Metabolic brain mapping in Alzheimer's disease using proton magnetic resonance spectroscopy

Meta-Analysis of Neurochemical Changes Estimated via Magnetic Resonance Spectroscopy in Mild Cognitive Impairment and Alzheimer's Disease

The changes of neurochemicals in mild cognitive impairment (MCI) and Alzheimer's disease (AD) patients has been observed via magnetic resonance spectroscopy in several studies. However, whether it exists the consistent pattern of changes of neurochemicals in the encephalic region during the progression of MCI to AD were still not clear. The study performed meta-analysis to investigate the patterns of neurochemical changes in the encephalic region in the progress of AD. We searched the PubMed, Embase, Cochrane Library, and Web of Science databases, and finally included 63 studies comprising 1,086 MCI patients, 1,256 AD patients, and 1,907 healthy controls. It showed that during the progression from MCI to AD, N-acetyl aspartate (NAA) decreased continuously in the posterior cingulate (PC) (SMD: −0.42 [95% CI: −0.62 to −0.21], z = −3.89, P < 0.05), NAA/Cr (creatine) was consistently reduced in PC (SMD: −0.58 [95% CI: −0.86 to −0.30], z = −4.06, P < 0.05) and hippocampus (SMD: −0.65 [95% CI: −1.11 to −0.12], z = −2.44, P < 0.05), while myo-inositol (mI) (SMD: 0.44 [95% CI: 0.26–0.61], z = 4.97, P < 0.05) and mI/Cr (SMD: 0.43 [95% CI: 0.17–0.68], z = 3.30, P < 0.05) were raised in PC. Furthermore, these results were further verified by a sustained decrease in the NAA/mI of PC (SMD: −0.94 [95% CI: −1.24 to −0.65], z = −6.26, P < 0.05). Therefore, the levels of NAA and mI were associated with the cognitive decline and might be used as potentially biomarkers to predict the possible progression from MCI to AD.

Systematic Review Registration:https://www.crd.york.ac.uk/PROSPERO/, identifier: CRD42020200308.

In vivo molecular imaging of neuroinflammation in Alzheimer's disease

It has become increasingly evident that neuroinflammation plays a critical role in the pathophysiology of Alzheimer's disease (AD) and other neurodegenerative disorders. Increased glial cell activation is consistently reported in both rodent models of AD and in AD patients. Moreover, recent genome wide association studies have revealed multiple genes associated with inflammation and immunity are significantly associated with an increased risk of AD development (e.g. TREM2). Non‐invasive in vivo detection and tracking of neuroinflammation is necessary to enhance our understanding of the contribution of neuroinflammation to the initiation and progression of AD. Importantly, accurate methods of quantifying neuroinflammation may aid early diagnosis and serve as an output for therapeutic monitoring and disease management. This review details current in vivo imaging biomarkers of neuroinflammation being explored and summarizes both pre‐clinical and clinical results from molecular imaging studies investigating the role of neuroinflammation in AD, with a focus on positron emission tomography and magnetic resonance spectroscopy (MRS).

Impaired brain metabolism and neurocognitive function in childhood leukemia survivors despite complete hormone supplementation in adulthood

Cranial radiotherapy is a known risk factor for neurocognitive impairment in survivors of childhood acute lymphoblastic leukemia (ALL). Understanding the nature of cognitive dysfunction during adulthood in ALL survivors is important as it has an impact on major life situations. Thirty-eight (21 women) ALL survivors were investigated 34 years after diagnosis. Median-age was 38 (27-46) years. All were treated with a CRT dose of 24Gy and 11 years (3-13) of complete hormone supplementation. Comparisons were made to 29 matched controls. Assessments of magnetic resonance spectroscopy (white and grey matter metabolic alterations), brain volume and neuropsychological tests were performed. ALL survivors demonstrate a generally lower performance in neuropsychological tests. ALL survivors scored lower than controls in vocabulary (p<0.001), memory (p<0.001), learning capacity (p<0.001), spatial ability (p<0.001), executive functions and attention (p<0.001) 34 years after ALL treatment. Compared to controls ALL survivors had reduced white matter (WM) (492 vs 536cm³, p<0.001) and grey matter (GM) volumes (525 vs 555cm³, p=0.001). ALL survivors had lower levels of WM N-acetyl aspartate/creatin (NAA/Cr) (1.48 vs 1.63, p=0.004), WM NAA+NAAG (N-acetylaspartylglutamate)/Cr (1.61 vs 1.85, p<0.001) and lower levels of GM NAA/Cr (1.18 vs 1.30, p=0.001) and GM NAA+NAAG/Cr (1.28 vs 1.34, p=0.01) compared to controls. ALL survivors had higher levels in WM MI (Myoinositol)/NAA (0.65 vs 0.56, p=0.01) concentrations compared to controls. There was a significantly negative correlation of years since ALL diagnosis to WM NAA+NAAG/Cr (r=-0.4, p=0.04) in ALL survivors. The present study shows impaired brain metabolism detected by MRS, reduced brain volumes and neurocognitive impairment in childhood ALL survivors treated with cranial radiotherapy and chemotherapy, despite complete hormone substitution. We also report an impairment of metabolites correlated to time since treatment and a progressive impairment in sustained attention, suggesting an accelerated aging in the irradiated brain. Following these survivors many decades, or throughout life, after treatment with cranial radiotherapy and chemotherapy is highly warranted for a broader understanding of long-term outcome in this patient group.

