激活可以抵抗高脂日粮和leptin缺失诱导的肥胖和脂肪肝,但脂质过氧化反应可能通过Nrf2-Akr1b10信号通路促进了肝癌发生.     

Time-restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high-fat diet

While diet-induced obesity has been exclusively attributed to increased caloric intake from fat, animals fed a high-fat diet (HFD) ad libitum (ad lib) eat frequently throughout day and night, disrupting the normal feeding cycle. To test whether obesity and metabolic diseases result from HFD or disruption of metabolic cycles, we subjected mice to either ad lib or time-restricted feeding (tRF) of a HFD for 8 hr per day. Mice under tRF consume equivalent calories from HFD as those with ad lib access yet are protected against obesity, hyperinsulinemia, hepatic steatosis, and inflammation and have improved motor coordination. The tRF regimen improved CREB, mTOR, and AMPK pathway function and oscillations of the circadian clock and their target genes' expression. These changes in catabolic and anabolic pathways altered liver metabolome and improved nutrient utilization and energy expenditure. We demonstrate in mice that tRF regimen is a nonpharmacological strategy against obesity and associated diseases.     

Role of Pregnane X Receptor in Obesity and Glucose Homeostasis in Male Mice

Clinical obesity is a complex metabolic disorder affecting one in three adults. Recent reports suggest that pregnane X receptor (PXR), a xenobiotic nuclear receptor important for defense against toxic agents and for eliminating drugs and other xenobiotics, may be involved in obesity. Noting differences in ligand specificities between human and mouse PXRs, the role of PXR in high fat diet (HFD)-induced obesity was examined using male PXR-humanized (hPXR) transgenic and PXR-knock-out (PXR-KO) mice in comparison to wild-type (WT) mice. After 16 weeks on either a control diet or HFD, WT mice showed greater weight gain, whereas PXR-KO mice gained less weight due to their resistance to HFD-induced decreases in adipose tissue peroxisome proliferator-activated receptor α and induction of hepatic carnitine palmitoyltransferase 1, suggesting increased energy metabolism. Interestingly, control-fed PXR-KO mice exhibited hepatomegaly, hyperinsulinemia, and hyperleptinemia but hypoadiponectinemia and lower adiponectin receptor R2 mRNA levels relative to WT mice. Evaluation of these biologic indicators in hPXR mice fed a control diet or HFD revealed further differences between the mouse and human receptors. Importantly, although HFD-fed hPXR mice were resistant to HFD-induced obesity, both PXR-KO and hPXR mice exhibited impaired induction of glucokinase involved in glucose utilization and displayed elevated fasting glucose levels and severely impaired glucose tolerance. Moreover, the basal hepatic levels of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase 1 were increased in hPXR mice compared with WT mice. Altogether, although the mouse PXR promotes HFD-induced obesity, the hPXR mouse carries a genetic predisposition for type 2 diabetes and thus provides a model for exploring the role of human PXR in the metabolic syndrome.     

Transgenic MSH overexpression attenuates the metabolic effects of a high-fat diet

To determine whether long-term melanocortinergic activation can attenuate the metabolic effects of a high fat diet, mice overexpressing an NH(2)-terminal POMC transgene that includes alpha- and gamma(3)-MSH were studied on either a 10% low-fat diet (LFD) or 45% high-fat diet (HFD). Weight gain was modestly reduced in transgenic (Tg-MSH) male and female mice vs. wild type (WT) on HFD (P < 0.05) but not LFD. Substantial reductions in body fat percentage were found in both male and female Tg-MSH mice on LFD (P < 0.05) and were more pronounced on HFD (P < 0.001). These changes occurred in the absence of significant feeding differences in most groups, consistent with effects of Tg-MSH on energy expenditure and partitioning. This is supported by indirect calorimetry studies demonstrating higher resting oxygen consumption and lower RQ in Tg-MSH mice on the HFD. Tg-MSH mice had lower fasting insulin levels and improved glucose tolerance on both diets. Histological and biochemical analyses revealed that hepatic fat accumulation was markedly reduced in Tg-MSH mice on the HFD. Tg-MSH also attenuated the increase in corticosterone induced by the HFD. Higher levels of Agrp mRNA, which might counteract effects of the transgene, were measured in Tg-MSH mice on LFD (P = 0.02) but not HFD. These data show that long-term melanocortin activation reduces body weight, adiposity, and hepatic fat accumulation and improves glucose metabolism, particularly in the setting of diet-induced obesity. Our results suggest that long-term melanocortinergic activation could serve as a potential strategy for the treatment of obesity and its deleterious metabolic consequences.     

