Stimulation Of Glucose Oxidation Research Articles

The polyunsaturated fatty acid docosahexaenoic affects mitochondrial function in prostate cancer cells

BackgroundProstate cancer (PCa) shows a rewired metabolism featuring increased fatty acid uptake and synthesis via de novo lipogenesis, both sharply related to mitochondrial physiology. The docosahexaenoic acid (DHA) is an omega-3 polyunsaturated fatty acid (PUFA) that exerts its antitumoral properties via different mechanisms, but its specific action on mitochondria in PCa is not clear. Therefore, we investigated whether the DHA modulates mitochondrial function in PCa cell lines.MethodsHere, we evaluated mitochondrial function of non-malignant PNT1A and the castration-resistant (CRPC) prostate 22Rv1 and PC3 cell lines in response to DHA incubation. For this purpose, we used Seahorse extracellular flux assay to assess mitochondria function, [14C]-glucose to evaluate its oxidation as well as its contribution to fatty acid synthesis, 1H-NMR for metabolite profile determination, MitoSOX for superoxide anion production, JC-1 for mitochondrial membrane polarization, mass spectrometry for determination of phosphatidylglycerol levels and composition, staining with MitoTracker dye to assess mitochondrial morphology under super-resolution in addition to Transmission Electron Microscopy, In-Cell ELISA for COX-I and SDH-A protein expression and flow cytometry (Annexin V and 7-AAD) for cell death estimation.ResultsIn all cell lines DHA decreased basal respiratory activity, ATP production, and the spare capacity in mitochondria. Also, the omega-3 induced mitochondrial hyperpolarization, ROS overproduction and changes in membrane phosphatidylglycerol composition. In PNT1A, DHA led to mitochondrial fragmentation and it increased glycolysis while in cancer cells it stimulated glucose oxidation, but decreased de novo lipogenesis specifically in 22Rv1, indicating a metabolic shift. In all cell lines, DHA modulated several metabolites related to energy metabolism and it was incorporated in phosphatidylglycerol, a precursor of cardiolipin, increasing the unsaturation index in the mitochondrial membrane. Accordingly, DHA triggered cell death mainly in PNT1A and 22Rv1.ConclusionIn conclusion, mitochondrial metabolism is significantly affected by the PUFA supplementation to the point that cells are not able to proliferate or survive under DHA-enriched condition. Moreover, combination of DHA supplementation with inhibition of metabolism-related pathways, such as de novo lipogenesis, may be synergistic in castration-resistant prostate cancer.

Stimulating cardiac glucose oxidation lessens the severity of heart failure in aged female mice.

Heart failure is a prevalent disease worldwide. While it is well accepted that heart failure involves changes in myocardial energetics, what alterations that occur in fatty acid oxidation and glucose oxidation in the failing heart remains controversial. The goal of the study are to define the energy metabolic profile in heart failure induced by obesity and hypertension in aged female mice, and to attempt to lessen the severity of heart failure by stimulating myocardial glucose oxidation. 13-Month-old C57BL/6 female mice were subjected to 10weeks of a 60% high-fat diet (HFD) with 0.5g/L of Nω-nitro-L-arginine methyl ester (L-NAME) administered via drinking water to induce obesity and hypertension. Isolated working hearts were perfused with radiolabeled energy substrates to directly measure rates of myocardial glucose oxidation and fatty acid oxidation. Additionally, a series of mice subjected to the obesity and hypertension protocol were treated with a pyruvate dehydrogenase kinase inhibitor (PDKi) to stimulate cardiac glucose oxidation. Aged female mice subjected to the obesity and hypertension protocol had increased body weight, glucose intolerance, elevated blood pressure, cardiac hypertrophy, systolic dysfunction, and decreased survival. While fatty acid oxidation rates were not altered in the failing hearts, insulin-stimulated glucose oxidation rates were markedly impaired. PDKi treatment increased cardiac glucose oxidation in heart failure mice, which was accompanied with improved systolic function and decreased cardiac hypertrophy. The primary energy metabolic change in heart failure induced by obesity and hypertension in aged female mice is a dramatic decrease in glucose oxidation. Stimulating glucose oxidation can lessen the severity of heart failure and exert overall functional benefits.

Stimulating myocardial pyruvate dehydrogenase activity fails to alleviate cardiac abnormalities in a mouse model of human Barth syndrome.

