Regulation of fatty acid uptake and metabolism in L6 skeletal muscle cells by resistin

An insight into the mechanistic role of (-)-Ampelopsin F from Vatica chinensis L. in inducing insulin secretion in pancreatic beta cells

Resveratrol oligomers, ranging from dimers to octamers, are formed through regioselective synthesis involving the phenoxy radical coupling of resveratrol building blocks, exhibiting remarkable therapeutic potential, including antidiabetic properties. In this study, we elucidate the mechanistic insights into the insulin secretion potential of a resveratrol dimer, (-)-Ampelopsin F (AmF), isolated from the acetone extract of Vatica chinensis L. stem bark in Pancreatic Beta-TC-6 cell lines. The AmF (50 µM) treated cells exhibited a 3.5-fold increase in insulin secretion potential as compared to unstimulated cells, which was achieved through the enhancement of mitochondrial membrane hyperpolarization, elevation of intracellular calcium concentration, and upregulation of GLUT2 and glucokinase expression in pancreatic Beta-TC-6 cell lines. Furthermore, AmF effectively inhibited the activity of DPP4, showcasing a 2.5-fold decrease compared to the control and a significant 6.5-fold reduction compared to the positive control. These findings emphasize AmF as a potential lead for the management of diabetes mellitus and point to its possible application in the next therapeutic initiatives.

Clinical impacts of sarcopenic obesity on chronic obstructive pulmonary disease: a cross-sectional study

BACKGROUND

Sarcopenia and obesity are two abnormal body composition phenotypes, and sarcopenic obesity (SO) is characterized by both low skeletal muscle mass (sarcopenia) and high adiposity (obesity). SO negatively influences the clinical status of patients with chronic obstructive pulmonary disease (COPD). However, the studies exploring the prevalence and clinical effects of SO in COPD patients are limited. Our study aimed to elucidate the prevalence and impact of SO on COPD patients.

METHODS

In this cross-sectional study, the pulmonary function, St. George's Respiratory Questionnaire, exercise tolerance, body composition, and serum levels of resistin and TNF-α were assessed in 198 COPD patients. The clinical value of serum resistin and TNF-α for predicting SO in patients with COPD was evaluated.

RESULTS

In the 198 patients with COPD, the prevalence rates of sarcopenia, obesity, and SO in COPD patients were 27.27%, 29.8%, and 9.6%, respectively. Patients with SO experienced more severe symptoms of dyspnea and worse health related quality of life. The expression of resistin increased in patients with SO compared to other patients. The AUC value of serum resistin level for predicting SO was 0.870 (95% CI: 0.799-0.940). BMI (OR: 1.474, 95% CI: 1.124-1.934) and resistin (OR: 1.001, 95% CI: 1.000-1.002) levels were independent risk factors of SO in patients with COPD in Multivariate analysis.

CONCLUSION

The prevalence rates of SO in COPD patients was 9.6%. COPD accompanied by SO is significantly associated with worse pulmonary function and poor physical performance. Serum resistin may be a potential adjunct for predicting SO in COPD patients.

Role of adipokines in sarcopenia

ABSTRACT

Sarcopenia is an age-related disease that mainly involves decreases in muscle mass, muscle strength and muscle function. At the same time, the body fat content increases with aging, especially the visceral fat content. Adipose tissue is an endocrine organ that secretes biologically active factors called adipokines, which act on local and distant tissues. Studies have revealed that some adipokines exert regulatory effects on muscle, such as higher serum leptin levels causing a decrease in muscle function and adiponectin inhibits the transcriptional activity of Forkhead box O3 (FoxO3) by activating peroxisome proliferators-activated receptor-γ coactivator -1α (PGC-1α) and sensitizing cells to insulin, thereby repressing atrophy-related genes (atrogin-1 and muscle RING finger 1 [MuRF1]) to prevent the loss of muscle mass. Here, we describe the effects on muscle of adipokines produced by adipose tissue, such as leptin, adiponectin, resistin, mucin and lipocalin-2, and discuss the importance of these adipokines for understanding the development of sarcopenia.

Interplay of skeletal muscle and adipose tissue: sarcopenic obesity

Sarcopenic obesity is becoming a global health concern, owing to the rising older population, causing cardiometabolic morbidity and mortality. Loss of muscle exceeding normal age-related changes has been revealed to be associated with obesity, aggravating each other through complex interactions. Physiological regeneration and proliferation of muscle tissue are achieved through harmonious processes of regulated inflammation, autophagy, muscle satellite cell proliferation, and signaling molecule function. Adipokines and myokines are signaling molecules from adipose tissue and muscle, respectively, that exert autocrine, paracrine, and endocrine effects on fat and muscle tissues. These signaling molecules interact with each other to regulate metabolic homeostasis. However, excessive adiposity creates pro-inflammatory conditions, leading to metabolic disorders and the disorganization of systemic homeostasis. Therefore, obesity impedes muscle tissue regeneration and induces the loss of muscle mass and function. Numerous studies have attempted to demonstrate the pathophysiological interaction between sarcopenia and obesity, but the interwoven matrix of the relationship between myokines and adipokines has made it difficult for researchers to understand them. This review briefly describes updated information about the crosstalk between muscle and adipose tissue.

The Mef2c/AdipoR1 axis is responsible for myogenic differentiation and is regulated by resistin in skeletal muscles

Previous studies have shown that accumulated lipid and insulin resistance emerges in skeletal muscle after the onset of obesity and diabetes. We have previously shown that resistin significantly increases lipid contents in C2C12 cells. However, studies evaluating the effects of resistin on skeletal muscle cells and tissues are limited; despite that, an understanding of resistin action and function on lipid alteration in skeletal muscle tissues is critical for understanding obesity-related diseases. In this study, we document that resistin increases lipid deposition both in vitro and in vivo. Further, resistin promotes fiber type transformation, decreases enzyme activities, inhibits myogenic differentiation, and decreases muscle grip and excise endurance. In addition, adiponectin signaling is activated during myocyte differentiation, but it is inhibited at elevated resistin concentrations. Mechanistic investigation revealed that mef2c is responsible for adiponectin signaling pathway inhibition by inhibiting adipoR1 expression at the transcriptional level. In conclusion, this is the first study to document that resistin increases ectopic lipid deposition in skeletal muscles via a mef2c-adipoR1 signaling pathway, which reveals for the first time the presence of crosstalk between resistin and adiponectin in skeletal muscles.

Adipose tissue adipokines and lipokines: Functions and regulatory mechanism in skeletal muscle development and homeostasis

Skeletal muscle plays important roles in normal biological activities and whole-body energy homeostasis in humans. The growth and development of skeletal muscle also directly influence meat production and meat quality in animal production. Therefore, regulating the development and homeostasis of skeletal muscle is crucial for human health and animal production. Adipose tissue, which includes white adipose tissue (WAT) and brown adipose tissue (BAT), not only functions as an energy reserve but also has attracted substantial attention because of its role as an endocrine organ. The novel signalling molecules known as "adipokines" and "lipokines" that are secreted by adipose tissue were identified through the secretomic technique, which broadened our understanding of the previously unknown crosstalk between adipose tissue and skeletal muscle. In this review, we summarize and discuss the secretory role of adipose tissues, both WAT and BAT, as well as the regulatory roles of various adipokines and lipokines in skeletal muscle development and homeostasis. We suggest that adipokines and lipokines have potential as drug candidates for the treatment of skeletal muscle dysfunction and related metabolic diseases and as promising nutrients for improving animal production.

