Brain energy rescue: an emerging therapeutic concept for neurodegenerative disorders of ageing

Regional changes with global brain hypometabolism indicates a physiological triage phenomenon and can explain shared pathophysiological events in Alzheimer's & small vessel diseases and delirium

While reduced global brain metabolism is known in aging, Alzheimer's disease (AD), small vessel disease (SVD) and delirium, explanation of regional brain metabolic (rBM) changes is a challenge. We hypothesized that this may be explained by "triage phenomenon", to preserve metabolic supply to vital brain areas. We studied changes in rBM in 69 patients with at least 5% decline in global brain metabolism during active lymphoma. There was significant decline in the rBM of the inferior parietal, precuneus, superior parietal, lateral occipital, primary visual cortices (P<0.001) and in the right lateral prefrontal cortex (P=0.01). Some areas showed no change; multiple areas had significantly increased rBM (e.g. medial prefrontal, anterior cingulate, pons, cerebellum and mesial temporal cortices; P<0.001). We conclude the existence of a physiological triage phenomenon and argue a new hypothetical model to explain the shared events in the pathophysiology of aging, AD, SVD and delirium.

Metabolic determinants of Alzheimer's disease: A focus on thermoregulation

Alzheimer's disease (AD) is a complex age-related neurodegenerative disease, associated with central and peripheral metabolic anomalies, such as impaired glucose utilization and insulin resistance. These observations led to a considerable interest not only in lifestyle-related interventions, but also in repurposing insulin and other anti-diabetic drugs to prevent or treat dementia. Body temperature is the oldest known metabolic readout and mechanisms underlying its maintenance fail in the elderly, when the incidence of AD rises. This raises the possibility that an age-associated thermoregulatory deficit contributes to energy failure underlying AD pathogenesis. Brown adipose tissue (BAT) plays a central role in thermogenesis and maintenance of body temperature. In recent years, the modulation of BAT activity has been increasingly demonstrated to regulate energy expenditure, insulin sensitivity and glucose utilization, which could also provide benefits for AD. Here, we review the evidence linking thermoregulation, BAT and insulin-related metabolic defects with AD, and we propose mechanisms through which correcting thermoregulatory impairments could slow the progression and delay the onset of AD.

Epidemiological and genetic overlap among biological aging clocks: New challenges in biogerontology

Estimators of biological age (BA) - defined as the hypothetical underlying age of an organism - have attracted more and more attention in the last years, especially after the advent of new algorithms based on machine learning and genetic markers. While different aging clocks reportedly predict mortality in the general population, very little is known on their overlap. Here we review the evidence reported so far to support the existence of a partial overlap among different BA acceleration estimators, both from an epidemiological and a genetic perspective. On the epidemiological side, we review evidence supporting shared and independent influence on mortality risk of different aging clocks - including telomere length, brain, blood and epigenetic aging - and provide an overview of how an important exposure like diet may affect the different aging systems. On the genetic side, we apply linkage disequilibrium score regression analyses to support the existence of partly shared genomic overlap among these aging clocks. Through multivariate analysis of published genetic associations with these clocks, we also identified the most associated variants, genes, and pathways, which may affect common mechanisms underlying biological aging of different systems within the body. Based on our analyses, the most implicated pathways were involved in inflammation, lipid and carbohydrate metabolism, suggesting them as potential molecular targets for future anti-aging interventions. Overall, this review is meant as a contribution to the knowledge on the overlap of aging clocks, trying to clarify their shared biological basis and epidemiological implications.

Nanotechnology-Based Drug Delivery Strategies to Repair the Mitochondrial Function in Neuroinflammatory and Neurodegenerative Diseases

Mitochondria are vital organelles in eukaryotic cells that control diverse physiological processes related to energy production, calcium homeostasis, the generation of reactive oxygen species, and cell death. Several studies have demonstrated that structural and functional mitochondrial disturbances are involved in the development of different neuroinflammatory (NI) and neurodegenerative (ND) diseases (NI&NDDs) such as multiple sclerosis, Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Remarkably, counteracting mitochondrial impairment by genetic or pharmacologic treatment ameliorates neurodegeneration and clinical disability in animal models of these diseases. Therefore, the development of nanosystems enabling the sustained and selective delivery of mitochondria-targeted drugs is a novel and effective strategy to tackle NI&NDDs. In this review, we outline the impact of mitochondrial dysfunction associated with unbalanced mitochondrial dynamics, altered mitophagy, oxidative stress, energy deficit, and proteinopathies in NI&NDDs. In addition, we review different strategies for selective mitochondria-specific ligand targeting and discuss novel nanomaterials, nanozymes, and drug-loaded nanosystems developed to repair mitochondrial function and their therapeutic benefits protecting against oxidative stress, restoring cell energy production, preventing cell death, inhibiting protein aggregates, and improving motor and cognitive disability in cellular and animal models of different NI&NDDs.

Sex differences in Alzheimer's disease: metabolic reprogramming and therapeutic intervention

Studies on the sporadic form of Alzheimer's disease (AD) have revealed three classes of risk factor: age, genetics, and sex. These risk factors point to a metabolic dysregulation as the origin of AD. Adaptive alterations in cerebral metabolism are the rationale for the Metabolic Reprogramming (MR) Theory of the origin of AD. The theory contends that the progression toward AD involves three adaptive events: a hypermetabolic phase, a prolonged prodromal phase, and a metabolic collapse. This article exploits the MR Theory to elucidate the effect of hormonal changes on the origin and progression of AD in women. The theory invokes bioenergetic signatures of the menopausal transition to propose sex-specific diagnostic program and therapeutic strategies.

Effects of Magnesium Orotate, Benfotiamine and a Combination of Vitamins on Mitochondrial and Cholinergic Function in the TgF344-AD Rat Model of Alzheimer's Disease

Glucose hypometabolism, mitochondrial dysfunction, and cholinergic deficits have been reported in early stages of Alzheimer’s disease (AD). Here, we examine these parameters in TgF344-AD rats, an Alzheimer model that carries amyloid precursor protein and presenilin-1 mutations, and of wild type F344 rats. In mitochondria isolated from rat hippocampi, we found reductions of complex I and oxidative phosphorylation in transgenic rats. Further impairments, also of complex II, were observed in aged (wild-type and transgenic) rats. Treatment with a “cocktail” containing magnesium orotate, benfotiamine, folic acid, cyanocobalamin, and cholecalciferol did not affect mitochondrial activities in wild-type rats but restored diminished activities in transgenic rats to wild-type levels. Glucose, lactate, and pyruvate levels were unchanged by age, genetic background, or treatment. Using microdialysis, we also investigated extracellular concentrations of acetylcholine that were strongly reduced in transgenic animals. Again, ACh levels in wild-type rats did not change upon treatment with nutrients, whereas the cocktail increased hippocampal acetylcholine levels under physiological stimulation. We conclude that TgF344-AD rats display a distinct mitochondrial and cholinergic dysfunction not unlike the findings in patients suffering from AD. This dysfunction can be partially corrected by the application of the “cocktail” which is particularly active in aged rats. We suggest that the TgF344-AD rat is a promising model to further investigate mitochondrial and cholinergic dysfunction and potential treatment approaches for AD.

Astrocytes in depression and Alzheimer's disease

Astrocytes are an abundant subgroup of cells in the central nervous system (CNS) that play a critical role in controlling neuronal circuits involved in emotion, learning, and memory. In clinical cases, multiple chronic brain diseases may cause psychosocial and cognitive impairment, such as depression and Alzheimer's disease (AD). For years, complex pathological conditions driven by depression and AD have been widely perceived to contribute to a high risk of disability, resulting in gradual loss of self-care ability, lower life qualities, and vast burden on human society. Interestingly, correlational research on depression and AD has shown that depression might be a prodrome of progressive degenerative neurological disease. As a kind of multifunctional glial cell in the CNS, astrocytes maintain physiological function via supporting neuronal cells, modulating pathologic niche, and regulating energy metabolism. Mounting evidence has shown that astrocytic dysfunction is involved in the progression of depression and AD. We herein review the current findings on the roles and mechanisms of astrocytes in the development of depression and AD, with an implication of potential therapeutic avenue for these diseases by targeting astrocytes.

A ketogenic supplement improves white matter energy supply and processing speed in mild cognitive impairment

INTRODUCTION

White matter (WM) energy supply is crucial for axonal function and myelin maintenance. An exogenous source of ketones, the brain's alternative fuel to glucose, bypasses the brain's glucose-specific energy deficit and improves cognitive outcomes in mild cognitive impairment (MCI). How an additional supply of ketones affects glucose or ketone uptake in specific WM fascicles in MCI has not previously been reported.

