Metabolites predict lesion formation and severity in relapsing-remitting multiple sclerosis.

BACKGROUND: Multiple sclerosis is characterized by white matter lesions, which are visualized with conventional T2-weighted magnetic resonance imaging (MRI). Little is known about local metabolic processes preceding the appearance and during the pathological development of new lesions. OBJECTIVE: To identify metabolite changes preceding white matter (WM) lesions and pathological severity of lesions over time. METHODS: A total of 59 relapsing-remitting multiple sclerosis (MS) patients were scanned four times, with 6-month intervals. Imaging included short-TE magnetic resonance spectroscopic imaging (MRSI) and diffusion tensor imaging (DTI). RESULTS: A total of 16 new lesions appeared within the MRSI slab in 12 patients. Glutamate increased (+1.0 mM (+19%), p = 0.039) 12 and 6 months before new lesions appeared. In these areas, the increase in creatine and choline 6 months before until lesion appearance was negatively correlated with radial diffusivity (ρ = -0.73, p = 0.002 and ρ = -0.72, p = 0.002). Increase in creatine also correlated with the increase of axial diffusivity in the same period (ρ = -0.53, p = 0.034). When splitting the lesions into "mild" and "severe" based on radial diffusivity, only mild lesions showed an increase in creatine and choline during lesion formation ( p = 0.039 and p = 0.008, respectively). CONCLUSION: Increased glutamate heralded the appearance of new T2-visible WM lesions. In pathologically "mild" lesions, an increase in creatine and choline was found during lesion formation.

Longitudinal absolute metabolite quantification of white and gray matter regions in healthy controls using proton MR spectroscopic imaging.

The purpose of this study was to evaluate quality parameters, metabolite concentrations and concentration ratios, and to investigate the reproducibility of quantitative proton magnetic resonance spectroscopic imaging ((1)H-MRSI) of selected white and gray matter regions of healthy adults. 2D-quantitative short-TE (1)H-MRSI spectra were obtained at 1.5T from the healthy human brain. Subjects (n = 12) were scanned twice with an interval of six months. Absolute metabolite concentrations were obtained based on coil loading, taking into account differences in sensitivity of the phased-array head coil. Spectral quality parameters, absolute metabolite concentrations, concentration ratios, and their reproducibility were determined and compared between time-points using a repeated measures general linear model. The quality of the spectra of selected brain areas was good, as determined by a mean spectral linewidth between 4.8 and 7.3 Hz (depending on the region). No significant differences between the two time-points were observed for spectral quality, concentrations, or concentration ratios. The mean intrasubject coefficient of variation (CoV) varied between 4.0 and 8.5% for total N-acetylaspartate, 7.2 and 10.8% for total creatine, 5.9 and 9.8% for myo-inositol, and 8.0 and 13.3% for choline, and remained below 20% for glutamate. CoV was generally lower when concentration ratios were considered. The study shows that longitudinal quantitative short-TE (1)H-MRSI generates reproducible absolute metabolite concentrations in healthy human white and gray matter. This may serve as a background for longitudinal clinical studies in adult patients.

Shifting imaging targets in multiple sclerosis: from inflammation to neurodegeneration.

Classically multiple sclerosis (MS) has been regarded as an auto-immune disease of the white matter in the central nervous system leading to severe disability over the course of several decades. Current therapeutic strategies in MS are mostly based on either immune suppression or immune modulation. Although effective in decreasing relapse frequency and severity as well as delaying disease progression, MS pathology ensues nonetheless. In the last decade it became evident that gray matter pathology plays an important role in disease progression and helps explaining certain aspects of MS-related disability such as cognitive decline. Conventional MRI outcome measures commonly used in clinical trials are sufficient to demonstrate an anti-inflammatory drug-effect but lack pathological specificity and are poor to moderate predictors of disability. In this article, we review new insights in gray matter pathology and functional reorganization in MS and how these novel fields in MS research may validate and establish new MRI outcome measures, aid in the development of new therapeutic strategies for neuroprotection and neurorepair, and may lead to development of novel predictive measures of disability and disease progression in MS.

Transient suppression of MLH1 allows effective single-nucleotide substitution by single-stranded DNA oligonucleotides.

Short synthetic single-stranded oligodeoxyribonucleotides (ssODNs) can be used to introduce subtle modifications into the genome of mouse embryonic stem cells (ESCs). We have previously shown that effective application of ssODN-mediated gene targeting in ESC requires (transient) suppression of DNA mismatch repair (MMR). However, whereas transient down-regulation of the mismatch recognition protein MSH2 allowed substitution of 3 or 4 nucleotides, 1 or 2 nucleotide substitutions were still suppressed. We now demonstrate that single- or dinucleotide substitution can effectively be achieved by transient down-regulation of the downstream MMR protein MLH1. By exploiting highly specific real-time PCR, we demonstrate the feasibility of substituting a single basepair in a non-selectable gene. However, disabling the MMR machinery may lead to inadvertent mutations. To obtain insight into the mutation rate associated with transient MMR suppression, we have compared the impact of transient and constitutive MMR deficiency on the repair of frameshift intermediates at mono- and dinucleotide repeats. Repair at these repeats relied on the substrate specificity and functional redundancy of the MSH2/MSH6 and MSH2/MSH3 MMR complexes. MLH1 knockdown increased the level of spontaneous mutagenesis, but modified ESCs remained germ line competent. Thus, transient MLH1 suppression provides a valuable extension of the MSH2 knockdown strategy, allowing rapid generation of mice carrying single basepair alterations in their genome.

Subcortical atrophy and cognition: sex effects in multiple sclerosis.

OBJECTIVES: Gray matter (GM) atrophy is common in multiple sclerosis (MS), as is cognitive dysfunction. Understanding the exact relationship between atrophy and cognition requires further investigation. The aim of this study was to investigate the relationship between subcortical GM atrophy and cognition in early relapsing onset MS. METHODS: Structural MRI and neuropsychological evaluations were performed in 120 patients (80 women) and 50 controls (30 women), part of an early inception cohort, 6 years postdiagnosis. Deep GM volumes were segmented automatically. Cognition was assessed in 7 domains. Stepwise linear regression was used to predict average cognition in the patient group. RESULTS: Most deep GM volumes were reduced in patients, with larger effects on average in men (-11%) than in women (-6.3%). Only the bilateral hippocampus, amygdala, and right nucleus accumbens in men, and right hippocampus and nucleus accumbens, bilateral amygdala, and putamen in women, showed no atrophy compared to controls. All cognitive domains except visuospatial memory were affected in men; none were significantly affected in women. In the MS group, average cognition was best predicted by thalamic volume, sex, and education (adjusted R(2) = 0.31), while lesion volume was not a significant predictor in the model. CONCLUSIONS: Six years postdiagnosis, almost all subcortical structures were affected by MS, especially in men. Cognition was most severely affected in male patients. Thalamic volume, sex, and education best predicted average cognition. These results underline the relevance of specific subcortical structures to cognition, as well as the relevance of (sex-specific) atrophy in MS.