Obesity-related derangements in metabolic regulation

Plasma fatty acid changes following consumption of dietary oils containing n-3, n-6, and n-9 fatty acids at different proportions: preliminary findings of the Canola Oil Multicenter Intervention Trial (COMIT)

Background

The Canola Oil Multicenter Intervention Trial (COMIT) was a randomized controlled crossover study designed to evaluate the effects of five diets that provided different oils and/or oil blends on cardiovascular disease (CVD) risk factors in individuals with abdominal obesity. The present objective is to report preliminary findings on plasma fatty acid profiles in volunteers with abdominal obesity, following the consumption of diets enriched with n-3, n-6 and n-9 fatty acids.

Methods

COMIT was conducted at three clinical sites, Winnipeg, Manitoba, Canada, Québec City, Québec, Canada and University Park, Pennsylvania, United States. Inclusion criteria were at least one of the followings: waist circumference (≥90 cm for males and ≥84 cm for females), and at least one other criterion: triglycerides ≥1.7 mmol/L, high density lipoprotein cholesterol <1 mmol/L (males) or <1.3 mmol/L (females), blood pressure ≥130 mmHg (systolic) and/or ≥85 mmHg (diastolic), and glucose ≥5.5 mmol/L. Weight-maintaining diets that included shakes with one of the dietary oil blends were provided during each of the five 30-day dietary phases. Dietary phases were separated by four-week washout periods. Treatment oils were canola oil, high oleic canola oil, high oleic canola oil enriched with docosahexaenoic acid (DHA), flax oil and safflower oil blend, and corn oil and safflower oil blend. A per protocol approach with a mixed model analysis was decided to be appropriate for data analysis.

Results

One hundred and seventy volunteers were randomized and 130 completed the study with a dropout rate of 23.5%. The mean plasma total DHA concentrations, which were analyzed among all participants as a measure of adherence, increased by more than 100% in the DHA-enriched phase, compared to other phases, demonstrating excellent dietary adherence.

Conclusions

Recruitment and retention strategies were effective in achieving a sufficient number of participants who completed the study protocol to enable sufficient statistical power to resolve small differences in outcome measures. It is expected that the study will generate important data thereby enhancing our understanding of the effects of n-3, n-6, and n-9 fatty acid-containing oils on CVD risks.

Trial registration

ClinicalTrials.gov NCT01351012.

Plasma metabolomic profiling suggests early indications for predisposition to latent insulin resistance in children conceived by ICSI

BACKGROUND

There have been increasing indications about an epigenetically-based elevated predisposition of assisted reproductive technology (ART) offspring to insulin resistance, which can lead to an unfavorable cardio-metabolic profile in adult life. However, the relevant long-term systematic molecular studies are limited, especially for the IntraCytoplasmic Sperm Injection (ICSI) method, introduced in 1992. In this study, we carefully defined a group of 42 prepubertal ICSI and 42 naturally conceived (NC) children. We assessed differences in their metabolic profile based on biochemical measurements, while, for a subgroup, plasma metabolomic analysis was also performed, investigating any relevant insulin resistance indices.

METHODS & RESULTS

Auxological and biochemical parameters of 42 6.8±2.1 yrs old ICSI-conceived and 42 age-matched controls were measured. Significant differences between the groups were determined using univariate and multivariate statistics, indicating low urea and low-grade inflammation markers (YKL-40, hsCRP) and high triiodothyronine (T3) in ICSI-children compared to controls. Moreover, plasma metabolomic analysis carried out for a subgroup of 10 ICSI- and 10 NC girls using Gas Chromatography-Mass Spectrometry (GC-MS) indicated clear differences between the two groups, characterized by 36 metabolites linked to obesity, insulin resistance and metabolic syndrome. Notably, the distinction between the two girl subgroups was accentuated when both their biochemical and metabolomic measurements were employed.

CONCLUSIONS

The present study contributes a large auxological and biochemical dataset of a well-defined group of pre-pubertal ICSI-conceived subjects to the research of the ART effect to the offspring's health. Moreover, it is the first time that the relevant usefulness of metabolomics was investigated. The acquired results are consistent with early insulin resistance in ICSI-offspring, paving the way for further systematic investigations. These data support that metabolomics may unravel metabolic differences before they become clinically or biochemically evident, underlining its utility in the ART research.

A withanolide coagulin-L inhibits adipogenesis modulating Wnt/β-catenin pathway and cell cycle in mitotic clonal expansion

Obesity is a result of adipocyte hypertrophy followed by hyperplasia. It is a risk factor for several metabolic disorders such as dyslipidemia, type-2 diabetes, hypertension, and cardiovascular diseases. Coagulanolides, particularly coagulin-L isolated from W. coagulan has earlier been reported for anti-hyperglycemic activity. In this study, we investigated the effect of coagulin-L on in vitro models of adipocyte differentiation including 3T3-L1 pre-adipocyte, mouse stromal mesenchymal C3H10T1/2 cells and bone marrow derived human mesenchymal stem cells (hMSCs). Our results showed that, coagulin-L reduces the expressions of peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα), the major transcription factors orchestrating adipocyte differentiation. Detailed analysis further proved that early exposure of coagulin-L is sufficient to cause significant inhibition during adipogenesis. Coagulin-L inhibited mitotic clonal expansion (MCE) by delayed entry in G1 to S phase transition and S-phase arrest. This MCE blockade was caused apparently by decreased phosphorylation of C/EBPβ, modulation in expression of cell cycle regulatory proteins, and upregulation of Wnt/β-catenin pathway, the early stage regulatory proteins of adipogenic induction. Taken together all evidences, a known anti-hyperglycemic agent coagulin-L has shown potential to inhibit adipogenesis significantly, which can be therapeutically exploited for treatment of obesity and metabolic syndrome.

Dietary intake of palmitate and oleate has broad impact on systemic and tissue lipid profiles in humans

BACKGROUND

Epidemiologic evidence has suggested that diets with a high ratio of palmitic acid (PA) to oleic acid (OA) increase risk of cardiovascular disease (CVD).

OBJECTIVE

To gain additional insights into the relative effect of dietary fatty acids and their metabolism on CVD risk, we sought to identify a metabolomic signature that tracks with diet-induced changes in blood lipid concentrations and whole-body fat oxidation.

DESIGN

We applied comprehensive metabolomic profiling tools to biological specimens collected from 18 healthy adults enrolled in a crossover trial that compared a 3-wk high-palmitic acid (HPA) with a low-palmitic acid and high-oleic acid (HOA) diet.

RESULTS

A principal components analysis of the data set including 329 variables measured in 15 subjects in the fasted state identified one factor, the principal components analysis factor in the fasted state (PCF1-Fasted), which was heavily weighted by the PA:OA ratio of serum and muscle lipids, that was affected by diet (P < 0.0001; HPA greater than HOA). One other factor, the additional principal components analysis factor in the fasted state (PCF2-Fasted), reflected a wide range of acylcarnitines and was affected by diet in women only (P = 0.0198; HPA greater than HOA). HOA lowered the ratio of serum low-density lipoprotein to high-density lipoprotein (LDL:HDL) in men and women, and adjustment for the PCF1-Fasted abolished the effect. In women only, adjustment for the PCF2-Fasted eliminated the HOA-diet effect on serum total- and LDL-cholesterol concentrations. The respiratory exchange ratio in the fasted state was lower with the HPA diet (P = 0.04), and the diet effect was eliminated after adjustment for the PCF1-Fasted. The messenger RNA expression of the cholesterol regulatory gene insulin-induced gene-1 was higher with the HOA diet (P = 0.008).

CONCLUSIONS

These results suggest that replacing dietary PA with OA reduces the blood LDL concentration and whole-body fat oxidation by modifying the saturation index of circulating and tissue lipids. In women, these effects are also associated with a higher production and accumulation of acylcarnitines, possibly reflecting a shift in fat catabolism.

