Alzheimer's disease pathology influences severity and topographical distribution of cerebral amyloid angiopathy

Towards a better diagnosis and treatment of dementia: Identifying common and distinct neuropathological mechanisms in Alzheimer's and vascular dementia

Alzheimer's disease (AD) and vascular dementia (VaD) together contribute to almost 90 % of all dementia cases leading to major health challenges of our time with a substantial global socioeconomic burden. While in AD, the improved understanding of Amyloid beta (Aß) mismetabolism and tau hyperphosphorylation as pathophysiological hallmarks has led to significant clinical breakthroughs, similar advances in VaD are lacking. After comparing the clinical presentation, including risk factors, disease patterns, course of diseases and further diagnostic parameters for both forms of dementia, we highlight the importance of shared pathomechanisms found in AD and VaD: Endothelial damage, blood brain barrier (BBB) breakdown and hypoperfusion inducing oxidative stress and inflammation and thus trophic uncoupling in the neurovascular unit. A dysfunctional endothelium and BBB lead to the accumulation of neurotoxic molecules and Aß through impaired clearance, which in turn leads to neurodegeneration. In this context we discuss possible neuropathological parameters, which might serve as biomarkers and thus improve diagnostic accuracy or reveal targets for novel therapeutic strategies for both forms of dementia.

Updated imaging markers in cerebral amyloid angiopathy: What radiologists need to know

Cerebral amyloid angiopathy (CAA) is an age-related small vessel disease pathologically characterized by the progressive accumulation of amyloid-beta (Aβ) peptide in cerebrovascular walls, affecting both cortical and leptomeningeal vessels. Amyloid deposition results in fragile vessels, which may lead to lobar intracerebral hemorrhage (ICH) and cognitive impairment. To evaluate the probability and severity of CAA, the imaging markers depicted on CT and MRI techniques are crucial, as brain pathological examination is highly invasive. Although the Boston criteria have established diagnostic value and have been updated to version 2.0, due to an aging population, the patients with CAA should also be assessed for their risk of future ICH or cognitive impairment. Furthermore, an increased awareness of CAA is essential when introducing anticoagulants for infarct in elderly patients or anti-amyloid antibodies for Alzheimer's disease, as these may worsen CAA-related hemorrhagic lesions. However, the radiological literature on CAA has not been comprehensively updated. Here, we review the imaging markers of CAA and clinical significance. We also discuss the clinical and imaging characteristics of CAA-related inflammation, amyloid-related imaging abnormalities, and iatrogenic-CAA.

Spatial Correlates of Dementia and Disability After Intracerebral Hemorrhage

BACKGROUND

Dementia and disability are highly prevalent after spontaneous intracerebral hemorrhage (ICH). Previous studies categorizing ICH by large anatomic boundaries have demonstrated that lobar ICH is associated with dementia, while ICH in the basal ganglia is associated with disability. This study aims to refine our understanding of the association between ICH location and post-ICH dementia and disability at a voxel level, which could improve the prognostic accuracy of these outcomes and provide mechanistic insights into post-ICH functional outcomes.

METHODS AND RESULTS

In this cohort study, we segmented the ICH lesions from the noncontrast computed tomography scans from 882 patients from the MGH-ICH (Massachusetts General Hospital ICH Study) as the discovery data set and from 146 patients from the Yale-ICH cohort as the validation data set. Using electronic health records and follow-up telephone interviews, incident dementia (International Classification of Diseases, Ninth Revision [ICD-9] codes of dementia or modified telephone interview for cognitive status <20) and disability (modified Rankin Scale score >2) were identified. The median follow-up times of the MGH-ICH and Yale-ICH cohorts were 2.9 (interquartile range, 1.0-5.8) years and 1.0 (interquartile range, 0.6-1.0) years, respectively. Two techniques of lesion symptom mapping were applied on the ICH lesions: sparse canonical correlation analysis for neuroimaging and voxel-based lesion symptom mappings. Dementia conversion after ICH was associated with ICH in the left temporo-occipital region (mean hazard ratio [HR], 3.62 [95% CI, 2.71-4.63]) and left superior longitudinal fasciculus (mean HR, 2.91 [95% CI, 2.40-3.52]). Development of disability after ICH was linked to the right cerebral peduncle (mean HR, 3.10 [95% CI, 2.44-3.94]), right pallidum (mean HR, 2.96 [95% CI, 1.99-4.25]), and right posterior limb of the internal capsule (mean HR, 2.54 [95% CI, 1.88-3.96]).

CONCLUSIONS

Specific distribution of ICH lesions is linked to development of dementia and disability after ICH. These insights have the potential to enhance clinical prognostic models for patients with ICH, facilitating more precise predictions of outcomes based on hemorrhage location.

The vascular contribution of apolipoprotein E to Alzheimer's disease

Alzheimer's disease, the most prevalent form of dementia, imposes a substantial societal burden. The persistent inadequacy of disease-modifying drugs targeting amyloid plaques and neurofibrillary tangles suggests the contribution of alternative pathogenic mechanisms. A frequently overlooked aspect is cerebrovascular dysfunction, which may manifest early in the progression of Alzheimer's disease pathology. Mounting evidence underscores the pivotal role of the apolipoprotein E gene, particularly the apolipoprotein ε4 allele as the strongest genetic risk factor for late-onset Alzheimer's disease, in the cerebrovascular pathology associated with Alzheimer's disease. In this review, we examine the evidence elucidating the cerebrovascular impact of both central and peripheral apolipoprotein E on the pathogenesis of Alzheimer's disease. We present a novel three-hit hypothesis, outlining potential mechanisms that shed light on the intricate relationship among different pathogenic events. Finally, we discuss prospective therapeutics targeting the cerebrovascular pathology associated with apolipoprotein E and explore their implications for future research endeavours.

Cognitive and psychological characteristics in patients with Cerebral Amyloid Angiopathy: a literature review

AIM

To review the current data on cognitive and psychological characteristics of patients with CAA and on the instruments used for their evaluation.

METHODS

A systematic search was performed in Embase, Scopus and PubMed with terms related to "cerebral amyloid angiopathy", "neuropsychological measures" and "patient-reported outcome measures" from January 2001 to December 2021.

RESULTS

Out of 2851 records, 18 articles were selected. The cognitive evaluation was present in all of which, while the psychological one only in five articles. The MMSE (Mini Mental State Examination), TMT (Trail Making Test), fluency test, verbal learning test, digit span, digit symbol and Rey figure tests were the most used cognitive tests, while executive function, memory, processing speed, visuospatial function, attention and language were the most frequent impaired cognitive functions. Depression was the most considered psychological factor usually measured with BDI (Beck Depression Inventory) and GDS (Geriatric Depression Scale).

