Vascular and metabolic dysfunction in Alzheimer's disease: a review

The effects of tea polyphenols on emotional homeostasis: Understanding dementia risk through stress, mood, attention & sleep

Decades of research provide evidence that certain phytochemicals in tea (Camellia sinensis) and other herbal beverages are protective against the development of sporadic types of dementia in later life. Since tea drinking is an economical and widely adopted social-cultural practice across all age groups, it is an ideal product to target in designing low-cost dietary interventions for Alzheimer's Disease (AD), the most prevalent form of dementia. In this review, we focus on the protective roles of tea-derived polyphenols and other phytochemicals on mood, the stress response, attention, and sleep, in keeping with the perspective that many early neuropathological events in AD may stem, in part, from allostatic overload. This approach aligns with the perspective that many forms of dementia, including AD, begin to take root in the brain decades prior to symptom onset, underscoring the need for early uptake of accessible and viable lifestyle interventions. The findings reviewed here suggest that consuming green and oolong tea can improve mood and reduce overall stress. However, given the caffeine content in tea and its association with stress reactivity, the effects of daily whole tea consumption on the emotional state are likely dose-dependent with an inverted-U relationship to wellbeing. Plant-based beverages that are to be consumed in high daily quantities for health purposes and which are naturally free of caffeine, such as Rooibos, may be more appropriate as a dietary supplement for managing emotional regulation over the lifetime.

Early Chronic Stress Induced Changes within the Locus Coeruleus in Sporadic Alzheimer's Disease

Chronic exposure to stress throughout the lifespan has been the focus of many studies on Alzheimer's disease (AD) because of the similarities between the biological mechanisms involved in chronic stress and the pathophysiology of AD. In fact, the earliest abnormality associated with the disease is the presence of phosphorylated tau protein in locus coeruleus neurons, a brain structure highly responsive to stress and perceived threat. Here, we introduce allostatic load as a useful concept for understanding many of the complex, interacting neuropathological changes involved in the AD degenerative process. In response to chronic stress, aberrant tau proteins that begin to accumulate within the locus coeruleus decades prior to symptom onset appear to represent a primary pathological event in the AD cascade, triggering a wide range of interacting brain changes involving neuronal excitotoxicity, endocrine alterations, inflammation, oxidative stress, and amyloid plaque exacerbation. While it is acknowledged that stress will not necessarily be the major precipitating factor in all cases, early tau-induced changes within the locus coeruleus-norepinephrine pathway suggests that a therapeutic window might exist for preventative measures aimed at managing stress and restoring balance within the HPA axis.

The Interaction Between Vascular Risk Factors, Cerebral Small Vessel Disease, and Amyloid Burden in Older Adults

BACKGROUND

Cerebral small vessel disease (SVD) and Alzheimer's disease pathology, namely amyloid-β (Aβ) deposition, commonly co-occur. Exactly how they interact remains uncertain.

OBJECTIVE

Using participants from the Alzheimer's Disease Neuroimaging Initiative (n = 216; mean age 73.29±7.08 years, 91 (42.1%) females), we examined whether the presence of vascular risk factors and/or baseline cerebral SVD was related to a greater burden of Aβ cross-sectionally, and at 24 months follow-up.

METHOD

Amyloid burden, assessed using 18F-florbetapir PET, was quantified as the global standardized uptake value ratio (SUVR). Multimodal imaging was used to strengthen the quantification of baseline SVD as a composite variable, which included white matter hyperintensity volume using MRI, and peak width of skeletonized mean diffusivity using diffusion tensor imaging. Structural equation modelling was used to analyze the associations between demographic factors, Apolipoprotein E ɛ4 carrier status, vascular risk factors, SVD burden and cerebral amyloid.

RESULTS

SVD burden had a direct association with Aβ burden cross-sectionally (coeff. = 0.229, p = 0.004), and an indirect effect over time (indirect coeff. = 0.235, p = 0.004). Of the vascular risk factors, a history of hypertension (coeff. = 0.094, p = 0.032) and a lower fasting glucose at baseline (coeff. = -0.027, p = 0.014) had a direct effect on Aβ burden at 24 months, but only the direct effect of glucose persisted after regularization.

CONCLUSION

While Aβ and SVD burden have an association cross-sectionally, SVD does not appear to directly influence the accumulation of Aβ longitudinally. Glucose regulation may be an important modifiable risk factor for Aβ accrual over time.

A metabolite panel that differentiates Alzheimer's disease from other dementia types

Introduction

Alzheimer's disease (AD) is associated with altered metabolites. This study aimed to determine the validity of using circulating metabolites to differentiate AD from other dementias.

Methods

Blood metabolites were measured in three data sets. Data set 1 (controls, 27; AD, 28) was used for analyzing differential metabolites. Data set 2 (controls, 93; AD, 92) was used to establish a diagnostic AD model with use of a metabolite panel. The model was applied to Data set 3 (controls, 76; AD, 76; other dementias, 205) to verify its capacity for differentiating AD from other dementias.

Results

Data set 1 revealed 7 upregulated and 77 downregulated metabolites. In Data set 2, a panel of 11 metabolites was included in a model that could distinguish AD from controls. In Data set 3, this panel was used to successfully differentiate AD from other dementias.

Discussion

This study revealed an AD‐specific panel of 11 metabolites that may be used for AD diagnosis.

Plasma High Density Lipoprotein Small Subclass is Reduced in Alzheimer's Disease Patients and Correlates with Cognitive Performance

Background:

The link between cholesterol and Alzheimer’s disease (AD) has received much attention, as evidence suggests high levels of cholesterol might be an AD risk factor. The carriage of cholesterol and lipids through the body is mediated via lipoproteins, some of which, particularly apolipoprotein E (ApoE), are intimately linked with AD. In humans, high density lipoprotein (HDL) is regarded as a “good” lipid complex due to its ability to enable clearance of excess cholesterol via ‘cholesterol reverse transport’, although its activities in the pathogenesis of AD are poorly understood. There are several subclasses of HDL; these range from the newly formed small HDL, to much larger HDL.

Objective:

We examined the major subclasses of HDL in healthy controls, mild cognitively impaired, and AD patients who were not taking statins to determine whether there were HDL profile differences between the groups, and whether HDL subclass levels correlated with plasma amyloid-β (Aβ) levels or brain Aβ deposition.

Methods:

Samples from AIBL cohort were used in this study. HDL subclass levels were assessed by Lipoprint while Aβ_1–42 levels were assessed by ELISA. Brain Aβ deposition was assessed by PET scan. Statistical analysis was performed using parametric and non-parametric tests.

Results:

We found that small HDL subclass is reduced in AD patients and it correlates with cognitive performance while plasma Aβ concentrations do not correlate with lipid profile or HDL subfraction levels.

Conclusion:

Our data indicate that AD patients exhibit altered plasma HDL profile and that HDL subclasses correlate with cognitive performances.

Role of Mitochondrial Dysfunction in the Pathology of Amyloid-β

Mitochondrial dysfunction has been widely reported in several neurodegenerative disorders, including in the brains of patients with Alzheimer's disease (AD), Parkinson's disease, and Huntington disease. An increasing number of studies have implicated altered glucose and energy metabolism in patients with AD. There is compelling evidence of abnormalities in some of the key mitochondrial enzymes involved in glucose metabolism, including the pyruvate dehydrogenase and α-ketoglutarate dehydrogenase complexes, which play a great significance role in the pathogenesis of AD. Changes in some of the enzyme activities of the mitochondria found in AD have been linked with the pathology of amyloid-β (Aβ). This review highlights the role of mitochondrial function in the production and clearance of Aβ and how the pathology of Aβ leads to a decrease in energy metabolism by affecting mitochondrial function.

