Evidence of elevated glutamate in multiple sclerosis using magnetic resonance spectroscopy at 3 T

Progressive multiple sclerosis and gray matter pathology: an MRI perspective

The evidence suggesting a role of extensive cortical demyelization and atrophy in progressive multiple sclerosis is rapidly increasing. Although conventional magnetic resonance imaging has had a huge impact on multiple sclerosis by enabling an earlier diagnosis, and by providing surrogate markers for monitoring disease response to anti-inflammatory/immunomodulatory treatments, it is limited by the low pathological specificity and the low sensitivity to both diffuse damage in normal-appearing white matter and focal and diffuse damage in gray matter. Advanced magnetic resonance imaging techniques can partially overcome these limitations by providing markers more specific to the underlying pathologic substrates and more sensitive to the structural and functional "occult" brain tissue damage in patients with multiple sclerosis. This review describes brain and spinal cord imaging studies of multiple sclerosis with particular emphasis on gray matter imaging in both secondary progressive and primary progressive multiple sclerosis, discusses the clinical implications of gray matter damage, and outlines current magnetic resonance imaging developments at high and ultrahigh magnetic field strength.

Glutamate and ATP signalling in white matter pathology

Excessive signalling by excitatory neurotransmitters like glutamate and ATP can be deleterious to neurons and oligodendroglia, and cause disease. In particular, sustained activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), kainate and N-methyl-d-aspartate (NMDA) receptors damages oligodendrocytes, a feature that depends entirely on Ca(2+) overload of the cytoplasm and that can be initiated by disruption of glutamate homeostasis. Thus, inhibition of glutamate uptake by activated microglia can compromise glutamate homeostasis and induce oligodendrocyte excitotoxicity. Moreover, non-lethal, brief activation of kainate receptors in oligodendrocytes rapidly sensitizes these cells to complement attack as a consequence of oxidative stress. In addition to glutamate, ATP signalling can directly trigger oligodendrocyte excitotoxicity via activation of Ca(2+) -permeable P2X7 purinergic receptors, which mediates ischaemic damage to white matter (WM) and causes lesions that are reminiscent of multiple sclerosis (MS) plaques. Conversely, blockade of P2X7 receptors attenuates post-ischaemic injury to WM and ameliorates chronic experimental autoimmune encephalomyelitis, a model of MS. Importantly, P2X7 expression is elevated in normal-appearing WM in patients with MS, suggesting that signalling through this receptor in oligodendrocytes may be enhanced in this disease. Altogether, these observations reveal novel mechanisms by which altered glutamate and ATP homeostasis can trigger oligodendrocyte death. This review aims at summarizing current knowledge about the mechanisms leading to WM damage as a consequence of altered neurotransmitter signalling, and their relevance to disease. This knowledge will generate new therapeutic avenues to treat more efficiently acute and chronic WM pathology.

Mechanisms of neuronal dysfunction and degeneration in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system. Due to its high prevalence, MS is the leading cause of non-traumatic neurological disability in young adults in the United States and Europe. The clinical disease course is variable and starts with reversible episodes of neurological disability in the third or fourth decade of life. This transforms into a disease of continuous and irreversible neurological decline by the sixth or seventh decade. Available therapies for MS patients have little benefit for patients who enter this irreversible phase of the disease. It is well established that irreversible loss of axons and neurons are the major cause of the irreversible and progressive neurological decline that most MS patients endure. This review discusses the etiology, mechanisms and progress made in determining the cause of axonal and neuronal loss in MS.

Neuroimaging in multiple sclerosis: neurotherapeutic implications

Imaging techniques, in particular magnetic resonance imaging (MRI), play an important role in the diagnosis and management of multiple sclerosis (MS) and related demyelinating diseases. Findings on MRI studies of the brain and spinal cord are critical for MS diagnosis, are used to monitor treatment response and may aid in predicting disease progression in individual patients. In addition, results of imaging studies serve as essential biomarkers in clinical trials of putative MS therapies and have led to important insights into disease pathophysiology. Although they are useful tools and provide in vivo measures of disease-related activity, there are some important limitations of MRI findings in MS, including the non-specific nature of detectable white matter changes, the poor correlation with clinical disability, the limited sensitivity and ability of standard measures of gadolinium enhancing lesions and T2 lesions to predict future clinical course, and the lack of validated biomarkers of long term outcomes. Advancements that hold promise for the future include new techniques that are sensitive to diffuse changes, the increased use of higher field scanners, measures that capture disease related changes in gray matter, and the use of combined structural and functional imaging approaches to assess the complex and evolving disease process that occurs during the course of MS.

MR spectroscopy and spectroscopic imaging of the brain

Magnetic resonance spectroscopy (MRS) and the related technique of magnetic resonance spectroscopic imaging (MRSI) are widely used in both clinical and preclinical research for the non-invasive evaluation of brain metabolism. They are also used in medical practice, although their ultimate clinical value continues to be a source of discussion. This chapter reviews the general information content of brain spectra and commonly used protocols for both MRS and MRSI and also touches on data analysis methods and quantitation. The main focus is on proton MRS for application in humans, but many of the methods are also applicable to other nuclei and studies of animal models as well.

Elevated cerebral glutamate and myo-inositol levels in cognitively normal middle-aged adults with metabolic syndrome

Metabolic syndrome (MetS) is a cluster of risk factors associated with significant cardiovascular morbidity and mortality and diminished cognitive function. Given that the cerebral mechanisms mediating the relationship between peripheral metabolic dysfunction and cognitive impairment are unknown, we set out to examine the relationship between diagnosis of metabolic syndrome and cerebral metabolism. Thirteen participants with MetS (aged 48 ± 6 years) and 25 healthy adults (aged 51 ± 6 years) underwent neuropsychological assessment, health screen and proton magnetic resonance spectroscopy ((1)H MRS) examining N-acetyl-aspartate (NAA), myo-inositol (mI), creatine (Cr), choline (Cho), and glutamate (Glu) concentrations in occipitoparietal grey matter. Cerebral metabolite ratios (NAA/Cr, Cho/Cr, mI/Cr, and Glu/Cr) of participants with MetS, defined by the International Diabetes Federation criteria, were compared with controls matched for age, education, cognition, and emotional function. There were no significant differences in global cognitive function, memory, language, and psychomotor performance between the groups. Diagnosis of MetS was associated with significantly higher mI/Cr (F(1,36) = 5.02, p = 0.031) and Glu/Cr ratio (F(1,36) = 4.81, p = 0.035). Even in cognitively normal adults, MetS is related to cerebral metabolic disturbances, a possible indication of early brain vulnerability. Longitudinal studies that begin in mid-life can help validate the use of (1)H MRS markers as indicators of long-term cognitive outcomes.

