C R Malloy

University of Texas Southwestern Medical Center, Dallas, Texas, United States

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Publications (240)997.09 Total impact

  • Jimin Ren, A Dean Sherry, Craig R Malloy
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    ABSTRACT: The goal of this study was to amplify the effects of magnetization exchange between γ-adenosine triphosphate (ATP) and inorganic phosphate (Pi) for evaluation of ATP synthesis rates in human skeletal muscle. The strategy works by simultaneously inverting the (31) P resonances of phosphocreatine (PCr) and ATP using a wide bandwidth, adiabatic inversion radiofrequency pulse followed by observing dynamic changes in intensity of the noninverted Pi signal versus the delay time between the inversion and observation pulses. This band inversion technique significantly delays recovery of γ-ATP magnetization; consequently, the exchange reaction, Pi ↔ γ-ATP, is readily detected and easily analyzed. The ATP synthesis rate measured from high-quality spectral data using this method was 0.073 ± 0.011 s(-1) in resting human skeletal muscle (N = 10). The T1 of Pi was 6.93 ± 1.90 s, consistent with the intrinsic T1 of Pi at this field. The apparent T1 of γ-ATP was 4.07 ± 0.32 s, about two-fold longer than its intrinsic T1 due to storage of magnetization in PCr. Band inversion provides an effective method to amplify the effects of magnetization transfer between γ-ATP and Pi. The resulting data can be easily analyzed to obtain the ATP synthesis rate using a two-site exchange model. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc. © 2014 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 12/2014; · 3.27 Impact Factor
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    ABSTRACT: The heart requires a continuous supply of energy but has little capacity for energy storage and thus relies on exogenous metabolic sources. We previously showed that cardiac MED13 modulates systemic energy homeostasis in mice. Here, we sought to define the extra-cardiac tissue(s) that respond to cardiac MED13 signaling. We show that cardiac overexpression of MED13 in transgenic (MED13cTg) mice confers a lean phenotype that is associated with increased lipid uptake, beta-oxidation and mitochondrial content in white adipose tissue (WAT) and liver. Cardiac expression of MED13 decreases metabolic gene expression in the heart but enhances them in WAT. Although exhibiting increased energy expenditure in the fed state, MED13cTg mice metabolically adapt to fasting. Furthermore, MED13cTg hearts oxidize fuel that is readily available, rendering them more efficient in the fed state. Parabiosis experiments in which circulations of wild-type and MED13cTg mice are joined, reveal that circulating factor(s) in MED13cTg mice promote enhanced metabolism and leanness. These findings demonstrate that MED13 acts within the heart to promote systemic energy expenditure in extra-cardiac energy depots and point to an unexplored metabolic communication system between the heart and other tissues. © 2014 The Authors. Published under the terms of the CC BY 4.0 license.
    EMBO Molecular Medicine 11/2014; · 7.80 Impact Factor
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    ABSTRACT: Glycogenolysis and gluconeogenesis are sensitive to nutritional state and the net direction of flux is controlled by multiple enzymatic steps. This delicate balance in the liver is disrupted by a variety of pathological states including cancer and diabetes mellitus. Hyperpolarized (HP) carbon-13 magnetic resonance (MR) is a new metabolic imaging technique that can probe intermediary metabolism nondestructively. There are currently no methods to rapidly distinguish livers in a gluconeogenic from glycogenolytic state. Here we use the gluconeogenic precursor dihydroxyacetone (DHA) to deliver hyperpolarized carbon-13 to the perfused mouse liver. DHA enters gluconeogenesis at the level of the trioses. Perfusion conditions were designed to establish either a gluconeogenic or glycogenolytic state. Unexpectedly we found that [2-(13)C]DHA was metabolized within a few seconds to the common intermediates and end-products of both glycolysis and gluconeogenesis under both conditions, including [2,5-(13)C]glucose, [2-(13)C]glycerol-3-phosphate, [2-(13)C]phosphoenolpyruvate (PEP), [2-(13)C]pyruvate, [2-(13)C]alanine, and [2-(13)C]lactate. [2-(13)C]Phosphoenolpyruvate, a key branch point in gluconeogenesis and glycolysis was monitored in functioning tissue for the first time. Observation of [2-(13)C]PEP was not anticipated as the free energy difference between PEP and pyruvate is large. Pyruvate kinase is the only regulatory step of the common glycolytic - gluconeogenic pathway that appears to exert significant control over the kinetics of any metabolites of DHA. A ratio of glycolytic to gluconeogenic products distinguished the gluconeogenic from glycogenolytic state in these functioning livers.
