Changes in N-acetylaspartate and myo-inositol detected in the cerebral cortex of hamsters with Creutzfeldt-Jakob disease

Metabolomic study of disease progression in scrapie prion infected mice; validation of a novel method for brain metabolite extraction

INTRODUCTION

Prion disease is a form of neurodegenerative disease caused by the misfolding and aggregation of cellular prion protein (PrP^C). The neurotoxicity of the misfolded form of prion protein, PrP^Sc still remains understudied. Here we try to investigate this issue using a metabolomics approach.

OBJECTIVES

The intention was to identify and quantify the small-in-size and water-soluble metabolites extracted from mice brains infected with the Rocky Mountain Laboratory isolate of mouse-adapted scrapie prions (RML) and track changes in these metabolites during disease evolution.

METHODS

A total of 73 mice were inoculated with RML prions or normal brain homogenate control; brains were harvested at 30, 60, 90, 120 and 150 days post-inoculation (dpi). We devised a high-efficiency metabolite extraction method and used nuclear magnetic resonance spectroscopy to identify and quantify 50 metabolites in the brain extracts. Data were analyzed using multivariate approach.

RESULTS

Brain metabolome profiles of RML infected animals displayed continuous changes throughout the course of disease. Among the analyzed metabolites, the most noteworthy changes included increases in myo-inositol and glutamine as well as decreases in 4-aminobutyrate, acetate, aspartate and taurine.

CONCLUSION

We report a novel metabolite extraction method for lipid-rich tissue. As all the major metabolites are identifiable and quantifiable by magnetic resonance spectroscopy, this study suggests that tracking of neurochemical profiles could be effective in monitoring the progression of neurodegenerative diseases and useful for assessing the efficacy of candidate therapeutics.

In Vivo Longitudinal (1)H MRS Study of Transgenic Mouse Models of Prion Disease in the Hippocampus and Cerebellum at 14.1 T

In vivo (1)H MR spectroscopy allows the non invasive characterization of brain metabolites and it has been used for studying brain metabolic changes in a wide range of neurodegenerative diseases. The prion diseases form a group of fatal neurodegenerative diseases, also described as transmissible spongiform encephalopathies. The mechanism by which prions elicit brain damage remains unclear and therefore different transgenic mouse models of prion disease were created. We performed an in vivo longitudinal (1)H MR spectroscopy study at 14.1 T with the aim to measure the neurochemical profile of Prnp -/- and PrPΔ32-121 mice in the hippocampus and cerebellum. Using high-field MR spectroscopy we were able to analyze in details the in vivo brain metabolites in Prnp -/- and PrPΔ32-121 mice. An increase of myo-inositol, glutamate and lactate concentrations with a decrease of N-acetylaspartate concentrations were observed providing additional information to the previous measurements.

The role of medical imaging in defining CNS abnormalities associated with HIV-infection and opportunistic infections

In this review of the current literature, we examine the role of medical imaging in providing new and relevant information on central nervous system (CNS) injury associated with human immunodeficiency virus (HIV) infection and various clinical manifestations of this injury. Common imaging modalities used to examine CNS injury in HIV infection include structural magnetic resonance imaging, magnetic resonance spectroscopy, diffusion tensor imaging, functional MRI, and positron emissions tomography. Clinical implications for the findings are discussed for each of these modalities individually and collectively. In addition, the direction for future studies is suggested in an attempt to provide possible methods that might answer the many questions that remain to be answered on the evolution and progression of CNS injury in the context of HIV infection.

Combined diffusion imaging and MR spectroscopy in the diagnosis of human prion diseases

BACKGROUND AND PURPOSE

The physiopathologic bases underlying the signal intensity changes and reduced diffusibility observed in prion diseases (TSEs) are still poorly understood. We evaluated the interest of MRS combined with DWI both as a diagnostic tool and a way to understand the mechanism underlying signal intensity and ADC changes in this setting.

MATERIALS AND METHODS

We designed a prospective study of multimodal MR imaging in patients with suspected TSEs. Forty-five patients with a suspicion of TSE and 11 age-matched healthy volunteers were included. The MR imaging protocol included T1, FLAIR, and DWI sequences. MRS was performed on the cerebellum, pulvinar, right lenticular nucleus, and frontal cortex. MR images were assessed visually, and ADC values were calculated.

