In vivo evidence of glutamate toxicity in multiple sclerosis

Association of Cortical Lesions With Regional Glutamate, GABA, N-Acetylaspartate, and Myoinositol Levels in Patients With Multiple Sclerosis

BACKGROUND AND OBJECTIVES

Cortical lesions contribute to disability in multiple sclerosis (MS), but their impact on regional neurotransmitter levels remains to be clarified. We tested the hypothesis that cortical lesions are associated with regional glutamate and gamma-aminobutyric acid (GABA) concentrations within the affected cortical region.

METHODS

In this cross-sectional study, we used structural 7T MRI to segment cortical lesions and 7T proton MR-spectroscopy of the bilateral sensorimotor hand areas to quantify regional GABA, glutamate, N-acetylaspartate, and myoinositol concentrations in patients with MS (inclusion criteria: diagnosis of relapsing-remitting [RR] or secondary progressive MS [SPMS]; age 18-80 years) and age and sex-matched healthy controls. Data were collected at a single center between August 2018 and September 2020. Linear mixed-effects models were used to test for associations between metabolite concentrations and cortical lesion volumes within the same MR-spectroscopy voxel.

RESULTS

Forty-seven patients with MS (34 RRMS, 13 SPMS; 45.1 ± 12.5 years; 31 women) and 23 healthy controls (44.4 ± 13 years, 15 women) were studied. In patients, higher regional glutamate and lower regional GABA concentrations were associated with larger cortical lesion volume within the MR-spectroscopy voxel [glutamate: 0.61 (95% CI 0.19-1.03) log(mm3), p = 0.005, GABA: -0.71 (-1.24 to -0.18) log(mm3), p = 0.01]. In addition, lower N-acetylaspartate levels [-0.37 (-0.67 to -0.07) log(mm3), p = 0.016] and higher myoinositol levels [0.48 (0.03-0.93) log(mm3), p = 0.037] were associated with a larger regional cortical lesion volume. Furthermore, glutamate concentrations were reduced in patients with SPMS compared with healthy participants [-0.75 (-1.3 to -0.19) mM, p = 0.005] and patients with RRMS [-0.55 (-1.07 to -0.02) mM, p = 0.04]. N-acetylaspartate levels were lower in both patients with RRMS [-0.81 (-1.39 to -0.24) mM, p = 0.003] and SPMS [-1.31 (-2.07 to -0.54) mM, p < 0.001] when compared with healthy controls. Creatine-normalized N-acetylaspartate levels were associated with performance in the 9-hole peg test of the contralateral hand [-0.004 (-0.007 to -0.002) log(s), p = 0.002], and reduced mean creatine-normalized glutamate was associated with increased Expanded Disability Status Scale (R = -0.39, p = 0.02).

DISCUSSION

Cortical lesions are associated with local increases in glutamate and a reduction in GABA concentration within the lesional or perilesional tissue. Further studies are needed to investigate the causal relationship between cortical lesions and changes in neurotransmitter concentrations.

Re-emergence of T lymphocyte-mediated synaptopathy in progressive multiple sclerosis

Background

Secondary progressive multiple sclerosis (SPMS) is defined by the irreversible accumulation of disability following a relapsing-remitting MS (RRMS) course. Despite treatments advances, a reliable tool able to capture the transition from RRMS to SPMS is lacking. A T cell chimeric MS model demonstrated that T cells derived from relapsing patients exacerbate excitatory transmission of central neurons, a synaptotoxic event absent during remitting stages. We hypothesized the re-emergence of T cell synaptotoxicity during SPMS and investigated the synaptoprotective effects of siponimod, a sphingosine 1-phosphate receptor (S1PR) modulator, known to reduce grey matter damage in SPMS patients.

Methods

Data from healthy controls (HC), SPMS patients, and siponimod-treated SPMS patients were collected. Chimeric experiments were performed incubating human T cells on murine cortico-striatal slices, and recording spontaneous glutamatergic activity from striatal neurons. Homologous chimeric experiments were executed incubating EAE mice T cells with siponimod and specific S1PR agonists or antagonists to identify the receptor involved in siponimod-mediated synaptic recovery.

Results

SPMS patient-derived T cells significantly increased the striatal excitatory synaptic transmission (n=40 synapses) compared to HC T cells (n=55 synapses), mimicking the glutamatergic alterations observed in active RRMS-T cells. Siponimod treatment rescued SPMS T cells synaptotoxicity (n=51 synapses). Homologous chimeric experiments highlighted S1P5R involvement in the siponimod's protective effects.

Conclusion

Transition from RRMS to SPMS involves the reappearance of T cell-mediated synaptotoxicity. Siponimod counteracts T cell-induced excitotoxicity, emphasizing the significance of inflammatory synaptopathy in progressive MS and its potential as a promising pharmacological target.

MicroRNA-92a-CPEB3 axis protects neurons against inflammatory neurodegeneration

Neuroinflammation causes neuronal injury in multiple sclerosis (MS) and other neurological diseases. MicroRNAs (miRNAs) are important modulators of neuronal stress responses, but knowledge about their contribution to neuronal protection or damage during inflammation is limited. Here, we constructed a regulatory miRNA-mRNA network of inflamed motor neurons by leveraging cell type-specific miRNA and mRNA sequencing of mice undergoing experimental autoimmune encephalomyelitis (EAE). We found robust induction of miR-92a in inflamed spinal cord neurons and identified cytoplasmic polyadenylation element-binding protein 3 (Cpeb3) as a key target of miR-92a-mediated posttranscriptional silencing. We detected CPEB3 repression in inflamed neurons in murine EAE and human MS. Moreover, both miR-92a delivery and Cpeb3 deletion protected neuronal cultures against excitotoxicity. Supporting a detrimental effect of Cpeb3 in vivo, neuron-specific deletion in conditional Cpeb3 knockout animals led to reduced inflammation-induced clinical disability in EAE. Together, we identified a neuroprotective miR-92a-Cpeb3 axis in neuroinflammation that might serve as potential treatment target to limit inflammation-induced neuronal damage.

In vivo cortical glutathione response to oral fumarate therapy in relapsing-remitting multiple sclerosis: A single-arm open-label phase IV trial using 7-Tesla 1H MRS

BACKGROUND

This is an open-label, single-arm, single-center pilot study using 7-Tesla in vivo proton magnetic resonance spectroscopy (1H MRS) to measure brain cortical glutathione concentration at baseline before and during the use of oral fumarates as a disease-modifying therapy for multiple sclerosis. The primary endpoint of this research was the change in prefrontal cortex glutathione concentration relative to a therapy-naïve baseline after one year of oral fumarate therapy.

METHODS

Brain glutathione concentrations were examined by 1H MRS in single prefrontal and occipital cortex cubic voxels (2.5 × 2.5 × 2.5 cm3) before and during initiation of oral fumarate therapy (120 mg b.i.d. for 7 days and 240 mg b.i.d. thereafter). Additional measurements of related metabolites glutamate, glutamine, myoinositol, total N-acetyl aspartate, and total choline were also acquired in voxels centered on the same regions. Seven relapsing-remitting multiple sclerosis patients (4 f / 3 m, age range 28-50 years, mean age 40 years) naïve to fumarate therapy were scanned at pre-therapy baseline and after 1, 3, 6 and 12 months of therapy. A group of 8 healthy volunteers (4 f / 4 m, age range 33-48 years, mean age 41 years) was also scanned at baseline and Month 6 to characterize 1H-MRS measurement reproducibility over a comparable time frame.

RESULTS

In the multiple sclerosis cohort, general linear models demonstrated a significant positive linear relationship between prefrontal glutathione and time either linearly across all time points (+0.05 ± 0.02 mM/month, t(27) = 2.6, p = 0.02) or specifically for factor variable Month 12 (+0.6 ± 0.3 mM/12 months, t(24) = 2.2, p = 0.04) relative to baseline. No such effects of time on glutathione concentration were demonstrated in the occipital cortex or in the healthy volunteer group. Changes in occipital total choline were further observed in the multiple sclerosis cohort as well as prefrontal total choline and occipital glutamine and myoinositol in the control cohort throughout the study duration.

CONCLUSIONS

While the open-label single-arm pilot study design and abbreviated control series cannot support firm conclusions about the influence of oral fumarate therapy independent of test-retest factors or normal biological variation in a state of either health or disease, these results do justify further investigation at a larger scale into the potential relationship between prefrontal cortex glutathione increases and oral fumarate therapy in relapsing-remitting multiple sclerosis.

Smouldering Lesion in MS: Microglia, Lymphocytes and Pathobiochemical Mechanisms

Multiple sclerosis (MS) is an immune-mediated, chronic inflammatory, demyelinating, and neurodegenerative disease of the central nervous system (CNS). Immune cell infiltration can lead to permanent activation of macrophages and microglia in the parenchyma, resulting in demyelination and neurodegeneration. Thus, neurodegeneration that begins with acute lymphocytic inflammation may progress to chronic inflammation. This chronic inflammation is thought to underlie the development of so-called smouldering lesions. These lesions evolve from acute inflammatory lesions and are associated with continuous low-grade demyelination and neurodegeneration over many years. Their presence is associated with poor disease prognosis and promotes the transition to progressive MS, which may later manifest clinically as progressive MS when neurodegeneration exceeds the upper limit of functional compensation. In smouldering lesions, in the presence of only moderate inflammatory activity, a toxic environment is clearly identifiable and contributes to the progressive degeneration of neurons, axons, and oligodendrocytes and, thus, to clinical disease progression. In addition to the cells of the immune system, the development of oxidative stress in MS lesions, mitochondrial damage, and hypoxia caused by the resulting energy deficit and iron accumulation are thought to play a role in this process. In addition to classical immune mediators, this chronic toxic environment contains high concentrations of oxidants and iron ions, as well as the excitatory neurotransmitter glutamate. In this review, we will discuss how these pathobiochemical markers and mechanisms, alone or in combination, lead to neuronal, axonal, and glial cell death and ultimately to the process of neuroinflammation and neurodegeneration, and then discuss the concepts and conclusions that emerge from these findings. Understanding the role of these pathobiochemical markers would be important to gain a better insight into the relationship between the clinical classification and the pathomechanism of MS.