Abnormal activity of the Na/Ca exchanger enhances glutamate transmission in experimental autoimmune encephalomyelitis

It is increasingly accepted that excessive glutamate release plays a key role in the pathophysiology of grey matter damage in multiple sclerosis (MS). The mechanisms causing abnormal glutamate transmission in this disorder are however largely unexplored. By means of electrophysiological recordings from single striatal neurons in slices, we found that the presymptomatic and acute phases of experimental autoimmune encephalomyelitis (EAE), a preclinical model of MS, are associated with enhanced synaptic release of glutamate. The reverse mode of action of axonal Na(+)/Ca(++) exchanger, secondary to abnormal functioning of voltage-dependent Na(+) channels, was identified as a major cause of this alteration. In fact, inhibition of the Na(+)/Ca(++) exchanger with bepridil or with KB-R7943, which selectively blocks the reverse mode of the exchanger, reduced the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) recorded from striatal neurons in EAE mice but not in control animals. In the presence of tetrodotoxin (TTX), a blocker of voltage-dependent Na(+) channels, the effect of bepridil was normalized in acute (25 days post-immunization) EAE mice, indicating that axonal accumulation of Na(+) ions flowing through voltage-dependent Na(+) channels plays a role in the abnormal activity of the Na(+)/Ca(++) exchanger in EAE. Our data reveal an important role of Na(+)/Ca(++) exchanger and of voltage-dependent Na(+) channels in the pathological process of EAE, and provide a rationale for the use of neuroprotective strategies since the very early stages of MS.

Proton MRS of large multiple sclerosis lesions reveals subtle changes in metabolite T(1) and area

The T(1) values of metabolites were measured in eight subjects with clinically definite multiple sclerosis (MS) having at least one large brain lesion (2.6 ± 0.7 mL) and in eight age- and sex-matched healthy controls. MRS examinations were conducted at 1.5 T using point-resolved spectroscopy (PRESS) (TE = 30 ms, TR = 530, 750, 1200, 1500, 3500, 5000 ms). Spectra were acquired from a voxel placed in the largest lesion in the subject with MS, and in a corresponding voxel (same size and region) in normal white matter (NWM) in the matched control, and were fitted using LCModel. As there are regional variations in metabolite and water T(1) and metabolite signal areas, careful placement of the control voxel was necessary to measure subtle differences between the lesions and NWM. The T(1) and T(1)-corrected signal areas of creatine were the same in MS lesions as in controls. The T(1) values of choline were significantly shorter in MS lesions located in occipital and parietal, but not in frontal, white matter. N-Acetylaspartate (NAA) and myoinositol T(1) values in MS lesions were similar to those in NWM; however, the area of myoinositol correlated directly with lesion water T(1), and the area of NAA correlated inversely with lesion water T(1). MR spectra acquired at short TR require T(1) correction of choline for accurate quantification. Careful voxel placement in controls to match lesion location in subjects with MS enables a clearer view of the subtle changes in lesions.

Imaging biomarkers in multiple sclerosis

Recent years have witnessed impressive advances in the use of magnetic resonance imaging (MRI) for the assessment of patients with multiple sclerosis (MS). Complementary to the clinical evaluation, conventional MRI provides crucial pieces of information for the diagnosis of MS. However, the correlation between the burden of lesions observed on conventional MRI scans and the clinical manifestations of the disease remains weak. The discrepancy between clinical and conventional MRI findings in MS is explained, at least partially, by the limited ability of conventional MRI to characterize and quantify the heterogeneous features of MS pathology. Other quantitative MR-based techniques, however, have the potential to overcome such a limitation of conventional MRI. Indeed, magnetization transfer MRI, diffusion tensor MRI, proton MR spectroscopy, and functional MRI are contributing to elucidate the mechanisms that underlie injury, repair, and functional adaptation in patients with MS. Such techniques are likely to benefit from the use of high-field MR systems and thus allow in the near future providing additional insight into all these aspects of the disease. This review summarizes how MRI is dramatically changing our understanding of the factors associated with the accumulation of irreversible disability in MS and highlights the reasons why they should be used more extensively in studies of disease evolution and clinical trials.

Genetic variation influences glutamate concentrations in brains of patients with multiple sclerosis

Glutamate is the main excitatory neurotransmitter in the mammalian brain. Appropriate transmission of nerve impulses through glutamatergic synapses is required throughout the brain and forms the basis of many processes including learning and memory. However, abnormally high levels of extracellular brain glutamate can lead to neuroaxonal cell death. We have previously reported elevated glutamate levels in the brains of patients suffering from multiple sclerosis. Here two complementary analyses to assess the extent of genomic control over glutamate levels were used. First, a genome-wide association analysis in 382 patients with multiple sclerosis using brain glutamate concentration as a quantitative trait was conducted. In a second approach, a protein interaction network was used to find associated genes within the same pathway. The top associated marker was rs794185 (P < 6.44 x 10(-7)), a non-coding single nucleotide polymorphism within the gene sulphatase modifying factor 1. Our pathway approach identified a module composed of 70 genes with high relevance to glutamate biology. Individuals carrying a higher number of associated alleles from genes in this module showed the highest levels of glutamate. These individuals also showed greater decreases in N-acetylaspartate and in brain volume over 1 year of follow-up. Patients were then stratified by the amount of annual brain volume loss and the same approach was performed in the 'high' (n = 250) and 'low' (n = 132) neurodegeneration groups. The association with rs794185 was highly significant in the group with high neurodegeneration. Further, results from the network-based pathway analysis remained largely unchanged even after stratification. Results from these analyses indicated that variance in the activity of neurochemical pathways implicated in neurodegeneration is explained, at least in part, by the inheritance of common genetic polymorphisms. Spectroscopy-based imaging provides a novel quantitative endophenotype for genetic association studies directed towards identifying new factors that contribute to the heterogeneity of clinical expression of multiple sclerosis.

