Reduced phospholipid breakdown in Alzheimer's brains: a 31P spectroscopy study

Frontal-temporal regional differences in brain energy metabolism and mitochondrial function using 31P MRS in older adults

Aging is a major risk for cognitive decline and transition to dementia. One well-known age-related change involves decreased brain efficiency and energy production, mediated in part by changes in mitochondrial function. Damaged or dysfunctional mitochondria have been implicated in the pathogenesis of age-related neurodegenerative conditions like Alzheimer's disease (AD). The aim of the current study was to investigate mitochondrial function over frontal and temporal regions in a sample of 70 cognitively normal older adults with subjective memory complaints and a first-degree family history of AD. We hypothesized cerebral mitochondrial function and energy metabolism would be greater in temporal as compared to frontal regions based on the high energy consumption in the temporal lobes (i.e., hippocampus). To test this hypothesis, we used phosphorous (31P) magnetic resonance spectroscopy (MRS) which is a non-invasive and powerful method for investigating in vivo mitochondrial function via high energy phosphates and phospholipid metabolism ratios. We used a single voxel method (left temporal and bilateral prefrontal) to achieve optimal sensitivity. Results of separate repeated measures analyses of variance showed 31P MRS ratios of static energy, energy reserve, energy consumption, energy demand, and phospholipid membrane metabolism were greater in the left temporal than bilateral prefrontal voxels. Our findings that all 31P MRS ratios were greater in temporal than bifrontal regions support our hypothesis. Future studies are needed to determine whether findings are related to cognition in older adults.

Systematic review of 31P-magnetic resonance spectroscopy studies of brain high energy phosphates and membrane phospholipids in aging and Alzheimer's disease

Many lines of evidence suggest that mitochondria have a central role in aging-related neurodegenerative diseases, such as Alzheimer's disease (AD). Mitochondrial dysfunction, cerebral energy dysmetabolism and oxidative damage increase with age, and are early event in AD pathophysiology and may precede amyloid beta (Aβ) plaques. In vivo probes of mitochondrial function and energy metabolism are therefore crucial to characterize the bioenergetic abnormalities underlying AD risk, and their relationship to pathophysiology and cognition. A majority of the research conducted in humans have used 18F-fluoro-deoxygluose (FDG) PET to image cerebral glucose metabolism (CMRglc), but key information regarding oxidative phosphorylation (OXPHOS), the process which generates 90% of the energy for the brain, cannot be assessed with this method. Thus, there is a crucial need for imaging tools to measure mitochondrial processes and OXPHOS in vivo in the human brain. 31Phosphorus-magnetic resonance spectroscopy (31P-MRS) is a non-invasive method which allows for the measurement of OXPHOS-related high-energy phosphates (HEP), including phosphocreatine (PCr), adenosine triphosphate (ATP), and inorganic phosphate (Pi), in addition to potential of hydrogen (pH), as well as components of phospholipid metabolism, such as phosphomonoesters (PMEs) and phosphodiesters (PDEs). Herein, we provide a systematic review of the existing literature utilizing the 31P-MRS methodology during the normal aging process and in patients with mild cognitive impairment (MCI) and AD, with an additional focus on individuals at risk for AD. We discuss the strengths and limitations of the technique, in addition to considering future directions toward validating the use of 31P-MRS measures as biomarkers for the early detection of AD.

Neurodegenerative Changes in the Brains of the 5xFAD Alzheimer’s Disease Model Mice Investigated by High-Field and High-Resolution Magnetic Resonance Imaging and Multi-Nuclei Magnetic Resonance Spectroscopy

This study aimed to investigate morphological and metabolic changes in the brains of 5xFAD mice. Structural magnetic resonance imaging (MRI) and 1H magnetic resonance spectroscopy (MRS) were obtained in 10- and 14-month-old 5xFAD and wild-type (WT) mice, while 31P MRS scans were acquired in 11-month-old mice. Significantly reduced gray matter (GM) was identified by voxel-based morphometry (VBM) in the thalamus, hypothalamus, and periaqueductal gray areas of 5xFAD mice compared to WT mice. Significant reductions in N-acetyl aspartate and elevation of myo-Inositol were revealed by the quantification of MRS in the hippocampus of 5xFAD mice, compared to WT. A significant reduction in NeuN-positive cells and elevation of Iba1- and GFAP-positive cells supported this observation. The reduction in phosphomonoester and elevation of phosphodiester was observed in 11-month-old 5xFAD mice, which might imply a sign of disruption in the membrane synthesis. Commonly reported 1H MRS features were replicated in the hippocampus of 14-month-old 5xFAD mice, and a sign of disruption in the membrane synthesis and elevation of breakdown were revealed in the whole brain of 5xFAD mice by 31P MRS. GM volume reduction was identified in the thalamus, hypothalamus, and periaqueductal gray areas of 5xFAD mice.

Sex and menopause impact 31P-Magnetic Resonance Spectroscopy brain mitochondrial function in association with 11C-PiB PET amyloid-beta load

Increasing evidence implicates sex and endocrine aging effects on brain bioenergetic aging in the greater lifetime risk of Alzheimer's disease (AD) in women. We conducted 31Phosphorus Magnetic Resonance Spectroscopy (31P-MRS) to assess the impact of sex and menopause on brain high-energy phosphates [adenosine triphosphate (ATP), phosphocreatine (PCr), inorganic phosphate (Pi)] and membrane phospholipids [phosphomonoesters/phosphodiesters (PME/PDE)] in 216 midlife cognitively normal individuals at risk for AD, 80% female. Ninety-seven participants completed amyloid-beta (Aβ) 11C-PiB PET. Women exhibited higher ATP utilization than men in AD-vulnerable frontal, posterior cingulate, fusiform, medial and lateral temporal regions (p < 0.001). This profile was evident in frontal cortex at the pre-menopausal and peri-menopausal stage and extended to the other regions at the post-menopausal stage (p = 0.001). Results were significant after multi-variable adjustment for age, APOE-4 status, midlife health indicators, history of hysterectomy/oophorectomy, use of menopause hormonal therapy, and total intracranial volume. While associations between ATP/PCr and Aβ load were not significant, individuals with the highest Aβ load were post-menopausal and peri-menopausal women with ATP/PCr ratios in the higher end of the distribution. No differences in Pi/PCr, Pi/ATP or PME/PDE were detected. Outcomes are consistent with dynamic bioenergetic brain adaptations that are associated with female sex and endocrine aging.