Early metabolic alterations in the normal‑appearing grey and white matter of patients with clinically isolated syndrome suggestive of multiple sclerosis: A proton MR spectroscopic study

Proton magnetic resonance spectroscopy (¹H-MRS) is an advanced method of examining metabolic profiles. The present study aimed to assess in vivo metabolite levels in areas of normal-appearing grey (thalamus) and white matter (centrum semiovale) using ¹H-MRS in patients with clinically isolated syndrome (CIS) suggestive of multiple sclerosis and compare them to healthy controls (HCs). Data from 35 patients with CIS (CIS group), of which 23 were untreated (CIS-untreated group) and 12 were treated (CIS-treated group) with disease-modifying-therapies (DMTs) at the time of ¹H-MRS, and from 28 age- and sex-matched HCs were collected using a 3.0 T MRI and single-voxel ¹H-MRS (point resolved spectroscopy sequence; repetition time, 2,000 msec; time to echo, 35 msec). Concentrations and ratios of total N-acetyl aspartate (tNAA), total creatine (tCr), total choline (tCho), myoinositol, glutamate (Glu), glutamine (Gln), Glu + Gln (Glx) and glutathione (Glth) were estimated in the thalamic-voxel (th) and centrum semiovale-voxel (cs). For the CIS group, the median duration from the first clinical attack to ¹H-MRS was 102 days (interquartile range, 89.5.-131.5). Compared with HCs, significantly lower Glx(cs) (P=0.014) and ratios of tCho/tCr(th) (P=0.026), Glu/tCr(cs) (P=0.040), Glx/tCr(cs) (P=0.004), Glx/tNAA(th) (P=0.043) and Glx/tNAA(cs) (P=0.015) were observed in the CIS group. No differences in tNAA levels were observed between the CIS and the HC groups; however, tNAA(cs) was higher in the CIS-treated than in the CIS-untreated group (P=0.028). Compared with those in HC group, decreased Glu(cs) (P=0.019) and Glx(cs) levels (P=0.014) and lower ratios for tCho/tCr(th) (P=0.015), Gln/tCr(th) (P=0.004), Glu/tCr(cs) (P=0.021), Glx/tCr(th) (P=0.041), Glx/tCr(cs) (P=0.003), Glx/tNAA(th) (P=0.030) and Glx/tNAA(cs) (P=0.015) were found in the CIS-untreated group. The present findings showed alterations in the normal-appearing grey and white matter of patients with CIS; moreover, the present results suggested an early indirect treatment effect of DMTs on the brain metabolic profile of these patients.

Glia Connect Inflammation and Neurodegeneration in Multiple Sclerosis

Multiple sclerosis (MS) is regarded as a chronic inflammatory disease that leads to demyelination and eventually to neurodegeneration. Activation of innate immune cells and other inflammatory cells in the brain and spinal cord of people with MS has been well described. However, with the innovation of technology in glial cell research, we have a deep understanding of the mechanisms of glial cells connecting inflammation and neurodegeneration in MS. In this review, we focus on the role of glial cells, including microglia, astrocytes, and oligodendrocytes, in the pathogenesis of MS. We mainly focus on the connection between glial cells and immune cells in the process of axonal damage and demyelinating neuron loss.

Glia Connect Inflammation and Neurodegeneration in Multiple Sclerosis

Multiple sclerosis (MS) is regarded as a chronic inflammatory disease that leads to demyelination and eventually to neurodegeneration. Activation of innate immune cells and other inflammatory cells in the brain and spinal cord of people with MS has been well described. However, with the innovation of technology in glial cell research, we have a deep understanding of the mechanisms of glial cells connecting inflammation and neurodegeneration in MS. In this review, we focus on the role of glial cells, including microglia, astrocytes, and oligodendrocytes, in the pathogenesis of MS. We mainly focus on the connection between glial cells and immune cells in the process of axonal damage and demyelinating neuron loss.

Imaging Methods Applicable in the Diagnostics of Alzheimer's Disease, Considering the Involvement of Insulin Resistance

Alzheimer's disease (AD) is an incurable neurodegenerative disease and the most frequently diagnosed type of dementia, characterized by (1) perturbed cerebral perfusion, vasculature, and cortical metabolism; (2) induced proinflammatory processes; and (3) the aggregation of amyloid beta and hyperphosphorylated Tau proteins. Subclinical AD changes are commonly detectable by using radiological and nuclear neuroimaging methods such as magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET), and single-photon emission computed tomography (SPECT). Furthermore, other valuable modalities exist (in particular, structural volumetric, diffusion, perfusion, functional, and metabolic magnetic resonance methods) that can advance the diagnostic algorithm of AD and our understanding of its pathogenesis. Recently, new insights into AD pathoetiology revealed that deranged insulin homeostasis in the brain may play a role in the onset and progression of the disease. AD-related brain insulin resistance is closely linked to systemic insulin homeostasis disorders caused by pancreas and/or liver dysfunction. Indeed, in recent studies, linkages between the development and onset of AD and the liver and/or pancreas have been established. Aside from standard radiological and nuclear neuroimaging methods and clinically fewer common methods of magnetic resonance, this article also discusses the use of new suggestive non-neuronal imaging modalities to assess AD-associated structural changes in the liver and pancreas. Studying these changes might be of great clinical importance because of their possible involvement in AD pathogenesis during the prodromal phase of the disease.

Brain spectroscopic measures of glutamatergic and neuronal metabolism and glial activation influence white matter integrity in bipolar depression

Bipolar disorder (BD) is associated with alterations in white matter (WM) microstructure, glutamatergic neurotransmission, and glia activity. Previous studies showed higher concentrations of glutamate (Glu), glutamate+glutamine (Glx), and reduced N-acetyl-aspartate (NAA) in BD. We investigated brain concentrations of Glu, Glx, NAA, mI as indirect marker of microglia activation, and Glx/NAA ratio as index of neuronal damage through 1H-MR, and WM integrity with Tract-Based Spatial Statistics in 93 depressed BD patients and 58 healthy controls (HC). We tested for linear effects of cited spectroscopic metabolites on DTI measures of WM integrity with general linear models for each group, then performing a conjunction analysis of Glx/NAA and mI concentration on the same measures. Statistical analyses (whole sample) revealed higher concentration of Glx/NAA, Glx and mI in BD patients compared to HC, and a positive association between mI and the ratio. DTI analyses (87 BD and 35 HC) showed a significant association of Glx/NAA ratio, and mI with WM microstructure. Conjunction analysis revealed a joint negative association between Glx/NAA and mI with fractional anisotropy. This is the first study showing an association between brain metabolites involved in neuronal damage, and glial activation and the alterations in WM consistently reported in BD.

1H-MRS neurometabolites and associations with neurite microstructures and cognitive functions in amnestic mild cognitive impairment

Alzheimer's disease (AD) pathogenesis is associated with alterations in neurometabolites and cortical microstructure. However, our understanding of alterations in neurochemicals in the prefrontal cortex and their relationship with changes in cortical microstructure in AD remains unclear. Here, we studied the levels of neurometabolites in the left dorsolateral prefrontal cortex (DLPFC) in healthy older adults and patients with amnestic Mild Cognitive Impairments (aMCI) using single-voxel proton-magnetic resonance spectroscopy (¹H-MRS). N-acetyl aspartate (NAA), glutamate+glutamate (Glx), Myo-inositol (mI), and γ-aminobutyric acid (GABA) brain metabolite levels were quantified relative to total creatine (tCr = Cr + PCr). aMCI had significantly decreased NAA/tCr, Glx/tCr, NAA/mI, and increased mI/tCr levels compared with healthy controls. Further, we leveraged advanced diffusion MRI to extract neurite properties in the left DLPFC and found a significant positive correlation between NAA/tCr, related to neuronal intracellular compartment, and neurite density (ICVF, intracellular volume fraction), and a negative correlation between mI/tCr and neurite orientation (ODI) only in healthy older adults. These data suggest a potential decoupling in the relationship between neurite microstructures and NAA and mI concentrations in DLPFC in the early stage of AD. Together, our results confirm altered DLPFC neurometabolites in prodromal phase of AD and provide unique evidence regarding the imbalance in the association between neurometabolites and neurite microstructure in early stage of AD.

Neurometabolic changes in multiple sclerosis: Fingolimod versus beta interferon or glatiramer acetate therapy

BACKGROUND AND PURPOSE

Fingolimod has been shown to be more effective in reducing relapse rate and disability than injectable therapies in clinical trials. An increase in N-acetylaspartate (NAA) as measured by MR spectroscopy is correlated with maintaining axonal metabolic functions. This study compared the neurometabolic and volumetric changes in relapsing-remitting multiple sclerosis (RRMS) patients on fingolimod or injectable therapies with healthy controls (HCs).

