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Chen J, Singh TK, Al Nemri S, Zaidi M, Billingsley KL, Park JM. Hyperpolarized [1- 13C]Acetyl-l-Carnitine Probes Tricarboxylic Acid Cycle Activity In Vivo. ACS Sens 2023; 8:2927-2932. [PMID: 37578472 PMCID: PMC11227661 DOI: 10.1021/acssensors.3c01046] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/15/2023]
Abstract
Mitochondrial oxidative phosphorylation (OXPHOS) is sensitive to a variety of biological factors, and dysregulated OXPHOS is observed during the development of numerous pathological conditions. ATP production via OXPHOS is intrinsically dependent on the availability of acetyl-coenzyme A (CoA), which can enter the tricarboxylic acid (TCA) cycle to drive the oxidative pathway. Acetyl-l-carnitine (ALCAR) is an interchangeable endogenous source of acetyl-CoA, and therefore, ALCAR-derived probes are uniquely positioned for the assessment of OXPHOS. In this report, we develop hyperpolarized (HP) [1-13C]ALCAR as a noninvasive probe to investigate cardiac TCA cycle activity in vivo. We initially synthesized the isotopically labeled substrate and demonstrated that the 13C nucleus maintained a suitable T1 value (50.1 ± 0.8 s at 3 T) and polarization levels (21.3 ± 5.3%) to execute in vivo metabolic measurements. HP [1-13C]ALCAR was employed for cardiac analyses of OXPHOS in rats under fed and fasted conditions. [5-13C]Glutamate was successfully detected, and the metabolite was used to analyze the TCA cycle activity in both nutritional states. These assessments were compared to analogous experiments with the HP [1-13C]pyruvate. Our report represents the first study to demonstrate that HP methods using [1-13C]ALCAR enable direct analyses of mitochondrial function and TCA cycle activity, which are fundamental to cardiac cell homeostasis.
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Affiliation(s)
- Jun Chen
- Advanced Imaging Research Center, The University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States
| | - Tamara K Singh
- Department of Chemistry and Biochemistry, California State University, Fullerton, California 92831, United States
| | - Sarah Al Nemri
- Advanced Imaging Research Center, The University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States
| | - Maheen Zaidi
- Advanced Imaging Research Center, The University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States
| | - Kelvin L Billingsley
- Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, Illinois 60660, United States
| | - Jae Mo Park
- Advanced Imaging Research Center, The University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States
- Department of Biomedical Engineering, The University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States
- Department of Radiology, The University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States
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Abstract
The heart is a biological pump that converts chemical to mechanical energy. This process of energy conversion is highly regulated to the extent that energy substrate metabolism matches energy use for contraction on a beat-to-beat basis. The biochemistry of cardiac metabolism includes the biochemistry of energy transfer, metabolic regulation, and transcriptional, translational as well as posttranslational control of enzymatic activities. Pathways of energy substrate metabolism in the heart are complex and dynamic, but all of them conform to the First Law of Thermodynamics. The perspectives expand on the overall idea that cardiac metabolism is inextricably linked to both physiology and molecular biology of the heart. The article ends with an outlook on emerging concepts of cardiac metabolism based on new molecular models and new analytical tools. © 2016 American Physiological Society. Compr Physiol 6:1675-1699, 2016.
