Magnetic resonance spectroscopy in Alzheimer's disease: focus on N-acetylaspartate

The CNS-Penetrant Soluble Guanylate Cyclase Stimulator CY6463 Reveals its Therapeutic Potential in Neurodegenerative Diseases

Effective treatments for neurodegenerative diseases remain elusive and are critically needed since the burden of these diseases increases across an aging global population. Nitric oxide (NO) is a gasotransmitter that binds to soluble guanylate cyclase (sGC) to produce cyclic guanosine monophosphate (cGMP). Impairment of this pathway has been demonstrated in neurodegenerative diseases. Normalizing deficient NO-cGMP signaling could address multiple pathophysiological features of neurodegenerative diseases. sGC stimulators are small molecules that synergize with NO, activate sGC, and increase cGMP production. Many systemic sGC stimulators have been characterized and advanced into clinical development for a variety of non-central nervous system (CNS) pathologies. Here, we disclose the discovery of CY6463, the first brain-penetrant sGC stimulator in clinical development for the treatment of neurodegenerative diseases, and demonstrate its ability to improve neuronal activity, mediate neuroprotection, and increase cognitive performance in preclinical models. In several cellular assays, CY6463 was demonstrated to be a potent stimulator of sGC. In agreement with the known effects of sGC stimulation in the vasculature, CY6463 elicits decreases in blood pressure in both rats and mice. Relative to a non-CNS penetrant sGC stimulator, rodents treated with CY6463 had higher cGMP levels in cerebrospinal fluid (CSF), functional-magnetic-resonance-imaging-blood-oxygen-level-dependent (fMRI-BOLD) signals, and cortical electroencephalographic (EEG) gamma-band oscillatory power. Additionally, CY6463 improved cognitive performance in a model of cognitive disruption induced by the administration of a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist. In models of neurodegeneration, CY6463 treatment increased long-term potentiation (LTP) in hippocampal slices from a Huntington’s disease mouse model and decreased the loss of dendritic spines in aged and Alzheimer’s disease mouse models. In a model of diet-induced obesity, CY6463 reduced markers of inflammation in the plasma. Furthermore, CY6463 elicited an additive increase in cortical gamma-band oscillatory power when co-administered with donepezil: the standard of care in Alzheimer’s disease. Together, these data support the clinical development of CY6463 as a novel treatment for neurodegenerative disorders.

Structural and Functional Alterations in Betel-Quid Chewers: A Systematic Review of Neuroimaging Findings

Background: A number of neuroimaging studies have investigated structural, metabolic, and functional connectivity changes in betel quid (BQ) chewers. We present a systematic review of neuroimaging studies with emphasis on key brain systems affected by BQ chewing to bring a better understanding on the neuro mechanisms involved in BQD. Methods: All BQ neuroimaging studies were identified by searching PubMed, EMBASE, and Google scholar for English articles published until March 2018 using the key words: Betel-quid, resting state, functional MRI, structural MRI, diffusion tensor imaging (DTI), and betel quid dependence basing on the PRISMA criteria. We also sought unpublished studies, and the rest were obtained from reference lists of the retrieved articles. All neuroimaging studies investigating brain structural, and functional alterations related to BQ chewing and BQ dependence were included. Our systematic review registration number is CRD42018092669. Results: A review of 12 studies showed that several systems in the brain of BQ chewers exhibited structural, metabolic, and functional alterations. BQ chewing was associated with alterations in the reward [areas in the midbrain, and prefrontal cortex (PFC)], impulsivity (anterior cingulate cortex, PFC) and cognitive (PFC, the default mode, frontotemporal, frontoparietal, occipital/temporal, occipital/parietal, temporal/limbic networks, hippocampal/hypothalamus, and the cerebellum) systems in the brain. BQ duration and severity of betel quid dependence were associated with majority of alterations in BQ chewers. Conclusion: Betel quid chewing is associated with brain alterations in structure, metabolism and function in the cognitive, reward, and impulsivity circuits which are greatly influenced by duration and severity of betel quid dependence.

