An anabolic state in the heart induced by arginine intubation

Using rat heart perfusion, we found that an anabolic state can be induced with a medium which includes glucose, carnitine, branched-chain amino acids and arginine after arginine intubation at a dose of 250 mg/kg body weight. It showed diminished levels of glutamine, glutamate, branched-chain oxoacids and phenylalanine (a marker of heart protein metabolism) release, reflecting anabolic changes occurring in the myocardium. While ornithine intubation caused a catabolic state in which the release of alanine and glutamate was increased but phenylalanine release was unchanged. This anabolic state may be a useful model providing for myocardial protection.     

Altered metabolism in cancer

Cancer cells have different metabolic requirements from their normal counterparts. Understanding the consequences of this differential metabolism requires a detailed understanding of glucose metabolism and its relation to energy production in cancer cells. A recent study in BMC Systems Biology by Vasquez et al. developed a mathematical model to assess some features of this altered metabolism. Here, we take a broader look at the regulation of energy metabolism in cancer cells, considering their anabolic as well as catabolic needs.     

Interleukin-15 increases glucose uptake in skeletal muscle. An antidiabetogenic effect of the cytokine

Previous studies have demonstrated that interleukin-15 (IL-15) has important anabolic effects on muscle protein metabolism. In the present investigation we have analysed the effects of IL-15 on glucose metabolism in skeletal muscle. Administration of a single dose of the cytokine (100 microg/kg body weight) resulted in a 32% increase on glucose uptake (as measured by the uptake of 2-deoxyglucose) in skeletal muscle. The effects observed on glucose uptake were direct since in vitro incubations of rat EDL muscles in the presence of the cytokine resulted in a 30% increase in glucose uptake. Similarly, IL-15 increased glucose uptake in C2C12 cell cultures, this being related with an increase in both glucose oxidation to CO2 and the incorporation into muscle lipid. The effects of the cytokine were associated with an increase in GLUT-4 mRNA, suggesting a higher effect in insulin sensitivity. In conclusion, the data presented here indicate that IL-15 facilitates glucose metabolism in skeletal muscle and, therefore, a possible role of the cytokine as an antidiabetogenic drug merits future investigations.     

The metabolic architecture of plant cells. Stability of central metabolism and flexibility of anabolic pathways during the growth cycle of tomato cells

The changes in the intermediary metabolism of plant cells were quantified according to growth conditions at three different stages of the growth cycle of tomato cell suspension. Eighteen fluxes of central metabolism were calculated from (13)C enrichments after near steady-state labeling by a metabolic model similar to that described in Dieuaide-Noubhani et al. (Dieuaide-Noubhani, M., Raffard, G., Canioni, P., Pradet, A., and Raymond, P. (1995) J. Biol. Chem. 270, 13147-13159), and 10 net fluxes were obtained directly from end-product accumulation rates. The absolute flux values of central metabolic pathways gradually slowed down with the decrease of glucose influx into the cells. However, the relative fluxes of glycolysis, the pentose-P pathway, and the tricarboxylic acid cycle remained unchanged during the culture cycle at 70, 28, and 40% of glucose influx, respectively, and the futile cycle of sucrose remained high at about 6-fold the glucose influx, independently from carbon nutritional conditions. This natural resistance to flux alterations is referred to as metabolic stability. The numerous anabolic pathways, including starch synthesis, hexose accumulation, biosynthesis of wall polysaccharides, and amino and organic acid biosynthesis were comparatively low and variable. The phosphoenolpyruvate carboxylase flux decreased 5-fold in absolute terms and 2-fold in relation to the glucose influx rate during the culture cycle. We conclude that anabolic fluxes constitute the flexible part of plant cell metabolism that can fluctuate in relation to cell demands for growth.     