METHODS

Ninety-eight RRMS (52 on fingolimod, 46 on injectable therapies (27 on glatiramer acetate and 19 on interferon) were age and sex-matched to 51 HCs. RRMS patients underwent cognitive, fatigue, and mental health assessments, as well as an Expanded disability status scale (EDSS). MRI/S was acquired from the hippocampus, posterior cingulate gyrus (PCG), and prefrontal cortex (PFC). Volumetric and neurometabolic measures were compared across cohorts using a univariate general linear model and correlated with clinical severity and neuropsychological scores.

RESULTS

Clinical parameters, MR-volumetric, and neurometabolic profiles showed no differences between treatment groups (p > .05). Compared to HCs, both RRMS cohorts showed volume changes in white matter (-13%), gray matter (-16%), and cerebral spinal fluid (CSF) (+17-23%), as well as reduced NAA (-17%, p = .001, hippocampus), (-7%, p = .001, PCG), and (-9%, p = .001, PFC). MRI/S metrics in three regions were moderately correlated with cognition and fatigue functions.

CONCLUSION

While both treatment arms showed overall similar volumetric and neurometabolic profiles, longitudinal studies are warranted to clarify neurometabolic changes and associations with treatment efficacy.

CEST MRI and MALDI imaging reveal metabolic alterations in the cervical lymph nodes of EAE mice

Background

Multiple sclerosis (MS) is a neurodegenerative disease, wherein aberrant immune cells target myelin-ensheathed nerves. Conventional magnetic resonance imaging (MRI) can be performed to monitor damage to the central nervous system that results from previous inflammation; however, these imaging biomarkers are not necessarily indicative of active, progressive stages of the disease. The immune cells responsible for MS are first activated and sensitized to myelin in lymph nodes (LNs). Here, we present a new strategy for monitoring active disease activity in MS, chemical exchange saturation transfer (CEST) MRI of LNs.

Methods and results

We studied the potential utility of conventional (T2-weighted) and CEST MRI to monitor changes in these LNs during disease progression in an experimental autoimmune encephalomyelitis (EAE) model. We found CEST signal changes corresponded temporally with disease activity. CEST signals at the 3.2 ppm frequency during the active stage of EAE correlated significantly with the cellular (flow cytometry) and metabolic (mass spectrometry imaging) composition of the LNs, as well as immune cell infiltration into brain and spinal cord tissue. Correlating primary metabolites as identified by matrix-assisted laser desorption/ionization (MALDI) imaging included alanine, lactate, leucine, malate, and phenylalanine.

Conclusions

Taken together, we demonstrate the utility of CEST MRI signal changes in superficial cervical LNs as a complementary imaging biomarker for monitoring disease activity in MS. CEST MRI biomarkers corresponded to disease activity, correlated with immune activation (surface markers, antigen-stimulated proliferation), and correlated with LN metabolite levels.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02493-z.

N-Methyl-D-Aspartate (NMDA)-Type Glutamate Receptors and Demyelinating Disorders: A Neuroimmune Perspective

N-methyl-D-aspartate receptors (NMDARs) are ionotropic glutamate receptors, highly important in regulating substantial physiologic processes in the brain and the nervous system, and disturbance in their function could contribute to different pathologies. Overstimulation and hyperactivity of NMDARs, termed as glutamate toxicity, could promote cell death and apoptosis. Meanwhile, their blockade could lead to dysfunction of the brain and nervous system as well. A growing body of evidence has demonstrated the prominent role of NMDARs in demyelinating disorders and anti-NMDAR encephalitis. Herein, we provide an overview of the role of NMDARs' dysfunction in the physiopathology of demyelinating disorders such as multiple sclerosis and neuromyelitis optica spectrum disorders.

Relaxation-Compensated Chemical Exchange Saturation Transfer MRI in the Brain at 7T: Application in Relapsing-Remitting Multiple Sclerosis

Chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) can probe tissue biochemistry in vivo with high resolution and sensitivity without requiring exogenous contrast agents. Applying CEST MRI at ultrahigh field provides advantages of increasing spectral resolution and improving sensitivity to metabolites with faster proton exchange rates such as glutamate, a critical neurotransmitter in the brain. Prior magnetic resonance spectroscopy and CEST MRI studies have revealed altered regulation of glutamate in patients with multiple sclerosis (MS). While CEST imaging facilitates new strategies for investigating the pathology underlying this complex and heterogeneous neurological disease, CEST signals are contaminated or diluted by concurrent effects (e.g., semi-solid magnetization transfer (MT) and direct water saturation) and are scaled by the T1 relaxation time of the free water pool which may also be altered in the context of disease. In this study of 20 relapsing-remitting MS patients and age- and sex-matched healthy volunteers, glutamate-weighted CEST data were acquired at 7.0 T. A Lorentzian fitting procedure was used to remove the asymmetric MT contribution from CEST z-spectra, and the apparent exchange-dependent relaxation (AREX) correction was applied using an R1 map derived from an inversion recovery sequence to further isolate glutamate-weighted CEST signals from concurrent effects. Associations between AREX and cognitive function were examined using the Minimal Assessment of Cognitive Function in MS battery. After isolating CEST effects from MT, direct water saturation, and T1 effects, glutamate-weighted AREX contrast remained higher in gray matter than in white matter, though the difference between these tissues decreased. Glutamate-weighted AREX in normal-appearing gray and white matter in MS patients did not differ from healthy gray and white matter but was significantly elevated in white matter lesions. AREX in some cortical regions and in white matter lesions correlated with disability and measures of cognitive function in MS patients. However, further studies with larger sample sizes are needed to confirm these relationships due to potential confounding effects. The application of MT and AREX corrections in this study demonstrates the importance of isolating CEST signals for more specific characterization of the contribution of metabolic changes to tissue pathology and symptoms in MS.

Steroid Sulfation in Neurodegenerative Diseases

Steroid sulfation and desulfation participates in the regulation of steroid bioactivity, metabolism and transport. The authors focused on sulfation and desulfation balance in three neurodegenerative diseases: Alzheimer´s disease (AD), Parkinson´s disease (PD), and multiple sclerosis (MS). Circulating steroid conjugates dominate their unconjugated counterparts, but unconjugated steroids outweigh their conjugated counterparts in the brain. Apart from the neurosteroid synthesis in the central nervous system (CNS), most brain steroids cross the blood-brain barrier (BBB) from the periphery and then may be further metabolized. Therefore, steroid levels in the periphery partly reflect the situation in the brain. The CNS steroids subsequently influence the neuronal excitability and have neuroprotective, neuroexcitatory, antidepressant and memory enhancing effects. They also exert anti-inflammatory and immunoprotective actions. Like the unconjugated steroids, the sulfated ones modulate various ligand-gated ion channels. Conjugation by sulfotransferases increases steroid water solubility and facilitates steroid transport. Steroid sulfates, having greater half-lives than their unconjugated counterparts, also serve as a steroid stock pool. Sulfotransferases are ubiquitous enzymes providing massive steroid sulfation in adrenal zona reticularis and zona fasciculata.. Steroid sulfatase hydrolyzing the steroid conjugates is exceedingly expressed in placenta but is ubiquitous in low amounts including brain capillaries of BBB which can rapidly hydrolyze the steroid sulfates coming across the BBB from the periphery. Lower dehydroepiandrosterone sulfate (DHEAS) plasma levels and reduced sulfotransferase activity are considered as risk factors in AD patients. The shifted balance towards unconjugated steroids can participate in the pathophysiology of PD and anti-inflammatory effects of DHEAS may counteract the MS.

Are Neurophysiological Biomarkers Able to Discriminate Multiple Sclerosis Clinical Subtypes?

Secondary progressive multiple sclerosis (SPMS) subtype is retrospectively diagnosed, and biomarkers of the SPMS are not available. We aimed to identify possible neurophysiological markers exploring grey matter structures that could be used in clinical practice to better identify SPMS. Fifty-five people with MS and 31 healthy controls underwent a transcranial magnetic stimulation protocol to test intracortical interneuron excitability in the primary motor cortex and somatosensory temporal discrimination threshold (STDT) to test sensory function encoded in cortical and deep grey matter nuclei. A logistic regression model was used to identify a combined neurophysiological index associated with the SP subtype. We observed that short intracortical inhibition (SICI) and STDT were the only variables that differentiated the RR from the SP subtype. The logistic regression model provided a formula to compute the probability of a subject being assigned to an SP subtype based on age and combined SICI and STDT values. While only STDT correlated with disability level at baseline evaluation, both SICI and STDT were associated with disability at follow-up. SICI and STDT abnormalities reflect age-dependent grey matter neurodegenerative processes that likely play a role in SPMS pathophysiology and may represent easily accessible neurophysiological biomarkers for the SPMS subtype.

Guanidinoacetate-creatine in secondary progressive multiple sclerosis: a case report

Acute secondary progressive multiple sclerosis (SPMS) is characterized by escalating neurological disability, with limited disease-modifying therapeutic options. A 48-year-old woman with acute SPMS being treated with interferon beta-1a and oral corticosteroids presented as a clinical outpatient with no disease-modifying effects after treatment. A decision was made to treat her with a combination of guanidinoacetate and creatine for 21 days. She had made clinical progress at follow-up, with the intensity of fatigue dropping from severe to mild. Magnetic resonance spectroscopy revealed increased brain choline, creatine, N-acetylaspartate, and glutathione. Patients with SPMS may benefit from guanidinoacetate-creatine treatment in terms of patient- and clinician-reported outcomes; this requires additional study.

