[18F]FDG PET signal is driven by astroglial glutamate transport

Common and divergent pathways in early stages of glutamate and tau-mediated toxicities in neurodegeneration

It has been shown that excitotoxicity and tau-mediated toxicities are major contributing factors to neuronal death in Alzheimer's disease (AD). The excitatory amino acid transporter 2 (EAAT2 or GLT-1), the major glutamate transporter in the brain that regulates glutamate levels synaptically and extrasynaptically, has been shown to be deficient in AD brains, leading to excitotoxicity and subsequent cell death. Similarly, buildup of neurofibrillary tangles, which consist of hyperphosphorylated tau protein, correlates with cognitive decline and neuronal atrophy in AD. However, common genes and pathways that are critical in the aforementioned toxicities have not been well elucidated. To investigate the impact of glutamate dyshomeostasis and tau accumulation on translational profiles of affected hippocampal neurons, we used mouse models of excitotoxicity and tau-mediated toxicities (GLT-1-/- and P301S, respectively) in conjunction with BAC-TRAP technology. Our data show that GLT-1 deficiency in CA3 pyramidal neurons leads to translational signatures characterized by dysregulation of pathways associated with synaptic plasticity and neuronal survival, while the P301S mutation induces changes in endocytic pathways and mitochondrial dysfunction. Finally, the commonly dysregulated pathways include impaired ion homeostasis and metabolic pathways. These common pathways may shed light on potential therapeutic targets for ameliorating glutamate and tau-mediated toxicities in AD.

Long Coronavirus Disease and the Brain: Molecular Neuroimaging Insights into Neurologic and Psychiatric Sequelae

The coronavirus disease 2019 (COVID-19) pandemic has led to a variety of health challenges, with "long COVID" emerging as a widespread and debilitating post-acute syndrome among a considerable number of infected patients. This PET review synthesizes current evidence of the neurologic and psychiatric sequelae of COVID. This review also explores the pathophysiological mechanisms of these results, including astrocyte dysfunction and glutamate dysregulation, as well as the multimodal comparison to MR imaging findings. The findings underscore the potential for long-term brain injury. Additionally, the authors discuss the role of advanced imaging multimodal techniques in diagnosing, monitoring, and guiding treatment strategies for long COVID.

Role of glia in delirium: proposed mechanisms and translational implications

Delirium is a common acute onset neurological syndrome characterised by transient fluctuations in cognition. It affects over 20% of medical inpatients and 50% of those critically ill. Delirium is associated with morbidity and mortality, causes distress to patients and carers, and has significant socioeconomic costs in ageing populations. Despite its clinical significance, the pathophysiology of delirium is understudied, and many underlying cellular mechanisms remain unknown. There are currently no effective pharmacological treatments which directly target underlying disease processes. Although many studies focus on neuronal dysfunction in delirium, glial cells, primarily astrocytes, microglia, and oligodendrocytes, and their associated systems, are increasingly implicated in delirium pathophysiology. In this review, we discuss current evidence which implicates glial cells in delirium, including biomarker studies, post-mortem tissue analyses and pre-clinical models. In particular, we focus on how astrocyte pathology, including aberrant brain energy metabolism and glymphatic dysfunction, reactive microglia, blood-brain barrier impairment, and white matter changes may contribute to the pathogenesis of delirium. We also outline limitations in this body of work and the unique challenges faced in identifying causative mechanisms in delirium. Finally, we discuss how established neuroimaging and single-cell techniques may provide further mechanistic insight at pre-clinical and clinical levels.

Impaired brain glucose metabolism as a biomarker for evaluation of dodecyl creatine ester in creatine transporter deficiency: Insights from patient brain-derived organoids and in vivo [18F]FDG PET imaging in a mouse model

Creatine transporter deficiency (CTD) is an inborn error of creatine (Cr) metabolism in which Cr is not properly distributed to the brain due to a mutation in the Cr transporter (CrT) SLC6A8 gene. CTD is associated with developmental delays and with neurological disability in children. Dodecyl creatine ester (DCE), as a Cr prodrug, is a promising drug to treat CTD after administration by the nasal route, taking advantage of the nose-to-brain pathway. In this study, the potential adaptive response to energy imbalance in glucose metabolism was investigated in CTD using both SLC6A8-deficient mice (CrT KO) and brain organoids derived from CTD patient cells. Longitudinal brain [18F]FDG PET imaging in CrT KO mice compared to wild-type mice demonstrated that CTD was associated with a significant loss and decline in brain glucose metabolism. In CrT KO mice, intranasal supplementation with DCE for a month significantly mitigated the decline in brain glucose metabolism compared to untreated (vehicle) animals. Mechanistic investigations in CrT KO mice and cerebral organoids derived from CTD patient cells suggest that intracellular trafficking of glucose transporter (Glut) may be altered by lack of activation of AMP-activated protein kinase (AMPK). Consistency between observations in the CrT KO mouse model and cerebral organoids derived from CTD patient cells supports the value of this new model for drug discovery and development. In addition, these results suggest that [18F]FDG PET imaging may offer a unique and minimally-invasive biomarker to monitor the impact of investigational treatment on CTD pathophysiology, with translational perspectives.

SNMMI Procedure Standard/EANM Practice Guideline for Brain [18F]FDG PET Imaging, Version 2.0

PREAMBLEThe Society of Nuclear Medicine and Molecular Imaging (SNMMI) is an international scientific and professional organization founded in 1954 to promote the science, technology, and practical application of nuclear medicine. The European Association of Nuclear Medicine (EANM) is a professional nonprofit medical association that facilitates communication worldwide between individuals pursuing clinical and research excellence in nuclear medicine. The EANM was founded in 1985. The EANM was founded in 1985. SNMMI and EANM members are physicians, technologists, and scientists specializing in the research and practice of nuclear medicine.The SNMMI and EANM will periodically define new guidelines for nuclear medicine practice to help advance the science of nuclear medicine and to improve the quality of service to patients throughout the world. Existing practice guidelines will be reviewed for revision or renewal, as appropriate, on their fifth anniversary or sooner, if indicated.Each practice guideline, representing a policy statement by the SNMMI/EANM, has undergone a thorough consensus process in which it has been subjected to extensive review. The SNMMI and EANM recognize that the safe and effective use of diagnostic nuclear medicine imaging requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guideline by those entities not providing these services is not authorized.These guidelines are an educational tool designed to assist practitioners in providing appropriate care for patients. They are not inflexible rules or requirements of practice and are not intended, nor should they be used, to establish a legal standard of care. For these reasons and those set forth below, both the SNMMI and the EANM caution against the use of these guidelines in litigation in which the clinical decisions of a practitioner are called into question.The ultimate judgment regarding the propriety of any specific procedure or course of action must be made by the physician or medical physicist in light of all the circumstances presented. Thus, there is no implication that an approach differing from the guidelines, standing alone, is below the standard of care. To the contrary, a conscientious practitioner may responsibly adopt a course of action different from that set forth in the guidelines when, in the reasonable judgment of the practitioner, such course of action is indicated by the condition of the patient, limitations of available resources, or advances in knowledge or technology subsequent to publication of the guidelines.The practice of medicine includes both the art and the science of the prevention, diagnosis, alleviation, and treatment of disease. The variety and complexity of human conditions make it impossible to always reach the most appropriate diagnosis or to predict with certainty a particular response to treatment.Therefore, it should be recognized that adherence to these guidelines will not ensure an accurate diagnosis or a successful outcome. All that should be expected is that the practitioner will follow a reasonable course of action based on current knowledge, available resources, and the needs of the patient to deliver effective and safe medical care. The sole purpose of these guidelines is to assist practitioners in achieving this objective.

Brain Metabolism in Health and Neurodegeneration: The Interplay Among Neurons and Astrocytes

The regulation of energy in the brain has garnered substantial attention in recent years due to its significant implications in various disorders and aging. The brain's energy metabolism is a dynamic and tightly regulated network that balances energy demand and supply by engaging complementary molecular pathways. The crosstalk among these pathways enables the system to switch its preferred fuel source based on substrate availability, activity levels, and cell state-related factors such as redox balance. Brain energy production relies on multi-cellular cooperation and is continuously supplied by fuel from the blood due to limited internal energy stores. Astrocytes, which interface with neurons and blood vessels, play a crucial role in coordinating the brain's metabolic activity, and their dysfunction can have detrimental effects on brain health. This review characterizes the major energy substrates (glucose, lactate, glycogen, ketones and lipids) in astrocyte metabolism and their role in brain health, focusing on recent developments in the field.

Astroglial glucose uptake determines brain FDG-PET alterations and metabolic connectivity during healthy aging in mice

PURPOSE

2-Fluorodeoxyglucose-PET (FDG-PET) is a powerful tool to study glucose metabolism in mammalian brains, but cellular sources of glucose uptake and metabolic connectivity during aging are not yet understood.

METHODS

Healthy wild-type mice of both sexes (2-21 months of age) received FDG-PET and cell sorting after in vivo tracer injection (scRadiotracing). FDG uptake per cell was quantified in isolated microglia, astrocytes and neurons. Cerebral FDG uptake and metabolic connectivity were determined by PET. A subset of mice received measurement of blood glucose levels to study associations with cellular FDG uptake during aging.