METHODS

This 6-month interventional study included MCI participants randomized to a placebo (n = 16) or ketogenic medium chain triglyceride (kMCT; n = 17) drink. A neurocognitive battery and brain imaging were performed pre- and post-intervention. WM fascicle uptake of ketone and glucose and structural properties were assessed using positron emission tomography and diffusion imaging, respectively.

RESULTS

Ketone uptake was increased in the kMCT group by 2.5- to 3.2-fold in all nine WM fascicles of interest (P < .001), an effect seen both in deep WM and in fascicle cortical endpoints. Improvement in processing speed was positively associated with WM ketone uptake globally and in individual fascicles, most importantly the fornix (r = +0.61; P = .014).

DISCUSSION

A 6-month kMCT supplement improved WM energy supply in MCI by increasing ketone uptake in WM fascicles. The significant positive association with processing speed suggests that ketones may have a role in myelin integrity in MCI.

Energy matters: presynaptic metabolism and the maintenance of synaptic transmission

Synaptic activity imposes large energy demands that are met by local adenosine triphosphate (ATP) synthesis through glycolysis and mitochondrial oxidative phosphorylation. ATP drives action potentials, supports synapse assembly and remodelling, and fuels synaptic vesicle filling and recycling, thus sustaining synaptic transmission. Given their polarized morphological features - including long axons and extensive branching in their terminal regions - neurons face exceptional challenges in maintaining presynaptic energy homeostasis, particularly during intensive synaptic activity. Recent studies have started to uncover the mechanisms and signalling pathways involved in activity-dependent and energy-sensitive regulation of presynaptic energetics, or 'synaptoenergetics'. These conceptual advances have established the energetic regulation of synaptic efficacy and plasticity as an exciting research field that is relevant to a range of neurological disorders associated with bioenergetic failure and synaptic dysfunction.

Down-regulation of EPB41L4A-AS1 mediated the brain aging and neurodegenerative diseases via damaging synthesis of NAD+ and ATP

Background

Aging and neurodegenerative diseases are typical metabolic-related processes. As a metabolism-related long non-coding RNA, EPB41L4A-AS has been reported to be potentially involved in the development of brain aging and neurodegenerative diseases. In this study, we sought to reveal the mechanisms of EPB41L4A-AS in aging and neurodegenerative diseases.

Methods

Human hippocampal gene expression profiles downloaded from the Genotype-Tissue Expression database were analyzed to obtain age-stratified differentially expressed genes; a weighted correlation network analysis algorithm was then used to construct a gene co-expression network of these differentially expressed genes to obtain gene clustering modules. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, protein–protein interaction network, and correlation analysis were used to reveal the role of EPB41L4A-AS1. The mechanism was verified using Gene Expression Omnibus dataset GSE5281 and biological experiments (construction of cell lines, Real-time quantitative PCR, Western blot, measurement of ATP and NAD⁺ levels, nicotinamide riboside treatment, Chromatin Immunoprecipitation) in neurons and glial-derived cells.

Results

EPB41L4A-AS1 was downregulated in aging and Alzheimer's disease. EPB41L4A-AS1 related genes were found to be enriched in the electron transport chain and NAD⁺ synthesis pathway. Furthermore, these genes were highly associated with neurodegenerative diseases and positively correlated with EPB41L4A-AS1. In addition, biological experiments proved that the downregulation of EPB41L4A-AS1 could reduce the expression of these genes via histone H3 lysine 27 acetylation, resulting in decreased NAD⁺ and ATP levels, while EPB41L4A-AS1 overexpression and nicotinamide riboside treatment could restore the NAD⁺ and ATP levels.

Conclusions

Downregulation of EPB41L4A-AS1 not only disturbs NAD⁺ biosynthesis but also affects ATP synthesis. As a result, the high demand for NAD⁺ and ATP in the brain cannot be met, promoting the development of brain aging and neurodegenerative diseases. However, overexpression of EPB41L4A-AS1 and nicotinamide riboside, a substrate of NAD⁺ synthesis, can reduce EPB41L4A-AS1 downregulation-mediated decrease of NAD⁺ and ATP synthesis. Our results provide new perspectives on the mechanisms underlying brain aging and neurodegenerative diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00705-2.

Transcriptomic Analysis of Laying Hens Revealed the Role of Aging-Related Genes during Forced Molting

Molting in birds provides us with an ideal genetic model for understanding aging and rejuvenation since birds present younger characteristics for reproduction and appearance after molting. Forced molting (FM) by fasting in chickens causes aging of their reproductive system and then promotes cell redevelopment by providing water and feed again. To reveal the genetic mechanism of rejuvenation, we detected blood hormone indexes and gene expression levels in the hypothalamus and ovary of hens from five different periods during FM. Three hormones were identified as participating in FM. Furthermore, the variation trends of gene expression levels in the hypothalamus and ovary at five different stages were found to be basically similar using transcriptome analysis. Among them, 45 genes were found to regulate cell aging during fasting stress and 12 genes were found to promote cell development during the recovery period in the hypothalamus. In addition, five hub genes (INO80D, HELZ, AGO4, ROCK2, and RFX7) were identified by WGCNA. FM can restart the reproductive function of aged hens by regulating expression levels of genes associated with aging and development. Our study not only enriches the theoretical basis of FM but also provides insights for the study of antiaging in humans and the conception mechanism in elderly women.

Oligodendrocytes enhance axonal energy metabolism by deacetylation of mitochondrial proteins through transcellular delivery of SIRT2

Neurons require mechanisms to maintain ATP homeostasis in axons, which are highly vulnerable to bioenergetic failure. Here, we elucidate a transcellular signaling mechanism by which oligodendrocytes support axonal energy metabolism via transcellular delivery of NAD-dependent deacetylase SIRT2. SIRT2 is undetectable in neurons but enriched in oligodendrocytes and released within exosomes. By deleting sirt2, knocking down SIRT2, or blocking exosome release, we demonstrate that transcellular delivery of SIRT2 is critical for axonal energy enhancement. Mass spectrometry and acetylation analyses indicate that neurons treated with oligodendrocyte-conditioned media from WT, but not sirt2-knockout, mice exhibit strong deacetylation of mitochondrial adenine nucleotide translocases 1 and 2 (ANT1/2). In vivo delivery of SIRT2-filled exosomes into myelinated axons rescues mitochondrial integrity in sirt2-knockout mouse spinal cords. Thus, our study reveals an oligodendrocyte-to-axon delivery of SIRT2, which enhances ATP production by deacetylating mitochondrial proteins, providing a target for boosting axonal bioenergetic metabolism in neurological disorders.

Conditional Knockout of Pdha1 in Mouse Hippocampus Impairs Cognitive Function: The Possible Involvement of Lactate

Background and Purpose: Neurodegenerative diseases are associated with metabolic disturbances. Pyruvate dehydrogenase E1 component subunit alpha (PDHA1) is an essential component in the process of glucose metabolism, and its deficiency exists in various diseases such as Alzheimer’s disease (AD), epilepsy, Leigh’s syndrome, and diabetes-associated cognitive decline. However, the exact role of PDHA1 deficiency in neurodegenerative diseases remains to be elucidated. In this study, we explored the effect of PDHA1 deficiency on cognitive function and its molecular mechanism.

Methods: A hippocampus-specific Pdha1 knockout (Pdha1^–/–) mouse model was established, and behavioral tests were used to evaluate the cognitive function of mice. Transmission electron microscopy (TEM) was performed to observe the morphological changes of the hippocampus. The lactate level in the hippocampus was measured. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting were used to explore the possible mechanism of the effect of PDHA1 on cognition.

Results:Pdha1 knockout damaged the spatial memory of mice and led to the ultrastructural disorder of hippocampal neurons. Lactate accumulation and abnormal lactate transport occurred in Pdha1^–/– mice, and the cyclic AMP-protein kinase A-cAMP response element-binding protein (cAMP/PKA/CREB) pathway was inhibited.

Conclusion: Lactate accumulation caused by PDHA1 deficiency in the hippocampus may impair cognitive function by inhibiting the cAMP/PKA/CREB pathway.