Reduced expression of plasma membrane calcium ATPase 2 and collapsin response mediator protein 1 promotes death of spinal cord neurons

The mechanisms underlying neuronal pathology and death in the spinal cord (SC) during inflammation remain elusive. We previously showed the important role of plasma membrane calcium ATPases (PMCAs) in the survival of SC neurons, in vitro. We also postulated that a decrease in PMCA2 expression could cause neuronal death during experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. The current studies were undertaken to define the specific contribution of PMCA2 to degeneration of SC neurons, the effectors downstream to PMCA2 mediating neuronal death and the triggers that reduce PMCA2 expression. We report that knockdown of PMCA2 in SC neurons decreases collapsin response mediator protein 1 (CRMP1) levels. This is followed by cell death. Silencing of CRMP1 expression also leads to neuronal loss. Kainic acid reduces both PMCA2 and CRMP1 levels and induces neuronal death. Administration of an alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA)/kainate receptor antagonist, at onset or peak of EAE, restores the decreased PMCA2 and CRMP1 levels to control values and ameliorates clinical deficits. Thus, our data link the reduction in PMCA2 expression with perturbations in the expression of CRMP1 and the ensuing death of SC neurons. This represents an additional mechanism underlying AMPA/kainate receptor-mediated excitotoxicity with relevance to neurodegeneration in EAE.

In vivo 1H NMR spectroscopy of the human brain at 9.4 T: initial results

In vivo proton NMR spectroscopy allows non-invasive detection and quantification of a wide range of biochemical compounds in the brain. Higher field strength is generally considered advantageous for spectroscopy due to increased signal-to-noise and increased spectral dispersion. So far (1)H NMR spectra have been reported in the human brain up to 7 T. In this study we show that excellent quality short echo time STEAM and LASER (1)H NMR spectra can be measured in the human brain at 9.4 T. The information content of the human brain spectra appears very similar to that measured in the past decade in rodent brains at the same field strength, in spite of broader linewidth in human brain. Compared to lower fields, the T(1) relaxation times of metabolites were slightly longer while T(2) relaxation values of metabolites were shorter (<100 ms) at 9.4 T. The linewidth of the total creatine (tCr) resonance at 3.03 ppm increased linearly with magnetic field (1.35 Hz/T from 1.5 T to 9.4 T), with a minimum achievable tCr linewidth of around 12.5 Hz at 9.4 T. At very high field, B(0) microsusceptibility effects are the main contributor to the minimum achievable linewidth.

Metabotropic glutamate receptor-4 modulates adaptive immunity and restrains neuroinflammation

High amounts of glutamate are found in the brains of people with multiple sclerosis, an inflammatory disease marked by progressive demyelination. Glutamate might affect neuroinflammation via effects on immune cells. Knockout mice lacking metabotropic glutamate receptor-4 (mGluR4) were markedly vulnerable to experimental autoimmune encephalomyelitis (EAE, a mouse model of multiple sclerosis) and developed responses dominated by interleukin-17-producing T helper (T(H)17) cells. In dendritic cells (DCs) from those mice, defective mGluR4 signaling-which would normally decrease intracellular cAMP formation-biased T(H) cell commitment to the T(H)17 phenotype. In wild-type mice, mGluR4 was constitutively expressed in all peripheral DCs, and this expression increased after cell activation. Treatment of wild-type mice with a selective mGluR4 enhancer increased EAE resistance via regulatory T (T(reg)) cells. The high amounts of glutamate in neuroinflammation might reflect a counterregulatory mechanism that is protective in nature and might be harnessed therapeutically for restricting immunopathology in multiple sclerosis.

Memantine for cognitive impairment in multiple sclerosis: a randomized placebo-controlled trial

BACKGROUND

Memantine, an NMDA antagonist, is effective for moderate to severe Alzheimer's disease.

OBJECTIVE

Determine whether memantine improves cognitive performance (CP) among subjects with multiple sclerosis (MS) and cognitive impairment (CI).

METHODS

This double-blind, randomized, placebo-controlled trial (Clinicaltrials.gov NCT00300716) compared memantine 10 mg twice a day (4 week titration followed by 12 weeks on the highest tolerated dose) with placebo. The primary outcome was the change from baseline to exit on the Paced Auditory Serial Addition Test (PASAT) and the California Verbal Learning Test-II (CVLT-II) Long Delay Free Recall (LDFR). Secondary outcomes included additional neuropsychological tests; self-report measures of quality of life, fatigue, and depression; and family/caregiver reports of subjects' CI and neuropsychiatric symptoms.

RESULTS

The differences between the groups on the change on the PASAT (placebo-memantine = 0.0 correct responses, 95% CI 3.4, 3.4; p = 0.9) and on CVLT-II LDFR (placebo-memantine =-0.6 words, 95% CI -2.1, 0.8; p = 0.4) as well as on the other cognitive tests were not significant. Subjects on memantine had no serious adverse events (AEs) but had more fatigue and neurological AEs as well as, per family members' reports, less cognitive improvement and greater neuropsychiatric symptoms than subjects on placebo.

CONCLUSION

Memantine 10 mg twice a day does not improve CP in subjects with MS, ages 18-65, without major depression, who have subjective cognitive complaints and perform worse than one SD below the mean on the PASAT or on the California Verbal Learning Test-II (total recall or delayed free recall).

Reduced creatine kinase B activity in multiple sclerosis normal appearing white matter

Background

Two studies using ³¹P-magnetic resonance spectroscopy (MRS) reported enhanced phosphocreatine (PCr) levels in normal appearing white matter (NAWM) of subjects with multiple sclerosis (MS), but this finding could not be properly explained.

Methodology/Principal Findings

We performed ³¹P-MRS and ¹H-MRS in the NAWM in 36 subjects, including 17 with progressive MS, 9 with benign MS, and 10 healthy controls. Compared to controls, PCr/β-ATP and PCr/total ³¹P ratios were significantly increased in subjects with progressive MS, but not with benign MS. There was no correlation between PCr ratios and the N-acetylaspartate/creatine ratio, suggesting that elevated PCr levels in NAWM were not secondary to axonal loss. In the central nervous system, PCr is degraded by creatine kinase B (CK-B), which in the white matter is confined to astrocytes. In homogenates of NAWM from 10 subjects with progressive MS and 10 controls without central nervous system disease, we measured CK-B levels with an ELISA, and measured its activity with an enzymatic assay kit. Compared to controls, both CK-B levels and activity were decreased in subjects with MS (22.41 versus 46.28 µg/ml; p = 0.0007, and 2.89 versus 7.76 U/l; p<0.0001).

