Increased glucose concentration in the hippocampus in early Alzheimer's disease following oral glucose ingestion

WNKs regulate mouse behavior and alter central nervous system glucose uptake and insulin signaling

Certain areas of the brain involved in episodic memory and behavior, such as the hippocampus, express high levels of insulin receptors and glucose transporter-4 (GLUT4) and are responsive to insulin. Insulin and neuronal glucose metabolism improve cognitive functions and regulate mood in humans. Insulin-dependent GLUT4 trafficking has been extensively studied in muscle and adipose tissue, but little work has demonstrated either how it is controlled in insulin-responsive brain regions or its mechanistic connection to cognitive functions. In this study, we demonstrate that inhibition of WNK (With-No-lysine (K)) kinases improves learning and memory in mice. Neuronal inhibition of WNK enhances in vivo hippocampal glucose uptake. Inhibition of WNK enhances insulin signaling output and insulin-dependent GLUT4 trafficking to the plasma membrane in mice primary neuronal cultures and hippocampal slices. Therefore, we propose that the extent of neuronal WNK kinase activity has an important influence on learning, memory and anxiety-related behaviors, in part, by modulation of neuronal insulin signaling.

Fuel for Thought? A Systematic Review of Neuroimaging Studies into Glucose Enhancement of Cognitive Performance

A transient improvement in cognitive performance can be observed following the ingestion of a glucose drink, a phenomenon known as the ‘glucose facilitation effect’. The effect has been studied thoroughly in the last three decades, but its neural underpinnings remain a matter of speculation. A systematic review was conducted to evaluate the current evidence from studies applying neuroimaging or neurophysiological methods to investigate the glucose enhancement effect. Eleven studies met the inclusion criteria of using neuroimaging in conjunction with cognitive outcomes. Six studies employed electroencephalography (EEG), four used functional magnetic resonance imaging (fMRI) and one employed functional near-infrared spectroscopy (fNIRS). All but one study reported modulation of neurophysiology or neuroimaging markers following glucose, while only five studies reported significant changes in cognitive outcomes. The evidence suggests that glucose administration enhances neurocognitive markers of episodic memory and attentional processes underpinned by medial temporal and frontal activation, sometimes in the absence of measurable behavioural effects. Further exploration of glucose facilitation using neuroimaging measures with increased sample sizes is warranted to replicate these findings.

Brain insulin resistance and altered brain glucose are related to memory impairments in schizophrenia

Memory is robustly impaired in schizophrenia (SZ) and related to functional outcome. Memory dysfunction has been shown to be related to altered brain glucose metabolism and brain insulin resistance in animal models and human studies of Alzheimer's disease. In this study, differences in brain glucose using magnetic resonance spectroscopy (MRS) and blood Extracellular Vesicle (EV) biomarkers of neuronal insulin resistance (i.e. Akt and signaling effectors) between SZ and controls were investigated, as well as whether these measures were related to memory impairments. Neuronal insulin resistance biomarkers showed a trend for being lower in SZ compared to controls, and memory measures were lower in SZ compared to controls. Occipital cortex glucose was higher in SZ compared to controls indicating lower brain glucose utilization. Linear regression analyses revealed significant relationships between neuronal insulin resistance biomarkers, memory measures, and brain glucose. More specifically, p70S6K, an insulin signaling effector, was related to verbal learning and brain MRS glucose in the SZ group. For the first time, we show that memory impairments in SZ may be related to brain glucose and brain insulin resistance. These data suggest that brain insulin resistance may play a role in the pathophysiology of learning and memory dysfunction in SZ.

