Insulin Sensitivity In Obese Rats Research Articles

Roux-en-Y Gastric Bypass Improves Insulin Sensitivity in Obese Rats with Type 2 Diabetes Mellitus by Regulating the Grin3a/AMPK Signal Axis in Hypothalamic Arcuate Nucleus.

The objective of this study was to explore the effects and related mechanisms of Roux-en-Y gastric bypass (RYGB) on insulin sensitivity in obese rats with type 2 diabetes mellitus (T2DM). The obese T2DM rat model was constructed by feeding a high-fat diet and injecting streptozotocin (STZ), and treated with RYGB. Grin3a shRNA was injected into the bilateral hypothalamic arcuate nucleus (ARC) to knockdown the Grin3a expression on T2DM rats. Eight weeks after operation, the body weight, fasting blood glucose (FBG), fasting serum insulin (FSI), homeostatic model assessment of insulin resistance (HOMA-IR), and plasma triglyceride (TG) levels were assessed. Hematoxylin & eosin (H&E) staining was adopted to observe the white adipose tissue (WAT) of rats. Western blot and qRT-PCR were used to detect the expression of Grin3a, adenosine 5' monophosphate-activated protein kinase (AMPK) and p-AMPK in ARC of rats. Later, the plasmid over-expressing or knocking down Grin3a was transfected into differentiated 3T3-L1 adipocytes, and the TG level and the formation of lipid droplets in adipocyte were assessed by TG kit and oil red O staining. The expression of lipogenic transcription factors in cells was detected by qRT-PCR. RYGB reduced FBG, FSI, HOMA-IR and plasma TG levels in T2DM rats while increasing Grin3a expression and p-AMPK/AMPK ratio in ARC. Knockdown of Grin3a not only reversed the decrease of FBG, FSI, HOMA-IR and plasma TG levels in T2DM rats induced by RYGB, but also reversed the up-regulation of p-AMPK/AMPK ratio in ARC affected by RYGB. Moreover, knocking down Grin3a significantly increased the TG level, promoted the formation of lipid droplets and up-regulated the expressions of lipogenic transcription factors in adipocytes. RYGB improved the insulin sensitivity, reduced the plasma TG level and lessens the fat accumulation in obese T2DM rats by regulating the Grin3a/AMPK signal in ARC.

Effect of electroacupuncture of "biaoben acupoint combination" on central sensitivity of cholecystokinin in obese rats with insulin resistance

To observe the effect of electroacupuncture (EA) of "biaoben acupoint combination" on appetite, body fat, insulin sensitivity and central sensitivity of cholecystokinin (CCK) in obese rats with insulin resistance (IR), and to explore the mechanism of EA on improving obesity with insulin resistance. Among the fifty 8-week-old healthy SPF male Wistar rats, 10 rats were randomly selected and fed with normal diet; after 8 weeks, 8 rats were randomly selected as a normal group. The remaining 40 rats were fed with high-fat diet to establish the model of obsesity IR; after 8 weeks, 24 rats with successful model of obsesity IR were randomly divided into a model group, an EA group and a sham EA group, 8 rats in each group. Eight weeks after model establishment, the rats in the EA group were intervened with EA at "Fenglong" (ST 40), "Zhongwan" (CV 12), "Guanyuan" (CV 4) and "Zusanli" (ST 36), with continuous wave, in frequency of 2 Hz, and current intensity of 1 mA, for 10 min each time. The rats in the sham EA group were intervened with EA at the points 5 mm next to the acupoints used in the EA group and no electricity was given; the sham EA was given for 10 min each time. Both the treatments were given once every other day for 8 weeks. The Lee's index and food intake were observed before the intervention as well as 2 weeks, 4 weeks, 6 weeks and 8 weeks into intervention; after the intervention, serum insulin (INS) and glucose infusion rate (GIR) were detected; serum cholecystokinin (CCK) level was detected by ELISA; c-fos expression in the area postrema (AP) and nucleus tractus solitarius (NTS) of medulla oblongata was detected by immunohistochemistry. Before the intervention as well as 2 weeks, 4 weeks, 6 weeks and 8 weeks into intervention, the Lee's index and food intake in the model group were higher than those in normal group (P<0.01). The Lee's index (6 weeks and 8 weeks into intervention) and food intake (4 weeks, 6 weeks and 8 weeks into intervention) in the EA group were lower than those in the model group and the sham EA group (P<0.05, P<0.01). After intervention, compared with the normal group, serum level of INS was increased (P<0.01), while GIR, serum CCK level, c-fos expression in AP and NTS in the model group were decreased (P<0.01, P<0.05). Compared with the model group and the sham EA group, serum level of INS in the EA group was decreased (P<0.01), and GIR, serum CCK level, c-fos expression in AP and NTS were increased (P<0.01, P<0.05). EA of "biaoben acupoint combination" could effectively reduce appetite, body fat and enhance insulin sensitivity in obese rats with IR. The mechanism may be related to the regulation of central sensitivity of CCK.

