Different patterns of N-acetylaspartate loss in subcortical ischemic vascular dementia and AD

Proposing a "Brain Health Checkup (BHC)" as a Global Potential "Standard of Care" to Overcome Reward Dysregulation in Primary Care Medicine: Coupling Genetic Risk Testing and Induction of "Dopamine Homeostasis"

In 2021, over 100,000 people died prematurely from opioid overdoses. Neuropsychiatric and cognitive impairments are underreported comorbidities of reward dysregulation due to genetic antecedents and epigenetic insults. Recent genome-wide association studies involving millions of subjects revealed frequent comorbidity with substance use disorder (SUD) in a sizeable meta-analysis of depression. It found significant associations with the expression of NEGR1 in the hypothalamus and DRD2 in the nucleus accumbens, among others. However, despite the rise in SUD and neuropsychiatric illness, there are currently no standard objective brain assessments being performed on a routine basis. The rationale for encouraging a standard objective Brain Health Check (BHC) is to have extensive data available to treat clinical syndromes in psychiatric patients. The BHC would consist of a group of reliable, accurate, cost-effective, objective assessments involving the following domains: Memory, Attention, Neuropsychiatry, and Neurological Imaging. Utilizing primarily PUBMED, over 36 years of virtually all the computerized and written-based assessments of Memory, Attention, Psychiatric, and Neurological imaging were reviewed, and the following assessments are recommended for use in the BHC: Central Nervous System Vital Signs (Memory), Test of Variables of Attention (Attention), Millon Clinical Multiaxial Inventory III (Neuropsychiatric), and Quantitative Electroencephalogram/P300/Evoked Potential (Neurological Imaging). Finally, we suggest continuing research into incorporating a new standard BHC coupled with qEEG/P300/Evoked Potentials and genetically guided precision induction of "dopamine homeostasis" to diagnose and treat reward dysregulation to prevent the consequences of dopamine dysregulation from being epigenetically passed on to generations of our children.

Discriminating subcortical ischemic vascular disease and Alzheimer's disease by diffusion kurtosis imaging in segregated thalamic regions

Differentiating between subcortical ischemic vascular disease (SIVD), Alzheimer's disease (AD), and normal cognition (NC) remains a challenge, and reliable neuroimaging biomarkers are needed. The current study, therefore, investigated the discriminative ability of diffusion kurtosis imaging (DKI) metrics in segregated thalamic regions and compare with diffusion tensor imaging (DTI) metrics. Twenty‐three SIVD patients, 30 AD patients, and 24 NC participants underwent brain magnetic resonance imaging. The DKI metrics including mean kurtosis (MK), axial kurtosis (K_axial) and radial kurtosis (K_radial) and the DTI metrics including diffusivity and fractional anisotropy (FA) were measured within the whole thalamus and segregated thalamic subregions. Strategic correlations by group, thalamo‐frontal connectivity, and canonical discriminant analysis (CDA) were used to demonstrate the discriminative ability of DKI for SIVD, AD, and NC. Whole and segregated thalamus analysis suggested that DKI metrics are less affected by white matter hyperintensities compared to DTI metrics. Segregated thalamic analysis showed that MK and K_radial were notably different between SIVD and AD/NC. The correlation analysis between K_axial and MK showed a nonsignificant relationship in SIVD group, a trend of negative relationship in AD group, and a significant positive relationship in NC group. A wider spatial distribution of thalamo‐frontal connectivity differences across groups was shown by MK compared to FA. CDA showed a discriminant power of 97.4% correct classification using all DKI metrics. Our findings support that DKI metrics could be more sensitive than DTI metrics to reflect microstructural changes within the gray matter, hence providing complementary information for currently outlined pathogenesis of SIVD and AD.

Effects of Alterations of Post-Mortem Delay and Other Tissue-Collection Variables on Metabolite Levels in Human and Rat Brain

The use of post-mortem human tissue is indispensable in studies investigating alterations in metabolite levels in neurodegenerative conditions such as Alzheimer's disease (AD). However, variability between samples may have unknown effects on metabolite concentrations. The aim of this study was to characterize the impact of such variables. Cingulate gyrus was obtained from AD cases and controls, from three brain banks. Gas chromatography-mass spectrometry (GC-MS) was used to measure and compare the levels of 66 identifiable metabolites in these tissues to determine effects of tissue-collection variables. The effect of PMD was further investigated by analysis of rat brain cortex and cerebellum collected following post-mortem delays (PMDs) of zero to 72 h. Metabolite levels between cases and controls were not replicable across cohorts with variable age- and gender-matching, PMD, and control Braak staging. Analysis of rat tissues found significant effects of PMD on 31 of 63 identified metabolites over periods up to 72 h. PMD must be kept under 24 h for metabolomics analyses on brain tissues to yield replicable results. Tissues should also be well age- and gender-matched, and Braak stage in controls should be kept to a minimum in order to minimize the impact of these variables in influencing metabolite variability.

Proton Magnetic Resonance Spectroscopy in Common Dementias-Current Status and Perspectives

Dementia occurs mainly in the elderly and is associated with cognitive decline and impairment of activities of daily living. The most common forms of dementia are Alzheimer's disease (AD), vascular dementia (VD), dementia with Lewy bodies (DLB), and frontotemporal dementia (FTD). To date, there are no causal options for therapy, but drug and non-drug treatments can positively modulate the course of the disease. Valid biomarkers are needed for the earliest possible and reliable diagnosis, but so far, such biomarkers have only been established for AD and require invasive and expensive procedures. In this context, proton magnetic resonance spectroscopy (¹H-MRS) provides a non-invasive and widely available technique for investigating the biochemical milieu of brain tissue in vivo. Numerous studies have been conducted for AD, but for VD, DLB, and FTD the number of studies is limited. Nevertheless, MRS can detect measurable metabolic alterations in common dementias. However, most of the studies conducted are too heterogeneous to assess the potential use of MRS technology in clinical applications. In the future, technological advances may increase the value of MRS in dementia diagnosis and treatment. This review summarizes the results of MRS studies conducted in common dementias and discusses the reasons for the lack of transfer into clinical routine.