Low peripheral mitochondrial DNA copy number during manic episodes of bipolar disorders is associated with disease severity and inflammation

Mitochondria (Mt) are intra-cellular components essential for cellular energy processes whose dysfunction may induce premature cellular senescence and/or inflammation, both observed in bipolar disorders (BD). We investigated mitochondrial DNA copy number (mtDNAcn) levels in patients with BD being in manic, depressive or euthymic phase and in healthy controls (HC) both characterized for the levels of blood-based inflammatory markers and stigma of pathogens. 312 patients with BD were compared to 180 HC. mtDNAcn were measured using a digital droplet PCR. Serum levels of 14 inflammatory molecules and 3 anti-infectious IgG stigma were respectively evaluated by electro-chemiluminescence, ELISA and dedicated immunoassays. The statistical analyses were performed using Spearman's correlation, Wilcoxon signed-rank and Kruskal-Wallis rank sum tests. P-values were adjusted for multiple testing with Benjamini-Hochberg method. We found low levels of mtDNAcn in BD patients as compared to HC (P = 0.008) especially during manic episodes (P = 0.0002). We also observed that low levels of mtDNAcn are negatively correlated with mood and psychotic scales (PANSS, YMRS and CGI) (adjusted P (Adj P) = 0.02, 0.003 and 0.05 respectively) and positively with the GAF severity scale (Adj P = 0.002). They were also correlated with high levels of both intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 (Adj P = 0.003 and 0.001) along with a trend toward increased IL-2, IL-10 and B2M circulating levels (Adj P = 0.05). Here, we report correlations between marker of mitochondria functioning and both clinical scales and inflammatory markers in BD patients experiencing manic episodes. If replicated, these finding might allow to predict transition between disease phases and to design accurate therapeutic options.

Metformin and cyanidin 3-O-galactoside from Aronia melanocarpa synergistically alleviate cognitive impairment in SAMP8 mice

Cyanidin 3-O-galactoside (Cy3Gal) from Aronia melanocarpa has been reported to alleviate cognitive impairment. Metformin for preventing the neurodegenerative disease is attracting increasing attention. However, the neuroprotective and metabolic health promoting both of their effects are not clear. We chose the senescence accelerated mouse prone 8 (SAMP8) as a model of spontaneous learning and memory impairment. This study aimed to investigate the synergistic neuroprotective effect of metformin and Cy3Gal by behavioral and histopathological assays and metabolite analysis in SAMP8 mice. The SAMR1 mice were the normal group, and the SAMP8 mice were divided into five groups, including the SAMP8 model group, the donepezil (1 mg kg^-1, ig) group, the metformin (100 mg kg^-1, ig) group, the Cy3Gal (25 mg kg^-1, ig) group, and the combination of metformin plus Cy3Gal (Met + Cy3Gal, 100 mg kg^-1, 25 mg kg^-1, ig) group. The behavior experiments showed that the SAMP8 mice treated with metformin and Cy3Gal showed improved spatial learning and memory compared to the SAMP8 model group. The number of neurons in the Met + Cy3Gal group was significantly higher than that in the SAMP8 group and the Met + Cy3Gal group showed significantly reduced Aβ aggregation in the brain, which was elevated in SAMP8 mice. Compared with SAMP8 mice, the Met + Cy3Gal group showed decreased indole, methyl esters and ketones and increased short-chain fatty acids and alcohols in feces and urine by regulating the fatty acid biosynthesis and degradation. This study confirmed the neuroprotective effects of coadministration of metformin and cyanidin 3-O-galactoside in the SAMP8 mice, and suggested its positive effect on postponing the progression of Alzheimer's disease.

Mitochondrial Electron Transport Chain Protein Abnormalities Detected in Plasma Extracellular Vesicles in Alzheimer's Disease

Mitochondria provide energy to neurons through oxidative phosphorylation and eliminate Reactive Oxygen Species (ROS) through Superoxide Dismutase 1 (SOD1). Dysfunctional mitochondria, manifesting decreased activity of electron transport chain (ETC) complexes and high ROS levels, are involved in Alzheimer’s disease (AD) pathogenesis. We hypothesized that neuronal mitochondrial dysfunction in AD is reflected in ETC and SOD1 levels and activity in plasma neuron-derived extracellular vesicles (NDEVs). We immunoprecipitated NDEVs targeting neuronal marker L1CAM from two cohorts: one including 22 individuals with early AD and 29 control subjects; and another including 14 individuals with early AD and 14 control subjects. In the first cohort, we measured levels of complexes I, III, IV, ATP synthase, and SOD1; in the second cohort, we measured levels and catalytic activity of complexes IV and ATP synthase. AD individuals had lower levels of complexes I (p < 0.0001), III (p < 0.0001), IV (p = 0.0061), and V (p < 0.0001), and SOD1 (p < 0.0001) compared to controls. AD individuals also had lower levels of catalytic activity of complex IV (p = 0.0214) and ATP synthase (p < 0.0001). NDEVs confirm quantitative and functional abnormalities in ECT complexes and SOD1 previously observed in AD models and during autopsy, opening the way for using them as biomarkers for mitochondrial dysfunction in AD.

Effects of aging on protein expression in mice brain microvessels: ROS scavengers, mRNA/protein stability, glycolytic enzymes, mitochondrial complexes, and basement membrane components

Differentially expressed (DE) proteins in the cortical microvessels (MVs) of young, middle-aged, and old male and female mice were evaluated using discovery-based proteomics analysis (> 4,200 quantified proteins/group). Most DE proteins (> 90%) showed no significant differences between the sexes; however, some significant DE proteins showing sexual differences in MVs decreased from young (8.3%), to middle-aged (3.7%), to old (0.5%) mice. Therefore, we combined male and female data for age-dependent comparisons but noted sex differences for examination. Key proteins involved in the oxidative stress response, mRNA or protein stability, basement membrane (BM) composition, aerobic glycolysis, and mitochondrial function were significantly altered with aging. Relative abundance of superoxide dismutase-1/-2, catalase and thioredoxin were reduced with aging. Proteins participating in either mRNA degradation or pre-mRNA splicing were significantly increased in old mice MVs, whereas protein stabilizing proteins decreased. Glycolytic proteins were not affected in middle age, but the relative abundance of these proteins decreased in MVs of old mice. Although most of the 41 examined proteins composing mitochondrial complexes I–V were reduced in old mice, six of these proteins showed a significant reduction in middle-aged mice, but the relative abundance increased in fourteen proteins. Nidogen, collagen, and laminin family members as well as perlecan showed differing patterns during aging, indicating BM reorganization starting in middle age. We suggest that increased oxidative stress during aging leads to adverse protein profile changes of brain cortical MVs that affect mRNA/protein stability, BM integrity, and ATP synthesis capacity.

The Spatiotemporal Coupling: Regional Energy Failure and Aberrant Proteins in Neurodegenerative Diseases

The spatial and temporal coordination of each element is a pivotal characteristic of systems, and the central nervous system (CNS) is not an exception. Glial elements and the vascular interface have been considered more recently, together with the extracellular matrix and the immune system. However, the knowledge of the single-element configuration is not sufficient to predict physiological or pathological long-lasting changes. Ionic currents, complex molecular cascades, genomic rearrangement, and the regional energy demand can be different even in neighboring cells of the same phenotype, and their differential expression could explain the region-specific progression of the most studied neurodegenerative diseases. We here reviewed the main nodes and edges of the system, which could be studied to develop a comprehensive knowledge of CNS plasticity from the neurovascular unit to the synaptic cleft. The future goal is to redefine the modeling of synaptic plasticity and achieve a better understanding of neurological diseases, pointing out cellular, subcellular, and molecular components that couple in specific neuroanatomical and functional regions.

Hippocampal disruptions of synaptic and astrocyte metabolism are primary events of early amyloid pathology in the 5xFAD mouse model of Alzheimer's disease

Alzheimer’s disease (AD) is an unremitting neurodegenerative disorder characterized by cerebral amyloid-β (Aβ) accumulation and gradual decline in cognitive function. Changes in brain energy metabolism arise in the preclinical phase of AD, suggesting an important metabolic component of early AD pathology. Neurons and astrocytes function in close metabolic collaboration, which is essential for the recycling of neurotransmitters in the synapse. However, this crucial metabolic interplay during the early stages of AD development has not been sufficiently investigated. Here, we provide an integrative analysis of cellular metabolism during the early stages of Aβ accumulation in the cerebral cortex and hippocampus of the 5xFAD mouse model of AD. Our electrophysiological examination revealed an increase in spontaneous excitatory signaling in the 5xFAD hippocampus. This hyperactive neuronal phenotype coincided with decreased hippocampal tricarboxylic acid (TCA) cycle metabolism mapped by stable ¹³C isotope tracing. Particularly, reduced astrocyte TCA cycle activity and decreased glutamine synthesis led to hampered neuronal GABA synthesis in the 5xFAD hippocampus. In contrast, the cerebral cortex of 5xFAD mice displayed an elevated capacity for oxidative glucose metabolism, which may suggest a metabolic compensation in this brain region. We found limited changes when we explored the brain proteome and metabolome of the 5xFAD mice, supporting that the functional metabolic disturbances between neurons and astrocytes are early primary events in AD pathology. In addition, synaptic mitochondrial and glycolytic function was selectively impaired in the 5xFAD hippocampus, whereas non-synaptic mitochondrial function was maintained. These findings were supported by ultrastructural analyses demonstrating disruptions in mitochondrial morphology, particularly in the 5xFAD hippocampus. Collectively, our study reveals complex regional and cell-specific metabolic adaptations in the early stages of amyloid pathology, which may be fundamental for the progressing synaptic dysfunctions in AD.