Distinct pathways regulate facilitated glucose transport in human articular chondrocytes during anabolic and catabolic responses

Articular cartilage is an avascular, non-insulin-sensitive tissue that utilizes glucose as the main energy source, a precursor for glycosaminoglycan synthesis, and a regulator of gene expression. Facilitated glucose transport represents the first rate-limiting step in glucose metabolism. Previously, we demonstrated that glucose transport in chondrocytes is regulated by proinflammatory cytokines via upregulation of GLUT mRNA and protein expression. The objective of the present study was to determine differences in molecular mechanisms regulating glucose transport in chondrocytes stimulated with the anabolic transforming growth factor-beta1 (TGF-beta1) vs. the catabolic and proinflammatory cytokine IL-1beta. Both TGF-beta1 and IL-1beta accelerate glucose transport in chondrocytes. Although both IL-1beta and TGF-beta1 enhance glucose transport in chondrocytes to a similar magnitude, IL-1beta induces significantly higher levels of lactate. TGF-beta1-stimulated glucose transport is not associated with increased expression or membrane incorporation of GLUT1, -3, -6, -8, and -10 and depends on PKC and ERK activation. In contrast, IL-1beta-stimulated glucose transport is accompanied by increased expression and membrane incorporation of GLUT1 and -6 and depends upon activation of PKC and p38 MAP kinase. In conclusion, anabolic and catabolic stimuli regulate facilitated glucose transport in human articular chondrocytes via different effector and signaling mechanisms, and they have distinct effects on glycolysis.     

The glucose effect: carbohydrate repression of enzyme induction, RNA synthesis, and glucocorticoid activity -- a role for cyclic AMP and cyclic GMP.

Feeding a variety of carbohydrates (but not all carbohydrates) to mammals results in blocking the induction of many enzymes involved in amino acid metabolism as well as stimulation of some enzymes which participate in glucose utilization. In addition, glucocorticoid activity, both catabolic and anabolic, is inhibited; alterations in nuclear morphology become apparent, and m-RNA synthesis is greatly depressed. Evidence clearly opposes the mediation of the glucose effect by insulin. In bacteria, similar events following glucose feeding are caused by a 90% drop in cyclic AMP levels. But only a relatively small (20%) reduction occurs in mammals; however, the concentration of the antagonist of cyclic AMP — cyclic GMP — is considerably increased, thereby producing a functional decrease in the activity of cyclic AMP. Some, not all, of the glucose effect can be reproduced by the administration of bromo-cyclic-GMP, indicating that part of the glucose effect is mediated by elevation of the guanosine cyclic nucleotide.     

Interleukin-15 increases glucose uptake in skeletal muscle An antidiabetogenic effect of the cytokine

Previous studies have demonstrated that interleukin-15 (IL-15) has important anabolic effects on muscle protein metabolism. In the present investigation we have analysed the effects of IL-15 on glucose metabolism in skeletal muscle. Administration of a single dose of the cytokine (100 μg/kg body weight) resulted in a 32% increase on glucose uptake (as measured by the uptake of 2-deoxyglucose) in skeletal muscle. The effects observed on glucose uptake were direct since in vitro incubations of rat EDL muscles in the presence of the cytokine resulted in a 30% increase in glucose uptake. Similarly, IL-15 increased glucose uptake in C2C12 cell cultures, this being related with an increase in both glucose oxidation to CO₂ and the incorporation into muscle lipid. The effects of the cytokine were associated with an increase in GLUT-4 mRNA, suggesting a higher effect in insulin sensitivity. In conclusion, the data presented here indicate that IL-15 facilitates glucose metabolism in skeletal muscle and, therefore, a possible role of the cytokine as an antidiabetogenic drug merits future investigations.     