Brain amyloid burden and cerebrovascular disease are synergistically associated with neurometabolism in cognitively unimpaired older adults

Alzheimer's disease (AD) is the most common cause of cognitive dysfunction in older adults. The pathological hallmarks of AD such as beta amyloid (Aβ) aggregation and neurometabolic change, as indicated by altered myo-inositol (mI) and N-acetylaspartate (NAA) levels, typically precede the onset of cognitive dysfunction by years. Furthermore, cerebrovascular disease occurs early in AD, but the interplay between vascular and neurometabolic brain change is largely unknown. Thirty cognitively normal older adults (age = 70 ± 5.6 years, Mini-Mental State Examination = 29.2 ± 1) received 11-C-Pittsburgh Compound B positron emission tomography for estimating Aβ-plaque density, 7 Tesla fluid-attenuated inversion recovery magnetic resonance imaging for quantifying white matter hyperintensity volume as a marker of small vessel cerebrovascular disease and high-resolution magnetic resonance spectroscopic imaging at 7 Tesla, based on free induction decay acquisition localized by outer volume suppression to investigate tissue-specific neurometabolism in the posterior cingulate and precuneus. Aβ (β = 0.45, p = 0.018) and white matter hyperintensities (β = 0.40, p = 0.046) were independently and interactively (β = -0.49, p = 0.026) associated with a higher ratio of mI over NAA (mI/NAA) in the posterior cingulate and precuneus gray matter but not in the white matter. Our data suggest that cerebrovascular disease and Aβ burden are synergistically associated with AD-related gray matter neurometabolism in older adults.

Multimodality Imaging Approaches in Alzheimer's disease. Part II: 1H MR spectroscopy, FDG PET and Amyloid PET

In this Part II review, as a complement to the Part I published in this supplement, the authors cover the imaging techniques that evaluates the Alzheimer's disease according to the different metabolic and molecular profiles. In this section MR spectroscopy, FDG-PET and amyloid PET are deeply discussed.

Decreased frontal lobe function in people with Internet addiction disorder

In our previous studies, we showed that frontal lobe and brainstem functions were abnormal in on-line game addicts. In this study, 14 students with Internet addiction disorder and 14 matched healthy controls underwent proton-magnetic resonance spectroscopy to measure cerebral function. Results demonstrated that the ratio of N-acetylaspartate to creatine decreased, but the ratio of cho-line-containing compounds to creatine increased in the bilateral frontal lobe white matter in people with Internet addiction disorder. However, these ratios were mostly unaltered in the brainstem, suggesting that frontal lobe function decreases in people with Internet addiction disorder.

Proton magnetic resonance spectroscopy and cognitive impairment in patients with ischemic white matter lesions

BACKGROUND

The purpose of this study is to investigate the relationship between the cognitive impairment and NAA/Cr and Cho/Cr ratios in the proton magnetic resonance spectroscopy ((1)HMRS), and to assess the importance of (1)HMRS in the early diagnosis of cognitive impairment in patients with ischemic white matter lesions (WMLs).

MATERIALS AND METHODS

A total of 45 patients (23 males and 22 females) with the ischemic WML were divided into mild WML group (n = 15), moderate WML group (n = 15), and severe WML group (n = 15). A total of 15 healthy controls (8 males and 7 females) with no WML on magnetic resonance imaging were included. (1)HMRS focusing on the frontal lobe white matter around the anterior horn of the lateral ventricle and Montreal Cognitive Assessment (MoCA) were conducted.

RESULTS

Patients with more severe WML had lower MoCA scores. The NAA/Cr ratio in (1)HMRS was reduced in all the patients and was strongly correlated with the total MoCA scores (r = 0.845, P < 0.001). The Cho/Cr ratio in (1)HMRS was increased in mild and moderate patients, was negatively correlated with the total MoCA scores (r = 0.907, P < 0.001). The Cho/Cr ratio was reduced in the severe patients and was positively correlated with the total MoCA scores (r = 0.937, P < 0.001). In addition, NAA/Cr and Cho/Cr ratios in (1)HMRS were changed in patients with the mild WML whose total MoCA scores were similar to the controls.

CONCLUSION

Our results suggest that NAA/Cr and Cho/Cr ratios in (1)HMRS are useful indicators for early diagnosis of ischemic WML and cognitive impairment in patients with ischemic WML.

Is overactive bladder a brain disease? The pathophysiological role of cerebral white matter in the elderly

Small-vessel disease of the brain affecting the deep white matter characteristically manifests with neurological syndromes, such as vascular dementia and vascular parkinsonism. There is, however, compelling evidence to suggest that white matter disease can cause overactive bladder and incontinence, and in some patients these might be the initial manifestation. As white matter disease increases significantly with age, and preferentially affects the prefrontal deep white matter, white matter disease becomes an anatomical substrate in the brain etiology of overactive bladder. Treatment entails the management of small-vessel disease risk factors and anticholinergic drugs that do not easily penetrate the blood-brain barrier, to improve bladder control. In short, when caring for elderly overactive-bladder patients, we should look at both the brain and the bladder.

