A damaged microcirculation contributes to neuronal cell death in Alzheimer's disease

Cerebral perfusion correlates with amyloid deposition in patients with mild cognitive impairment due to Alzheimer's disease

BACKGROUND

Changes in cerebral blood flow (CBF) may contribute to the initial stages of the pathophysiological process in patients with Alzheimer's disease (AD). Hypoperfusion has been observed in several brain regions in patients with mild cognitive impairment (MCI). However, the clinical significance of CBF changes in the early stages of AD is currently unclear.

OBJECTIVES

The aim of this study was to investigate the characteristics, diagnostic value and cognitive correlation of cerebral perfusion measured with arterial spin labeling (ASL) magnetic resonance imaging (MRI) in patients with MCI due to AD.

DESIGN, SETTING AND PARTICIPANTS

A total of fifty-nine MCI patients and 49 cognitively unimpaired controls (CUCs) were recruited and underwent multimodal MRI scans, including pseudocontinuous ASL, and neurocognitive testing. MCI patients were dichotomously classified according to the presence of amyloid deposition on 11C-labelled Pittsburgh compound B (PiB) positron emission tomography (PET).

MEASUREMENTS

The differences in CBF and expression of the AD-related perfusion pattern (ADRP), established by spatial covariance analysis in our previous study, were compared between the PiB+ MCI group and the CUC group and between the PiB+ and PiB- MCI groups. The diagnostic accuracy and correlations with cognitive function scores for CBF and ADRP expression were further analyzed.

RESULTS

Hypoperfusion in the precuneus and posterior cingulate cortex (PCC) was more characteristic of patients with MCI due to AD than of those with non-AD-related MCI. The relative regional CBF value of the left precuneus best distinguished patients with MCI due to AD from CUCs and patients with MCI due to non-AD conditions. Cerebral perfusion, as indicated by either the relative regional CBF or the expression score of the ADRP, was strongly correlated with certain cognitive function scores.

CONCLUSIONS

Here, we show that changes in CBF in the precuneus/PCC are promising MRI biomarkers for the identification of an AD etiology in patients with MCI. ASL, a noninvasive and cost-effective tool, has broad application prospects in the screening and early diagnosis of AD.

Inflammation and DNA methylation in Alzheimer's disease: mechanisms of epigenetic remodelling by immune cell oxidants in the ageing brain

Alzheimer's disease is a neurodegenerative disease involving memory impairment, confusion, and behavioural changes. The disease is characterised by the accumulation of amyloid beta plaques and neurofibrillary tangles in the brain, which disrupt normal neuronal function. There is no known cure for Alzheimer's disease and due to increasing life expectancy, occurrence is projected to rise over the coming decades. The causes of Alzheimer's disease are multifactorial with inflammation, oxidative stress, genetic and epigenetic variation, and cerebrovascular abnormalities among the strongest contributors. We review the current literature surrounding inflammation and epigenetics in Alzheimer's disease, with a focus on how oxidants from infiltrating immune cells have the potential to alter DNA methylation profiles in the ageing brain.

TWCOM: an R package for inference of cell-cell communication on spatially resolved transcriptomics data

Summary

The inference of cell-cell communication is important, as it unveils the intricate cellular behaviors at the molecular level, providing crucial insights essential for understanding complex biological processes and informing targeted interventions in various pathological contexts. Here, we present TWCOM, an R package that implements a Tweedie distribution-based model for accurate cell-cell communication inference. Operating under a generalized additive model framework, TWCOM adeptly handles both single-cell resolution and spot-based spatially resolved transcriptomics data, providing a versatile tool for robust biological sample analysis.

Availability and implementation

The R package TWCOM is available at https://github.com/dongyuanwu/TWCOM. Comprehensive documentation is included with the package.

Endothelial dysfunction in neurodegenerative disease: Is endothelial inflammation an overlooked druggable target?

Neurological diseases with a neurodegenerative component have been associated with alterations in the cerebrovasculature. At the anatomical level, these are centred around changes in cerebral blood flow and vessel organisation. At the molecular level, there is extensive expression of cellular adhesion molecules and increased release of pro-inflammatory mediators. Together, these has been found to negatively impact blood-brain barrier integrity. Systemic inflammation has been found to accelerate and exacerbate endothelial dysfunction, neuroinflammation and degeneration. Here, we review the role of cerebrovasculature dysfunction in neurodegenerative disease and discuss the potential contribution of intermittent pro-inflammatory systemic disease in causing endothelial pathology, highlighting a possible mechanism that may allow broad-spectrum therapeutic targeting in the future.

Neuroinflammation in Alzheimer's disease: insights from peripheral immune cells

Alzheimer's disease (AD) is a serious brain disorder characterized by the presence of beta-amyloid plaques, tau pathology, inflammation, neurodegeneration, and cerebrovascular dysfunction. The presence of chronic neuroinflammation, breaches in the blood-brain barrier (BBB), and increased levels of inflammatory mediators are central to the pathogenesis of AD. These factors promote the penetration of immune cells into the brain, potentially exacerbating clinical symptoms and neuronal death in AD patients. While microglia, the resident immune cells of the central nervous system (CNS), play a crucial role in AD, recent evidence suggests the infiltration of cerebral vessels and parenchyma by peripheral immune cells, including neutrophils, T lymphocytes, B lymphocytes, NK cells, and monocytes in AD. These cells participate in the regulation of immunity and inflammation, which is expected to play a huge role in future immunotherapy. Given the crucial role of peripheral immune cells in AD, this article seeks to offer a comprehensive overview of their contributions to neuroinflammation in the disease. Understanding the role of these cells in the neuroinflammatory response is vital for developing new diagnostic markers and therapeutic targets to enhance the diagnosis and treatment of AD patients.

Interactions between nanoparticles and pathological changes of vascular in Alzheimer's disease

Emerging evidence suggests that vascular pathological changes play a pivotal role in the pathogenesis of Alzheimer's disease (AD). The dysfunction of the cerebral vasculature occurs in the early course of AD, characterized by alterations in vascular morphology, diminished cerebral blood flow (CBF), impairment of the neurovascular unit (NVU), vasculature inflammation, and cerebral amyloid angiopathy. Vascular dysfunction not only facilitates the influx of neurotoxic substances into the brain, triggering inflammation and immune responses but also hampers the efflux of toxic proteins such as Aβ from the brain, thereby contributing to neurodegenerative changes in AD. Furthermore, these vascular changes significantly impact drug delivery and distribution within the brain. Therefore, developing targeted delivery systems or therapeutic strategies based on vascular alterations may potentially represent a novel breakthrough in AD treatment. This review comprehensively examines various aspects of vascular alterations in AD and outlines the current interactions between nanoparticles and pathological changes of vascular.

Thinking outside the black box: are the brain endothelial cells the new main target in Alzheimer's disease?

The blood-brain barrier is the interface through which the brain interacts with the milieu and consists mainly of a sophisticated network of brain endothelial cells that forms blood vessels and selectively moves molecules inside and outside the brain through multiple mechanisms of transport. Although brain endothelial cell function is crucial for brain homeostasis, their role in neurodegenerative diseases has historically not been considered with the same importance as other brain cells such as microglia, astroglia, neurons, or even molecules such as amyloid beta, Tau, or alpha-synuclein. Alzheimer's disease is the most common neurodegenerative disease, and brain endothelial cell dysfunction has been reported by several groups. However, its impairment has barely been considered as a potential therapeutic target. Here we review the most recent advances in the relationship between Alzheimer's disease and brain endothelial cells commitment and analyze the possible mechanisms through which their alterations contribute to this neurodegenerative disease, highlighting their inflammatory phenotype and the possibility of an impaired secretory pattern of brain endothelial cells that could contribute to the progression of this ailment. Finally, we discuss why shall brain endothelial cells be appreciated as a therapeutic target instead of solely an obstacle for delivering treatments to the injured brain in Alzheimer's disease.

