Krebs Cycle (Kreb + cycle)

Distribution by Scientific Domains

Selected Abstracts

13C-breath tests for clinical investigation of liver mitochondrial function

Ignazio Grattagliano
Eur J Clin Invest 2010; 40 (9): 843,850 Abstract Background, Mitochondria play a major role in cell energetic metabolism; therefore, mitochondrial dysfunction inevitably participates in or even determines the onset and progression of chronic liver diseases. The assessment of mitochondrial function in vivo, by providing more insight into the pathogenesis of liver diseases, would be a helpful tool to study specific hepatic functions and to develop rational diagnostic, prognostic and therapeutic strategies. Design, This review focuses on the utility of breath tests to assess mitochondrial function in humans and experimental animals. Results, The introduction in the clinical setting of specific breath tests may allow elegantly and noninvasively overcoming the difficulties caused by previous complex techniques and might provide clinically relevant information, i.e the effects of drugs on mitochondria. Substrates meeting this requirement are alpha-keto-isocaproic acid and methionine that are both decarboxylated by mitochondria. Long-and medium-chain fatty acids that are metabolized through the Krebs cycle, and benzoic acid which undergoes glycine conjugation, may also reflect the function of mitochondria. Conclusions, Breath tests to assess in vivo mitochondrial function in humans represent a potentially useful diagnostic and prognostic tool in clinical investigation. [source]

Effects of aluminum on activity of Krebs cycle enzymes and glutamate dehydrogenase in rat brain homogenate

FEBS JOURNAL, Issue 10 2000
P. Zatta
Aluminum is a neurotoxic agent for animals and humans that has been implicated as an etiological factor in several neurodegenerative diseases and as a destabilizer of cell membranes. Due to its high reactivity, Al3+ is able to interfere with several biological functions, including enzymatic activities in key metabolic pathways. In this paper we report that, among the enzymes that constitute the Krebs cycle, only two are activated by aluminum: ,-ketoglutarate dehydrogenase and succinate dehydrogenase. In contrast, aconitase, shows decreased activity in the presence of the metal ion. Al3+ also inhibits glutamate dehydrogenase, an allosteric enzyme that is closely linked to the Krebs cycle. A possible correlation between aluminum, the Krebs cycle and aging processes is discussed. [source]

Phosphorylation status of pyruvate dehydrogenase distinguishes metabolic phenotypes of cultured rat brain astrocytes and neurons

GLIA, Issue 10 2010
Nader D. Halim
Abstract Glucose metabolism in nervous tissue has been proposed to occur in a compartmentalized manner with astrocytes contributing largely to glycolysis and neurons being the primary site of glucose oxidation. However, mammalian astrocytes and neurons both contain mitochondria, and it remains unclear why in culture neurons oxidize glucose, lactate, and pyruvate to a much larger extent than astrocytes. The objective of this study was to determine whether pyruvate metabolism is differentially regulated in cultured neurons versus astrocytes. Expression of all components of the pyruvate dehydrogenase complex (PDC), the rate-limiting step for pyruvate entry into the Krebs cycle, was determined in cultured astrocytes and neurons. In addition, regulation of PDC enzymatic activity in the two cell types via protein phosphorylation was examined. We show that all components of the PDC are expressed in both cell types in culture, but that PDC activity is kept strongly inhibited in astrocytes through phosphorylation of the pyruvate dehydrogenase alpha subunit (PDH,). In contrast, neuronal PDC operates close to maximal levels with much lower levels of phosphorlyated PDH,. Dephosphorylation of astrocytic PDH, restores PDC activity and lowers lactate production. Our findings suggest that the glucose metabolism of astrocytes and neurons may be far more flexible than previously believed. 2010 Wiley-Liss, Inc. [source]

Mitochondrial A, A potential cause of metabolic dysfunction in Alzheimer's disease