Physical Exercise and Alzheimer's Disease: Effects on Pathophysiological Molecular Pathways of the Disease

Alzheimer’s disease (AD), the most common form of neurodegenerative dementia in adults worldwide, is a multifactorial and heterogeneous disorder characterized by the interaction of genetic and epigenetic factors and the dysregulation of numerous intracellular signaling and cellular/molecular pathways. The introduction of the systems biology framework is revolutionizing the study of complex diseases by allowing the identification and integration of cellular/molecular pathways and networks of interaction. Here, we reviewed the relationship between physical activity and the next pathophysiological processes involved in the risk of developing AD, based on some crucial molecular pathways and biological process dysregulated in AD: (1) Immune system and inflammation; (2) Endothelial function and cerebrovascular insufficiency; (3) Apoptosis and cell death; (4) Intercellular communication; (5) Metabolism, oxidative stress and neurotoxicity; (6) DNA damage and repair; (7) Cytoskeleton and membrane proteins; (8) Synaptic plasticity. Moreover, we highlighted the increasingly relevant role played by advanced neuroimaging technologies, including structural/functional magnetic resonance imaging, diffusion tensor imaging, and arterial spin labelling, in exploring the link between AD and physical exercise. Regular physical exercise seems to have a protective effect against AD by inhibiting different pathophysiological molecular pathways implicated in AD.

Increased Carotid Intima-Media Thickness was not Associated With Cognitive Dysfunction After Off-Pump Coronary Surgery in Older Adult Patients Without Carotid Stenosis

Increased carotid intima-media thickness (C-IMT), a marker of atherosclerosis, is known to be associated with cerebrovascular and cortical abnormalities and cognitive impairment. This prospective observational study investigated the association between increased C-IMT and postoperative cognitive dysfunction (POCD) in older adult patients undergoing off-pump coronary artery bypass surgery. A total of 201 patients (57 females, 144 males; >60 years) were classified into increased (n = 105) or normal (n = 96) C-IMT groups by a cut-off value of 0.9 mm (bilateral C-IMT mean). Cognitive function was serially assessed with the Korean Mini-Mental State Examination, and Korean Montreal Cognitive Assessment scores preoperatively and at 7 days and 3 months postoperatively. POCD was defined as the deterioration of 1 standard deviation in at least one of the postoperative tests compared with their corresponding baseline scores. Independent risk factors for POCD were evaluated using multivariable analysis. Overall, POCD occurred in 46 patients (23%) over the 3 months. The incidences of POCD at 7 days and 3 months after surgery were similar, and there was no difference in both Korean Mini-Mental State Examination and Korean Montreal Cognitive Assessment test scores before and after surgery between groups. Chronic obstructive lung disease and intraoperative hyperglycemia episodes (>180 mg/dL), but not increased C-IMT, were independent risk factors for POCD. Unlike in nonsurgical cohorts, increased C-IMT was not significantly associated with the occurrence of POCD in older adult patients undergoing off-pump coronary artery bypass surgery.

Caffeic acid protects against Aβ toxicity and prolongs lifespan in Caenorhabditis elegans models

Caffeic acid may alleviate Aβ-induced toxicity and increase lifespan by increasing signaling pathway-associated oxidative stress and regulating metabolism in C. elegans.

NCX1 and EAAC1 transporters are involved in the protective action of glutamate in an in vitro Alzheimer's disease-like model

Increasing evidence suggests that metabolic dysfunctions are at the roots of neurodegenerative disorders such as Alzheimer's disease (AD). In particular, defects in cerebral glucose metabolism, which have been often noted even before the occurrence of clinical symptoms and histopathological lesions, are now regarded as critical contributors to the pathogenesis of AD. Hence, the stimulation of energy metabolism, by enhancing the availability of specific metabolites, might be an alternative way to improve ATP synthesis and to positively affect AD progression. For instance, glutamate may serve as an intermediary metabolite for ATP synthesis through the tricarboxylic acid (TCA) cycle and the oxidative phosphorylation. We have recently shown that two transporters are critical for the anaplerotic use of glutamate: the Na⁺-dependent Excitatory Amino Acids Carrier 1 (EAAC1) and the Na⁺-Ca²⁺ exchanger 1 (NCX1). Therefore, in the present study, we established an AD-like phenotype by perturbing glucose metabolism in both primary rat cortical neurons and retinoic acid (RA)-differentiated SH-SY5Y cells, and we explored the potential of glutamate to halt cell damage by monitoring neurotoxicity, AD markers, ATP synthesis, cytosolic Ca²⁺ levels and EAAC1/NCX1 functional activities. We found that glutamate significantly increased ATP production and cell survival, reduced the increase of AD biomarkers (amyloid β protein and the hyperphosphorylated form of tau protein), and recovered the increase of NCX reverse-mode activity. The RNA silencing of either EAAC1 or NCX1 caused the loss of the beneficial effects of glutamate, suggesting the requirement of a functional interplay between these transporters for glutamate-induced protection. Remarkably, our results indicate, as proof-of-principle, that facilitating the use of alternative fuels, like glutamate, may be an effective approach to overcome deficits in glucose utilization and significantly slow down neuronal degenerative process in AD.

Implementation of Imaging Methods in Evaluation of T2DM-Correlated Brain Alterations and Cognitive Dysfunction

Introduction:

There has been mounting evidence that type 2 diabetes mellitus (T2DM) populations are prone to aberrant brain functionality and cognitive deficits. Hyperglycemic status and insulin resistance, among other factors, have been associated with compromised brain neural congruity, leading to lower cognitive performance.

Aim:

The aim of the present paper is to provide a comprehensive review of imaging techniques and their applicability in detection of brain changes in the setting of T2DM.

Methods:

A search of PubMed electronic database was followed. Primary search terms included “imaging methods”, “type 2 diabetes” and “cognitive impairment”.

Results:

A range of imaging modalities that can be of value in depiction of diabetes-mediated structural and functional brain aberrations.

Conclusion:

An increasingly body of research points to the adverse effect T2DM exerts on brain integrity and higher cognitive skills. Findings support the role of imaging techniques in delineation of brain divergence in middle-aged and older diabetic populations.

Higher physiological vulnerability to hypoxic exposure with advancing age in the human brain

The aging brain is associated with atrophy along with functional and metabolic changes. In this study, we examined age-related changes in resting brain functions and the vulnerability of brain physiology to hypoxic exposure in humans in vivo. Brain functions were examined in 81 healthy humans (aged 18-62 years) by acquisitions of gray and white matter volumes, cerebral blood flow, cerebral oxygen consumption, and concentrations of lactate, N-acetylaspartate, and glutamate+glutamine using magnetic resonance imaging and spectroscopy. We observed impaired cerebral blood flow reactivity in response to inhalation of hypoxic air (p = 0.029) with advancing age along with decreased cerebral oxygen consumption (p = 0.036), and increased lactate concentration (p = 0.009), indicating tissue hypoxia and impaired metabolism. Diminished resilience to hypoxia and consequently increased vulnerability to metabolic stress could be a key part of declining brain health with age. Furthermore, we observed increased resting cerebral lactate concentration with advancing age (p = 0.007), which might reflect inhibited brain clearance of waste products.

Review of Alterations in Perlecan-Associated Vascular Risk Factors in Dementia

Perlecan is a heparan sulfate proteoglycan protein in the extracellular matrix that structurally and biochemically supports the cerebrovasculature by dynamically responding to changes in cerebral blood flow. These changes in perlecan expression seem to be contradictory, ranging from neuroprotective and angiogenic to thrombotic and linked to lipid retention. This review investigates perlecan's influence on risk factors such as diabetes, hypertension, and amyloid that effect Vascular contributions to Cognitive Impairment and Dementia (VCID). VCID, a comorbidity with diverse etiology in sporadic Alzheimer's disease (AD), is thought to be a major factor that drives the overall clinical burden of dementia. Accordingly, changes in perlecan expression and distribution in response to VCID appears to be injury, risk factor, location, sex, age, and perlecan domain dependent. While great effort has been made to understand the role of perlecan in VCID, additional studies are needed to increase our understanding of perlecan's role in health and in cerebrovascular disease.

