Brain metabolic stress and neuroinflammation at the basis of cognitive impairment in Alzheimer's disease

A bibliometric analysis on the health behaviors related to mild cognitive impairment

Background

Mild cognitive impairment (MCI) is commonly defined as a transitional subclinical state between normal aging and dementia. A growing body of research indicates that health behaviors may play a protective role against cognitive decline and could potentially slow down the progression from MCI to dementia. The aim of this study is to conduct a bibliometric analysis of literature focusing on health behaviors and MCI to summarize the factors and evidence regarding the influence of health behaviors on MCI.

Methods

The study performed a bibliometric analysis by retrieving publications from the Science Citation Index and Social Sciences Citation Index sub-databases within the Web of Science Core Collection. Utilizing VOSviewer and CiteSpace software, a total of 2,843 eligible articles underwent co-citation, co-keywords, and clustering analyses. This methodology aimed to investigate the current status, trends, major research questions, and potential future directions within the research domain.

Results

The bibliometric analysis indicates that research on healthy behaviors in individuals with MCI originated in 2002 and experienced rapid growth in 2014, reflecting the increasing global interest in this area. The United States emerged as the primary contributor, accounting for more than one-third of the total scientific output with 982 articles. Journals that published the most articles on MCI-related health behaviors included "Journal of Alzheimer's Disease," "Neurobiology of Aging," "Frontiers in Aging Neuroscience," and other geriatrics-related journals. High-impact papers identified by VOSviewer predominantly cover concepts related to MCI, such as diagnostic criteria, assessment, and multifactorial interventions. Co-occurrence keyword analysis highlights five research hotspots in health behavior associated with MCI: exercise, diet, risk factors and preventive measures for dementia, cognitive decline-related biomarkers, and clinical trials.

Conclusion

This study provides a comprehensive review of literature on health behavior in individuals with MCI, emphasizing influential documents and journals. It outlines research trends and key focal points, offering valuable insights for researchers to comprehend significant contributions and steer future studies.

Orthosiphon aristatus (Blume) Miq. Extracts attenuate Alzheimer-like pathology through anti-inflammatory, anti-oxidative, and β-amyloid inhibitory activities

ETHNOPHARMACOLOGICAL RELEVANCE

Orthosiphon aristatus (Blume) Miq. (OA) is a traditional folk-herb, which is usually used to treat acute and chronic nephritis, epilepsy, cystitis, and other diseases. Phenols and flavonoids are the main active compound compounds of OA, with proven anti-inflammatory and antioxidant activities.

AIMS OF THIS STUDY

Based on evidenced therapeutic activities, we aimed to investigate the impact of OA on Alzheimer's disease (AD) which is the most common age-related neurodegenerative disease, and the pathological features include accumulation of beta-amyloid (Aβ) and neurofibrillary tangles (NFT).

MATERIALS AND METHODS

OA was extracted with water, methanol, chloroform, and ethyl acetate, and determined its total flavonoid and phenolic contents. Initially, Aβ1-42 based cytotoxicity was induced in BV2 cells and C6 cells to investigate the therapeutic impact of OA therapy by MTT, RT-PCR, Western blot, and ELISA. Further, Aβ1-42 Oligomer (400 pmol)-induced AD mice model was established to evaluate the impact of OA extract on improving learning and memory impairment.

RESULTS

The results showed that the extract of OA could increase cell survival, inhibit the expression of TNF-α, IL-6, IL-1β, COX-2, and iNOS, and increase BDNF levels. We infer that the OA extract may attenuate Aβ-induced cytotoxicity by retarding the production of inflammatory-related factors. In the animal behavior test, the number of mice entering darkroom and the time of arriving at the platform were significantly reduced, indicating the learning and memory-improving ability of OA extract.

CONCLUSIONS

These findings imply that the OA ethanolic extract demonstrated an improving effect on memory and hence could serve as a potential therapeutic target for the treatment of neurodegenerative diseases like AD.

Semaglutide ameliorates cognition and glucose metabolism dysfunction in the 3xTg mouse model of Alzheimer's disease via the GLP-1R/SIRT1/GLUT4 pathway

Disorders of brain glucose metabolism is known to affect brain activity in neurodegenerative diseases including Alzheimer's disease (AD). Furthermore, recent evidence has shown an association between AD and type 2 diabetes. Numerous reports have found that glucagon-like peptide-1 (GLP-1) receptor agonists improve the cognitive behavior and pathological features in AD patients and animals, which may be related to the improvement of glucose metabolism in the brain. However, the mechanism by which GLP-1 agonists improve the brain glucose metabolism in AD patients remains unclear. In this study, we found that SIRT1 is closely related to expression of GLP-1R in hippocampus of 3xTg mice. Therefore, we used semaglutide, a novel GLP-1R agonist currently undergoing two phase 3 clinical trials in AD patients, to observe the effect of SIRT1 after semaglutide treatment in 3XTg mice and HT22 cells, and to explore the mechanism of SIRT1 in the glucose metabolism disorders of AD. The mice were injected with semaglutide on alternate days for 30 days, followed by behavioral experiments including open field test, new object recognition test, and Y-maze. The content of glucose in the brain was also measured by using 18FDG-PET-CT scans. We measured the expression of Aβ and tau in the hippocampus, observed the expression of GLUT4 which is downstream of SIRT1, and tested the Glucose oxidase assay (GOD-POD) and Hexokinase (HK) in HT22 cells. Here, we found in the 3xTg mouse model of AD and in cultured HT22 mouse neurons that SIRT1 signaling is involved in the impairment of glucose metabolism in AD. Semaglutide can increased the expression levels of SIRT1 and GLUT4 in the hippocampus of 3xTg mice, accompanied by an improvement in learning and memory, decreased in Aβ plaques and neurofibrillary tangles. In addition, we further demonstrated that semaglutide improved glucose metabolism in the brain of 3xTg mice in vitro, semaglutide promoted glycolysis and improved glycolytic disorders, and increased the membrane translocation of GLUT4 in cultured HT22 cells. These effects were blocked by the SIRT1 inhibitor (EX527). These findings indicate that semaglutide can regulate the expression of GLUT4 to mediate glucose transport through SIRT1, thereby improving glucose metabolism dysfunction in AD mice and cells. The present study suggests that SIRT1/GLUT4 signaling pathway may be an important mechanism for GLP-1R to promote glucose metabolism in the brain, providing a reliable strategy for effective therapy of AD.

Amyloid-β Pathology-Specific Cytokine Secretion Suppresses Neuronal Mitochondrial Metabolism

Introduction

Neuroinflammation and metabolic dysfunction are early alterations in Alzheimer's disease (AD) brain that are thought to contribute to disease onset and progression. Glial activation due to protein deposition results in cytokine secretion and shifts in brain metabolism, which have been observed in AD patients. However, the mechanism by which this immunometabolic feedback loop can injure neurons and cause neurodegeneration remains unclear.

Methods

We used Luminex XMAP technology to quantify hippocampal cytokine concentrations in the 5xFAD mouse model of AD at milestone timepoints in disease development. We used partial least squares regression to build cytokine signatures predictive of disease progression, as compared to healthy aging in wild-type littermates. We applied the disease-defining cytokine signature to wild-type primary neuron cultures and measured downstream changes in gene expression using the NanoString nCounter system and mitochondrial function using the Seahorse Extracellular Flux live-cell analyzer.

Results

We identified a pattern of up-regulated IFNγ, IP-10/CXCL10, and IL-9 as predictive of advanced disease. When healthy neurons were exposed to these cytokines in proportions found in diseased brain, gene expression of mitochondrial electron transport chain complexes, including ATP synthase, was suppressed. In live cells, basal and maximal mitochondrial respiration were impaired following cytokine stimulation.

Conclusions

We identify a pattern of cytokine secretion predictive of progressing amyloid-β pathology in the 5xFAD mouse model of AD that reduces expression of mitochondrial electron transport complexes and impairs mitochondrial respiration in healthy neurons. We establish a mechanistic link between disease-specific immune cues and impaired neuronal metabolism, potentially causing neuronal vulnerability and susceptibility to degeneration in AD.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-023-00782-y.

Preface: Special issue "Brain Proteostasis in Health and Disease"

This preface introduces the Journal of Neurochemistry Special Issue on Brain Proteostasis. Adequate control of protein homeostasis, or proteostasis, has been at the center stage of brain physiology, and its deregulation may contribute to brain diseases, including several neuropsychiatric and neurodegenerative conditions. Therefore, delineating the processes underlying protein synthesis, folding, stability, function, and degradation in brain cells is key to promoting brain function and identifying effective therapeutic options for neurological disorders. This special issue comprises four review articles and four original articles covering the roles of protein homeostasis in several mechanisms that are of relevance to sleep, depression, stroke, dementia, and COVID-19. Thus, these articles highlight different aspects of proteostasis regulation in the brain and present important evidence on this growing and exciting field.