RESULTS

Cerebral FDG-PET signals in healthy mice increased linearly with age. Cellular FDG uptake of neurons increased between 2 and 12 months of age, followed by a strong decrease towards late ages. Contrarily, FDG uptake in microglia and astrocytes exhibited a U-shaped function with respect to age, comprising the predominant cellular source of higher cerebral FDG uptake in the later stages. Metabolic connectivity was closely associated with the ratio of glucose uptake in astroglial cells relative to neurons. Cellular FDG uptake was not associated with blood glucose levels and increasing FDG brain uptake as a function of age was still observed after adjusting for blood glucose levels.

CONCLUSION

Trajectories of astroglial glucose uptake drive brain FDG-PET alterations and metabolic connectivity during aging.

Recent developments and challenges in positron emission tomography imaging of gliosis in chronic neuropathic pain

ABSTRACT

Understanding the mechanisms that underpin the transition from acute to chronic pain is critical for the development of more effective and targeted treatments. There is growing interest in the contribution of glial cells to this process, with cross-sectional preclinical studies demonstrating specific changes in these cell types capturing targeted timepoints from the acute phase and the chronic phase. In vivo longitudinal assessment of the development and evolution of these changes in experimental animals and humans has presented a significant challenge. Recent technological advances in preclinical and clinical positron emission tomography, including the development of specific radiotracers for gliosis, offer great promise for the field. These advances now permit tracking of glial changes over time and provide the ability to relate these changes to pain-relevant symptomology, comorbid psychiatric conditions, and treatment outcomes at both a group and an individual level. In this article, we summarize evidence for gliosis in the transition from acute to chronic pain and provide an overview of the specific radiotracers available to measure this process, highlighting their potential, particularly when combined with ex vivo / in vitro techniques, to understand the pathophysiology of chronic neuropathic pain. These complementary investigations can be used to bridge the existing gap in the field concerning the contribution of gliosis to neuropathic pain and identify potential targets for interventions.

Omics-derived biological modules reflect metabolic brain changes in Alzheimer's disease

INTRODUCTION

Brain glucose hypometabolism, indexed by the fluorodeoxyglucose positron emission tomography ([18F]FDG-PET) imaging, is a metabolic signature of Alzheimer's disease (AD). However, the underlying biological pathways involved in these metabolic changes remain elusive.

METHODS

Here, we integrated [18F]FDG-PET images with blood and hippocampal transcriptomic data from cognitively unimpaired (CU, n = 445) and cognitively impaired (CI, n = 749) individuals using modular dimension reduction techniques and voxel-wise linear regression analysis.

RESULTS

Our results showed that multiple transcriptomic modules are associated with brain [18F]FDG-PET metabolism, with the top hits being a protein serine/threonine kinase activity gene cluster (peak-t(223) = 4.86, P value < 0.001) and zinc-finger-related regulatory units (peak-t(223) = 3.90, P value < 0.001).

DISCUSSION

By integrating transcriptomics with PET imaging data, we identified that serine/threonine kinase activity-associated genes and zinc-finger-related regulatory units are highly associated with brain metabolic changes in AD.

HIGHLIGHTS

We conducted an integrated analysis of system-based transcriptomics and fluorodeoxyglucose positron emission tomography ([18F]FDG-PET) at the voxel level in Alzheimer's disease (AD). The biological process of serine/threonine kinase activity was the most associated with [18F]FDG-PET in the AD brain. Serine/threonine kinase activity alterations are associated with brain vulnerable regions in AD [18F]FDG-PET. Zinc-finger transcription factor targets were associated with AD brain [18F]FDG-PET metabolism.

Regional desynchronization of microglial activity is associated with cognitive decline in Alzheimer's disease

BACKGROUND

Microglial activation is one hallmark of Alzheimer disease (AD) neuropathology but the impact of the regional interplay of microglia cells in the brain is poorly understood. We hypothesized that microglial activation is regionally synchronized in the healthy brain but experiences regional desynchronization with ongoing neurodegenerative disease. We addressed the existence of a microglia connectome and investigated microglial desynchronization as an AD biomarker.

METHODS

To validate the concept, we performed microglia depletion in mice to test whether interregional correlation coefficients (ICCs) of 18 kDa translocator protein (TSPO)-PET change when microglia are cleared. Next, we evaluated the influence of dysfunctional microglia and AD pathophysiology on TSPO-PET ICCs in the mouse brain, followed by translation to a human AD-continuum dataset. We correlated a personalized microglia desynchronization index with cognitive performance. Finally, we performed single-cell radiotracing (scRadiotracing) in mice to ensure the microglial source of the measured desynchronization.

RESULTS

Microglia-depleted mice showed a strong ICC reduction in all brain compartments, indicating microglia-specific desynchronization. AD mouse models demonstrated significant reductions of microglial synchronicity, associated with increasing variability of cellular radiotracer uptake in pathologically altered brain regions. Humans within the AD-continuum indicated a stage-depended reduction of microglia synchronicity associated with cognitive decline. scRadiotracing in mice showed that the increased TSPO signal was attributed to microglia.

CONCLUSION

Using TSPO-PET imaging of mice with depleted microglia and scRadiotracing in an amyloid model, we provide first evidence that a microglia connectome can be assessed in the mouse brain. Microglia synchronicity is closely associated with cognitive decline in AD and could serve as an independent personalized biomarker for disease progression.

Early brain neuroinflammatory and metabolic changes identified by dual tracer microPET imaging in mice with acute liver injury

Background

Acute liver injury (ALI) that progresses into acute liver failure (ALF) is a life-threatening condition with an increasing incidence and associated costs. Acetaminophen (N-acetyl-p-aminophenol, APAP) overdosing is among the leading causes of ALI and ALF in the Northern Hemisphere. Brain dysfunction defined as hepatic encephalopathy is one of the main diagnostic criteria for ALF. While neuroinflammation and brain metabolic alterations significantly contribute to hepatic encephalopathy, their evaluation at early stages of ALI remained challenging. To provide insights, we utilized post-mortem analysis and non-invasive brain micro positron emission tomography (microPET) imaging of mice with APAP-induced ALI.

Methods

Male C57BL/6 mice were treated with vehicle or APAP (600 mg/kg, i.p.). Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), liver damage (using H&E staining), hepatic and serum IL-6 levels, and hippocampal IBA1 (using immunolabeling) were evaluated at 24h and 48h. Vehicle and APAP treated animals also underwent microPET imaging utilizing a dual tracer approach, including [11C]-peripheral benzodiazepine receptor ([11C]PBR28) to assess microglia/astrocyte activation and [18F]-fluoro-2-deoxy-2-D-glucose ([18F]FDG) to assess energy metabolism. Brain images were pre-processed and evaluated using conjunction and individual tracer uptake analysis.

Results

APAP-induced ALI and hepatic and systemic inflammation were detected at 24h and 48h by significantly elevated serum ALT and AST levels, hepatocellular damage, and increased hepatic and serum IL-6 levels. In parallel, increased microglial numbers, indicative for neuroinflammation were observed in the hippocampus of APAP-treated mice. MicroPET imaging revealed overlapping increases in [11C]PBR28 and [18F]FDG uptake in the hippocampus, thalamus, and habenular nucleus indicating microglial/astroglial activation and increased energy metabolism in APAP-treated mice (vs. vehicle-treated mice) at 24h. Similar significant increases were also found in the hypothalamus, thalamus, and cerebellum at 48h. The individual tracer uptake analyses (APAP vs vehicle) at 24h and 48h confirmed increases in these brain areas and indicated additional tracer- and region-specific effects including hippocampal alterations.

Conclusion

Peripheral manifestations of APAP-induced ALI in mice are associated with brain neuroinflammatory and metabolic alterations at relatively early stages of disease progression, which can be non-invasively evaluated using microPET imaging and conjunction analysis. These findings support further PET-based investigations of brain function in ALI/ALF that may inform timely therapeutic interventions.

PET imaging of synaptic vesicle glycoprotein 2 subtype A for neurological recovery in ischemic stroke

PURPOSE

[18F]SynVesT-1 is a novel radiopharmaceutical for assessing synaptic density in vivo. This study aims to investigate the potential of [18F]SynVesT-1 positron emission tomography (PET) in evaluating neurological recovery in the rat model of ischemic stroke, and to compare its performance with [18F]FDG PET.

METHODS

Sprague-Dawley rats were subjected to photothrombotic cerebral infarction, and safinamide was administered intraperitoneally from day 3 to day 14 post-stroke to alleviate neurological deficits. Cylinder test and forelimb placing test were performed to assess the neurological function. MRI, [18F]SynVesT-1 PET/CT and [18F]FDG PET/CT imaging were used to evaluate infarct volume, synaptic density, and cerebral glucose metabolism pre- and post-treatment. [18F]SynVesT-1 and [18F]FDG PET images were compared using Statistical Parametric Mapping (SPM) and region of interest (ROI)-based analysis. Post-mortem histological analysis was performed to validate PET images.

RESULTS

Safinamide treatment improved behavioral outcomes in stroke-damaged rats. Both [18F]SynVesT-1 and [18F]FDG PET detected stroke-induced injury, with the injured region being significantly larger in [18F]FDG PET than in [18F]SynVesT-1 PET. Compared with the saline group, radiotracer uptake in the injured area significantly increased in [18F]SynVesT-1 PET after safinamide treatment, whereas no notable change was observed in [18F]FDG PET. Additionally, [18F]SynVesT-1 PET imaging showed a better correlation with neurological function recovery than [18F]FDG PET. Post-mortem analysis revealed increased neuronal numbers, synaptic density, and synaptic neuroplasticity, as well as decreased glia activation in the stroke-injured area after treatment.