Deuterium Metabolic Imaging of the Healthy and Diseased Brain

Altered brain metabolism contributes to pathophysiology in cerebrovascular and neurodegenerative diseases such as stroke and Alzheimer's disease. Current clinical tools to study brain metabolism rely on positron emission tomography (PET) requiring specific hardware and radiotracers, or magnetic resonance spectroscopy (MRS) involving technical complexity. In this review we highlight deuterium metabolic imaging (DMI) as a novel translational technique for assessment of brain metabolism, with examples from brain tumor and stroke studies. DMI is an MRS-based method that enables detection of deuterated substrates, such as glucose, and their metabolic products, such as lactate, glutamate and glutamine. It provides additional detail of downstream metabolites compared to analogous approaches like fluorodeoxyglucose (FDG)-PET, and can be implemented and executed on clinical and preclinical MR systems. We foresee that DMI, with future improvements in spatial and temporal resolutions, holds promise to become a valuable MR imaging (MRI) method for non-invasive mapping of glucose uptake and its downstream metabolites in healthy and diseased brain.

Brain energy failure in dementia syndromes: Opportunities and challenges for glucagon-like peptide-1 receptor agonists

Medications for type 2 diabetes (T2DM) offer a promising path for discovery and development of effective interventions for dementia syndromes. A common feature of dementia syndromes is an energy failure due to reduced energy supply to neurons and is associated with synaptic loss and results in cognitive decline and behavioral changes. Among diabetes medications, glucagon‐like peptide‐1 (GLP‐1) receptor agonists (RAs) promote protective effects on vascular, microglial, and neuronal functions. In this review, we present evidence from animal models, imaging studies, and clinical trials that support developing GLP‐1 RAs for dementia syndromes. The review examines how changes in brain energy metabolism differ in conditions of insulin resistance and T2DM from dementia and underscores the challenges that arise from the heterogeneity of dementia syndromes. The development of GLP‐1 RAs as dementia therapies requires a deeper understanding of the regional changes in brain energy homeostasis guided by novel imaging biomarkers.

Metabolic and Signaling Roles of Ketone Bodies in Health and Disease

Ketone bodies play significant roles in organismal energy homeostasis, serving as oxidative fuels, modulators of redox potential, lipogenic precursors, and signals, primarily during states of low carbohydrate availability. Efforts to enhance wellness and ameliorate disease via nutritional, chronobiological, and pharmacological interventions have markedly intensified interest in ketone body metabolism. The two ketone body redox partners, acetoacetate and D-β-hydroxybutyrate, serve distinct metabolic and signaling roles in biological systems. We discuss the pleiotropic roles played by both of these ketones in health and disease. While enthusiasm is warranted, prudent procession through therapeutic applications of ketogenic and ketone therapies is also advised, as a range of metabolic and signaling consequences continue to emerge. Organ-specific and cell-type-specific effects of ketone bodies are important to consider as prospective therapeutic and wellness applications increase.

Relieving Cellular Energy Stress in Aging, Neurodegenerative, and Metabolic Diseases, SIRT1 as a Therapeutic and Promising Node

The intracellular energy state will alter under the influence of physiological or pathological stimuli. In response to this change, cells usually mobilize various molecules and their mechanisms to promote the stability of the intracellular energy status. Mitochondria are the main source of ATP. Previous studies have found that the function of mitochondria is impaired in aging, neurodegenerative diseases, and metabolic diseases, and the damaged mitochondria bring lower ATP production, which further worsens the progression of the disease. Silent information regulator-1 (SIRT1) is a multipotent molecule that participates in the regulation of important biological processes in cells, including cellular metabolism, cell senescence, and inflammation. In this review, we mainly discuss that promoting the expression and activity of SIRT1 contributes to alleviating the energy stress produced by physiological and pathological conditions. The review also discusses the mechanism of precise regulation of SIRT1 expression and activity in various dimensions. Finally, according to the characteristics of this mechanism in promoting the recovery of mitochondrial function, the relationship between current pharmacological preparations and aging, neurodegenerative diseases, metabolic diseases, and other diseases was analyzed.

Functional Metabolic Mapping Reveals Highly Active Branched-Chain Amino Acid Metabolism in Human Astrocytes, Which Is Impaired in iPSC-Derived Astrocytes in Alzheimer's Disease

The branched-chain amino acids (BCAAs) leucine, isoleucine, and valine are important nitrogen donors for synthesis of glutamate, the main excitatory neurotransmitter in the brain. The glutamate carbon skeleton originates from the tricarboxylic acid (TCA) cycle intermediate α-ketoglutarate, while the amino group is derived from nitrogen donors such as the BCAAs. Disturbances in neurotransmitter homeostasis, mainly of glutamate, are strongly implicated in the pathophysiology of Alzheimer's disease (AD). The divergent BCAA metabolism in different cell types of the human brain is poorly understood, and so is the involvement of astrocytic and neuronal BCAA metabolism in AD. The goal of this study is to provide the first functional characterization of BCAA metabolism in human brain tissue and to investigate BCAA metabolism in AD pathophysiology using astrocytes and neurons derived from human-induced pluripotent stem cells (hiPSCs). Mapping of BCAA metabolism was performed using mass spectrometry and enriched [¹⁵N] and [¹³C] isotopes of leucine, isoleucine, and valine in acutely isolated slices of surgically resected cerebral cortical tissue from human brain and in hiPSC-derived brain cells carrying mutations in either amyloid precursor protein (APP) or presenilin-1 (PSEN-1). We revealed that both human astrocytes of acutely isolated cerebral cortical slices and hiPSC-derived astrocytes were capable of oxidatively metabolizing the carbon skeleton of BCAAs, particularly to support glutamine synthesis. Interestingly, hiPSC-derived astrocytes with APP and PSEN-1 mutations exhibited decreased amino acid synthesis of glutamate, glutamine, and aspartate derived from leucine metabolism. These results clearly demonstrate that there is an active BCAA metabolism in human astrocytes, and that leucine metabolism is selectively impaired in astrocytes derived from the hiPSC models of AD. This impairment in astrocytic BCAA metabolism may contribute to neurotransmitter and energetic imbalances in the AD brain.

Impairments in Brain Bioenergetics in Aging and Tau Pathology: A Chicken and Egg Situation?

The brain is the most energy-consuming organ of the body and impairments in brain energy metabolism will affect neuronal functionality and viability. Brain aging is marked by defects in energetic metabolism. Abnormal tau protein is a hallmark of tauopathies, including Alzheimer's disease (AD). Pathological tau was shown to induce bioenergetic impairments by affecting mitochondrial function. Although it is now clear that mutations in the tau-coding gene lead to tau pathology, the causes of abnormal tau phosphorylation and aggregation in non-familial tauopathies, such as sporadic AD, remain elusive. Strikingly, both tau pathology and brain hypometabolism correlate with cognitive impairments in AD. The aim of this review is to discuss the link between age-related decrease in brain metabolism and tau pathology. In particular, the following points will be discussed: (i) the common bioenergetic features observed during brain aging and tauopathies; (ii) how age-related bioenergetic defects affect tau pathology; (iii) the influence of lifestyle factors known to modulate brain bioenergetics on tau pathology. The findings compiled here suggest that age-related bioenergetic defects may trigger abnormal tau phosphorylation/aggregation and cognitive impairments after passing a pathological threshold. Understanding the effects of aging on brain metabolism may therefore help to identify disease-modifying strategies against tau-induced neurodegeneration.

Nuclear and Mitochondrial Genome, Epigenome and Gut Microbiome: Emerging Molecular Biomarkers for Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is currently the second most common neurodegenerative disorder, burdening about 10 million elderly individuals worldwide. The multifactorial nature of PD poses a difficult obstacle for understanding the mechanisms involved in its onset and progression. Currently, diagnosis depends on the appearance of clinical signs, some of which are shared among various neurologic disorders, hindering early diagnosis. There are no effective tools to prevent PD onset, detect the disease in early stages or accurately report the risk of disease progression. Hence, there is an increasing demand for biomarkers that may identify disease onset and progression, as treatment-based medicine may not be the best approach for PD. Over the last few decades, the search for molecular markers to predict susceptibility, aid in accurate diagnosis and evaluate the progress of PD have intensified, but strategies aimed to improve individualized patient care have not yet been established.

CONCLUSIONS

Genomic variation, regulation by epigenomic mechanisms, as well as the influence of the host gut microbiome seem to have a crucial role in the onset and progress of PD, thus are considered potential biomarkers. As such, the human nuclear and mitochondrial genome, epigenome, and the host gut microbiome might be the key elements to the rise of personalized medicine for PD patients.