Metabolomics-A Promising Approach to Pituitary Adenomas

Background: Metabolomics-the novel science that evaluates the multitude of low-molecular-weight metabolites in a biological system, provides new data on pathogenic mechanisms of diseases, including endocrine tumors. Although development of metabolomic profiling in pituitary disorders is at an early stage, it seems to be a promising approach in the near future in identifying specific disease biomarkers and understanding cellular signaling networks. Objectives: To review the metabolomic profile and the contributions of metabolomics in pituitary adenomas (PA). Methods: A systematic review was conducted via PubMed, Web of Science Core Collection and Scopus databases, summarizing studies that have described metabolomic aspects of PA. Results: Liquid chromatography tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR) spectrometry, which are traditional techniques employed in metabolomics, suggest amino acids metabolism appears to be primarily altered in PA. N-acetyl aspartate, choline-containing compounds and creatine appear as highly effective in differentiating PA from healthy tissue. Deoxycholic and 4-pyridoxic acids, 3-methyladipate, short chain fatty acids and glucose-6-phosphate unveil metabolite biomarkers in patients with Cushing's disease. Phosphoethanolamine, N-acetyl aspartate and myo-inositol are down regulated in prolactinoma, whereas aspartate, glutamate and glutamine are up regulated. Phosphoethanolamine, taurine, alanine, choline-containing compounds, homocysteine, and methionine were up regulated in unclassified PA across studies. Intraoperative use of ultra high mass resolution matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI), which allows localization and delineation between functional PA and healthy pituitary tissue, may contribute to achievement of complete tumor resection in addition to preservation of pituitary cell lines and vasopressin secretory cells, thus avoiding postoperative diabetes insipidus. Conclusion: Implementation of ultra high performance metabolomics analysis techniques in the study of PA will significantly improve diagnosis and, potentially, the therapeutic approach, by identifying highly specific disease biomarkers in addition to novel molecular pathogenic mechanisms. Ultra high mass resolution MALDI-MSI emerges as a helpful clinical tool in the neurosurgical treatment of pituitary tumors. Therefore, metabolomics appears to be a science with a promising prospect in the sphere of PA, and a starting point in pituitary care.

[The cholinergic deficiency syndrome in patients with depressed consciousness after severe brain injury]

AIM

To determine the clinical and electrophysiological (EEG) signs of cholinergic deficiency in the process of recovery of consciousness in patients with severe brain injury.

MATERIAL AND METHODS

Thirty-seven people (24 men and 13 women, mean age 32±14 years) were studied. A comprehensive study included assessment of neurological status, mental activity, and EEG.

RESULTS AND CONCLUSION

A set of neurological symptoms, including reduced muscle tone, autonomic disorders (dry mucous membranes and skin, tachycardia, hypotension, gastrointestinal tract), eye movement disorders, that were,in accordance with the literature, characteristicof the cholinergic deficiency syndrome was found. This syndrome was detected against the background of a comatose state, akinetic mutism and mutism with understanding of speech, disintegration of speech, disorientation and amnestic decline. EEG revealed stable over time (months) characteristic changes: slowing and asymmetric alpha activity, equivalent dipole sources of hippocampal and stem localization, persistent strengthening of intra-hemispheric coherent connections, especially on the left side. The regression of the cholinergic deficiency syndrome was accompanied by an increase of regularity, capacity and frequency of alpha-activity (from 7-8 to 9-10 Hz), prevalence of equivalent dipole sources in the hippocampus with their appearance in the occipital cortex, normalization of connections with right-brain coherence with the preservation of their pathologically high values on the left side.

Neurometabolic characteristics in the anterior cingulate gyrus of Alzheimer's disease patients with depression: a (1)H magnetic resonance spectroscopy study

BACKGROUND

Depression is a common comorbid psychiatric symptom in patients with Alzheimer's disease (AD), and the prevalence of depression is higher among people with AD compared with healthy older adults. Comorbid depression in AD may increase the risk of cognitive decline, impair patients' function, and reduce their quality of life. However, the mechanisms of depression in AD remain unclear. Here, our aim was to identify neurometabolic characteristics in the brain that are associated with depression in patients with mild AD.

METHODS

Thirty-seven patients were evaluated using the Neuropsychiatric Inventory (NPI) and Hamilton Depression Rating Scale (HAMD-17), and divided into two groups: 17 AD patients with depression (D-AD) and 20 non-depressed AD patients (nD-AD). Using proton magnetic resonance spectroscopy, we characterized neurometabolites in the anterior cingulate gyrus (ACG) of D-AD and nD-AD patients.

RESULTS

Compared with nD-AD patients, D-AD patients showed lower N-acetylaspartate/creatine (NAA/Cr) and higher myo-inositol/creatine (mI/Cr) in the left ACG. NPI score correlated with NAA/Cr and mI/Cr in the left ACG, while HAMD correlated with NAA/Cr.

CONCLUSIONS

Our findings show neurometabolic alterations in D-AD patients. Thus, D-AD pathogenesis may be attributed to abnormal activity of neurons and glial cells in the left ACG.