Altered Microcirculation in Alzheimer's Disease Assessed by Machine Learning Applied to Functional Thermal Imaging Data

Alzheimer's disease (AD) is characterized by progressive memory failures accompanied by microcirculation alterations. Particularly, impaired endothelial microvascular responsiveness and altered flow motion patterns have been observed in AD patients. Of note, the endothelium influences the vascular tone and also the small superficial blood vessels, which can be evaluated through infrared thermography (IRT). The advantage of IRT with respect to other techniques relies on its contactless features and its capability to preserve spatial information of the peripheral microcirculation. The aim of the study is to investigate peripheral microcirculation impairments in AD patients with respect to age-matched healthy controls (HCs) at resting state, through IRT and machine learning (ML) approaches. Particularly, several classifiers were tested, employing as regressors the power of the nose tip temperature time course in different physiological frequency bands. Among the ML classifiers tested, the Decision Tree Classifier (DTC) delivered the best cross-validated accuracy (accuracy = 82%) when discriminating between AD and HCs. The results further demonstrate the alteration of microvascular patterns in AD in the early stages of the pathology, and the capability of IRT to assess vascular impairments. These findings could be exploited in clinical practice, fostering the employment of IRT as a support for the early diagnosis of AD.

SSAO/VAP-1 in Cerebrovascular Disorders: A Potential Therapeutic Target for Stroke and Alzheimer's Disease

The semicarbazide-sensitive amine oxidase (SSAO), also known as vascular adhesion protein-1 (VAP-1) or primary amine oxidase (PrAO), is a deaminating enzyme highly expressed in vessels that generates harmful products as a result of its enzymatic activity. As a multifunctional enzyme, it is also involved in inflammation through its ability to bind and promote the transmigration of circulating leukocytes into inflamed tissues. Inflammation is present in different systemic and cerebral diseases, including stroke and Alzheimer’s disease (AD). These pathologies show important affectations on cerebral vessels, together with increased SSAO levels. This review summarizes the main roles of SSAO/VAP-1 in human physiology and pathophysiology and discusses the mechanisms by which it can affect the onset and progression of both stroke and AD. As there is an evident interrelationship between stroke and AD, basically through the vascular system dysfunction, the possibility that SSAO/VAP-1 could be involved in the transition between these two pathologies is suggested. Hence, its inhibition is proposed to be an interesting therapeutical approach to the brain damage induced in these both cerebral pathologies.

PET Imaging of Neutrophils Infiltration in Alzheimer's Disease Transgenic Mice

Neutrophils are important components in the innate immune system. Neutrophil hyperactivation is regarded as a characteristic of Alzheimer's disease (AD). But in vivo imaging tools observing neutrophil activity in AD dynamically is lacking. This study aimed to identify neutrophil infiltration in AD transgenic mice. We used the AD triple-mutant transgenic mouse model and identified the genotype with RT-PCR. Behavioral experiments including an open-field test, a Morris water maze, and a Y-maze test were performed to evaluate the status of this AD model. ¹⁸F-AV45, ¹⁸F-PM-PBB3, ⁶⁸Ga-PEG-cFLFLFK, and ¹⁸F-DPA714 were synthesized according to previous reports. We employed microPET to detect tracer uptake in the AD model and the control mice at different stages. Western blotting was used to observe the expression of functional proteins. We proved the successful establishment of AD models by RT-PCR, behavioral tests, and ¹⁸F-AV45 and ¹⁸F-PM-PBB3 PET imaging. We found an increased neutrophil accumulation in the brains of the AD mice through ⁶⁸Ga-PEG-cFLFLFK PET imaging and Western blot assay. Our studies also demonstrated an elevated level of CAP37, which is produced by neutrophils, in the AD brain, and treatment with CAP37 promoted the expression of Iba1, iNOS, and COX-2 in BV2 cultures. Furthermore, our ¹⁸F-DPA714 PET imaging studies verified the raised activation of microglia in the brain of transgenic AD mice. Collectively, our findings indicate the increased activity of neutrophils in the brain and heart of AD model mice, ⁶⁸Ga-PEG-cFLFLFK PET imaging represents a sensitive method to observe the status of neutrophils in AD, and infiltrated neutrophils can induce the activation of microglia by releasing CAP37 and blocking the activity of neutrophils may be beneficial for the control of AD progression.

Renal Contributions in the Pathophysiology and Neuropathological Substrates Shared by Chronic Kidney Disease and Alzheimer's Disease

Chronic kidney disease and Alzheimer's disease are chronic conditions highly prevalent in elderly communities and societies, and a diagnosis of them is devastating and life changing. Demanding therapies and changes, such as non-compliance, cognitive impairment, and non-cognitive anomalies, may lead to supplementary symptoms and subsequent worsening of well-being and quality of life, impacting the socio-economic status of both patient and family. In recent decades, additional hypotheses have attempted to clarify the connection between these two diseases, multifactorial in their nature, but even so, the mechanisms behind this link are still elusive. In this paper, we sought to highlight the current understanding of the mechanisms for cognitive decline in patients with these concurrent pathologies and provide insight into the relationship between markers related to these disease entities and whether the potential biomarkers for renal function may be used for the diagnosis of Alzheimer's disease. Exploring detailed knowledge of etiologies, heterogeneity of risk factors, and neuropathological processes associated with these conditions opens opportunities for the development of new therapies and biomarkers to delay or slow their progression and validation of whether the setting of chronic kidney disease could be a potential determinant for cognitive damage in Alzheimer's disease.

In vitro modeling of the neurovascular unit: advances in the field

The blood–brain barrier (BBB) is a fundamental component of the central nervous system. Its functional and structural integrity is vital in maintaining the homeostasis of the brain microenvironment. On the other hand, the BBB is also a major hindering obstacle for the delivery of effective therapies to treat disorders of the Central Nervous System (CNS). Over time, various model systems have been established to simulate the complexities of the BBB. The development of realistic in vitro BBB models that accurately mimic the physiological characteristics of the brain microcapillaries in situ is of fundamental importance not only in CNS drug discovery but also in translational research. Successful modeling of the Neurovascular Unit (NVU) would provide an invaluable tool that would aid in dissecting out the pathological factors, mechanisms of action, and corresponding targets prodromal to the onset of CNS disorders. The field of BBB in vitro modeling has seen many fundamental changes in the last few years with the introduction of novel tools and methods to improve existing models and enable new ones. The development of CNS organoids, organ-on-chip, spheroids, 3D printed microfluidics, and other innovative technologies have the potential to advance the field of BBB and NVU modeling. Therefore, in this review, summarize the advances and progress in the design and application of functional in vitro BBB platforms with a focus on rapidly advancing technologies.

Anti-interleukin-17A and anti-interleukin-23 antibodies may be effective against Alzheimer's disease: Role of neutrophils in the pathogenesis

INTRODUCTION

Despite the remarkable progress achieved in the research on Alzheimer's disease (AD), its exact pathogenesis is not fully understood and effective therapies do not currently exist. In order to find effective therapy for AD, I ranged extensively over the literature and found an important paper by Tiffany and colleagues.

