Cerebral blood flow and metabolic rate of oxygen, glucose, lactate, pyruvate, ketone bodies and amino acids

Lower GLUT1 and unchanged MCT1 in Alzheimer's disease cerebrovasculature

The brain is a highly demanding organ, utilizing mainly glucose but also ketone bodies as sources of energy. Glucose transporter-1 (GLUT1) and monocarboxylates transporter-1 (MCT1) respectively transport glucose and ketone bodies across the blood-brain barrier. While reduced glucose uptake by the brain is one of the earliest signs of Alzheimer's disease (AD), no change in the uptake of ketone bodies has been evidenced yet. To probe for changes in GLUT1 and MCT1, we performed Western immunoblotting in microvessel extracts from the parietal cortex of 60 participants of the Religious Orders Study. Participants clinically diagnosed with AD had lower cerebrovascular levels of GLUT1, whereas MCT1 remained unchanged. GLUT1 reduction was associated with lower cognitive scores. No such association was found for MCT1. GLUT1 was inversely correlated with neuritic plaques and cerebrovascular β-secretase-derived fragment levels. No other significant associations were found between both transporters, markers of Aβ and tau pathologies, sex, age at death or apolipoprotein-ε4 genotype. These results suggest that, while a deficit of GLUT1 may underlie the reduced transport of glucose to the brain in AD, no such impairment occurs for MCT1. This study thus supports the exploration of ketone bodies as an alternative energy source for the aging brain.

Cholecystokinin (CCK): a neuromodulator with therapeutic potential in Alzheimer's and Parkinson's disease

Cholecystokinin (CCK) is a neuropeptide modulating digestion, glucose levels, neurotransmitters and memory. Recent studies suggest that CCK exhibits neuroprotective effects in Alzheimer's disease (AD) and Parkinson's disease (PD). Thus, we review the physiological function and therapeutic potential of CCK. The neuropeptide facilitates hippocampal glutamate release and gates GABAergic basket cell activity, which improves declarative memory acquisition, but inhibits consolidation. Cortical CCK alters recognition memory and enhances audio-visual processing. By stimulating CCK-1 receptors (CCK-1Rs), sulphated CCK-8 elicits dopamine release in the substantia nigra and striatum. In the mesolimbic pathway, CCK release is triggered by dopamine and terminates reward responses via CCK-2Rs. Importantly, activation of hippocampal and nigral CCK-2Rs is neuroprotective by evoking AMPK activation, expression of mitochondrial fusion modulators and autophagy. Other benefits include vagus nerve/CCK-1R-mediated expression of brain-derived neurotrophic factor, intestinal protection and suppression of inflammation. We also discuss caveats and the therapeutic combination of CCK with other peptide hormones.

NOX-induced oxidative stress is a primary trigger of major neurodegenerative disorders

Neurodegenerative diseases (NDDs) causing cognitive impairment and dementia are difficult to treat due to the lack of understanding of primary initiating factors. Meanwhile, major sporadic NDDs share many risk factors and exhibit similar pathologies in their early stages, indicating the existence of common initiation pathways. Glucose hypometabolism associated with oxidative stress is one such primary, early and shared pathology, and a likely major cause of detrimental disease-associated cascades; targeting this common pathology may therefore be an effective preventative strategy for most sporadic NDDs. However, its exact cause and trigger remain unclear. Recent research suggests that early oxidative stress caused by NADPH oxidase (NOX) activation is a shared initiating mechanism among major sporadic NDDs and could prove to be the long-sought ubiquitous NDD trigger. We focus on two major NDDs - Alzheimer's disease (AD) and Parkinson's disease (PD), as well as on acquired epilepsy which is an increasingly recognized comorbidity in NDDs. We also discuss available data suggesting the relevance of the proposed mechanisms to other NDDs. We delve into the commonalities among these NDDs in neuroinflammation and NOX involvement to identify potential therapeutic targets and gain a deeper understanding of the underlying causes of NDDs.

The Role of Ketogenic Diet in the Treatment of Neurological Diseases

Over a hundred years of study on the favourable effect of ketogenic diets in the treatment of epilepsy have contributed to a long-lasting discussion on its potential influence on other neurological diseases. A significant increase in the number of scientific studies in that field has been currently observed. The aim of this paper is a widespread, thorough analysis of the available scientific evidence in respect of the role of the ketogenic diet in the therapy of neurological diseases such as: epilepsy, Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS) and migraine. A wide range of the mechanisms of action of the ketogenic diet has been demonstrated in neurological diseases, including, among other effects, its influence on the reduction in inflammatory conditions and the amount of reactive oxygen species (ROS), the restoration of the myelin sheath of the neurons, the formation and regeneration of mitochondria, neuronal metabolism, the provision of an alternative source of energy for neurons (ketone bodies), the reduction in glucose and insulin concentrations, the reduction in amyloid plaques, the induction of autophagy, the alleviation of microglia activation, the reduction in excessive neuronal activation, the modulation of intestinal microbiota, the expression of genes, dopamine production and the increase in glutamine conversion into GABA. The studies discussed (including randomised controlled studies), conducted in neurological patients, have stressed the effectiveness of the ketogenic diet in the treatment of epilepsy and have demonstrated its promising therapeutic potential in Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS) and migraine. A frequent advantage of the diet was demonstrated over non-ketogenic diets (in the control groups) in the therapy of neurological diseases, with simultaneous safety and feasibility when conducting the nutritional model.

The neuroprotective effects of glucagon-like peptide 1 in Alzheimer's and Parkinson's disease: An in-depth review

Currently, there is no disease-modifying treatment available for Alzheimer's and Parkinson's disease (AD and PD) and that includes the highly controversial approval of the Aβ-targeting antibody aducanumab for the treatment of AD. Hence, there is still an unmet need for a neuroprotective drug treatment in both AD and PD. Type 2 diabetes is a risk factor for both AD and PD. Glucagon-like peptide 1 (GLP-1) is a peptide hormone and growth factor that has shown neuroprotective effects in preclinical studies, and the success of GLP-1 mimetics in phase II clinical trials in AD and PD has raised new hope. GLP-1 mimetics are currently on the market as treatments for type 2 diabetes. GLP-1 analogs are safe, well tolerated, resistant to desensitization and well characterized in the clinic. Herein, we review the existing evidence and illustrate the neuroprotective pathways that are induced following GLP-1R activation in neurons, microglia and astrocytes. The latter include synaptic protection, improvements in cognition, learning and motor function, amyloid pathology-ameliorating properties (Aβ, Tau, and α-synuclein), the suppression of Ca2+ deregulation and ER stress, potent anti-inflammatory effects, the blockage of oxidative stress, mitochondrial dysfunction and apoptosis pathways, enhancements in the neuronal insulin sensitivity and energy metabolism, functional improvements in autophagy and mitophagy, elevated BDNF and glial cell line-derived neurotrophic factor (GDNF) synthesis as well as neurogenesis. The many beneficial features of GLP-1R and GLP-1/GIPR dual agonists encourage the development of novel drug treatments for AD and PD.