7.0T nuclear magnetic resonance evaluation of the amyloid beta (1-40) animal model of Alzheimer's disease: comparison of cytology verification

3.0T magnetic resonance spectroscopic imaging is a commonly used method in the research of brain function in Alzheimer's disease. However, the role of 7.0T high-field magnetic resonance spectroscopic imaging in brain function of Alzheimer's disease remains unclear. In this study, 7.0T magnetic resonance spectroscopy showed that in the hippocampus of Alzheimer's disease rats, the N-acetylaspartate wave crest was reduced, and the creatine and choline wave crest was elevated. This finding was further supported by hematoxylin-eosin staining, which showed a loss of hippocampal neurons and more glial cells. Moreover, electron microscopy showed neuronal shrinkage and mitochondrial rupture, and scanning electron microscopy revealed small size hippocampal synaptic vesicles, incomplete synaptic structure, and reduced number. Overall, the results revealed that 7.0T high-field nuclear magnetic resonance spectroscopy detected the lesions and functional changes in hippocampal neurons of Alzheimer's disease rats in vivo, allowing the possibility for assessing the success rate and grading of the amyloid beta (1-40) animal model of Alzheimer's disease.

Unraveling amyloid toxicity pathway in NIH3T3 cells by a combined proteomic and 1 H-NMR metabonomic approach

A range of debilitating human diseases is known to be associated with the formation of stable highly organized protein aggregates known as amyloid fibrils. The early prefibrillar aggregates behave as cytotoxic agents and their toxicity appears to result from an intrinsic ability to impair fundamental cellular processes by interacting with cellular membranes, causing oxidative stress and increase in free Ca(2+) that lead to apoptotic or necrotic cell death. However, specific signaling pathways that underlie amyloid pathogenicity remain still unclear. This work aimed to clarify cell impairment induced by amyloid aggregated. To this end, we used a combined proteomic and one-dimensional (1) H-NMR approach on NIH-3T3 cells exposed to prefibrillar aggregates from the amyloidogenic apomyoglobin mutant W7FW14F. The results indicated that cell exposure to prefibrillar aggregates induces changes of the expression level of proteins and metabolites involved in stress response. The majority of the proteins and metabolites detected are reported to be related to oxidative stress, perturbation of calcium homeostasis, apoptotic and survival pathways, and membrane damage. In conclusion, the combined proteomic and (1) H-NMR metabonomic approach, described in this study, contributes to unveil novel proteins and metabolites that could take part to the general framework of the toxicity induced by amyloid aggregates. These findings offer new insights in therapeutic and diagnostic opportunities.

Current strategies in the discovery of small-molecule biomarkers for Alzheimer’s disease

With the number of patients suffering from Alzheimer’s disease rapidly increasing, there is a major requirement for an accurate biomarker capable of diagnosing the disease early. Much of the research is focused on protein and genetic approaches; however, small molecules may provide viable marker molecules. Examples that support this approach include known abnormalities in lipid metabolism, glucose utilization and oxidative stress, which have been demonstrated in patients suffering from the disease. Therefore, by-products of this irregular metabolism may provide accurate biomarkers. In this review we present the current approaches previously published in the literature used to investigate potential small-molecule and metabolite markers, and report their findings. A wide range of techniques are discussed, including separation approaches (LC, GC and CE), magnetic resonance technologies (NMR and magnetic resonance spectroscopy), and immunoassays.

A metabolomic study of the CRND8 transgenic mouse model of Alzheimer's disease

Alzheimer's disease is the most common neurodegenerative disease of the central nervous system characterized by a progressive loss in memory and deterioration of cognitive functions. In this study the transgenic mouse TgCRND8, which encodes a mutant form of the amyloid precursor protein 695 with both the Swedish and Indiana mutations and develops extracellular amyloid beta-peptide deposits as early as 2-3 months, was investigated. Extract from eight brain regions (cortex, frontal cortex, cerebellum, hippocampus, olfactory bulb, pons, midbrain and striatum) were studied using (1)H NMR spectroscopy. Analysis of the NMR spectra discriminated control from APP695 tissues in hippocampus, cortex, frontal cortex, midbrain and cerebellum, with hippocampal and cortical region being most affected. The analysis of the corresponding loading plots for these brain regions indicated a decrease in N-acetyl-L-aspartate, glutamate, glutamine, taurine (exception hippocampus), gamma-amino butyric acid, choline and phosphocholine (combined resonances), creatine, phosphocreatine and succinate in hippocampus, cortex, frontal cortex (exception gamma-amino butyric acid) and midbrain of affected animals. An increase in lactate, aspartate, glycine (except in midbrain) and other amino acids including alanine (exception frontal cortex), leucine, iso-leucine, valine and water soluble free fatty acids (0.8-0.9 and 1.2-1.3 ppm) were observed in the TgCRND8 mice. Our findings demonstrate that the perturbations in metabolism are more widespread and include the cerebellum and midbrain. Furthermore, metabolic perturbations are associated with a wide range of metabolites which could improve the diagnosis and monitoring of the progression of Alzheimer's disease.