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Affiliation(s)
- Heinrich Taegtmeyer
- Division of Cardiology, Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston
| | - Truong Lam
- Division of Cardiology, Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston
| | - Giovanni Davogustto
- Division of Cardiology, Department of Internal Medicine, McGovern Medical School at The University of Texas Health Science Center at Houston
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Bastiaansen JAM, Merritt ME, Comment A. Measuring changes in substrate utilization in the myocardium in response to fasting using hyperpolarized [1-(13)C]butyrate and [1-(13)C]pyruvate. Sci Rep 2016; 6:25573. [PMID: 27150735 PMCID: PMC4858671 DOI: 10.1038/srep25573] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Accepted: 04/20/2016] [Indexed: 12/26/2022] Open
Abstract
Cardiac dysfunction is often associated with a shift in substrate preference for ATP production. Hyperpolarized (HP) 13C magnetic resonance spectroscopy (MRS) has the unique ability to detect real-time metabolic changes in vivo due to its high sensitivity and specificity. Here a protocol using HP [1-13C]pyruvate and [1-13C]butyrate is used to measure carbohydrate versus fatty acid metabolism in vivo. Metabolic changes in fed and fasted Sprague Dawley rats (n = 36) were studied at 9.4 T after tail vein injections. Pyruvate and butyrate competed for acetyl-CoA production, as evidenced by significant changes in [13C]bicarbonate (−48%), [1-13C]acetylcarnitine (+113%), and [5-13C]glutamate (−63%), following fasting. Butyrate uptake was unaffected by fasting, as indicated by [1-13C]butyrylcarnitine. Mitochondrial pseudoketogenesis facilitated the labeling of the ketone bodies [1-13C]acetoacetate and [1-13C]β-hydroxybutyryate, without evidence of true ketogenesis. HP [1-13C]acetoacetate was increased in fasting (250%) but decreased during pyruvate co-injection (−82%). Combining HP 13C technology and co-administration of separate imaging agents enables noninvasive and simultaneous monitoring of both fatty acid and carbohydrate oxidation. This protocol illustrates a novel method for assessing metabolic flux through different enzymatic pathways simultaneously and enables mechanistic studies of the changing myocardial energetics often associated with disease.
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Affiliation(s)
- Jessica A M Bastiaansen
- Department of Radiology, University Hospital Lausanne (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland.,Laboratory of Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | - Matthew E Merritt
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
| | - Arnaud Comment
- Institute of Physics of Biological Systems, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
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Kuzmiak-Glancy S, Jaimes R, Wengrowski AM, Kay MW. Oxygen demand of perfused heart preparations: how electromechanical function and inadequate oxygenation affect physiology and optical measurements. Exp Physiol 2016; 100:603-16. [PMID: 25865254 DOI: 10.1113/ep085042] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Accepted: 04/09/2015] [Indexed: 01/22/2023]
Abstract
NEW FINDINGS What is the topic of this review? This review discusses how the function and electrophysiology of isolated perfused hearts are affected by oxygenation and energy utilization. The impact of oxygenation on fluorescence measurements in perfused hearts is also discussed. What advances does it highlight? Recent studies have illuminated the inherent differences in electromechanical function, energy utilization rate and oxygen requirements between the primary types of excised heart preparations. A summary and analysis of how these variables affect experimental results are necessary to elevate the physiological relevance of these approaches in order to advance the field of whole-heart research. The ex vivo perfused heart recreates important aspects of in vivo conditions to provide insight into whole-organ function. In this review we discuss multiple types of ex vivo heart preparations, explain how closely each mimic in vivo function, and discuss how changes in electromechanical function and inadequate oxygenation of ex vivo perfused hearts may affect measurements of physiology. Hearts that perform physiological work have high oxygen demand and are likely to experience hypoxia when perfused with a crystalloid perfusate. Adequate myocardial oxygenation is critically important for obtaining physiologically relevant measurements, so when designing experiments the type of ex vivo preparation and the capacity of perfusate to deliver oxygen must be carefully considered. When workload is low, such as during interventions that inhibit contraction, oxygen demand is also low, which could dramatically alter a physiological response to experimental variables. Changes in oxygenation also alter the optical properties of cardiac tissue, an effect that may influence optical signals measured from both endogenous and exogenous fluorophores. Careful consideration of oxygen supply, working condition, and wavelengths used to acquire optical signals is critical for obtaining physiologically relevant measurements during ex vivo perfused heart studies.