Barth syndrome (BTHS) is a rare genetic disorder due to mutations in the TAFAZZIN gene, leading to impaired maturation of cardiolipin and thereby adversely affecting mitochondrial function and energy metabolism, often resulting in cardiomyopathy. In a murine model of BTHS involving short-hairpin RNA mediated knockdown of Tafazzin (TazKD mice), myocardial glucose oxidation rates were markedly reduced, likely secondary to an impairment in the activity of pyruvate dehydrogenase (PDH), the rate-limiting enzyme of glucose oxidation. Furthermore, TazKD mice exhibited cardiac hypertrophy with minimal cardiac dysfunction. Because the stimulation of myocardial glucose oxidation has been shown to alleviate diabetic cardiomyopathy and heart failure, we hypothesized that stimulating PDH activity would alleviate the cardiac hypertrophy present in TazKD mice. In order to address our hypothesis, 6-week-old male TazKD mice and their wild-type (WT) littermates were treated with dichloroacetate (DCA; 70 mM in the drinking water), which stimulates PDH activity via inhibiting PDH kinase to prevent inhibitory phosphorylation of PDH. We utilized ultrasound echocardiography to assess cardiac function and left ventricular wall structure in all mice prior to and following 6-weeks of treatment. Consistent with systemic activation of PDH and glucose oxidation, DCA treatment improved glycemia in both TazKD mice and their WT littermates, and decreased PDH phosphorylation equivalently at all 3 of its inhibitory sites (serine 293/300/232). However, DCA treatment had no impact on left ventricular structure, or systolic and diastolic function in TazKD mice. Therefore, it is unlikely that stimulating glucose oxidation is a viable target to improve BTHS-related cardiomyopathy.

Short-Chain Fatty Acids in the Metabolism of Heart Failure - Rethinking the Fat Stigma.

Heart failure (HF) remains a disease with immense global health burden. During the development of HF, the myocardium and therefore cardiac metabolism undergoes specific changes, with decreased long-chain fatty acid oxidation and increased anaerobic glycolysis, diminishing the overall energy yield. Based on the dogma that the failing heart is oxygen-deprived and on the fact that carbohydrates are more oxygen-efficient than FA, metabolic HF drugs have so far aimed to stimulate glucose oxidation or inhibit FA oxidation. Unfortunately, these treatments have failed to provide meaningful clinical benefits. We believe it is time to rethink the concept that fat is harmful to the failing heart. In this review we discuss accumulating evidence that short-chain fatty acids (SCFAs) may be an effective fuel for the failing heart. In contrast to long-chain fatty acids, SCFAs are readily taken up and oxidized by the heart and could serve as a nutraceutical treatment strategy. In addition, we discuss how SCFAs activate pathways that increase long chain fatty acid oxidation, which could help increase the overall energy availability. Another potential beneficial effect we discuss lies within the anti-inflammatory effect of SCFAs, which has shown to inhibit cardiac fibrosis – a key pathological process in the development of HF.

Anti-hyperglycemic potential of alginate oligosaccharide in a high glucose-induced zebrafish model

The anti-hyperglycemic activity of alginate oligosaccharide (AOS) and its mechanism were elucidated in a hyperglycemic zebrafish model. The model was prepared by inducing high glucose in zebrafish for the study. AOS treatment significantly reduced blood glucose level and delayed mortality in hyperglycemic zebrafish. To explain the anti-hyperglycemic mechanism of AOS, a comparative proteomic analysis was performed in three groups (control, hyperglycemic, AOS-treated hyperglycemic) of zebrafish. Among 639 identified proteins, 72 proteins modulated by AOS treatment were classified into key biofunctional categories, including energy metabolism and survival. Ingenuity pathway analysis predicted that AOS treatment inhibits lactic acid production by suppressing hypoxia inducible factor 1 subunit a (HIF1A) via modulating insulin receptor (INSR), sirtuin 1 (SIRT1) and lactate dehydrogenase A (LDHA); and induces glucose oxidation by enhancing pyruvate dehydrogenase 1 (PDHA1) via decreasing pyruvate dehydrogenase kinase isoform 2 (PDK2). Subsequently, RT-qPCR analysis verified the reduction of hif1a, pdk2 and ldha gene expression, and the elevation of insr and sirt1 expression by AOS treatment in hyperglycemic zebrafish. In conclusion, AOS could be an alternative therapeutic agent to ameliorate hyperglycemia by stimulating glucose oxidation and suppressing lactic acid pathway.

A novel Ag/Zn bimetallic MOF as a superior sensitive biosensing platform for HCV-RNA electrochemical detection

A new label-free electrochemical biosensor was progressed for direct detection of unamplified HCV nucleic acid based on silver/zinc bimetallic metal–organic framework (Ag/Zn-MOF). Several physico-chemical techniques were used to confirm the structure and morphology. The prepared bimetallic-MOF was cast on the glassy carbon electrode (GCE) and treated with the capture probe of HCV. Then, treated with bovine serum albumin (BSA) to passivate the surface, which is ready for hybridization process once the HCV target nucleic acid was added. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used as an evidence for the successful stepwise formation of the desired biosensor. In addition, a differential pulse voltammetry (DPV) measurement was used in the presence of glucose as an electrochemical catalytic indicator. The results confirmed that the bimetallic MOF's catalytic activity stimulated glucose oxidation to gluconolactone, resulting in electrochemical signal amplification. The proposed HCV electrochemical biosensor has several advantages ease of use; low cost; high selectivity and sensitivity; a linear detection ranges from 1 fM to 100 nM; and ultra-low detection limit (0.64 fM). To date, this is the first electrochemical HCV-biosensor report based on bimetallic-MOF. Consequently, this assay opens the door for designing more electrochemical biosensors regarding the electrical and catalytic activity of bimetallic-MOF.