¹H- and ¹³C-NMR spectroscopy of Thy-1-APPSL mice brain extracts indicates metabolic changes in Alzheimer's disease

Biochemical alterations underlying the symptoms and pathomechanisms of Alzheimer's disease (AD) are not fully understood. However, alterations of glucose metabolism and mitochondrial dysfunction certainly play an important role. (1)H- and (13)C-NMR spectroscopy exhibits promising results in providing information about those alterations in vivo in patients and animals, especially regarding the mitochondrial tricarboxylic acid (TCA) cycle. Accordingly, transgenic mice expressing mutant human amyloid precursor protein (APP(SL))-serving as a model of neuropathological changes in AD-were examined with in vitro 1D (1)H- and 2D (1)H-(13)C-HSQC-NMR spectroscopy after oral administration of 1-(13)C-glucose and acquisition of brain material after 30 min. Perchloric acid extracts were measured using a 500 MHz spectrometer, providing more detailed information compared to in vivo spectra achievable nowadays. Area under curve (AUC) data of metabolite peaks were obtained and normalized in relation to the creatine signal, serving as internal reference. Besides confirming well-known metabolic alterations in AD like decreased N-acetylaspartate (NAA)/Creatine (Cr) ratio, new findings such as a decrease in phosphorylcholine (PC) are presented. Glutamate (Glu) and glutamine (Gln) concentrations were decreased while γ-aminobutyric acid (GABA) was elevated in Thy1-APP(SL) mice. (13)C-NMR spectroscopy revealed a shift in the Glx-2/Glx-4-ratio-where Glx represents a combined Glu/Gln-signal-towards Glx-2 in AD. These findings correlated well with the NAA/Cr-ratio. The Gln-4/Glu-4-ratio is altered in favor of Glu. Our findings suggest that glutamine synthetase (GS), which is predominantly present in glial cells may be impaired in the brain of Thy1-APP(SL) transgenic mice. Since GS is an ATP-dependent enzyme, mitochondrial dysfunction might contribute to reduced activity, which might also account for the increased metabolism of glutamate via the GABA shunt, a metabolic pathway to bypass intra-mitochondrial α-ketoglutarate-dehydrogenase, resulting in elevated GABA levels.

Various MRS application tools for Alzheimer disease and mild cognitive impairment

MR spectroscopy is a noninvasive technique that allows the detection of several naturally occurring compounds (metabolites) from well-defined regions of interest within the human brain. Alzheimer disease, a progressive neurodegenerative disorder, is the most common cause of dementia in the elderly. During the past 20 years, multiple studies have been performed on MR spectroscopy in patients with both mild cognitive impairment and Alzheimer disease. Generally, MR spectroscopy studies have found decreased N-acetylaspartate and increased myo-inositol in both patients with mild cognitive impairment and Alzheimer disease, with greater changes in Alzheimer disease than in mild cognitive impairment. This review summarizes the information content of proton brain MR spectroscopy and its related technical aspects, as well as applications of MR spectroscopy to mild cognitive impairment and Alzheimer disease. While MR spectroscopy may have some value in the differential diagnosis of dementias and assessing prognosis, more likely its role in the near future will be predominantly as a tool for monitoring disease response or progression in treatment trials. More work is needed to evaluate the role of MR spectroscopy as a biomarker in Alzheimer disease and its relationship to other imaging modalities.