    The Journal of biological chemistry. 10/2014;
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    ABSTRACT: Flux through pyruvate dehydrogenase (PDH) in the heart may be reduced by various forms of injury to the myocardium, or by oxidation of alternative substrates in normal heart tissue. It is important to distinguish these two mechanisms because imaging of flux through PDH based on the appearance of hyperpolarized (HP) [(13)C]bicarbonate derived from HP [1-(13)C]pyruvate has been proposed as a method for identifying viable myocardium. The efficacy of propionate for increasing PDH flux in the setting of PDH inhibition by an alternative substrate was studied using isotopomer analysis paired with exams using HP [1-(13)C]pyruvate. Hearts from C57/bl6 mice were supplied with acetate (2 mM) and glucose (8.25 mM). (13)C NMR spectra were acquired in a cryogenically cooled probe at 14.1 Tesla. After addition of hyperpolarized [1-(13)C]pyruvate, (13)C NMR signals from lactate, alanine, malate, and aspartate were easily detected, in addition to small signals from bicarbonate and CO2. The addition of propionate (2 mM) increased appearance of HP [(13)C]bicarbonate >30-fold without change in O2 consumption. Isotopomer analysis of extracts from the freeze-clamped hearts indicated that acetate was the preferred substrate for energy production, glucose contribution to energy production was minimal, and anaplerosis was stimulated in the presence of propionate. Under conditions where production of acetyl-CoA is dominated by the availability of an alternative substrate, acetate, propionate markedly stimulated PDH flux as detected by the appearance of hyperpolarized [(13)C]bicarbonate from metabolism of hyperpolarized [1-(13)C]pyruvate.
    AJP Heart and Circulatory Physiology 10/2014; 307(8):H1134-41. · 4.01 Impact Factor
  • Eunsook S Jin, A Dean Sherry, Craig R Malloy
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    ABSTRACT: After exposure to [U-13C3]glycerol, the liver produces primarily [1,2,3-13C3]- and [4,5,6-13C3]glucose in equal proportions through gluconeogenesis from the level of trioses. Other 13C labeling patterns occur as a consequence of alternative pathways for glucose production. The pentose phosphate pathway (PPP), metabolism in the citric acid cycle, incomplete equilibration by triose phosphate isomerase, or the transaldolase reaction all interact to produce complex 13C labeling patterns in exported glucose. Here we investigated 13C labeling in plasma glucose in rats given [U-13C3]glycerol under various nutritional conditions. Blood was drawn at multiple time points to extract glucose for NMR analysis. Since the transaldolase reaction and incomplete equilibrium by triose phosphate isomerase cannot break a 13C-13C bond within the trioses contributing to glucose, the appearance of [1,2-13C2]-, [2,3-13C2]-, [5,6-13C2]- and [4,5-13C2]glucose provides direct evidence for metabolism of glycerol in the citric acid cycle or the PPP but not an influence of either triose phosphate isomerase or the transaldolase reaction. In all animals, [1,2-13C2]glucose / [2,3-13C2]glucose was significantly greater than [5,6-13C2]glucose / [4,5-13C2]glucose, a relationship that can only arise from gluconeogenesis followed by passage of substrates through the PPP. In summary, the hepatic PPP in vivo can be detected by 13C distribution in blood glucose after [U-13C3]glycerol administration.