Ketones: potential to achieve brain energy rescue and sustain cognitive health during ageing

Alzheimer’s disease (AD) is the most common major neurocognitive disorder of ageing. Although largely ignored until about a decade ago, accumulating evidence suggests that deteriorating brain energy metabolism plays a key role in the development and/or progression of AD-associated cognitive decline. Brain glucose hypometabolism is a well-established biomarker in AD but was mostly assumed to be a consequence of neuronal dysfunction and death. However, its presence in cognitively asymptomatic populations at higher risk of AD strongly suggests that it is actually a pre-symptomatic component in the development of AD. The question then arises as to whether progressive AD-related cognitive decline could be prevented or slowed down by correcting or bypassing this progressive ‘brain energy gap’. In this review, we provide an overview of research on brain glucose and ketone metabolism in AD and its prodromal condition – mild cognitive impairment (MCI) – to provide a clearer basis for proposing keto-therapeutics as a strategy for brain energy rescue in AD. We also discuss studies using ketogenic interventions and their impact on plasma ketone levels, brain energetics and cognitive performance in MCI and AD. Given that exercise has several overlapping metabolic effects with ketones, we propose that in combination these two approaches might be synergistic for brain health during ageing. As cause-and-effect relationships between the different hallmarks of AD are emerging, further research efforts should focus on optimising the efficacy, acceptability and accessibility of keto-therapeutics in AD and populations at risk of AD.

Potential for Ketotherapies as Amyloid-Regulating Treatment in Individuals at Risk for Alzheimer’s Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative condition characterized by clinical decline in memory and other cognitive functions. A classic AD neuropathological hallmark includes the accumulation of amyloid-β (Aβ) plaques, which may precede onset of clinical symptoms by over a decade. Efforts to prevent or treat AD frequently emphasize decreasing Aβ through various mechanisms, but such approaches have yet to establish compelling interventions. It is still not understood exactly why Aβ accumulates in AD, but it is hypothesized that Aβ and other downstream pathological events are a result of impaired bioenergetics, which can also manifest prior to cognitive decline. Evidence suggests that individuals with AD and at high risk for AD have functional brain ketone metabolism and ketotherapies (KTs), dietary approaches that produce ketone bodies for energy metabolism, may affect AD pathology by targeting impaired brain bioenergetics. Cognitively normal individuals with elevated brain Aβ, deemed “preclinical AD,” and older adults with peripheral metabolic impairments are ideal candidates to test whether KTs modulate AD biology as they have impaired mitochondrial function, perturbed brain glucose metabolism, and elevated risk for rapid Aβ accumulation and symptomatic AD. Here, we discuss the link between brain bioenergetics and Aβ, as well as the potential for KTs to influence AD risk and progression.

Is the Brain Undernourished in Alzheimer's Disease?

Cerebrospinal fluid (CSF) amino acid (AA) levels and CSF/plasma AA ratios in Alzheimer Disease (AD) in relation to nutritional state are not known. Methods: In 30 fasting patients with AD (46% males, 74.4 ± 8.2 years; 3.4 ± 3.2 years from diagnosis) and nine control (CTRL) matched subjects, CSF and venous blood samples were drawn for AA measurements. Patients were stratified according to nutritional state (Mini Nutritional Assessment, MNA, scores). Results: Total CSF/plasma AA ratios were lower in the AD subpopulations than in NON-AD (p < 0.003 to 0.017. In combined malnourished (16.7%; MNA < 17) and at risk for malnutrition (36.6%, MNA 17−24) groups (CG), compared to CTRL, all essential amino acids (EAAs) and 30% of non-EAAs were lower (p < 0.018 to 0.0001), whereas in normo-nourished ADs (46.7%, MNA > 24) the CSF levels of 10% of EAAs and 25% of NON-EAAs were decreased (p < 0.05 to 0.00021). CG compared to normo-nourished ADs, had lower CSF aspartic acid, glutamic acid and Branched-Chain AA levels (all, p < 0.05 to 0.003). CSF/plasma AA ratios were <1 in NON-AD but even lower in the AD population. Conclusions: Compared to CTRL, ADs had decreased CSF AA Levels and CSF/plasma AA ratios, the degree of which depended on nutritional state.

Disentangling Mitochondria in Alzheimer's Disease

Alzheimer's disease (AD) is a major cause of dementia in older adults and is fast becoming a major societal and economic burden due to an increase in life expectancy. Age seems to be the major factor driving AD, and currently, only symptomatic treatments are available. AD has a complex etiology, although mitochondrial dysfunction, oxidative stress, inflammation, and metabolic abnormalities have been widely and deeply investigated as plausible mechanisms for its neuropathology. Aβ plaques and hyperphosphorylated tau aggregates, along with cognitive deficits and behavioral problems, are the hallmarks of the disease. Restoration of mitochondrial bioenergetics, prevention of oxidative stress, and diet and exercise seem to be effective in reducing Aβ and in ameliorating learning and memory problems. Many mitochondria-targeted antioxidants have been tested in AD and are currently in development. However, larger streamlined clinical studies are needed to provide hard evidence of benefits in AD. This review discusses the causative factors, as well as potential therapeutics employed in the treatment of AD.

Aβ initiates brain hypometabolism, network dysfunction and behavioral abnormalities via NOX2-induced oxidative stress in mice

A predominant trigger and driver of sporadic Alzheimer’s disease (AD) is the synergy of brain oxidative stress and glucose hypometabolism starting at early preclinical stages. Oxidative stress damages macromolecules, while glucose hypometabolism impairs cellular energy supply and antioxidant defense. However, the exact cause of AD-associated glucose hypometabolism and its network consequences have remained unknown. Here we report NADPH oxidase 2 (NOX2) activation as the main initiating mechanism behind Aβ_1-42-related glucose hypometabolism and network dysfunction. We utilize a combination of electrophysiology with real-time recordings of metabolic transients both ex- and in-vivo to show that Aβ_1-42 induces oxidative stress and acutely reduces cellular glucose consumption followed by long-lasting network hyperactivity and abnormalities in the animal behavioral profile. Critically, all of these pathological changes were prevented by the novel bioavailable NOX2 antagonist GSK2795039. Our data provide direct experimental evidence for causes and consequences of AD-related brain glucose hypometabolism, and suggest that targeting NOX2-mediated oxidative stress is a promising approach to both the prevention and treatment of AD.

Anton Malkov, Irina Popova et al. demonstrate that beta-amyloid application induces oxidative stress and reduces glucose consumption in the mouse brain, leading to network hyperactivity and behavioral changes—pathologies similar to those observed early on in Alzheimer’s disease patients. Inhibition of NADPH oxidase 2 (NOX2) rescued these phenotypes, suggesting that NOX2 may represent an important therapeutic target for Alzheimer’s disease.