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Affiliation(s)
- Sarah Kuzmiak-Glancy
- Department of Biomedical Engineering, The George Washington University, Washington, DC, USA
| | - Rafael Jaimes
- Department of Biomedical Engineering, The George Washington University, Washington, DC, USA
| | - Anastasia M Wengrowski
- Department of Biomedical Engineering, The George Washington University, Washington, DC, USA
| | - Matthew W Kay
- Department of Biomedical Engineering, The George Washington University, Washington, DC, USA.,Department of Pharmacology and Physiology, The George Washington University, Washington, DC, USA
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Bastiaansen JA, Cheng T, Lei H, Gruetter R, Comment A. Direct noninvasive estimation of myocardial tricarboxylic acid cycle flux in vivo using hyperpolarized 13C magnetic resonance. J Mol Cell Cardiol 2015; 87:129-37. [DOI: 10.1016/j.yjmcc.2015.08.012] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Revised: 07/27/2015] [Accepted: 08/12/2015] [Indexed: 11/28/2022]
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Jin ES, Sherry AD, Malloy CR. Evidence for transaldolase activity in the isolated heart supplied with [U-13C3]glycerol. J Biol Chem 2012; 288:2914-22. [PMID: 23235149 DOI: 10.1074/jbc.m112.409441] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Studies of glycerol metabolism in the heart have largely emphasized its role in triglyceride synthesis. However, glycerol may also be oxidized in the citric acid cycle, and glycogen synthesis from glycerol has been reported in the nonmammalian myocardium. The intent of this study was to test the hypothesis that glycerol may be metabolized to glycogen in mammalian heart. Isolated rat hearts were supplied with a mixture of substrates including glucose, lactate, pyruvate, octanoate, [U-(13)C(3)]glycerol, and (2)H(2)O to probe various metabolic pathways including glycerol oxidation, glycolysis, the pentose phosphate pathway, and carbon sources of stored glycogen. NMR analysis confirmed that glycogen production from the level of the citric acid cycle did not occur and that the glycerol contribution to oxidation in the citric acid cycle was negligible in the presence of alternative substrates. Quite unexpectedly, (13)C from [U-(13)C(3)]glycerol appeared in glycogen in carbon positions 4-6 of glucosyl units but none in positions 1-3. The extent of [4,5,6-(13)C(3)]glucosyl unit enrichment in glycogen was enhanced by insulin but decreased by H(2)O(2). Given that triose phosphate isomerase is generally assumed to fully equilibrate carbon tracers in the triose pool, the marked (13)C asymmetry in glycogen can only be attributed to conversion of [U-(13)C(3)]glycerol to [U-(13)C(3)]dihydroxyacetone phosphate and [U-(13)C(3)]glyceraldehyde 3-phosphate followed by rearrangements in the nonoxidative branch of the pentose phosphate pathway involving transaldolase that places this (13)C-enriched 3-carbon unit only in the bottom half of hexose phosphate molecules contributing to glycogen.
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Affiliation(s)
- Eunsook S Jin
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
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Moreno KX, Sabelhaus SM, Merritt ME, Sherry AD, Malloy CR. Competition of pyruvate with physiological substrates for oxidation by the heart: implications for studies with hyperpolarized [1-13C]pyruvate. Am J Physiol Heart Circ Physiol 2010; 298:H1556-64. [PMID: 20207817 DOI: 10.1152/ajpheart.00656.2009] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Carbon 13 nuclear magnetic resonance (NMR) isotopomer analysis was used to measure the rates of oxidation of long-chain fatty acids, ketones, and pyruvate to determine the minimum pyruvate concentration ([pyruvate]) needed to suppress oxidation of these alternative substrates. Substrate mixtures were chosen to represent either the fed or fasted state. At physiological [pyruvate], fatty acids and ketones supplied the overwhelming majority of acetyl-CoA. Under conditions mimicking the fed state, 3 mM pyruvate provided approximately 80% of acetyl-CoA, but under fasting conditions 6 mM pyruvate contributed only 33% of acetyl-CoA. Higher [pyruvate], 10-25 mM, was associated with transient reduced cardiac output, but overall hemodynamic performance was unchanged after equilibration. These observations suggested that 3-6 mM pyruvate in the coronary arteries would be an appropriate target for studies with hyperpolarized [1-(13)C]pyruvate. However, the metabolic products of 3 mM hyperpolarized [1-(13)C]pyruvate could not be detected in the isolated heart during perfusion with a physiological mixture of substrates including 3% albumin. In the presence of albumin even at high concentrations of pyruvate, 20 mM, hyperpolarized H(13)CO(3)(-) could be detected only in the absence of competing substrates. Highly purified albumin (but not albumin from plasma) substantially reduced the longitudinal relaxation time of [1-(13)C]pyruvate. In conclusion, studies of cardiac metabolism using hyperpolarized [1-(13)C]pyruvate are sensitive to the effects of competing substrates on pyruvate oxidation.