CONCLUSIONS

The results of this study might be used in clinical practice as a guide to choose cognitive and psychological instruments and integrate them in the clinical evaluation. The results might also be used in the research field for studies investigating the impact of cognitive and psychological variables on the disease course and for consensus studies aimed at define a standardized evaluation of these aspects.

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.

Prevalence of Concomitant Pathologies in Parkinson's Disease: Implications for Prognosis, Diagnosis, and Insights into Common Pathogenic Mechanisms

Pathologies characteristic of Alzheimer's disease (i.e., hyperphosphorylated tau and amyloid-β (Aβ) plaques), cardiovascular disease, and limbic predominant TDP-43 encephalopathy (LATE) often co-exist in patients with Parkinson's disease (PD), in addition to Lewy body pathology (α-synuclein). Numerous studies point to a putative synergistic relationship between hyperphosphorylation tau, Aβ, cardiovascular lesions, and TDP-43 with α-synuclein, which may alter the stereotypical pattern of pathological progression and accelerate cognitive decline. Here we discuss the prevalence and relationships between common concomitant pathologies observed in PD. In addition, we highlight shared genetic risk factors and developing biomarkers that may provide better diagnostic accuracy for patients with PD that have co-existing pathologies. The tremendous heterogeneity observed across the PD spectrum is most likely caused by the complex interplay between pathogenic, genetic, and environmental factors, and increasing our understanding of how these relate to idiopathic PD will drive research into finding accurate diagnostic tools and disease modifying therapies.

Familial cerebral amyloid disorders with prominent white matter involvement

Familial cerebral amyloid disorders are characterized by the accumulation of fibrillar protein aggregates, which deposit in the parenchyma as plaques and in the vasculature as cerebral amyloid angiopathy (CAA). Amyloid β (Aβ) is the most common of these amyloid proteins, accumulating in familial and sporadic forms of Alzheimer's disease and CAA. However, there are also a number of rare, hereditary, non-Aβ cerebral amyloidosis. The clinical manifestations of these familial cerebral amyloid disorders are diverse, including cognitive or neuropsychiatric presentations, intracerebral hemorrhage, seizures, myoclonus, headache, ataxia, and spasticity. Some mutations are associated with extensive white matter hyperintensities on imaging, which may or may not be accompanied by hemorrhagic imaging markers of CAA; others are associated with occipital calcification. We describe the clinical, imaging, and pathologic features of these disorders and discuss putative disease mechanisms. Familial disorders of cerebral amyloid accumulation offer unique insights into the contributions of vascular and parenchymal amyloid to pathogenesis and the pathways underlying white matter involvement in neurodegeneration. With Aβ immunotherapies now entering the clinical realm, gaining a deeper understanding of these processes and the relationships between genotype and phenotype has never been more relevant.

Monomeric C-reactive protein: A novel biomarker predicting neurodegenerative disease and vascular dysfunction

Circulating C-reactive protein (pCRP) concentrations rise dramatically during both acute (e.g., following stroke) or chronic infection and disease (e.g., autoimmune conditions such as lupus), providing complement fixation through C1q protein binding. It is now known, that on exposure to the membranes of activated immune cells (and microvesicles and platelets), or damaged/dysfunctional tissue, it undergoes lysophosphocholine (LPC)-phospholipase-C-dependent dissociation to the monomeric form (mCRP), concomitantly becoming biologically active. We review histological, immunohistochemical, and morphological/topological studies of post-mortem brain tissue from individuals with neuroinflammatory disease, showing that mCRP becomes stably distributed within the parenchyma, and resident in the arterial intima and lumen, being "released" from damaged, hemorrhagic vessels into the extracellular matrix. The possible de novo synthesis via neurons, endothelial cells, and glia is also considered. In vitro, in vivo, and human tissue co-localization analyses have linked mCRP to neurovascular dysfunction, vascular activation resulting in increased permeability, and leakage, compromise of blood brain barrier function, buildup of toxic proteins including tau and beta amyloid (Aβ), association with and capacity to "manufacture" Aβ-mCRP-hybrid plaques, and, greater susceptibility to neurodegeneration and dementia. Recently, several studies linked chronic CRP/mCRP systemic expression in autoimmune disease with increased risk of dementia and the mechanisms through which this occurs are investigated here. The neurovascular unit mediates correct intramural periarterial drainage, evidence is provided here that suggests a critical impact of mCRP on neurovascular elements that could suggest its participation in the earliest stages of dysfunction and conclude that further investigation is warranted. We discuss future therapeutic options aimed at inhibiting the pCRP-LPC mediated dissociation associated with brain pathology, for example, compound 1,6-bis-PC, injected intravenously, prevented mCRP deposition and associated damage, after temporary left anterior descending artery ligation and myocardial infarction in a rat model.

Amyloid-β (Aβ) immunotherapy induced microhemorrhages are associated with activated perivascular macrophages and peripheral monocyte recruitment in Alzheimer's disease mice

BACKGROUND

Amyloid-related imaging abnormalities (ARIA) have been identified as the most common and serious adverse events resulting from pathological changes in the cerebral vasculature during several recent anti-amyloid-β (Aβ) immunotherapy trials. However, the precise cellular and molecular mechanisms underlying how amyloid immunotherapy enhances cerebral amyloid angiopathy (CAA)-mediated alterations in vascular permeability and microhemorrhages are not currently understood. Interestingly, brain perivascular macrophages have been implicated in regulating CAA deposition and cerebrovascular function however, further investigations are required to understand how perivascular macrophages play a role in enhancing CAA-related vascular permeability and microhemorrhages associated with amyloid immunotherapy.

METHODS

In this study, we examined immune responses induced by amyloid-targeting antibodies and CAA-induced microhemorrhages using histology and gene expression analyses in Alzheimer's disease (AD) mouse models and primary culture systems.

RESULTS

In the present study, we demonstrate that anti-Aβ (3D6) immunotherapy leads to the formation of an antibody immune complex with vascular amyloid deposits and induces the activation of CD169+ perivascular macrophages. We show that macrophages activated by antibody mediated Fc receptor signaling have increased expression of inflammatory signaling and extracellular matrix remodeling genes such as Timp1 and MMP9 in vitro and confirm these key findings in vivo. Finally, we demonstrate enhanced vascular permeability of plasma proteins and recruitment of inflammatory monocytes around vascular amyloid deposits, which are associated with hemosiderin deposits from cerebral microhemorrhages, suggesting the multidimensional roles of activated perivascular macrophages in response to Aβ immunotherapy.