The Role of Transcranial Magnetic Stimulation as a Surrogate Marker of Disease Activity in Patients with Multiple Sclerosis: A Literature Review

OBJECTIVE

Multiple sclerosis (MS) is a chronic, immune-mediated inflammatory disease of the central nervous system (CNS) characterized by demyelination, axonal degeneration, and cognitive impairment. It also has an important impact on the quality of life of patients and their family members. We sought to determine if transcranial magnetic stimulation (TMS) is a valid instrument for determining disease progression activity in patients with MS.

METHODS

A literature search of the PubMed database was conducted using the terms "multiple sclerosis," "transcranial magnetic stimulation," and "neurophysiological parameters."

RESULTS

Neurophysiological parameters, such as sensitivity to demyelination and the strength of excitatory and inhibitory synaptic interactions in the cerebral cortex, can be identified through TMS in patients affected by MS. These objective parameters can be correlated with the progression of disease and provide reliable indices for the severity of illness and the efficacy of drugs used to treat MS in clinical trials.

CONCLUSION

The discovery of specific and detailed neurophysiological parameters as surrogate endpoints for disease activity could represent an important step in clinical trials. Changes in cortical connectivity have already been demonstrated in MS, but in clinical practice, other measures are typically used to evaluate disease activity. We speculate that TMS might be more effective in identifying disease progression that leads to long-term disability, compared to standard surrogate markers, since it represents a direct measure of synaptic transmission(s) in MS.

Myelin-associated glycoprotein activation triggers glutamate uptake by oligodendrocytes in vitro and contributes to ameliorate glutamate-mediated toxicity in vivo

BACKGROUND

Myelin-associated glycoprotein (MAG) is a key molecule involved in the nurturing effect of myelin on ensheathed axons. MAG also inhibits axon outgrowth after injury. In preclinical stroke models, administration of a function-blocking anti-MAG monoclonal antibody (mAb) aimed to improve axon regeneration demonstrated reduced lesion volumes and a rapid clinical improvement, suggesting a mechanism of immediate neuroprotection rather than enhanced axon regeneration. In addition, it has been reported that antibody-mediated crosslinking of MAG can protect oligodendrocytes (OLs) against glutamate (Glu) overload by unknown mechanisms.

PURPOSE

To unravel the molecular mechanisms underlying the protective effect of anti-MAG therapy with a focus on neuroprotection against Glu toxicity.

RESULTS

MAG activation (via antibody crosslinking) triggered the clearance of extracellular Glu by its uptake into OLs via high affinity excitatory amino acid transporters. This resulted not only in protection of OLs but also nearby neurons. MAG activation led to a PKC-dependent activation of factor Nrf2 (nuclear-erythroid related factor-2) leading to antioxidant responses including increased mRNA expression of metabolic enzymes from the glutathione biosynthetic pathway and the regulatory chain of cystine/Glu antiporter system xc^- increasing reduced glutathione (GSH), the main antioxidant in cells. The efficacy of early anti-MAG mAb administration was demonstrated in a preclinical model of excitotoxicity induced by intrastriatal Glu administration and extended to a model of Experimental Autoimmune Encephalitis showing axonal damage secondary to demyelination.

CONCLUSIONS

MAG activation triggers Glu uptake into OLs under conditions of Glu overload and induces a robust protective antioxidant response.

In vivo evidence of differential frontal cortex metabolic abnormalities in progressive and relapsing-remitting multiple sclerosis

The pathophysiology of progressive multiple sclerosis remains elusive, significantly limiting available disease-modifying therapies. Proton MRS (¹ H-MRS) enables in vivo measurement of small molecules implicated in multiple sclerosis, but its application to key metabolites glutamate, γ-aminobutyric acid (GABA), and glutathione has been sparse. We employed, at 7 T, a previously validated ¹ H-MRS protocol to measure glutamate, GABA, and glutathione, as well as glutamine, N-acetyl aspartate, choline, and myoinositol, in the frontal cortex of individuals with relapsing-remitting (N = 26) or progressive (N = 21) multiple sclerosis or healthy control adults (N = 25) in a cross-sectional analysis. Only individuals with progressive multiple sclerosis demonstrated reduced glutamate (F_2,65  = 3.424, p = 0.04; 12.40 ± 0.62 mM versus control 13.17 ± 0.95 mM, p = 0.03) but not glutamine (F_2,65  = 0.352, p = 0.7; 4.71 ± 0.35 mM versus control 4.84 ± 0.42 mM), reduced GABA (F_2,65  = 3.89, p = 0.03; 1.29 ± 0.23 mM versus control 1.47 ± 0.25 mM, p = 0.05), and possibly reduced glutathione (F_2,65  = 0.352, p = 0.056; 2.23 ± 0.46 mM versus control 2.51 ± 0.48 mM, p < 0.1). As a group, multiple sclerosis patients demonstrated significant negative correlations between disease duration and glutamate or GABA (ρ = -0.4, p = 0.02) but not glutamine or glutathione. Alone, only relapsing-remitting multiple sclerosis patients exhibited a significant negative correlation between disease duration and GABA (ρ = -0.5, p = 0.03). Taken together, these results indicate that frontal cortex metabolism is differentially disturbed in progressive and relapsing-remitting multiple sclerosis.

A Multi-Ligand Imaging Study Exploring GABAergic Receptor Expression and Inflammation in Multiple Sclerosis

PURPOSE

The γ-aminobutyric acid (GABA) is the main inhibitory neurotransmitter and essential for normal brain function. The GABAergic system has been shown to have immunomodulatory effects and respond adaptively to excitatory toxicity. The association of the GABAergic system and inflammation in patients with multiple sclerosis (MS) remains unknown. In this pilot study, the in vivo relationship between GABA_A binding and the innate immune response is explored using positron emission tomography (PET) with [¹¹C] flumazenil (FMZ) and [¹¹C]-PK11195 PET (PK-PET), a measure of activated microglia/macrophages.

PROCEDURES

Sixteen MS patients had dynamic FMZ-PET and PK-PET imaging. Ten age-matched healthy controls (HC) had a single FMZ-PET. GABA_A receptor binding was calculated using Logan reference model with the pons as reference. Distribution of volume ratio (VTr) for PK-PET was calculated using image-derived input function. A hierarchical linear model was fitted to assess the linear association between PK-PET and FMZ-PET among six cortical regions of interest.

RESULTS

GABA_A receptor binding was higher throughout the cortex in MS patients (5.72 ± 0.91) as compared with HC (4.70 ± 0.41) (p = 0.002). A significant correlation was found between FMZ binding and PK-PET within the cortex (r = 0.61, p < 0.001) and among the occipital (r = 0.61, p = 0.012), parietal (r = 0.49, p = 0.041), and cingulate (r = 0.32, p = 0.006) regions.

CONCLUSIONS

A higher GABA_A receptor density in MS subjects compared with HC was observed and correlated with innate immune activity. Our observations demonstrate that immune-driven GABAergic abnormalities may be present in MS.

HIV-induced neuroinflammation inhibits oligodendrocyte maturation via glutamate-dependent activation of the PERK arm of the integrated stress response

Despite combined antiretroviral therapy (cART), HIV-associated neurocognitive disorder (HAND) affects 30-50% of HIV-positive patients. Importantly, persistent white matter pathologies, specifically corpus callosum thinning and disruption of white matter microstructures observed in patients with HAND despite viral control through cART, raise the possibility that HIV infection in the setting of suboptimal cART may perturb oligodendrocyte (OL) maturation, function and/or survival, influencing HAND persistence in the cART era. To examine the effect of HIV infection on OL maturation, we used supernatants of primary human monocyte-derived macrophages infected with HIV (HIV/MDMs) to treat primary cultures of rat oligodendrocyte precursor cells (OPCs) during their differentiation to mature OLs. Using immunostaining for lineage-specific markers, we found that HIV/MDMs significantly inhibited OPC maturation. Based on our previous studies, we examined the potential role of several signaling pathways, including ionotropic glutamate receptors and the integrated stress response (ISR), and found that AMPA receptors (AMPAR)/kainic acid (KA) receptors (KARs) mediated the HIV/MDMs-induced defect in OL maturation. We also found that the treatment of OPC cultures with glutamate or AMPAR/KAR agonists phenocopied this effect. Blocking ISR activation, specifically the PERK arm of the ISR, protected OPCs from HIV/MDMs-mediated inhibition of OL maturation. Further, while glutamate, AMPA, and KA activated the ISR, inhibition of AMPAR/KAR activation prevented ISR induction in OPCs and rescued OL maturation. Collectively, these data identify glutamate signaling via ISR activation as a potential therapeutic pathway to ameliorate white matter pathologies in HAND and highlight the need for further investigation of their contribution to cognitive impairment.

In Vivo Molecular Changes in the Retina of Patients With Multiple Sclerosis

Purpose

Raman spectroscopy allows molecular changes to be quantified in vivo from the tissues like the retina. Here we aimed to assess the metabolic changes in the retina of patients with multiple sclerosis (MS).