RESULTS AND CONCLUSION

Neuroinflammation has been proposed as a possible cause or driving force of AD. The discovery by Tiffany et al. that amyloid β (Aβ) is a formylpeptide receptor 2 agonist indicated that Aβ is a potent chemoattractant for phagocytic leukocytes. Therefore, in all likelihood Aβ attracts peripheral blood neutrophils, monocytes, as well as microglia cells in brain parenchyma, and activates them. However, the role of microglia cells and their precursor monocytes in AD pathogenesis remains elusive. Recently, neutrophils were found to be present in areas with Aβ deposits in AD brain and in transgenic AD model mice. Because brain is vulnerable to the effects of reactive oxygen species (ROS) and neutrophils secrete a large amount of ROS, neutrophils look like a driving force of AD. Therefore, a possibility arises that anti-IL-17A and anti-IL-23 antibodies are effective against AD, because these antibodies can be thought to interfere with neutrophil trafficking from the bone marrow to the blood circulation and thus inhibit neutrophil infiltration into AD brain. Clinical studies using anti-IL-17A and anti-IL-23 antibodies in patients with AD are required.

Vascular Dysfunction in Alzheimer's Disease: A Prelude to the Pathological Process or a Consequence of It?

Alzheimer's disease (AD) is the most prevalent form of dementia. Despite decades of research following several theoretical and clinical lines, all existing treatments for the disorder are purely symptomatic. AD research has traditionally been focused on neuronal and glial dysfunction. Although there is a wealth of evidence pointing to a significant vascular component in the disease, this angle has been relatively poorly explored. In this review, we consider the various aspects of vascular dysfunction in AD, which has a significant impact on brain metabolism and homeostasis and the clearance of β-amyloid and other toxic metabolites. This may potentially precede the onset of the hallmark pathophysiological and cognitive symptoms of the disease. Pathological changes in vessel haemodynamics, angiogenesis, vascular cell function, vascular coverage, blood-brain barrier permeability and immune cell migration may be related to amyloid toxicity, oxidative stress and apolipoprotein E (APOE) genotype. These vascular deficits may in turn contribute to parenchymal amyloid deposition, neurotoxicity, glial activation and metabolic dysfunction in multiple cell types. A vicious feedback cycle ensues, with progressively worsening neuronal and vascular pathology through the course of the disease. Thus, a better appreciation for the importance of vascular dysfunction in AD may open new avenues for research and therapy.

The value of whole-brain CT perfusion imaging and CT angiography using a 320-slice CT scanner in the diagnosis of MCI and AD patients

OBJECTIVES

To validate the value of whole-brain computed tomography perfusion (CTP) and CT angiography (CTA) in the diagnosis of mild cognitive impairment (MCI) and Alzheimer's disease (AD).

METHODS

Whole-brain CTP and four-dimensional CT angiography (4D-CTA) images were acquired in 30 MCI, 35 mild AD patients, 35 moderate AD patients, 30 severe AD patients and 50 normal controls (NC). Cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), time to peak (TTP), and correlation between CTP and 4D-CTA were analysed.

RESULTS

Elevated CBF in the left frontal and temporal cortex was found in MCI compared with the NC group. However, TTP was increased in the left hippocampus in mild AD patients compared with NC. In moderate and severe AD patients, hypoperfusion was found in multiple brain areas compared with NC. Finally, we found that the extent of arterial stenosis was negatively correlated with CBF in partial cerebral cortex and hippocampus, and positively correlated with TTP in these areas of AD and MCI patients.

CONCLUSIONS

Our findings suggest that whole-brain CTP and 4D-CTA could serve as a diagnostic modality in distinguishing MCI and AD, and predicting conversion from MCI based on TTP of left hippocampus.

KEY POINTS

• Whole-brain perfusion using the full 160-mm width of 320 detector rows • Provide clinical experience of 320-row CT in cerebrovascular disorders of Alzheimer's disease • Initial combined 4D CTA-CTP data analysed perfusion and correlated with CT angiography • Whole-brain CTP and 4D-CTA have high value for monitoring MCI to AD progression • TTP in the left hippocampus may predict the transition from MCI to AD.

NETosis in Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the progressive deterioration of cognitive functions. Its neuropathological features include amyloid-β (Aβ) accumulation, the formation of neurofibrillary tangles, and the loss of neurons and synapses. Neuroinflammation is a well-established feature of AD pathogenesis, and a better understanding of its mechanisms could facilitate the development of new therapeutic approaches. Recent studies in transgenic mouse models of AD have shown that neutrophils adhere to blood vessels and migrate inside the parenchyma. Moreover, studies in human AD subjects have also shown that neutrophils adhere and spread inside brain vessels and invade the parenchyma, suggesting these cells play a role in AD pathogenesis. Indeed, neutrophil depletion and the therapeutic inhibition of neutrophil trafficking, achieved by blocking LFA-1 integrin in AD mouse models, significantly reduced memory loss and the neuropathological features of AD. We observed that neutrophils release neutrophil extracellular traps (NETs) inside blood vessels and in the parenchyma of AD mice, potentially harming the blood–brain barrier and neural cells. Furthermore, confocal microscopy confirmed the presence of NETs inside the cortical vessels and parenchyma of subjects with AD, providing more evidence that neutrophils and NETs play a role in AD-related tissue destruction. The discovery of NETs inside the AD brain suggests that these formations may exacerbate neuro-inflammatory processes, promoting vascular and parenchymal damage during AD. The inhibition of NET formation has achieved therapeutic benefits in several models of chronic inflammatory diseases, including autoimmune diseases affecting the brain. Therefore, the targeting of NETs may delay AD pathogenesis and offer a novel approach for the treatment of this increasingly prevalent disease.

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.

Imaging of Leukocyte Trafficking in Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder and is characterized by a progressive decline of cognitive functions. The neuropathological features of AD include amyloid beta (Aβ) deposition, intracellular neurofibrillary tangles derived from the cytoskeletal hyperphosphorylated tau protein, amyloid angiopathy, the loss of synapses, and neuronal degeneration. In the last decade, inflammation has emerged as a key feature of AD, but most studies have focused on the role of microglia-driven neuroinflammation mechanisms. A dysfunctional blood-brain barrier has also been implicated in the pathogenesis of AD, and several studies have demonstrated that the vascular deposition of Aβ induces the expression of adhesion molecules and alters the expression of tight junction proteins, potentially facilitating the transmigration of circulating leukocytes. Two-photon laser scanning microscopy (TPLSM) has become an indispensable tool to dissect the molecular mechanisms controlling leukocyte trafficking in the central nervous system (CNS). Recent TPLSM studies have shown that vascular deposition of Aβ in the CNS promotes intraluminal neutrophil adhesion and crawling on the brain endothelium and also that neutrophils extravasate in the parenchyma preferentially in areas with Aβ deposits. These studies have also highlighted a role for LFA-1 integrin in neutrophil accumulation in the CNS of AD-like disease models, revealing that LFA-1 inhibition reduces the corresponding cognitive deficit and AD neuropathology. In this article, we consider how current imaging techniques can help to unravel new inflammation mechanisms in the pathogenesis of AD and identify novel therapeutic strategies to treat the disease by interfering with leukocyte trafficking mechanisms.

Compromised endothelium-dependent hyperpolarization-mediated dilations can be rescued by NS309 in obese Zucker rats

OBJECTIVE

NO and a non-NO/prostacyclin EDH mechanism are major contributors of vascular tone and cerebral blood flow. However, the effect of metabolic syndrome on EDH-mediated responses in cerebral vessels remains unknown and may offer another avenue for therapeutic targeting. The purpose of this study was to investigate EDH-dependent responses in cerebral arteries during metabolic syndrome.

METHODS

EDH-dependent dilations were assessed in MCAs isolated from nondiabetic obese and lean Zucker rats in the presence and absence of NS309, an activator of SKCa and IKCa channels. IKCa channel expression and activity were assessed by western blotting and pressure myography, respectively.

RESULTS

EDH-mediated dilations were significantly attenuated in the obese compared to the lean Zucker rat MCA. Luminal delivery of 1 μM NS309 enhanced EDH-mediated responses in lean and obese Zucker cerebral vessels. Both dose-dependent dilations to luminal NS309 and IKCa protein expression in pooled cerebral arteries were comparable between the two groups.