A Placebo-Controlled, Parallel-Group, Randomized Clinical Trial of AC-1204 in Mild-to-Moderate Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is characterized by amyloid-β plaques, neurofibrillary tangles, and regional cerebral glucose hypometabolism. Providing an alternative metabolic substrate, such as ketone bodies, may be a viable therapeutic option.

OBJECTIVE

The objective was to determine the efficacy and safety of the AC-1204 formulation of caprylic triglyceride administered daily for 26 weeks in APOE4 non-carrier participants with mild-to-moderate AD.

METHODS

In a double-blind, placebo-controlled, randomized study (AC-12-010, NOURISH AD, NCT01741194), 413 patients with mild-to-moderate probable AD were stratified by APOE genotype and randomized (1 : 1) to receive either placebo or AC-1204 for 26 weeks. The primary outcome was the change from baseline to week 26 on the 11-item Alzheimer's Disease Assessment Scale - Cognitive subscale (ADAS-Cog11) among APOE4 non-carriers. The key secondary outcome was the change from baseline to week 26 in the Alzheimer's Disease Cooperative Study - Clinician's Global Impression of Change scale.

RESULTS

Administration of AC-1204 was safe and well-tolerated. Mean changes from baseline in the primary outcome at 26 weeks in ADAS-Cog11 for placebo (n = 138) was 0.0 and for AC-1204 (n = 137) was 0.6 (LS differences of mean - 0.761, p = 0.2458) and secondary outcome measures failed to detect any drug effects.

CONCLUSION

The AC-1204 formulation of caprylic triglyceride failed to improve cognition or functional ability in subjects with mild-to-moderate AD. The lack of efficacy observed in this study may have several contributing factors including a lower ketone body formation from AC-1204 than expected and a lack of decline in the patients receiving placebo.

Glycolytic Metabolism, Brain Resilience, and Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of age-related dementia. Despite decades of research, the etiology and pathogenesis of AD are not well understood. Brain glucose hypometabolism has long been recognized as a prominent anomaly that occurs in the preclinical stage of AD. Recent studies suggest that glycolytic metabolism, the cytoplasmic pathway of the breakdown of glucose, may play a critical role in the development of AD. Glycolysis is essential for a variety of neural activities in the brain, including energy production, synaptic transmission, and redox homeostasis. Decreased glycolytic flux has been shown to correlate with the severity of amyloid and tau pathology in both preclinical and clinical AD patients. Moreover, increased glucose accumulation found in the brains of AD patients supports the hypothesis that glycolytic deficit may be a contributor to the development of this phenotype. Brain hyperglycemia also provides a plausible explanation for the well-documented link between AD and diabetes. Humans possess three primary variants of the apolipoprotein E (ApoE) gene - ApoE∗ϵ2, ApoE∗ϵ3, and ApoE∗ϵ4 - that confer differential susceptibility to AD. Recent findings indicate that neuronal glycolysis is significantly affected by human ApoE isoforms and glycolytic robustness may serve as a major mechanism that renders an ApoE2-bearing brain more resistant against the neurodegenerative risks for AD. In addition to AD, glycolytic dysfunction has been observed in other neurodegenerative diseases, including Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis, strengthening the concept of glycolytic dysfunction as a common pathway leading to neurodegeneration. Taken together, these advances highlight a promising translational opportunity that involves targeting glycolysis to bolster brain metabolic resilience and by such to alter the course of brain aging or disease development to prevent or reduce the risks for not only AD but also other neurodegenerative diseases.

Therapies for Alzheimer's disease: a metabolic perspective

Alzheimer's disease (AD) is one of the most common forms of dementia in the elderly. Currently, there are over 50 million cases of dementia worldwide and it is expected that it will reach 136 million by 2050. AD is described as a neurodegenerative disease that gradually compromises memory and learning capacity. Patients often exhibit brain glucose hypometabolism and are more susceptible to develop type 2 diabetes or insulin resistance in comparison with age-matched controls. This suggests that there is a link between both pathologies. Glucose metabolism and the tricarboxylic acid cycle are tightly related to mitochondrial performance and energy production. Impairment of both these pathways can evoke oxidative damage on mitochondria and key proteins linked to several hallmarks of AD. Glycation is also another type of post-translational modification often reported in AD, which might impair the function of proteins that participate in metabolic pathways thought to be involved in this illness. Despite needing further research, therapies based on insulin treatment, usage of anti-diabetes drugs or some form of dietary intervention, have shown to be promising therapeutic approaches for AD in its early stages of progression and will be unveiled in this paper.

Acylated Ghrelin as a Multi-Targeted Therapy for Alzheimer's and Parkinson's Disease

Much thought has been given to the impact of Amyloid Beta, Tau and Alpha-Synuclein in the development of Alzheimer's disease (AD) and Parkinson's disease (PD), yet the clinical failures of the recent decades indicate that there are further pathological mechanisms at work. Indeed, besides amyloids, AD and PD are characterized by the culminative interplay of oxidative stress, mitochondrial dysfunction and hyperfission, defective autophagy and mitophagy, systemic inflammation, BBB and vascular damage, demyelination, cerebral insulin resistance, the loss of dopamine production in PD, impaired neurogenesis and, of course, widespread axonal, synaptic and neuronal degeneration that leads to cognitive and motor impediments. Interestingly, the acylated form of the hormone ghrelin has shown the potential to ameliorate the latter pathologic changes, although some studies indicate a few complications that need to be considered in the long-term administration of the hormone. As such, this review will illustrate the wide-ranging neuroprotective properties of acylated ghrelin and critically evaluate the hormone's therapeutic benefits for the treatment of AD and PD.

Effects of Ketone Bodies on Brain Metabolism and Function in Neurodegenerative Diseases

Under normal physiological conditions the brain primarily utilizes glucose for ATP generation. However, in situations where glucose is sparse, e.g., during prolonged fasting, ketone bodies become an important energy source for the brain. The brain’s utilization of ketones seems to depend mainly on the concentration in the blood, thus many dietary approaches such as ketogenic diets, ingestion of ketogenic medium-chain fatty acids or exogenous ketones, facilitate significant changes in the brain’s metabolism. Therefore, these approaches may ameliorate the energy crisis in neurodegenerative diseases, which are characterized by a deterioration of the brain’s glucose metabolism, providing a therapeutic advantage in these diseases. Most clinical studies examining the neuroprotective role of ketone bodies have been conducted in patients with Alzheimer’s disease, where brain imaging studies support the notion of enhancing brain energy metabolism with ketones. Likewise, a few studies show modest functional improvements in patients with Parkinson’s disease and cognitive benefits in patients with—or at risk of—Alzheimer’s disease after ketogenic interventions. Here, we summarize current knowledge on how ketogenic interventions support brain metabolism and discuss the therapeutic role of ketones in neurodegenerative disease, emphasizing clinical data.