CONCLUSION

[18F]SynVesT-1 PET effectively quantified spatiotemporal dynamics of synaptic density in the rat model of stroke, and showed different capabilities in detecting stroke injury and neurological recovery compared with [18F]FDG PET. The utilization of [18F]SynVesT-1 PET holds promise as a potential non-invasive biomarker for evaluating ischemic stroke in conjunction with [18F]FDG PET.

A lactate-dependent shift of glycolysis mediates synaptic and cognitive processes in male mice

Astrocytes control brain activity via both metabolic processes and gliotransmission, but the physiological links between these functions are scantly known. Here we show that endogenous activation of astrocyte type-1 cannabinoid (CB1) receptors determines a shift of glycolysis towards the lactate-dependent production of D-serine, thereby gating synaptic and cognitive functions in male mice. Mutant mice lacking the CB1 receptor gene in astrocytes (GFAP-CB1-KO) are impaired in novel object recognition (NOR) memory. This phenotype is rescued by the gliotransmitter D-serine, by its precursor L-serine, and also by lactate and 3,5-DHBA, an agonist of the lactate receptor HCAR1. Such lactate-dependent effect is abolished when the astrocyte-specific phosphorylated-pathway (PP), which diverts glycolysis towards L-serine synthesis, is blocked. Consistently, lactate and 3,5-DHBA promoted the co-agonist binding site occupancy of CA1 post-synaptic NMDA receptors in hippocampal slices in a PP-dependent manner. Thus, a tight cross-talk between astrocytic energy metabolism and gliotransmission determines synaptic and cognitive processes.

Synaptic signaling modeled by functional connectivity predicts metabolic demands of the human brain

PURPOSE

The human brain is characterized by interacting large-scale functional networks fueled by glucose metabolism. Since former studies could not sufficiently clarify how these functional connections shape glucose metabolism, we aimed to provide a neurophysiologically-based approach.

METHODS

51 healthy volunteers underwent simultaneous PET/MRI to obtain BOLD functional connectivity and [18F]FDG glucose metabolism. These multimodal imaging proxies of fMRI and PET were combined in a whole-brain extension of metabolic connectivity mapping. Specifically, functional connectivity of all brain regions were used as input to explain glucose metabolism of a given target region. This enabled the modeling of postsynaptic energy demands by incoming signals from distinct brain regions.

RESULTS

Functional connectivity input explained a substantial part of metabolic demands but with pronounced regional variations (34 - 76%). During cognitive task performance this multimodal association revealed a shift to higher network integration compared to resting state. In healthy aging, a dedifferentiation (decreased segregated/modular structure of the brain) of brain networks during rest was observed. Furthermore, by including data from mRNA maps, [11C]UCB-J synaptic density and aerobic glycolysis (oxygen-to-glucose index from PET data), we show that whole-brain functional input reflects non-oxidative, on-demand metabolism of synaptic signaling. The metabolically-derived directionality of functional inputs further marked them as top-down predictions. In addition, the approach uncovered formerly hidden networks with superior efficiency through metabolically informed network partitioning.

CONCLUSIONS

Applying multimodal imaging, we decipher a crucial part of the metabolic and neurophysiological basis of functional connections in the brain as interregional on-demand synaptic signaling fueled by anaerobic metabolism. The observed task- and age-related effects indicate promising future applications to characterize human brain function and clinical alterations.

Brain Glucose Metabolism as a Readout of the Central Nervous System Impact of Cigarette Smoke Exposure and Withdrawal and the Effects of NFL-101, as an Immune-Based Drug Candidate for Smoking Cessation Therapy

Neuroimaging biomarkers are needed to investigate the impact of smoking withdrawal on brain function. NFL-101 is a denicotinized aqueous extract of tobacco leaves currently investigated as an immune-based smoking cessation therapy in humans. However, the immune response to NFL-101 and its ability to induce significant changes in brain function remain to be demonstrated. Brain glucose metabolism was investigated using [18F]fluoro-deoxy-glucose ([18F]FDG) PET imaging in a mouse model of cigarette smoke exposure (CSE, 4-week whole-body inhalation, twice daily). Compared with control animals, the relative uptake of [18F]FDG in CSE mice was decreased in the thalamus and brain stem (p < 0.001, n = 14 per group) and increased in the hippocampus, cortex, cerebellum, and olfactory bulb (p < 0.001). NFL-101 induced a humoral immune response (specific IgGs) in mice and activated human natural-killer lymphocytes in vitro. In CSE mice, but not in control mice, single-dose NFL-101 significantly increased [18F]FDG uptake in the thalamus (p < 0.01), thus restoring normal brain glucose metabolism after 2-day withdrawal in this nicotinic receptor-rich region. In tobacco research, [18F]FDG PET imaging provides a quantitative method to evaluate changes in the brain function associated with the withdrawal phase. This method also showed the CNS effects of NFL-101, with translational perspectives for future clinical evaluation in smokers.

Role of F-18 FDG PET-CT in neuropsychiatric systemic lupus erythematosus

BACKGROUND

Neuropsychiatric systemic lupus erythematosus (NPSLE) is a major contributor to morbidity and mortality in systemic lupus erythematosus (SLE) patients. To date no single clinical, laboratory or imaging test has proven accurate for NPSLE diagnosis which is a testament to the intricate and multifactorial pathophysiological mechanisms suspected to exist. Functional imaging with FDG PET-CT has shown promise in NPSLE diagnosis, detecting abnormalities prior to changes evident on anatomical imaging. Research indicates that NPSLE may be more aggressive in people of African descent with higher mortality rates, making rapid and correct diagnosis even more important in the African context.

METHODS

In this narrative review, we provide a thorough appraisal of the current literature on the role of FDG PET-CT in NPSLE. Large, well-known databases were searched using appropriate search terms. Manual searches of references of retrieved literature were also included.

FINDINGS

A total of 73 article abstracts were assessed, yielding 26 papers that were directly relevant to the topic of FDG PET-CT in NPSLE. Results suggest that FDG PET-CT is a sensitive imaging test for NPSLE diagnosis and may play a role in assessing treatment response. It is complementary to routine anatomical imaging, particularly in diffuse manifestations of the disease. Newer quantitative analyses are commonly used for interpretation and can detect even subtle abnormalities, missed on visual inspection. Findings of group-wise analyses of FDG PET-CT scans in NPSLE patients are important in furthering our understanding of the complicated pathophysiological mechanisms involved. Limitations of FDG PET-CT include its lack of specificity, high cost and poor access.

CONCLUSION

FDG PET-CT is a sensitive test for NPSLE diagnosis but is hampered by lack of specificity. It is a valuable tool for clinicians managing SLE patients, particularly when anatomical imaging is negative. Its exact application will depend on the local context and clinical scenario.

Is Cancer Metabolism an Atavism?

The atavistic theory of cancer posits that cancer emerges and progresses through the reversion of cellular phenotypes to more ancestral types with genomic and epigenetic changes deactivating recently evolved genetic modules and activating ancient survival mechanisms. This theory aims at explaining the known cancer hallmarks and the paradox of cancer's predictable progression despite the randomness of genetic mutations. Lineweaver and colleagues recently proposed the Serial Atavism Model (SAM), an enhanced version of the atavistic theory, which suggests that cancer progression involves multiple atavistic reversions where cells regress through evolutionary stages, losing recently evolved traits first and reactivating primitive ones later. The Warburg effect, where cancer cells upregulate glycolysis and lactate production in the presence of oxygen instead of using oxidative phosphorylation, is one of the key feature of the SAM. It is associated with the metabolism of ancient cells living on Earth before the oxygenation of the atmosphere. This review addresses the question of whether cancer metabolism can be considered as an atavistic reversion. By analyzing several known characteristics of cancer metabolism, we reach the conclusion that this version of the atavistic theory does not provide an adequate conceptual frame for cancer research. Cancer metabolism spans a whole spectrum of metabolic states which cannot be fully explained by a sequential reversion to an ancient state. Moreover, we interrogate the nature of cancer metabolism and discuss its characteristics within the framework of the SAM.

Imaging brain glucose metabolism in vivo reveals propionate as a major anaplerotic substrate in pyruvate dehydrogenase deficiency

A vexing problem in mitochondrial medicine is our limited capacity to evaluate the extent of brain disease in vivo. This limitation has hindered our understanding of the mechanisms that underlie the imaging phenotype in the brain of patients with mitochondrial diseases and our capacity to identify new biomarkers and therapeutic targets. Using comprehensive imaging, we analyzed the metabolic network that drives the brain structural and metabolic features of a mouse model of pyruvate dehydrogenase deficiency (PDHD). As the disease progressed in this animal, in vivo brain glucose uptake and glycolysis increased. Propionate served as a major anaplerotic substrate, predominantly metabolized by glial cells. A combination of propionate and a ketogenic diet extended lifespan, improved neuropathology, and ameliorated motor deficits in these animals. Together, intermediary metabolism is quite distinct in the PDHD brain-it plays a key role in the imaging phenotype, and it may uncover new treatments for this condition.

Diagnostic performance of molecular imaging methods in predicting the progression from mild cognitive impairment to dementia: an updated systematic review

PURPOSE

Epidemiological and logistical reasons are slowing the clinical validation of the molecular imaging biomarkers in the initial stages of neurocognitive disorders. We provide an updated systematic review of the recent advances (2017-2022), highlighting methodological shortcomings.