Effect of electroacupuncture on SIRT1/NF-κB signaling pathway in adipose tissue of obese rats

To explore the effect of electroacupuncture (EA) on insulin sensitivity, adipose tissue inflammatory reaction and silent information regulation factor 1(SIRT1)/nuclear factor kappa B (NF-κB) signaling pathway in obese rats. A total of 100 SPF-grade Wistar male rats were collected. Thirteen rats of them were selected randomly as the normal group and fed with common forage, and the rest rats were fed with high-fat forage. Eight weeks later, 39 rats that met the obesity criteria were randomized into a model group, an EA group and a sham-EA group, 13 rats in each one. In each group, 3 rats were collected randomly and the hyperinsulinemic-euglycemic clamp was exerted to record glucose infusion rate (GIR) so as to determine insulin sensitivity. Afterwards, in the EA group, EA was applied to "Zusanli" (ST 36), "Fenglong" (ST 40), "Zhongwan" (CV 12) and "Guanyuan" (CV 4), stimulated with continuous wave, 2 Hz in frequency, 1 mA in current intensity, for 15 min. The treatment was given once every 2 days, 3 times a week, for 8 weeks totally. In the sham-EA group, the needles were inserted shallowly at the sites, 5 mm lateral to each of the acupoints stimulated in the EA group, and the electrodes were attached to the needle handles, but without electric stimulation exerted. The rest management was the same as the EA group. Before and after intervention, the body mass and the insulin sensitivity were measured. After intervention, the white adipose tissue was collected from the kidney in the rats. Western blot was adopted to detect the relative protein expressions of SIRT1, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and acetylated NF-κB (Ac-NFκB). The real-time fluorescence quantitative PCR was used to detect the mRNA expressions of SIRT1, IL-6 and TNF-α. The immunofluorescence double labeling method was applied to detect the co-expression of SIRT1 and Ac-NFκB in adipose tissue. After fed with high-fat forage for 8 weeks, the body mass was significantly increased and GIR decreased in the rats of the model group as compared with the normal group (P<0.01), suggesting that the model of obese rat with insulin resistance was successfully established. After 8-week intervention, compared with the model group, the body mass was reduced and GIR increased in the rats of the EA group (P<0.01). The differences were not significant statistically in comparison between the sham-EA group and the model group (P>0.05). Compared with the normal group, in the model group, the protein and mRNA expressions of SIRT1 in adipose tissue were decreased, and the protein expression of Ac-NFκB increased, the protein and mRNA expressions of IL-6 and TNF-α increased (P<0.05, P<0.01). Compared with the model group, in the EA group, the protein and mRNA expressions of SIRT1 in adipose tissue were increased significantly, the protein expression of Ac-NFκB decreased, and the protein and mRNA expressions of IL-6 and TNF-α significantly decreased (P<0.05, P<0.01). There was no significant difference in each index between the sham-EA group and the model group (P>0.05). The results of immunofluorescence double labeling showed that SIRT1 and Ac-NFκB were co-expressed in adipose tissue. Electroacupuncture significantly reduces the body mass, inflammatory reaction conditions of adipose tissue and improves insulin sensitivity in obese rats. Regarding the potential mechanism, after the activation of SIRT1/NF-κB signaling pathway by electroacupuncture, and down-regulates the transcription of downstream inflammatory factors.

A combination of borage seed oil and quercetin reduces fat accumulation and improves insulin sensitivity in obese rats.