CONCLUSIONS

Our results suggest that pharmacological targeting of IKCa channels can rescue EDH-mediated dilations in obese Zucker rat MCAs. Compromised EDH-mediated dilations in obesity are not due to impaired IKCa channel expression or activity.

The link between cardiovascular risk, Alzheimer's disease, and mild cognitive impairment: support from recent functional neuroimaging studies

OBJECTIVE

To review functional neuroimaging studies about the relationship between cardiovascular risk factors (CVRFs), Alzheimer's disease (AD), and mild cognitive impairment (MCI).

METHODS

We performed a comprehensive literature search to identify articles in the neuroimaging field addressing CVRF in AD and MCI. We included studies that used positron emission tomography (PET), single photon emission computerized tomography (SPECT), or functional magnetic resonance imaging (fMRI).

RESULTS

CVRFs have been considered risk factors for cognitive decline, MCI, and AD. Patterns of AD-like changes in brain function have been found in association with several CVRFs (both regarding individual risk factors and also composite CVRF measures). In vivo assessment of AD-related pathology with amyloid imaging techniques provided further evidence linking CVRFs and AD, but there is still limited information resulting from this new technology.

CONCLUSION

There is a large body of evidence from functional neuroimaging studies supporting the hypothesis that CVRFs may play a causal role in the pathophysiology of AD. A major limitation of most studies is their cross-sectional design; future longitudinal studies using multiple imaging modalities are expected to better document changes in CVRF-related brain function patterns and provide a clearer picture of the complex relationship between aging, CVRFs, and AD.

Pericyte function in the physiological central nervous system

Damage to the central nervous system (CNS) leads to disruption of the vascular network, causing vascular dysfunction. Vascular dysfunction is the major event in the pathogenesis of CNS diseases and is closely associated with the severity of neuronal dysfunction. The suppression of vascular dysfunction has been considered a promising avenue to limit damage to the CNS, leading to efforts to clarify the cellular and molecular basis of vascular homeostasis maintenance. A reduction of trophic support and oxygen delivery due to circulatory insufficiency has long been regarded as a major cause of vascular damage. Moreover, recent studies provide a new perspective on the importance of the structural stability of blood vessels in CNS diseases. This updated article discusses emerging information on the key role of vascular integrity in CNS diseases, specially focusing on pericyte function.

Magnetic resonance angiography and vascular corrosion casting as tools in biomedical research: application to transgenic mice modeling Alzheimer's disease

In vivo imaging technologies are presently receiving considerable attention in the biomedical and pharmaceutical research areas. One of the principal imaging modalities is magnetic resonance imaging (MRI). The multiparametric nature of MRI enables anatomical, functional and even molecular information to be obtained non-invasively from intact organisms at high spatial resolution. Here we describe the use of one MRI modality, namely angiography (MRA), to non-invasively study the arterial vascular architecture of APP23 transgenic mice modeling Alzheimer's disease. Because the spatial resolution of the technique is limited, the in vivo studies are complemented by a powerful analysis of the vasculature using vascular corrosion casting. Both techniques revealed age-dependent blood flow alterations and cerebrovascular abnormalities in these mice. Our experience suggests that MRA complemented by cast analysis are important tools to describe vascular alterations and test new therapy concepts in animal models of AD. Furthermore, being non-invasive, MRA can also be applied to studies in patients suffering from this disease.

Aging enhances vascular dysfunction induced by the Alzheimer's peptide β-amyloid

Aging is a major risk factor for Alzheimer's disease and the evidence suggests a role for cerebrovascular pathology in cognitive dysfunction. The hypothesis in this study is that aging is a significant risk factor in the effect of the Alzheimer peptide beta-amyloid on endothelium-dependent function of cerebral and peripheral vessels. The diameter response to acetylcholine, an endothelium-dependent vasodilator, was recorded in pressurized segments of rat posterior cerebral vessels from mature (3 months) and aged (20 months) rats. The threshold concentration of beta-amyloid for a significant decrease in the response to acetylcholine was lower in vessels from aged rats (10(-9) M) than in vessels from mature rats (10(-8) M). The threshold concentration of beta-amyloid for a significant decrease in the sensitivity to acetylcholine was lower for ring segments of aorta from aged rats (10(-10) M) than for aorta from mature rats (10(-8) M). Structural changes of the endothelium were first observed in electron micrographs of aorta from aged rats when the concentration of beta-amyloid was 10(-8) M, whereas structural changes in aorta from mature rats did not occur until the concentration of beta-amyloid was increased to 10(-7) M. The results suggest that aging increases the susceptibility of cerebral and peripheral blood vessels to beta-amyloid related dysfunction and that functional change precedes structural change.

Cardiovascular risk in cognitively preserved elderlies is associated with glucose hypometabolism in the posterior cingulate cortex and precuneus regardless of brain atrophy and apolipoprotein gene variations

Cardiovascular risk factors (CVRF) possibly contribute to the emergence of Alzheimer's disease (AD). Fluorodeoxyglucose-positron emission tomography (FDG-PET) has been widely used to demonstrate specific patterns of reduced cerebral metabolic rates of glucose (CMRgl) in subjects with AD and in non-demented carriers of the apolipoprotein ε4 (APOE ε4) allele, the major genetic risk factor for AD. However, functional neuroimaging studies investigating the impact of CVRF on cerebral metabolism have been scarce to date. The present FDG-PET study investigated 59 cognitively preserved elderlies divided into three groups according to their cardiovascular risk based on the Framingham 10-year risk Coronary Heart Disease Risk Profile (low-, medium-, and high-risk) to examine whether different levels of CVRF would be associated with reduced CMRgl, involving the same brain regions affected in early stages of AD. Functional imaging data were corrected for partial volume effects to avoid confounding effects due to regional brain atrophy, and all analyses included the presence of the APOE ε4 allele as a confounding covariate. Significant cerebral metabolism reductions were detected in the high-risk group when compared to the low-risk group in the left precuneus and posterior cingulate gyrus. This suggests that findings of brain hypometabolism similar to those seen in subjects with AD can be detected in association with the severity of cardiovascular risk in cognitively preserved individuals. Thus, a greater knowledge about how such factors influence brain functioning in healthy subjects over time may provide important insigths for the future development of strategies aimed at delaying or preventing the vascular-related triggering of pathologic brain changes in the AD.

Cerebral microvascular endothelium and the pathogenesis of neurodegenerative diseases

Diseases of the central nervous system (CNS) pose a significant health challenge, but despite their diversity, they share many common features and mechanisms. For example, endothelial dysfunction has been implicated as a crucial event in the development of several CNS disorders, such as Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, multiple sclerosis, human immunodeficiency virus (HIV)-1-associated neurocognitive disorder and traumatic brain injury. Breakdown of the blood–brain barrier (BBB) as a result of disruption of tight junctions and transporters, leads to increased leukocyte transmigration and is an early event in the pathology of these disorders. The brain endothelium is highly reactive because it serves as both a source of, and a target for, inflammatory proteins and reactive oxygen species. BBB breakdown thus leads to neuroinflammation and oxidative stress, which are implicated in the pathogenesis of CNS disease. Furthermore, the physiology and pathophysiology of endothelial cells are closely linked to the functioning of their mitochondria, and mitochondrial dysfunction is another important mediator of disease pathology in the brain. The high concentration of mitochondria in cerebrovascular endothelial cells might account for the sensitivity of the BBB to oxidant stressors. Here, we discuss how greater understanding of the role of BBB function could lead to new therapeutic approaches for diseases of the CNS that target the dynamic properties of brain endothelial cells.