Dysregulation of CO2-Driven Heart-Rate Chemoreflex Is Related Closely to Impaired CO2 Dynamic Vasomotor Reactivity in Mild Cognitive Impairment Patients

BACKGROUND

Significant reduction of dynamic vasomotor reactivity (DVR) was recently reported in patients with amnestic mild cognitive impairment (MCI) relative to age-matched controls. These results were obtained via a novel approach that utilizes data-based predictive dynamic models to quantify DVR.

OBJECTIVE

Using the same methodological approach, we seek to quantify the dynamic effects of the CO2-driven chemoreflex and baroreflex upon heart-rate in order to examine their possible correlation with the observed DVR impairment in each MCI patient.

METHODS

The employed approach utilizes time-series data to obtain subject-specific predictive input-output models of the dynamic effects of changes in arterial blood pressure and end-tidal CO2 (putative "inputs") upon cerebral blood flow velocity in large cerebral arteries, cortical tissue oxygenation, and heart-rate (putative "outputs").

RESULTS

There was significant dysregulation of CO2-driven heart-rate chemoreflex (p = 0.0031), but not of baroreflex (p = 0.5061), in MCI patients relative to age-matched controls. The model-based index of CO2-driven heart-rate chemoreflex gain (CRG) correlated significantly with the DVR index in large cerebral arteries (p = 0.0146), but not with the DVR index in small/micro-cortical vessels (p = 0.1066). This suggests that DVR impairment in small/micro-cortical vessels is not mainly due to CO2-driven heart-rate chemoreflex dysregulation, but to other factors (possibly dysfunction of neurovascular coupling).

CONCLUSION

Improved delineation between MCI patients and controls is achieved by combining the DVR index for small/micro-cortical vessels with the CRG index (p = 2×10-5). There is significant correlation (p < 0.01) between neuropsychological test scores and model-based DVR indices. Combining neuropsychological scores with DVR indices reduces the composite diagnostic index p-value (p∼10-10).

Summative Effects of Vascular Risk Factors on the Progression of Alzheimer Disease

OBJECTIVES

To investigate the summative effects of vascular risk factors (VRFs) on the progression of Alzheimer disease (AD).

DESIGN

Longitudinal follow-up cohort study.

SETTING

AD patients from two teaching hospitals in Taiwan with 3-year follow-ups.

PARTICIPANTS

A total of 330 AD patients with a mean age of 80.7 years, a mean Mini-Mental State Examination (MMSE) score 18.7, and a mean Clinical Dementia Rating Sum of Boxes (CDRSB) score of 6.9.

MEASUREMENTS

All patients completed a clinically functional assessment and a neuropsychological test battery at baseline and yearly follow-ups. The VRF burden was combined into a summative VRF index at baseline (ie, having one, two, or more VRFs); VRFs included coronary heart disease, cardiac arrhythmia, hypertension, cerebrovascular disease, diabetes mellitus, obesity, smoking, and physical inactivity. The generalized estimating equation (GEE) method was used to analyze the correlations between the VRFs and longitudinal MMSE and CDRSB changes.

RESULTS

The results of the GEE adjusted for age, years of education, sex, disease duration, baseline MMSE score, time, apolipoprotein E (APOE) ε4 carrier status, use of medications (acetylcholinesterase inhibitors or N-methyl-D-aspartate receptor antagonists), and hospitalization rates and showed that patients with more than three VRFs had more rapid cognitive decline than patients without VRFs (MMSE, P = .02; CDRSB, P = .001) as well as patients with three or fewer VRFs (MMSE, P = .009; CDRSB, P = .02). Subsequent analyses of APOE ε4 carriers with more than three VRFs also showed their more rapid cognitive decline compared with patients without VRFs (MMSE, P = .02; CDRSB, P = .001) and patients with three or fewer VRFs (MMSE, P = .009; CDRSB, P = .02), but no significant difference was found in APOE ε4 noncarriers.

CONCLUSION

Multiple VRFs have summative effects on the progression of AD, especially in APOE ε4 carriers. J Am Geriatr Soc 68:129-136, 2019.

The Vascular Hypothesis of Alzheimer's Disease: A Key to Preclinical Prediction of Dementia Using Neuroimaging

The vascular hypothesis of Alzheimer's disease (VHAD) was proposed 24 years ago from observations made in our laboratory using aging rats subjected to chronic brain hypoperfusion. In recent years, VHAD has become a mother-lode to numerous neuroimaging studies targeting cerebral hemodynamic changes, particularly brain hypoperfusion in elderly patients at risk of developing Alzheimer's disease (AD). There is a growing consensus among neuroradiologists that brain hypoperfusion is likely involved in the pathogenesis of AD and that disturbed cerebral blood flow (CBF) can serve as a key biomarker for predicting conversion of mild cognitive impairment to AD. The use of cerebral hypoperfusion as a preclinical predictor of AD is becoming decisive in stratifying low and high risk patients that may develop cognitive decline and for assessing the effectiveness of therapeutic interventions. There is currently an international research drive from neuroimaging groups to seek new perspectives that can broaden our understanding of AD and improve lifestyle. Diverse neuroimaging methods are currently being used to monitor normal and dyscognitive brain activity. Some techniques are very powerful and can detect, diagnose, quantify, prognose, and predict cognitive decline before AD onset, even from a healthy cognitive state. Multimodal imaging offers new insights in the treatment and prevention of cognitive decline during advanced aging and better understanding of the functional and structural organization of the human brain. This review discusses the impact the VHAD and CBF are having on the neuroimaging technology that can usher practical strategies to help prevent AD.

Chinese Herbal Medicine Xueshuantong Enhances Cerebral Blood Flow and Improves Neural Functions in Alzheimer's Disease Mice

Reduced cerebral blood flow in Alzheimer's disease (AD) may occur in early AD, which contributes to the pathogenesis and/or pathological progression of AD. Reversing this deficit may have therapeutic potential. Certain traditional Chinese herbal medicines (e.g., Saponin and its major component Xueshuantong [XST]) increase blood flow in humans, but whether they could be effective in treating AD patients has not been tested. We found that systemic XST injection elevated cerebral blood flow in APP/PS1 transgenic mice using two-photon time-lapse imaging in the same microvessels before and after injection. Subchronic XST treatment led to improved spatial learning and memory and motor performance in the APP/PS1 mice, suggesting improved neural plasticity and functions. Two-photon time lapse imaging of the same plaques revealed a reduction in plaque size after XST treatment. In addition, western blots experiments showed that XST treatment led to reduced processing of amyloid-β protein precursor (AβPP) and enhanced clearance of amyloid-β (Aβ) without altering the total level of AβPP. We also found increased synapse density in the immediate vicinity of amyloid plaques, suggesting enhanced synaptic function. We conclude that targeting cerebral blood flow can be an effective strategy in treating AD.

Tortuous Paths of Insulin Signaling and Mitochondria in Alzheimer's Disease

Due to the exponential growth of aging population worldwide, neurodegenerative diseases became a major public health concern. Among them, Alzheimer's disease (AD) prevails as the most common in the elderly, rendering it a research priority. After several decades considering the brain as an insulin-insensitive organ, recent advances proved a central role for this hormone in learning and memory processes and showed that AD shares a high number of features with systemic conditions characterized by insulin resistance. Mitochondrial dysfunction has also been widely demonstrated to play a major role in AD development supporting the idea that this neurodegenerative disease is characterized by a pronounced metabolic dysregulation. This chapter is intended to discuss evidence demonstrating the key role of insulin signaling and mitochondrial anomalies in AD.

Does arterial hypertension influence the onset of Huntington's disease?