Conclusions/Significance

Our results suggest that PCr metabolism in the NAWM in MS is impaired due to decreased CK-B levels. Our findings raise the possibility that a defective PCr metabolism in astrocytes might contribute to the degeneration of oligodendrocytes and axons in MS.

The AMPA receptor as a therapeutic target: current perspectives and emerging possibilities

The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) is a subtype of the ionotropic glutamate receptors that plays a prominent role in neurotransmission and is widespread throughout the CNS. Because of this, its malfunction can result in a multitude of nervous system diseases. This review looks at compounds that are able to modulate AMPAR function by binding to one of several sites on the receptor that either downregulate its function (competitive, noncompetitive and uncompetitive antagonists) or upregulate its function (positive modulators). It will also give an account of the various diseases that have implicated AMPAR dysfunction and how specific types of AMPAR modulator may be beneficial in their treatment. The AMPAR remains an unexploited but important therapeutic target.

Brain metabolite proton T2 mapping at 3.0 T in relapsing-remitting multiple sclerosis

PURPOSE

To test the hypothesis that T2 signals in lesions and normal-appearing tissue are sufficiently similar that signal variations represent true variations in metabolite concentration.

MATERIALS AND METHODS

The T2 distributions of N-acetylaspartate (NAA), creatine (Cr), and choline (Cho) at 3.0 T were mapped in the brain of 10 relapsing-remitting (RR) MS patients of 0.3-12 years disease duration with multivoxel (four sections of 80 1-cm(3) voxels) point-resolved proton spectroscopy imaging in a two-point protocol. Institutional review board approval and written informed consent were obtained; the study was Health Insurance Portability and Accountability-compliant. Mixed-model analysis of variance was performed to compare brain regions and lesion types for each metabolite; a Wilcoxon test was performed to compare observed T2 values with age-based predictions.

RESULTS

The T2 histograms from 320 voxels in each patient were similar in peak position for mean values (+/- standard error) for NAA (250 msec +/- 9), Cr (166 msec +/- 3), and Cho (221 msec +/- 6); shape was characterized by full width at half maximum values of 174 msec +/- 11, 98 msec +/- 3, and 143 msec +/- 5, respectively. Regional T2 values in white matter (WM; 298 msec +/- 6, 162 msec +/- 1, and 222 msec +/- 4 for NAA, Cr, and Cho, respectively) were all significantly longer than in gray matter (GM; 221 msec +/- 7, 143 msec +/- 4, and 205 msec +/- 8, respectively) but not different from isointense (313 msec +/- 24, 188 msec +/- 12, and 238 msec +/- 17, respectively) or hypointense (296 msec +/- 27, 163 msec +/- 12, and 199 msec +/- 12, respectively) lesions, except for the Cho value for hypointense lesion, which was significantly lower. When compared with corresponding values in healthy contemporaries, these T2 values were shorter by 18%, 8%, and 14% in GM and by 21%, 12%, and 13% in WM for NAA, Cr, and Cho, respectively.

CONCLUSION

For the purpose of metabolic quantification at 3.0 T and echo times of less than 100 msec, an average T2 value per metabolite should suffice for any brain region and lesion regardless of disease duration, age, or disability in any RR MS patient and their controls. (c) RSNA, 2010.

Advanced magnetic resonance imaging techniques to better understand multiple sclerosis

Magnetic resonance imaging (MRI) has considerably improved the diagnosis and monitoring of multiple sclerosis (MS). Conventional MRI such as T₂-weighted and gadolinium-enhanced T₁-weighted sequences detect focal lesions of the white matter, damage of the blood-brain barrier, and tissue loss and inflammatory activity within lesions. However, these conventional MRI metrics lack the specificity required for characterizing the underlying pathophysiology, especially diffuse damage occurring throughout the whole central nervous system. To overcome these limitations, advanced MRI techniques have been developed to get more sensitive and specific parameters of focal and diffuse brain damage. Among these techniques, magnetization transfer imaging, diffusion MRI, functional MRI, and magnetic resonance spectroscopy are the most significant. In this article, we provide an overview of these advanced MRI techniques and their contribution to the better characterization and understanding of MS.

Optimized glutamate detection at 3T

PURPOSE

To identify the pulse sequence and acquisition parameters that result in the most accurate and repeatable measurements of glutamate (Glu) concentration in the brain at 3T.

MATERIALS AND METHODS

Simulations were performed to compare the accuracy and repeatability of 11 pulse sequences and acquisition parameters, within four general classes (PRESS, STEAM, Carr-Purcell PRESS [CPRESS] and TE averaged PRESS [JPRESS]), the majority of which were previously suggested as optimal for Glu detection. Three of the simulated acquisitions were implemented in a clinical scanner and measures of repeatability in vivo were compared to their simulated values.

RESULTS

Good agreement was demonstrated between simulated and experimentally determined measures of repeatability. Among the acquisitions considered, a CPRESS sequence with minimal echo time, together with, possibly, a short TE PRESS sequence, result in the most repeatable within session Glu measurements, while slightly overestimating the Glu concentration. Excellent accuracy is demonstrated by the simulations for a JPRESS sequence, at the expense of lower repeatability than optimal PRESS or CPRESS sequences.

CONCLUSION

Further proof of concept is presented toward validation of a simulation approach to understand pulse sequence performance in measuring the concentration of a given metabolite. Improved within session Glu measurement repeatability is predicted for CPRESS and demonstrated in vivo.

1H-MRS for the diagnosis of acute disseminated encephalomyelitis: insight into the acute-disease stage

BACKGROUND

Acute disseminated encephalomyelitis (ADEM) is a demyelinating disorder of the central nervous system (CNS). Differentiating ADEM from other inflammatory disorders, such as multiple sclerosis, is not always conclusive using conventional MRI.

OBJECTIVE

To evaluate longitudinal magnetic resonance spectroscopy (MRS) changes that distinguish ADEM from other inflammatory disorders.

MATERIALS AND METHODS

MRI/MRS scans were performed in seven patients with ADEM during the acute and chronic phases of the disease.

