Increase In AMP-activated Protein Kinase Research Articles

Curcumin-dependent phenotypic transformation of microglia mediates resistance to pseudorabies-induced encephalitis

Pseudorabies virus (PRV) causes viral encephalitis, a devastating disease with high mortality worldwide. Curcumin (CUR) can reduce inflammatory damage by altering the phenotype of microglia; however, whether and how these changes mediate resistance to PRV-induced encephalitis is still unclear. In this study, BV2 cells were infected with/without PRV for 24 h and further treated with/without CUR for 24 h. The results indicated that CUR promoted the polarization of PRV-infected BV2 cells from the M1 phenotype to the M2 phenotype and reversed PRV-induced mitochondrial dysfunction. Furthermore, M1 BV2 cell secretions induced signalling pathways leading to apoptosis in PC-12 neuronal cells, and this effect was abrogated by the secretions of M2 BV2 cells. RNA sequencing and bioinformatics analysis predicted that this phenotypic shift may be due to changes in energy metabolism. Furthermore, Western blot analysis showed that CUR inhibited the increase in AMP-activated protein kinase (AMPK) phosphorylation, glycolysis, and triacylglycerol synthesis and the reduction in oxidative phosphorylation induced by PRV infection. Moreover, the ATP levels in M2 BV2 cells were higher than those in M1 cells. Furthermore, CUR prevented the increase in mortality, elevated body temperature, slowed growth, nervous system excitation, brain tissue congestion, vascular cuffing, and other symptoms of PRV-induced encephalitis in vivo. Thus, this study demonstrated that CUR protected against PRV-induced viral encephalitis by switching the phenotype of BV2 cells, thereby protecting neurons from inflammatory injury, and this effect was mediated by improving mitochondrial function and the AMPK/NF-κB p65-energy metabolism-related pathway.

Distinct Plasma Immune Profile in ALS Implicates sTNFR-II in pAMPK/Leptin Homeostasis

Amyotrophic lateral sclerosis (ALS) is a clinically highly heterogeneous disease with a survival rate ranging from months to decades. Evidence suggests that a systemic deregulation of immune response may play a role and affect disease progression. Here, we measured 62 different immune/metabolic mediators in plasma of sporadic ALS (sALS) patients. We show that, at the protein level, the majority of immune mediators including a metabolic sensor, leptin, were significantly decreased in the plasma of sALS patients and in two animal models of the disease. Next, we found that a subset of patients with rapidly progressing ALS develop a distinct plasma assess immune-metabolic molecular signature characterized by a differential increase in soluble tumor necrosis factor receptor II (sTNF-RII) and chemokine (C-C motif) ligand 16 (CCL16) and further decrease in the levels of leptin, mostly dysregulated in male patients. Consistent with in vivo findings, exposure of human adipocytes to sALS plasma and/or sTNF-RII alone, induced a significant deregulation in leptin production/homeostasis and was associated with a robust increase in AMP-activated protein kinase (AMPK) phosphorylation. Conversely, treatment with an AMPK inhibitor restored leptin production in human adipocytes. Together, this study provides evidence of a distinct plasma immune profile in sALS which affects adipocyte function and leptin signaling. Furthermore, our results suggest that targeting the sTNF-RII/AMPK/leptin pathway in adipocytes may help restore assess immune-metabolic homeostasis in ALS.

Beneficial effects of SGLT2 inhibitor on metabolic inflexibility and visceral fat amount in animal model of obese type 2 diabetes