Influence of comorbidities in idiopathic normal pressure hydrocephalus - research and clinical care. A report of the ISHCSF task force on comorbidities in INPH

Idiopathic normal pressure hydrocephalus (INPH) is a syndrome of ventriculomegaly, gait impairment, cognitive decline and incontinence that occurs in an elderly population prone to many types of comorbidities. Identification of the comorbidities is thus an important part of the clinical management of INPH patients. In 2011, a task force was appointed by the International Society for Hydrocephalus and Cerebrospinal Fluid Disorders (ISHCSF) with the objective to compile an evidence-based expert analysis of what we know and what we need to know regarding comorbidities in INPH. This article is the final report of the task force. The expert panel conducted a comprehensive review of the literature. After weighing the evidence, the various proposals were discussed and the final document was approved by all the task force members and represents a consensus of expert opinions. Recommendations regarding the following topics are given: I. Musculoskeletal conditions; II. Urinary problems; III. Vascular disease including risk factors, Binswanger disease, and white matter hyperintensities; IV. Mild cognitive impairment and Alzheimer disease including biopsies; V. Other dementias (frontotemporal dementia, Lewy body, Parkinson); VI. Psychiatric and behavioral disorders; VII. Brain imaging; VIII. How to investigate and quantify. The task force concluded that comorbidity can be an important predictor of prognosis and post-operative outcome in INPH. Reported differences in outcomes among various INPH cohorts may be partly explained by variation in the rate and types of comorbidities at different hydrocephalus centers. Identification of comorbidities should thus be a central part of the clinical management of INPH where a detailed history, physical examination, and targeted investigations are the basis for diagnosis and grading. Future INPH research should focus on the contribution of comorbidity to overall morbidity, mortality and long-term outcomes.

Magnetic resonance spectroscopy in Alzheimer's disease

Aging is the primary risk factor for dementia. With increasing life expectancy and aging populations worldwide, dementia is becoming one of the significant public health problems of the century. The most common pathology underlying dementia in older adults is Alzheimer's disease. Proton magnetic resonance spectroscopy (MRS) may provide a window into the biochemical changes associated with the loss of neuronal integrity and other neurodegenerative pathology that involve the brain before the manifestations of cognitive impairment in patients who are at risk for Alzheimer's disease. This review focuses on proton MRS studies in normal aging, mild cognitive impairment, and dementia, and how proton MRS metabolite levels may be potential biomarkers for early diagnosis of dementia-related pathologic changes in the brain.

Neuroimaging in dementia

As treatment of neurodegenerative disease moves toward therapies aimed at specific molecular abnormalities, the importance of early and accurate diagnosis will increase, as will the need for sensitive measures for tracking disease progression. Brain imaging, using MRI and PET scanning, offers a variety of highly reliable techniques that examine the structure, chemical content, metabolic state, and functional capacity of the brain. For all the major neurodegenerative disorders, relatively specific findings can be identified with some or all of these techniques. New approaches for imaging specific molecular pathology likely will revolutionize brain imaging and be combined with established imaging approaches to obtain a complete molecular, structural, and metabolic characterization, which could be used to improve diagnosis, and to stage each patient and follow disease progression and response to treatment.

Vascular incontinence: incontinence in the elderly due to ischemic white matter changes

This review article introduces the new concept of vascular incontinence, a disorder of bladder control resulting from cerebral white matter disease (WMD). The concept is based on the original observation in 1999 of a correlation between the severity of leukoareosis or WMD, urinary symptoms, gait disorder and cognitive impairment. Over the last 20 years, the realization that WMD is not a benign incidental finding in the elderly has become generally accepted and several studies have pointed to an association between geriatric syndromes and this type of pathology. The main brunt of WMD is in the frontal regions, a region recognized to be crucial for bladder control. Other disorders should be excluded, both neurological and urological, such as normal-pressure hydrocephalus, progressive supranuclear palsy, etc., and prostatic hyperplasia, physical stress incontinence, nocturnal polyuria, etc. Treatment involves management of small vessel disease risk factors and anticholinergic drugs that do not easily penetrate the blood brain barrier to improve bladder control.

The profile of hippocampal metabolites differs between Alzheimer's disease and subcortical ischemic vascular dementia, as measured by proton magnetic resonance spectroscopy

Alzheimer's disease (AD) and subcortical ischemic vascular dementia (SIVD) have overlapping pathologies and risk factors, but their underlying neurodegenerative mechanisms are basically different. We performed magnetic resonance spectroscopy (MRS) to study metabolite differences between the two diseases in vivo. The subjects were 31 patients with SIVD and 99 with AD. Additionally, 45 elderly subjects were recruited as controls. We measured N-acetylaspartate (NAA), glutamine and glutamate (Glx), and myoinositol (mIns) concentration quantitatively using a 1.5-T MR scanner. N-acetylaspartate and Glx concentrations decreased in the hippocampus and cingulate/precuneal cortices (PCC) in both AD and SIVD patients, and the NAA decrease in the hippocampus was more prominent in AD than in SIVD. Interestingly, the pattern of mIns concentration changes differed between the two disorders; mIns was increased in AD but not increased in SIVD. If one differentiates between AD and SIVD by the mIns concentration in the hippocampus, the area under the receiver operating characteristic curve was 0.95, suggesting a high potential for discrimination. Our results suggest that proton MRS can provide useful information to differentiate between AD and SIVD. The difference of mIns concentrations in the hippocampus and PCC seems to reflect the different neurodegenerative mechanisms of the two disorders.

Neuroimaging in dementia

Dementia is a common illness with an incidence that is rising as the aged population increases. There are a number of neurodegenerative diseases that cause dementia, including Alzheimer's disease, dementia with Lewy bodies, and frontotemporal dementia, which is subdivided into the behavioral variant, the semantic variant, and nonfluent variant. Numerous other neurodegenerative illnesses have an associated dementia, including corticobasal degeneration, Creutzfeldt-Jakob disease, Huntington's disease, progressive supranuclear palsy, multiple system atrophy, Parkinson's disease dementia, and amyotrophic lateral sclerosis. Vascular dementia and AIDS dementia are secondary dementias. Diagnostic criteria have relied on a constellation of symptoms, but the definite diagnosis remains a pathologic one. As treatments become available and target specific molecular abnormalities, differentiating amongst the various primary dementias early on becomes essential. The role of imaging in dementia has traditionally been directed at ruling out treatable and reversible etiologies and not to use imaging to better understand the pathophysiology of the different dementias. Different brain imaging techniques allow the examination of the structure, biochemistry, metabolic state, and functional capacity of the brain. All of the major neurodegenerative disorders have relatively specific imaging findings that can be identified. New imaging techniques carry the hope of revolutionizing the diagnosis of neurodegenerative disease so as to obtain a complete molecular, structural, and metabolic characterization, which could be used to improve diagnosis and to stage each patient and follow disease progression and response to treatment. Structural and functional imaging modalities contribute to the diagnosis and understanding of the different dementias.