CONCLUSIONS

In summary, our study establishes a connection between Aβ antibodies engaged at CAA deposits, the activation of perivascular macrophages, and the upregulation of genes involved in vascular permeability. However, the implications of this phenomenon on the susceptibility to microhemorrhages remain to be fully elucidated. Further investigations are warranted to determine the precise role of CD169 + perivascular macrophages in enhancing CAA-mediated vascular permeability, extravasation of plasma proteins, and infiltration of immune cells associated with microhemorrhages.

Sex-Specific Patterns of Cerebral Atrophy and Enlarged Perivascular Spaces in Patients with Cerebral Amyloid Angiopathy and Dementia

BACKGROUND AND PURPOSE

Cerebral amyloid angiopathy is characterized by amyloid β deposition in leptomeningeal and superficial cortical vessels. Cognitive impairment is common and may occur independent of concomitant Alzheimer disease neuropathology. It is still unknown which neuroimaging findings are associated with dementia in cerebral amyloid angiopathy and whether they are modulated by sex. This study compared MR imaging markers in patients with cerebral amyloid angiopathy with dementia or mild cognitive impairment or who are cognitively unimpaired and explored sex-specific differences.

MATERIALS AND METHODS

We studied 58 patients with cerebral amyloid angiopathy selected from the cerebrovascular and memory outpatient clinics. Clinical characteristics were collected from clinical records. Cerebral amyloid angiopathy was diagnosed on MR imaging on the basis of the Boston criteria. Visual rating scores for atrophy and other imaging features were independently assessed by 2 senior neuroradiologists.

RESULTS

Medial temporal lobe atrophy was higher for those with cerebral amyloid angiopathy with dementia versus those cognitively unimpaired (P = .015), but not for those with mild cognitive impairment. This effect was mainly driven by higher atrophy in men with dementia, compared with women with and without dementia (P = .034, P = .012; respectively) and with men without dementia (P = .012). Enlarged perivascular spaces in the centrum semiovale were more frequent in women with dementia versus men with and without dementia (P = .021, P = .011; respectively) and women without dementia (P = .011).

CONCLUSIONS

Medial temporal lobe atrophy was more prominent in men with dementia, whereas women showed a higher number of enlarged perivascular spaces in the centrum semiovale. Overall, this finding suggests differential pathophysiologic mechanisms with sex-specific neuroimaging patterns in cerebral amyloid angiopathy.

Morphological characteristics differentiate dementia with Lewy bodies from Parkinson disease with and without dementia

Dementia with Lewy bodies (DLB) and Parkinson disease (PD) with and without dementia are entities of a spectrum of Lewy body diseases. About 26.3% of all PD patients develop dementia increasing up to 83%. Parkinson disease-dementia (PDD) and DLB share many clinical and morphological features that separate them from non-demented PD (PDND). Clinically distinguished by the temporal sequence of motor and cognitive symptoms, the pathology of PDD and DLB includes variable combinations of Lewy body (LB) and Alzheimer (AD) lesions, both being more severe in DLB, but much less frequent and less severe in PDND. The objective of this study was to investigate the morphological differences between these three groups. 290 patients with pathologically confirmed PD were reviewed. 190 of them had clinical dementia; 110 met the neuropathological criteria of PDD and 80 of DLB. The major demographic and clinical data were obtained from medical records. Neuropathology included semiquantitative assessment of LB and AD pathologies including cerebral amyloid angiopathy (CAA). PDD patients were significantly older than PDND and DLB ones (83.9 vs 77.9 years, p < 0.05); the age of DLB patients was between them (80.0 years), while the disease duration was shortest in DLB. Brain weight was lowest in DLB, which showed higher Braak LB scores (mean 5.2 vs 4.2) and highest Braak tau stages (mean 5.2 vs 4.4 and 2.3, respectively). Thal Aβ phases were also highest in DLB (mean 4.1 vs 3.0 and 1.8, respectively). Major findings were frequency and degree of CAA, being highest in DLB (95% vs 50% and 24%, with scores 2.9 vs 0.7 and 0.3, respectively), whereas other small vessel lesions showed no significant differences. Striatal Aβ deposits also differentiated DLB from the other groups. This and other studies of larger cohorts of PD patients indicate that the association of CAA and cortical tau-but less-LB pathologies are associated with more severe cognitive decline and worse prognosis that distinguish DLB from PDD and PDND. The particular impact of both CAA and tau pathology supports the concept of a pathogenic continuum ranging from PDND to DLB + AD within the spectrum of age-related synucleinopathies.

Cerebrospinal fluid biomarkers for cerebral amyloid angiopathy

Integrating cerebrospinal fluid-biomarkers into diagnostic workup of patients with sporadic cerebral amyloid angiopathy may support early and correct identification. We aimed to identify and validate clinical- and cerebrospinal fluid-biomarkers for in vivo diagnosis of cerebral amyloid angiopathy. This observational cohort study screened 2795 consecutive patients admitted for cognitive complaints to the academic departments of neurology and psychiatry over a 10-year period (2009-2018). We included 372 patients with available hemosiderin-sensitive MR imaging and cerebrospinal fluid-based neurochemical dementia diagnostics, i.e. Aβ40, Aβ42, t-tau, p-tau. We investigated the association of clinical- and cerebrospinal fluid-biomarkers with the MRI-based diagnosis of cerebral amyloid angiopathy, applying confounder-adjusted modelling, receiver operating characteristic and unsupervised cluster analyses. We identified 67 patients with cerebral amyloid angiopathy, 76 patients with Alzheimer's disease, 75 patients with mild cognitive impairment due to Alzheimer's disease, 76 patients with mild cognitive impairment with unlikely Alzheimer's disease and 78 healthy controls. Patients with cerebral amyloid angiopathy showed a specific cerebrospinal fluid pattern: average concentration of Aß40 [13 792 pg/ml (10 081-18 063)] was decreased compared to all controls (P < 0.05); Aß42 [634 pg/ml (492-834)] was comparable to Alzheimer's disease and mild cognitive impairment due to Alzheimer's disease (P = 0.10, P = 0.93) but decreased compared to mild cognitive impairment and healthy controls (both P < 0.001); p-tau [67.3 pg/ml (42.9-91.9)] and t-tau [468 pg/ml (275-698)] were decreased compared to Alzheimer's disease (P < 0.001, P = 0.001) and mild cognitive impairment due to Alzheimer's disease (P = 0.001, P = 0.07), but elevated compared to mild cognitive impairment and healthy controls (both P < 0.001). Multivariate modelling validated independent clinical association of cerebral amyloid angiopathy with older age [odds-ratio: 1.06, 95% confidence interval (1.02-1.10), P < 0.01], prior lobar intracerebral haemorrhage [14.00 (2.64-74.19), P < 0.01], prior ischaemic stroke [3.36 (1.58-7.11), P < 0.01], transient focal neurologic episodes (TFNEs) [4.19 (1.06-16.64), P = 0.04] and gait disturbance [2.82 (1.11-7.15), P = 0.03]. For cerebrospinal fluid-biomarkers per 1 pg/ml, both lower Aß40 [0.9999 (0.9998-1.0000), P < 0.01] and lower Aß42 levels [0.9989 (0.9980-0.9998), P = 0.01] provided an independent association with cerebral amyloid angiopathy controlled for all aforementioned clinical confounders. Both amyloid biomarkers showed good discrimination for diagnosis of cerebral amyloid angiopathy among adjusted receiver operating characteristic analyses (area under the receiver operating characteristic curves, Aß40: 0.80 (0.73-0.86), P < 0.001; Aß42: 0.81 (0.75-0.88), P < 0.001). Unsupervised Euclidian clustering of all cerebrospinal fluid-biomarker-profiles resulted in distinct segregation of cerebral amyloid angiopathy patients from all controls. Together, we demonstrate that a distinctive set of cerebrospinal fluid-biomarkers effectively differentiate cerebral amyloid angiopathy patients from patients with Alzheimer's disease, mild cognitive impairment with or without underlying Alzheimer's disease, and healthy controls. Integrating our findings into a multiparametric approach may facilitate diagnosing cerebral amyloid angiopathy, and may aid clinical decision-making, but warrants future prospective validation.

