Enhanced insulin-stimulated glycogen synthesis in response to insulin, metformin or rosiglitazone is associated with increased mRNA expression of GLUT4 and peroxisomal proliferator activator receptor gamma co-activator 1

Aims/hypothesis The aim of this study was to determine the effect of several antidiabetic agents on insulin-stimulated glycogen synthesis, as well as on mRNA expression.Methods Cultured primary human skeletal myotubes obtained from six healthy subjects were treated for 4 or 8 days without or with glucose (25 mmol/l), insulin (400 pmol/l), rosiglitazone (10 mol/l), metformin (20 mol/l) or the AMP-activated kinase activator 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) (200 mol/l). After this, insulin-stimulated glycogen synthesis was determined. mRNA levels of the glucose transporters GLUT1 and GLUT4, the peroxisomal proliferator activator receptor gamma (PPAR gamma) co-activator 1 (PGC1) and the myocyte-specific enhancer factors (MEF2), MEF2A, MEF2C and MEF2D were determined using real-time PCR analysis after 8 days exposure to the various antidiabetic agents.Results Insulin-stimulated glycogen synthesis was significantly increased in cultured human myotubes treated with insulin, rosiglitazone or metformin for 8 days, compared with non-treated cells. Furthermore, an 8-day exposure of myotubes to 25 mmol/l glucose impaired insulin-stimulated glycogen synthesis. In contrast, treatment with AICAR was without effect on insulin-mediated glycogen synthesis. Exposure to insulin, rosiglitazone or metformin increased mRNA expression of PGC1 and GLUT4, while AICAR or 25 mmol/l glucose treatment increased GLUT1 mRNA expression. Metformin also increased mRNA expression of the MEF2 isoforms.Conclusions/interpretation Enhanced insulin-stimulated glycogen synthesis in human skeletal muscle cell culture coincides with increased GLUT4 and PGC1 mRNA expression following treatment with various antidiabetic agents. These data show that chronic treatment of human myotubes with insulin, metformin or rosiglitazone has a direct positive effect on insulin action and mRNA expression.     

Treatment of Lesch–Nyhan disease with S-adenosylmethionine: Experience with five young Malaysians,including a girl

Background: Lesch–Nyhan disease (LND) is a rare X-linked recessive neurogenetic disorder caused by deficiency of the purine salvage enzyme hypoxanthine phosphoribosyltransferase (HPRT, EC 2.4.2.8) which is responsible for recycling purine bases into purine nucleotides. Affected individuals have hyperuricemia leading to gout and urolithiasis, accompanied by a characteristic severe neurobehavioural phenotype with compulsive self-mutilation, extrapyramidal motor disturbances and cognitive impairment. Aim: For its theoretical therapeutic potential to replenish the brain purine nucleotide pool, oral supplementation with S-adenosylmethionine (SAMe) was trialed in 5 Malaysian children with LND, comprising 4 related Malay children from 2 families, including an LND girl, and a Chinese Malaysian boy. Results: Dramatic reductions of self-injury and aggressive behaviour, as well as a milder reduction of dystonia, were observed in all 5 patients. Other LND neurological symptoms did not improve during SAMe therapy. Discussion: Molecular mechanisms proposed for LND neuropathology include GTP depletion in the brain leading to impaired dopamine synthesis, dysfunction of G-protein-mediated signal transduction, and defective developmental programming of dopamine neurons. The improvement of our LND patients on SAMe, particularly the hallmark self-injurious behaviour, echoed clinical progress reported with another purine nucleotide depletion disorder, Arts Syndrome, but contrasted lack of benefit with the purine disorder adenylosuccinate lyase deficiency. This first report of a trial of SAMe therapy in LND children showed remarkably encouraging results that warrant larger studies.     