    The Journal of biological chemistry. 10/2014;
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    ABSTRACT: Context: The ability of insulin to suppress hepatic glucose production is impaired among subjects with increased intrahepatic triglycerides (IHTG). However, little is known about the roles of insulin on the supporting fluxes of glucose production among patients with fatty liver. Objective: To evaluate the effects of insulin on fluxes through the three potential sources of plasma glucose (glycerol, the citric acid cycle, and glycogen) among patients with fatty liver. Design, settings, participants, and intervention: Nineteen men with a range of IHTG (∼0.5% - 23%) were studied after an overnight fast and during hyperinsulinemia using MR spectroscopy and stable isotope tracers. Main Outcome Measures: IHTG, gluconeogenesis from glycerol, gluconeogenesis from the citric acid cycle, glycogenolysis, and (13)C-labeled glucose produced from the citric acid cycle during hyperinsulinemia were measured. Results: Men with high IHTG had higher fluxes through all pathways contributing to glucose production during hyperinsulinemia compared to men with low IHTG, but they had similar fluxes after the fast. Consequently, men with fatty liver had impaired insulin efficiency in suppressing total glucose production as well as fluxes through all three biochemical pathways contributing to glucose. The detection of glucose isotopomers with (13)C arising from [U-(13)C3]propionate ingested during hyperinsulinemia demonstrated continuous gluconeogenesis from the citric acid cycle in all subjects. Conclusions: These findings challenge the concept that individual glucose production pathways are selectively dysregulated during hepatic insulin resistance. Overproduction of glucose during hyperinsulinemia in men with fatty liver results from inadequate suppression of all the supporting fluxes of glucose production in response to insulin.
    The Journal of clinical endocrinology and metabolism. 09/2014;
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    ABSTRACT: The 13C labeling patterns in glutamate and glutamine from brain tissue are quite different after infusion of a mixture of 13C-enriched glucose and acetate. Two processes contribute to this observation, oxidation of acetate by astrocytes but not neurons, and preferential incorporation of α-ketoglutarate into glutamate in neurons, and incorporation of α-ketoglutarate into glutamine in astrocytes. The acetate:glucose ratio, introduced previously for analysis of a single 13C NMR spectrum, provides a useful index of acetate and glucose oxidation in the brain tissue. However, quantitation of relative substrate oxidation at the cell compartment level has not been reported. A simple mathematical method is presented to quantify the ratio of acetate to glucose oxidation in astrocytes, based on the standard assumption that neurons do not oxidize acetate. Mice were infused with [1,2-13C]acetate and [1,6-13C]glucose, and proton decoupled 13C NMR spectra of cortex extracts were acquired. A fit of those spectra to the model indicated that 13C-labeled acetate and glucose contributed approximately equally to acetyl-CoA (0.96) in astrocytes. Since this method relies on a single 13C NMR spectrum, it can be readily applied to multiple physiologic and pathologic conditions.This article is protected by copyright. All rights reserved.
    Journal of Neurochemistry 09/2014; · 3.97 Impact Factor
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    ABSTRACT: PurposeThe diseased myocardium lacks metabolic flexibility and responds to stimuli differently compared with healthy hearts. Here, we report the use of hyperpolarized 13C NMR spectroscopy to detect sudden changes in cardiac metabolism in isolated, perfused rat hearts in response to adrenergic stimulation.Methods Metabolism of hyperpolarized [1-13C]pyruvate was investigated in perfused rat hearts. The hearts were stimulated in situ by isoproterenol shortly after the administration of hyperpolarized [1-13C]pyruvate. The hyperpolarized 13C NMR results were corroborated with 1H NMR spectroscopy of tissue extracts.ResultsAddition of isoproterenol to hearts after equilibration of hyperpolarized [1-13C]pyruvate into the existing lactate pool resulted in a sudden, rapid increase in hyperpolarized [1-13C]lactate signal within seconds after exposure to drug. The hyperpolarized H13CO3− and hyperpolarized [1-13C]alanine signals were not affected by the isoproterenol-induced elevated cardiac workload. Separate experiments confirmed that the new hyperpolarized [1-13C]lactate signal that arises after stimulation by isoproterenol reflects a sudden increase in total tissue lactate derived from glycogen.Conclusion These results suggest that hyperpolarized pyruvate and 13C MRS may be useful for detecting abnormal glycogen metabolism in intact tissues. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 08/2014; · 3.27 Impact Factor