Huntington’s disease (HD) age of onset (AO) is mainly determined by the length of the CAG repeat expansion in the huntingtin gene. The remaining AO variability has been attributed to other little-known factors. A factor that has been associated with other neurodegenerative diseases is arterial hypertension (AHT). The aim of this study is to evaluate the contribution of AHT to the AO of HD. We used data from a cohort of 630 European HD patients with adult onset collected by the REGISTRY project of the European Huntington’s Disease Network. Multiple linear regression and ANOVA, controlling for the CAG repeat number of the expanded allele (CAGexp) of each patient, were performed to assess the association between the AHT condition and the AO of the motor symptoms (mAO). The results showed a significant association between AHT and mAO, especially when we only considered the patients diagnosed with AHT prior to manifesting any HD signs (pre-HD AHT). Remarkably, despite the low number of cases, those patients developed motor symptoms 5–8 years later than normotensive patients in the most frequent CAGexp range (40–44). AHT is an age-related condition and consequently, the age of the patient at the time of data collection could be a confounder variable. However, given that most pre-HD AHT patients included in our study had started treatment with antihypertensive drugs prior to the onset of HD, and that antihypertensive drugs have been suggested to confer a neuroprotective effect in other neurodegenerative diseases, raises the interest in elucidating the impact of AHT and/or AHT treatment in HD age of onset in further studies. A confirmation of our results in a larger sample set would open the possibility to significantly improve HD management.

Changes in Blood Factors and Ultrasound Findings in Mild Cognitive Impairment and Dementia

The present study aimed to assess the changes in blood factors and ultrasound measures of atherosclerosis burden patient with mild cognitive impairment (MCI) and dementia. Peripheral blood samples and ultrasonography findings were obtained for 53 enrolled participants. Flow cytometry was used to evaluate levels of activated platelets and platelet-leukocyte aggregates (PLAs). The number of platelets expressing p-selectin was correlated with intima media thickness (IMT) and plaque number in both the MCI and dementia groups. The number of platelets expressing p-selectin glycoprotein ligand (PSGL) was strongly correlated with IMT in patients with MCI, whereas the number of platelets expressing PGSL was correlated with plaque number rather than IMT in patients with dementia. PLAs was associated with both IMT and plaque number in patients with MCI but not in those with dementia. Our findings demonstrate that alterations in IMT and plaque number are associated with an increased risk of cognitive decline as well as conversion from MCI to dementia and that blood factor analysis may aid to detect the severity of cognitive decline.

Evaluation of Metabolic and Synaptic Dysfunction Hypotheses of Alzheimer's Disease (AD): A Meta-Analysis of CSF Markers

BACKGROUND

Alzheimer's disease (AD) is currently incurable and a majority of investigational drugs have failed clinical trials. One explanation for this failure may be the invalidity of hypotheses focusing on amyloid to explain AD pathogenesis. Recently, hypotheses which are centered on synaptic and metabolic dysfunction are increasingly implicated in AD.

OBJECTIVE

Evaluate AD hypotheses by comparing neurotransmitter and metabolite marker concentrations in normal versus AD CSF.

METHODS

Meta-analysis allows for statistical comparison of pooled, existing cerebrospinal fluid (CSF) marker data extracted from multiple publications, to obtain a more reliable estimate of concentrations. This method also provides a unique opportunity to rapidly validate AD hypotheses using the resulting CSF concentration data. Hubmed, Pubmed and Google Scholar were comprehensively searched for published English articles, without date restrictions, for the keywords "AD", "CSF", and "human" plus markers selected for synaptic and metabolic pathways. Synaptic markers were acetylcholine, gamma-aminobutyric acid (GABA), glutamine, and glycine. Metabolic markers were glutathione, glucose, lactate, pyruvate, and 8 other amino acids. Only studies that measured markers in AD and controls (Ctl), provided means, standard errors/deviation, and subject numbers were included. Data were extracted by six authors and reviewed by two others for accuracy. Data were pooled using ratio of means (RoM of AD/Ctl) and random effects meta-analysis using Cochrane Collaboration's Review Manager software.

RESULTS

Of the 435 identified publications, after exclusion and removal of duplicates, 35 articles were included comprising a total of 605 AD patients and 585 controls. The following markers of synaptic and metabolic pathways were significantly changed in AD/controls: acetylcholine (RoM 0.36, 95% CI 0.24-0.53, p<0.00001), GABA (0.74, 0.58-0.94, p<0.01), pyruvate (0.48, 0.24-0.94, p=0.03), glutathione (1.11, 1.01- 1.21, p=0.03), alanine (1.10, 0.98-1.23, p=0.09), and lower levels of significance for lactate (1.2, 1.00-1.47, p=0.05). Of note, CSF glucose and glutamate levels in AD were not significantly different than that of the controls.

CONCLUSION

This study provides proof of concept for the use of meta-analysis validation of AD hypotheses, specifically via robust evidence for the cholinergic hypothesis of AD. Our data disagree with the other synaptic hypotheses of glutamate excitotoxicity and GABAergic resistance to neurodegeneration, given observed unchanged glutamate levels and decreased GABA levels. With regards to metabolic hypotheses, the data supported upregulation of anaerobic glycolysis, pentose phosphate pathway (glutathione), and anaplerosis of the tricarboxylic acid cycle using glutamate. Future applications of meta-analysis indicate the possibility of further in silico evaluation and generation of novel hypotheses in the AD field.

Regional association of pCASL-MRI with FDG-PET and PiB-PET in people at risk for autosomal dominant Alzheimer's disease

Autosomal dominant Alzheimer's disease (ADAD) is a small subset of Alzheimer's disease that is genetically determined with 100% penetrance. It provides a valuable window into studying the course of pathologic processes that leads to dementia. Arterial spin labeling (ASL) MRI is a potential AD imaging marker that non-invasively measures cerebral perfusion. In this study, we investigated the relationship of cerebral blood flow measured by pseudo-continuous ASL (pCASL) MRI with measures of cerebral metabolism (FDG PET) and amyloid deposition (Pittsburgh Compound B (PiB) PET). Thirty-one participants at risk for ADAD (age 39 ± 13 years, 19 females) were recruited into this study, and 21 of them received both MRI and FDG and PiB PET scans. Considerable variability was observed in regional correlations between ASL-CBF and FDG across subjects. Both regional hypo-perfusion and hypo-metabolism were associated with amyloid deposition. Cross-sectional analyses of each biomarker as a function of the estimated years to expected dementia diagnosis indicated an inverse relationship of both perfusion and glucose metabolism with amyloid deposition during AD development. These findings indicate that neurovascular dysfunction is associated with amyloid pathology, and also indicate that ASL CBF may serve as a sensitive early biomarker for AD. The direct comparison among the three biomarkers provides complementary information for understanding the pathophysiological process of AD.

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Regional associations of three imaging biomarkers (pCASL-MRI, FDG-PET and PiB-PET) are studied in persons at risk for ADAD.

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PiB-PET shows different spatial pattern compared to pCASL-MRI and FDG-PET.

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There is considerable variability among regional correlations between pCASL and FDG.

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Both regional hypo-perfusion and hypo-metabolism are associated with amyloid deposition.

A Translational Systems Pharmacology Model for Aβ Kinetics in Mouse, Monkey, and Human

A mechanistic model of amyloid beta production, degradation, and distribution was constructed for mouse, monkey, and human, calibrated and externally verified across multiple datasets. Simulations of single‐dose avagacestat treatment demonstrate that the Aβ₄₂ brain inhibition may exceed that in cerebrospinal fluid (CSF). The dose that achieves 50% CSF Aβ₄₀ inhibition for humans (both healthy and with Alzheimer's disease (AD)) is about 1 mpk, one order of magnitude lower than for mouse (10 mpk), mainly because of differences in pharmacokinetics. The predicted maximal percent of brain Aβ₄₂ inhibition after single‐dose avagacestat is higher for AD subjects (about 60%) than for healthy individuals (about 45%). The probability of achieving a normal physiological level for Aβ₄₂ in brain (1 nM) during multiple avagacestat dosing can be increased by using a dosing regimen that achieves higher exposure. The proposed model allows prediction of brain pharmacodynamics for different species given differing dosing regimens.