BackgroundObesity and type 2 diabetes mellitus (T2DM) are often accompanied with a disrupted diurnal rhythm of eating and sustained anabolic state, leading to metabolic inflexibility. In the present study, we plan to investigate effects of a sodium glucose co-transporter 2 (SGLT2) inhibitor, canagliflozin (CANA), on such a metabolic inflexibility, especially on fat metabolism, in the obese type 2 diabetic rats. Materials and methodsFive-week-old male SDT (Spontaneously Diabetic Torii) fatty rats as a model of obesity and T2DM and Sprague-Dawley (SD) rats were treated by either CANA (10 mg/kg) or saline (vehicle) orally for 14 days. Then, after the measurement of respiratory quotient (RQ) and visceral and subcutaneous fat volumes, rats were euthanized and blood and tissue samples were collected. ResultsThe treatment by CANA significantly enhanced β-ketone concentration in the blood during light period in the SDT fatty rats with no effect on blood glucose concentration. The CANA treatment significantly reduced visceral fat volume in the SDT fatty rats. A diurnal rhythm of RQ was severely disrupted and persistently high throughout the day in the vehicle-treated SDT fatty rats. By the administration of CANA clearly restored the disrupted diurnal rhythm of RQ with a revival of the nadir during light period. Quantitative real-time RT-PCR revealed a significant increase of AMP-activated protein kinase and decrease of acetyl-CoA carboxylase-1 expression in the liver, and a significant increase of hormone sensitive lipase and uncoupling protein-2 expression in the white adipose tissue by the treatment of CANA in the SDT fatty rats. ConclusionCANA as a SGLT2i reduced visceral fat amount via the enhancement of fat oxidation during the light period, leading to an amelioration of metabolic inflexibility in an obese diabetic model. A novel mechanism of CANA prompts the possibility that this new class of anti-diabetic agent could be a promising anti-obesity agent as well.

Adiponectin Alleviates Intestinal Fibrosis by Enhancing AMP-Activated Protein Kinase Phosphorylation.

Intestinal fibrosis is a common complication of Crohn's disease (CD). Adiponectin reportedly exerts anti-inflammatory effects in various disease models, including colitis models. In this study, we aimed to determine the effects of adiponectin on intestinal fibrosis and the underlying mechanisms. A murine model of intestinal fibrosis was established by administering increasing doses of 2,4,6-trinitrobenzene sulfonic acid to Balb/c mice via enema for 7 weeks. Primary human fibroblasts were isolated from the colon tissues of patients with CD. The fibroblasts were incubated with transforming growth factor (TGF)-β1 to establish a fibrosis model in vitro. Pathway inhibitors were used to verify the potential signaling pathways involved in the anti-fibrogenic effect of adiponectin. Compared with the normal mesentery, adiponectin expression was significantly increased in the hypertrophic mesentery of patients with CD. Intraperitoneal injection of adiponectin significantly decreased the activity of myeloperoxidase and the expression of pro-inflammatory cytokines (tumor necrosis factor α and interleukin 6) in the colon of fibrosis model mice, whereas the expression of the anti-inflammatory cytokine interleukin 10 was substantially increased. Moreover, adiponectin treatment inhibited colon shortening, decreased colon weight, and reduced fibrotic protein deposition in the model mice. Adiponectin reduced the phosphorylation of Smad2 and collagen deposition induced by TGF-β1 in primary human intestinal fibroblasts, with an increase in AMP-activated protein kinase (AMPK) phosphorylation. Furthermore, this phenomenon was reversed by the AMPK inhibitor. Adiponectin can protect against intestinal fibrosis by enhancing the phosphorylation of AMPK and inhibiting the activity of the TGF-β1/Smad signaling pathway.

Exercise-induced AMPK activation and IL-6 muscle production are disturbed in adiponectin knockout mice

BackgroundAdiponectin exhibits anti-inflammatory actions and is mainly expressed in adipose tissue. However, recent studies have shown that adiponectin can also be secreted by skeletal muscle fibers with autocrine and paracrine effects. ObjectivesTo analyze the role of adiponectin in the metabolic and inflammatory response of skeletal muscle after acute exhaustive aerobic exercise. MethodsC57BL/6 (WT) and adiponectin knockout (AdKO) mice underwent four days of treadmill running adaptation and at the fifth day, they performed an incremental maximum test to determine the maximum speed (Vmax). Acute exercise consisted of one hour at 60% Vmax. Mice were euthanatized 2 and 24 h after acute exercise session. ResultsSerum and gastrocnemius adiponectin increased after 2-hours of acute exercise. NEFA concentrations were lower in non-exercise AdKO, and decreased 2-hours after exercise only in WT. No differences were found in muscle triacylglycerol content; however, glycogen content was higher in AdKO in non-exercise (p-value = 0.005). WT showed an increase in AMP-activated protein kinase (AMPK) phosphorylation 2-hours after exercise and its level went back to normal after 24-hours. Otherwise, exercise was not able to modify AMPK in the same way as in AdKO. WT showed an increase in the phosphorylation of ACC (Ser79) 2-hours after exercise and return to normal after 24-hours of exercise (p-value < 0.05), kinects that was not observed in AdKO mice. IL-10 and IL-6 concentration was completely different among genotypes. In WT, these cytokines were increased at 2 (p-value < 0.01) and 24 h (p-value < 0.001) after exercise when compared with AdKO. NF-κBp65 protein and gene expression were not different between genotypes. ConclusionAdiponectin influences muscle metabolism, mainly by the decrease in exercise-induced AMPK phosphorylation, inflammatory profile and IL-6 in the muscle.

