Predominant abnormality in cerebral glucose utilization in late-onset dementia of the Alzheimer type: a cross-sectional comparison against advanced late-onset and incipient early-onset cases

Proteomic Analysis of a Rat Streptozotocin Model Shows Dysregulated Biological Pathways Implicated in Alzheimer's Disease

Alzheimer's Disease (AD) is an age-related neurodegenerative disorder characterized by progressive memory loss and cognitive impairment, affecting 35 million individuals worldwide. Intracerebroventricular (ICV) injection of low to moderate doses of streptozotocin (STZ) in adult male Wistar rats can reproduce classical physiopathological hallmarks of AD. This biological model is known as ICV-STZ. Most studies are focused on the description of behavioral and morphological aspects of the ICV-STZ model. However, knowledge regarding the molecular aspects of the ICV-STZ model is still incipient. Therefore, this work is a first attempt to provide a wide proteome description of the ICV-STZ model based on mass spectrometry (MS). To achieve that, samples from the pre-frontal cortex (PFC) and hippocampus (HPC) of the ICV-STZ model and control (wild-type) were used. Differential protein abundance, pathway, and network analysis were performed based on the protein identification and quantification of the samples. Our analysis revealed dysregulated biological pathways implicated in the early stages of late-onset Alzheimer's disease (LOAD), based on differentially abundant proteins (DAPs). Some of these DAPs had their mRNA expression further investigated through qRT-PCR. Our results shed light on the AD onset and demonstrate the ICV-STZ as a valid model for LOAD proteome description.

Lysophosphatidylcholines are associated with P-tau181 levels in early stages of Alzheimer's Disease

Background

We profiled circulating plasma metabolites to identify systemic biochemical changes in clinical and biomarker-assisted diagnosis of Alzheimer's disease (AD).

Methods

We used an untargeted approach with liquid chromatography coupled to high-resolution mass spectrometry to measure small molecule plasma metabolites from 150 clinically diagnosed AD patients and 567 age-matched healthy elderly of Caribbean Hispanic ancestry. Plasma biomarkers of AD were measured including P-tau181, Aβ40, Aβ42, total-tau, neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP). Association of individual and co-abundant modules of metabolites were tested with clinical diagnosis of AD, as well as biologically-defined AD pathological process based on P-tau181 and other biomarker levels.

Results

Over 6000 metabolomic features were measured with high accuracy. First principal component (PC) of lysophosphatidylcholines (lysoPC) that bind to or interact with docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and arachidonic acid (AHA) was associated with decreased risk of AD (OR = 0.91 [0.89-0.96], p = 2e-04). Association was restricted to individuals without an APOE ε4 allele (OR = 0.89 [0.84-0.94], p = 8.7e-05). Among individuals carrying at least one APOE ε4 allele, PC4 of lysoPCs moderately increased risk of AD (OR = 1.37 [1.16-1.6], p = 1e-04). Essential amino acids including tyrosine metabolism pathways were enriched among metabolites associated with P-tau181 levels and heparan and keratan sulfate degradation pathways were associated with Aβ42/Aβ40 ratio.

Conclusions

Unbiased metabolic profiling can identify critical metabolites and pathways associated with β-amyloid and phosphotau pathology. We also observed an APOE-ε4 dependent association of lysoPCs with AD and biologically based diagnostic criteria may aid in the identification of unique pathogenic mechanisms.

Lysophosphatidylcholines are associated with P-tau181 levels in early stages of Alzheimer's Disease

Background

We investigated systemic biochemical changes in Alzheimer's disease (AD) by investigating the relationship between circulating plasma metabolites and both clinical and biomarker-assisted diagnosis of AD.

Methods

We used an untargeted approach with liquid chromatography coupled to high-resolution mass spectrometry to measure exogenous and endogenous small molecule metabolites in plasma from 150 individuals clinically diagnosed with AD and 567 age-matched elderly without dementia of Caribbean Hispanic ancestry. Plasma biomarkers of AD were also measured including P-tau181, Aβ40, Aβ42, total tau, neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP). Association of individual and co-expressed modules of metabolites were tested with the clinical diagnosis of AD, as well as biologically-defined AD pathological process based on P-tau181 and other biomarker levels.

Results

Over 4000 metabolomic features were measured with high accuracy. First principal component (PC) of lysophosphatidylcholines (lysoPC) that bind to or interact with docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and arachidonic acid (AHA) was associated with decreased risk of AD (OR=0.91 [0.89-0.96], p=2e-04). Restricted to individuals without an APOE ε4 allele (OR=0.89 [0.84-0.94], p= 8.7e-05), the association remained. Among individuals carrying at least one APOE ε4 allele, PC4 of lysoPCs moderately increased risk of AD (OR=1.37 [1.16-1.6], p=1e-04). Essential amino acids including tyrosine metabolism pathways were enriched among metabolites associated with P-tau181 levels and heparan and keratan sulfate degradation pathways were associated with Aβ42/Aβ40 ratio reflecting different pathways enriched in early and middle stages of disease.

Conclusions

Our findings indicate that unbiased metabolic profiling can identify critical metabolites and pathways associated with β-amyloid and phosphotau pathology. We also observed an APOE ε4 dependent association of lysoPCs with AD and that biologically-based diagnostic criteria may aid in the identification of unique pathogenic mechanisms.

Altered cerebral blood flow in older adults with Alzheimer's disease: a systematic review

The prevalence of Alzheimer's disease is projected to reach 13 million in the U.S. by 2050. Although major efforts have been made to avoid this outcome, so far there are no treatments that can stop or reverse the progressive cognitive decline that defines Alzheimer's disease. The utilization of preventative treatment before significant cognitive decline has occurred may ultimately be the solution, necessitating a reliable biomarker of preclinical/prodromal disease stages to determine which older adults are most at risk. Quantitative cerebral blood flow is a promising potential early biomarker for Alzheimer's disease, but the spatiotemporal patterns of altered cerebral blood flow in Alzheimer's disease are not fully understood. The current systematic review compiles the findings of 81 original studies that compared resting gray matter cerebral blood flow in older adults with mild cognitive impairment or Alzheimer's disease and that of cognitively normal older adults and/or assessed the relationship between cerebral blood flow and objective cognitive function. Individuals with Alzheimer's disease had relatively decreased cerebral blood flow in all brain regions investigated, especially the temporoparietal and posterior cingulate, while individuals with mild cognitive impairment had consistent results of decreased cerebral blood flow in the posterior cingulate but more mixed results in other regions, especially the frontal lobe. Most papers reported a positive correlation between regional cerebral blood flow and cognitive function. This review highlights the need for more studies assessing cerebral blood flow changes both spatially and temporally over the course of Alzheimer's disease, as well as the importance of including potential confounding factors in these analyses.