Body mass index and risk of age-related cataract: a meta-analysis of prospective cohort studies

Background

Age-related cataract (ARC) is the leading cause of blindness in the world. The relationship between body mass index (BMI) and risk of ARC is controversial across observational studies. We therefore performed this meta-analysis to evaluate the association between BMI and risk of ARC.

Methods

Eligible studies were identified through an electronic search of PubMed, Embase and the Cochrane Library. We pooled study-specific relative risks (RRs) and 95% confidence intervals (CIs) to determine the risk of ARC associated with BMI categories and per 1 kg/m² increase in BMI.

Results

A total of 17 prospective cohort studies were included in the meta-analysis. The pooled RRs of ARC were 1.08 (95% CI, 1.01–1.16) for overweight and 1.19 (95% CI, 1.10–1.28) for obesity compared with normal weight. These findings were robust when stratified by sex, sample source, outcome types and confounders, while significantly differed by assessment of BMI and ARC, and duration of follow-up. The summary RR suggested that per 1 kg/m² increase in BMI was associated with a 2% increased risk of ARC (RR 1.02, 95% CI 1.01–1.03). Pooled estimates of RRs consistently indicated a trend for subjects with a high BMI to develop posterior subcapsular cataracts (RR 1.19, 95% CI 1.06–1.35, for overweight; RR 1.50, 95% CI 1.24–1.81, for obesity; RR 1.04, 95% CI 1.01–1.06, per 1 kg/m² increase in BMI) other than nuclear or cortical cataracts.

Conclusions

The overall findings suggest that elevated BMI may increase the risk of ARC, especially posterior subcapsular cataracts. Further trials are needed to investigate the effect of weight reduction in obese populations on the risk of ARC.

Mitochondrial alteration in type 2 diabetes and obesity: an epigenetic link

The growing epidemic of type 2 diabetes mellitus (T2DM) and obesity is largely attributed to the current lifestyle of over-consumption and physical inactivity. As the primary platform controlling metabolic and energy homeostasis, mitochondria show aberrant changes in T2DM and obese subjects. While the underlying mechanism is under extensive investigation, epigenetic regulation is now emerging to play an important role in mitochondrial biogenesis, function, and dynamics. In line with lifestyle modifications preventing mitochondrial alterations and metabolic disorders, exercise has been shown to change DNA methylation of the promoter of PGC1α to favor gene expression responsible for mitochondrial biogenesis and function. In this article we discuss the epigenetic mechanism of mitochondrial alteration in T2DM and obesity, and the effects of lifestyle on epigenetic regulation. Future studies designed to further explore and integrate the epigenetic mechanisms with lifestyle modification may lead to interdisciplinary interventions and novel preventive options for mitochondrial alteration and metabolic disorders.

Alleviating Effects of Baechu Kimchi Added Ecklonia cava on Postprandial Hyperglycemia in Diabetic Mice

In this study, we investigated the inhibitory effects of Baechu kimchi added Ecklonia cava on the activities of α-glucosidase and α-amylase and its alleviating effect on the postprandial hyperglycemia in STZ-induced diabetic mice. Baechu kimchi added Ecklonia cava (BKE, 15%) was fermented at 5°C for 28 days. Optimum ripened BKE was used in this study as it showed the strongest inhibitory activities on α-glucosidase and α-amylase by fermentation time among the BKEs in our previous study. The BKE was extracted with 80% methanol and the extract solution was concentrated, and then used in this study. The BKE extract showed higher inhibitory activities than Baechu kimchi extract against α-glucosidase and α-amylase. The IC₅₀ values of the BKE extract against α-glucosidase and α-amylase were 0.58 and 0.35 mg/mL, respectively; BKE exhibited a lower α-glucosidase inhibitory activity but a higher α-amylase inhibitory activity than those of acarbose. The BKE extract alleviated postprandial hyperglycemia caused by starch loading in normal and streptozotocin-induced diabetic mice. Furthermore, the BKE extract significantly lowered the incremental area under the curve in both normal and diabetic mice (P<0.05). These results indicated that the BKE extract may delay carbohydrate digestion and thus glucose absorption.

Chronic high glucose and pyruvate levels differentially affect mitochondrial bioenergetics and fuel-stimulated insulin secretion from clonal INS-1 832/13 cells

Glucotoxicity in pancreatic β-cells is a well established pathogenetic process in type 2 diabetes. It has been suggested that metabolism-derived reactive oxygen species perturb the β-cell transcriptional machinery. Less is known about altered mitochondrial function in this condition. We used INS-1 832/13 cells cultured for 48 h in 2.8 mm glucose (low-G), 16.7 mm glucose (high-G), or 2.8 mm glucose plus 13.9 mm pyruvate (high-P) to identify metabolic perturbations. High-G cells showed decreased responsiveness, relative to low-G cells, with respect to mitochondrial membrane hyperpolarization, plasma membrane depolarization, and insulin secretion, when stimulated acutely with 16.7 mm glucose or 10 mm pyruvate. In contrast, high-P cells were functionally unimpaired, eliminating chronic provision of saturating mitochondrial substrate as a cause of glucotoxicity. Although cellular insulin content was depleted in high-G cells, relative to low-G and high-P cells, cellular functions were largely recovered following a further 24-h culture in low-G medium. After 2 h at 2.8 mm glucose, high-G cells did not retain increased levels of glycolytic or TCA cycle intermediates but nevertheless displayed increased glycolysis, increased respiration, and an increased mitochondrial proton leak relative to low-G and high-P cells. This notwithstanding, titration of low-G cells with low protonophore concentrations, monitoring respiration and insulin secretion in parallel, showed that the perturbed insulin secretion of high-G cells could not be accounted for by increased proton leak. The present study supports the idea that glucose-induced disturbances of stimulus-secretion coupling by extramitochondrial metabolism upstream of pyruvate, rather than exhaustion from metabolic overload, underlie glucotoxicity in insulin-producing cells.

PPARα and Sirt1 mediate erythropoietin action in increasing metabolic activity and browning of white adipocytes to protect against obesity and metabolic disorders

Erythropoietin (EPO) has shown beneficial effects in the regulation of obesity and metabolic syndrome; however, the detailed mechanism is still largely unknown. Here, we created mice with adipocyte-specific deletion of EPO receptor. These mice exhibited obesity and decreased glucose tolerance and insulin sensitivity, especially when fed a high-fat diet. Moreover, EPO increased oxidative metabolism, fatty acid oxidation, and key metabolic genes in adipocytes and in white adipose tissue from diet-induced obese wild-type mice. Increased metabolic activity by EPO is associated with induction of brown fat-like features in white adipocytes, as demonstrated by increases in brown fat gene expression, mitochondrial content, and uncoupled respiration. Peroxisome proliferator-activated receptor (PPAR)α was found to mediate EPO activity because a PPARα antagonist impaired EPO-mediated induction of brown fat-like gene expression and uncoupled respiration. PPARα also cooperates with Sirt1 activated by EPO through modulating the NAD+ level to regulate metabolic activity. PPARα targets, including PPARγ coactivator 1α, uncoupling protein 1, and carnitine palmitoyltransferase 1α, were increased by EPO but impaired by Sirt1 knockdown. Sirt1 knockdown also attenuated adipose response to EPO. Collectively, EPO, as a novel regulator of adipose energy homeostasis via these metabolism coregulators, provides a potential therapeutic strategy to protect against obesity and metabolic disorders.

Palmitate increases Nur77 expression by modulating ZBP89 and Sp1 binding to the Nur77 proximal promoter in pancreatic β-cells

Nur77 is a stress sensor in pancreatic β-cells, which negatively regulates glucose-stimulated insulin secretion. We recently showed that a lipotoxic shock caused by exposure of β-cells to the saturated fatty acid palmitate strongly increases Nur77 expression. Here, using dual luciferase reporter assays and Nur77 promoter deletion constructs, we identified a regulatory cassette between -1534 and -1512 bp upstream from the translational start site mediating Nur77 promoter activation in response to palmitate exposure. Chromatin immunoprecipitation, transient transfection and siRNA-mediated knockdown assays revealed that palmitate induced Nur77 promoter activation involves Sp1 recruitment and ZBP89 release from the gene promoter.