Pathophysiology, cellular and molecular mechanisms of large and small vessel diseases

Cerebrovascular disease (CVD) is the second most common cause of cognitive impairment and dementia in aged population. CVD presents in a myriad number of clinical ways based on the functional location of pathology. While primary clinical emphasis has been placed on motor, speech and visual deficits, vascular cognitive decline is a vastly under recognized and devastating condition afflicting millions of Americans. CVD, a disease of the blood vessels that supply blood to brain involves an integration between small and large vessels. Cerebral large vessel diseases (LVD) are associated with atherosclerosis, artery-to-artery embolism, intracardiac embolism and a large vessel stroke leading to substantial functional disability. Cerebral small vessel disease (SVD) is critically involved in stroke, brain hemorrhages, cognitive decline and functional loss in elderly patients. An evolving understanding of cellular and molecular mechanisms emphasizes that inflammatory vascular changes contribute to systemic pathologic conditions of the central nervous systems (CNS), with specific clinical presentations including, cognitive decline. Advances in an understanding of pathophysiology of disease processes and therapeutic interventions may help improve outcomes. This review will focus on large and small vessels diseases and their relationship to vascular cognitive decline, atherosclerosis, stroke, and inflammatory neurodegeneration. We will also emphasize the molecular and cellular mechanisms, as well as genetic and epigenetic factors associated with LVD and SVD.

Neuropathology of central nervous system involvement in TTR amyloidosis

Hereditary transthyretin amyloidosis (ATTRv) is a systemic disease caused by the accumulation of misfolded transthyretin (TTR). It usually presents with an adult-onset progressive axonal peripheral neuropathy and cardiomyopathy. In the central nervous system (CNS), variant TTR is produced by the choroid plexus and accumulates in the leptomeninges. CNS symptoms have been increasingly recognized in this population, including transient focal neurological episodes and stroke, particularly in patients with the V30M mutation and longstanding disease. The prevalence, pathophysiology, and progression of CNS involvement remain to be clarified. The present work explores if there is a recognizable sequence of CNS TTR deposition in ATTRv. We studied the topographical and severity distribution of TTR deposition in 16 patients with ATTRv, aged 27-69 years and with a mean disease duration of 10.9 years (range: 3-29). Our results suggest that CNS pathological involvement in V30M ATTRv occurs early in the disease course, probably starting in pre-symptomatic phases, and follows a distinct sequence. Leptomeninges and subarachnoid meningeal vessels are affected earlier, then followed by perforating cortical vessels and subpial deposition, and finally by deposition in the subependymal and basal ganglia vessels near the ependymal lining. Brainstem and spinal cord show early and severe involvement, with amyloid subpial deposition already seen in initial stages. Despite massive superficial amyloid deposition, no parenchymal deposition outside subpial or subependymal regions was found. Additionally, vascular lesions or superficial cortical siderosis were not frequent. Future studies with more patients from different populations and TTR mutations will be important to confirm these findings. Defining stages of TTR pathology in the CNS may be useful to better understand pathogenic mechanisms leading to symptoms and to interpret neuroimaging biomarkers.

Imaging markers of cerebral amyloid angiopathy and hypertensive arteriopathy differentiate Alzheimer disease subtypes synergistically

Background

Both cerebral amyloid angiopathy (CAA) and hypertensive arteriopathy (HA) are related to cognitive impairment and dementia. This study aimed to clarify CAA- and HA-related small vessel disease (SVD) imaging marker associations with cognitive dysfunction and Alzheimer disease (AD) subtypes.

Methods

A sample of 137 subjects with clinically diagnosed late-onset AD identified from the dementia registry of a single center from January 2017 to October 2021 were enrolled. Semi-quantitative imaging changes (visual rating scale grading) suggestive of SVD were analyzed singularly and compositely, and their correlations with cognitive domains and AD subtypes were examined.

Results

Patients with typical and limbic-predominant AD subtypes had worse cognitive performance and higher dementia severity than minimal-atrophy subtype patients. Deep white matter hyperintensity (WMH) presence correlated inversely with short-term memory (STM) performance. The three composite SVD scores correlated with different cognitive domains and had distinct associations with AD subtypes. After adjusting for relevant demographic factors, multivariate logistic regression (using minimal-atrophy subtype as the reference condition) revealed the following: associations of the typical subtype with periventricular WMH [odds ratio (OR) 2.62; 95% confidence interval (CI), 1.23–5.57, p = 0.012], global SVD score (OR 1.67; 95%CI, 1.11–2.52, p = 0.009), and HA-SVD score (OR 1.93; 95%CI, 1.10–3.52, p = 0.034); associations of limbic-predominant subtype with HA-SVD score (OR 2.57; 95%CI, 1.23–5.37, p = 0.012) and most global and domain-specific cognitive scores; and an association of hippocampal-sparing subtype with HA-SVD score (OR 3.30; 95%CI, 1.58–6.85, p = 0.001).

Conclusion

Composite SVD imaging markers reflect overall CAA and/or HA severity and may have differential associations with cognitive domains and AD subtypes. Our finding supports the possibility that the clinical AD subtypes may reflect differing burdens of underlying CAA and HA microangiopathologies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-01083-8.

Distinct tau neuropathology and cellular profiles of an APOE3 Christchurch homozygote protected against autosomal dominant Alzheimer's dementia

We describe in vivo follow-up PET imaging and postmortem findings from an autosomal dominant Alzheimer's disease (ADAD) PSEN1 E280A carrier who was also homozygous for the APOE3 Christchurch (APOE3ch) variant and was protected against Alzheimer's symptoms for almost three decades beyond the expected age of onset. We identified a distinct anatomical pattern of tau pathology with atypical accumulation in vivo and unusual postmortem regional distribution characterized by sparing in the frontal cortex and severe pathology in the occipital cortex. The frontal cortex and the hippocampus, less affected than the occipital cortex by tau pathology, contained Related Orphan Receptor B (RORB) positive neurons, homeostatic astrocytes and higher APOE expression. The occipital cortex, the only cortical region showing cerebral amyloid angiopathy (CAA), exhibited a distinctive chronic inflammatory microglial profile and lower APOE expression. Thus, the Christchurch variant may impact the distribution of tau pathology, modulate age at onset, severity, progression, and clinical presentation of ADAD, suggesting possible therapeutic strategies.

Are there morphological differences between Parkinson's disease-dementia and dementia with Lewy bodies?

Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB) are two major neurocognitive disorders in the spectrum of Lewy body diseases that overlap in many clinical and neuropathological features, although they show several differences. Clinically distinguished mainly based on the duration of parkinsonism prior to development of dementia, their morphology is characterized by a variable combination of Lewy body (LB) and Alzheimer's disease (AD) pathologies, the latter usually being more frequent and severe in DLB.

OBJECTIVE

The aims of the study were to investigate essential neuropathological differences between PDD and DLB in a larger cohort of autopsy cases.

METHODS

110 PDD autopsy cases were compared with 78 DLB cases. The major demographic, clinical (duration of illness, final MMSE) and neuropathological data were assessed retrospectively. Neuropathological studies used standardized methods and immunohistochemistry for phospho-tau, β-amyloid (Aß) and α-synuclein, with semiquantitative assessment of the major histological lesions.

RESULTS

PDD patients were significantly older at death than DLB ones (mean 83.9 vs. 79.8 years), with a significantly longer disease duration (mean 9.2 vs. 6.7 years). Braak LB scores and particularly neuritic Braak stages were significantly higher in the DLB group (mean 5.1and 5.1 vs. 4.2 and 4.4, respectively), as were Thal Aβ phases (mean 4.1 vs. 3.0). Diffuse striatal Aβ plaques were considerable in 55% and moderate in 45% of DLB cases, but were extremely rare in PDD. The most significant differences concerned the frequency and degree of cerebral amyloid angiopathy (CAA), being significantly higher in DLB (98.7 vs. 50%, and mean degree of 2.9 vs. 0.72, respectively). Worse prognosis in DLB than in PDD was linked to both increased Braak neuritic stages and more severe CAA.

INTERPRETATION

These and other recent studies imply the association of CAA, more severe concomitant AD pathology, and striatal Aβ load with cognitive decline and more rapid disease process that distinguishes DLB from PDD, while the influence of other cerebrovascular diseases or co-pathologies in both disorders was not specifically examined. The importance of both CAA and tau pathology in DLB and much less in PDD supports the concept of a pathogenetic continuum from Parkinson's disease (PD) - > PDD - > DLB - > DLB + AD and subtypes of AD with LB pathology within the spectrum of age-related proteinopathies.

Psychiatric symptoms of frontotemporal dementia and subcortical (co-)pathology burden: new insights

Three subtypes of distinct pathological proteins accumulate throughout multiple brain regions and shape the heterogeneous clinical presentation of frontotemporal lobar degeneration (FTLD). Besides the main pathological subtypes, co-occurring pathologies are common in FTLD brain donors. The objective of this study was to investigate how the location and burden of (co-)pathology correlate to early psychiatric and behavioural symptoms of FTLD. Eighty-seven brain donors from The Netherlands Brain Bank cohort (2008-2017) diagnosed with FTLD were included: 46 FTLD-TAR DNA-binding protein 43 (FTLD-TDP), 34 FTLD-tau, and seven FTLD-fused-in-sarcoma (FTLD-FUS). Post-mortem brain tissue was dissected into 20 standard regions and stained for phosphorylated TDP-43, phosphorylated tau, FUS, amyloid-β, and α-synuclein. The burden of each pathological protein in each brain region was assessed with a semi-quantitative score. Clinical records were reviewed for early psychiatric and behavioural symptoms. Whole-brain clinico-pathological partial correlations were calculated (local false discovery rate threshold = 0.01). Elaborating on the results, we validated one finding using a quantitative assessment of TDP-43 pathology in the granular layer of the hippocampus in FTLD-TDP brain donors with (n = 15) and without (n = 15) hallucinations. In subcortical regions, the presence of psychiatric symptoms showed positive correlations with increased hippocampal pathology burden: hallucinations with TDP-43 in the granular layer (R = 0.33), mania with TDP-43 in CA1 (R = 0.35), depression with TDP-43 in CA3 and with parahippocampal tau (R = 0.30 and R = 0.23), and delusions with CA3 tau (R = 0.26) and subicular amyloid-β (R = 0.25). Behavioural disinhibition showed positive correlations with tau burden in the thalamus (R = 0.29) and with both TDP-43 and amyloid-β burden in the subthalamus (R = 0.23 and R = 0.24). In the brainstem, the presence of α-synuclein co-pathology in the substantia nigra correlated with disinhibition (R = 0.24), tau pathology in the substantia nigra correlated with depression (R = 0.25) and in the locus coeruleus with both depression and perseverative/compulsive behaviour (R = 0.26 and R = 0.32). The quantitative assessment of TDP-43 in the granular layer validated the higher burden of TDP-43 pathology in brain donors with hallucinations compared to those without hallucinations (P = 0.007). Our results show that psychiatric symptoms of FTLD are linked to subcortical pathology burden in the hippocampus, and hallucinations are linked to a higher burden of TDP-43 in the granular layer. Co-occurring non-FTLD pathologies in subcortical regions could contribute to configuring the clinical phenotype of FTLD.

Cryo-EM structures of amyloid-β 42 filaments from human brains

[Figure: see text].

Comparison of Cerebral Cortex Transcriptome Profiles in Ischemic Stroke and Alzheimer’s Disease Models

Ischemic stroke and Alzheimer’s disease (AD) are representative geriatric diseases with a rapidly increasing prevalence worldwide. Recent studies have reported an association between ischemic stroke neuropathology and AD neuropathology. Ischemic stroke shares some similar characteristics with AD, such as glia activation-induced neuroinflammation, amyloid beta accumulation, and neuronal cell loss, as well as some common risk factors with AD progression. Although there are considerable similarities in neuropathology between ischemic stroke and AD, no studies have ever compared specific genetic changes of brain cortex between ischemic stroke and AD. Therefore, in this study, I compared the cerebral cortex transcriptome profile of 5xFAD mice, an AD mouse model, with those of middle cerebral artery occlusion (MCAO) mice, an ischemic stroke mouse model. The data showed that the expression of many genes with important functional implications in MCAO mouse brain cortex were related to synaptic dysfunction and neuronal cell death in 5xFAD mouse model. In addition, changes in various protein-coding RNAs involved in synaptic plasticity, amyloid beta accumulation, neurogenesis, neuronal differentiation, glial activation, inflammation and neurite outgrowth were observed. The findings could serve as an important basis for further studies to elucidate the pathophysiology of AD in patients with ischemic stroke.

Histopathological Analysis of Cerebrovascular Lesions Associated With Aging

Cerebrovascular disease (CVD) has been associated with cognitive impairment. Yet, our understanding of vascular contribution to cognitive decline has been limited by heterogeneity of definitions and assessment, as well as its occurrence in cognitively healthy aging. Therefore, we aimed to establish the natural progression of CVD associated with aging. We conducted a retrospective observational study of 63 cognitively healthy participants aged 19-84 years selected through the histological archives of the CHU de Québec. Assessment of CVD lesions was performed independently by 3 observers blinded to clinical data using the Vascular Cognitive Impairment Neuropathology Guidelines (VCING). We found moderate to almost perfect interobserver agreement for most regional CVD scores. Atherosclerosis (ρ = 0.758) and arteriolosclerosis (ρ = 0.708) showed the greatest significant association with age, followed by perivascular hemosiderin deposits (ρ = 0.432) and cerebral amyloid angiopathy (CAA; ρ = 0.392). Amyloid and tau pathologies were both associated with higher CVD load, but only CAA remained significantly associated with amyloid plaques after controlling for age. Altogether, these findings support the presence of multiple CVD lesions in the brains of cognitively healthy adults, the burden of which increases with age and can be quantified in a reproducible manner using standardized histological scales such as the VCING.

Frontal white matter lesions in Alzheimer's disease are associated with both small vessel disease and AD-associated cortical pathology

Cerebral white matter lesions (WML) encompass axonal loss and demyelination and are assumed to be associated with small vessel disease (SVD)-related ischaemia. However, our previous study in the parietal lobe white matter revealed that WML in Alzheimer's disease (AD) are linked with degenerative axonal loss secondary to the deposition of cortical AD pathology. Furthermore, neuroimaging data suggest that pathomechanisms for the development of WML differ between anterior and posterior lobes with AD-associated degenerative mechanism driving posterior white matter disruption, and both AD-associated degenerative and vascular mechanisms contributed to anterior matter disruption. In this pilot study, we used human post-mortem brain tissue to investigate the composition and aetiology of frontal WML from AD and non-demented controls to determine if frontal WML are SVD-associated and to reveal any regional differences in the pathogenesis of WML. Frontal WML tissue sections from 40 human post-mortem brains (AD, n = 19; controls, n = 21) were quantitatively assessed for demyelination, axonal loss, cortical hyperphosphorylated tau (HPτ) and amyloid-beta (Aβ) burden, and arteriolosclerosis as a measure of SVD. Biochemical assessment included Wallerian degeneration-associated protease calpain and the myelin-associated glycoprotein to proteolipid protein ratio as a measure of ante-mortem ischaemia. Arteriolosclerosis severity was found to be associated with and a significant predictor of frontal WML severity in both AD and non-demented controls. Interesting, frontal axonal loss was also associated with HPτ and calpain levels were associated with increasing Aβ burden in the AD group, suggestive of an additional degenerative influence. To conclude, this pilot data suggest that frontal WML in AD may result from both increased arteriolosclerosis and AD-associated degenerative changes. These preliminary findings in combination with previously published data tentatively indicate regional differences in the aetiology of WML in AD, which should be considered in the clinical diagnosis of dementia subtypes: posterior WML maybe associated with degenerative mechanisms secondary to AD pathology, while anterior WML could be associated with both SVD-associated and degenerative mechanisms.

Spatial and temporal intracerebral hemorrhage patterns in Dutch-type hereditary cerebral amyloid angiopathy

Aim

To investigate whether there is a topographical and temporal pattern of index and recurrent intracerebral hemorrhages (ICH) in Dutch-type hereditary Cerebral Amyloid Angiopathy (D-CAA) to increase our understanding on CAA-related ICH development.

Methods

We included patients with DNA confirmed D-CAA or a history with ≥1 lobar ICH and ≥1 first-degree relative with D-CAA. Topographical pattern was studied by location (proportion frontal/parietal/temporal/occipital; infra/supratentorial and occurrence ratios relative to lobe volume) and volume of index and recurrent ICHs were determined on CT. Temporal pattern was examined by time between recurrent ICHs was retrieved from medical records.

Results

We included 72 patients with D-CAA (mean age at index ICH 55 years) with in total 214 ICH. The median follow-up time was 7 years (range 0.8 to 28 years). All ICH were lobar and supratentorial. The index ICH was most frequently located in the occipital lobe (34% vs. 22% in the other three lobes; with index ICH occurrence ratios relative to lobe volume of 1.9 for occipital, 1.0 for temporal, 1.2 for parietal, and 0.5 for frontal, p = 0.001). In 16/47 (34%) patients with multiple ICH, the second ICH was located in the same lobe as the index ICH. The median time-interval between subsequent ICH was #1-2 ICH 27 months, #2-3 ICH 14 months, and #3-4 ICH 7 months (p = 0.6) There was no difference in volume between index and recurrent ICHs.

Conclusions

We found that index and recurrent ICHs in D-CAA have a preference for the occipital lobe and are least frequent in the frontal lobe, which adds to the existing knowledge of histopathological studies on amyloid load in CAA. Surprisingly, there was no acceleration in time nor gradual increase of hematoma volume between subsequent ICHs.