Mitochondrial dysfunction, oxidative stress, neuroinflammation, and metabolic alterations in the progression of Alzheimer's disease: A meta-analysis of in vivo magnetic resonance spectroscopy studies

Accumulating evidence demonstrates that metabolic changes in the brain associated with neuroinflammation, oxidative stress, and mitochondrial dysfunction play an important role in the pathophysiology of mild cognitive impairment (MCI) and Alzheimer's disease (AD). However, the neural signatures associated with these metabolic alterations and underlying molecular mechanisms are still elusive. Accordingly, we reviewed the literature on in vivo human brain ¹H and ³¹P-MRS studies and use meta-analyses to identify patterns of brain metabolic alterations in MCI and AD. 40 and 39 studies on MCI and AD, respectively, were classified according to brain regions. Our results indicate decreased N-acetyl aspartate and creatine but increased myo-inositol levels in both MCI and AD, decreased glutathione level in MCI as well as disrupted energy metabolism in AD. In addition, the hippocampus shows the strongest alterations in most of these metabolites. This meta-analysis also illustrates progressive metabolite alterations from MCI to AD. Taken together, it suggests that 1) neuroinflammation and oxidative stress may occur in the early stages of AD, and likely precede neuron loss in its progression; 2) the hippocampus is a sensitive region of interest for early diagnosis and monitoring the response of interventions; 3) targeting bioenergetics associated with neuroinflammation/oxidative stress is a promising approach for treating AD.

Phosphate Brain Energy Metabolism and Cognition in Alzheimer's Disease: A Spectroscopy Study Using Whole-Brain Volume-Coil 31Phosphorus Magnetic Resonance Spectroscopy at 7Tesla

Introduction

Mitochondrial dysfunction is a neurometabolic hallmark signaling abnormal brain energy metabolism (BEM) targeted as a potential early marker of Alzheimer’s disease (AD). Advanced imaging technologies, such as ³¹phosphorus magnetic resonance spectroscopy (³¹P MRS) at ultra-high-field (UHF) magnetic strength 7T, provide sensitive phosphate-BEM (p-BEM) data with precision. The study’s first goal was to develop a methodology to measure phosphate energy and membrane metabolites simultaneously across the whole-brain using volume-coil ³¹P MRS at 7T in three groups-cognitively normal (CN), amnestic mild cognitive impairment (aMCI), and AD. The second aim investigated whether p-BEM markers in the four brain regions-frontal, temporal, parietal, and occipital were significantly different across the three groups. The final goal examined correspondence between the p-BEM markers and cognition in the three groups.

Methods

Forty-one participants (CN = 15, aMCI = 15, AD = 11) were enrolled and completed cognitive assessment and scan. The cognitive domains included executive function (EF), memory, attention, visuospatial skills, and language. The p-BEM markers were measured using energy reserve index (PCr/t-ATP), energy consumption index (intracellular_Pi/t-ATP), metabolic state indicator (intracellular_Pi/PCr), and regulatory co-factors [magnesium (Mg²⁺) and intracellular pH].

Results

Thirteen metabolites were measured simultaneously from the whole brain for all three group with high spectral resolution at UHF. In the aMCI group, a lower p-BEM was observed compared to CN group based on two markers, i.e., energy reserve (p = 0.009) and energy consumption (p = 0.05) indices; whereas in AD a significant increase was found in metabolic stress indicator (p = 0.007) and lower Mg²⁺ (p = 0.004) in the temporal lobes compared to aMCI using ANOVA between group analytical approach. Finally, using a linear mixed model, a significant positive correlation was found between Mg²⁺ and cognitive performance of memory (p = 0.013), EF (p = 0.023), and attention (p = 0.0003) in CN but not in aMCI or AD.

Conclusion

To our knowledge, this is the first study to show that it is possible to measure p-BEM in vivo with precision at UHF across the three groups. Moreover, the findings suggest that p-BEM may be compromised in aMCI even before an AD diagnosis, which in future studies should explore to examine whether this energy crisis contributes to some of the earliest neuropathophysiologic changes in AD.

Relationship of Parieto-Occipital Brain Energy Phosphate Metabolism and Cognition Using 31P MRS at 7-Tesla in Amnestic Mild Cognitive Impairment

Background

The human brain has high energy requirements that continuously support healthy neuronal activity and cognition. A disruption in brain energy metabolism (BEM) may contribute to early neuropathological changes such as accumulation of β-amyloid and tau in vulnerable populations. One such population is amnestic mild cognitive impairment (aMCI) where some individuals are at risk for developing dementia, i.e. Alzheimer’s disease (AD). Recent advances in imaging technology are providing new avenues to measure BEM accurately using 31phosphorus magnetic resonance spectroscopy (31P MRS) at ultra-high-field (UHF) magnetic strength 7-Tesla. This study investigates whether a methodology using partial volume-coil 31P MRS at 7T over parieto-occipital lobes can accurately quantify high-energy phosphate and membrane phospholipid metabolites in aMCI. A secondary objective was to explore BEM and membrane phospholipid indices’ correspondence with cognitive performance in domains of executive function (EF), memory, attention, and visuospatial skills in aMCI, a heterogeneous population.

Methods

19 aMCI participants enrolled in the study completed cognitive assessment and 31P MRS scan. BEM indices were measured using three energy indicators: energy reserve (PCr/t-ATP), energy consumption (intracellular_Pi/t-ATP), and metabolic state (PCr/intracellular_Pi) along with regulatory co-factors of BEM-intracellular Mg^{2 +} and pH; whereas the ratio of phosphomonoesters (PMEs) to phosphodiesters (PDEs) – membrane phospholipid indicator.