RESULTS

Among the 45 suspected cases, 31 fulfilled the criteria for probable or definite TSEs (19 sCJDs, 3 iCJDs, 2 vCJDs, and 7 genetic TSEs); and 14 were classified as AltDs. High signals in the cortex and/or basal ganglia were observed in 26/31 patients with TSEs on FLAIR and 29/31 patients on DWI. In the basal ganglia, high DWI signals corresponded to a decreased ADC. Metabolic alterations, increased mIns, and decreased NAA were observed in all patients with TSEs. ADC values and metabolic changes were not correlated; this finding suggests that neuronal stress (vacuolization), neuronal loss, and astrogliosis do not alone explain the decrease of ADC.

CONCLUSIONS

MRS combined with other MR imaging is of interest in the diagnosis of TSE and provides useful information for understanding physiopathologic processes underlying prion diseases.

Role of myo-inositol by magnetic resonance spectroscopy in early diagnosis of Alzheimer's disease in APP/PS1 transgenic mice

BACKGROUND/AIMS

To explore the potential value of myo-inositol (mIns), which is regarded as a biomarker for early diagnosis of Alzheimer's disease, in APP/PS1 transgenic (tg) mice detected by (1)H-MRS.

METHODS

(1)H-MRS was performed in 30 APP/PS1 tg mice and 20 wild-type (wt) littermates at 3, 5 and 8 months of age. Areas under the peak of N-acetylaspartate (NAA), mIns and creatine (Cr) in the frontal cortex and hippocampus were measured, and the NAA/Cr and mIns/Cr ratios were analyzed quantitatively.

RESULTS

Compared with the wt mice, the mIns/Cr ratio of the 3-month-old tg mice was significantly higher (p < 0.05), and pathology showed activation and proliferation of astrocytes in the frontal cortex and hippocampus. The concentration of NAA was significantly lower at 8 and 8 months of age (p < 0.05). According to the threshold of mIns/Cr that was adopted to separate the tg from the wt mice, the rate of correct predictions was 82, 94 and 95%, respectively, for 3, 5 and 8 months.

CONCLUSION

Of the early AD metabolites as detected by (1)H-MRS, mIns is the most valuable marker for assessment of AD. Quantitative analysis of mIns may provide important clues for early diagnosis of AD.

Cerebral ependymoma in a patient with multiple sclerosis case report and critical review of the literature

BACKGROUND

The concurrence of multiple sclerosis (MS) and brain tumors is a rare but well-recognized condition. The radiologic evidence of the progressive evolution of a mega-plaque in a tumor has never been described. We report the first case of such an occurrence.

METHODS

A 27-year-old woman with a diagnosis of MS was referred to us for an intense frontal headache. Magnetic resonance imaging showed a mass lesion in correspondence of a black hole lesion previously diagnosed. The patient was operated on, with complete removal of the tumor documented by an intraoperative MRI. The histologic examination evidenced an ependymoma. Postoperative radiotherapy was performed.

RESULTS

The patient is well and recurrence-free at 2 years follow-up.

CONCLUSIONS

The present case, documenting the transformation of a mega-plaque into a tumor, suggests a cause-effect relationship between MS and brain tumors.

MRI and MRS alterations in the preclinical phase of murine prion disease: association with neuropathological and behavioural changes

Prion diseases are fatal chronic neurodegenerative diseases. Previous qualitative magnetic resonance imaging (MRI) and spectroscopy (MRS) studies report conflicting results in the symptomatic stages of the disease, but little work has been carried out during the earlier stages of the disease. Here we have used the murine ME7 model of prion disease to quantitatively investigate MRI and MRS changes during the period prior to the onset of overt clinical signs (20+ weeks) and have correlated these with pathological and behavioural abnormalities. Using in vivo MRI, at the later stages of the preclinical period (18 weeks) the diffusion of tissue water was significantly reduced, coinciding with significant microglial activation and behavioural hyperactivity. Using in vivo MRS, we found early (12 weeks) decreases in the ratio of N-acetyl aspartate to both choline (NAA/Cho) and creatine (NAA/Cr) in the thalamus and hippocampus, which were associated with early behavioural deficits. Ex vivo MRS of brain extracts confirmed and extended these findings, showing early (8-12 weeks) decreases in both the neuronal metabolites NAA and glutamate, and the metabolic metabolites lactate and glucose. Increases in the glial metabolite myo-inositol were observed at later stages when microglial and astrocyte activation is substantial. These changes in MRI and MRS signals, which precede overt clinical signs of disease, could provide insights into the pathogenesis of this disease and may enable early detection of pathology.