The Relationship between the Static and Dynamic Balance of the Body, the Influence of Eyesight and Muscle Tension in the Cervical Spine in CAA Patients-A Pilot Study

Cerebral amyloid angiopathy (CAA) is one form of disease of the small vessels of the brain and can cause frequent cerebral hemorrhages as well as other types of stroke. The aim of the study was to analyze the static and dynamic balance of the body and changes in the tension of selected muscles of the cervical spine in patients with CAA after stroke, depending on visual control or its absence, compared to healthy volunteers. Eight stroke patients and eight healthy subjects were examined. The functional Unterberger test and the Biodex SD platform were used to test the dynamic equilibrium, on which the static equilibrium was also assessed. Muscle tension was tested with the Luna EMG device. In static tests, the LC muscle (longus colli) was significantly more active with and without visual control (p = 0.016; p = 0.002), and in dynamic tests, significantly higher results for MOS (p = 0.046) were noted. The comparison of the groups led to the conclusion that the more functional deficits, the more difficult it is to keep balance, also with eye control.

Cognitive Dysfunction in Cats: Update on Neuropathological and Behavioural Changes Plus Clinical Management

Cognitive dysfunction syndrome (CDS) is an established condition in cats that shares many similarities with human Alzheimer's disease (AD), where cognitive decline ultimately results in dementia. Cats with CDS display behavioural abnormalities, including excessive Vocalisation, altered Interaction with owners (increased affection/attention), altered Sleep-wake cycles, House-soiling, Disorientation (spatial and/or temporal), alterations in Activity, Anxiety, and/or Learning/memory deficits (i.e., VISHDAAL). These cats develop neuropathologies, such as accumulation of β-amyloid and hyperphosphorylated tau deposits. Because of its similarities to those in the brains of people with cognitive impairment and AD, the domestic cat could be a natural model for human dementia studies. It is important to diagnose CDS promptly in cats, ruling out other causes for these behavioural changes, to provide effective management. Interventions include environmental enrichment (e.g., easy access to key resources, calming pheromones), dietary supplementations (e.g., Senilife, Aktivait for cats, SAMe), specific diets (e.g., containing antioxidants, medium-chain triglycerides) and, potentially, medication (e.g., selegiline or propentofylline). This article reviews the literature about CDS in cats, its causes, neuropathology, clinical signs, diagnosis and potential management options. By doing so, it furthers our understanding of this condition and allows improved health, welfare and quality of life of affected cats.

Cerebral Amyloid Angiopathy in Amyloid-Positive Patients from a Memory Clinic Cohort

BACKGROUND

The overlap between cerebral amyloid angiopathy (CAA) and Alzheimer's disease (AD) is frequent and relevant for patients with cognitive impairment.

OBJECTIVE

To assess the role of the diagnosis of CAA on the phenotype of amyloid-β (Aβ) positive patients from a university-hospital memory clinic.

METHODS

Consecutive patients referred for suspected cognitive impairment, screened for Aβ pathological changes in cerebrospinal fluid (CSF), with available MRI and neuropsychological results were included. We determined the association between probable CAA and clinical, neuropsychological (at presentation and after a mean follow-up of 17 months in a sub-sample) and MRI (atrophy, white matter hyperintensities, perivascular spaces) characteristics.

RESULTS

Of 218 amyloid-positive patients, 8.3% fulfilled criteria for probable CAA. A multivariable logistic regression showed an independent association of probable CAA with lower Aβ1-42 (adjusted odds ratio [aOR] = 0.94, 95% confidence interval [95% CI] = 0.90-0.98, p = 0.003), and Aβ1-40 (aOR = 0.98, 95% CI=0.97-0.99 p = 0.017) levels in CSF, and presence of severe burden of enlarged perivascular spaces (EPVS) in the centrum semiovale (aOR = 3.67, 95% CI = 1.21-11.15, p = 0.022). Linear mixed-model analysis showed that both groups significantly deteriorated in global clinical severity, executive function and memory. Nevertheless, the presence of probable CAA did not differently affect the rate of cognitive decline.

CONCLUSION

The presence of probable CAA in Aβ positive patients was associated with lower Aβ1-42 and Aβ1-40 CSF levels and increased centrum semiovale EPVS burden, but did not independently influence clinical phenotype nor the rate of cognitive decline within our follow-up time window.

Incident stroke in patients with Alzheimer's disease: systematic review and meta-analysis

Vascular mechanisms are increasingly recognized in the pathophysiology of Alzheimer's disease (AD), but less is known about the occurrence of stroke in AD patients. We aimed to quantify the risk of stroke in patients with AD and compare the incidence rates (IR) of stroke in individuals without AD. Systematic search of Embase and MEDLINE between 1970 and 2020. Inclusion criteria: reports with ≥ 50 patients with non-familial AD, which reported the occurrence of stroke (all types) and/or ischemic stroke and/or intracerebral hemorrhage (ICH) during follow-up. Meta-analyses of pooled data using random-effects model were performed. IR were calculated for each study. Incidence rate ratios (IRR) were calculated for studies presenting a control-group without AD. Among 5109 retrieved studies, 29 (0.6%) fulfilled the inclusion criteria, reporting a total of 61,824 AD patients. In AD patients the IR were 15.4/1000 person-years for stroke (all types), 13.0/1000 person-years for ischemic stroke and 3.4/1000 person-years for ICH. When compared to controls without AD, incidence rate for ICH in AD patients was significantly higher (IRR = 1.67, 95%CI 1.43-1.96), but similar for ischemic stroke. Incident stroke is not a rare event in AD population. AD is associated with an increased risk of intracerebral hemorrhage which warrants further clarification.