Results

31P MRS scan showed thirteen well-resolved peaks with precise quantification of the phosphorus metabolites at UHF. The higher BEM indices were associated with lower cognitive performance of memory [(energy reserve indicator: CVLT p = 0.004), (metabolic state indicator: CVLT p = 0.007)], executive function [(metabolic state indicator: TOSL (p = 0.044)], and attention [(pH: selective auditory task, p = 0.044)]. The finding of an inverse relationship observed in the parieto-occipital lobes suggests an association between neuronal energy markers with cognition in aMCI.

Conclusion

The significant contribution of this preliminary research was to establish the feasibility of utilizing a methodology at UHF to accurately measure high-energy phosphate and membrane phospholipid metabolites in a population with heterogeneous outcomes. This work offers a novel approach for future work to further elucidate early dementia biomarkers or precursors to the downstream accumulation of amyloid and tau using the combination of MRS-PET imaging modalities in AD.

Three plasma metabolites in elderly patients differentiate mild cognitive impairment and Alzheimer's disease: a pilot study

The metabolomic profile of patients with Alzheimer's disease (AD) and mild cognitive impairment (MCI) may suggest potential diagnostic biomarkers and provide information on the pathophysiology of dementia. Our aim was to quantify plasmatic metabolites of AD patients, MCI and controls. We investigated the metabolomic profile-using the AbsoluteIDQ®p180 assay-of 79 older adults with primary cognitive impairment (34 AD and 20 MCI) and 25 healthy elders (controls). A cluster analysis revealed that a combination C12-DC, C12 and PCaaC26:0 could differentiate the patients according to diagnostic. Future studies should combine metabolomic profiles with other biomarkers to identify diagnostic groups.

C-type lectin-like receptor 2 and zonulin are associated with mild cognitive impairment and Alzheimer's disease

OBJECTIVE

Increased permeability and changes in gut microbiota contributed to the pathogenesis of Alzheimer's disease (AD). Zonulin is a key modulator that regulates intestinal barrier function. Peripheral platelet alterations have been involved in AD pathology. C-type lectin-like receptor 2 (CLEC-2) is a receptor on the platelet surface for activation. The purpose of this study was to determine zonulin and CLEC-2 levels in mild cognitive impairment (MCI) and AD, and investigate the relationship between zonulin and CLEC-2.

METHODS

In this study, CLEC-2 and zonulin levels were measured using ELISA assay in 110 AD patients, 110 MCI patients, and 110 non-demented control subjects.

RESULTS

Increased CLEC-2 and zonulin levels were observed in MCI and AD patients. Furthermore, AD patients had higher CLEC-2 and zonulin levels compared with MCI patients. In addition, CLEC-2 levels were positively correlated with zonulin levels, after adjusting confounding factors (r = .592, P < .001). Multivariate analysis revealed that increased CLEC-2 and zonulin levels were significantly associated with reduced Mini-Mental State Examination (MMSE) score.

CONCLUSIONS

C-type lectin-like receptor 2 is correlated with zonulin after adjusting confounding covariates. Moreover, increased CLEC-2 and zonulin are the significant factors for reduced MMSE score in MCI and AD. Further studies are needed.

The validity and reliability of the CAMDEX-DS for assessing dementia in adults with Down syndrome in Brazil

Objective:

Alzheimer’s disease occurs at a higher prevalence and an earlier age in individuals with Down syndrome (DS) than typically developing individuals. However, diagnosing dementia in individuals with intellectual disability remains a challenge due to pre-existing cognitive deficits. The aim of this study was to investigate the validity and reliability of the Brazilian version of the Cambridge Examination for Mental Disorders of Older People with Down’s syndrome and Others with Intellectual Disabilities (CAMDEX-DS) for individuals with DS.

Methods:

Two psychiatrists, working independently, evaluated 92 adults with DS ≥ 30 years of age. The concurrent validity of the CAMDEX-DS was analyzed in relation to the gold standard of established international criteria. In a subgroup of 20 subjects, the concurrent validity of the CAMDEX-DS was analyzed in relation to an independent objective assessment of cognitive decline over three years. We analyzed the inter-rater reliability of cognitive assessment.

Results:

The diagnostic accuracy of the CAMDEX-DS compared to the gold standard was 96.7%. CAMDEX-DS-based diagnosis was considered consistent with cognitive decline. The probability of a participant with dementia having cognitive decline was 83%. Inter-rater reliability for the participant assessment was good, with a kappa of > 0.8 for 93% of the CAMDEX-DS items.

Conclusion:

The CAMDEX-DS can be considered the first valid and reliable instrument for evaluating dementia in adults with DS in Brazil. Its use in such individuals could improve clinical practice and research.

Altered brain high-energy phosphate metabolism in mild Alzheimer's disease: A 3-dimensional 31P MR spectroscopic imaging study

In Alzheimer's disease (AD), defects in essential metabolic processes for energy supply and phospholipid membrane function have been implicated in the pathological process. However, post-mortem investigations are generally limited to late stage disease and prone to tissue decay artifacts. In vivo assessments of high energy phosphates, tissue pH and phospholipid metabolites are possible by phosphorus MR spectroscopy (³¹P–MRS), but so far only small studies, mostly focusing on single brain regions, have been performed. Therefore, we assessed phospholipid and energy metabolism in multiple brain regions of 31 early stage AD patients and 31 age- and gender-matched controls using ³¹P–MRS imaging. An increase of phosphocreatine (PCr) was found in AD patients compared with controls in the retrosplenial cortex, and both hippocampi, but not in the anterior cingulate cortex. While PCr/inorganic phosphate and pH were also increased in AD, no changes were found for phospholipid metabolites. This study showed that PCr levels are specifically increased in regions that show early degeneration in AD. Together with an increased pH, this indicates an altered energy metabolism in mild AD.