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Affiliation(s)
- Karlos X Moreno
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390, USA
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Merritt ME, Harrison C, Storey C, Sherry AD, Malloy CR. Inhibition of carbohydrate oxidation during the first minute of reperfusion after brief ischemia: NMR detection of hyperpolarized 13CO2 and H13CO3-. Magn Reson Med 2009; 60:1029-36. [PMID: 18956454 DOI: 10.1002/mrm.21760] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Isolated rat hearts were studied by (31)P NMR and (13)C NMR. Hyperpolarized [1-(13)C]pyruvate was supplied to control normoxic hearts and production of [1-(13)C]lactate, [1-(13)C]alanine, (13)CO(2) and H(13)CO(-) (3) was monitored with 1-s temporal resolution. Hearts were also subjected to 10 min of global ischemia followed by reperfusion. Developed pressure, heart rate, oxygen consumption, [ATP], [phosphocreatine], and pH recovered within 3 min after the ischemic period. During the first 90 s of reperfusion, [1-(13)C]alanine and [1-(13)C]lactate appeared rapidly, demonstrating metabolism of pyruvate through two enzymes largely confined to the cytosol, alanine aminotransferase, and lactate dehydrogenase. (13)CO(2) and H(13)CO(-) (3) were not detected. Late after ischemia and reperfusion, the products of pyruvate dehydrogenase, (13)CO(2) and H(13)CO(-) (3) were easily detected. Using this multinuclear NMR approach, we established that during the first 90 s of reperfusion PDH flux is essentially zero and recovers within 20 min in reversibly-injured myocardium.
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Affiliation(s)
- Matthew E Merritt
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
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9
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Hyperpolarized 13C allows a direct measure of flux through a single enzyme-catalyzed step by NMR. Proc Natl Acad Sci U S A 2007; 104:19773-7. [PMID: 18056642 DOI: 10.1073/pnas.0706235104] [Citation(s) in RCA: 222] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
(13)C NMR is a powerful tool for monitoring metabolic fluxes in vivo. The recent availability of automated dynamic nuclear polarization equipment for hyperpolarizing (13)C nuclei now offers the potential to measure metabolic fluxes through select enzyme-catalyzed steps with substantially improved sensitivity. Here, we investigated the metabolism of hyperpolarized [1-(13)C(1)]pyruvate in a widely used model for physiology and pharmacology, the perfused rat heart. Dissolved (13)CO(2), the immediate product of the first step of the reaction catalyzed by pyruvate dehydrogenase, was observed with a temporal resolution of approximately 1 s along with H(13)CO(3)(-), the hydrated form of (13)CO(2) generated catalytically by carbonic anhydrase. In hearts presented with the medium-chain fatty acid octanoate in addition to hyperpolarized [1-(13)C(1)]pyruvate, production of (13)CO(2) and H(13)CO(3)(-) was suppressed by approximately 90%, whereas the signal from [1-(13)C(1)]lactate was enhanced. In separate experiments, it was shown that O(2) consumption and tricarboxylic acid (TCA) cycle flux were unchanged in the presence of added octanoate. Thus, the rate of appearance of (13)CO(2) and H(13)CO(3)(-) from [1-(13)C(1)]pyruvate does not reflect production of CO(2) in the TCA cycle but rather reflects flux through pyruvate dehydrogenase exclusively.