Neurovascular dysfunction, inflammation and endothelial activation: implications for the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is an age-related disorder characterized by progressive cognitive decline and dementia. Alzheimer's disease is an increasingly prevalent disease with 5.3 million people in the United States currently affected. This number is a 10 percent increase from previous estimates and is projected to sharply increase to 8 million by 2030; it is the sixth-leading cause of death. In the United States the direct and indirect costs of Alzheimer's and other dementias to Medicare, Medicaid and businesses amount to more than $172 billion each year. Despite intense research efforts, effective disease-modifying therapies for this devastating disease remain elusive. At present, the few agents that are FDA-approved for the treatment of AD have demonstrated only modest effects in modifying clinical symptoms for relatively short periods and none has shown a clear effect on disease progression. New therapeutic approaches are desperately needed. Although the idea that vascular defects are present in AD and may be important in disease pathogenesis was suggested over 25 years ago, little work has focused on an active role for cerebrovascular mechanisms in the pathogenesis of AD. Nevertheless, increasing literature supports a vascular-neuronal axis in AD as shared risk factors for both AD and atherosclerotic cardiovascular disease implicate vascular mechanisms in the development and/or progression of AD. Also, chronic inflammation is closely associated with cardiovascular disease, as well as a broad spectrum of neurodegenerative diseases of aging including AD. In this review we summarize data regarding, cardiovascular risk factors and vascular abnormalities, neuro- and vascular-inflammation, and brain endothelial dysfunction in AD. We conclude that the endothelial interface, a highly synthetic bioreactor that produces a large number of soluble factors, is functionally altered in AD and contributes to a noxious CNS milieu by releasing inflammatory and neurotoxic species.

High-resolution magnetic resonance angiography in the mouse using a nanoparticle blood-pool contrast agent

High-resolution magnetic resonance angiography is already a useful tool for studying mouse models of human disease. Magnetic resonance angiography in the mouse is typically performed using time-of-flight contrast. In this work, a new long-circulating blood-pool contrast agent-a liposomal nanoparticle with surface-conjugated gadolinium (SC-Gd liposomes)-was evaluated for use in mouse neurovascular magnetic resonance angiography. A total of 12 mice were imaged. Scan parameters were optimized for both time-of-flight and SC-Gd contrast. Compared to time-of-flight contrast, SC-Gd liposomes (0.08 mmol/kg) enabled improved small-vessel contrast-to-noise ratio, larger field of view, shorter scan time, and imaging of venous structures. For a limited field of view, time-of-flight and SC-Gd were not significantly different; however, SC-Gd provided better contrast-to-noise ratio when the field of view encompassed the whole brain (P < 0.001) or the whole neurovascular axis (P < 0.001). SC-Gd allowed acquisition of high-resolution magnetic resonance angiography (52 x 52 x 100 micrometer(3) or 0.27 nL), with 123% higher (P < 0.001) contrast-to-noise ratio in comparable scan time ( approximately 45 min). Alternatively, SC-Gd liposomes could be used to acquire high-resolution magnetic resonance angiography (0.27 nL) with 32% higher contrast-to-noise ratio (P < 0.001) in 75% shorter scan time (12 min).

Brain endothelial cells synthesize neurotoxic thrombin in Alzheimer's disease

Alzheimer's disease (AD) is characterized by neuronal death; thus, identifying neurotoxic proteins and their source is central to understanding and treating AD. The multifunctional protease thrombin is neurotoxic and found in AD senile plaques. The objective of this study was to determine whether brain endothelial cells can synthesize thrombin and thus be a source of this neurotoxin in AD brains. Microvessels were isolated from AD patient brains and from age-matched controls. Reverse transcription-PCR demonstrated that thrombin message was highly expressed in microvessels from AD brains but was not detectable in control vessels. Similarly, Western blot analysis of microvessels showed that the thrombin protein was highly expressed in AD- but not control-derived microvessels. In addition, high levels of thrombin were detected in cerebrospinal fluid obtained from AD but not control patients, and sections from AD brains showed reactivity to thrombin antibody in blood vessel walls but not in vessels from controls. Finally, we examined the ability of brain endothelial cells in culture to synthesize thrombin and showed that oxidative stress or cell signaling perturbations led to increased expression of thrombin mRNA in these cells. The results demonstrate, for the first time, that brain endothelial cells can synthesize thrombin, and suggest that novel therapeutics targeting vascular stabilization that prevent or decrease release of thrombin could prove useful in treating this neurodegenerative disease.

Cortical hypoperfusion in the B6.PS2APP mouse model for Alzheimer's disease: comprehensive phenotyping of vascular and tissular parameters by MRI

Function and morphology of the cerebral vasculature were studied in the amyloid (Abeta) plaque-containing double-transgenic (TG) B6.PS2APP Alzheimer's disease (AD) mouse model with MRI at an age range of 10 to 17 months. Perfusion, blood volume, and average vessel geometry were assessed in the brain and compared to age-matched controls (wild-type [WT] C57Bl/6). Additionally, the MR relaxation times T(1), T(2), and T(2)* were measured to detect potential pathological changes that might be associated with Abeta plaque depositions. Both decreased perfusion and decreased blood volume were observed in the occipital cortex in B6.PS2APP mice as compared to controls. A significant decrease in T(1) and T(2) was found in the frontal cortex and in the subiculum/parasubiculum. Immunohistochemistry confirmed plaque depositions in the cortex and in the subiculum/parasubiculum. In summary, our data indicate a reduced blood supply of B6.PS2APP mice in the occipital cortex that parallels the findings in cortical regions of patients with AD.

Brain ischemia and ischemic blood-brain barrier as etiological factors in sporadic Alzheimer's disease

The development of neuronal death and amyloid plaques is a characteristic feature of ischemic- and Alzheimer-type dementia. An important aspect of neuronal loss and amyloid plaques are their topography and neuropathogenesis. This review was performed to present the hypothesis that different fragments of blood-borne amyloid precursor protein are able to enter the ischemic blood-brain barrier. Chronic disruption of the blood-brain barrier after ischemic injury was shown. As an effect of chronic ischemic blood-brain barrier injury, a visible connection of amyloid plaques with neurovasculature was observed. This neuropathology appears to have similar distribution and mechanisms to Alzheimer's disease. The usefulness of rival ischemic theory in elucidating the neuropathogenesis of amyloid plaques formation and neuronal death in Alzheimer's disorder is discussed.

Altered expression of zonula occludens-2 precedes increased blood-brain barrier permeability in a murine model of fulminant hepatic failure

Brain edema secondary to increased blood-brain barrier (BBB) permeability is a lethal complication in fulminant hepatic failure (FHF). Intact tight junctions (TJ) between brain capillary endothelial cells are critical for normal BBB function. However, the role of TJ in FHF has not been explored. We hypothesized that alterations in the composition of TJ proteins would result in increased BBB permeability in FHF. In this study, FHF was induced in C57BL/6J mice by using azoxymethane. BBB permeability was assessed with sodium fluorescein. Expression of TJ proteins was determined by Western blot, and their cellular distribution was examined using immunofluorescent microscopy. Comatose FHF mice had significant cerebral sodium fluorescein extravasation compared with control and precoma FHF mice, indicating increased BBB permeability. Western blot analysis showed a significant decrease in zonula occludens (ZO)-2 expression starting in the precoma stage. Immunofluorescent microscopy showed a significantly altered distribution pattern of ZO-2 in isolated microvessels from precoma FHF mice. These changes were more prominent in comatose FHF animals. Significant alterations in ZO-2 expression and distribution in the tight junctions preceded the increased BBB permeability in FHF mice. These results suggest that ZO-2 may play an important role in the pathogenesis of brain edema in FHF.