•

Phosphocreatine and pH are increased in mild Alzheimer's disease.

•

Phosphocreatine increase occurs in early affected brain regions.

•

Brain energy metabolism may be altered in mild Alzheimer's disease.

•

Phospholipid and energy metabolites as well as pH, differ across brain regions.

The medical food Souvenaid affects brain phospholipid metabolism in mild Alzheimer's disease: results from a randomized controlled trial

Background

Synaptic dysfunction contributes to cognitive impairment in Alzheimer’s disease and may be countered by increased intake of nutrients that target brain phospholipid metabolism. In this study, we explored whether the medical food Souvenaid affects brain phospholipid metabolism in patients with Alzheimer’s disease.

Methods

Thirty-four drug-naive patients with mild Alzheimer’s disease (Mini Mental State Examination score ≥20) were enrolled in this exploratory, double-blind, randomized controlled study. Before and after 4-week intervention with Souvenaid or an isocaloric control product, phosphorus and proton magnetic resonance spectroscopy (MRS) was performed to assess surrogate measures of phospholipid synthesis and breakdown (phosphomonoesters [PME] and phosphodiesters [PDEs]), neural integrity (N-acetyl aspartate), gliosis (myo-inositol), and choline metabolism (choline-containing compounds [tCho]). The main outcome parameters were PME and PDE signal intensities and the PME/PDE ratio.

Results

MRS data from 33 patients (60–86 years old; 42% males; Souvenaid arm n = 16; control arm n = 17) were analyzed. PME/PDE and tCho were higher after 4 weeks of Souvenaid compared with control (PME/PDE least squares [LS] mean difference [95% CI] 0.18 [0.06–0.30], p = 0.005; tCho LS mean difference [95% CI] 0.01 [0.00–0.02], p = 0.019). No significant differences were observed in the other MRS outcome parameters.

Conclusions

MRS reveals that Souvenaid affects brain phospholipid metabolism in mild Alzheimer’s disease, in line with findings in preclinical studies.

Trial registration

Netherlands Trial Register, NTR3346. Registered on 13 March 2012.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0286-2) contains supplementary material, which is available to authorized users.

Clinical applications at ultrahigh field (7 T). Where does it make the difference?

Presently, three major MR vendors provide commercial 7-T units for clinical research under ethical permission, with the number of operating 7-T systems having increased to over 50. This rapid increase indicates the growing interest in ultrahigh-field MRI because of improved clinical results with regard to morphological as well as functional and metabolic capabilities. As the signal-to-noise ratio scales linearly with the field strength (B0 ) of the scanner, the most obvious application at 7 T is to obtain higher spatial resolution in the brain, musculoskeletal system and breast. Of specific clinical interest for neuro-applications is the cerebral cortex at 7 T, for the detection of changes in cortical structure as a sign of early dementia, as well as for the visualization of cortical microinfarcts and cortical plaques in multiple sclerosis. In the imaging of the hippocampus, even subfields of the internal hippocampal anatomy and pathology can be visualized with excellent resolution. The dynamic and static blood oxygenation level-dependent contrast increases linearly with the field strength, which significantly improves the pre-surgical evaluation of eloquent areas before tumor removal. Using susceptibility-weighted imaging, the plaque-vessel relationship and iron accumulation in multiple sclerosis can be visualized for the first time. Multi-nuclear clinical applications, such as sodium imaging for the evaluation of repair tissue quality after cartilage transplantation and (31) P spectroscopy for the differentiation between non-alcoholic benign liver disease and potentially progressive steatohepatitis, are only possible at ultrahigh fields. Although neuro- and musculoskeletal imaging have already demonstrated the clinical superiority of ultrahigh fields, whole-body clinical applications at 7 T are still limited, mainly because of the lack of suitable coils. The purpose of this article was therefore to review the clinical studies that have been performed thus far at 7 T, compared with 3 T, as well as those studies performed at 7 T that cannot be routinely performed at 3 T. Copyright © 2015 John Wiley & Sons, Ltd.

Whole-body radiofrequency coil for (31) P MRSI at 7 T

Widespread use of ultrahigh-field (31) P MRSI in clinical studies is hindered by the limited field of view and non-uniform radiofrequency (RF) field obtained from surface transceivers. The non-uniform RF field necessitates the use of high specific absorption rate (SAR)-demanding adiabatic RF pulses, limiting the signal-to-noise ratio (SNR) per unit of time. Here, we demonstrate the feasibility of using a body-sized volume RF coil at 7 T, which enables uniform excitation and ultrafast power calibration by pick-up probes. The performance of the body coil is examined by bench tests, and phantom and in vivo measurements in a 7-T MRI scanner. The accuracy of power calibration with pick-up probes is analyzed at a clinical 3-T MR system with a close to identical (1) H body coil integrated at the MR system. Finally, we demonstrate high-quality three-dimensional (31) P MRSI of the human body at 7 T within 5 min of data acquisition that includes RF power calibration. Copyright © 2016 John Wiley & Sons, Ltd.

Increased iPLA2 activity and levels of phosphorylated GSK3B in platelets are associated with donepezil treatment in Alzheimer's disease patients

Reduced phospholipase A2 (PLA2) activity and increased phosphorylation of glycogen synthase kinase 3B (GSK3B) participate in the production of beta-amyloid plaques and of neurofibrillary tangles, which are two neuropathological hallmarks of Alzheimer's disease (AD). Experimental evidences suggest a neuroprotective effect of the cholinesterase inhibitor donepezil in the treatment the disease. The aims of the present study were to evaluate in AD patients the effects of treatment with donepezil on PLA2 activity and GSK3B level. Thirty patients with AD were treated during 6 months with 10 mg daily of donepezil. Radio-enzymatic assays were used to measure PLA2 activity and Elisa assays for GSK3B level, both in platelets. Before treatment and after 3 and 6 months on donepezil, AD patients underwent a cognitive assessment and platelet samples were collected. Values were compared to a healthy control group of 42 sex- and age-matched elderly individuals. Before treatment, iPLA2 activity was lower in patients with AD as compared to controls (p < 0.001). At baseline, no differences were found in GSK3B level between both groups. After 3 and 6 months of treatment, we found a significant increase in iPLA2 activity (p = 0.015 and p < 0.001, respectively). iPLA2 increment was related to the cognitive improvement during treatment (p = 0.037). After 6 months, we found an increase in phosphorylated GSK3B (p = 0.02). The present findings suggest two possible mechanisms by which donepezil delays the progression of AD. The increment of iPLA2 activity may reduce the production of beta-amyloid plaques, whereas the phosphorylation of GSK3B inactivates the enzyme, reducing thus the phosphorylation of tau protein.