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Sharma N, Okere IC, Brunengraber DZ, McElfresh TA, King KL, Sterk JP, Huang H, Chandler MP, Stanley WC. Regulation of pyruvate dehydrogenase activity and citric acid cycle intermediates during high cardiac power generation. J Physiol 2004; 562:593-603. [PMID: 15550462 PMCID: PMC1665507 DOI: 10.1113/jphysiol.2004.075713] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
A high rate of cardiac work increases citric acid cycle (CAC) turnover and flux through pyruvate dehydrogenase (PDH); however, the mechanisms for these effects are poorly understood. We tested the hypotheses that an increase in cardiac energy expenditure: (1) activates PDH and reduces the product/substrate ratios ([NADH]/[NAD(+)] and [acetyl-CoA]/[CoA-SH]); and (2) increases the content of CAC intermediates. Measurements were made in anaesthetized pigs under control conditions and during 15 min of a high cardiac workload induced by dobutamine (Dob). A third group was made hyperglycaemic (14 mm) to stimulate flux through PDH during the high work state (Dob + Glu). Glucose and fatty acid oxidation were measured with (14)C-glucose and (3)H-oleate. Compared with control, the high workload groups had a similar increase in myocardial oxygen consumption ( and cardiac power. Dob increased PDH activity and glucose oxidation above control, but did not reduce the [NADH]/[NAD(+)] and [acetyl-CoA]/[CoA-SH] ratios, and there were no differences between the Dob and Dob + Glu groups. An additional group was treated with Dob + Glu and oxfenicine (Oxf) to inhibit fatty acid oxidation: this increased [CoA-SH] and glucose oxidation compared with Dob; however, there was no further activation of PDH or decrease in the [NADH]/[NAD(+)] ratio. Content of the 4-carbon CAC intermediates succinate, fumarate and malate increased 3-fold with Dob, but there was no change in citrate content, and the Dob + Glu and Dob + Glu + Oxf groups were not different from Dob. In conclusion, compared with normal conditions, at high myocardial energy expenditure (1) the increase in flux through PDH is regulated by activation of the enzyme complex and continues to be partially controlled through inhibition by fatty acid oxidation, and (2) there is expansion of the CAC pool size at the level of 4-carbon intermediates that is largely independent of myocardial fatty acid oxidation.
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Affiliation(s)
- Naveen Sharma
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4970, USA
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Panchal AR, Comte B, Huang H, Kerwin T, Darvish A, des Rosiers C, Brunengraber H, Stanley WC. Partitioning of pyruvate between oxidation and anaplerosis in swine hearts. Am J Physiol Heart Circ Physiol 2000; 279:H2390-8. [PMID: 11045976 DOI: 10.1152/ajpheart.2000.279.5.h2390] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The goal of this study was to measure flux through pyruvate carboxylation and decarboxylation in the heart in vivo. These rates were measured in the anterior wall of normal anesthetized swine hearts by infusing [U-(13)C(3)]lactate and/or [U-(13)C(3)] pyruvate into the left anterior descending (LAD) coronary artery. After 1 h, the tissue was freeze-clamped and analyzed by gas chromatography-mass spectrometry for the mass isotopomer distribution of citrate and its oxaloacetate moiety. LAD blood pyruvate and lactate enrichments and concentrations were constant after 15 min of infusion. Under near-normal physiological concentrations of lactate and pyruvate, pyruvate carboxylation and decarboxylation accounted for 4.7 +/- 0.3 and 41.5 +/- 2.0% of citrate formation, respectively. Similar relative fluxes were found when arterial pyruvate was raised from 0.2 to 1.1 mM. Addition of 1 mM octanoate to 1 mM pyruvate inhibited pyruvate decarboxylation by 93% without affecting carboxylation. The absence of M1 and M2 pyruvate demonstrated net irreversible pyruvate carboxylation. Under our experimental conditions we found that pyruvate carboxylation in the in vivo heart accounts for at least 3-6% of the citric acid cycle flux despite considerable variation in the flux through pyruvate decarboxylation.