IUBMB LIFE, Issue 12 2006
Xi Chen
Abstract Deficits in mitochondrial function are a characteristic finding in Alzheimer's disease (AD), though the mechanism remains to be clarified. Recent studies revealed that amyloid , peptide (A,) gains access into mitochondrial matrix, which was much more pronounced in both AD brain and transgenic mutant APP mice than in normal controls. A, progressively accumulates in mitochondria and mediates mitochondrial toxicity. Interaction of mitochondrial A, with mitochondrial enzymes such as amyloid , binding alcohol dehydrogenase (ABAD) exaggerates mitochondrial stress by inhibiting the enzyme activity, releasing reactive oxygen species (ROS), and affecting glycolytic, Krebs cycle and/or the respiratory chain pathways through the accumulation of deleterious intermediate metabolites. The pathways proposed may play a key role in the pathogenesis of this devastating neurodegenerative disorder, Alzheimer's disease. iubmb Life, 58: 686-694, 2006 [source]

Distribution of carbon-14 labeled C60 ([14C]C60) in the pregnant and in the lactating dam and the effect of C60 exposure on the biochemical profile of urine

Susan C. J. Sumner
Abstract This study was conducted to determine the distribution of [14C]C60 in the pregnant rat and fetuses, and in the lactating rat and offspring. Pregnant rats were dosed on gestation day (gd) 15 and lactating rats were dosed on postnatal day (pnd) 8 via tail vein injection with a suspension of ,0.3,mg [14C]C60,kg,1 body weight prepared in polyvinylpyrrolidone (PVP), or with PVP alone. Tissues were collected at 24 and 48 h after dosing. The largest portion of the administered dose was detected in the liver (,43%, pregnant dam; ,35%, lactating dam) and lung (,25%, lactating dam). Radioactivity (,6%) was distributed to the reproductive tract, placenta and fetuses of the pregnant dam. Lactating rats had radioactivity distributed to the milk (3140,dpm,g,1 tissue, 24,h; 1620,dpm,g,1 tissue, 48,h), and to the pups' GI tract (2.8%, 24,h; 4.4% 48,h) and liver (<1%). Blood radioactivity was significant at 24,h (14,19%) and at 48,h (7%) after dosing; largely accounted for in the plasma fraction. Less that 4% of the dose was recovered in the maternal spleen, heart, brain, urine or feces. Metabolomics analysis of urine indicated that dams exposed to [14C]C60 had decreased metabolites derived from the Krebs cycle and increased metabolites derived from the urea cycle or glycolysis, as well as alterations in the levels of some sulfur-containing amino acids and purine/pyrimidine metabolites. This study demonstrated that [14C]C60 crosses the placenta and is transmitted to offspring via the dam's milk and subsequently systemically absorbed. Copyright 2009 John Wiley & Sons, Ltd. [source]

Proteomic Analysis Demonstrates Adolescent Vulnerability to Lasting Hippocampal Changes Following Chronic Alcohol Consumption

ALCOHOLISM, Issue 1 2009
Garth A. Hargreaves
Background:, Excessive teenage alcohol consumption is of great concern because alcohol may adversely alter the developmental trajectory of the brain. The aim of the present study was to assess whether chronic intermittent alcohol intake during the adolescent period alters hippocampal protein expression to a greater extent than during adulthood. Methods:, Adolescent [postnatal day (PND) 27] and adult (PND 55) male Wistar rats were given 8 hours daily access to beer (4.44% ethanol v/v) in addition to ad libitum food and water for 4 weeks. From a large subject pool, subgroups of adolescent and adult rats were selected that displayed equivalent alcohol intake (average of 6.1 g/kg/day ethanol). The 4 weeks of alcohol access were followed by a 2-week alcohol-free washout period after which the hippocampus was analyzed using 2-DE proteomics. Results:, Beer consumption by the adult group resulted in modest hippocampal changes relative to alcohol nave adult controls. The only changes observed were an up-regulation of citrate synthase (a precursor to the Krebs cycle) and fatty acid binding protein (which facilitates fatty acid metabolism). In contrast, adolescent rats consuming alcohol showed more widespread hippocampal changes relative to adolescent controls. These included an increase in cytoskeletal protein T-complex protein 1 subunit epsilon (TCP-1) and a decrease in the expression of 10 other proteins, including glyceraldehyde-3-phosphate dehydrogenase (GAPDH), triose phosphate isomerise, alpha-enolase, and phosphoglycerate kinase 1 (all involved in glycolysis); glutamate dehydrogenase 1 (an important regulator of glutamate); methylmalonate-semialdehyde dehydrogenase (involved in aldehyde detoxification); ubiquitin carboxyl-terminal hydrolase isozyme L1 (a regulator of protein degradation); and synapsin 2 (involved in synaptogenesis and neurotransmitter release). Conclusions:, These results suggest the adolescent hippocampus is more vulnerable to lasting proteomic changes following repeated alcohol exposure. The proteins most affected include those related to glycolysis, glutamate metabolism, neurodegeneration, synaptic function, and cytoskeletal structure. [source]

