Brain atrophy and cognitive impairment in multiple sclerosis: a review

Effects of Dimethyl Fumarate on Brain Atrophy in Relapsing-Remitting Multiple Sclerosis: Pooled Analysis Phase 3 DEFINE and CONFIRM Studies

Objective

In the pivotal DEFINE and CONFIRM trials for dimethyl fumarate (DMF), patterns of brain volume changes were different, potentially due to low sample sizes and because MRIs were analyzed at two different reading centers. We evaluated effects of DMF on brain volume change in patients with multiple sclerosis (MS) through reanalysis of pooled images from DEFINE/CONFIRM trials in one reading center.

Methods

MRIs from DEFINE/CONFIRM at weeks 0, 24, 48, and 96 from patients randomized to twice-daily DMF or placebo (PBO) were reanalyzed at the Cleveland Clinic to measure brain parenchymal fraction (BPF). To account for pseudoatrophy, brain volume estimates were re-baselined to calculate changes for weeks 48–96.

Results

Across studies, 301 and 314 patients receiving DMF and PBO, respectively, had analyzable MRIs. In weeks 0–48, mean ± SE percentage change in BPF was −0.44 ± 0.04 vs. −0.34 ± 0.04% in DMF vs. PBO, respectively, whereas in weeks 48–96, mean ± SE percentage change in BPF was −0.27 ± 0.03 vs. −0.41 ± 0.04% in DMF vs. PBO, respectively. The mixed-effect model for repeated measures showed similar results: in weeks 48–96, estimated change (95% confidence interval) in BPF was −0.0021 (−0.0027, −0.0016) for DMF vs. −0.0033 (−0.0039, −0.0028) for PBO (35.9% reduction; p = 0.0025).

Conclusions

The lower rate of whole brain volume loss with DMF in this pooled BPF analysis in the second year vs. PBO is consistent with its effects on relapses, disability, and MRI lesions. Brain volume changes in the first year may be explained by pseudoatrophy effects also described in other MS clinical trials.

Effect of fingolimod vs interferon treatment on OCT measurements and cognitive function in RRMS

OBJECTIVE

To explore prospectively through OCT the rate of retinal layer changes in relapsing-remitting multiple sclerosis patients followed up on fingolimod or interferon, as well as the treatments' differential effects on cognitive tests scores.

METHODS

This prospective observational study enrolled 128 stable RRMS patients treated either with fingolimod (n = 71) or interferon (n = 56). Symbol-Digit Modality Test and retinal OCT scans were obtained at baseline and every 6 to 12 months. A subgroup of patients underwent expanded cognitive tests annually (Brief visual-spatial memory-total recall, BVMT-delayed recall, and Montreal Cognitive Assessment). Retinal-OCT scans were also obtained from 22 age- and sex-matched healthy controls. Mixed effects regression was used to study annualized changes in retinal layers and cognitive function, including differences between treatment groups. Correlations between annualized changes in retinal measurements and cognitive scores were also explored.

RESULTS

Fingolimod treated patients showed no significant difference in the rate of thinning of all retinal layers when compared to healthy controls and had significantly less GCIPL thinning when compared to interferons. SDMT scores improved similarly among both RRMS treatment groups. However, interferon but not fingolimod treated patients had significant decline in MOCA and total recall scores. We also found correlations between the annualized change in GCIPL thickness and annualized change in MOCA scores, and similar correlations with annualized change in total recall scores.

CONCLUSION

Fingolimod has a potential role in reducing retinal neurodegeneration in RRMS. Longitudinal OCT measures appear to be sensitive to changes in cognitive function and may be useful for monitoring neuroprotective therapies.

Future Brain and Spinal Cord Volumetric Imaging in the Clinic for Monitoring Treatment Response in MS

PURPOSE OF REVIEW

Volumetric analysis of brain imaging has emerged as a standard approach used in clinical research, e.g., in the field of multiple sclerosis (MS), but its application in individual disease course monitoring is still hampered by biological and technical limitations. This review summarizes novel developments in volumetric imaging on the road towards clinical application to eventually monitor treatment response in patients with MS.

