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.     

Long-term effects of ovariectomy on osteoporosis and obesity in estrogen-receptor-β-deleted mice

Untreated BERKO mice demonstrate few abnormalities in bone phenotype and recent ovariectomy has few effects on various bone characteristics in these mice. Long-term studies on the bone phenotype of intact and ovariectomized mice are unavailable. Using quantitative computed tomography (qCT), we determined various parameters of the metaphysis of the tibia in sham-ovariectomized (intact) and ovariectomized BERKO and wildtype mice. Body weight and estrogen-regulated fat were also measured. Mice underwent surgery (ovariectomy or sham) at 3 mo of age, and qCT analysis was performed every 2 to 4 mo until mice were 12 mo old. Ovariectomized wildtype mice gained body weight and their fat depot increased in size within 2 mo after ovariectomy. Obesity developed later in ovariectomized BERKO mice, which became significantly heavier than their wildtype counterparts. Ovariectomized wildtype mice lost trabecular density more rapidly than did ovariectomized BERKO mice, which did not show similar loss in trabecular density until at least 7 mo after ovariectomy. At the latest studied time point (9 mo after surgery), cortical area was significantly larger in ovariectomized BERKO mice than ovariectomized wildtype mice. The absence of ERβ in ovariectomized BERKO mice during the first 3 to 5 mo after ovariectomy had protective effects against obesity and trabecular rarification; this protective effect disappeared at later time points.     

Oral treatment with γ-aminobutyric acid improves glucose tolerance and insulin sensitivity by inhibiting inflammation in high fat diet-fed mice

Adipocyte and β-cell dysfunction and macrophage-related chronic inflammation are critical for the development of obesity-related insulin resistance and type 2 diabetes mellitus (T2DM), which can be negatively regulated by Tregs. Our previous studies and those of others have shown that activation of γ-aminobutyric acid (GABA) receptors inhibits inflammation in mice. However, whether GABA could modulate high fat diet (HFD)-induced obesity, glucose intolerance and insulin resistance has not been explored. Here, we show that although oral treatment with GABA does not affect water and food consumption it inhibits the HFD-induced gain in body weights in C57BL/6 mice. Furthermore, oral treatment with GABA significantly reduced the concentrations of fasting blood glucose, and improved glucose tolerance and insulin sensitivity in the HFD-fed mice. More importantly, after the onset of obesity and T2DM, oral treatment with GABA inhibited the continual HFD-induced gain in body weights, reduced the concentrations of fasting blood glucose and improved glucose tolerance and insulin sensitivity in mice. In addition, oral treatment with GABA reduced the epididymal fat mass, adipocyte size, and the frequency of macrophage infiltrates in the adipose tissues of HFD-fed mice. Notably, oral treatment with GABA significantly increased the frequency of CD4(+)Foxp3(+) Tregs in mice. Collectively, our data indicated that activation of peripheral GABA receptors inhibited the HFD-induced glucose intolerance, insulin resistance, and obesity by inhibiting obesity-related inflammation and up-regulating Treg responses in vivo. Given that GABA is safe for human consumption, activators of GABA receptors may be valuable for the prevention of obesity and intervention of T2DM in the clinic.     

Effects of high fat diet induced obesity on peripheral nerve regeneration and levels of GAP 43 and TGF-β in rats

The increasing frequency of obesity is important because of its accompanying related health problems. The effects of obesity on peripheral nerves have not been elucidated. We investigated the effects of obesity on sciatic nerve regeneration using electrophysiology, stereology, immunohistochemistry, histopathology and functional tests. We used control, obese, control injured and obese injured groups of rats. Electrophysiological results showed that nerve conduction velocity and EMG were same in the experimental groups, but the amplitude of the compound action potential of the control group was significantly higher than that of the obese group. Examination of the nerves showed that the control and obese groups had both larger axon diameters and thicker myelin sheaths. The number of myelinated axons was decreased in both of the injured groups. Axon diameters and myelin sheath thicknesses of the control injured group were significantly greater those of the obese injured group. There were no significant differences in functional tests among the groups. Although growth associated protein 43 immunostaining in the control injured group was significantly greater than that of the obese injured group, no significant difference was observed between the control and obese groups. There was no significant difference in immunohistochemical staining for transforming growth factor beta 3 between the control injured and obese injured groups. Our results suggest that obesity may affect peripheral nerve regeneration negatively after crush injury.     