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    ABSTRACT: Introduction: Metabolic imaging (18 F-fluoro-deoxyglucose, FDG-PET) is widely used to monitor treatment response of many cancers. However, its use in neuro-oncology has been limited. Although 18 FDG-PET imaging can accurately monitor the transition of indolent, low-grade gliomas, to high-grade (Glioblastoma, GBM) disease which is associated with rapid proliferation, it has consistently failed to reflect treatment response when patients are clearly 'stable' from a clinical and radiographic perspective, following concurrent radiation (RT) and chemotherapy (temozolomide,TMZ). It is hypothesized that the transition from indolent to rapid growth, which requires increased metabolic resources to support macromolecule synthesis, is associated with a switch from oxidative metabolism to aerobic glycolysis (Warburg effect). If this is correct, then it is reasonable to hypothesize that the 18 FDG-PET metabolic profile post-treatment, stable GBM should reflect a lower bioenergetic demand, similar to a low-grade tumor. This, however, does not reflect clinical experience. Rather, stable GBMs most often show persistent high uptake of 18 FDG and this has limited utility of 18 FDG-PET in the management of gliomas. Thus there is a discrepancy between non-proliferating GBM and high uptake of 18 FDG. Here we directly tested the assumption that fast growing GBM will have a fundamentally different metabolic profile compared to proliferation-arrested tumors. Using a human orthotopic mouse model of GBM (HOT) that shows a cytostatic response to TMZ, we compared the 13 C-NMR profiles of TMZ treated and untreated GBM following infusion of 13 C-glucose. Methods: The GBM HOT mouse model was produced by isolating tumor cells from freshly resected human surgical specimens and stereotactically injecting them into 6-week-old NOD/SCID mouse brain. Seven individual HOT lines were used for these studies, 1 mouse for treatment and vehicle from each line. Neurologically symptomatic mice were treated with TMZ at clinically equivalent dose (20 mg/kg x 5 days, equivalent to one cycle of standard care), or vehicle. Tracer studies were performed 3 days later. After a priming bolus, awake mice were infused with [U-13 C] glucose for 150 minutes, then deeply anesthetized and cardiac perfused with ice-cold PBS. Tumor and non-tumor bearing brain regions were rapidly dissected and freeze-clamped. Proton–decoupled 13 C NMR spectra of tissue extracts were acquired at 150 MHz (600 MHz) with 2 H field-frequency lock. Results: Histopathological analysis confirmed that TMZ induced a dramatic inhibition of GBM cell proliferation in the treated tumors (MiB-1 6% vs vehicle 65%). Representative 13 C NMR spectra of tissue extracts are shown in Fig.1. Multiplets in glutamate C4 indicate oxidation of glucose in the citric acid cycle. No significant difference was observed between TMZ treated and untreated (-TMZ) for any line (data not shown). Similarly, the full 13 C spectrum including enrichment in lactate (LAC), alanine (ALA), glutamate (GLU) and glutamine (GLN) were similar (data not shown). It is important to note that the absence of significant changes in the metabolic profile of GBM cells in vivo by TMZ induced cell-cycle arrest was associated with clear evidence of DNA damage mediated p53-p21 activation. This observation is remarkable for the fact that p53 is regarded as how tumor cells utilize respiratory and glycolytic pathways. Conclusion: Deregulation of tumor metabolism has been intimately linked to cell proliferation. Here we report, contrary to expectation, that following chemotherapy induced arrest, dormant GBM continue to exhibit high rates of glucose oxidation in vivo. This observation may in part explain why PET studies have failed to be prognostic of therapeutic response and raises the possibility that metabolic profiles of tumor are determined by their mutational and differentiation status and not simply proliferation rate. Fig.1 13 C-NMR spectra from TMZ-treated (upper panel) and untreated (vehicle; lower panel). Carbon 4 (C4) of Glutamate (Glu) and Glutamine (Gln) . Similar pattern of multiplets are seen in both spectra. Abbrev: D45 (doublet 45), S (singlet), Q (quartet).