RANTES upregulation in the Alzheimer's disease brain: a possible neuroprotective role

Numerous studies demonstrate inflammatory proteins in the brain and microcirculation in Alzheimer's disease (AD) and implicate inflammation in disease pathogenesis. However, emerging literature suggests that neuroinflammation can also be neuroprotective. The chemokine RANTES has been implicated in neurodegenerative diseases including AD. The objectives of this study are to determine the expression of RANTES in AD microvessels, its regulation in endothelial cells and its effects on neuronal survival. Our data show elevated expression of RANTES in the cerebral microcirculation of AD patients. Treatment of neurons in vitro with RANTES results in an increase in cell survival and a neuroprotective effect against the toxicity of thrombin and sodium nitroprusside. Oxidative stress upregulates RANTES expression in rat brain endothelial cells. Developing strategies to augment neuroprotection and diminish inflammatory activation of multifunctional mediators such as RANTES holds promise for the development of novel neuroprotective therapeutics in AD.

Thrombin-induced oxidative stress contributes to the death of hippocampal neurons: role of neuronal NADPH oxidase

The present study investigated whether thrombin can induce the production of reactive oxygen species (ROS) through activation of neuronal NADPH oxidase and whether this contributes to oxidative damage and consequently to neurodegeneration. Immunocytochemical and biochemical evidence demonstrated that, in neuron-enriched hippocampal cultures, thrombin induces neurodegeneration in a dose-dependent manner. In parallel, ROS production was evident as assessed by analyzing DCF and hydroethidine. Real-time PCR analysis, at various time points after thrombin treatment, also demonstrated that expression of NADPH oxidase subunits (p47(phox) and p67(phox)) occurs. In addition, Western blot analysis and double-label immunocytochemistry showed an up-regulation in the expression of cytosolic components (Rac 1 and p67(phox)), the translocation of cytosolic proteins (p47(phox) and p67(phox)) to the membrane, and the localization of gp91(phox) or p47(phox) expression in hippocampal neurons of cultures and CA1 layer. The thrombin-induced ROS production, protein oxidation, and loss of cultured hippocampal neurons were partially attenuated by an NADPH oxidase inhibitor and/or by several antioxidants. Collectively, the present study is the first to demonstrate that, in cultured hippocampal neurons, thrombin-induced neurotoxicity is, at least in part, caused by neuronal NADPH oxidase-mediated oxidative stress. This strongly suggests that thrombin can act as an endogenous neurotoxin, and inhibitors of thrombin and/or antioxidants can be useful agents for treating oxidative stress-mediated hippocampal neurodegenerative diseases, such as Alzheimer's disease.

Dicholine salt of succinic acid, a neuronal insulin sensitizer, ameliorates cognitive deficits in rodent models of normal aging, chronic cerebral hypoperfusion, and beta-amyloid peptide-(25-35)-induced amnesia

BACKGROUND

Accumulated evidence suggests that insulin resistance and impairments in cerebral insulin receptor signaling may contribute to age-related cognitive deficits and Alzheimer's disease. The enhancement of insulin receptor signaling is, therefore, a promising strategy for the treatment of age-related cognitive disorders. The mitochondrial respiratory chain, being involved in insulin-stimulated H2O2 production, has been identified recently as a potential target for the enhancement of insulin signaling. The aim of the present study is to examine: (1) whether a specific respiratory substrate, dicholine salt of succinic acid (CS), can enhance insulin-stimulated insulin receptor autophosphorylation in neurons, and (2) whether CS can ameliorate cognitive deficits of various origins in animal models.

RESULTS

In a primary culture of cerebellar granule neurons, CS significantly enhanced insulin-stimulated insulin receptor autophosphorylation. In animal models, CS significantly ameliorated cognitive deficits, when administered intraperitoneally for 7 days. In 16-month-old middle-aged C57Bl/6 mice (a model of normal aging), CS enhanced spatial learning in the Morris water maze, spontaneous locomotor activity, passive avoidance performance, and increased brain N-acetylaspartate/creatine levels, as compared to the age-matched control (saline). In rats with chronic cerebral hypoperfusion, CS enhanced spatial learning, passive avoidance performance, and increased brain N-acetylaspartate/creatine levels, as compared to control rats (saline). In rats with beta-amyloid peptide-(25-35)-induced amnesia, CS enhanced passive avoidance performance and increased activity of brain choline acetyltransferase, as compared to control rats (saline). In all used models, CS effects lasted beyond the seven-day treatment period and were found to be significant about two weeks following the treatment.

CONCLUSION

The results of the present study suggest that dicholine salt of succinic acid, a novel neuronal insulin sensitizer, ameliorates cognitive deficits and neuronal dysfunctions in animal models relevant to age-related cognitive impairments, vascular dementia, and Alzheimer's disease.

ApoE deficiency leads to a progressive age-dependent blood-brain barrier leakage

Previously, we reported a defect in the blood-brain barrier (BBB) of apolipoprotein E-deficient (apoE-/-) mice (24). Here, we investigate BBB permeability in wild-type (WT) and apoE-/- mice as a function of age. Both WT and apoE-/- mice showed significantly increased cortical BBB leakage with age. However, in apoE-/- mice, the leakage increased at a 3.7 x higher rate compared with WT mice. Surprisingly, the cerebellum showed significantly more leakage than other brain regions across age, while there was no difference between the two hemispheres. To determine the contribution of tissue- vs. blood-borne apoE to vascular permeability, we generated chimeric mice by bone marrow transplantation and measured their BBB leakage. These experiments suggest that both blood- and tissue-derived apoE are equally important for BBB function. In sum, we find an age-dependent defect in the BBB that is exacerbated in apoE-/- mice. Since vascular defects are found in patients with age-related neurodegenerative diseases, such as Alzheimer's, age-related BBB leakage could underlie these defects and may thus be an important contributor to the cumulative neuronal damage of these diseases.

Pravastatin reduces microvascular basal lamina damage following focal cerebral ischemia and reperfusion

Transient ischemia has been shown to damage the basal lamina of the cerebral microvasculature. Other studies proved statins to be beneficial to non-cerebral microvessels. The aim of this study was to determine whether pravastatin pretreatment ameliorates microvascular basal lamina damage following transient ischemia. Using the suture model, we subjected 15 rats to focal ischemia (3 h) and reperfusion (24 h). Rats received pravastatin (20 mg/kg/day) or saline for 4 weeks prior to the experiment. The outcome was determined by a behavior test and the infarct size. Collagen type IV, a marker for an intact basal lamina, and hemoglobin extravasation were measured by Western blot analysis. A ratio (in percentage) between ischemic and contralateral hemispheres was calculated. Pravastatin pretreatment resulted in a significantly better neurological outcome and reduced infarct size (15 +/- 0.5 and 59 +/- 10 mm(3), respectively) compared with controls (12.25 +/- 0.4 and 167 +/- 13 mm(3), respectively, P < 0.01 for both). In controls, loss of collagen type IV was seen in the basal ganglia and in the cortex (43 +/- 4 and 64 +/- 5%, respectively). Pravastatin prevented significant collagen loss (basal ganglia: 106 +/- 17%; cortex: 112 +/- 14%, P < 0.01 for both) and significantly reduced the hemoglobin extravasation compared with controls in the basal ganglia (198 +/- 49 vs. 553 +/- 47%, P < 0.01). Pravastatin pretreatment resulted in a reduction of microvascular basal lamina damage and hemoglobin extravasation following transient ischemia. Pravastatin seems to protect the cerebral microvascular system.