Neurochemistry of drug action: insights from proton magnetic resonance spectroscopic imaging and their relevance to addiction

Proton magnetic resonance spectroscopy ((1)H MRS) is a noninvasive imaging technique that permits measurement of particular compounds or metabolites within the tissue of interest. In the brain, (1)H MRS provides a snapshot of the neurochemical environment within a defined volume of interest. A search of the literature demonstrates the widespread utility of this technique for characterizing tumors, tracking the progress of neurodegenerative disease, and for understanding the neurobiological basis of psychiatric disorders. As of relatively recently, (1)H MRS has found its way into substance abuse research, and it is beginning to become recognized as a valuable complement in the brain imaging toolbox that also contains positron emission tomography, single-photon-emission computed tomography, and functional magnetic resonance imaging. Drug abuse studies using (1)H MRS have identified several biochemical changes in the brain. The most consistent alterations across drug class were reductions in N-acetylaspartate and elevations in myo-inositol, whereas changes in choline, creatine, and amino acid transmitters also were abundant. Together, the studies discussed herein provide evidence that drugs of abuse may have a profound effect on neuronal health, energy metabolism and maintenance, inflammatory processes, cell membrane turnover, and neurotransmission, and these biochemical changes may underlie the neuropathology within brain tissue that subsequently gives rise to the cognitive and behavioral impairments associated with drug addiction.

Neuroimaging Studies in Alzheimer's Disease

Alzheimer's Disease (AD) is a progressive neurodegenerative disease associated with memory loss and gradual behavioral, functional and cognitive impairment. Conventional imaging studies, such as magnetic resonance or computed tomography have played a secondary role in AD diagnosis: While other causes of memory loss and cognitive deficit can be evaluated by these imaging methods, AD structural changes are not detected until very late in the course of the disease. Recent and more precise techniques have been developed to detect subtle changes not visualized with those imaging methods. This article presents a review of the neuroimaging techniques used as a diagnostic aid for AD.

Proton magnetic resonance spectroscopy in dementias and mild cognitive impairment

With the anticipated increase in dementias due to the aging demographic of industrialized nations, biomarkers for neurodegenerative diseases are increasingly important as new therapies are being developed for clinical trials. Proton MR spectroscopy ((1)H MRS) appears poised to be a viable means of tracking brain metabolic changes due to neurodegenerative diseases and potentially as a biomarker for treatment effects in clinical therapeutic trials. This review highlights the body of literature investigating brain metabolic abnormalities in Alzheimer's disease, amnestic mild cognitive impairment, frontotemporal dementia, vascular dementia, Lewy body dementia, and Parkinson's disease dementia. In particular, the review addresses the viability of (1)H MRS to discriminate among dementias, to measure disease progression, and to measure the effects of pharmacological treatments. While findings to date are encouraging, more study is needed in longitudinal patterns of brain metabolic changes, correspondence with changes in clinical markers of disease progression, and sensitivity of (1)H MRS measures to treatment effects. Such developments will hopefully benefit the search for effective treatments of dementias in the twenty-first century.

Molecular Imaging and Magnetic Resonance Imaging in Early Diagnosis of Alzheimer's Disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is the most common cause of dementia in the elderly. Magnetic resonance (MR) or computed tomography (CT) imaging is recommended for routine evaluation of dementias. The development of molecular imaging agents and the new techniques of MR for AD are critically important for early diagnosis, neuropathogenesis studies and assessing treatment efficacy in AD. Neuroimaging using nuclear medicine techniques such as SPECT, PET and MR spectroscopy has the potential to characterize the biomarkers for Alzheimer's disease. The present review summarizes the results of radionuclide imaging and MR imaging in AD.

Longitudinal multimodal imaging in mild to moderate Alzheimer disease: a pilot study with memantine

OBJECTIVE

To study the feasibility of multimodal neuroimaging in mild to moderate Alzheimer disease (AD) and to estimate the size of possible treatment effects of memantine on potential functional, structural and metabolic biomarkers of disease progression.

METHODS

In this randomised, double-blind, placebo-controlled pilot study, 36 patients with moderate AD received 52 weeks of memantine (20 mg/day) or placebo. Patients were re-evaluated after 26 and 52 weeks to measure the change from baseline in several outcome measures including global and regional glucose metabolism, total brain and hippocampal volumes, as well as chemical shift imaging-derived global and regional N-acetylaspartate and myoinositol concentrations.

RESULTS

In the total population, global glucose metabolism decreased by 2.3% (p<0.01), total brain volume by 2.1% (p<0.001) and hippocampal volume by 2.7% (p<0.01) after 52 weeks. Chemical shift imaging (CSI) spectra were severely affected by patient-induced artefacts and highly variable. Patients receiving memantine showed less decline in glucose metabolism in all brain areas than patients on placebo. Their loss of hippocampal volume was substantially smaller (2.4% vs 4.0%). No between-group differences were seen for changes in total brain volume.