Nutrients for neurocognition in health and disease: measures, methodologies and mechanisms

Effective pharmaceutical treatments for age-related cognitive decline have proved elusive. There is, however, compelling evidence that nutritional status and supplementation could play crucial roles in modifying the expression of cognitive change through the lifespan. Subjective memory impairment and mild cognitive impairment can be harbingers of dementia but this is by no means inevitable. Neurocognitive change is influenced by a variety of processes, many of which are involved in other aspects of systemic health, including cardiovascular function. Importantly, many of these processes are governed by mechanisms which may be modified by specific classes of bioactive nutrients. There is increasing, converging evidence from controlled trials that nutritional interventions can improve mood and cognitive function in both clinical and healthy populations. Specific examples include selected botanical extracts such as the flavonoids. Some nutritional supplements (e.g. broad-spectrum micronutrient supplementation) appear to support improved cognitive function, possibly through redressing insufficient nutrient status (i.e. suboptimal but above the threshold for frank deficiency). Recent mechanistic research has unveiled physiologically plausible, modifiable, cognition-relevant targets for nutrition and nutraceuticals. These include processes involved in both systemic and central vascular function, inflammation, metabolism, central activation, improved neural efficiency and angiogenesis. The advent and development of human neuroimaging methodology have greatly aided our understanding of the core central mechanisms of cognitive change. Different imaging modalities can provide insights into modifiable central mechanisms which may be targeted by bioactive nutrients. The latter may contribute to slowing age-related decline through supporting neurocognitive scaffolding mechanisms.

Crocin attenuates acute hypobaric hypoxia-induced cognitive deficits of rats

This study investigated whether crocin exerted neuroprotective effects against acute hypobaric hypoxia at high altitude in vivo and determined the underlying mechanisms. Male Sprague-Dawley rats were randomly assigned to a normoxic group，a hypoxic group, and three crocin groups at three different doses. The rats were transferred from 50m to 4200m for 3 days after treatment with crocin for 3 days. The learning and memory of the rat were evaluated with the Morris water maze test. Transmission electron microscope (TEM) was used to analyze the changes in the ultrastructure of hippocampal neurons. Peroxisome proliferator-activated receptor-γ co-activator 1α (PGC-1α) and sirtuin-1 (SIRT1) levels were determined using immunohistochemical staining and western blotting. The escape latency of the crocin group was shorter than that of the hypoxic group, while the frequency of the rats reaching the platform was significantly higher in the crocin group. The structures of nerve cells and mitochondria were destroyed in the hypoxic group, but were repaired in the crocin groups. The expressions of PGC-1α and SIRT1 were decreased in the hypoxic group, but were increased in the crocin group. All the effects improved by crocin were dose-dependent. Crocin attenuates acute hypobaric hypoxia-induced cognitive deficits in rats, accompanied by repairing the structures of hippocampal neurons and improving PGC-1α and SIRT1 levels.

Lower brain and blood nutrient status in Alzheimer's disease: Results from meta-analyses

INTRODUCTION

Alzheimer's disease (AD) patients are at risk of nutritional insufficiencies because of physiological and psychological factors. Recently, we showed the results of the meta-analyses indicating lower plasma levels of vitamins A, B12, C, E, and folate in AD patients compared with cognitively intact elderly controls (controls). Now, additional and more extensive literature searches were performed selecting studies which compare blood and brain/cerebrospinal fluid (CSF) levels of vitamins, minerals, trace elements, micronutrients, and fatty acids in AD patients versus controls.

METHODS

The literature published after 1980 in Cochrane Central Register of Controlled Trials, Medline, and Embase electronic databases was systematically analyzed using Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines to detect studies meeting the selection criteria. Search terms used are as follows: AD patients, Controls, vitamins, minerals, trace elements, micronutrients, and fatty acids. Random-effects meta-analyses using a linear mixed model with correction for age differences between AD patients and controls were performed when four or more publications were retrieved for a specific nutrient.

RESULTS

Random-effects meta-analyses of 116 selected publications showed significant lower CSF/brain levels of docosahexaenoic acid (DHA), choline-containing lipids, folate, vitamin B12, vitamin C, and vitamin E. In addition, AD patients showed lower circulatory levels of DHA, eicosapentaenoic acid, choline as phosphatidylcholine, and selenium.

CONCLUSION

The current data show that patients with AD have lower CSF/brain availability of DHA, choline, vitamin B12, folate, vitamin C, and vitamin E. Directionally, brain nutrient status appears to parallel the lower circulatory nutrient status; however, more studies are required measuring simultaneously circulatory and central nutrient status to obtain better insight in this observation. The brain is dependent on nutrient supply from the circulation, which in combination with nutrient involvement in AD-pathophysiological mechanisms suggests that patients with AD may have specific nutritional requirements. This hypothesis could be tested using a multicomponent nutritional intervention.