Sex differences in the progression of glucose metabolism dysfunction in Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disease characterized by amyloid plaques and impaired brain metabolism. Because women have a higher prevalence of AD than men, sex differences are of great interest. Using cross-sectional and longitudinal data, we showed sex-dependent metabolic dysregulations in the brains of AD patients. Cohort 1 (South Korean, n = 181) underwent Pittsburgh compound B-PET, fluorodeoxyglucose-PET, magnetic resonance imaging, and blood biomarker (plasma tau and beta-amyloid 42 and 40) measurements at baseline and two-year follow-ups. Transcriptome analysis of data from Cohorts 2 and 3 (European, n = 78; Singaporean, n = 18) revealed sex differences in AD-related alterations in brain metabolism. In women (but not in men), all imaging indicators displayed consistent correlation curves with AD progression. At the two-year follow-up, clear brain metabolic impairment was revealed only in women, and the plasma beta-amyloid 42/40 ratio was a possible biomarker for brain metabolism in women. Furthermore, our transcriptome analysis revealed sex differences in transcriptomes and metabolism in the brains of AD patients as well as a molecular network of 25 female-specific glucose metabolic genes (FGGs). We discovered four key-attractor FGG genes (ALDOA, ENO2, PRKACB, and PPP2R5D) that were associated with amyloid/tau-related genes (APP, MAPT, BACE1, and BACE2). Furthermore, these genes successfully distinguished amyloid positivity in women. Understanding sex differences in the pathogenesis of AD and considering these differences will improve development of effective diagnostics and therapeutic treatments for AD.

Alzheimer's disease-specific cytokine secretion suppresses neuronal mitochondrial metabolism

Introduction

Neuroinflammation and metabolic dysfunction are early alterations in Alzheimer's disease brain that are thought to contribute to disease onset and progression. Glial activation due to protein deposition results in cytokine secretion and shifts in brain metabolism, which have been observed in Alzheimer's disease patients. However, the mechanism by which this immunometabolic feedback loop can injure neurons and cause neurodegeneration remains unclear.

Methods

We used Luminex XMAP technology to quantify hippocampal cytokine concentrations in the 5xFAD mouse model of Alzheimer's disease at milestone timepoints in disease development. We used partial least squares regression to build cytokine signatures predictive of disease progression, as compared to healthy aging in wild-type littermates. We applied the disease-defining cytokine signature to wild-type primary neuron cultures and measured downstream changes in gene expression using the NanoString nCounter system and mitochondrial function using the Seahorse Extracellular Flux live-cell analyzer.

Results

We identified a pattern of up-regulated IFNγ, IP-10, and IL-9 as predictive of advanced disease. When healthy neurons were exposed to these cytokines in proportions found in diseased brain, gene expression of mitochondrial electron transport chain complexes, including ATP synthase, was suppressed. In live cells, basal and maximal mitochondrial respiration were impaired following cytokine stimulation.

Conclusions

An Alzheimer's disease-specific pattern of cytokine secretion reduces expression of mitochondrial electron transport complexes and impairs mitochondrial respiration in healthy neurons. We establish a mechanistic link between disease-specific immune cues and impaired neuronal metabolism, potentially causing neuronal vulnerability and susceptibility to degeneration in Alzheimer's disease.

Modeling integrated stress, sleep, fear and neuroimmune responses: Relevance for understanding trauma and stress-related disorders

Sleep and stress have complex interactions that are implicated in both physical diseases and psychiatric disorders. These interactions can be modulated by learning and memory, and involve additional interactions with the neuroimmune system. In this paper, we propose that stressful challenges induce integrated responses across multiple systems that can vary depending on situational variables in which the initial stress was experienced, and with the ability of the individual to cope with stress- and fear-inducing challenges. Differences in coping may involve differences in resilience and vulnerability and/or whether the stressful context allows adaptive learning and responses. We provide data demonstrating both common (corticosterone, SIH and fear behaviors) and distinguishing (sleep and neuroimmune) responses that are associated with an individual's ability to respond and relative resilience and vulnerability. We discuss neurocircuitry regulating integrated stress, sleep, neuroimmune and fear responses, and show that responses can be modulated at the neural level. Finally, we discuss factors that need to be considered in models of integrated stress responses and their relevance for understanding stress-related disorders in humans.

Curcumin-Nicotinate Attenuates Hippocampal Synaptogenesis Dysfunction in Hyperlipidemia Rats by the BDNF/TrkB/CREB Pathway: Involving Idol/LDLR Signaling to Eliminate Aβ Deposition

Hyperlipidemia has been demonstrated to evoke Alzheimer disease (AD) pathologies such as Amyloid-β (Aβ) deposition and synaptogenesis dysfunction in the hippocampus. Curcumin gives protection against anti-amyloid properties and synaptogenesis dysfunction. Curcumin-Nicotinate (CurTn), a new type of curcumin derivative, ameliorates cognitive impairment by rescuing autophagic flux in the CA1 hippocampus of diabetic rats. However, whether Curtn possesses an antagonistic effect on AD-related pathologies in the hippocampus induced by hyperlipidemia remains ill-defined. The present study aims to investigate whether CurTn alleviates synaptogenesis dysfunction by promoting the activation of brain-derived neurotrophic factor (BDNF)/tyrosine kinase receptor B (TrkB)/cAMP-response element binding protein (CREB) signaling and whether the underlying fundamental mechanism involves the elimination of Aβ deposition due to Idol/low-density lipoprotein receptor (LDLR) signaling in the hippocampus of high-fat diet (HFD)-induced hyperlipidemia rats. The results demonstrated that CurTn not only improved synaptogenesis dysfunction in the hippocampus of HFD rats, as evidenced by the increases in the expressions of synapse-related proteins postsynaptic density protein 95 (PSD-95), synapsin-1, and Glutamate receptor 1 (GluR1), but also activated BDNF/TrkB/CREB signaling, as evidenced by the elevation of the expressions of BDNF, pTrkB, and CREB. Moreover, CurTn modulated the Idol/LDLR pathway in the hippocampus of HFD rats, as evidenced by the decreased expression of Idol and the increased expression of LDLR. Furthermore, CurTn eliminated the deposition of Aβ, as evidenced by the reduction in the content of Aβ40 and Aβ42. These results reveal that CurTn may attenuate synaptogenesis dysfunction by activating BDNF/TrkB/CREB signaling, as the possible result of the modulation of Idol/LDLR signaling to eliminate Aβ deposition in the hippocampus of HFD rats.

Age-linked suppression of lipoxin A4 associates with cognitive deficits in mice and humans

Age increases the risk for cognitive impairment and is the single major risk factor for Alzheimer's disease (AD), the most prevalent form of dementia in the elderly. The pathophysiological processes triggered by aging that render the brain vulnerable to dementia involve, at least in part, changes in inflammatory mediators. Here we show that lipoxin A4 (LXA4), a lipid mediator of inflammation resolution known to stimulate endocannabinoid signaling in the brain, is reduced in the aging central nervous system. We demonstrate that genetic suppression of 5-lipoxygenase (5-LOX), the enzyme mediating LXA4 synthesis, promotes learning impairment in mice. Conversely, administration of exogenous LXA4 attenuated cytokine production and memory loss induced by inflammation in mice. We further show that cerebrospinal fluid LXA4 is reduced in patients with dementia and positively associated with cognitive performance, brain-derived neurotrophic factor (BDNF), and AD-linked amyloid-β. Our findings suggest that reduced LXA4 levels may lead to vulnerability to age-related cognitive disorders and that promoting LXA4 signaling may comprise an effective strategy to prevent early cognitive decline in AD.

Immunotherapies for Alzheimer’s Disease—A Review

Alzheimer’s disease (AD) is a chronic neurodegenerative disorder that falls under the umbrella of dementia and is characterised by the presence of highly neurotoxic amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFTs) of tau protein within the brain. Historically, treatments for AD have consisted of medications that can slow the progression of symptoms but not halt or reverse them. The shortcomings of conventional drugs have led to a growing need for novel, effective approaches to the treatment of AD. In recent years, immunotherapies have been at the forefront of these efforts. Briefly, immunotherapies utilise the immune system of the patient to treat a condition, with common immunotherapies for AD consisting of the use of monoclonal antibodies or vaccines. Most of these treatments target the production and deposition of Aβ due to its neurotoxicity, but treatments specifically targeting tau protein are being researched as well. These treatments have had great variance in their efficacy and safety, leading to a constant need for the research and development of new safe and effective treatments.