Insulin directly stimulates mitochondrial glucose oxidation in the heart

BackgroundGlucose oxidation is a major contributor to myocardial energy production and its contribution is orchestrated by insulin. While insulin can increase glucose oxidation indirectly by enhancing glucose uptake and glycolysis, it also directly stimulates mitochondrial glucose oxidation, independent of increasing glucose uptake or glycolysis, through activating mitochondrial pyruvate dehydrogenase (PDH), the rate-limiting enzyme of glucose oxidation. However, how insulin directly stimulates PDH is not known. To determine this, we characterized the impacts of modifying mitochondrial insulin signaling kinases, namely protein kinase B (Akt), protein kinase C-delta (PKC-δ) and glycogen synthase kinase-3 beta (GSK-3β), on the direct insulin stimulation of glucose oxidation.MethodsWe employed an isolated working mouse heart model to measure the effect of insulin on cardiac glycolysis, glucose oxidation and fatty acid oxidation and how that could be affected when mitochondrial Akt, PKC-δ or GSK-3β is disturbed using pharmacological modulators. We also used differential centrifugation to isolate mitochondrial and cytosol fraction to examine the activity of Akt, PKC-δ and GSK-3β between these fractions. Data were analyzed using unpaired t-test and two-way ANOVA.ResultsHere we show that insulin-stimulated phosphorylation of mitochondrial Akt is a prerequisite for transducing insulin’s direct stimulation of glucose oxidation. Inhibition of mitochondrial Akt completely abolishes insulin-stimulated glucose oxidation, independent of glucose uptake or glycolysis. We also show a novel role of mitochondrial PKC-δ in modulating mitochondrial glucose oxidation. Inhibition of mitochondrial PKC-δ mimics insulin stimulation of glucose oxidation and mitochondrial Akt. We also demonstrate that inhibition of mitochondrial GSK3β phosphorylation does not influence insulin-stimulated glucose oxidation.ConclusionWe identify, for the first time, insulin-stimulated mitochondrial Akt as a prerequisite transmitter of the insulin signal that directly stimulates cardiac glucose oxidation. These novel findings suggest that targeting mitochondrial Akt is a potential therapeutic approach to enhance cardiac insulin sensitivity in condition such as heart failure, diabetes and obesity.

α1-Adrenergic receptors increase glucose oxidation under normal and ischemic conditions in adult mouse cardiomyocytes

The role of catecholamine receptors in cardiac energy metabolism is unknown. α1-adrenergic receptors (α1-ARs) have been identified to play a role in whole body metabolism but its role in cardiac energy metabolism has not been explored. We used freshly prepared primary adult mouse cardiomyocytes and incubated with either 14C-palmitate or 14C-glucose tracers to measure oxidation rates in the presence or absence of phenylephrine, an α1-AR agonist (with β and α2-AR blockers) under normal cell culture conditions. 14CO2 released was collected over a 10 min period in covered tissue culture plates using a 1 M hyamine hydroxide solution placed in well cups, counted by scintillation and converted into nmoles/hr. We found that phenylephrine stimulated glucose oxidation but not fatty acid oxidation in adult primary cardiomyocytes. α1-AR stimulated glucose oxidation was blocked by the AMPK inhibitor, dorsomorphin dihydrochloride, and the PKC inhibitor, rottlerin. Ischemic conditions were induced by lowering the glucose concentration from 22.5 mM to 1.375 mM. Under ischemic conditions, we found that phenylephrine also increased glucose oxidation. We report a direct role of α1-ARs in regulating glucose oxidation under normal and ischemic conditions that may lead to new therapeutic approaches in treating ischemia.

Perturbations in myocardial energy metabolism in the ischemic heart

As an organ that must continuously pump oxygenated blood throughout the body, the heart has an enormous metabolic demand, which is primarily met via oxidative metabolism of fatty acids and carbohydrates. Because of its high metabolic demand, during times of reduced oxygen supply such as ischemia, the heart becomes highly susceptible to injury, and if flow is not re-established, myocardial tissue is lost and can result in death (myocardial infarction). Of interest, both myocardial ischemia and reperfusion are associated with a number of perturbations in energy metabolism that contribute to the pathology of ischemic heart disease. This includes marked elevations in glycolysis to counteract the reduction in oxidative metabolism, whereas fatty acids predominate as the primary fuel source for residual oxidative metabolism. During the early stages of cardiac recovery after successful reperfusion of the ischemic heart, fatty acid oxidation rates also rapidly recover at the expense of low glucose oxidation rates. These metabolic perturbations increase myocardial acidosis due to glycolysis being uncoupled from glucose oxidation, which impairs cardiac efficiency. As such, therapeutic approaches to stimulate glucose oxidation or inhibit fatty acid oxidation have the potential to correct dysregulated myocardial energy metabolism during ischemia and reperfusion, which improves cardiac efficiency and may lead to improved clinical outcomes in people with ischemic heart disease. L