Hippocampal neurochemical changes in senescent mice induced with chronic injection of D-galactose and NaNO₂: an in vitro high-resolution NMR spectroscopy study at 9.4T

Proton magnetic resonance spectroscopy (¹H-MRS) has been used to provide useful information about the neurochemical changes reflecting early pathological alterations in Alzheimer's disease (AD) brain. In this study, we have longitudinally measured the hippocampal neurochemical profile in vitro in senescent mice induced with chronic injection of D-Galactose and NaNO₂, at different time point from day 30 to day 70 with a 10-day interval. Pathological brain alterations induced by D-Galactose and NaNO₂ were monitored through hematoxylin and eosin (HE) staining, Congo red staining and bielschowsky silver staining, and the cognition deficits were assessed via Morris Water Maze (MWM) test. This D-galactose and NaNO₂ treated mouse model, characterized by an early-onset memory dysfunction, a robust neuronal loss, amyloid plaques and neurofibrillary tangles in hippocampal subdivision, well mimics a prodromal Alzheimer's phenotype. Consistent with previously published in vivo ¹H MRS findings in human AD patients and AD transgenic mice, our in vitro ¹H MRS on the perchloric acid extractions of hippocampus in senescent mice observed significant decreases of N-acetylaspartate (NAA) and Glutamate (Glu) but an increase in Myo-inositol (mIns). Elevated mIns occurred prior to the reduction of NAA and Glu during the progression of aging. In addition, changes in mIns, NAA and Glu were found to precede pathological abnormalities. Overall, our in vitro findings in senescent mice validated the concept that hippocampal neurochemical alternations preceded the pathological changes of the brain, and could serve as potential markers of AD progression. Reductions of NAA and Glu can be interpreted in terms of neuronal degeneration and dysfunctions in glutamatergic activity that may contribute to the pathophysiological mechanisms underlying AD. Elevated mIns might be related to glial activation. Further experiments are needed to explore the potential value of mIns in the early diagnosis of AD, to verify whether glial cell proliferation occurs earlier than neuronal changes.

Magnetic resonance spectroscopy in vivo of neurochemicals in a transgenic model of Alzheimer's disease: a longitudinal study of metabolites, relaxation time, and behavioral analysis in TASTPM and wild-type mice

Alzheimer's disease (AD) is the most common form of dementia in the elderly. Due to ongoing advances in our understanding of the underlying pathology of AD, many potential new targets for therapeutics are becoming available. Transgenic mouse models of AD have helped in furthering our understanding of AD and also provide a vehicle for preclinical testing of new, putative disease-modifying therapeutics, which may have potential for translation to use in clinical trials. To identify possible translational biomarkers, we have studied the longitudinal cerebral metabolic pattern of the TASTPM transgenic AD mouse, a double transgenic mouse overexpressing human mutant amyloid precursor protein (hAPP695swe) and presenilin-1 (M146V) by (1) H magnetic resonance spectroscopy, along with concurrent brain T1 /T2 mapping and behavioral testing. We found significant differences in creatine, glutamate, N-acetylaspartate, choline-containing compounds, and myo-inositol between TASTPM and wild-type mice. In the case of N-acetylaspartate and myo-inositol, there were similarities to differences detected in human AD. T1 /T2 values were shorter overall in TASTPM mice, indicating possible differences in water content between TASTPM and wild-type mice. In older TASTPM mice, exploratory behavior became more random, indicating a possible memory deficiency. The decrease in behavioral performance correlated in the transgenic group with higher expression of myo-inositol.

N-acetylaspartate, choline, myoinositol, glutamine and glutamate (glx) concentration changes in proton MR spectroscopy (1H MRS) in patients with mild cognitive impairment (MCI)

Background

Purpose of study was evaluation of regional metabolic disorders using ¹H MRS in patients with MCI, as a predictor of clinical conversion to dementia based on clinical follow-up.

Material/Methods

The study group consisted of 31 subjects with diagnosis of MCI based on criteria the Mayo Clinic Group. ¹H MRS was performed with a single-voxel method using PRESS sequence. The volume of interest (VOI) was located in the hippocampal formation and posterior part of the cingulated gyrus.

Results

Patients had annual clinical control at least twice. At the beginning, 9 had amnestic MCI and the others had multidomain MCI. During follow-up (median 3 yrs) 8 subjects had stable disease (SD), 13 had disease progression (DP) and 10 develop Alzheimer disease (AD). Baseline metabolic ratios (¹H MRS) between 3 groups indicated significant difference (P<0.05) in left frontal lobe in mI/H₂0 ratio, between patients with SD (0.27) and DP. In comparing the groups with DP and AD, a significant difference in NAA/Cr (1.77 vs. 1.43) was found. A significant difference within left temporal external lobes was found between SD and DP in NAA/H₂O ratio (0.55 vs. 0.51). An additional significant difference within medial temporal lobe was found between DP and AD in Glx/H₂O ratio (0.44 vs. 0.34) on the right side.