Insulin-induced activation of atypical protein kinase C, but not protein kinase B, is maintained in diabetic (ob/ob and Goto-Kakazaki) liver. Contrasting insulin signaling patterns in liver versus muscle define phenotypes of type 2 diabetic and high fat-induced insulin-resistant states

Insulin resistance in type 2 diabetes is characterized by defects in muscle glucose uptake and hepatic overproduction of both glucose and lipids. These hepatic defects are perplexing because insulin normally suppresses glucose production and increases lipid synthesis in the liver. To understand the mechanisms for these seemingly paradoxical defects, we examined the activation of atypical protein kinase C (aPKC) and protein kinase B (PKB), two key signaling factors that operate downstream of phosphatidylinositol 3-kinase and regulate various insulin-sensitive metabolic processes. Livers and muscles of three insulin-resistant rodent models were studied. In livers of type 2 diabetic non-obese Goto-Kakazaki rats and ob/ob-diabetic mice, the activation of PKB was impaired, whereas activation of aPKC was surprisingly maintained. In livers of non-diabetic high fatfed mice, the activation of both aPKC and PKB was maintained. In contrast to the maintenance of aPKC activation in the liver, insulin activation of aPKC was impaired in muscles of Goto-Kakazaki-diabetic rats and ob/ob-diabetic and non-diabetic high fat-fed mice. These findings suggest that, at least in these rodent models, (a) defects in aPKC activation contribute importantly to skeletal muscle insulin resistance observed in both high fat feeding and type 2 diabetes; (b) insulin signaling defects in muscle are not necessarily accompanied by similar defects in liver; (c) defects in hepatic PKB activation occur in association with, and probably contribute importantly to, the development of overt diabetes; and (d) maintenance of hepatic aPKC activation may explain the continued effectiveness of insulin for stimulating certain metabolic actions in the liver.     

Dietary sphingomyelin attenuates hepatic steatosis and adipose tissue inflammation in high-fat-diet-induced obese mice

Western-type diets can induce obesity and related conditions such as dyslipidemia, insulin resistance and hepatic steatosis. We evaluated the effects of milk sphingomyelin (SM) and egg SM on diet-induced obesity, the development of hepatic steatosis and adipose inflammation in C57BL/6J mice fed a high-fat, cholesterol-enriched diet for 10 weeks. Mice were fed a low-fat diet (10% kcal from fat) (n=10), a high-fat diet (60% kcal from fat) (HFD, n=14) or a high-fat diet modified to contain either 0.1% (w/w) milk SM (n=14) or 0.1% (w/w) egg SM (n=14). After 10 weeks, egg SM ameliorated weight gain, hypercholesterolemia and hyperglycemia induced by HFD. Both egg SM and milk SM attenuated hepatic steatosis development, with significantly lower hepatic triglycerides (TGs) and cholesterol relative to HFD. This reduction in hepatic steatosis was stronger with egg SM supplementation relative to milk SM. Reductions in hepatic TGs observed with dietary SM were associated with lower hepatic mRNA expression of PPARγ-related genes: Scd1 and Pparg2 in both SM groups, and Cd36 and Fabp4 with egg SM. Egg SM and, to a lesser extent, milk SM reduced inflammation and markers of macrophage infiltration in adipose tissue. Egg SM also reduced skeletal muscle TG content compared to HFD. Overall, the current study provides evidence of dietary SM improving metabolic complications associated with diet-induced obesity in mice. Further research is warranted to understand the differences in bioactivity observed between egg and milk SM.     