The metabolic properties of omega-6 fatty acid consumption are being increasingly accepted. We had previously observed that supplementation with a borage seed oil (BSO), as a source of linoleic (18:2n-6; LA) and gamma-linolenic (18:3n-6; GLA) acids, reduces body weight and visceral adiposity and improves insulin sensitivity in a diet-induced obesity model of Wistar rats. Here, it was investigated whether the anti-obesogenic properties of BSO could be maintained in a pre-obese model of rats, and if these effects are enhanced by a combination with low doses of quercetin, together with its potential role in the regulation of the adipocyte biology. The combination of BSO and quercetin during 8 weeks was able to ameliorate glucose intolerance and insulin resistance, and to improve liver steatosis. Although no effects were observed on body weight, animals supplemented with this combination exhibited a lower proportion of visceral adiposity. In addition, in vitro differentiation of epididymal adipose-precursor cells of the BSO-treated animals exhibited a down-regulation of Fasn, Glut4, Pparg and Srebp1 genes, in comparison with the control group. Finally, in vitro evaluation of the components of BSO demonstrated that the anti-adipogenic activity of quercetin was significantly potentiated by the combination with both LA and GLA through the down-regulation of different adipogenesis-key genes in 3T3-L1 cells. All these data suggest that omega-6 fatty acids LA and GLA, and their natural sources such as BSO, could be combined with quercetin to potentiate their effects in the prevention of the excess of adiposity and the insulin resistance.

Potential Anti-obesogenic Effects of Ginkgo biloba Observed in Epididymal White Adipose Tissue of Obese Rats.

Exacerbated expansion of adipose tissue seen in diet-induced obesity leads to endocrine dysfunction and disturbance in adipokine secretion, with such abnormal profile positively associated with type 2 diabetes and other mild chronic inflammatory conditions. Ginkgo biloba extract (GbE), a mixture of polyphenols with antioxidant properties, has been recently investigated in a variety of experimental models of endocrine dysfunction, with several potentially beneficial effects identified, including improvement in insulin sensitivity in obese rats, and reduction of weight gain in ovariectomy-induced obesity and diet-induced obesity. The aim of this study was to investigate in high fat diet-induced obese male rats the effects of GbE supplementation for 2 weeks on adipocyte volume and adipose tissue lipid accumulation. GbE supplementation was effective in reducing energy intake in obese rats compared to the saline-treated placebo group. Epididymal adipocyte volume was reduced in GbE-supplemented rats, as were epididymal [1-14C]-acetate incorporation into fatty acids, perilipin (Plin 1) and fatty acid synthase (Fasn) mRNA, and FAS protein levels. Adipocyte hypertrophy in obesity is associated with insulin resistance, and in the present study we observed a reduction in the adipocyte volume of GbE-supplemented obese rats to dimensions equivalent to adipocytes from non-obese rats. GbE supplementation significantly reduced acetate accumulation and tended to reduce [3H]-oleate incorporation, into epididymal adipose tissue, suggesting a potentially anti-obesogenic effect in longer term therapies. Further studies that investigate the effects of GbE supplementation in other experimental models are required to fully elucidate its suggested beneficial effects on mild chronic inflammatory conditions.

Obesity Induced by High Fat Diet Impairs Glucose Tolerance and Insulin Sensitivity in Rats

Introduction: Obesity is a chronic disease, besides a risk factor for cardiovascular diseases, nowadays, it is characterized as a worldwide epidemic. The food imbalance and physical inactivity are factors that contribute to the emergence of obesity as well as diabetes. Objective: To evaluate the injury on glucose tolerance and insulin sensitivity in obese rats induced by high fat diet. Methodology: Male Rats Wistar (8 weeks old) were submitted to the standard diet (chow group, 11.8% kcal-Lipids; n = 5) and dietary intervention with high fat diet during 8 weeks (HFD group, 58.4% kcal-Lipids; n= 5). It was evaluated the body weight weekly, and fasting and fed blood glucose. At the end of the experimental period, was measured the glucose tolerance, insulin sensitivity and gluconeogenesis. After the animal sacrifice, it was analyzed relative weight of white adipose tissue, as well as the adipocytes diameter (epididymal white adipose tissue) and circulating levels of leptin. Results and Discussion: The group HFD presented higher body weight (from the 2nd week of diet), an increase accumulation of epididymal and perirenal white adipose tissue. In addition, in these animals, it was observed a significant increase in the adipocytes diameter and the levels of leptin in plasma when compared to animals chow, indicating obesity with increased release of cytokines. In HFD group, the fasting blood glucose levels were significantly higher in the 6th week of high fat diet consumption compared to the chow group. Adding up to the frame of obesity, at the end of the 8th week of high fat diet consumption, the obese group had higher fasting plasma glucose in fed state, glucose intolerance, insulin resistance, as well as increased gluconeogenesis as compared with the chow group. Conclusion: Obesity with adipocyte hypertrophy, induced by high fat diet, induces glycemic damages, as the elevation of blood glucose, glucose intolerance and lower insulin sensitivity in rats.