Pharmacological effects and mechanisms of tannic acid

In recent years, increasing attention has been paid to the pharmacological efficacy of tannins. Tannic acid (TA), the simplest hydrolysable tannin that has been approved by the FDA as a safe food additive, is one of the most important components of these traditional medicines. Studies have shown that TA displays a wide range of pharmacological activities, such as anti-inflammatory, neuroprotective, antitumor, cardioprotective, and anti-pathogenic effects. Here, we summarize the known pharmacological effects and associated mechanisms of TA. We focus on the effect and mechanism of TA in various animal models of inflammatory disease and organ, brain, and cardiovascular injury. Moreover, we discuss the possible molecular targets and signaling pathways of TA, in addition to the pharmacological effects of TA-based nanoparticles and TA in combination with chemotherapeutic drugs.

Resilient Hippocampal Gamma Rhythmogenesis and Parvalbumin-Expressing Interneuron Function Before and After Plaque Burden in 5xFAD Alzheimer's Disease Model

Recent studies have implicated impaired Parvalbumin Fast-Spiking Interneuron (PVIN) function as a precipitating factor underlying abnormalities in network synchrony, oscillatory rhythms, and cognition associated with Alzheimer's disease (AD). However, a complete developmental investigation of potential gamma deficits, induced by commonly used carbachol or kainate in ex vivo slice preparations, within AD model mice is lacking. We examined gamma oscillations using field recordings in acute hippocampal slices from 5xFAD and control mice, through the period of developing pathology, starting at 3 months of age, when there is minimal plaque presence in the hippocampus, through to 12+ months of age, when plaque burden is high. In addition, we examined PVIN participation in gamma rhythms using targeted cell-attached recordings of genetically-reported PVINs, in both wild type and mutant mice. In parallel, a developmental immunohistochemical characterisation probing the PVIN-associated expression of PV and perineuronal nets (PNNs) was compared between control and 5xFAD mice. Remarkably, this comprehensive longitudinal evaluation failed to reveal any obvious correlations between PVIN deficits (electrical and molecular), circuit rhythmogenesis (gamma frequency and power), and Aβ deposits/plaque formation. By 6-12 months, 5xFAD animals have extensive plaque formation throughout the hippocampus. However, a deficit in gamma oscillatory power was only evident in the oldest 5xFAD animals (12+ months), and only when using kainate, and not carbachol, to induce the oscillations. We found no difference in PV firing or phase preference during kainate-induced oscillations in younger or older 5xFAD mice compared to control, and a reduction of PV and PNNs only in the oldest 5xFAD mice. The lack of a clear relationship between PVIN function, network rhythmicity, and plaque formation in our study highlights an unexpected resilience in PVIN function in the face of extensive plaque pathology associated with this model, calling into question the presumptive link between PVIN pathology and Alzheimer's progression.

JNK1 and JNK3: divergent functions in hippocampal metabolic-cognitive function

Background and aim

The appearance of alterations in normal metabolic activity has been increasingly considered a risk factor for the development of sporadic and late-onset neurodegenerative diseases. In this report, we induced chronic metabolic stress by feeding of a high-fat diet (HFD) in order to study its consequences in cognition. We also studied the effects of a loss of function of isoforms 1 and 3 of the c-Jun N-terminal Kinases (JNK), stress and cell death response elements.

Methods

Animals were fed either with conventional chow or with HFD, from their weaning until their sacrifice at 9 months. Before sacrifice, body weight, intraperitoneal glucose and insulin tolerance test (IP-GTT and IP‑ITT) were performed to evaluate peripheral biometrics. Additionally, cognitive behavioral tests and analysis of spine density were performed to assess cognitive function. Molecular studies were carried out to confirm the effects of metabolic stressors in the hippocampus relative to cognitive loss.

Results

Our studies demonstrated that HFD in Jnk3^−/− lead to synergetic responses. Loss of function of JNK3 led to increased body weight, especially when exposed to an HFD and they had significantly decreased response to insulin. These mice also showed increased stress in the endoplasmic reticulum and diminished cognitive capacity. However, loss of function of JNK1 promoted normal or heightened energetic metabolism and preserved cognitive function even when chronically metabolically stressed.

Conclusions

Downregulation of JNK3 does not seem to be a suitable target for the modulation of energetic-cognitive dysregulations while loss of function of JNK1 seems to promote a good metabolic-cognitive profile, just like resistance to the negative effects of chronic feeding with HFD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00471-y.

Improving mouse models for the study of Alzheimer's disease

Alzheimer's disease (AD) is a complex neurodegenerative disease whose risk is influenced by genetic and environmental factors. Although a number of pathological hallmarks have been extensively studied over the last several decades, a complete picture of disease initiation and progression remains unclear. We now understand that numerous cell types and systems are involved in AD pathogenesis, and that this cellular profile may present differently for each individual, making the creation of relevant mouse models challenging. However, with increasingly diverse data made available by genome-wide association studies, we can identify and examine new genes and pathways involved in genetic risk for AD, many of which involve vascular health and inflammation. When developing mouse models, it is critical to assess (1) an aging timeline that represents onset and progression in humans, (2) genetic variants and context, (3) environmental factors present in human populations that result in both neuropathological and functional changes-themes that we address in this chapter.

Glucose Metabolism, Neural Cell Senescence and Alzheimer’s Disease

Alzheimer’s disease (AD), an elderly neurodegenerative disorder with a high incidence and progressive memory decline, is one of the most expensive, lethal, and burdening diseases. To date, the pathogenesis of AD has not been fully illustrated. Emerging studies have revealed that cellular senescence and abnormal glucose metabolism in the brain are the early hallmarks of AD. Moreover, cellular senescence and glucose metabolism disturbance in the brain of AD patients may precede amyloid-β deposition or Tau protein phosphorylation. Thus, metabolic reprogramming targeting senescent microglia and astrocytes may be a novel strategy for AD intervention and treatment. Here, we recapitulate the relationships between neural cell senescence and abnormal glucose metabolism (e.g., insulin signaling, glucose and lactate metabolism) in AD. We then discuss the potential perspective of metabolic reprogramming towards an AD intervention, providing a theoretical basis for the further exploration of the pathogenesis of and therapeutic approach toward AD.

Oleuropein-Rich Olive Leaf Extract Attenuates Neuroinflammation in the Alzheimer's Disease Mouse Model

Alzheimer's disease (AD) is the most common form of dementia among several neurodegenerative disorders afflicting the elderly. AD is characterized by the deposition of extracellular amyloid-β (Aβ) plaques, disrupted blood-brain barrier (BBB), and neuroinflammation. Several studies have demonstrated the health benefits of olive oil and olive leaf extract (OLE) due to their polyphenolic content. The main phenolic compound in OLE is glycosylated oleuropein (OLG), while the aglycon form of oleuropein (OLA) exists in much lower amounts. This work aimed to evaluate the effect of a low dose of OLG-rich OLE and the mechanism(s) that contributed to the observed beneficial effects against Aβ pathology in the homozygous 5xFAD mouse model. Mice were fed with OLE-enriched diet (695 μg/kg body weight/day) for 3 months, starting at 3 months old. Overall findings demonstrated that OLE reduced neuroinflammation by inhibiting the NF-κB pathway and suppressing the activation of NLRP3 inflammasomes and RAGE/HMGB1 pathways. In addition, OLE reduced total Aβ brain levels due to increased clearance and reduced production of Aβ and enhanced BBB integrity and function, which collectively improved the memory function. Thus, the consumption of OLE as a dietary supplement is expected to stop and/or slow the progression of AD.

Dysmetabolism and Neurodegeneration: Trick or Treat?

Accumulating evidence suggests the existence of a strong link between metabolic syndrome and neurodegeneration. Indeed, epidemiologic studies have described solid associations between metabolic syndrome and neurodegeneration, whereas animal models contributed for the clarification of the mechanistic underlying the complex relationships between these conditions, having the development of an insulin resistance state a pivotal role in this relationship. Herein, we review in a concise manner the association between metabolic syndrome and neurodegeneration. We start by providing concepts regarding the role of insulin and insulin signaling pathways as well as the pathophysiological mechanisms that are in the genesis of metabolic diseases. Then, we focus on the role of insulin in the brain, with special attention to its function in the regulation of brain glucose metabolism, feeding, and cognition. Moreover, we extensively report on the association between neurodegeneration and metabolic diseases, with a particular emphasis on the evidence observed in animal models of dysmetabolism induced by hypercaloric diets. We also debate on strategies to prevent and/or delay neurodegeneration through the normalization of whole-body glucose homeostasis, particularly via the modulation of the carotid bodies, organs known to be key in connecting the periphery with the brain.