RECENT FINDINGS

In addition to the assessment of whole-brain volume changes, recent work was focused on the volumetry of specific compartments and substructures of the central nervous system (CNS) in MS. This included volumetric imaging of the deep brain structures and of the spinal cord white and gray matter. Volume changes of the latter indeed independently correlate with clinical outcome measures especially in progressive MS. Ultrahigh field MRI and quantitative MRI added to this trend by providing a better visualization of small compartments on highly resolving MR images as well as microstructural information. New developments in volumetric imaging have the potential to improve sensitivity as well as specificity in detecting and hence monitoring disease-related CNS volume changes in MS.

Clinical significance of cortical lesions in patients with multiple sclerosis: A neuropsychological and neuroimaging study

INTRODUCTION

This study aims to investigate the association between the presence and frequency of cortical lesions (CLs), and the clinical and psychological features of multiple sclerosis (MS).

METHODS

A total of 19 patients with MS were examined using double inversion recovery (DIR) sequences with 3T magnetic resonance imaging (MRI) and classified into two groups: CL and non-CL. In-house software was used to quantitatively determine the atrophy of each brain region. Activities of daily living (ADL) were estimated using the Kurtzke Expanded Disability Status Scale (EDSS). Cognitive function was assessed using the following tests: Mini-Mental State Examination (MMSE), Trail Making Test (TMT), and Paced Auditory Serial Addition Task (PASAT). Z-scores were used to assess significant differences in the neuropsychological test outcomes between the groups.

RESULTS

Six of 19 patients had subcortical and deep WM lesions (non-CL group; diagnosed with relapsing-remitting MS). Thirteen of 19 patients had both subcortical and cortical lesions (CL group; 9-relapsing-remitting MS; 4-primary/secondary progressive MS). There were no significant differences in age, education, and disease duration, but EDSS scores were significantly higher in the CL group compared to the non-CL group. There were no significant differences in gray and white matter volume between the CL and the non-CL groups, but the white matter lesion volume was significantly higher in the CL group compared to the non-CL group. Neuropsychological tests showed significant performance worsening in the CL group as compared to the standard values for healthy individuals in their age group, especially in the TMT data.

CONCLUSIONS

Progressive MS, which was associated with decreased physical functioning, ADL, and cognitive impairment, was found in patients in the CL group.

CCL5-Glutamate Cross-Talk in Astrocyte-Neuron Communication in Multiple Sclerosis

The immune system (IS) and the central nervous system (CNS) are functionally coupled, and a large number of endogenous molecules (i.e., the chemokines for the IS and the classic neurotransmitters for the CNS) are shared in common between the two systems. These interactions are key elements for the elucidation of the pathogenesis of central inflammatory diseases. In recent years, evidence has been provided supporting the role of chemokines as modulators of central neurotransmission. It is the case of the chemokines CCL2 and CXCL12 that control pre- and/or post-synaptically the chemical transmission. This article aims to review the functional cross-talk linking another endogenous pro-inflammatory factor released by glial cells, i.e., the chemokine Regulated upon Activation Normal T-cell Expressed and Secreted (CCL5) and the principal neurotransmitter in CNS (i.e., glutamate) in physiological and pathological conditions. In particular, the review discusses preclinical data concerning the role of CCL5 as a modulator of central glutamatergic transmission in healthy and demyelinating disorders. The CCL5-mediated control of glutamate release at chemical synapses could be relevant either to the onset of psychiatric symptoms that often accompany the development of multiple sclerosis (MS), but also it might indirectly give a rationale for the progression of inflammation and demyelination. The impact of disease-modifying therapies for the cure of MS on the endogenous availability of CCL5 in CNS will be also summarized. We apologize in advance for omission in our coverage of the existing literature.