Conclusions

¹H MRS seems to be sensitive method allows prediction of which patients are liable to progress from MCI to AD. Combined with other biomarkers of disease staging, it is an important approach in the preclinical AD diagnosis, as well as the assessment of dementia progression.

Effects of Alzheimer's disease transgenes on neurochemical expression in the mouse brain determined by ¹H MRS in vitro

Transgenic models of human disease can be used to understand pathology and to discover biomarkers of disease presence, progression and response to therapy. Here we report a study of longitudinal metabolic differences between TASTPM transgenic Alzheimer's disease (AD) mice and their wild type counterparts using (1)H magnetic resonance spectroscopy (MRS) to look for potential biomarkers for use in AD research and drug discovery. Chloroform methanol extractions were performed on the brains of mice aged between 3 and 18 months. (1)H MR spectra were recorded from the aqueous fractions. Absolute metabolite concentrations, determined from resonance integrals relative to an internal standard, were analysed by 2-way ANOVA (genotype x age). Significant effects of age alone were identified for creatine, glutamine and total choline-containing compounds. There was a marked increase in creatine in the oldest (15-18 mo) TASTPM mice. The increase in creatine was unexpected and may be caused by osmotic stress in older animals as plaque load increases. Care should be taken when using creatine as a reference metabolite during scans of these animals in vivo. A significant effect of genotype alone was identified for myo-inositol (MI), which was higher in TASTPM mice at all ages. Succinate, glycerophosphocholine and choline all showed significant effects of age and genotype. No significant effects were detected in N-acetylaspartate (NAA) levels. Increased MI could be a marker of gliosis or microglial activation in TASTPM mice, but the absence of an age dependence for MI levels means it may be a biomarker of disease, but not of disease progression. Decreased succinate is indicative of disrupted neuronal energy metabolism, an effect that has been seen in human AD.

Three-dimensional magnetic resonance spectroscopic imaging in the substantia nigra of healthy controls and patients with Parkinson's disease

OBJECTIVES

To investigate the substantia nigra in patients with Parkinson's disease three-dimensional magnetic resonance spectroscopic imaging with high spatial resolution at 3 Tesla was performed. Regional variations of spectroscopic data between the rostral and caudal regions of the substantia nigra as well as the midbrain tegmentum areas were evaluated in healthy controls and patients with Parkinson's disease.

METHODS

Nine patients with Parkinson's disease and eight age- and gender-matched healthy controls were included in this study. Data were acquired by using three-dimensional magnetic resonance spectroscopic imaging measurements. The ratios between rostral and caudal voxels of the substantia nigra as well as the midbrain tegmentum areas were calculated for the main-metabolites N-acetyl aspartate, creatine, choline, and myo-inositol. Additionally, the metabolite/creatine ratios were calculated.

RESULTS

In all subjects spectra of acceptable quality could be obtained with a nominal voxel size of 0.252 ml. The calculated rostral-to-caudal ratios of the metabolites as well as of the metabolite/creatine ratios showed with exception of choline/creatine ratio significant differences between healthy controls and patients with Parkinson's disease.

CONCLUSIONS

The findings from this study indicate that regional variations in N-acetyl aspartate/creatine ratios in the regions of the substantia nigra may differentiate patients with Parkinson's disease and healthy controls.

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.

Executive function is associated with brain proton magnetic resonance spectroscopy in amnestic mild cognitive impairment

Persons with amnestic mild cognitive impairment (MCI) show deficits on executive function measures, although the neuroanatomic basis of executive function in MCI is unknown. We investigated cognitive correlates of 3-tesla proton magnetic resonance spectroscopy (MRS) of the posterior cingulate gyrus in 26 MCI patients. Posterior cingulate ratio of myo-inositol to creatine (mI/Cr) was negatively correlated (-.51) with spontaneous clock drawing. This relationship was not attenuated after accounting for age, overall cognitive function, or memory performance. This finding suggests a role for the posterior cingulate in executive function in MCI. Proton MRS may offer a means to track neurometabolic changes associated with cognitive impairment in MCI.

[Proton spectroscopy in Alzheimer's disease and cognitive impairment not dementia: a community study]

OBJECTIVE

To describe the proton magnetic resonance spectroscopy (1H-ERM) data in Alzheimer's disease (AD) and Cognitive Impairment Not Dementia (CIND) in a community sample.