Platelets, a reliable source for peripheral Alzheimer's disease biomarkers?

Peripheral biomarkers play an indispensable role in quick and reliable diagnoses of any kind of disease. With the population ageing, the number of people suffering from age-related diseases is expected to rise dramatically over the coming decades. In particular, all types of cognitive deficits, such as Alzheimer's disease, will increase. Alzheimer's disease is characterised mainly by coexistence of amyloid plaques and neurofibrillary tangles in brain. Reliable identification of such molecular characteristics antemortem, however, is problematic due to restricted availability of appropriate sample material and definitive diagnosis is only possible postmortem. Currently, the best molecular biomarkers available for antemortem diagnosis originate from cerebrospinal fluid. Though, this is not convenient for routine diagnosis because of the required invasive lumbar puncture. As a consequence, there is a growing demand for additional peripheral biomarkers in a more readily accessible sample material. Blood platelets, due to shared biochemical properties with neurons, can constitute an attractive alternative as discussed here. This review summarises potential platelet Alzheimer's disease biomarkers, their role, implication, and alteration in the disease. For easy comparison of their performance, the Hedge effect size was calculated whenever data were available.

Flip-angle mapping of 31P coils by steady-state MR spectroscopic imaging

PURPOSE

Phosphorus ((31)P) MR spectroscopic imaging (MRSI) is primarily applied with sensitive, surface radiofrequency (RF) coils that provide inhomogeneous excitation RF field (B1(+)) and rough localization due to their B1(+) and sensitivity (B1(-)) profiles. A careful and time-consuming pulse adjustment and an accurate knowledge of flip angle (FA) are mandatory for quantification corrections.

MATERIALS AND METHODS

In this study, a simple, fast, and universal (31)P B1(+) mapping method is proposed, which requires fast steady-state MRSI (typically one sixth of normal measurement time) in addition to the typical MRSI acquired within the examination protocol. The FA maps are calculated from the ratio of the signal intensities acquired by these two measurements and were used to correct for the influence of B1(+) on the metabolite maps.

RESULTS

In vitro tests were performed on two scanners (3 and 7 Tesla) using a surface and a volume coil. The calculated FA maps were in good agreement with adjusted nominal FAs and the theoretical calculation using the Biot-Savart law. The method was successfully tested in vivo in the calf muscle and the brain of healthy volunteers (n = 4). The corrected metabolite maps show higher homogeneity compared with their noncorrected versions.

CONCLUSION

The calculated FA maps helped with B1(+) inhomogeneity corrections of acquired in vivo data, and should also be useful with optimization and testing of pulse performances, or with the construction quality tests of new dual-channel (1)H/(31)P coils.

Mean platelet volume and platelet distribution width in vascular dementia and Alzheimer's disease

Activated platelets play a substantial role in Alzheimer's disease (AD) and atherothrombosis. Mean platelet volume (MPV) is an early marker of platelet activation, which is linked to a variety of pro-thrombotic and pro-inflammatory diseases. This study is to examine the association between platelet indices and vascular dementia (VaD) and AD. In this cross-sectional study, we investigated the levels of platelet count, MPV, and platelet distribution width (PDW) in 150 VaD patients, 110 AD patients, and 150 non-demented controls. MPV and PDW were significantly lower in patients with VaD and AD as compared with controls. The decrease in PDW for AD patients as compared with VaD patients was also significant (p < 0.001). In addition, there was a positive correlation between Mini-Mental State Examination (MMSE) and MPV and PDW, after adjusting confounding factors (r = 0.532 for MPV and r = 0.425 for PDW, p < 0.001 for both). Multivariate regression analysis showed that MPV and PDW were significantly associated with MMSE (β = 0.366 for MPV and β = 0.273 for PDW, p < 0.001 for both). In conclusion, MPV and PDW were both decreased in VaD and AD. PDW levels were significantly lower in AD as compared to those in VaD. Our findings suggest that PDW in combination with MMSE scores could be potential indicators for distinguishing VaD from AD.

Decreased mean platelet volume and platelet distribution width are associated with mild cognitive impairment and Alzheimer's disease

Neuroinflammation is a critical driving force underlying mild cognitive impairment (MCI) and Alzheimer's disease (AD) pathologies. Activated platelets play an important role in neuroinflammation and have been implicated in AD pathogenic mechanisms. Mean platelet volume (MPV), a marker of platelet activation, is involved in the pathophysiology of a variety of pro-inflammatory diseases. However, little research has been conducted to investigate the relationship between platelet indices and MCI and AD pathogenesis. In this cross-sectional study, we investigated the levels of platelet count, MPV and platelet distribution width (PDW) in 120 AD patients, 120 MCI patients, and 120 non-demented controls. Our study showed that MPV and PDW were significantly lower in patients with AD as compared with either MCI or controls. Moreover, MCI patients had lower MPV and PDW values compared with the controls (P < 0.001). In addition, there is a positive correlation between mini-mental state examination (MMSE) and MPV and PDW, after adjusting age, gender, and body mass index (r = 0.576, P < 0.001 for MPV; r = 0.465, P < 0.001 for PDW, respectively). Multivariate analysis showed that MPV and PDW were significantly associated with MMSE (β = 0.462; P < 0.001 for MPV; β = 0.245; P < 0.001 for PDW; respectively). In conclusion, MPV and PDW were decreased in MCI and AD patients. Further prospective research is warranted to determine the potential clinical application of MPV and PDW as biomarkers in the early diagnosis of AD.