N-Acetylaspartate in the CNS: from neurodiagnostics to neurobiology

The brain is unique among organs in many respects, including its mechanisms of lipid synthesis and energy production. The nervous system-specific metabolite N-acetylaspartate (NAA), which is synthesized from aspartate and acetyl-coenzyme A in neurons, appears to be a key link in these distinct biochemical features of CNS metabolism. During early postnatal central nervous system (CNS) development, the expression of lipogenic enzymes in oligodendrocytes, including the NAA-degrading enzyme aspartoacylase (ASPA), is increased along with increased NAA production in neurons. NAA is transported from neurons to the cytoplasm of oligodendrocytes, where ASPA cleaves the acetate moiety for use in fatty acid and steroid synthesis. The fatty acids and steroids produced then go on to be used as building blocks for myelin lipid synthesis. Mutations in the gene for ASPA result in the fatal leukodystrophy Canavan disease, for which there is currently no effective treatment. Once postnatal myelination is completed, NAA may continue to be involved in myelin lipid turnover in adults, but it also appears to adopt other roles, including a bioenergetic role in neuronal mitochondria. NAA and ATP metabolism appear to be linked indirectly, whereby acetylation of aspartate may facilitate its removal from neuronal mitochondria, thus favoring conversion of glutamate to alpha ketoglutarate which can enter the tricarboxylic acid cycle for energy production. In its role as a mechanism for enhancing mitochondrial energy production from glutamate, NAA is in a key position to act as a magnetic resonance spectroscopy marker for neuronal health, viability and number. Evidence suggests that NAA is a direct precursor for the enzymatic synthesis of the neuron specific dipeptide N-acetylaspartylglutamate, the most concentrated neuropeptide in the human brain. Other proposed roles for NAA include neuronal osmoregulation and axon-glial signaling. We propose that NAA may also be involved in brain nitrogen balance. Further research will be required to more fully understand the biochemical functions served by NAA in CNS development and activity, and additional functions are likely to be discovered.

The imaging appearance of Creutzfeldt-Jakob disease caused by the E200K mutation

The E200K mutation on chromosome 20 can cause familial Creutzfeldt-Jakob disease (CJD). Patients with this mutation are clinically similar to those with sporadic CJD, but their imaging features are not well documented. We report here the quantitative and qualitative evaluation of the magnetic resonance (MR) imaging characteristics of this unique group of patients using three-dimensional spoiled gradient recalled (SPGR) echo images, diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) measurements, MR spectroscopy and a fluid-attenuated inversion recovery (FLAIR) sequence. The SPGR and ADC data were analyzed with SPM99. ANCOVA and regression models were used for a region-of-interest (ROI) analysis of ADC and metabolic ratios. CJD patients had a decreased fraction of gray matter and an increased fraction of cerebrospinal fluid (P=.001) in the cortex and cerebellum and increased ADC values in the cortex (P<.001). Focal decreases of ADC were found in the putamen via ROI analysis (548+/-83 vs. 709+/-9 microm(2)/s, P=.02). N-acetyl aspartate (NAA) was generally reduced, with the NAA/Cho ratio lowest in the cingulate gyrus. Qualitative assessment revealed hyperintensities on FLAIR, DWI or both in the putamen (three out of four patients), caudate (three out of four patients) and thalamus. These results provide a framework for future study of patients with genetically defined familial CJD.

Regional brain metabolite abnormalities in inherited prion disease and asymptomatic gene carriers demonstrated in vivo by quantitative proton magnetic resonance spectroscopy

INTRODUCTION

Inherited prion diseases are caused by mutations in the gene which codes for prion protein (PrP), leading to proliferation of abnormal PrP isomers in the brain and neurodegeneration; they include Gerstmann-Sträussler-Scheinker disease (GSS), fatal familial insomnia (FFI) and familial Creutzfeldt-Jakob disease (fCJD).

