C R Malloy

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

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Publications (224)961.54 Total impact

  • [Show abstract] [Hide abstract]
    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: 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: 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
  • Jimin Ren, A Dean Sherry, Craig R Malloy
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    ABSTRACT: Despite its importance in energy metabolism, lactate in human skeletal muscle has been difficult to detect by noninvasive (1) H-magnetic resonance spectroscopy mainly due to interference from large water and lipid signals. Long echo-time acquisitions at 7 T effectively attenuates the water and lipid signals in forearm muscle allowing direct observation of both lactate resonances, the methine at 4.09 ppm and the methyl at 1.31 ppm. Using this approach, we were able to monitor lactate dynamics at a temporal resolution of 32 s. While lactate was not detectable at rest, immediately after an acute period of exercise to fatigue the forearm muscle, lactate rose to a level comparable to that of creatine (∼30 mmol/kg wet weight). In a typical (1) H-magnetic resonance spectrum collected using a echo-time of 140 ms, the lactate methine and methyl resonances both appear as doublets with an unusually large splitting of ∼20 Hz due to residual dipolar coupling. During muscle recovery following exercise, the lactate signals decay rapidly with a time constant of t(½) = 2.0 ± 0.6 min (n = 12 subjects). This fast and simple lactate detection method may prove valuable for monitoring lactate metabolism in cancer and in sports medicine applications. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 11/2012; · 3.27 Impact Factor
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    ABSTRACT: The goal of this work was to test feasibility of using galvinoxyl (2,6-di-tert-butyl-α-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy) as a polarizing agent for dissolution dynamic nuclear polarization (DNP) NMR spectroscopy. We have found that galvinoxyl is reasonably soluble in ethyl acetate, chloroform, or acetone and the solutions formed good glasses when mixed together or with other solvents such as dimethyl sulfoxide. W-band electron spin resonance (ESR) measurements revealed that galvinoxyl has an ESR linewidth D intermediate between that of carbon-centered free radical trityl OX063 and the nitroxide-based 4-oxo-TEMPO, thus the DNP with galvinoxyl for nuclei with low gyromagnetic ratio γ such as (13)C and (15)N is expected to proceed predominantly via the thermal mixing process. The optimum radical concentration that would afford the highest (13)C nuclear polarization (approximately 6% for [1-(13)C]ethyl acetate) at 3.35T and 1.4K was found to be around 40mM. After dissolution, large liquid-state NMR enhancements were achieved for a number of (13)C and (15)N compounds with long spin-lattice relaxation time T(1). In addition, the hydrophobic galvinoxyl free radical can be easily filtered out from the dissolution liquid when water is used as the solvent. These results indicate that galvinoxyl can be considered as an easily available free radical polarizing agent for routine dissolution DNP-NMR spectroscopy.
    Journal of Magnetic Resonance 11/2012; 227C:14-19. · 2.30 Impact Factor
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    ABSTRACT: It has been postulated that triheptanoin can ameliorate seizures by supplying the tricarboxylic acid cycle with both acetyl-CoA for energy production and propionyl-CoA to replenish cycle intermediates. These potential effects may also be important in other disorders associated with impaired glucose metabolism because glucose supplies, in addition to acetyl-CoA, pyruvate, which fulfills biosynthetic demands via carboxylation. In patients with glucose transporter type I deficiency (G1D), ketogenic diet fat (a source only of acetyl-CoA) reduces seizures, but other symptoms persist, providing the motivation for studying heptanoate metabolism. In this work, metabolism of infused [5,6,7-(13)C(3)]heptanoate was examined in the normal mouse brain and in G1D by (13)C-nuclear magnetic resonance spectroscopy, gas chromatography-mass spectrometry (GC-MS), and liquid chromatography-mass spectrometry (LC-MS). In both groups, plasma glucose was enriched in (13)C, confirming gluconeogenesis from heptanoate. Acetyl-CoA and glutamine levels became significantly higher in the brain of G1D mice relative to normal mice. In addition, brain glutamine concentration and (13)C enrichment were also greater when compared with glutamate in both animal groups, suggesting that heptanoate and/or C5 ketones are primarily metabolized by glia. These results enlighten the mechanism of heptanoate metabolism in the normal and glucose-deficient brain and encourage further studies to elucidate its potential antiepileptic effects in disorders of energy metabolism.Journal of Cerebral Blood Flow & Metabolism advance online publication, 17 October 2012; doi:10.1038/jcbfm.2012.151.
    Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 10/2012; · 5.46 Impact Factor
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    ABSTRACT: OBJECTIVE: A three-day high-fat diet induces hepatic steatosis and hepatic insulin resistance in rats without altering fasting plasma glucose concentration or the rate of glucose production. However, as the nutrient profile available to the liver is substantially altered by a high-fat diet, we hypothesized that the relative fluxes supporting hepatic glucose production would be altered. MATERIALS/METHODS: To test this hypothesis, we used multiple tracers ([3,4-(13)C(2)]glucose, (2)H(2)O, and [U-(13)C(3)]propionate) followed by NMR analysis of blood glucose to quantify net glucose production and the contributions of glycogen and key gluconeogenesis precursors in 4-5-h fasted rats. RESULTS: NMR analysis demonstrated that the majority of blood glucose was derived from glycogen and the citric acid cycle, while a smaller fraction of glucose was derived from glycerol in both controls and high-fat-fed animals. High-fat feeding was associated with a two-fold increase in plasma glycerol concentration and an increase in the contribution (both fractional and absolute) of glycerol-gluconeogenesis. The increase in gluconeogenesis from glycerol tended to be balanced by a decrease in glycogenolysis. The absolute fluxes associated with the citric acid cycle including gluconeogenesis from the cycle intermediates, pyruvate cycling and the citric acid cycle flux itself, were not altered by this short high-fat diet. CONCLUSIONS: A short term high-fat diet altered the specific pathways for hepatic glucose production without influencing the overall rate of glucose production or flux in the citric acid cycle.
    Metabolism: clinical and experimental 09/2012; · 3.10 Impact Factor
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    ABSTRACT: The pyruvate dehydrogenase complex (PDC), required for complete glucose oxidation, is essential for brain development. Although PDC deficiency is associated with a severe clinical syndrome, little is known about its effects on either substrate oxidation or synthesis of key metabolites such as glutamate and glutamine. Computational simulations of brain metabolism indicated that a 25% reduction in flux through PDC and a corresponding increase in flux from an alternative source of acetyl-CoA would substantially alter the (13)C NMR spectrum obtained from brain tissue. Therefore, we evaluated metabolism of [1,6-(13)C(2)]glucose (oxidized by both neurons and glia) and [1,2-(13)C(2)]acetate (an energy source that bypasses PDC) in the cerebral cortex of adult mice mildly and selectively deficient in brain PDC activity, a viable model that recapitulates the human disorder. Intravenous infusions were performed in conscious mice and extracts of brain tissue were studied by (13)C NMR. We hypothesized that mice deficient in PDC must increase the proportion of energy derived from acetate metabolism in the brain. Unexpectedly, the distribution of (13)C in glutamate and glutamine, a measure of the relative flux of acetate and glucose into the citric acid cycle, was not altered. The (13)C labeling pattern in glutamate differed significantly from glutamine, indicating preferential oxidation of [1,2-(13)C]acetate relative to [1,6-(13)C]glucose by a readily discernible metabolic domain of the brain of both normal and mutant mice, presumably glia. These findings illustrate that metabolic compartmentation is preserved in the PDC-deficient cerebral cortex, probably reflecting intact neuron-glia metabolic interactions, and that a reduction in brain PDC activity sufficient to induce cerebral dysgenesis during development does not appreciably disrupt energy metabolism in the mature brain.
    Neurochemistry International 08/2012; · 2.66 Impact Factor
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    ABSTRACT: Dysregulated metabolism is a hallmark of cancer cell lines, but little is known about the fate of glucose and other nutrients in tumors growing in their native microenvironment. To study tumor metabolism in vivo, we used an orthotopic mouse model of primary human glioblastoma (GBM). We infused (13)C-labeled nutrients into mice bearing three independent GBM lines, each with a distinct set of mutations. All three lines displayed glycolysis, as expected for aggressive tumors. They also displayed unexpected metabolic complexity, oxidizing glucose via pyruvate dehydrogenase and the citric acid cycle, and using glucose to supply anaplerosis and other biosynthetic activities. Comparing the tumors to surrounding brain revealed obvious metabolic differences, notably the accumulation of a large glutamine pool within the tumors. Many of these same activities were conserved in cells cultured ex vivo from the tumors. Thus GBM cells utilize mitochondrial glucose oxidation during aggressive tumor growth in vivo.