The impact of uremic toxins on Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia, pathologically characterized by accumulation of senile plaques and neurofibrillary tangles. Chronic kidney disease (CKD) is highly prevalent in elderly population closely associated with occurrence of dementia. Recent epidemiological and experimental studies suggest a potential association of CKD with AD. Both diseases share a panel of identical risk factors, such as type 2 diabetes; and hypertension. However, the relationship between CKD and AD is unclear. Lower clearance of a panel of uremic toxin including cystatin-C, guanidine, and adiponectin due to CKD is implied to contribute to AD pathogenesis. In this review we summarize the current evidence from epidemiological, experimental and clinical studies on the potential contribution of uremic toxins to AD pathogenesis. We describe outstanding questions and propose an outlook on the link between uremic toxins and AD.

Myocardial infarction coincides with increased NOX2 and Nε-(carboxymethyl) lysine expression in the cerebral microvasculature

Background

Myocardial infarction (MI) is associated with mental health disorders, in which neuroinflammation and cerebral microvascular dysfunction may play a role. Previously, we have shown that the proinflammatory factors N^ε-(carboxymethyl)lysine (CML) and NADPH oxidase 2 (NOX2) are increased in the human infarcted heart microvasculature. The aim of this study was to analyse the presence of CML and NOX2 in the cerebral microvasculature of patients with MI.

Methods

Brain tissue was obtained at autopsy from 24 patients with MI and nine control patients. According to their infarct age, patients with MI were divided into three groups: 3–6 hours old (phase I), 6 hours–5 days old (phase II) and 5–14 days old (phase III). CML and NOX2 in the microvasculature were studied through immunohistochemical analysis.

Results

We observed a 2.5-fold increase in cerebral microvascular CML in patients with phase II and phase III MI (phase II: 21.39±7.91, p=0.004; phase III: 24.21±10.37, p=0.0007) compared with non-MI controls (8.55±2.98). NOX2 was increased in microvessels in patients with phase II MI (p=0.002) and phase III MI (p=0.04) compared with controls. No correlation was found between CML and NOX2 (r=0.58, p=0.13).

Conclusions

MI coincides with an increased presence of CML and NOX2 in the brain microvasculature. These data point to proinflammatory alterations in the brain microvasculature that may underlie MI-associated mental health disorders.

Optimizing Use of Neuroimaging Tools in Evaluation of Prodromal Alzheimer's Disease and Related Disorders

Alzheimer's disease (AD) is the most common neurodegenerative disease and is characterized by preclinical, pre-dementia, and dementia phases. Progression of the disease leads to cognitive decline and is associated with loss of functional independence, personality changes, and behavioral disturbances. Current guidelines for AD diagnosis include the use of neuroimaging tools as biomarkers for identifying and monitoring pathological changes. Various imaging modalities, namely magnetic resonance imaging (MRI), fluorodeoxyglucose-positron emission tomography (FDG-PET) and PET with amyloid-beta tracers are available to facilitate early accurate diagnoses. Enhancing diagnosis in the early stages of the disease can allow for timely interventions that can delay progression of the disease. This paper will discuss the characteristic findings associated with each of the imaging tools for patients with AD, with a focus on FDG-PET due to its established accuracy in assisting with the differential diagnosis of dementia and discussion of other methods including MRI. Diagnostically-relevant features to aid clinicians in making a differential diagnosis will also be pointed out and multimodal imaging will be reviewed. We also discuss the role of quantification software in interpretation of brain imaging. Lastly, to guide evaluation of patients presenting with cognitive deficits, an algorithm for optimal integration of these imaging tools will be shared. Molecular imaging modalities used in dementia evaluations hold promise toward identifying AD-related pathology before symptoms are fully in evidence. The work describes state of the art functional and molecular imaging methods for AD. It will also overview a clinically applicable quantitative method for reproducible assessments of such scans in the early identification of AD.

Cerebrospinal Fluid Neurotransmitters, Cytokines, and Chemokines in Alzheimer's and Lewy Body Diseases

BACKGROUND

Alzheimer's disease (AD) and Lewy body disease (LBD) are complex neurodegenerative disorders that have been associated with brain inflammation and impaired neurotransmission.

OBJECTIVE

We aimed to determine concentrations of multiple cytokines, chemokines, and neurotransmitters previously associated with brain inflammation and synapse function in cerebrospinal fluid (CSF) from AD and LBD patients.

METHODS

We examined a panel of 50 analytes comprising neurotransmitters, cytokines, chemokines, and hormones in CSF in a cohort of patients diagnosed with mild cognitive impairment (MCI), AD, LBD, or non-demented controls (NDC).

RESULTS

Among neurotransmitters, noradrenaline (NA) was increased in AD CSF, while homovanillic acid (HVA), a dopamine metabolite, was reduced in both AD and LBD CSF relative to NDC. Six cytokines/chemokines out of 30 investigated were reliably detected in CSF. CSF vascular endothelial growth factor (VEGF) was significantly reduced in LBD patients relative to NDC.

CONCLUSIONS

CSF alterations in NA, HVA, and VEGF in AD and LBD may reflect pathogenic features of these disorders and provide tools for improved diagnosis. Future studies are warranted to replicate current findings in larger, multicenter cohorts.

Metformin: A Growing Journey from Glycemic Control to the Treatment of Alzheimer's Disease and Depression

Metabolic stress, transduced as an altered cellular redox and energy status, presents as the main culprit in many diseases, including diabetes. However, its role in the pathology of neurological disorders is still not fully elucidated. Metformin, a biguanide compound, is an FDA approved antidiabetic drug generally used for the treatment of type 2 diabetes. The recently described wide spectrum of action executed by this drug suggests a potential therapeutic benefit in a panoply of disorders. Current studies imply that metformin could play a neuroprotective role by reversing hallmarks of brain injury (metabolic dysfunction, neuronal dystrophy and cellular loss), in addition to cognitive and behavioral alterations that accompany the onset of certain brain diseases such as Alzheimer's disease (AD) and depression. However, the mechanisms by which metformin exerts its protective effect in neurodegenerative disorders are not yet fully elucidated. The aim of this review is to reexamine the mechanisms through which metformin performs its function while concentrating on its effect on reestablishing homeostasis in a metabolically disturbed milieu. We will also highlight the importance of metabolic stress, not only as a component of many neurological disorders, but also as a primary driving force for neural insult. Of interest, we will explore the involvement of metabolic stress in the pathobiology of AD and depression. The derangement in major metabolic pathways, including AMPK, insulin and glucose transporters, will be explored and the potential therapeutic effects of metformin administration on the reversal of brain injury in such metabolism dependent diseases will be exposed.

Keeping the ageing brain wired: a role for purine signalling in regulating cellular metabolism in oligodendrocyte progenitors

White matter (WM) is a highly prominent feature in the human cerebrum and is comprised of bundles of myelinated axons that form the connectome of the brain. Myelin is formed by oligodendrocytes and is essential for rapid neuronal electrical communication that underlies the massive computing power of the human brain. Oligodendrocytes are generated throughout life by oligodendrocyte precursor cells (OPCs), which are identified by expression of the chondroitin sulphate proteoglycan NG2 (Cspg4), and are often termed NG2-glia. Adult NG2+ OPCs are slowly proliferating cells that have the stem cell-like property of self-renewal and differentiation into a pool of 'late OPCs' or 'differentiation committed' OPCs(COPs) identified by specific expression of the G-protein-coupled receptor GPR17, which are capable of differentiation into myelinating oligodendrocytes. In the adult brain, these reservoirs of OPCs and COPs ensure rapid myelination of new neuronal connections formed in response to neuronal signalling, which underpins learning and cognitive function. However, there is an age-related decline in myelination that is associated with a loss of neuronal function and cognitive decline. The underlying causes of myelin loss in ageing are manifold, but a key factor is the decay in OPC 'stemness' and a decline in their replenishment of COPs, which results in the ultimate failure of myelin regeneration. These changes in ageing OPCs are underpinned by dysregulation of neuronal signalling and OPC metabolic function. Here, we highlight the role of purine signalling in regulating OPC self-renewal and the potential importance of GPR17 and the P2X7 receptor subtype in age-related changes in OPC metabolism. Moreover, age is the main factor in the failure of myelination in chronic multiple sclerosis and myelin loss in Alzheimer's disease, hence understanding the importance of purine signalling in OPC regeneration and myelination is critical for developing new strategies for promoting repair in age-dependent neuropathology.

