Detection of glutathione in the human brain in vivo by means of double quantum coherence filtering

In vivo GABA detection with improved selectivity and sensitivity by localized double quantum filter technique at 4.1T

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter for the normal function of mammal and human brain. It is difficult to detect GABA signal with the conventional single quantum technique due to its relatively low concentration and overlapping with other signals from creatine (Cr), glutathione (GSH), as well as macromolecules. Using a high-selective read pulse, DANTE, and at the facility of increased sensitivity and chemical shift resolution at high-field 4.1T, GABA editing by double quantum filter (DQF) with robust suppression of Cr and GSH was achieved. Our editing efficiency of 40-50% was achievable on a GABA phantom (50 mM GABA and 61 mM choline). Furthermore, GABA editing spectra were acquired with echo time TE = 77 ms, and any possible macromolecular contamination to GABA editing spectra was found to be negligible. This high-field DQF setup was applied to 11 healthy volunteers, and the mean GABA level was measured to be 1.12 +/- 0.15 mM in the occipital lobe in reference to 7.1 mM Cr concentration.

In vivo 1H NMR spectroscopy of individual human brain metabolites at moderate field strengths

This article reviews spectral editing techniques for in vivo 1H NMR spectroscopy of human brain tissue at moderate field strengths of 1.5-3 Tesla. Various aspects of 1H NMR spectroscopy are discussed with regard to in vivo applications. The parameter set [delta, J, n] (delta being the relative chemical shift, J the scalar coupling constant and n the number of coupled spins) is used to characterize the spin systems under investigation and to classify the editing techniques that are used in in vivo 1H NMR spectroscopy.

Analysis of glutathione: implication in redox and detoxification

BACKGROUND

Glutathione is a ubiquitous thiol-containing tripeptide, which plays a central role in cell biology. It is implicated in the cellular defence against xenobiotics and naturally occurring deleterious compounds, such as free radicals and hydroperoxides. Glutathione status is a highly sensitive indicator of cell functionality and viability. Its levels in human tissues normally range from 0.1 to 10 mM, being most concentrated in liver (up to 10 mM) and in the spleen, kidney, lens, erythrocytes and leukocytes. In humans, GSH depletion is linked to a number of disease states including cancer, neurodegenerative and cardiovascular diseases. The present review proposes an analysis of the current knowledge about the methodologies for measuring glutathione in human biological samples and their feasibility as routine methods in clinical chemistry. Furthermore, it elucidates the fundamental role of glutathione in pathophysiological conditions and its implication in redox and detoxification process.

TESTS AVAILABLE

Several methods have been optimised in order to identify and quantify glutathione forms in human biological samples. They include spectrophotometric, fluorometric and bioluminometric assays, often applied to HPLC analysis. Recently, a liquid chromatography-mass spectrometry technique for glutathione determination has been developed that, however, suffers from the lack of total automation and the high cost of the equipment.

CONCLUSION

Glutathione is a critical factor in protecting organisms against toxicity and disease. This review may turn useful for analysing the glutathione homeostasis, whose impairment represents an indicator of tissue oxidative status in human subjects.

Measurement of reduced glutathione (GSH) in human brain using LCModel analysis of difference-edited spectra

The concentration of reduced glutathione (GSH), an antioxidant, may be altered in various brain diseases. MEGA-PRESS was used to edit for the (1)H NMR signal from GSH in the occipital lobe of 12 normal humans. In all studies, GSH was clearly detected with a spectral pattern consistent with spectra acquired from a phantom containing GSH. Retention of singlet resonances in the subspectra, a key advantage of this difference-editing technique, provided an unambiguous reference for the offset and phase of the edited signal. Linear combination model (LCModel) analysis provided an unbiased means for quantifying signal contribution from edited metabolites. GSH concentration was estimated from the in vivo spectra as 1.3 +/- 0.2 micro mol/g (mean +/- SD, n = 12).