The Effect of Exercise on Serum Resistin and Leptin Values in Rats Fed with a High Fat Diet

Aim: This study was performed to investigate the effect of exercise on serum resistin and leptin values in rats fed with a high-fat diet. Material and Method: 24 Wistar albino male rats were used in the study. They were randomly divided into 4 groups, with 6 rats in each group. The groups were determined as the control group (C), exercise group (E), high-fat diet (HFD) group, and high-fat diet + exercise (HFDE) Group. Results: When the findings obtained in this study were evaluated statistically, it was determined that the resistin values were similar in the C, E and HFDE groups, and higher in the HFD group compared to the other groups. It was observed that resistin value increased with high-fat diet and decreased with exercise. When evaluated in terms of leptin levels, the C and E groups showed similarity, while the HFD and HFDE groups showed similarity with each other. Although exercise decreased the leptin level, which was highly increased with a high-fat diet, it was not statistically significant. Conclusion: It has been determined that feeding with a high-fat diet causes an increase in serum resistin and leptin levels, and exercise provides a significant decrease in resistin values, but is not effective in leptin levels.

Targeting adipokines in polycystic ovary syndrome and related metabolic disorders: from experimental insights to clinical studies

Polycystic ovary syndrome (PCOS) affects approximately 15% of women of reproductive age worldwide. It is the most prevalent endocrine disorder with marked risks for female infertility, type 2 diabetes mellitus (T2DM), psychiatric disorders and gynecological cancers. Although the pathophysiology of PCOS remains largely elusive, growing evidence suggests a close link with obesity and its related metabolic disorders. As a highly active endocrine cell population, hypertrophic adipocytes in obesity have disturbed production of a vast array of adipokines, biologically active peptides that exert pleiotropic effects on homeostatic regulation of glucose and lipid metabolism. In parallel with their crucial roles in the pathophysiology of obesity-induced metabolic diseases, adipokines have recently been identified as promising targets for novel therapeutic strategies for multiple diseases. Current treatments for PCOS are suboptimal with insufficient alleviation of all symptoms. Novel findings in adipokine-targeted agents may provide important insight into the development of new drugs for PCOS. This Review presents an overview of the current understanding of mechanisms that link PCOS to obesity and highlights emerging evidence of adipose-ovary crosstalk as a pivotal mediator of PCOS pathogenesis. We summarize recent findings of preclinical and clinical studies that reveal the therapeutic potential of adipokine-targeted novel approaches to PCOS and its related metabolic disorders. We also discuss the critical gaps in knowledge that need to be addressed to guide the development of adipokine-based novel therapies for PCOS.

The Relation between Resistin (-420C/G) Single Nucleotide Variant, Resistin Serum Concentration, Carbohydrate, and Lipid Parameters and Fried Food Taste Preference in Patients with Hypertriglyceridemia

BACKGROUND

Resistin is a proinflammatory adipokine involved in metabolic disorders. Its interplay with hypertriglyceridemia remains to be elucidated. We aimed to evaluate the relationship between resistin (-420C/G) single nucleotide variant (SNV) and metabolic parameters and preference for fried food consumption in hypertriglyceridemia.

METHODS

The study enrolled 179 hypertriglyceridemic (HTG) and 182 normotriglyceridemic (NTG) patients. Anthropometric measurements, serum resistin, insulin and fasting glucose concentration, a homeostatic model assessment-insulin resistance (HOMA-IR), triglycerides (TG), cholesterol concentration, and fried food taste preference (FP) or other cooking methods preference (OP) were assessed in the study. Genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

HTG and NTG groups did not differ significantly in serum resistin concentration; HTG individuals demonstrated significantly increased serum levels of TG, glucose, total cholesterol (TCH), and HOMA-IR and decreased HDL cholesterol. Resistin, insulin, glucose, HOMA-IR, and cholesterol fractions were similar among particular resistin genotypes in HTG, NTG, FP, or OP groups. TG and TCH concentrations differ significantly among CG and CC genotypes in the FP group. Considering the FP group, GG and CG genotypes appeared more frequently in hyperlipidemic (OR 2.6 95% CI; 1.16-5.82; p = 0.01; significant after Bonferroni correction) than in NTG patients. Multivariable logistic regression models showed that the G allele and CG genotype of SNV (-420C/G), adjusted for selected confounders such as fried food preference, increased the odds of hypertriglyceridemia about twofold.

CONCLUSIONS

Allele G and CG genotype of resistin SNV (-420C/G) are linked with the preference for fried food taste in hypertriglyceridemic patients.

The Exocyst Is Required for CD36 Fatty Acid Translocase Trafficking and Free Fatty Acid Uptake in Skeletal Muscle Cells

In obesity, chronic membrane-localization of CD36 free fatty acid (FFA) translocase, but not other FFA transporters, enhances FFA uptake and intracellular lipid accumulation. This ectopic lipid accumulation promotes insulin resistance by inhibiting insulin-induced GLUT4 glucose transporter trafficking and glucose uptake. GLUT4 and CD36 cell surface delivery is triggered by insulin- and contraction-induced signaling, which share conserved downstream effectors. While we have gathered detailed knowledge on GLUT4 trafficking, the mechanisms regulating CD36 membrane delivery and subsequent FFA uptake in skeletal muscle are not fully understood. The exocyst trafficking complex facilitates the docking of membrane-bound vesicles, a process underlying the controlled surface delivery of fuel transporters. The exocyst regulates insulin-induced glucose uptake via GLUT4 membrane trafficking in adipocytes and skeletal muscle cells and plays a role in lipid uptake in adipocytes. Based on the high degree of conservation of the GLUT4 and CD36 trafficking mechanisms in adipose and skeletal muscle tissue, we hypothesized that the exocyst also contributes to lipid uptake in skeletal muscle and acts through the targeted plasma membrane delivery of CD36 in response to insulin and contraction. Here, we show that the exocyst complex is necessary for insulin- and contraction-induced CD36 membrane trafficking and FFA uptake in muscle cells.

The Molecular Effects of BDNF Synthesis on Skeletal Muscle: A Mini-Review

The brain-derived neurotrophic factor (BDNF) is a member of the nerve growth factor family which is generated mainly by the brain. Its main role involve synaptic modulation, neurogenesis, neuron survival, immune regulation, myocardial contraction, and angiogenesis in the brain. Together with the encephalon, some peripheral tissues synthesize BDNF like skeletal muscle. On this tissue, this neurotrophin participates on cellular mechanisms related to muscle function maintenance and plasticity as reported on recent scientific works. Moreover, during exercise stimuli the BDNF contributes directly to strengthening neuromuscular junctions, muscle regeneration, insulin-regulated glucose uptake and β-oxidation processes in muscle tissue. Given its vital relevance on many physiological mechanisms, the current mini-review focuses on discussing up-to-date knowledge about BDNF production in skeletal muscle and how this neurotrophin impacts skeletal muscle biology.

The water extract of Radix scutellariae, its total flavonoids and baicalin inhibited CYP7A1 expression, improved bile acid, and glycolipid metabolism in T2DM mice

ETHNOPHARMACOLOGICAL RELEVANCE

Radix scutellariae (the root of Scutellaria baicalensis Georgi), is a traditional Chinese medicine (TCM) used to treat type 2 diabetes mellitus (T2DM). Abundant flavonoids are the antidiabetic components of Radix scutellariae, of which baicalin (Baicalein 7-O-glucuronide, BG) is the major bioactive component. Our previous studies found that the water extract of Radix scutellariae (WESB) could exert hypoglycemic and hypolipidemic efficacies by adjusting the ileum FXR-medicated interaction between gut microbiota and bile acid (BA) metabolism. However, it remains unclear whether WESB and its biologically active ingredients exert an antidiabetic effect through bile acid signaling mediated by FXR-CYP7A1.

AIMS OF THE STUDY

To explore the mechanism of WESB and its total flavonoids (TF) further and BG on BA signals and glycolipid metabolism in T2DM mice.

