Melissa Terpstra

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 1H 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 μmol/g (mean ± SD, n = 12). Magn Reson Med 50:19–23, 2003.

Direct in vivo measurement of human cerebral GABA concentration using MEGA-editing at 7 Tesla

Spectral editing of the GABA spin system is hampered by coediting of macromolecule (MM) coherences. To reduce contamination arising from MMs in spectra edited for GABA, the highest field strength currently available for human experimentation (7 Tesla) and MEGA‐based editing were used. Despite judicious choice of experimental parameters, MM contamination was found to arise from field drifts. When the MM contribution was accounted for, [GABA] = 0.75 ± 0.14 μmol/g (mean ± SD, N = 16) relative to 8 μmol/g creatine (Cr), whereas without accounting for the MM signal [GABA*] = 0.88 ± 0.23 μmol/g (mean ± SD, N = 16). Incorporating the direct experimental assessment of MM contamination to the edited GABA signal substantially reduced the variance of the measurement, resulting in concentrations that were in excellent agreement with previous 13C labeling experiments. Magn Reson Med 47:1009–1012, 2002.

N-acetylcysteine boosts brain and blood glutathione in gaucher and Parkinson diseases

Objective This study aimed to determine if the antioxidant N-acetylcysteine (NAC) is able to alter peripheral and central redox capabilities in patients with Parkinson disease (PD) or Gaucher disease (GD). Methods The study included nondemented adult subjects: 3 with PD, 3 with GD, and 3 healthy controls. Baseline brain glutathione (GSH) concentrations were measured using 7-T magnetic resonance spectroscopy (MRS). Baseline blood reduced-to-oxidized GSH ratios were determined for each subject. Brain GSH concentrations and blood redox ratios were then determined during and at specified time points after a single, 150-mg/kg NAC infusion. Results N-acetylcysteine increased blood GSH redox ratios in those with PD and GD and healthy controls, which was followed by an increase in brain GSH concentrations in all subjects. Conclusions This is the first demonstration that with MRS, it is possible to directly measure and monitor increases in brain GSH levels in the human brain in response to a single, intravenous administration of NAC. This work shows the potential utility of MRS monitoring, which could assist in determining dosing regimens for clinical trials of this potentially useful antioxidant therapy for PD disease, GD, and other neurodegenerative disorders.

Proton MRS of the unilateral substantia nigra in the human brain at 4 tesla: Detection of high GABA concentrations

Parkinsons disease (PD) is characterized by loss of dopaminergic neurons in the substantia nigra (SN), the cause of which is unknown. Characterization of early SN pathology could prove beneficial in the treatment and diagnosis of PD. The present study shows that with the use of short‐echo (5 ms) Stimulated‐Echo Acquisition Mode (STEAM) spectroscopy and LCModel, a neurochemical profile consisting of 10 metabolites, including γ‐aminobutyric acid (GABA), glutamate (Glu), and glutathione (GSH), can be measured from the unilateral SN at 4 tesla. The neurochemical profile of the SN is unique and characterized by a fourfold higher GABA/Glu ratio compared to the cortex, in excellent agreement with established neurochemistry. The presence of elevated GABA levels in SN was validated with the use of editing, suggesting that partial volume effects were greatly reduced. These findings establish the feasibility of obtaining a neurochemical profile of the unilateral human SN by single‐voxel spectroscopy in small volumes. Magn Reson Med, 2006.

Regional neurochemical profiles in the human brain measured by ¹H MRS at 7 T using local B₁ shimming.

Increased sensitivity and chemical shift dispersion at ultra‐high magnetic fields enable the precise quantification of an extended range of brain metabolites from 1H MRS. However, all previous neurochemical profiling studies using single‐voxel MRS at 7 T have been limited to data acquired from the occipital lobe with half‐volume coils. The challenges of 1H MRS of the human brain at 7 T include short T2 and complex B1 distribution that imposes limitations on the maximum achievable B1 strength. In this study, the feasibility of acquiring and quantifying short‐echo (TE = 8 ms), single‐voxel 1H MR spectra from multiple brain regions was demonstrated by utilizing a 16‐channel transceiver array coil with 16 independent transmit channels, allowing local transmit B1 (B1+) shimming. Spectra were acquired from volumes of interest of 1–8 mL in brain regions that are of interest for various neurological disorders: frontal white matter, posterior cingulate, putamen, substantia nigra, pons and cerebellar vermis. Local B1+ shimming substantially increased the transmit efficiency, especially in the peripheral and ventral brain regions. By optimizing a STEAM sequence for utilization with a 16‐channel coil, artifact‐free spectra were acquired with a small chemical shift displacement error (<5% /ppm/direction) from all regions. The high signal‐to‐noise ratio enabled the quantification of neurochemical profiles consisting of at least nine metabolites, including γ‐aminobutyric acid, glutamate and glutathione, in all brain regions. Significant differences in neurochemical profiles were observed between brain regions. For example, γ‐aminobutyric acid levels were highest in the substantia nigra, total creatine was highest in the cerebellar vermis and total choline was highest in the pons, consistent with the known biochemistry of these regions. These findings demonstrate that single‐voxel 1H MRS at ultra‐high field can reliably detect region‐specific neurochemical patterns in the human brain, and has the potential to objectively detect alterations in neurochemical profiles associated with neurological diseases. Copyright