AMPK induces regulatory innate lymphoid cells after traumatic brain injury

The CNS is regarded as an immunoprivileged organ, evading routine immune surveillance; however, the coordinated development of immune responses profoundly influences outcomes after brain injury. Innate lymphoid cells (ILCs) are cytokine-producing cells that are critical for the initiation, modulation, and resolution of inflammation, but the functional relevance and mechanistic regulation of ILCs are unexplored after acute brain injury. We demonstrate increased proliferation of all ILC subtypes within the meninges for up to 1 year after experimental traumatic brain injury (TBI) while ILCs were present within resected dura and elevated within cerebrospinal fluid (CSF) of moderate-to-severe TBI patients. In line with energetic derangements after TBI, inhibition of the metabolic regulator, AMPK, increased meningeal ILC expansion, whereas AMPK activation suppressed proinflammatory ILC1/ILC3 and increased the frequency of IL-10-expressing ILC2 after TBI. Moreover, intracisternal administration of IL-33 activated AMPK, expanded ILC2, and suppressed ILC1 and ILC3 within the meninges of WT and Rag1-/- mice, but not Rag1-/- IL2rg-/- mice. Taken together, we identify AMPK as a brake on the expansion of proinflammatory, CNS-resident ILCs after brain injury. These findings establish a mechanistic framework whereby immunometabolic modulation of ILCs may direct the specificity, timing, and magnitude of cerebral immunity.

Amyloid Beta Peptide Is an Endogenous Negative Allosteric Modulator of Leptin Receptor

INTRODUCTION

Metabolic dysfunction is now recognized as a pivotal component of Alzheimer's disease (AD), the most common dementia worldwide. However, the precise molecular mechanisms linking metabolic dysfunction to AD remain elusive.

OBJECTIVE

Here, we investigated the direct impact of soluble oligomeric amyloid beta (Aβ) peptides, the main molecular hallmark of AD, on the leptin system, a major component of central energy metabolism regulation.

METHODS

We developed a new time-resolved fluorescence resonance energy transfer-based Aβ binding assay for the leptin receptor (LepR) and studied the effect of Aβ on LepR function in several in vitro assays. The in vivo effect of Aβ on LepR function was studied in an Aβ-specific AD mouse model and in pro-opiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus.

RESULTS

We revealed specific and high-affinity (Ki = 0.1 nM) binding of Aβ to LepR. Pharmacological characterization of this interaction showed that Aβ binds allosterically to the extracellular domain of LepR and negatively affects receptor function. Negative allosteric modulation of LepR by Aβ was detected at the level of signaling pathways (STAT-3, AKT, and ERK) in vitroand in vivo. Importantly, the leptin-induced response of POMC neurons, key players in the regulation of metabolic function, was completely abolished in the presence of Aβ.

CONCLUSION

Our data indicate that Aβ is a negative allosteric modulator of LepR, resulting in impaired leptin action, and qualify LepR as a new and direct target of Aβ oligomers. Preventing the interaction of Aβ with LepR might improve both the metabolic and cognitive dysfunctions in AD condition.

Diabetic Cognitive Dysfunction: From Bench to Clinic

Type 2 diabetes increases the risk of developing cognitive dysfunction in the elderly in the form of short-term memory and executive function impairment. Genetic and diet-induced models of type 2 diabetes further support this link, displaying deficits in working memory, learning, and memory performance. The risk factors for diabetic cognitive dysfunction include vascular disease, hypoglycaemia, hyperlipidaemia, adiposity, insulin resistance, lifestyle factors, and genetic factors. Using neuronal imaging technologies, diabetic patients with cognitive dysfunction show atrophy of the whole brain, particularly the grey matter, hippocampus and amygdala; increased volume of the ventricular and white matter; brain infarcts; impaired network integrity; abnormal microstructure; and reduced cerebral blood flow and amplitude of low-frequency fluctuations. The pathogenesis of type 2 diabetes with cognitive dysfunction involves hyperglycaemia, macrovascular and microvascular diseases, insulin resistance, inflammation, apoptosis, and disorders of neurotransmitters. Large clinical trials may offer further proof of biomarkers and risk factors for diabetic cognitive dysfunction. Advanced neuronal imaging technologies and novel disease animal models will assist in elucidating the precise pathogenesis and to provide better therapeutic interventions and treatment.

Altered functional connectivity of brain regions based on a meta-analysis in patients with T2DM: A resting-state fMRI study

OBJECTIVE

To explore the neural mechanisms of brain impairment in type 2 diabetes mellitus (T2DM), abnormal changes to the functional connections between brain regions in the resting state were investigated based on a meta-analysis.

METHODS

Resting-state functional magnetic resonance imaging (fMRI) and neuropsychological assessment were performed on 38 patients with T2DM and 33 healthy controls (HCs). Functional connectivity between regions based on a meta-analysis and other voxels in the brain was calculated and compared between the two groups using a two-sample t test. A correlation analysis was conducted between clinical/cognitive variables and functional connection values from the regions with significant differences in the above comparison.

RESULTS

Patients in the T2DM group showed a significantly decreased functional connection between the right posterior cerebellum and the right middle/inferior occipital gyrus, left middle temporal gyrus, left superior frontal gyrus, left middle frontal gyrus, left insula, left precuneus, and right paracentral lobule/left precuneus when compared with HC group. The functional connection values between the right insula and left medial frontal gyrus, left supplementary motor area, and between the left lingual gyrus and right middle/inferior occipital gyrus in patients with T2DM were significantly decreased. Moreover, the functional connection values between the right posterior cerebellum and left middle frontal gyrus, and between the right posterior cerebellum and left precuneus were negatively correlated with HbA1c in the T2DM group (r = -.356, p = .03; r = -.334, p = .043).

CONCLUSIONS

Our study showed a wide range of cerebellar-cerebral circuit abnormalities in patients with T2DM, which provides a new direction to investigate the neuropathological mechanisms of T2DM from the perspective of the cerebellum.

Dietary Inflammatory Potential and the Risk of Neurodegenerative Diseases in Adults

Nutrition and diet have been suggested to enhance or inhibit cognitive performance and the risk of several neurodegenerative diseases. We conducted a systematic review to elucidate the relationship between the inflammatory capacity of a person's diet and the risk of incident neurodegenerative diseases. We searched major medical databases for articles published through June 30, 2018. Original, full-text, English-language articles on studies with human participants which investigated the link between dietary inflammatory potential and risk of developing neurodegenerative diseases were included. Duplicate and irrelevant studies were removed, and data were compiled through critical analysis. Initially, 457 articles were collected via the searching method, of which 196 studies remained after removal of duplicates. Fourteen articles were screened and found to be relevant to the scope of the review. After critical analysis, 10 were included in the final review. In all studies but one, a higher dietary inflammatory index (DII) was related to higher risk of developing neurodegenerative disease symptoms, including memory and cognition decline and multiple sclerosis. Of 3 studies that assessed the association of DII with levels of circulating inflammation markers, 2 indicated that DII was positively correlated with inflammatory marker levels. Low literacy, an unhealthy lifestyle, and individual nutritional status were the factors involved in a diet with inflammatory potential. These findings enhance confidence that DII is an appropriate tool for measurement of dietary inflammatory potential and validate the role of diets with inflammatory potential in the pathophysiology of neurodegenerative diseases. DII may be correlated with levels of circulating inflammatory markers.

Cerebrospinal fluid irisin correlates with amyloid-β, BDNF, and cognition in Alzheimer's disease

INTRODUCTION

Irisin is a novel hormone originally identified for its role as a regulator of peripheral metabolism and recently found to protect synapses and rescue memory in mouse models of Alzheimer's disease (AD). However, whether and how cerebrospinal fluid (CSF) irisin varies in relation to canonical AD biomarkers and cognition in humans remains unknown.

METHODS

We determined CSF levels of irisin and brain-derived neurotrophic factor (BDNF) and examined their correlations with CSF amyloid beta (Aβ)42, total tau, and Mini-Mental State Exam (MMSE) scores in a cohort comprising AD patients (n = 14) and non-demented controls (NDC; n = 25).

RESULTS

CSF irisin correlated positively with BDNF, Aβ42, and MMSE scores, but not with CSF total tau.

DISCUSSION

Results indicate that CSF irisin and BDNF are directly correlated with Aβ pathology and cognition in AD.