METHODS

Studies reporting the diagnostic accuracy values of the molecular imaging techniques (i.e., amyloid-, tau-, [18F]FDG-PETs, DaT-SPECT, and cardiac [123I]-MIBG scintigraphy) in predicting progression from mild cognitive impairment (MCI) to dementia were selected according to the Preferred Reporting Items for a Systematic Review and Meta-Analysis (PRISMA) method and evaluated with the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool. Main eligibility criteria were as follows: (1) ≥ 50 subjects with MCI, (2) follow-up ≥ 3 years, (3) gold standard: progression to dementia or diagnosis on pathology, and (4) measures of prospective accuracy.

RESULTS

Sensitivity (SE) and specificity (SP) in predicting progression to dementia, mainly to Alzheimer's dementia were 43-100% and 63-94% for [18F]FDG-PET and 64-94% and 48-93% for amyloid-PET. Longitudinal studies were lacking for less common disorders (Dementia with Lewy bodies-DLB and Frontotemporal lobe degeneration-FTLD) and for tau-PET, DaT-SPECT, and [123I]-MIBG scintigraphy. Therefore, the accuracy values from cross-sectional studies in a smaller sample of subjects (n > 20, also including mild dementia stage) were chosen as surrogate outcomes. DaT-SPECT showed 47-100% SE and 71-100% SP in differentiating Lewy body disease (LBD) from non-LBD conditions; tau-PET: 88% SE and 100% SP in differentiating DLB from Posterior Cortical Atrophy. [123I]-MIBG scintigraphy differentiated LBD from non-LBD conditions with 47-100% SE and 71-100% SP.

CONCLUSION

Molecular imaging has a moderate-to-good accuracy in predicting the progression of MCI to Alzheimer's dementia. Longitudinal studies are sparse in non-AD conditions, requiring additional efforts in these settings.

Cerebrospinal fluid NPTX2 changes and relationship with regional brain metabolism metrics across mild cognitive impairment due to Alzheimer's disease

BACKGROUND

Neuronal pentraxin-2 (NPTX2), crucial for synaptic functioning, declines in cerebrospinal fluid (CSF) as cognition deteriorates. The variations of CSF NPTX2 across mild cognitive impairment (MCI) due to Alzheimer's disease (AD) and its association with brain metabolism remain elusive, albeit relevant for patient stratification and pathophysiological insights.

METHODS

We retrospectively analyzed 49 MCI-AD patients grouped by time until dementia (EMCI, n = 34 progressing within 2 years; LMCI, n = 15 progressing later/stable at follow-up). We analyzed demographic variables, cognitive status (MMSE score), and CSF NPTX2 levels using a commercial ELISA assay in EMCI, LMCI, and a control group of age-/sex-matched individuals with other non-dementing disorders (OND). Using [18F]FDG PET scans for voxel-based analysis, we explored correlations between regional brain metabolism metrics and CSF NPTX2 levels in MCI-AD patients, accounting for age.

RESULTS

Baseline and follow-up MMSE scores were lower in LMCI than EMCI (p value = 0.006 and p < 0.001). EMCI exhibited significantly higher CSF NPTX2 values than both LMCI (p = 0.028) and OND (p = 0.006). We found a significant positive correlation between NPTX2 values and metabolism of bilateral precuneus in MCI-AD patients (p < 0.005 at voxel level, p < 0.05 with family-wise error correction at the cluster level).

CONCLUSIONS

Higher CSF NPTX2 in EMCI compared to controls and LMCI suggests compensatory synaptic responses to initial AD pathology. Disease progression sees these mechanisms overwhelmed, lowering CSF NPTX2 approaching dementia. Positive CSF NPTX2 correlation with precuneus glucose metabolism links to AD-related metabolic changes across MCI course. These findings posit CSF NPTX2 as a promising biomarker for both AD staging and progression risk stratification.

Astroglial activation: Current concepts and future directions

Astrocytes are abundantly and ubiquitously expressed cell types with diverse functions throughout the central nervous system. Astrocytes show remarkable plasticity and exhibit morphological, molecular, and functional remodeling in response to injury, disease, or infection of the central nervous system, as evident in neurodegenerative diseases. Astroglial mediated inflammation plays a prominent role in the pathogenesis of neurodegenerative diseases. This review focus on the role of astrocytes as essential players in neuroinflammation and discuss their morphological and functional heterogeneity in the normal central nervous system and explore the spatial and temporal variations in astroglial phenotypes observed under different disease conditions. This review discusses the intimate relationship of astrocytes to pathological hallmarks of neurodegenerative diseases. Finally, this review considers the putative therapeutic strategies that can be deployed to modulate the astroglial functions in neurodegenerative diseases. HIGHLIGHTS: Astroglia mediated neuroinflammation plays a key role in the pathogenesis of neurodegenerative diseases. Activated astrocytes exhibit diverse phenotypes in a region-specific manner in brain and interact with β-amyloid, tau, and α-synuclein species as well as with microglia and neuronal circuits. Activated astrocytes are likely to influence the trajectory of disease progression of neurodegenerative diseases, as determined by the stage of disease, individual susceptibility, and state of astroglial priming. Modulation of astroglial activation may be a therapeutic strategy at various stages in the trajectory of neurodegenerative diseases to modify the disease course.

Tracing synaptic loss in Alzheimer's brain with SV2A PET-tracer UCB-J

INTRODUCTION

Synaptic loss is an early prominent feature of Alzheimer's disease (AD). The recently developed novel synaptic vesicle 2A protein (SV2A) PET-tracer UCB-J has shown great promise in tracking synaptic loss in AD. However, there have been discrepancies between the findings and a lack of mechanistic insight.

METHODS

Here we report the first extensive pre-clinical validation studies for UCB-J in control (CN; n = 11) and AD (n = 11) brains using a multidimensional approach of post-mortem brain imaging techniques, radioligand binding, and biochemical studies.

RESULTS AND DISCUSSION

We demonstrate that UCB-J could target SV2A protein with high specificity and depict synaptic loss at synaptosome levels in AD brain regions compared to CNs. UCB-J showed highest synaptic loss in AD hippocampus followed in descending order by frontal cortex, temporal cortex, parietal cortex, and cerebellum. 3H-UCB-J large brain-section autoradiography and cellular/subcellular fractions binding studies indicated potential off-target interaction with phosphorylated tau (p-tau) species in AD brains, which could have subsequent clinical implications for imaging studies.

HIGHLIGHTS

Synaptic positron emission tomography (PET)-tracer UCB-J could target synaptic vesicle 2A protein (SV2A) with high specificity in Alzheimer's disease (AD) and control brains. Synaptic PET-tracer UCB-J could depict synaptic loss at synaptosome levels in AD brain regions compared to control. Potential off-target interaction of UCB-J with phosphorylated tau (p-tau) species at cellular/subcellular levels could have subsequent clinical implications for imaging studies, warranting further investigations.

Maternal environmental enrichment protects neonatal brains from hypoxic-ischemic challenge by mitigating brain energetic dysfunction and modulating glial cell responses

There is evidence that maternal milieu and changes in environmental factors during the prenatal period may exert a lasting impact on the brain health of the newborn, even in case of neonatal brain hypoxia-ischemia (HI). The present study aimed to investigate the effects of maternal environmental enrichment (EE) on HI-induced energetic and metabolic failure, along with subsequent neural cell responses in the early postnatal period. Male Wistar pups born to dams exposed to maternal EE or standard conditions (SC) were randomly divided into Sham-SC, HI-SC, Sham-EE, and HI-EE groups. Neonatal HI was induced on postnatal day (PND) 3. The Na+,K+-ATPase activity, mitochondrial function and neuroinflammatory related-proteins were assessed at 24 h and 48 h after HI. MicroPET-FDG scans were used to measure glucose uptake at three time points: 24 h post-HI, PND18, and PND24. Moreover, neuronal preservation and glial cell responses were evaluated at PND18. After HI, animals exposed to maternal EE showed an increase in Na+,K+-ATPase activity, preservation of mitochondrial potential/mass ratio, and a reduction in mitochondrial swelling. Glucose uptake was preserved in HI-EE animals from PND18 onwards. Maternal EE attenuated HI-induced cell degeneration, white matter injury, and reduced astrocyte immunofluorescence. Moreover, the HI-EE group exhibited elevated levels of IL-10 and a reduction in Iba-1 positive cells. Data suggested that the regulation of AKT/ERK1/2 signaling pathways could be involved in the effects of maternal EE. This study evidenced that antenatal environmental stimuli could promote bioenergetic and neural resilience in the offspring against early HI damage, supporting the translational value of pregnancy-focused environmental treatments.

Insulin-stimulated brain glucose uptake correlates with brain metabolites in severe obesity: A combined neuroimaging study

The human brain undergoes metabolic adaptations in obesity, but the underlying mechanisms have remained largely unknown. We compared concentrations of often reported brain metabolites measured with magnetic resonance spectroscopy (1H-MRS, 3 T MRI) in the occipital lobe in subjects with obesity and lean controls under different metabolic conditions (fasting, insulin clamp, following weight loss). Brain glucose uptake (BGU) quantified with 18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET)) was also performed in a subset of subjects during clamp. In dataset A, 48 participants were studied during fasting with brain 1H-MRS, while in dataset B 21 participants underwent paired brain 1H-MRS acquisitions under fasting and clamp conditions. In dataset C 16 subjects underwent brain 18F-FDG-PET and 1H-MRS during clamp. In the fasting state, total N-acetylaspartate was lower in subjects with obesity, while brain myo-inositol increased in response to hyperinsulinemia similarly in both lean participants and subjects with obesity. During clamp, BGU correlated positively with brain glutamine/glutamate, total choline, and total creatine levels. Following weight loss, brain creatine levels were increased, whereas increases in other metabolites remained not significant. To conclude, insulin signaling and glucose metabolism are significantly coupled with several of the changes in brain metabolites that occur in obesity.