Type 2 diabetes mellitus in the pathophysiology of Alzheimer's disease

Both Alzheimer's disease (AD) and type 2 diabetes mellitus (DM) are two common forms of disease worldwide and many studies indicate that people with diabetes, especially DM, are at higher risk of developing AD. AD is characterized by progressive cognitive decline and accumulation of β-amyloid (Aβ) forming senile plaques. DM is a metabolic disorder characterized by hyperglycemia in the context of insulin resistance and relative lack of insulin. Both diseases also share common characteristics such as loss of cognitive function and inflammation. Inflammation resulting from Aβ further induces production of Aβ_1-42 peptides. Inflammation due to overnutrition induces insulin resistance and consequently DM. Memory deficit and a decrease in GLUT4 and hippocampal insulin signaling have been observed in animal models of insulin resistance. The objective of this review was to show the shared characteristics of AD and DM.

Shared Neuropathological Characteristics of Obesity, Type 2 Diabetes and Alzheimer's Disease: Impacts on Cognitive Decline

In the past few decades, the prevalence of obesity and type 2 diabetes mellitus (T2DM), as well as older individuals at risk for Alzheimer’s disease (AD), has increased. While the consumption of diets high in fat (total and saturated) have been linked to increased risk of AD, diets rich in antioxidants, polyunsaturated fats, and omega-3 fatty acids are associated with decreased risk. Additionally, AD patients are at increased risk for developing T2DM. Recent research suggests that there are stronger similarities between AD and T2DM than have previously been considered. Here we review the neurocognitive and inflammatory effects of high-fat diet consumption, its relationship to AD, and the treatment potential of dietary interventions that may decrease risk of cognitive decline and other associated neuropathological changes, such as insulin resistance, oxidative stress, and chronic inflammatory processes.

Metabolic Alterations Associated to Brain Dysfunction in Diabetes

From epidemiological studies it is known that diabetes patients display increased risk of developing dementia. Moreover, cognitive impairment and Alzheimer's disease (AD) are also accompanied by impaired glucose homeostasis and insulin signalling. Although there is plenty of evidence for a connection between insulin-resistant diabetes and AD, definitive linking mechanisms remain elusive. Cerebrovascular complications of diabetes, alterations in glucose homeostasis and insulin signalling, as well as recurrent hypoglycaemia are the factors that most likely affect brain function and structure. While difficult to study in patients, the mechanisms by which diabetes leads to brain dysfunction have been investigated in experimental models that display phenotypes of the disease. The present article reviews the impact of diabetes and AD on brain structure and function, and discusses recent findings from translational studies in animal models that link insulin resistance to metabolic alterations that underlie brain dysfunction. Such modifications of brain metabolism are likely to occur at early stages of neurodegeneration and impact regional neurochemical profiles and constitute non-invasive biomarkers detectable by magnetic resonance spectroscopy (MRS).

Brain hypometabolism triggers PHF-like phosphorylation of tau, a major hallmark of Alzheimer's disease pathology

Sporadic Alzheimer's disease (AD) is a chronic progressive neurodegenerative disorder of unknown cause characterized by fibrillar accumulation of the Aß-peptide and aggregates of the microtubule-associated protein tau in a hyperphosphorylated form. Already at preclinical stages, AD is characterized by hypometabolic states which are a good predictor of cognitive decline. Here, we summarize recent evidence derived from the study of hibernating animals that brain hypometabolism can trigger PHF-like hyperphosphorylation of tau. We put forward the concept that particular types of neurons respond to a hypometabolic state with an elevated phosphorylation of tau protein which represents a physiological mechanism involved in regulating synaptic gain. If, in contrast to hibernation, the hypometabolic state is not terminated after a definite time but rather persists and progresses, the elevated phosphorylation of tau protein endures and the protective reaction associated with it might turn into a pathological cascade leading to neurodegeneration.

