Ashish Jindal

Metabolism of [U-13 C]glucose in human brain tumors in vivo.

Glioblastomas and brain metastases demonstrate avid uptake of 2‐[18F]fluoro‐2‐deoxyglucose by positron emission tomography and display perturbations of intracellular metabolite pools by 1H 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‐[18F]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 13C 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 13C NMR spectroscopy and enables the analysis of intermediary metabolism in diverse cancers growing in their native microenvironment. Copyright

Comparison of kinetic models for analysis of pyruvate‐to‐lactate exchange by hyperpolarized 13C NMR

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 [1‐13C]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 T1 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

DNP by Thermal Mixing under Optimized Conditions Yields >60 000-fold Enhancement of 89Y NMR Signal

Hyperpolarized (89)Y complexes are attractive NMR spectroscopy and MR imaging probes due to the exceptionally long spin-lattice relaxation time (T(1) ≈ 10 min) of the (89)Y nucleus. However, in vivo imaging of (89)Y has not yet been realized because of the low NMR signal enhancement levels previously achieved for this ultra low-γ(n) nucleus. Here, we report liquid-state (89)Y NMR signal enhancements over 60,000 times the thermal signal at 298 K in a 9.4 T magnet, achieved after the dynamic nuclear polarization (DNP) of Y(III) complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) samples at 3.35 T and 1.4 K. The (89)Y DNP was shown to proceed by thermal mixing and the liquid state (89)Y NMR signal enhancement was maximized by (i) establishing the optimal microwave irradiation frequency, (ii) optimizing the glassing matrix, (iii) choosing a radical with negligible inhomogeneous line broadening contribution to the ESR linewidth, and (iv) addition of an electron T(1e) relaxation agent. The highest enhancements were achieved using a trityl OX063 radical combined with a gadolinium relaxation agent in water-glycerol matrix. Co-polarization of (89)YDOTA and sodium [1-(13)C]pyruvate showed that both (89)Y and (13)C nuclear species acquired the same spin temperature, consistent with thermal mixing theory of DNP. This methodology may be applicable for the optimization of DNP of other low-γ(n) nuclei.

BDPA: an efficient polarizing agent for fast dissolution dynamic nuclear polarization NMR spectroscopy.

Keywords: dynamic nuclear polarization ; hyperpolarization ; NMR spectroscopy ; radicals ; relaxation ; Signal Reference EPFL-ARTICLE-169192doi:10.1002/chem.201102037View record in Web of Science Record created on 2011-10-03, modified on 2017-05-12

Hyperpolarized 89Y Complexes as pH sensitive NMR Probes

Hyperpolarization can increase the sensitivity of NMR/MRI experiments, but the primary limitation is the T(1) decay of magnetization. Due to its long T(1), the hyperpolarized (89)Y nucleus makes an excellent candidate as an in vivo spectroscopy/imaging probe. Here we report the (89)Y chemical shift dependence upon pH for two hyperpolarized (89)Y(III) complexes and demonstrate how such complexes can be used as sensitive spectroscopy/imaging agents to measure pH.

Glucose metabolism via the pentose phosphate pathway, glycolysis and Krebs cycle in an orthotopic mouse model of human brain tumors.

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 [1,2‐13C2]glucose. The [3‐13C]lactate/[2,3‐13C2]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, 13C–13C 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, 13C 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 patients 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 13C‐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

Modified gaseous electronics conference reference cell for the study of plasma-surface-gas interactions

The inductively coupled plasma (ICP) gaseous electronics conference (GEC) reference cell provides a standard system for the study of plasma sciences. In this article, we present a version of the ICP GEC cell that has been designed to allow studies of the interactions between a plasma, gas-phase chemistry, and surface-phase chemistry. Specifically, this modified GEC reference cell has specially designed interior walls that can be heated/cooled (10 to 200 °C) and moved. In addition, these walls can be coated with various materials (Al2O3, SiO2, Si, etc.). Design specifications and initial results are presented. These initial results provide an indication of the flexibility of this modified tool and the types of experiments that it should allow.