Monitoring synaptic pathology in Alzheimer's disease through fluid and PET imaging biomarkers: a comprehensive review and future perspectives

Alzheimer's disease (AD) is currently constrained by limited clinical treatment options. The initial pathophysiological event, which can be traced back to decades before the clinical symptoms become apparent, involves the excessive accumulation of amyloid-beta (Aβ), a peptide comprised of 40-42 amino acids, in extraneuronal plaques within the brain. Biochemical and histological studies have shown that overaccumulation of Aβ instigates an aberrant escalation in the phosphorylation and secretion of tau, a microtubule-binding axonal protein. The accumulation of hyperphosphorylated tau into intraneuronal neurofibrillary tangles is in turn correlated with microglial dysfunction and reactive astrocytosis, culminating in synaptic dysfunction and neurodegeneration. As neurodegeneration progresses, it gives rise to mild clinical symptoms of AD, which may eventually evolve into overt dementia. Synaptic loss in AD may develop even before tau alteration and in response to possible elevations in soluble oligomeric forms of Aβ associated with early AD. These findings largely rely on post-mortem autopsy examinations, which typically involve a limited number of patients. Over the past decade, a range of fluid biomarkers such as neurogranin, α-synuclein, visinin-like protein 1 (VILIP-1), neuronal pentraxin 2, and β-synuclein, along with positron emission tomography (PET) markers like synaptic vesicle glycoprotein 2A, have been developed. These advancements have facilitated the exploration of how synaptic markers in AD patients correlate with cognitive impairment. However, fluid biomarkers indicating synaptic loss have only been validated in cerebrospinal fluid (CSF), not in plasma, with the exception of VILIP-1. The most promising PET radiotracer, [11C]UCB-J, currently faces significant challenges hindering its widespread clinical use, primarily due to the necessity of a cyclotron. As such, additional research geared toward the exploration of synaptic pathology biomarkers is crucial. This will not only enable their extensive clinical application, but also refine the optimization process of AD pharmacological trials.

Astrocytic Na+, K+ ATPases in physiology and pathophysiology

The Na+, K+ ATPases play a fundamental role in the homeostatic functions of astrocytes. After a brief historic prologue and discussion of the subunit composition and localization of the astrocytic Na+, K+ ATPases, the review focuses on the role of the astrocytic Na+, K+ pumps in extracellular K+ and glutamate homeostasis, intracellular Na+ and Ca2+ homeostasis and signaling, regulation of synaptic transmission and neurometabolic coupling between astrocytes and neurons. Loss-of-function mutations in the gene encoding the astrocytic α2 Na+, K+ ATPase cause a rare monogenic form of migraine with aura (familial hemiplegic migraine type 2). On the other hand, the α2 Na+, K+ ATPase is upregulated in spinal cord and brain samples from amyotrophic lateral sclerosis and Alzheimer disease patients, respectively. In the last part, the review focuses on i) the migraine relevant phenotypes shown by familial hemiplegic migraine type 2 knock-in mice with 50 % reduced expression of the astrocytic α2 Na+, K+ ATPase and the insights into the pathophysiology of migraine obtained from these genetic mouse models, and ii) the evidence that upregulation of the astrocytic α2 Na+, K+ ATPase in mouse models of amyotrophic lateral sclerosis and Alzheimer disease promotes neuroinflammation and contributes to progressive neurodegeneration.

In vivo PET of synaptic density as potential diagnostic marker for cognitive disorders: prospective comparison with current imaging markers for neuronal dysfunction and relation to symptomatology - study protocol

BACKGROUND

18F-FDG brain PET is clinically used for differential diagnosis in cognitive dysfunction of unclear etiology and for exclusion of a neurodegenerative cause in patients with cognitive impairment in late-life psychiatric disorders. 18F-FDG PET measures regional glucose metabolism, which represents a combination of neuronal/synaptic activity but also astrocytic activity and neuroinflammation. Recently, imaging of synaptic vesicle protein 2 A (SV2A) has become available and was shown to be a proxy of synaptic density. This prospective study will investigate the use of 18F-SynVesT-1 for imaging SV2A and its discriminative power for differential diagnosis in cognitive disorders in a head-to-head comparison to 18F-FDG PET. In addition, simultaneous PET/MR allows an evaluation of contributing factors and the additional value of advanced MRI imaging to FDG/SV2A PET imaging will be investigated. In this work, the study design and protocol are depicted.

METHODS

In this prospective, multimodal imaging study, 110 patients with uncertain diagnosis of cognitive impairment who are referred for 18F-FDG PET brain imaging in their diagnostic work-up in a tertiary memory clinic will be recruited. In addition, 40 healthy volunteers (HV) between 18 and 85 years (M/F) will be included. All study participants will undergo simultaneous 18F-SynVesT-1 PET/MR and an extensive neuropsychological evaluation. Amyloid status will be measured by PET using 18FNAV4694, in HV above 50 years of age. Structural T1-weighted and T2-weighted fluid-attenuated inversion recovery MR images, triple-tagging arterial spin labeling (ASL) and resting-state functional MRI (rs-fMRI) will be obtained. The study has been registered on ClinicalTrials.gov (NCT05384353) and is approved by the local Research Ethics Committee.

DISCUSSION

The main endpoint of the study will be the comparison of the diagnostic accuracy between 18F-SynVesT-1 and 18F-FDG PET in cognitive disorders with uncertain etiology and in exclusion of a neurodegenerative cause in patients with cognitive impairment in late-life psychiatric disorders. The strength of the relationship between cognition and imaging data will be assessed, as well as the potential incremental diagnostic value of including MR volumetry, ASL perfusion and rs-fMRI.

Validity and value of metabolic connectivity in mouse models of β-amyloid and tauopathy

Among functional imaging methods, metabolic connectivity (MC) is increasingly used for investigation of regional network changes to examine the pathophysiology of neurodegenerative diseases such as Alzheimer's disease (AD) or movement disorders. Hitherto, MC was mostly used in clinical studies, but only a few studies demonstrated the usefulness of MC in the rodent brain. The goal of the current work was to analyze and validate metabolic regional network alterations in three different mouse models of neurodegenerative diseases (β-amyloid and tau) by use of 2-deoxy-2-[18F]fluoro-d-glucose positron emission tomography (FDG-PET) imaging. We compared the results of FDG-µPET MC with conventional VOI-based analysis and behavioral assessment in the Morris water maze (MWM). The impact of awake versus anesthesia conditions on MC read-outs was studied and the robustness of MC data deriving from different scanners was tested. MC proved to be an accurate and robust indicator of functional connectivity loss when sample sizes ≥12 were considered. MC readouts were robust across scanners and in awake/ anesthesia conditions. MC loss was observed throughout all brain regions in tauopathy mice, whereas β-amyloid indicated MC loss mainly in spatial learning areas and subcortical networks. This study established a methodological basis for the utilization of MC in different β-amyloid and tau mouse models. MC has the potential to serve as a read-out of pathological changes within neuronal networks in these models.

The value of FDG combined with PiB PET in the diagnosis of patients with cognitive impairment in a memory clinic

AIMS

To analyze the value of 18 F-fluorodeoxyglucose (FDG) positron emission tomography (PET) combined with amyloid PET in cognitive impairment diagnosis.

METHODS

A total of 187 patients with dementia or mild cognitive impairment (MCI) who underwent 11 C-Pittsburgh compound B (PiB) and FDG PET scans in a memory clinic were included in the final analysis.

RESULTS

Amyloid-positive and amyloid-negative dementia patient groups showed a significant difference in the proportion of individuals presenting temporoparietal cortex (p < 0.001) and posterior cingulate/precuneus cortex (p < 0.001) hypometabolism. The sensitivity and specificity of this hypometabolic pattern for identifying amyloid pathology were 72.61% and 77.97%, respectively, in patients clinically diagnosed with AD and 60.87% and 76.19%, respectively, in patients with MCI. The initial diagnosis was changed in 32.17% of patients with dementia after considering both PiB and FDG results. There was a significant difference in both the proportion of patients showing the hypometabolic pattern and PiB positivity between dementia conversion patients and patients with a stable diagnosis of MCI (p < 0.05).

CONCLUSION

Temporoparietal and posterior cingulate/precuneus cortex hypometabolism on FDG PET suggested amyloid pathology in patients with cognitive impairment and is helpful in diagnostic decision-making and predicting AD dementia conversion from MCI, particularly when combined with amyloid PET.

Short-term consumption of highly processed diets varying in macronutrient content impair the sense of smell and brain metabolism in mice

OBJECTIVE

Food processing greatly contributed to increased food safety, diversity, and accessibility. However, the prevalence of highly palatable and highly processed food in our modern diet has exacerbated obesity rates and contributed to a global health crisis. While accumulating evidence suggests that chronic consumption of such foods is detrimental to sensory and neural physiology, it is unclear whether its short-term intake has adverse effects. Here, we assessed how short-term consumption (<2 months) of three diets varying in composition and macronutrient content influence olfaction and brain metabolism in mice.