Effects of dietary restriction on neuroinflammation in neurodegenerative diseases

Recent and accumulating work in experimental animal models and humans shows that diet has a much more pervasive and prominent role than previously thought in modulating neuroinflammatory and neurodegenerative mechanisms leading to some of the most common chronic central nervous system (CNS) diseases. Chronic or intermittent food restriction has profound effects in shaping brain and peripheral metabolism, immunity, and gut microbiome biology. Interactions among calorie intake, meal frequency, diet quality, and the gut microbiome modulate specific metabolic and molecular pathways that regulate cellular, tissue, and organ homeostasis as well as inflammation during normal brain aging and CNS neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis, among others. This review discusses these findings and their potential application to the prevention and treatment of CNS neuroinflammatory diseases and the promotion of healthy brain aging.

Serum proBDNF Is Associated With Changes in the Ketone Body β-Hydroxybutyrate and Shows Superior Repeatability Over Mature BDNF: Secondary Outcomes From a Cross-Over Trial in Healthy Older Adults

Background: β-hydroxybutyrate (BHB) can upregulate brain-derived neurotrophic factor (BDNF) in mice, but little is known about the associations between BHB and BDNF in humans. The primary aim here was to investigate whether ketosis (i.e., raised BHB levels), induced by a ketogenic supplement, influences serum levels of mature BDNF (mBDNF) and its precursor proBDNF in healthy older adults. A secondary aim was to determine the intra-individual stability (repeatability) of those biomarkers, measured as intra-class correlation coefficients (ICC).

Method: Three of the arms in a 6-arm randomized cross-over trial were used for the current sub-study. Fifteen healthy volunteers, 65–75 y, 53% women, were tested once a week. Test oils, mixed in coffee and cream, were ingested after a 12-h fast. Labeled by their level of ketosis, the arms provided: sunflower oil (lowK); coconut oil (midK); caprylic acid + coconut oil (highK). Repeated blood samples were collected for 4 h after ingestion. Serum BDNF levels were analyzed for changes from baseline to 1, 2 and 4 h to compare the arms. Individual associations between BHB and BDNF were analyzed cross-sectionally and for a delayed response (changes in BHB 0–2 h to changes in BDNF at 0–4 h). ICC estimates were calculated from baseline levels from the three study days.

Results: proBDNF increased more in highK vs. lowK between 0 and 4 h (z-score: β = 0.25, 95% CI 0.07–0.44; p = 0.007). Individual change in BHB 0–2 h, predicted change in proBDNF 0–4 h, (β = 0.40, CI 0.12–0.67; p = 0.006). Change in mBDNF was lower in highK vs. lowK at 0–2 h (β = −0.88, CI −1.37 to −0.40; p < 0.001) and cumulatively 0–4 h (β = −1.01, CI −1.75 to −0.27; p = 0.01), but this could not be predicted by BHB levels. ICC was 0.96 (95% CI 0.92–0.99) for proBDNF, and 0.72 (CI 0.47–0.89) for mBDNF.

Conclusions: The findings support a link between changes in peripheral BHB and proBDNF in healthy older adults. For mBDNF, changes differed between arms but independent to BHB levels. Replication is warranted due to the small sample. Excellent repeatability encourages future investigations on proBDNF as a predictor of brain health.

Clinical Trial Registration:ClinicalTrials.gov, NCT03904433.

Creatine transporter deficiency impairs stress adaptation and brain energetics homeostasis

The creatine transporter (CrT) maintains brain creatine (Cr) levels, but the effects of its deficiency on energetics adaptation under stress remain unclear. There are also no effective treatments for CrT deficiency, the second most common cause of X-linked intellectual disabilities. Herein, we examined the consequences of CrT deficiency in brain energetics and stress-adaptation responses plus the effects of intranasal Cr supplementation. We found that CrT-deficient (CrT^–/y) mice harbored dendritic spine and synaptic dysgenesis. Nurtured newborn CrT^–/y mice maintained baseline brain ATP levels, with a trend toward signaling imbalance between the p-AMPK/autophagy and mTOR pathways. Starvation elevated the signaling imbalance and reduced brain ATP levels in P3 CrT^–/y mice. Similarly, CrT^–/y neurons and P10 CrT^–/y mice showed an imbalance between autophagy and mTOR signaling pathways and greater susceptibility to cerebral hypoxia-ischemia and ischemic insults. Notably, intranasal administration of Cr after cerebral ischemia increased the brain Cr/N-acetylaspartate ratio, partially averted the signaling imbalance, and reduced infarct size more potently than intraperitoneal Cr injection. These findings suggest important functions for CrT and Cr in preserving the homeostasis of brain energetics in stress conditions. Moreover, intranasal Cr supplementation may be an effective treatment for congenital CrT deficiency and acute brain injury.

Mitochondrial dysfunctions in neurodegenerative diseases: role in disease pathogenesis, strategies for analysis and therapeutic prospects

Fundamental organelles that occur in every cell type with the exception of mammal erythrocytes, the mitochondria are required for multiple pivotal processes that include the production of biological energy, the biosynthesis of reactive oxygen species, the control of calcium homeostasis, and the triggering of cell death. The disruption of anyone of these processes has been shown to impact strongly the function of all cells, but especially of neurons. In this review, we discuss the role of the mitochondria impairment in the development of the neurodegenerative diseases Amyotrophic Lateral Sclerosis, Parkinson's disease and Alzheimer's disease. We highlight how mitochondria disruption revolves around the processes that underlie the mitochondria's life cycle: fusion, fission, production of reactive oxygen species and energy failure. Both genetic and sporadic forms of neurodegenerative diseases are unavoidably accompanied with and often caused by the dysfunction in one or more of the key mitochondrial processes. Therefore, in order to get in depth insights into their health status in neurodegenerative diseases, we need to focus into innovative strategies aimed at characterizing the various mitochondrial processes. Current techniques include Mitostress, Mitotracker, transmission electron microscopy, oxidative stress assays along with expression measurement of the proteins that maintain the mitochondrial health. We will also discuss a panel of approaches aimed at mitigating the mitochondrial dysfunction. These include canonical drugs, natural compounds, supplements, lifestyle interventions and innovative approaches as mitochondria transplantation and gene therapy. In conclusion, because mitochondria are fundamental organelles necessary for virtually all the cell functions and are severely impaired in neurodegenerative diseases, it is critical to develop novel methods to measure the mitochondrial state, and novel therapeutic strategies aimed at improving their health.

Astrocyte metabolism of the medium-chain fatty acids octanoic acid and decanoic acid promotes GABA synthesis in neurons via elevated glutamine supply

The medium-chain fatty acids octanoic acid (C8) and decanoic acid (C10) are gaining attention as beneficial brain fuels in several neurological disorders. The protective effects of C8 and C10 have been proposed to be driven by hepatic production of ketone bodies. However, plasma ketone levels correlates poorly with the cerebral effects of C8 and C10, suggesting that additional mechanism are in place. Here we investigated cellular C8 and C10 metabolism in the brain and explored how the protective effects of C8 and C10 may be linked to cellular metabolism. Using dynamic isotope labeling, with [U-¹³C]C8 and [U-¹³C]C10 as metabolic substrates, we show that both C8 and C10 are oxidatively metabolized in mouse brain slices. The ¹³C enrichment from metabolism of [U-¹³C]C8 and [U-¹³C]C10 was particularly prominent in glutamine, suggesting that C8 and C10 metabolism primarily occurs in astrocytes. This finding was corroborated in cultured astrocytes in which C8 increased the respiration linked to ATP production, whereas C10 elevated the mitochondrial proton leak. When C8 and C10 were provided together as metabolic substrates in brain slices, metabolism of C10 was predominant over that of C8. Furthermore, metabolism of both [U-¹³C]C8 and [U-¹³C]C10 was unaffected by etomoxir indicating that it is independent of carnitine palmitoyltransferase I (CPT-1). Finally, we show that inhibition of glutamine synthesis selectively reduced ¹³C accumulation in GABA from [U-¹³C]C8 and [U-¹³C]C10 metabolism in brain slices, demonstrating that the glutamine generated from astrocyte C8 and C10 metabolism is utilized for neuronal GABA synthesis. Collectively, the results show that cerebral C8 and C10 metabolism is linked to the metabolic coupling of neurons and astrocytes, which may serve as a protective metabolic mechanism of C8 and C10 supplementation in neurological disorders.