Cerebral blood flow in ischemic vascular dementia and Alzheimer's disease, measured by arterial spin-labeling magnetic resonance imaging

BACKGROUND

Our objectives were to compare the effects of subcortical ischemic vascular dementia (SIVD) and Alzheimer's disease (AD) on cerebral blood flow (CBF), and then to analyze the relationship between CBF and subcortical vascular disease, measured as volume of white-matter lesions (WMLs).

METHODS

Eight mildly demented patients with SIVD (mean +/- SD; aged 77 +/- 8 years; Mini-Mental State Examination score 26 +/- 3 years) and 14 patients with AD were compared with 18 cognitively normal elderly subjects. All subjects had CBF measured using arterial spin-labeling magnetic resonance imaging, and brain volumes were assessed using structural magnetic resonance imaging.

RESULTS

AD and SIVD showed marked CBF reductions in the frontal (P = 0.001) and parietal (P = 0.001) cortices. In SIVD, increased subcortical WMLs were associated with reduced CBF in the frontal cortex (P = 0.04), in addition to cortical atrophy (frontal, P = 0.05; parietal, P = 0.03).

CONCLUSIONS

Subcortical vascular disease is associated with reduced CBF in the cortex, irrespective of brain atrophy.

Ways toward an early diagnosis in Alzheimer's disease: the Alzheimer's Disease Neuroimaging Initiative (ADNI)

With the increasing life expectancy in developed countries, the incidence of Alzheimer's disease (AD) and thus its socioeconomic impact are growing. Increasing knowledge over the last years about the pathomechanisms involved in AD allow for the development of specific treatment strategies aimed at slowing down or even preventing neuronal death in AD. However, this requires also that (1) AD can be diagnosed with high accuracy, because non-AD dementias would not benefit from an AD-specific treatment; (2) AD can be diagnosed in very early stages when any intervention would be most effective; and (3) treatment efficacy can be reliably and meaningfully monitored. Although there currently is no ideal biomarker that would fulfill all these requirements, there is increasing evidence that a combination of currently existing neuroimaging and cerebrospinal fluid (CSF) and blood biomarkers can provide important complementary information and thus contribute to a more accurate and earlier diagnosis of AD. The Alzheimer's Disease Neuroimaging Initiative (ADNI) is exploring which combinations of these biomarkers are the most powerful for diagnosis of AD and monitoring of treatment effects.

Frontal and periventricular brain white matter lesions and cortical deafferentation of cholinergic and other neuromodulatory axonal projections

White matter fiber bundles form a spatial pattern defined by anatomical and functional architecture. Structural lesions in the white matter may cause clinical symptoms because of disruption of fiber tracts. The clinical significance will depend on the anatomic location of such lesions and whether the functional integrity of specific fiber bundles is affected. Unlike more acute lesions of stroke or multiple sclerosis that may cause sudden sensorimotor deficits, white matter lesions of aging manifest with more subtle and gradual symptoms that are often cognitive in nature. Such cognitive symptoms have been explained by strategically located white matter lesions in the deep forebrain that may disrupt cholinergic projection fibers at their proximal origin. Recent in vivo imaging studies provide supportive evidence that periventricular white matter lesions are associated with cortical cholinergic deafferentation in elderly with leukoaraiosis. White matter lesions at the frontal horns, so-called "capping," are in close proximity to cholinergic axons that originate in the basal forebrain. Therefore, these lesions may result in more significant cortical deafferentation because of the more proximal axonal disruption. A unique anatomic feature common to all cortical projections from subcortical neuromodulator systems (that not only include the cholinergic but also the monoaminergic systems, such as dopamine, serotonin, and norepinephrine) is that the proximal axons largely pass through the deep forebrain before fanning out to the cortex. It is thus plausible that deep frontal white matter lesions may result in not only cholinergic but also variable monoaminergic cortical deafferentation.

Blood pressure and dementia - a comprehensive review

Alzheimer's disease (AD) and vascular dementia (VaD) are important causes of cognitive decline in the elderly. As a result of an ageing population worldwide, the incidence of dementia is expected to rise exponentially over the coming decades. Vascular risk factors are implicated in the pathogenesis of both AD and VaD. Hypertension in midlife is particularly associated with an increased risk of developing dementia. One might hope the treatment of high blood pressure in midlife would reduce the risk of developing dementia, as it does the risk of stroke. Divergent results have been reported in studies examining this effect, with the evidence suggesting that certain antihypertensives confer benefits beyond others. This implies that certain drugs may have neuroprotective properties separate to their blood pressure lowering capabilities. Recent trials have added to our understanding of these relationships.

Proton magnetic resonance spectroscopy of late-life major depressive disorder

The primary goal of this study was to examine the biochemical abnormalities of late-life major depression by using 3-tesla (3-T) proton magnetic resonance spectroscopy ((1)H-MRS). The antidepressant effects on the biochemical abnormalities were investigated as well. Study participants were 27 elderly patients with major depressive disorders (among which 9 were on antidepressant medication) and 19 comparison elderly subjects. (1)H-MRS spectra were acquired from voxels that were placed in the left frontal white matter, left periventricular white matter, and left basal ganglia. Ratios of N-acetylaspartate (NAA), choline (Cho) and myo-inositol to creatine were calculated. Patients with late-life major depressive disorder had a significantly lower NAA/creatine ratio in the left frontal white matter, and higher Cho/creatine and myo-inositol/creatine ratios in the left basal ganglia when compared with the control subjects. The myo-inositol correlated with global cognitive function among the patients. The biochemical abnormalities in late-life major depressive disorder were found on the left side of the frontal white matter and the basal ganglia. Neuron degeneration in the frontal white matter and second messenger system dysfunction or glial dysfunction in the basal ganglia are suggested to be associated with late-life depression.