The metabolic network of Lactococcus lactis: distribution of (14)C-labeled substrates between catabolic and anabolic pathways

Lactococcus lactis NCDO 2118 was grown in a simple synthetic medium containing only six essential amino acids and glucose as carbon substrates to determine qualitatively and quantitatively the carbon fluxes into the metabolic network. The specific rates of substrate consumption, product formation, and biomass synthesis, calculated during the exponential growth phase, represented the carbon fluxes within the catabolic and anabolic pathways. The macromolecular composition of the biomass was measured to distribute the global anabolic flux into the specific anabolic pathways. Finally, the distribution of radiolabeled substrates, both into the excreted fermentation end products and into the different macromolecular fractions of biomass, was monitored. The classical end products of lactic acid metabolism (lactate, formate, and acetate) were labeled with glucose, which did not label other excreted products, and to a lesser extent with serine, which was deaminated to pyruvate and represented approximately 10% of the pyruvate flux. Other minor products, keto and hydroxy acids, were produced from glutamate and branched-chain amino acids via deamination and subsequent decarboxylation and/or reduction. Glucose labeled all biomass fractions and accounted for 66% of the cellular carbon, although this represented only 5% of the consumed glucose.     

Respiratory pathways and oxygen toxicity in Phanerochaete chrysosporium

Phanerochaete chrysosporium maintained on glucose as the carbon source contained severely impaired mitochondria that were characterised by the loss of both succinate dehydrogenase and cytochrome oxidase activities. These cells maintained a constant value for energy charge using anaerobic metabolism. Cells with these properties express lignin peroxidase when supplied with a pure oxygen atmosphere, which may reflect a response to accumulating reactive oxygen species. Cells maintained on cellulose retained fully functional mitochondria, but expressed lignin peroxidase without being exposed to a pure oxygen atmosphere. In the cells maintained on cellulose, mitochondrial function may be limited by the supply of glucose, leading to the accumulation of reactive oxygen species.     

Precursors for liver gluconeogenesis in periparturient dairy cows

The review is based on a compiled data set from studies quantifying liver release of glucose concomitant with uptake of amino acids (AA) and other glucogenic precursors in periparturient dairy cows. It has become dogma that AAs are significant contributors to liver gluconeogenesis in early lactation, presumably accounting for the observed lack of glucogenic precursors to balance estimated glucose need. Until recently, there has been paucity in quantitative data on liver nutrient metabolism in the periparturient period. Propionate is the quantitatively most important glucogenic precursor throughout the periparturient period. However, the immediate post partum increment in liver release of glucose is not followed by an equivalent increment in propionate uptake, because of the lower rate of increment in feed intake compared with the rate of increment in requirements for milk synthesis. The quantitative data on liver metabolism of AA do not support the hypothesis that the rapid post partum increase in net liver release of glucose is supported by increased utilisation of AA for gluconeogenesis. Only alanine is likely to contribute to liver release of glucose through its role in the inter-organ transfer of nitrogen from catabolised AA. AAs seem to be prioritised for anabolic purposes, indicating the relevance of investigating effects of supplying additional protein to post partum dairy cows. Combining data from quantitative and qualitative experimental techniques on L-lactate metabolism point to the conclusion that the quantitatively most important adaptation of metabolism to support the increased glucose demand in the immediate post partum period is endogenous recycling of glucogenic carbon through lactate. This is mediated by a dual site of adaptation of metabolism in the liver and in the peripheral tissues, where the liver affinity for L-lactate is increased and glucose metabolism in peripheral tissues is shifted towards L-lactate formation over complete oxidation.     

Involvement of nitrogen metabolism in the triggering of ethanol fermentation in aerobic chemostat cultures of Saccharomyces cerevisiae.