Genistein stimulates fatty acid oxidation in a leptin receptor-independent manner through the JAK2-mediated phosphorylation and activation of AMPK in skeletal muscle

Obesity is a public health problem that contributes to the development of insulin resistance, which is associated with an excessive accumulation of lipids in skeletal muscle tissue. There is evidence that soy protein can decrease the ectopic accumulation of lipids and improves insulin sensitivity; however, it is unknown whether soy isoflavones, particularly genistein, can stimulate fatty acid oxidation in the skeletal muscle. Thus, we studied the mechanism by which genistein stimulates fatty acid oxidation in the skeletal muscle. We showed that genistein induced the expression of genes of fatty acid oxidation in the skeletal muscle of Zucker fa/fa rats and in leptin receptor (ObR)-silenced C2C12 myotubes through AMPK phosphorylation. Furthermore, the genistein-mediated AMPK phosphorylation occurred via JAK2, which was possibly activated through a mechanism that involved cAMP. Additionally, the genistein-mediated induction of fatty acid oxidation genes involved PGC1α and PPARδ. As a result, we observed that genistein increased fatty acid oxidation in both the control and silenced C2C12 myotubes, as well as a decrease in the RER in mice, suggesting that genistein can be used in strategies to decrease lipid accumulation in the skeletal muscle.

Effect of Regular Exercise on the Histochemical Changes of d-Galactose-Induced Oxidative Renal Injury in High-Fat Diet-Fed Rats

Renal lipid accumulation exhibits slowly developing chronic kidney disease and is associated with increased oxidative stress. The impact of exercise on the obese- and oxidative stress-related renal disease is not well understood. The purpose of this study was to investigate whether a high-fat diet (HFD) would accelerate d-galactose-induced aging process in rat kidney and to examine the preventive effect of regular exercise on the obese- and oxidative stress-related renal disease. Oxidative stress was induced by an administration of d-galactose (100 mg/kg intraperitoneally injected) for 9 weeks, and d-galactose-treated rats were also fed with a high-fat diet (60% kcal as fat) for 9 weeks to induce obesity. We investigated the efficacy of regular exercise in reducing renal injury by analyzing Nε-carboxymethyllysine (CML), 8-hydroxygluanine (8-OHdG) and apoptosis. When rats were fed with a HFD for 9 weeks in d-galactose-treated rats, an increased CML accumulation, oxidative DNA damage and renal podocyte loss were observed in renal glomerular cells and tubular epithelial cells. However, the regular exercise restored all these renal changes in HFD plus d-galactose-treated rats. Our data suggested that long-term HFD may accelerate the deposition of lipoxidation adducts and oxidative renal injury in d-galactose-treated rats. The regular exercise protects against obese- and oxidative stress-related renal injury by inhibiting this lipoxidation burden.

Androgen receptor (AR) pathophysiological roles in androgen-related diseases in skin, bone/muscle, metabolic syndrome and neuron/immune systems: lessons learned from mice lacking AR in specific cells

The androgen receptor (AR) is expressed ubiquitously and plays a variety of roles in a vast number of physiological and pathophysiological processes. Recent studies of AR knockout (ARKO) mouse models, particularly the cell type- or tissue-specific ARKO models, have uncovered many AR cell type- or tissue-specific pathophysiological roles in mice, which otherwise would not be delineated from conventional castration and androgen insensitivity syndrome studies. Thus, the AR in various specific cell types plays pivotal roles in production and maturation of immune cells, bone mineralization, and muscle growth. In metabolism, the ARs in brain, particularly in the hypothalamus, and the liver appear to participate in regulation of insulin sensitivity and glucose homeostasis. The AR also plays key roles in cutaneous wound healing and cardiovascular diseases, including atherosclerosis and abdominal aortic aneurysm. This article will discuss the results obtained from the total, cell type-, or tissue-specific ARKO models. The understanding of AR cell type- or tissue-specific physiological and pathophysiological roles using these in vivo mouse models will provide useful information in uncovering AR roles in humans and eventually help us to develop better therapies via targeting the AR or its downstream signaling molecules to combat androgen/AR-related diseases.

Metformin inhibits the growth of human pancreatic cancer xenografts

OBJECTIVE

Pancreatic ductal adenocarcinoma is a devastating disease, with an overall 5-year survival rate of only 3% to 5%. As the current therapies offer very limited survival benefits, novel therapeutic strategies are urgently required to treat this disease. Here, we determined whether metformin administration inhibits the growth of PANC-1 and MiaPaCa-2 tumor xenografts in vivo.

METHODS

Different xenograft models, including orthotopic implantation, were used to determine whether intraperitoneal or oral administration of metformin inhibits the growth of pancreatic cancer in vivo.

RESULTS

We demonstrate that metformin given once daily intraperitoneally at various doses (50-250 mg/kg) to nude mice inhibited the growth of PANC-1 xenografts in a dose-dependent manner. A significant effect of metformin was obtained at 50 mg/kg and maximal effect at 200 mg/kg. Metformin administration also caused a significant reduction in the phosphorylation of ribosomal S6 protein and ERK in these xenografts. Metformin also inhibited the growth of pancreatic cancer xenografts when administered orally (2.5 mg/mL) either before or after tumor implantation. Importantly, oral administration of metformin also inhibited the growth of MiaPaCa-2 tumors xenografted orthotopically.

CONCLUSIONS

The studies presented here provide further evidence indicating that metformin offers a potential novel approach for pancreatic ductal adenocarcinoma prevention and therapy.

Mediating lipid biosynthesis: implications for cardiovascular disease

Dysregulation of lipid homeostasis is a risk factor for cardiovascular disease (CVD). Thus, understanding the molecular mechanisms of maintaining lipid homeostasis may aid the discovery of novel targets for treating CVD. MED15 and cyclin-dependent kinase-8 (CDK8) are subunits of the Mediator complex, which contains multiple proteins and functions as a transcriptional cofactor. Mediator can positively or negatively regulate gene expression, depending on the contexts and its associated transcription factors. Recent studies revealed a critical role of MED15 and CDK8 in regulating sterol regulatory element-binding protein (SREBP) transcription factors, which are master activators for genes that are responsible for lipid biosynthesis. Here, we review the function of MED15 and CDK8 in regulating lipid homeostasis and discuss the implications for CVD.

Host gene expression profiling and in vivo cytokine studies to characterize the role of linezolid and vancomycin in methicillin-resistant Staphylococcus aureus (MRSA) murine sepsis model

Linezolid (L), a potent antibiotic for Methicillin Resistant Staphylococcus aureus (MRSA), inhibits bacterial protein synthesis. By contrast, vancomycin (V) is a cell wall active agent. Here, we used a murine sepsis model to test the hypothesis that L treatment is associated with differences in bacterial and host characteristics as compared to V. Mice were injected with S. aureus USA300, and then intravenously treated with 25 mg/kg of either L or V at 2 hours post infection (hpi). In vivo alpha-hemolysin production was reduced in both L and V-treated mice compared to untreated mice but the reduction did not reach the statistical significance [P = 0.12 for L; P = 0.70 for V). PVL was significantly reduced in L-treated mice compared to untreated mice (P = 0.02). However the reduction of in vivo PVL did not reach the statistical significance in V- treated mice compared to untreated mice (P = 0.27). Both antibiotics significantly reduced IL-1β production [P = 0.001 for L; P = 0.006 for V]. IL-6 was significantly reduced with L but not V antibiotic treatment [P<0.001 for L; P = 0.11 for V]. Neither treatment significantly reduced production of TNF-α. Whole-blood gene expression profiling showed no significant effect of L and V on uninfected mice. In S. aureus-infected mice, L altered the expression of a greater number of genes than V (95 vs. 42; P = 0.001). Pathway analysis for the differentially expressed genes identified toll-like receptor signaling pathway to be common to each S. aureus-infected comparison. Expression of immunomodulatory genes like Cxcl9, Cxcl10, Il1r2, Cd14 and Nfkbia was different among the treatment groups. Glycerolipid metabolism pathway was uniquely associated with L treatment in S. aureus infection. This study demonstrates that, as compared to V, treatment with L is associated with reduced levels of toxin production, differences in host inflammatory response, and distinct host gene expression characteristics in MRSA sepsis.