METHODS

The diets tested included a grain-based standard chow diet (CHOW; 54% carbohydrate, 32% protein, 14% fat; #8604 Teklad Rodent diet , Envigo Inc.), a highly processed control diet (hpCTR; 70% carbohydrate, 20% protein, 10% fat; #D12450B, Research Diets Inc.), and a highly processed high-fat diet (hpHFD; 20% carbohydrate, 20% protein, 60% fat; #D12492, Research Diets Inc.). We performed behavioral and metabolic phenotyping, electro-olfactogram (EOG) recordings, brain glucose metabolism imaging, and mitochondrial respirometry in different brain regions. We also performed RNA-sequencing (RNA-seq) in the nose and across several brain regions, and conducted differential expression analysis, gene ontology, and network analysis.

RESULTS

We show that short-term consumption of the two highly processed diets, but not the grain-based diet, regardless of macronutrient content, adversely affects odor-guided behaviors, physiological responses to odorants, transcriptional profiles in the olfactory mucosa and brain regions, and brain glucose metabolism and mitochondrial respiration.

CONCLUSIONS

Even short periods of highly processed food consumption are sufficient to cause early olfactory and brain abnormalities, which has the potential to alter food choices and influence the risk of developing metabolic disease.

Homeostasis to Allostasis: Prefrontal Astrocyte Roles in Cognitive Flexibility and Stress Biology

In the intricate landscape of neurophysiology, astrocytes have been traditionally cast as homeostatic cells; however, their mechanistic involvement in allostasis-particularly how they modulate the adaptive response to stress and its accumulative impact that disrupts cognitive functions and precipitates psychiatric disorders-is now starting to be unraveled. Here, we address the gap by positing astrocytes as crucial allostatic players whose molecular adaptations underlie cognitive flexibility in stress-related neuropsychiatric conditions. We review how astrocytes, responding to stress mediators such as glucocorticoid and epinephrine/norepinephrine, undergo morphological and functional transformations that parallel the maladaptive changes. Our synthesis of recent findings reveals that these glial changes, especially in the metabolically demanding prefrontal cortex, may underlie some of the neuropsychiatric mechanisms characterized by the disruption of energy metabolism and astrocytic networks, compromised glutamate clearance, and diminished synaptic support. We argue that astrocytes extend beyond their homeostatic role, actively participating in the brain's allostatic response, especially by modulating energy substrates critical for cognitive functions.

Mass spectrometry in cerebrospinal fluid uncovers association of glycolysis biomarkers with Alzheimer's disease in a large clinical sample

Alzheimer's disease (AD) is a complex and heterogeneous neurodegenerative disorder with contributions from multiple pathophysiological pathways. One of the long-recognized and important features of AD is disrupted cerebral glucose metabolism, but the underlying molecular basis remains unclear. In this study, unbiased mass spectrometry was used to survey CSF from a large clinical cohort, comparing patients who are either cognitively unimpaired (CU; n = 68), suffering from mild-cognitive impairment or dementia from AD (MCI-AD, n = 95; DEM-AD, n = 72), or other causes (MCI-other, n = 77; DEM-other, n = 23), or Normal Pressure Hydrocephalus (NPH, n = 57). The results revealed changes related to altered glucose metabolism. In particular, two glycolytic enzymes, pyruvate kinase (PKM) and aldolase A (ALDOA), were found to be upregulated in CSF from patients with AD compared to those with other neurological conditions. Increases in full-length PKM and ALDOA levels in CSF were confirmed with immunoblotting. Levels of these enzymes furthermore correlated negatively with CSF glucose in matching CSF samples. PKM levels were also found to be increased in AD in publicly available brain-tissue data. These results indicate that ALDOA and PKM may act as technically-robust potential biomarkers of glucose metabolism dysregulation in AD.

Metabolic remodeling in astrocytes: Paving the path to brain tumor development

The brain is a highly metabolic organ, composed of multiple cell classes, that controls crucial functions of the body. Although neurons have traditionally been the main protagonist, astrocytes have gained significant attention over the last decade. In this regard, astrocytes are a type of glial cells that have recently emerged as critical regulators of central nervous system (CNS) function and play a significant role in maintaining brain energy metabolism. However, in certain scenarios, astrocyte behavior can go awry, which poses a significant threat to brain integrity and function. This is definitively the case for mutations that turn normal astrocytes and astrocytic precursors into gliomas, an aggressive type of brain tumor. In addition, healthy astrocytes can interact with tumor cells, becoming part of the tumor microenvironment and influencing disease progression. In this review, we discuss the recent evidence suggesting that disturbed metabolism in astrocytes can contribute to the development and progression of fatal human diseases such as cancer. Emphasis is placed on detailing the molecular bases and metabolic pathways of this disease and highlighting unique metabolic vulnerabilities that can potentially be exploited to develop successful therapeutic opportunities.

Aquaporin-4 Deficiency is Associated with Cognitive Impairment and Alterations in astrocyte-neuron Lactate Shuttle

Cognitive impairment refers to notable declines in cognitive abilities including memory, language, and emotional stability leading to the inability to accomplish essential activities of daily living. Astrocytes play an important role in cognitive function, and homeostasis of the astrocyte-neuron lactate shuttle (ANLS) system is essential for maintaining cognitive functions. Aquaporin-4 (AQP-4) is a water channel expressed in astrocytes and has been shown to be associated with various brain disorders, but the direct relationship between learning, memory, and AQP-4 is unclear. We examined the relationship between AQP-4 and cognitive functions related to learning and memory. Mice with genetic deletion of AQP-4 showed significant behavioral and emotional changes including hyperactivity and instability, and impaired cognitive functions such as spatial learning and memory retention. 18 F-FDG PET imaging showed significant metabolic changes in the brains of AQP-4 knockout mice such as reductions in glucose absorption. Such metabolic changes in the brain seemed to be the direct results of changes in the expression of metabolite transporters, as the mRNA levels of multiple glucose and lactate transporters in astrocytes and neurons were significantly decreased in the cortex and hippocampus of AQP-4 knockout mice. Indeed, AQP-4 knockout mice showed significantly higher accumulation of both glucose and lactate in their brains compared with wild-type mice. Our results show that the deficiency of AQP-4 can cause problems in the metabolic function of astrocytes and lead to cognitive impairment, and that the deficiency of AQP4 in astrocyte endfeet can cause abnormalities in the ANLS system.

Effects of bariatric surgery and dietary interventions for obesity on brain neurotransmitter systems and metabolism: A systematic review of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies

This systematic review collates studies of dietary or bariatric surgery interventions for obesity using positron emission tomography and single-photon emission computed tomography. Of 604 publications identified, 22 met inclusion criteria. Twelve studies assessed bariatric surgery (seven gastric bypass, five gastric bypass/sleeve gastrectomy), and ten dietary interventions (six low-calorie diet, three very low-calorie diet, one prolonged fasting). Thirteen studies examined neurotransmitter systems (six used tracers for dopamine DRD2/3 receptors: two each for 11 C-raclopride, 18 F-fallypride, 123 I-IBZM; one for dopamine transporter, 123 I-FP-CIT; one used tracer for serotonin 5-HT2A receptor, 18 F-altanserin; two used tracers for serotonin transporter, 11 C-DASB or 123 I-FP-CIT; two used tracer for μ-opioid receptor, 11 C-carfentanil; one used tracer for noradrenaline transporter, 11 C-MRB); seven studies assessed glucose uptake using 18 F-fluorodeoxyglucose; four studies assessed regional cerebral blood flow using 15 O-H2 O (one study also used arterial spin labeling); and two studies measured fatty acid uptake using 18 F-FTHA and one using 11 C-palmitate. The review summarizes findings and correlations with clinical outcomes, eating behavior, and mechanistic mediators. The small number of studies using each tracer and intervention, lack of dietary intervention control groups in any surgical studies, heterogeneity in time since intervention and degree of weight loss, and small sample sizes hindered the drawing of robust conclusions across studies.

Advanced brain imaging for the diagnosis of Alzheimer disease

PURPOSE OF REVIEW

The purpose is to review the latest advances of brain imaging for the diagnosis of Alzheimer disease (AD).

RECENT FINDINGS

Brain imaging techniques provide valuable and complementary information to support the diagnosis of Alzheimer disease in clinical and research settings. The recent FDA accelerated approvals of aducanumab, lecanemab and donanemab made amyloid-PET critical in helping determine the optimal window for anti-amyloid therapeutic interventions. Tau-PET, on the other hand, is considered of key importance for the tracking of disease progression and for monitoring therapeutic interventions in clinical trials. PET imaging for microglial activation, astrocyte reactivity and synaptic degeneration are still new techniques only used in the research field, and more studies are needed to validate their use in the clinical diagnosis of AD. Finally, artificial intelligence has opened new prospective in the early detection of AD using MRI modalities.

SUMMARY

Brain imaging techniques using PET improve our understanding of the different AD-related pathologies and their relationship with each other along the course of disease. With more robust validation, machine learning and deep learning algorithms could be integrated with neuroimaging modalities to serve as valuable tools for clinicians to make early diagnosis and prognosis of AD.