CONCLUSIONS

The results support the use of multimodal imaging including MRI and positron emission tomography (PET) to monitor the progression of moderate AD. CSI yielded unreliable longitudinal results. The data suggest that memantine has potentially protective effects in AD and they can be used for planning larger confirmatory studies on the cerebral effects of memantine.

Anteroposterior hippocampal metabolic heterogeneity: three-dimensional multivoxel proton 1H MR spectroscopic imaging--initial findings

PURPOSE

To quantify proton magnetic resonance (MR) spectroscopy-detectable metabolite concentrations along anteroposterior axis of hippocampus in healthy young and elderly subjects.

MATERIALS AND METHODS

Young (three women, three men; age range, 25-35 years) and elderly (four women, two men; age range, 68-72 years) groups underwent MR imaging and proton MR spectroscopic imaging at 3 T in this HIPAA-compliant prospective study and gave institutional review board-approved written consent. Volume of interest was centered on and tilted parallel to hippocampal anteroposterior plane. Absolute N-acetylaspartate (NAA), choline, and creatine levels were obtained in each voxel, with phantom replacement.

RESULTS

Mean NAA, creatine, and choline concentrations in the young group were higher in posterior hippocampus (12.9 mmol/L +/- 2.0 [standard deviation], 7.8 mmol/L +/- 1.2, 2.3 mmol/L +/- 0.4, respectively) than anterior hippocampus (8.0 mmol/L +/- 1.1, 6.0 mmol/L +/- 1.4, 1.5 mmol/L +/- 0.2; P = .005, .02, and .0002, respectively). In the elderly group, mean concentrations were higher in posterior hippocampus (8.6 mmol/L +/- 0.9, 5.6 mmol/L +/- 0.6, 1.5 mmol/L +/- 0.2, respectively) than anterior hippocampus (7.2 mmol/L +/- 1.0, 2.4 mmol/L +/- 0.3, 1.0 mmol/L +/- 0.2; P = .006, .0001, .04, respectively). Mean concentrations were significantly higher in the young group (13.2 mmol/L +/- 1.0, 7.4 mmol/L +/- 0.8, 2.1 mmol/L +/- 0.3, respectively) than in the elderly group (9.0 mmol/L +/- 1.0, 5.8 mmol/L +/- 0.8, 1.8 mmol/L +/- 0.3; P = .0001, .01, .05, respectively). Posteroanterior metabolic gradients differed: NAA decreased faster in the young group (-1.0 mmol/L x cm(-1)) than the elderly group (-0.7 mmol/L x cm(-1)); creatine and choline concentrations decreased faster in the elderly group (-0.8 and -0.058 mmol/L x cm(-1), respectively) than the young group (-0.16 and -0.008 mmol/L x cm(-1), respectively). No left-right metabolic differences were found.

CONCLUSION

Significant metabolic heterogeneity was observed between groups and along anteroposterior axis of healthy hippocampus in both groups. Age matching and consistent voxel placement are important for correct comparisons of both absolute metabolic levels and metabolite ratios in longitudinal intra- and intersubject cross-sectional studies.

Brain N-acetylaspartate is reduced in Parkinson disease with dementia

Persons with Parkinson disease (PD) are at risk of developing dementia. Of the dementias affecting patients with PD, PD with dementia (PDD) is not well understood, although brain imaging studies to date have observed characteristic patterns of brain atrophy. Metabolic differences have been observed in magnetic resonance spectroscopy (MRS) studies comparing patients with PDD to nondemented PD patients, although it is unclear whether PDD patients have abnormally low MRS ratios compared with healthy age-matched adults. In this study, 12 patients with PDD, 12 patients with PD and no dementia, and 12 age-matched healthy older adults underwent MRS of the posterior cingulate gyrus. Patients with PDD showed lower N-acetylaspartate/creatine (NAA/Cr) compared with controls (P=0.004) and compared with nondemented PD patients (P=0.003). No abnormalities were observed in choline/Cr or myo-Inositol/Cr. NAA/Cr was correlated with mental status in patients with PD and in patients with PDD (r=0.56; P=0.029). The findings suggest that reduced NAA/Cr of the posterior cingulate could be used as a marker for dementia in patients with PD. Future studies investigating the utility of brain MRS as a predictor of dementia in PD and comparing brain metabolism in PDD with other dementias seem warranted.

Memantine decreases hippocampal glutamate levels: a magnetic resonance spectroscopy study

Glutamate (Glu) is associated with excitotoxic cell damage. Memantine modulates the glutamate induced excitotoxicity in Alzheimer's disease (AD). No information is available as to the influence of memantine on in vivo brain glutamate levels. Hippocampal Glu levels were measured in cognitively impaired and normal individuals (n=10) before and after 6 months of memantine treatment, using three dimensional high spatial resolution (0.5 cm(3) voxels) proton magnetic resonance spectroscopy at 3 T. These measurements were also repeated in a non-treated cognitively normal group (n=6). Treatment with memantine decreased Glu/Cr (creatine) ratio in the left hippocampal region. Memantine reduced hippocampal glutamate levels, which may be consistent with its anti-excitotoxic property.