Mitochondrial dynamics in the regulation of nutrient utilization and energy expenditure

Mitochondrial fusion, fission, and mitophagy form an essential axis of mitochondrial quality control. However, quality control might not be the only task carried out by mitochondrial dynamics. Recent studies link mitochondrial dynamics to the balance between energy demand and nutrient supply, suggesting changes in mitochondrial architecture as a mechanism for bioenergetic adaptation to metabolic demands. By favoring either connected or fragmented architectures, mitochondrial dynamics regulates bioenergetic efficiency and energy expenditure. Placement of bioenergetic adaptation and quality control as competing tasks of mitochondrial dynamics might provide a new mechanism, linking excess nutrient environment to progressive mitochondrial dysfunction, common to age-related diseases.

A lipidomics analysis of the relationship between dietary fatty acid composition and insulin sensitivity in young adults

Relative to diets enriched in palmitic acid (PA), diets rich in oleic acid (OA) are associated with reduced risk of type 2 diabetes. To gain insight into mechanisms underlying these observations, we applied comprehensive lipidomic profiling to specimens collected from healthy adults enrolled in a randomized, crossover trial comparing a high-PA diet to a low-PA/high-OA (HOA) diet. Effects on insulin sensitivity (SI) and disposition index (DI) were assessed by intravenous glucose tolerance testing. In women, but not men, SI and DI were higher during HOA. The effect of HOA on SI correlated positively with physical fitness upon enrollment. Principal components analysis of either fasted or fed-state metabolites identified one factor affected by diet and heavily weighted by the PA/OA ratio of serum and muscle lipids. In women, this factor correlated inversely with SI in the fasted and fed states. Medium-chain acylcarnitines emerged as strong negative correlates of SI, and the HOA diet was accompanied by lower serum and muscle ceramide concentrations and reductions in molecular biomarkers of inflammatory and oxidative stress. This study provides evidence that the dietary PA/OA ratio impacts diabetes risk in women.

Adiponectin corrects high-fat diet-induced disturbances in muscle metabolomic profile and whole-body glucose homeostasis

We provide here a detailed and comprehensive analysis of skeletal muscle metabolomic profiles in response to adiponectin in adiponectin knockout (AdKO) mice after high-fat-diet (HFD) feeding. Hyperinsulinemic-euglycemic clamp studies showed that adiponectin administration corrected HFD-induced defects in post/basal insulin stimulated R(d) and insulin signaling in skeletal muscle. Lipidomic profiling of skeletal muscle from HFD-fed mice indicated elevated triacylglycerol and diacylglycerol species (16:0-18:1, 18:1, and 18:0-18:2) as well as acetyl coA, all of which were mitigated by adiponectin. HFD induced elevated levels of various ceramides, but these were not significantly altered by adiponectin. Adiponectin corrected the altered branched-chain amino acid metabolism caused by HFD and corrected increases across a range of glycerolipids, fatty acids, and various lysolipids. Adiponectin also reversed induction of the pentose phosphate pathway by HFD. Analysis of muscle mitochondrial structure indicated that adiponectin treatment corrected HFD-induced pathological changes. In summary, we show an unbiased comprehensive metabolomic profile of skeletal muscle from AdKO mice subjected to HFD with or without adiponectin and relate these to changes in whole-body glucose handling, insulin signaling, and mitochondrial structure and function. Our data revealed a key signature of relatively normalized muscle metabolism across multiple metabolic pathways with adiponectin supplementation under the HFD condition.

Oxidative stress in diabetes

Oxidative stress and diabetes, both Type 1 and Type 2 as well as their related conditions have been extensively studied. As diabetes, obesity and metabolic syndrome have reached at epidemic levels, there is a huge need and effort to understand the detailed molecular mechanisms of the possible redox imbalance, underlying the cause of pathology and progression of the disease. These studies provide new insights at cellular and subcellular levels to design effective clinical interventions. This chapter is intended to emphasize the latest knowledge and current evidence on the role of oxidative stress in diabetes as well as to discuss some key questions that are currently under discussion.

Carnitine and acylcarnitines: pharmacokinetic, pharmacological and clinical aspects

L-Carnitine (levocarnitine) is a naturally occurring compound found in all mammalian species. The most important biological function of L-carnitine is in the transport of fatty acids into the mitochondria for subsequent β-oxidation, a process which results in the esterification of L-carnitine to form acylcarnitine derivatives. As such, the endogenous carnitine pool is comprised of L-carnitine and various short-, medium- and long-chain acylcarnitines. The physiological importance of L-carnitine and its obligatory role in the mitochondrial metabolism of fatty acids has been clearly established; however, more recently, additional functions of the carnitine system have been described, including the removal of excess acyl groups from the body and the modulation of intracellular coenzyme A (CoA) homeostasis. In light of this, acylcarnitines cannot simply be considered by-products of the enzymatic carnitine transfer system, but provide indirect evidence of altered mitochondrial metabolism. Consequently, examination of the contribution of L-carnitine and acylcarnitines to the endogenous carnitine pool (i.e. carnitine pool composition) is critical in order to adequately characterize metabolic status. The concentrations of L-carnitine and its esters are maintained within relatively narrow limits for normal biological functioning in their pivotal roles in fatty acid oxidation and maintenance of free CoA availability. The homeostasis of carnitine is multifaceted with concentrations achieved and maintained by a combination of oral absorption, de novo biosynthesis, carrier-mediated distribution into tissues and extensive, but saturable, renal tubular reabsorption. Various disorders of carnitine insufficiency have been described but ultimately all result in impaired entry of fatty acids into the mitochondria and consequently disturbed lipid oxidation. Given the sensitivity of acylcarnitine concentrations and the relative carnitine pool composition in reflecting the intramitochondrial acyl-CoA to free CoA ratio (and, hence, any disturbances in mitochondrial metabolism), the relative contribution of L-carnitine and acylcarnitines within the total carnitine pool is therefore considered critical in the identification of mitochondria dysfunction. Although there is considerable research in the literature focused on disorders of carnitine insufficiency, relatively few have examined relative carnitine pool composition in these conditions; consequently, the complexity of these disorders may not be fully understood. Similarly, although important studies have been conducted establishing the pharmacokinetics of exogenous carnitine and short-chain carnitine esters in healthy volunteers, few studies have examined carnitine pharmacokinetics in patient groups. Furthermore, the impact of L-carnitine administration on the kinetics of acylcarnitines has not been established. Given the importance of L-carnitine as well as acylcarnitines in maintaining normal mitochondrial function, this review seeks to examine previous research associated with the homeostasis and pharmacokinetics of L-carnitine and its esters, and highlight potential areas of future research.

Effects of physical training with different intensities of effort on lipid metabolism in rats submitted to the neonatal application of alloxan

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a chronic disease that is characterized by insulin resistance. Its development is directly connected with the inability of insulin to exert its action, not just on carbohydrate metabolism but also on primarily on lipid metabolism. The present study aimed to compare the effects of continuous, intermittent, and strength training on serum and tissue variables on the lipid metabolism of alloxan rats.