Turn up the power –pharmacological activation of mitochondrial biogenesis in mouse models

The oxidative phosphorylation (OXPHOS) system in mitochondria is responsible for the generation of the majority of cellular energy in the form of ATP. Patients with genetic OXPHOS disorders form the largest group of inborn errors of metabolism. Unfortunately, there is still a lack of efficient therapies for these disorders other than management of symptoms. Developing therapies has been complicated because, although the total group of OXPHOS patients is relatively large, there is enormous clinical and genetic heterogeneity within this patient population. Thus there has been a lot of interest in generating relevant mouse models for the different kinds of OXPHOS disorders. The most common treatment strategies tested in these mouse models have aimed to up-regulate mitochondrial biogenesis, in order to increase the residual OXPHOS activity present in affected animals and thereby to ameliorate the energy deficiency. Drugs such as bezafibrate, resveratrol and AICAR target the master regulator of mitochondrial biogenesis PGC-1α either directly or indirectly to manipulate mitochondrial metabolism. This review will summarize the outcome of preclinical treatment trials with these drugs in mouse models of OXPHOS disorders and discuss similar treatments in a number of mouse models of common diseases in which pathology is closely linked to mitochondrial dysfunction. In the majority of these studies the pharmacological activation of the PGC-1α axis shows true potential as therapy; however, other effects besides mitochondrial biogenesis may be contributing to this as well.

Linked Articles

This article is part of a themed issue on Mitochondrial Pharmacology: Energy, Injury & Beyond. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2014.171.issue-8     

Role of AMPK in pancreatic beta cell function

Pharmacological activation of AMP activated kinase (AMPK) by metformin has proven to be a beneficial therapeutic approach for the treatment of type II diabetes. Despite improved glucose regulation achieved by administration of small molecule activators of AMPK, the potential negative impact of enhanced AMPK activity on insulin secretion by the pancreatic beta cell is an important consideration. In this review, we discuss our current understanding of the role of AMPK in central functions of the pancreatic beta cell, including glucose-stimulated insulin secretion (GSIS), proliferation, and survival. In addition we discuss the controversy surrounding the role of AMPK in insulin secretion, underscoring the merits and caveats of methods used to date.     

Adenosine induces apoptosis in the human gastric cancer cells via an intrinsic pathway relevant to activation of AMP-activated protein kinase

Extracellular adenosine significantly reduced cell viability in a dose (0.1-20mM)- and treatment time (24-72h)-dependent manner in GT3-TKB cells, a human gastric cancer cell line. Nuclei of cells were reactive to Hoechst 33342, a marker of apoptosis, and an anti-single-stranded DNA. Adenosine-induced GT3-TKB cell death was significantly inhibited by dipyridamole, an inhibitor of adenosine transporter, and 5'-amino-5'-deoxyadenosine, an inhibitor of adenosine kinase, but the effect was not affected by theophylline, a broad inhibitor of adenosine receptors, 8-cyclopentyltheophylline, an inhibitor of A(1) adenosine receptors or 3,7-dimethyl-1-propargylxanthine, an inhibitor of A(2a) adenosine receptors. Adenosine had no effect on mitochondrial membrane potentials. The effect of adenosine on GT3-TKB cell death was not inhibited by a pancaspase inhibitor or inhibitors of caspase-1,-3,-4,-8, and -9. 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR), an activator of AMP-activated protein kinase (AMPK), significantly reduced GT3-TKB cell viability, but the AICAR action was not reinforced in the presence of adenosine. The results of the present study, thus, suggest that extracellular adenosine induces apoptosis in GT3-TKB cells by its uptake into cells and conversion to AMP followed by activation of AMPK, regardless of caspase activation linked to the mitochondria and the endoplasmic reticulum.     