To Keto or Not to Keto? A Systematic Review of Randomized Controlled Trials Assessing the Effects of Ketogenic Therapy on Alzheimer Disease

Alzheimer disease (AD) is a global health concern with the majority of pharmacotherapy choices consisting of symptomatic treatment. Recently, ketogenic therapies have been tested in randomized controlled trials (RCTs), focusing on delaying disease progression and ameliorating cognitive function. The present systematic review aimed to aggregate the results of trials examining the effects of ketogenic therapy on patients with AD/mild cognitive impairment (MCI). A systematic search was conducted on PubMed, CENTRAL, clinicaltrials.gov, and gray literature for RCTs performed on adults, published in English until 1 April, 2019, assessing the effects of ketogenic therapy on MCI and/or AD compared against placebo, usual diet, or meals lacking ketogenic agents. Two researchers independently extracted data and assessed risk of bias with the Cochrane tool. A total of 10 RCTs were identified, fulfilling the inclusion criteria. Interventions were heterogeneous, acute or long term (45-180 d), including adherence to a ketogenic diet, intake of ready-to-consume drinks, medium-chain triglyceride (MCT) powder for drinks preparation, yoghurt enriched with MCTs, MCT capsules, and ketogenic formulas/meals. The use of ketoneurotherapeutics proved effective in improving general cognition using the Alzheimer's Disease Assessment Scale-Cognitive, in interventions of either duration. In addition, long-term ketogenic therapy improved episodic and secondary memory. Psychological health, executive ability, and attention were not improved. Increases in blood ketone concentrations were unanimous and correlated to the neurocognitive battery based on various tests. Cerebral ketone uptake and utilization were improved, as indicated by the global brain cerebral metabolic rate for ketones and [11C] acetoacetate. Ketone concentrations and cognitive performance differed between APOE ε4(+) and APOE ε4(-) participants, indicating a delayed response among the former and an improved response among the latter. Although research on the subject is still in the early stages and highly heterogeneous in terms of study design, interventions, and outcome measures, ketogenic therapy appears promising in improving both acute and long-term cognition among patients with AD/MCI. This systematic review was registered at www.crd.york.ac.uk/prospero as CRD42019128311.

Age and Ketogenic Diet Have Dissociable Effects on Synapse-Related Gene Expression Between Hippocampal Subregions

As the number of individuals living beyond the age of 65 is rapidly increasing, so is the need to develop strategies to combat the age-related cognitive decline that may threaten independent living. Although the link between altered neuronal signaling and age-related cognitive impairments is not completely understood, it is evident that declining cognitive abilities are at least partially due to synaptic dysfunction. Aging is accompanied by well-documented changes in both excitatory and inhibitory synaptic signaling across species. Age-related synaptic alterations are not uniform across the brain, however, with different regions showing unique patterns of vulnerability in advanced age. In the hippocampus, increased activity within the CA3 subregion has been observed across species, and this can be reversed with anti-epileptic medication. In contrast to CA3, the dentate gyrus shows reduced activity with age and declining metabolic activity. Ketogenic diets have been shown to decrease seizure incidence and severity in epilepsy, improve metabolic function in diabetes type II, and improve cognitive function in aged rats. This link between neuronal activity and metabolism suggests that metabolic interventions may be able to ameliorate synaptic signaling deficits accompanying advanced age. We therefore investigated the ability of a dietary regimen capable of inducing nutritional ketosis and improving cognition to alter synapse-related gene expression across the dentate gyrus, CA3 and CA1 subregions of the hippocampus. Following 12 weeks of a ketogenic or calorie-matched standard diet, RTq-PCR was used to quantify expression levels of excitatory and inhibitory synaptic signaling genes within CA1, CA3 and dentate gyrus. While there were no age or diet-related changes in CA1 gene expression, expression levels were significantly altered within CA3 by age and within the dentate gyrus by diet for several genes involved in presynaptic glutamate regulation and postsynaptic excitation and plasticity. These data demonstrate subregion-specific alterations in synaptic signaling with age and the potential for a ketogenic diet to alter these processes in dissociable ways across different brain structures that are uniquely vulnerable in older animals.

Dietary Neuroketotherapeutics for Alzheimer's Disease: An Evidence Update and the Potential Role for Diet Quality

Alzheimer’s disease (AD) is a devastating neurodegenerative disease with growing prevalence as the global population ages. Currently available treatments for AD have minimal efficacy and there are no proven treatments for its prodrome, mild cognitive impairment (MCI). AD etiology is not well understood and various hypotheses of disease pathogenesis are currently under investigation. A consistent hallmark in patients with AD is reduced brain glucose utilization; however, evidence suggests that brain ketone metabolism remains unimpaired, thus, there is a great deal of increased interest in the potential value of ketone-inducing therapies for the treatment of AD (neuroketotherapeutics; NKT). The goal of this review was to discuss dietary NKT approaches and mechanisms by which they exert a possible therapeutic benefit, update the evidence available on NKTs in AD and consider a potential role of diet quality in the clinical use of dietary NKTs. Whether NKTs affect AD symptoms through the restoration of bioenergetics, the direct and indirect modulation of antioxidant and inflammation pathways, or both, preliminary positive evidence suggests that further study of dietary NKTs as a disease-modifying treatment in AD is warranted.

Ketogenic Medium Chain Triglycerides Increase Brain Energy Metabolism in Alzheimer's Disease

BACKGROUND

In Alzheimer's disease (AD), it is unknown whether the brain can utilize additional ketones as fuel when they are derived from a medium chain triglyceride (MCT) supplement.

OBJECTIVE

To assess whether brain ketone uptake in AD increases in response to MCT as it would in young healthy adults.

METHODS

Mild-moderate AD patients sequentially consumed 30 g/d of two different MCT supplements, both for one month: a mixture of caprylic (55%) and capric acids (35%) (n = 11), followed by a wash-out and then tricaprylin (95%; n = 6). Brain ketone (11C-acetoacetate) and glucose (FDG) uptake were quantified by PET before and after each MCT intervention.

RESULTS

Brain ketone consumption doubled on both types of MCT supplement. The slope of the relationship between plasma ketones and brain ketone uptake was the same as in healthy young adults. Both types of MCT increased total brain energy metabolism by increasing ketone supply without affecting brain glucose utilization.

CONCLUSION

Ketones from MCT compensate for the brain glucose deficit in AD in direct proportion to the level of plasma ketones achieved.

Integration of probabilistic regulatory networks into constraint-based models of metabolism with applications to Alzheimer's disease

Background

Mathematical models of biological networks can provide important predictions and insights into complex disease. Constraint-based models of cellular metabolism and probabilistic models of gene regulatory networks are two distinct areas that have progressed rapidly in parallel over the past decade. In principle, gene regulatory networks and metabolic networks underly the same complex phenotypes and diseases. However, systematic integration of these two model systems remains a fundamental challenge.