METHODS

Wistar rats were divided into eight groups: sedentary alloxan (SA), sedentary control (SC), continuous training alloxan (CA), intermittent training alloxan (IA), strength training alloxan (StA), continuous training control (CC), intermittent training control (IC) and strength training control (StC). Alloxan (250 mg/kg bw) was injected into neonatal rats at 6 days of age. The continuous training protocol consisted of 12 weeks of swimming training for 1 uninterrupted hour/day, five days/week, supporting a load that was 5% bw. The intermittent training protocol consisted of 12 weeks of swimming training with 30 s of activity interrupted by 30 s of rest, for a total of 20 min/day, five days/week, supporting a load that was 15% bw. The strength-training protocol consisted of 12 weeks of training, five days/week with 4 sets of 10 jumps in water with 1 min rest between sets, supporting a load that was a 50% bw.

RESULTS

At 28 days, the alloxan animals exhibited higher insulin resistance as measured by the disappearance of glucose serum (% Kitt/min) during the ITT. At 120 days, the sedentary alloxan animals showed higher FFA values than continuous and intermittent training alloxan. In addition, the alloxan animals that underwent intermittent and strength training showed lower FFA values compared to the corresponding controls. The continuous training protocol was less effective than the strength training protocol for reducing the levels of total cholesterol in the alloxan animals. Serum total lipid values revealed that intermittent training increased serum levels in alloxan animals

CONCLUSION

Thus, it was concluded that physical training at different intensities of effort is of great importance in attenuation and control of changes in the lipid metabolism in alloxan animals.

MitoNEET-driven alterations in adipocyte mitochondrial activity reveal a crucial adaptive process that preserves insulin sensitivity in obesity

We examined mouse models with altered adipocyte expression of mitoNEET, a protein residing in the mitochondrial outer membrane, to probe its impact on mitochondrial function and subsequent cellular responses. We found that overexpression of mitoNEET enhances lipid uptake and storage, leading to an expansion of the mass of adipose tissue. Despite the resulting massive obesity, benign aspects of adipose tissue expansion prevail, and insulin sensitivity is preserved. Mechanistically, we also found that mitoNEET inhibits mitochondrial iron transport into the matrix and, because iron is a rate-limiting component for electron transport, lowers the rate of β-oxidation. This effect is associated with a lower mitochondrial membrane potential and lower levels of reactive oxygen species-induced damage, along with increased production of adiponectin. Conversely, a reduction in mitoNEET expression enhances mitochondrial respiratory capacity through enhanced iron content in the matrix, ultimately corresponding to less weight gain on a high-fat diet. However, this reduction in mitoNEET expression also causes heightened oxidative stress and glucose intolerance. Thus, manipulation of mitochondrial function by varying mitoNEET expression markedly affects the dynamics of cellular and whole-body lipid homeostasis.

Mitochondrial dysfunction in white adipose tissue

Although mitochondria in brown adipose tissue and their role in non-shivering thermogenesis have been widely studied, we have only a limited understanding of the relevance of mitochondria in white adipose tissue (WAT) for cellular homeostasis of the adipocyte and their impact upon systemic energy homeostasis. A better understanding of the regulatory role that white adipocyte mitochondria play in the regulation of whole-body physiology becomes increasingly important. WAT mitochondrial biogenesis can effectively be induced pharmacologically using a number of agents, including PPARγ agonists. Through their ability to influence key biochemical processes central to the adipocyte, such as fatty acid (FA) esterification and lipogenesis, as well as their impact upon the production and release of key adipokines, mitochondria play a crucial role in determining systemic insulin sensitivity.

Skeletal muscle SIRT1 and the genetics of metabolic health: therapeutic activation by pharmaceuticals and exercise

Silent mating type information regulation 2 homolog 1 (SIRT1) is implicated in the control of skeletal muscle mitochondrial content and function through deacetylation of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and participation in the SIRT1/PGC-1α axis. The SIRT1/PGC-1α axis control of skeletal muscle mitochondrial biogenesis is an important therapeutic target for obesity and obesity-related metabolic dysfunction, as skeletal muscle mitochondrial dysfunction is implicated in the pathogenesis of multiple metabolic diseases. This review will establish the importance of the SIRT1/PGC-1α axis in the control of skeletal muscle mitochondrial biogenesis, and explore possible pharmacological and physiological interventions designed to activate SIRT1 and the SIRT1/PGC-1α axis in order to prevent and/or treat obesity and obesity-related metabolic disease. The current evidence supports a role for therapeutic activation of SIRT1 and the SIRT1/PGC-1α axis by both pharmaceuticals and exercise in the treatment and prevention of metabolic disease. Future research should be directed toward the feasibility of pharmaceutical activation of SIRT1 in humans and refining exercise prescriptions for optimal SIRT1 activation.

α-Glucosidase- and α-amylase-inhibitory activities of phlorotannins from Eisenia bicyclis

BACKGROUND

In an effort to develop alternative therapeutic agents, strong inhibitory activity against α-glucosidase and α-amylase was detected in Eisenia bicyclis methanolic extract.

RESULTS

In this study, two phlorotannins were isolated from E. bicyclis and characterised by chromatography and nuclear magnetic resonance. The active substances were identified as fucofuroeckol A (FF) and dioxinodehydroeckol (DD). To the authors' knowledge, this is the first report of the identification of these substances in E. bicyclis. However, to date, no antidiabetic activity of FF and DD has been reported. Both phlorotannins demonstrated significant inhibitory activity against α-glucosidase and α-amylase. FF showed potent antidiabetic activity, with IC(50) values of 131.34 nmol L(-1) against α-glucosidase and 42.91 µmol L(-1) against α-amylase. The corresponding IC(50) values of DD were 93.33 nmol L(-1) and 472.7 µmol L(-1) . Furthermore, kinetic analysis revealed that FF and DD exhibited non-competitive inhibitory activity against α-glucosidase.

CONCLUSION

These results suggest that FF and DD may be candidates for the development of an antidiabetic pharmaceutical agent or food additive.

AMP-activated protein kinase: an emerging drug target to regulate imbalances in lipid and carbohydrate metabolism to treat cardio-metabolic diseases

The adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor of energy metabolism at the cellular as well as whole-body level. It is activated by low energy status that triggers a switch from ATP-consuming anabolic pathways to ATP-producing catabolic pathways. AMPK is involved in a wide range of biological activities that normalizes lipid, glucose, and energy imbalances. These pathways are dysregulated in patients with metabolic syndrome (MetS), which represents a clustering of major cardiovascular risk factors including diabetes, lipid abnormalities, and energy imbalances. Clearly, there is an unmet medical need to find a molecule to treat alarming number of patients with MetS. AMPK, with multifaceted activities in various tissues, has emerged as an attractive drug target to manage lipid and glucose abnormalities and maintain energy homeostasis. A number of AMPK activators have been tested in preclinical models, but many of them have yet to reach to the clinic. This review focuses on the structure-function and role of AMPK in lipid, carbohydrate, and energy metabolism. The mode of action of AMPK activators, mechanism of anti-inflammatory activities, and preclinical and clinical findings as well as future prospects of AMPK as a drug target in treating cardio-metabolic disease are discussed.

Regulation of lipogenesis by cyclin-dependent kinase 8-mediated control of SREBP-1

Altered lipid metabolism underlies several major human diseases, including obesity and type 2 diabetes. However, lipid metabolism pathophysiology remains poorly understood at the molecular level. Insulin is the primary stimulator of hepatic lipogenesis through activation of the SREBP-1c transcription factor. Here we identified cyclin-dependent kinase 8 (CDK8) and its regulatory partner cyclin C (CycC) as negative regulators of the lipogenic pathway in Drosophila, mammalian hepatocytes, and mouse liver. The inhibitory effect of CDK8 and CycC on de novo lipogenesis was mediated through CDK8 phosphorylation of nuclear SREBP-1c at a conserved threonine residue. Phosphorylation by CDK8 enhanced SREBP-1c ubiquitination and protein degradation. Importantly, consistent with the physiologic regulation of lipid biosynthesis, CDK8 and CycC proteins were rapidly downregulated by feeding and insulin, resulting in decreased SREBP-1c phosphorylation. Moreover, overexpression of CycC efficiently suppressed insulin and feeding-induced lipogenic gene expression. Taken together, these results demonstrate that CDK8 and CycC function as evolutionarily conserved components of the insulin signaling pathway in regulating lipid homeostasis.