Thyroid hormone treatment reduces inflammatory cytokines in mesenteric adipose tissue improving insulin sensitivity of obese rats

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Chronic insulin infusion induces reversible glucose intolerance in lean rats yet ameliorates glucose intolerance in obese rats

BackgroundAlthough insulin resistance (IR) is a key factor in the pathogenesis of type 2 diabetes (T2D), the precise role of insulin in the development of IR remains unclear. Therefore, we investigated whether chronic basal insulin infusion is causative in the development of glucose intolerance. MethodsNormoglycemic lean rats surgically instrumented with i.v. catheters were infused with insulin (3mU/kg/min) or physiological saline for 6weeks. At infusion-end, plasma insulin levels along with glucose tolerance were assessed. ResultsSix weeks of insulin infusion induced glucose intolerance and impaired insulin response in healthy rats. Interestingly, the effects of chronic insulin infusion were completely normalized following 24h withdrawal of exogenous insulin and plasma insulin response to glucose challenge was enhanced, suggesting improved insulin secretory capacity. As a result of this finding, we assessed whether the effects of insulin therapy followed by a washout could ameliorate established glucose intolerance in obese rats. Obese rats were similarly instrumented and infused with insulin or physiological saline for 7days followed by 24h washout. Seven day-insulin therapy in obese rats significantly improved glucose tolerance, which was attributed to improved insulin secretory capacity and improved insulin signaling in liver and skeletal muscle. ConclusionModerate infusion of insulin alone is sufficient to cause glucose intolerance and impair endogenous insulin secretory capacity, whereas short-term, intensive insulin therapy followed by insulin removal effectively improves glucose tolerance, insulin response and peripheral insulin sensitivity in obese rats. General significanceNew insight into the link between insulin and glucose intolerance may optimize T2D management.

Muscle adaptation in obese rats exposed to chronic hypoxia (1167.3)

Chronic hypoxia decreases fasting glucose and increases glucose utilization in lean and obese rats. Hypoxia increases insulin sensitivity in obese rats, but insulin resistance remains higher compared to lean rats exposed to hypoxia (figure). Skeletal muscle plays an important role in glucose metabolism; thus changes in insulin pathway and mitochondrial metabolism may impact skeletal muscle glucose uptake. We evaluated the adaptation of skeletal muscle to chronic hypoxia in lean and obese rats. We hypothesized that obese rats have less mitochondrial protein content and decreased activation of the ERK/MAPK pathway, one of the components of the insulin‐signaling cascade. For this purpose, Sprague‐Dawley rats were fed with normal chow diet or high‐fat diet (45% Kcal from fat) for 24 weeks in a normoxic environment. Rats were then exposed to hypobaric hypoxia (simulated altitude of 4500m) for 3 weeks. Triceps surae muscles were removed at the end of the hypoxia exposure and processed for western blot analysis. Mitochondrial protein content was evaluated using a monoclonal antibody against the subunit α of complex V. Contrary to our hypothesis, obese rats have a higher mitochondrial protein content than lean rats (35% higher, p=0.025). There was no difference in the activation of the ERK/MAPK pathway between the groups. Further studies are required to elucidate how chronic hypoxia affects glucose metabolism in obese rats.$graphic_082DEB25‐E5FC‐41C5‐820C‐9A23528E6536$Grant Funding Source: Supported by FINCyT (No 046‐FINCyT‐PITEI‐2010) and NIH (K23DK100533)

Fenofibrate increases serum vaspin by upregulating its expression in adipose tissue