DNA-PK and P38 MAPK: A Kinase Collusion in Alzheimer's Disease?

The pathogenesis of Alzheimer's disease (AD), characterized by prevalent neuronal death and extracellular deposit of amyloid plaques, is poorly understood. DNA lesions downstream of reduced DNA repair ability have been reported in AD brains. Neurons predominantly use a mechanism to repair double-strand DNA breaks (DSB), which is non-homologous end joining (NHEJ). NHEJ requires DNA-dependent protein kinase (DNA-PK) activity. DNA-PK is a holoenzyme comprising the p460 kD catalytic subunit (DNA-PKcs) and its activator Ku, a heterodimer of p86 and p70 subunits. Ku first binds and then recruits DNA-PKcs to double-stranded DNA ends before NHEJ process begins. Studies have shown reduced NHEJ activity as well as DNA-PKcs and Ku protein levels in AD brains suggesting possible contribution of unrepaired DSB to AD development. However, normal aging brains also show reduced DNA-PKcs and Ku levels thus challenging the notion of any direct link between NHEJ and AD. Another kinase, p38 MAPK is induced by various DNA damaging agents and DSB itself. Increased DNA damage with aging could induce p38 MAPK and its induction may be sustained when DNA repair is compromised in the brain with reduced DNA-PK activity. Combined, these two events may potentially set the stage for an awry nervous system approaching AD.

Comparison of Model-Based Indices of Cerebral Autoregulation and Vasomotor Reactivity Using Transcranial Doppler versus Near-Infrared Spectroscopy in Patients with Amnestic Mild Cognitive Impairment

We recently introduced model-based "physiomarkers" of dynamic cerebral autoregulation and CO2 vasomotor reactivity as an aid for diagnosis of early-stage Alzheimer's disease (AD) [1], where significant impairment of dynamic vasomotor reactivity (DVR) was observed in early-stage AD patients relative to age-matched controls. Milder impairment of DVR was shown in patients with amnestic mild cognitive impairment (MCI) using the same approach in a subsequent study [2]. The advocated approach utilizes subject-specific data-based models of cerebral hemodynamics to quantify the dynamic effects of resting-state changes in arterial blood pressure and end-tidal CO2 (the putative inputs) upon cerebral blood flow velocity (the putative output) measured at the middle cerebral artery via transcranial Doppler (TCD). The obtained input-output models are then used to compute model-based indices of DCA and DVR from model-predicted responses to an input pressure pulse or an input CO2 pulse, respectively. In this paper, we compare these model-based indices of DVR and DCA in 46 amnestic MCI patients, relative to 20 age-matched controls, using TCD measurements with their counterparts using Near-Infrared Spectroscopy (NIRS) measurements of blood oxygenation at the lateral prefrontal cortex in 43 patients and 22 age-matched controls. The goal of the study is to assess whether NIRS measurements can be used instead of TCD measurements to obtain model-based physiomarkers with comparable diagnostic utility. The results corroborate this view in terms of the ability of either output to yield model-based physiomarkers that can differentiate the group of aMCI patients from age-matched healthy controls.

Cerebral hypoperfusion and glucose hypometabolism: Key pathophysiological modulators promote neurodegeneration, cognitive impairment, and Alzheimer's disease

Aging, hypertension, diabetes, hypoxia/obstructive sleep apnea (OSA), obesity, vitamin B12/folate deficiency, depression, and traumatic brain injury synergistically promote diverse pathological mechanisms including cerebral hypoperfusion and glucose hypometabolism. These risk factors trigger neuroinflammation and oxidative-nitrosative stress that in turn decrease nitric oxide and enhance endothelin, Amyloid-β deposition, cerebral amyloid angiopathy, and blood-brain barrier disruption. Proinflammatory cytokines, endothelin-1, and oxidative-nitrosative stress trigger several pathological feedforward and feedback loops. These upstream factors persist in the brain for decades, upregulating amyloid and tau, before the cognitive decline. These cascades lead to neuronal Ca²⁺ increase, neurodegeneration, cognitive/memory decline, and Alzheimer's disease (AD). However, strategies are available to attenuate cerebral hypoperfusion and glucose hypometabolism and ameliorate cognitive decline. AD is the leading cause of dementia among the elderly. There is significant evidence that pathways involving inflammation and oxidative-nitrosative stress (ONS) play a key pathophysiological role in promoting cognitive dysfunction. Aging and several comorbid conditions mentioned above promote diverse pathologies. These include inflammation, ONS, hypoperfusion, and hypometabolism in the brain. In AD, chronic cerebral hypoperfusion and glucose hypometabolism precede decades before the cognitive decline. These comorbid disease conditions may share and synergistically activate these pathophysiological pathways. Inflammation upregulates cerebrovascular pathology through proinflammatory cytokines, endothelin-1, and nitric oxide (NO). Inflammation-triggered ONS promotes long-term damage involving fatty acids, proteins, DNA, and mitochondria; these amplify and perpetuate several feedforward and feedback pathological loops. The latter includes dysfunctional energy metabolism (compromised mitochondrial ATP production), amyloid-β generation, endothelial dysfunction, and blood-brain-barrier disruption. These lead to decreased cerebral blood flow and chronic cerebral hypoperfusion- that would modulate metabolic dysfunction and neurodegeneration. In essence, hypoperfusion deprives the brain from its two paramount trophic substances, viz., oxygen and nutrients. Consequently, the brain suffers from synaptic dysfunction and neuronal degeneration/loss, leading to both gray and white matter atrophy, cognitive dysfunction, and AD. This Review underscores the importance of treating the above-mentioned comorbid disease conditions to attenuate inflammation and ONS and ameliorate decreased cerebral blood flow and hypometabolism. Additionally, several strategies are described here to control chronic hypoperfusion of the brain and enhance cognition. © 2016 Wiley Periodicals, Inc.

Endocrine Risk Factors for Cognitive Impairment

Cognitive impairment, including Alzheimer's disease and other kinds of dementia, is a major health problem in older adults worldwide. Although numerous investigators have attempted to develop effective treatment modalities or drugs, there is no reasonably efficacious strategy for preventing or recovering from cognitive impairment. Therefore, modifiable risk factors for cognitive impairment have received attention, and the growing literature of metabolic risk factors for cognitive impairment has expanded from epidemiology to molecular pathogenesis and therapeutic management. This review focuses on the epidemiological evidence for the association between cognitive impairment and several endocrine risk factors, including insulin resistance, dyslipidemia, thyroid dysfunction, vitamin D deficiency, and subclinical atherosclerosis. Researches suggesting possible mechanisms for this association are reviewed. The research investigating modifiable endocrine risk factors for cognitive impairment provides clues for understanding the pathogenesis of cognitive impairment and developing novel treatment modalities. However, so far, interventional studies investigating the beneficial effect of the "modification" of these "modifiable risk factors" on cognitive impairment have reported variable results. Therefore, well-designed, randomized prospective interventional studies are needed.

The Role of Sleep and Sleep Disorders in the Development, Diagnosis, and Management of Neurocognitive Disorders

It is becoming increasingly apparent that sleep plays an important role in the maintenance, disease prevention, repair, and restoration of both mind and body. The sleep and wake cycles are controlled by the pacemaker activity of the superchiasmic nucleus in the hypothalamus but can be disrupted by diseases of the nervous system causing disordered sleep. A lack of sleep has been associated with an increase in all-cause mortality. Likewise, sleep disturbances and sleep disorders may disrupt neuronal pathways and have an impact on neurological diseases. Sleep deprivation studies in normal subjects demonstrate that a lack of sleep can cause attention and working memory impairment. Moreover, untreated sleep disturbances and sleep disorders such as obstructive sleep apnoe (OSA) can also lead to cognitive impairment. Poor sleep and sleep disorders may present a significant risk factor for the development of dementia. In this review, the underlying mechanisms and the role of sleep and sleep disorders in the development of neurocognitive disorders [dementia and mild cognitive impairment (MCI)] and how the presence of sleep disorders could direct the process of diagnosis and management of neurocognitive disorders will be discussed.