Genetic and environmental influences on body fat distribution, fasting insulin levels and CVD: are the influences shared?

Central body fat distribution has been shown to be related to hyperinsulinemia, insulin resistance, hypertriglyceridemia, and atherosclerosis to a greater degree than general obesity. There are known to be both genetic and environmental effects on all components of this clustering. Whether these genetic effects are due to one set of genes in common to the components or whether genetic influences on insulin resistance and/or general/abdominal fatness 'turn on' other genes that affect other components of the syndrome is not clear. We analyzed data from the Swedish Adoption/Twin Study of Aging (60% female; monozygotic = 116, dizygotic = 202; average age 65 years) to determine whether there were genetic and/or environmental factors shared among general body fat distribution, abdominal body fat distribution, fasting insulin levels and cardiovascular disease. We found additive genetic effects in males to be significantly different from those in females with genetic effects accounting for variance in waist-hip ratio (males = 28%; females = 49%), body mass index (males = 58%; females = 73%), fasting insulin levels (FI) (males = 27%; females = 49%), and cardiovascular disease (CVD) (males = 18%; females = 37%). There were also shared genetic and environmental effects among all the variables except CVD, but a majority of the genetic variance for these measures was trait specific.     

Lycopene attenuates body weight gain through induction of browning via regulation of peroxisome proliferator-activated receptor γ in high-fat diet-induced obese mice

Lycopene (LYC), one of the major carotenoids in tomatoes, has been preclinically and clinically used to obesity and type 2 diabetes management. However, whether its ability of countering body weight gain is related to induction of brown-like adipocyte phenotype in white adipose tissues (WAT) remains largely unknown. Activation of peroxisome proliferator-activated receptor γ (PPARγ) serves the brown-like phenotype conversion and energy expenditure. Here, we show that LYC treatment promotes glucose consumption and improves insulin sensitivity, as well as fosters white adipocytes browning through up-regulating mRNA and protein expression levels of PPARγ, uncoupling protein 1, PPARγ coactivator-1α and PR domain-containing 16 in the differentiated 3T3-L1 adipocytes and primary adipocytes, as well as in the WAT of HFD-exposed obese mice. In addition, LYC treatment attenuates body weight gain and improves serum lipid profiles as well as promotes brown adipose tissue activation in obese mice. Moreover, PPARγ is induced with LYC intervention in mitochondria respiration and browning in white adipocytes and tissues. Taken together, these results suggest that LYC counteracts obesity and improves glucose and lipid metabolism through induction of the browning via up-regulation of PPARγ, which offers a new perspective of this compound to combat obesity and obesity-related disorders.     

PKCδ is activated in the liver of obese Zucker rats and mediates diet-induced whole body insulin resistance and hepatocyte cellular insulin resistance

Insulin resistance can arise when pathological levels of free fatty acids (FFAs) and proinflammatory cytokines disrupt insulin signaling. Protein kinase C delta (PKCδ) is a FFA- and a proinflammatory cytokine-regulated protein kinase that is associated with inhibition of insulin signaling and action. To gain insight into the role of PKCδ in insulin resistance, PKCδ activation was studied in a genetic model of obesity-linked insulin resistance. PKCδ was found to be activated in the liver of obese insulin-resistant Zucker rats and in isolated cultured hepatocytes. PKCδ was further studied in PKCδ-null mice and their wild-type littermates fed a high-fat or control diet for 10 weeks. PKCδ-null mice on a high-fat diet had improved insulin sensitivity and hepatic insulin signaling compared to wild-type littermates. Additionally, the deleterious effect of a high-fat diet on glucose tolerance in wild-type mice was completely blocked in PKCδ-null mice. To directly test the role of PKCδ in cellular insulin resistance, primary hepatocytes from the high-fat diet mice were isolated and stimulated with insulin. Primary hepatocytes from PKCδ-null mice had improved insulin-stimulated Akt and FOXO phosphorylation compared to hepatocytes from wild-type littermates. Consistent with this result, tumor necrosis factor alpha-mediated inhibition of insulin signaling was blocked in PKCδ knockdown primary hepatocytes. These results indicate that PKCδ plays a role in insulin resistance and is consistent with the hypothesis that PKCδ is a negative regulator of insulin signaling and thus may be a therapeutic target for the treatment of type 2 diabetes.     