Overexpression of Akt1 enhances adipogenesis and leads to lipoma formation in zebrafish

Background

Obesity is a complex, multifactorial disorder influenced by the interaction of genetic, epigenetic, and environmental factors. Obesity increases the risk of contracting many chronic diseases or metabolic syndrome. Researchers have established several mammalian models of obesity to study its underlying mechanism. However, a lower vertebrate model for conveniently performing drug screening against obesity remains elusive. The specific aim of this study was to create a zebrafish obesity model by over expressing the insulin signaling hub of the Akt1 gene.

Methodology/Principal Findings

Skin oncogenic transformation screening shows that a stable zebrafish transgenic of Tg(krt4Hsa.myrAkt1)^cy18 displays severely obese phenotypes at the adult stage. In Tg(krt4:Hsa.myrAkt1)^cy18, the expression of exogenous human constitutively active Akt1 (myrAkt1) can activate endogenous downstream targets of mTOR, GSK-3α/β, and 70S6K. During the embryonic to larval transitory phase, the specific over expression of myrAkt1 in skin can promote hypertrophic and hyperplastic growth. From 21 hour post-fertilization (hpf) onwards, myrAkt1 transgene was ectopically expressed in several mesenchymal derived tissues. This may be the result of the integration position effect. Tg(krt4:Hsa.myrAkt1)^cy18 caused a rapid increase of body weight, hyperplastic growth of adipocytes, abnormal accumulation of fat tissues, and blood glucose intolerance at the adult stage. Real-time RT-PCR analysis showed the majority of key genes on regulating adipogenesis, adipocytokine, and inflammation are highly upregulated in Tg(krt4:Hsa.myrAkt1)^cy18. In contrast, the myogenesis- and skeletogenesis-related gene transcripts are significantly downregulated in Tg(krt4:Hsa.myrAkt1)^cy18, suggesting that excess adipocyte differentiation occurs at the expense of other mesenchymal derived tissues.

Conclusion/Significance

Collectively, the findings of this study provide direct evidence that Akt1 signaling plays an important role in balancing normal levels of fat tissue in vivo. The obese zebrafish examined in this study could be a new powerful model to screen novel drugs for the treatment of human obesity.

Brain-derived neurotrophic factor as a regulator of systemic and brain energy metabolism and cardiovascular health

Overweight sedentary individuals are at increased risk for cardiovascular disease, diabetes, and some neurological disorders. Beneficial effects of dietary energy restriction (DER) and exercise on brain structural plasticity and behaviors have been demonstrated in animal models of aging and acute (stroke and trauma) and chronic (Alzheimer's and Parkinson's diseases) neurological disorders. The findings described later, and evolutionary considerations, suggest brain-derived neurotrophic factor (BDNF) plays a critical role in the integration and optimization of behavioral and metabolic responses to environments with limited energy resources and intense competition. In particular, BDNF signaling mediates adaptive responses of the central, autonomic, and peripheral nervous systems from exercise and DER. In the hypothalamus, BDNF inhibits food intake and increases energy expenditure. By promoting synaptic plasticity and neurogenesis in the hippocampus, BDNF mediates exercise- and DER-induced improvements in cognitive function and neuroprotection. DER improves cardiovascular stress adaptation by a mechanism involving enhancement of brainstem cholinergic activity. Collectively, findings reviewed in this paper provide a rationale for targeting BDNF signaling for novel therapeutic interventions in a range of metabolic and neurological disorders.

BNip3 regulates mitochondrial function and lipid metabolism in the liver

BNip3 localizes to the outer mitochondrial membrane, where it functions in mitophagy and mitochondrial dynamics. While the BNip3 protein is constitutively expressed in adult liver from fed mice, we have shown that its expression is superinduced by fasting of mice, consistent with a role in responses to nutrient deprivation. Loss of BNip3 resulted in increased lipid synthesis in the liver that was associated with elevated ATP levels, reduced AMP-regulated kinase (AMPK) activity, and increased expression of lipogenic enzymes. Conversely, there was reduced β-oxidation of fatty acids in BNip3 null liver and also defective glucose output under fasting conditions. These metabolic defects in BNip3 null liver were linked to increased mitochondrial mass and increased hepatocellular respiration in the presence of glucose. However, despite elevated mitochondrial mass, an increased proportion of mitochondria exhibited loss of mitochondrial membrane potential, abnormal structure, and reduced oxygen consumption. Elevated reactive oxygen species, inflammation, and features of steatohepatitis were also observed in the livers of BNip3 null mice. These results identify a role for BNip3 in limiting mitochondrial mass and maintaining mitochondrial integrity in the liver that has consequences for lipid metabolism and disease.

Metabolic syndrome as a risk factor for neurological disorders

The metabolic syndrome is a cluster of common pathologies: abdominal obesity linked to an excess of visceral fat, insulin resistance, dyslipidemia and hypertension. At the molecular level, metabolic syndrome is accompanied not only by dysregulation in the expression of adipokines (cytokines and chemokines), but also by alterations in levels of leptin, a peptide hormone released by white adipose tissue. These changes modulate immune response and inflammation that lead to alterations in the hypothalamic 'bodyweight/appetite/satiety set point,' resulting in the initiation and development of metabolic syndrome. Metabolic syndrome is a risk factor for neurological disorders such as stroke, depression and Alzheimer's disease. The molecular mechanism underlying the mirror relationship between metabolic syndrome and neurological disorders is not fully understood. However, it is becoming increasingly evident that all cellular and biochemical alterations observed in metabolic syndrome like impairment of endothelial cell function, abnormality in essential fatty acid metabolism and alterations in lipid mediators along with abnormal insulin/leptin signaling may represent a pathological bridge between metabolic syndrome and neurological disorders such as stroke, Alzheimer's disease and depression. The purpose of this review is not only to describe the involvement of brain in the pathogenesis of metabolic syndrome, but also to link the pathogenesis of metabolic syndrome with neurochemical changes in stroke, Alzheimer's disease and depression to a wider audience of neuroscientists with the hope that this discussion will initiate more studies on the relationship between metabolic syndrome and neurological disorders.

Toward a unifying hypothesis of metabolic syndrome

Despite a lack of consistent diagnostic criteria, the metabolic syndrome (MetS) is increasingly evident in children and adolescents, portending a tsunami of chronic disease and mortality as this generation ages. The diagnostic criteria for MetS apply absolute cutoffs to continuous variables and fail to take into account aging, pubertal changes, and race/ethnicity. We attempt to define MetS mechanistically to determine its specific etiologies and to identify targets for therapy. Whereas the majority of studies document a relationship of visceral fat to insulin resistance, ectopic liver fat correlates better with dysfunctional insulin dynamics from which the rest of MetS derives. In contrast to the systemic metabolism of glucose, the liver is the primary metabolic clearinghouse for 4 specific foodstuffs that have been associated with the development of MetS: trans-fats, branched-chain amino acids, ethanol, and fructose. These 4 substrates (1) are not insulin regulated and (2) deliver metabolic intermediates to hepatic mitochondria without an appropriate "pop-off" mechanism for excess substrate, enhancing lipogenesis and ectopic adipose storage. Excessive fatty acid derivatives interfere with hepatic insulin signal transduction. Reactive oxygen species accumulate, which cannot be quenched by adjacent peroxisomes; these reactive oxygen species reach the endoplasmic reticulum, leading to a compensatory process termed the "unfolded protein response," driving further insulin resistance and eventually insulin deficiency. No obvious drug target exists in this pathway; thus, the only rational therapeutic approaches remain (1) altering hepatic substrate availability (dietary modification), (2) reducing hepatic substrate flux (high fiber), or (3) increasing mitochondrial efficiency (exercise).