Platelet biomarkers in Alzheimer’s disease

The search for diagnostic and prognostic markers in Alzheimer’s disease (AD) has been an area of active research in the last decades. Biochemical markers are correlates of intracerebral changes that can be identified in biological fluids, namely: peripheral blood (total blood, red and white blood cells, platelets, plasma and serum), saliva, urine and cerebrospinal fluid. An important feature of a biomarker is that it can be measured objectively and evaluated as (1) an indicator of disease mechanisms (markers of core pathogenic processes or the expression of downstream effects of these processes), or (2) biochemical responses to pharmacological or therapeutic intervention, which can be indicative of disease modification. Platelets have been used in neuropharmacological models since the mid-fifties, as they share several homeostatic functions with neurons, such as accumulation and release of neurotransmitters, responsiveness to variations in calcium concentration, and expression of membrane-bound compounds. Recent studies have shown that platelets also express several components related to the pathogenesis of AD, in particular to the amyloid cascade and the regulation of oxidative stress: thus they can be used in the search for biomarkers of the disease process. For instance, platelets are the most important source of circulating forms of the amyloid precursor protein and other important proteins such as Tau and glycogen synthase kinase-3B. Moreover, platelets express enzymes involved in membrane homeostasis (e.g., phospholipase A₂), and markers of the inflammatory process and oxidative stress. In this review we summarize the available literature and discuss evidence concerning the potential use of platelet markers in AD.

Fully adiabatic 31P 2D-CSI with reduced chemical shift displacement error at 7 T--GOIA-1D-ISIS/2D-CSI

A fully adiabatic phosphorus (31P) two-dimensional (2D) chemical shift spectroscopic imaging sequence with reduced chemical shift displacement error for 7 T, based on 1D-image-selected in vivo spectroscopy, combined with 2D-chemical shift spectroscopic imaging selection, was developed. Slice-selective excitation was achieved by a spatially selective broadband GOIA-W(16,4) inversion pulse with an interleaved subtraction scheme before nonselective adiabatic excitation, and followed by 2D phase encoding. The use of GOIA-W(16,4) pulses (bandwidth 4.3-21.6 kHz for 10-50 mm slices) reduced the chemical shift displacement error in the slice direction ∼1.5-7.7 fold, compared to conventional 2D-chemical shift spectroscopic imaging with Sinc3 selective pulses (2.8 kHz). This reduction was experimentally demonstrated with measurements of an MR spectroscopy localization phantom and with experimental evaluation of pulse profiles. In vivo experiments in clinically acceptable measurement times were demonstrated in the calf muscle (nominal voxel volume, 5.65 ml in 6 min 53 s), brain (10 ml, 6 min 32 s), and liver (8.33 ml, 8 min 14 s) of healthy volunteers at 7 T. High reproducibility was found in the calf muscle at 7 T. In combination with adiabatic excitation, this sequence is insensitive to the B1 inhomogeneities associated with surface coils. This sequence, which is termed GOIA-1D-ISIS/2D-CSI (goISICS), has the potential to be applied in both clinical research and in the clinical routine.

Inhibition of phospholipase A₂ in rat brain modifies different membrane fluidity parameters in opposite ways

Fluidity is an important neuronal membrane property and it is influenced by the concentration of polyunsaturated fatty acids (PUFAs) in membrane phospholipids. Phospholipase A(2) (PLA(2)) is a key enzyme in membrane phospholipid metabolism, generating free PUFAs. In Alzheimer disease (AD), reduced PLA(2) activity, specifically of calcium-dependent cytosolic PLA(2) (cPLA(2)) and calcium-independent intracellular PLA(2) (iPLA(2)), and phospholipid metabolism was reported in the frontal cortex and hippocampus. This study investigated the effects of in vivo infusion of the dual cPLA(2) and iPLA(2) inhibitor MAFP into rat brain on PLA(2) activity and membrane fluidity parameters in the postmortem frontal cortex and dorsal hippocampus. PLA(2) activity was measured by radioenzymatic assay and membrane fluidity was determined by fluorescence anisotropy technique using three different probes: DPH, TMA-DPH, and pyrene. MAFP significantly inhibited PLA(2) activity, reduced the flexibility of fatty acyl chains (indicated by increased DPH anisotropy), increased the fluidity in the lipid-water interface (indicated by decreased TMA-DPH anisotropy), and increased the lipid lateral diffusion in the hydrocarbon core (represented by pyrene excimer formation) of membranes in both brain areas. The findings suggest that reduced cPLA(2) and iPLA(2) activities in AD brain might contribute to the cognitive impairment, in part, through alterations in membrane fluidity parameters.

A new experimental approach and signal processing scheme for the detection and quantitation of ³¹P brain neurochemicals from in vivo MRS studies using dual tuned (¹H/³¹P) head coil

Brain (31)P-neurometabolites play an important role in energy and membrane metabolism. Unambiguous identification and quantification of these neurochemicals in different brain regions would be a great aid in advancing the understanding of metabolic processes in the nervous system. Phosphomonoester (PME), consisting of phosphoethanolamine (PE) and phosphocholine (PC), is the "building block" for membranes, while phosphodiesters (PDE), consisting of glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE) metabolites are involved in the membrane breakdown process. In the clinical setting, generating well-resolved spectra for PC, PE, GPC, and GPE could be crucial phospholipids in providing information regarding membrane metabolism. We present here a new experimental approach for generating well-resolved (31)P spectra for PC and PE as well as for GPC, GPE, and other (31)P metabolites. Our results (based on uni-dimensional (1D) and multi-voxel (31)P studies) indicate that an intermediate excitation pulse angle (35°) is best suited to obtain well-resolved PC/PE and GPC/GPE resonance peaks. Our novel signal processing scheme allows generating metabolite maps of different phospholipids include PC/PE and GPC/GPE using the 'time-domain-frequency-domain' method as referred to in the MATLAB programming language.