MATERIALS AND METHODS

The antidiabetic effects of WESB, TF and BG were evaluated by indexing the body weight, fasting blood glucose (FBG) and oral glucose tolerance test (OGTT) in HFD/STZ-induced (high-fat diet and streptozocin) diabetic mice, and comparing them with the positive control (metformin). The lipids in the mouse liver and the total bile acids (TBA) in the mouse liver and bile were detected by commercial kits. The concentration of BAs in the mouse feces was determined by liquid chromatography-tandem mass spectrometry. The protein expression levels of cholesterol 7α-hydroxylase (CYP7A1), farnesol X receptor (FXR), etc., in the liver and/or ileum, play a key role in the BAs metabolism of T2DM mice were evaluated by immunoblot analysis.

RESULTS

The hyperglycemia and impaired glucose tolerance of T2DM mice were improved after WESB, TF and BG treatment. Especially after BG administration, the levels of low-density lipoprotein-cholesterol (LDL-c) and total glyceride (TG) in the T2DM mouse liver were significantly decreased (p < 0.05). While the level of high-density lipoprotein cholesterol (HDL-c) was significant increased (p < 0.001). Meanwhile, the levels of TBA in both the liver and bile of T2DM mice were significantly decreased by BG (p < 0.05). Moreover, the high expression of CYP7A1 in the liver of T2DM mice was significantly inhibited by WESB, TF and BG (p < 0.05), and the high expression of FXR in the ileum of T2DM mice was significantly inhibited by TF (p < 0.05).

CONCLUSION

These results indicated that the hypoglycemic effects of WESB, TF and BG might be exerted by inhibiting the expression of CYP7A1 in T2DM mice, and TF inhibited expression of intestinal FXR by inducing changes in fecal BA profile. BG significantly improved hepatic lipid metabolism. Moreover, BG reduced lipid accumulation in the liver and bile by inhibiting the expression of CYP7A1 in T2DM mice. These findings provide useful explanations for the antidiabetic mechanism of Radix scutellariae.

Resistin: A journey from metabolism to cancer

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Resistin levels have been associated with several pathological disorders such as metabolic disorders, cancers etc.

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Resistin exists in three isoforms namely RELM-α, β and γ.

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High resistin level activates inflammatory pathways, promotes metabolic disorders and is associated with carcinogenesis.

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Increase in the resistin level impairs the therapeutic response by inducing stemness or resistance, in cancer cells.

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Conventional drugs which alter resistin level could have therapeutic implications in several pathological disorders.

Resistin, a small secretory molecule, has been implicated to play an important role in the development of insulin resistance under obese condition. For the past few decades, it has been linked to various cellular and metabolic functions. It has been associated with diseases like metabolic disorders, cardiovascular diseases and cancers. Numerous clinical studies have indicated an increased serum resistin level in pathological disorders which have been reported to increase mortality rate in comparison to low resistin expressing subjects. Various molecular studies suggest resistin plays a pivotal role in proliferation, metastasis, angiogenesis, inflammation as well as in regulating metabolism in cancer cells. Therefore, understanding the role of resistin and elucidating its’ associated molecular mechanism will give a better insight into the management of these disorders. In this article, we summarize the diverse roles of resistin in pathological disorders based on the available literature, clinicopathological data, and a compiled study from various databases. The article mainly provides comprehensive information of its role as a target in different treatment modalities in pre as well as post-clinical studies.

Recent advances and future avenues in understanding the role of adipose tissue cross talk in mediating skeletal muscle mass and function with ageing

Sarcopenia, broadly defined as the age-related decline in skeletal muscle mass, quality, and function, is associated with chronic low-grade inflammation and an increased likelihood of adverse health outcomes. The regulation of skeletal muscle mass with ageing is complex and necessitates a delicate balance between muscle protein synthesis and degradation. The secretion and transfer of cytokines, long non-coding RNAs (lncRNAs) and microRNAs (miRNAs), both discretely and within extracellular vesicles, have emerged as important communication channels between tissues. Some of these factors have been implicated in regulating skeletal muscle mass, function, and pathologies and may be perturbed by excessive adiposity. Indeed, adipose tissue participates in a broad spectrum of inter-organ communication and obesity promotes the accumulation of macrophages, cellular senescence, and the production and secretion of pro-inflammatory factors. Pertinently, age-related sarcopenia has been reported to be more prevalent in obesity; however, such effects are confounded by comorbidities and physical activity level. In this review, we provide evidence that adiposity may exacerbate age-related sarcopenia and outline some emerging concepts of adipose-skeletal muscle communication including the secretion and processing of novel myokines and adipokines and the role of extracellular vesicles in mediating inter-tissue cross talk via lncRNAs and miRNAs in the context of sarcopenia, ageing, and obesity. Further research using advances in proteomics, transcriptomics, and techniques to investigate extracellular vesicles, with an emphasis on translational, longitudinal human studies, is required to better understand the physiological significance of these factors, the impact of obesity upon them, and their potential as therapeutic targets in combating muscle wasting.

Relationships between placental adiponectin, leptin, visfatin and resistin and birthweight in cattle

Adipokines can affect intrauterine development while calf birthweight (CBW) is a breeding standard of calves, which reflects the status of fetal intrauterine development. To explore the correlation between placental adipokines and CBW, 54 healthy Chinese Holstein cows were used in the present study. The cows were grouped according to the CBW of their calves. Placentas were collected immediately after delivery and enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction were used to detect the placental expression levels of adiponectin, leptin, visfatin and resistin. Our results show that the mRNA transcription and blood placental content of adiponectin, leptin, visfatin and resistin increased with increasing CBW. The analysis showed that the mRNA transcription levels of placental adiponectin, leptin and resistin were positively correlated with CBW. The mRNA and protein expression levels of adiponectin, leptin and visfatin between the three groups were significantly correlated. Placental resistin mRNA levels correlated positively with adiponectin mRNA, but not leptin or visfatin. The protein expression levels of resistin were significantly positively correlated with those of adiponectin, leptin and visfatin. These results suggest that placental adipokines play important roles in regulating calf intrauterine growth.

Metabolic cross-talk between skeletal muscle and adipose tissue in high-intensity interval training vs. moderate-intensity continuous training by regulation of PGC-1α

PURPOSE

An imbalance in the production of adipokines and myokines impairs the energy expenditure, increases adipocyte and develops metabolic pathologies. Physical exercise is able to regulate the secretion of myokines and adipokines. The present study considers the metabolic cross talk between skeletal muscle and adipose tissue in high-intensity interval training vs. moderate-intensity continuous training by regulation of PGC-1α.

METHODS

A sample of 32 male Wistar rats (8 weeks old with mean weight 250 ± 55 g) were divided into four groups randomly: control of base (CO), control of 8 weeks (CO8w), moderate-intensity continuous training (MICT), and high-intensity interval training (HIIT). The rats were fed with standard chow diet. The CO group was killed at the start of the study and the CO8w group was kept alive for the same time as the experimental groups, but did not participate in any exercise. MICT and HIIT groups for 8 weeks were placed under the moderate-intensity continuous training (15-60 min, with speed of 15-30 m/min) and high-intensity interval training (8-4 intense period for 1 min, with speed of 28-55 m/min, with 3-7 slow-intensity period for 1 min, with a speed of 12-30 m/min) for 8 weeks, respectively. To measure the levels of serum irisin, nesfatin, and resistin the ELISA method was used and real-time PCR method was used to evaluate the relative expression of soleus PGC-1α gene mRNA.

RESULTS

The levels of irisin and nesfatin significantly increased in the HIIT compared with control groups (p = 0.001). Resistin values in both training groups showed a significant decrease compared to the control groups (p = 0.005). The level of PGC-1α gene expression in both HIIT and MICT groups was significantly increased in comparison with the control groups (p = 0.001).

DISCUSSION

The results showed that HIIT and MICT increase the transcription of the PGC-1α gene and possibly the increased expression of this gene after HIIT and MICT plays a central role in the secretion of skeletal muscle myokines and adipokines of adipose tissue.