Fenofibrate is a peroxisome proliferator-activated receptor-α that has been clinically used to treat dyslipidemia and insulin resistance. To better understand the molecular mechanisms underlying fenofibrate action, we investigated whether fenofibrate affects serum levels of vaspin, an adipocytokine that has recently been shown to link obesity and insulin resistance. Fenofibrate treatment significantly increased serum vaspin levels of dyslipidemic patients, which correlated with reduced body weight and increased insulin sensitivity. To elucidate the biochemical mechanisms of fenofibrate action, we investigated the effect of fenofibrate on vaspin mRNA and protein expressions in obese rats. Fenofibrate greatly increased vaspin mRNA and protein levels in visceral adipose tissue consisting of retroperitoneal, mesenteric, and periepididymal adipose tissue but not in the subcutaneous adipose tissue, which correlated with increased serum vaspin levels and increased insulin sensitivity in obese rats. Consistent with a direct effect on vaspin expression, fenofibrate treatment significantly increased the mRNA and protein expression levels of vaspin in 3T3-L1 adipocytes. Together, our results demonstrate for the first time that fenofibrate upregulates vaspin expression in dyslipidemic human subjects and suggest that upregulation of vaspin expression in adipocytes may provide a mechanism by which fenofibrate improves insulin sensitivity in dyslipidemic patients.

Dietary leucine improves whole-body insulin sensitivity independent of body fat in diet-induced obese Sprague–Dawley rats

Dairy foods and dietary calcium (Ca) are potential regulators of body weight and insulin sensitivity. The specific components of dairy responsible for these actions are not known but may include leucine. Our objective was to determine the effect of dietary protein (casein, skim milk or leucine) and Ca level [low, 0.67% (LC) or high, 2.4% (HC)] on adiposity and insulin sensitivity. Obesity was induced in Sprague–Dawley rats with a 6-week period of high-fat/high-sucrose (HFHS) diet intake. Rats were randomly assigned to one of six HFHS diets for 8 weeks where dietary protein was provided as casein, skim milk or casein enriched with leucine, and contained either LC or HC. Body composition via dual-energy x-ray absorptiometry and insulin sensitivity via euglycemic–hyperinsulinemic clamp were measured. Microarray was used to assess gene expression in liver and skeletal muscle. Rats fed leucine had greater insulin sensitivity than those fed casein or skim milk (P<.05). Dietary protein differentially regulated hepatic and skeletal muscle genes associated with insulin, peroxisome proliferator-activated receptor and mammalian target of rapamycin pathways. Specifically, two key genes responsible for insulin sensitivity, hepatic insulin receptor substrate (IRS) and protein kinase B (Akt), were altered in hepatic tissue in response to leucine. Rats fed skim milk and leucine diets had lower body weight compared to those fed casein (P<.05). HC reduced fat mass compared to LC (P<.05). While skim milk and leucine both reduced fat mass, only leucine improved insulin sensitivity compared to casein. Differential expression of genes such as IRS and Akt may be responsible for changes in insulin sensitivity in obese rats.

Effects of food pattern change and physical exercise on cafeteria diet-induced obesity in female rats

Obesity affects a large number of people around the world and appears to be the result of changes in food intake, eating habits and physical activity levels. Changes in dietary patterns and physical exercise are therefore strongly recommended to treat obesity and its complications. The present study tested the hypothesis that obesity and metabolic changes produced by a cafeteria diet can be prevented with dietary changes and/or physical exercise. A total of fifty-six female Wistar rats underwent one of five treatments: chow diet; cafeteria diet; cafeteria diet followed by a chow diet; cafeteria diet plus exercise; cafeteria diet followed by a chow diet plus exercise. The duration of the experiment was 34 weeks. The cafeteria diet resulted in higher energy intake, weight gain, increased visceral adipose tissue and liver weight, and insulin resistance. The cafeteria diet followed by the chow diet resulted in energy intake, body weight, visceral adipose tissue and liver weight and insulin sensitivity equal to that of the controls. Exercise increased total energy intake at week 34, but produced no changes in the animals' body weight or adipose tissue mass. However, insulin sensitivity in animals subjected to exercise and the diet was similar to that of the controls. The present study found that exposure to palatable food caused obesity and insulin resistance and a diet change was sufficient to prevent cafeteria diet-induced obesity and to maintain insulin sensitivity at normal levels. In addition, exercise resulted in normal insulin sensitivity in obese rats. These results may help to develop new approaches for the treatment of obesity and type 2 diabetes mellitus.