Methods

We built a Raman spectroscopy prototype by connecting a scanning laser ophthalmoscope to a spectrophotometer. We defined the spectra of 10 molecules participating on energy supply, axon biology, or synaptic damage, which have been shown to be altered in the brain of patients with MS: cytochrome C, flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide (NADH), N-acetyl-aspartate (NAA), excitotoxicity, glutamate, amyloid β (Aβ), τ and α-synuclein (SNCA), phosphatidyl-ethanolamine, and phosphatidyl-choline. We studied these molecules in a prospective cohort of patients with MS, either in the chronic phase or during relapses of acute optic neuritis (AON).

Results

Significant changes to all these molecules were associated with age in healthy individuals. There was a significant decrease in NADH and a trend toward a decrease in NAA in patients with MS, as well as an increase in Aβ compared with healthy controls. Moreover, NADH and FAD increased over time in a longitudinal analysis of patients with MS, whereas Aβ diminished. In patients with acute retinal inflammation due to AON, there was a significant increase in FAD and a decrease in SNCA in the affected retina. Moreover, glutamate levels increased in the affected eyes after a 6-month follow-up.

Conclusions

Alterations of molecules related to axonal degeneration are observed during neuroinflammation and show dynamic changes over time, suggesting progressive neurodegeneration.

Met carriers of the BDNF Val66Met polymorphism show reduced Glx/NAA in the pregenual ACC in two independent cohorts

The Met allele of the Val66Met SNP of the BDNF gene (rs6265) is associated with impaired activity-dependent release of brain-derived neurotrophic factor (BDNF), resulting in reduced synaptic plasticity, impaired glutamatergic neurotransmission, and morphological changes. While previous work has demonstrated Val66Met effects on magnetic resonance spectroscopy (MRS) markers of either glutamatergic metabolism (Glx) or neuronal integrity (NAA), no study has investigated Val66Met effects on these related processes simultaneously. As these metabolites share a metabolic pathway, the Glx/NAA ratio may be a more sensitive marker of changes associated with the Val66Met SNP. This ratio is increased in psychiatric disorders linked to decreased functioning in the anterior cingulate cortex (ACC). In this study, we investigated the correlation of the Val66Met polymorphism of the BDNF gene with Glx/NAA in the pregenual anterior cingulate cortex (pgACC) using MRS at 3 Tesla (T) (n = 30, all males) and 7 T (n = 98, 40 females). In both cohorts, Met carriers had lower Glx/NAA compared to Val homozygotes. Follow-up analyses using absolute quantification revealed that the Met carriers do not show decreased pgACC glutamate or glutamine levels, but instead show increased NAA compared to the Val homozygotes. This finding may in part explain conflicting evidence for Val66Met as a risk factor for developing psychiatric illnesses.

Neuroimaging Correlates of Cognitive Dysfunction in Adults with Multiple Sclerosis

Cognitive impairment is a frequent and meaningful symptom in multiple sclerosis (MS), caused by the accrual of brain structural damage only partially counteracted by effective functional reorganization. As both these aspects can be successfully investigated through the application of advanced neuroimaging, here, we offer an up-to-date overview of the latest findings on structural, functional and metabolic correlates of cognitive impairment in adults with MS, focusing on the mechanisms sustaining damage accrual and on the identification of useful imaging markers of cognitive decline.

Memantine for Multiple Sclerosis: A Systematic Review and Meta-Analysis of Randomized Trials

Background: Multiple sclerosis (MS), a disabling demyelinating disease of the central nervous system, is associated with cognitive impairment, spasticity, and fatigue. There are still no established guidelines on the management of MS-related sequela. Memantine has the potential to reduce glutamate toxicity, thereby reducing consequent cognitive impairment, spasticity, and fatigue.

Objectives: This study aims to determine the efficacy and safety of memantine in preventing cognitive impairment, reducing spasticity and fatigue, and controlling disability in MS patients through a review of relevant randomized trials.

Methods: MEDLINE, CENTRAL, Scopus, Embase, LILACS, ClinicalTrials.gov, and HERDIN were searched from inception to May 2020 for relevant trials.

Results: The search yielded 203 articles; four studies were included in the analysis. Pooled evidence shows that memantine compared with placebo does not significantly improve PASAT, ASS, MFIS, and EDSS scores of patients with MS. Memantine is associated with mild adverse drug events such as dizziness, fatigue, and anxiety.

Conclusion: There is not enough evidence to support the efficacy of memantine in preventing cognitive decline, controlling spasticity, reducing fatigue, and preventing disability. Future researches should consider the different MS subtypes, effect of co-administration of disease-modifying therapies, longer duration of administration, and more sensitive outcome measures to evaluate the potential benefit of memantine in MS.

Neuroinflammation in the normal-appearing white matter (NAWM) of the multiple sclerosis brain causes abnormalities at the nodes of Ranvier

Changes to the structure of nodes of Ranvier in the normal-appearing white matter (NAWM) of multiple sclerosis (MS) brains are associated with chronic inflammation. We show that the paranodal domains in MS NAWM are longer on average than control, with Kv1.2 channels dislocated into the paranode. These pathological features are reproduced in a model of chronic meningeal inflammation generated by the injection of lentiviral vectors for the lymphotoxin-α (LTα) and interferon-γ (IFNγ) genes. We show that tumour necrosis factor (TNF), IFNγ, and glutamate can provoke paranodal elongation in cerebellar slice cultures, which could be reversed by an N-methyl-D-aspartate (NMDA) receptor blocker. When these changes were inserted into a computational model to simulate axonal conduction, a rapid decrease in velocity was observed, reaching conduction failure in small diameter axons. We suggest that glial cells activated by pro-inflammatory cytokines can produce high levels of glutamate, which triggers paranodal pathology, contributing to axonal damage and conduction deficits.

Current thinking on the mechanisms by which multiple sclerosis gives rise to cumulative neurological disability revolves largely around focal lesions of inflammation and demyelination. However, some of the debilitating symptoms, such as severe fatigue, might be better explained by a more diffuse pathology. This study shows that paranodes in the white matter become abnormal as a result of neuroinflammation, which may be the result of the action of cytokines that cause glia to release glutamate.

Temporal Changes in In Vivo Glutamate Signal during Demyelination and Remyelination in the Corpus Callosum: A Glutamate-Weighted Chemical Exchange Saturation Transfer Imaging Study

BACKGROUND

Glutamate-weighted chemical exchange saturation transfer (GluCEST) is a useful imaging tool that can be used to detect changes in glutamate levels in vivo and could also be helpful in the diagnosis of brain myelin changes. We investigated glutamate level changes in the cerebral white matter of a rat model of cuprizone-administered demyelination and remyelination using GluCEST.

METHOD

We used a 7 T pre-clinical magnetic resonance imaging (MRI) system. The rats were divided into the normal control (CTRL), cuprizone-administered demyelination (CPZ_DM), and remyelination (CPZ_RM) groups. GluCEST data were analyzed using the conventional magnetization transfer ratio asymmetry in the corpus callosum. Immunohistochemistry and transmission electron microscopy analyses were also performed to investigate the myelinated axon changes in each group.

RESULTS

The quantified GluCEST signals differed significantly between the CPZ_DM and CTRL groups (-7.25 ± 1.42% vs. -2.84 ± 1.30%; p = 0.001). The increased GluCEST signals in the CPZ_DM group decreased after remyelination (-6.52 ± 1.95% in CPZ_RM) to levels that did not differ significantly from those in the CTRL group (p = 0.734).

CONCLUSION

The apparent temporal signal changes in GluCEST imaging during demyelination and remyelination demonstrated the potential usefulness of GluCEST imaging as a tool to monitor the myelination process.

Astrocyte Glutamate Uptake and Water Homeostasis Are Dysregulated in the Hippocampus of Multiple Sclerosis Patients With Seizures

While seizure disorders are more prevalent among multiple sclerosis (MS) patients than the population overall and prognosticate earlier death & disability, their etiology remains unclear. Translational data indicate perturbed expression of astrocytic molecules contributing to homeostatic neuronal excitability, including water channels (AQP4) and synaptic glutamate transporters (EAAT2), in a mouse model of MS with seizures (MS+S). However, astrocytes in MS+S have not been examined. To assess the translational relevance of astrocyte dysfunction observed in a mouse model of MS+S, demyelinated lesion burden, astrogliosis, and astrocytic biomarkers (AQP4/EAAT2/ connexin-CX43) were evaluated by immunohistochemistry in postmortem hippocampi from MS & MS+S donors. Lesion burden was comparable in MS & MS+S cohorts, but astrogliosis was elevated in MS+S CA1 with a concomitant decrease in EAAT2 signal intensity. AQP4 signal declined in MS+S CA1 & CA3 with a loss of perivascular AQP4 in CA1. CX43 expression was increased in CA3. Together, these data suggest that hippocampal astrocytes from MS+S patients display regional differences in expression of molecules associated with glutamate buffering and water homeostasis that could exacerbate neuronal hyperexcitability. Importantly, mislocalization of CA1 perivascular AQP4 seen in MS+S is analogous to epileptic hippocampi without a history of MS, suggesting convergent pathophysiology. Furthermore, as neuropathology was concentrated in MS+S CA1, future study is warranted to determine the pathophysiology driving regional differences in glial function in the context of seizures during demyelinating disease.

NAA is a Marker of Disability in Secondary-Progressive MS: A Proton MR Spectroscopic Imaging Study

BACKGROUND AND PURPOSE

The secondary progressive phase of multiple sclerosis is characterised by disability progression due to processes that lead to neurodegeneration. Surrogate markers such as those derived from MRI are beneficial in understanding the pathophysiology that drives disease progression and its relationship to clinical disability. We undertook a 1H-MRS imaging study in a large secondary progressive MS (SPMS) cohort, to examine whether metabolic markers of brain injury are associated with measures of disability, both physical and cognitive.