METHODS

We studied two patients with symptomatic inherited prion disease (P102L) and two pre-symptomatic P102L gene carriers using quantitative magnetic resonance spectroscopy (MRS). Short echo time spectra were acquired from the thalamus, caudate region and frontal white matter, metabolite levels and ratios were measured and z-scores calculated for individual patients relative to age-matched normal controls. MRS data were compared with structural magnetic resonance imaging.

RESULTS

One fCJD case had generalised atrophy and showed increased levels of myo-inositol (MI) in the thalamus (z=3.7). The other had decreased levels of N-acetylaspartate (z=4) and diffuse signal abnormality in the frontal white matter. Both asymptomatic gene carriers had normal imaging, but increased frontal white matter MI (z=4.3, 4.1), and one also had increased MI in the caudate (z=5.3).

CONCLUSION

Isolated MI abnormalities in asymptomatic gene carriers are a novel finding and may reflect early glial proliferation, prior to significant neuronal damage. MRS provides potential non-invasive surrogate markers of early disease and progression in inherited prion disease.

Preclinical metabolic changes in mouse prion diseases detected by 1H-nuclear magnetic resonance spectroscopy

Magnetic resonance spectroscopy studies in animal models of prion disease are very few and concern terminal stages of infection. In order to study earlier stages of the disease, we used in-vivo magnetic resonance spectroscopy in a mouse model of scrapie and, for the first time, in mice infected with a bovine spongiform encephalopathy strain. In bovine spongiform encephalopathy-infected mice, we observed an increase in myo-inositol preceding clinical signs by 20 days, followed by a decrease in N-acetylaspartate at advanced stages. In scrapie-infected mice, changes in N-acetylaspartate and myo-inositol were detected at the beginning of the symptomatic phase. These results show that magnetic resonance spectroscopy is a valuable tool for detecting subtle metabolic changes associated to gliosis and neuronal dysfunction in prion diseases.

Short TE Quantitative Proton Magnetic Resonance Spectroscopy in Variant Creutzfeldt-Jakob Disease

Variant Creutzfeldt-Jakob disease (vCJD) is a fatal neurodegenerative disorder. Clinical diagnosis is difficult in the early stages as the disease often presents with non-specific psychiatric and neurological symptoms. To investigate the diagnostic potential of quantitative short TE in vivo MRS, and the nature and anatomical distribution of biochemical abnormalities in vCJD, localised single-voxel spectra (TE/TR 30 ms/2,000 ms) were acquired from three brain regions: thalami, caudate nuclei and frontal white matter. Metabolite concentrations and ratios from three patients with definite or probable vCJD were compared with eight normal age-matched controls. Abnormal signal on T2-weighted MRI was apparent in the pulvinar region in all vCJD patients; this region also showed greatly increased myo-inositol [MI] (mean 2.5-fold, P=0.01) and decreased N-acetyl-aspartate (NAA; mean 2-fold, P=0.01). Two patients also showed increased [MI] (z=17, 11; one with decreased NAA, z=-12) in normal-appearing caudate nuclei. The magnitude of metabolite abnormalities in the thalami in moderately advanced vCJD suggests a potential role in earlier diagnosis. Short TE protocols allow the measurement of MI, which adds discriminant power to the MRS examination.

Monitoring disease progression in transgenic mouse models of Alzheimer's disease with proton magnetic resonance spectroscopy

Currently no definitive biomarker of Alzheimer's disease (AD) is available, and this impedes both clinical diagnosis in humans and drug discovery in transgenic animal models. Proton magnetic resonance spectroscopy ((1)H MRS) provides a noninvasive way to investigate in vivo neurochemical abnormalities. Each observable metabolite can potentially provide information about unique in vivo pathological processes at the molecular or cellular level. In this study, the age-dependent 1H MRS profile of transgenic AD mice was compared to that of wild-type mice. Twenty-seven APP-PS1 mice (which coexpress mutated human presenilin 1 and amyloid-beta precursor protein) and 30 wild-type mice age 66-904 days were examined, some repeatedly. A reduction in the levels of N-acetylaspartate and glutamate, compared with total creatine levels, was found in APP-PS1 mice with advancing age. The most striking finding was a dramatic increase in the concentration of myo-inositol with age in APP-PS1 mice, which was not observed in wild-type mice. The age-dependent neurochemical changes observed in APP-PS1 mice agree with results obtained from in vivo human MRS studies. Among the different transgenic mouse models of AD that have been studied with 1H MRS, APP-PS1 mice seem to best match the neurochemical profile exhibited in human AD. 1H MRS could serve as a sensitive in vivo surrogate indicator of therapeutic efficacy in trials of agents designed to reduce neurotoxicity due to microglial activation. Because of its noninvasive and repeatable nature, MRS in transgenic models of AD could substantially accelerate drug discovery for this disease.