In vivo NMR studies of neurodegenerative diseases in transgenic and rodent models

In vivo magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) provide unique quality to attain neurochemical, physiological, anatomical, and functional information non-invasively. These techniques have been increasingly applied to biomedical research and clinical usage in diagnosis and prognosis of diseases. The ability of MRS to detect early yet subtle changes of neurochemicals in vivo permits the use of this technology for the study of cerebral metabolism in physiological and pathological conditions. Recent advances in MR technology have further extended its use to assess the etiology and progression of neurodegeneration. This review focuses on the current technical advances and the applications of MRS and MRI in the study of neurodegenerative disease animal models including amyotrophic lateral sclerosis, Alzheimer's, Huntington's, and Parkinson's diseases. Enhanced MR measurable neurochemical parameters in vivo are described in regard to their importance in neurodegenerative disorders and their investigation into the metabolic alterations accompanying the pathogenesis of neurodegeneration.

Detection of elevated glutathione in meningiomas by quantitative in vivo 1H MRS

Glutathione has major roles in removing free radicals and toxins from normal tissues, but its presence in tumor cells hinders the effectiveness of many anticancer therapies. Analysis of short echo time brain tumor (1)H spectra at 1.5 T using a linear combination of metabolite spectra (LCModel) suggested a significant contribution of glutathione to meningioma spectra. By in vivo MRS (TE = 30 ms, TR = 2020 ms), reduced glutathione was found to be significantly elevated in meningiomas (3.3 +/- 1.5 mM, Mann Whitney, P < 0.005) compared to normal white matter (1.2 +/- 0.15 mM) and low-grade gliomas (1.0 +/- 0.26 mM), in agreement with published histofluorescence studies of tumor biopsies. Glx concentrations were also found to be elevated in meningiomas compared to astrocytomas or normal white matter, indicative of metabolic differences. The ability to noninvasively quantify reduced glutathione in vivo may aid selection of treatment therapies and also provide an indication of tumor aggressiveness.

In vivo monitoring of hepatic glutathione in anesthetized rats by 13C NMR

A method for in vivo (13)C NMR monitoring of hepatic glutathione (GSH) in intact, anesthetized rats has been developed. Studies were conducted using a triple-tuned, surgically implanted surface coil designed for this animal model. The coil permitted complete decoupling and sufficient resolution in the (13)C NMR spectrum to monitor the time course of hepatic (13)C-metabolites of intravenously administered 2-(13)C-glycine, particularly GSH at 44.2 ppm and serine signals at 61.1 and 57.2 ppm, respectively. It further allowed concomitant monitoring of high-energy phosphagens and intracellular pH by (31)P NMR. To confirm in vivo NMR peak assignments, we compared high-resolution 2D (1)H[(13)C] heteronuclear multiple quantum coherence and 1D (13)C spectra of hepatic perchloric acid extracts to those of authentic standards. The fractional isotopic enrichment of hepatic (13)C-glycine increased exponentially at a rate of 1.68 h(-1) and reached its plateau level of 81% in 2 h. The (13)C fractional isotopic enrichment of GSH increased exponentially at a rate of 0.316 h(-1) and reached 55% after 4 h of 2-(13)C-glycine infusion, but without achieving a plateau. To confirm that the resonance at 44.2 ppm resulted from GSH, a rat was given an intravenous dose of 2-oxothiazolidine-4-carboxylic acid (OTC), a cysteine precursor that increases intracellular GSH. As expected, with OTC administration the hepatic (13)C GSH-to-glycine peak area increased more than sevenfold.

In vivo GABA+ measurement at 1.5T using a PRESS-localized double quantum filter

A point-resolved spectroscopy (PRESS)-localized double quantum filter was implemented on a 1.5T clinical scanner for the estimation of gamma-amino butyric acid (GABA) concentrations in vivo. Several calibrations were found to be necessary for consistent results to be obtained. The apparent filter yield was approximately 38%; filter strength was sufficient to reduce the singlet metabolite peaks in vivo to below the level of the noise. Metabolite-nulled experiments were performed, which confirmed that significant overlap occurred between macromolecule signals and the GABA resonance at 3.1 ppm. Although the multiplet arm at 2.9 ppm was confirmed to be relatively free of contamination with macromolecules, some contribution from these and from peptides is likely to remain; therefore, the term GABA+ is used. GABA+ concentrations were estimated relative to creatine (Cr) at the same echo time (TE) in a group of controls, studied on two occasions. The GABA+ concentration in 35-ml regions of interest (ROIs) in the occipital lobe was found to be 1.4 +/- 0.2 mM, with scan-rescan repeatability of 38%.