The Link between Oxidative Stress, Mitochondrial Dysfunction and Neuroinflammation in the Pathophysiology of Alzheimer's Disease: Therapeutic Implications and Future Perspectives

Alzheimer's disease (AD), the most common form of dementia, has increasing incidence, increasing mortality rates, and poses a huge burden on healthcare. None of the currently approved drugs for the treatment of AD influence disease progression. Many clinical trials aiming at inhibiting amyloid plaque formation, increasing amyloid beta clearance, or inhibiting neurofibrillary tangle pathology yielded inconclusive results or failed. Meanwhile, research has identified many interlinked vicious cascades implicating oxidative stress, mitochondrial dysfunction, and chronic neuroinflammation, and has pointed to novel therapeutic targets such as improving mitochondrial bioenergetics and quality control, diminishing oxidative stress, or modulating the neuroinflammatory pathways. Many novel molecules tested in vitro or in animal models have proven efficient, but their translation into clinic needs further research regarding appropriate doses, delivery routes, and possible side effects. Cell-based therapies and extracellular vesicle-mediated delivery of messenger RNAs and microRNAs seem also promising strategies allowing to target specific signaling pathways, but need further research regarding the most appropriate harvesting and culture methods as well as control of the possible tumorigenic side effects. The rapidly developing area of nanotechnology could improve drug delivery and also be used in early diagnosis.

Prediction value of the genetic risk of type 2 diabetes on the amnestic mild cognitive impairment conversion to Alzheimer’s disease

Amnestic mild cognitive impairment (aMCI) and Type 2 diabetes mellitus (T2DM) are both important risk factors for Alzheimer’s disease (AD). We aimed to investigate whether a T2DM-specific polygenic risk score (PRS_sT2DM) can predict the conversion of aMCI to AD and further explore the underlying neurological mechanism. All aMCI patients were from the Alzheimer’s disease Neuroimaging Initiative (ADNI) database and were divided into conversion (aMCI-C, n = 164) and stable (aMCI-S, n = 222) groups. PRS_sT2DM was calculated by PRSice-2 software to explore the predictive efficacy of the aMCI conversion to AD. We found that PRS_sT2DM could independently predict the aMCI conversion to AD after removing the common variants of these two diseases. PRS_sT2DM was significantly negatively correlated with gray matter volume (GMV) of the right superior frontal gyrus in the aMCI-C group. In all aMCI patients, PRS_sT2DM was significantly negatively correlated with the cortical volume of the right superior occipital gyrus. The cortical volume of the right superior occipital gyrus could significantly mediate the association between PRS_sT2DM and aMCI conversion. Gene-based analysis showed that T2DM-specific genes are highly expressed in cortical neurons and involved in ion and protein binding, neural development and generation, cell junction and projection, and PI3K-Akt and MAPK signaling pathway, which might increase the aMCI conversion by affecting the Tau phosphorylation and amyloid-beta (Aβ) accumulation. Therefore, the PRS_sT2DM could be used as a measure to predict the conversion of aMCI to AD.

A New Hypothesis for Alzheimer’s Disease: The Lipid Invasion Model

This paper proposes a new hypothesis for Alzheimer’s disease (AD)—the lipid invasion model. It argues that AD results from external influx of free fatty acids (FFAs) and lipid-rich lipoproteins into the brain, following disruption of the blood-brain barrier (BBB). The lipid invasion model explains how the influx of albumin-bound FFAs via a disrupted BBB induces bioenergetic changes and oxidative stress, stimulates microglia-driven neuroinflammation, and causes anterograde amnesia. It also explains how the influx of external lipoproteins, which are much larger and more lipid-rich, especially more cholesterol-rich, than those normally present in the brain, causes endosomal-lysosomal abnormalities and overproduction of the peptide amyloid-β (Aβ). This leads to the formation of amyloid plaques and neurofibrillary tangles, the most well-known hallmarks of AD. The lipid invasion model argues that a key role of the BBB is protecting the brain from external lipid access. It shows how the BBB can be damaged by excess Aβ, as well as by most other known risk factors for AD, including aging, apolipoprotein E4 (APOE4), and lifestyle factors such as hypertension, smoking, obesity, diabetes, chronic sleep deprivation, stress, and head injury. The lipid invasion model gives a new rationale for what we already know about AD, explaining its many associated risk factors and neuropathologies, including some that are less well-accounted for in other explanations of AD. It offers new insights and suggests new ways to prevent, detect, and treat this destructive disease and potentially other neurodegenerative diseases.

Kisspeptin-13 prevented the electrophysiological alterations induced by Amyloid-Beta pathology in rat: Possible involvement of stromal interaction molecules and pCREB

Alzheimer's disease (AD) is a progressive neurological disease that slowly causing memory impairments with no effective treatment. We have recently reported that kisspeptin-13 (KP-13) ameliorates Aβ toxicity-induced memory deficit in rats. Here, the possible cellular impact of kisspeptin receptor activation in a rat model of the early stage AD was assessed using whole-cell patch-clamp recording from CA1 pyramidal neurons and molecular approaches. Compared to neurons from the control group, cells from the Aβ-treated group displayed spontaneous and evoked hyperexcitability with lower spike frequency adaptation. These cells had also a lower sag ratio in response to hyperpolarizing prepulse current delivered before a depolarizing current injection. Neurons from the Aβ-treated group exhibited short spike onset latency, lower rheobase and short utilization time compared with those in the control group. Furthermore, phase plot analysis of action potential showed that Aβ treatment affected the action potential features. These electrophysiological changes induced by Aβ were associated with increased expression of stromal interaction molecules (STIMs), particularly (STIM2) and decreased pCREB/CREB ratio. Treatment with KP-13 following Aβ injection into the entorhinal cortex, however, prevented the excitatory effect of Aβ on spontaneous and evoked neuronal activity, increased the latency of onset, enhanced the sag ratio, increased the rheobase and utilization time, and prevented the changes induced Aβ on spike parameters. In addition, the KP-13 application after Aβ treatment reduced the expression of STIMs and increased the pCREB/CREB ratio compared to those receiving Aβ treatment alone. In summary, these results provide evidence that activation of kisspeptin receptor may be effective against pathology of Aβ.

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.

Alzheimer's Disease and Epilepsy: A Perspective on the Opportunities for Overlapping Therapeutic Innovation

Early-onset Alzheimer's disease (AD) is associated with variants in amyloid precursor protein (APP) and presenilin (PSEN) 1 and 2. It is increasingly recognized that patients with AD experience undiagnosed focal seizures. These AD patients with reported seizures may have worsened disease trajectory. Seizures in epilepsy can also lead to cognitive deficits, neuroinflammation, and neurodegeneration. Epilepsy is roughly three times more common in individuals aged 65 and older. Due to the numerous available antiseizure drugs (ASDs), treatment of seizures has been proposed to reduce the burden of AD. More work is needed to establish the functional impact of seizures in AD to determine whether ASDs could be a rational therapeutic strategy. The efficacy of ASDs in aged animals is not routinely studied, despite the fact that the elderly represents the fastest growing demographic with epilepsy. This leaves a particular gap in understanding the discrete pathophysiological overlap between hyperexcitability and aging, and AD more specifically. Most of our preclinical knowledge of hyperexcitability in AD has come from mouse models that overexpress APP. While these studies have been invaluable, other drivers underlie AD, e.g. PSEN2. A diversity of animal models should be more frequently integrated into the study of hyperexcitability in AD, which could be particularly beneficial to identify novel therapies. Specifically, AD-associated risk genes, in particular PSENs, altogether represent underexplored contributors to hyperexcitability. This review assesses the available studies of ASDs administration in clinical AD populations and preclinical studies with AD-associated models and offers a perspective on the opportunities for further therapeutic innovation.

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.