Different Brain Regions are Infected with Fungi in Alzheimer's Disease

The possibility that Alzheimer's disease (AD) has a microbial aetiology has been proposed by several researchers. Here, we provide evidence that tissue from the central nervous system (CNS) of AD patients contain fungal cells and hyphae. Fungal material can be detected both intra- and extracellularly using specific antibodies against several fungi. Different brain regions including external frontal cortex, cerebellar hemisphere, entorhinal cortex/hippocampus and choroid plexus contain fungal material, which is absent in brain tissue from control individuals. Analysis of brain sections from ten additional AD patients reveals that all are infected with fungi. Fungal infection is also observed in blood vessels, which may explain the vascular pathology frequently detected in AD patients. Sequencing of fungal DNA extracted from frozen CNS samples identifies several fungal species. Collectively, our findings provide compelling evidence for the existence of fungal infection in the CNS from AD patients, but not in control individuals.

Angiotensin receptor blockers and risk of dementia: cohort study in UK Clinical Practice Research Datalink

Aims

This was a cohort study to evaluate whether individuals exposed to angiotensin receptor blockers have a reduced risk of dementia compared with those exposed to angiotensin-converting enzyme inhibitors.

Methods

The study included new users of angiotensin receptor blockers or angiotensin-converting enzyme inhibitors (from 1995 to 2010) from UK primary care practices contributing to the Clinical Research Practice Datalink. The association between exposure to angiotensin receptor blockers and the risk of incident dementia was analysed using a Cox model, adjusting for age, sex, body mass index, diabetes, hypertension, heart failure, statin use, socioeconomic status, alcohol, smoking, number of consultations and calendar year.

Results

A total of 426 089 persons were included in the primary analysis, with 45 541 persons exposed to angiotensin receptor blockers and the remainder to angiotensin-converting enzyme inhibitors. The total number of new diagnoses of dementia was 6517. There was weak evidence of a decreased risk of dementia with exposure to angiotensin receptor blockers, with follow-up beginning at 1 year after the start of treatment (adjusted hazard ratio 0.92, 95% confidence interval 0.85–1.00). An analysis restricted to the first 12 months after the index date showed a larger effect on dementia risk (adjusted hazard ratio 0.60, 95% confidence interval 0.50–0.72).

Conclusions

A small reduction in dementia risk was seen with angiotensin receptor blockers in comparison to angiotensin-converting enzyme inhibitors. However, the strongest association was seen in early follow-up, suggesting that the inverse association is unlikely to be causal, but instead reflects other important but unmeasured differences between angiotensin receptor blocker and angiotensin-converting enzyme inhibitor users.

Insulin resistance predicts brain amyloid deposition in late middle-aged adults

BACKGROUND

Insulin resistance (IR) increases Alzheimer's disease (AD) risk. IR is related to greater amyloid burden post-mortem and increased deposition within areas affected by early AD. No studies have examined if IR is associated with an in vivo index of amyloid in the human brain in late middle-aged participants at risk for AD.

METHODS

Asymptomatic, late middle-aged adults (N = 186) from the Wisconsin Registry for Alzheimer's Prevention underwent [C-11]Pittsburgh compound B (PiB) positron emission tomography. The cross-sectional design tested the interaction between insulin resistance and glycemic status on PiB distribution volume ratio in three regions of interest (frontal, parietal, and temporal).

RESULTS

In participants with normoglycemia but not hyperglycemia, higher insulin resistance corresponded to higher PiB uptake in frontal and temporal areas, reflecting increased amyloid deposition.

CONCLUSIONS

This is the first human study to demonstrate that insulin resistance may contribute to amyloid deposition in brain regions affected by AD.

Flos Puerariae Extract Ameliorates Cognitive Impairment in Streptozotocin-Induced Diabetic Mice

Objective. The effects of Flos Puerariae extract (FPE) on cognitive impairment associated with diabetes were assessed in C57BL/6J mice. Methods. Experimental diabetic mice model was induced by one injection of 50 mg/kg streptozotocin (STZ) for 5 days consecutively. FPE was orally administrated at the dosages of 50, 100, or 200 mg/kg/day, respectively. The learning and memory ability was assessed by Morris water maze test. Body weight, blood glucose, free fatty acid (FFA) and total cholesterol (TCH) in serum, malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and acetylcholinesterase (AChE) activities in cerebral cortex and hippocampus were also measured. Results. Oral administration of FPE significantly improved cognitive deficits in STZ-induced diabetic mice. FPE treatment also maintained body weight and ameliorated hyperglycemia and dyslipidemia in diabetic mice. Additionally, decreased MDA level, enhanced CAT, and GSH-Px activities in cerebral cortex or hippocampus, as well as alleviated AChE activity in cerebral cortex, were found in diabetic mice supplemented with FPE. Conclusion. This study suggests that FPE ameliorates memory deficits in experimental diabetic mice, at least partly through the normalization of metabolic abnormalities, ameliorated oxidative stress, and AChE activity in brain.

Carotid intima-media thickness is associated with the progression of cognitive impairment in older adults

BACKGROUND AND PURPOSE

We investigated the association between cardiovascular risk factors, including carotid intima-media thickness (CIMT), and future risk of mild cognitive impairment (MCI) and dementia in elderly subjects.

METHODS

We conducted a population-based prospective study as a part of the Korean Longitudinal Study on Health and Aging. Our study included 348 participants who were nondemented at the baseline (mean age, 71.7±6.3 years) and underwent cognitive evaluation at the 5-year follow-up. Baseline cardiovascular risk factors were compared according to the development of MCI or dementia during the study period.

RESULTS

At the baseline evaluation, 278 subjects were cognitively normal and 70 subjects had MCI. Diagnoses of cognitive function either remained unchanged or improved during the study period in 292 subjects (nonprogression group), whereas 56 subjects showed progression of cognitive impairment to MCI or dementia (progression group). The progression group exhibited a higher prevalence of hypertension and greater CIMT compared with the nonprogression group. Other baseline cardiovascular risk factors, including sex, body mass index, diabetes mellitus, insulin resistance, total cholesterol, waist-to-hip ratio, visceral fat, pulse wave velocity, and ankle-brachial index, were not significantly different between 2 groups. The association between greater baseline CIMT and the progression of cognitive impairment was maintained after adjustment for conventional baseline risk factors of cognitive impairment. Greater baseline CIMT was also independently associated with the development of MCI in the subjects whose baseline cognitive function was normal.

CONCLUSIONS

Greater baseline CIMT was independently associated with the risk of cognitive impairment, such as MCI and dementia in elderly subjects.

Increased cerebral vascular reactivity in the tau expressing rTg4510 mouse: evidence against the role of tau pathology to impair vascular health in Alzheimer's disease

Vascular abnormalities are a key feature of Alzheimer's disease (AD). Imaging of cerebral vascular reactivity (CVR) is a powerful tool to investigate vascular health in clinical populations although the cause of reduced CVR in AD patients is not fully understood. We investigated the specific role of tau pathology in CVR derangement in AD using the rTg4510 mouse model. We observed an increase in CVR in cortical regions with tau pathology. These data suggest that tau pathology alone does not produce the clinically observed decreases in CVR and implicates amyloid pathology as the dominant etiology of impaired CVR in AD patients.