Discrimination of white matter lesions and multiple sclerosis plaques by short echo quantitative 1H—magnetic resonance spectroscopy

Multiple sclerosis (MS) plaques and age related white matter lesions (WML) are of similar morphological appearance on T2 weighted MRI. Therefore their differentiation is sometimes crucial. Proton magnetic resonance spectroscopy ((1)H-MRS) adds metabolic information to conventional imaging and may help to distinguish inflammatory MS plaques from vascular related WML. This study was performed to evaluate the metabolite pattern in MS plaques and WML. 15 MS patients, 14 elderly individuals with WML and 16 controls were investigated by conventional MRI and short echo quantitative (1)H-MRS (TE: 30ms, TR: 3000ms). The mean metabolite concentrations in normal control white matter (NCWM), MS plaques and WML were: t-NAA: 8.96 mmol/l (SD: 0.93) vs 6.79 mmol/l (SD: 1.99) vs 7.18 mmol/l (SD: 1.41); Cho:1.66 mmol/l (SD: 0.4) vs 1.49 mmol/l (SD: 0.45) vs 1.46 mmol/l (SD: 0.34); PCr:5.64 mmol/l (SD: 0.83) vs 4.9mmol/l (SD: 1.3) vs 4.95 mmol/l (SD: 0.86); myo-Ins: 4.57 mmol/l (SD:1.05) vs 6.34 mmol/l (SD: 2.03) vs 4.5 mmol/l (SD: 0.96). t-NAA reduction in MS plaques and WML was significant compared with controls (p <or= 0.001). MS plaques showed significantly elevated myo- Ins concentrations compared with controls (p = 0.002) and to WML (p = 0.003). In summary MS plaques and WML show a decrease in their t-NAA concentrations compared with controls. Elevated concentrations of myo-Ins in MS plaques but not in WML makes this metabolite of special interest for their differentiation.

Understanding pathogenesis and treatment of HIV dementia: a role for magnetic resonance?

HIV dementia (HIVD) is among the most common and most feared neurological complications of AIDS. In vitro studies have identified a constellation of potentially neurotoxic inflammatory and non-inflammatory pathways, one or more of which could underlie HIVD. Magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) studies can distinguish between inflammatory and non-inflammatory pathways in vivo and suggest that either or both might be active in different patients or at different times in the same patient. This could perhaps explain the variability in HIVD development, progression and response to therapy. These findings also suggest that MRI and MRS can identify patients at risk for HIVD and predict response to therapy.

Quantitative 1H MRS imaging 14 years after presenting with a clinically isolated syndrome suggestive of multiple sclerosis

clinically isolated syndromes (CIS) are events suggestive for emerging multiple sclerosis (MS). A majority of patients develop MS within months or years whilst others remain clinically isolated. The goal of this study was to investigate whether biochemical metabolites detectable by 'H magnetic resonance spectroscopy (MRS) may serve to distinguish between these two groups. We investigated 41 patients 14 years after presentation with a CIS and 21 controls with combined quantitative short echo 'H MRS and magnetic resonance imaging (MRI) and assessed disability according to the Expanded Disability Status Scale (EDSS). At follow-up, 32 had developed MS, and 9 still had CIS. Compared with controls, MS patients demonstrated significantly higher concentrations of myo-inositol (Ins) in normal appearing white matter (NAWM) and lesions. Lesions also demonstrated a reduced N-acetyl-aspartate (NAA) level and an increase in choline-containing compounds (Cho). The NAWM Ins concentration was correlated with EDSS (r = 0.48, p = 0.005). MS normal appearing cortical grey matter (CGM) exhibited a decreased NAA. Patients who remained CIS did not differ significantly from controls in any MRS measure. Metabolite changes in normal appearing white and grey matter in MS indicate diffuse involvement of the entire MS brain, which was not seen in the persisting CIS patients. Elevated Ins in MS NAWM appeared functionally relevant It may indicate glial cell proliferation or gliosis.