Decreased expression of the reduced folate carrier and folypolyglutamate synthetase is the basis for acquired resistance to the pemetrexed antifolate (LY231514) in an L1210 murine leukemia cell line

Pemetrexed (LY231514) is a new-generation antifolate that, in its polyglutamyl forms, is a potent inhibitor of thymidylate synthase and glycinamide ribonucleotide formyltransferase (GAR transformylase). This study explored the mechanisms of resistance to pemetrexed in L1210 murine leukemia cells using chemical mutagenesis with 5-formyltetrahydrofolate (5-formylTHF) as the growth substrate. A cell line, MTA-13, was identified that was 8.5-fold resistant to pemetrexed with comparable cross-resistance to ZD1694 (Tomudex) and lesser cross-resistance (5-fold) to ZD9331 [(2S)-2-(O-fluoro-p-[N-(2,7-dimethyl-4-oxo-3,4-dihydro-quinazolin-6-ylmethyl)-N-(prop-2-ynyl)amino]benzamido)-4-(tetrazol-5-yl)-butyric acid], DDATHF (dideazatetrahydrofolate) (3.5-fold), and methotrexate (MTX) (2.7-fold) but comparable sensitivity to trimetrexate. Influx of pemetrexed, MTX, and 5-formylTHF into MTA-13 cells was decreased by 56, 47, and 38% compared to wild-type cells. Folate receptor expression was negligible in both cell lines. Net drug uptake declined within 15min to a slower, constant rate over the next 45min, reflecting the rate of accumulation of pemetrexed polyglutamate derivatives. This rate in the MTA-13 line was half that of the wild-type cells. Accumulation of 50nM [3H]pemetrexed, 25nM [3H]5-formylTHF, or 50nM [3H]DDATHF after 3 days was decreased to 35, 46, and 56% the level of L1210 cells. The reduced folate carrier (RFC) message and protein were decreased by 50%, and folypolyglutamate synthetase (FPGS) message was decreased by 65% in MTA-13 cells. No mutations were detected in either protein by DNA sequence analysis. There was a slight decrease (approximately 25%) in thymidylate synthase mRNA, without mutations in the protein, and there was no change in GAR transformylase message. The data indicate that resistance to pemetrexed in the MTA-13 cell line was due to changes in both RFC and FPGS expression, two proteins that act in tandem to regulate polyglutamation of folates and antifolates in cells, resulting in cellular depletion of these active pemetrexed congeners.     

The different time courses of reading different levels of Chinese characters: an ERP study

AMP-activated protein kinase (AMPK) is an energy sensor that is activated by the increase of intracellular AMP:ATP ratio. AMPK in the hypothalamic arcuate nucleus (ARC) is activated during fasting and the activation of AMPK stimulates food intake. To clarify the pathway underlying AMPK-induced feeding, we monitored the activity of single ARC neurons by measuring cytosolic Ca(2+) concentration ([Ca(2+)](i)) with fura-2 fluorescence imaging. An AMPK activator, AICA-riboside (AICAR), at 200 μM increased [Ca(2+)](i) in 24% of ARC neurons. AMPK and acetyl CoA carboxylase were phosphorylated in the neurons with [Ca(2+)](i) responses to AICAR. AICAR-induced [Ca(2+)](i) increases were inhibited by Ca(2+)-free condition but not by thapsigargin, suggesting that AICAR increases [Ca(2+)](i) through Ca(2+) influx from extracellular space. Among AICAR-responding ARC neurons, 38% were neuropeptide Y (NPY)-immunoreactive neurons while no proopiomelanocortin (POMC)-immunoreactive neuron was observed. Intracerebroventricular administration of AICAR increased food intake, and the AICAR-induced food intake was abolished by the co-administration of NPY Y1 receptor antagonist, 1229U91. These results indicate that the activation of AMPK leads to the activation of ARC NPY neurons through Ca(2+) influx, thereby causing NPY-dependent food intake. These mechanisms could be implicated in the stimulation of food intake by physiological orexigenic substances.     