The preventive effect of deep sea water on the development of cancerous skin cells through the induction of autophagic cell death in UVB-damaged HaCaT keratinocyte

Ultraviolet light (UV) is a major inducer of skin cancer. Therefore, recovery and removal of UV-damaged skin cells are important in the prevention of skin carcinogenesis. Here, we investigated the effect of deep sea water (DSW) in HaCaT keratinocyte exposed by UVB (λ = 290∼320 nm). The result showed that UVB-induced cell death was reinforced by DSW treatment in a hardness-dependent manner. Furthermore, the increase of cell death by DSW was associated with the down-regulation of survivin and RAD51 expressions induced by UVB. Moreover, we confirmed the inhibition of H2 A.X phosphorylation, a marker for double-stranded DNA damage, and the enhancement of LC3-II and SQSTM1/p62 expressions by DSW administration in UVB-radiated HaCaT keratinocyte. The results imply that the enhancement of UVB-induced cell death by DSW is associated with autophagy. Therefore, we further explored the regulation of autophagy-regulating proteins and apoptosis-related factors expression. Phosphorylation of mammalian target of rapamycin (mTOR), ribosomal protein S6, and S6 kinase by UVB radiation were regressed via DSW treatment, underlying the increase of AMP-activated protein kinase (AMPK) phosphorylation. Furthermore, UVB-enhanced nuclear factor κB (NF-κB) and c-Jun N-terminal kinase (JNK) phosphorylations were increased with DSW treatment. Contrastingly, DSW lessened the Ser15 phosphorylation of p53 and cleavage of poly (ADP-ribose) polymerase induced by UVB radiation. Consequently, the results demonstrate that DSW enhances UVB-damaged skin cell clearance through the activation of autophagic cell death underlying the regulation of AMP-activated protein kinase (AMPK)/mTOR signaling as well as NF-κB and JNK phosphorylations. In conclusion, this investigation suggests that DSW is a potent candidate for the prevention of UV-induced skin cancer development.

Glucagon Receptor Antagonism Improves Glucose Metabolism and Cardiac Function by Promoting AMP-Mediated Protein Kinase in Diabetic Mice

SUMMARYThe antidiabetic potential of glucagon receptor antagonism presents an opportunity for use in an insulin-centric clinical environment. To investigate the metabolic effects of glucagon receptor antagonism in type 2 diabetes, we treated Leprdb/db and Lepob/ob mice with REMD 2.59, a human monoclonal antibody and competitive antagonist of the glucagon receptor. As expected, REMD 2.59 suppresses hepatic glucose production and improves glycemia. Surprisingly, it also enhances insulin action in both liver and skeletal muscle, coinciding with an increase in AMP-activated protein kinase (AMPK)-mediated lipid oxidation. Furthermore, weekly REMD 2.59 treatment over a period of months protects against diabetic cardiomyopathy. These functional improvements are not derived simply from correcting the systemic milieu; nondiabetic mice with cardiac-specific overexpression of lipoprotein lipase also show improvements in contractile function after REMD 2.59 treatment. These observations suggest that hyperglucagonemia enables lipotoxic conditions, allowing the development of insulin resistance and cardiac dysfunction during disease progression.