Metformin a Potential Pharmacological Strategy in Late Onset Alzheimer's Disease Treatment

Alzheimer's disease (AD) is one of the most devastating brain disorders. Currently, there are no effective treatments to stop the disease progression and it is becoming a major public health concern. Several risk factors are involved in the progression of AD, modifying neuronal circuits and brain cognition, and eventually leading to neuronal death. Among them, obesity and type 2 diabetes mellitus (T2DM) have attracted increasing attention, since brain insulin resistance can contribute to neurodegeneration. Consequently, AD has been referred to "type 3 diabetes" and antidiabetic medications such as intranasal insulin, glitazones, metformin or liraglutide are being tested as possible alternatives. Metformin, a first line antihyperglycemic medication, is a 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK) activator hypothesized to act as a geroprotective agent. However, studies on its association with age-related cognitive decline have shown controversial results with positive and negative findings. In spite of this, metformin shows positive benefits such as anti-inflammatory effects, accelerated neurogenesis, strengthened memory, and prolonged life expectancy. Moreover, it has been recently demonstrated that metformin enhances synaptophysin, sirtuin-1, AMPK, and brain-derived neuronal factor (BDNF) immunoreactivity, which are essential markers of plasticity. The present review discusses the numerous studies which have explored (1) the neuropathological hallmarks of AD, (2) association of type 2 diabetes with AD, and (3) the potential therapeutic effects of metformin on AD and preclinical models.

Amyotrophic lateral sclerosis alters the metabolic aging profile in patient derived fibroblasts

Aging is a major risk factor for neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). As metabolic alterations are a hallmark of aging and have previously been observed in ALS, it is important to examine the effect of aging in the context of ALS metabolic function. Here, using a newly established phenotypic metabolic approach, we examined the effect of aging on the metabolic profile of fibroblasts derived from ALS cases compared to controls. We found that ALS fibroblasts have an altered metabolic profile, which is influenced by age. In control cases, we found significant increases with age in NADH metabolism in the presence of several metabolites including lactic acid, trehalose, uridine and fructose, which was not recapitulated in ALS cases. Conversely, we found a reduction of NADH metabolism with age of biopsy, age of onset and age of death in the presence of glycogen in the ALS cohort. Furthermore, we found that NADH production correlated with disease progression rates in relation to a number of metabolites including inosine and α-ketoglutaric acid. Inosine or α-ketoglutaric acid supplementation in ALS fibroblasts was bioenergetically favourable. Overall, we found aging related defects in energy substrates that feed carbon into glycolysis at various points as well as the tricarboxylic acid (TCA) cycle in ALS fibroblasts, which was validated in induced neuronal progenitor cell derived iAstrocytes. Our results suggest that supplementing those pathways may protect against age related metabolic dysfunction in ALS.

Alzheimer's disease alters oligodendrocytic glycolytic and ketolytic gene expression

INTRODUCTION

Sporadic Alzheimer's disease (AD) is strongly correlated with impaired brain glucose metabolism, which may affect AD onset and progression. Ketolysis has been suggested as an alternative pathway to fuel the brain.

METHODS

RNA-seq profiles of post mortem AD brains were used to determine whether dysfunctional AD brain metabolism can be determined by impairments in glycolytic and ketolytic gene expression. Data were obtained from the Knight Alzheimer's Disease Research Center (62 cases; 13 controls), Mount Sinai Brain Bank (110 cases; 44 controls), and the Mayo Clinic Brain Bank (80 cases; 76 controls), and were normalized to cell type: astrocytes, microglia, neurons, oligodendrocytes.

RESULTS

In oligodendrocytes, both glycolytic and ketolytic pathways were significantly impaired in AD brains. Ketolytic gene expression was not significantly altered in neurons, astrocytes, and microglia.

DISCUSSION

Oligodendrocytes may contribute to brain hypometabolism observed in AD. These results are suggestive of a potential link between hypometabolism and dysmyelination in disease physiology. Additionally, ketones may be therapeutic in AD due to their ability to fuel neurons despite impaired glycolytic metabolism.

Pericytes: Intrinsic Transportation Engineers of the CNS Microcirculation

Pericytes in the brain are candidate regulators of microcirculatory blood flow because they are strategically positioned along the microvasculature, contain contractile proteins, respond rapidly to neuronal activation, and synchronize microvascular dynamics and neurovascular coupling within the capillary network. Analyses of mice with defects in pericyte generation demonstrate that pericytes are necessary for the formation of the blood-brain barrier, development of the glymphatic system, immune homeostasis, and white matter function. The development, identity, specialization, and progeny of different subtypes of pericytes, however, remain unclear. Pericytes perform brain-wide 'transportation engineering' functions in the capillary network, instructing, integrating, and coordinating signals within the cellular communicome in the neurovascular unit to efficiently distribute oxygen and nutrients ('goods and services') throughout the microvasculature ('transportation grid'). In this review, we identify emerging challenges in pericyte biology and shed light on potential pericyte-targeted therapeutic strategies.

Astrocyte-neuron metabolic cooperation shapes brain activity

The brain has almost no energy reserve, but its activity coordinates organismal function, a burden that requires precise coupling between neurotransmission and energy metabolism. Deciphering how the brain accomplishes this complex task is crucial to understand central facets of human physiology and disease mechanisms. Each type of neural cell displays a peculiar metabolic signature, forcing the intercellular exchange of metabolites that serve as both energy precursors and paracrine signals. The paradigm of this biological feature is the astrocyte-neuron couple, in which the glycolytic metabolism of astrocytes contrasts with the mitochondrial oxidative activity of neurons. Astrocytes generate abundant mitochondrial reactive oxygen species and shuttle to neurons glycolytically derived metabolites, such as L-lactate and L-serine, which sustain energy needs, conserve redox status, and modulate neurotransmitter-receptor activity. Conversely, early disruption of this metabolic cooperation may contribute to the initiation or progression of several neurological diseases, thus requiring innovative therapies to preserve brain energetics.

Dietary medium chain triglycerides for management of epilepsy: New data from human, dog, and rodent studies

Many studies show that glucose metabolism in epileptic brain areas can be impaired. Energy is crucial to maintain normal brain function, including ion and neurotransmitter balances. Energy deficits can lead to disruption of ion gradients, which can trigger neuronal depolarization and generation of seizures. Thus, perturbed metabolic processing of glucose in epileptogenic brain areas indicates a specific nutritional need for people and animals with epilepsy, as they are likely to benefit from auxiliary brain fuels other than glucose. Ketogenic diets provide the ketone bodies acetoacetate and β-hydroxybutyrate, which can be used as auxiliary fuel by the brain. In approximately 50% children and adults with certain types of epilepsy, who can tolerate and maintain these dietary regimens, seizure frequency can be effectively reduced. More recent data demonstrate that addition of medium chain triglycerides (MCTs), which provide the medium chain fatty acids octanoic and decanoic acid, as well as ketone bodies as auxiliary brain energy, can be beneficial in rodent seizure models, and dogs and humans with epilepsy. Here, this evidence is reviewed, including tolerance in 65% of humans, efficacy studies in dogs, possible anticonvulsant mechanisms of actions of MCTs, and specifically decanoic acid as well as metabolic and antioxidant mechanisms. In conclusion, MCTs are a promising adjunct to standard pharmacological treatment for both humans and dogs with epilepsy, as they lack central nervous system side effects found with current antiepileptic drugs. There is now a need for larger clinical trials in children, adults, and dogs to find the ideal composition and doses of MCTs and the types of epilepsy that respond best.

TLR2- and TLR3-activated microglia induce different levels of neuronal network dysfunction in a context-dependent manner

Recognition of pathogen- or damage-associated molecular patterns (PAMPs, DAMPs) by innate Toll-like receptors (TLRs) is central to the activation of microglia (brain macrophages) in many CNS diseases. Notably, TLR-mediated microglial activation is complex and modulated by additional exogenous and endogenous immunological signals. The impact of different microglial reactive phenotypes on electrical activity and neurotransmission is widely unknown, however. We explored the effects of TLR ligands on microglia and neuronal network function in rat organotypic hippocampal slice cultures (in situ), i.e., postnatal cortical tissue lacking adaptive immunity. Single exposure of slice cultures to TLR2 or TLR3 ligands [PGN, poly(I:C)] for 2-3 days induced moderate microglial activation featuring IL-6 and TNF-α release and only mild alterations of fast neuronal gamma band oscillations (30-70 Hz) that are fundamental to higher cognitive functions, such as perception, memory and behavior. Paired exposure to TLR3/TLR2 or TLR3/TLR4 ligands (LPS) induced nitric oxide (NO) release, enhanced TNF-α release, and associated with advanced network dysfunction, including slowing to the beta frequency band (12-30 Hz) and neural bursts (hyperexcitability). Paired exposure to a TLR ligand and the leukocyte cytokine IFN-γ enhanced NO release and associated with severe network dysfunction, albeit sensitive parvalbumin- and somatostatin-positive inhibitory interneurons were preserved. Notably, the neuronal disturbance was prevented by either microglial depletion or pharmacological inhibition of oxidant-producing enzymes, inducible NO synthase (iNOS) and NADPH oxidase. In conclusion, TLR-activated microglia can induce different levels of neuronal network dysfunction, in which severe dysfunction is mainly caused by reactive oxygen and nitrogen species rather than proinflammatory cytokines. Our findings provide a mechanistic insight into microglial activation and functional neuronal network impairment, with relevance to neuroinflammation and neurodegeneration observed in, e.g., meningoencephalitis, multiple sclerosis and Alzheimer's disease.