LEVEL OF EVIDENCE

No Level of evidence: Animal study.

Engineered skeletal muscles for disease modeling and drug discovery

Skeletal muscle is the largest organ of human body with several important roles in everyday movement and metabolic homeostasis. The limited ability of small animal models of muscle disease to accurately predict drug efficacy and toxicity in humans has prompted the development in vitro models of human skeletal muscle that fatefully recapitulate cell and tissue level functions and drug responses. We first review methods for development of three-dimensional engineered muscle tissues and organ-on-a-chip microphysiological systems and discuss their potential utility in drug discovery research and development of new regenerative therapies. Furthermore, we describe strategies to increase the functional maturation of engineered muscle, and motivate the importance of incorporating multiple tissue types on the same chip to model organ cross-talk and generate more predictive drug development platforms. Finally, we review the ability of available in vitro systems to model diseases such as type II diabetes, Duchenne muscular dystrophy, Pompe disease, and dysferlinopathy.

Isolation and characterization of resveratrol oligomers from the stem bark of Hopea ponga (Dennst.) Mabb. And their antidiabetic effect by modulation of digestive enzymes, protein glycation and glucose uptake in L6 myocytes

ETHNOPHARMACOLOGICAL RELEVANCE

Hopea ponga (Dennst.) Mabb. Is used in traditional herbal formulations for diabetes complications. The aim of this study is to evaluate the antidiabetic effect of extracts and compounds from H. ponga.

MATERIALS AND METHODS

Silica gel column chromatography was performed to identify various chemical components of the plant extract. Different extracts of H. ponga and isolated compounds were screened for their antidiabetic effect by modulation of digestive enzymes and protein glycation. The effect of glucose uptake by the compounds and the pathways through which the compounds mediate the glucose uptake potential were confirmed by fluorescent microscopy, flow cytometry and western blot analysis.

RESULTS

Acetone and ethanol extracts of the stem bark of Hopea ponga (Dennst.) Mabb. Afforded six resveratrol oligomers namely, E-resveratrol (1), (-)-ε-viniferin (2), (-)-α-viniferin (3), trihydroxyphenanthrene glucoside (THPG) (4), vaticaphenol A (5), (-)-hopeaphenol (6), along with four phytosterols. The structures were determined on the basis of spectroscopic analyses including nuclear magnetic resonance (NMR) spectroscopy and high resolution mass spectrometry (HRMS) data. Compounds 1-5 and 7-10 were tested for their α-glucosidase, α-amylase and glycation inhibitiory activities. All the resveratrol oligomers (1-5) showed prominent α-glucosidase inhibition with IC₅₀ values, 12.56 ± 1.00, 23.98 ± 1.11, 7.17 ± 1.10, 31.74 ± 0.42 and 16.95 ± 0.39 μM, respectively. Molecular docking studies also supported the observed α-glucosidase inhibition. Compound 3 displayed IC₅₀ values of 4.85 ± 0.06 and 27.10 ± 0.04 μM in α-amylase and glycation inhibitory assays activity. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay revealed that the compounds 3 and 4 were found to be less toxic at a concentration of 100 μM (<10%) and 25 μM (<20%), respectively. The effect of glucose uptake performed by 2-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (2-NBDG) in L6 myoblast were measured by fluorescent microscopy and flow cytometry. The compounds 3 and 4 showed 2-NBDG uptake of 49.6% and 38.8% respectively. By examining the molecular pathway through which the compounds elicit their glucose uptake potential, it was observed that both the compounds mainly act via AMPK pathway.

CONCLUSION

This is the first report on the isolation of compounds from H. ponga. Altogether, the results of this study reveal the antidiabetic effects of H. ponga extracts and isolated compounds promoting traditional use of this plant in the treatment of diabetes.

Effect of 6-gingerol on AMPK- NF-κB axis in high fat diet fed rats

OBJECTIVES

Adenosine monophosphate (AMP)-activated protein kinase (AMPK) plays a central role in metabolic homeostasis and regulation of inflammatory responses through attenuation of nuclear factor kappa-B (NF-κB), Thus AMPK may be a promising pharmacologic target for the treatment of various chronic inflammatory diseases. We examined the effect of 6-gingerol, an active ingredient of ginger on AMPK-NF-κB pathway in high fat diet (HFD) rats in comparison to fish oil.

METHODS

Protein levels of AMPK-α1 and phosphorylated AMPK-α1 were measured by western blot while Sirtuin 6 (Sirt-6), resistin and P65 were estimated by RT-PCR, TNF-α was determined by ELISA, FFAs were estimated chemically as well as the enzymatic determination of the metabolic parameters.

RESULTS

6-Gingerol substantially enhanced phosphorylated AMPK-α1 more than fish oil and reduced the P65 via upregulation of Sirt-6 and downregulation of resistin, and resulted in attenuation of the inflammatory molecules P65, FFAs and TNF-α more than fish oil treated groups but in an insignificant statistical manner, those effects were accompanied by a substantial hypoglycemic effect.

CONCLUSION

Gingerol treatment effectively modulated the state of inflammatory privilege in HFD group and the metabolic disorders via targeting the AMPK-NF-κB pathway, through an increment in the SIRT-6 and substantial decrement in resistin levels.

Myokines and adipokines: Involvement in the crosstalk between skeletal muscle and adipose tissue

Skeletal muscle and adipose tissue are the two largest organs in the body. Skeletal muscle is an effector organ, and adipose tissue is an organ that stores energy; in addition, they are endocrine organs that secrete cytokines, namely myokines and adipokines, respectively. Myokines consist of myostatin, interleukin (IL)-8, IL-15, irisin, fibroblast growth factor 21, and myonectin; adipokines include leptin, adiponectin, resistin, chemerin, and visfatin. Furthermore, certain cytokines, such as IL-6 and tumor necrosis factor-α, are released by both skeletal muscle and adipose tissue and exhibit a bioactive effect; thus, they are called adipo-myokines. Recently, novel myokines or adipokines were identified through the secretomic technique, which has expanded our knowledge on the previously unknown functions of skeletal muscle and adipose tissue and provide a new avenue of investigation for obesity treatment or animal production. This review focuses on the roles of and crosstalk between myokines and adipokines in skeletal muscle and adipose tissue that modulate the molecular events in the metabolic homeostasis of the whole body.

Oleate dose-dependently regulates palmitate metabolism and insulin signaling in C2C12 myotubes

Because the protective effect of oleate against palmitate-induced insulin resistance may be lessened in skeletal muscle once cell metabolism is overloaded by fatty acids (FAs), we examined the impact of varying amounts of oleate on palmitate metabolic channeling and insulin signaling in C2C12 myotubes. Cells were exposed to 0.5mM of palmitate and to increasing doses of oleate (0.05, 0.25 and 0.5mM). Impacts of FA treatments on radio-labelled FA fluxes, on cellular content in diacylglycerols (DAG), triacylglycerols (TAG), ceramides, acylcarnitines, on PKCθ, MAPKs (ERK1/2, p38) and NF-ΚB activation, and on insulin-dependent Akt phosphorylation were examined. Low dose of oleate (0.05mM) was sufficient to improve palmitate complete oxidation to CO₂ (+29%, P<0.05) and to alter the cellular acylcarnitine profile. Insulin-induced Akt phosphorylation was 48% higher in that condition vs. palmitate alone (p<0.01). Although DAG and ceramide contents were significantly decreased with 0.05mM of oleate vs. palmitate alone (-47 and -28%, respectively, p<0.01), 0.25mM of oleate was required to decrease p38 MAPK and PKCθ phosphorylation, thus further improving the insulin signaling (+32%, p<0.05). By contrast, increasing oleate concentration from 0.25 to 0.5mM, thus increasing total amount of FA from 0.75 to 1mM, deteriorated the insulin signaling pathway (-30%, p<0.01). This was observed despite low contents in DAG and ceramides, and enhanced palmitate incorporation into TAG (+27%, p<0.05). This was associated with increased incomplete FA β-oxidation and impairment of acylcarnitine profile. In conclusion, these combined data place mitochondrial β-oxidation at the center of the regulation of muscle insulin sensitivity, besides p38 MAPK and PKCθ.