MATERIALS AND METHODS

A cross-sectional analysis of individuals with secondary-progressive MS was performed in 119 participants. They underwent ¹H-MR spectroscopy to obtain estimated concentrations and ratios to total Cr for total NAA, mIns, Glx, and total Cho in normal-appearing WM and GM. Clinical outcome measures chosen were the following: Paced Auditory Serial Addition Test, Symbol Digit Modalities Test, Nine-Hole Peg Test, Timed 25-foot Walk Test, and the Expanded Disability Status Scale. The relationship between these neurometabolites and clinical disability measures was initially examined using Spearman rank correlations. Significant associations were then further analyzed in multiple regression models adjusting for age, sex, disease duration, T2 lesion load, normalized brain volume, and occurrence of relapses in 2 years preceding study entry.

RESULTS

Significant associations, which were then confirmed by multiple linear regression, were found in normal-appearing WM for total NAA (tNAA)/total Cr (tCr) and the Nine-Hole Peg Test (ρ = 0.23; 95% CI, 0.06-0.40); tNAA and tNAA/tCr and the Paced Auditory Serial Addition Test (ρ = 0.21; 95% CI, 0.03-0.38) (ρ = 0.19; 95% CI, 0.01-0.36); mIns/tCr and the Paced Auditory Serial Addition Test, (ρ = -0.23; 95% CI, -0.39 to -0.05); and in GM for tCho and the Paced Auditory Serial Addition Test (ρ = -0.24; 95% CI, -0.40 to -0.06). No other GM or normal-appearing WM relationships were found with any metabolite, with associations found during initial correlation testing losing significance after multiple linear regression analysis.

CONCLUSIONS

This study suggests that metabolic markers of neuroaxonal integrity and astrogliosis in normal-appearing WM and membrane turnover in GM may act as markers of disability in secondary-progressive MS.

Signal alterations of glutamate-weighted chemical exchange saturation transfer MRI in lysophosphatidylcholine-induced demyelination in the rat brain

PURPOSE

To compare in vivo glutamate-weighted chemical exchange saturation transfer (GluCEST-weighted) signal changes between in a rat model of demyelinated multiple sclerosis and control groups.

PROCEDURES

Using a pre-clinical 7 T magnetic resonance imaging (MRI) system, CEST imaging was applied to a toxin (lysophosphatidylcholine; LPC) induced rat (MS_LPC) and control (CTRL) groups to compare in vivo glutamate signal changes. The GluCEST-weighted signals were analyzed based on the magnetization transfer ratio asymmetry approach at 3.0 ppm on the region-of-interests (ROIs) in the corpus callosum and hippocampus at each hemispheric region.

RESULTS

GluCEST-weighted signals were significantly changed between the CTRL and MS_LPC groups, while higher glutamate signals were indicated in the MS_LPC than the CTRL group ([MS_LPC / CTRL]; hippocampus: [6.159 ± 0.790 / 4.336 ± 0.446] and corpus callosum: [-3.545 ± 0.945 / -6.038 ± 0.620], all p = 0.001).

CONCLUSIONS

Our results show increased GluCEST-weighted signals in the LPC-induced demyelination rat brain compared with control. GluCEST-weighted imaging could be a useful tool for defining a biomarker to estimate the glutamate-related metabolism in MS.

Current Methods of Magnetic Resonance for Noninvasive Assessment of Molecular Aspects of Pathoetiology in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease with expanding axonal and neuronal degeneration in the central nervous system leading to motoric dysfunctions, psychical disability, and cognitive impairment during MS progression. The exact cascade of pathological processes (inflammation, demyelination, excitotoxicity, diffuse neuro-axonal degeneration, oxidative and metabolic stress, etc.) causing MS onset is still not fully understood, although several accompanying biomarkers are particularly suitable for the detection of early subclinical changes. Magnetic resonance (MR) methods are generally considered to be the most sensitive diagnostic tools. Their advantages include their noninvasive nature and their ability to image tissue in vivo. In particular, MR spectroscopy (proton 1H and phosphorus 31P MRS) is a powerful analytical tool for the detection and analysis of biomedically relevant metabolites, amino acids, and bioelements, and thus for providing information about neuro-axonal degradation, demyelination, reactive gliosis, mitochondrial and neurotransmitter failure, cellular energetic and membrane alternation, and the imbalance of magnesium homeostasis in specific tissues. Furthermore, the MR relaxometry-based detection of accumulated biogenic iron in the brain tissue is useful in disease evaluation. The early description and understanding of the developing pathological process might be critical for establishing clinically effective MS-modifying therapies.

Central Modulation of Selective Sphingosine-1-Phosphate Receptor 1 Ameliorates Experimental Multiple Sclerosis

Future treatments of multiple sclerosis (MS), a chronic autoimmune neurodegenerative disease of the central nervous system (CNS), aim for simultaneous early targeting of peripheral immune function and neuroinflammation. Sphingosine-1-phosphate (S1P) receptor modulators are among the most promising drugs with both “immunological” and “non-immunological” actions. Selective S1P receptor modulators have been recently approved for MS and shown clinical efficacy in its mouse model, the experimental autoimmune encephalomyelitis (EAE). Here, we investigated the anti-inflammatory/neuroprotective effects of ozanimod (RPC1063), a S1P_1/5 modulator recently approved in the United States for the treatment of MS, by performing ex vivo studies in EAE brain. Electrophysiological experiments, supported by molecular and immunofluorescence analysis, revealed that ozanimod was able to dampen the EAE glutamatergic synaptic alterations, through attenuation of local inflammatory response driven by activated microglia and infiltrating T cells, the main CNS-cellular players of EAE synaptopathy. Electrophysiological studies with selective S1P₁ (AUY954) and S1P₅ (A971432) agonists suggested that S1P₁ modulation is the main driver of the anti-excitotoxic activity mediated by ozanimod. Accordingly, in vivo intra-cerebroventricular treatment of EAE mice with AUY954 ameliorated clinical disability. Altogether these results strengthened the relevance of S1P₁ agonists as immunomodulatory and neuroprotective drugs for MS therapy.

Effect of sildenafil on neuroinflammation and synaptic plasticity pathways in experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic immuno-inflammatory disease of the central nervous system characterized by demyelination and axonal damage. Cognitive changes are common in individuals with MS since inflammatory molecules secreted by microglia interfere with the physiological mechanisms of synaptic plasticity. According to previous data, inhibition of PDE5 promotes the accumulation of cGMP, which inhibits neuroinflammation and seems to improve synaptic plasticity and memory. The present study aimed to evaluate the effect of sildenafil on the signaling pathways of neuroinflammation and synaptic plasticity in experimental autoimmune encephalomyelitis (EAE). C57BL/6 mice were divided into three experimental groups (n = 10/group): (a) Control; (b) EAE; (c) EAE + sild (25 mg/kg/21 days). Sildenafil was able to delay the onset and attenuate the severity of the clinical symptoms of EAE. The drug also reduced the infiltration of CD4+ T lymphocytes and their respective IL-17 and TNF-α cytokines. Moreover, sildenafil reduced neuroinflammation in the hippocampus (assessed by the reduction of inflammatory markers IL-1β, pIKBα and pNFkB and reactive gliosis, as well as elevating the inhibitory cytokines TGF-β and IL-10). Moreover, sildenafil induced increased levels of NeuN, BDNF and pCREB, protein kinases (PKA, PKG, and pERK) and synaptophysin, and modulated the expression of the glutamate receptors AMPA and NMDA. The present findings demonstrated that sildenafil has therapeutic potential for cognitive deficit associated with multiple sclerosis.

Altered anterior cingulate glutamatergic metabolism in depressed adolescents with current suicidal ideation

The anterior cingulate cortex (ACC) is involved in emotion regulation and salience processing. Prior research has implicated ACC dysfunction in suicidal ideation (SI) and suicidal behavior. This study aimed to quantify ACC glutamatergic concentrations and to examine relationships with SI in a sample of healthy and depressed adolescents. Forty adolescents underwent clinical evaluation and proton magnetic resonance spectroscopy (1H-MRS) at 3 T, utilizing a 2-dimensional J-averaged PRESS sequence sampling a medial pregenual ACC voxel. Cerebrospinal fluid-corrected ACC metabolite concentrations were compared between healthy control (HC, n = 16), depressed without SI (Dep/SI-, n = 13), and depressed with SI (Dep/SI+, n = 11) youth using general linear models covarying for age, sex, and psychotropic medication use. Relationships between ACC metabolites and continuous measures of SI were examined using multiple linear regressions. ROC analysis was used to determine the ability of glutamate+glutamine (Glx) and the N-acetylaspartate (NAA)/Glx ratio to discriminate Dep/SI- and Dep/SI+ adolescents. Dep/SI+ adolescents had higher Glx than Dep/SI- participants (padj = 0.012) and had lower NAA/Glx than both Dep/SI- (padj = 0.002) and HC adolescents (padj = 0.039). There were significant relationships between SI intensity and Glx (pFDR = 0.026), SI severity and NAA/Glx (pFDR = 0.012), and SI intensity and NAA/Glx (pFDR = 0.004). ACC Glx and NAA/Glx discriminated Dep/SI- from Dep/SI+ participants. Uncoupled NAA-glutamatergic metabolism in the ACC may play a role in suicidal ideation and behavior. Longitudinal studies are needed to establish whether aberrant glutamatergic metabolism corresponds to acute or chronic suicide risk. Glutamatergic biomarkers may be promising targets for novel risk assessment and interventional strategies for suicidal ideation and behavior.