Fundamental Neurochemistry Review: Microglial immunometabolism in traumatic brain injury

Traumatic brain injury (TBI) is a devastating neurological disorder caused by a physical impact to the brain that promotes diffuse damage and chronic neurodegeneration. Key mechanisms believed to support secondary brain injury include mitochondrial dysfunction and chronic neuroinflammation. Microglia and brain-infiltrating macrophages are responsible for neuroinflammatory cytokine and reactive oxygen species (ROS) production after TBI. Their production is associated with loss of homeostatic microglial functions such as immunosurveillance, phagocytosis, and immune resolution. Beyond providing energy support, mitochondrial metabolic pathways reprogram the pro- and anti-inflammatory machinery in immune cells, providing a critical immunometabolic axis capable of regulating immunologic response to noxious stimuli. In the brain, the capacity to adapt to different environmental stimuli derives, in part, from microglia's ability to recognize and respond to changes in extracellular and intracellular metabolite levels. This capacity is met by an equally plastic metabolism, capable of altering immune function. Microglial pro-inflammatory activation is associated with decreased mitochondrial respiration, whereas anti-inflammatory microglial polarization is supported by increased oxidative metabolism. These metabolic adaptations contribute to neuroimmune responses, placing mitochondria as a central regulator of post-traumatic neuroinflammation. Although it is established that profound neurometabolic changes occur following TBI, key questions related to metabolic shifts in microglia remain unresolved. These include (a) the nature of microglial mitochondrial dysfunction after TBI, (b) the hierarchical positions of different metabolic pathways such as glycolysis, pentose phosphate pathway, glutaminolysis, and lipid oxidation during secondary injury and recovery, and (c) how immunometabolism alters microglial phenotypes, culminating in chronic non-resolving neuroinflammation. In this basic neurochemistry review article, we describe the contributions of immunometabolism to TBI, detail primary evidence of mitochondrial dysfunction and metabolic impairments in microglia and macrophages, discuss how major metabolic pathways contribute to post-traumatic neuroinflammation, and set out future directions toward advancing immunometabolic phenotyping in TBI.

Tracking reactive astrogliosis in autosomal dominant and sporadic Alzheimer's disease with multi-modal PET and plasma GFAP

BACKGROUND

Plasma assays for the detection of Alzheimer's disease neuropathological changes are receiving ever increasing interest. The concentration of plasma glial fibrillary acidic protein (GFAP) has been suggested as a potential marker of astrocytes or recently, amyloid-β burden, although this hypothesis remains unproven. We compared plasma GFAP levels with the astrocyte tracer 11C-Deuterium-L-Deprenyl (11C-DED) in a multi-modal PET design in participants with sporadic and Autosomal Dominant Alzheimer's disease.

METHODS

Twenty-four individuals from families with known Autosomal Dominant Alzheimer's Disease mutations (mutation carriers = 10; non-carriers = 14) and fifteen patients with sporadic Alzheimer's disease were included. The individuals underwent PET imaging with 11C-DED, 11C-PIB and 18F-FDG, as markers of reactive astrogliosis, amyloid-β deposition, and glucose metabolism, respectively, and plasma sampling for measuring GFAP concentrations. Twenty-one participants from the Autosomal Dominant Alzheimer's Disease group underwent follow-up plasma sampling and ten of these participants underwent follow-up PET imaging.

RESULTS

In mutation carriers, plasma GFAP levels and 11C-PIB binding increased, while 11C-DED binding and 18F-FDG uptake significantly decreased across the estimated years to symptom onset. Cross-sectionally, plasma GFAP demonstrated a negative correlation with 11C-DED binding in both mutation carriers and patients with sporadic disease. Plasma GFAP indicated cross-sectionally a significant positive correlation with 11C-PIB binding and a significant negative correlation with 18F-FDG in the whole sample. The longitudinal levels of 11C-DED binding showed a significant negative correlation with longitudinal plasma GFAP concentrations over the follow-up interval.

CONCLUSIONS

Plasma GFAP concentration and astrocyte 11C-DED brain binding levels followed divergent trajectories and may reflect different underlying processes. The strong negative association between plasma GFAP and 11C-DED binding in Autosomal Dominant and sporadic Alzheimer's disease brains may indicate that if both are markers of reactive astrogliosis, they may detect different states or subtypes of astrogliosis. Increased 11C-DED brain binding seems to be an earlier phenomenon in Alzheimer's disease progression than increased plasma GFAP concentration.

The consequences of neurodegenerative disease on neuron-astrocyte metabolic and redox interactions

Brain metabolic pathways relating to bioenergetic and redox homeostasis are closely linked, and deficits in these pathways are thought to occur in many neurodegenerative diseases. Astrocytes play important roles in both processes, and growing evidence suggests that neuron-astrocyte intercellular signalling ensures brain bioenergetic and redox homeostasis in health. Moreover, alterations to this crosstalk have been observed in the context of neurodegenerative pathology. In this review, we summarise the current understanding of how neuron-astrocyte interactions influence brain metabolism and antioxidant functions in health as well as during neurodegeneration. It is apparent that deleterious and adaptive protective responses alter brain metabolism in disease, and that knowledge of both may illuminate targets for future therapeutic interventions.

Fatty acid oxidation organizes mitochondrial supercomplexes to sustain astrocytic ROS and cognition

Having direct access to brain vasculature, astrocytes can take up available blood nutrients and metabolize them to fulfil their own energy needs and deliver metabolic intermediates to local synapses1,2. These glial cells should be, therefore, metabolically adaptable to swap different substrates. However, in vitro and in vivo studies consistently show that astrocytes are primarily glycolytic3-7, suggesting glucose is their main metabolic precursor. Notably, transcriptomic data8,9 and in vitro10 studies reveal that mouse astrocytes are capable of mitochondrially oxidizing fatty acids and that they can detoxify excess neuronal-derived fatty acids in disease models11,12. Still, the factual metabolic advantage of fatty acid use by astrocytes and its physiological impact on higher-order cerebral functions remain unknown. Here, we show that knockout of carnitine-palmitoyl transferase-1A (CPT1A)-a key enzyme of mitochondrial fatty acid oxidation-in adult mouse astrocytes causes cognitive impairment. Mechanistically, decreased fatty acid oxidation rewired astrocytic pyruvate metabolism to facilitate electron flux through a super-assembled mitochondrial respiratory chain, resulting in attenuation of reactive oxygen species formation. Thus, astrocytes naturally metabolize fatty acids to preserve the mitochondrial respiratory chain in an energetically inefficient disassembled conformation that secures signalling reactive oxygen species and sustains cognitive performance.

Assessment of synaptic loss in mouse models of β-amyloid and tau pathology using [18F]UCB-H PET imaging

OBJECTIVE

In preclinical research, the use of [18F]Fluorodesoxyglucose (FDG) as a biomarker for neurodegeneration may induce bias due to enhanced glucose uptake by immune cells. In this study, we sought to investigate synaptic vesicle glycoprotein 2A (SV2A) PET with [18F]UCB-H as an alternative preclinical biomarker for neurodegenerative processes in two mouse models representing the pathological hallmarks of Alzheimer's disease (AD).

METHODS

A total of 29 PS2APP, 20 P301S and 12 wild-type mice aged 4.4 to 19.8 months received a dynamic [18F]UCB-H SV2A-PET scan (14.7 ± 1.5 MBq) 0-60 min post injection. Quantification of tracer uptake in cortical, cerebellar and brainstem target regions was implemented by calculating relative volumes of distribution (VT) from an image-derived-input-function (IDIF). [18F]UCB-H binding was compared across all target regions between transgenic and wild-type mice. Additional static scans were performed in a subset of mice to compare [18F]FDG and [18F]GE180 (18 kDa translocator protein tracer as a surrogate for microglial activation) standardized uptake values (SUV) with [18F]UCB-H binding at different ages. Following the final scan, a subset of mouse brains was immunohistochemically stained with synaptic markers for gold standard validation of the PET results.

RESULTS

[18F]UCB-H binding in all target regions was significantly reduced in 8-months old P301S transgenic mice when compared to wild-type controls (temporal lobe: p = 0.014; cerebellum: p = 0.0018; brainstem: p = 0.0014). Significantly lower SV2A tracer uptake was also observed in 13-months (temporal lobe: p = 0.0080; cerebellum: p = 0.006) and 19-months old (temporal lobe: p = 0.0042; cerebellum: p = 0.011) PS2APP transgenic versus wild-type mice, whereas the brainstem revealed no significantly altered [18F]UCB-H binding. Immunohistochemical analyses of post-mortem mouse brain tissue confirmed the SV2A PET findings. Correlational analyses of [18F]UCB-H and [18F]FDG using Pearson's correlation coefficient revealed a significant negative association in the PS2APP mouse model (R = -0.26, p = 0.018). Exploratory analyses further stressed microglial activation as a potential reason for this inverse relationship, since [18F]FDG and [18F]GE180 quantification were positively correlated in this cohort (R = 0.36, p = 0.0076).

CONCLUSION

[18F]UCB-H reliably depicts progressive synaptic loss in PS2APP and P301S transgenic mice, potentially qualifying as a more reliable alternative to [18F]FDG as a biomarker for assessment of neurodegeneration in preclinical research.