(13)C metabolic flux analysis shows that resistin impairs the metabolic response to insulin in L6E9 myotubes

Background

It has been suggested that the adipokine resistin links obesity and insulin resistance, although how resistin acts on muscle metabolism is controversial. We aimed to quantitatively analyse the effects of resistin on the glucose metabolic flux profile and on insulin response in L6E9 myotubes at the metabolic level using a tracer-based metabolomic approach and our in-house developed software, Isodyn.

Results

Resistin significantly increased glucose uptake and glycolysis, altering pyruvate utilisation by the cell. In the presence of resistin, insulin only slightly increased glucose uptake and glycolysis, and did not alter the flux profile around pyruvate induced by resistin. Resistin prevented the increase in gene expression in pyruvate dehydrogenase-E1 and the sharp decrease in gene expression in cytosolic phosphoenolpyruvate carboxykinase-1 induced by insulin.

Conclusions

These data suggest that resistin impairs the metabolic activation of insulin. This impairment cannot be explained by the activity of a single enzyme, but instead due to reorganisation of the whole metabolic flux distribution.

AMPK regulation of fatty acid metabolism and mitochondrial biogenesis: implications for obesity

Skeletal muscle plays an important role in regulating whole-body energy expenditure given it is a major site for glucose and lipid oxidation. Obesity and type 2 diabetes are causally linked through their association with skeletal muscle insulin resistance, while conversely exercise is known to improve whole body glucose homeostasis simultaneously with muscle insulin sensitivity. Exercise activates skeletal muscle AMP-activated protein kinase (AMPK). AMPK plays a role in regulating exercise capacity, skeletal muscle mitochondrial content and contraction-stimulated glucose uptake. Skeletal muscle AMPK is also thought to be important for regulating fatty acid metabolism; however, direct genetic evidence in this area is currently lacking. This review will discuss the current paradigms regarding the influence of AMPK in regulating skeletal muscle fatty acid metabolism and mitochondrial biogenesis at rest and during exercise, and highlight the potential implications in the development of insulin resistance.

Aspirin prevents resistin-induced endothelial dysfunction by modulating AMPK, ROS, and Akt/eNOS signaling

BACKGROUND

Resistin, an adipocytokine, plays a potential role in cardiovascular disease and may contribute to increased atherosclerotic risk by modulating the activity of endothelial cells. A growing body of evidence suggests that aspirin is a potent antioxidant. We investigated whether aspirin mitigates resistin-induced endothelial dysfunction via modulation of reactive oxygen species (ROS) generation and explored the role that AMP-activated protein kinase (AMPK), a negative regulator of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, plays in the suppressive effects of aspirin on resistin-induced endothelial dysfunction.

METHODS

Human umbilical vein endothelial cells (HUVECs) were pretreated with various doses of aspirin (10-500 μg/mL) for 2 hours and then incubated with resistin (100 ng/mL) for an additional 48 hours. Fluorescence produced by the oxidation of dihydroethidium (DHE) was used to quantify the production of superoxide in situ; superoxide dismutase (SOD) and catalase activities were determined by an enzymatic assay; and protein levels of AMPK-mediated downstream signaling were investigated by Western blot.

RESULTS

Treatment of HUVECs with resistin for 48 hours resulted in a 2.9-fold increase in superoxide production; however, pretreatment with aspirin resulted in a dose-dependent decrease in production of superoxide (10-500 μg/mL; n = 3 experiments; all P < .05). Resistin also suppressed the activity of superoxide dismutase and catalase by nearly 50%; that result, however, was not observed in HUVECs that had been pretreated with aspirin at a concentration of 500 μg/mL. The membrane translocation assay showed that the levels of NADPH oxidase subunits p47(phox)and Rac-1 in membrane fractions of HUVECs were threefold to fourfold higher in cells that had been treated with resistin for 1 hour than in untreated cells; however, pretreatment with aspirin markedly inhibited resistin-induced membrane assembly of NADPH oxidase via modulating AMPK-suppressed PKC-α activation. Application of AMPKα1-specific siRNA resulted in increased activation of PKC-α and p47(phox). In addition, resistin significantly decreased AMPK-mediated downstream Akt/endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) signaling and induced the phosphorylation of p38 mitogen-activated protein kinases, which in turn activated NF-κB-mediated inflammatory responses such as the release of interleukin (IL)-6 and IL-8, the overexpression of adhesion molecules, and stimulation of monocytic THP-1 cell attachment to HUVECs (2.5-fold vs control; n = 3 experiments). Furthermore, resistin downregulated eNOS and upregulated inducible NO synthase (iNOS) expression, thereby augmenting the formation of NO and protein nitrosylation. Pretreatment with aspirin, however, exerted significant cytoprotective effects in a dose-dependent manner (P < .05).

CONCLUSIONS

Our findings suggest a direct connection between adipocytokines and endothelial dysfunction and provide further insight into the protective effects of aspirin in obese individuals with endothelial dysfunction.

Association of circulating resistin with metabolic risk factors in Indian females having metabolic syndrome

Role of resistin in insulin sensitivity and metabolic syndrome (MetS) is controversial till date. Increased serum resistin levels are associated with MetS and insulin resistance. The aim of this study was to investigate the relationship between serum resistin levels with markers of the MetS in females. In a cross-sectional study, a total of 170 healthy female subjects were selected for the study. Out of which 71 (age 31.59 ± 4.88 years) were with MetS and 99 (age 31.75 ± 6.34 years) were without MetS. Different parameters of MetS and serum resistin level were measured according to the standard protocols as given in NCEP ATP III 2001 guideline. Serum resistin levels were significantly higher in subjects with MetS when compared with subjects without MetS [13.54 ± 4.14 ng/ml (n = 71) vs. 7.42 ± 2.31 ng/ml (n = 99); P ≤ 0.001]. Resistin levels were positively associated with waist circumference, systolic and diastolic blood pressure, plasma glucose, waist/hip ratio, serum triglycerides, serum cholesterol, serum VLDL, plasma insulin, and insulin resistance, while it was negatively associated with high-density lipoprotein. This study demonstrates a positive correlation between resistin and factors of MetS except high-density lipoprotein which was found to be negatively correlated in Indian female subjects.

FATP4 contributes as an enzyme to the basal and insulin-mediated fatty acid uptake of C₂C₁₂ muscle cells

The function of membrane proteins in long-chain fatty acid transport is controversial. The acyl-CoA synthetase fatty acid transport protein-4 (FATP4) has been suggested to facilitate fatty acid uptake indirectly by its enzymatic activity, or directly by transport across the plasma membrane. Here, we investigated the function of FATP4 in basal and insulin mediated fatty acid uptake in C(2)C(12) muscle cells, a model system relevant for fatty acid metabolism. Stable expression of exogenous FATP4 resulted in a twofold higher fatty acyl-CoA synthetase activity, and cellular uptake of oleate was enhanced similarly. Kinetic analysis demonstrated that FATP4 allowed the cells to reach apparent saturation of fatty acid uptake at a twofold higher level compared with control. Short-term treatment with insulin increased fatty acid uptake in line with previous reports. Surprisingly, insulin increased the acyl-CoA synthetase activity of C(2)C(12) cells within minutes. This effect was sensitive to inhibition of insulin signaling by wortmannin. Affinity purified FATP4 prepared from insulin-treated cells showed an enhanced enzyme activity, suggesting it constitutes a novel target of short-term metabolic regulation by insulin. This offers a new mechanistic explanation for the concomitantly observed enhanced fatty acid uptake. FATP4 was colocalized to the endoplasmic reticulum by double immunofluorescence and subcellular fractionation, clearly distinct from the plasma membrane. Importantly, neither differentiation into myotubes nor insulin treatment changed the localization of FATP4. We conclude that FATP4 functions by its intrinsic enzymatic activity. This is in line with the concept that intracellular metabolism plays a significant role in cellular fatty acid uptake.