Similarities and Differences in the Pattern of Tau Hyperphosphorylation in Physiological and Pathological Conditions: Impacts on the Elaboration of Therapies to Prevent Tau Pathology

Tau protein, a neuronal microtubule-associated protein, becomes hyperphosphorylated in several neurodegenerative diseases called tauopathies. Hyperphosphorylation of tau is correlated to its redistribution from the axon to the somato-dendritic compartment at early stages of tauopathies. Interestingly, tau hyperphosphorylation begins in different regions of the brain in each tauopathy. In some regions, both neurons and glial cells develop tau hyperphosphorylation. Tau hyperphosphorylation is also observed in physiological conditions such as hibernation and brain development. In the first section of present article, we will review the spatiotemporal and cellular distribution of hyperphosphorylated tau in the most frequent tauopathies. In the second section, we will compare the pattern of tau hyperphosphorylation in physiological and pathological conditions and discuss the sites that could play a pivotal role in the conversion of non-toxic to toxic forms of hyperphosphorylated tau. Furthermore, we will discuss the role of hyperphosphorylated tau in physiological and pathological conditions and the fact that tau hyperphosphorylation is reversible in physiological conditions but not in a pathological ones. In the third section, we will speculate how the differences and similarities between hyperphosphorylated tau in physiological and pathological conditions could impact the elaboration of therapies to prevent tau pathology. In the fourth section, the different therapeutic approaches using tau as a direct or indirect therapeutic target will be presented.

Molecular Mechanisms and Genetics of Oxidative Stress in Alzheimer's Disease

Alzheimer’s disease is the most common neurodegenerative disorder that can cause dementia in elderly over 60 years of age. One of the disease hallmarks is oxidative stress which interconnects with other processes such as amyloid-β deposition, tau hyperphosphorylation, and tangle formation. This review discusses current thoughts on molecular mechanisms that may relate oxidative stress to Alzheimer’s disease and identifies genetic factors observed from in vitro, in vivo, and clinical studies that may be associated with Alzheimer’s disease-related oxidative stress.

The Importance of Understanding Amylin Signaling Mechanisms for Therapeutic Development in the Treatment of Alzheimer's Disease

Type II Diabetes (T2D) is a major risk factor for Alzheimer's Disease (AD). These two diseases share several pathological features, including amyloid accumulation, inflammation, oxidative stress, cell death and cognitive decline. The metabolic hormone amylin and amyloid-beta are both amyloids known to self-aggregate in T2D and AD, respectively, and are thought to be the main pathogenic entities in their respective diseases. Furthermore, studies suggest amylin's ability to seed amyloid-beta aggregation, the activation of common signaling cascades in the pancreas and the brain, and the ability of amyloid beta to signal through amylin receptors (AMYR), at least in vitro. However, paradoxically, non-aggregating forms of amylin such as pramlintide are given to treat T2D and functional and neuroprotective benefits of amylin and pramlintide administration have been reported in AD transgenic mice. These paradoxical results beget a deeper study of the complex nature of amylin's signaling through the several AMYR subtypes and other receptors associated with amylin effects to be able to fully understand its potential role in mediating AD development and/or prevention. The goal of this review is to provide such critical insight to begin to elucidate how the complex nature of this hormone's signaling may explain its equally complex relationship with T2D and mechanisms of AD pathogenesis.

Effect of amylin on memory and central insulin resistance in a rat model of Alzheimer's disease

Context: Alzheimer's disease is strongly associated with brain insulin signalling.Objective: Investigating the effect of amylin as a novel treatment in streptozotocin (STZ) rat model of AD.Materials and methods: Alzheimer's disease (AD) was induced in albino rats by intracerebroventricular injection of STZ (3 mg/kg). Rats received either amylin analogue (Pramlintide 200 μg/kg/day) or Metformin (30 mg/kg/day) for 5 weeks.Results: Both Pramlintide and Metformin improve learning and memory through enhancing insulin signalling (p-IR and p-PI3K) which lead to lowering level of CSF glucose, phosphorylated tau proteins, and amyloid-β peptide (Aβ) in hippocampus.Conclusions: Insulin sensitisers as Metformin and Pramlintide can improve learning and memory and decrease the pathological changes in STZ induced rat model of AD. However, Pramlintide is superior to Metformin in some memory tests which related to its action as an amylin analogue. Amylin improves learning and memory through an independent effect other than insulin sensitisation.

Cerebral Fructose Metabolism as a Potential Mechanism Driving Alzheimer's Disease

The loss of cognitive function in Alzheimer's disease is pathologically linked with neurofibrillary tangles, amyloid deposition, and loss of neuronal communication. Cerebral insulin resistance and mitochondrial dysfunction have emerged as important contributors to pathogenesis supporting our hypothesis that cerebral fructose metabolism is a key initiating pathway for Alzheimer's disease. Fructose is unique among nutrients because it activates a survival pathway to protect animals from starvation by lowering energy in cells in association with adenosine monophosphate degradation to uric acid. The fall in energy from fructose metabolism stimulates foraging and food intake while reducing energy and oxygen needs by decreasing mitochondrial function, stimulating glycolysis, and inducing insulin resistance. When fructose metabolism is overactivated systemically, such as from excessive fructose intake, this can lead to obesity and diabetes. Herein, we present evidence that Alzheimer's disease may be driven by overactivation of cerebral fructose metabolism, in which the source of fructose is largely from endogenous production in the brain. Thus, the reduction in mitochondrial energy production is hampered by neuronal glycolysis that is inadequate, resulting in progressive loss of cerebral energy levels required for neurons to remain functional and viable. In essence, we propose that Alzheimer's disease is a modern disease driven by changes in dietary lifestyle in which fructose can disrupt cerebral metabolism and neuronal function. Inhibition of intracerebral fructose metabolism could provide a novel way to prevent and treat this disease.

Exposure of ultrafine particulate matter causes glutathione redox imbalance in the hippocampus: A neurometabolic susceptibility to Alzheimer's pathology

Particulate matter (PM) exposure is related to an increased risk of sporadic Alzheimer's disease (AD), the pathogenesis of which is explained by chronic neurometabolic disturbance. Therefore, PM-induced alterations in neurometabolism might herald AD. We aimed to identify brain region-specific changes in metabolic pathways associated with ultrafine particle (UFP) exposure and to determine whether such metabolic alterations are linked to susceptibility to AD. We constructed UFP exposure chambers and generated UFP by the pyrolysis method, which produces no toxic oxidized by-products of combustion, such as NOx and CO. Twenty male C57BL6 mice (11-12 months old) were exposed either to UFP or room air in the chambers for 3 weeks. One week following completion of UFP exposure, regional brain tissues, including the olfactory bulb, cortex, hippocampus, and cerebellum, were obtained and analyzed by metabolomics based on GC-MS and LC-MS, western blot analysis, and immunohistochemistry. Our results demonstrated that the metabolomic phenotype was distinct within the 4 different anatomical regions following UFP exposure. The highest level of metabolic change was identified in the hippocampus, a vulnerable region involved in AD pathogenesis. In this region, one of the key changes was perturbed redox homeostasis via alterations in the methionine-glutathione pathway. UFP exposure also induced oxidative stress and neuroinflammation, and importantly, increased Alzheimer's beta-amyloid levels in the hippocampus. These results suggest that inhaled UFP-induced perturbation in hippocampal redox homeostasis has a role in the pathogenesis of AD. Therefore, chronic exposure to UFP should be regarded as a cumulative environmental risk factor for sporadic AD.