METHOD

We investigated subjects with AD (n=6), CIND (n=7) and normal control (n=7). 1H-ERM was performed with single voxel (8 cm3) placed in temporal, parietal and occipital regions and studied metabolites were: N-acetylaspartate (NAA), creatine (Cr), choline (Cho) and myo-inositol (mI).

RESULTS

NAA concentration was higher in control subjects than AD and intermediated in CIND patients. Cho parietal plus occipital and Cr parietal plus Cho occipital classified correctly 92.3% of subjects Control vs AD. Temporal mI classified 78.6% of subjects between Control vs CIND.

CONCLUSION

Spectroscopy can be used in the diagnosis and follow-up of individuals with cognitive impairment; evaluation of community subjects may show different patterns of brain metabolites distribution.

Stigmatization in Alzheimer's disease research on African American elders

Stigmatization in research sustains the spread of the silent epidemic of Alzheimer's disease (AD) in African American populations. Researchers use stereotypes and inappropriate assumptions to select a paradigm to examine the symptoms of AD. This paradigm fails to encompass the symptoms as manifested by African American elders. Yet, stigmatization can be minimized by recognizing the genetic heterogeneity of the symptoms within the general population, especially those manifested by African American elders. Thus, researchers can utilize pioneering genetic analyses to identify other paradigms critical in the assessment and proactive treatment of the symptoms of AD needed for this vulnerable population.

Pathological aging of the brain: an overview

The number of elderly people is increasing rapidly and, therefore, an increase in neurodegenerative and cerebrovascular disorders causing dementia is expected. Alzheimer disease (AD) is the most common cause of dementia. Vascular dementia, dementia with Lewy bodies, and frontotemporal dementia are the most frequent causes after AD, but a large proportion of patients have a combination of degenerative and vascular brain pathology. Characteristic magnetic resonance (MR) imaging findings can contribute to the identification of different diseases causing dementia. The MR imaging protocol should include axial T2-weighted images (T2-WI), axial fluid-attenuated inversion recovery (FLAIR) or proton density-weighted images, and axial gradient-echo T2*-weighted images, for the detection of cerebrovascular pathology. Structural neuroimaging in dementia is focused on detection of brain atrophy, especially in the medial temporal lobe, for which coronal high resolution T1-weighted images perpendicular to the long axis of the temporal lobe are extremely important. Single photon emission computed tomography and positron emission tomography may have added value in the diagnosis of dementia and may become more important in the future, due to the development of radioligands for in vivo detection of AD pathology. New functional MR techniques and serial volumetric imaging studies to identify subtle brain abnormalities may also provide surrogate markers for pathologic processes that occur in diseases causing dementia and, in conjunction with clinical evaluation, may enable a more rigorous and early diagnosis, approaching the accuracy of neuropathology.

A Review of 1H MR Spectroscopy Findings in Alzheimer's Disease

Hydrogen-1 MR spectroscopy (MRS) studies demonstrate metabolic differences between patients who have Alzheimer's disease (AD) and cognitive normal age-matched controls. Clinical MRS also shows regional variations in metabolites between patients who have AD and those who have other dementias. Single-voxel and volumetric standard MRS techniques and automated data processing software are available for clinical MR scanners. Improvements in specificity and sensitivity of AD diagnosis, using MRS techniques as an adjunct to clinical imaging, are under evaluation. Multiparametric data analyses show, however, that metabolite changes correlate with in-vitro, postmortem, and metabolic changes and to changes in or predictions of cognitive scores.

Quantitative neuropathologic correlates of changes in ratio of N-acetylaspartate to creatine in macaque brain

PURPOSE

To elucidate the neuropathologic basis of transient changes in the ratio of N-acetylaspartate (NAA) to creatine (Cr) in the primate brain by using a simian immunodeficiency virus (SIV)-infected macaque model of the neurologic manifestation of acquired immune deficiency syndrome.