High field (1)H MRS of the hippocampus after donepezil treatment in Alzheimer disease

The purpose of this study was to measure metabolite level changes in patients with newly diagnosed Alzheimer Disease (AD) following four months of donepezil treatment. A small number of cognitively normal elderly subjects were also scanned longitudinally (twice within one year) to assess the reproducibility. Short echo-time (1)H magnetic resonance spectra were acquired at 4.0 T in the right hippocampus. Subjects were scanned at the time of first diagnosis (prior to receiving donepezil) and then following four months of donepezil treatment (5 mg/day for the first month, 10 mg/day thereafter). Changes in absolute metabolite levels and metabolite ratios were quantified and compared. There was no change in measured cognitive function following four months of donepezil treatment in the AD patients. Decreased levels of N-acetylaspartate, choline, N-acetylaspartate/creatine, choline/creatine, and myo-inositol/creatine were observed in AD patients after four months of treatment. Cognitively normal elderly subjects showed an increase in myo-inositol/choline ratio following one year. The reduced levels of N-acetylaspartate in AD patients indicates continued decline in neuronal function and/or integrity. However decreased levels of choline and myo-inositol/creatine ratio may indicate a positive treatment effect.

Magnetic resonance approaches to brain aging and Alzheimer disease-associated neuropathology

The noninvasive, nonradioactive, quantitative nature of magnetic resonance techniques has propelled them to the forefront of neuroscience and neuropsychiatric research. In particular, recent advances have confirmed their enormous potential in patients with Alzheimer disease (AD). Structural and functional magnetic resonance (MR) imaging have demonstrated significant correlation with clinical outcomes and underlying pathology and are used increasingly in the AD clinic. This review will highlight the role of high-resolution structural MR imaging and functional magnetic resonance imaging in the identification of atrophic and hemodynamic changes in AD and their potential as diagnostic biomarkers and surrogates of therapeutic response. Advanced MR techniques based on diffusion, perfusion, and neurochemical abnormalities in the aging brain will be presented briefly. These newer techniques continue to expand our understanding of neuropathology in the aging brain and are likely to play an important clinical role in the future.

1H MRS-detectable metabolic brain changes and reduced impulsive behavior in adult rats exposed to methylphenidate during adolescence

Administration of methylphenidate (MPH, Ritalin) to children affected by attention deficit hyperactivity disorder (ADHD) is an elective therapy, which however raises concerns for public health, due to possible persistent neuro-behavioral alterations. We investigated potential long-term consequences at adulthood of MPH exposure during adolescence, by means of behavioral and brain MRS assessment in drug-free state. Wistar adolescent rats (30- to 44-day-old) were treated with MPH (0 or 2 mg/kg once/day for 14 days) and then left undisturbed until adulthood. Levels of impulsive behavior were assessed in the intolerance-to-delay task: Food-restricted rats were tested in operant chambers with two nose-poking holes, delivering one food pellet immediately, or five pellets after a delay whose length was increased over days. MPH-exposed animals showed a less marked shifting profile from the large/late to the small/soon reward, suggesting reduced basal levels of impulsivity, compared to controls. In vivo MRI-guided 1H MRS examinations at 4.7 T in anaesthetised animals revealed long-term biochemical changes in the dorsal striatum (STR), nucleus accumbens (NAcc), and prefrontal cortex (PFC) of MPH-exposed rats. Notably, total creatine and taurine, metabolites respectively involved in bioenergetics and synaptic efficiency, were up-regulated in the STR and conversely down-regulated in the NAcc of MPH-exposed rats. A strong correlation was evident between non-phosphorylated creatine in the STR and behavioral impulsivity. Moreover, unaltered total creatine and increased phospho-creatine/creatine ratio were detected in the PFC, suggesting improved cortical energetic performance. Because of this enduring rearrangement in the forebrain function, MPH-exposed animals may be more efficient when faced with delay of reinforcement. In summary, MPH exposure during adolescence produced enduring MRS-detectable biochemical modifications in brain reward-related circuits, which may account for increased self-control capacity of adult rats.