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Affiliation(s)
- A R Panchal
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106-4970, USA
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Yu X, Alpert NM, Lewandowski ED. Modeling enrichment kinetics from dynamic 13C-NMR spectra: theoretical analysis and practical considerations. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 272:C2037-48. [PMID: 9227433 DOI: 10.1152/ajpcell.1997.272.6.c2037] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Measurements of oxidative metabolism in the heart from dynamic 13C nuclear magnetic resonance (NMR) spectroscopy rely on 13C turnover in the NMR-detectable glutamate pool. A kinetic model was developed for the analysis of isotope turnover to determine tricarboxylic acid cycle flux (VTCA) and the interconversion rate between alpha-ketoglutarate and glutamate (F1) by fitting the model to NMR data of glutamate enrichment. The results of data fitting are highly reproducible when the noise level is within 10%, making this model applicable to single or grouped experiments. The values for VTCA and F1 were unchanged whether obtained from least-squares fitting of the model to mean experimental enrichment data with standard deviations in the cost function (VTCA = 10.52 mumol.min-1.g dry wt-1, F1 = 10.67 mumol.min-1.g dry wt-1) or to the individual enrichment values for each heart with the NMR noise level in the cost function (VTCA = 10.67 mumol.min-1.g dry wt-1, F1 = 10.18 mumol.min-1.g dry wt-1). Computer simulation and theoretical analysis indicate that glutamate enrichment kinetics are insensitive to the fractional enrichment of acetyl-CoA and changes in small intermediate pools (< 1 mumol/g dry wt). Therefore, high-resolution NMR analysis of tissue extracts and biochemical assays for intermediates at low concentrations are unnecessary. However, a high correlation between VTCA and F1 exists, as anticipated from competition for alpha-ketoglutarate, which indicates the utility of introducing independent experimental constraints into the data fitting for accurate quantification.
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Affiliation(s)
- X Yu
- Nuclear Magnetic Resonance Center, Massachusetts General Hospital, Boston, USA
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Utility and Limitations of [18F]2-Deoxy-2-Fluoro-D-Glucose for the Assessment of Flux through Metabolic Pathways in Heart Muscle: A Critical Appraisal. ACTA ACUST UNITED AC 1996. [DOI: 10.1007/978-1-4613-1233-8_4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/28/2023]
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15
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Hotchkiss RS, Song SK, Neil JJ, Chen RD, Manchester JK, Karl IE, Lowry OH, Ackerman JJ. Sepsis does not impair tricarboxylic acid cycle in the heart. THE AMERICAN JOURNAL OF PHYSIOLOGY 1991; 260:C50-7. [PMID: 1987781 DOI: 10.1152/ajpcell.1991.260.1.c50] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Sepsis has been reported to cause mitochondrial dysfunction and inhibition of key enzymes that regulate the tricarboxylic acid (TCA) cycle. We investigated the effect of sepsis on high-energy phosphates, glycolytic and TCA cycle intermediates, and specific amino acids that are involved in regulating the size of the TCA cycle pool during changes in metabolic state of the heart. Sepsis was induced in 12 female rats by the cecal ligation and perforation technique under halothane anesthesia; seven control rats underwent cecal manipulation without ligation. At 36-42 h postsurgery, the rats were reanesthetized, the chest was opened, and the hearts were freeze-clamped. Perchloric acid extracts of the hearts were analyzed with fluorometric enzymatic methods and 31P nuclear magnetic resonance spectroscopy. There were no significant differences in the levels of the TCA cycle intermediates or high-energy phosphates between the septic and control rats. The major metabolic changes were the 28% decrease in alanine and the 31% decrease in glutamate in the septic hearts compared with control (P less than 0.05 and P less than 0.005, respectively). Phosphocholine, a component of membrane phospholipids, was increased by 91% in the septic hearts (P less than 0.01). We conclude that sepsis does not impair the TCA cycle or induce significant cellular ischemia in the heart. The increase in phosphocholine may represent significant cellular membrane disruption during sepsis.
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Affiliation(s)
- R S Hotchkiss
- Department of Anesthesiology, Washington University School of Medicine, St. Louis 63110
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16
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Boyer B, Odessey R. Quantitative control analysis of branched-chain 2-oxo acid dehydrogenase complex activity by feedback inhibition. Biochem J 1990; 271:523-8. [PMID: 2241928 PMCID: PMC1149586 DOI: 10.1042/bj2710523] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The potential for branched-chain 2-oxo acid dehydrogenase complex (BCOADC) activity to be controlled by feedback inhibition was investigated by calculating the Elasticity Coefficients for several feedback inhibitors. We suggest that feedback inhibition is a quantitatively important regulatory mechanism by which branched-chain 2-oxo acid dehydrogenase activity is regulated. The potential for control of enzyme activity is greater for NADH than for the acyl-CoA products, and suggests that factors that alter the redox potential may physiologically regulate BCOADC activity through a feedback inhibitory mechanism in vivo. Local pH may also be an important regulatory control factor.