    ISMRM, Milan, Italy; 05/2014
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    ABSTRACT: Target audience: Researchers and clinicians studying metabolism in brain tumors. Purpose: Brain tumors in situ are exposed to intermediate-and long-chain fatty acids, as well as lactate, carbohydrates and other substrates for energy production in mitochondria. The overwhelming majority of studies in tumor metabolism focus on conversion of glucose to lactate, and the preferred model is isolated cells in culture. However, there is growing evidence that cells lines conditioned to culture may not correctly reflect metabolism in situ, and some tumors appear capable of oxidizing substrates other than glucose. Furthermore, the enzymes for β-oxidation of fatty acids are present in some malignancies, and there is general agreement that tumor oncogenes reprogram intermediary metabolism. In this study, our previously described human orthotopic tumor (HOT) glioblastoma GBM mouse models were studied by 13 C NMR isotopomer analysis to assess whether β-oxidation is active. Since animals (and patients) with advanced malignancies are often undernourished, the effects of hepatic gluconeogenesis on 13 C-labeling in plasma glucose, also available to the tumor, was evaluated. Materials and Methods: All studies were performed with approval of the local Institutional Review Board and Animal Care Committee. Six individual HOT models, all isocitrate dehydrogenase wild type, were used. Expression analysis for the common driver GBM mutations, c-Met, EGFR, P53 and PDGFRα, was performed for each human and paired HOT mouse line and at least one example of each of the common driver mutations was chosen. Three metastatic cancers to the brain were also studied; breast cancer (estrogen receptor and progesterone receptor negative, HER2-neu positive), adenocarcinoma of the lung (EGFR, Ras, BRAF wild type), and endometrial cancer. One mouse from each of the eight representative tumors was examined. MRI was used to monitor tumor growth. When animals had difficulty walking or began to lose weight, MRI and 18
    ISMRM, Milan, Italy; 05/2014
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    ABSTRACT: PurposeTo develop an inversion pulse-based, chemical exchange saturation transfer-like method for detection of 31P magnetization exchanges among all nuclear magnetic resonance visible metabolites suitable for providing an integrated kinetic analysis of phosphorus exchange reactions in vivo.Methods The exchange kinetics by inversion transfer (EKIT) sequence includes application of a frequency-selective inversion pulse arrayed over the range of relevant 31P frequencies, followed by a constant delay and a hard readout pulse. A series of EKIT spectra, each given by a plot of Z-magnetization for each metabolite of interest versus frequency of the inversion pulse, can be generated from this single data set.ResultsEKIT spectra reflect chemical exchange due to known biochemical reactions, cross-relaxation effects, and relayed magnetization transfers due to both processes. The rate constants derived from EKIT data collected on resting human skeletal muscle were: ATP synthesis via ATP synthase (0.050 ± 0.016 s−1), ATP synthesis via creatine kinase (0.264 ± 0.023 s−1), and cross-relaxation between neighboring spin pairs within ATP (0.164 ± 0.022 s−1).ConclusionEKIT provides a simple, alternative method to detect chemical exchange, cross relaxation, and relayed magnetization transfer effects in human skeletal muscle at 7 T. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 04/2014; · 3.27 Impact Factor
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    ABSTRACT: To demonstrate the use of forced current excitation (FCE) to create homogeneous excitation of the breast at 7 tesla, insensitive to the effects of asymmetries in the electrical environment. FCE was implemented on two breast coils: one for quadrature (1) H imaging and one for proton-decoupled (13) C spectroscopy. Both were a Helmholtz-saddle combination, with the saddle tuned to 298 MHz for imaging and 75 MHz for spectroscopy. Bench measurements were acquired to demonstrate the ability to force equal currents on elements in the presence of asymmetric loading to improve homogeneity. Modeling and temperature measurements were conducted per safety protocol. B1 mapping, imaging, and proton-decoupled (13) C spectroscopy were demonstrated in vivo. Using FCE to ensure balanced currents on elements enabled straightforward tuning and maintaining of isolation between quadrature elements of the coil. Modeling and bench measurements confirmed homogeneity of the field, which resulted in images with excellent fat suppression and in broadband proton-decoupled carbon-13 spectra. FCE is a straightforward approach to ensure equal currents on multiple coil elements and a homogeneous excitation field, insensitive to the effects of asymmetries in the electrical environment. This enabled effective breast imaging and proton-decoupled carbon-13 spectroscopy at 7T. J. Magn. Reson. Imaging 2014. © 2014 Wiley Periodicals, Inc.