Results

In this work, we address this challenge by fusing probabilistic models of gene regulatory networks into constraint-based models of metabolism. The novel approach utilizes probabilistic reasoning in BN models of regulatory networks serves as the “glue” that enables a natural interface between the two systems. Probabilistic reasoning is used to predict and quantify system-wide effects of perturbation to the regulatory network in the form of constraints for flux variability analysis. In this setting, both regulatory and metabolic networks inherently account for uncertainty. Applications leverage constraint-based metabolic models of brain metabolism and gene regulatory networks parameterized by gene expression data from the hippocampus to investigate the role of the HIF-1 pathway in Alzheimer’s disease. Integrated models support HIF-1A as effective target to reduce the effects of hypoxia in Alzheimer’s disease. However, HIF-1A activation is far less effective in shifting metabolism when compared to brain metabolism in healthy controls.

Conclusions

The direct integration of probabilistic regulatory networks into constraint-based models of metabolism provides novel insights into how perturbations in the regulatory network may influence metabolic states. Predictive modeling of enzymatic activity can be facilitated using probabilistic reasoning, thereby extending the predictive capacity of the network. This framework for model integration is generalizable to other systems.

Electronic supplementary material

The online version of this article (10.1186/s12859-019-2872-8) contains supplementary material, which is available to authorized users.

A short-term intervention combining aerobic exercise with medium-chain triglycerides (MCT) is more ketogenic than either MCT or aerobic exercise alone: a comparison of normoglycemic and prediabetic older women

The objectives of this study were to determine (i) whether a 5-day aerobic exercise (AE) program combined with a medium-chain triglyceride (MCT) supplement would increase the plasma ketone response in older women more than either intervention alone and (ii) whether ketonemia after these combined or separate treatments was alike in normoglycemic (NG) and prediabetic (PD) women. Older women (NG, n = 10; PD, n = 9) underwent a 4-h metabolic study after each of 4 different treatments: (i) no treatment (control), (ii) 5 days of MCT alone (30 g·day^-1), (iii) 1 session of 30 min of AE alone, and (iv) 5 days of MCT and AE combined (MCT+AE). Blood was sampled every 30 min over 4 h for analysis. In NG, MCT+AE induced the highest area under the curve (AUC) for plasma ketones (835 ± 341 μmol·h·L^-1); this value was 69% higher than that observed with MCT alone (P < 0.05). AUCs were not different between MCT alone and MCT+AE in PD, but both treatments induced a significantly higher AUC than the control or AE alone (P < 0.05). Although there was a trend towards a higher ketone AUC in NG versus PD with AE alone (P = 0.091), there was no significant difference between the ketone AUCs in PD and NG. In conclusion, MCT+AE was more ketogenic in older women than MCT or AE alone. MCT+AE had a synergistic effect on ketonemia in NG but not in PD. Whether improving insulin sensitivity with a longer term AE intervention can improve the ketogenic effect of MCT in PD and thereby increase brain ketone uptake in older people merits further investigation.

APOE and Alzheimer's Disease: Neuroimaging of Metabolic and Cerebrovascular Dysfunction

Apolipoprotein E4 (ApoE4) is the strongest genetic risk factor for late onset Alzheimer’s Disease (AD), and is associated with impairments in cerebral metabolism and cerebrovascular function. A substantial body of literature now points to E4 as a driver of multiple impairments seen in AD, including blunted brain insulin signaling, mismanagement of brain cholesterol and fatty acids, reductions in blood brain barrier (BBB) integrity, and decreased cerebral glucose uptake. Various neuroimaging techniques, in particular positron emission topography (PET) and magnetic resonance imaging (MRI), have been instrumental in characterizing these metabolic and vascular deficits associated with this important AD risk factor. In the current mini-review article, we summarize the known effects of APOE on cerebral metabolism and cerebrovascular function, with a special emphasis on recent findings via neuroimaging approaches.

Inverse relationship between brain glucose and ketone metabolism in adults during short-term moderate dietary ketosis: A dual tracer quantitative positron emission tomography study

Ketones (principally β-hydroxybutyrate and acetoacetate (AcAc)) are an important alternative fuel to glucose for the human brain, but their utilisation by the brain remains poorly understood. Our objective was to use positron emission tomography (PET) to assess the impact of diet-induced moderate ketosis on cerebral metabolic rate of acetoacetate (CMRa) and glucose (CMRglc) in healthy adults. Ten participants (35 ± 15 y) received a very high fat ketogenic diet (KD) (4.5:1; lipid:protein plus carbohydrates) for four days. CMRa and CMRglc were quantified by PET before and after the KD with the tracers, ¹¹C-AcAc and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG), respectively. During the KD, plasma ketones increased 8-fold ( p = 0.005) while plasma glucose decreased by 24% ( p = 0.005). CMRa increased 6-fold ( p = 0.005), whereas CMRglc decreased by 20% ( p = 0.014) on the KD. Plasma ketones were positively correlated with CMRa (r = 0.93; p < 0.0001). After four days on the KD, CMRa represented 17% of whole brain energy requirements in healthy adults with a 2-fold difference across brain regions (12-24%). The CMR of ketones (AcAc and β-hydroxybutyrate combined) while on the KD was estimated to represent about 33% of brain energy requirements or approximately double the CMRa. Whether increased ketone availability raises CMR of ketones to the same extent in older people as observed here or in conditions in which chronic brain glucose hypometabolism is present remains to be determined.

The vicious circle of hypometabolism in neurodegenerative diseases: Ways and mechanisms of metabolic correction

Hypometabolism, characterized by decreased brain glucose consumption, is a common feature of many neurodegenerative diseases. Initial hypometabolic brain state, created by characteristic risk factors, may predispose the brain to acquired epilepsy and sporadic Alzheimer's and Parkinson's diseases, which are the focus of this review. Analysis of available data suggests that deficient glucose metabolism is likely a primary initiating factor for these diseases, and that resulting neuronal dysfunction further promotes the metabolic imbalance, establishing an effective positive feedback loop and a downward spiral of disease progression. Therefore, metabolic correction leading to the normalization of abnormalities in glucose metabolism may be an efficient tool to treat the neurological disorders by counteracting their primary pathological mechanisms. Published and preliminary experimental results on this approach for treating Alzheimer's disease and epilepsy models support the efficacy of metabolic correction, confirming the highly promising nature of the strategy. © 2017 Wiley Periodicals, Inc.