Prophylactic versus Therapeutic Fingolimod: Restoration of Presynaptic Defects in Mice Suffering from Experimental Autoimmune Encephalomyelitis

Fingolimod, the first oral, disease-modifying therapy for MS, has been recently proposed to modulate glutamate transmission in the central nervous system (CNS) of mice suffering from Experimental Autoimmune Encephalomyelitis (EAE) and in MS patients. Our study aims at investigating whether oral fingolimod recovers presynaptic defects that occur at different stages of disease in the CNS of EAE mice. In vivo prophylactic (0.3 mg/kg for 14 days, from the 7th day post immunization, d.p.i, the drug dissolved in the drinking water) fingolimod significantly reduced the clinical symptoms and the anxiety-related behaviour in EAE mice. Spinal cord inflammation, demyelination and glial cell activation are markers of EAE progression. These signs were ameliorated following oral fingolimod administration. Glutamate exocytosis was shown to be impaired in cortical and spinal cord terminals isolated from EAE mice at 21 ± 1 d.p.i., while GABA alteration emerged only at the spinal cord level. Prophylactic fingolimod recovered these presynaptic defects, restoring altered glutamate and GABA release efficiency. The beneficial effect occurred in a dose-dependent, region-specific manner, since lower (0.1-0.03 mg/kg) doses restored, although to a different extent, synaptic defects in cortical but not spinal cord terminals. A delayed reduction of glutamate, but not of GABA, exocytosis was observed in hippocampal terminals of EAE mice at 35 d.p.i. Therapeutic (0.3 mg/kg, from 21 d.p.i. for 14 days) fingolimod restored glutamate exocytosis in the cortex and in the hippocampus of EAE mice at 35 ± 1 d.p.i. but not in the spinal cord, where also GABAergic defects remained unmodified. These results improve our knowledge of the molecular events accounting for the beneficial effects elicited by fingolimod in demyelinating disorders.

Correlation between white matter damage and gray matter lesions in multiple sclerosis patients

We observed the characteristics of white matter fibers and gray matter in multiple sclerosis patients, to identify changes in diffusion tensor imaging fractional anisotropy values following white matter fiber injury. We analyzed the correlation between fractional anisotropy values and changes in whole-brain gray matter volume. The participants included 20 patients with relapsing-remitting multiple sclerosis and 20 healthy volunteers as controls. All subjects underwent head magnetic resonance imaging and diffusion tensor imaging. Our results revealed that fractional anisotropy values decreased and gray matter volumes were reduced in the genu and splenium of corpus callosum, left anterior thalamic radiation, hippocampus, uncinate fasciculus, right corticospinal tract, bilateral cingulate gyri, and inferior longitudinal fasciculus in multiple sclerosis patients. Gray matter volumes were significantly different between the two groups in the right frontal lobe (superior frontal, middle frontal, precentral, and orbital gyri), right parietal lobe (postcentral and inferior parietal gyri), right temporal lobe (caudate nucleus), right occipital lobe (middle occipital gyrus), right insula, right parahippocampal gyrus, and left cingulate gyrus. The voxel sizes of atrophic gray matter positively correlated with fractional anisotropy values in white matter association fibers in the patient group. These findings suggest that white matter fiber bundles are extensively injured in multiple sclerosis patients. The main areas of gray matter atrophy in multiple sclerosis are the frontal lobe, parietal lobe, caudate nucleus, parahippocampal gyrus, and cingulate gyrus. Gray matter atrophy is strongly associated with white matter injury in multiple sclerosis patients, particularly with injury to association fibers.

Presynaptic, release-regulating mGlu2 -preferring and mGlu3 -preferring autoreceptors in CNS: pharmacological profiles and functional roles in demyelinating disease

BACKGROUND AND PURPOSE

Presynaptic, release-regulating metabotropic glutamate 2 and 3 (mGlu2/3) autoreceptors exist in the CNS. They represent suitable targets for therapeutic approaches to central diseases that are typified by hyperglutamatergicity. The availability of specific ligands able to differentiate between mGlu2 and mGlu3 subunits allows us to further characterize these autoreceptors. In this study we investigated the pharmacological profile of mGlu2/3 receptors in selected CNS regions and evaluated their functions in mice with experimental autoimmune encephalomyelitis (EAE).