MATERIALS AND METHODS

This study was approved by the Massachusetts General Hospital Subcommittee on Research and Animal Care and the Institutional Animal Care and Use Committee of Harvard University. Rhesus macaques infected with SIV were evaluated during the 1st month of infection. A total of 11 animals were studied, including four control animals, three animals sacrificed 12 days after infection, three animals sacrificed 14 days after infection, and one animal sacrificed 28 days after infection. All animals underwent in vivo proton ((1)H) magnetic resonance (MR) spectroscopy, and postmortem frontal lobe tissue was investigated by using high-spectral-resolution (1)H MR spectroscopy of brain extracts. In addition, quantitative neuropathologic analyses were performed. Stereologic analysis was performed to determine neuronal counts, and immunohistochemical analysis was performed to analyze three neuronal markers: synaptophysin, microtubule-associated protein 2 (MAP2), and calbindin. Analysis of variance (ANOVA) was used to determine substantial changes in neuropathologic and MR spectroscopic markers. Spearman rank correlations were calculated between plasma viral load and neuropathologic and spectroscopic markers.

RESULTS

During acute infection with SIV, the macaque brain exhibited significant changes in NAA/Cr (P < .02, ANOVA) and synaptophysin (P < .013, ANOVA). There was no significant change in the concentration of Cr. No significant changes were found in neuronal counts or other immunohistochemical neuronal markers. With the Spearman rank test, a significant direct correlation was detected between synaptophysin and ex vivo NAA/Cr (r(s) = 0.72, P < .013). No correlation between NAA/Cr and neuronal counts, calbindin, or MAP2 was found.

CONCLUSION

NAA/Cr is a sensitive marker of neuronal injury, not necessarily neuronal loss, and best correlates with synaptophysin, a marker of synaptodendritic dysfunction.

Straightforward relative quantitation and age-related human standards of N-acetylaspartate at the centrum semiovale level by CSI (1)H-MRS

1H-MRS was aimed to monitor metabolite concentrations in homogeneous interaxial slices of cerebral matter at the centrum semiovale level in healthy volunteers. NAA (N-acetylaspartate + N-acetylglutamate), Cr (creatine + phosphocreatine), and Cho (choline + acetylcholine) were evaluated by resonance integrations. Using Cr as an internal standard, NAA/Cr ratio was considered as a relative measure of concentration. CSI sequence explored volunteer's interaxial slices of white and gray matter by means of 8 x 8 matrices of (1)H-NMR spectra. NAA/Cr integral ratios were averaged over the whole spectral matrix to obtain the Index of NAA at Centrum Semiovale (INACS) of each individual. Indexes of the sixty-eight healthy volunteers, divided into three groups by age, showed good intraindividual reproducibility, and were virtually unaffected by small shifts or bendings of the interaxial slice analyzed. The INACSs were used to estimate Age-Sectorial INACS Ranges (ASIR), the intervals that, on the basis of a normal statistical distribution, should comprise 95% of the age-matched healthy population. Individual INACSs, compared to accurately defined ASIRs taken as standards, could early detect subtle, diffuse neuronal or axonal damage within centrum semiovale interaxial slices. Periodic inspection of INACS could also allow monitoring of progressive neuronal or axonal degeneration.

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.

Quantification of neurons in Alzheimer and control brains with ex vivo high resolution magic angle spinning proton magnetic resonance spectroscopy and stereology

Samples from human brains were examined with both stereologic methods for neuronal counting and high resolution magic angle spinning (HRMAS) proton magnetic resonance spectroscopy (1HMRS) for quantification of cellular metabolites. A statistically significant linear correlation between neuronal density and the concentration of N-acetylaspartate (NAA) in the superior temporal sulcus (STS) area was observed. Although NAA has been widely utilized as a neuronal marker in in vivo MRS, an emerging sub-discipline of diagnostic neuroradiology, the experimental proof of the unilateral relationship between NAA and neurons has yet to be confirmed. The observed correlation provides experimental evidence that NAA concentration is proportional to the neuronal density. Metabolite ratios measured from the STS area were compared to those from frontal association cortex for their sensitivities in differentiating Alzheimer disease brains from control brains.

Barriers to Alzheimer disease drug discovery and drug development in the pharmaceutical industry

The drug development process in the pharmaceutical industry has evolved from separate programs, specific for each country, into one coordinated, global development scheme. As a result, such a development program must meet regulatory requirements for all countries in which approval for the new drug will be sought. Barriers to Alzheimer disease (AD) drug discovery and development in the pharmaceutical industry can be categorized as (1) regulatory, (2) logistical, and (3) drug development issues. Some of the regulatory barriers could be overcome by international harmonization of guidelines for the development of antidementia drugs. The logistical issues can be reduced through international collaboration in the conduct of clinical studies, and the developmental issues can be addressed by using an expedited drug development plan that not only can reduce the time but also the resources required to develop the drug.