Genome-Scale Reconstruction of the Human Astrocyte Metabolic Network

Astrocytes are the most abundant cells of the central nervous system; they have a predominant role in maintaining brain metabolism. In this sense, abnormal metabolic states have been found in different neuropathological diseases. Determination of metabolic states of astrocytes is difficult to model using current experimental approaches given the high number of reactions and metabolites present. Thus, genome-scale metabolic networks derived from transcriptomic data can be used as a framework to elucidate how astrocytes modulate human brain metabolic states during normal conditions and in neurodegenerative diseases. We performed a Genome-Scale Reconstruction of the Human Astrocyte Metabolic Network with the purpose of elucidating a significant portion of the metabolic map of the astrocyte. This is the first global high-quality, manually curated metabolic reconstruction network of a human astrocyte. It includes 5,007 metabolites and 5,659 reactions distributed among 8 cell compartments, (extracellular, cytoplasm, mitochondria, endoplasmic reticle, Golgi apparatus, lysosome, peroxisome and nucleus). Using the reconstructed network, the metabolic capabilities of human astrocytes were calculated and compared both in normal and ischemic conditions. We identified reactions activated in these two states, which can be useful for understanding the astrocytic pathways that are affected during brain disease. Additionally, we also showed that the obtained flux distributions in the model, are in accordance with literature-based findings. Up to date, this is the most complete representation of the human astrocyte in terms of inclusion of genes, proteins, reactions and metabolic pathways, being a useful guide for in-silico analysis of several metabolic behaviors of the astrocyte during normal and pathologic states.

Can Ketones Help Rescue Brain Fuel Supply in Later Life? Implications for Cognitive Health during Aging and the Treatment of Alzheimer's Disease

We propose that brain energy deficit is an important pre-symptomatic feature of Alzheimer's disease (AD) that requires closer attention in the development of AD therapeutics. Our rationale is fourfold: (i) Glucose uptake is lower in the frontal cortex of people >65 years-old despite cognitive scores that are normal for age. (ii) The regional deficit in brain glucose uptake is present in adults <40 years-old who have genetic or lifestyle risk factors for AD but in whom cognitive decline has not yet started. Examples include young adult carriers of presenilin-1 or apolipoprotein E4, and young adults with mild insulin resistance or with a maternal family history of AD. (iii) Regional brain glucose uptake is impaired in AD and mild cognitive impairment (MCI), but brain uptake of ketones (beta-hydroxybutyrate and acetoacetate), remains the same in AD and MCI as in cognitively healthy age-matched controls. These observations point to a brain fuel deficit which appears to be specific to glucose, precedes cognitive decline associated with AD, and becomes more severe as MCI progresses toward AD. Since glucose is the brain's main fuel, we suggest that gradual brain glucose exhaustion is contributing significantly to the onset or progression of AD. (iv) Interventions that raise ketone availability to the brain improve cognitive outcomes in both MCI and AD as well as in acute experimental hypoglycemia. Ketones are the brain's main alternative fuel to glucose and brain ketone uptake is still normal in MCI and in early AD, which would help explain why ketogenic interventions improve some cognitive outcomes in MCI and AD. We suggest that the brain energy deficit needs to be overcome in order to successfully develop more effective therapeutics for AD. At present, oral ketogenic supplements are the most promising means of achieving this goal.

Understanding the physiology of the ageing individual: computational modelling of changes in metabolism and endurance

Ageing and lifespan are strongly affected by metabolism. The maximal possible uptake of oxygen is not only a good predictor of performance in endurance sports, but also of life expectancy. Figuratively speaking, healthy ageing is a competitive sport. Although the root cause of ageing is damage to macromolecules, it is the balance with repair processes that is decisive. Reduced or intermittent nutrition, hormones and intracellular signalling pathways that regulate metabolism have strong effects on ageing. Homeostatic regulatory processes tend to keep the environment of the cells within relatively narrow bounds. On the other hand, the body is constantly adapting to physical activity and food consumption. Spontaneous fluctuations in heart rate and other processes indicate youth and health. A (homeo)dynamic aspect of homeostasis deteriorates with age. We are now in a position to develop computational models of human metabolism and the dynamics of heart rhythm and oxygen transport that will advance our understanding of ageing. Computational modelling of the connections between dietary restriction, metabolism and protein turnover may increase insight into homeostasis of the proteins in our body. In this way, the computational reconstruction of human physiological processes, the Physiome, can help prevent frailty and age-related disease.

Can ketones compensate for deteriorating brain glucose uptake during aging? Implications for the risk and treatment of Alzheimer's disease

Brain glucose uptake is impaired in Alzheimer's disease (AD). A key question is whether cognitive decline can be delayed if this brain energy defect is at least partly corrected or bypassed early in the disease. The principal ketones (also called ketone bodies), β-hydroxybutyrate and acetoacetate, are the brain's main physiological alternative fuel to glucose. Three studies in mild-to-moderate AD have shown that, unlike with glucose, brain ketone uptake is not different from that in healthy age-matched controls. Published clinical trials demonstrate that increasing ketone availability to the brain via moderate nutritional ketosis has a modest beneficial effect on cognitive outcomes in mild-to-moderate AD and in mild cognitive impairment. Nutritional ketosis can be safely achieved by a high-fat ketogenic diet, by supplements providing 20-70 g/day of medium-chain triglycerides containing the eight- and ten-carbon fatty acids octanoate and decanoate, or by ketone esters. Given the acute dependence of the brain on its energy supply, it seems reasonable that the development of therapeutic strategies aimed at AD mandates consideration of how the underlying problem of deteriorating brain fuel supply can be corrected or delayed.

Ketogenic response to cotreatment with bezafibrate and medium chain triacylglycerols in healthy humans

OBJECTIVES

The aim of this study was to compare the ketogenic effect of the peroxisome proliferator-activated receptor-α stimulator, bezafibrate (BEZA), alone or in combination with medium-chain triacylglycerols (MCTs) in healthy adults.

METHODS

Eighteen healthy adults completed the study: 10 were given a therapeutic dose of BEZA (400 mg/d) for 8 wk followed by a further 4 wk of BEZA (400 mg/d) plus MCT (60 g/d). Eight other participants were given MCT alone (60 g/d) for 4 wk. All participants underwent identical metabolic study days: (a) pretreatment (the control), and after (b) BEZA combined with MCT (BEZA+MCT) or (c) an equal dose of MCT only. On the metabolic study days, a standard breakfast and lunch were given and blood samples were taken hourly to measure plasma ketones, glucose, and fatty acids.

RESULTS

The combination of BEZA+MCT increased ketones twofold during the metabolic study day. The addition of BEZA increased early ketogenic efficiency of MCT by 2.5-fold but did not result in higher peak or mean concentration of ketones during the metabolic study day. No other differences were seen in plasma metabolites or insulin during metabolic study days. On the final metabolic study day, MCT or BEZA+MCT had different effects on the plasma acetoacetate-to-β-hydroxybutyrate ratio compared with control.