Cocoa Flavanols and Brain Perfusion

Foods and beverages rich in flavonoids are being heralded as potential preventive agents for a range of pathologic conditions, ranging from hypertension to coronary heart disease to stroke and dementia. We and others have demonstrated that short-term ingestion of cocoa, particularly rich in the subclass of flavonoids known as flavanols, induced a consistent and striking peripheral vasodilation in healthy people, improving endothelial function in a nitric oxide-dependent manner. The vasodilator response was reversed by N-nitro-L-arginine methyl ester, an arginine analog that blocks nitric oxide synthesis. Flavanol-poor cocoa induced much smaller responses. Because impairment of endothelial function is a nearly universal accompaniment of the aging process, we examined the peripheral vasodilator response to flavanol-rich cocoa in healthy older subjects. Observations point to a favorable response among the older. Together with peripheral vascular disease, cerebrovascular disease is responsible for significant mortality with advancing age. An association of decreased cerebral perfusion with dementia has been recently highlighted. The prospect of increasing cerebral perfusion with cocoa flavanols is extremely promising. Our still preliminary data hold out the promise that the cerebral blood supply in the elderly participates in the vasodilator response. With the modalities of transcranial Doppler and MRI, we have the capabilities of analyzing the potential benefits of flavanols on brain perfusion and, subsequently, on cognition.

Bosentan preserves endothelial function in mice overexpressing APP

This study was designed to test the hypothesis that Alzheimer's disease (AD) is associated with endothelial dysfunction and that chronic endothelin-1 antagonism preserves endothelial function in mice overexpressing the AD amyloid precursor protein (APP). Three groups of mice were studied: C57BL/6 (normal control, n = 6), transgenic mice overexpressing APP (Tg2576, n = 5), and Tg2576 mice fed Bosentan (100 mg/(kg day)(-1)), a combined endothelin A and B receptor antagonist, for 4 months (Tg2576+Bosentan, n = 5). Mice were sacrificed at the age of 7 months. In vitro, the endothelium-dependent aortic vasorelaxation was significantly attenuated in Tg2576 mice as compared to C57BL/6 and Tg2576+Bosentan mice. In contrast, Tg2576+Bosentan and C57BL/6 mice showed similar endothelium-dependent aortic vasorelaxation. Similarly, endothelium-dependent carotid vasorelaxation was significantly attenuated in Tg2576 mice compared to C57BL/6 and Tg2576+Bosentan mice. There was no difference between the three groups in the response to nitroprusside. The current study demonstrates the presence of endothelial dysfunction in both carotid and aortic arteries in mice overexpressing APP and suggests a pathophysiological role for the endogenous endothelin system in AD.

Thrombin-induced oxidative stress contributes to the death of hippocampal neurons in vivo: role of microglial NADPH oxidase

The present study investigated whether thrombin, a potent microglial activator, can induce reactive oxygen species (ROS) generation through activation of microglial NADPH oxidase and if this may contribute to oxidative damage and consequent neurodegeneration. Seven days after intrahippocampal injection of thrombin, Nissl staining and immunohistochemistry using the neuronal-specific nuclear protein NeuN revealed a significant loss in hippocampal CA1 neurons. In parallel, thrombin-activated microglia, assessed by OX-42 and OX-6 immunohistochemistry, and ROS production, assessed by hydroethidine histochemistry, were observed in the hippocampal CA1 area in which degeneration of hippocampal neurons occurred. Reverse transcription-PCR at various time points after thrombin administration demonstrated an early and transient expression of inducible nitric oxide synthase (iNOS) and several proinflammatory cytokines. Western blot analysis and double-label immunohistochemistry showed an increase in the expression of and the localization of iNOS within microglia. Additional studies demonstrated that thrombin induced the upregulation of membrane (gp91(phox)) and cytosolic (p47(phox) and p67(phox)) components, translocation of cytosolic proteins (p47(phox), p67(phox), and Rac1) to the membrane, and p67(phox) expression of the NADPH oxidase in microglia in the hippocampus in vivo, indicating the activation of NADPH oxidase. The thrombin-induced oxidation of proteins and loss of hippocampal CA1 neurons were partially inhibited by an NADPH oxidase inhibitor and by an antioxidant. To our knowledge, the present study is the first to demonstrate that thrombin-induced neurotoxicity in the hippocampus in vivo is caused by microglial NADPH oxidase-mediated oxidative stress. This suggests that thrombin inhibition or enhancing antioxidants may be beneficial for the treatment of neurodegenerative diseases, such as Alzheimer's disease, that are associated with microglial-derived oxidative damage.

Acute anoxia induces tau dephosphorylation in rat brain slices and its possible underlying mechanisms

Abnormal phosphorylation of microtubule-associated protein tau plays a critical role in Alzheimer's disease (AD), together with a distinct decrease of energy metabolism in the affected brain regions. To explore the effect of acute energy crisis on tau phosphorylation and the underlying mechanisms, we incubated rat brain slices in artificial cerebrospinal fluid (aCSF) at 37 degrees C with or without an oxygen supply, or in aCSF with low glucose concentrations. Then, the levels of total, phosphorylated and unphosphorylated tau, as well as the activities and levels of protein phosphatase (PP)-1, PP-2A, glycogen synthase kinase 3 (GSK-3), extracellular signal-regulated protein kinase (ERK) and C-jun amino terminal kinase (JNK), were measured. It was found, unexpectedly, that tau was significantly dephosphorylated at Ser396/Ser404 (PHF-1), Ser422 (R145), Ser199/Ser202 (Tau-1), Thr181 (AT270), Ser202/Thr205 (AT8) and Thr231 (AT180) by acute anoxia for 30 min or 120 min. The activity of PP-2A and the level of dephosphorylated PP-2A catalytic subunit at tyrosine 307 (Tyr307) were simultaneously increased. The active forms of ERK1/2 and JNK1/2 were decreased under anoxic incubation. The PP-2A inhibitor, okadaic acid (OA, 0.75 microm), completely prevented tau from acute anoxia-induced dephosphorylation and restored the active forms of ERK1/2 and JNK1/2 to the control level. The activities and protein levels of GSK-3 and PP-1 showed no change during acute anoxia. These data suggest that acute anoxia induces tau dephosphorylation, and that PP-2A may play a key role in tau dephosphorylation induced by acute anoxia.

Decreased release of the angiogenic peptide vascular endothelial growth factor in Alzheimer's disease: recovering effect with insulin and DHEA sulfate

Changes of vascular endothelial growth factor (VEGF) secretion have recently been demonstrated in patients with Alzheimer's disease (AD). Since VEGF has been involved in brain angiogenesis, neuroprotection and cerebromicrovascular exchange of substrates and nutrients, the study of VEGF could have important relapses into the pathogenesis and treatment of AD. Within this context, 35 healthy subjects (16 of young and 19 of old age), 18 patients with dementia of the vascular type (VAD) and 22 with dementia of the Alzheimer's type (AD) were included in the study. VEGF levels were determined in the supernates of circulating natural killer (NK) immune cells isolated by immunomagnetic separation (pure CD16 + CD56 + NK cells at a final density of 7.75 x 10(6) cells/ml). VEGF was measured in spontaneous conditions (without modulation) and after exposure of NK cells with IL-2, lipopolysaccharide (LPS), dehydroepiandrosterone sulfate (DHEAS), LPS + insulin, amyloid-beta (Abeta) fragment 1-42, the inactive sequence Abeta(40-1) and Abeta(1-42) + insulin. A significant decrease in VEGF released by NK cells was demonstrated in AD subjects compared to the other groups. No differences of VEGF levels were found between healthy subjects of old age and the VAD group. The incubation with LPS and DHEAS significantly increased, in a dose-dependent manner, VEGF levels in AD as well as in healthy subjects of young and old age and in VAD patients. The incubation of NK cells with Abeta(1-42) completely suppressed VEGF generation in AD subjects, also reducing VEGF release in the other groups. The co-incubation of NK with LPS + insulin, at different molar concentrations, significantly restored (4- and 6-fold increase from LPS alone) VEGF in AD, also enhancing VEGF secretion in healthy subjects and the VAD group, while the co-incubation of NK with Abeta(1-42) + insulin promptly abolished the negative effects of Abeta(1-42) on VEGF release. These data might suggest that the decreased VEGF secretion by peripheral immune cells of AD subjects could have a negative role for brain angiogenesis, neuroprotection and for brain microvascular permeability to nutrients, increasing brain frailty towards hypoxic injuries. On the contrary, insulin and DHEAS could have beneficial effects in AD, as well as in VAD and in physiological aging, by increasing, in a dose-dependent fashion, VEGF availability by peripheral and resident immune and endothelial cells, so contributing to increase its circulating pool.