An Exploratory Analysis of Potential New Biomarkers of Cognitive Function

We examined the relationship between serially measured, novel serum biomarkers and a measure of cognitive functioning in older adults. We assayed stored serum samples from two Fels Longitudinal Study visits in N = 100 adult participants (visit 1 ages 59.3 ± 8.5 years; 53% female), and Montreal Cognitive Assessment (MoCA) scores also assessed at the second visit. Assays included acylcarnitines, amino acids, and 2-hydroxybutyric acid (b-HBA). Cross-sectional correlations between acylcarnitines and amino acids and MoCA were identified. Serial change in short-chain acylcarnitines and visit 2 MoCA were also correlated. Participants with MoCA scores <26 were more likely to have an increase in short-chain acylcarnitines between visits 1 and 2 [adjusted odds ratio (OR) = 5.24; 95% confidence interval (CI) 1.07-25.9]. b-HBA was also correlated with acylcarnitines. Several cross-sectional and serial associations between novel serum biomarkers and cognitive functioning were identified. b-HBA may also be a cost-effective marker of dysregulation associated with cognitive decline.

Neuroprotective Effects of Amylin Analogues on Alzheimer's Disease Pathogenesis and Cognition

Type II diabetes (T2D) has been identified as a major risk factor for the development of Alzheimer's disease (AD). Interestingly, both AD and T2D have similar characteristics including amyloid peptide aggregation, decreased metabolism, and increased oxidative stress and inflammation. Despite their prevalence, therapies for these diseases are limited. To date, most therapies for AD have targeted amyloid-β or tau. Unfortunately, most of these clinical trials have been largely unsuccessful, creating a crucial need for novel therapies. A number of studies have shown that metabolic hormone therapies are effective at ameliorating high blood glucose levels in diabetics as well as improving cognitive function in AD and mild cognitive impairment patients. Pramlintide, a synthetic analogue of the pancreatic hormone amylin, has been developed and used for years now as a treatment for both type I diabetes and T2D due to the loss of β-islet cells responsible for producing amylin. Importantly, recent data demonstrates its potential therapeutic role for AD as well. This review aims at addressing parallels between T2D and AD at a pathological and functional level, focusing on amylin signaling as a key, overlapping mediator in both diseases. The potential therapeutic use of this hormone to treat AD will also be explored from a mechanistic viewpoint.

Moderate protective effect of Kyotorphin against the late consequences of intracerebroventricular streptozotocin model of Alzheimer's disease

The established decrease in the level of endogenous kyotorphin (KTP) into the cerebrospinal fluid of patients with an advanced stage of Alzheimer's disease (AD) and the found neuroprotective activity of KTP suggested its participation in the pathophysiology of the disease. We aimed to study the effects of subchronic intracerebroventricular (ICV) treatment (14 days) with KTP on the behavioral, biochemical and histological changes in rats with streptozotocin (STZ-ICV)-induced model of sporadic AD (sAD). Three months after the administration of STZ-ICV, rats developed increased locomotor activity, decreased level of anxiety, impaired spatial and working memory. Histological data from the STZ-ICV group demonstrated decreased number of neurons in the CA1 and CA3 subfields of the hippocampus. The STZ-ICV group was characterized with a decrease of total protein content in the hippocampus and the prefrontal cortex as well as increased levels of the carbonylated proteins in the hippocampus. KTP treatment of STZ-ICV rats normalized anxiety level and regained object recognition memory. KTP abolished the protein loss in prefrontal cortex and decrease the neuronal loss in the CA3 subfield of the hippocampus. STZ-ICV rats, treated with KTP, did not show significant changes in the levels of the carbonylated proteins in specific brain structures or in motor activity and spatial memory compared to the saline-treated STZ-ICV group. Our data show a moderate and selective protective effect of a subchronic ICV administration of the dipeptide KTP on the pathological changes induced by an experimental model of sAD in rats.

Crucial players in Alzheimer's disease and diabetes mellitus: Friends or foes?

Alzheimer's disease (AD) and diabetes mellitus, especially type 2 (T2DM), are very common and widespread diseases in contemporary societies, and their incidence is steadily on the increase. T2DM is a multiple metabolic disorder, with several mechanisms including hyperglycaemia, insulin resistance, insulin receptor and insulin growth factor disturbances, glucose toxicity, formation of advanced glycation end products (AGEs) and the activity of their receptors. AD is the most common form of dementia, characterized by the accumulation of extracellular beta amyloid peptide aggregates and intracellular hyper-phosphorylated tau proteins, which are thought to drive and/or accelerate inflammatory and oxidative stress processes leading to neurodegeneration. The aim of this paper is to provide a comprehensive review of the evidence linking T2DM to the onset and development of AD and highlight the unknown or poorly studied "nooks and crannies" of this interesting relationship, hence providing an opportunity to stimulate new ideas for the analysis of comorbidities between AD and DM. Despite, indication of possible biomarkers of early diagnosis of T2DM and AD, this review is also an attempt to answer the question as to whether the crucial factors in the development of both conditions support the link between DM and AD.

Apelin-13 Suppresses Neuroinflammation Against Cognitive Deficit in a Streptozotocin-Induced Rat Model of Alzheimer's Disease Through Activation of BDNF-TrkB Signaling Pathway

Alzheimer’s disease (AD), a progressive neurodegenerative disease characterized by impairments of cognitive function as a result of synaptic deficits and neuronal loss, is associated with inflammation. Apelin-13, a predominant neuropeptide with inhibiting effect on inflammation, has beneficial effects on cognition memory and neuronal damage. However, whether apelin-13 can protect neurons to ameliorate cognitive deficits in AD by inhibiting the inflammatory response remains largely unknown. To test this hypothesis, rats were intracerebroventricularly (ICV) injected with streptozotocin (3 mg/kg) alone or in combination with apelin-13 (2 μg). And tyrosine receptor kinase B (TrkB) blocker K252a (200 nM) was administrated 10 min before apelin injection. Furthermore, cognitive performance was assessed by new object recognition (NOR) and Y-maze tests. Protein expression of apelin, APJ, microglial marker (IBA1), astroglia marker (GFAP), interleukin 1 beta (IL-1β), tumor necrosis factor-α (TNF-α), synaptophysin (SYP), brain-derived neurotrophic factor (BDNF), TrkB, phospho-TrkB (p-TrkB) in the hippocampus were examined by western blotting or immunohistochemistry. And the gene expression of IBA1, GFAP, IL-1β, TNF-α, and SYP were detected by real-time quantitative polymerase chain reaction (PCR). Inflammatory disorder in the hippocampus was tested by hematoxylin and eosin (H&E) staining. The enzyme-linked immunosorbent assay (ELISA) was used to study the expression level of acetylcholine. And the activity of acetylcholinesterase was detected by Acetylcholinesterase Assay Kit. We observed that apelin/APJ signaling was downregulated in the hippocampus of rats administrated with STZ. Apelin-13 was found to significantly ameliorate STZ-induced AD-like phenotypes including congnitive deficit, cholinergic disfunction and the damage of neuron and synaptic plasticity. Moreover, apelin-13 inhibited microglia and astrocyte activation, reduced IL-1β and TNF-α expression and hippocampal BDNF/TrkB expression deficit in AD rats. Finally, apelin-13-mediated effects were blocked by TrkB receptor antagonist K252a. These results suggest that apelin-13 upregulates BDNF/TrkB pathway against cognitive deficit in a STZ-induced rat model of sporadic AD by attenuating inflammation.