CONCLUSIONS

BEZA mildly potentiated the ketogenic action of MCT but did not increase peak plasma ketone concentration or overall ketone production during the metabolic study day.

Brain aerobic glycolysis functions and Alzheimer's disease

Genetic, biochemical, pathological, and biomarker data demonstrate that Alzheimer's disease (AD) pathology, including the initiation and progressive buildup of insoluble forms of beta-amyloid (Aβ), appears to begin ~ 10-15 years prior to the onset of cognitive decline associated with AD. Metabolic dysfunction, a prominent feature of the evolving brain pathology, is reflected in a decline of total glucose utilization. Despite decades of interest in declining glucose use in AD no detailed consideration had been given to the possibility that this decline is not just a decline in energy consumption but rather in glycolysis alone. Glycolysis is a multi-step process that prepares the glucose molecule for oxidative phosphorylation and the generation of energy. In the normal brain, glycolysis exceeds that required for the needs of oxidative phosphorylation. Because it is occurring in a setting with adequate oxygen available for oxidative phosphorylation it is often referred to as aerobic glycolysis (AG). AG is a biomarker of a group of metabolic functions broadly supporting biosynthesis and neuroprotection. The distribution of AG in normal young adults correlates spatially with Aβ deposition in AD patients and cognitively normal individuals with elevated Aβ. In transgenic mice extracellular fluid Aβ and lactate, a marker of AG, vary in parallel regionally and with changes in activity. Reducing neuronal activity locally in transgenic mice attenuates plaque formation suggesting that plaque formation is an activity dependent process associated with aerobic glycolysis.

Systematic analysis of transcription-level effects of neurodegenerative diseases on human brain metabolism by a newly reconstructed brain-specific metabolic network

Network-oriented analysis is essential to identify those parts of a cell affected by a given perturbation. The effect of neurodegenerative perturbations in the form of diseases of brain metabolism was investigated by using a newly reconstructed brain-specific metabolic network. The developed stoichiometric model correctly represents healthy brain metabolism, and includes 630 metabolic reactions in and between astrocytes and neurons, which are controlled by 570 genes. The integration of transcriptome data of six neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, multiple sclerosis, schizophrenia) with the model was performed to identify reporter features specific and common for these diseases, which revealed metabolites and pathways around which the most significant changes occur. The identified metabolites are potential biomarkers for the pathology of the related diseases. Our model indicated perturbations in oxidative stress, energy metabolism including TCA cycle and lipid metabolism as well as several amino acid related pathways, in agreement with the role of these pathways in the studied diseases. The computational prediction of transcription factors that commonly regulate the reporter metabolites was achieved through binding-site analysis. Literature support for the identified transcription factors such as USF1, SP1 and those from FOX families are known from the literature to have regulatory roles in the identified reporter metabolic pathways as well as in the neurodegenerative diseases. In essence, the reconstructed brain model enables the elucidation of effects of a perturbation on brain metabolism and the illumination of possible machineries in which a specific metabolite or pathway acts as a regulatory spot for cellular reorganization.

Is there in vivo evidence for amino acid shuttles carrying ammonia from neurons to astrocytes?

The high in vivo flux of the glutamate/glutamine cycle puts a strong demand on the return of ammonia released by phosphate activated glutaminase from the neurons to the astrocytes in order to maintain nitrogen balance. In this paper we review several amino acid shuttles that have been proposed for balancing the nitrogen flows between neurons and astrocytes in the glutamate/glutamine cycle. All of these cycles depend on the directionality of glutamate dehydrogenase, catalyzing reductive glutamate synthesis (forward reaction) in the neuron in order to capture the ammonia released by phosphate activated glutaminase, while catalyzing oxidative deamination of glutamate (reverse reaction) in the astrocytes to release ammonia for glutamine synthesis. Reanalysis of results from in vivo experiments using (13)N and (15)N labeled ammonia and (15)N leucine in rats suggests that the maximum flux of the alanine/lactate or branched chain amino acid/branched chain amino acid transaminase shuttles between neurons and astrocytes are approximately 3-5 times lower than would be required to account for the ammonia transfer from neurons to astrocytes needed for glutamine synthesis (amide nitrogen) to sustain the glutamate/glutamine cycle. However, in the rat brain both the total ammonia fixation rate by glutamate dehydrogenase and the total branched chain amino acid transaminase activity are sufficient to support a branched chain amino acid/branched chain keto acid shuttle, as proposed by Hutson and coworkers, which would support the de novo synthesis of glutamine in the astrocyte to replace the ~20 % of neurotransmitter glutamate that is oxidized. A higher fraction of the nitrogen needs of total glutamate neurotransmitter cycling could be supported by hybrid cycles in which glutamate and tricarboxylic acid cycle intermediates act as a nitrogen shuttle. A limitation of all in vivo studies in animals conducted to date is that none have shown transfer of nitrogen for glutamine amide synthesis, either as free ammonia or via an amino acid from the neurons to the astrocytes. Future work will be needed, perhaps using methods for selectively labeling nitrogen in neurons, to conclusively establish the rate of amino acid nitrogen shuttles in vivo and their coupling to the glutamate/glutamine cycle.

Brain fuel metabolism, aging, and Alzheimer's disease

Lower brain glucose metabolism is present before the onset of clinically measurable cognitive decline in two groups of people at risk of Alzheimer's disease--carriers of apolipoprotein E4, and in those with a maternal family history of AD. Supported by emerging evidence from in vitro and animal studies, these reports suggest that brain hypometabolism may precede and therefore contribute to the neuropathologic cascade leading to cognitive decline in AD. The reason brain hypometabolism develops is unclear but may include defects in brain glucose transport, disrupted glycolysis, and/or impaired mitochondrial function. Methodologic issues presently preclude knowing with certainty whether or not aging in the absence of cognitive impairment is necessarily associated with lower brain glucose metabolism. Nevertheless, aging appears to increase the risk of deteriorating systemic control of glucose utilization, which, in turn, may increase the risk of declining brain glucose uptake, at least in some brain regions. A contributing role of deteriorating glucose availability to or metabolism by the brain in AD does not exclude the opposite effect, i.e., that neurodegenerative processes in AD further decrease brain glucose metabolism because of reduced synaptic functionality and hence reduced energy needs, thereby completing a vicious cycle. Strategies to reduce the risk of AD by breaking this cycle should aim to (1) improve insulin sensitivity by improving systemic glucose utilization, or (2) bypass deteriorating brain glucose metabolism using approaches that safely induce mild, sustainable ketonemia.