RESULTS

Partial recovery was detected between the acute and chronic phases in choline/creatine ratio. Major elevation of lipids and reduction in myo-inositol/creatine ratio was detected in all patients during the acute phase, followed by a reduction in lipids peak and elevation above normal in myo-inositol/creatine ratio during the chronic phase.

CONCLUSION

Consistent and unique MRS changes in metabolite ratios between the acute and chronic presentations of the disease were found. To the best of our knowledge, these patterns have not been described in other inflammatory disorders and might assist in the early diagnosis of ADEM.

Lower glutamate levels in rostral anterior cingulate of chronic cocaine users - A (1)H-MRS study using TE-averaged PRESS at 3 T with an optimized quantification strategy

Previous studies have shown significantly lower metabolism and functional activity in the anterior cingulate cortex (ACC) of human cocaine addicts. The present study examined whether this ACC hypoactivity is associated with altered glutamate (Glu), the primary excitatory neurotransmitter in the central nervous system (CNS), which has been recently implicated in drug addiction. Participants comprised 14 chronic cocaine addicts and 14 matched healthy volunteers who were examined using (1)H magnetic resonance spectroscopy at 3 T. A new quantification strategy for echo time (TE)-averaged point-resolved spectroscopy (PRESS) was applied to disentangle relaxation effects from J-evolution of coupled spin systems such as Glu. The concentrations of Glu as well as N-acetyl aspartate (NAA), total creatine (tCr), choline-containing compounds (tCho), and myo-inositol (Ins) were estimated from both groups. Glu/tCr was significantly lower in chronic cocaine users compared to control subjects and was significantly correlated with years of cocaine use. Glu/tCr was also positively correlated with NAA/tCr. NAA/tCr significantly decreased with age but was not significantly different between the two groups. These findings suggest a metabolic/neurotransmitter dysregulation associated with cocaine addiction and support a possible therapeutic intervention strategy aimed at normalizing the Glu transmission and function in the treatment of cocaine addiction.

Axonal degeneration in multiple sclerosis: the mitochondrial hypothesis

Multiple sclerosis (MS) is a chronic disease of the central nervous system, affecting more than 2 million people worldwide. Traditionally considered an inflammatory demyelinating disease, recent evidence now points to axonal degeneration as crucial to the development of irreversible disability. Studies show that axonal degeneration occurs throughout the entire course of MS. Although the specific mechanisms causing axonal damage may differ at various stages, mitochondrial failure seems to be a common underlying theme. This review addresses the mitochondrial hypothesis for axonal degeneration in MS, highlighting the mechanisms by which mitochondrial dysfunction leads to axonal disruption in acute inflammatory lesions and the chronic axonopathy in progressive MS. Emphasis is placed on Ca(2+), free radical production, and permeability transition pore opening as key players in mitochondrial failure, axonal transport impairment, and subsequent axonal degeneration. In addition, the role of mitochondria as therapeutic targets for neuroprotection in MS is addressed.

Glutamate excitotoxicity inflicts paranodal myelin splitting and retraction

Paranodal myelin damage is observed in white matter injury. However the culprit for such damage remains unknown. By coherent anti-Stokes Raman scattering imaging of myelin sheath in fresh tissues with sub-micron resolution, we observed significant paranodal myelin splitting and retraction following glutamate application both ex vivo and in vivo. Multimodal multiphoton imaging further showed that glutamate application broke axo-glial junctions and exposed juxtaparanodal K⁺ channels, resulting in axonal conduction deficit that was demonstrated by compound action potential measurements. The use of 4-aminopyridine, a broad-spectrum K⁺ channel blocker, effectively recovered both the amplitude and width of compound action potentials. Using CARS imaging as a quantitative readout of nodal length to diameter ratio, the same kind of paranodal myelin retraction was observed with applications of Ca²⁺ ionophore A23187. Moreover, exclusion of Ca²⁺ from the medium or application of calpain inhibitor abolished paranodal myelin retraction during glutamate exposure. Examinations of glutamate receptor agonists and antagonists further showed that the paranodal myelin damage was mediated by NMDA and kainate receptors. These results suggest that an increased level of glutamate in diseased white matter could impair paranodal myelin through receptor-mediated Ca²⁺ overloading and subsequent calpain activation.

3 T MRI relaxometry detects T2 prolongation in the cerebral normal-appearing white matter in multiple sclerosis

MRI at 3 T has increased sensitivity in detecting overt multiple sclerosis (MS) brain lesions; a growing body of data suggests clinically relevant damage occurs in the normal-appearing white matter (NAWM). We tested a novel pulse sequence to determine whether 3 T MRI spin-spin relaxometry detected damage in NAWM of MS patients (n=13) vs. age-matched normal controls [(NL) (n=11)]. Baseline characteristics of the MS group were: age (mean+/-SD) 42.5+/-5.4 (range 33-51 years), disease duration 9.0+/-6.4 (range 1-22 years), Expanded Disability Status Scale score 2.5+/-1.7 (range 1-6.5). Brain MRI measures, obtained at 3 T, included global and regional NAWM transverse relaxation rate [R2 (=1/T2)], derived from 3D fast spin-echo T2 prepared images, and global white matter volume fraction derived from SPGR images. The regional NAWM areas investigated were the frontal lobe, parietal lobe, and the genu and splenium of the corpus callosum. Mean NAWM R2 was lower (indicating T2 prolongation) in MS than NL in the whole brain (p=0.00047), frontal NAWM (p=0.00015), parietal NAWM (p=0.0069) and callosal genu (p=0.0019). Similarly, R2 histogram peak position was lower in NAWM in MS than NL in the whole brain (p=0.019). However, the normalized WM volume fractions were similar in both MS and NL (p>0.1). This pilot study suggests that a novel 3D fast spin-echo pulse sequence at 3 T, used to derive R2 relaxation maps, can detect tissue damage in the global and regional cerebral NAWM of MS patients that is missed by conventional lesion and atrophy measures. Such findings may represent demyelination, inflammation, glial proliferation and axonal loss.