Selective reduction of N-acetylaspartate in medial temporal and parietal lobes in AD

BACKGROUND

Both AD and normal aging cause brain atrophy, limiting the ability of MRI to distinguish between AD and age-related brain tissue loss. MRS imaging (MRSI) measures the neuronal marker N-acetylaspartate (NAA), which could help assess brain change in AD and aging.

OBJECTIVES

To determine the effects of AD on concentrations of NAA, and choline- and creatine-containing compounds in different brain regions and to assess the extent NAA in combination with volume measurements by MRI improves discrimination between AD patients and cognitively normal subjects.

METHODS

Fifty-six patients with AD (mean age: 75.6 +/- 8.0 years) and 54 cognitively normal subjects (mean age: 74.3 +/- 8.1 years) were studied using MRSI and MRI.

RESULTS

NAA concentration was less in patients with AD compared with healthy subjects by 21% (p < 0.0001) in the medial temporal lobe and by 13% to 18% (p < 0.003) in parietal lobe gray matter (GM), but was not changed significantly in white matter and frontal lobe GM. In addition to lower NAA, AD patients had 29% smaller hippocampi and 11% less cortical GM than healthy subjects. Classification of AD and healthy subjects increased significantly from 89% accuracy using hippocampal volume alone to 95% accuracy using hippocampal volume and NAA together.

CONCLUSION

In addition to brain atrophy, NAA reductions occur in regions that are predominantly impacted by AD pathology.

[Alzheimer's disease and magnetic resonance spectroscopy of the hippocampus]

OBJECTIVE

Acquisition of data of magnetic resonance metabolite spectrum of the hippocampal formation (hippocampus-hc) in the elderly, normal and with Alzheimer's disease (AD).

METHOD

Subjects matched for age: a. normal sample (n=20), CDR=0, and b. AD sample (n=40), CDR 1 and 2.

TECHNIQUE

Signa Horizon LX-GE, 1.5T, 1H-MRS with automated software PROBE/SV, VOI: hc (right and left); single voxel (2x2x2cm); TR 1500ms/TE 50ms; PRESS; metabolites: N-acetylaspartate (Naa), choline (Cho), creatine (Cr), myo-inositol (mI).

RESULTS

The present data relate to the ratios of Naa, Cho and mI, with Cr taken as reference, and the mI/Naa ratio. The study showed reduction of Naa, increase of mI and of the mI/Naa ratio, and not consistent results for Cho. The results of the whole sample of AD patients compared to the pooled normal mean +/- sd were significant for Naa, mI and mI/Naa (p<0.01). Accuracy in relation to the individual values of both samples showed satisfactory levels of sensitivity, specificity and positive predictive value.

CONCLUSION

The present results can be used as a helpful tool to detect pathologic changes of the hippocampus in AD, and allowing greater accuracy and an earlier diagnosis of this disease.

Relation between 1H MR spectroscopic imaging and regional cerebral glucose metabolism in Alzheimer's disease

1 H Magnetic resonance spectroscopic imaging (MRSI) and positron emission tomography (PET) of (18) F-2-fluoro-2-deoxy-D-glucose (FDG) were performed in 18 patients with probable Alzheimer's disease (AD) and 3 normal controls. We measured the distribution and relative signal intensities of N-acetyl aspartate (NAA; a presumed neuronal marker), choline residues (Cho) representing cellular membrane compounds and of creatine-containing metabolites (Cr), and correlated these to regional cerebral glucose metabolism (rCMRGI) after coregistration of both imaging-techniques. The pattern of choline was significantly different between AD and normals (p < 0.01). RCMRGI was significantly related to Cho/Cr (r=-0.21, p<.05) and NAA/Cho quotients (r=0.35, p<.001). Our results suggest that in AD reduced neuronal energy performance and membrane abnormalities contribute to metabolic deterioration.

Patterns of cortical activity and memory performance in Alzheimer's disease

BACKGROUND

Declarative memory changes are the hallmark of Alzheimer's disease, although their functional neuroanatomy is not restricted to a single structure. Factor analysis provides statistical methods for evaluating patterns of cerebral changes in regional glucose uptake.

METHODS

Thirty-three Alzheimer's patients and 33 age- and gender-matched control subjects were studied with magnetic resonance imaging and positron emission tomography with [(18)F] deoxyglucose. During the tracer-uptake period, subjects performed a serial verbal learning task. Cortical activity was measured in 32 regions of interest, four in each lobe on both hemispheres.