高糖环境对大鼠肾小球系膜细胞AMPK表达及活性的影响

 目的 观察高糖环境下肾小球系膜细胞AMP活化蛋白激酶（AMPK）表达和活性的变化及这种变化与系膜细胞增殖的关系。  方法 实验分4组：对照组（糖浓度5.6mmol/L）,高糖组（22.0mmol/L）,低浓度5-氨基-4-氨甲酰咪唑核苷（AICAR）组（0.5mmol/L AICAR+高糖）,高浓度AICAR组（1.0mmol/L AICAR+高糖）。观察24h后,应用MTT法检测细胞增殖,流式细胞仪检测细胞周期,RT-PCR法测定AMPKα1、α2亚单位mRNA水平,Westernblot法测定总AMPKα蛋白及磷酸化AMPKα蛋白水平。  结果 与对照组比较,高糖组细胞增殖趋势明显（P＜0.01）,且S期的细胞百分数增加（P＜0.01）;RT-PCR显示,高糖组AMPKα1、α2亚单位的mRNA水平低于对照组;总AMPKα蛋白水平及磷酸化AMPKα蛋白水平亦较低;特异性AMPK激活剂AICAR可抑制高糖诱导的细胞增殖（P＜0.01）,使S期的细胞百分数下降,并能增强AMPKα1、α2亚单位的mRNA表达水平及总AMPKα蛋白水平和磷酸化AMPKα蛋白水平。 结论  高糖环境下AMPKα1、α2 mRNA表达水平低下,AMPK蛋白的表达及活性降低;高糖诱导的系膜细胞增殖与AMPK表达及活性降低有关。     

Fatty acid synthase gene regulation in primary hypothalamic neurons

Understanding the mechanisms that regulate feeding is critical to the development of therapeutic interventions for obesity. Many studies indicate that enzymes within fatty acid metabolic pathways may serve as targets for pharmacological tools to treat this epidemic. We, and others have previously demonstrated that C75, a fatty acid synthase (FAS) inhibitor, induced significant anorexia and weight loss by both central and peripheral mechanisms. Because the hypothalamus is important in the regulation of homeostatic processes for feeding control, we have identified pathways that alter the gene expression of FAS in primary hypothalamic neuronal cultures. Insulin, glucose and AICAR (an activator of AMP-activated protein kinase) affected changes in hypothalamic FAS mRNA, which may be regulated via the SREBP1c dependent or independent pathway.     

Insulin signalling downstream of protein kinase B is potentiated by 5′AMP-activated protein kinase in rat hearts in vivo

Aims/hypothesis 5′AMP-activated protein kinase (AMPK) and insulin stimulate glucose transport in heart and muscle. AMPK acts in an additive manner with insulin to increase glucose uptake, thereby suggesting that AMPK activation may be a useful strategy for ameliorating glucose uptake, especially in cases of insulin resistance. In order to characterise interactions between the insulin- and AMPK-signalling pathways, we investigated the effects of AMPK activation on insulin signalling in the rat heart in vivo. Methods Male rats (350–400 g) were injected with 1 g/kg 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) or 250 mg/kg metformin in order to activate AMPK. Rats were administered insulin 30 min later and after another 30 min their hearts were removed. The activities and phosphorylation levels of components of the insulin-signalling pathway were subsequently analysed in individual rat hearts. Results AICAR and metformin administration activated AMPK and enhanced insulin signalling downstream of protein kinase B in rat hearts in vivo. Insulin-induced phosphorylation of glycogen synthase kinase 3 (GSK3) β, p70 S6 kinase (p70^S6K)(Thr389) and IRS1(Ser636/639) were significantly increased following AMPK activation. To the best of our knowledge, this is the first report of heightened insulin responses of GSK3β and p70^S6K following AMPK activation. In addition, we found that AMPK inhibits insulin stimulation of IRS1-associated phosphatidylinositol 3-kinase activity, and that AMPK activates atypical protein kinase C and extracellular signal-regulated kinase in the heart. Conclusions/interpretations Our data are indicative of differential effects of AMPK on the activation of components in the cardiac insulin-signalling pathway. These intriguing observations are critical for characterisation of the crosstalk between AMPK and insulin signalling.