[Magnetic resonance imaging of central nervous system inflammation]

Magnetic resonance imaging (MRI) is widely used to explore central nervous system inflammatory disorders, especially multiple sclerosis (MS). Advanced MRI methods are bringing more sensitive and specific tools for each step of the inflammatory process. In this review, we discuss the different MRI approaches for inflammatory disorders exploration, especially MS. We give particular emphasize on sensibility and specificity of each MRI approach and we also discuss the current knowledge concerning biological and histopathological substratum that could explain MRI signal with each modality.

In vivo evidence for alcohol-induced neurochemical changes in rat brain without protracted withdrawal, pronounced thiamine deficiency, or severe liver damage

Magnetic resonance spectroscopy (MRS) studies in human alcoholics report decreases in N-acetylaspartate (NAA) and choline-containing (Cho) compounds. Whether alterations in brain metabolite levels are attributable to alcohol per se or to physiological effects of protracted withdrawal or impaired nutritional or liver status remains unclear. Longitudinal effects of alcohol on brain metabolites measured in basal ganglia with single-voxel MRS were investigated in sibling pairs of wild-type Wistar rats, with one rat per pair exposed to escalating doses of vaporized alcohol, the other to vapor chamber air. MRS was conducted before alcohol exposure and twice during exposure. After 16 weeks of alcohol exposure, rats achieved average blood alcohol levels (BALs) of approximately 293 mg per 100 ml and had higher Cho and a trend for higher glutamine+glutamate (Glx) than controls. After 24 weeks of alcohol exposure, BALs rose to approximately 445 mg per 100 ml, and alcohol-exposed rats had higher Cho, Glx, and glutamate than controls. Thiamine and thiamine monophosphate levels were significantly lower in the alcohol than the control group but did not reach levels low enough to be considered clinically relevant. Histologically, livers of alcohol-exposed rats exhibited greater steatosis and lower glycogenosis than controls, but were not cirrhotic. This study demonstrates a specific pattern of neurobiochemical changes suggesting excessive membrane turnover or inflammation, indicated by high Cho, and alterations to glutamate homeostasis in the rat brain in response to extended vaporized alcohol exposure. Thus, we provide novel in vivo evidence for alcohol exposure as causing changes in brain chemistry in the absence of protracted withdrawal, pronounced thiamine deficiency, or severe liver damage.

Inflammation triggers synaptic alteration and degeneration in experimental autoimmune encephalomyelitis

Neurodegeneration is the irremediable pathological event occurring during chronic inflammatory diseases of the CNS. Here we show that, in experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis, inflammation is capable in enhancing glutamate transmission in the striatum and in promoting synaptic degeneration and dendritic spine loss. These alterations occur early in the disease course, are independent of demyelination, and are strongly associated with massive release of tumor necrosis factor-alpha from activated microglia. CNS invasion by myelin-specific blood-borne immune cells is the triggering event, and the downregulation of the early gene Arc/Arg3.1, leading to the abnormal expression and phosphorylation of AMPA receptors, represents a culminating step in this cascade of neurodegenerative events. Accordingly, EAE-induced synaptopathy subsided during pharmacological blockade of AMPA receptors. Our data establish a link between neuroinflammation and synaptic degeneration and calls for early neuroprotective therapies in chronic inflammatory diseases of the CNS.

Evidence of reduced glutamate in the frontal lobe of HIV-seropositive patients

Neurological complications associated with the acquired immunodeficiency syndrome, in particular, HIV-associated dementia, continue to plague those infected. We report our finding that the concentration of brain Glu is reduced in the frontal white matter region in this condition. In addition, our data appear to absolve highly active retroviral therapy (HAART) from blame, as drug-naïve patients were equally affected. Our findings suggest that Glu neurotransmission is abnormal and may be a key target for early interventions to reduce the later incidence of neurocognitive impairment and dementia among HIV-seropositive patients.

High field MRI in the diagnosis of multiple sclerosis: high field-high yield?

Following the approval of the U.S. Food and Drug Administration (FDA), high field magnetic resonance imaging (MRI) has been increasingly incorporated into the clinical setting. Especially in the field of neuroimaging, the number of high field MRI applications has been increased dramatically. Taking advantage on increased signal-to-noise ratio (SNR) and chemical shift, higher magnetic field strengths offer new perspectives particularly in brain imaging and also challenges in terms of several technical and physical consequences. Over the past few years, many applications of high field MRI in patients with suspected and definite multiple sclerosis (MS) have been reported including conventional and quantitative MRI methods. Conventional pulse sequences at 3 T offers higher lesion detection rates when compared to 1.5 T, particularly in anatomic regions which are important for the diagnosis of patients with MS. MR spectroscopy at 3 T is characterized by an improved spectral resolution due to increased chemical shift allowing a better quantification of metabolites. It detects significant axonal damage already in patients presenting with clinically isolated syndromes and can quantify metabolites of special interest such as glutamate which is technically difficult to quantify at lower field strengths. Furthermore, the higher susceptibility and SNR offer advantages in the field of functional MRI and diffusion tensor imaging. The recently introduced new generation of ultra-high field systems beyond 3 T allows scanning in submillimeter resolution and gives new insights into in vivo MS pathology on MRI. The objectives of this article are to review the current knowledge and level of evidence concerning the application of high field MRI in MS and to give some ideas of research perspectives in the future.

Gray matter pathology in (chronic) MS: modern views on an early observation

Involvement of the gray matter (GM) in the pathology of multiple sclerosis (MS) was already recognized in the early days of MS research, but the detection of (cortical) GM lesions under the microscope and with magnetic resonance imaging (MRI) techniques was initially suboptimal and could only recently be enhanced. The visualization of GM lesions in vivo opens new doors for studies focusing on clinical, especially cognitive, effects of GM pathology, as well as for monitoring of neuroprotective treatment. However, so far little is known about what causes GM pathology. In this review, several pathogenetic mechanisms will be discussed, affecting the MS brain both from the 'outside-in' and from the 'inside-out'. Also, the use and reliability of MRI atrophy measures as a monitoring tool for GM damage in the therapeutic setting will be reviewed.

Proton magnetic resonance spectroscopy in multiple sclerosis

Proton magnetic resonance spectroscopy ((1)H-MRS) provides tissue metabolic information in vivo. This article reviews the role of MRS-determined metabolic alterations in lesions, normal-appearing white matter, gray matter, and spinal cord in advancing our knowledge of pathologic changes in multiple sclerosis (MS). In addition, the role of MRS in objectively evaluating therapeutic efficacy is reviewed. This potential metabolic information makes MRS a unique tool to follow MS disease evolution, understand its pathogenesis, evaluate the disease severity, establish a prognosis, and objectively evaluate the efficacy of therapeutic interventions.