Increased platelet GSK3B activity in patients with mild cognitive impairment and Alzheimer's disease

The disruption of glycogen synthase kinase 3-beta (GSK3B) homeostasis has implications in the pathophysiology of neuropsychiatric disorders, namely Alzheimer's disease (AD). GSK3B activity is increased within the AD brain, favoring the hyperphosphorylation of microtubule-associated protein Tau and the formation of neurofibrillary tangles. Such abnormality has also been detected in leukocytes of patients with cognitive disorders. The aim of the present study was to determine the expression of total and phosphorylated GSK3B at protein level in platelets of older adults with varying degrees of cognitive impairment, and to compare GSK3B activity in patients with AD, mild cognitive impairment (MCI) and healthy controls. Sixty-nine older adults were included (24 patients with mild to moderate AD, 22 patients with amnestic MCI and 23 elderly controls). The expression of platelet GSK3B (total- and Ser-9 phosphorylated GSK3B) was determined by Western blot. GSK3B activity was indirectly assessed by means of the proportion between phospho-GSK3B to total GSK3B (GSK3B ratio), the former representing the inactive form of the enzyme. Ser-9 phosphorylated GSK3B was significantly reduced in patients with MCI and AD as compared to controls (p=0.04). Platelet GSK3B ratio was significantly decreased in patients with MCI and AD (p=0.04), and positively correlated with scores on memory tests (r=0.298, p=0.01). In conclusion, we corroborate previous evidence of increased GSK activity in peripheral tissues of patients with MCI and AD, and further propose that platelet GSK may be an alternative peripheral biomarker of this abnormality, provided samples are adequately handled in order to preclude platelet activation.

Differential roles of phospholipases A2 in neuronal death and neurogenesis: implications for Alzheimer disease

The involvement of phospholipase A(2) (PLA(2)) in Alzheimer disease (AD) was first investigated nearly 15 years ago. Over the years, several PLA(2) isoforms have been detected in brain tissue: calcium-dependent secreted PLA(2) or sPLA(2) (IIA, IIC, IIE, V, X, and XII), calcium-dependent cytosolic PLA(2) or cPLA(2) (IVA, IVB, and IVC), and calcium-independent PLA(2) or iPLA(2) (VIA and VIB). Additionally, numerous in vivo and in vitro studies have suggested the role of different brain PLA(2) in both physiological and pathological events. This review aimed to summarize the findings in the literature relating the different brain PLA(2) isoforms with alterations found in AD, such as neuronal cell death and impaired neurogenesis process. The review showed that sPLA(2)-IIA, sPLA(2)-V and cPLA(2)-IVA are involved in neuronal death, whereas sPLA(2)-III and sPLA(2)-X are related to the process of neurogenesis, and that the cPLA(2) and iPLA(2) groups can be involved in both neuronal death and neurogenesis. In AD, there are reports of reduced activity of the cPLA(2) and iPLA(2) groups and increased expression of sPLA(2)-IIA and cPLA(2)-IVA. The findings suggest that the inhibition of cPLA(2) and iPLA(2) isoforms (yet to be determined) might contribute to impaired neurogenesis, whereas stimulation of sPLA(2)-IIA and cPLA(2)-IVA might contribute to neurodegeneration in AD.

Phospholipase A2 activation as a therapeutic approach for cognitive enhancement in early-stage Alzheimer disease

RATIONALE

Alzheimer disease (AD) is the leading cause of dementia in the elderly and has no known cure. Evidence suggests that reduced activity of specific subtypes of intracellular phospholipases A2 (cPLA2 and iPLA2) is an early event in AD and may contribute to memory impairment and neuropathology in the disease.

OBJECTIVE

The objective of this study was to review the literature focusing on the therapeutic role of PLA2 stimulation by cognitive training and positive modulators, or of supplementation with arachidonic acid (PLA2 product) in facilitating memory function and synaptic transmission and plasticity in either research animals or human subjects.

METHODS

MEDLINE database was searched (no date restrictions) for published articles using the keywords Alzheimer disease (mild, moderate, severe), mild cognitive impairment, healthy elderly, rats, mice, phospholipase A(2), phospholipid metabolism, phosphatidylcholine, arachidonic acid, cognitive training, learning, memory, long-term potentiation, protein kinases, dietary lipid compounds, cell proliferation, neurogenesis, and neuritogenesis. Reference lists of the identified articles were checked to select additional studies of interest.

RESULTS

Overall, the data suggest that PLA2 activation is induced in the healthy brain during learning and memory. Furthermore, learning seems to regulate endogenous neurogenesis, which has been observed in AD brains. Finally, PLA2 appears to be implicated in homeostatic processes related to neurite outgrowth and differentiation in both neurodevelopmental processes and response to neuronal injury.

CONCLUSION

The use of positive modulators of PLA2 (especially of cPLA2 and iPLA2) or supplementation with dietary lipid compounds (e.g., arachidonic acid) in combination with cognitive training could be a valuable therapeutic strategy for cognitive enhancement in early-stage AD.

Cholinergic and glutamatergic alterations beginning at the early stages of Alzheimer disease: participation of the phospholipase A2 enzyme

RATIONALE

Alzheimer disease (AD), a progressive neurodegenerative disorder, is the leading cause of dementia in the elderly. A combination of cholinergic and glutamatergic dysfunction appears to underlie the symptomatology of AD, and thus, treatment strategies should address impairments in both systems. Evidence suggests the involvement of phospholipase A(2) (PLA(2)) enzyme in memory impairment and neurodegeneration in AD via actions on both cholinergic and glutamatergic systems.

OBJECTIVES

To review cholinergic and glutamatergic alterations underlying cognitive impairment and neuropathology in AD and attempt to link PLA(2) with such alterations.