    Cell metabolism 06/2012; 15(6):827-37. · 17.35 Impact Factor
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    ABSTRACT: Hyperpolarized [1-(13)C]pyruvate has become an important diagnostic tracer of normal and aberrant cellular metabolism for in vitro and in vivo NMR spectroscopy (MRS) and imaging (MRI). In pursuit of achieving high NMR signal enhancements in dynamic nuclear polarization (DNP) experiments, we have performed an extensive investigation of the influence of Gd(3+) doping, a parameter previously reported to improve hyperpolarized NMR signals, on the DNP of this compound. [1-(13)C]Pyruvate samples were doped with varying amounts of Gd(3+) and fixed optimal concentrations of free radical polarizing agents commonly used in fast dissolution DNP: trityl OX063 (15 mM), 4-oxo-TEMPO (40 mM), and BDPA (40 mM). In general, we have observed three regions of interest, namely, (i) a monotonic increase in DNP-enhanced nuclear polarization P(dnp) upon increasing the Gd(3+) concentration until a certain threshold concentration c(1) (1-2 mM) is reached, (ii) a region of roughly constant maximum P(dnp) from c(1) until a concentration threshold c(2) (4-5 mM), and (iii) a monotonic decrease in P(dnp) at Gd(3+) concentration c > c(2). Of the three free radical polarizing agents used, trityl OX063 gave the best response to Gd(3+) doping, with a 300% increase in the solid-state nuclear polarization, whereas addition of the optimum Gd(3+) concentration on BDPA and 4-oxo-TEMPO-doped samples only yielded a relatively modest 5-20% increase in the base DNP-enhanced polarization. The increase in P(dnp) due to Gd(3+) doping is ascribed to the decrease in the electronic spin-lattice relaxation T(1e) of the free radical electrons, which plays a role in achieving lower spin temperature T(s) of the nuclear Zeeman system. These results are discussed qualitatively in terms of the spin temperature model of DNP.
    The Journal of Physical Chemistry A 05/2012; 116(21):5129-38. · 2.77 Impact Factor
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    ABSTRACT: A trimethylamine (TMA) moiety is present in carnitine and acetylcarnitine, and both molecules play critical roles in muscle metabolism. At 7 T, the chemical shift dispersion was sufficient to routinely resolve the TMA signals from carnitine at 3.20 and from acetylcarnitine at 3.17 ppm in the (1) H-MRS (Magnetic Resonance Spectroscopy) of human soleus muscle with a temporal resolution of about 2 min. In healthy, sedentary adults, the concentration of acetylcarnitine increased nearly 10-fold, to 4.1 ± 1.0 mmol/kg, in soleus muscle after 5 min of calf-raise exercise and recovered to a baseline concentration of 0.5 ± 0.3 mmol/kg. While the half-time for decay of acetylcarnitine was the same whether measured from the TMA signal (18.8 ± 5.6 min) or measured from the methyl signal (19.4 ± 6.1 min), the detection of acetylcarnitine by its TMA signal in soleus has the advantage of higher sensitivity and without overlapping from lipid signals. Although the activity of carnitine acetyltransferase is sufficient to allow equilibrium between carnitine and coenzyme-A pools, the exchange in TMA signal between carnitine and acetylcarnitine is slow in soleus following exercise on 7T (1) H-NMR time scale. The TMA signal provides a simple and direct measure of the relative amounts of carnitine and acetylcarnitine. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 04/2012; · 3.27 Impact Factor
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    ABSTRACT: The activity of specific enzyme-catalyzed reactions may be detected in vivo by (13)  C NMR of hyperpolarized (HP) substrates. The signals from HP substrates and products, acquired over time, have been fitted to a number of different mathematical models to determine fluxes, but these models have not been critically compared. In this study, two-pool and three-pool first-order models were constructed to measure flux through lactate dehydrogenase in isolated glioblastoma cells by NMR detection of lactate and pyruvate following the addition of HP [1-(13) C]pyruvate. Mass spectrometry (MS) was used to independently monitor (13)  C enrichment in intra- and extracellular lactate. Six models were evaluated using time-dependent pyruvate C2 and lactate C1 HP NMR data acquired by the use of selective excitation pulses, plus (13)  C enrichment data from intracellular and extracellular lactate measured by MS. A three-pool bidirectional model provided the most accurate description of pyruvate metabolism in these cells. With computed values for T(1) of pyruvate and lactate, as well as the effect of pulsing, the initial flux through lactate dehydrogenase was well determined by both the two-pool bidirectional and unidirectional models when only HP data were available. The three-pool model was necessary to fit the combined data from both MS and HP, but the simpler two-pool exchange model was sufficient to determine the (13)  C lactate concentration when the lactate appearance was measured only by HP. Copyright © 2012 John Wiley & Sons, Ltd.