Large-scale in silico modeling of metabolic interactions between cell types in the human brain

Metabolic interactions between multiple cell types are difficult to model using existing approaches. Here we present a workflow that integrates gene expression data, proteomics data and literature-based manual curation to model human metabolism within and between different types of cells. Transport reactions are used to account for the transfer of metabolites between models of different cell types via the interstitial fluid. We apply the method to create models of brain energy metabolism that recapitulate metabolic interactions between astrocytes and various neuron types relevant to Alzheimer's disease. Analysis of the models identifies genes and pathways that may explain observed experimental phenomena, including the differential effects of the disease on cell types and regions of the brain. Constraint-based modeling can thus contribute to the study and analysis of multicellular metabolic processes in the human tissue microenvironment and provide detailed mechanistic insight into high-throughput data analysis.

Ablation of the locus coeruleus increases oxidative stress in tg-2576 transgenic but not wild-type mice

Mice transgenic for production of excessive or mutant forms of beta-amyloid differ from patients with Alzheimer's disease in the degree of inflammation, oxidative damage, and alteration of intermediary metabolism, as well as the paucity or absence of neuronal atrophy and cognitive impairment. Previous observers have suggested that differences in inflammatory response reflect a discrepancy in the state of the locus coeruleus (LC), loss of which is an early change in Alzheimer's disease but which is preserved in the transgenic mice. In this paper, we extend these observations by examining the effects of the LC on markers of oxidative stress and intermediary metabolism. We compare four groups: wild-type or Tg2576 Aβ transgenic mice injected with DSP4 or vehicle. Of greatest interest were metabolites different between ablated and intact transgenics, but not between ablated and intact wild-type animals. The Tg2576_DSP4 mice were distinguished from the other three groups by oxidative stress and altered energy metabolism. These observations provide further support for the hypothesis that Tg2576 Aβ transgenic mice with this ablation may be a more congruent model of Alzheimer's disease than are transgenics with an intact LC.

Region-specific effects on brain metabolites of hypoxia and hyperoxia overlaid on cerebral ischemia in young and old rats: a quantitative proton magnetic resonance spectroscopy study

Background

Both hypoxia and hyperoxia, deregulating the oxidative balance, may play a role in the pathology of neurodegenerative disorders underlain by cerebral ischemia. In the present study, quantitative proton magnetic resonance spectroscopy was used to evaluate regional metabolic alterations, following a 24-hour hypoxic or hyperoxic exposure on the background of ischemic brain insult, in two contrasting age-groups of rats: young - 3 months old and aged - 24 months old.

Methods

Cerebral ischemia was induced by ligation of the right common carotid artery. Concentrations of eight metabolites (alanine, choline-containing compounds, total creatine, γ-aminobutyric acid, glutamate, lactate, myo-inositol and N-acetylaspartate) were quantified from extracts in three different brain regions (fronto-parietal and occipital cortices and the hippocampus) from both hemispheres.

Results

In the control normoxic condition, there were significant increases in lactate and myo-inositol concentrations in the hippocampus of the aged rats, compared with the respective values in the young ones. In the ischemia-hypoxia condition, the most prevalent changes in the brain metabolites were found in the hippocampal regions of both young and aged rats; but the effects were more evident in the aged animals. The ischemia-hyperoxia procedure caused less dedicated changes in the brain metabolites, which may reflect more limited tissue damage.

Conclusions

We conclude that the hippocampus turns out to be particularly susceptible to hypoxia overlaid on cerebral ischemia and that old age further increases this susceptibility.

Measurements of the anaplerotic rate in the human cerebral cortex using 13C magnetic resonance spectroscopy and [1-13C] and [2-13C] glucose

Recent studies in rodent and human cerebral cortex have shown that glutamate-glutamine neurotransmitter cycling is rapid and the major pathway of neuronal glutamate repletion. The rate of the cycle remains controversial in humans, because glutamine may come either from cycling or from anaplerosis via glial pyruvate carboxylase. Most studies have determined cycling from isotopic labeling of glutamine and glutamate using a [1-(13)C]glucose tracer, which provides label through neuronal and glial pyruvate dehydrogenase or via glial pyruvate carboxylase. To measure the anaplerotic contribution, we measured (13)C incorporation into glutamate and glutamine in the occipital-parietal region of awake humans while infusing [2-(13)C]glucose, which labels the C2 and C3 positions of glutamine and glutamate exclusively via pyruvate carboxylase. Relative to [1-(13)C]glucose, [2-(13)C]glucose provided little label to C2 and C3 glutamine and glutamate. Metabolic modeling of the labeling data indicated that pyruvate carboxylase accounts for 6 +/- 4% of the rate of glutamine synthesis, or 0.02 micromol/g/min. Comparison with estimates of human brain glutamine efflux suggests that the majority of the pyruvate carboxylase flux is used for replacing glutamate lost due to glial oxidation and therefore can be considered to support neurotransmitter trafficking. These results are consistent with observations made with arterial-venous differences and radiotracer methods.

Regional changes in the metabolite profile after long-term hypoxia-ischemia in brains of young and aged rats: a quantitative proton MRS study

Quantitative proton magnetic resonance spectroscopy (MRS) was used to determine region-specific metabolic changes in young and aged animals subjected to a long-term hypoxic-ischemic injury. Focal ischemia, which was studied as an experimental stroke model, was induced in 3- and 24-month-old rats by unilateral common carotid artery occlusion associated with 24 h of hypoxia. Eight metabolites were quantified from extracts in three different brain regions (hippocampus, frontoparietal and occipital cortices) from both the ipsilateral and contralateral sides. Our findings showed significant differences in lactate and myo-inositol concentration values in the hippocampus of the aged rats as compared to the same area of the young adult group under normoxic conditions. After hypoxia-ischemia (HI), the most relevant changes in metabolite concentrations were found in the hippocampal region of both young and aged groups as compared to their age-matched controls. Of the three brain areas under investigation, the hippocampus proved to be particularly susceptible to the prolonged hypoxia-ischemia perturbation. The effects were more evident in the aged animals.

Normal pressure hydrocephalus and cerebral blood flow: a review

Normal pressure hydrocephalus is a neurological disease which poses both diagnostic and therapeutic problems for the clinician. The measurement and characterisation of cerebral blood flow has been proposed as a tool for resolving such problems as well as elucidating its pathophysiology. We review the results of studies in which this tool has been applied to normal pressure hydrocephalus patients and consider the merits of the techniques that have been utilised. Finally, consideration is given to feasible future studies and the methods that could be employed in the study of cerebral blood flow and metabolism in patients with normal pressure hydrocephalus.

Weight loss in cancer and Alzheimer's disease is mediated by a similar pathway

Weight loss, despite adequate caloric intake, occurs in Alzheimer's disease and cancer. Similar alterations of biochemistry accompany the weight loss in both diseases, and this suggests a common pathway of weight loss. If this hypothesis is correct, then drugs that prevent weight loss in cancer should also prevent weight loss in Alzheimer's disease. Megestrol acetate prevents weight loss in human and animal cancers. Omega 3 fatty acids prevent weight loss in animal models of cancer. Both compounds might prevent weight loss in Alzheimer patients.