METHODS

Medline databases were searched (no date restrictions) for published articles with links among the terms Alzheimer disease (mild, moderate, severe), mild cognitive impairment, choline acetyltransferase, acetylcholinesterase, NGF, NGF receptor, muscarinic receptor, nicotinic receptor, NMDA, AMPA, metabotropic glutamate receptor, atrophy, glucose metabolism, phospholipid metabolism, sphingolipid, membrane fluidity, phospholipase A(2), arachidonic acid, attention, memory, long-term potentiation, beta-amyloid, tau, inflammation, and reactive species. Reference lists of the identified articles were checked to identify additional studies of interest.

RESULTS

Overall, results suggest the hypothesis that persistent inhibition of cPLA(2) and iPLA(2) isoforms at early stages of AD may play a central role in memory deficits and beta-amyloid production through down-regulation of cholinergic and glutamate receptors. As the disease progresses, beta-amyloid induced up-regulation of cPLA(2) and sPLA(2) isoforms may play critical roles in inflammation and oxidative stress, thus participating in the neurodegenerative process.

CONCLUSION

Activation and inhibition of specific PLA(2) isoforms at different stages of AD could be of therapeutic importance and delay cognitive dysfunction and neurodegeneration.

Cognitive training increases platelet PLA2 activity in healthy elderly subjects

Phospholipases A(2) (PLA(2)) are ubiquitous enzymes involved in membrane fatty acid metabolism and intracellular signalling. Recent studies have shown that PLA(2) subtypes are implicated in the modulation of pathways related to memory acquisition and retrieval. We investigated the effects of cognitive training on platelet PLA(2) activity in healthy elderly individuals. Twenty-three cognitively unimpaired older adults were randomly assigned to receive memory training or standard outpatient care only. Both groups were cognitively assessed by the same protocol, and the experimental group (EG) underwent a four-session memory training intervention. Pre- and post-test measures included prose and list recall, WAIS-III digit symbol, strategy use measures and platelet PLA(2) group activity. After cognitive training, patients in the EG group had significant increase in cytosolic, calcium-dependent PLA(2) (cPLA(2)), extracellular (or secreted), calcium-dependent PLA(2) (sPLA(2)), total platelet PLA(2) activity, and significant decrease in platelet calcium-independent PLA(2) (iPLA(2)) activity. Our results suggest that memory training may have a modulating effect in PLA(2)-mediated biological systems associated with cognitive functions and neurodegenerative diseases.

MR spectroscopy in neurodegenerative disease

Unlike traditional, tracer-based methods of molecular imaging, magnetic resonance spectroscopy (MRS) is based on the behavior of specific nuclei within a magnetic field and the general principle that the resonant frequency depends on the nucleus' immediate chemical environment. Most clinical MRS research has concentrated on the metabolites visible with proton spectroscopy and measured in specified tissue volumes in the brain. This methodology has been applied in various neurodegenerative disorders, most frequently utilizing measures of N-acetylaspartate as a neuronal marker. At short echo times, additional compounds can be quantified, including myo-inositol, a putative marker for neuroglia, the excitatory neurotransmitter glutamate and its metabolic counterpart glutamine, and the inhibitory neurotransmitter gamma-aminobutyric acid. 31P-MRS can be used to study high-energy phosphate metabolites, providing an in vivo assessment of tissue bioenergetic status. This review discusses the application of these techniques to patients with neurodegenerative disorders, including Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis.

Inhibition of phospholipase A2 reduces neurite outgrowth and neuronal viability

Phospholipase A2 (PLA(2)) has been implicated in neurodevelopmental processes and in the early development of the nervous system. We investigated the effects of the inhibition of calcium-dependent and calcium-independent subtypes of cytosolic PLA2 (cPLA2 and iPLA2) on the development and viability of primary cultures of cortical and hippocampal neurons. PLA2 in these cultures was continuously inhibited with methylarachidonyl-fluorophosphonate (MAFP), an irreversible inhibitor of cPLA2 and iPLA2, or with bromoenol lactone (BEL), an irreversible selective iPLA2 inhibitor. The effect of PLA2 inhibitors on the development of neuronal cultures was ascertained by total cell count and morphological characterisation. Neuronal viability was quantified with MTT assays. Inhibition of PLA2 resulted in reduction of neuritogenesis and neuronal viability, disrupting neuronal homeostasis and leading to neuronal death. We conclude that the functional integrity of both calcium-dependent and calcium-independent cytosolic PLA2 is necessary for the in vitro development of cortical and hippocampal neurons.

The role of phospholipase A2 in neuronal homeostasis and memory formation: implications for the pathogenesis of Alzheimer's disease

Phospholipase A(2) (PLA(2)) is a key enzyme in cerebral phospholipid metabolism. Preliminary post-mortem studies have shown that PLA(2) activity is decreased in frontal and parietal areas of the AD brain, which is in accordance with recent (31)P-Magnetic Resonance Spectroscopy evidence of reduced phospholipid turnover in the pre-frontal cortex of moderately demented AD patients. Such abnormality may also be observed in peripheral cells, and reduced PLA(2) activity in platelet membranes of AD patients, and correlates with the severity of dementia. In rat hippocampal slices, PLA(2) has been implicated in mechanisms of synaptic plasticity. In adult rats, the stereotaxic injection of PLA(2) inhibitors in the CA1 area of hippocampus impaired, in a dose-dependent manner, the formation of short- and long-term memory. Additionally, such inhibition resulted in a reduction of the fluidity of hippocampal membranes. In primary cultures of cortical and hippocampal neurons, the inhibition of PLA(2) precluded neurite outgrowth, and the sustained inhibition of the enzyme in mature cultures lead to loss of viability. Taken together, these findings reinforce the involvement of PLA(2) enzymes in neurodevelopment and neurodegeneration processes, and further suggest that reduced PLA(2) activity, probably reducing membrane phospholipids breakdown, may contribute to the memory impairment in AD.