Control Of Oxidative Metabolism Research Articles

Natriuretic peptides control of skeletal muscle oxidative metabolism

Besides their well-known effect in the regulation of blood volume, natriuretic peptides have emerged during the last two decades as key metabolic hormones linking cardiac function to energy metabolism. Recent work from our laboratory underscores a new role of these peptides in the control of oxidative metabolism in skeletal muscle and open novel perspectives in the field of chronic diseases affecting skeletal muscles.

16. DEVELOPMENTAL BIOMARKERS OF ENVIRONMENTAL ADVERSITY AND EPIGENETIC RISK FOR MAJOR PSYCHIATRIC DISORDERS: CLUES TO PATHOGENESIS

Overall : Interaction between genetic risks and environmental adversities such as childhood trauma may underlie the etiology of psychiatric disorders. Mechanisms underpinning these interactions are poorly understood. This panel will present new data supporting a model in which epigenetic modifications and increased oxidative stress lead to altered trajectories and patients’ stratification. Helen Fisher will introduce the field, how exposure to severe stress may have immediate as well as long-lasting damaging effects on learning, behaviour, and health, and has been implicated in the development of psychosis. She will present epigenome-wide analyses of poly-victimisation across childhood and adolescence, utilising data from the Environmental Risk (E-Risk) Longitudinal Twin Study, an epidemiological study of 2,232 children (1,116 twin pairs) born in 1994–1995 in England and Wales and followed to 18 years of age. Results related to associations with DNA methylation in peripheral blood at age 18 years, specific forms of victimization and candidate genes in the stress response will be discussed. Luis Alameda will show that childhood trauma (sexual, physical and emotional abuse) engages oxidative stress in a cohort of early psychosis patients (n=118). Patients with high peripheral oxidation status were found to have smaller hippocampal volumes and more severe clinical symptoms, while those with lower oxidation status evidenced a compensatory antioxidant regulation and better cognition. Linear discrimination analysis highlights blood oxidation status together with childhood trauma as markers for poorer psychopathological profile, allowing patients’ stratification. Oussama Kebir will present the first longitudinal prospective study of genomic DNA methylation during psychotic transition in help-seeking young individuals (14 converters, 25 non converters). Alterations in gene promoters and pathways relevant for psychosis, including oxidative stress regulation, axon guidance and inflammatory pathways were observed. In particularly, antioxidant defense gene GTSTM5 is differentially methylated through time and two other genes of GST family might be differentially methylated after conversion to psychosis. These findings suggest that conversion to psychosis may depend on the specific control of oxidative metabolism and regulation between these genes. Darina Czamara will report on how cord blood methylation is affected by genetic and prenatal environment. Analysis on SNP (G) and environmental (E) effects as well as on GxE and G+E were performed using Illumina’s Human Omni Express Exom as well as the 450k DNA methylation array in a cohort of 817 Finnish newborns. G and the combination of G and E explained DNA methylation best, environment alone was almost never the best predictor. Furthermore, epigenetic gestational age was associated with prenatal environment as well as with childhood psychiatric problem at age 3 indicating that it might be used as a potential biomarker.Overall, these new results suggest new biomarkers of environmental and genetic adversity that are related to pathogenic mechanisms, including epigenetic, oxidative stress and structural abnormalities, in epidemiological studies and psychiatric disorders. These biomarkers offer the potential for individualized early intervention and preventive strategies.