Treinamento resistido reduz inflamação em músculo esquelético e melhora a sensibilidade à insulina periférica em ratos obesos induzidos por dieta hiperlipídica

To determine if resistive exercise protocol can modulate Tnf-α, SOCS3 and glucose transporter GLUT4 genes expression in skeletal muscle, and peripheral insulin sensitivity in obese rats induced by hyperlipidic diet. Wistar obese rats induced by hyperlipidic diet were subjected a resistive exercise protocol as jump squat. Insulin sensitivity and mRNA content of Tnf-α, SOCS3 and GLUT4 were assayed and compared among the groups: obese sedentary (OS) and exercised (OE), control sedentary (CS) and exercised (CE). The mRNA content of Tnf-α and SOCS3 has increased in skeletal muscle from OS and has decreased in OE group. The protein and GLUT4 mRNA contents were correlated but they did not change among the groups. Peripheral insulin sensitivity has increased in the OE compared to OS group. The resistive exercise reverses the peripheral insulin resistance and the inflammatory state in skeletal muscle from diet-induced obese rats.

Low fish oil intake improves insulin sensitivity, lipid profile and muscle metabolism on insulin resistant MSG-obese rats

BackgroundObesity is commonly associated with diabetes, cardiovascular diseases and cancer. The purpose of this study was to determinate the effect of a lower dose of fish oil supplementation on insulin sensitivity, lipid profile, and muscle metabolism in obese rats.MethodsMonosodium glutamate (MSG) (4 mg/g body weight) was injected in neonatal Wistar male rats. Three-month-old rats were divided in normal-weight control group (C), coconut fat-treated normal weight group (CO), fish oil-treated normal weight group (FO), obese control group (Ob), coconut fat-treated obese group (ObCO) and fish oil-treated obese group (ObFO). Obese insulin-resistant rats were supplemented with fish oil or coconut fat (1 g/kg/day) for 4 weeks. Insulin sensitivity, fasting blood biochemicals parameters, and skeletal muscle glucose metabolism were analyzed.ResultsObese animals (Ob) presented higher Index Lee and 2.5 fold epididymal and retroperitoneal adipose tissue than C. Insulin sensitivity test (Kitt) showed that fish oil supplementation was able to maintain insulin sensitivity of obese rats (ObFO) similar to C. There were no changes in glucose and HDL-cholesterol levels amongst groups. Yet, ObFO revealed lower levels of total cholesterol (TC; 30%) and triacylglycerol (TG; 33%) compared to Ob. Finally, since exposed to insulin, ObFO skeletal muscle revealed an increase of 10% in lactate production, 38% in glycogen synthesis and 39% in oxidation of glucose compared to Ob.ConclusionsLow dose of fish oil supplementation (1 g/kg/day) was able to reduce TC and TG levels, in addition to improved systemic and muscle insulin sensitivity. These results lend credence to the benefits of n-3 fatty acids upon the deleterious effects of insulin resistance mechanisms.

Multi-tissue, selective PPARγ modulation of insulin sensitivity and metabolic pathways in obese rats.

Peroxisome proliferator-activated receptor-γ (PPARγ) ligands, including the insulin-sensitizing thiazolidinedione drugs, transcriptionally regulate hundreds of genes. Little is known about the relationship between PPARγ ligand-specific modulation of cellular mechanisms and insulin sensitization. We characterized the insulin sensitivity and multitissue gene expression profiles of lean and insulin-resistant, obese Zucker rats untreated or treated with one of four PPARγ ligands (pioglitazone, rosiglitazone, troglitazone, and AG-035029). We analyzed the transcriptional profiles of adipose tissue, skeletal muscle, and liver from the rats and determined whether ligand treatment insulin-sensitizing potency was related to ligand treatment-induced alteration of functional pathways. Ligand treatments improved insulin sensitivity in obese rats to varying degrees. Adipose tissue profiles revealed ligand treatment-selective modulation of inflammatory and branched-chain amino acid (BCAA) metabolic pathways, which correlated with ligand treatment-specific insulin-sensitizing potency. Skeletal muscle profiles showed that obese rats exhibited elevated expression of adipocyte and slow-twitch fiber markers, which further increased after ligand treatment, but the magnitude of the treatment-induced changes was not correlated with insulin sensitization. Although PPARγ ligand treatments heterogeneously improved dysregulated expression of cholesterol and fatty acid biosynthetic pathways in obese rat liver, these alterations were not correlated with ligand insulin-sensitizing potency. PPARγ ligand treatment-specific insulin-sensitizing potency correlated with modulation of adipose tissue inflammatory and BCAA metabolic pathways, suggesting a functional relationship between these pathways and whole body insulin sensitivity. Other PPARγ ligand treatment-induced functional pathway changes were detected in adipose tissue, skeletal muscle, and liver profiles but were not related to degree of insulin sensitization.