Qishen granules exerts cardioprotective effects on rats with heart failure via regulating fatty acid and glucose metabolism

BackgroundQishen granules (QSG) has been applied to treat heart failure (HF) for decades. Our previous transcriptomics study has suggested that Qishen granules (QSG) could regulate the pathways of cardiac energy metabolism in HF, but the specific regulatory mechanism has not yet been clarified. This study was to investigate the potential mechanism of QSG in regulating myocardial fatty acid (FA) and glucose metabolism in a rat model of HF.MethodsThe model of HF was induced by left anterior descending coronary artery ligation. Cardiac structure and function were assessed by cine magnetic resonance imaging (MRI) and echocardiography. Level of glucose metabolism was non-invasively evaluated by 18F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT). Blood lipid levels were determined by enzymatic analysis. The mitochondrial ultrastructure was observed with a transmission electron microscope. The critical proteins related to FA metabolism, glucose metabolism and mitochondrial function were measured by western blotting. The ANOVA followed by a Fisher’s LSD test was used for within-group comparisons.ResultsQSG ameliorated cardiac functions and attenuated myocardial remodeling in HF model. The levels of serum TC, TG and LDL-C were significantly reduced by QSG. The proteins mediating FA uptake, transportation into mitochondria and β-oxidation (FAT/CD36, CPT1A, ACADL, ACADM, ACAA2 and SCP2) as well as the upstreaming transcriptional regulators of FA metabolism (PPARα, RXRα, RXRβ and RXRγ) were up-regulated by QSG. As to glucose metabolism, QSG inhibited glycolytic activity by decreasing LDHA, while stimulated glucose oxidation by decreasing PDK4. Furthermore, QSG could facilitate tricarboxylic acid cycle, promote the transportation of ATP from mitochondria to cytoplasm and restore the mitochondrial function by increasing SUCLA2, CKMT2 and PGC-1α and decreasing UCP2 simultaneously.ConclusionQSG improved myocardial energy metabolism through increasing FA metabolism,inhibiting uncoupling of glycolysis from glucose oxidation.

Abstract 868: A Cardiac Specific Branched Chain Aminotransferase Deletion Increases Insulin Stimulated Glucose Oxidation in the Mouse Heart

Impaired branched chain amino acid (BCAA) oxidation at the level of downstream BCAA catabolic enzymes cause cardiac insulin resistance and dysfunction. However, it is not known whether it is the accumulation of BCAAs or branched chain keto acids (BCKAs) due to impaired cardiac BCAA oxidation that result in these cardiac metabolic detrimental effects. Our objective was to inhibit cardiac branched chain aminotransferase (BCATm), the first enzyme in the BCAA oxidative pathway, which functions to produce BCKAs. We anticipate deletion of upstream BCAA catabolic enzyme will result in reduced cardiac BCAA oxidation and increase BCAAs but decrease BCKAs. Ten-week-old BCATm cardiac specific knockout (BCATm -/- ) male mice and their α-MHC-Cre expressing wildtype littermates (WT-Cre +/+ ) received 6 intraperitoneal injections of tamoxifen (50 mg/kg). All mice were allowed a 6-week washout post-tamoxifen, following which 16-week-old mice were used to assess cardiac energy metabolism. Isolated working hearts were perfused with oxygenated Krebs–Henseleit solution, consisting of either 5mM [5- 3 H/U- 14 C] glucose, 0.8mM palmitate, 3%BSA, 0.5mM BCAA for glycolysis and glucose oxidation measurements, or 0.5mM glucose, 0.8mM [9,10- 3 H] palmitate, 3%BSA and 0.5mM [U- 14 C] BCAA from combination of 0.15mM leucine/isoleucine and 0.2mM valine for fatty acid oxidation and BCAA oxidation measurements respectively. There was no body weight, glucose tolerance or cardiac function differences observed in BCATm -/- mice compared to WT-Cre +/+ mice (control). As expected, cardiac BCAA oxidation was significantly reduced in BCATm -/- mice compared to control, however, adding insulin after 30 min of perfusion did not change BCAA oxidation rates. Interestingly, glucose oxidation was significantly higher in BCATm -/- mice. Adding insulin further increased glucose oxidation in BCATm -/- mice. Additionally, the contribution of glucose oxidation to ATP production was significantly higher in the BCATm -/- mice compared to control. We conclude that impaired BCAA oxidation due to the upstream catabolic enzyme deletion increases cardiac insulin sensitivity. This also indicates that accumulation of BCKAs, not BCAAs, may be primarily contributing to cardiac insulin resistance.