α-Linolenic acid-enriched butter attenuated high fat diet-induced insulin resistance and inflammation by promoting bioconversion of n-3 PUFA and subsequent oxylipin formation

α-Linolenic acid (ALA) is an essential fatty acid and the precursor for long-chain n-3 PUFA. However, biosynthesis of n-3 PUFA is limited in a Western diet likely due to an overabundance of n-6 PUFA. We hypothesized that dietary reduction of n-6/n-3 PUFA ratio is sufficient to promote the biosynthesis of long-chain n-3 PUFA, leading to an attenuation of high fat (HF) diet-induced obesity and inflammation. C57BL/6 J mice were fed a HF diet from ALA-enriched butter (n3Bu, n-6/n-3=1) in comparison with isocaloric HF diets from either conventional butter lacking both ALA and LA (Bu, n-6/n-3=6), or margarine containing a similar amount of ALA and abundant LA (Ma, n-6/n-3=6). Targeted lipidomic analyses revealed that n3Bu feeding promoted the bioconversion of long-chain n-3 PUFA and their oxygenated metabolites (oxylipins) derived from ALA and EPA. The n3Bu supplementation attenuated hepatic TG accumulation and adipose tissue inflammation, resulting in improved insulin sensitivity. Decreased inflammation by n3Bu feeding was attributed to the suppression of NF-κB activation and M1 macrophage polarization. Collectively, our work suggests that dietary reduction of the n-6/n-3 PUFA ratio, as well as total n-3 PUFA consumed, is a crucial determinant that facilitates n-3 PUFA biosynthesis and subsequent lipidomic modifications, thereby conferring metabolic benefits against obesity-induced inflammation and insulin resistance.     

Exercise is more effective than diet control in preventing high fat diet-induced β-amyloid deposition and memory deficit in amyloid precursor protein transgenic mice

Accumulating evidence suggests that some dietary patterns, specifically high fat diet (HFD), increase the risk of developing sporadic Alzheimer disease (AD). Thus, interventions targeting HFD-induced metabolic dysfunctions may be effective in preventing the development of AD. We previously demonstrated that amyloid precursor protein (APP)-overexpressing transgenic mice fed HFD showed worsening of cognitive function when compared with control APP mice on normal diet. Moreover, we reported that voluntary exercise ameliorates HFD-induced memory impairment and β-amyloid (Aβ) deposition. In the present study, we conducted diet control to ameliorate the metabolic abnormality caused by HFD on APP transgenic mice and compared the effect of diet control on cognitive function with that of voluntary exercise as well as that of combined (diet control plus exercise) treatment. Surprisingly, we found that exercise was more effective than diet control, although both exercise and diet control ameliorated HFD-induced memory deficit and Aβ deposition. The production of Aβ was not different between the exercise- and the diet control-treated mice. On the other hand, exercise specifically strengthened the activity of neprilysin, the Aβ-degrading enzyme, the level of which was significantly correlated with that of deposited Aβ in our mice. Notably, the effect of the combination treatment (exercise and diet control) on memory and amyloid pathology was not significantly different from that of exercise alone. These studies provide solid evidence that exercise is a useful intervention to rescue HFD-induced aggravation of cognitive decline in transgenic model mice of AD.     

PPARδ activation attenuates hepatic steatosis in Ldlr?/? mice by enhanced fat oxidation,reduced lipogenesis,and improved insulin sensitivity