In vivo magnetic resonance spectroscopy and its application to neuropsychiatric disorders

In vivo magnetic resonance spectroscopy (MRS) is the only noninvasive imaging technique that can directly assess the living biochemistry in localized brain regions. In the past decade, spectroscopy studies have shown biochemical alterations in various neuropsychiatric disorders. These first-generation studies have, in most cases, been exploratory but have provided insightful biochemical information that has furthered our understanding of different brain disorders. This review provides a brief description of spectroscopy, followed by a literature review of key spectroscopy findings in schizophrenia, affective disorders, and autism. In schizophrenia, phosphorus spectroscopy studies have shown altered metabolism of membrane phospholipids (MPL) during the early course of the illness, which is consistent with a neurodevelopmental abnormality around the critical period of adolescence when the illness typically begins. Children and adolescents who are at increased genetic risk for schizophrenia show similar MPL alterations, suggesting that schizophrenia subjects with a genetic predisposition may have a premorbid neurodevelopmental abnormality. Independent of medication status, bipolar subjects in the depressive state tended to have higher MPL precursor levels and a deficit of high-energy phosphate metabolites, which also is consistent with major depression, though these results varied. Further bipolar studies are needed to investigate alterations at the early stage. Lastly, associations between prefrontal metabolism of high-energy phosphate and MPL and neuropsychological performance and reduced N-acetylaspartate in the temporal and cerebellum regions have been reported in individuals with autism. These findings are consistent with developmental alterations in the temporal lobe and in the cerebellum of persons with autism. This paper discusses recent findings of new functions of N-acetylaspartate.

In vivo GABA editing using a novel doubly selective multiple quantum filter

A novel multiple quantum filtering method is proposed that uses a doubly selective pulse termed Delays Alternating with Nutations for Tailored Excitation (DANTE) for multiple quantum preparation. This method selectively prepares GABA-3 and GABA-4 into a multiple quantum state and suppresses all other resonances at 3.0 ppm in each single scan. Phantom tests demonstrated excellent GABA signal retention and complete suppression of overlapping metabolites. It is shown using numerical simulations that overlapping macromolecules are suppressed because the frequency of the first upfield 2pi rotation of the doubly selective DANTE pulse coincides with that of the macromolecules at 1.72 ppm. Excellent suppression of overlapping macromolecules was demonstrated in vivo. Using this method the concentration of GABA in the occipital lobe of healthy volunteers was measured to be 1.21 +/- 0.28 micromol/mL (mean +/-SD, N = 9).

Metabolic changes in quinolinic acid-lesioned rat striatum detected non-invasively by in vivo (1)H NMR spectroscopy

Intrastriatal injection of quinolinic acid (QA) provides an animal model of Huntington disease. In vivo (1)H NMR spectroscopy was used to measure the neurochemical profile non-invasively in seven animals 5 days after unilateral injection of 150 nmol of QA. Concentration changes of 16 metabolites were measured from 22 microl volume at 9.4 T. The increase of glutamine ((+25 +/- 14)%, mean +/- SD, n = 7) and decrease of glutamate (-12 +/- 5)%, N-acetylaspartate (-17 +/- 6)%, taurine (-14 +/- 6)% and total creatine (-9 +/- 3%) were discernible in each individual animal (P < 0.005, paired t-test). Metabolite concentrations in control striata were in excellent agreement with biochemical literature. The change in glutamate plus glutamine was not significant, implying a shift in the glutamate-glutamine interconversion, consistent with a metabolic defect at the level of neuronal-glial metabolic trafficking. The most significant indicator of the lesion, however, were the changes in glutathione ((-19 +/- 9)%, P < 0.002)), consistent with oxidative stress. From a comparison with biochemical literature we conclude that high-resolution in vivo (1)H NMR spectroscopy accurately reflects the neurochemical changes induced by a relatively modest dose of QA, which permits one to longitudinally follow mitochondrial function, oxidative stress and glial-neuronal metabolic trafficking as well as the effects of treatment in this model of Huntington disease.