Exercise Protects against Diet-Induced Insulin Resistance through Downregulation of Protein Kinase Cβ in Mice

Physical exercise is an important and effective therapy for diabetes. However, its underlying mechanism is not fully understood. Protein kinase Cβ (PKCβ) has been suggested to be involved in the pathogenesis of obesity and insulin resistance, but the role of PKCβ in exercise-induced improvements in insulin resistance is completely unknown. In this study, we evaluated the involvement of PKCβ in exercise-attenuated insulin resistance in high-fat diet (HFD)-fed mice. PKCβ^-/- and wild-type mice were fed a HFD with or without exercise training. PKC protein expression, body and tissue weight change, glucose and insulin tolerance, metabolic rate, mitochondria size and number, adipose inflammation, and AKT activation were determined to evaluate insulin sensitivity and metabolic changes after intervention. PKCβ expression decreased in both skeletal muscle and liver tissue after exercise. Exercise and PKCβ deficiency can alleviate HFD-induced insulin resistance, as evidenced by improved insulin tolerance. In addition, fat accumulation and mitochondrial dysfunction induced by HFD were also ameliorated by both exercise and PKCβ deficiency. On the other hand, exercise had little effect on PKCβ^-/- mice. Further, our data indicated improved activation of AKT, the downstream signal molecule of insulin, in skeletal muscle and liver of exercised mice, whereas PKCβ deficiency blunted the difference between sedentary and exercised mice. These results suggest that downregulation of PKCβ contributes to exercise-induced improvement of insulin resistance in HFD-fed mice.     

Neonatal exposure to leptin augments diet-induced obesity in leptin-deficient Ob/Ob mice

Objective: Epidemiological evidence has revealed that undernutrition in utero is closely associated with obesity and related detrimental metabolic sequelae in adulthood. Recently, using a wild‐type (wt) mouse model in which offspring were exposed to intrauterine undernutrition (UN offspring), we reported that the premature leptin surge during neonatal growth promotes lifelong changes in energy regulating circuitry in the hypothalamus, thus playing an important role in the development of pronounced obesity on a high‐fat diet (HFD) in adulthood. Here, we further evaluate the essential involvement of leptin in the developmental origins of obesity using leptin‐deficient ob/ob mice. Methods and Procedures: We assessed the progression of obesity on an HFD in adult leptin‐deficient ob/ob male mice that were exposed to intrauterine undernutrition by maternal food restriction (ob/ob UN offspring) or to leptin treatment during the neonatal period; this treatment is comparable to the premature leptin surge observed in the wt‐UN offspring. Results: On an HFD, the body weight of the male ob/ob UN offspring paralleled that of the ob/ob offspring exposed to normal intrauterine nutrition (ob/ob NN offspring). In contrast, early exposure to leptin in the ob/ob NN offspring during early neonatal growth reproduced the development of pronounced obesity on an HFD in adulthood. Discussion: The presence of leptin and associated energy regulation are indispensable in the acceleration of obesity on an HFD caused by undernutrition in utero. The premature leptin surge plays an essential role in the developmental origins of obesity as a programming signal during the early neonatal period.     

β‐Aminoisobutyric Acid Prevents Diet‐induced Obesity in Mice With Partial Leptin Deficiency

β‐Aminoisobutyric acid (BAIBA), a thymine catabolite, increases fatty acid oxidation (FAO) in liver and reduces the gain of body fat mass in Swiss (lean) mice fed a standard chow. We determined whether BAIBA could prevent obesity and related metabolic disorders in different murine models. To this end, BAIBA (100 or 500 mg/kg/day) was administered for 4 months in mice totally deficient in leptin (ob/ob). BAIBA (100 mg/kg/day) was also given for 4 months in wild‐type (+/+) mice and mice partially deficient in leptin (ob/+) fed a high‐calorie (HC) diet. BAIBA did not limit obesity and hepatic steatosis in ob/ob mice, but reduced liver cytolysis and inflammation. In ob/+ mice fed the HC diet, BAIBA fully prevented, or limited, the gain of body fat, steatosis and necroinflammation, glucose intolerance, and hypertriglyceridemia. Plasma β‐hydroxybutyrate was increased, whereas expression of carnitine palmitoyltransferase‐1 was augmented in liver and white adipose tissue. Acetyl‐CoA carboxylase was more phosphorylated, and de novo lipogenesis was less induced in liver. These favorable effects of BAIBA in ob/+ mice were associated with a restoration of plasma leptin levels. The reduction of body adiposity afforded by BAIBA was less marked in +/+ mice. Finally, BAIBA significantly stimulated the secretion of leptin in isolated ob/+ adipose cells, but not in +/+ cells. Thus, BAIBA could limit triglyceride accretion in tissues through a leptin‐dependent stimulation of FAO. As partial leptin deficiency is not uncommon in the general population, supplementation with BAIBA may help to prevent diet‐induced obesity and related metabolic disorders in low leptin secretors.     