    Journal of Magnetic Resonance Imaging 01/2014; · 2.57 Impact Factor
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    ABSTRACT: Metabolic reprogramming facilitates cancer cell growth, so quantitative metabolic flux measurements could produce useful biomarkers. However, current methods to analyze flux in vivo provide either a steady-state overview of relative activities (infusion of 13C and analysis of extracted metabolites) or a dynamic view of a few reactions (hyperpolarized 13C spectroscopy). Moreover, while hyperpolarization has successfully quantified pyruvate-lactate exchanges, its ability to assess mitochondrial pyruvate metabolism is unproven in cancer. Here, we combined 13C hyperpolarization and isotopomer analysis to quantify multiple fates of pyruvate simultaneously. Two cancer cell lines with divergent pyruvate metabolism were incubated with thermally-polarized [3-13C]pyruvate for several hours, then briefly exposed to hyperpolarized [1-13C]pyruvate during acquisition of NMR spectra, using selective excitation to maximize detection of H[13C]O3- and [1-13C]lactate. Metabolites were then extracted and subjected to isotopomer analysis to determine relative rates of pathways involving [3-13C]pyruvate. Quantitation of hyperpolarized H[13C]O3- provided a single definitive metabolic rate, which was then used to convert relative rates derived from isotopomer analysis into quantitative fluxes. This revealed that H[13C]O3- appearance reflects activity of pyruvate dehydrogenase (PDH) rather than pyruvate carboxylation followed by subsequent decarboxylation reactions. Glucose substantially altered [1-13C]pyruvate metabolism, enhancing exchanges with [1-13C]lactate and suppressing H[13C]O3- formation. Furthermore, inhibiting Akt, an oncogenic kinase that stimulates glycolysis, reversed these effects, indicating that metabolism of pyruvate by both LDH and PDH is subject to the acute effects of oncogenic signaling on glycolysis. The data suggest that combining 13C isotopomer analyses and dynamic hyperpolarized 13C spectroscopy may enable quantitative flux measurements in living tumors.
    Journal of Biological Chemistry 01/2014; · 4.65 Impact Factor
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    ABSTRACT: PurposeTo enable high spatial and temporal breast imaging resolution via combined use of high field MRI, array coils, and forced current excitation (FCE) multi channel transmit. Materials and MethodsA unilateral 16-channel receive array insert was designed for use in a transmit volume coil optimized for quadrature operation with dual-transmit RF shimming at 7T. Signal-to-noise ratio (SNR) maps, g-factor maps, and high spatial and temporal resolution in vivo images were acquired to demonstrate the utility of the coil architecture. ResultsThe dual-transmit FCE coil provided homogeneous excitation and the array provided an increase in average SNR of 3.3 times (max 10.8, min 1.5) compared to the volume coil in transmit/receive mode. High resolution accelerated in vivo breast imaging demonstrated the ability to achieve isotropic spatial resolution of 0.5 mm within clinically relevant 90 s scan times, as well as the ability to perform 1.0 mm isotropic resolution imaging, 7 s per dynamics, with the use of bidirectional SENSE acceleration of up to R = 9. Conclusion The FCE design of the transmit coil easily accommodates the addition of a sixteen channel array coil. The improved spatial and temporal resolution provided by the high-field array coil with FCE dual-channel transmit will ultimately be beneficial in lesion detection and characterization.
    PLoS ONE 01/2014; 9(11):e113969. · 3.53 Impact Factor
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    ABSTRACT: Carbon-13 magnetic resonance spectroscopy (13C MRS) offers a noninvasive method to assess glycogen levels in skeletal muscle and to identify excess glycogen accumulation in patients with glycogen storage disease (GSD). Despite the clinical potential of the method, it is currently not widely used for diagnosis or for follow-up of treatment. While it is possible to perform acceptable 13C MRS at lower fields, the low natural abundance of 13C and the inherently low signal-to-noise ratio of 13C MRS makes it desirable to utilize the advantage of increased signal strength offered by ultra-high fields for more accurate measurements. Concomitant with this advantage, however, ultra-high fields present unique technical challenges that need to be addressed when studying glycogen. In particular, the question of measurement reproducibility needs to be answered so as to give investigators insight into meaningful inter-subject glycogen differences. We measured muscle glycogen levels in vivo in the calf muscle in three patients with McArdle disease (MD), one patient with phosphofructokinase deficiency (PFKD) and four healthy controls by performing 13C MRS at 7T. Absolute quantification of the MRS signal was achieved by using a reference phantom with known concentration of metabolites. Muscle glycogen concentration was increased in GSD patients (31.5±2.9 g/kg w. w.) compared with controls (12.4±2.2 g/kg w. w.). In three GSD patients glycogen was also determined biochemically in muscle homogenates from needle biopsies and showed a similar 2.5-fold increase in muscle glycogen concentration in GSD patients compared with controls. Repeated inter-subject glycogen measurements yield a coefficient of variability of 5.18%, while repeated phantom measurements yield a lower 3.2% system variability. We conclude that noninvasive ultra-high field 13C MRS provides a valuable, highly reproducible tool for quantitative assessment of glycogen levels in health and disease.