Localized two-dimensional shift correlated MR spectroscopy of human brain

A two-dimensional (2D) chemical shift correlated MR spectroscopic (COSY) sequence integrated into a new volume localization technique (90 degrees -180 degrees -90 degrees ) is proposed for whole-body MR spectroscopy (MRS). Using the product operator formalism, a theoretical calculation of the volume localization as well as the coherence transfer efficiencies in 2D MRS is presented. Phantom model solutions were used to test and optimize the efficiency of the proposed sequence. A combination of different MRI transmit/receive RF coils was used: a head MRI coil and a 3" surface coil receive combined with a body coil transmit. The J cross-peaks due to N-acetyl aspartate (NAA), glutamate/glutamine (Glx), myo-inositol (mI), creatine (Cr), choline (Ch), aspartate (Asp), gamma-aminobutyrate (GABA), taurine (Tau), glutathione (GSH), threonine (Thr), and macromolecules (MM) were identified. The cross-peak intensities excited by the proposed 2D sequence were asymmetric with respect to the diagonal peaks. Localized COSY (L-COSY) spectra of cerebral prefrontal and occipital gray/white matter regions in 15 healthy controls are presented. Magn Reson Med 46:58-67, 2001.

The effects of slice-selective excitation/refocusing in localized spectral editing with gradient-selected double-quantum coherence transfer

Spectral editing using gradient-selected double-quantum filtering (DQF) with PRESS localization has been used for selective observation of metabolites in vivo. In previous studies using localized DQF sequences, it is generally assumed that the slice-selective pulses used in the sequence have no roles in coherence transfer, and do not interfere with DQF. To validate this assumption, the effects of slice-selective excitation/refocusing on DQF were investigated in DQF lactate editing sequences combined with PRESS localization. Contrary to the previous assumption, the results show that, due to chemical shift displacement artifact and J coupling, slice selection in DQF does interfere with coherence transfer, affecting both the accuracy of spatial localization and the detection sensitivity adversely. In the case of lactate editing, the effects of this interference can be accounted for simply by adjusting the strength of the slice-selection gradients and by using narrowband slice-selective refocusing pulses.

Improved selectivity of double quantum coherence filtering for the detection of glutathione in the human brain in vivo

An improved double quantum coherence (DQC) filter for the selective in vivo detection of glutathione (GSH) in the human brain at 1.5 Tesla is presented. The goal was to minimize contamination of the DQC-filtered GSH signal at 2.9 ppm with contributions arising from GABA. The modification consists of tailoring the frequency response of the read pulse, which converts DQC into anti-phase single quantum coherence in such a way that the GABA beta and gamma resonances at 3.0 and 1.9 ppm, respectively, remain unaffected. An implementation incorporating a Dante pulse train is used for in vitro tests as well as for in vivo applications. Magn Reson Med 45:708-710, 2001.

Unique in vivo applications of spin traps

The ultimate goal of in vivo electron spin resonance (ESR) spin trapping is to provide a window to the characterization and quantification of free radicals with time within living organisms. However, the practical application of in vivo ESR to systems involving reactive oxygen radicals has proven challenging. Some of these limitations relate to instrument sensitivity and particularly to the relative stability of these radicals and their nitrone adducts, as well as toxicity limitations with dosing. Our aim here is to review the strengths and weaknesses of both traditional and in vivo ESR spin trapping and to describe new approaches that couple the strengths of spin trapping with methodologies that promise to overcome some of the problems, in particular that of radical adduct decomposition. The new, complementary techniques include: (i) NMR spin trapping, which monitors new NMR lines resulting from diamagnetic products of radical spin adduct degradation and reduction, (ii) detection of *NO by ESR with dithiocarbamate: Fe(II) "spin trap-like" complexes, (iii) MRI spin trapping, which images the dithiocarbamate: Fe(II)-NO complexes by proton relaxation contrast enhancement, and (iv) the use of ESR to follow the reactions of sulfhydryl groups with dithiol biradical spin labels to form "thiol spin label adducts," for monitoring intracellular redox states of glutathione and other thiols. Although some of these approaches are in their infancy, they show promise of adding to the arsenal of techniques to measure and possibly "image" oxidative stress in living organisms in real time.