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Affiliation(s)
- B Boyer
- Louisiana State University Medical Center, Department of Physiology, New Orleans 70112
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18
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Relations between the energy state of the myocardium and release of some products of anaerobic metabolism during underperfusion. Pflugers Arch 1990; 416:434-41. [PMID: 2399116 DOI: 10.1007/bf00370751] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The relations between parameters of cellular energy and the release of succinate, alanine and creatine from isolated, isovolumic guinea pig hearts were studied during underperfusion (0.2 ml/min) with glucose or acetate. The heart work index (the product of the left ventricular pressure and the heart rate), tissue ATP and phosphocreatine contents did not depend upon the nature of the substrate when coronary flow was 19 ml/min. However, 50 min underperfusion with acetate resulted in a twofold increase in diastolic pressure, while glucose prevented the development of contracture. A more rapid ATP depletion accompanied by an increased succinate and creatine release was observed during underperfusion with acetate as compared with glucose. Succinate and alanine accumulation in myocardial effluent was related to a decrease in tissue ATP, while creatine release showed a close, inverse correlation with the tissue phosphocreatine/creatine ratio. Hyperbolic and linear relations were found between these indices for glucose- and acetate-perfused hearts, respectively. The results suggest that the determination of succinate, creatine and alanine in myocardial effluent may be used for assessment of the energy status of the ischemic heart.
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19
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Bagger JP. Effects of antianginal drugs on myocardial energy metabolism in coronary artery disease. PHARMACOLOGY & TOXICOLOGY 1990; 66 Suppl 4:1-31. [PMID: 2181432 DOI: 10.1111/j.1600-0773.1990.tb01609.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- J P Bagger
- Department of Cardiology, Skejby Sygehus, Aarhus, Denmark
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Birkhahn RH, Awad S, Klaunig JE, Thomford NR. Interaction of ketosis and liver regeneration in the rat. J Surg Res 1989; 47:427-32. [PMID: 2509817 DOI: 10.1016/0022-4804(89)90096-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Monoacetoacetin, the monoglyceride of acetoacetate, was investigated as a nutritional support for the regenerating liver. Following partial hepatectomy, rats were either fed an oral diet ad libitum or administered by total parenteral feeding glucose alone, monoacetoacetin-glucose mixture, or lipid emulsion-glucose for the nonprotein calories. Five rats from each treatment were killed at 6-hr intervals beginning 12 hr after partial hepatectomy and ending at 72 hr. The number of cells synthesizing DNA and the number of cells in mitosis were compared. Rats fed orally or infused with glucose alone or with lipid emulsion had similar parameters throughout. Rats infused with monoacetoacetin had approximately double the number of cells in mitosis and DNA synthesis compared to the other treatments. This stimulation by monoacetoacetin persisted 72 hr. It was concluded from the data that acetoacetate was the agent responsible for increased DNA synthesis and mitosis, but the mechanism for the stimulation was not identified.
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Affiliation(s)
- R H Birkhahn
- Department of Surgery, Medical College of Ohio, Toledo 43699
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Wiesner RJ, Kreutzer U, Rösen P, Grieshaber MK. Subcellular distribution of malate-aspartate cycle intermediates during normoxia and anoxia in the heart. BIOCHIMICA ET BIOPHYSICA ACTA 1988; 936:114-23. [PMID: 2902879 DOI: 10.1016/0005-2728(88)90258-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The subcellular distribution of adenine nucleotides, phosphocreatine and intermediates of the malate-aspartate cycle was investigated in adult rat heart myocytes under normoxia and anoxia. Cytosolic and mitochondrial concentrations of metabolites were determined by a fractionation method using digitonin. Under normoxia, cytosolic/mitochondrial gradients were found for ATP (c/m = 4), AMP (c/m less than 0.01), citrate (c/m = 0.5), aspartate (c/m = 3), glutamate (c/m = 2), while phosphocreatine and glutamine were confined to the cytosolic space. No gradients were found for malate and 2-oxoglutarate. The results show that the transport of electrons from the cytosol into the mitochondria is supported by the glutamate gradient and by a high glutamate/aspartate ratio inside the mitochondria (Glu/Asp = 15) which is maintained by the energy-dependent Glu-Asp exchange across the mitochondrial membrane. Under anoxia, cytosolic glutamate is transaminated with pyruvate, yielding alanine and 2-oxoglutarate, which is oxidized to succinate inside the mitochondria and leaves the cell. The data indicate that stimulation of transamination is caused by a mass action effect following a decrease in cytosolic 2-oxoglutarate which may be due to succinate-2-oxoglutarate exchange across the mitochondrial membrane. Inhibition of the energy-dependent inward transport of glutamate may support this process.