Safety and efficacy of memantine for multiple sclerosis-related fatigue: A pilot randomized, double-blind placebo-controlled trial

BACKGROUND

Fatigue is one of the most common symptoms in patients with multiple sclerosis (MS). Currently, there is no approved medication for MS-related fatigue.

OBJECTIVE

In this study, we aim to evaluate the safety and efficacy of memantine for improving fatigue in patients with MS.

METHODS

This was a pilot randomized, double-blind, placebo-controlled clinical trial. Eligible patients with relapsing-remitting MS (RRMS) according to the McDonald criteria were randomized to receive either memantine (20 mg/day) or placebo and were assessed at baseline and three months after treatment. The change in the severity of fatigue was determined by the Modified Fatigue Impact Scale (MFIS).

RESULTS

Sixty-four patients were randomly allocated to the memantine (n = 32) and placebo (n = 32) groups. Sixteen patients in the memantine group and 24 patients in the placebo group completed the study. The mean [95% CI] absolute change in MFIS scores from baseline did not differ significantly between the memantine (-5.8 [-12.7 to 1.0]) and placebo (-4.0 [-10.6 to 2.7]) groups (between-group difference: -1.9 [-11.7 to 7.8], P = .702). No serious adverse events were reported, except for dizziness and sedation in four patients in the experimental arm, which resulted in discontinuation.

CONCLUSION

This trial failed to prove any clinical efficacy of memantine for the management of MS-related fatigue. Although memantine was generally well-tolerated, adverse events were among the major causes of dropout in this study.

Astrocytes Are Required for Oligodendrocyte Survival and Maintenance of Myelin Compaction and Integrity

Astrocytes have been implicated in regulating oligodendrocyte development and myelination in vitro, although their functions in vivo remain less well defined. Using a novel approach to locally ablate GFAP+ astrocytes, we demonstrate that astrocytes are required for normal CNS myelin compaction during development, and for maintaining myelin integrity in the adult. Transient ablation of GFAP+ astrocytes in the mouse spinal cord during the first postnatal week reduced the numbers of mature oligodendrocytes and inhibited myelin formation, while prolonged ablation resulted in myelin that lacked compaction and structural integrity. Ablation of GFAP+ astrocytes in the adult spinal cord resulted in the rapid, local loss of myelin integrity and regional demyelination. The loss of myelin integrity induced by astrocyte ablation was greatly reduced by NMDA receptor antagonists, both in vitro and in vivo, suggesting that myelin stability was affected by elevation of local glutamate levels following astrocyte ablation. Furthermore, targeted delivery of glutamate into adult spinal cord white matter resulted in reduction of myelin basic protein expression and localized disruption of myelin compaction which was also reduced by NMDA receptor blockade. The pathology induced by localized astrocyte loss and elevated exogenous glutamate, supports the concept that astrocytes are critical for maintenance of myelin integrity in the adult CNS and may be primary targets in the initiation of demyelinating diseases of the CNS, such as Neuromyelitis Optica (NMO).

Reduction of AMPA receptor activity on mature oligodendrocytes attenuates loss of myelinated axons in autoimmune neuroinflammation

Glutamate dysregulation occurs in multiple sclerosis (MS), but whether excitotoxic mechanisms in mature oligodendrocytes contribute to demyelination and axonal injury is unexplored. Although current treatments modulate the immune system, long-term disability ensues, highlighting the need for neuroprotection. Glutamate is elevated before T2-visible white matter lesions appear in MS. We previously reported that myelin-reactive T cells provoke microglia to release glutamate from the system xc - transporter promoting myelin degradation in experimental autoimmune encephalomyelitis (EAE). Here, we explore the target for glutamate in mature oligodendrocytes. Most glutamate-stimulated calcium influx into oligodendrocyte somas is AMPA receptor (AMPAR)-mediated, and genetic deletion of AMPAR subunit GluA4 decreased intracellular calcium responses. Inducible deletion of GluA4 on mature oligodendrocytes attenuated EAE and loss of myelinated axons was selectively reduced compared to unmyelinated axons. These data link AMPAR signaling in mature oligodendrocytes to the pathophysiology of myelinated axons, demonstrating glutamate regulation as a potential neuroprotective strategy in MS.

Detecting neurodegenerative pathology in multiple sclerosis before irreversible brain tissue loss sets in

Background

Multiple sclerosis (MS) is a complex chronic inflammatory and degenerative disorder of the central nervous system. Accelerated brain volume loss, or also termed atrophy, is currently emerging as a popular imaging marker of neurodegeneration in affected patients, but, unfortunately, can only be reliably interpreted at the time when irreversible tissue damage likely has already occurred. Timing of treatment decisions based on brain atrophy may therefore be viewed as suboptimal.

Main body

This Narrative Review focuses on alternative techniques with the potential of detecting neurodegenerative events in the brain of subjects with MS prior to the atrophic stage. First, metabolic and molecular imaging provide the opportunity to identify early subcellular changes associated with energy dysfunction, which is an assumed core mechanism of axonal degeneration in MS. Second, cerebral hypoperfusion has been observed throughout the entire clinical spectrum of the disorder but it remains an open question whether this serves as an alternative marker of reduced metabolic activity, or exists as an independent contributing process, mediated by endothelin-1 hyperexpression. Third, both metabolic and perfusion alterations may lead to repercussions at the level of network performance and structural connectivity, respectively assessable by functional and diffusion tensor imaging. Fourth and finally, elevated body fluid levels of neurofilaments are gaining interest as a biochemical mirror of axonal damage in a wide range of neurological conditions, with early rises in patients with MS appearing to be predictive of future brain atrophy.

Conclusions

Recent findings from the fields of advanced neuroradiology and neurochemistry provide the promising prospect of demonstrating degenerative brain pathology in patients with MS before atrophy has installed. Although the overall level of evidence on the presented topic is still preliminary, this Review may pave the way for further longitudinal and multimodal studies exploring the relationships between the abovementioned measures, possibly leading to novel insights in early disease mechanisms and therapeutic intervention strategies.

Quantifying the Metabolic Signature of Multiple Sclerosis by in vivo Proton Magnetic Resonance Spectroscopy: Current Challenges and Future Outlook in the Translation From Proton Signal to Diagnostic Biomarker

Proton magnetic resonance spectroscopy (¹H-MRS) offers a growing variety of methods for querying potential diagnostic biomarkers of multiple sclerosis in living central nervous system tissue. For the past three decades, ¹H-MRS has enabled the acquisition of a rich dataset suggestive of numerous metabolic alterations in lesions, normal-appearing white matter, gray matter, and spinal cord of individuals with multiple sclerosis, but this body of information is not free of seeming internal contradiction. The use of ¹H-MRS signals as diagnostic biomarkers depends on reproducible and generalizable sensitivity and specificity to disease state that can be confounded by a multitude of influences, including experiment group classification and demographics; acquisition sequence; spectral quality and quantifiability; the contribution of macromolecules and lipids to the spectroscopic baseline; spectral quantification pipeline; voxel tissue and lesion composition; T₁ and T₂ relaxation; B₁ field characteristics; and other features of study design, spectral acquisition and processing, and metabolite quantification about which the experimenter may possess imperfect or incomplete information. The direct comparison of ¹H-MRS data from individuals with and without multiple sclerosis poses a special challenge in this regard, as several lines of evidence suggest that experimental cohorts may differ significantly in some of these parameters. We review the existing findings of in vivo¹H-MRS on central nervous system metabolic abnormalities in multiple sclerosis and its subtypes within the context of study design, spectral acquisition and processing, and metabolite quantification and offer an outlook on technical considerations, including the growing use of machine learning, by future investigations into diagnostic biomarkers of multiple sclerosis measurable by ¹H-MRS.

Glutamine antagonism attenuates physical and cognitive deficits in a model of MS

OBJECTIVE

To measure the impact of JHU-083, a novel prodrug of the glutamine antagonist 6-diazo-5-oxo-l-norleucine, on immune cell proliferation and activation, along with physical and cognitive impairments associated with the experimental autoimmune encephalomyelitis (EAE) mouse model of MS.

METHODS

Splenic-derived T cells and bone marrow-derived dendritic cells (DCs) were cultured, activated, and treated daily with vehicle or JHU-083. Proliferation and activation were measured via flow cytometry and IncuCyte live cell analysis. C57BL/6 mice were immunized for EAE. Vehicle or JHU-083 was administered orally every other day either from the time of immunization in the prevention paradigm or from the time of disease onset in the treatment paradigm. Disease scores and body weight were monitored. In the treatment paradigm, cognition was evaluated using the Barnes maze test.

RESULTS

JHU-083 selectively inhibits T-cell proliferation and decreases T-cell activation, with no effect on DCs. In vivo, orally administered JHU-083 significantly decreases EAE severity in both prevention and treatment paradigms and reverses EAE-induced cognitive impairment.

CONCLUSIONS

JHU-083, a well-tolerated, brain penetrable glutamine antagonist, is a promising novel treatment for both the physical and cognitive deficits of MS.