An (un)paralleled process?

exercise is challenged because classical biochemical models are unable to explain the increased rate of oxidative ATP production on the basis of altered concentrations of respiratory substrates alone. The paper by Zoladz et al. (2013) exploresparallelactivationtheoryinhuman skeletal muscle by applying innovative reasoning,asfollows:(i) adaptationtofaster oxygenuptakekineticsfollowingendurance exercise training, observed in as few as two training sessions, occurs more rapidly than theexpansionofthemitochondrialvolume, suggesting enhancements of allosteric control in mitochondrial energy supply; and (ii) following training, a more tightly controlled, metabolically stable, parallel system would be accompanied by a reduction in the energy demands of exercise. The data show convincing support for these hypotheses, in that moderateintensity exercise training speeded the kinetics aerobic adjustment during exercise by almost 25% and reduced the oxygen cost of the exercise by nearly 5%; these effects were observed in the absence of changes in markers of mitochondrial respiratory capacity or biogenesis. These human data are consistent with features of parallel control recently demonstrated in single Xenopus myocytes (Gandra et al. 2012) andinthegastrocnemius‐superficialdigital flexorcomplexofthedog(W¨ ustetal.2011). Considering the wide interest in the control of oxidative metabolism during exercise, the molecular mechanisms contributing to kinetic control of oxidative phosphorylation in vivo have received relatively little attention. As such, the training-induced reduction in sarcoplasmic

Regulation of skeletal muscle lipolysis and oxidative metabolism by the co-lipase CGI-58

We investigated here the specific role of CGI-58 in the regulation of energy metabolism in skeletal muscle. We first examined CGI-58 protein expression in various muscle types in mice, and next modulated CGI-58 expression during overexpression and knockdown studies in human primary myotubes and evaluated the consequences on oxidative metabolism. We observed a preferential expression of CGI-58 in oxidative muscles in mice consistent with triacylglycerol hydrolase activity. We next showed by pulse-chase that CGI-58 overexpression increased by more than 2-fold the rate of triacylglycerol (TAG) hydrolysis, as well as TAG-derived fatty acid (FA) release and oxidation. Oppositely, CGI-58 silencing reduced TAG hydrolysis and TAG-derived FA release and oxidation (-77%, P < 0.001), whereas it increased glucose oxidation and glycogen synthesis. Interestingly, modulations of CGI-58 expression and FA release are reflected by changes in pyruvate dehydrogenase kinase 4 gene expression. This regulation involves the activation of the peroxisome proliferator activating receptor-δ (PPARδ) by lipolysis products. Altogether, these data reveal that CGI-58 plays a limiting role in the control of oxidative metabolism by modulating FA availability and the expression of PPARδ-target genes, and highlight an important metabolic function of CGI-58 in skeletal muscle.

Age‐ and sex‐related differences in muscle phosphocreatine and oxygenation kinetics during high‐intensity exercise in adolescents and adults

The aim of this investigation was to examine the adaptation of the muscle phosphates (e.g. phosphocreatine (PCr) and ADP) implicated in regulating oxidative phosphorylation, and oxygenation at the onset of high intensity exercise in children and adults. The hypotheses were threefold: primary PCr kinetics would be faster in children than adults; the amplitude of the PCr slow component would be attenuated in children; and the amplitude of the deoxyhaemoglobin/myoglobin (HHb) slow component would be reduced in children. Eleven children (5 girls, 6 boys, 13 +/- 1 years) and 11 adults (5 women, 6 men, 24 +/- 4 years) completed two to four constant work rate exercise tests within a 1.5 T MR scanner. Quadriceps muscle energetics during high intensity exercise were monitored using (31)P-MRS. Muscle oxygenation was monitored using near-infrared spectroscopy. The time constant for the PCr response was not significantly different in boys (31 +/- 10 s), girls (31 +/- 10 s), men (44 +/- 20 s) or women (29 +/- 14 s, main effects: age, p = 0.37, sex, p = 0.25). The amplitude of the PCr slow component relative to end-exercise PCr was not significantly different between children (23 +/- 23%) and adults (17 +/- 13%, p = 0.47). End-exercise [PCr] was significantly lower, and [ADP] higher, in females (18 +/- 4 mM and 53 +/- 16 microM) than males (23 +/- 4 mM, p = 0.02 and 37 +/- 11 microM, p = 0.02), but did not differ with age ([PCr]: p = 0.96, [ADP]: p = 0.72). The mean response time for muscle tissue deoxygenation was significantly faster in children (22 +/- 4 s) than adults (27 +/- 7 s, p = 0.01). The results of this study show that the control of oxidative metabolism at the onset of high intensity exercise is adult-like in 13-year-old children, but that matching of oxygen delivery to extraction is more precise in adults.