We have investigated whether central nitrogen metabolism may influence the triggering of ethanol fermentation in Saccharomyces cerevisiae strain CEN.PK122 grown in the presence of different N-sources (ammonia, glutamate, or glutamine) under conditions in which the carbon to nitrogen (C : N) ratio was varied. An exhaustive quantitative evaluation of yeast physiology and metabolic behavior through metabolic flux analysis (MFA) was undertaken. It is shown that ethanol fermentation is triggered at dilution rates, D (growth rate), significantly lower (D=0.070 and 0.074 h(-1) for glutamate and glutamine, respectively, and D=0.109 h(-1) for ammonia) under N- than C-limitation (approximately 0.18 h(-1) for all N-sources). A characteristic specific rate of glucose influx, q(Glc), for each N-source at Dc, i.e., just before the onset of respirofermentative metabolism, was determined (approximately 2.0, 1.5, and 2.5, for ammonia, glutamate, and glutamine, respectively). This q(Glc) was independent of the nutritional limitation though dependent on the nature of the N-source. The onset of fermentation occurs when this "threshold q(Glc)" is overcome. The saturation of respiratory activity appears not to be associated with the onset of fermentation since q(O(2)) continued to increase after Dc. It was remarkable that under respirofermentative conditions in C-limited chemostat cultures, the glucose consumed was almost completely fermented with biomass being synthesized from glutamate through gluconeogenesis. The results obtained show that the enzyme activities involved in central nitrogen metabolism do not appear to participate in the control of the overflow in carbon catabolism, which is driven toward ethanol production. The role of nitrogen metabolism in the onset of ethanol fermentation would rather be realized through its involvement in setting the anabolic fluxes directed to nitrogenous macromolecules. It seems that nitrogen-related anabolic fluxes would determine when the threshold glucose consumption rate is achieved after which ethanol fermentation is triggered.     

Metabolism of glucose by preimplantation mouse embryos in the presence of glucagon, insulin, epinephrine, cAMP, theophylline and caffeine

Neither insulin nor epinephrine influenced the incorporation of glucose into the acid-soluble or acid-insoluble glycogen pool of mouse embryos at the morula-early blastocyst stage during 5 h culture in the presence of radiolabelled glucose. During a 5 h chase culture of pulse-labelled embryos at this stage of development, acid-soluble glycogen labelled during the pulse was not utilized by the embryo but acid-insoluble glycogen was reduced. Addition of glucagon, insulin, epinephrine, cAMP, theophylline or caffeine during chase culture had no effect on the turnover of label in the glycogen pools of the embryo. These results indicate that the turnover of embryonic glycogen observed in vivo is not due to the direct effect of the hormones that regulate glycogen metabolism in the mother. Insulin was found to stimulate incorporation of glucose into non-glycogen macromolecules during both pulse and chase culture. Thus, whilst an effect of insulin on glycogen metabolism was absent, the anabolic effects of this hormone appear to have been expressed in the embryo at this stage of development.     

Effects of growth hormone in patients with chronic renal failure: experience in children and adults

Recombinant human growth hormone (GH) has proven effective in promoting growth in short children with chronic renal failure before and after renal transplantation. The action of GH and its mediator insulin-like growth factor 1 on body composition, protein, glucose and bone metabolism offers additional therapeutic options. One might be the improvement of the catabolic state in adults with end-stage renal failure. In few pilot studies and two placebo-controlled studies of 6 months duration, GH treatment in adults on dialysis showed clear anabolic effects resulting in a significant increase in lean body mass.     

Short-term metabolome dynamics and carbon, electron, and ATP balances in chemostat-grown Saccharomyces cerevisiae CEN.PK 113-7D following a glucose pulse

The in vivo kinetics in Saccharomyces cerevisiae CEN.PK 113-7D was evaluated during a 300-second transient period after applying a glucose pulse to an aerobic, carbon-limited chemostat culture. We quantified the responses of extracellular metabolites, intracellular intermediates in primary metabolism, intracellular free amino acids, and in vivo rates of O(2) uptake and CO(2) evolution. With these measurements, dynamic carbon, electron, and ATP balances were set up to identify major carbon, electron, and energy sinks during the postpulse period. There were three distinct metabolic phases during this time. In phase I (0 to 50 seconds after the pulse), the carbon/electron balances closed up to 85%. The accumulation of glycolytic and storage compounds accounted for 60% of the consumed glucose, caused an energy depletion, and may have led to a temporary decrease in the anabolic flux. In phase II (50 to 150 seconds), the fermentative metabolism gradually became the most important carbon/electron sink. In phase III (150 to 300 seconds), 29% of the carbon uptake was not identified in the measurements, and the ATP balance had a large surplus. These results indicate an increase in the anabolic flux, which is consistent with macroscopic balances of extracellular fluxes and the observed increase in CO(2) evolution associated with nonfermentative metabolism. The identified metabolic processes involving major carbon, electron, and energy sinks must be taken into account in in vivo kinetic models based on short-term dynamic metabolome responses.     