The endocannabinoid anandamide from immunomodulation to neuroprotection. Implications for multiple sclerosis

Over the last decade, the endocannabinoid system (ECS) has emerged as a potential target for multiple sclerosis (MS) management. A growing amount of evidence suggests that cannabinoids may be neuroprotective during CNS inflammation. Advances in the understanding of the physiology and pharmacology of the ECS have potentiated the interest of several components of this system as useful biological targets for disease management. Alterations of the ECS have been recently implicated in a number of neuroinflammatory and neurodegenerative conditions, so that the pharmacological modulation of cannabinoid (CB) receptors and/or of the enzymes controlling synthesis, transport, and degradation of these lipid mediators is considered an option to treat several neurological diseases. This chapter focuses on our current understanding of the function of anandamide (AEA), its biological and therapeutic implications, as well as a description of its effects on neuroimmune modulation.

Impact of fluoxetine on the human brain in multiple sclerosis as quantified by proton magnetic resonance spectroscopy and diffusion tensor imaging

The antidepressant fluoxetine stimulates astrocytic glycogenolysis, which serves as an energy source for axons. In multiple sclerosis patients fluoxetine administration may improve energy supply in neuron cells and thus inhibit axonal degeneration. In a preliminary pilot study, 15 patients with multiple sclerosis (MS) were examined by diffusion tensor imaging (DTI) and (1)H magnetic resonance spectroscopy (MRS) in order to quantify the brain tissue diffusion properties (fractional anisotropy, apparent diffusion coefficient) and metabolite levels (choline, creatine and N-acetylaspartate) in cortical gray matter brain tissue, in normal appearing white matter and in white matter lesions. After oral administration of fluoxetine (20 mg/day) for 1 week, the DTI and MRS measurements were repeated and after treatment with a higher dose (40 mg/day) during the next week, a third series of DTI/MRS examinations was performed in order to assess any changes in diffusion properties and metabolism. One trend was observed in gray matter tissue, a decrease of choline measured at weeks 1 and 2 (significant in a subgroup of 11 relapsing remitting/secondary progressive MS patients). In white matter lesions, the apparent diffusion coefficient was increased at week 1 and N-acetylaspartate was increased at week 2 (both significant). These preliminary results provide evidence of a neuroprotective effect of fluoxetine in MS by the observed partial normalization of the structure-related MRS parameter N-acetylaspartate in white matter lesions.

Genotype-Phenotype correlations in multiple sclerosis: HLA genes influence disease severity inferred by 1HMR spectroscopy and MRI measures

Genetic susceptibility to multiple sclerosis (MS) is associated with the human leukocyte antigen (HLA) DRB1*1501 allele. Here we show a clear association between DRB1*1501 carrier status and four domains of disease severity in an investigation of genotype-phenotype associations in 505 robust, clinically well characterized MS patients evaluated cross-sectionally: (i) a reduction in the N-acetyl-aspartate (NAA) concentration within normal appearing white matter (NAWM) via (1)HMR spectroscopy (P = 0.025), (ii) an increase in the volume of white matter (WM) lesions utilizing conventional anatomical MRI techniques (1,127 mm(3); P = 0.031), (iii) a reduction in normalized brain parenchymal volume (nBPV) (P = 0.023), and (iv) impairments in cognitive function as measured by the Paced Auditory Serial Addition Test (PASAT-3) performance (Mean Z Score: DRB1*1501+: 0.110 versus DRB1*1501-: 0.048; P = 0.004). In addition, DRB1*1501+ patients had significantly more women (74% versus 63%; P = 0.009) and a younger mean age at disease onset (32.4 years versus 34.3 years; P = 0.025). Our findings suggest that DRB1*1501 increases disease severity in MS by facilitating the development of more T2-foci, thereby increasing the potential for irreversible axonal compromise and subsequent neuronal degeneration, as suggested by the reduction of NAA concentrations in NAWM, ultimately leading to a decline in brain volume. These structural aberrations may explain the significant differences in cognitive performance observed between DRB1*1501 groups. The overall goal of a deep phenotypic approach to MS is to develop an array of meaningful biomarkers to monitor the course of the disease, predict future disease behaviour, determine when treatment is necessary, and perhaps to more effectively recommend an available therapeutic intervention.

Autoantibodies and neurodegeneration in multiple sclerosis

Neurodegeneration develops in association with inflammation and demyelination in multiple sclerosis. Available data suggest that the progressive neuroaxonal loss begins in the earliest stages of the disease and underlies the accumulation of clinical disability. The loss of neurons and their processes is driven by a complex molecular mechanism involving cellular and humoral immune histotoxicity, demyelination, reduced neurotrophic support, metabolic impairment, and altered intracellular processes. Here we survey available data concerning the role of autoreactive immunoglobulins in neurotoxicity. A better understanding of molecular pathways leading to immune-mediated neurodegeneration may have key importance in the successful treatment of the disease.

Comparison of T(1) and T(2) metabolite relaxation times in glioma and normal brain at 3T

PURPOSE

To measure T(1) and T(2) relaxation times of metabolites in glioma patients at 3T and to investigate how these values influence the observed metabolite levels.

MATERIALS AND METHODS

A total of 23 patients with gliomas and 10 volunteers were studied with single-voxel two-dimensional (2D) J-resolved point-resolved spectral selection (PRESS) using a 3T MR scanner. Voxels were chosen in normal appearing white matter (WM) and in regions of tumor. The T(1) and T(2) of choline containing compounds (Cho), creatine (Cr), and N-acetyl aspartate (NAA) were estimated.

RESULTS

Metabolite T(1) relaxation values in gliomas were not significantly different from values in normal WM. The T(2) of Cho and Cr were statistically significantly longer for grade 4 gliomas than for normal WM but the T(2) of NAA was similar. These differences were large enough to impact the corrections of metabolite levels for relaxation times with tumor grade in terms of metabolite ratios (P < 0.001).