Structural and Functional Alterations in Mitochondria-Associated Membranes (MAMs) and in Mitochondria Activate Stress Response Mechanisms in an In Vitro Model of Alzheimer's Disease

Alzheimer’s disease (AD) is characterized by the accumulation of extracellular plaques composed by amyloid-β (Aβ) and intracellular neurofibrillary tangles of hyperphosphorylated tau. AD-related neurodegenerative mechanisms involve early changes of mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) and impairment of cellular events modulated by these subcellular domains. In this study, we characterized the structural and functional alterations at MAM, mitochondria, and ER/microsomes in a mouse neuroblastoma cell line (N2A) overexpressing the human amyloid precursor protein (APP) with the familial Swedish mutation (APPswe). Proteins levels were determined by Western blot, ER-mitochondria contacts were quantified by transmission electron microscopy, and Ca²⁺ homeostasis and mitochondria function were analyzed using fluorescent probes and Seahorse assays. In this in vitro AD model, we found APP accumulated in MAM and mitochondria, and altered levels of proteins implicated in ER-mitochondria tethering, Ca²⁺ signaling, mitochondrial dynamics, biogenesis and protein import, as well as in the stress response. Moreover, we observed a decreased number of close ER-mitochondria contacts, activation of the ER unfolded protein response, reduced Ca²⁺ transfer from ER to mitochondria, and impaired mitochondrial function. Together, these results demonstrate that several subcellular alterations occur in AD-like neuronal cells, which supports that the defective ER-mitochondria crosstalk is an important player in AD physiopathology.

Glutamate metabolism and recycling at the excitatory synapse in health and neurodegeneration

Glutamate is the primary excitatory neurotransmitter of the brain. Cellular homeostasis of glutamate is of paramount importance for normal brain function and relies on an intricate metabolic collaboration between neurons and astrocytes. Glutamate is extensively recycled between neurons and astrocytes in a process known as the glutamate-glutamine cycle. The recycling of glutamate is closely linked to brain energy metabolism and is essential to sustain glutamatergic neurotransmission. However, a considerable amount of glutamate is also metabolized and serves as a metabolic hub connecting glucose and amino acid metabolism in both neurons and astrocytes. Disruptions in glutamate clearance, leading to neuronal overstimulation and excitotoxicity, have been implicated in several neurodegenerative diseases. Furthermore, the link between brain energy homeostasis and glutamate metabolism is gaining attention in several neurological conditions. In this review, we provide an overview of the dynamics of synaptic glutamate homeostasis and the underlying metabolic processes with a cellular focus on neurons and astrocytes. In particular, we review the recently discovered role of neuronal glutamate uptake in synaptic glutamate homeostasis and discuss current advances in cellular glutamate metabolism in the context of Alzheimer's disease and Huntington's disease. Understanding the intricate regulation of glutamate-dependent metabolic processes at the synapse will not only increase our insight into the metabolic mechanisms of glutamate homeostasis, but may reveal new metabolic targets to ameliorate neurodegeneration.

Reappraisal of metabolic dysfunction in neurodegeneration: Focus on mitochondrial function and calcium signaling

The cellular and molecular mechanisms that drive neurodegeneration remain poorly defined. Recent clinical trial failures, difficult diagnosis, uncertain etiology, and lack of curative therapies prompted us to re-examine other hypotheses of neurodegenerative pathogenesis. Recent reports establish that mitochondrial and calcium dysregulation occur early in many neurodegenerative diseases (NDDs), including Alzheimer's disease, Parkinson's disease, Huntington's disease, and others. However, causal molecular evidence of mitochondrial and metabolic contributions to pathogenesis remains insufficient. Here we summarize the data supporting the hypothesis that mitochondrial and metabolic dysfunction result from diverse etiologies of neuropathology. We provide a current and comprehensive review of the literature and interpret that defective mitochondrial metabolism is upstream and primary to protein aggregation and other dogmatic hypotheses of NDDs. Finally, we identify gaps in knowledge and propose therapeutic modulation of mCa2+ exchange and mitochondrial function to alleviate metabolic impairments and treat NDDs.

Mild cognitive impairment: when nutrition helps brain energy rescue-a report from the EuGMS 2020 Congress

BACKGROUND

Mild cognitive impairment (MCI) is characterized by a decline in cognition and mainly affects older individuals above the age of 60. The global incidence of MCI varies, but it is often underdiagnosed and untreated. There is a distinct lack of approved pharmacologic options to treat MCI. There is, however, evidence to support the efficacy of nutritional interventions, such as ketogenic supplements/diets, which offer ketones as an alternative energy source to brain cells. This article explores the effect of ketones on metabolic activity in the brain and the mechanisms by which ketogenic medium-chain triglycerides (kMCTs) induce ketosis in patients with MCI.

KEY TAKEAWAYS

This article reviews the effect of ketogenic supplements/diets on brain metabolism, including evidence supporting the efficacy of ketones as an efficient fuel for the brain. It discusses the use of oral nutritional ketogenic supplements, with particular reference to the 6-month randomized controlled BENEFIC trial, which showed that consumption of a kMCT drink, BrainXpert Energy Complex, improved cognitive performance in individuals with MCI compared with placebo.

CONCLUSION

While there is a need for more long-term studies, results from the BENEFIC trial revealed the benefits of a brain-specific ketogenic supplement, as a nutritional intervention, on cognitive performance in individuals with MCI.

Mitoprotective Effects of Centella asiatica (L.) Urb.: Anti-Inflammatory and Neuroprotective Opportunities in Neurodegenerative Disease

Natural products remain a crucial source of drug discovery for accessible and affordable solutions for healthy aging. Centella asiatica (L.) Urb. (CA) is an important medicinal plant with a wide range of ethnomedicinal uses. Past in vivo and in vitro studies have shown that the plant extract and its key components, such as asiatic acid, asiaticoside, madecassic acid and madecassoside, exhibit a range of anti-inflammatory, neuroprotective, and cognitive benefits mechanistically linked to mitoprotective and antioxidant properties of the plant. Mitochondrial dysfunction and oxidative stress are key drivers of aging and neurodegenerative disease, including Alzheimer’s disease and Parkinson’s disease. Here we appraise the growing body of evidence that the mitoprotective and antioxidative effects of CA may potentially be harnessed for the treatment of brain aging and neurodegenerative disease.

Intranasal 15d-PGJ2 ameliorates brain glucose hypometabolism via PPARγ-dependent activation of PGC-1α/GLUT4 signalling in APP/PS1 transgenic mice

Targeting the common molecular mechanism of type 2 diabetes mellitus and Alzheimer's disease (AD), including dysregulation of glucose metabolism, insulin resistance, and neuroinflammation, might be an efficient treatment strategy for AD. Previous studies have shown that 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2), an endogenous PPARγ agonist, has anti-inflammatory, insulin sensitizing and anti-diabetic effects. However, whether 15d-PGJ2 has beneficial effects on AD remains to be elucidated. In the present study, we found that intranasal administration of 15d-PGJ2 (300 ng/30 μL/day) for 3 months significantly inhibited Aβ plaques, suppressed neuroinflammation, and attenuated cognitive deficits in APP/PS1 transgenic mice. Interestingly, 15d-PGJ2 treatment could increase brain glucose uptake, as detected by ¹⁸F-FDG microPET imaging, and co-localization of GLUT4 and NeuN in the hippocampus of APP/PS1 mice. Furthermore, 15d-PGJ2 markedly increased the expression of PPARγ and PGC-1α, upregulated GLUT4, and decreased the phosphorylation of IRS-1 (Ser616) in the hippocampus of APP/PS1 mice. Importantly, co-administration of a PPARγ antagonist GW9662 abrogated these protective effects of 15d-PGJ2. Collectively, intranasal 15d-PGJ2 conferred protective effects against AD by activating PPARγ-dependent PGC-1α/GLUT4 signalling. The PPARγ agonist 15d-PGJ2 might be a potential therapeutic drug for AD.

New insights into human prefrontal cortex aging with a lipidomics approach

INTRODUCTION

Human prefrontal cortex (hPFC) is a recent evolutionarily developed brain region involved in cognitive functions. Human cognitive functions decline during aging. Yet the molecular mechanisms underlying the functional deterioration of the neural cells of this brain region still remain to be fully described.