Insights into the molecular mechanisms of the anti-atherogenic actions of flavonoids in normal and obese mice

Obesity is a major and independent risk factor for cardiovascular disease and it is strongly associated with the development of dyslipidemia, insulin resistance and type 2 diabetes. Flavonoids, a diverse group of polyphenol compounds of plant origin widely distributed in human diet, have been reported to have numerous health benefits, although the mechanisms underlying these effects have remained obscure. We analyzed the effects of chronic dietary supplementation with flavonoids extracted from cranberry (FLS) in normal and obese C57/BL6 mice compared to mice maintained on the same diets lacking FLS. Obese mice supplemented with flavonoids showed an amelioration of insulin resistance and plasma lipid profile, and a reduction of visceral fat mass. We provide evidence that the adiponectin-AMPK pathway is the main mediator of the improvement of these metabolic disorders. In contrast, the reduced plasma atherogenic cholesterol observed in normal mice under FLS seems to be due to a downregulation of the hepatic cholesterol synthesis pathway. Overall, we demonstrate for the first time that the molecular mechanisms underlying the beneficial effects of flavonoids are determined by the metabolic state.

Iron in fatty liver and in the metabolic syndrome: a promising therapeutic target

The dysmetabolic iron overload syndrome (DIOS) is now a frequent finding in the general population, as is detected in about one third of patients with nonalcoholic fatty liver disease (NAFLD) and the metabolic syndrome. The pathogenesis is related to altered regulation of iron transport associated with steatosis, insulin resistance, and subclinical inflammation, often in the presence of predisposing genetic factors. Evidence is accumulating that excessive body iron plays a causal role in insulin resistance through still undefined mechanisms that probably involve a reduced ability to burn carbohydrates and altered function of adipose tissue. Furthermore, DIOS may facilitate the evolution to type 2 diabetes by altering beta-cell function, the progression of cardiovascular disease by contributing to the recruitment and activation of macrophages within arterial lesions, and the natural history of liver disease by inducing oxidative stress in hepatocytes, activation of hepatic stellate cells, and malignant transformation by promotion of cell growth and DNA damage. Based on these premises, the association among DIOS, metabolic syndrome, and NAFLD is being investigated as a new risk factor to predict the development of overt cardiovascular and hepatic diseases, and possibly hepatocellular carcinoma, but most importantly, represents also a treatable condition. Indeed, iron depletion, most frequently achieved by phlebotomy, has been shown to decrease metabolic alterations and liver enzymes in controlled studies in NAFLD. Additional studies are warranted to evaluate the potential of iron reductive therapy on hard clinical outcomes in patients with DIOS.

In vivo and in vitro insulin and fasting control of the transmembrane fatty acid transport proteins in Atlantic salmon (Salmo salar)

We have examined the nutritional and insulin regulation of the mRNA expression of transmembrane fatty acid (FA) transporters [FA transport protein-1 (FATP1) and CD36] together with the lipoprotein lipase (LPL), the cytosolic FA carrier FA binding protein (FABP3), and mitochondrial FA-CoA and -carnitine palmitoyl transferase carriers (CPT)1 and -2 in Atlantic salmon tissues and myocyte cell culture. Two weeks of fasting diminished FATP1, CD36, and LPL in adipose tissue, suggesting a reduction in FA uptake, while FABP3 increased in liver, probably enhancing the transport of FA to the mitochondria. Insulin injection decreased FATP1 and CD36 in white and red muscles, while both transporters were upregulated in the adipose tissue in agreement with the role of insulin-inhibiting muscle FA oxidation and stimulating adipose fat stores. Serum deprivation of 48 h in Atlantic salmon myotubes increased FATP1, FABP3, and CPT-2, while CPT-1 was diminished. In myotubes, insulin induced FATP1 expression but decreased CD36, FABP3, and LPL, suggesting that FATP1 could be more involved in the insulin-stimulated FA uptake. Insulin increased the FA uptake in myotubes mediated, at least in part, through the relocation of FATP1 protein to the plasma membrane. Overall, Atlantic salmon FA transporters are regulated by fasting and insulin on in vivo and in vitro models.

Lipid metabolism in mammalian tissues and its control by retinoic acid

Evidence has accumulated that specific retinoids impact on developmental and biochemical processes influencing mammalian adiposity including adipogenesis, lipogenesis, adaptive thermogenesis, lipolysis and fatty acid oxidation in tissues. Treatment with retinoic acid, in particular, has been shown to reduce body fat and improve insulin sensitivity in lean and obese rodents by enhancing fat mobilization and energy utilization systemically, in tissues including brown and white adipose tissues, skeletal muscle and the liver. Nevertheless, controversial data have been reported, particularly regarding retinoids' effects on hepatic lipid and lipoprotein metabolism and blood lipid profile. Moreover, the molecular mechanisms underlying retinoid effects on lipid metabolism are complex and remain incompletely understood. Here, we present a brief overview of mammalian lipid metabolism and its control, introduce mechanisms through which retinoids can impact on lipid metabolism, and review reported activities of retinoids on different aspects of lipid metabolism in key tissues, focusing on retinoic acid. Possible implications of this knowledge in the context of the management of obesity and the metabolic syndrome are also addressed. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.

AMP-activated protein kinase and metabolic control

AMP-activated protein kinase AMP-activated protein kinase (AMPK AMPK ), a phylogenetically conserved serine/threonine protein kinase, is a major regulator of cellular and whole-body energy homeostasis that coordinates metabolic pathways in order to balance nutrient supply with energy demand. It is now recognized that pharmacological activation of AMPK improves blood glucose homeostasis, lipid profile, and blood pressure in insulin-resistant rodents. Indeed, AMPK activation mimics the beneficial effects of physical activity or those of calorie restriction calorie restriction by acting on multiple cellular targets. In addition, it is now demonstrated that AMPK is one of the probable (albeit indirect) targets of major antidiabetic drugs drugs including the biguanides (metformin metformin ) and thiazolidinedione thiazolidinedione s, as well as of insulin-sensitizing adipokines (e.g., adiponectin adiponectin ). Taken together, such findings highlight the logic underlying the concept of targeting the AMPK pathway for the treatment of metabolic syndrome and type 2 diabetes.

The Role of Genetic Variation in Muscle Strength

Skeletal muscle is an important link to an individual’s health and quality of life. The primary clinical interest in skeletal muscle is muscle strength. Muscle strength is a complex trait, influenced by biological, morphological, psychological, and environmental factors. Muscle strength is highly variable among individuals and has a strong genetic component. Though several genetic variants have been associated with muscle strength, genes comprising this genetic component are generally unknown. Research examining associations between genetic variants and muscle strength suffers from scientific challenges such as lack of replication, population stratification, and complexity of defining muscle phenotypes. Additionally, non-scientific challenges such as privacy and protection of genetic information and the questionable value of direct-to-consumer genetic marketing exist. How these challenges will influence research examining genetics and muscle strength is uncertain. Findings from this research may lead to improved treatment for muscle-related disease as well as improved health and quality of life. This may be realized through the development of genetic profiles that clinicians can implement into personalized treatment plans. This review will summarize the current literature regarding genetic variation and muscle strength. The authors’ focus will be on the muscle strength response to resistance training. Additionally, the authors discuss challenges and implications of this research.