Glutathione in disease

Altered glutathione metabolism in association with increased oxidative stress has been implicated in the pathogenesis of many diseases. However, whether strategies aimed at restoring glutathione concentration and homeostasis are effective in ameliorating or modifying the natural history of these states is unknown. In this review we discuss the pathogenic role for altered glutathione metabolism in such diseases as protein energy malnutrition, seizures, Alzheimer's disease, Parkinson's disease, sickle cell anaemia, chronic diseases associated with ageing and the infected state. In addition, we discuss the efficacy of glutathione precursors in restoring glutathione homeostasis both in vitro and in vivo.

Schizophrenia: glutathione deficit in cerebrospinal fluid and prefrontal cortex in vivo

Schizophrenia is a major psychiatric disease, which affects the centre of the personality, with severe problems of perception, cognition as well as affective and social behaviour. In cerebrospinal fluid of drug-free schizophrenic patients, a significant decrease in the level of total glutathione (GSH) by 27% (P<0.05) was observed as compared to controls, in keeping with the reported reduced level of its metabolite gamma-glutamylglutamine. With a new non-invasive proton magnetic resonance spectroscopy methodology, GSH level in medial prefrontal cortex of schizophrenic patients was found to be 52% (P = 0.0012) lower than in controls. GSH plays a fundamental role in protecting cells from damage by reactive oxygen species generated among others by the metabolism of dopamine. A deficit in GSH would lead to degenerative processes in the surrounding of dopaminergic terminals resulting in loss of connectivity. GSH also potentiates the N-methyl-D-aspartate (NMDA) receptor response to glutamate, an effect presumably reduced by a GSH deficit, leading to a situation similar to the application of phencyclidine (PCP). Thus, a GSH hypothesis might integrate many established biological aspects of schizophrenia.

Methods for measuring glutathione concentration and rate of synthesis

Altered gamma-glutamylcysteinylglycine homeostasis has been implicated in a wide variety of human diseases. The measurement of the rates of synthesis or loss of gamma-glutamylcysteinylglycine is necessary in order to make meaningful inferences about changes in gamma-glutamylcysteinylglycine concentration in these diseased states. In this review, we discuss methods for measuring gamma-glutamylcysteinylglycine concentration in biological samples as well as how improvements in the sensitivity of gas chromatography-mass spectrometric analyses have permitted the development of new and convenient stable isotope tracer methods for the in-vivo measurement of gamma-glutamylcysteinylglycine kinetics.

Single-shot, three-dimensional "non-echo" localization method for in vivo NMR spectroscopy

Metabolite signals with short T(1) or T(2) are difficult to localize with full sensitivity. This limitation was overcome with the development and implementation of a single-shot, complete three-dimensional "non-echo" localization method with reduced sensitivity to spatial B(1) variation, which is suitable for measuring signals with very short T(1) or T(2), e.g., the (13)C NMR signals of glycogen. The proposed method is based on a T(1)-optimized outer volume suppression scheme using pulses of the hyperbolic secant type applied at different power levels, which is robust over a fivefold range of T(1). Strong lipid, muscle glycogen, and glucose signals originating outside the rat brain were suppressed. Signals of glycogen, aspartate, glutathione, GABA C4, N-acetyl aspartate as well as the C3 and C4 signals of glutamate and glutamine with resolved homonuclear (13)C-(13)C coupling were fully resolved in vivo at 9.4 Tesla using higher-order shimming. The method can be extended to other nuclei and to localized MRS of humans.