Conversion of MCI to dementia: Role of proton magnetic resonance spectroscopy

Mild cognitive impairment (MCI) represents a heterogeneous group of cognitive disturbances at high risk of dementia. The amnestic subtype (aMCI) might be a prodromal state of Alzheimer's disease (AD). The aim of this study is the identification, by proton magnetic resonance spectroscopy (1H MRS), of modifications in brain metabolites able to detect subjects with aMCI at risk of conversion towards AD. Twenty-five subjects with aMCI and 29 normal elderly were enrolled; they underwent a comprehensive clinical and instrumental assessment, a cerebral 1H MRS scan to measure N-acetyl aspartate (NAA), choline (Cho), myo-inositol (mI) and creatine (Cr) in the paratrigonal white matter, bilaterally. After 1 year, 5 MCI subjects became demented (progressive MCI, pMCI). Their baseline levels of metabolites were compared with those evaluated in stable MCI (sMCI) and in controls. We observed a significant difference of the NAA/Cr ratio between pMCI (1.48+/-0.08) and sMCI (1.65+/-0.12) and between pMCI and controls (1.63+/-0.16) in the left hemisphere, suggesting that this metabolic alteration can be detected before the clinical appearance of dementia.

Alzheimer's disease and proton magnetic resonance spectroscopy of limbic regions: a suggestion of a clinical-spectroscopic staging

OBJECTIVE

To compare magnetic resonance proton spectroscopic with clinical data and to propose a spectroscopic staging of Alzheimer's disease (AD).

METHOD

Subjects (n = 46), normals (12) and with AD (34), paired to age (CDR0-CDR3); AD diagnosis according to DSM-IV/NINCDS-ADRDA criteria; 1H-MRS with Signa Horizon LX-GE, 1.5T; single voxel at hippocampal region/HCR and posterior cingulate area/PCA.

RESULTS

Statistically significant decrease (p < 0.01) only of Naa/Cr--at HCR among the CDR0, CDR1+CDR2, and CDR3, and at PCA between CDR0 and CDR1+CDR2 in relation to CDR3.

CONCLUSION

The HCR is the first to show Naa reduction (CDR1). The PCA suffers later (CDR3). These values decline progressively according to the severity stages. Considering the disparities between the HCR and PCA it is possible to suggest a spectroscopic (metabolite) staging (MS) of AD, as follows: MS0 (-CDR0) = both normal HCR and PCA, MS1-2 (approximately CDR1-2) = abnormal HCR and normal PCA, and MS3 (approximately CDR3) = both abnormal HCR and PCA. These results make possible the early diagnosis, to follow the degenerative process throughout the course, and to suggest a spectroscopic staging related to the clinical stages of AD.

Intraindividual variability of striatal (1)H-MRS brain metabolite measurements at 3 T

PURPOSE

To measure possible positional and diurnal physiological effects on brain metabolites in single-voxel proton magnetic resonance spectroscopy ((1)H-MRS) measurements of the right and left striatum.

METHODS

(1)H-MRS measurements were performed in 10 healthy adult volunteers using a short echo PRESS sequence (TE=30 ms, TR=3000 ms). Each individual was scanned during both morning and afternoon hours. Regions of interest were right and left striatum. To control for systematic drift in scanner performance, (1)H-MRS measurements of a standard phantom solution were also acquired. Statistical analysis was performed using a repeated measures analysis of variance that included three within-subject factors: metabolite (N-acetyl-aspartate [NAA] or creatine [Cr]), laterality (left or right caudate) and time (morning or afternoon).

RESULTS

A significant interaction (P<.016) between time of day and metabolite levels was observed. Further exploration of this finding revealed a significant difference between morning and afternoon levels of NAA (P<.044) but not Cr. In addition, no significant morning-to-afternoon differences were observed for the (1)H-MRS phantom measurements.

CONCLUSIONS

Systematic variation due to scanner performance does not account for the changes observed in repeated measurements of striatal NAA levels. This difference may be accounted for by either repositioning effects or circadian physiological effects. Further studies are required to learn whether time of day standardization of (1)H-MRS acquisitions may contribute to improved reproducibility of measurements.

Quantitative 1H magnetic resonance spectroscopic imaging determines therapeutic immunization efficacy in an animal model of Parkinson's disease

Nigrostriatal degeneration, the pathological hallmark of Parkinson's disease (PD), is mirrored by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication. MPTP-treated animals show the common behavioral, motor, and pathological features of human disease. We demonstrated previously that adoptive transfer of Copaxone (Cop-1) immune cells protected the nigrostriatal dopaminergic pathway in MPTP-intoxicated mice. Herein, we evaluated this protection by quantitative proton magnetic resonance spectroscopic imaging (1H MRSI). 1H MRSI performed in MPTP-treated mice demonstrated that N-acetyl aspartate (NAA) was significantly diminished in the substantia nigra pars compacta (SNpc) and striatum, regions most affected in human disease. When the same regions were coregistered with immunohistochemical stains for tyrosine hydroxylase, numbers of neuronal bodies and termini were similarly diminished. MPTP-intoxicated animals that received Cop-1 immune cells showed NAA levels, in the SNpc and striatum, nearly equivalent to PBS-treated animals. Moreover, adoptive transfer of immune cells from ovalbumin-immunized to MPTP-treated mice failed to alter NAA levels or protect dopaminergic neurons and their projections. These results demonstrate that 1H MRSI can evaluate dopaminergic degeneration and its protection by Cop-1 immunization strategies. Most importantly, the results provide a monitoring system to assess therapeutic outcomes for PD.