    PLoS ONE 01/2014; 9(10):e108706. · 3.53 Impact Factor
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    ABSTRACT: We have performed temperature-dependent electron spin resonance (ESR) measurements of the stable free radical trityl OX063, an efficient polarizing agent for dissolution dynamic nuclear polarization (DNP), at the optimum DNP concentration (15 mM). We have found that (i) when compared to the W-band electron spin-lattice relaxation rate T1e(-1) of other free radicals used in DNP at the same concentration, trityl OX063 has slower T1e(-1) than BDPA and 4-oxo-TEMPO. At T > 20 K, the T1e(-1)vs. T data of trityl OX063 appears to follow a power law dependence close to the Raman process prediction whereas at T < 10 K, electronic relaxation slows and approaches the direct process behaviour. (ii) Gd(3+) doping, a factor known to enhance DNP, of trityl OX063 samples measured at W-band resulted in monotonic increases of T1e(-1) especially at temperatures below 20-40 K while the ESR lineshapes remained essentially unchanged. (iii) The high frequency ESR spectrum can be fitted with an axial g-tensor with a slight g-anisotropy: gx = gy = 2.00319(3) and gz = 2.00258(3). Although the ESR linewidth D monotonically increases with field, the temperature-dependent T1e(-1) is almost unchanged as the ESR frequency is increased from 9.5 GHz to 95 GHz, but becomes faster at 240 GHz and 336 GHz. The ESR properties of trityl OX063 reported here may provide insights into the efficiency of DNP of low-γ nuclei performed at various magnetic fields, from 0.35 T to 12 T.
    Physical Chemistry Chemical Physics 05/2013; · 4.20 Impact Factor
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    ABSTRACT: Two variants of a widely used two-compartment model were prepared for fitting the time course of [1,6-(13)C2]glucose metabolism in rat brain. Features common to most models were included, but in one model the enrichment of the substrates entering the glia and neuronal citric acid cycles was allowed to differ. Furthermore, the models included the capacity to analyze multiplets arising from (13)C spin-spin coupling, known to improve parameter estimates in heart. Data analyzed were from a literature report providing time courses of [1,6-(13)C2]glucose metabolism. Four analyses were used, two comparing the effect of different pyruvate enrichment in glia and neurons, and two for determining the effect of multiplets present in the data. When fit independently, the enrichment in glial pyruvate was less than in neurons. In the absence of multiplets, fit quality and parameter values were typical of those in the literature, whereas the multiplet curves were not modeled well. This prompted the use of robust statistical analysis (the Kolmogorov-Smirnov test of goodness of fit) to determine whether individual curves were modeled appropriately. At least 50% of the curves in each experiment were considered poorly fit. It was concluded that the model does not include all metabolic features required to analyze the data.Journal of Cerebral Blood Flow & Metabolism advance online publication, 8 May 2013; doi:10.1038/jcbfm.2013.67.
    Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 05/2013; · 5.46 Impact Factor
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    ABSTRACT: 2-Hydroxyglutarate (2HG) is produced in gliomas with mutations of isocitrate dehydrogenase (IDH) 1 and 2. The (1) H resonances of the J-coupled spins of 2HG are extensively overlapped with signals from other metabolites. Here, we report a comparative study at 3 T of the utility of the point-resolved spectroscopy sequence with a standard short TE (35 ms) and a long TE (97 ms), which had been theoretically designed for the detection of the 2HG 2.25-ppm resonance. The performance of the methods is evaluated using data from phantoms, seven healthy volunteers and 22 subjects with IDH-mutated gliomas. The results indicate that TE = 97 ms provides higher detectability of 2HG than TE = 35 ms, and that this improved capability is gained when data are analyzed with basis spectra that include the effects of the volume localizing radiofrequency and gradient pulses. Copyright © 2013 John Wiley & Sons, Ltd.