Control of oxidative metabolism in volume-overloaded rat hearts: effect of propionyl-L-carnitine.

The objective of the present work was the assessment of metabolic events responsible for the improvement of hemodynamic function of volume-overloaded hearts from rats receiving propionyl-L-carnitine. A severe cardiac hypertrophy was induced in 2-mo-old rats by surgical opening of an aortocaval communication. Three months later, during in vitro perfusions with 1.2 mM palmitate, 11 mM glucose, and 10 IU/l insulin, the mechanical performance and overall energy turnover (myocardial O2 consumption) of hypertrophied rat hearts were significantly decreased under conditions of moderate and high workloads. These changes in cardiac energetics paralleled the decrease in total tissue carnitine content and alterations in exogenous palmitate oxidation. The oxidative utilization of glucose was also slightly depressed in volume-overloaded hearts while steady-state glycolysis rates increased, especially in hearts subjected to high mechanical loads. This slowing of metabolic pathways involved in acetyl-CoA generation resulted in decreased NADH availability and in an apparent substrate limitation of oxidative phosphorylation suggested by a failure of cytosolic unbound ADP to drive respiration. Long-term administration of propionyl-L-carnitine normalized the degree of reduction of mitochondrial pyridine nucleotides and improved the kinetics of mitochondrial ATP production in volume-overloaded hearts. The resulting acceleration of energy turnover was essentially related to improved oxidative utilization of glucose, but steady-state palmitate oxidation rates also increased in severely hypertrophied hearts. This concomitant acceleration of glucose and palmitate oxidation may be related to the particular experimental conditions (high exogenous palmitate concentrations, elevated workloads) used in this study. We assume that the increase in intracellular carnitine, together with a stimulation of acetyl-CoA demands related to high workloads, creates conditions that are compatible with the simultaneous relief of pyruvate dehydrogenase and carnitine palmitoyltransferase I. The resulting increase in the rate of steady-state ATP production improves, in turn, the mechanical activity of volume-overloaded hearts.

Control of oxidative metabolism in volume-overloaded rat hearts: effect of pretreatment with propionyl-L-carnitine.

Chronic mechanic overloading of the heart has been shown to lead to a significant depletion of tissue carnitine (1,2) that is possibly related to impaired carnitine transport to the myocardium (3, 4). At the same time, the ability of chronically overloaded hearts to oxidize exogenous palmitate is diminished (5, 6). This decrease of long-chain fatty acid utilization is accompanied by reduced myocardial oxygen consumption (MVO2) and gives rise to an impaired mechanical activity during in vitro perfusions (6, 7). Most of the above quoted alterations disappear when exogenous palmitate is replaced by octanoate, a short-chain fatty acid that has free access to mitochondrial matrix (8). This suggests that the respiratory chain of volume-overloaded rat hearts perfused in presence of long-chain fatty acids may be actually substrate limited (7). In this work, we tried to improve NADH delivery to respiratory chain by a prolonged treatment of volume-overloaded rats with millimolar concentrations of propionyl-L-carnitine (9). It has been shown that the administration of this compound significantly increases both blood plasma concentrations and myocardial tissue levels of L-carnitine (10, 11). This, in turn, may improve long chain fatty acid utilization (5) and glucose oxidation (12) via a decreased acetyl-CoA/CoA ratio (13, 14). The control and volume-overloaded hearts were perfused with 11 mM glucose and 1.2 mM palmitate (2.4 mM octanoate) over a range of left ventricular work loads, leading to a progressive increase in the myocardial V02 (7). The respective relationships between the rates of oxidative phosphorylation and different intracellular energy parameters ((cytosolic phosphorylation potential (ATP/ADPf.Pi), ADPf, and mitochondrial NAD+/NADH ratio)) as obtained in control and volume-overloaded hearts were compared for each metabolic condition examined. The effects of the pretreatment with propionyl-L-carnitine on the kinetics of oxidative phosphorylation were tested under conditions of a high work load (heart ejecting against an increased aortic resistance related to the clamp of the aortic outflow line) as described previously (6, 7).