Fibroblast Growth Factor 21 Action in the Brain Increases Energy Expenditure and Insulin Sensitivity in Obese Rats

OBJECTIVEThe hormone fibroblast growth factor 21 (FGF21) exerts diverse, beneficial effects on energy balance and insulin sensitivity when administered systemically to rodents with diet-induced obesity (DIO). The current studies investigate whether central FGF21 treatment recapitulates these effects.RESEARCH DESIGN AND METHODSAfter preliminary dose-finding studies, either saline vehicle or recombinant human FGF21 (0.4 μg/day) was infused continuously for 2 weeks into the lateral cerebral ventricle of male Wistar rats rendered obese by high-fat feeding. Study end points included measures of energy balance (body weight, body composition, food intake, energy expenditure, and circulating and hepatic lipids) and glucose metabolism (insulin tolerance test, euglycemic-hyperinsulinemic clamp, and hepatic expression of genes involved in glucose metabolism).RESULTSCompared with vehicle, continuous intracerebroventricular infusion of FGF21 increased both food intake and energy expenditure in rats with DIO, such that neither body weight nor body composition was altered. Despite unchanged body fat content, rats treated with intracerebroventricular FGF21 displayed a robust increase of insulin sensitivity due to increased insulin-induced suppression of both hepatic glucose production and gluconeogenic gene expression, with no change of glucose utilization.CONCLUSIONSFGF21 action in the brain increases hepatic insulin sensitivity and metabolic rate in rats with DIO. These findings identify the central nervous system as a potentially important target for the beneficial effects of FGF21 in the treatment of diabetes and obesity.

Fenofibrate reduces serum retinol-binding protein-4 by suppressing its expression in adipose tissue

Fenofibrate is a peroxisome proliferator-activated receptor-alpha (PPARalpha) activator that has been clinically used to treat dyslipidemia and insulin resistance. To better understand the molecular mechanisms underlying fenofibrate action, we investigated whether fenofibrate affects serum levels of retinol-binding protein-4 (RBP4), an adipocytokine that has recently been shown to link obesity and insulin resistance. Fenofibrate treatment significantly decreased serum RBP4 levels of dyslipidemic patients, which correlated with reduced body weight and increased insulin sensitivity. To elucidate the biochemical mechanisms of fenofibrate action, we investigated the effect of fenofibrate on RBP4 expression in obese rats. Fenofibrate greatly decreased RBP4 mRNA levels in adipose tissue but not in the liver, which correlated with decreased serum RBP4 levels and increased insulin sensitivity in obese rats. Consistent with a direct effect on RBP4 expression, fenofibrate treatment significantly reduced the mRNA expression levels of RPB4 in 3T3-L1 adipocytes. Together, our results demonstrate for the first time that fenofibrate inhibits RPB4 expression in dyslipidemic human subjects and suggest that inhibition of RBP4 expression in adipocytes may provide a mechanism by which fenofibrate improves insulin sensitivity in dyslipidemic patients.