TOF-SIMS analysis of lipid accumulation in the skeletal muscle of ob/ob mice

Skeletal muscle lipid accumulation is associated with several chronic metabolic disorders, including obesity, insulin resistance (IR) and type 2 diabetes. The aim of this study is to evaluate whether static imaging time-of-flight-secondary-ion mass spectrometry (TOF-SIMS) equipped with a Bismuth-cluster ion source can be used for studying skeletal muscle lipid accumulation associated with obesity. Mouse gastrocnemius muscle tissues in 10-week-old obese ob/ob (n = 8) and lean wild-type C57/BL6 (n = 6) mice were analyzed by TOF-SIMS. Our results showed that signal intensities of fatty acids (FAs) and diacylglycerols (DAGs) were significantly increased in skeletal muscle of the obese ob/ob mice as compared to the lean wild-type mice. These differences were revealed through a global analytical approach, principal component analysis (PCA) of TOF-SIMS spectra, and ion-specific TOF-SIMS images. Region-of-interest (ROI) analysis showed that FA signal intensities within the muscle cell were significantly increased in ob/ob mice. Moreover, analysis of the ratio between different FA peaks revealed changes in monounsaturated FAs (MUFAs) and polyunsaturated FAs (PUFAs), which is in agreement with previous reports on obesity. These changes in FA composition were also reflected in the ratio of different DAGs or phosphatidylcholines (PCs) that contain different FA residues. Imaging TOF-SIMS together with PCA of TOF-SIMS spectra is a promising tool for studying skeletal muscle lipid accumulation associated with obesity.     

Voglibose administration regulates body weight and energy intake in high fat-induced obese mice

We tested whether long-term administration of voglibose (VO) prevents diet induced obesity in addition to hypoglycemic effects in high fat fed mice and further investigated the underlying mechanisms by which voglibose exerts its weight lowering effect. Male C57BL/6 mice were fed ad libitum for 12 weeks with the control diet (CTL), high-fat diet (HFD) or the HFD with VO supplementations. Blood lipid profile, plasma leptin levels and hepatic triglyceride content, as well as expressions of genes involved in appetite and mitochondrial function were examined. The results showed that VO significantly reduced body weight, fat mass and energy intakes in high fat fed mice. VO showed improved metabolic profiles including blood glucose, triglyceride and free fatty acid. Elevated levels of plasma leptin in HFD were significantly reduced with the VO, furthermore, VO modulated the hypothalamic expressions of leptin receptors and appetite related genes. VO showed the upregulated expressions of PGC-1 in the liver and epididymal adipose tissue. In conclusion, VO may exert antiobesity properties through reductions in energy intake and improvement in mitochondrial function, indicating that VO has potential therapeutic use in patients with obesity, type 2 diabetes, and related complications.     

MKR mice are resistant to the metabolic actions of both insulin and adiponectin: discordance between insulin resistance and adiponectin responsiveness

Most rodent models of insulin resistance are accompanied by decreased circulating adiponectin levels. Adiponectin treatment improves the metabolic phenotype by increasing fatty acid oxidation in skeletal muscle and suppressing hepatic glucose production. Muscle IGF-I receptor (IGF-IR)-lysine-arginine (MKR) mice expressing dominant-negative mutant IGF-IRs in skeletal muscle are diabetic with insulin resistance in muscle, liver, and adipose tissue. Adiponectin levels are elevated in MKR mice, suggesting an unusual discordance between insulin resistance and adiponectin responsiveness. Therefore, we investigated the metabolic actions of adiponectin in MKR mice. MKR and ob/ob mice were treated both acutely (28 microg/g) and chronically (for 2 wk) with full-length adiponectin. Acute hypoglycemic effects of adiponectin were evident only in ob/ob mice but not in MKR mice. Chronic adiponectin treatment significantly improved both insulin sensitivity and glucose tolerance in ob/ob but not in MKR mice. Adiponectin receptor mRNA levels and adiponectin-stimulated phosphorylation of AMPK in skeletal muscle and liver were similar among MKR, wild-type, and ob/ob mice. Thus MKR mice are adiponectin resistant despite normal expression of adiponectin receptors and normal AMPK phosphorylation in muscle and liver. MKR mice may be a useful model for dissecting relationships between insulin resistance and adiponectin action in regulation of glucose homeostasis.     