Utilization of citrate and lactate through a lactate dehydrogenase and ATP-regulated pathway in boar spermatozoa

Antonio Medrano
Abstract Incubation of boar spermatozoa in Krebs,Ringer,Henseleit medium with either 10 mM lactate or 10 mM citrate induced a fast and robust increase in the intracellular levels of ATP in both cases, which reached a peak after 30 sec of incubation. Utilization of both citrate and lactate resulted in the export of CO2 to the extracellular medium, indicating that both substrates were metabolized through the Krebs cycle. Incubation with citrate resulted in the generation of extracellular lactate, which was inhibited in the presence of phenylacetic acid. This indicates that lactate is produced through the pyruvate carboxylase step. In addition, there was also a significant increase in tyrosine phosphorylation induced by both citrate and lactate. Boar sperm has a sperm-specific isoform of lactate dehydrogenase (LDH), mainly located in the principal piece of the tail. Kinetic studies showed that boar sperm has at least two distinct LDH activities. The major activity (with an estimated Km of 0.51 mM) was located in the supernatants of sperm extracts. The minor LDH activity (with an estimated Km of 5.9 mM) was associated with the nonsoluble fraction of sperm extracts. Our results indicate that boar sperm efficiently metabolizes citrate and lactate through a metabolic pathway regulated by LDH. Mol. Reprod. Dev. 2005 Wiley-Liss, Inc. [source]

Integration of [U- 13C]glucose and 2H2O for quantification of hepatic glucose production and gluconeogenesis

Rui Perdigoto
Abstract Glucose metabolism in five healthy subjects fasted for 16,h was measured with a combination of [U- 13C]glucose and 2H2O tracers. Phenylbutyric acid was also provided to sample hepatic glutamine for the presence of 13C-isotopomers derived from the incorporation of [U- 13C]glucose products into the hepatic Krebs cycle. Glucose production (GP) was quantified by 13C NMR analysis of the monoacetone derivative of plasma glucose following a primed infusion of [U- 13C]glucose and provided reasonable estimates (1.90,,0.19,mg/kg/min with a range of 1.60,2.15,mg/kg/min). The same derivative yielded measurements of plasma glucose 2H-enrichment from 2H2O by 2H NMR from which the contribution of glycogenolytic and gluconeogenic fluxes to GP was obtained (0.87,,0.14 and 1.03,,0.10,mg/kg/min, respectively). Hepatic glutamine 13C-isotopomers representing multiply-enriched oxaloacetate and [U- 13C]acetyl-CoA were identified as multiplets in the 13C NMR signals of the glutamine moiety of urinary phenylacetylglutamine, demonstrating entry of the [U- 13C]glucose tracer into both oxidative and anaplerotic pathways of the hepatic Krebs cycle. These isotopomers contributed 0.1,0.2% excess enrichment to carbons 2 and 3 and ,0.05% to carbon 4 of glutamine. Copyright 2003 John Wiley & Sons, Ltd. [source]

The Effect of Irradiance on Carboxylating/Decarboxylating Enzymes and Fumarase Activities in Mesembryanthemum crystallinum L. Exposed to Salinity Stress