Abstract 856: Mitochondrial Protein Kinase B (akt) Translocation Mediates Insulin-stimulated Cardiac Glucose Oxidation

Introduction: Insulin stimulates glucose oxidation, an effect which is associated with simulating pyruvate dehydrogenase (PDH). However, how the insulin signal is transduced from the cell membrane to the mitochondria to stimulate PDH is not known. Protein kinase B (Akt), protein kinase C-delta (PKCδ) and glycogen synthase kinase-3beta (GSK-3β) are main components of the cytosolic insulin signalling pathway and it has been suggested that they can be translocated to the mitochondria following insulin receptor activation in noncardiac tissue. Therefore, we investigated whether any of these kinases has a role mediated cardiac insulin-stimulated glucose oxidation in the heart. Methods and Results: Male and female C57BL/6 mice were anesthetized and hearts were collected and perfused in the isolated working heart mode. Hearts were perfused with [5- 3 H] glucose and [U- 14 C] glucose to simultaneously measure glycolysis and glucose oxidation rates, respectively, in the presence and absence of insulin. Insulin enhanced the phosphorylation and translocation of Akt Ser473 , PKCδ Tyr311 and GSK-3β Ser9 to the cardiac mitochondria along with enhancing PDH activity by decreasing its phosphorylation. Pharmacological inhibition of Akt using AktiVIII completely abolish the stimulatory effect of insulin on cardiac glucose oxidation rates (354 ± 145 vs 2307 ± 185 nmol. g dry wt -1 . min -1 in vehicle-treated hearts, p<0.05). However, pharmacological inhibition of either PKCδ or GSK-3β using Bisindolylmaleimide I or 3F8, respectively, did not have a significant effect on insulin-stimulated glucose oxidation rates. None of the pharmacological inhibitors had any significant effect on cardiac glycolysis. Conclusion: Insulin mediates its stimulatory effect on cardiac glucose oxidation via a mechanism which involve the activation and translocation of Akt to the mitochondria.

Metabolic interventions for the prevention and treatment of daptomycin non-susceptibility in Staphylococcus aureus.

A major developing problem in the treatment of Staphylococcus aureus infections is the emergence of resistance during treatment with daptomycin. Previous metabolomic analyses of isogenic S. aureus strains prior to and after evolution into a daptomycin non-susceptible (DapNS) state provided important metabolic information about this transition (e.g. perturbations of the tricarboxylic acid cycle). To assess the significance of these metabolic changes, in vitro susceptibility to daptomycin was determined in daptomycin-susceptible (DapS) and DapNSS. aureus strains cultivated with metabolic inhibitors targeting these changes. Only inhibitors that are approved for use in humans were chosen (i.e. fosfomycin, valproate, trimetazidine and 6-mercaptopurine) to assess the importance of metabolic pathways for daptomycin non-susceptibility. The ability of these inhibitors to forestall the emergence of DapNS strains was also assessed. The combination of daptomycin and fosfomycin synergistically killed both DapS and DapNS strains in vitro and enhanced the in vivo outcome against a DapNS strain in experimental endocarditis. Interestingly, fosfomycin acts on the peptidoglycan biosynthetic enzyme UDP-N-acetylglucosamine enolpyruvyl transferase (MurA); however, it also had a significant effect on the enzymatic activity of enolase, an essential enzyme in S. aureus. While fosfomycin acted synergistically with daptomycin, it failed to prevent the in vitro evolution of daptomycin non-susceptibility. In contrast, trimetazidine, an anti-angina drug that stimulates glucose oxidation, abolished the ability of DapSS. aureus strains to transition to a DapNS state. These data reveal that metabolic adaptations associated with DapNS strains can be targeted to prevent the emergence of and/or reverse pre-existing resistance to daptomycin.

Targeting the glucagon receptor improves cardiac function and enhances insulin sensitivity following a myocardial infarction