The nuclear orphan receptor Nur77 is a lipotoxicity sensor regulating glucose-induced insulin secretion in pancreatic β-cells

The NR4A orphan nuclear receptors Nur77, Nurr1, and Nor1 exert multiple cellular and metabolic functions. These transcriptional regulators are activated in response to extracellular stresses, including lipotoxic fatty acids (FA) and proinflammatory cytokines. The contribution of NR4As to β-cell pathophysiology is, however, unknown. We have therefore examined the role of NR4As as downstream contributors to FA-induced β-cell dysfunctions. Human pancreatic islets and insulinoma β-cells were used to determine transcriptional programs elicited by NR4A, which were compared to those triggered by palmitate treatment. Functional studies evaluated the consequence of an increased NR4A expression on insulin biosynthesis and secretion and cell viability in insulinoma β-cells. FA and cytokine treatment increased NR4A expression in pancreatic β-cells, with Nur77 being most highly inducible in murine β-cells. Nur77, Nurr1, or Nor1 modulated common and distinct clusters of genes involved notably in cation homeostasis and insulin gene transcription. By altering zinc homeostasis, insulin gene transcription, and secretion, Nur77 was found to be a major transcriptional mediator of part of FA-induced β-cell dysfunctions. The repressive role of Nur77 in insulin gene regulation was tracked down to protein-protein interaction with FoxO1, a pivotal integrator of the insulin gene regulatory network. The present study identifies a member of the NR4A nuclear receptor subclass, Nur77/NR4A1, as a modulator of pancreatic β-cell biology. Together with its previously documented role in liver and muscle, its role in β-cells establishes Nur77 as an important integrator of glucose metabolism.

Disruption of the chemokine-like receptor-1 (CMKLR1) gene is associated with reduced adiposity and glucose intolerance

Adipose tissue secretes a variety of bioactive signaling molecules, termed adipokines, which regulate numerous biological functions including appetite, energy balance, glucose homeostasis, and inflammation. Chemerin is a novel adipokine that regulates adipocyte differentiation and metabolism by binding to and activating the G protein-coupled receptor, chemokine like receptor-1 (CMKLR1). In the present study, we investigated the impact of CMKLR1 deficiency on adipose development, glucose homeostasis, and inflammation in vivo. Herein we report that regardless of diet (low or high fat), CMKLR1(-/-) mice had lower food consumption, total body mass, and percent body fat compared with wild-type controls. CMKLR1(-/-) mice also exhibited decreased hepatic and white adipose tissue TNFα and IL-6 mRNA levels coincident with decreased hepatic dendritic cell infiltration, decreased adipose CD3+ T cells, and increased adipose natural killer cells. CMKLR1(-/-) mice were glucose intolerant compared with wild-type mice, and this was associated with decreased glucose stimulated insulin secretion as well as decreased skeletal muscle and white adipose tissue glucose uptake. Collectively these data provide compelling evidence that CMKLR1 influences adipose tissue development, inflammation, and glucose homeostasis and may contribute to the metabolic derangement characteristic of obesity and obesity-related diseases.

PGC-1α and exercise in the control of body weight

The increasing prevalence of obesity and its comorbidities represents a major threat to human health globally. Pharmacological treatments exist to achieve weight loss, but the subsequent weight maintenance is prone to fail in the long run. Accordingly, efficient new strategies to persistently control body weight need to be elaborated. Exercise and dietary interventions constitute classical approaches to reduce and maintain body weight, yet people suffering from metabolic diseases are often unwilling or unable to move adequately. The administration of drugs that partially mimic exercise adaptation might circumvent this problem by easing and supporting physical activity. The thermogenic peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) largely mediates the adaptive response of skeletal muscle to endurance exercise and is a potential target for such interventions. Here, we review the role of PGC-1α in mediating exercise adaptation, coordinating metabolic circuits and enhancing thermogenic capacity in skeletal muscle. We suggest a combination of elevated muscle PGC-1α and exercise as a modified approach for the efficient long-term control of body weight and the treatment of the metabolic syndrome.

Regulation of SREBP-Mediated Gene Expression

The sterol regulatory element-binding proteins (SREBPs) play an important role in regulating lipid homeostasis. Translated as inactive precursors that are localized in the endoplasmic reticulum (ER) membrane, SREBPs are activated through a proteolytic process in response to intracellular demands for lipids. The cleaved amino-terminal fragments of SREBPs then translocate into the nucleus as homodimers and stimulate the transcription of target genes by binding to the sterol response elements (SREs) in their promoters. Numerous studies using cell culture or genetically modified mouse models have demonstrated that the major target genes of SREBPs include rate-limiting enzymes in the pathways of fatty acid and cholesterol biosynthesis as well as the low-density lipoprotein (LDL) receptor. The proteolytic maturation of SREBPs has been well studied in the past. However, recent studies have also improved our understanding on the regulation of nuclear SREBPs. In the nucleus, SREBPs interact with specific transcriptional cofactors, such as CBP/p300 and the Mediator complex, resulting in stimulation or inhibition of their transcriptional activities. In addition, nuclear SREBP protein stability is dynamically regulated by phosphorylation and acetylation. Such protein-protein interactions and post-translational modifications elegantly link the extracellular signals, such as insulin, or intracellular signals, such as oxidative stress, to lipid biosynthesis by modulating the transcriptional activity of SREBPs. Under normal physiological states, lipid homeostasis is strictly maintained. However, the SREBP pathways are often dysregulated in pathophysiological conditions, such as obesity, type 2 diabetes, and fatty liver diseases. Thus, the novel regulatory mechanisms of SREBPs may provide new opportunities for fighting these metabolic diseases.

Aerobic exercise training conserves insulin sensitivity for 1 yr following weight loss in overweight women

The objectives of this study were to 1) identify the independent effects of exercise (aerobic or resistance training) and weight loss on whole body insulin sensitivity and 2) determine if aerobic or resistance training would be more successful for maintaining improved whole body insulin sensitivity 1 yr following weight loss. Subjects were 97 healthy, premenopausal women, body mass index (BMI) 27-30 kg/m(2). Following randomized assignment to one of three groups, diet only, diet + aerobic, or diet + resistance training until a BMI <25 kg/m(2) was achieved, body composition, fat distribution, and whole body insulin sensitivity were determined at baseline, in the weight reduced state, and at 1-yr follow up. The whole body insulin sensitivity index (S(I)) was determined using a frequently sampled intravenous glucose tolerance test. Results of repeated-measures ANOVA indicated a significant improvement in S(I) following weight loss. However, there were no group or group×time interactions. At 1-yr follow up, there were no significant time or group interactions for S(I;) however, there was a significant group×time interaction for S(I). Post hoc analysis revealed that women in the aerobic training group showed a significant increased S(I) from weight reduced to 1-yr follow up (P < 0.05), which was independent of intra-abdominal adipose tissue and %fat. No significant differences in S(I) from weight reduced to 1-yr follow up were observed for diet only or diet + resistance groups. Additionally, multiple linear regression analysis revealed that change in whole body insulin sensitivity from baseline to 1-yr follow up was independently associated with the change in Vo(2max) from baseline to 1-yr follow up (P < 0.05). These results suggest that long-term aerobic exercise training may conserve improvements in S(I) following weight loss and that maintaining cardiovascular fitness following weight loss may be important for maintaining improvements in S(I).

The arrestin domain-containing 3 protein regulates body mass and energy expenditure

A human genome-wide linkage scan for obesity identified a linkage peak on chromosome 5q13-15. Positional cloning revealed an association of a rare haplotype to high body-mass index (BMI) in males but not females. The risk locus contains a single gene, "arrestin domain-containing 3" (ARRDC3), an uncharacterized α-arrestin. Inactivating Arrdc3 in mice led to a striking resistance to obesity, with greater impact on male mice. Mice with decreased ARRDC3 levels were protected from obesity due to increased energy expenditure through increased activity levels and increased thermogenesis of both brown and white adipose tissues. ARRDC3 interacted directly with β-adrenergic receptors, and loss of ARRDC3 increased the response to β-adrenergic stimulation in isolated adipose tissue. These results demonstrate that ARRDC3 is a gender-sensitive regulator of obesity and energy expenditure and reveal a surprising diversity for arrestin family protein functions.