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Affiliation(s)
- R J Wiesner
- Institut für Zoologie, Lehrstuhl für Tierphysiologie, Düsseldorf, F.R.G
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Evaluation of carbon flux and substrate selection through alternate pathways involving the citric acid cycle of the heart by 13C NMR spectroscopy. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(18)68590-4] [Citation(s) in RCA: 261] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Birkhahn RH, Askari A, Thomford NR. The influence of ketosis on the metabolic response to skeletal trauma. J Surg Res 1988; 44:160-5. [PMID: 3123802 DOI: 10.1016/0022-4804(88)90044-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Intravenous glucose and ketone body feeding were compared for their potential in altering urinary nitrogen losses by the traumatized rat. Eighteen male rats were traumatized by bilateral femoral fracture. The rats were fed totally by vein for 3 days prior and 3 days after injury and the infusion rate was held constant over the 6 days of infusion. Group GT rats were fed glucose as the source of nonprotein energy while group MT rats were fed a mixture of 72% monoacetoacetin (the monoglyceride of acetoacetate)-28% glucose for the nonprotein energy. Total urinary nitrogen excretion on a 24-hr basis was measured for each of the 6 days of intravenous feeding. On the third day post-trauma, each rat was evaluated for leucine kinetics using a continuous infusion of L-[1-14C]leucine and measurement of breath and plasma specific activities. Rats from group MT were hyperketonemic and normoglycemic and rats from group GT were normoketonemic and hyperglycemic. Urinary nitrogen losses, leucine oxidation, and leucine turnover were similar for the two groups. We conclude that ketone bodies are as good an intravenous source of energy as is glucose, and the ketone bodies do not cause hyperglycemia.
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Affiliation(s)
- R H Birkhahn
- Department of Surgery, Medical College of Ohio, Toledo 43699
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Malloy CR, Sherry AD, Jeffrey FM. Carbon flux through citric acid cycle pathways in perfused heart by 13C NMR spectroscopy. FEBS Lett 1987; 212:58-62. [PMID: 2879743 DOI: 10.1016/0014-5793(87)81556-9] [Citation(s) in RCA: 138] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Mathematical models of the TCA cycle derived previously for 14C tracer studies have been extended to 13C NMR to measure the 13C fractional enrichment of [2-13C]acetyl-CoA entering the cycle and the relative activities of the oxidative versus anaplerotic pathways. The analysis is based upon the steady-state enrichment of 13C into the glutamate carbons. Hearts perfused with [2-13C]acetate show low but significant activity of the anaplerotic pathways. Activation of two different anaplerotic pathways is demonstrated by addition of unlabeled propionate or pyruvate to hearts perfused with [2-13C]acetate. In each case, the amount of [2-13C]acetate being oxidized and the relative carbon flux through anaplerotic versus oxidative pathways are evaluated.
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Kerckaert I, Roels F. Myocardial H2O2 production in the unanaesthetized rat. Influence of fasting, myocardial load and inhibition of superoxide dismutase and monoamine oxidase. Basic Res Cardiol 1986; 81:83-91. [PMID: 3013154 DOI: 10.1007/bf01907430] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Myocardial H2O2 production was studied by means of the in vivo administration of aminotriazole (AT), which inactivates the catalase-H2O2 complex compound I. Measurements of the residual catalase activity in male and female rats indicate that beta-oxidation of fatty acids in peroxisomes does not contribute in a substantial way to energy production in response to fasting or to an increased myocardial load, despite previous data on peroxisomes in myocardium. Superoxide dismutase (SOD) inhibition by diethyldithiocarbamate demonstrates that SOD participates in the production of H2O2 in physiological conditions. Such a role was not demonstrated for monoamine oxidase through inhibition by phenelzine.
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