Theories of schizophrenia: a genetic-inflammatory-vascular synthesis

BACKGROUND

Schizophrenia, a relatively common psychiatric syndrome, affects virtually all brain functions yet has eluded explanation for more than 100 years. Whether by developmental and/or degenerative processes, abnormalities of neurons and their synaptic connections have been the recent focus of attention. However, our inability to fathom the pathophysiology of schizophrenia forces us to challenge our theoretical models and beliefs. A search for a more satisfying model to explain aspects of schizophrenia uncovers clues pointing to genetically mediated CNS microvascular inflammatory disease.

DISCUSSION

A vascular component to a theory of schizophrenia posits that the physiologic abnormalities leading to illness involve disruption of the exquisitely precise regulation of the delivery of energy and oxygen required for normal brain function. The theory further proposes that abnormalities of CNS metabolism arise because genetically modulated inflammatory reactions damage the microvascular system of the brain in reaction to environmental agents, including infections, hypoxia, and physical trauma. Damage may accumulate with repeated exposure to triggering agents resulting in exacerbation and deterioration, or healing with their removal. There are clear examples of genetic polymorphisms in inflammatory regulators leading to exaggerated inflammatory responses. There is also ample evidence that inflammatory vascular disease of the brain can lead to psychosis, often waxing and waning, and exhibiting a fluctuating course, as seen in schizophrenia. Disturbances of CNS blood flow have repeatedly been observed in people with schizophrenia using old and new technologies. To account for the myriad of behavioral and other curious findings in schizophrenia such as minor physical anomalies, or reported decreased rates of rheumatoid arthritis and highly visible nail fold capillaries, we would have to evoke a process that is systemic such as the vascular and immune/inflammatory systems.

SUMMARY

A vascular-inflammatory theory of schizophrenia brings together environmental and genetic factors in a way that can explain the diversity of symptoms and outcomes observed. If these ideas are confirmed, they would lead in new directions for treatments or preventions by avoiding inducers of inflammation or by way of inflammatory modulating agents, thus preventing exaggerated inflammation and consequent triggering of a psychotic episode in genetically predisposed persons.

Age-dependent cerebrovascular abnormalities and blood flow disturbances in APP23 mice modeling Alzheimer's disease

Neuropathological changes associated with Alzheimer's disease (AD) such as amyloidplaques, cerebral amyloid angiopathy, and related pathologies are reproduced in APP23 transgenic mice overexpressing amyloid precursor protein (APP) with the Swedish mutation. Magnetic resonance angiography (MRA) was applied to probe, in vivo, the cerebral arterial hemodynamics of these mice. Flow voids were detected at the internal carotid artery of 11-month-old APP23 mice. At the age of 20 months, additional flow disturbances were observed in large arteries at the circle of Willis. Vascular corrosion casts obtained from the same mice revealed that vessel elimination, deformation, or both had taken place at the sites where flow voids were detected by MRA. The detailed three-dimensional architecture of the vasculature visible in the casts assisted the identification of smaller vessels most likely formed as substitution or anastomosis within the circle of Willis. Angiograms and corrosion casts from nontransgenic, age-matched mice manifested no major abnormalities in the cerebrovascular arterial flow pattern. Because no transgene overexpression has been found in the cerebrovasculature of APP23 mice and no deposits of amyloid-beta (Abeta) were observed in large arteries in the region of the circle of Willis, the present results suggest that soluble Abeta may exert deleterious effects on the vasculature. Our findings support the idea that cerebral circulatory abnormalities evolving progressively could contribute to AD pathogenesis. The study also shows the power of MRA to identify changes of vascular function in genetically engineered mice. MRA as a noninvasive technique could be applied to test new therapeutic concepts in animal models of AD and in humans.

Microvascular basal lamina antigen loss after traumatic brain injury in the rat

The loss of microvascular basal lamina antigen is known to be a consequence of cerebral ischemia, but little information is available on its role in traumatic brain injury (TBI). The aim of our study was (1) to test the hypothesis that there is damage to the basal lamina of brain microvasculature after TBI, (2) to localize microvascular damage, and (3) to compare this loss with that in ischemia. Rats (n=14) were either sham operated (n=5) or subjected to fluid percussion injury (n=9; TBI=1.5 atm) and killed after 0 (n=5, sham), 12 (n=4), or 24 h (n=5). Collagen-type-IV immunoreactivity and a digital image-processing system were used to localize and quantify the number of stained vascular elements and the total collagen stained area. Western blot was used to compare collagen-type-IV content on the traumatic and nontraumatic brain side. The cortex of animals subjected to TBI and killed after 24 h showed a reduction in the area of stained collagen amounting to 19+/-4% (p<0.009) and a reduction in the total number of microvessels identified by collagen stain (29+/-6%; p<0.02). The Western blot revealed a 31+/-6% (p<0.03) reduction of collagen, compared to the mirror cortical area after 24 h. No significant reduction was found in the group that survived 12 h or in basal ganglia in both groups. TBI causes microvascular basal lamina damage. Whereas TBI affected only cortical areas, cerebral ischemia also induced microvascular basal lamina damage in the basal ganglia. After 24 h, the extent of severe basal lamina damage due to TBI was less severe than in ischemia.

Association of HFE mutations with neurodegeneration and oxidative stress in Alzheimer's disease and correlation with APOE

Oxidative stress enhanced by transition metals such as iron forms an attractive hypothesis for neurodegeneration in Alzheimer's Disease (AD). Iron is increased in the brain in AD, but whether this is a primary abnormality or the result of secondary accumulation is unclear. Among several genetic loci associated with AD, the locus at chromosome 6p21 contains the hereditary hemochromatosis gene HFE. To determine whether a genetic predisposition to iron accumulation is associated with AD, we evaluated three hemochromatosis-associated HFE mutations and APOE in cognitively and histopathologically evaluated subjects with AD, mild cognitive impairment (MCI), non-demented controls with AD-like pathologic changes defined by Braak stage > or = 3 (high pathology controls (HPC)), and non-demented controls without significant histologic changes (low-pathology controls (LPC)). In a subset, we examined ventricular (CSF) fluid F(2)-isoprostane (F(2)-IsoP) levels, a marker of lipid peroxidation. Seventeen subjects demonstrated homozygous or compound heterozygous HFE mutations, 13 (9.4%) in the AD/MCI group (P = 0.019 vs. LPC) and four (20%) in the HPC group (P = 0.006, P < 0.05 with Bonferroni correction vs. LPC). In contrast, the APOE4 allele frequency was increased only in the AD/MCI patients (P < 10(-3) vs. HPC, P < 10(-6) vs. LPC). F(2)-IsoP levels were increased in AD subjects with any HFE mutation versus wild type HFE (P = 0.027). Although confirmation is required, these findings suggest that HFE mutations are associated with increased oxidative stress and Braak stage, and that HFE and APOE genotypes are different between AD patients, high pathology and low pathology controls.