    NMR in Biomedicine 04/2013; · 3.45 Impact Factor
  • Eunsook S Jin, A Dean Sherry, Craig R Malloy
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    ABSTRACT: During hepatic lipogenesis, the glycerol backbone of acylglycerols originates from one of three sources: glucose, glycerol, or substrates passing through the citric acid cycle via glyceroneogenesis. The relative contribution of each substrate source to glycerol in rat liver acylglycerols was determined using 13C-enriched substrates and NMR. Animals received a fixed mixture of glucose, glycerol and lactate; one group received [U-13C6]glucose, another received [U-13C3]glycerol, and the third received [U-13C3]lactate. After three hours, the liver was harvested to extract fats and the glycerol moiety from hydrolyzed acylglycerols was analyzed by 13C NMR. In either fed or fasted animals, glucose and glycerol provided the majority of the glycerol backbone carbons while the contribution of lactate was small. In fed animals, glucose contributed > 50% of total newly synthesized glycerol backbone and 35% of this contribution occurred after glucose had passed through the citric acid cycle. By comparison, the glycerol contribution was ~40% and, of this, 17% of the exogenous glycerol first passed through the cycle. In fasted animals, exogenous glycerol became the major contributor to acylgycerols. The contribution from exogenous lactate did increase in fasted animals, but its overall contribution remained small. The contributions of glucose and glycerol that had passed through the citric acid cycle first increased in fasted animals from 35% to 71% for glucose and from 17% to 24% for glycerol. Thus, a substantial fraction from both substrate sources passed through the cycle prior to incorporation into the glycerol moiety of acylglycerols in the liver.
    Journal of Biological Chemistry 04/2013; · 4.65 Impact Factor
  • Eunsook S Jin, A Dean Sherry, Craig R Malloy
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    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 non-mammalian 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-13C3]glycerol, and 2H2O 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, 13C from [U-13C3]glycerol appeared in glycogen in carbon positions 4-6 of glucosyl units, but none in positions 1-3. The extent of [4,5,6-13C3]glucosyl unit enrichment in glycogen was enhanced by insulin, but decreased by H2O2. Given that triose phosphate isomerase is generally assumed to fully equilibrate carbon tracers in the triose pool, the marked 13C-asymmetry in glycogen can only be attributed to conversion of [U-13C3]glycerol to [U-13C3]dihydroxyacetone phosphate and [U-13C3]glyceraldehyde 3-phosphate followed by rearrangements in the non-oxidative branch of the pentose phosphate pathway involving transaldolase that places this 13C-enriched 3-carbon unit only in the bottom half of hexose phosphate molecules contributing to glycogen.
    Journal of Biological Chemistry 12/2012; · 4.65 Impact Factor

Publication Stats

4k Citations
997.09 Total Impact Points

Institutions

  • 1989–2014
    • University of Texas Southwestern Medical Center
      • • Research Center for Advanced Imaging
      • • Department of Radiology
      • • Division of General Internal Medicine
      • • Department of Internal Medicine
      Dallas, Texas, United States
  • 2011
    • University of California, San Francisco
      • Department of Radiology and Biomedical Imaging
      San Francisco, CA, United States
  • 1987–2009
    • University of Texas at Dallas
      • Chemistry
      Dallas, TX, United States
  • 2007
    • Johns Hopkins Medicine
      Baltimore, Maryland, United States
  • 2005
    • Center for Magnetic Resonance Research Minnesota, USA
      Minneapolis, Minnesota, United States
  • 1999–2004
    • University of Coimbra
      • Faculdade de Ciências e Tecnologia
      Coimbra, Distrito de Coimbra, Portugal
  • 2000
    • University of Pennsylvania
      • Department of Radiology
      Philadelphia, PA, United States
  • 1994
    • University of Pécs
      Fuenfkirchen, Baranya county, Hungary
  • 1988
    • Texas Tech University Health Sciences Center
      • Department of Internal Medicine
      Lubbock, TX, United States
    • University of Oxford
      • Department of Biochemistry
      Oxford, ENG, United Kingdom
  • 1985–1987
    • University of Texas Health Science Center at Tyler
      Tyler, Texas, United States