Magnetic resonance spectroscopy in schizophrenia: methodological issues and findings--part I

Our knowledge of the biological basis of schizophrenia has significantly increased with the contribution of in vivo proton and phosphorus magnetic resonance spectroscopy (MRS), a noninvasive tool that can assess the biochemistry from a localized region in the human body. Studies thus far suggest altered membrane phospholipid metabolism at the early stage of illness and reduced N-acetylaspartate, a measure of neuronal volume/viability in chronic schizophrenia. Inconsistencies remain in the literature, in part due to the complexities in the MRS methodology. These complexities of in vivo spectroscopy make it important to understand the issues surrounding the design of spectroscopy protocols to best address hypotheses of interest. This review addresses these issues, including 1) understanding biochemistry and the physiologic significance of metabolites; 2) the influence of acquisition parameters combined with spin-spin and spin-lattice relaxation effects on the MRS signal; 3) the composition of spectral peaks and the degree of overlapping peaks, including the broader underlying peaks; 4) factors affecting the signal-to-noise ratio; 5) the various types of localization schemes; and 6) the objectives to produce accurate and reproducible quantification results. The ability to fully exploit the potentials of in vivo spectroscopy should lead to a protocol best optimized to address the hypotheses of interest.

Single-quantum coherence filter for strongly coupled spin systems for localized (1)H NMR spectroscopy

A pulse sequence for localized in vivo (1)H NMR spectroscopy is presented, which selectively filters single-quantum coherence built up by strongly coupled spin systems. Uncoupled and weakly coupled spin systems do not contribute to the signal output. Analytical calculations using a product operator description of the strongly coupled AB spin system as well as in vitro tests demonstrate that the proposed filter produces a signal output for a strongly coupled AB spin system, whereas the resonances of a weakly coupled AX spin system and of uncoupled spins are widely suppressed. As a potential application, the detection of the strongly coupled AA'BB' spin system of taurine at 1.5 T is discussed.

Off-resonance effects of the radiofrequency pulses used in spectral editing with double-quantum coherence transfer

Spectral editing using gradient selected double-quantum (DQ) coherence transfer is often used for the selective observation of metabolites in vivo. In attempting to optimize the detection sensitivity of a conventional DQ spectral editing sequence, the effects of using radiofrequency (RF) pulses that are not at the resonance frequency of the observed peaks were investigated both theoretically and experimentally. The results show that spectral editing using pulses at the frequency of the observed resonance does not necessarily give the optimal detection sensitivity. At 7 T, the detection sensitivity of lactate observed using a DQ editing method can be increased by up to 30% by setting the RF pulses off resonance at the proper frequency. The results also suggest that slice selective RF pulses used in DQ spectral editing combined with PRESS localization may have slice profiles different from those when the same pulses are used for standard PRESS spatial localization.

Proton NMR chemical shifts and coupling constants for brain metabolites

Proton NMR chemical shift and J-coupling values are presented for 35 metabolites that can be detected by in vivo or in vitro NMR studies of mammalian brain. Measurements were obtained using high-field NMR spectra of metabolites in solution, under conditions typical for normal physiological temperature and pH. This information is presented with an accuracy that is suitable for computer simulation of metabolite spectra to be used as basis functions of a parametric spectral analysis procedure. This procedure is verified by the analysis of a rat brain extract spectrum, using the measured spectral parameters. In addition, the metabolite structures and example spectra are presented, and clinical applications and MR spectroscopic measurements of these metabolites are reviewed.

Simultaneous spectral editing for gamma-aminobutyric acid and taurine using double quantum coherence transfer

Conventional double quantum (DQ) editing techniques recover resonances of one metabolite at a time and are thus inefficient for monitoring metabolic changes involving several metabolites. A DQ coherence transfer double editing sequence using a dual-band DQ coherence read pulse is described here. The sequence permits simultaneous spectral editing for two metabolites with similar J coupling constants in a single scan. Simultaneous editing for taurine and gamma-aminobutyric acid (GABA) is demonstrated using solution phantoms and rat brain tissue. Selectivity of the double editing sequence for the target metabolites is as good as that achieved using conventional DQ editing which selects each metabolite individually. With experimental parameters of the double editing sequence chosen to optimize GABA editing, the sensitivity for GABA detection is the same as that with GABA editing only, while the sensitivity for taurine detection is decreased slightly compared to that with taurine editing only.