CONCLUSION

The differential increase in T(2) for Cho and Cr relative to NAA means that the ratios of Cho/NAA and Cr/NAA are higher in tumor at longer echo times (TEs) relative to values in normal appearing brain. Having this information may be useful in defining the acquisition parameters for optimizing contrast between tumor and normal tissue in MR spectroscopic imaging (MRSI) data, in which limited time is available and only one TE can be used.

MRI in multiple sclerosis: current status and future prospects

Many promising MRI approaches for research or clinical management of multiple sclerosis (MS) have recently emerged, or are under development or refinement. Advanced MRI methods need to be assessed to determine whether they allow earlier diagnosis or better identification of phenotypes. Improved post-processing should allow more efficient and complete extraction of information from images. Magnetic resonance spectroscopy should improve in sensitivity and specificity with higher field strengths and should enable the detection of a wider array of metabolites. Diffusion imaging is moving closer to the goal of defining structural connectivity and, thereby, determining the functional significance of lesions at specific locations. Cell-specific imaging now seems feasible with new magnetic resonance contrast agents. The imaging of myelin water fraction brings the hope of providing a specific measure of myelin content. Ultra-high-field MRI increases sensitivity, but also presents new technical challenges. Here, we review these recent developments in MRI for MS, and also look forward to refinements in spinal-cord imaging, optic-nerve imaging, perfusion MRI, and functional MRI. Advances in MRI should improve our ability to diagnose, monitor, and understand the pathophysiology of MS.

Regional variations and the effects of age and gender on glutamate concentrations in the human brain

Proton magnetic resonance spectroscopy was performed at 3 T using the echo time-averaged point-resolved spectroscopy method to determine the effects of age, gender and brain region on glutamate (Glu) concentrations in the healthy human brain. Thirty healthy men and 20 healthy women aged between 21 and 71 years were studied. Significant regional variations of Glu concentrations were observed. Glu concentration in the gray matter (GM) was approximately 25% higher than that in the white matter. Significant age-dependent decreases in Glu concentrations were observed in the basal ganglia (r=-0.75, P<.001) and parietal GM (r=-0.66, P<.001) of men but not those of women. Our findings demonstrate regional variations of Glu concentrations and suggest that the male brain may be more vulnerable to aging than the female brain. Our results also highlight the importance of brain region, age and gender matching in clinical studies.

The inflammatory cytokine, interleukin-1 beta, mediates loss of astroglial glutamate transport and drives excitotoxic motor neuron injury in the spinal cord during acute viral encephalomyelitis

Astrocytes remove glutamate from the synaptic cleft via specific transporters, and impaired glutamate reuptake may promote excitotoxic neuronal injury. In a model of viral encephalomyelitis caused by neuroadapted Sindbis virus (NSV), mice develop acute paralysis and spinal motor neuron degeneration inhibited by the AMPA receptor antagonist, NBQX. To investigate disrupted glutamate homeostasis in the spinal cord, expression of the main astroglial glutamate transporter, GLT-1, was examined. GLT-1 levels declined in the spinal cord during acute infection while GFAP expression was preserved. There was simultaneous production of inflammatory cytokines at this site, and susceptible animals treated with drugs that blocked IL-1beta release also limited paralysis and prevented the loss of GLT-1 expression. Conversely, infection of resistant mice that develop mild paralysis following NSV challenge showed higher baseline GLT-1 levels as well as lower production of IL-1beta and relatively preserved GLT-1 expression in the spinal cord compared to susceptible hosts. Finally, spinal cord GLT-1 expression was largely maintained following infection of IL-1beta-deficient animals. Together, these data show that IL-1beta inhibits astrocyte glutamate transport in the spinal cord during viral encephalomyelitis. They provide one of the strongest in vivo links between innate immune responses and the development of excitotoxicity demonstrated to date.

Pharmacogenomics of the response to IFN-β in multiple sclerosis: ramifications from the first genome-wide screen

Evaluation of: Byun E, Caillier SJ, Montalban X et al.: Genome-wide pharmacogenomic analysis of the response to interferon-β therapy in multiple sclerosis. Arch. Neurol. 65(3) 337–344 (2008). Specifically, IFN-β is the most widely used disease-modifying therapy for the treatment of multiple sclerosis. The main benefits of the therapy, fewer and less severe relapses as well as delayed disease progression, are seen in only approximately 50% of the patients. Genetic polymorphisms may constitute in-built determinants of individual differences in response to IFN-β. Prior attempts to identify such ‘predictors of response’ were hypothesis-driven in that they were based on preselection of candidate genes associated with Type I interferon pathways. In the present study, the authors performed the first ever nonbiased genome-wide association screen in an attempt to identify response-predictive SNPs. Using a robust four-stage completion strategy coupled to advanced SNP ranking/clustering algorithms, 18 significant SNPs were identified, many of which are located in genes that have never before been linked clearly to Type I interferon biology or therapeutic effects. While this study was not designed per se so as to validate earlier findings, genes arising from previous pharmacogenomic studies were generally not confirmed. This is due to major discrepancies between interstudy sets of used SNPs, but may also reflect differential strategies for ascertainment of response to IFN-β, or simply Type I/II errors. The 100-K SNP screen by Byun et al. hallmarks a new stage of pharmacogenomics research applied to multiple sclerosis treatments. Through the judicious implementation of DNA pooling on SNP microarrays, it vividly demonstrates that informative genome-wide pharmacogenomic screens can be performed at a fraction of the cost of individual microarray genotyping. Although, unquestionably, higher-density SNP screens and further replication studies are needed, this study is instrumental in bringing the concept of personalized medicine a (small) step closer to the multiple sclerosis patient. In addition, it has generated a flurry of novel information of likely importance in furthering our understanding of Type I interferon biology.

Association of an EAAT2 polymorphism with higher glutamate concentration in relapsing multiple sclerosis

Glutamate excitotoxicity contributes to oligodendrocyte and tissue damage in multiple sclerosis (MS). Here, we have examined if glutamate homeostasis is altered in plasma from MS patients. We initially observed that plasma glutamate levels are elevated in MS patients as compared to control subjects. In addition, we have studied the presence of a polymorphism sited in the promoter of the glutamate transporter EAAT2 whose mutant genotype results in lower transporter expression. We found that the polymorphism is not associated with the risk to develop MS. However, it is associated with higher glutamate plasma levels during the course of a relapse. These findings suggest that glutamate homeostasis is compromised in MS and that carrying this mutation may contribute to this alteration in relapsing MS.