Short-Term Metabolome Dynamics and Carbon, Electron, and ATP Balances in Chemostat-Grown Saccharomyces cerevisiae CEN.PK 113-7D following a Glucose Pulse

The in vivo kinetics in Saccharomyces cerevisiae CEN.PK 113-7D was evaluated during a 300-second transient period after applying a glucose pulse to an aerobic, carbon-limited chemostat culture. We quantified the responses of extracellular metabolites, intracellular intermediates in primary metabolism, intracellular free amino acids, and in vivo rates of O₂ uptake and CO₂ evolution. With these measurements, dynamic carbon, electron, and ATP balances were set up to identify major carbon, electron, and energy sinks during the postpulse period. There were three distinct metabolic phases during this time. In phase I (0 to 50 seconds after the pulse), the carbon/electron balances closed up to 85%. The accumulation of glycolytic and storage compounds accounted for 60% of the consumed glucose, caused an energy depletion, and may have led to a temporary decrease in the anabolic flux. In phase II (50 to 150 seconds), the fermentative metabolism gradually became the most important carbon/electron sink. In phase III (150 to 300 seconds), 29% of the carbon uptake was not identified in the measurements, and the ATP balance had a large surplus. These results indicate an increase in the anabolic flux, which is consistent with macroscopic balances of extracellular fluxes and the observed increase in CO₂ evolution associated with nonfermentative metabolism. The identified metabolic processes involving major carbon, electron, and energy sinks must be taken into account in in vivo kinetic models based on short-term dynamic metabolome responses.     

Effect of zwf gene knockout on the metabolism of Escherichia coli grown on glucose or acetate

The mutant deficient in glucose-6-phosphate dehydrogenase (G6PDH) was constructed by disrupting zwf gene by one-step inactivation protocol using polymerase chain reaction primers. The knockout of zwf gene was shown to have different influence on the metabolism of Escherichia coli grown on glucose or acetate. The decreased rates of substrate uptake and CO(2) production were found for the mutant grown on acetate, whereas these two rates were increased during the growth on glucose. The metabolic flux analysis based on (13)C-labeling experiments indicates that the metabolism of the mutant grown on glucose is related to the higher flux via tricorboxylic acid (TCA) cycle to generate anabolic reducing equivalents normally provided by the oxidative pentose phosphate pathway. However, the metabolism of the mutant grown on acetate shows a lower flux towards the TCA cycle as compared with the parent strain. The decreased flux through TCA cycle is associated with an increased flux via the glyoxylate shunt, by which the carbon source can bypass the two decarboxylative steps of TCA cycle in which CO(2) is released, thus conserving more carbon for biosynthesis in response to the decreased uptake rate of the carbon source.     

Heterogeneity in tumor cell energetic metabolome at different cell cycle phases of human colon cancer cell lines

In this present study, the efficacy of metabolomics as a tool for tumor cell energetics for in vitro cell cultures was demonstrated with full competence for the first time by elucidating the anabolic and energy-yielding segments of glycolysis and glutaminolysis, which constitute a part of energy metabolism in tumor cells. By synchronizing colon cancer cells SW480 and SW620 in culture, the metabolome specific to cell cycle phases was analyzed using nuclear magnetic resonance spectroscopy. At the G₁/S transition of the cell cycle (i.e. transition from cell growth to duplication of genetic material), the majority of the energy production was realized by glycolysis through a high channeling of glucose carbons towards lactate. During the late S phase, the majority of energy was produced by glutaminolysis through a high channeling of glutamine carbons towards lactate, while the glucose carbons were channeled towards bio-synthetic pathways. These results indicate that the metabolism of proliferating cells is heterogeneous throughout the cell cycle and can be better interpreted on the basis of different cell cycle phases. These findings could be exploited for the development of a tool for tumor diagnosis as well as for targeting tumors.