Proton magnetic resonance spectroscopic evaluation of brain tumor metabolism

Magnetic resonance imaging (MRI) is the neuroimaging method of choice for the noninvasive monitoring of patients with brain tumors due to the enormous amount of information it yields regarding the morphologic features of the lesion and surrounding parenchyma. Over the past decade, proton magnetic resonance spectroscopy (1H-MRS), which uses the same technology as MRI and can be performed during a routine clinical imaging examination, has been used to glean information about the metabolic status of the brain. Accurate interpretation of 1H-MRS data from individual patients requires an understanding of the various techniques for acquiring the data, the physiologic basis of the metabolic signatures obtained from different types of tumors, and the specificity of the technique. This review covers the basic physics of 1H-MRS, the spectral and physiological characteristics of the metabolites that are typically measured in various types of brain tumors, and the clinical utility of 1H-MRS with respect to diagnosis, therapeutic planning, and the assessment of response to treatment.

Neuroimaging and early diagnosis of Alzheimer disease: a look to the future

Alzheimer disease (AD), a progressive neurodegenerative disorder, is the most common cause of dementia in the elderly. Current consensus statements have emphasized the need for early recognition and the fact that a diagnosis of AD can be made with high accuracy by using clinical, neuropsychologic, and imaging assessments. Magnetic resonance (MR) or computed tomographic (CT) imaging is recommended for the routine evaluation of AD. Coronal MR images can be useful to document or quantify atrophy of the hippocampus and entorhinal cortex, both of which occur early in the disease process. Both volumetric and subtraction MR techniques can be used to quantify and monitor dementia progression and rates of regional atrophy. MR measures are also increasingly being used to monitor treatment effects in clinical trials of cognitive enhancers and antidementia agents. Positron emission tomography (PET) and single photon emission CT offer value in the differential diagnosis of AD from other cortical and subcortical dementias and may also offer prognostic value. In addition, PET studies have demonstrated that subtle abnormalities may be apparent in the prodromal stages of AD and in subjects who carry susceptibility genes. PET ligands are in late-stage development for demonstration of amyloid plaques, and human studies have already begun. Functional MR-based memory challenge tests are in development as well.

Advanced brain imaging procedures and human memory disorder

The impact of advanced brain imaging procedures in the field of human memory disorder is reviewed, with particular emphasis on current and potential applications that may impact upon the diagnosis and management of memory-disordered patients. While both advanced structural, resting physiological and functional physiological brain imaging procedures have been applied to conditions where memory disorder is a major feature, the specific implications of research findings for diagnosis and treatment in routine clinical practice remain tentative and promising, but not yet substantive enough to inform clinical decisions to a significant degree. In terms of diagnostic applications, several promising areas include dementia, epilepsy, and transient amnesic states. In the case of applications in treatment settings, advanced brain imaging procedures may help to monitor neural correlates of spontaneous recovery or progression of memory function, and may also help in the planning and monitoring of therapeutic intervention.

A comprehensive review of proton magnetic resonance spectroscopy studies in dementia and Parkinson's disease

We reviewed the literature of proton magnetic resonance spectroscopy (MRS) in dementia and Parkinson's disease (PD) and quantitatively compared the reported values of the markers N-acetyl aspartate (NAA), choline, and myo-Inositol between control and disease groups. We analysed a total of 27 reports in dementia. Combining the quantitative data from these showed a relative decrease of 15% in NAA level in the temporal lobe tissue in patients with Alzheimer's disease (AD) compared with controls. The rest of the brain showed a seemingly uniform 10% decrease in NAA levels in AD compared with controls. myo-Inositol was raised by about 15%, again uniformly throughout the brain, but there was no evidence for changed levels of choline. We found 15 reports of MRS in PD, which show a small decrease (5%) in the NAA level in the lentiform nucleus compared with controls. In progressive supranuclear palsy (PSP), there is a greater decrease in NAA levels in the frontal region and the lentiform nucleus. This may aid in the diagnosis of PSP. Further research is needed to determine spectroscopic changes in other dementias, to monitor how markers change with disease progression and to establish clinical utility.

Current awareness

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of NMR in biomedicine. Each bibliography is divided into 9 sections: 1 Books, Reviews ' Symposia; 2 General; 3 Technology; 4 Brain and Nerves; 5 Neuropathology; 6 Cancer; 7 Cardiac, Vascular and Respiratory Systems; 8 Liver, Kidney and Other Organs; 9 Muscle and Orthopaedic. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted.