Cerebral beta amyloid angiopathy is a risk factor for cerebral ischemic infarction. A case control study in human brain biopsies

Prevalence, distribution, and severity of cerebral amyloid angiopathy differ between Lewy body diseases and Alzheimer's disease

Dementia with Lewy bodies (DLB), Parkinson's disease dementia (PDD), and Parkinson's disease (PD) collectively known as Lewy body diseases (LBDs) are neuropathologically characterised by α-synuclein deposits (Lewy bodies and Lewy neurites). However, LBDs also exhibit pathology associated with Alzheimer's disease (AD) (i.e. hyperphosphorylated tau and amyloid β (Aβ). Aβ can be deposited in the walls of blood vessels in the brains of individuals with AD, termed cerebral amyloid angiopathy (CAA). The aim of this study was to investigate the type and distribution of CAA in DLB, PDD, and PD and determine if this differs from AD. CAA type, severity, and topographical distribution was assessed in 94 AD, 30 DLB, 17 PDD, and 11 PD cases, and APOE genotype evaluated in a subset of cases where available. 96.3% AD cases, 70% DLB cases and 82.4% PDD cases exhibited CAA (type 1 or type 2). However only 45.5% PD cases had CAA. Type 1 CAA accounted for 37.2% of AD cases, 10% of DLB cases, and 5.9% of PDD cases, and was not observed in PD cases. There was a hierarchical topographical distribution in regions affected by CAA where AD and DLB displayed the same distribution pattern that differed from PDD and PD. APOE ε4 was associated with severity of CAA in AD cases. Topographical patterns and severity of CAA in DLB more closely resembled AD rather than PDD, and as type 1 CAA is associated with clinical dementia in AD, further investigations are warranted into whether the increased presence of type 1 CAA in DLB compared to PDD are related to the onset of cognitive symptoms and is a distinguishing factor between LBDs. Possible alignment of the the topographical distribution of CAA and microbleeds in DLB warrants further investigation. CAA in DLB more closely resembles AD rather than PDD or PD, and should be taken into consideration when stratifying patients for clinical trials or designing disease modifying therapies.

[A case of multiple small cerebral infarcts in the cerebellum and bilateral cerebrum, diagnosed with amyloid angiopathy by brain biopsy]

An 82-year-old woman had been suffering from progressive forgetfulness and abnormal speech and behavior for One month. Findings of the MRI of the head indicated scattered small cerebral infarcts in the cerebellum and in bilateral cerebral cortex/subcortical white matter. After admission, she experienced a subcortical hemorrhage, and the percentage of small cerebral infarcts increased over time. Based on the suspicion of central primary vasculitis or malignant lymphoma, we performed a brain biopsy targeting the right temporal lobe hemorrhage site, and the patient was diagnosed with cerebral amyloid angiopathy (CAA). We conclude that CAA can cause multiple small progressive cerebral infarcts.

Transcriptomic analysis of frontotemporal lobar degeneration with TDP-43 pathology reveals cellular alterations across multiple brain regions

Frontotemporal lobar degeneration (FTLD) is a group of heterogeneous neurodegenerative disorders affecting the frontal and temporal lobes of the brain. Nuclear loss and cytoplasmic aggregation of the RNA-binding protein TDP-43 represents the major FTLD pathology, known as FTLD-TDP. To date, there is no effective treatment for FTLD-TDP due to an incomplete understanding of the molecular mechanisms underlying disease development. Here we compared postmortem tissue RNA-seq transcriptomes from the frontal cortex, temporal cortex, and cerebellum between 28 controls and 30 FTLD-TDP patients to profile changes in cell-type composition, gene expression and transcript usage. We observed downregulation of neuronal markers in all three regions of the brain, accompanied by upregulation of microglia, astrocytes, and oligodendrocytes, as well as endothelial cells and pericytes, suggesting shifts in both immune activation and within the vasculature. We validate our estimates of neuronal loss using neuropathological atrophy scores and show that neuronal loss in the cortex can be mainly attributed to excitatory neurons, and that increases in microglial and endothelial cell expression are highly correlated with neuronal loss. All our analyses identified a strong involvement of the cerebellum in the neurodegenerative process of FTLD-TDP. Altogether, our data provides a detailed landscape of gene expression alterations to help unravel relevant disease mechanisms in FTLD.

Regional Associations of Cortical Superficial Siderosis and β-Amyloid-Positron-Emission-Tomography Positivity in Patients With Cerebral Amyloid Angiopathy

Objective

This is a cross-sectional study to evaluate whether β-amyloid-(Aβ)-PET positivity and cortical superficial siderosis (cSS) in patients with cerebral amyloid angiopathy (CAA) are regionally colocalized.

Methods

Ten patients with probable or possible CAA (73.3 ± 10.9 years, 40% women) underwent MRI examination with a gradient-echo-T2*-weighted-imaging sequence to detect cSS and ¹⁸F-florbetaben PET examination to detect fibrillar Aβ. In all cortical regions of the Hammers Atlas, cSS positivity (MRI: ITK-SNAP segmentation) and Aβ-PET positivity (PET: ≥ mean value + 2 standard deviations of 14 healthy controls) were defined. Regional agreement of cSS- and Aβ-PET positivity was evaluated. Aβ-PET quantification was compared between cSS-positive and corresponding contralateral cSS-negative atlas regions. Furthermore, the Aβ-PET quantification of cSS-positive regions was evaluated in voxels close to cSS and in direct cSS voxels.

Results

cSS- and Aβ-PET positivity did not indicate similarity of their regional patterns, despite a minor association between the frequency of Aβ-positive patients and the frequency of cSS-positive patients within individual regions (r_s = 0.277, p = 0.032). However, this association was driven by temporal regions lacking cSS- and Aβ-PET positivity. When analyzing all composite brain regions, Aβ-PET values in regions close to cSS were significantly higher than in regions directly affected with cSS (p < 0.0001). However, Aβ-PET values in regions close to cSS were not different when compared to corresponding contralateral cSS-negative regions (p = 0.603).

Conclusion

In this cross-sectional study, cSS and Aβ-PET positivity did not show regional association in patients with CAA and deserve further exploitation in longitudinal designs. In clinical routine, a specific cross-sectional evaluation of Aβ-PET in cSS-positive regions is probably not useful for visual reading of Aβ-PETs in patients with CAA.

Neuroinflammation as a Key Driver of Secondary Neurodegeneration Following Stroke?

Ischaemic stroke involves the rapid onset of focal neurological dysfunction, most commonly due to an arterial blockage in a specific region of the brain. Stroke is a leading cause of death and common cause of disability, with over 17 million people worldwide suffering from a stroke each year. It is now well-documented that neuroinflammation and immune mediators play a key role in acute and long-term neuronal tissue damage and healing, not only in the infarct core but also in distal regions. Importantly, in these distal regions, termed sites of secondary neurodegeneration (SND), spikes in neuroinflammation may be seen sometime after the initial stroke onset, but prior to the presence of the neuronal tissue damage within these regions. However, it is key to acknowledge that, despite the mounting information describing neuroinflammation following ischaemic stroke, the exact mechanisms whereby inflammatory cells and their mediators drive stroke-induced neuroinflammation are still not fully understood. As a result, current anti-inflammatory treatments have failed to show efficacy in clinical trials. In this review we discuss the complexities of post-stroke neuroinflammation, specifically how it affects neuronal tissue and post-stroke outcome acutely, chronically, and in sites of SND. We then discuss current and previously assessed anti-inflammatory therapies, with a particular focus on how failed anti-inflammatories may be repurposed to target SND-associated neuroinflammation.

Protein Aggregation in the Pathogenesis of Ischemic Stroke

Despite the distinction between ischemic stroke and neurodegenerative disorders, they share numerous pathophysiologies particularly those mediated by inflammation and oxidative stress. Although protein aggregation is considered to be a hallmark of neurodegenerative diseases, the formation of protein aggregates can be also induced within a short time after cerebral ischemia, aggravating cerebral ischemic injury. Protein aggregation uncovers a previously unappreciated molecular overlap between neurodegenerative diseases and ischemic stroke. Unfortunately, compared with neurodegenerative disease, mechanism of protein aggregation after cerebral ischemia and how this can be averted remain unclear. This review highlights current understanding on protein aggregation and its intrinsic role in ischemic stroke.

A1 reactive astrocytes and a loss of TREM2 are associated with an early stage of pathology in a mouse model of cerebral amyloid angiopathy

Background

Cerebral amyloid angiopathy (CAA) is typified by the cerebrovascular deposition of amyloid. The mechanisms underlying the contribution of CAA to neurodegeneration are not currently understood. Although CAA is highly associated with the accumulation of amyloid beta (Aβ), other amyloids are known to associate with the vasculature. Alzheimer’s disease (AD) is characterized by parenchymal Aβ deposition, intracellular accumulation of tau, and significant neuroinflammation. CAA increases with age and is present in 85–95% of individuals with AD. A substantial amount of research has focused on understanding the connection between parenchymal amyloid and glial activation and neuroinflammation, while associations between vascular amyloid pathology and glial reactivity remain understudied.

Methods

Here, we dissect the glial and immune responses associated with early-stage CAA with histological, biochemical, and gene expression analyses in a mouse model of familial Danish dementia (FDD), a neurodegenerative disease characterized by the vascular accumulation of Danish amyloid (ADan). Findings observed in this CAA mouse model were complemented with primary culture assays.

Results

We demonstrate that early-stage CAA is associated with dysregulation in immune response networks and lipid processing, severe astrogliosis with an A1 astrocytic phenotype, and decreased levels of TREM2 with no reactive microgliosis. Our results also indicate how cholesterol accumulation and ApoE are associated with vascular amyloid deposits at the early stages of pathology. We also demonstrate A1 astrocytic mediation of TREM2 and microglia homeostasis.

Conclusion

The initial glial response associated with early-stage CAA is characterized by the upregulation of A1 astrocytes without significant microglial reactivity. Gene expression analysis revealed that several AD risk factors involved in immune response and lipid processing may also play a preponderant role in CAA. This study contributes to the increasing evidence that brain cholesterol metabolism, ApoE, and TREM2 signaling are major players in the pathogenesis of AD-related dementias, including CAA. Understanding the basis for possible differential effects of glial response, ApoE, and TREM2 signaling on parenchymal plaques versus vascular amyloid deposits provides important insight for developing future therapeutic interventions.

The Amyloid-Tau-Neuroinflammation Axis in the Context of Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA) is typified by the cerebrovascular deposition of amyloid. Currently, there is no clear understanding of the mechanisms underlying the contribution of CAA to neurodegeneration. Despite the fact that CAA is highly associated with the accumulation of Aβ, other types of amyloids have been shown to associate with the vasculature. Interestingly, in many cases, vascular amyloidosis has been associated with an active immune response and perivascular deposition of hyperphosphorylated tau. Despite the fact that in Alzheimer’s disease (AD) a major focus of research has been the understanding of the connection between parenchymal amyloid plaques, tau aggregates in the form of neurofibrillary tangles (NFTs), and immune activation, the contribution of tau and neuroinflammation to neurodegeneration associated with CAA remains understudied. In this review, we discussed the existing evidence regarding the amyloid diversity in CAA and its relation to tau pathology and immune response, as well as the possible contribution of molecular and cellular mechanisms, previously associated with parenchymal amyloid in AD and AD-related dementias, to the pathogenesis of CAA. The detailed understanding of the “amyloid-tau-neuroinflammation” axis in the context of CAA could open the opportunity to develop therapeutic interventions for dementias associated with CAA that are currently being proposed for AD and AD-related dementias.

Neurovascular Ageing and Age-Related Diseases

Proper functioning of the brain is dependent on integrity of the cerebral vasculature. During ageing, a number of factors including aortic or arterial stiffness, autonomic dysregulation, neurovascular uncoupling and blood-brain barrier (BBB) damage will define the dynamics of brain blood flow and local perfusion. The nature and extent of ageing-related cerebrovascular changes, the degree of involvement of the heart and extracranial vessels and the consequent location of tissue pathology may vary considerably. Atheromatous disease retarding flow is a common vascular insult, which increases exponentially with increasing age. Arteriolosclerosis characterized as a prominent feature of small vessel disease is one of the first changes to occur during the natural history of cerebrovascular pathology. At the capillary level, the cerebral endothelium, which forms the BBB undergoes changes including reduced cytoplasm, fewer mitochondria, loss of tight junctions and thickened basement membranes with collagenosis. Astrocyte end-feet protecting the BBB retract as part of the clasmatodendrotic response whereas pericyte coverage is altered. The consequences of these microvascular changes are lacunar infarcts, cortical and subcortical microinfarcts, microbleeds and diffuse white matter disease, which involves myelin loss and axonal abnormalities. The deeper structures are particularly vulnerable because of the relatively reduced density of the microvascular network formed by perforating and penetrating end arteries. Ultimately, the integrity of both the neurovascular and gliovascular units is compromised such that there is an overall synergistic effect reflecting on ageing associated cerebral perfusion and permeability. More than one protagonist appears to be involved in ageing-related cognitive dysfunction characteristically associated with the neurocognitive disorders.

Multiple infarcts and hemorrhages in the central nervous system of a dog with cerebral amyloid angiopathy: a case report

Background

β-amyloid (Aβ) can accumulate in the brain of aged dogs, and within vessels walls, the disease is called cerebral amyloid angiopathy (CAA). In humans, Alzheimer’s disease and CAA are strongly correlated with cerebrovascular disease. However, in dogs, this association has not been extensively studied yet. The present report highlights the pathological and clinical features of a concomitant cerebrovascular disease and amyloid precursor protein (APP) accumulation in the brain of a dog.

Case presentation

A female, 16-year-old, Standard Poodle with a one-year history of cognitive deficits presented with an acute onset of right-sided postural reaction deficit and circling, left-sided head tilt, positional nystagmus, and ataxia. Due to poor prognosis the dog was euthanized, and pathological examination of the brain revealed an acute lacunar infarction within the thalamus extending to rostral colliculus. Additional findings included subacute and chronic areas of ischemia throughout the brain and areas of hemorrhage within the medulla. Immunolabeling revealed APP deposition within intraparenchymal vessels of frontal, temporal and occipital cortex, hippocampus, diencephalon, mesencephalon and myelencephalon, besides meningeal vessels walls. Glial fibrillary acidic protein (GFAP) immunolabeling showed marked astrocytosis around the acute area of infarction and within chronic areas of ischemia. Histological examination of the brain along with immunohistochemistry results showed a concomitant APP, which is an Aβ precursor, accumulation within the neuroparenchyma and vessels (CAA) with histological evidences of a cerebrovascular disease in an aged dog.

Conclusions

This report shows that APP accumulation in the brain can occur concomitantly to a severe cerebrovascular disease in a dog. Further studies are necessary to elucidate if cerebrovascular disease is associated with Aβ accumulation in the brain of dogs.

The pathology and pathophysiology of vascular dementia

Vascular dementia (VaD) is widely recognised as the second most common type of dementia. Consensus and accurate diagnosis of clinically suspected VaD relies on wide-ranging clinical, neuropsychological and neuroimaging measures in life but more importantly pathological confirmation. Factors defining subtypes of VaD include the nature and extent of vascular pathologies, degree of involvement of extra and intracranial vessels and the anatomical location of tissue changes as well as time after the initial vascular event. Atherosclerotic and cardioembolic diseases combined appear the most common subtypes of vascular brain injury. In recent years, cerebral small vessel disease (SVD) has gained prominence worldwide as an important substrate of cognitive impairment. SVD is characterised by arteriolosclerosis, lacunar infarcts and cortical and subcortical microinfarcts and diffuse white matter changes, which involve myelin loss and axonal abnormalities. Global brain atrophy and focal degeneration of the cerebrum including medial temporal lobe atrophy are also features of VaD similar to Alzheimer's disease. Hereditary arteriopathies have provided insights into the mechanisms of dementia particularly how arteriolosclerosis, a major contributor of SVD promotes cognitive impairment. Recently developed and validated neuropathology guidelines indicated that the best predictors of vascular cognitive impairment were small or lacunar infarcts, microinfarcts, perivascular space dilation, myelin loss, arteriolosclerosis and leptomeningeal cerebral amyloid angiopathy. While these substrates do not suggest high specificity, VaD is likely defined by key neuronal and dendro-synaptic changes resulting in executive dysfunction and related cognitive deficits. Greater understanding of the molecular pathology is needed to clearly define microvascular disease and vascular substrates of dementia. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Small vessel disease, neurovascular regulation and cognitive impairment: post-mortem studies reveal a complex relationship, still poorly understood

The contribution of vascular disease to cognitive impairment is under-recognized and the pathogenesis is poorly understood. This information gap has multiple causes, including a lack of post-mortem validation of clinical diagnoses of vascular cognitive impairment (VCI) or vascular dementia (VaD), the exclusion of cases with concomitant neurodegenerative disease when diagnosing VCI/VaD, and a lack of standardization of neuropathological assessment protocols for vascular disease. Other contributors include a focus on end-stage destructive lesions to the exclusion of more subtle types of diffuse brain injury, on structural abnormalities of arteries and arterioles to the exclusion of non-structural abnormalities and capillary damage, and the use of post-mortem sampling strategies that are biased towards the identification of neurodegenerative pathologies. Recent studies have demonstrated the value of detailed neuropathology in characterizing vascular contributions to cognitive impairment (e.g. in diabetes), and highlight the importance of diffuse white matter changes, capillary damage and vasoregulatory abnormalities in VCI/VaD. The use of standardized, evidence-based post-mortem assessment protocols and the inclusion of biochemical as well as morphological methods in neuropathological studies should improve the accuracy of determination of the contribution of vascular disease to cognitive impairment and clarify the relative contribution of different pathogenic processes to the tissue damage.

Cerebral Hypoperfusion and the Energy Deficit in Alzheimer's Disease

There is a perfusion deficit in Alzheimer's disease (AD), commencing in the precuneus and spreading to other parts of the cerebral cortex. The deficit anticipates the development of dementia, contributes to brain damage, and is caused by both functional and structural abnormalities of the cerebral vasculature. Most of the abnormalities are probably secondary to the accumulation of Aβ but the consequent hypoperfusion may, in turn, increase Aβ production. In the early stages of disease, abnormalities that cause vasoconstriction predominate. These include cholinergic vascular denervation, inhibition of endothelial nitric oxide synthase, increased production of endothelin-1 production and possibly also of angiotensin II. Patients with AD also have an increased prevalence of structural disease of cerebral microvessels, particularly CAA and capillary damage, and particularly in the later stages of disease these are likely to make an important contribution to the cerebral hypoperfusion. The metabolic abnormalities that cause early vascular dysfunction offer several targets for therapeutic intervention. However, for intervention to be effective it probably needs to be early. Prolonged cerebral hypoperfusion may induce compensatory circulatory changes that are themselves damaging, including hypertension and small vessel disease. This has implications for the use of antihypertensive drugs once there is accumulation of Aβ within the brain.

Update on Vascular Dementia

Vascular dementia (VaD) is a major contributor to the dementia syndrome and is described as having problems with reasoning, planning, judgment, and memory caused by impaired blood flow to the brain and damage to the blood vessels resulting from events such as stroke. There are a variety of etiologies that contribute to the development of vascular cognitive impairment and VaD, and these are often associated with other dementia-related pathologies such as Alzheimer disease. The diagnosis of VaD is difficult due to the number and types of lesions and their locations in the brain. Factors that increase the risk of vascular diseases such as stroke, high blood pressure, high cholesterol, and smoking also raise the risk of VaD. Therefore, controlling these risk factors can help lower the chances of developing VaD. This update describes the subtypes of VaD, with details of their complex presentation, associated pathological lesions, and issues with diagnosis, prevention, and treatment.

Shared genetic contribution to Ischaemic Stroke and Alzheimer's Disease

OBJECTIVE

Increasing evidence suggests epidemiological and pathological links between Alzheimer's disease (AD) and Ischaemic Stroke (IS). We investigated the evidence that shared genetic factors underpin the two diseases.

METHODS

Using genome wide association study (GWAS) data from METASTROKE+ (15,916 IS cases and 68,826 controls) and IGAP (17,008 AD cases and 37,154 controls), we evaluated known associations with AD and IS. On the subset of data for which we could obtain compatible genotype-level data (4,610 IS cases, 1,281 AD cases and 14,320 controls), we estimated the genome-wide genetic correlation (rG) between AD and IS, and the three subtypes (cardioembolic, small vessel, large vessel), using genome-wide SNP data. We then performed a meta-analysis and pathway analysis in the combined AD and small vessel stroke datasets to identify the SNPs and molecular pathways through which disease risk may be conferred.

RESULTS

We found evidence of a shared genetic contribution between AD and small vessel stroke (rG(SE)=0.37(0.17); p=0.011). Conversely, there was no evidence to support shared genetic factors in AD and IS overall, or with the other stroke subtypes. Of the known GWAS associations with IS or AD, none reached significance for association with the other trait (or stroke subtypes). A meta-analysis of AD IGAP and METASTROKE+ small vessel stroke GWAS data highlighted a region (ATP5H/KCTD2/ICT1), associated with both diseases (p=1.8x10-8 ). A pathway analysis identified four associated pathways, involving cholesterol transport and immune response.

INTERPRETATION

Our findings indicate shared genetic susceptibility to AD and small vessel stroke and highlight potential causal pathways and loci. This article is protected by copyright. All rights reserved.

Vascular cognitive impairment and dementia

Vascular contributions to cognitive impairment are receiving heightened attention as potentially modifiable factors for dementias of later life. These factors have now been linked not only to vascular cognitive disorders but also Alzheimer's disease. In this chapter we review 3 related topics that address vascular contributions to cognitive impairment: 1. vascular pathogenesis and mechanisms; 2. neuropsychological and neuroimaging phenotypic manifestations of cerebrovascular disease; and 3. prospects for prevention of cognitive impairment of later life based on cardiovascular and stroke risk modification. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Neuropathological diagnosis of vascular cognitive impairment and vascular dementia with implications for Alzheimer's disease

Vascular dementia (VaD) is recognised as a neurocognitive disorder, which is explained by numerous vascular causes in the general absence of other pathologies. The heterogeneity of cerebrovascular disease makes it challenging to elucidate the neuropathological substrates and mechanisms of VaD as well as vascular cognitive impairment (VCI). Consensus and accurate diagnosis of VaD relies on wide-ranging clinical, neuropsychometric and neuroimaging measures with subsequent pathological confirmation. Pathological diagnosis of suspected clinical VaD requires adequate postmortem brain sampling and rigorous assessment methods to identify important substrates. Factors that define the subtypes of VaD include the nature and extent of vascular pathologies, degree of involvement of extra and intracranial vessels and the anatomical location of tissue changes. Atherosclerotic and cardioembolic diseases appear the most common substrates of vascular brain injury or infarction. Small vessel disease characterised by arteriolosclerosis and lacunar infarcts also causes cortical and subcortical microinfarcts, which appear to be the most robust substrates of cognitive impairment. Diffuse WM changes with loss of myelin and axonal abnormalities are common to almost all subtypes of VaD. Medial temporal lobe and hippocampal atrophy accompanied by variable hippocampal sclerosis are also features of VaD as they are of Alzheimer’s disease. Recent observations suggest that there is a vascular basis for neuronal atrophy in both the temporal and frontal lobes in VaD that is entirely independent of any Alzheimer pathology. Further knowledge on specific neuronal and dendro-synaptic changes in key regions resulting in executive dysfunction and other cognitive deficits, which define VCI and VaD, needs to be gathered. Hereditary arteriopathies such as cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy or CADASIL have provided insights into the mechanisms of dementia associated with cerebral small vessel disease. Greater understanding of the neurochemical and molecular investigations is needed to better define microvascular disease and vascular substrates of dementia. The investigation of relevant animal models would be valuable in exploring the pathogenesis as well as prevention of the vascular causes of cognitive impairment.

Cerebrovascular disease in ageing and Alzheimer's disease

Cerebrovascular disease (CVD) and Alzheimer’s disease (AD) have more in common than their association with ageing. They share risk factors and overlap neuropathologically. Most patients with AD have Aβ amyloid angiopathy and degenerative changes affecting capillaries, and many have ischaemic parenchymal abnormalities. Structural vascular disease contributes to the ischaemic abnormalities in some patients with AD. However, the stereotyped progression of hypoperfusion in this disease, affecting first the precuneus and cingulate gyrus, then the frontal and temporal cortex and lastly the occipital cortex, suggests that other factors are more important, particularly in early disease. Whilst demand for oxygen and glucose falls in late disease, functional MRI, near infrared spectroscopy to measure the saturation of haemoglobin by oxygen, and biochemical analysis of myelin proteins with differential susceptibility to reduced oxygenation have all shown that the reduction in blood flow in AD is primarily a problem of inadequate blood supply, not reduced metabolic demand. Increasing evidence points to non-structural vascular dysfunction rather than structural abnormalities of vessel walls as the main cause of cerebral hypoperfusion in AD. Several mediators are probably responsible. One that is emerging as a major contributor is the vasoconstrictor endothelin-1 (EDN1). Whilst there is clearly an additive component to the clinical and pathological effects of hypoperfusion and AD, experimental and clinical observations suggest that the disease processes also interact mechanistically at a cellular level in a manner that exacerbates both. The elucidation of some of the mechanisms responsible for hypoperfusion in AD and for the interactions between CVD and AD has led to the identification of several novel therapeutic approaches that have the potential to ameliorate ischaemic damage and slow the progression of neurodegenerative disease.

APOE and cerebral amyloid angiopathy in community-dwelling older persons

Both cerebral amyloid angiopathy and Alzheimer's disease pathology involve abnormal β-amyloid processing. We aim to elucidate the relationship of the apolipoprotein E (APOE) genotypes with amyloid angiopathy in the presence of variable amounts of Alzheimer's pathology. Data came from 1062 autopsied subjects from 2 community-based studies of aging. Common neuropathologies including Alzheimer's disease and amyloid angiopathy were assessed using uniform methods. APOE was genotyped by sequencing the 2 polymorphisms in codons 112 and 158 of exon 4. We examined the associations of APOE with amyloid angiopathy using ordinal logistic regression analyses, controlling for demographics and subsequently Alzheimer's and other common pathologies. Moderate to severe amyloid angiopathy was identified in 35.2% (n = 374) of the subjects; 15.3% (n = 162) of the subjects were APOE ε2 carriers; and 26.1% (n = 277) ε4 carriers. Adjusting for demographics, the presence of ε4 allele, but not ε2, was associated with more severe amyloid angiopathy. After further adjustment for Alzheimer's pathology, both ε2 (odds ratio 1.707, 95% confidence interval 1.236-2.358, p = 0.001) and ε4 (odds ratio 2.284, 95% confidence interval 1.730-3.014, p < 0.001) were independently associated with amyloid angiopathy. The results were confirmed by path analysis. Furthermore, APOE ε4 carriers, but not ε2 carriers, were more likely to have capillary amyloid angiopathy. Accounting for capillary involvement did not alter the APOE associations with amyloid angiopathy. We conclude that both APOE ε2 and ε4 alleles are associated with more severe cerebral amyloid angiopathy, and the direct effect of ε2 is masked by the allele's negative association with comorbid Alzheimer's pathology. APOE ε4, but not ε2, is associated with capillary amyloid angiopathy.

Matrix metalloproteinase 9-mediated intracerebral hemorrhage induced by cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA), the deposition of amyloid-β in cerebrovascular walls, is the most common cause of lobar hemorrhagic stroke. Previous studies show that cerebrovascular amyloid-β induces expression and activation of matrix metalloproteinase 9 (MMP-9) in cerebral vessels of amyloid precursor protein transgenic mice. Here, we extended these findings and evaluated MMP-9 expression in postmortem brain tissues of human CAA cases. MMP-9 colocalized with CAA, correlated with the severity of the vascular pathology, and was detected in proximity to microbleeds. We characterized a novel assay using longitudinal multiphoton microscopy and a novel tracer to visualize and quantify the magnitude and kinetics of hemorrhages in three dimensions in living mouse brains. We demonstrated that topical application of recombinant MMP-9 resulted in a time- and dose-dependent cerebral hemorrhage. Amyloid precursor protein mice with significant CAA developed more extensive hemorrhages which also appeared sooner after exposure to MMP-9. Our data suggest an important role for MMP-9 in development of hemorrhages in the setting of CAA. Inhibition of MMP-9 may present a preventive strategy for CAA-associated hemorrhage.

Cerebral amyloid angiopathy, subcortical white matter disease and dementia: literature review and study in OPTIMA

Cerebral amyloid angiopathy (CAA) is of increasing clinical and research interest as the ability to detect it and its consequences by neuroimaging in living subjects has advanced. There is also increasing interest in understanding its possible role in the development of intracerebral hemorrhage, Alzheimer's disease (AD) and vascular dementia. In this article, the literature on this subject is reviewed and novel findings relating CAA to subcortical white matter damage in 224 subjects in the Oxford project to Investigate Memory and Ageing (OPTIMA) are reported. The relationship between CAA and subcortical tissue damage in the OPTIMA subjects was found to be critically dependent on ApoE genotype, there being a positive relationship between measures of CAA and subcortical small vessel disease in ApoEε4 carriers and a significant negative relationship in ApoEε2 carriers. These findings draw attention, as have many other studies, to the importance of ApoE genotype as a major risk factor not only for dementia but also for damage to blood vessels in the aging brain.

Nontraumatic convexal subarachnoid hemorrhage concomitant with acute ischemic stroke

BACKGROUND

Nontraumatic convexal subarachnoid hemorrhage (cSAH) rarely occurs subsequent to acute ischemic stroke. The incidence, clinical background characteristics, and outcomes in acute ischemic stroke patients with cSAH were investigated.

METHODS

Our stroke center database was reviewed to identify patients with acute ischemic stroke/transient ischemic attack (TIA) who demonstrated acute cSAH within 14 days of admission between 2005 and 2011. Background characteristics, clinical course, and outcomes at discharge and 3 months after onset were investigated in these patients.

RESULTS

Of 4953 acute stroke/TIA patients, cSAH was observed in 8 (.14%) patients (7 men, mean age 71 years): 7 were detected incidentally, and the other was found immediately after a convulsion. Two patients died during their hospital stay, 1 died after discharge, and 3 were dependent at 3 months. Major artery occlusion or severe stenosis was observed in 5 patients. Two patients subsequently developed subcortical hemorrhage. On gradient echo imaging, lobar cerebral microbleeds were observed in 2 patients, and chronic superficial siderosis was observed in 2 patients.

CONCLUSIONS

In this retrospective review of cases with ischemic stroke and cSAH, over half of patients had occlusion of major arteries. Cerebral amyloid angiopathy was suggested by magnetic resonance imaging findings and subsequent events in 3 patients. The overall outcome was unfavorable although the causal relationship with cSAH was unclear.

Blood platelets in the progression of Alzheimer's disease

Alzheimer's disease (AD) is characterized by neurotoxic amyloid-ß plaque formation in brain parenchyma and cerebral blood vessels known as cerebral amyloid angiopathy (CAA). Besides CAA, AD is strongly related to vascular diseases such as stroke and atherosclerosis. Cerebrovascular dysfunction occurs in AD patients leading to alterations in blood flow that might play an important role in AD pathology with neuronal loss and memory deficits. Platelets are the major players in hemostasis and thrombosis, but are also involved in neuroinflammatory diseases like AD. For many years, platelets were accepted as peripheral model to study the pathophysiology of AD because platelets display the enzymatic activities to generate amyloid-ß (Aß) peptides. In addition, platelets are considered to be a biomarker for early diagnosis of AD. Effects of Aß peptides on platelets and the impact of platelets in the progression of AD remained, however, ill-defined. The present study explored the cellular mechanisms triggered by Aß in platelets. Treatment of platelets with Aß led to platelet activation and enhanced generation of reactive oxygen species (ROS) and membrane scrambling, suggesting enhanced platelet apoptosis. More important, platelets modulate soluble Aß into fibrillar structures that were absorbed by apoptotic but not vital platelets. This together with enhanced platelet adhesion under flow ex vivo and in vivo and platelet accumulation at amyloid deposits of cerebral vessels of AD transgenic mice suggested that platelets are major contributors of CAA inducing platelet thrombus formation at vascular amyloid plaques leading to vessel occlusion critical for cerebrovascular events like stroke.

Assessing white matter ischemic damage in dementia patients by measurement of myelin proteins

White matter ischemia is difficult to quantify histologically. Myelin-associated glycoprotein (MAG) is highly susceptible to ischemia, being expressed only adaxonally, far from the oligodendrocyte cell body. Myelin-basic protein (MBP) and proteolipid protein (PLP) are expressed throughout the myelin sheath. We compared MAG, MBP, and PLP levels in parietal white matter homogenates from 17 vascular dementia (VaD), 49 Alzheimer's disease (AD), and 33 control brains, after assessing the post-mortem stability of these proteins. Small vessel disease (SVD) and cerebral amyloid angiopathy (CAA) severity had been assessed in paraffin sections. The concentration of MAG remained stable post-mortem, declined with increasing SVD, and was significantly lower in VaD than controls. The concentration of MBP fell progressively post-mortem, limiting its diagnostic utility in this context. Proteolipid protein was stable post-mortem and increased significantly with SVD severity. The MAG/PLP ratio declined significantly with SVD and CAA severity. The MAG and PLP levels and MAG/PLP did not differ significantly between AD and control brains. We validated the utility of MAG and MAG/PLP measurements on analysis of 74 frontal white matter samples from an Oxford cohort in which SVD had previously been scored. MAG concentration and the MAG/PLP ratio are useful post-mortem measures of ante-mortem white matter ischemia.

Cerebral Amyloidal Angiopathy--a disease with implications for neurology and psychiatry

Cerebral Amyloidal Angiopathy (CAA), which occurs sporadically in most cases but can also occur hereditarily, belongs to the group amyloidoses and is characterized by the deposition and accumulation of beta-amyloid (Aβ) in smaller arterial vessels of the brain. The deposition of Aβ leads to degenerative changes in the cerebral vessel system (thickening of the vessel wall, microaneurysm, constriction of vascular lumen, dissection), which favour the development of the clinical symptomatology most often associated with CAA. Besides haemorrhages, cerebral ischaemia, transient neurological symptoms, leukoencephalopathy as well as cognitive decline and even dementia may appear in connection with CAA. A definite diagnosis of CAA can only be made on the basis of a pathological assessment, even though diagnostic findings of cerebral neuroimaging and clinical symptoms allow the diagnosis of a probable CAA. At present, no causal therapy options are available. Although CAA is placed within the range of neurological illnesses, psychiatric symptoms such as cognitive impairment, personality change or behavioural problems as well as depression are plausible clinical manifestations of CAA and may even dominate the clinical picture. Apart from epidemiological, pathogenetical, clinical and diagnostical aspects, possible psychiatric implications of CAA are discussed in the review article.

Vascular dementia: different forms of vessel disorders contribute to the development of dementia in the elderly brain

The diagnosis of vascular dementia (VaD) describes a group of various vessel disorders with different types of vascular lesions that finally contribute to the development of dementia. Most common forms of VaD in the elderly brain are subcortical vascular encephalopathy, strategic infarct dementia, and the multi infarct encephalopathy. Hereditary forms of VaD are rare. Most common is the cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Sporadic forms of VaD are caused by degenerative vessel disorders such as atherosclerosis, small vessel disease (SVD) including small vessel arteriosclerosis, arteriolosclerosis, and lipohyalinosis, and cerebral amyloid angiopathy (CAA). Less frequently inflammatory vessel disorders and tumor-associated vessel lesions (e.g. angiocentric T-cell or angiotropic large cell lymphoma) can cause symptoms of dementia. Here, we review and discuss the impact of vessel disorders to distinct vascular brain tissue lesions and to the development of dementia in elderly individuals. The impact of coexisting neurodegenerative pathology in the elderly brain to VaD as well as the correlation between SVD and CAA expansion in the brain parenchyma with that of Alzheimer's disease (AD)-related pathology is highlighted. We conclude that "pure" VaD is rare and most frequently caused by infarctions. However, there is a significant contribution of vascular lesions and vessel pathology to the development of dementia that may go beyond tissue damage due to vascular lesions. Insufficient blood blow and alterations of the perivascular drainage mechanisms of the brain may also lead to a reduced protein clearance from extracellular space and subsequent increase of proteins in the brain parenchyma, such as the amyloid β-protein, and foster, thereby, the development of AD-related neurodegeneration. As such, it seems to be important for clinical practice to consider treatment of potentially coexisting AD pathology in cognitively impaired patients with vascular lesions.

Vascular dementia: Current concepts and nomenclature harmonization

Several types of cerebrovascular lesions are associated with cognitive decline, but the role of each type in dementia manifestation has yet to be determined. One of the greatest barriers of conducting clinicopathological studies in vascular dementia concerns the overlapping of nomenclature for these lesions. The aim of the present review was to discuss current nomenclature for cerebrovascular lesions and suggest modifications to allow better diagnostic reproducibility in this field.

Contrast-enhanced magnetic resonance microangiography reveals remodeling of the cerebral microvasculature in transgenic ArcAβ mice

Amyloid-β (Aβ) deposition in the cerebral vasculature is accompanied by remodeling which has a profound influence on vascular integrity and function. In the current study we have quantitatively assessed the age-dependent changes of the cortical vasculature in the arcAβ model of cerebral amyloidosis. To estimate the density of the cortical microvasculature in vivo, we used contrast-enhanced magnetic resonance microangiography (CE-μMRA). Three-dimensional gradient echo datasets with 60 μm isotropic resolution were acquired in 4- and 24-month-old arcAβ mice and compared with wild-type (wt) control mice of the same age before and after administration of superparamagnetic iron oxide nanoparticles. After segmentation of the cortical vasculature from difference images, an automated algorithm was applied for assessing the number and size distribution of intracortical vessels. With CE-μMRA, cerebral arteries and veins with a diameter of less than the nominal pixel resolution (60 μm) can be visualized. A significant age-dependent reduction in the number of functional intracortical microvessels (radii of 20-80 μm) has been observed in 24-month-old arcAβ mice compared with age-matched wt mice, whereas there was no difference between transgenic and wt mice of 4 months of age. Immunohistochemistry demonstrated strong fibrinogen and Aβ deposition in small- and medium-sized vessels, but not in large cerebral arteries, of 24-month-old arcAβ mice. The reduced density of transcortical vessels may thus be attributed to impaired perfusion and vascular occlusion caused by deposition of Aβ and fibrin. The study demonstrated that remodeling of the cerebrovasculature can be monitored noninvasively with CE-μMRA in mice.

Amyloid triggers extensive cerebral angiogenesis causing blood brain barrier permeability and hypervascularity in Alzheimer's disease

Evidence of reduced blood-brain barrier (BBB) integrity preceding other Alzheimer's disease (AD) pathology provides a strong link between cerebrovascular angiopathy and AD. However, the "Vascular hypothesis", holds that BBB leakiness in AD is likely due to hypoxia and neuroinflammation leading to vascular deterioration and apoptosis. We propose an alternative hypothesis: amyloidogenesis promotes extensive neoangiogenesis leading to increased vascular permeability and subsequent hypervascularization in AD. Cerebrovascular integrity was characterized in Tg2576 AD model mice that overexpress the human amyloid precursor protein (APP) containing the double missense mutations, APPsw, found in a Swedish family, that causes early-onset AD. The expression of tight junction (TJ) proteins, occludin and ZO-1, were examined in conjunction with markers of apoptosis and angiogenesis. In aged Tg2576 AD mice, a significant increase in the incidence of disrupted TJs, compared to age matched wild-type littermates and young mice of both genotypes, was directly linked to an increased microvascular density but not apoptosis, which strongly supports amyloidogenic triggered hypervascularity as the basis for BBB disruption. Hypervascularity in human patients was corroborated in a comparison of postmortem brain tissues from AD and controls. Our results demonstrate that amylodogenesis mediates BBB disruption and leakiness through promoting neoangiogenesis and hypervascularity, resulting in the redistribution of TJs that maintain the barrier and thus, provides a new paradigm for integrating vascular remodeling with the pathophysiology observed in AD. Thus the extensive angiogenesis identified in AD brain, exhibits parallels to the neovascularity evident in the pathophysiology of other diseases such as age-related macular degeneration.

Review: sporadic cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) may result from focal to widespread amyloid-β protein (Aβ) deposition within leptomeningeal and intracortical cerebral blood vessels. In addition, pericapillary Aβ refers to Aβ depositions in the glia limitans and adjacent neuropil, whereas in capillary CAA Aβ depositions are present in the capillary wall. CAA may cause lobar intracerebral haemorrhages and microbleeds. Hypoperfusion and reduced vascular autoregulation due to CAA might cause infarcts and white matter lesions. CAA thus causes vascular lesions that potentially lead to (vascular) dementia and may further contribute to dementia by impeding the clearance of solutes out of the brain and transport of nutrients across the blood brain barrier. Severe CAA is an independent risk factor for cognitive decline. The clinical diagnosis of CAA is based on the assessment of associated cerebrovascular lesions. In addition, perivascular spaces in the white matter and reduced concentrations of both Aβ(40) and Aβ(42) in cerebrospinal fluid may prove to be suggestive for CAA. Transgenic mouse models that overexpress human Aβ precursor protein show parenchymal Aβ and CAA, thus corroborating the current concept of CAA pathogenesis: neuronal Aβ enters the perivascular drainage pathway and may accumulate in vessel walls due to increased amounts and/or decreased clearance of Aβ, respectively. We suggest that pericapillary Aβ represents early impairment of the perivascular drainage pathway while capillary CAA is associated with decreased transendothelial clearance of Aβ. CAA plays an important role in the multimorbid condition of the ageing brain but its contribution to neurodegeneration remains to be elucidated.

Amyloidosis presenting as pulmonary infarcts: a case report

Amyloidosis is a multisystem disease characterized by extracellular deposition of complex protein-polysaccharide in a β-pleated configuration. The imaging features in the thorax are well described and are traditionally divided into tracheobronchial, nodular parenchymal, and diffuse alveolar septal subtypes. We describe an unusual case of pulmonary amyloidosis presenting with hemoptysis as a result of pulmonary infarcts related to vascular deposition. With this case, we show that amyloidosis should be considered (along with embolic disease) when vascular insults (infarcts) are seen in multiple vascular territories.

Tau, prions and Aβ: the triad of neurodegeneration

This article highlights the features that connect prion diseases with other cerebral amyloidoses and how these relate to neurodegeneration, with focus on tau phosphorylation. It also discusses similarities between prion disease and Alzheimer's disease: mechanisms of amyloid formation, neurotoxicity, pathways involved in triggering tau phosphorylation, links to cell cycle pathways and neuronal apoptosis. We review previous evidence of prion diseases triggering hyperphosphorylation of tau, and complement these findings with cases from our collection of genetic, sporadic and transmitted forms of prion diseases. This includes the novel finding that tau phosphorylation consistently occurs in sporadic CJD, in the absence of amyloid plaques.

Fibrinogen and beta-amyloid association alters thrombosis and fibrinolysis: a possible contributing factor to Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder in which vascular pathology plays an important role. Since the beta-amyloid peptide (Abeta) is a critical factor in this disease, we examined its relationship to fibrin clot formation in AD. In vitro and in vivo experiments showed that fibrin clots formed in the presence of Abeta are structurally abnormal and resistant to degradation. Fibrin(ogen) was observed in blood vessels positive for amyloid in mouse and human AD samples, and intravital brain imaging of clot formation and dissolution revealed abnormal thrombosis and fibrinolysis in AD mice. Moreover, depletion of fibrinogen lessened cerebral amyloid angiopathy pathology and reduced cognitive impairment in AD mice. These experiments suggest that one important contribution of Abeta to AD is via its effects on fibrin clots, implicating fibrin(ogen) as a potential critical factor in this disease.

Prevalence of dementia disorders in the oldest-old: an autopsy study

The prevalence of Alzheimer disease (AD) and vascular dementia (VD) increases with advancing age, but less so after age 90 years. A retrospective hospital-based study of the relative prevalence of different disorders was performed in 1,110 consecutive autopsy cases of demented elderly in Vienna, Austria (66% females, MMSE <20; mean age 83.3 +/- 5.4 SD years). It assessed clinical, general autopsy data and neuropathology including immunohistochemistry. Neuropathologic diagnosis followed current consensus criteria. Four age groups (7-10th decade) were evaluated. In the total cohort AD pathology was seen in 82.9% ("pure" AD 42.9%; AD + other pathologies 39.9%), VD in 10.8% (mixed dementia, MIX, i.e. AD + vascular encephalopathy in 5.5%); other disorders in 5.7%, and negative pathology in 0.8%. The relative prevalence of AD increased from age 60 to 89 years and decreased slightly after age 90+, while "pure" VD diagnosed in the presence of vascular encephalopathy of different types with low neuritic AD pathology (Braak stages <3; mean 1.2-1.6) decreased progressively from age 60 to 90+; 85-95% of these patients had histories of diabetes, morphologic signs of hypertension, 65% myocardial infarction/cardiac decompensation, and 75% a history of stroke(s). Morphologic subtypes, subcortical arteriosclerotic (the most frequent), multi-infarct encephalopathy, and strategic infarct dementia showed no age-related differences. The relative prevalence of AD + Lewy pathology remained fairly constant with increasing age. Mixed dementia and AD with minor cerebrovascular lesions increased significantly with age, while other dementias decreased. This retrospective study using strict morphologic criteria confirmed increased prevalence of AD with age, but mild decline at age 90+, and progressive decline of VD, while AD + vascular pathologies including MIX showed considerable age-related increase, confirming that mixed pathologies account for most dementia cases in very old persons. A prospective clinicopathologic study in oldest-old subjects showed a significant increase in both AD and cerebral amyloid angiopathy (CAA), but decrease in VD over age 85, while in a small group of old subjects CAA without considerable AD pathology may be an independent risk factor for cognitive decline.

Vascular pathology in the aged human brain

Cerebral atherosclerosis (AS), small vessel disease (SVD), and cerebral amyloid angiopathy (CAA) are the most prevalent arterial disorders in the aged brain. Pathogenetically, AS and SVD share similar mechanisms: plasma protein leakage into the vessel wall, accumulation of lipid-containing macrophages, and fibrosis of the vessel wall. CAA, on the other hand, is characterized by the deposition of the amyloid β-protein in the vessel wall. Despite these differences between CAA, AS and SVD, apolipoprotein E (apoE) is involved in all three disorders. Such a pathogenetic link may explain the correlations between AS, SVD, CAA, and Alzheimer’s disease in the brains of elderly individuals reported in the literature. In addition, AS, SVD, and CAA can lead to tissue lesions such as hemorrhage and infarction. Moreover, intracerebral SVD leads to plasma protein leakage into the damaged vessel wall and into the perivascular space resulting in a blood–brain barrier (BBB) dysfunction. This SVD-related BBB dysfunction is considered to cause white matter lesions (WMLs) and lacunar infarcts. In this review, we demonstrate the relationship between AS, SVD, and CAA as well as their contribution to the development of vascular tissue lesions and we emphasize an important role for apoE in the pathogenesis of vessel disorders and vascular tissue lesions as well as for BBB dysfunction on WML and lacunar infarct development.

Cerebral microinfarcts associated with severe cerebral beta-amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is common in elderly individuals, especially those affected with Alzheimer's disease. Eighteen brains with severe SCAA (SCAA) were compared with 21 brains with mild CAA (MCAA) to investigate whether the presence of SCAA in the brains of demented patients was associated with a higher burden of old microinfarcts than those with MCAA. Immunohistochemistry for CD68 was employed to highlight old microinfarcts in tissue blocks from various brain regions. Old microinfarcts, manually counted by light microscopy, were present in 14 of 18 SCAA brains and in 7 of 21 MCAA brains (P = 0.01, two-tailed Fisher's exact test). The average number of old microinfarcts across geographic regions in each brain ranged from 0 to 1.95 (mean rank 24.94, sum of ranks 449) in the SCAA group, and from 0 to 0.35 (mean rank 15.76, sum of ranks 331) in the MCAA group (P = 0.008, two-tailed Mann-Whitney U-test). Frequent old microinfarcts in demented individuals with severe CAA may contribute a vascular component to the cognitive impairment in these patients.

Genetics and molecular pathogenesis of sporadic and hereditary cerebral amyloid angiopathies

In cerebral amyloid angiopathy (CAA), amyloid fibrils deposit in walls of arteries, arterioles and less frequently in veins and capillaries of the central nervous system, often resulting in secondary degenerative vascular changes. Although the amyloid-beta peptide is by far the commonest amyloid subunit implicated in sporadic and rarely in hereditary forms of CAA, a number of other proteins may also be involved in rare familial diseases in which CAA is also a characteristic morphological feature. These latter proteins include the ABri and ADan subunits in familial British dementia and familial Danish dementia, respectively, which are also known under the umbrella term BRI2 gene-related dementias, variant cystatin C in hereditary cerebral haemorrhage with amyloidosis of Icelandic-type, variant transthyretins in meningo-vascular amyloidosis, disease-associated prion protein (PrP(Sc)) in hereditary prion disease with premature stop codon mutations and mutated gelsolin (AGel) in familial amyloidosis of Finnish type. In this review, the characteristic morphological features of the different CAAs is described and the implication of the biochemical, genetic and transgenic animal data for the pathogenesis of CAA is discussed.

Beta-amyloid, blood vessels, and brain function

Cerebrovascular disease and Alzheimer disease are common diseases of aging and frequently coexist in the same brain. Accumulating evidence suggests that the presence of brain infarction, including silent infarction, influences the course of Alzheimer disease. Conversely, there is evidence that beta-amyloid can impair blood vessel function. Vascular beta-amyloid deposition, also known as cerebral amyloid angiopathy, is associated with vascular dysfunction in animal and human studies. Alzheimer disease is associated with morphological changes in capillary networks, and soluble beta-amyloid produces abnormal vascular responses to physiological and pharmacological stimuli. In this review, we discuss current evidence linking beta-amyloid metabolism with vascular function and morphological changes in animals and humans.

Silent ischemic infarcts are associated with hemorrhage burden in cerebral amyloid angiopathy

BACKGROUND

Neuropathologic studies suggest an association between cerebral amyloid angiopathy (CAA) and small ischemic infarctions as well as hemorrhages. We examined the prevalence and associated risk factors for infarcts detected by diffusion-weighted imaging (DWI).

METHODS

We performed retrospective analysis of MR images from 78 subjects with a diagnosis of probable CAA and a similar aged group of 55 subjects with Alzheimer disease or mild cognitive impairment (AD/MCI) for comparison. DWI and apparent diffusion coefficient (ADC) maps were inspected for acute or subacute infarcts. We also examined the association between DWI lesions and demographic variables, conventional vascular risk factors, and radiographic markers of CAA severity such as number of hemorrhages on gradient-echo MRI and volume of T2-hyperintense white matter lesions.

RESULTS

Twelve of 78 subjects with CAA (15%) had a total of 17 DWI-hyperintense lesions consistent with subacute cerebral infarctions vs 0 of 55 subjects with AD/MCI (p = 0.001). The DWI lesions were located primarily in cortex and subcortical white matter. CAA subjects with DWI lesions had a higher median number of total hemorrhages (22 vs 4, p = 0.025) and no difference in white matter hyperintensity volume or conventional vascular risk factors compared to subjects with CAA without lesions.

CONCLUSIONS

MRI evidence of small subacute infarcts is present in a substantial proportion of living patients with advanced cerebral amyloid angiopathy (CAA). The presence of these lesions is associated with a higher burden of hemorrhages, but not with conventional vascular risk factors. This suggests that advanced CAA predisposes to ischemic infarction as well as intracerebral hemorrhage.

Hereditary and sporadic forms of abeta-cerebrovascular amyloidosis and relevant transgenic mouse models

Cerebral amyloid angiopathy (CAA) refers to the specific deposition of amyloid fibrils in the leptomeningeal and cerebral blood vessel walls, often causing secondary vascular degenerative changes. Although many kinds of peptides are known to be deposited as vascular amyloid, amyloid-beta (Abeta)-CAA is the most common type associated with normal aging, sporadic CAA, Alzheimer's disease (AD) and Down's syndrome. Moreover, Abeta-CAA is also associated with rare hereditary cerebrovascular amyloidosis due to mutations within the Abeta domain of the amyloid precursor protein (APP) such as Dutch and Flemish APP mutations. Genetics and clinicopathological studies on these familial diseases as well as sporadic conditions have already shown that CAA not only causes haemorrhagic and ischemic strokes, but also leads to progressive dementia. Transgenic mouse models based on familial AD mutations have also successfully reproduced many of the features found in human disease, providing us with important insights into the pathogenesis of CAA. Importantly, such studies have pointed out that specific vastopic Abeta variants or an unaltered Abeta42/Abeta40 ratio favor vascular Abeta deposition over parenchymal plaques, but higher than critical levels of Abeta40 are also observed to be anti-amyloidogenic. These data would be important in the development of therapies targeting amyloid in vessels.