PPARδ regulates systemic lipid homeostasis and inflammation, but its role in hepatic lipid metabolism remains unclear. Here, we examine whether intervening with a selective PPARδ agonist corrects hepatic steatosis induced by a high-fat, cholesterol-containing (HFHC) diet. Ldlr^−/− mice were fed a chow or HFHC diet (42% fat, 0.2% cholesterol) for 4 weeks. For an additional 8 weeks, the HFHC group was fed HFHC or HFHC plus GW1516 (3 mg/kg/day). GW1516-intervention significantly attenuated liver TG accumulation by induction of FA β-oxidation and attenuation of FA synthesis. In primary mouse hepatocytes, GW1516 treatment stimulated AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) phosphorylation in WT hepatocytes, but not AMPKβ1^−/− hepatocytes. However, FA oxidation was only partially reduced in AMPKβ1^−/− hepatocytes, suggesting an AMPK-independent contribution to the GW1516 effect. Similarly, PPARδ-mediated attenuation of FA synthesis was partially due to AMPK activation, as GW1516 reduced lipogenesis in WT hepatocytes but not AMPKβ1^−/− hepatocytes. HFHC-fed animals were hyperinsulinemic and exhibited selective hepatic insulin resistance, which contributed to elevated fasting FA synthesis and hyperglycemia. GW1516 intervention normalized fasting hyperinsulinemia and selective hepatic insulin resistance and attenuated fasting FA synthesis and hyperglycemia. The HFHC diet polarized the liver toward a proinflammatory M1 state, which was reversed by GW1516 intervention. Thus, PPARδ agonist treatment inhibits the progression of preestablished hepatic steatosis.     

Inherited non-autosomal effects on body fat in F2 mice derived from an AKR/J × SWR/J cross

In this study we describe the contribution of matrilineal and patrilineal effects on the adiposity, body weight, and on the weights of individual fat pads in F₂ male mice derived from an SWR/J × AKR/J cross. AKR/J mice become obese after 12 weeks on a high-fat diet, whereas SWR/J mice remain relatively lean. Here we report that mice with AKR maternal and AKR paternal grandmothers have significantly larger epidydimal and retroperitoneal fat pads than those with SWR maternal and paternal grandmothers. However, grandparental strain had no effect on the overall adiposity (AI) or the weights of the inguinal, subcutaneous or mesenteric fat pads. The strain of the paternal grandparents had a small but significant effect on body weight. These effects can be attributed to in utero effects, imprinting effects, cytoplasmic and/or Y chromosome transmission of factors controlling body fat. We also describe the presence of a quantitative trait locus (QTL) on Chromosome X, close to DXMit174, which is linked to adiposity, body weight, and to the weights of the individual fat depots. However, this QTL is not responsible for the grandparental strain effects described above. Received: 3 March 1997 / Accepted: 5 May 1997     

Ameliorative effect of vanadyl(IV)–ascorbate complex on high-fat high-sucrose diet-induced hyperglycemia,insulin resistance,and oxidative stress in mice

There is mounting evidence demonstrating causative links between hyperglycemia, oxidative stress, and insulin resistance, the core pathophysiological features of type 2 diabetes mellitus. Using a combinational approach, we synthesized a vanadium–antioxidant (i.e., l-ascorbic acid) complex and examined its effect on insulin resistance and oxidative stress. This study was designed to examine whether vanadyl(IV)-ascorbate complex (VOAsc) would reduce oxidative stress, hyperglycemia, and insulin resistance in high-fat high-sucrose diet (HFSD)-induced type 2 diabetes in mice. Male C57BL/6J mice were fed a HFSD for 12 weeks to induce insulin resistance, rendering them diabetic. Diabetic mice were treated with rosiglitazone, sodium l-ascorbate, or VOAsc. At the end of treatment, fasting blood glucose, fasting serum insulin, homeostasis model assessment-insulin resistance index, and serum adipocytokine levels were measured. Serum levels of nitric oxide (NO) parameters were also determined. The liver was isolated and used for determination of malondialdehyde, reduced glutathione, and catalase levels, and superoxide dismutase and glutathione peroxidase activities. VOAsc groups exhibited significant reductions in serum adipocytokine and NO levels, and oxidative stress parameters compared to the corresponding values in the untreated diabetic mice. The results indicated that VOAsc is non-toxic. In conclusion, we identified VOAsc as a potentially effective adjunct therapy for the management of type 2 diabetes.     

The obese Göttingen minipig as a model of the metabolic syndrome: dietary effects on obesity, insulin sensitivity, and growth hormone profile