The Increase of AMP-activated Protein Kinase during Physical Activities can Reduce Symptoms of Autistic Children

Autism spectrum disorders (ASD) are one of the neurodevelopmental disorders. About one-five of children diagnosed with ASD have regression autism. Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is precisely control the balance of ATP metabolism in mitochondria, the organelle that show dysfunction in regressive autism. Studies have shown that this sensor kinase can be effective in axonal growth. It has been suggested that exercise is one of the most powerful factors that increase mitochondrial activity and the amount of AMPK. Above the mentioned, we hypothesized that the physical activities can increase mitochondrial activity and reduce the symptoms of autistic children.

Stress tolerance in the green crab, Carcinus maenas exposed to waste water treatment plant effluent

Wastewater treatment plant effluent (WTPE) is commonly discharged into marine environments. We investigated the effect of WTPE on the stress tolerance of the green crab Carcinus maenas. Crabs were placed in 5 and 20% of WTPE and incubated for 4 days and then underwent an anoxia challenge for 1 hour. 20% WTPE‐exposed crabs showed decreased treadmill running endurance (145±76 and 316±179 sec, respectively), righting response (8.9±8.4 and 3.5±5.7 sec), and oxygen consumption (0.067±0.012 and 0.064±0.009 µmol/g/min). Glutathione‐S‐transferase (GST) activity, as an indicator for oxidative stress, was increased in WTPE exposed crabs (0.9±0.46, 3.3±0.52 and 2.25±1.84 units/mg protein for control, 5% and 20%, respectively). Gene expression assessed by qPCR revealed only a 1.5 fold increase in AMP‐activated protein kinase (AMPK), as an indicator of cellular energy stress, and a 1.3 fold increase in HSP70, as a general stress marker, for the 20% WTPE treated animals. Overall, there was very little change in the selected stress parameters after exposure to WTPE, paired with anoxia. This is different than observed in a parallel study using the blue mussel, Mytilus edulis, which showed diminished performance at the whole animal and cellular level after exposure to WTPE. Our data indicate that WTPE does not diminish the performance of the green crab, but that of other species. Therefore, WTPE might aid in the success of the invasive green crab in dominating new environments. Further studies will continue to explore this.Supported by an APS summer fellowship to G.P. and a Maine SeaGrant Project Development grant to M.F.

The Increase of AMP-activated Protein Kinase during Physical Activitiescan Reduce Symptoms of Autistic Children

Autism spectrum disorders (ASD) are one of the neurodevelopmental disorders. About one-five of children diagnosed with ASD have regression autism. Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is precisely control the balance of ATP metabolism in mitochondria, the organelle that show dysfunction in regressive autism. Studies have shown that this sensor kinase can be effective in axonal growth. It has been suggested that exercise is one of the most powerful factors that increase mitochondrial activity and the amount of AMPK. Above the mentioned, we hypothesized that the physical activities can increase mitochondrial activity and reduce the symptoms of autistic children.

Phloridzin improves lipoprotein lipase activity in stress-loaded mice via AMPK phosphorylation

Long-term stress exposure can lead to disturbed homeostasis and cause many life-style diseases. Phloridzin possesses various bioactivities, but the understanding of the effects of phloridzin on stress-related lipid metabolism disorder is limited. Our results demonstrate that phloridzin improved plasma lipoprotein lipase (LPL) activity and triglyceride metabolism in restrained mice. A decrease of angiopoietin-like protein 4 (ANGPTL4) mRNA expression and an increase of AMP-activated protein kinase (AMPK) phosphorylation were observed after phloridzin treatment. After inhibiting AMPK phosphorylation, the effects of phloridzin on the amelioration of plasma LPL activity and suppression of ANGPTL4 expression were blocked. In addition, cardiac AMPK phosphorylation, plasma LPL activity and ANGPTL4 expression were also affected by phloridzin, even if the glucocorticoid receptor was blocked. Taken together, the down-regulation of ANGPTL4 expression by phloridzin was probably via a direct activation of AMPK pathway. This discovery can provide a biochemical and nutritional basis for the use of phloridzin-containing food and beverage in daily life.