Mammalian Target of Rapamycin at the Crossroad Between Alzheimer's Disease and Diabetes

Accumulating evidence suggests that Alzheimer's disease may manifest as a metabolic disorder with pathology and/or dysfunction in numerous tissues. Adults with Alzheimer's disease suffer with significantly more comorbidities than demographically matched Medicare beneficiaries (Zhao et al, BMC Health Serv Res 8:108, 2008b). Reciprocally, comorbid health conditions increase the risk of developing Alzheimer's disease (Haaksma et al, PLoS One 12(5):e0177044, 2017). Type 2 diabetes mellitus is especially notable as the disease shares many overlapping pathologies observed in patients with Alzheimer's disease, including hyperglycemia, hyperinsulinemia, insulin resistance, glucose intolerance, dyslipidemia, inflammation, and cognitive dysfunction, as described in Chap. 8 of this book (Yoshitake et al, Neurology 45(6):1161-1168, 1995; Leibson et al, Am J Epidemiol 145(4):301-308, 1997; Ott et al, Neurology 53(9):1937-1942, 1999; Voisin et al, Rev Med Interne 24(Suppl 3):288s-291s, 2003; Janson et al. Diabetes 53(2):474-481, 2004; Ristow M, J Mol Med (Berl) 82(8):510-529, 2004; Whitmer et al, BMJ 330(7504):1360, 2005, Curr Alzheimer Res 4(2):103-109, 2007; Ohara et al, Neurology 77(12):1126-1134, 2011). Although nondiabetic older adults also experience age-related cognitive decline, diabetes is uniquely associated with a twofold increased risk of Alzheimer's disease, as described in Chap. 2 of this book (Yoshitake et al, Neurology 45(6):1161-1168, 1995; Leibson et al, Am J Epidemiol 145(4):301-308, 1997; Ott et al. Neurology 53(9):1937-1942, 1999; Ohara et al, Neurology 77(12):1126-1134, 2011). Good glycemic control has been shown to improve cognitive status (Cukierman-et al, Diabetes Care 32(2):221-226, 2009), and the use of insulin sensitizers is correlated with a lower rate of cognitive decline in older adults (Morris JK, Burns JM, Curr Neurol Neurosci Rep 12(5):520-527, 2012). At the molecular level, the mechanistic/mammalian target of rapamycin (mTOR) plays a key role in maintaining energy homeostasis. Nutrient availability and cellular stress information, both extracellular and intracellular, are integrated and transduced through mTOR signaling pathways. Aberrant regulation of mTOR occurs in the brains of patients with Alzheimer's disease and in numerous tissues of individuals with type 2 diabetes (Mannaa et al, J Mol Med (Berl) 91(10):1167-1175, 2013). Moreover, modulating mTOR activity with a pharmacological inhibitor, rapamycin, provides wide-ranging health benefits, including healthy life span extension in numerous model organisms (Vellai et al, Nature 426(6967):620, 2003; Jia et al, Development 131(16):3897-3906, 2004; Kapahi et al, Curr Biol 14(10):885-890, 2004; Kaeberlein et al, Science 310(5751):1193-1196, 2005; Powers et al, Genes Dev 20(2):174-184, 2006; Harrison et al, Nature 460(7253):392-395, 2009; Selman et al, Science 326(5949):140-144, 2009; Sharp ZD, Strong R, J Gerontol A Biol Sci Med Sci 65(6):580-589, 2010), which underscores its importance to overall organismal health and longevity. In this chapter, we discuss the physiological role of mTOR signaling and the consequences of mTOR dysregulation in the brain and peripheral tissues, with emphasis on its relevance to the development of Alzheimer's disease and link to type 2 diabetes.

Insulin Peptides as Mediators of the Impact of Life Style in Alzheimer's disease

The search for the cause of Alzheimer's disease (AD), that affects millions of people worldwide, is currently one of the most important scientific endeavors from a clinical perspective. There are so many mechanisms proposed, and so disparate changes observed, that it is becoming a challenging task to provide a comprehensive view of possible pathogenic processes in AD. Tauopathy (intracellular neurofibrillary tangles) and amyloidosis (extracellular amyloid plaques) are the anatomical hallmarks of the disease, and the formation of these proteinaceous aggregates in specific brain areas is widely held as the ultimate pathogenic mechanism. However, the triggers of this dysproteostasis process remain unknown. Further, neurofibrillary tangles and plaques may only constitute the last stages of a process of still uncertain origin. Thus, without an established knowledge of its etiology, and no cure in the horizon, prevention - or merely delaying its development, has become a last-resort goal in AD research. As with other success stories in preventive medicine, epidemiological studies have provided basic knowledge of risk factors in AD that may contribute to understand its etiology. Disregarding old age, gender, and ApoE4 genotype as non preventable risk factors, there are diverse life-style traits - many of them closely related to cardiovascular health, that have been associated to AD risk. Most prominent among them are diet, physical and mental activity, exposure to stress, and sleep/wake patterns. We argue that all these life-style factors engage insulinergic pathways that affect brain function, providing a potentially unifying thread for life-style and AD risk. Although further studies are needed to firmly establish a link between faulty insulinergic function and AD, we herein summarize the evidence that this link should be thoroughly considered.

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.

Oral inflammation and infection, and chronic medical diseases: implications for the elderly

Oral diseases, such as caries and periodontitis, not only have local effects on the dentition and on tooth-supporting tissues but also may impact a number of systemic conditions. Emerging evidence suggests that poor oral health influences the initiation and/or progression of diseases such as atherosclerosis (with sequelae including myocardial infarction and stoke), diabetes mellitus and neurodegenerative diseases (such as Alzheimer's disease, rheumatoid arthritis and others). Aspiration of oropharyngeal (including periodontal) bacteria causes pneumonia, especially in hospitalized patients and the elderly, and may influence the course of chronic obstructive pulmonary disease. This article addresses several pertinent aspects related to the medical implications of periodontal disease in the elderly. There is moderate evidence that improved oral hygiene may help prevent aspiration pneumonia in high-risk patients. For other medical conditions, because of the absence of well-designed randomized clinical trials in elderly patients, no specific guidance can be provided regarding oral hygiene or periodontal interventions that enhance the medical management of older adults.

Diabetes Mellitus and Alzheimer's Disease: The Protection of Epigallocatechin-3-gallate in Streptozotocin Injection-Induced Models

Diabetes mellitus is considered as a risk factor of Alzheimer’s disease (AD), the front runner of neurodegenerative disorders. Streptozotocin (STZ) is a toxin for pancreatic β-cell, which can construct a model of insulin deficient diabetes through intraperitoneal or intravenous injection. A model generated by intracerebroventricular STZ (icv-STZ) also shows numerous aspects of sporadic AD. The protective roles of tea polyphenols epigallocatechin-3-gallate (EGCG) on both two diseases were researched by some scientists. This review highlights the link between diabetes and AD and recent studies on STZ injection-induced models, and also discusses the protection of EGCG to clarify its treatment in STZ-induced diabetes and AD.