EXPERIMENTAL APPROACH

The comparative analysis of presynaptic mGlu2/3 autoreceptors was performed by determining the effect of selective mGlu2/3 receptor agonist(s) and antagonist(s) on the release of [(3)H]-D-aspartate from cortical and spinal cord synaptosomes in superfusion. In EAE mice, mGlu2/3 autoreceptor-mediated release functions were investigated and effects of in vivo LY379268 administration on impaired glutamate release examined ex vivo.

KEY RESULTS

Western blot analysis and confocal microscopy confirmed the presence of presynaptic mGlu2/3 receptor proteins. Cortical synaptosomes possessed LY541850-sensitive, NAAG-insensitive autoreceptors having low affinity for LY379268, while LY541850-insensitive, NAAG-sensitive autoreceptors with high affinity for LY379268 existed in spinal cord terminals. In EAE mice, mGlu2/3 autoreceptors completely lost their inhibitory activity in cortical, but not in spinal cord synaptosomes. In vivo LY379268 administration restored the glutamate exocytosis capability in spinal cord but not in cortical terminals in EAE mice.

CONCLUSIONS AND IMPLICATIONS

We propose the existence of mGlu2-preferring and mGlu3-preferring autoreceptors in mouse cortex and spinal cord respectively. The mGlu3 -preferring autoreceptors could represent a target for new pharmacological approaches for treating demyelinating diseases.

Multiple sclerosis

Due to its sensitivity to the different multiple sclerosis (MS)-related abnormalities, magnetic resonance imaging (MRI) has become an established tool to diagnose MS and to monitor its evolution. MRI has been included in the diagnostic workup of patients with clinically isolated syndromes suggestive of MS, and ad hoc criteria have been proposed and are regularly updated. In patients with definite MS, the ability of conventional MRI techniques to explain patients' clinical status and progression of disability is still suboptimal. Several advanced MRI-based technologies have been applied to estimate overall MS burden in the different phases of the disease. Their use has allowed the heterogeneity of MS pathology in focal lesions, normal-appearing white matter and gray matter to be graded in vivo. Recently, additional features of MS pathology, including macrophage infiltration and abnormal iron deposition, have become quantifiable. All of this, combined with functional imaging techniques, is improving our understanding of the mechanisms associated with MS evolution. In the near future, the use of ultrahigh-field systems is likely to provide additional insight into disease pathophysiology. However, the utility of advanced MRI techniques in clinical trial monitoring and in assessing individual patients' response to treatment still needs to be assessed.

Association between a genetic variant of type-1 cannabinoid receptor and inflammatory neurodegeneration in multiple sclerosis

Genetic ablation of type-1 cannabinoid receptors (CB1Rs) exacerbates the neurodegenerative damage of experimental autoimmune encephalomyelitis, the rodent model of multiple sclerosis (MS). To address the role on CB1Rs in the pathophysiology of human MS, we first investigated the impact of AAT trinucleotide short tandem repeat polymorphism of CNR1 gene on CB1R cell expression, and secondly on the inflammatory neurodegeneration process responsible for irreversible disability in MS patients. We found that MS patients with long AAT repeats within the CNR1 gene (≥12 in both alleles) had more pronounced neuronal degeneration in response to inflammatory white matter damage both in the optic nerve and in the cortex. Optical Coherence Tomography (OCT), in fact, showed more severe alterations of the retinal nerve fiber layer (RNFL) thickness and of the macular volume (MV) after an episode of optic neuritis in MS patients carrying the long AAT genotype of CNR1. MS patients with long AAT repeats also had magnetic resonance imaging (MRI) evidence of increased gray matter damage in response to inflammatory lesions of the white matter, especially in areas with a major role in cognition. In parallel, visual abilities evaluated at the low contrast acuity test, and cognitive performances were negatively influenced by the long AAT CNR1 genotype in our sample of MS patients. Our results demonstrate the biological relevance of the (AAT)n CNR1 repeats in the inflammatory neurodegenerative damage of MS.