RESULTS

Factor analysis with varimax rotation identified seven factors explaining 80% of the variance ("parietal cortex," "occipital cortex," "right temporo-prefrontal areas," "frontal cortex," "motor strip," "left temporal cortex," and "posterior temporal cortex"). Relative to control subjects, Alzheimer's patients showed significantly reduced values on the factors occipital cortex, right temporo-prefrontal areas, frontal cortex, and left temporal cortex. The factor temporo-prefrontal areas showed large differences between patients with good and poor performance, but little difference when control subjects were similarly divided.

CONCLUSIONS

Findings suggest that Alzheimer's disease is characterized by altered patterns of cortical activity, rather than deficits in a single location, and emphasize the importance of right temporo-prefrontal circuitry for understanding memory deficits.

Magnetic resonance imaging and magnetic resonance spectroscopy in dementias

This article reviews recent studies of magnetic resonance imaging and magnetic resonance spectroscopy in dementia, including Alzheimer's disease, frontotemporal dementia, dementia with Lewy bodies, idiopathic Parkinson's disease, Huntington's disease, and vascular dementia. Magnetic resonance imaging and magnetic resonance spectroscopy can detect structural alteration and biochemical abnormalities in the brain of demented subjects and may help in the differential diagnosis and early detection of affected individuals, monitoring disease progression, and evaluation of therapeutic effect.

Brain abnormalities in Gulf War syndrome: evaluation with 1H MR spectroscopy

PURPOSE

To test for neuronal brain damage in the basal ganglia and brainstem in Gulf War veterans by using magnetic resonance (MR) spectroscopy.

MATERIALS AND METHODS

Twenty-two Gulf War veterans with one of three factor analysis-derived syndromes (case patients); 18 well veterans matched for age, sex, and education level (control subjects); and six Gulf War veterans with syndrome 2 from a different population (replication sample) underwent long echo time (272 msec) proton (hydrogen 1) MR spectroscopy on a 4 x 2 x 2-cm voxel in the basal ganglia bilaterally and a 2 x 2 x 2-cm voxel in the pons. Syndromes 1-3 are described as "impaired cognition," "confusion-ataxia," and "central pain," respectively.

RESULTS

The N-acetylaspartate-to-creatine (NAA/Cr) ratio, which reflects functional neuronal mass, was significantly lower in the basal ganglia and brainstem of Gulf War veterans with the three syndromes than in those structures of the control subjects (P =.007). The finding was corroborated in the replication sample (P =.002). Veterans with syndrome 2 (the most severe clinically) had evidence of decreased NAA/Cr in both the basal ganglia and the brainstem; those with syndrome 1, in the basal ganglia only; and those with syndrome 3, in the brainstem only.

CONCLUSION

Veterans with different Gulf War syndromes have biochemical evidence of neuronal damage in different distributions in the basal ganglia and brainstem.

Brain biochemistry using magnetic resonance spectroscopy: relevance to psychiatric illness in the elderly

Magnetic resonance spectroscopy (MRS) allows for the noninvasive study of cerebral biochemistry. It has been used to investigate cerebral metabolic changes associated with mental illness in vivo and in vitro. In this review, we will discuss the application of MRS to psychiatric illness in the elderly. Following a brief description of the basic principles of MRS, the use of phosphorus (31P) and proton (1H) MRS to enable a better understanding of normal brain aging, dementia (Alzheimer's disease, multiple subcortical infarct dementia, Down syndrome, frontotemporal dementia, vascular dementia, age-associated memory impairment, and other dementias), major depression, and electroconvulsive therapy is detailed.

Magnetic resonance spectroscopy in toxic encephalopathy and neurodegeneration

Magnetic resonance spectroscopy allows neurochemistry to be probed noninvasively in vivo. Recent advances in our understanding of the biochemical significance of the various neurochemicals that are observable allow a variety of pathologic states of relevance to encephalopathies and neurodegenerative disorders to be observed. Measurements of brain glutamate and glutamine allow observation of neuronal/glial substrate cycling and ammonia detoxification. Myo-inositol allows changes in cerebral osmolarity and gliosis to be observed. N-acetylaspartate is a marker of neuronal health and number. Lactate allows nonoxidative glycolysis to be observed. These molecules are now being used to ask etiologic questions that are of relevance to encephalopathies and neurodegeneration, as well to probe longitudinally both natural history and therapeutic interventions in these conditions. Combined with recent advances in anatomic magnetic resonance imaging as well as perfusion magnetic resonance imaging, magnetic resonance spectroscopy has the potential to aid greatly in our understanding of neuronal dysfunction in a wide variety of neurologic pathologies, even in single patients.