An APPL1-AMPK signaling axis mediates beneficial metabolic effects of adiponectin in the heart

Adiponectin promotes cardioprotection by various mechanisms, and this study used primary cardiomyocytes and the isolated working perfused heart to investigate cardiometabolic effects. We show in adult cardiomyocytes that adiponectin increased CD36 translocation and fatty acid uptake as well as insulin-stimulated glucose transport and Akt phosphorylation. Coimmunoprecipitation showed that adiponectin enhanced association of AdipoR1 with APPL1, subsequent binding of APPL1 with AMPKα2, which led to phosphorylation and inhibition of ACC and increased fatty acid oxidation. Using siRNA to effectively knockdown APPL1 in neonatal cardiomyocytes, we demonstrated an essential role for APPL1 in mediating increased fatty acid uptake and oxidation by adiponectin. Importantly, enhanced fatty acid oxidation in conjunction with AMPK and ACC phosphorylation was also observed in the isolated working heart. Despite increasing fatty acid oxidation and myocardial oxygen consumption, adiponectin increased hydraulic work and maintained cardiac efficiency. In summary, the present study documents several beneficial metabolic effects mediated by adiponectin in the heart and provides novel insight into the mechanisms behind these effects, in particular the importance of APPL1.

Circulating and local visfatin/Nampt/PBEF levels in spontaneously hypertensive rats, stroke-prone spontaneously hypertensive rats and Wistar-Kyoto rats

Visfatin (also known as nicotinamide phosphoribosyltransferase and pre-B cell colony-enhancing factor) is a multifunctional protein. Visfatin has been reported to be involved in several biological processes in the cardiovascular system, . However, the role of visfatin in hypertension is still unclear. In this study, we examined the circulating and local adipose visfatin levels in spontaneously hypertensive rats (SHR), stroke-prone spontaneously hypertensive rats (SHR-SP), and in their normotensive control Wistar-Kyoto (WKY). SHR and SHR-SP rats exhibited lower body weight, lower fat tissue and hypolipidemia. No differences of serum visfatin levels were observed in SHR/SHR-SP and WKY. Serum visfatin levels did not correlate to serum glucose, lipids, insulin, and fat pad weights, but significantly correlated to weights of skeletal muscle. Visfatin expression in visceral fat tissue was slightly lower in SHR-SP compared with that in WKY. Moreover, there were no significant differences of visfatin expression in skeletal muscles among WKY, SHR and SHR-SP. Finally, visfatin protein was detected in L6 rat skeletal muscle cell culture medium, indicating that visfatin was secreted from skeletal muscle cells. Thus, our results may provide useful information for understanding the characteristic of visfatin in hypertensive models, and support the view that visfatin may be a myokine.

AMPK inhibition in health and disease

All living organisms depend on dynamic mechanisms that repeatedly reassess the status of amassed energy, in order to adapt energy supply to demand. The AMP-activated protein kinase (AMPK) alphabetagamma heterotrimer has emerged as an important integrator of signals managing energy balance. Control of AMPK activity involves allosteric AMP and ATP regulation, auto-inhibitory features and phosphorylation of its catalytic (alpha) and regulatory (beta and gamma) subunits. AMPK has a prominent role not only as a peripheral sensor but also in the central nervous system as a multifunctional metabolic regulator. AMPK represents an ideal second messenger for reporting cellular energy state. For this reason, activated AMPK acts as a protective response to energy stress in numerous systems. However, AMPK inhibition also actively participates in the control of whole body energy homeostasis. In this review, we discuss recent findings that support the role and function of AMPK inhibition under physiological and pathological states.

Relationship between resistin and aPAI-1 levels with insulin resistance in Saudi children

BACKGROUND

Association of resistin with insulin resistance (IR) in humans is still controversial and few studies have investigated the association of plasminogen activator inhibitor-1 (PAI-1) with IR in children. The purpose of the present study was therefore to evaluate serum levels of resistin and active PAI-1 (aPAI-1) in Saudi children and their association with the various obesity-related complications.

METHODS

In this cross-sectional study, 73 boys and 77 girls with varying body mass index (BMI) were recruited. They were assessed for anthropometric measures and fasting serum levels of glucose, insulin, lipid profile, resistin, angiotensin II (ANG II) and aPAI-1.

RESULTS

Resistin was positively correlated with hips (r = 0.33, P < 0.01), waist (r = 0.23, P < 0.05) and BMI (r = 0.33, P < 0.01). The association of resistin with the markers of obesity was also significant in girls but lost significance in boys. aPAI-1 was positively correlated with total cholesterol (r = 0.24; P < 0.01), triglycerides (r = 0.2, P < 0.05), HOMA-IR (r = 0.26, P < 0.01) and insulin (r = 0.26, P < 0.01). The significant association of aPAI-1 with IR was also true in girls but lost significance in boys.

CONCLUSION

Resistin is not correlated with IR and further studies are needed to explore the role of resistin especially in childhood obesity. In contrast, increased levels of PAI-1 may contribute to the risk of cardiovascular diseases related to obesity and insulin resistance in children. The observed gender-related differences in the association between resistin, aPAI-1 with obesity markers and IR could be attributed to sexual dimorphism in body fat distribution.

Activation of AMP-activated protein kinase signaling pathway by adiponectin and insulin in mouse adipocytes: requirement of acyl-CoA synthetases FATP1 and Acsl1 and association with an elevation in AMP/ATP ratio

Adiponectin activates AMP-activated protein kinase (AMPK) in adipocytes, but the underlying mechanism remains unclear. Here we tested the hypothesis that AMP, generated in activating fatty acids to their CoA derivatives, catalyzed by acyl-CoA synthetases, is involved in AMPK activation by adiponectin. Moreover, in adipocytes, insulin affects the subcellular localization of acyl-CoA synthetase FATP1. Thus, we also tested whether insulin activates AMPK in these cells and, if so, whether it activates through a similar mechanism. We examined these hypotheses by measuring the AMP/ATP ratio and AMPK activation on adiponectin and insulin stimulation and after knocking down acyl-CoA synthetases in adipocytes. We show that adiponectin activation of AMPK is accompanied by an ∼2-fold increase in the cellular AMP/ATP ratio. Moreover, FATP1 and Acsl1, the 2 major acyl-CoA synthetase isoforms in adipocytes, are essential for AMPK activation by adiponectin. We also show that after 40 min. insulin activated AMPK in adipocytes, which was coupled with a 5-fold increase in the cellular AMP/ATP ratio. Knockdown studies show that FATP1 and Acsl1 are required for these processes, as well as for stimulation of long-chain fatty acid uptake by adiponection and insulin. These studies demonstrate that a change in cellular energy state is associated with AMPK activation by both adiponectin and insulin, which requires the activity of FATP1 and Acsl1.

Membrane Fatty Acid Transporters as Regulators of Lipid Metabolism: Implications for Metabolic Disease

Long-chain fatty acids and lipids serve a wide variety of functions in mammalian homeostasis, particularly in the formation and dynamic properties of biological membranes and as fuels for energy production in tissues such as heart and skeletal muscle. On the other hand, long-chain fatty acid metabolites may exert toxic effects on cellular functions and cause cell injury. Therefore, fatty acid uptake into the cell and intracellular handling need to be carefully controlled. In the last few years, our knowledge of the regulation of cellular fatty acid uptake has dramatically increased. Notably, fatty acid uptake was found to occur by a mechanism that resembles that of cellular glucose uptake. Thus, following an acute stimulus, particularly insulin or muscle contraction, specific fatty acid transporters translocate from intracellular stores to the plasma membrane to facilitate fatty acid uptake, just as these same stimuli recruit glucose transporters to increase glucose uptake. This regulatory mechanism is important to clear lipids from the circulation postprandially and to rapidly facilitate substrate provision when the metabolic demands of heart and muscle are increased by contractile activity. Studies in both humans and animal models have implicated fatty acid transporters in the pathogenesis of diseases such as the progression of obesity to insulin resistance and type 2 diabetes. As a result, membrane fatty acid transporters are now being regarded as a promising therapeutic target to redirect lipid fluxes in the body in an organ-specific fashion.