Normal-appearing white matter permeability distinguishes poor cognitive performance in processing speed and working memory

BACKGROUND AND PURPOSE

Secondary-progressive MS is characterized by reduced acute inflammation and contrast enhancement but with increased axonal degeneration and cognitive/clinical disability that worsens with advanced disease. Relative recirculation, extracted from DSC is a surrogate measure of BBB integrity. We hypothesized that normal-appearing white matter relative recirculation is reduced in cognitively impaired compared with nonimpaired secondary-progressive MS, reflecting more advanced disease.

MATERIALS AND METHODS

Cognitive performance was classified as impaired or nonimpaired by use of Minimal Assessment of Cognitive Function In MS test components. Demographic data, brain parenchymal fraction, WM lesion fraction, and weighted mean normal-appearing white matter relative recirculation were compared in cognitively dichotomized groups. Univariate and multivariate logistic regressions were used to study the association between cognitive test results and normal-appearing white matter relative recirculation.

RESULTS

The mean (SD) age of 36 patients with secondary-progressive MS studied was 55.9 ± 9.3 years; 13 of 36 (36%) patients were male. A highly significant difference between normal-appearing white matter relative recirculation and WM lesion relative recirculation was present for all patients (P < .001). Normal-appearing white matter relative recirculation in impaired patients was significantly lower than in nonimpaired subjects for the Symbol Digit Modalities Test (P = .007), Controlled Word Association Test (P = .008), and Paced Auditory Serial Addition Test (P = .024). The Expanded Disability Status Scale demonstrated an inverse correlation with normal-appearing white matter relative recirculation (r = -0.319, P = .075). After adjustment for confounders, significant normal-appearing white matter relative recirculation reduction persisted for the Symbol Digit Modalities Test (P = .023) and the Paced Auditory Serial Addition Test (P = .047) but not for the Controlled Word Association Test (P = .13) in impaired patients.

CONCLUSIONS

Significant normal-appearing white matter relative recirculation reduction exists in cognitively impaired patients with secondary-progressive MS, localizing to the domains of processing speed and working memory.

Cortical pathology and cognitive impairment in multiple sclerosis

Cognitive impairment constitutes a relevant clinical aspect of multiple sclerosis (MS). Depending on the disease phase and type, 40-65% of MS patients develop various degrees of cognitive dysfunction. Pathological and MRI studies have failed to demonstrate the existence of a strict relationship between cognitive impairment and subcortical white matter pathology. The correlation is also poor when MRI metrics of whole brain (white plus gray matter) atrophy are considered. Over the last decade, increasing observations have provided evidence of a primary role of cortical pathology - that is, inflammatory focal lesions (cortical lesions) and atrophy (cortical thickness) - in determining global and/or selective cognitive disability in MS. By applying a new semi-automated software (Freesurfer) to analyze the global and regional cortical thickness and the double inversion recovery sequence to identify cortical lesions, it has been observed that specific cognitive deficits, such as memory impairment, attention deficits and reduced mental processing speed, could be better explained by cortical structural abnormalities rather than subcortical white matter lesions. Therefore, MRI evaluation of cortical pathology should be included in the routine examination of MS patients, especially those with initial signs/symptoms of cognitive dysfunctions.

MR imaging of multiple sclerosis

Owing to its ability to depict the pathologic features of multiple sclerosis (MS) in exquisite detail, conventional magnetic resonance (MR) imaging has become an established tool in the diagnosis of this disease and in monitoring its evolution. MR imaging has been formally included in the diagnostic work-up of patients who present with a clinically isolated syndrome suggestive of MS, and ad hoc diagnostic criteria have been proposed and are updated on a regular basis. In patients with established MS and in those participating in treatment trials, examinations performed with conventional MR pulse sequences provide objective measures to monitor disease activity and progression; however, they have a limited prognostic role. This has driven the application of newer MR imaging technologies, including higher-field-strength MR units, to estimate overall MS burden and mechanisms of recovery in patients at different stages of the disease. These techniques have allowed in vivo assessment of the heterogeneity of MS pathologic features in focal lesions and in normal-appearing tissues. More recently, some of the finer details of MS, including macrophage infiltration and abnormal iron deposition, have become quantifiable with MR imaging. The utility of these modern MR techniques in clinical trial monitoring and in the assessment of the individual patient's response to treatment still need to be evaluated.