Understanding the synthesis of DEGVE pulsed plasmas for application to ultra thin biocompatible interfaces.

There is interest in the development of novel surface treatments for biocompatibility and non-fouling behaviors on various surfaces of in vivo devices. Polyethylene glycol thin films have shown promise as non-fouling passivation layers for such devices. Studies of the surface chemistry and non-fouling effectiveness of plasma deposited di(ethylene glycol) vinyl ether (DEGVE) films have observed that non-fouling performance is maximized when plasma deposition occurs at low values of average power, (<5W). [Y.J. Wu, R.B. Timmons, J.S. Jen, Frank E. Molock, Non-fouling surfaces produced by gas phase pulsed plasma polymerization of an ultra low molecular weight ethylene oxide containing monomer, Colloids and Surfaces B: Biointerfaces 18 (2000) 235-248.] Chemical properties of plasma deposited films were directly attributed to the complex interactions occurring within the gas phase. In order to better understand the deposition process, as well as the significance of the conclusions drawn by Wu et al. [Y.J. Wu, R.B. Timmons, J.S. Jen, Frank E. Molock, Non-fouling surfaces produced by gas phase pulsed plasma polymerization of an ultra low molecular weight ethylene oxide containing monomer, Colloids and Surfaces B: Biointerfaces 18 (2000) 235-248.] an investigation of the gas phase behavior in DEGVE pulsed plasma discharges was performed. Infrared spectra were used to characterize the chemical composition and dissociative behavior of DEGVE plasmas across a range of average powers. This allowed for the construction of a dissociative model of the DEGVE monomer in the plasma discharge. Analysis of the observed dissociative pattern demonstrates the presence of key daughter species which would account for the observations made on deposited DEGVE films by Wu et al. [Y.J. Wu, R.B. Timmons, J.S. Jen, Frank E. Molock, Non-fouling surfaces produced by gas phase pulsed plasma polymerization of an ultra low molecular weight ethylene oxide containing monomer, Colloids and Surfaces B: Biointerfaces 18 (2000) 235-248.].

Measurement of glycine in human prefrontal brain by point-resolved spectroscopy at 7.0 tesla in vivo

Measurement of glycine in human frontal brain by an optimized point‐resolved spectroscopy sequence at 7 T is reported. Echo time dependencies of the overlapping coupled resonances of myo‐inositol, free choline, and threonine were investigated with density matrix simulations, incorporating the slice‐selective radiofrequency and gradient pulses. The numerical simulations indicated that the selectivity of the 3.55‐ppm glycine singlet is maximized at (TE1, TE2) = (101, 51) ms. Phantom experiments indicated that the myo‐inositol peak amplitude between 3.5 and 3.6 ppm is reduced by a factor of 30 following the optimized point‐resolved spectroscopy, as predicted by the simulation. From LCModel analyses, the glycine concentration in the medial prefrontal cortex in healthy adults was estimated, with a mean Cramér‐Rao lower bound of 7 ± 1% (mean ± standard deviation; n = 7), to be 0.8 ± 0.1 mM, with reference to total creatine at 8 mM. Magn Reson Med, 2009.

In situ Fourier transform infrared characterization of the plasma chemistry in varying pulsed cycles of a 1,3-butadiene discharge in an inductively coupled gaseous electronics conference cell

In situ Fourier transform infrared spectroscopy is used to characterize the plasma chemistry of pulsed 1,3-butadiene (H2CCHCHCH2) discharges subject to varying percentages of the duty cycle in a gaseous electronics conference cell. Variations in densities associated with the major observed spectral bands are closely examined as a function of duty cycle. The possible dissociation mechanisms responsible for all observed vibrations are investigated. For example, the data show that about 44% of CH2 stretching vibrations during continuous wave biasing are due to free CH2 daughter species, while only bound CH2 are observed during pulsing of the discharge. This indicates that only the π bond of the CC bond is cleaved during pulsed mode operation, with the σ being cleaved during cw biasing.