Grape pomace reduces the severity of non-alcoholic hepatic steatosis and the development of steatohepatitis by improving insulin sensitivity and reducing ectopic fat deposition in mice

While non-alcoholic fatty liver disease (NAFLD) represents the common cause of chronic liver disease, specific therapies are currently unavailable. The wine industry produces millions of tons of residue (pomace), which contains high levels of bioactive phytochemicals. The aim of this study was to clarify the potential benefits of grape pomace for the treatment of NAFLD at different levels of severity, and to clarify the mechanism of action. C57Bl/6 mice were given high fat diet (HFD) or western diet (WD) as models of obesity and hepatic steatosis or steatohepatitis, respectively, with or without pomace supplementation (50–250 mg/day). Pomace inhibited food intake, and reduced serum leptin and body weight gain. Ectopic fat deposition was reduced, while white adipose tissue mass was preserved. In addition, pomace improved glucose tolerance and insulin sensitivity, prevented the development of adipose tissue inflammation, and reduced hepatic steatosis. Higher expression of genes involved in fatty acids transport and oxidation was observed in adipose tissue, while lipogenic genes were attenuated in the liver of pomace-treated mice. In WD-fed mice, pomace reduced the severity of hepatic steatosis and inflammation and improved blood lipid profile, but was ineffective in reversing hepatic damage of advanced NASH. In conclusion, pomace improved insulin sensitivity and reduced ectopic fat deposition, leading to a healthier metabolic profile. Pomace may hold the potential as a supplement with beneficial health outcomes for the prevention and treatment of hepatic steatosis and other obesity-related pathologies.     

Pioglitazone ameliorates insulin resistance and diabetes by both adiponectin-dependent and -independent pathways

Thiazolidinediones have been shown to up-regulate adiponectin expression in white adipose tissue and plasma adiponectin levels, and these up-regulations have been proposed to be a major mechanism of the thiazolidinedione-induced amelioration of insulin resistance linked to obesity. To test this hypothesis, we generated adiponectin knock-out (adipo-/-) ob/ob mice with a C57B/6 background. After 14 days of 10 mg/kg pioglitazone, the insulin resistance and diabetes of ob/ob mice were significantly improved in association with significant up-regulation of serum adiponectin levels. Amelioration of insulin resistance in ob/ob mice was attributed to decreased glucose production and increased AMP-activated protein kinase in the liver but not to increased glucose uptake in skeletal muscle. In contrast, insulin resistance and diabetes were not improved in adipo-/-ob/ob mice. After 14 days of 30 mg/kg pioglitazone, insulin resistance and diabetes of ob/ob mice were again significantly ameliorated, which was attributed not only to decreased glucose production in the liver but also to increased glucose uptake in skeletal muscle. Interestingly, adipo-/-ob/ob mice also displayed significant amelioration of insulin resistance and diabetes, which was attributed to increased glucose uptake in skeletal muscle but not to decreased glucose production in the liver. The serum-free fatty acid and triglyceride levels as well as adipocyte sizes in ob/ob and adipo-/-ob/ob mice were unchanged after 10 mg/kg pioglitazone but were significantly reduced to a similar degree after 30 mg/kg pioglitazone. Moreover, the expressions of TNFalpha and resistin in adipose tissues of ob/ob and adipo-/-ob/ob mice were unchanged after 10 mg/kg pioglitazone but were decreased after 30 mg/kg pioglitazone. Thus, pioglitazone-induced amelioration of insulin resistance and diabetes may occur adiponectin dependently in the liver and adiponectin independently in skeletal muscle.