Metabolic disturbances in diseases with neurological involvement

Degeneration of specific neuronal populations and progressive nervous system dysfunction characterize neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. These findings are also reported in inherited diseases such as phenylketonuria and glutaric aciduria type I. The involvement of mitochondrial dysfunction in these diseases was reported, elicited by genetic alterations, exogenous toxins or buildup of toxic metabolites. In this review we shall discuss some metabolic alterations related to the pathophysiology of diseases with neurological involvement and aging process. These findings may help identifying early disease biomarkers and lead to more effective therapies to improve the quality of life of the patients affected by these devastating illnesses.

Advances in high-field magnetic resonance spectroscopy in Alzheimer's disease

Alzheimer's disease (AD) affects several important molecules in brain metabolism. The resulting neurochemical changes can be quantified non-invasively in localized brain regions using in vivo single-voxel proton magnetic resonance spectroscopy (SV 1H MRS). Although the often heralded diagnostic potential of MRS in AD largely remains unfulfilled, more recent use of high magnetic fields has led to significantly improved signal-to-noise ratios and spectral resolutions, thereby allowing clinical applications with increased measurement reliability. The present article provides a comprehensive review of SV 1H MRS studies on AD at high magnetic fields (3.0 Tesla and above). This review suggests that patterned regional differences and longitudinal alterations in several neurometabolites are associated with clinically established AD. Changes in multiple metabolites are identifiable even at early stages of AD development. By combining information of neurochemicals in different brain regions revealing either pathological or compensatory changes, high field MRS can be evaluated in AD diagnosis and in the detection of treatment effects. To achieve this, standardization of data acquisition and analytical approaches is needed.

Caloric intake, dietary lifestyles, macronutrient composition, and alzheimer' disease dementia

Alzheimer's disease is a devastating neurodegenerative condition currently affecting over 5 million elderly individuals in the United States. There is much evidence suggesting that certain dietary lifestyles can help to prevent and possibly treat Alzheimer's disease. In this paper, we discuss how certain cardiovascular and diabetic conditions can induce an increased susceptibility for Alzheimer's disease and the mechanisms through which this occurs. We further discuss how the consumption of certain foods or food components can help to reduce one's risk for Alzheimer's disease and may possibly be developed as a therapeutic agent.

The physiological link between metabolic rate depression and tau phosphorylation in mammalian hibernation

Abnormal phosphorylation and aggregation of tau protein are hallmarks of a variety of neurological disorders, including Alzheimer's disease (AD). Increased tau phosphorylation is assumed to represent an early event in pathogenesis and a pivotal aspect for aggregation and formation of neurofibrillary tangles. However, the regulation of tau phosphorylation in vivo and the causes for its increased stage of phosphorylation in AD are still not well understood, a fact that is primarily based on the lack of adequate animal models. Recently we described the reversible formation of highly phosphorylated tau protein in hibernating European ground squirrels. Hence, mammalian hibernation represents a model system very well suited to study molecular mechanisms of both tau phosphorylation and dephosphorylation under in vivo physiological conditions. Here, we analysed the extent and kinetics of hibernation-state dependent tau phosphorylation in various brain regions of three species of hibernating mammals: arctic ground squirrels, Syrian hamsters and black bears. Overall, tau protein was highly phosphorylated in torpor states and phosphorylation levels decreased after arousal in all species. Differences between brain regions, hibernation-states and phosphosites were observed with respect to degree and kinetics of tau phosphorylation. Furthermore, we tested the phosphate net turnover of tau protein to analyse potential alterations in kinase and/or phosphatase activities during hibernation. Our results demonstrate that the hibernation-state dependent phosphorylation of tau protein is specifically regulated but involves, in addition, passive, temperature driven regulatory mechanisms. By determining the activity-state profile for key enzymes of tau phosphorylation we could identify kinases potentially involved in the differentially regulated, reversible tau phosphorylation that occurs during hibernation. We show that in black bears hibernation is associated with conformational changes of highly phosphorylated tau protein that are typically related to neuropathological alterations. The particular hibernation characteristics of black bears with a continuous torpor period and an only slightly decreased body temperature, therefore, potentially reflects the limitations of this adaptive reaction pattern and, thus, might indicate a transitional state of a physiological process.

PGC-1alpha expression decreases in the Alzheimer disease brain as a function of dementia

OBJECTIVES

To explore mechanisms through which altered peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC-1alpha) expression may influence Alzheimer disease (AD) amyloid neuropathology and to test the hypothesis that promotion of PGC-1alpha expression in neurons might be developed as a novel therapeutic strategy in AD.