Cerebrovascular and mitochondrial abnormalities in Alzheimer's disease: a brief overview

Multiple lines of evidence suggest that vascular alterations contribute to Alzheimer's disease (AD) pathogenesis. It is also well established that mitochondrial abnormalities occur early in course of AD. Here, we give an overview of the vascular and mitochondrial abnormalities occurring in AD, including mitochondrial alterations in vascular endothelial cells within the brain, which is emerging as a common feature that bridges cerebral vasculature and mitochondrial metabolism.

A viral vector expressing hypoxia-inducible factor 1 alpha inhibits hippocampal neuronal apoptosis

Hypoxia-inducible factor 1 (HIF-1) attenuates amyloid-beta protein neurotoxicity and decreases apoptosis induced by oxidative stress or hypoxia in cortical neurons. In this study, we constructed a recombinant adeno-associated virus (rAAV) vector expressing the human HIF-1α gene (rAAV-HIF-1α), and tested the assumption that rAAV-HIF-1α represses hippocampal neuronal apoptosis induced by amyloid-beta protein. Our results confirmed that rAAV-HIF-1α significantly reduces apoptosis induced by amyloid-beta protein in primary cultured hippocampal neurons. Direct intracerebral rAAV-HIF-1α administration also induced robust and prolonged HIF-1α production in rat hippocampus. Single rAAV-HIF-1α administration resulted in decreased apoptosis of hippocampal neurons in an Alzheimer's disease rat model established by intracerebroventricular injection of aggregated amyloid-beta protein (25-35). Our in vitro and in vivo findings demonstrate that HIF-1 has potential for attenuating hippocampal neuronal apoptosis induced by amyloid-beta protein, and provides experimental support for treatment of neurodegenerative diseases using gene therapy.

Is Alzheimer's disease related to metabolic syndrome? A Wnt signaling conundrum

Alzheimer's disease (AD) is the most common cause of dementia, affecting more than 36 million people worldwide. AD is characterized by a progressive loss of cognitive functions. For years, it has been thought that age is the main risk factor for AD. Recent studies suggest that life style factors, including nutritional behaviors, play a critical role in the onset of dementia. Evidence about the relationship between nutritional behavior and AD includes the role of conditions such as obesity, hypertension, dyslipidemia and elevated glucose levels. The coexistence of some of these cardio-metabolic risk factors is generally known as metabolic syndrome (MS). Some clinical studies support the role of MS in the onset of AD. However, the cross-talk between the molecular signaling implicated in these disorders is unknown. In the present review, we focus on the molecular correlates that support the relationship between MS and the onset of AD. We also discuss relevant issues such as the role of leptin, insulin and renin-angiotensin signaling in the brain and the possible role of Wnt signaling in both MS and AD. We discuss the evidence supporting the use of ob/ob mice, high-fructose diets, aortic coarctation-induced hypertension and Octodon degus, which spontaneously develops β-amyloid deposits and metabolic derangements, as suitable animal models to address the relationships between MS and AD. Finally, we examine emergent data supporting the role of Wnt signaling in the modulation of AD and MS, implicating this pathway as a therapeutic target in both conditions.

Repair of oxidative DNA damage, cell-cycle regulation and neuronal death may influence the clinical manifestation of Alzheimer's disease

Alzheimer’s disease (AD) is characterized by progressive cognitive decline associated with a featured neuropathology (neuritic plaques and neurofibrillary tangles). Several studies have implicated oxidative damage to DNA, DNA repair, and altered cell-cycle regulation in addition to cell death in AD post-mitotic neurons. However, there is a lack of studies that systematically assess those biological processes in patients with AD neuropathology but with no evidence of cognitive impairment. We evaluated markers of oxidative DNA damage (8-OHdG, H2AX), DNA repair (p53, BRCA1, PTEN), and cell-cycle (Cdk1, Cdk4, Cdk5, Cyclin B1, Cyclin D1, p27^Kip1, phospho-Rb and E2F1) through immunohistochemistry and cell death through TUNEL in autopsy hippocampal tissue samples arrayed in a tissue microarray (TMA) composed of three groups: I) “clinical-pathological AD” (CP-AD) - subjects with neuropathological AD (Braak≥IV and CERAD = B or C) and clinical dementia (CDR≥2, IQCODE>3.8); II) “pathological AD” (P-AD) - subjects with neuropathological AD (Braak≥IV and CERAD = B or C) and without cognitive impairment (CDR 0, IQCODE<3.2); and III) “normal aging” (N) - subjects without neuropathological AD (Braak≤II and CERAD 0 or A) and with normal cognitive function (CDR 0, IQCODE<3.2). Our results show that high levels of oxidative DNA damage are present in all groups. However, significant reductions in DNA repair and cell-cycle inhibition markers and increases in cell-cycle progression and cell death markers in subjects with CP-AD were detected when compared to both P-AD and N groups, whereas there were no significant differences in the studied markers between P-AD individuals and N subjects. This study indicates that, even in the setting of pathological AD, healthy cognition may be associated with a preserved repair to DNA damage, cell-cycle regulation, and cell death in post-mitotic neurons.

Model-based physiomarkers of cerebral hemodynamics in patients with mild cognitive impairment

In our previous studies, we have introduced model-based "functional biomarkers" or "physiomarkers" of cerebral hemodynamics that hold promise for improved diagnosis of early-stage Alzheimer's disease (AD). The advocated methodology utilizes subject-specific data-based dynamic nonlinear models of cerebral hemodynamics to compute indices (serving as possible diagnostic physiomarkers) that quantify the state of cerebral blood flow autoregulation to pressure-changes (CFAP) and cerebral CO2 vasomotor reactivity (CVMR) in each subject. The model is estimated from beat-to-beat measurements of mean arterial blood pressure, mean cerebral blood flow velocity and end-tidal CO2, which can be made reliably and non-invasively under resting conditions. In a previous study, it was found that a CVMR index quantifying the impairment in CO2 vasomotor reactivity correlates with clinical indications of early AD, offering the prospect of a potentially useful diagnostic tool. In this paper, we explore the use of the same model-based indices for patients with amnestic Mild Cognitive Impairment (MCI), a preclinical stage of AD, relative to a control subjects and clinical cognitive assessments. It was found that the model-based CVMR values were lower for MCI patients relative to the control subjects.

Pharmacogenomics of Alzheimer's disease: novel therapeutic strategies for drug development

Alzheimer's disease (AD) is a major problem of health and disability, with a relevant economic impact on our society. Despite important advances in pathogenesis, diagnosis, and treatment, its primary causes still remain elusive, accurate biomarkers are not well characterized, and the available pharmacological treatments are not cost-effective. As a complex disorder, AD is a polygenic and multifactorial clinical entity in which hundreds of defective genes distributed across the human genome may contribute to its pathogenesis. Diverse environmental factors, cerebrovascular dysfunction, and epigenetic phenomena, together with structural and functional genomic dysfunctions, lead to amyloid deposition, neurofibrillary tangle formation, and premature neuronal death, the major neuropathological hallmarks of AD. Future perspectives for the global management of AD predict that genomics and proteomics may help in the search for reliable biomarkers. In practical terms, the therapeutic response to conventional drugs (cholinesterase inhibitors, multifactorial strategies) is genotype-specific. Genomic factors potentially involved in AD pharmacogenomics include at least five categories of gene clusters: (1) genes associated with disease pathogenesis; (2) genes associated with the mechanism of action of drugs; (3) genes associated with drug metabolism (phase I and II reactions); (4) genes associated with drug transporters; and (5) pleiotropic genes involved in multifaceted cascades and metabolic reactions. The implementation of pharmacogenomic strategies will contribute to optimize drug development and therapeutics in AD and related disorders.