The therapeutic potential of metabolic hormones in the treatment of age-related cognitive decline and Alzheimer's disease

Aging leads to a number of physiological alterations, specifically changes in circulating hormone levels, increases in fat deposition, decreases in metabolism, changes in inflammatory responses, and reductions in growth factors. These progressive changes in physiology and metabolism are exacerbated by modern culture and Western diet and give rise to diseases such as obesity, metabolic syndrome, and type 2 (non-insulin-dependent) diabetes (T2D). These age and lifestyle-related metabolic diseases are often accompanied by insulin and leptin resistance, as well as aberrant amylin production and signaling. Many of these alterations in hormone production and signaling are directly influenced by an increase in both oxidative stress and inflammation. Importantly, changes in hormone production and signaling have direct effects on brain function and the development of age-related neurologic disorders. Therefore, this review aims to present evidence on the effects that diet and metabolic disease have on age-related cognitive decline and the development of cognitive diseases, particularly Alzheimer disease. This review will focus on the metabolic hormones insulin, leptin, and amylin and their role in cognitive decline, as well as the therapeutic potential of these hormones in treating cognitive disease. Future investigations targeting the long-term effects of insulin and leptin treatment may reveal evidence to reduce risk of cognitive decline and Alzheimer disease.

Is Alzheimer's disease a Type 3 Diabetes? A critical appraisal

Recently researchers proposed the term 'Type-3-Diabetes' for Alzheimer's disease (ad) because of the shared molecular and cellular features among Type-1-Diabetes, Type-2-Diabetes and insulin resistance associated with memory deficits and cognitive decline in elderly individuals. Recent clinical and basic studies on patients with diabetes and AD revealed previously unreported cellular and pathological among diabetes, insulin resistance and AD. These studies are also strengthened by various basic biological studies that decipher the effects of insulin in the pathology of AD through cellular and molecular mechanisms. For instance, insulin is involved in the activation of glycogen synthase kinase 3β, which in turn causes phosphorylation of tau, which involved in the formation of neurofibrillary tangles. Interestingly, insulin also plays a crucial role in the formation amyloid plaques. In this review, we discussed significant shared mechanisms between AD and diabetes and we also provided therapeutic avenues for diabetes and AD. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.

Intracerebroventricular Streptozotocin Injections as a Model of Alzheimer's Disease: in Search of a Relevant Mechanism

Streptozotocin (STZ), a glucosamine-nitrosourea compound derived from soil bacteria and originally developed as an anticancer agent, in 1963 has been found to induce diabetes in experimental animals. Since then, systemic application of STZ became the most frequently studied experimental model of insulin-dependent (type 1) diabetes. The compound is selectively toxic toward insulin-producing pancreatic beta cells, which is explained as the result of its cellular uptake by the low-affinity glucose transporter 2 (GLUT2) protein located in their cell membranes. STZ cytotoxicity is mainly due to DNA alkylation which results in cellular necrosis. Besides pancreatic beta cells, STZ applied systemically damages also other organs expressing GLUT2, such as kidney and liver, whereas brain is not affected directly because blood-brain barrier lacks this transporter protein. However, single or double intracerebroventricular (icv) STZ injection(s) chronically decrease cerebral glucose uptake and produce multiple other effects that resemble molecular, pathological, and behavioral features of Alzheimer's disease (AD). Taking into consideration that glucose hypometabolism is an early and persistent sign of AD and that Alzheimer's brains present features of impaired insulin signaling, icv STZ injections are exploited by some investigators as a non-transgenic model of this disease and used for preclinical testing of pharmacological therapies for AD. While it has been assumed that icv STZ produces cerebral glucose hypometabolism and other effects directly through desensitizing brain insulin receptors, the evidence for such mechanism is poor. On the other hand, early data on insulin immunoreactivity showed intense insulin expression in the rodent brain, and the possibility of local production of insulin in the mammalian brain has never been conclusively excluded. Also, there are GLUT2-expressing cells in the brain, in particular in the circumventricular organs and hypothalamus; some of these cells may be involved in glucose sensing. Thus, icv STZ may damage brain glucose insulin producing cells and/or brain glucose sensors. Mechanistic explanation of the mode of action of icv STZ, which is currently lacking, would provide a valuable contribution to the field of animal models of Alzheimer's disease.

Medium-chain plasma acylcarnitines, ketone levels, cognition, and gray matter volumes in healthy elderly, mildly cognitively impaired, or Alzheimer's disease subjects

Aging, amyloid deposition, and tau-related pathology are key contributors to the onset and progression of Alzheimer's disease (AD). However, AD is also associated with brain hypometabolism and deficits of mitochondrial bioenergetics. Plasma acylcarnitines (ACCs) are indirect indices of altered fatty acid beta-oxidation, and ketogenesis has been found to be decreased on aging. Furthermore, in elderly subjects, alterations in plasma levels of specific ACCs have been suggested to predict conversion to mild cognitive impairment (MCI) or AD. In this study, we assayed plasma profiles of ACCs in a cohort of healthy elderly control, MCI subjects, and AD patients. Compared with healthy controls or MCI subjects, AD patients showed significant lower plasma levels of several medium-chain ACCs. Furthermore, in AD patients, these lower concentrations were associated with lower prefrontal gray matter volumes and the presence of cognitive impairment. Interestingly, lower levels of medium-chain ACCs were also found to be associated with lower plasma levels of 2-hydroxybutyric acid. Overall, these findings suggest that altered metabolism of medium-chain ACCs and impaired ketogenesis can be metabolic features of AD.

Lipoic acid improves neuronal insulin signalling and rescues cognitive function regulating VGlut1 expression in high-fat-fed rats: Implications for Alzheimer's disease

The concept of central insulin resistance and dysfunctional insulin signalling in sporadic Alzheimer's disease (AD) is now widely accepted and diabetes is recognized as one of the main risk factors for developing AD. Moreover, some lines of evidence indicated that VGlut1 is impaired in frontal regions of AD patients and this impairment is correlated with the progression of cognitive decline in AD. The present work hypothesizes that ketosis associated to insulin resistance could interfere with the normal activity of VGlut1 and its role in the release of glutamate in the hippocampus, which might ultimately lead to cognitive deficits. High fat diet (HFD) rats showed memory impairments and both peripheral (as shown by increased fasting plasma insulin levels and HOMA index) and hippocampal (as shown by decreased activation of insulin receptor, IRS-1 and pAkt) insulin pathway alterations, accompanied by increased ketone bodies production. All these effects were counteracted by α-lipoic acid (LA) administration. VGlut1 levels were significantly decreased in the hippocampus of HFD rats, and this decrease was reversed by LA. Altogether, the present results suggest that HFD induced alterations in central insulin signalling could switch metabolism to produce ketone bodies, which in turn, in the hippocampus, might lead to a decreased expression of VGlut1, and therefore to a decreased release of glutamate and hence, to the glutamatergic deficit described in AD. The ability of LA treatment to prevent the alterations in insulin signalling in this model of HFD might represent a possible new therapeutic target for the treatment of AD.

Novel GLP-1 (Glucagon-Like Peptide-1) Analogues and Insulin in the Treatment for Alzheimer's Disease and Other Neurodegenerative Diseases

The link between diabetes mellitus and Alzheimer's disease (AD) has been known for the last few decades. Since insulin and insulin receptors are known to be present in the brain, the downstream signalling as well as the effect of hyperinsulinemia have been extensively studied in both AD and Parkinson's disease. Glucagon-like peptide-1 (GLP-1) is a hormone belonging to the incretin family, and its receptors (GLP-1Rs) can be found in pancreatic cells and in vascular endothelium. Interestingly, GLP-1Rs are found in the neuronal cell body and dendrites in the central nervous system (CNS), in particular in the hypothalamus, hippocampus, cerebral cortex and olfactory bulb. Several studies have shown the importance of both insulin and GLP-1 signalling on cognitive function, and many preclinical studies have been performed to evaluate the potential protective role of GLP-1 on the brain. Here we review the underlying mechanism of insulin and GLP-1 signalling in the CNS, as well as the preclinical data for the use of GLP-1 analogues such as liraglutide, exenatide and lixisenatide in neurodegenerative diseases.