Sustained activation of PPARα by endogenous ligands increases hepatic fatty acid oxidation and prevents obesity in ob/ob mice

Obesity, a major health concern, results from an imbalance between energy intake and expenditure. Leptin-deficient ob/ob mice are paradigmatic of obesity, resulting from excess energy intake and storage. Mice lacking acyl-CoA oxidase 1 (Acox1), the first enzyme of the peroxisomal fatty acid β-oxidation system, are characterized by increased energy expenditure and a lean body phenotype caused by sustained activation of peroxisome proliferator-activated receptor α (PPARα) by endogenous ligands in liver that remain unmetabolized in the absence of Acox1. We generated ob/ob mice deficient in Acox1 (Acox1(-/-)) to determine how the activation of PPARα by endogenous ligands might affect the obesity of ob/ob mice. In contrast to Acox1(-/-) (14.3±1.2 g at 6 mo) and the Acox1-deficient (ob/ob) double-mutant mice (23.8±4.6 g at 6 mo), the ob/ob mice are severely obese (54.3±3.2 g at 6 mo) and had significantly more (P<0.01) epididymal fat content. The resistance of Acox1(-/-)/ob/ob mice to obesity is due to increased PPARα-mediated up-regulation of genes involved in fatty acid oxidation in liver. Activation of PPARα in Acox1-deficient ob/ob mice also reduces serum glucose and insulin (P<0.05) and improves glucose tolerance and insulin sensitivity. Further, PPARα activation reduces hepatic steatosis and increases hepatocellular regenerative response in Acox1(-/-)/ob/ob mice at a more accelerated pace than in mice lacking only Acox1. However, Acox1(-/-)/ob/ob mice manifest hepatic endoplasmic reticulum (ER) stress and also develop hepatocellular carcinomas (8 of 8 mice) similar to those observed in Acox1(-/-) mice (10 of 10 mice), but unlike in ob/ob (0 of 14 mice) and OB/OB (0 of 6 mice) mice, suggesting that superimposed ER stress and PPARα activation contribute to carcinogenesis in a fatty liver. Finally, absence of Acox1 in ob/ob mice can impart resistance to high-fat diet (60% fat)-induced obesity, and their liver had significantly (P<0.01) more cell proliferation. These studies with Acox1(-/-)/ob/ob mice indicate that sustained activation of lipid-sensing nuclear receptor PPARα attenuates obesity and restores glucose homeostasis by ameliorating insulin resistance but increases the risk for liver cancer development, in part related to excess energy combustion.

Berberine protects against high fat diet-induced dysfunction in muscle mitochondria by inducing SIRT1-dependent mitochondrial biogenesis

Berberine (BBR) has recently been shown to improve insulin sensitivity in rodent models of insulin resistance. Although this effect was explained partly through an observed activation of AMP-activated protein kinase (AMPK), the upstream and downstream mediators of this phenotype were not explored. Here, we show that BBR supplementation reverts mitochondrial dysfunction induced by High Fat Diet (HFD) and hyperglycemia in skeletal muscle, in part due to an increase in mitochondrial biogenesis. Furthermore, we observe that the prevention of mitochondrial dysfunction by BBR, the increase in mitochondrial biogenesis, as well as BBR-induced AMPK activation, are blocked in cells in which SIRT1 has been knocked-down. Taken together, these data reveal an important role for SIRT1 and mitochondrial biogenesis in the preventive effects of BBR on diet-induced insulin resistance.

Deficiency of MGAT2 increases energy expenditure without high-fat feeding and protects genetically obese mice from excessive weight gain

Acyl CoA:monoacylglycerol acyltransferase 2 (MGAT2) is thought to be crucial for dietary fat absorption. Indeed, mice lacking the enzyme (Mogat2(-/-)) are resistant to obesity and other metabolic disorders induced by high-fat feeding. However, these mice absorb normal quantities of fat. To explore whether a high level of dietary fat is an essential part of the underlying mechanism(s), we examined metabolic responses of Mogat2(-/-) mice to diets containing varying levels of fat. Mogat2(-/-) mice exhibited 10-15% increases in energy expenditure compared with wild-type littermates; although high levels of dietary fat exacerbated the effect, this phenotype was expressed even on a fat-free diet. When deprived of food, Mogat2(-/-) mice expended energy and lost weight like wild-type controls. To determine whether MGAT2 deficiency protects against obesity in the absence of high-fat feeding, we crossed Mogat2(-/-) mice with genetically obese Agouti mice. MGAT2 deficiency increased energy expenditure and prevented these mice from gaining excess weight. Our results suggest that MGAT2 modulates energy expenditure through multiple mechanisms, including one independent of dietary fat; these findings also raise the prospect of inhibiting MGAT2 as a strategy for combating obesity and related metabolic disorders resulting from excessive calorie intake.

Association between life-span extension by caloric restriction and thiol redox state in two different strains of mice

The hypothesis that the life-extending effect of caloric restriction (CR) is associated with an attenuation of the age-related pro-oxidant shift in the thiol redox state was tested employing a novel experimental design. Amounts of GSH, GSSG, and protein mixed disulfides (Pr-SSG) in the skeletal muscle and liver were compared between two strains of mice that have similar life spans when fed ad libitum (AL), but different life spans under the standard CR regimen. The life span of one strain, C57BL/6, is extended under CR, whereas it remains unaffected in the other strain, DBA/2. Mice were fed AL or 40% less food starting at 4 months and compared at 6 and 24 months of age. The amounts of GSSG and Pr-SSG increased and the GSH:GSSG ratios decreased with age in both strains of AL-fed mice. CR prevented these age-related changes in the C57BL/6, whose life span is extended by CR, but not in the DBA/2 mice, in which it remains unaffected. CR enhanced the activity of glutamate-cysteine ligase in the C57BL/6, but not in the DBA/2 mice. The results suggest that longevity extension by CR may be associated with the attenuation of age-related pro-oxidizing shifts in the thiol redox state.

Human obesity is characterized by defective fat storage and enhanced muscle fatty acid oxidation, and trimetazidine gradually counteracts these abnormalities

An impaired ability to store fatty acids (FA) in subcutaneous adipose tissue (SAT) may be implicated in the pathogenesis of obesity-related diseases via overexposure of lean tissues and production of free radicals from FA oxidation (FAO). We studied regional FA metabolism in skeletal muscle and adipose tissue in humans and investigated the long-term effects of the FAO inhibitor trimetazidine on glucose and FA metabolism. Positron emission tomography (PET) and [(11)C]palmitate were used to compare FA metabolism in SAT and skeletal muscle between eight obese and eight nonobese subjects (BMI ≥/< 30 kg/m(2)). A subgroup of nine subjects underwent a 1-mo trimetazidine administration. PET with [(11)C]palmitate and [(18)F]fluorodeoxyglucose, indirect calorimetry, and MRI before and after this period were performed to characterize glucose and FA metabolism, fat masses, skeletal muscle triglyceride, and creatine contents. Obesity was characterized by a 100% elevation in FAO and a defect in the FA esterification rate constant (P < 0.05) in skeletal muscle. FA esterification was reduced by ~70% in SAT (P < 0.001) in obese vs. control subjects. The degrees of obesity and insulin resistance were both negatively associated with esterification-related parameters and positively with FAO (P < 0.05). Trimetazidine increased skeletal muscle FA esterification (P < 0.01) and mildly upregulated glucose phosphorylation (P = 0.066). Our data suggest that human obesity is characterized by a defect in tissue FA storage capability, which is accompanied by a (potentially compensatory) elevation in skeletal muscle FAO; trimetazidine diverted FA from oxidative to nonoxidative pathways and provoked an initial activation of glucose metabolism in skeletal muscle.