S 23521 Decreases Food Intake and Body Weight Gain in Diet‐Induced Obese Rats

To investigate the effect of S 23521, a new glucagon-like peptide-1-(7-36) amide analogue, on food intake and body weight gain in obese rats, as well as on gene expression of several proteins involved in energy homeostasis. Lean and diet-induced obese rats were treated with either S 23521 or vehicle. S 23521 was given either intraperitoneally (10 or 100 microg/kg) or subcutaneously (100 microg/kg) for 14 and 20 days, respectively. Because the low-dose treatment did not affect food intake and body weight, the subcutaneous treatment at high dose was selected to test the effect on selected end-points. Treated obese rats significantly decreased their cumulative energy intake in relation to vehicle-treated counterparts (3401 +/- 65 vs. 3898 +/- 72 kcal/kg per 20 days; p < 0.05). Moreover, their body weight gain was reduced by 110%, adiposity was reduced by 20%, and plasma triglyceride levels were reduced by 38%. The treatment also improved glucose tolerance and insulin sensitivity of obese rats. Regarding gene expression, no changes in uncoupling protein-1, uncoupling protein-3, leptin, resistin, and peroxisome proliferator-activated receptor (PPAR)-gamma were observed. S 23521 is an effective glucagon-like peptide-1-(7-36) amide analogue, which induced a decrease in energy intake, body weight, and adiposity in a rat model of diet-induced obesity. In addition, the treatment also improved glucose tolerance and insulin sensitivity of obese rats. These results strongly support S 23521 as a putative molecule for the treatment of obesity.

Dehydroepiandrosterone decreases serum tumor necrosis factor-alpha and restores insulin sensitivity: independent effect from secondary weight reduction in genetically obese Zucker fatty rats.

Dehydroepiandrosterone (DHEA) and its sulfate ester are the most abundant circulating adrenal steroids in humans. Administration of DHEA has been reported to have beneficial effects on obesity, hyperlipidemia, diabetes, and atherosclerosis in obese rodents, although its effects on insulin resistance have not been fully elucidated. In this study, the effects of DHEA treatment on insulin sensitivity were investigated in genetically obese Zucker rats, an animal model of insulin resistance, using the euglycemic clamp technique. After 0.4% DHEA was administered for 10 days to female obese Zucker rats aged 16 weeks, body weight and plasma insulin decreased and glucose disposal rate (GDR), which was normally reduced in obese rats, rose significantly compared with age- and sex-matched control obese rats. On the other hand, although the pair-fed obese rats also showed levels of weight reduction similar to those of DHEA-treated rats, the increase in GDR of DHEA-treated rats was significantly greater than in pair-fed rats, suggesting a direct ameliorating effect of DHEA on insulin sensitivity of obese rats. Serum concentration of tumor necrosis factor (TNF)-alpha, one of cytokines causing insulin resistance, was also reduced significantly in DHEA-treated, but not in pair-fed obese rats. In conclusion, our results suggest that DHEA treatment reduces body weight and serum TNF-alpha independently, and that both may ameliorate insulin resistance in obese Zucker fatty rats.

Dehydroepiandrosterone Decreases Serum Tumor Necrosis Factor- and Restores Insulin Sensitivity: Independent Effect from Secondary Weight Reduction in Genetically Obese Zucker Fatty Rats

Dehydroepiandrosterone (DHEA) and its sulfate ester are the most abundant circulating adrenal steroids in humans. Administration of DHEA has been reported to have beneficial effects on obesity, hyperlipidemia, diabetes, and atherosclerosis in obese rodents, although its effects on insulin resistance have not been fully elucidated. In this study, the effects of DHEA treatment on insulin sensitivity were investigated in genetically obese Zucker rats, an animal model of insulin resistance, using the euglycemic clamp technique. After 0.4% DHEA was administered for 10 days to female obese Zucker rats aged 16 weeks, body weight and plasma insulin decreased and glucose disposal rate (GDR), which was normally reduced in obese rats, rose significantly compared with age- and sex-matched control obese rats. On the other hand, although the pair-fed obese rats also showed levels of weight reduction similar to those of DHEA-treated rats, the increase in GDR of DHEA-treated rats was significantly greater than in pair-fed rats, suggesting a direct ameliorating effect of DHEA on insulin sensitivity of obese rats. Serum concentration of tumor necrosis factor (TNF)-α, one of cytokines causing insulin resistance, was also reduced significantly in DHEA-treated, but not in pair-fed obese rats. In conclusion, our results suggest that DHEA treatment reduces body weight and serum TNF-α independently, and that both may ameliorate insulin resistance in obese Zucker fatty rats.