PLANT BIOLOGY, Issue 1 2001
Z. Miszalski
Abstract: In Mesembryanthemum crystallinum plants, treated for 9 days with 0.4 M NaCl at low light intensities (80 - 90 or 95 - 100 ,E m -2 s -1; , = 400 - 700 nm), no day/night malate level differences (,malate) were detected. At high light (385 - 400 ,E m -2 s -1) strong stimulation of PEPC activity, accompanied by a ,malate of 11.3 mM, demonstrated the presence of CAM metabolism. This indicates that, to evolve day/night differences in malate concentration, high light is required. Salt treatment at low light induces and increases the activity of NAD- and NADP-malic enzymes by as much as 3.7- and 3.9-fold, while at high light these values reach 6.4- and 17.7-fold, respectively. The induction of activity of both malic enzymes and PEPC (phospoenolpyruvate carboxylase) take place before ,malate is detectable. An increase in SOD (superoxide dismutase) was observed in plants cultivated at high light in both control and salt-treated plants. However, in salt-treated plants this effect was more pronounced. Carboxylating and decarboxylating enzymes seem to be induced by a combination of different signals, i.e., salt and light intensity. Plants performing CAM, after the decrease of activity of both the decarboxylating enzymes at the beginning of the light period, showed an increase in these enzymes in darkness when the malate pool reaches higher levels. In CAM plants the activity of fumarase (Krebs cycle) is much lower than that in C3 plants. The role of mitochondria in CAM plants is discussed. [source]

Dynamics of the Dictyostelium discoideum mitochondrial proteome during vegetative growth, starvation and early stages of development

Malgorzata Czarna
Abstract In this study, a quantitative comparative proteomics approach has been used to analyze the Dictyostelium discoideum mitochondrial proteome variations during vegetative growth, starvation and the early stages of development. Application of 2-D DIGE technology allowed the detection of around 2000 protein spots on each 2-D gel with 180 proteins exhibiting significant changes in their expression level. In total, 96 proteins (51 unique and 45 redundant) were unambiguously identified. We show that the D. discoideum mitochondrial proteome adaptations mainly affect energy metabolism enzymes (the Krebs cycle, anaplerotic pathways, the oxidative phosphorylation system and energy dissipation), proteins involved in developmental and signaling processes as well as in protein biosynthesis and fate. The most striking observations were the opposite regulation of expression of citrate synthase and aconitase and the very large variation in the expression of the alternative oxidase that highlighted the importance of citrate and alternative oxidase in the physiology of the development of D. discoideum. Mitochondrial energy states measured in vivo with MitoTracker Orange CMRos showed an increase in mitochondrial membrane polarization during D. discoideum starvation and starvation-induced development. [source]

Alterations in Brain Glucose Utilization Accompanying Elevations in Blood Ethanol and Acetate Concentrations in the Rat

ALCOHOLISM, Issue 2 2010
Robert J. Pawlosky
Background:, Previous studies in humans have shown that alcohol consumption decreased the rate of brain glucose utilization. We investigated whether the major metabolite of ethanol, acetate, could account for this observation by providing an alternate to glucose as an energy substrate for brain and the metabolic consequences of that shift. Methods:, Rats were infused with solutions of sodium acetate, ethanol, or saline containing 13C-2-glucose as a tracer elevating the blood ethanol (BEC) and blood acetate (BAcC) concentrations. After an hour, blood was sampled and the brains of animals were removed by freeze blowing. Tissue samples were analyzed for the intermediates of glucose metabolism, Krebs' cycle, acyl-coenzyme A (CoA) compounds, and amino acids. Results:, Mean peak BEC and BAcC were approximately 25 and 0.8 mM, respectively, in ethanol-infused animals. Peak blood BAcC increased to 12 mM in acetate-infused animals. Both ethanol and acetate infused animals had a lower uptake of 13C-glucose into the brain compared to controls and the concentration of brain 13C-glucose-6-phosphate varied inversely with the BAcC. There were higher concentrations of brain malonyl-CoA and somewhat lower levels of free Mg2+ in ethanol-treated animals compared to saline controls. In acetate-infused animals the concentrations of brain lactate, ,-ketoglutarate, and fumarate were higher. Moreover, the free cytosolic [NAD+]/[NADH] was lower, the free mitochondrial [NAD+]/[NADH] and [CoQ]/[CoQH2] were oxidized and the ,G, of ATP lowered by acetate infusion from ,61.4 kJ to ,59.9 kJ/mol. Conclusions:, Animals with elevated levels of blood ethanol or acetate had decreased 13C-glucose uptake into the brain. In acetate-infused animals elevated BAcC were associated with a decrease in 13C-glucose phosphorylation. The co-ordinate decrease in free cytosolic NAD, oxidation of mitochondrial NAD and Q couples and the decrease in ,G, of ATP was similar to administration of uncoupling agents indicating that the metabolism of acetate in brain caused the mitochondrial voltage dependent pore to form. [source]