White Matter Lipids as a Ketogenic Fuel Supply in Aging Female Brain: Implications for Alzheimer's Disease

White matter degeneration is a pathological hallmark of neurodegenerative diseases including Alzheimer's. Age remains the greatest risk factor for Alzheimer's and the prevalence of age-related late onset Alzheimer's is greatest in females. We investigated mechanisms underlying white matter degeneration in an animal model consistent with the sex at greatest Alzheimer's risk. Results of these analyses demonstrated decline in mitochondrial respiration, increased mitochondrial hydrogen peroxide production and cytosolic-phospholipase-A₂ sphingomyelinase pathway activation during female brain aging. Electron microscopic and lipidomic analyses confirmed myelin degeneration. An increase in fatty acids and mitochondrial fatty acid metabolism machinery was coincident with a rise in brain ketone bodies and decline in plasma ketone bodies. This mechanistic pathway and its chronologically phased activation, links mitochondrial dysfunction early in aging with later age development of white matter degeneration. The catabolism of myelin lipids to generate ketone bodies can be viewed as a systems level adaptive response to address brain fuel and energy demand. Elucidation of the initiating factors and the mechanistic pathway leading to white matter catabolism in the aging female brain provides potential therapeutic targets to prevent and treat demyelinating diseases such as Alzheimer's and multiple sclerosis. Targeting stages of disease and associated mechanisms will be critical.

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Mitochondrial dysfunction activates mechanisms for catabolism of myelin lipids to generate ketone bodies for ATP production.

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Mechanisms leading to ketone body driven energy production in brain coincide with stages of reproductive aging in females.

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Sequential activation of myelin catabolism pathway during aging provides multiple therapeutic targets and windows of efficacy.

The mechanisms underlying white matter degeneration, a hallmark of multiple neurodegenerative diseases including Alzheimer's, remain unclear. Herein we provide a mechanistic pathway, spanning multiple transitions of aging, that links mitochondrial dysfunction early in aging with later age white matter degeneration. Catabolism of myelin lipids to generate ketone bodies can be viewed as an adaptive survival response to address brain fuel and energy demand. Women are at greatest risk of late-onset-AD, thus, our analyses in female brain address mechanisms of AD pathology and therapeutic targets to prevent, delay and treat AD in the sex most affected with potential relevance to men.

Quantification of normal cerebral oxygen extraction and oxygen metabolism by phase-based MRI susceptometry: evaluation of repeatability using two different imaging protocols

INTRODUCTION

Global oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO₂ ) were quantified in a test-retest study. Cerebral blood flow (CBF) data, required for CMRO₂ estimation, were obtained using dynamic susceptibility contrast MRI (DSC-MRI). OEF and CMRO₂ were quantified using two separate data sets, that is, conventional high-resolution (HR) gradient echo (GRE) phase maps as well as echo planar imaging (EPI) phase maps taken from the baseline (precontrast) part of the DSC-MRI time series. The EPI phase data were included to elucidate whether an extra HR-GRE scan is needed to obtain information about OEF and CMRO₂ , or if this information can be extracted from the DSC-MRI experiment only.

METHODS

Twenty healthy volunteers were scanned using 3 T MRI on two occasions. Oxygen saturation levels were obtained from phase data measured in the great cerebral vein of Galen, based on HR-GRE as well as EPI phase maps. In combination with DSC-MRI CBF, this allowed for calculation of OEF and CMRO₂ .

RESULTS

High-resolution-gradient echo- and EPI-based phase images resulted in similar OEF spread and repeatability, with coefficients of variation/intraclass correlation coefficients of 0·26/0·95 and 0·23/0·81, respectively. Absolute OEF values (HR-GRE: 0·40 ± 0·11, EPI: 0·35 ± 0·08) were consistent with literature data. CMRO₂ showed similar repeatability, somewhat increased spread and reasonable absolute values (HR-GRE: 3·23 ± 1·26 ml O₂ /100 g min^-1 , EPI: 2·79 ± 0·89 ml O₂ /100 g min^-1 ).

DISCUSSION

In general, the results obtained by HR-GRE and EPI showed comparable characteristics. The EPI methodology could potentially be improved using a slightly modified DSC-MRI protocol (e.g. with regard to spatial resolution and slice gap).

Insulin resistance, neuroinflammation, and Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. Pathologically, it is characterized by degeneration of neurons and synapses, the deposition of extracellular plaques consisting of aggregated amyloid-β (Aβ) peptides, and intracellular neurofibrillary tangles made up of hyperphosphorylated tau protein. Recently, the spotlights have been centered on two characteristics of AD, neuroinflammation and insulin resistance. Because both of these pathways play roles in synaptic dysfunction and neurodegeneration, they become potential targets for therapeutic intervention that could impede the progression of the disease. Here, we present an overview of the traditional amyloid hypothesis, as well as emerging data on both inflammatory and impaired insulin signaling pathways in AD. It becomes evident that more than one concurrent treatment can be synergistic and various combinations should be discussed as a potential therapeutic strategy to correct the anomalies in AD. Insulin resistance, Aβ/tau pathologies, neuroinflammation, and dysregulation of central nervous system homeostasis are intertwined processes that together create the complex pathology of AD and should be considered as a whole picture.

Rodent models of neuroinflammation for Alzheimer's disease

Alzheimer's disease remains incurable, and the failures of current disease-modifying strategies for Alzheimer's disease could be attributed to a lack of in vivo models that recapitulate the underlying etiology of late-onset Alzheimer's disease. The etiology of late-onset Alzheimer's disease is not based on mutations related to amyloid-β (Aβ) or tau production which are currently the basis of in vivo models of Alzheimer's disease. It has recently been suggested that mechanisms like chronic neuroinflammation may occur prior to amyloid-β and tau pathologies in late-onset Alzheimer's disease. The aim of this study is to analyze the characteristics of rodent models of neuroinflammation in late-onset Alzheimer's disease. Our search criteria were based on characteristics of an idealistic disease model that should recapitulate causes, symptoms, and lesions in a chronological order similar to the actual disease. Therefore, a model based on the inflammation hypothesis of late-onset Alzheimer's disease should include the following features: (i) primary chronic neuroinflammation, (ii) manifestations of memory and cognitive impairment, and (iii) late development of tau and Aβ pathologies. The following models fit the pre-defined criteria: lipopolysaccharide- and PolyI:C-induced models of immune challenge; streptozotocin-, okadaic acid-, and colchicine neurotoxin-induced neuroinflammation models, as well as interleukin-1β, anti-nerve growth factor and p25 transgenic models. Among these models, streptozotocin, PolyI:C-induced, and p25 neuroinflammation models are compatible with the inflammation hypothesis of Alzheimer's disease.

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.

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.