Magnetic resonance spectroscopy performance for detection of dementia, Alzheimer's disease and mild cognitive impairment in a community-based survey

BACKGROUND/AIMS

To evaluate (1)H-labelled magnetic resonance spectroscopy (MRS) in patients with a low Mini Mental State Examination (MMSE) score identified during a dementia community-based survey.

METHODS

A population sample of 1,500 individuals (>64 years old) was randomly selected. Two hundred and fifteen individuals (MMSE < or =24) were sorted into clinical groups: dementia, Alzheimer's disease, mild cognitive impairment (MCI), normal. Up to 56 of these individuals attended the MRS appointment. Two single-voxel sequences (TR 1,500, TE 35/144 ms) were carried out in the posterior cingulate gyrus of each individual, and the ratios N-acetylaspartate (NAA)/creatine (Cr), choline (Cho)/Cr, myo-inositol (mI)/Cr, NAA/mI and NAA/Cho were compared statistically. The ability of MRS to distinguish clinical groups was assessed by receiver-operating characteristics analysis. Cognition effects on metabolite ratios were estimated, with gender and cognition as categorical variables and age as a continuous covariate.

RESULTS

NAA/Cr and NAA/Cho ratios were lower in dementia or Alzheimer's disease than in MCI and normal groups. The NAA/Cr ratio at TE 35 ms performed best when distinguishing dementia or Alzheimer's disease from non-demented subjects (cut-off point 1.40). MRS could not distinguish between MCI patients and normal subjects. Dementia was an independent predictor of metabolite values.

CONCLUSION

In a population sample, conventional MRS still proved to be a useful tool for dementia discrimination, but it is potentially far less useful as a surrogate marker for MCI.

Effects of Alzheimer disease on fronto-parietal brain N-acetyl aspartate and myo-inositol using magnetic resonance spectroscopic imaging

Previous magnetic resonance (MR) spectroscopy studies of Alzheimer disease (AD) reporting reduced N-acetyl aspartate (NAA) and increased myo-Inositol (mI) used single voxel techniques, which have limited ability to assess the regional distribution of the metabolite abnormalities. The objective of this study was to determine the regional distribution of NAA and mI alterations in AD by using MR spectroscopic imaging. Fourteen patients with AD and 22 cognitively normal elderly were studied using structural MR imaging and MR spectroscopic imaging. Changes of NAA, mI, and various metabolite ratios were measured in frontal and parietal lobe gray matter (GM) and white matter. This study found: (1) when compared with cognitively normal subjects, AD patients had increased mI and mI/creatine (Cr) ratios primarily in parietal lobe GM, whereas frontal lobe GM and white matter were spared; (2) in the same region where mI was increased, AD patients had also decreased NAA and NAA/Cr ratios, replicating previous findings; (3) however, increased mI or mI/Cr ratios did not correlate with decreased NAA or NAA/Cr ratios; and (4) using mI/Cr and NAA/Cr together improved sensitivity and specificity to AD from control as compared with NAA/Cr alone. In conclusion, decreased NAA and increased mI in AD are primarily localized in parietal lobe GM regions. However, the NAA and mI changes are not correlated with each other, suggesting that they represent different processes that might help staging of AD.

White matter changes compromise prefrontal cortex function in healthy elderly individuals

Changes in memory function in elderly individuals are often attributed to dysfunction of the prefrontal cortex (PFC). One mechanism for this dysfunction may be disruption of white matter tracts that connect the PFC with its anatomical targets. Here, we tested the hypothesis that white matter degeneration is associated with reduced prefrontal activation. We used white matter hyperintensities (WMH), a magnetic resonance imaging (MRI) finding associated with cerebrovascular disease in elderly individuals, as a marker for white matter degeneration. Specifically, we used structural MRI to quantify the extent of WMH in a group of cognitively normal elderly individuals and tested whether these measures were predictive of the magnitude of prefrontal activity (fMRI) observed during performance of an episodic retrieval task and a verbal working memory task. We also examined the effects of WMH located in the dorsolateral frontal regions with the hypothesis that dorsal PFC WMH would be strongly associated with not only PFC function, but also with areas that are anatomically and functionally linked to the PFC in a task-dependent manner. Results showed that increases in both global and regional dorsal PFC WMH volume were associated with decreases in PFC activity. In addition, dorsal PFC WMH volume was associated with decreased activity in medial temporal and anterior cingulate regions during episodic retrieval and decreased activity in the posterior parietal and anterior cingulate cortex during working memory performance. These results suggest that disruption of white matter tracts, especially within the PFC, may be a mechanism for age-related changes in memory functioning.

Comprehensive processing, display and analysis for in vivo MR spectroscopic imaging

Image reconstruction for magnetic resonance spectroscopic imaging (MRSI) requires specialized spatial and spectral data processing methods and benefits from the use of several sources of prior information that are not commonly available, including MRI-derived tissue segmentation, morphological analysis and spectral characteristics of the observed metabolites. In addition, incorporating information obtained from MRI data can enhance the display of low-resolution metabolite images and multiparametric and regional statistical analysis methods can improve detection of altered metabolite distributions. As a result, full MRSI processing and analysis can involve multiple processing steps and several different data types. In this paper, a processing environment is described that integrates and automates these data processing and analysis functions for imaging of proton metabolite distributions in the normal human brain. The capabilities include normalization of metabolite signal intensities and transformation into a common spatial reference frame, thereby allowing the formation of a database of MR-measured human metabolite values as a function of acquisition, spatial and subject parameters. This development is carried out under the MIDAS project (Metabolite Imaging and Data Analysis System), which provides an integrated set of MRI and MRSI processing functions. It is anticipated that further development and distribution of these capabilities will facilitate more widespread use of MRSI for diagnostic imaging, encourage the development of standardized MRSI acquisition, processing and analysis methods and enable improved mapping of metabolite distributions in the human brain.