Visualizing reactive astrocyte-neuron interaction in Alzheimer's disease using 11C-acetate and 18F-FDG

Reactive astrogliosis is a hallmark of Alzheimer's disease (AD). However, a clinically validated neuroimaging probe to visualize the reactive astrogliosis is yet to be discovered. Here, we show that PET imaging with 11C-acetate and 18F-fluorodeoxyglucose (18F-FDG) functionally visualizes the reactive astrocyte-mediated neuronal hypometabolism in the brains with neuroinflammation and AD. To investigate the alterations of acetate and glucose metabolism in the diseased brains and their impact on the AD pathology, we adopted multifaceted approaches including microPET imaging, autoradiography, immunohistochemistry, metabolomics, and electrophysiology. Two AD rodent models, APP/PS1 and 5xFAD transgenic mice, one adenovirus-induced rat model of reactive astrogliosis, and post-mortem human brain tissues were used in this study. We further curated a proof-of-concept human study that included 11C-acetate and 18F-FDG PET imaging analyses along with neuropsychological assessments from 11 AD patients and 10 healthy control subjects. We demonstrate that reactive astrocytes excessively absorb acetate through elevated monocarboxylate transporter-1 (MCT1) in rodent models of both reactive astrogliosis and AD. The elevated acetate uptake is associated with reactive astrogliosis and boosts the aberrant astrocytic GABA synthesis when amyloid-β is present. The excessive astrocytic GABA subsequently suppresses neuronal activity, which could lead to glucose uptake through decreased glucose transporter-3 in the diseased brains. We further demonstrate that 11C-acetate uptake was significantly increased in the entorhinal cortex, hippocampus and temporo-parietal neocortex of the AD patients compared to the healthy controls, while 18F-FDG uptake was significantly reduced in the same regions. Additionally, we discover a strong correlation between the patients' cognitive function and the PET signals of both 11C-acetate and 18F-FDG. We demonstrate the potential value of PET imaging with 11C-acetate and 18F-FDG by visualizing reactive astrogliosis and the associated neuronal glucose hypometablosim for AD patients. Our findings further suggest that the acetate-boosted reactive astrocyte-neuron interaction could contribute to the cognitive decline in AD.

Mass Spectrometry in Cerebrospinal Fluid Uncovers Association of Glycolysis Biomarkers with Alzheimer's Disease in a Large Clinical Sample

Background

Alzheimer's disease (AD) is a complex heterogenous neurodegenerative disorder, characterized by multiple pathophysiologies, including disruptions in brain metabolism. Defining markers for patient stratification across these pathophysiologies is an important step towards personalized treatment of AD. Efficient brain glucose metabolism is essential to sustain neuronal activity, but hypometabolism is consistently observed in AD. The molecular changes underlying these observations remain unclear. Recent studies have indicated dysregulation of several glycolysis markers in AD cerebrospinal fluid and tissue.

Methods

In this study, unbiased mass spectrometry was used to perform a deep proteomic survey of cerebrospinal fluid (CSF) from a large-scale clinically complex cohort to uncover changes related to impaired glucose metabolism.

Results

Two glycolytic enzymes, Pyruvate kinase (PKM) and Aldolase A (ALDOA) were found to be specifically upregulated in AD CSF compared to other non-AD groups. Presence of full-length protein of these enzymes in CSF was confirmed through immunoblotting. Levels of tryptic peptides of these enzymes correlated significantly with CSF glucose and CSF lactate in matching CSF samples.

Conclusions

The results presented here indicate a general dysregulation of glucose metabolism in the brain in AD. We highlight two markers ALDOA and PKM that may act as potential functionally-relevant biomarkers of glucose metabolism dysregulation in AD.

Refueling the post COVID-19 brain: potential role of ketogenic medium chain triglyceride supplementation: an hypothesis

COVID-19 infection causes cognitive changes in the acute phase, but also after apparent recovery. Over fifty post (long)-COVID symptoms are described, including cognitive dysfunction ("brain fog") precluding return to pre-COVID level of function, with rates twice as high in females. Additionally, the predominant demographic affected by these symptoms is younger and still in the workforce. Lack of ability to work, even for six months, has significant socio-economic consequences. This cognitive dysfunction is associated with impaired cerebral glucose metabolism, assessed using 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET), showing brain regions that are abnormal compared to age and sex matched controls. In other cognitive conditions such as Alzheimer's disease (AD), typical patterns of cerebral glucose hypometabolism, frontal hypometabolism and cerebellar hypermetabolism are common. Similar FDG-PET changes have also been observed in post-COVID-19, raising the possibility of a similar etiology. Ketone bodies (B-hydroxybutyrate, acetoacetate and acetone) are produced endogenously with very low carbohydrate intake or fasting. They improve brain energy metabolism in the face of cerebral glucose hypometabolism in other conditions [mild cognitive impairment (MCI) and AD]. Long-term low carbohydrate intake or prolonged fasting is not usually feasible. Medium chain triglyceride (MCT) is an exogenous route to nutritional ketosis. Research has supported their efficacy in managing intractable seizures, and cognitive impairment in MCI and AD. We hypothesize that cerebral glucose hypometabolism associated with post COVID-19 infection can be mitigated with MCT supplementation, with the prediction that cognitive function would also improve. Although there is some suggestion that post COVID-19 cognitive symptoms may diminish over time, in many individuals this may take more than six months. If MCT supplementation is able to speed the cognitive recovery, this will impact importantly on quality of life. MCT is readily available and, compared to pharmaceutical interventions, is cost-effective. Research shows general tolerability with dose titration. MCT is a component of enteral and parenteral nutrition supplements, including in pediatrics, so has a long record of safety in vulnerable populations. It is not associated with weight gain or adverse changes in lipid profiles. This hypothesis serves to encourage the development of clinical trials evaluating the impact of MCT supplementation on the duration and severity of post COVID-19 cognitive symptoms.

Multimodal comparisons of QSM and PET in neurodegeneration and aging

Quantitative susceptibility mapping (QSM) has been used to study susceptibility changes that may occur based on tissue composition and mineral deposition. Iron is a primary contributor to changes in magnetic susceptibility and of particular interest in applications of QSM to neurodegeneration and aging. Iron can contribute to neurodegeneration through inflammatory processes and via interaction with aggregation of disease-related proteins. To better understand the local susceptibility changes observed on QSM, its signal has been studied in association with other imaging metrics such as positron emission tomography (PET). The associations of QSM and PET may provide insight into the pathophysiology of disease processes, such as the role of iron in aging and neurodegeneration, and help to determine the diagnostic utility of QSM as an indirect indicator of disease processes typically evaluated with PET. In this review we discuss the proposed mechanisms and summarize prior studies of the associations of QSM and amyloid PET, tau PET, TSPO PET, FDG-PET, 15O-PET, and F-DOPA PET in evaluation of neurologic diseases with a focus on aging and neurodegeneration.

Effect of Obesity and Osteocalcin on Brain Glucose Metabolism in Healthy Participants

We evaluated the effects of obesity and osteocalcin on glucose metabolism in the brain. A total of 179 healthy men were enrolled in this study. After preprocessing positron emission tomography images, including by performing coregistration, spatial normalization, and smoothing, regression analysis was conducted to identify the correlation between body mass index, osteocalcin, and brain glucose metabolism. Body mass index was positively correlated with brain glucose metabolism in the anterior lobe of the right cerebellum, the anterior and posterior lobes of the left cerebellum, the right middle frontal gyrus (Brodmann area 9), the right cingulate gyrus (Brodmann area 32), the right anterior cingulate (Brodmann area 32), the left middle frontal gyrus (Brodmann area 10), and the subgyral area of the left frontal lobe. Osteocalcin was negatively correlated with glucose metabolism in the anterior lobe of the left cerebellum. Body mass index was positively correlated with brain glucose metabolism in the prefrontal cortex and cerebellum. Osteocalcin levels were negatively correlated with brain glucose metabolism in the left cerebellum.

Astrocyte Signature in Alzheimer's Disease Continuum through a Multi-PET Tracer Imaging Perspective

Reactive astrogliosis is an early event in the continuum of Alzheimer's disease (AD). Current advances in positron emission tomography (PET) imaging provide ways of assessing reactive astrogliosis in the living brain. In this review, we revisit clinical PET imaging and in vitro findings using the multi-tracer approach, and point out that reactive astrogliosis precedes the deposition of Aβ plaques, tau pathology, and neurodegeneration in AD. Furthermore, considering the current view of reactive astrogliosis heterogeneity-more than one subtype of astrocyte involved-in AD, we discuss how astrocytic body fluid biomarkers might fit into trajectories different from that of astrocytic PET imaging. Future research focusing on the development of innovative astrocytic PET radiotracers and fluid biomarkers may provide further insights into the heterogeneity of reactive astrogliosis and improve the detection of AD in its early stages.

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.

16p11.2 haploinsufficiency reduces mitochondrial biogenesis in brain endothelial cells and alters brain metabolism in adult mice

Neurovascular abnormalities in mouse models of 16p11.2 deletion autism syndrome are reminiscent of alterations reported in murine models of glucose transporter deficiency, including reduced brain angiogenesis and behavioral alterations. Yet, whether cerebrovascular alterations in 16p11.2^df/+ mice affect brain metabolism is unknown. Here, we report that anesthetized 16p11.2^df/+ mice display elevated brain glucose uptake, a phenomenon recapitulated in mice with endothelial-specific 16p11.2 haplodeficiency. Awake 16p11.2^df/+ mice display attenuated relative fluctuations of extracellular brain glucose following systemic glucose administration. Targeted metabolomics on cerebral cortex extracts reveals enhanced metabolic responses to systemic glucose in 16p11.2^df/+ mice that also display reduced mitochondria number in brain endothelial cells. This is not associated with changes in mitochondria fusion or fission proteins, but 16p11.2^df/+ brain endothelial cells lack the splice variant NT-PGC-1α, suggesting defective mitochondrial biogenesis. We propose that altered brain metabolism in 16p11.2^df/+ mice is compensatory to endothelial dysfunction, shedding light on previously unknown adaptative responses.