Type 3 diabetes is sporadic Alzheimer׳s disease: mini-review

Alzheimer׳s disease (AD) is the most common cause of dementia in North America. Growing evidence supports the concept that AD is a metabolic disease mediated by impairments in brain insulin responsiveness, glucose utilization, and energy metabolism, which lead to increased oxidative stress, inflammation, and worsening of insulin resistance. In addition, metabolic derangements directly contribute to the structural, functional, molecular, and biochemical abnormalities that characterize AD, including neuronal loss, synaptic disconnection, tau hyperphosphorylation, and amyloid-beta accumulation. Because the fundamental abnormalities in AD represent effects of brain insulin resistance and deficiency, and the molecular and biochemical consequences overlap with Type 1 and Type 2 diabetes, we suggest the term "Type 3 diabetes" to account for the underlying abnormalities associated with AD-type neurodegeneration. In light of the rapid increases in sporadic AD prevalence rates and vastly expanded use of nitrites and nitrates in foods and agricultural products over the past 30-40 years, the potential role of nitrosamine exposures as mediators of Type 3 diabetes is discussed.

Gene expression profiles of entorhinal cortex in Alzheimer's disease

The incidence of Alzheimer's disease (AD) has been increasing in the recent years but the underlying mechanisms remain uncertain. This study aimed to analyze the differentially expressed genes (DEGs) in entorhinal cortex with AD and identify featured genes related to AD. Gene expression profile GSE5281 was downloaded from Gene Expression Omnibus, including 10 AD and 13 control samples. Differentially expressed genes were identified by Student t test including 119 upregulated and 591 downregulated DEGs. Then, we obtained 14 enrichment Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways among which 11 pathways were significantly enriched (adjusted P value < .05). The KEGG pathway network which was constructed by 14 KEGG pathways showed that 6-phosphofructokinase, muscle type, phosphoglucomutase 1, aldolase A, and adolase C had high degree. Glycometabolism pathways network which was constructed by 4 glycometabolism pathways showed that adenosine triphosphate (ATP) synthase, H+transporting, mitochondrial F1 complex ATP5B, ATP5C1, ATP5D, and ATP5G1 had high degree related to ATP metabolism. These findings suggested that these genes with high degree may be the underlying potential therapeutic targets for AD.

Relationships between diabetes and cognitive impairment

Epidemics of obesity, diabetes, nonalcoholic fatty liver disease, and cognitive impairment/Alzheimer disease have emerged over the past 3 to 4 decades. These diseases share in common target-organ insulin resistance with a constellation of molecular and biochemical abnormalities that lead to organ/tissue degeneration over time. This article discusses the fundamental links among these diseases and how peripheral organ insulin resistance diseases contribute to cognitive impairment and neurodegeneration. A future role of endocrinologists and diabetologists could be to provide integrative diagnostic and treatment approaches for this collection of diseases that seem to share pathophysiological and pathogenetic bases.

Brain metabolic dysfunction at the core of Alzheimer's disease

Growing evidence supports the concept that Alzheimer's disease (AD) is fundamentally a metabolic disease with molecular and biochemical features that correspond with diabetes mellitus and other peripheral insulin resistance disorders. Brain insulin/IGF resistance and its consequences can readily account for most of the structural and functional abnormalities in AD. However, disease pathogenesis is complicated by the fact that AD can occur as a separate disease process, or arise in association with systemic insulin resistance diseases, including diabetes, obesity, and non-alcoholic fatty liver disease. Whether primary or secondary in origin, brain insulin/IGF resistance initiates a cascade of neurodegeneration that is propagated by metabolic dysfunction, increased oxidative and ER stress, neuro-inflammation, impaired cell survival, and dysregulated lipid metabolism. These injurious processes compromise neuronal and glial functions, reduce neurotransmitter homeostasis, and cause toxic oligomeric pTau and (amyloid beta peptide of amyloid beta precursor protein) AβPP-Aβ fibrils and insoluble aggregates (neurofibrillary tangles and plaques) to accumulate in brain. AD progresses due to: (1) activation of a harmful positive feedback loop that progressively worsens the effects of insulin resistance; and (2) the formation of ROS- and RNS-related lipid, protein, and DNA adducts that permanently damage basic cellular and molecular functions. Epidemiologic data suggest that insulin resistance diseases, including AD, are exposure-related in etiology. Furthermore, experimental and lifestyle trend data suggest chronic low-level nitrosamine exposures are responsible. These concepts offer opportunities to discover and implement new treatments and devise preventive measures to conquer the AD and other insulin resistance disease epidemics.

Attenuation of oxidative damage-associated cognitive decline by Withania somnifera in rat model of streptozotocin-induced cognitive impairment

Oxidative stress is a critical contributing factor to age-related neurodegenerative disorders. Therefore, the inhibition of oxidative damage, responsible for chronic detrimental neurodegeneration, is an important strategy for neuroprotective therapy. Withania somnifera (WS) extract has been reported to have potent antioxidant and free radical quenching properties in various disease conditions. The present study evaluated the hypothesis that WS extract would reduce oxidative stress-associated neurodegeneration after intracerebroventricular injection of streptozotocin (ICV-STZ) in rats. To test this hypothesis, male Wistar rats were pretreated with WS extract at doses of 100, 200, and 300 mg/kg body weight once daily for 3 weeks. On day 22nd, the rats were infused bilaterally with ICV-STZ injection (3 mg/kg body weight) in normal saline while sham group received only saline. Two weeks after the lesioning, STZ-infused rats showed cognitive impairment in the Morris water maze test. The rats were sacrificed after 3 weeks of the lesioning for the estimation of the contents of lipid peroxidation, reduced glutathione, and activities of glutathione reductase, glutathione peroxidase, and catalase. Pretreatment with WS extract attenuated behavioral, biochemical, and histological alterations significantly in dose-dependent manner in the hippocampus and cerebral cortex of ICV-STZ-infused rats. These results suggest that WS affords a beneficial effect on cognitive deficit by ameliorating oxidative damage induced by streptozotocin in a model of cognitive impairment.

CSF and Brain Indices of Insulin Resistance, Oxidative Stress and Neuro-Inflammation in Early versus Late Alzheimer's Disease

Alzheimer’s disease (AD) is characterized by progressive impairments in cognitive and behavioral functions with deficits in learning, memory and executive reasoning. Growing evidence points toward brain insulin and insulin-like growth factor (IGF) resistance-mediated metabolic derangements as critical etiologic factors in AD. This suggests that indices of insulin/IGF resistance and their consequences, i.e. oxidative stress, neuro-inflammation, and reduced neuronal plasticity, should be included in biomarker panels for AD. Herein, we examine a range of metabolic, inflammatory, stress, and neuronal plasticity related proteins in early AD, late AD, and aged control postmortem brain, postmortem ventricular fluid (VF), and clinical cerebrospinal fluid (CSF) samples. In AD brain, VF, and CSF samples the trends with respect to alterations in metabolic, neurotrophin, and stress indices were similar, but for pro-inflammatory cytokines, the patterns were discordant. With the greater severities of dementia and neurodegeneration, the differences from control were more pronounced for late AD (VF and brain) than early or moderate AD (brain, VF and CSF). The findings suggest that the inclusion of metabolic, neurotrophin, stress biomarkers in AβPP-Aβ+pTau CSF-based panels could provide more information about the status and progression of neurodegeneration, as well as aid in predicting progression from early- to late-stage AD. Furthermore, standardized multi-targeted molecular assays of neurodegeneration could help streamline postmortem diagnoses, including assessments of AD severity and pathology.