    NMR in Biomedicine 03/2012; 25(11):1286-94. · 3.45 Impact Factor
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    ABSTRACT: Glioblastomas and brain metastases demonstrate avid uptake of 2-[(18) F]fluoro-2-deoxyglucose by positron emission tomography and display perturbations of intracellular metabolite pools by (1) H MRS. These observations suggest that metabolic reprogramming contributes to brain tumor growth in vivo. The Warburg effect, excess metabolism of glucose to lactate in the presence of oxygen, is a hallmark of cancer cells in culture. 2-[(18) F]Fluoro-2-deoxyglucose-positive tumors are assumed to metabolize glucose in a similar manner, with high rates of lactate formation relative to mitochondrial glucose oxidation, but few studies have specifically examined the metabolic fates of glucose in vivo. In particular, the capacity of human brain cancers to oxidize glucose in the tricarboxylic acid cycle is unknown. Here, we studied the metabolism of human brain tumors in situ. [U-(13)  C]Glucose (uniformly labeled glucose, i.e. d-glucose labeled with (13)  C in all six carbons) was infused during surgical resection, and tumor samples were subsequently subjected to (13) C NMR spectroscopy. The analysis of tumor metabolites revealed lactate production, as expected. We also determined that pyruvate dehydrogenase, turnover of the tricarboxylic acid cycle, anaplerosis and de novo glutamine and glycine synthesis contributed significantly to the ultimate disposition of glucose carbon. Surprisingly, less than 50% of the acetyl-coenzyme A pool was derived from blood-borne glucose, suggesting that additional substrates contribute to tumor bioenergetics. This study illustrates a convenient approach that capitalizes on the high information content of (13) C NMR spectroscopy and enables the analysis of intermediary metabolism in diverse cancers growing in their native microenvironment. Copyright © 2012 John Wiley & Sons, Ltd.
    NMR in Biomedicine 03/2012; 25(11):1234-44. · 3.45 Impact Factor
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    ABSTRACT: It has been hypothesized that increased flux through the pentose phosphate pathway (PPP) is required to support the metabolic demands of rapid malignant cell growth. Using orthotopic mouse models of human glioblastoma (GBM) and renal cell carcinoma metastatic to brain, we estimated the activity of the PPP relative to glycolysis by infusing [1,2-(13) C(2) ]glucose. The [3-(13) C]lactate/[2,3-(13) C(2) ]lactate ratio was similar for both the GBM and brain metastasis and their respective surrounding brains (GBM, 0.197 ± 0.011 and 0.195 ± 0.033, respectively (p = 1); metastasis: 0.126 and 0.119 ± 0.033, respectively). This suggests that the rate of glycolysis is significantly greater than the PPP flux in these tumors, and that the PPP flux into the lactate pool is similar in both tumors. Remarkably, (13) C-(13) C coupling was observed in molecules derived from Krebs cycle intermediates in both tumor types, denoting glucose oxidation. In the renal cell carcinoma, in contrast with GBM, (13) C multiplets of γ-aminobutyric acid (GABA) differed from its precursor glutamate, suggesting that GABA did not derive from a common glutamate precursor pool. In addition, the orthotopic renal tumor, the patient's primary renal mass and brain metastasis were all strongly immunopositive for the 67-kDa isoform of glutamate decarboxylase, as were 84% of tumors on a renal cell carcinoma tissue microarray of the same histology, suggesting that GABA synthesis is cell autonomous in at least a subset of renal cell carcinomas. Taken together, these data demonstrate that (13) C-labeled glucose can be used in orthotopic mouse models to study tumor metabolism in vivo and to ascertain new metabolic targets for cancer diagnosis and therapy. Copyright © 2012 John Wiley & Sons, Ltd.
    NMR in Biomedicine 03/2012; 25(10):1177-86. · 3.45 Impact Factor

Publication Stats

4k Citations
961.54 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
  • 1986–1988
    • University of Oxford
      • Department of Biochemistry
      Oxford, ENG, United Kingdom
  • 1985–1987
    • University of Texas Health Science Center at Tyler
      Tyler, Texas, United States