Cerebrovascular dysfunction in amyloid precursor protein transgenic mice: contribution of soluble and insoluble amyloid-beta peptide, partial restoration via gamma-secretase inhibition

The contributing effect of cerebrovascular pathology in Alzheimer's disease (AD) has become increasingly appreciated. Recent evidence suggests that amyloid-beta peptide (Abeta), the same peptide found in neuritic plaques of AD, may play a role via its vasoactive properties. Several studies have examined young Tg2576 mice expressing mutant amyloid precursor protein (APP) and having elevated levels of soluble Abeta but no cerebral amyloid angiopathy (CAA). These studies suggest but do not prove that soluble Abeta can significantly impair the cerebral circulation. Other studies examining older Tg2576 mice having extensive CAA found even greater cerebrovascular dysfunction, suggesting that CAA is likely to further impair vascular function. Herein, we examined vasodilatory responses in young and older Tg2576 mice to further assess the roles of soluble and insoluble Abeta on vessel function. We found that (1) vascular impairment was present in both young and older Tg2576 mice; (2) a strong correlation between CAA severity and vessel reactivity exists; (3) a surprisingly small amount of CAA led to marked reduction or complete loss of vessel function; 4) CAA-induced vasomotor impairment resulted from dysfunction rather than loss or disruption of vascular smooth muscle cells; and 5) acute depletion of Abeta improved vessel function in young and to a lesser degree older Tg2576 mice. These results strongly suggest that both soluble and insoluble Abeta cause cerebrovascular dysfunction, that mechanisms other than Abeta-induced alteration in vessel integrity are responsible, and that anti-Abeta therapy may have beneficial vascular effects in addition to positive effects on parenchymal amyloid.

Cerebral amyloid angiopathy: pathogenetic mechanisms and link to dense amyloid plaques

Cerebral amyloid angiopathy (CAA) of the amyloid-beta (Abeta) type is the most common form of sporadic CAA and is now also accepted as an early and integral part of Alzheimer's disease (AD) pathogenesis. Cerebral amyloid angiopathy is a risk factor for haemorrhagic stroke and is believed to independently contribute to dementia. Rare forms of hereditary cerebral amyloidosis caused by mutations within the Abeta domain of amyloid precursor protein (APP) have been identified, where mutant Abeta preferably deposits in vessels because of a decreased fibrillogenic potential and/or increased vasotopicity. A review of factors involved in CAA caused by wild-type Abeta suggests that increased Abeta levels in brain without an increased Abeta42/Abeta40 ratio is one of the most important prerequisites for vascular amyloidosis. This is exemplified by CAA observed in APP duplication and Down's syndrome patients, neprilysin polymorphism patients and knockout mice and Swedish APP (KM670/671NL) mice. Select presenilin mutations also lead to a prominent CAA, and importantly, presenilin mutations are shown to have varied effects on the production of Abeta40, the predominant amyloid found in CAA. Conversely, APP mutations such as Austrian APP (T714I) drastically decrease Abeta40 production and are deficient in CAA. Apolipoprotein E-epsilon4 is also shown to be a risk factor for CAA, and this might be because of its specific role in the aggregation of Abeta40. Recent data also suggest that dense-core senile plaques in humans and dense plaques in transgenic mice, composed predominantly of Abeta40, associate with vessels. This review highlights some of these aspects of genetics and biochemistry of CAA and pathological descriptions linked to a prominent CAA and/or dense plaques in humans and relevant mouse models and discusses how this knowledge has led to a better understanding of the processes involved in vascular amyloidosis, and in causing dementia, and thus has important therapeutic implications.

Topographical distribution of cerebral amyloid angiopathy and its effect on cognitive decline are influenced by Alzheimer disease pathology

Cerebral amyloid angiopathy (CAA) is defined by beta-amyloid peptide (Abeta) depositions in cerebral vessels and is associated with Alzheimer disease (AD). It has been suggested that severe CAA is an independent risk factor for cognitive decline. 171 autopsy brains underwent standardized neuropathological assessment, the patients age ranged from 54 to 104 years (mean age: 83.9 years, +/-9.2, 59.6% female, 56.1% clinically demented). Using immunohistochemistry, the severity of Abeta depositions in vessels was assessed semiquantitatively in the frontal, frontobasal, hippocampal, and occipital region, respectively. CAA was present in 117 cases (68.4%), with the occipital region being affected significantly stronger than other regions. The overall incidence of CAA was significantly higher in cases with high grade neuritic AD pathology (ADP) compared to those with low grade or no ADP. The severity of CAA significantly increased with increasing ADP, with CAA in the occipital region increasing significantly stronger than that in other regions. The association of CAA and clinical dementia failed to remain statistically significant when adjusting for concomitant ADP. However, in cases devoid of any ADP CAA was significantly associated with the presence of clinical dementia. These results indicate a strong association of AD with CAA, but do not unequivocally support reports suggesting CAA to be an independent risk factor for cognitive decline, except for a subgroup of demented patients lacking any ADP.

The enigma of vascular cognitive disorder and vascular dementia

The prevalence, morphology and pathogenesis of vascular dementia (VaD), recently termed vascular cognitive impairment, are a matter of discussion, and currently used clinical diagnostic criteria show moderate sensitivity (average 50%) and variable specificity (range 64-98%). In Western clinic-based series, VaD is suggested in 8-10% of cognitively impaired aged subjects. Its prevalence in autopsy series varies from 0.03 to 58%, with reasonable values of 8-15%, while in Japan it is seen in 22-35%. Neuropathologic changes associated with cognitive impairment include multifocal and/or diffuse disease and focal lesions: multi-infarct encephalopathy, white matter lesions or arteriosclerotic subcortical (leuko)encephalopathy, multilacunar state, mixed cortico-subcortical type, borderline/watershed lesions, rare granular cortical atrophy, post-ischemic encephalopathy and hippocampal sclerosis. They result from systemic, cardiac and local large or small vessel disease. Recent data indicate that cognitive decline is commonly associated with widespread small ischemic/vascular lesions (microinfarcts, lacunes) throughout the brain with predominant involvement of subcortical and functionally important brain areas. Their pathogenesis is multifactorial, and their pathophysiology affects neuronal networks involved in cognition, memory, behavior and executive functioning. Vascular lesions often coexist with Alzheimer disease (AD) and other pathologies. Minor cerebrovascular lesions, except for severe amyloid angiopathy, appear not essential for cognitive decline in full-blown AD, while both mild Alzheimer pathology and small vessel disease may interact synergistically. The lesion pattern of "pure" VaD, related to arteriosclerosis and microangiopathies, differs from that in mixed-type dementia (AD with vascular encephalopathy), more often showing large infarcts, which suggests different pathogenesis of both types of lesions. Due to the high variability of cerebrovascular pathology and its causative factors, no validated neuropathologic criteria for VaD are available, and a large variability across laboratories still exists in the procedures for morphologic examination and histology techniques.

Clinical phenotypes of Cerebral Amyloid Angiopathy

The term Cerebral Amyloid Angiopathy (CAA) is used to describe the pathological changes occurring in cerebral blood vessels, both leptomeningeal and cortical that result from the deposition of amyloid proteins. This CNS vasculopathy is associated with a spectrum of clinical phenotypes that include both ischemic and hemorrhagic presentations. Dementia, cognitive impairment and transient neurological symptoms or signs are also being increasingly recognized as part of the CAA clinical spectrum. This review covers the clinical, pathological and neuroimaging aspects of CAA.