Protective effects of Akkermansia muciniphila on cognitive deficits and amyloid pathology in a mouse model of Alzheimer's disease

Objective

Alzheimer’s disease (AD) is a global health problem without effective methods to alleviate the disease progression. Amyloid β-protein (Aβ) is widely accepted as a key biomarker for AD. Metabolic syndromes, including obesity and insulin resistance, are key high risk factors for AD. Akkermansia muciniphila (Akk), the only representative human gut microbe in the genus Verrucomicrobia, can prevent the weight gain caused by a high-fat diet, repair the damaged integrity of the intestinal epithelium barrier, reduce endotoxin levels in blood and improve insulin resistance. The aim of this study is to explore the impact of Akk administration in AD model mice in different diets.

Methods

APP/PS1 mice were fed either a normal chow diet or a high-fat diet and were treated with Akk by gavage each day for 6 months. The impacts of Akk on glucose metabolism, intestinal barrier and lipid metabolism in the mouse model of AD were determined. Changes in brain pathology and neuroethology were also analyzed.

Results

Akk effectively reduced the fasting blood glucose and serum diamine oxidase levels, and alleviated the reduction of colonic mucus cells in APP/PS1 mice. After treatment with Akk, the APP/PS1 mice showed obviously reduced blood lipid levels, improved hepatic steatosis and scapular brown fat whitening. Moreover, Akk promoted the reduction of Aβ 40–42 levels in the cerebral cortex of APP/PS1 mice, shortened the study time and improved the completion rate in Y-maze tests.

Conclusion

Akk effectively improved glucose tolerance, intestine barrier dysfunction and dyslipidemia in AD model mice. Our study results suggested that Akk could delay the pathological changes in the brain and relieve impairment of spatial learning and memory in AD model mice, which provides a new strategy for prevention and treatment of AD.

APP/PS1 mice display alterations in physiological processes after treated with Akk. It is showed that the damaged integrity of the intestinal epithelium barrier is repaired, leading to obviously reduced blood glucose and lipid levels, improved hepatic steatosis, insulin resistance and scapular brown fat whitening, which are beneficial to reduce Aβ 40–42 levels in the brain of APP/PS1 mice.

Phytochemicals against TNFα-Mediated Neuroinflammatory Diseases

Tumor necrosis factor-alpha (TNF-α) is a well-known pro-inflammatory cytokine responsible for the modulation of the immune system. TNF-α plays a critical role in almost every type of inflammatory disorder, including central nervous system (CNS) diseases. Although TNF-α is a well-studied component of inflammatory responses, its functioning in diverse cell types is still unclear. TNF-α functions through its two main receptors: tumor necrosis factor receptor 1 and 2 (TNFR1, TNFR2), also known as p55 and p75, respectively. Normally, the functions of soluble TNF-α-induced TNFR1 activation are reported to be pro-inflammatory and apoptotic. While TNF-α mediated TNFR2 activation has a dual role. Several synthetic drugs used as inhibitors of TNF-α for diverse inflammatory diseases possess serious adverse effects, which make patients and researchers turn their focus toward natural medicines, phytochemicals in particular. Phytochemicals targeting TNF-α can significantly improve disease conditions involving TNF-α with fewer side effects. Here, we reviewed known TNF-α inhibitors, as well as lately studied phytochemicals, with a role in inhibiting TNF-α itself, and TNF-α-mediated signaling in inflammatory diseases focusing mainly on CNS disorders.

Natural Compounds as Beneficial Antioxidant Agents in Neurodegenerative Disorders: A Focus on Alzheimer's Disease

The positive role of nutrition in chronic neurodegenerative diseases (NDs) suggests that dietary interventions represent helpful tools for preventing NDs. In particular, diets enriched with natural compounds have become an increasingly attractive, non-invasive, and inexpensive option to support a healthy brain and to potentially treat NDs. Bioactive compounds found in vegetables or microalgae possess special properties able to counteract oxidative stress, which is involved as a triggering factor in neurodegeneration. Here, we briefly review the relevant experimental data on curcuminoids, silymarin, chlorogenic acid, and compounds derived from the microalga Aphanizomenon flos aquae (AFA) which have been demonstrated to possess encouraging beneficial effects on neurodegeneration, in particular on Alzheimer's disease models.

Prognosis and Interplay of Cognitive Impairment and Sarcopenia in Older Adults Discharged from Acute Care Hospitals

Sarcopenia and cognitive impairment are associated with an increased risk of negative outcomes, but their prognostic interplay has not been investigated so far. We aimed to investigate the prognostic interaction of sarcopenia and cognitive impairment concerning 12-month mortality among older patients discharged from acute care wards in Italy. Our series consisted of 624 patients (age = 80.1 ± 7.0 years, 56.1% women) enrolled in a prospective observational study. Sarcopenia was defined following the European Working Group on Sarcopenia in Older People (EWGSOP) criteria. Cognitive impairment was defined as age- and education-adjusted Mini-Mental State Examination (MMSE) score < 24 or recorded diagnosis of dementia. The study outcome was all-cause mortality during 12-month follow-up. The combination of sarcopenia and cognitive ability was tested against participants with intact cognitive ability and without sarcopenia. Overall, 159 patients (25.5%) were identified as having sarcopenia, and 323 (51.8%) were cognitively impaired. During the follow-up, 79 patients (12.7%) died. After adjusting for potential confounders, the combination of sarcopenia and cognitive impairment has been found associated with increased mortality (HR = 2.12, 95% CI = 1.05-4.13). Such association was also confirmed after excluding patients with dementia (HR = 2.13, 95% CI = 1.06-4.17), underweight (HR = 2.18, 95% CI = 1.03-3.91), high comorbidity burden (HR = 2.63, 95% CI = 1.09-6.32), and severe disability (HR = 2.88, 95% CI = 1.10-5.73). The co-occurrence of sarcopenia and cognitive impairment may predict 1-year mortality in older patients discharged from acute care hospitals.

Geraniin Attenuates Lipopolysaccharide-Induced Cognitive Impairment in Mice by Inhibiting Toll-Like Receptor 4 Activation

Geraniin has been reported to possess potent anti-inflammatory properties and to modulate the macrophage polarization. This study sought to evaluate the protective effects and underlying mechanisms of geraniin on lipopolysaccharide (LPS)-induced neuroinflammation and neurobiological alternations as well as cognitive impairment. Daily intragastrical administration with geraniin (20 mg kg^-1 day^-1) for 14 days significantly prolonged the duration in the target quadrant (26.53 ± 2.03 versus 37.09 ± 3.27%; p < 0.05) and increased crossing-target number (1.93 ± 0.22 versus 3.08 ± 0.17; p < 0.01) in the probe test of LPS-treated mice. Geraniin also ameliorated LPS-elicited neural/synaptic impairments and decreased levels of LPS-induced Aβ generation (p < 0.05), amyloid precursor protein (APP) (p < 0.05) and β-site amyloid precursor protein cleavage enzyme 1 (BACE1) (p < 0.05). Furthermore, geraniin suppressed the production of pro-inflammatory cytokines, including tumor necrosis factor α (TNF-α) (9.85 ± 0.58 versus 5.20 ± 0.52 pg/mg of protein; p < 0.01), interleukin (IL)-1β (16.31 ± 0.67 versus 8.62 ± 0.46 pg/mg of protein; p < 0.01), and IL-6 (12.12 ± 0.45 versus 7.43 ± 0.32 pg/mg of protein; p < 0.05), and inhibited glial cell activation. Moreover, geraniin effectively polarized the microglia toward an anti-inflammatory M2 phenotype. Further study revealed that geraniin targeted toll-like receptor 4 (TLR4)-mediated signaling and decreased the production of pro-inflammatory cytokines in BV-2 microglial cells. These results indicate that geraniin mitigates LPS-elicited neural/synaptic neurodegeneration, amyloidogenesis, neuroinflammation, and cognitive impairment and suggest geraniin as a therapeutic option for neuroinflammation-associated neurological disorders, such as Alzheimer's disease.

Ageing as a risk factor for neurodegenerative disease

Ageing is the primary risk factor for most neurodegenerative diseases, including Alzheimer disease (AD) and Parkinson disease (PD). One in ten individuals aged ≥65 years has AD and its prevalence continues to increase with increasing age. Few or no effective treatments are available for ageing-related neurodegenerative diseases, which tend to progress in an irreversible manner and are associated with large socioeconomic and personal costs. This Review discusses the pathogenesis of AD, PD and other neurodegenerative diseases, and describes their associations with the nine biological hallmarks of ageing: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, mitochondrial dysfunction, cellular senescence, deregulated nutrient sensing, stem cell exhaustion and altered intercellular communication. The central biological mechanisms of ageing and their potential as targets of novel therapies for neurodegenerative diseases are also discussed, with potential therapies including NAD⁺ precursors, mitophagy inducers and inhibitors of cellular senescence.