Is NAA reduction in normal contralateral cerebral tissue in stroke patients dependent on underlying risk factors?

BACKGROUND AND PURPOSE

This retrospective study investigated the dependence of N-acetyl aspartate (NAA) ratios on risk factors for cerebral vasculopathy such as sex, age, hypertension, diabetes mellitus, carotid stenosis, and dyslipidaemia, which may have affected brain vessels and induced metabolic brain abnormalities prior to stroke. We hypothesise that in stroke patients metabolic alterations in the apparently normal contralateral brain are dependent on the presence or not of such risk factors.

METHODS

Fifty nine patients (31 male, 28 female: 58.8+/-16.1 years old) with cortical middle cerebral artery (MCA) territory infarction were included. Long echo time chemical shift imaging spectroscopy was carried out on a Siemens 1.5 T Magnetom Vision scanner using a multi-voxel PRESS technique. Metabolite ratios (NAA/choline, NAA/creatine, lactate/choline, etc) were studied using uni- and multivariate analyses with respect to common risk factors. The influence of age, stroke lesion size, and time since stroke was studied using a linear regression approach.

RESULTS

Age, sex, and hypertension all appeared to individually influence metabolite ratios, although only hypertension was significant after multivariate analysis. In both basal ganglia and periventricular white matter regions in apparently normal contralateral brain, the NAA/choline ratio was significantly lower in hypertensive (1.37+/-0.16 and 1.50+/-0.19, respectively) than in normotensive patients (1.72+/-0.19 and 1.85+/-0.15, respectively).

CONCLUSIONS

Regarding MCA infarction, contralateral tissue remote from the lesion behaves abnormally in the presence of hypertension, the NAA ratios in hypertensive patients being significantly lower. These data suggest that hypertension may compromise the use of contralateral tissue data as a reference for comparison with ischaemic tissue.

White Matter Changes Compromise Prefrontal Cortex Function in Healthy Elderly Individuals

Changes in memory function in elderly individuals are often attributed to dysfunction of the prefrontal cortex (PFC). One mechanism for this dysfunction may be disruption of white matter tracts that connect the PFC with its anatomical targets. Here, we tested the hypothesis that white matter degeneration is associated with reduced prefrontal activation. We used white matter hyperintensities (WMH), a magnetic resonance imaging (MRI) finding associated with cerebrovascular disease in elderly individuals, as a marker for white matter degeneration. Specifically, we used structural MRI to quantify the extent of WMH in a group of cognitively normal elderly individuals and tested whether these measures were predictive of the magnitude of prefrontal activity (fMRI) observed during performance of an episodic retrieval task and a verbal working memory task. We also examined the effects of WMH located in the dorsolateral frontal regions with the hypothesis that dorsal PFC WMH would be strongly associated with not only PFC function, but also with areas that are anatomically and functionally linked to the PFC in a task-dependent manner. Results showed that increases in both global and regional dorsal PFC WMH volume were associated with decreases in PFC activity. In addition, dorsal PFC WMH volume was associated with decreased activity in medial temporal and anterior cingulate regions during episodic retrieval and decreased activity in the posterior parietal and anterior cingulate cortex during working memory performance. These results suggest that disruption of white matter tracts, especially within the PFC, may be a mechanism for age-related changes in memory functioning.

1H MR spectroscopy in common dementias

OBJECTIVE

To determine the 1H MR spectroscopic (MRS) findings and intergroup differences among common dementias: Alzheimer disease (AD), vascular dementia (VaD), dementia with Lewy bodies (DLB), and frontotemporal lobar degeneration (FTLD).

METHODS

The authors consecutively recruited 206 normal elderly subjects and 121 patients with AD, 41 with FTLD, 20 with DLB, and 8 with VaD. The 1H MRS metabolite ratio changes in common dementias were evaluated with respect to normal and also differences among the common dementias.

RESULTS

N-acetylaspartate (NAA)/creatine (Cr) was lower than normal in patients with AD, FTLD, and VaD. Myo-inositol (mI)/Cr was higher than normal in patients with AD and FTLD. Choline (Cho)/Cr was higher than normal in patients with AD, FTLD, and DLB. There were no metabolite differences between patients with AD and FTLD or between patients with DLB and VaD. NAA/Cr was lower in patients with AD and FTLD than DLB. MI/Cr was higher in patients with AD and FTLD than VaD. MI/Cr was also higher in patients with FTLD than DLB.

CONCLUSIONS

NAA/Cr levels are decreased in dementias that are characterized by neuron loss, such as AD, FTLD, and VaD. MI/Cr levels are elevated in dementias that are pathologically characterized by gliosis, such as AD and FTLD. Cho/Cr levels are elevated in dementias that are characterized by a profound cholinergic deficit, such as AD and DLB.

Measurement of brain metabolites by 1H magnetic resonance spectroscopy in patients with schizophrenia: a systematic review and meta-analysis

A systematic review of the literature identified 64 published English-language papers that used proton (1H) magnetic resonance spectroscopy to measure N-acetylaspartate (NAA) concurrently in healthy controls and in patients with a diagnosis of schizophrenia (SZ). A total of 1209 controls and 1256 patients have been evaluated, with 88% of studies carried out at 1.5 T field strength, and 77% of studies focused on patients with chronic SZ. There is consistent evidence that NAA is reduced in a broad range of tissues in the SZ brain. Broad consensus (> or =10 studies) is emerging that NAA levels are reduced > or =5% in hippocampus and in both cortical gray matter (GM) and white matter (WM) of the frontal lobe. There is no evidence to support a hypothesis that relative NAA levels are reduced to a different degree in frontal lobe GM and WM, nor is there robust evidence of a difference in NAA levels between patients with first-episode and chronic SZ. Study reliability may be a problem, as most studies appear to be underpowered. With simple assumptions about the inherent difference in NAA levels between patients and controls, it can be calculated that a minimum sample size of approximately 39 patients and 39 controls is required for acceptable statistical power. Only three of 64 studies included enough subjects to have 80% power to detect a 10% NAA reduction in patients, and no studies were adequately powered to detect a 5% NAA reduction with 80% power.