AREAS COVERED

In this review, we explore the role of lipids in hPFC aging. Firstly, we briefly consider the approaches used to identify lipid species in brain tissue with special attention paid to a lipidomics analysis. Then, as the evolution process has conferred a specific lipid profile on the hPFC, we consider the lipidome of hPFC. In addition, the role of lipids in hPFC aging, and in particular, the cognitive decline associated with aging, is discussed. Finally, nutritional and pharmacological interventions designed to modulate this process are examined. It is suggested that the dysfunction of key cellular processes secondarily to the damage of lipid membrane underlies the cognitive decline of hPFC during aging.

EXPERT OPINION

Lipidomics methods are and will continue to be key tools in the effort to gain additional insights into the aging of the human brain.

Glucose metabolic crosstalk and regulation in brain function and diseases

Brain glucose metabolism, including glycolysis, the pentose phosphate pathway, and glycogen turnover, produces ATP for energetic support and provides the precursors for the synthesis of biological macromolecules. Although glucose metabolism in neurons and astrocytes has been extensively studied, the glucose metabolism of microglia and oligodendrocytes, and their interactions with neurons and astrocytes, remain critical to understand brain function. Brain regions with heterogeneous cell composition and cell-type-specific profiles of glucose metabolism suggest that metabolic networks within the brain are complex. Signal transduction proteins including those in the Wnt, GSK-3β, PI3K-AKT, and AMPK pathways are involved in regulating these networks. Additionally, glycolytic enzymes and metabolites, such as hexokinase 2, acetyl-CoA, and enolase 2, are implicated in the modulation of cellular function, microglial activation, glycation, and acetylation of biomolecules. Given these extensive networks, glucose metabolism dysfunction in the whole brain or specific cell types is strongly associated with neurologic pathology including ischemic brain injury and neurodegenerative disorders. This review characterizes the glucose metabolism networks of the brain based on molecular signaling and cellular and regional interactions, and elucidates glucose metabolism-based mechanisms of neurological diseases and therapeutic approaches that may ameliorate metabolic abnormalities in those diseases.

The effect of a 6-month ketogenic medium-chain triglyceride supplement on plasma cardiometabolic and inflammatory markers in mild cognitive impairment

INTRODUCTION

Mild cognitive impairment (MCI) is often accompanied by metabolic abnormalities and inflammation that might play a role in the development of cognitive impairment. The use of ketogenic medium-chain triglycerides (kMCT) to improve cognition in this population has shown promising results but remains controversial because of the potentially detrimental effect of elevated intake of saturated fatty acids on cardiovascular (CV) health and perhaps inflammatory processes. The primary aim of this secondary data analysis report is to describe changes in cardiometabolic markers and peripheral inflammation during a 6-month kMCT intervention in MCI.

METHODS

Thirty-nine participants with MCI completed the intervention of 30 g/day of either a kMCT drink or calorie-matched placebo (high-oleic acid) for 6 months. Plasma concentrations of cardiometabolic and inflammatory markers were collected before (fasting state) and after the intervention (2 h following the last drink).

RESULTS

A mixed model ANOVA analysis revealed a time by group interaction for ketones (P < 0.001), plasma 8:0 and 10:0 acids (both P < 0.001) and IL-8 (P = 0.002) with follow up comparison revealing a significant increase in the kMCT group (+48%, P = 0.005), (+3,800 and +4,900%, both P < 0.001) and (+147%, P < 0.001) respectively. A main effect of time was observed for insulin (P = 0.004), triglycerides (P = 0.011) and non-esterified fatty acids (P = 0.036).

CONCLUSION

Under these study conditions, 30 g/d of kMCT taken for six months and up to 2-hour before post-intervention testing had minimal effect on an extensive profile of circulating cardiometabolic and inflammatory markers as compared to a placebo calorie-matched drink. Our results support the safety kMCT supplementation in individuals with MCI. The clinical significance of the observed increase in circulating IL-8 levels is presently unknown and awaits future studies.

Impact of supplementation with vitamins B6 , B12 , and/or folic acid on the reduction of homocysteine levels in patients with mild cognitive impairment: A systematic review

Hyperhomocysteinemia is an independent predictor of the risk for cognitive decline and may be a result of low levels of vitamins B₁₂ , B₆ , and folate. Previous findings suggest that adequate intake of these vitamins may reduce homocysteine levels. This review aimed to assess the effects of treatment with vitamins B_6, B₁₂ , and/or folic acid in the homocysteine levels in patients with mild cognitive impairment (MCI). A systematic literature review was conducted in EMBASE, MEDLINE®, PsycINFO, and Cochrane Central Register of Controlled Trials. The research question was formulated using the Population, Intervention, Comparison, and Outcome (PICO) framework: in patients with MCI (P); what is the efficacy of vitamins B₆ , B₁₂ , and/or folic acid intake (I); compared with baseline values, and/or compared with controls (C); in reducing homocysteine levels from baseline (O). A total of eight primary studies with a total of 1,140 participants were included in the review. Four were randomized controlled trials, one was a quasi-controlled trial, and three were observational studies. All studies included folic acid in their intervention, seven vitamin B₁₂ , and four vitamin B₆ . Mean (SD) length of the intervention period was 18.8 (19.3) months, ranging from 1 to 60 months. All studies showed a statistically significant decrease in homocysteine levels in groups treated with vitamins B_6, B₁₂ , and/or folic acid compared to controls, with a mean decline of homocysteine concentration of 31.9% in the intervention arms whereas it increased by 0.7% in the control arm. This review identified evidence of a reduction of plasma homocysteine levels in MCI patients taking vitamins B_6, B₁₂ , and/or folic acid supplements, with statistically significant declines being observed after 1 month of supplementation. Findings support that supplementation with these vitamins might be an option to reduce homocysteine levels in people with MCI and elevated plasma homocysteine.

Brain energy metabolism and neurodegeneration: hints from CSF lactate levels in dementias

Mitochondrial dysfunction is pivotal in the development of neurodegenerative dementias, causing cellular death alongside disease-specific pathogenic cascades. Holding cerebrospinal fluid (CSF) lactates as an indirect measure of brain metabolic activity, we first compared CSF lactate levels from patients with Alzheimer's disease (AD)-stratified according to the ATN system and epsilon genotype-frontotemporal dementia (FTD) and dementia with Lewy body (DLB) to findings from healthy controls. With respect to controls, we detected lower CSF lactates in patients with AD and FTD but comparable levels in patients with DLB. Second, a correlation analysis between CSF lactates and biomarkers of neurodegeneration identified an inverse correlation between lactates and levels of t-tau and p-tau only in the Alzheimer's continuum. The reduction of CSF lactate correlates to the advent of tauopathy and cellular death in AD, implying that Aβ pathology alone is not sufficient to induce neuronal metabolic impairment. The metabolic impairment in FTD patients has a similar explanation, as it is likely due to fast neuronal degeneration in the disease. The absence of CSF lactate reduction in patients with DLB may be related to the prevalent subcortical localization of the pathology.

Inhibition of α-Synuclein Accumulation Improves Neuronal Apoptosis and Delayed Postoperative Cognitive Recovery in Aged Mice

Delayed neurocognitive recovery (dNCR) is a major complication after anesthesia and surgery in older adults. Alpha-synuclein (α-syn; encoded by the gene, SNCA) has recently been shown to play an important role in hippocampus-dependent working memory. Aggregated forms of α-syn are associated with multiple neurotoxic mechanisms, such as mitochondrial dysfunction and cell death. In this study, we found that blocking α-syn improved both mitochondrial function and mitochondria-dependent neuronal apoptosis in a mouse model of dNCR. Various forms of α-syn (including total α-syn, phosphorylated-Ser129-α-syn, and oligomers) were upregulated in hippocampal tissue and extracted mitochondria after surgical challenge. Clenbuterol is a novel transcription modulator of Scna. Clenbuterol significantly attenuated surgery-induced progressive accumulation of various toxic α-syn forms in the hippocampus, as well as mitochondrial damage and memory deficits in aged mice following surgery. We also observed excessive mitochondrial α-syn accumulation and increased mitochondria-mediated apoptosis in vitro using nerve growth factor-differentiated PC12 cells and primary hippocampal neurons exposed to lipopolysaccharide. To further validate the neuroprotective effect of α-syn inhibition, we used a lentiviral Snca-shRNA (Lv-shSnca) to knockdown Snca. Of note, Lv-shSnca transfection significantly inhibited neuronal apoptosis mediated by the mitochondrial apoptosis pathway in neurons exposed to lipopolysaccharide. This α-syn inhibition improved the disruption to mitochondrial morphology and function, as well as decreased levels of apoptosis. Our results suggest that targeting pathological α-syn may achieve neuroprotection through regulation of mitochondrial homeostasis and suppression of apoptosis in the aged hippocampus, further strengthening the therapeutic potential of targeting α-syn for dNCR.