High fat diet worsens the adverse effects of antibiotic on intestinal health in juvenile Nile tilapia (Oreochromis niloticus)

Antibiotics and high fat diets are commonly used independently in global aquaculture production for fish health management and to spare the use of costly protein as energy sources, respectively, causing relatively similar metabolic effects and stresses. However, it is unknown whether dietary high fat worsens or attenuates the adverse effects caused by antibiotics in fish. We determined the ability of high fat diet to influence the adverse effects of oxytetracycline on Nile tilapia, Oreochromis niloticus. Thirty Nile tilapia weighing 8.45 ± 0.15 g were fed on medium fat (MF; 70 g/kg) and high fat (HF; 120 g/kg) diets and the same fat levels supplemented with 2.00 g/kg diet of OTC (80 mg/kg body weight/day) hereafter, MFO and HFO for 65 days. The general growth performance, feed efficiency and intestinal health of fish were evaluated. The Nile tilapia fed on HFO diet had significantly lower growth rate, body protein content and feed efficiency compared to those fed on MFO diet. Dietary HFO affected the intestine histomorphology, which decreased dramatically the tight junction proteins of Nile tilapia and induced microbiota dysbiosis compared to MFO diet. The Nile tilapia fed on HFO diet had increased oxidative stress, which stimulated drug detoxification response, caused endoplasmic reticulum stress and apoptosis compared to those fed on MFO diet. The new findings from our study demonstrate that, the adverse effects of antibiotics in fish are different at medium and high fat contents. Feeding fish with high fat diets with antibiotics worsen the adverse effects. This enlightens our understanding on the risks of antibiotics misuse and also suggests that antibiotics should be more strictly limited in aquaculture, in which high fat diets are currently widely used in fish production worldwide.

Dysglycemia, Not Altered Sex Steroid Hormones, Affects Cognitive Function in Polycystic Ovary Syndrome

Context

Polycystic ovary syndrome (PCOS) is a complex endocrine condition characterized by multiple reproductive and metabolic abnormalities. Because individual reproductive and metabolic abnormalities modulate working memory in the general population, there is growing interest in whether cognitive function is dually and negatively affected in PCOS.

Objective

To examine the association of reproductive and metabolic features with cognitive function in women with and without PCOS.

Design

An observational, cross-sectional study was conducted at an academic clinical research center in North America between 2006 and 2009. Common tests of working memory (i.e., manual dexterity, perceptual speed, and visuospatial ability) were performed by women with PCOS (n = 40) and control subjects (n = 40). Markers of sex steroid hormones, ovulatory function, and cardiometabolic health were also assessed.

Results

Reduced visuospatial ability was observed in women with PCOS compared with control subjects (P < 0.01). Reduced visuospatial ability was linked to higher levels of hemoglobin A1c in the entire study cohort, independent of body mass index or PCOS status. No associations were observed between visuospatial ability and reproductive features, after controlling for confounding variables.

Conclusion

Our findings support a role for glycemic control, and not PCOS per se, in cognitive dysfunction in women of reproductive age. Additional studies are needed to understand the short- and long-term effects of dysglycemia on brain health in women with PCOS, given their increased propensity for metabolic comorbidities, compared with control subjects.

Metabolic Dysfunction in Alzheimer's Disease: From Basic Neurobiology to Clinical Approaches

Clinical trials have extensively failed to find effective treatments for Alzheimer's disease (AD) so far. Even after decades of AD research, there are still limited options for treating dementia. Mounting evidence has indicated that AD patients develop central and peripheral metabolic dysfunction, and the underpinnings of such events have recently begun to emerge. Basic and preclinical studies have unveiled key pathophysiological mechanisms that include aberrant brain stress signaling, inflammation, and impaired insulin sensitivity. These findings are in accordance with clinical and neuropathological data suggesting that AD patients undergo central and peripheral metabolic deregulation. Here, we review recent basic and clinical findings indicating that metabolic defects are central to AD pathophysiology. We further propose a view for future therapeutics that incorporates metabolic defects as a core feature of AD pathogenesis. This approach could improve disease understanding and therapy development through drug repurposing and/or identification of novel metabolic targets.

The Amyloid-β Oligomer Hypothesis: Beginning of the Third Decade

The amyloid-β oligomer (AβO) hypothesis was introduced in 1998. It proposed that the brain damage leading to Alzheimer’s disease (AD) was instigated by soluble, ligand-like AβOs. This hypothesis was based on the discovery that fibril-free synthetic preparations of AβOs were potent CNS neurotoxins that rapidly inhibited long-term potentiation and, with time, caused selective nerve cell death (Lambert et al., 1998). The mechanism was attributed to disrupted signaling involving the tyrosine-protein kinase Fyn, mediated by an unknown toxin receptor. Over 4,000 articles concerning AβOs have been published since then, including more than 400 reviews. AβOs have been shown to accumulate in an AD-dependent manner in human and animal model brain tissue and, experimentally, to impair learning and memory and instigate major facets of AD neuropathology, including tau pathology, synapse deterioration and loss, inflammation, and oxidative damage. As reviewed by Hayden and Teplow in 2013, the AβO hypothesis “has all but supplanted the amyloid cascade.” Despite the emerging understanding of the role played by AβOs in AD pathogenesis, AβOs have not yet received the clinical attention given to amyloid plaques, which have been at the core of major attempts at therapeutics and diagnostics but are no longer regarded as the most pathogenic form of Aβ. However, if the momentum of AβO research continues, particularly efforts to elucidate key aspects of structure, a clear path to a successful disease modifying therapy can be envisioned. Ensuring that lessons learned from recent, late-stage clinical failures are applied appropriately throughout therapeutic development will further enable the likelihood of a successful therapy in the near-term.

Kinetic and thermodynamic study of beta-Boswellic acid interaction with Tau protein investigated by surface plasmon resonance and molecular modeling methods

Introduction: Beta-Boswellic acid (BBA) is a pentacyclic terpene which has been obtained from frankincense and its beneficial effects on neurodegenerative disorders such as Alzheimer’s disease (AD) have been addressed.

Methods: In the present study, thermodynamic and kinetic aspects of BBA interaction with Tau protein as one of the important proteins involved in AD in the absence and presence of glucose has been investigated using surface plasmon resonance (SPR) method. Tau protein was immobilized onto the carboxy methyl dextran chip and its binding interactions with BBA were studied at physiological pH at various temperatures. Glucose interference with these interactions was also investigated.

Results: Results showed that BBA forms a stable complex with Tau (K_D=8.45×10^-7 M) at 298 K. Molecular modeling analysis showed a hydrophobic interaction between BBA and HVPGGG segment of R₂ and R₄ repeated domains of Tau.

Conclusion: The binding affinity increased by temperature enhancement, while it decreased significantly in the presence of glucose. Both association and dissociation of the BBA-Tau complex were accompanied with an entropic activation barrier; however, positive enthalpy and entropy changes revealed that hydrophobic bonding is the main force involved in the interaction.

MST1 Regulates Neuronal Cell Death via JNK/Casp3 Signaling Pathway in HFD Mouse Brain and HT22 Cells

Oxidative stress has been considered as the main mediator in neurodegenerative diseases. A high-fat diet (HFD) and metabolic diseases result in oxidative stress generation, leading to various neurodegenerative diseases via molecular mechanisms that remain largely unknown. Protein kinases play an important role in the homeostasis between cell survival and cell apoptosis. The mammalian sterile 20-like kinase-1 (MST1) protein kinase plays an important role in cellular apoptosis in different organ systems, including the central nervous system. In this study, we evaluated the MST1/c-Jun N-terminal kinase (JNK) dependent oxidative damage mediated cognitive dysfunction in HFD-fed mice and stress-induced hippocampal HT22 (mice hippocampal) cells. Our Western blot and immunofluorescence results indicate that HFD and stress-induced hippocampal HT22 cells activate MST1/JNK/Caspase-3 (Casp-3) signaling, which regulates neuronal cell apoptosis and beta-amyloid-cleaving enzyme (BACE1) expression and leads to impaired cognition. Moreover, MST1 expression inhibition by shRNA significantly reduced JNK/Casp-3 signaling. Our in vivo and in vitro experiments mimicking metabolic stress, such as a high-fat diet, hyperglycemia, and an inflammatory response, determined that MST1 plays a key regulatory role in neuronal cell death and cognition, suggesting that MST1 could be a potential therapeutic target for numerous neurodegenerative diseases.