A comparative study of the different N-acetylaspartate measures of the medial temporal lobe in Alzheimer's disease

OBJECTIVE

To investigate group differences and correlations and to determine the sensitivity and specificity of different measures of the neuronal marker N-acetylaspartate (NAA) in the medial temporal lobe of Alzheimer's Disease (AD) patients.

METHODS

The metabolic ratio NAA/creatine (Cr), the absolute concentration of NAA referenced against brain tissue (BT) water and NAA multiplied with the amount of BT in the proton magnetic resonance spectroscopy (1H-MRS) voxel were assessed in patients and healthy controls with a single-voxel 1H-MRS protocol.

RESULTS

All measures were significantly lower in AD patients compared with controls. NAA/Cr and NAA correlated weakly, and there was no correlation of NAA with the amount of BT in the voxel. The highest specificity (87%) at a sensitivity of 80% was observed for NAA multiplied with the amount of BT in the voxel. There was no correlation of the MMSE with any of the NAA parameters.

CONCLUSIONS

NAA/Cr does not reflect NAA concentration very well. NAA is not correlated with brain atrophy. The BT volume in the 1H-MRS voxel in combination with the concentration of NAA discriminates AD from healthy controls sufficiently.

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.

Reduced medial temporal lobe N-acetylaspartate in cognitively impaired but nondemented patients

BACKGROUND

N-acetylaspartate (NAA) in the medial temporal lobe (MTL) and parietal lobe gray matter (GM) is diminished in Alzheimer disease (AD). Because NAA is considered a marker of neuronal integrity, reduced medial temporal and parietal lobe NAA could be an early indication of dementia-related pathology in elderly individuals.

OBJECTIVES

1) To determine whether cognitively impaired but nondemented (CIND) elderly individuals exhibit a similar pattern of reduced medial temporal and parietal lobe NAA as AD patients. 2) To compare regional NAA patterns, hippocampal and neocortical gray matter (GM) volumes in CIND patients who remained cognitively stable and those who became demented over 3.6 years of follow-up. 3) To examine the relationship between memory performance, medial temporal lobe NAA, and hippocampal volume.

METHODS

Seventeen CIND, 24 AD, and 24 cognitively normal subjects were studied using MRSI and MRI.

RESULTS

Relative to controls, CIND patients had reduced MTL NAA (19 to 21%, p = 0.005), hippocampal (11 to 14%, p < or = 0.04), and neocortical GM (5%, p = 0.05) volumes. CIND patients who later became demented had less MTL NAA (26%, p = 0.01), hippocampal (17 to 23%, p < or = 0.05), and neocortical GM (13%, p = 0.02) volumes than controls, but there were no significant differences between stable CIND patients and controls. MTL NAA in combination with hippocampal volume improved discrimination of CIND and controls over hippocampal volume alone. In AD and CIND patients, decreased MTL NAA correlated significantly with impaired memory performance.

CONCLUSION

Reduced medial temporal lobe N-acetylaspartate, together with reduced hippocampal and neocortical gray matter volumes, may be early indications of dementia-related pathology in subjects at high risk for developing dementia.

Correlates of hippocampal neuron number in Alzheimer's disease and ischemic vascular dementia

The cornu ammonis 1 region of the hippocampus (CA1) sector of hippocampus is vulnerable to both Alzheimer's disease (AD)-type neurofibrillary degeneration and anoxia-ischemia. The objective of this article is to compare number and size of neurons in CA1 in AD versus ischemic vascular dementia. Unbiased stereological methods were used to estimate the number and volume of neurons in 28 autopsy-derived brain samples. For each case, the entire hippocampus from one cerebral hemisphere was sliced into 5mm slabs (5-7 slabs/case), cut into 50 microm sections, and stained with gallocyanine. Using the optical dissector, we systematically sampled the number and size of neurons throughout the extent of CA1 and CA2. The total number of neurons was significantly less in AD compared with ischemic vascular dementia (p < 0.02), but there was no significant difference in neuron size. The greatest loss of neurons was observed in two cases with combined AD and hippocampal sclerosis. Regardless of causative diagnosis, the number of CA1 neurons correlates with magnetic resonance imaging-derived hippocampal volume (r = 0.72; p < 0.001) and memory score (r = 0.62; p < 0.01). We conclude that although CA1 neuron loss is more consistently observed in AD than ischemic vascular dementia, severity of loss shows the expected correlation with structure and function across causative subtype. Reductions in magnetic resonance imaging-derived hippocampal volume reflect loss, rather than shrinkage, of CA1 neurons.

Coregistration of quantitative proton magnetic resonance spectroscopic imaging with neuropathological and neurophysiological analyses defines the extent of neuronal impairments in murine human immunodeficiency virus type-1 encephalitis

Relatively few immune-activated and virus-infected mononuclear phagocytes (MP; perivascular macrophages and microglia) may affect widespread neuronal dysfunction during human immunodeficiency virus type 1 (HIV-1)-associated dementia (HAD). Indeed, histopathological evidence of neuronal dropout often belies the extent of cognitive impairment. To define relationships between neuronal function and histopathology, proton magnetic resonance spectroscopic imaging (1H MRSI) and hippocampal long-term potentiation (LTP) were compared with neuronal and glial immunohistology in a murine model of HIV-1 encephalitis (HIVE). HIV-1(ADA)-infected human monocyte-derived macrophages (MDM) were stereotactically injected into the subcortex of severe combined immunodeficient (SCID) mice. Sham-operated and unmanipulated mice served as controls. Seven days after cell injection, brain histological analyses revealed a focal giant cell encephalitis, with reactive astrocytes, microgliosis, and neuronal dropout. Strikingly, significant reductions in N-acetyl aspartate concentration ([NAA]) and LTP levels in HIVE mice were in both injected and contralateral hemispheres and in brain subregions, including the hippocampus, where neuropathology was limited or absent. The data support the importance of 1H MRSI as a tool for assessing neuronal function for HAD. The data also demonstrate that a highly focal encephalitis can produce global deficits for neuronal function and metabolism.