Personalized Medicine of Alzheimer’s Disease

Alzheimer’s disease (AD) is a major problem of health and disability, with a relevant economic impact on society (e.g., €177 billion in Europe). Despite important advances in pathogenesis, diagnosis, and treatment, The primary causes of AD remain elusive, accurate biomarkers are not well characterized, and available pharmacological treatments are not cost-effective. As a complex disorder, AD is polygenic and multifactorial: hundreds of defective genes distributed across the human genome may contribute to its pathogenesis (with the participation of diverse environmental factors, cerebrovascular dysfunction, and epigenetic phenomena) and lead to amyloid deposition, neurofibrillary tangle formation, and premature neuronal death. Future perspectives for the global management of AD predict that structural and functional genomics and proteomics may help in the search for reliable biomarkers, and that pharmacogenomics may be an option in optimizing drug development and therapeutics.

Glutathione prevents free fatty acids-induced oxidative stress and apoptosis in human brain vascular endothelial cells through Akt pathway

AIMS

The damage of human brain vascular endothelial cells (HBVECs) is the key pathogenesis of diabetes-associated cerebral vascular complications. The aim of this study was to elucidate the effects of glutathione (GSH) on free fatty acids (FFAs)-induced HBVECs apoptosis, oxidative stress, and the involved possible signaling pathway.

METHODS

After culturing HBVECs for 72 h with GSH and FFAs, we determined cell proliferation by CCK8, detected apoptosis by caspase-3 and Annexin V-FITC/PI staining, and judged oxygen stress by determining the reactive oxygen species (ROS) and the mitochondrial membrane potential (MMP). We investigated whether the Akt pathway was involved in FFAs-induced signaling pathway alteration and whether GSH influenced the above effects.

RESULTS

After being cultured in 200 μM FFAs for 72 h, the HBVECs proliferation significantly decreased; HBVECs apoptosis increased; the ROS levels increased; and the HBVECs MMP subsequently decreased. FFAs induced a significant decrease in phosphorylated active Akt. These alterations were obviously prevented when 1 mM GSH was added to culture medium containing FFAs, and the above effects of GSH were blocked by Akt inhibitor.

CONCLUSION

GSH may prevent FFAs-induced HBVECs damage, oxidative stress, and apoptosis through activating the Akt pathway.

β-Amyloid-induced cognitive dysfunction impairs glucose homeostasis by increasing insulin resistance and decreasing β-cell mass in non-diabetic and diabetic rats

OBJECTIVE

β-Amyloid accumulation in the brain may impair glucose homeostasis in both the brain and peripheral tissues. The present study investigated whether β-amyloid deposition in the hippocampus impairs glucose homeostasis by altering insulin sensitivity, glucose-stimulated insulin secretion or β-cell mass.

METHODS

Male rats were divided into two groups: a non-diabetic sham group and a diabetic partial pancreatectomized (Px) group. Each group was then subdivided into three treatment groups that received intra-CA1 infusions of β-amyloid (25-35; AMY), β-amyloid (35-25; RAMY; non-plaque forming), or saline at a rate of 3.6 nmol/day for 14 days.

RESULTS

After 4weeks, cognitive function measured by passive avoidance and water maze tests was impaired in non-diabetic rats that received AMY compared with rats that received saline or RAMY. Furthermore, diabetes exacerbated cognitive dysfunction in AMY-infused rats. This was associated with the hyperphosphorylation of tau as a result of attenuated insulin signaling (pAkt→pGSK) through decreased phosphorylation of cAMP responding element binding protein in the hippocampus of non-diabetic and diabetic rats. AMY exacerbated whole-body and hepatic insulin resistance in non-diabetic and diabetic rats. However, AMY potentiated glucose-stimulated insulin secretion in non-diabetic and diabetic rats, but caused decreased β-cell mass via increased β-cell apoptosis and decreased β-cell proliferation. As a result, glucose homeostasis was maintained by potentiating insulin secretion in diabetic rats, but may not be sustainable with further decreases in β-cell mass.

CONCLUSION

Cognitive dysfunction attributable to β-amyloid accumulation in the hippocampus might be related to disturbed glucose homeostasis due to increased insulin resistance and decreased β-cell mass.

Model-based quantification of cerebral hemodynamics as a physiomarker for Alzheimer's disease?

Previous studies have found that Alzheimer's disease (AD) impairs cerebral vascular function, even at early stages of the disease. This offers the prospect of a useful diagnostic method for AD, if cerebral vascular dysfunction can be quantified reliably within practical clinical constraints. We present a recently developed methodology that utilizes a data-based dynamic nonlinear closed-loop model of cerebral hemodynamics to compute "physiomarkers" quantifying the state of cerebral flow autoregulation to pressure-changes (CA) and cerebral CO2 vasomotor reactivity (CVMR) in each subject. This model is estimated from beat-to-beat measurements of mean arterial blood pressure, mean cerebral blood flow velocity and end-tidal CO2, which can be made reliably and non-invasively under resting conditions. This model may also take an open-loop form and comparisons are made with the closed-loop counterpart. The proposed model-based physiomarkers take the form of two indices that quantify the gain of the CA and CVMR processes in each subject. It was found in an initial set of clinical data that the CVMR index delineates AD patients from control subjects and, therefore, may prove useful in the improved diagnosis of early-stage AD.

Metabolic syndrome and cognitive decline in early Alzheimer's disease and healthy older adults

Metabolic syndrome (MetS) is a cluster of risk factors (i.e., abdominal obesity, hypertension, dyslipidemia, glucose and insulin dysregulation) that is associated with cardiovascular disease, diabetes, and dementia. Recent studies addressing the association of MetS with cognitive performance and risk for dementia report mixed results. An important step in clarifying these conflicting results is determining whether cognition is influenced by the effects of individual MetS components versus the additive effects of multiple components. We assessed the effect of MetS on cognitive performance and decline over two years in 75 cases of early Alzheimer's disease (AD) and 73 healthy older adult controls in the Brain Aging Project. Using factor analytic techniques, we compared the effect of a combined MetS factor to the effect of individual MetS components on change in attention, verbal memory, and mental status. In healthy controls, a combined MetS factor did not significantly predict cognitive performance, though higher insulin predicted poorer cognitive performance outcomes. In the AD group, higher scores on a combined MetS factor predicted better cognitive outcomes. Our findings suggest that MetS does not have the same association with cognitive decline in healthy older adults and those with early AD. We suggest that individual MetS components should not be evaluated in isolation and that careful methodological approaches are needed to understand the timing and non-linear relationships among these components over time.

Integrative EEG biomarkers predict progression to Alzheimer's disease at the MCI stage

Alzheimer's disease (AD) is a devastating disorder of increasing prevalence in modern society. Mild cognitive impairment (MCI) is considered a transitional stage between normal aging and AD; however, not all subjects with MCI progress to AD. Prediction of conversion to AD at an early stage would enable an earlier, and potentially more effective, treatment of AD. Electroencephalography (EEG) biomarkers would provide a non-invasive and relatively cheap screening tool to predict conversion to AD; however, traditional EEG biomarkers have not been considered accurate enough to be useful in clinical practice. Here, we aim to combine the information from multiple EEG biomarkers into a diagnostic classification index in order to improve the accuracy of predicting conversion from MCI to AD within a 2-year period. We followed 86 patients initially diagnosed with MCI for 2 years during which 25 patients converted to AD. We show that multiple EEG biomarkers mainly related to activity in the beta-frequency range (13–30 Hz) can predict conversion from MCI to AD. Importantly, by integrating six EEG biomarkers into a diagnostic index using logistic regression the prediction improved compared with the classification using the individual biomarkers, with a sensitivity of 88% and specificity of 82%, compared with a sensitivity of 64% and specificity of 62% of the best individual biomarker in this index. In order to identify this diagnostic index we developed a data mining approach implemented in the Neurophysiological Biomarker Toolbox (http://www.nbtwiki.net/). We suggest that this approach can be used to identify optimal combinations of biomarkers (integrative biomarkers) also in other modalities. Potentially, these integrative biomarkers could be more sensitive to disease progression and response to therapeutic intervention.