The objective of the study reported here was to induce obesity in the female G?ttingen minipig to establish a model of the human metabolic syndrome. Nine- to ten-month-old female G?ttingen minipigs received a high-fat high-energy (HFE) diet or a low-fat, low-energy (LFE) diet. The energy contents derived from fat were 55 and 13 %, respectively. After 5 weeks, animals were subjected to dual energy x-ray absorptiometry (DEXA) scanning, intravenous glucose tolerance testing (IVGTT), and 6-h growth hormone profile recording. After treatment, mean body weight of pigs of the LFE group was 21.0 +/- 0.4 kg, and was 26.8 +/- 0.2 kg in pigs of the HFE group (P < 0.0001). The DEXA scanning indicated that the fat content of the LFE group was 10.0 +/- 1.2 % versus 15.2 +/- 0.7 % in the HFE group (P < 0.003). Triglycerides concentration was significantly (P < 0.05) increased in pigs of the HFE group (0.24 +/- 0.03 mM), compared with that in pigs of the LFE group (0.13 +/- 0.04 mM). Preprandial plasma glucose and insulin concentrations were not affected, but insulin area under the curve during IVGTT was significantly high in the obese animals. Growth hormone (GH) secretion was low in both groups of pigs. The obese minipig shares some of the metabolic impairments seen in obese humans, and may thus serve as a model of the metabolic syndrome.     

The beneficial effects of α-cyclodextrin on blood lipids and weight loss in healthy humans

α‐Cyclodextrin (α‐CD) is a soluble fiber derived from corn. It has previously been reported that early intervention with Mirafit fbcx, a trademarked name for α‐CD, has beneficial effects on weight management in obese individuals with type 2 diabetes, and that it preferentially reduces blood levels of saturated and trans fats in the LDL receptor knockout mice. The current investigation involves overweight but not obese nondiabetic individuals and was intended to confirm the effects of α‐CD on both weight management and improving blood lipid levels. Forty‐one healthy adults (age: 41.4 ± 13.6 years) participated in this 2‐month, double‐blinded, crossover study. In 28 compliant participants (8 males and 20 females), when the active phase was compared to the control phase, there were significant decreases in body weight (?0.4 ± 0.2 kg, P < 0.05), serum total cholesterol (mean ± s.e.m., ?0.295 ± 0.10 mmol/l, 5.3%, P < 0.02) and low‐density lipoprotein (LDL) cholesterol (?0.23 ± 0.11 mmol/l, ?6.7%, P < 0.05). Apolipoprotein B (Apo B) (?0.0404 ± 0.02 g/l, ?5.6%, P = 0.06) and insulin levels also decreased by 9.5% (?0.16 ± 0.08 pmol/l, P = 0.06) while blood glucose and leptin levels did not change. These results suggest that α‐CD exerts its beneficial health effects on body weight and blood lipid profile in healthy nonobese individuals, as previously reported in obese individuals with type 2 diabetes.     

Chronic effects of β2 agonists on body composition and protein synthesis in the rat

Chronic treatment of rats with the ₂-adrenergic agonists clenbuterol and fenoterol over 16–19 d raised energy intake, expenditure, and body weight gain but did not affect fat or energy deposition, and body protein gain was increased by 50 and 18%, respectively. Both drugs increased the protein content and mitochondrial GDP-binding capacity of brown adipose tissue. Clenbuterol did not affect plasma insulin, growth hormone, or triiodothyronine levels, although insulin levels were reduced by fenoterol. Both drugs caused hypertrophy of skeletal muscle (gastrocnemius), and muscle protein synthesis in vivo (fractional rate) was elevated by 34 and 26% in clenbuterol and fenoteroltreated rats, respectively.     

Intestine-specific expression of acyl CoA:diacylglycerol acyltransferase 1 reverses resistance to diet-induced hepatic steatosis and obesity in Dgat1−/− mice

Mice deficient in acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), a key enzyme in triacylglycerol (TG) biosynthesis, are resistant to high-fat (HF) diet-induced hepatic steatosis and obesity. DGAT1-deficient (Dgat1^−/−) mice have no defect in quantitative absorption of dietary fat; however, they have abnormally high levels of TG stored in the cytoplasm of enterocytes, and they have a reduced postprandial triglyceridemic response. We generated mice expressing DGAT1 only in the intestine (Dgat1^IntONLY) to determine whether this phenotype contributes to resistance to HF diet-induced hepatic steatosis and obesity in Dgat1^−/− mice. Despite lacking DGAT1 in liver and adipose tissue, we found that Dgat1^IntONLY mice are not resistant to HF diet-induced hepatic steatosis or obesity. The results presented demonstrate that intestinal DGAT1 stimulates dietary fat secretion out of enterocytes and that altering this cellular function alters the fate of dietary fat in specific tissues.