Liver, but Not Muscle, Has an Entrainable Metabolic Memory

Hyperglycemia in the hospitalized setting is common, especially in patients that receive nutritional support either continuously or intermittently. As the liver and muscle are the major sites of glucose disposal, we hypothesized their metabolic adaptations are sensitive to the pattern of nutrient delivery. Chronically catheterized, well-controlled depancreatized dogs were placed on one of three isocaloric diets: regular chow diet once daily (Chow) or a simple nutrient diet (ND) that was given either once daily (ND-4) or infused continuously (ND-C). Intraportal insulin was infused to maintain euglycemia. After 5 days net hepatic (NHGU) and muscle (MGU) glucose uptake and oxidation were assessed at euglycemia (120 mg/dl) and hyperglycemia (200 mg/dl) in the presence of basal insulin. While hyperglycemia increased both NHGU and MGU in Chow, NHGU was amplified in both groups receiving ND. The increase was associated with enhanced activation of glycogen synthase, glucose oxidation and suppression of pyruvate dehydrogenase kinase-4 (PDK-4). Accelerated glucose-dependent muscle glucose uptake was only evident with ND-C. This was associated with a decrease in PDK-4 expression and an increase in AMP-activated protein kinase (AMPK) phosphorylation. Interestingly, ND-C markedly increased hepatic FGF-21 expression. Thus, augmentation of carbohydrate disposal in the liver, as opposed to the muscle, is not dependent on the pattern of nutrient delivery.

The Increase of AMP-activated Protein Kinase during Exercise and its Effect on Reducing Parkinson’s Disease Symptoms

The Increase of AMP-activated Protein Kinase during Exercise and its Effect on Reducing Parkinson’s Disease Symptoms

Dietary intake of green tea polyphenols regulates insulin sensitivity with an increase in AMP‐activated protein kinase α content and changes in mitochondrial respiratory complexes

The intake of food rich in polyphenols is related to a lower incidence in almost all chronic degenerative diseases. However, relatively little is known about the molecular mechanisms involved in its antioxidant properties. The aim of this study was to determine whether the mechanism of action of polyphenols could be related to a modulation in energy uptake and metabolism, and further induced mitochondrial changes. For this purpose, male C57BL6 mice were fed during 3 months with a tea-based beverage rich in polyphenols. Insulin sensitivity, tissue oxidative damage biomarkers, as well as energy-related signaling pathways were determined to evaluate its mechanism of action. As a result, a tissue- and protein-specific subtle reduction in oxidative damage was observed. Skeletal muscle showed mitochondrial changes in respiratory complexes and an increase in AMP-activated protein kinase α levels, suggesting reduced energy availability. These changes were also associated with adipose tissue cellular metabolism. This was confirmed by a decline in the potential of energy uptake, evidenced by a diminished intestinal and systemic absorption of carbohydrates together with an inhibition of insulin sensitivity. Our results suggest that the mechanisms of action of green tea polyphenols may be related to their ability to modulate energy uptake leading to mitochondrial adaptations possibly responsible for the changes in protein oxidative damage.

A comprehensive assessment of mitochondrial protein synthesis and cellular proliferation with age and caloric restriction

It is proposed that caloric restriction (CR) increases mitochondrial biogenesis. However, it is not clear why CR increases an energetically costly biosynthetic process. We hypothesized that 40% CR would decrease mitochondrial protein synthesis and would be regulated by translational rather than transcriptional mechanisms. We assessed cumulative mitochondrial protein synthesis over 6 weeks and its transcriptional and translational regulation in the liver, heart, and skeletal muscle of young (6 month), middle (12 month), and old (24 month) male B6D2F1 mice that were lifelong CR or ad lib (AL) controls. Mitochondrial protein synthesis was not different between AL and CR (fractional synthesis over 6 weeks (range): liver, 91-100%; heart, 74-85%; skeletal muscle, 53-72%) despite a decreased cellular proliferation in liver and heart with CR. With CR, there was an increase in AMP-activated protein kinase phosphorylation/total (P:T) in heart and liver, and an increase in peroxisome proliferator-activated receptor gamma coactivator 1-α mRNA in all tissues, but not protein. Ribosomal protein S6 was decreased with CR. In conclusion, CR maintained mitochondrial protein synthesis while decreasing cellular proliferation during a time of energetic stress, which is consistent with the concept that CR increases somatic maintenance. Alternative mechanisms to global translation initiation may be responsible for selective translation of mitochondrial proteins.