Kinetic analysis of dynamic 13C NMR spectra: metabolic flux, regulation, and compartmentation in hearts

Control of oxidative metabolism was studied using 13C NMR spectroscopy to detect rate-limiting steps in 13C labeling of glutamate. 13C NMR spectra were acquired every 1 or 2 min from isolated rabbit hearts perfused with either 2.5 mM [2-13C]acetate or 2.5 mM [2-13C]butyrate with or without KCl arrest. Tricarboxylic acid cycle flux (VTCA) and the exchange rate between alpha-ketoglutarate and glutamate (F1) were determined by least-square fitting of a kinetic model to NMR data. Rates were compared to measured kinetics of the cardiac glutamate-oxaloacetate transaminase (GOT). Despite similar oxygen use, hearts oxidizing butyrate instead of acetate showed delayed incorporation of 13C label into glutamate and lower VTCA, because of the influence of beta-oxidation: butyrate = 7.1 +/- 0.2 mumol/min/g dry wt; acetate = 10.1 +/- 0.2; butyrate + KCl = 1.8 +/- 0.1; acetate + KCl = 3.1 +/- 0.1 (mean +/- SD). F1 ranged from a low of 4.4 +/- 1.0 mumol/min/g (butyrate + KCl) to 9.3 +/- 0.6 (acetate), at least 20-fold slower than GOT flux, and proved to be rate limiting for isotope turnover in the glutamate pool. Therefore, dynamic 13C NMR observations were sensitive not only to TCA cycle flux but also to the interconversion between TCA cycle intermediates and glutamate.

Intracellular [Ca 2+] and Vo 2 after manipulation of the Free-energy of the Na +/Ca 2+-exchanger in isolated rat ventricular myocytes

We have investigated whether the Na+/Ca(2+)-exchanger has a functional regulatory role in the control of oxidative metabolism in suspensions of isolated rat ventricular myocytes. Therefore we simultaneously measured intracellular [Ca2+] ([Ca2+]i) with Indo-1 and respiratory rate (Vo2) after abrupt manipulation of the free-energy of the Na+/Ca(2+)-exchanger (delta Gexch). The average fraction of viable myocytes was about 90% (82% rod-shaped plus 8% viable round cells). delta Gexch was manipulated either by an abrupt decrease of [Na+]o (in combination with an increase of [K+]o or [Ca2+]o) or by changing membrane potential and/or intracellular cation activities with the use of gramicidin or veratridine. A change of extracellular cation composition caused a transient increase of [Ca2+]i and Vo2, with peak values after 30 to 40 s and a new steady state near control values after 180 to 240 s. Peak values of the transients were associated with the magnitude of the thermodynamic disturbance. Inhibition of sodium-pump activity with ouabain greatly enhanced peak values and reduced the rate of return to a new steady state. Reversal of the initial disturbance of delta Gexch by restoring [Na+]o or reduction of [Ca2+]o during the time course of the transients greatly accelerated return to a new steady-state. An increase of sarcolemmal sodium permeability with the Na-channel ligand veratridine or manipulation of [Na+]i and [K+]i with the Na+/K(+)-exchanger gramicidin caused monophasic increase of both [Ca2+]i and Vo2. The relationship between VO2 and [Ca2+]i was the same, irrespective of the nature of the intervention (either extracellular or intracellular manipulation of delta Gexch). We conclude that cytoplasmic [Ca2+] (thermodynamically controlled by the Na+/Ca(2+)-exchanger) is a major regulator of the respiratory rate in (quiescent) myocytes.