Berberine improves free-fatty-acid-induced insulin resistance in L6 myotubes through inhibiting peroxisome proliferator-activated receptor gamma and fatty acid transferase expressions

The plant alkaloid berberine (BBR) has been reported to have antidiabetic effect in humans and animals. However, the mechanism of action is not well understood. The present study was conducted to determine the effect and mechanism of action of BBR on the free-fatty-acid (FFA)-induced insulin resistance in muscle cells. The FFA-induced insulin-resistant cell model was established in L6 myotubes by treating them with 250 mumol/L of palmitic acid. The inclusion of FFA in the medium increased peroxisome proliferator-activated receptor gamma (PPARgamma) and fatty acid transferase (FAT/CD36) expressions by 26% and 50% and decreased glucose consumption by 43% and insulin-mediated glucose uptake by 63%, respectively. Berberine treatment increased the glucose consumption and insulin-stimulated glucose uptake in normal cells and improved glucose uptake in the FFA-induced insulin-resistant cells. The improved glucose uptake by BBR was accompanied with a dose-dependent decrease in PPARgamma and FAT/CD36 protein expressions. In insulin-resistant myotubes, BBR (5 micromol/L) decreased PPARgamma and FAT/CD36 proteins by 31% and 24%, whereas PPARgamma antagonist GW9662 reduced both proteins by 56% and 46%, respectively. In contrast, PPARgamma agonist rosiglitazone increased the expression of PPARgamma and FAT/CD36 by 34% and 21%, respectively. Our results suggest that BBR improves the FFA-induced insulin resistance in myotubes through inhibiting fatty acid uptake at least in part by reducing PPARgamma and FAT/CD36 expressions.

AMPK in Health and Disease

The function and survival of all organisms is dependent on the dynamic control of energy metabolism, when energy demand is matched to energy supply. The AMP-activated protein kinase (AMPK) alphabetagamma heterotrimer has emerged as an important integrator of signals that control energy balance through the regulation of multiple biochemical pathways in all eukaryotes. In this review, we begin with the discovery of the AMPK family and discuss the recent structural studies that have revealed the molecular basis for AMP binding to the enzyme's gamma subunit. AMPK's regulation involves autoinhibitory features and phosphorylation of both the catalytic alpha subunit and the beta-targeting subunit. We review the role of AMPK at the cellular level through examination of its many substrates and discuss how it controls cellular energy balance. We look at how AMPK integrates stress responses such as exercise as well as nutrient and hormonal signals to control food intake, energy expenditure, and substrate utilization at the whole body level. Lastly, we review the possible role of AMPK in multiple common diseases and the role of the new age of drugs targeting AMPK signaling.

Oligomeric resistin impairs insulin and AICAR-stimulated glucose uptake in mouse skeletal muscle by inhibiting GLUT4 translocation

The hormone resistin is elevated in obesity and impairs glucose homeostasis. Here, we examined the effect of oligomerized human resistin on insulin signaling and glucose metabolism in skeletal muscle and myotubes. This was investigated by incubating mouse extensor digitorum longus (EDL) and soleus muscles and L6 myotubes with physiological concentrations of resistin and assessing insulin-stimulated glucose uptake, cellular signaling, suppressor of cytokine signaling 3 (SOCS-3) mRNA, and GLUT4 translocation. We found that resistin at a concentration of 30 ng/ml decreased insulin-stimulated glucose uptake by 30-40% in soleus muscle and myotubes, whereas in EDL muscle insulin-stimulated glucose uptake was impaired at a resistin concentration of 100 ng/ml. Impaired insulin-stimulated glucose uptake was not associated with reduced Akt phosphorylation or IRS-1 protein or increased SOCS-3 mRNA expression. To further investigate the site(s) at which resistin impairs glucose uptake we treated myotubes and skeletal muscle with the AMPK activator 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR) and found that, although resistin did not impair AMPK activation, it reduced AICAR-stimulated glucose uptake. These data suggested that resistin impairs glucose uptake at a point common to insulin and AMPK signaling pathways, and we thus measured AS160/TBC1D4 Thr(642) phosphorylation and GLUT4 translocation in myotubes. Resistin did not impair TBC1D4 phosphorylation but did reduce both insulin and AICAR-stimulated GLUT4 plasma membrane translocation. We conclude that resistin impairs insulin-stimulated glucose uptake by mechanisms involving reduced plasma membrane GLUT4 translocation but independent of the proximal insulin-signaling cascade, AMPK, and SOCS-3.

Adipokines in nonalcoholic steatohepatitis: from pathogenesis to implications in diagnosis and therapy

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome and can vary from benign steatosis to end-stage liver disease. The pathogenesis of non-alcoholic steatohepatitis (NASH) is currently thought to involve a multiple-hit process with the first hit being the accumulation of liver fat which is followed by the development of necroinflammation and fibrosis. There is mounting evidence that cytokines secreted from adipose tissue, namely, adipokines, are implicated in the pathogenesis and progression of NAFLD. In the current review, we explore the role of these adipokines, particularly leptin, adiponectin, resistin, tumor necrosis factor-a, and interleukin-6 in NASH, as elucidated in experimental models and clinical practice. We also comment on their potential use as noninvasive markers for differentiating simple fatty liver from NASH as well as on their potential future therapeutic role in patients with NASH.

Insulin resistance and fuel homeostasis: the role of AMP-activated protein kinase

The worldwide prevalence of type 2 diabetes (T2D) and related disorders of the metabolic syndrome (MS) has reached epidemic proportions. Insulin resistance (IR) is a major perturbation that characterizes these disorders. Extra-adipose accumulation of lipid, particularly within the liver and skeletal muscle, is closely linked with the development of IR. The AMP-activated protein kinase (AMPK) pathway plays an important role in the regulation of both lipid and glucose metabolism. Through its effects to increase fatty acid oxidation and inhibit lipogenesis, AMPK activity in the liver and skeletal muscle could be expected to ameliorate lipid accumulation and associated IR in these tissues. In addition, AMPK promotes glucose uptake into skeletal muscle and suppresses glucose output from the liver via insulin-independent mechanisms. These characteristics make AMPK a highly attractive target for the development of strategies to curb the prevalence and costs of T2D. Recent insights into the regulation of AMPK and mechanisms by which it modulates fuel metabolism in liver and skeletal muscle are discussed here. In addition, we consider the arguments for and against the hypothesis that dysfunctional AMPK contributes to IR. Finally we review studies which assess AMPK as an appropriate target for the prevention and treatment of T2D and MS.

AMPK-dependent hormonal regulation of whole-body energy metabolism

AMP-dependent protein kinase (AMPK) is an evolutionarily conserved serine/threonine protein kinase central to the regulation of energy balance at both the cellular and whole-body levels. In its classical role as an intracellular metabolic stress-sensing kinase, AMPK switches on fatty acid oxidation and glucose uptake in muscle, while switching off hepatic gluconeogenesis. AMPK also has a broader role in metabolism through the control of appetite. Regulation of AMPK activity at the whole-body level is coordinated by a growing number of hormones and cytokines secreted from adipose tissue, skeletal muscle, pancreas and the gut including leptin, adiponectin, insulin, interluekin-6, resistin, TNF-alpha and ghrelin. Understanding how these secreted signalling proteins regulate AMPK activity to control fatty acid oxidation, glucose uptake, gluconeogenesis and appetite may yield therapeutic treatments for metabolic disorders such as diabetes, insulin resistance and obesity.