White matter lesions are associated with cortical atrophy more than entorhinal and hippocampal atrophy

The goal of this study was to examine the relationship between subcortical vascular disease and brain atrophy in patients with Alzheimer's disease (AD) and mixed dementia (i.e., AD and subcortical vascular disease together). MRI was performed on 77 cognitively normal (CN) subjects, 50 AD and 13 mixed dementia patients. Subcortical vascular disease was determined by white matter hyperintensities (WMH) volume and presence of subcortical lacunes. Brain atrophy was measured using total brain cortical gray matter (CGM), entorhinal cortex (ERC) and hippocampal volumes. CGM volume, but not ERC or hippocampal volume was inversely related to WMH volume in patients and controls. In contrast, no relationship was detected between CGM, ERC, or hippocampal volumes and subcortical lacunes. Furthermore, no interaction was found between WMH and diagnosis on cortical atrophy, implying that WMH affect cortical atrophy indifferently of group. These results suggest that subcortical vascular disease, manifested as WMH, may affect cortical atrophy more than ERC and hippocampal atrophy. Further, AD pathology and subcortical vascular disease may independently affect cortical atrophy.

1H MRS in stroke patients with and without cognitive impairment

The pathophysiological basis of cognitive impairment in patients with cerebrovascular disease (CVD) is not well understood, particularly in relation to the role of non-infarction ischemic change and associated Alzheimer-type pathology. We used single voxel 1H MRS to determine the differences in brain neurometabolites in non-infarcted frontal white matter and occipito-parietal gray matter of 48 stroke patients with or without cognitive impairment and 60 elderly controls. The results showed that there were no significant neurometabolite differences between the stroke cohort and healthy elderly controls, but there was a difference in NAA/H2O between the stroke patients that had cognitive impairment (vascular dementia (VaD) and vascular cognitive impairment (VCI)) compared with those patients with no impairment. This was significant in the occipito-parietal gray matter, but not in the frontal white matter, although the results were in the same direction for the latter. This suggests that cognitive impairment in stroke patients may be related to cortical neuronal dysfunction rather than purely subcortical change. Moreover, cortical regions not obviously infarcted may have dysfunctional neurons, the pathophysiological basis for which needs further study.

High-field magnetic resonance imaging of brain iron: birth of a biomarker?

The brain has an unusually high concentration of iron, which is distributed in an unusual pattern unlike that in any other organ. The physiological role of this iron and the reasons for this pattern of distribution are not yet understood. There is increasing evidence that several neurodegenerative diseases are associated with altered brain iron metabolism. Understanding these dysmetabolic conditions may provide important information for their diagnosis and treatment. For many years the iron distribution in the human brain could be studied effectively only under postmortem conditions. This situation was changed dramatically by the finding that T2-weighted MR imaging at high field strength (initially 1.5 T) appears to demonstrate the pattern of iron distribution in normal brains and that this imaging technique can detect changes in brain iron concentrations associated with disease states. Up to the present time this imaging capability has been utilized in many research applications but it has not yet been widely applied in the routine diagnosis and management of neurodegenerative disorders. However, recent advances in the basic science of brain iron metabolism, the clinical understanding of neurodegenerative diseases and in MRI technology, particularly in the availability of clinical scanners operating at the higher field strength of 3 T, suggest that iron-dependent MR imaging may soon provide biomarkers capable of characterizing the presence and progression of important neurological disorders. Such biomarkers may be of crucial assistance in the development and utilization of effective new therapies for Alzheimer's and Parkinson's diseases, multiple sclerosis and other iron-related CNS disorders which are difficult to diagnose and treat.

Phosphate-related energy compounds are not exhausted in chronically hypoperfused rat brain cortex after cortical spreading depression

Long-term bilateral common carotid occlusion (BCCAO) in rats induces brain hypoperfusion and structural injury, and could have relevance as a model of vascular dementia in which cortical metabolism is reduced. The present study was designed to assess whether phosphate-related energy compounds and blood supplies are markedly affected by KCI-induced cortical spreading depression (CSD), which leads to metabolic and cerebral blood flow changes in rats with chronic BCCAO, by means of near-infrared spectroscopy and phosphorus magnetic resonance spectroscopy. Male Wistar rats were divided into 4 groups: BCCAO for 1 week (n = 6) and 4 weeks (n = 15), and sham operation for 1 week (n = 7) and 4 weeks (n = 7). The phosphocreatine (Pcr) index (PCr/PCr+Pi) and intracellular pH (pHi) were measured pre-CSD, just after KCl application, and at 20 and 40 minutes after CSD. Brains were evaluated by histology with hematoxylin and eosin and immunohistochemical reaction for glial fibrillary acidic protein (GFAP). Rapid signal changes of oxy-, deoxy-, and total hemoglobin were observed in all KCl-applied brains. The PCr index and pHi values in BCCAO were not different than those in control rats. The percentage of vacuolated area in the optic tract and percentage values of GFAP-positive area in the frontoparietal cortex were significantly increased in BCCAO. The generation of CSD was seen in regions of cortical gliosis induced by BCCAO, and severe energy exhaustion did not occur during or after CSD. Our results may suggest that the functional interaction of neurons and glia is sustained even in brain tissue where the metabolic state of neurons is impaired and astrocytes are proliferated.