BackgroundIn heart failure the myocardium becomes insulin resistant which negatively influences cardiac energy metabolism and function, while increasing cardiac insulin signalling improves cardiac function and prevents adverse remodelling in the failing heart. Glucagon’s action on cardiac glucose and lipid homeostasis counteract that of insulin’s action. We hypothesised that pharmacological antagonism of myocardial glucagon action, using a human monoclonal antibody (mAb A) against glucagon receptor (GCGR), a G-protein coupled receptor, will enhance insulin sensitivity and improve cardiac energy metabolism and function post myocardial infarction (MI).MethodsMale C57BL/6 mice were subjected to a permanent left anterior descending coronary artery ligation to induce MI, following which they received either saline or mAb A (4 mg kg−1 week−1 starting at 1 week post-MI) for 3 weeks.ResultsEchocardiographic assessment at 4 weeks post-MI showed that mAb A treatment improved % ejection fraction (40.0 ± 2.3% vs 30.7 ± 1.7% in vehicle-treated MI heart, p < 0.05) and limited adverse remodelling (LV mass: 129 ± 7 vs 176 ± 14 mg in vehicle-treated MI hearts, p < 0.05) post MI. In isolated working hearts an increase in insulin-stimulated glucose oxidation was evident in the mAb A-treated MI hearts (1661 ± 192 vs 924 ± 165 nmol g dry wt−1 min−1 in vehicle-treated MI hearts, p < 0.05), concomitant with a decrease in ketone oxidation and fatty acid oxidation rates. The increase in insulin stimulated glucose oxidation was accompanied by activation of the IRS-1/Akt/AS160/GSK-3β pathway, an increase in GLUT4 expression and a reduction in pyruvate dehydrogenase phosphorylation. This enhancement in insulin sensitivity occurred in parallel with a reduction in cardiac branched chain amino acids content (374 ± 27 vs 183 ± 41 µmol g protein−1 in vehicle-treated MI hearts, p < 0.05) and inhibition of the mTOR/P70S6K hypertrophic signalling pathway. The MI-induced increase in the phosphorylation of transforming growth factor β-activated kinase 1 (p-TAK1) and p38 MAPK was also reduced by mAb A treatment.ConclusionsmAb A-mediated cardioprotection post-myocardial infarction is associated with improved insulin sensitivity and a selective enhancement of glucose oxidation via, at least in part, enhancing branched chain amino acids catabolism. Antagonizing glucagon action represents a novel and effective pharmacological intervention to alleviate cardiac dysfunction and adverse remodelling post-myocardial infarction.

α-1 acid glycoprotein inhibits insulin responses by glucose oxidation, protein synthesis and protein breakdown in mouse C2C12 myotubes

Increased plasma α-1 acid glycoprotein (AGP) is correlated with reduced growth rates in neonatal swine. The specific physiological mechanisms contributing to this relationship are unknown. This study was performed to determine if AGP can modify muscle metabolism by examining glucose oxidation and protein synthesis in the C2C12 muscle cell line. Cells were used for experiments 4 days post-fusion as myotubes. Myotubes were exposed to AGP for 24 h, with the last 4 h used to monitor 14C-glucose oxidation or to measure protein synthesis by incorporation of 3H-tyrosine. Treatment of C2C12 myotubes with mouse AGP (100 µg/ml) reduced glucose oxidation (P<0.01, n=3 trials), whereas bovine insulin (1 µM) stimulated glucose oxidation (P<0.05, n=3 trials). Treatment with AGP in combination with insulin reduced 14C-glucose oxidation (P<0.05, n=3 trials), similar to the effect of AGP alone. Glucose transport, as measured by 3H-deoxyglucose uptake, was increased by 38% with 1 µM insulin (P<0.05, n=3 trials), whereas AGP alone increased glucose uptake by 36% (P<0.05, n=3 trials). The combination of insulin and AGP in the medium resulted in an 88% increase in glucose uptake (P<0.01, n=3 trials). Protein synthesis was measured by 3H-tyrosine incorporation into C2C12 myotubes. Insulin stimulated a 18% increase in 3H-tyrosine incorporation (P<0.05, n=6 trials). The incorporation of 3H-tyrosine into myotubes was reduced by 20% with AGP incubation (P<0.01, n=6 trials), like the 20% decrease in 3H-tyrosine incorporation in response to the combination of AGP and insulin (P<0.01, n=6 trials). Protein breakdown, as measured by the release of 3H-tyrosine from C2C12 myotubes, was reduced 27% by insulin (P<0.01, n=6 trials). Treatment with AGP had no effect on protein breakdown (P>0.05, n=6 trials), whereas incubation with both AGP and insulin reduced 3H-tyrosine release by 15% (P<0.01, n=6 trials). First, these data indicate that the acute phase protein AGP can interact with the skeletal muscle to reduce glucose oxidation, but this is not the result of an effect on glucose transport. Second, AGP can specifically reduce protein synthesis. Lastly, AGP can inhibit insulin-stimulated glucose oxidation, protein synthesis and breakdown.

Treading slowly through hypoxic waters: dichloroacetate to the rescue!

Metabolic flexibility is compromised during myocardial hypoxia and the development of heart failure. In this issue of The Journal of Physiology, Handzlik and colleagues provide novel findings that demonstrate how chronic hypoxia increases the susceptibility of the heart to acute hypoxia, although chronic hypoxia interestingly displays preserved pyruvate dehydrogenase (PDH) function (Handzlik et al. 2018). They also found that increasing PDH activity with the PDH kinase inhibitor dichloroacetate (DCA) improves the chronically hypoxic heart's tolerance to acute hypoxia, thereby reinforcing the importance of cardiac metabolic flexibility. In the setting of heart failure, a potential end stage of chronic hypoxia, cardiac energy metabolism becomes perturbed and inflexible, with energy production being both insufficient and inefficient. More specifically, the failing heart's energy metabolism is characterized by an increase in glycolysis and, concurrently, a significant reduction in glucose oxidation (for which PDH is the rate-limiting enzyme) (Figure 1). As such, there is therapeutic potential to stimulate glucose oxidation to improve the failing heart's energy production and efficiency. This study provides evidence for a beneficial effect of DCA treatment, administered concurrently with chronic hypoxia, for improving acetyl-carnitine stores to pre-emptively protect against acute hypoxic attacks. However, while the findings of Handzlik and colleagues demonstrate promising potential for DCA in the setting of chronic hypoxia, extrapolation to the pathophysiological setting of heart failure may be premature. During hypoxia and the development of heart failure, glycolysis increases and glucose oxidation decreases. DCA treatment increases glucose oxidation and can eventually improve the metabolic flexibility of the heart. Combining NAD+ precursors with DCA may have further benefits to increase mitochondrial quality and quantity as well. We previously demonstrated that acute treatment with DCA during reperfusion of ischaemic hearts has a beneficial effect on functional recovery, due to an increase in PDH activity and glucose oxidation (Lopaschuk et al. 1993). Handzlik et al. also observed that DCA treatment during chronic hypoxia can improve functional recovery during a subsequent acute hypoxic episode. However, although an acute hypoxic episode decreased functional recovery of chronically hypoxic hearts, this was curiously accompanied by an increase in PDH activity in the untreated hearts. Furthermore, while DCA treatment improved functional recovery following acute hypoxia, it did not further increase PDH activity. Additionally, glycolytic flux increased as expected with acute hypoxia, as did lactate efflux. On the contrary though, DCA treatment did not decrease lactate efflux, even though glycolytic flux was slightly decreased, suggesting that glucose oxidation was not increased with DCA treatment. Another interesting finding was that glycolytic flux normalized to function was inhibited by DCA treatment during acute hypoxia and reoxygenation but no changes in PDH activity following DCA treatment were observed. This suggests that the benefits of DCA on heart function may not originate from a DCA-induced increase in glucose oxidation. Unfortunately, direct measurements of glucose oxidation rates were not made in this study, which would help define the therapeutic mechanism and implication of DCA in the setting of chronic hypoxia and its potential applications in the failing heart. Cardiac mitochondrial function can be compromised in diabetes and obesity. Mitochondria are the main role-players in maintaining metabolic flexibility; however, manipulation of the mitochondrial acetyl-carnitines via DCA administration may only be a temporary solution for improving cardiac function. Furthermore, the effects of prolonging mitochondrial oxidative phosphorylation during acute hypoxia remain unclear. Regardless of the disease state, in a naive heart, pre-adaptation with adverse mitochondrial respiration may be an effective therapeutic approach to consider. However, making mitochondria solely dependent on PDH flux and the acetyl-carnitine pool may be a rate-limiting approach in the context of aging. An important factor to consider for future therapeutic approaches is the age-dependent decrease in mitochondrial number and function as well as different disease states. A major metabolic cofactor, NAD+, and its precursors (nicotinamide mononucleotide, NMN, and nicotinamide riboside, NR) have been shown to improve mitochondrial function and biogenesis in obesity, diabetes and in aging leading to considerable mitochondrial adaptation when metabolism is impaired (Uddin et al. 2017). Therefore, improving cardiac adaptations to acute hypoxic conditions or heart failure is a unique approach; however, future studies of combining DCA with NMN, NR or CD38 inhibitor (an NADase) could potentially make more mitochondria quantitatively and qualitatively to improve cardiac hypoxic tolerance. None declared. All authors have approved the final version of the manuscript and agree to be accountable for all aspects of the work. All persons designated as authors qualify for authorship, and all those who qualify for authorship are listed.

Zinc stimulates glucose oxidation and glycemic control by modulating the insulin signaling pathway in human and mouse skeletal muscle cell lines.

Zinc is a metal ion that is an essential cell signaling molecule. Highlighting this, zinc is an insulin mimetic, activating cellular pathways that regulate cellular homeostasis and physiological responses. Previous studies have linked dysfunctional zinc signaling with several disease states including cancer, obesity, cardiovascular disease and type 2 diabetes. The present study evaluated the insulin-like effects of zinc on cell signaling molecules including tyrosine, PRSA40, Akt, ERK1/2, SHP-2, GSK-3β and p38, and glucose oxidation in human and mouse skeletal muscle cells. Insulin and zinc independently led to the phosphorylation of these proteins over a 60-minute time course in both mouse and human skeletal muscle cells. Similarly, utilizing a protein array we identified that zinc could active the phosphorylation of p38, ERK1/2 and GSK-3B in human and ERK1/2 and GSK-3B in mouse skeletal muscle cells. Glucose oxidation assays were performed on skeletal muscle cells treated with insulin, zinc, or a combination of both and resulted in a significant induction of glucose consumption in mouse (p<0.01) and human (p<0.05) skeletal muscle cells when treated with zinc alone. Insulin, as expected, increased glucose oxidation in mouse (p<0.001) and human (0.001) skeletal muscle cells, however the combination of zinc and insulin did not augment glucose consumption in these cells. Zinc acts as an insulin mimetic, activating key molecules implicated in cell signaling to maintain glucose homeostasis in mouse and human skeletal muscle cells. Zinc is an important metal ion implicated in several biological processes. The role of zinc as an insulin memetic in activating key signaling molecules involved in glucose homeostasis could provide opportunities to utilize this ion therapeutically in treating disorders associated with dysfunctional zinc signaling.

Acute exposure of primary rat soleus muscle to zilpaterol HCl (β2 adrenergic agonist), TNFα, or IL-6 in culture increases glucose oxidation rates independent of the impact on insulin signaling or glucose uptake

Recent studies show that adrenergic agonists and inflammatory cytokines can stimulate skeletal muscle glucose uptake, but it is unclear if glucose oxidation is similarly increased. Thus, the objective of this study was to determine the effects of ractopamine HCl (β1 agonist), zilpaterol HCl (β2 agonist), TNFα, and IL-6 on glucose uptake and oxidation rates in unstimulated and insulin-stimulated soleus muscle strips from adult Sprague-Dawley rats. Effects on phosphorylation of Akt (phospho-Akt), p38 MAPK (phospho-p38), and p44/42 MAPK (phospho-p44/42) was also determined. Incubation with insulin increased (P<0.05) glucose uptake by ∼47%, glucose oxidation by ∼32%, and phospho-Akt by ∼238%. Insulin also increased (P<0.05) phospho-p38, but only after 2h in incubation. Muscle incubated with β2 agonist alone exhibited ∼20% less (P<0.05) glucose uptake but ∼32% greater (P<0.05) glucose oxidation than unstimulated muscle. Moreover, co-incubation with insulin+β2 agonist increased (P<0.05) glucose oxidation and phospho-Akt compared to insulin alone. Conversely, β1 agonist did not appear to affect basal or insulin-stimulated glucose metabolism, and neither β agonist affected phospho-p44/42. TNFα and IL-6 increased (P<0.05) glucose oxidation by ∼23% and ∼33%, respectively, in the absence of insulin. This coincided with increased (P<0.05) phospho-p38 and phospho-p44/42 but not phospho-Akt. Furthermore, co-incubation of muscle with insulin+either cytokine yielded glucose oxidation rates that were similar to insulin alone, despite lower (P<0.05) phospho-Akt. Importantly, cytokine-mediated increases in glucose oxidation rates were not concomitant with greater glucose uptake. These results show that acute β2 adrenergic stimulation, but not β1 stimulation, directly increases fractional glucose oxidation in the absence of insulin and synergistically increases glucose oxidation when combined with insulin. The cytokines, TNFα and IL-6, likewise directly increased glucose oxidation in the absence of insulin, but were not additive in combination with insulin and in fact appeared to disrupt Akt-mediated insulin signaling. Rather, cytokines appear to be acting through MAPKs to elicit effects on glucose oxidation. Regardless, stimulation of glucose oxidation by these key stress factors did not rely upon greater glucose uptake, which may promote metabolic efficiency during acute stress by increasing fractional glucose oxidation without increasing total glucose consumption by muscle.

Glucose oxidation positively regulates glucose uptake and improves cardiac function recovery after myocardial reperfusion.

Myocardial reperfusion decreases glucose oxidation and uncouples glucose oxidation from glycolysis. Therapies that increase glucose oxidation lessen myocardial ischemia-reperfusion (I/R) injury. However, the regulation of glucose uptake during reperfusion remains poorly understood. We found that glucose uptake was remarkably diminished in the myocardium following reperfusion in Sprague-Dawley rats as detected by 18F-labeled and fluorescent-labeled glucose analogs, even though GLUT1 was upregulated by threefold and GLUT4 translocation remained unchanged compared with those of sham-treated rats. The decreased glucose uptake was accompanied by suppressed glucose oxidation. Interestingly, stimulating glucose oxidation by inhibition of pyruvate dehydrogenase kinase 4 (PDK4), a rate-limiting enzyme for glucose oxidation, increased glucose uptake and alleviated I/R injury. In vitro data in neonatal myocytes showed that PDK4 overexpression decreased glucose uptake, whereas its knockdown increased glucose uptake, suggesting that PDK4 has a role in regulating glucose uptake. Moreover, inhibition of PDK4 increased myocardial glucose uptake with concomitant enhancement of cardiac insulin sensitivity following myocardial I/R. These results showed that the suppressed glucose oxidation mediated by PDK4 contributes to the reduced glucose uptake in the myocardium following reperfusion, and enhancement of glucose uptake exerts cardioprotection. The findings suggest that stimulating glucose oxidation via PDK4 could be an efficient approach to improve recovery from myocardial I/R injury.

December 2016 at a glance: cardiac metabolism, myocarditis, right ventricular function and prognostic markers.

December 2016 at a glance: cardiac metabolism, myocarditis, right ventricular function and prognostic markers.