Control of oxidative metabolism in volume-overloaded rat hearts: effects of different lipid substrates

The relationship between intracellular energy parameters and myocardial O2 consumption (VO2) was studied in control and volume-overloaded hearts perfused with different lipid substrates and over a range of left ventricular work loads. In control hearts, a unique linear relationship between log of cytosolic [ATP]/[ADPf].[Pi] (where [ADPf] is concentration of free ADP) and myocardial VO2 was observed between low and high work loads for both fatty acids studied. In volume-overloaded hearts perfused in the presence of exogenous palmitate, the slope of the relationship between log [ATP]/[ADPf].[Pi] and myocardial VO2 was considerably depressed. It would seem that, under these conditions, much of the thermodynamic control of respiratory chain function has been lost. When myocardial VO2 was expressed as a function of cytosolic ADPf, the cytosolic ADPf was not regulatory. This may be related to a substrate limitation of the respiratory chain, as suggested by an excessive oxidation of pyridine nucleotides. When octanoate, instead of palmitate, was used, most of the above limitation of the respiration disappeared. With this substrate, the reduction of mitochondrial pyridine nucleotides in volume-overloaded hearts was similar to that in controls, and the linear relationship between log [ATP]/[ADPf].[Pi] and myocardial VO2 reappeared over the range of work loads studied. The above failure of cytosolic phosphate potential and ADPf to drive respiration when mitochondrial NADH is low fits well with the integrated model of kinetic regulation, as proposed by recent nuclear magnetic resonance studies. our results also indicate that, even at high respiratory rates, free-energy change of ATP synthesis of volume-overloaded hearts can be protected by use of an appropriate substrate. This, in turn, prevents contractile failure.

Interaction between (-)naloxone and morphine in modifying superoxide generation from human granulocytes.

The effect of the opioid agonist morphine and of the (-) and (+) stereoisomers of the antagonist naloxone were studied on superoxide generation from human granulocytes. Morphine or naloxone had no effect on basal or phorbol 12-myristate 13-acetate (PMA)-stimulated superoxide generation. Combined equimolar (-)naloxone and morphine concentrations (0.1 pM-0.1 microM) inhibited PMA-stimulated superoxide generation, while combined (+)naloxone and morphine had no effect. The stereospecific effect of naloxone suggests the involvement of opioid receptors. Thus, inhibition of superoxide generation by combined (-)naloxone and morphine could result from the unmasking of non opioid effects of morphine. It is suggested that the opioid control of oxidative metabolism in human granulocytes could involve multiple receptors mediating opposite effects.

Separation of nucleotides in homogenates of octopus retina by ion-pair reversed-phase liquid chromatography and identification by mass spectrometry

An isocratic ion-pair reversed-phase liquid chromatographic method has been developed for the determination of thirteen nucleotides including cyclic AMP and cyclic GMP. The resolution capability of this method was evaluated successfully using homogenates of octopus retina, the aim being to elucidate the role of nucleotides (particularly ADP and ATP) in the control of oxidative metabolism. To overcome the inherent lack of specificity of ultraviolet detection we used the coupling of liquid chromatography with mass spectrometry, via a thermospray interface, to confirm the identity of the nucleotides of interest in the biological samples.

Oxygen control of oxidative metabolism

Oxygen control of oxidative metabolism

Control of oxidative metabolism and oxygen delivery in human skeletal muscle: a steady-state analysis of the work/energy cost transfer function.

The concept of transfer function for organ performance (work output vs. biochemical input) is developed for skeletal and cardiac muscle under steady-state exercise conditions. For metabolic control by the ADP concentration, the transfer function approximates a Michaelis-Menten hyperbola. Variation of the work identifies metabolic operating points on the transfer function corresponding to ADP concentrations or to a ratio of inorganic phosphate to phosphocreatine that can be determined by phosphorus nuclear magnetic resonance. This operating point is characterized by the fraction (V/Vmax) of maximal activity of oxidative metabolism in the steady state. This quantity appears to be useful in predicting the degree to which metabolic homeostasis is effective; poorly controlled metabolic states can readily be identified and are used in the diagnosis and therapy of metabolic disease in the organs of neonates and adults.