Detection of an antioxidant profile in the human brain in vivo via double editing with MEGA-PRESS

Vitamin C (ascorbate) and glutathione (GSH) are the two most concentrated non‐enzymatic antioxidants in the human brain. Double editing with (DEW) MEGA‐PRESS at 4T was designed in this study to measure both antioxidants in the same amount of time previously required to measure one. In the occipital lobe of four human subjects, resolved ascorbate (Asc) and GSH resonances were detected repeatedly and simultaneously using DEW MEGA‐PRESS. The Asc and GSH concentrations measured using LCModel analysis of DEW MEGA‐PRESS spectra were 0.8 ± 0.1 and 1.0 ± 0.1 μmol/g (mean ± SD), with average Cramer‐Rao lower bounds (CRLB) of 10% and 7%, respectively. Aside from the effects of J‐modulation at a common echo time (TE), double editing did not compromise sensitivity. To determine the extent to which the oxidized forms of Asc and GSH contribute to DEW MEGA‐PRESS spectra in vivo, chemical shifts and coupling constants for dehydroascorbate (DHA) and oxidized glutathione (GSSG) were measured at physiologic pH and temperature. DHA does not contribute to the 3.73 ppm DEW MEGA‐PRESS Asc resonance. GSSG contributions to the DEW MEGA‐PRESS GSH resonance (3.0 ppm) are negligible under physiologic conditions, and would be evidenced by a distinct GSSG resonance (3.3 ppm) at exceptionally high concentrations. Magn Reson Med, 2006.

Relationships Among Lactate Concentration, Blood Flow and Histopathologic Profiles in Rat C6 Glioma

Increased capacity for glycolytic metabolism is a well‐known characteristic of neoplastic cells. Because lactic acid is the end product of glycolysis, in vivo MRS measurements of tumor lactate concentration ([lac]t) may provide valuable information about tumor metabolism, which will aid the development of therapies and the clinical diagnosis and treatment of tumors. In the present study, several hemodynamic and histologic parameters were evaluated with respect to their influence on [lac]t. Pronounced differences in [lac]t in two distinct populations of tumors suggested a putative perfusion threshold. Above this threshold, [lac]t was independent of hemodynamic and histologic factors including tumor blood flow (measured using MRS and the method of D2O washout), extent of necrosis and inflammatory cell infiltrate. Thus, for most tumors, [lac]t was not determined by any one single factor such as hypoxia, venous clearance, glucose supply, extent of necrosis or degree of inflammatory cell infiltrate. Rather, [lac]t may be equilibrated, at least in part, by an interplay of forces involving hemodynamics and substrate supply. In general, the data are consistent with the hypothesis that elevated lactate in most tumors is related to the high glycolytic activity of adequately perfused, viable neoplastic cells.

Noninvasive quantification of ascorbate and glutathione concentration in the elderly human brain

In this study, ascorbate (Asc) and glutathione (GSH) concentrations were quantified noninvasively using double‐edited 1H MRS at 4 T in the occipital cortex of healthy young [age (mean ± standard deviation) = 20.4 ± 1.4 years] and elderly (age = 76.6 ± 6.1 years) human subjects. Elderly subjects had a lower GSH concentration than younger subjects (p < 0.05). The Asc concentration was not significantly associated with age. Furthermore, the lactate (Lac) concentration was higher in elderly than young subjects. Lower GSH and higher Lac concentrations are indications of defective protection against oxidative damage and impaired mitochondrial respiration. The extent to which the observed concentration differences could be associated with physiological differences and methodological artifacts is discussed. In conclusion, GSH and Asc concentrations were compared noninvasively for the first time in young vs elderly subjects. Copyright

1H NMR detection of vitamin C in human brain in vivo

Vitamin C (ascorbate) is well established as an essential nutrient that functions as an antioxidant. Since it is present in the human brain at detectable concentrations, this study was designed to detect and quantify ascorbate in the human brain in vivo using 1H NMR spectroscopy (MRS). Ascorbate was consistently detected in all five study subjects, and was measured using MEGA‐PRESS difference editing. The in vivo resonance pattern was consistent with that of ascorbate based on position, line width, peak pattern, and relative intensity. Metabolites with a potential for coediting were assessed using phantom solutions. The putative resonances of myo‐inositol, lactate, glycerophosphocholine, phosphocholine, and phosphoethanolamine were detected at positions distinct from those of ascorbate. This study represents the first in vivo detection of vitamin C in the human brain using 1H MRS. A concentration of 1.3 ± 0.3 μmol/g (mean ± SD, N = 4) was estimated. Magn Reson Med 51:225–229, 2004.

Test-retest reproducibility of neurochemical profiles with short-echo, single-voxel MR spectroscopy at 3T and 7T

To determine the test‐retest reproducibility of neurochemical concentrations obtained with a highly optimized, short‐echo, single‐voxel proton MR spectroscopy (MRS) pulse sequence at 3T and 7T using state‐of‐the‐art hardware.