Advances in brain imaging in multiple sclerosis

Brain imaging is increasingly used to support clinicians in diagnosing multiple sclerosis (MS) and monitoring its progression. However, the role of magnetic resonance imaging (MRI) in MS goes far beyond its clinical application. Indeed, advanced imaging techniques have helped to detect different components of MS pathogenesis in vivo, which is now considered a heterogeneous process characterized by widespread damage of the central nervous system, rather than multifocal demyelination of white matter. Recently, MRI biomarkers more sensitive to disease activity than clinical disability outcome measures, have been used to monitor response to anti-inflammatory agents in patients with relapsing-remitting MS. Similarly, MRI markers of neurodegeneration exhibit the potential as primary and secondary outcomes in clinical trials for progressive phenotypes. This review will summarize recent advances in brain neuroimaging in MS from the research setting to clinical applications.

Developing therapeutic strategies to promote myelin repair in multiple sclerosis

Introduction: Approved disease-modifying therapies for multiple sclerosis (MS) lessen inflammatory disease activity that causes relapses and MRI lesions. However, chronic inflammation and demyelination lead to axonal degeneration and neuronal loss, for which there currently is no effective treatment. There has been increasing interest in developing repair-promoting strategies, but there are important unanswered questions regarding the mechanisms and appropriate methods to evaluate these treatments. Areas covered: The rationale for remyelinating agents in MS is discussed, with an overview of both myelin physiology and endogenous repair mechanisms. This is followed by a discussion of the identification and development of potential remyelinating drugs. Potential biomarkers of remyelination are reviewed, including considerations regarding measuring remyelination in clinical trials. Information and data were obtained from a search of recent literature through PubMed. Peer-reviewed original articles and review articles were included. Expert opinion: There are several obstacles to the translation of potential remyelinating agents to clinical trials, particularly uncertainty regarding the most appropriate study population and method to monitor remyelination. Refinements in clinical trial design and outcome measurement, potentially via advanced imaging techniques, are needed to optimize detection of repair in patients with MS.

Neuronal methylome reveals CREB-associated neuro-axonal impairment in multiple sclerosis

Background

Due to limited access to brain tissue, the precise mechanisms underlying neuro-axonal dysfunction in neurological disorders such as multiple sclerosis (MS) are largely unknown. In that context, profiling DNA methylation, which is a stable and cell type-specific regulatory epigenetic mark of genome activity, offers a unique opportunity to characterize the molecular mechanisms underpinning brain pathology in situ. We examined DNA methylation patterns of neuronal nuclei isolated from post-mortem brain tissue to infer processes that occur in neurons of MS patients.

Results

We isolated subcortical neuronal nuclei from post-mortem white matter tissue of MS patients and non-neurological controls using flow cytometry. We examined bulk DNA methylation changes (total n = 29) and further disentangled true DNA methylation (5mC) from neuron-specific DNA hydroxymethylation (5hmC) (n = 17), using Illumina Infinium 450K arrays. We performed neuronal sub-type deconvolution using glutamate and GABA methylation profiles to further reduce neuronal sample heterogeneity. In total, we identified 2811 and 1534 significant (genome-wide adjusted P value < 0.05) differentially methylated and hydroxymethylated positions between MS patients and controls. We found striking hypo-5mC and hyper-5hmC changes occurring mainly within gene bodies, which correlated with reduced transcriptional activity, assessed using published RNAseq data from bulk brain tissue of MS patients and controls. Pathway analyses of the two cohorts implicated dysregulation of genes involved in axonal guidance and synaptic plasticity, with meta-analysis confirming CREB signalling as the most highly enriched pathway underlying these processes. We functionally investigated DNA methylation changes of CREB signalling-related genes by immunohistofluoresence of phosphorylated CREB in neurons from brain sections of a subcohort of MS patients and controls (n = 15). Notably, DNA methylation changes associated with a reduction of CREB activity in white matter neurons of MS patients compared to controls.

Conclusions

Our data demonstrate that investigating 5mC and 5hmC modifications separately allows the discovery of a substantial fraction of changes occurring in neurons, which can escape traditional bisulfite-based DNA methylation analysis. Collectively, our findings indicate that neurons of MS patients acquire sustained hypo-5mC and hyper-5hmC, which may impair CREB-mediated neuro-axonal integrity, in turn relating to clinical symptoms.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0678-1) contains supplementary material, which is available to authorized users.

Increased glutamate and deep brain atrophy can predict the severity of multiple sclerosis

OBJECTIVE

In multiple sclerosis (MS), deep grey matter (DGM) atrophy has been recognised as a crucial component of the disease that presents early and it has been associated with disability. Although the precise mechanism underlying grey matter atrophy is unknown, several hypotheses have been postulated. Our previous research pointed to correlations of hypothalamic metabolic alterations with clinical outcomes of MS, therefore we decided to further test the relationship of these alterations with DGM atrophy.

METHODS

We used ¹H-Magnetic Resonance spectroscopy (¹H-MRS) of the hypothalamus to test its metabolites in 26 patients with RRMS and 22 healthy age-matched controls. DGM atrophy was evaluated by simple planimetry of third ventricular width on the hypothalamic level (3VW) in T1 weighted MRI pictures. Metabolite ratios of N-acetyl aspartate (NAA), choline (Cho), glutamate and glutamine (Glx), myo-inositol (mIns) and creatine (Cr) were correlated with Multiple Sclerosis Severity Scale (MSSS) and 3VW.

RESULTS

Metabolite concentrations were compared between patients and controls using multiple regression models allowing for age, 3VW and metabolites. It revealed that the only relevant predictors of MSSS were 3VW and Glx/NAA. At a significance level of P<0.05, a unit increase of 3VW was associated with a 0.35 increase of MSSS, for a typical value of Glx/NAA; P value 0.0039. A unit increase of Glx/NAA was associated with a 0.93 increase of MSSS, for a typical value of atrophy; P value 0.090. There were significant linear correlations between Glx/Cr and MSSS, Glx/NAA and MSSS, and between mIns/NAA and 3VW.

CONCLUSIONS

The results suggest that both NAA and Glx are associated with neurodegeneration of hypothalamic DGM and severe disease course. Glx related ¹H-MRS parameters seem to be superior to other metabolites in determining disease burden, independently of otherwise powerful 3VW planimetry. Significantly increased mIns/NAA in MS patients compared to controls point to gliosis, which parallels the atrophy of hypothalamic DGM.

Magnetic resonance markers of tissue damage related to connectivity disruption in multiple sclerosis

Patients with multiple sclerosis (MS) display reduced structural connectivity among brain regions, but the pathogenic mechanisms underlying network disruption are still unknown. We aimed to investigate the association between the loss of diffusion-based structural connectivity, measured with graph theory metrics, and magnetic resonance (MR) markers of microstructural damage. Moreover, we evaluated the cognitive consequences of connectivity changes. We analysed the frontoparietal network in 102 MS participants and 25 healthy volunteers (HV). MR measures included radial diffusivity (RD), as marker of demyelination, and ratios of myo-inositol, N-acetylaspartate and glutamate+glutamine with creatine in white (WM) and grey matter as markers of astrogliosis, neuroaxonal integrity and glutamatergic neurotoxicity. Patients showed decreased global and local efficiency, and increased assortativity (p < 0.01) of the network, as well as increased RD and myo-inositol, and decreased N-acetylaspartate in WM compared with HV (p < 0.05). In patients, the age-adjusted OR of presenting abnormal global and local efficiency was increased for each increment of 0.01 points in RD and myo-inositol, while it was decreased for each increment of 0.01 points in N-acetylaspartate (the increase of N-acetylaspartate reduced the risk of having abnormal connectivity), all in WM. In a multiple logistic regression analysis, the OR of presenting abnormal global efficiency was 0.95 (95% confidence interval, CI: 0.91–0.99, p = 0.011) for each 0.01 increase in N-acetylaspartate, and the OR of presenting abnormal local efficiency was 1.39 (95% CI: 1.14–1.71, p = 0.001) for each 0.01 increase in RD. Patients with abnormal efficiency had worse performance in attention, working memory and processing speed (p < 0.05). In conclusion, patients with MS exhibit decreased structural network efficiency driven by diffuse microstructural impairment of the WM, probably related to demyelination, astroglial and neuroaxonal damage. The accumulation of neuroaxonal pathological burden seems to magnify the risk of global network collapse, while demyelination may contribute to the regional disorganization. These network modifications have negative consequences on cognition.

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The pathogenic mechanisms underlying structural network disruption in MS are unknown.

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The microstructural damage of the white matter contributes to network impairment.

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The worsening of global efficiency is associated with markers of neuroaxonal burden.

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Local efficiency impairment is related to MR measures of demyelination.

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The described network modifications contribute to cognitive dysfunction.

Magnetic Resonance Imaging in Multiple Sclerosis

Since its technical development in the early 1980s, magnetic resonance imaging (MRI) has quickly been adopted as an essential tool in supporting the diagnosis, longitudinal monitoring, evaluation of therapeutic response, and scientific investigations in multiple sclerosis (MS). The clinical usage of MRI has increased in parallel with technical innovations in the technique itself; the widespread adoption of clinically routine MRI at 1.5T has allowed sensitive qualitative and quantitative assessments of macroscopic central nervous system (CNS) inflammatory demyelinating lesions and tissue atrophy. However, conventional MRI lesion measures lack specificity for the underlying MS pathology and only weakly correlate with clinical status. Higher field strength units and newer, advanced MRI techniques offer increased sensitivity and specificity in the detection of disease activity and disease severity. This review summarizes the current status and future prospects regarding the role of MRI in the characterization of MS-related brain and spinal cord involvement.