Insulin treatment protects the brain against neuroinflammation by reducing cerebral cytokines and modulating mitochondrial function

In the central nervous system, glial cells protect the brain against neuronal stress by inducing inflammatory responses; namely, intracellular signaling and cytokine production. However, chronic inflammation is often associated with degenerative diseases that can damage hormone signaling and mitochondrial function. Lipopolysaccharide (LPS) induces neuroinflammation by stimulating the production of interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α); moreover, it generates oxidative stress and impairs cognitive functions. The aim of the present study was to assess the therapeutic efficacy of intracerebroventricular (i.c.v.) injections of insulin against neuroinflammation. Inflammation was first induced in male Wistar rats (60 days old, n = 12/group) through an intraperitoneal injection of 0.1 mg/kg LPS. The i.c.v. insulin treatment at a 0.5 mU dose was initiated 4 h later and administered once a day for 5 days. Thereafter, the spatial memory of the rats was assessed, and the hippocampus and cortex were later dissected for biochemical analyses. Our results showed that LPS induced cognitive function impairments, but the insulin treatment reversed these effects. Whereas the levels of brain-derived neurotrophic factor and beta-nerve growth factor in the hippocampus were not altered by LPS, they were decreased in the cortex by insulin. The IL-1β and TNF-α levels were increased in the cortex and hippocampus following exposure to LPS, but insulin reversed these effects. Evaluation of the H₂O₂levels and mitochondrial membrane potential revealed that LPS modulated mitochondrial function, an effect that was also reversed by insulin. Moreover, LPS induced oxidative stress by decreasing the superoxide dismutase and catalase activities and glutathione and sulfhydryl levels. Furthermore, the levels of oxidative stress probes/markers (i.e.,2',7'-dichlorodihydrofluoresceindiacetateand nitrite) were higher in the LPS-treated rats. These effects were all reversed in the cortex and hippocampus by insulin treatment. Our results suggest a potential role for insulin as a therapeutic drug against inflammatory diseases associated with mitochondrial dysfunction in the brain.

Understanding the link between insulin resistance and Alzheimer's disease: Insights from animal models

Alzheimer's disease (AD) is a devastating neurodegenerative disease affecting millions of people worldwide. AD is characterized by a profound impairment of higher cognitive functions and still lacks any effective disease-modifying treatment. Defective insulin signaling has been implicated in AD pathophysiology, but the mechanisms underlying this process are not fully understood. Here, we review the molecular mechanisms underlying defective brain insulin signaling in rodent models of AD, and in a non-human primate (NHP) model of the disease that recapitulates features observed in AD brains. We further highlight similarities between the NHP and human brains and discuss why NHP models of AD are important to understand disease mechanisms and to improve the translation of effective therapies to humans. We discuss how studies using different animal models have contributed to elucidate the link between insulin resistance and AD.

Role of brain c-Jun N-terminal kinase 2 in the control of the insulin receptor and its relationship with cognitive performance in a high-fat diet pre-clinical model

Insulin resistance has negative consequences on the physiological functioning of the nervous system. The appearance of type 3 diabetes in the brain leads to the development of the sporadic form of Alzheimer's disease. The c-Jun N-terminal kinases (JNK), a subfamily of the Mitogen Activated Protein Kinases, are enzymes composed by three different isoforms with differential modulatory activity against the insulin receptor (IR) and its substrate. This research focused on understanding the regulatory role of JNK2 on the IR, as well as study the effect of a high-fat diet (HFD) in the brain. Our observations determined how JNK2 ablation did not induce compensatory responses in the expression of the other isoforms but led to an increase in JNKs total activity. HFD-fed animals also showed an increased activity profile of the JNKs. These animals also displayed endoplasmic reticulum stress and up-regulation of the protein tyrosine phosphatase 1B (PTP1B) and the suppressor of cytokine signalling 3 protein. Consequently, a reduction in insulin sensitivity was detected and it is correlated with a decrease on the signalling of the IR. Moreover, cognitive impairment was observed in all groups but only wild-type genotype animals fed with HFD showed neuroinflammatory responses. In conclusion, HFD and JNK2 absence cause alterations in normal cognitive activity by altering the signalling of the IR. These affectations are related to the appearance of endoplasmic reticulum stress and an increase in the levels of inhibitory proteins like PTP1B and suppressor of cytokine signalling 3 protein. Cover Image for this issue: doi: 10.1111/jnc.14502.

Metabolism and inflammation: implications for traumatic brain injury therapeutics

INTRODUCTION

Traumatic Brain Injury (TBI) is a leading cause of death and disability in young people, affecting 69 million people annually, worldwide. The initial trauma disrupts brain homeostasis resulting in metabolic dysfunction and an inflammatory cascade, which can then promote further neurodegenerative effects for months or years, as a 'secondary' injury. Effective targeting of the cerebral inflammatory system is challenging due to its complex, pleiotropic nature. Cell metabolism plays a key role in many diseases, and increased disturbance in the TBI metabolic state is associated with poorer patient outcomes. Investigating critical metabolic pathways, and their links to inflammation, can potentially identify supplements which alter the brain's long-term response to TBI and improve recovery. Areas covered: The authors provide an overview of literature on metabolism and inflammation following TBI, and from relevant pre-clinical and clinical studies, propose therapeutic strategies. Expert opinion: There is still no specific active drug treatment for TBI. Changes in metabolic and inflammatory states have been reported after TBI and appear linked. Understanding more about abnormal cerebral metabolism following TBI, and its relationship with cerebral inflammation, will provide essential information for designing therapies, with implications for neurocritical care and for alleviating long-term disability and neurodegeneration in post-TBI patients.

Multi-faceted therapeutic strategy for treatment of Alzheimer's disease by concurrent administration of etodolac and α-tocopherol

Alzheimer's disease (AD) is a complex neurodegenerative disorder with multiple dysfunctional pathways. Therefore, a sophisticated treatment strategy that simultaneously targets multiple brain cell types and disease pathways could be advantageous for effective intervention. To elucidate an effective treatment, we developed an in vitro high-throughput screening (HTS) assay to evaluate candidate drugs for their ability to enhance the integrity of the blood-brain barrier (BBB) and improve clearance of amyloid-β (Aβ) using a cell-based BBB model. Results from HTS identified etodolac and α-tocopherol as promising drugs for further investigation. Both drugs were tested separately and in combination for the purpose of targeting multiple pathways including neuroinflammation and oxidative stress. In vitro studies assessed the effects of etodolac and α-tocopherol individually and collectively for BBB integrity and Aβ transport, synaptic markers and Aβ production in APP-transfected neuronal cells, as well as effects on inflammation and oxidative stress in astrocytes. Transgenic 5XFAD mice were used to translate in vitro results of etodolac and α-tocopherol independently and with concurrent administration. Compared to either drug alone, the combination significantly enhanced the BBB function, decreased total Aβ load correlated with increased expression of major transport proteins, promoted APP processing towards the neuroprotective and non-amyloidogenic pathway, induced synaptic markers expression, and significantly reduced neuroinflammation and oxidative stress both in vitro and in vivo. Collective findings demonstrated the combination produced mixed interaction showing additive, less than additive or synergistic effects on the evaluated markers. In conclusion, this study highlights the significance of combination therapy to simultaneously target multiple disease pathways, and suggest the repurposing and combination of etodolac and α-tocopherol as a novel therapeutic strategy against AD.

The Role of Leptin and Adiponectin in Obesity-Associated Cognitive Decline and Alzheimer's Disease

Cross-talk between adipose tissue and central nervous system (CNS) underlies the increased risk of obese people to develop brain diseases such as cognitive and mood disorders. Detailed mechanisms for how peripheral changes caused by adipose tissue accumulation in obesity impact the CNS to cause brain dysfunction are poorly understood. Adipokines are a large group of substances secreted by the white adipose tissue to regulate a wide range of homeostatic processes including, but not limited to, energy metabolism and immunity. Obesity is characterized by a generalized change in the levels of circulating adipokines due to abnormal accumulation and dysfunction of adipose tissue. Altered adipokine levels underlie complications of obesity as well as the increased risk for the development of obesity-related comorbidities such as type 2 diabetes, cardiovascular and neurodegenerative diseases. Here, we review the literature for the role of adipokines as key mediators of the communication between periphery and CNS in health and disease. We will focus on the actions of leptin and adiponectin, two of the most abundant and well studied adipokines, in the brain, with particular emphasis on how altered signaling of these adipokines in obesity may lead to cognitive dysfunction and augmented risk for Alzheimer's disease. A better understanding of adipokine biology in brain disorders may prove of major relevance to diagnostic, prevention and therapy.