Rhodiola rosea extracts and salidroside decrease the growth of bladder cancer cell lines via inhibition of the mTOR pathway and induction of autophagy

The incidence of human urinary bladder cancer increases markedly with age, suggesting a mechanistic connection between aging and bladder carcinogenesis and a potential use of anti-aging agents in bladder cancer chemoprevention. Rhodiola rosea, growing in high altitude or cold regions of the world, has been reported to have anti-aging effects in Drosophila. We demonstrated that a R. rosea extract and one of its bioactive components, salidroside, inhibited the growth of bladder cancer cell lines with a minimal effect on nonmalignant bladder epithelial cells TEU-2. Interestingly, the R. rosea extract and salidroside component exhibited a selective ability to inhibit the growth of p53 knockout primary mouse embryo fibroblasts (p53-/- MEFs) compared to their wild-type counterparts. The growth inhibitory effects of the R. rosea extract and salidroside were, however, attenuated in TSC2 and p53 double knock MEFs (TSC2-/-, p53-/- MEFs), suggesting that TSC2 protein is, at least in part, required for the growth inhibitory effects of the R. rosea extract and salidroside. The R. rosea extract and salidroside treatment of UMUC3 cells resulted in an increase of AMP-activated protein kinase (AMPK)-α phosphorylation and a decrease of 4E-BP1 phosphorylation, leading to increased binding of 4E-BP1 to m7 GTP. These results indicate that the R. rosea extract and salidroside inhibit translation initiation. Furthermore, both the R. rosea extract and salidroside treatment of UMUC3 cells caused a significant percentage of cells undergoing autophagy. Therefore, the R. rosea extract and salidroside deserve further study as novel agents for chemoprevention of bladder carcinogenesis.

An active part of Artemisia sacrorum Ledeb. inhibits adipogenesis via the AMPK signaling pathway in 3T3-L1 adipocytes

Artemisia sacrorum Ledeb. (Compositae) (ASL) has long been used in Oriental folk medicine to treat diverse hepatic diseases. In this study, we investigated the effect of ASL on adipocyte differentiation in 3T3-L1 cells. ASL significantly suppressed 3T3-L1 differentiation in a concentration-dependent manner. A significant increase of AMP-activated protein kinase (AMPK) was observed when the cells were treated with ASL. Activation of AMPK was also demonstrated by measuring the phosphorylation of acetyl-CoA carboxylase, a substrate of AMPK. These effects were abolished by pre-treatment with the AMPK inhibitor, compound C. In addition, ASL down-regulated the adipogenesis-related gene expression of the sterol regulatory element-binding protein 1c (SREBP1c) and its target genes, such as fatty acid synthase (FAS), stearoyl-CoA desaturase 1 (SCD1) and glycerol-3-phosphate acyltransferase (GPAT) in a concentration-dependent manner. These effects were abolished by pre-treatment with compound C. ASL significantly reduced the gene expression of the peroxisome proliferator-activated receptor γ (PPARγ) and of the CCAAT/enhancer binding protein-α (C/EBPα), two key transcription factors in adipogenesis. Meanwhile, adipocyte fatty acid binding protein (aP2) gene expression was also reduced in a concentration-dependent manner. These findings indicated that ASL exerts anti-adipogenic activity via AMPK activation and may act to prevent obesity.