DESIGN

Case-control. Patients Human postmortem brain (hippocampal formation) samples from AD cases and age-matched non-AD cases.

RESULTS

Using genome-wide complementary DNA microarray analysis, we found that PGC-1alpha messenger RNA expression was significantly decreased as a function of progression of clinical dementia in the AD brain. Following confirmatory real-time polymerase chain reaction assay, we continued to explore the role of PGC-1alpha in clinical dementia and found that PGC-1alpha protein content was negatively associated with both AD-type neuritic plaque pathology and beta-amyloid (Abeta)(X-42) contents. Moreover, we found that the predicted elevation of amyloidogenic Abeta(1-42) and Abeta(1-40) peptide accumulation in embryonic cortico-hippocampal neurons derived from Tg2576 AD mice under hyperglycemic conditions (glucose level, 182-273 mg/dL) coincided with a dose-dependent attenuation in PGC-1alpha expression. Most importantly, we found that the reconstitution of exogenous PGC-1alpha expression in Tg2576 neurons attenuated the hyperglycemic-mediated beta-amyloidogenesis through mechanisms involving the promotion of the "nonamyloidogenic" alpha-secretase processing of amyloid precursor protein through the attenuation of the forkheadlike transcription factor 1 (FoxO3a) expression.

CONCLUSION

Therapeutic preservation of neuronal PGC-1alpha expression promotes the nonamyloidogenic processing of amyloid precursor protein precluding the generation of amyloidogenic Abeta peptides.

Metabolic syndrome and the role of dietary lifestyles in Alzheimer's disease

Since Alzheimer's disease (AD) has no cure or preventive treatment, an urgent need exists to find a means of preventing, delaying the onset, or reversing the course of the disease. Clinical and epidemiological evidence suggests that lifestyle factors, especially nutrition, may be crucial in controlling AD. Unhealthy lifestyle choices lead to an increasing incidence of obesity, dyslipidemia and hypertension--components of the metabolic syndrome. These disorders can also be linked to AD. Recent research supports the hypothesis that calorie intake, among other non-genetic factors, can influence the risk of clinical dementia. In animal studies, high calorie intake in the form of saturated fat promoted AD-type amyloidosis, while calorie restriction via reduced carbohydrate intake prevented it. Pending further study, it is prudent to recommend to those at risk for AD--e.g. with a family history or features of metabolic syndrome, such as obesity, insulin insensitivity, etc.--to avoid foods and beverages with added sugars; to eat whole, unrefined foods with natural fats, especially fish, nuts and seeds, olives and olive oil; and to minimize foods that disrupt insulin and blood sugar balance.

Hibernation model of tau phosphorylation in hamsters: selective vulnerability of cholinergic basal forebrain neurons - implications for Alzheimer's disease

Neurofibrillar tangles made up of 'paired helical filaments' (PHFs) consisting of hyperphosphorylated microtubule-associated protein tau are major hallmarks of Alzheimer's disease (AD). Tangle formation selectively affects certain neuronal types and systematically progresses throughout numerous brain areas, which reflects a hierarchy of neuronal vulnerability and provides the basis for the neuropathological staging of disease severity. Mechanisms underlying this selective neuronal vulnerability are unknown. We showed previously that reversible PHF-like phosphorylation of tau occurs during obligate hibernation. Here we extend these findings to facultative hibernators such as Syrian hamsters (Mesocricetus auratus) forced into hibernation. In this model, we showed in the basal forebrain projection system that cholinergic neurons are selectively affected by PHF-like phosphorylated tau, while gamma-aminobutyric acid (GABA)ergic neurons are largely spared, which shows strong parallels to the situation in AD. Formation of PHF-tau in these neurons apparently does not affect their function as pacemaker for terminating hibernation. We conclude that although formation of PHF-like phosphorylated tau in the mammalian brain follows a certain hierarchy, affecting some neurons more frequently than others, it is not necessarily associated with impaired neuronal function and viability. This indicates a more general link between PHF-like phosphorylation of tau and the adaptation of neurons under conditions of a 'vita minima'.