Korean red ginseng attenuates hepatic lipid accumulation via AMPK activation in human hepatoma cells

In this study, we examined Korean red ginseng (KRG) extract affects on the lipid metabolism in HepG2 cells. Increase in AMP-activated protein kinase (AMPK) phosphorylation was observed when the cells were treated with KRG. Activation of AMPK was also demonstrated by measuring the phosphorylation of acetyl-CoA caboxylase (ACC), a substrate of AMPK. KRG down-regulated gene expressions of sterol regulatory element binding protein 1c (SREBP1c) and its target proteins, such as fatty acid synthase (FAS) and stearoyl-CoA desaturase (SCD1) in time- and dose-dependent fashions. In contrast, gene expressions of peroxisome proliferator-activated receptor α (PPARα) and CD36 were increased. These effects were reversed in the presence of compound C, an AMPK inhibitor. However, there were no differences in gene expressions of SREBP2, 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, and low-density-lipoprotein receptor (LDLR). Taken together, KRG induced supression of SREBP1c and activation of PPARα via AMPK and these effects seem to be one of anti-hyperlipidemic mechanism of KRG in HepG2 cells.

Compound K, Intestinal Metabolite of Ginsenoside, Attenuates Hepatic Lipid Accumulation via AMPK Activation in Human Hepatoma Cells

Compound K (CK) is a major intestinal metabolite of ginsenosides derived from ginseng radix. Although antidiabetic and antihyperlipidemic activities of CK have been investigated in recent years, action mechanism of CK remains poorly understood. Therefore, we examined whether CK affects the lipid metabolism in insulin-resistant HepG2 human hepatoma cells. In this study, a significant increase in AMP-activated protein kinase (AMPK) was observed when the cells were treated with CK. Activation of AMPK was also demonstrated by measuring the phosphorylation of acetyl-CoA carboxylase (ACC), a substrate of AMPK. CK attenuated gene expression of sterol regulatory element-binding protein 1c (SREBP1c) in time- and dose-dependent manners. Genes for fatty acid synthase (FAS) and stearoyl-CoA desaturase 1 (SCD1), well-known target molecules of SREBP1c, were also suppressed. In contrast, gene expressions of peroxisome proliferator-activated receptor alpha (PPAR-alpha) and CD36 were increased. These effects were reversed by treatment of compound C, an AMPK inhibitor. However, there were no differences in gene expressions of SREBP2, hydroxymethyl glutaryl CoA reductase (HMGR), and low-density-lipoprotein receptor (LDLR). Taken together, AMPK mediates CK induced suppression and activation of SREBP1c and PPAR-alpha, respectively, and these effects seem to be one of antidiabetic and/or antihyperlipidemic mechanisms of CK in insulin-resistant HepG2 human hepatoma cells.

Acute physical exercise reverses S‐nitrosation of the insulin receptor, insulin receptor substrate 1 and protein kinase B/Akt in diet‐induced obese Wistar rats

Early evidence demonstrates that exogenous nitric oxide (NO) and the NO produced by inducible nitric oxide synthase (iNOS) can induce insulin resistance. Here, we investigated whether this insulin resistance, mediated by S-nitrosation of proteins involved in early steps of the insulin signal transduction pathway, could be reversed by acute physical exercise. Rats on a high-fat diet were subjected to swimming for two 3 h-long bouts, separated by a 45 min rest period. Two or 16 h after the exercise protocol the rats were killed and proteins from the insulin signalling pathway were analysed by immunoprecipitation and immunoblotting. We demonstrated that a high-fat diet led to an increase in the iNOS protein level and S-nitrosation of insulin receptor beta (IR beta), insulin receptor substrate 1 (IRS1) and Akt. Interestingly, an acute bout of exercise reduced iNOS expression and S-nitrosation of proteins involved in the early steps of insulin action, and improved insulin sensitivity in diet-induced obesity rats. Furthermore, administration of GSNO (NO donor) prevents this improvement in insulin action and the use of an inhibitor of iNOS (L-N6-(1-iminoethyl)lysine; L-NIL) simulates the effects of exercise on insulin action, insulin signalling and S-nitrosation of IR beta, IRS1 and Akt. In summary, a single bout of exercise reverses insulin sensitivity in diet-induced obese rats by improving the insulin signalling pathway, in parallel with a decrease in iNOS expression and in the S-nitrosation of IR/IRS1/Akt. The decrease in iNOS protein expression in the muscle of diet-induced obese rats after an acute bout of exercise was accompanied by an increase in AMP-activated protein kinase (AMPK) activity. These results provide new insights into the mechanism by which exercise restores insulin sensitivity.