APOE immunotherapy reduces cerebral amyloid angiopathy and amyloid plaques while improving cerebrovascular function

The ε4 allele of the apolipoprotein E (APOE) gene is the strongest genetic risk factor for late-onset Alzheimer's disease (AD) and greatly influences the development of amyloid-β (Aβ) pathology. Our current study investigated the potential therapeutic effects of the anti-human APOE antibody HAE-4, which selectively recognizes human APOE that is co-deposited with Aβ in cerebral amyloid angiopathy (CAA) and parenchymal amyloid pathology. In addition, we tested whether HAE-4 provoked brain hemorrhages, a component of amyloid-related imaging abnormalities (ARIA). ARIA is an adverse effect secondary to treatment with anti-Aβ antibodies that can occur in blood vessels with CAA. We used 5XFAD mice expressing human APOE4 ^+/+ (5XE4) that have prominent CAA and parenchymal plaque pathology to assess the efficacy of HAE-4 compared to an Aβ antibody that removes parenchymal Aβ but increases ARIA in humans. In chronically treated 5XE4 mice, HAE-4 reduced Aβ deposition including CAA compared to a control antibody, whereas the anti-Aβ antibody had no effect on CAA. Furthermore, the anti-Aβ antibody exacerbated microhemorrhage severity, which highly correlated with reactive astrocytes surrounding CAA. In contrast, HAE-4 did not stimulate microhemorrhages and instead rescued CAA-induced cerebrovascular dysfunction in leptomeningeal arteries in vivo. HAE-4 not only reduced amyloid but also dampened reactive microglial, astrocytic, and proinflammatory-associated genes in the cortex. These results suggest that targeting APOE in the core of both CAA and plaques could ameliorate amyloid pathology while protecting cerebrovascular integrity and function.

Visuospatial dysfunction is associated with posterior distribution of white matter damage in non-demented cerebral amyloid angiopathy

BACKGROUND AND PURPOSE

Cerebral amyloid angiopathy (CAA) is a well-recognized contributor to cognitive decline in the elderly. The posterior cortical predilection of CAA pathology would cause visuospatial dysfunction, which is still underexplored. We aimed to investigate whether the visuospatial dysfunction in CAA is associated with the posterior distribution of small vessel disease (SVD) imaging markers.

METHODS

We recruited 60 non-demented CAA cases from a Chinese prospective cohort and 30 cases with non-CAA SVD as controls. We used the Visual Object and Space Perception (VOSP) battery to evaluate visuospatial abilities, and multivariable regression models to assess their associations with SVD imaging markers.

RESULTS

There was visuospatial dysfunction, especially visual object perception impairment, in CAA compared to controls (Z-score of VOSP: -0.11 ± 0.66 vs. 0.22 ± 0.54, p = 0.023). The VOSP score in CAA was independently related to the fronto-occipital gradient of white matter hyperintensity volumes (coefficient = 0.03, 95% confidence interval [CI] = 0.003-0.05, p = 0.030) and mean fractional anisotropy values on diffusion tensor imaging (coefficient = 4.72, 95% CI = 0.97-8.48, p = 0.015), but not the severity of global SVD imaging markers or the gradient of lobar cerebral microbleeds with adjustments for age and global cognition score.

CONCLUSIONS

This finding suggests that the damage of posterior white matter rather than global disease severity may be a major contributor to visuospatial dysfunction in CAA.

The existence of Aβ strains and their potential for driving phenotypic heterogeneity in Alzheimer's disease

Reminiscent of the human prion diseases, there is considerable clinical and pathological variability in Alzheimer's disease, the most common human neurodegenerative condition. As in prion disorders, protein misfolding and aggregation is a hallmark feature of Alzheimer's disease, where the initiating event is thought to be the self-assembly of Aβ peptide into aggregates that deposit in the central nervous system. Emerging evidence suggests that Aβ, similar to the prion protein, can polymerize into a conformationally diverse spectrum of aggregate strains both in vitro and within the brain. Moreover, certain types of Aβ aggregates exhibit key hallmarks of prion strains including divergent biochemical attributes and the ability to induce distinct pathological phenotypes when intracerebrally injected into mouse models. In this review, we discuss the evidence demonstrating that Aβ can assemble into distinct strains of aggregates and how such strains may be primary drivers of the phenotypic heterogeneity in Alzheimer's disease.

Significance of cerebral amyloid angiopathy and other co-morbidities in Lewy body diseases

Lewy body dementia (LBD) and Parkinson's disease-dementia (PDD) are two major neurocognitive disorders with Lewy bodies (LB) of unknown etiology. There is considerable clinical and pathological overlap between these two conditions that are clinically distinguished based on the duration of Parkinsonism prior to development of dementia. Their morphology is characterized by a variable combination of LB and Alzheimer's disease (AD) pathologies. Cerebral amyloid angiopathy (CAA), very common in aged persons and particularly in AD, is increasingly recognized for its association with both pathologies and dementia. To investigate neuropathological differences between LB diseases with and without dementia, 110 PDD and 60 LBD cases were compared with 60 Parkinson's disease (PD) cases without dementia (PDND). The major demographic and neuropathological data were assessed retrospectively. PDD patients were significantly older than PDND ones (83.9 vs 77.8 years; p < 0.05); the age of LB patients was in between both groups (mean 80.2 years), while the duration of disease was LBD < PDD < PDND (mean 6.7 vs 12.5 and 14.3 years). LBD patients had higher neuritic Braak stages (mean 5.1 vs 4.5 and 4.0, respectively), LB scores (mean 5.3 vs 4.2 and 4.0, respectively), and Thal amyloid phases (mean 4.1 vs 3.0 and 2.3, respectively) than the two other groups. CAA was more common in LBD than in the PDD and PDND groups (93 vs 50 and 21.7%, respectively). Its severity was significantly greater in LBD than in PDD and PDND (p < 0.01), involving mainly the occipital lobes. Moreover, striatal Aβ deposition highly differentiated LBD brains from PDD. Braak neurofibrillary tangle (NFT) stages, CAA, and less Thal Aβ phases were positively correlated with LB pathology (p < 0.05), which was significantly higher in LBD than in PDD < PDND. Survival analysis showed worse prognosis in LBD than in PDD (and PDND), which was linked to both increased Braak tau stages and more severe CAA. These and other recent studies imply the association of CAA-and both tau and LB pathologies-with cognitive decline and more rapid disease progression that distinguishes LBD from PDD (and PDND).

Biphasic Effects of Ethanol Exposure on Waste Metabolites Clearance in the CNS

We have shown that the effects of low-dose ethanol promote the clearance of waste metabolites, such as amyloid-beta (Aβ) proteins, from the brain through the perivascular space (PVS). We demonstrated that dilative reactivity of arterial smooth muscle and endothelial cells regulate this clearance. These findings indicate the importance of blood-brain barrier (BBB) transvascular clearance of large size metabolites from the central nervous system (CNS), where the lymphatic clearance system is absent. We next examined the contrasting effects of acute low-dose and chronic moderate ethanol exposure on BBB-associated perivascular clearance. We injected a high molecular weight fluorescent dye into the interstitial space or directly into the cerebrospinal fluid (CSF). Bio-distribution of this tracer was then examined in different brain regions by multiphoton imaging and whole brain tissue section scanning. Ethanol-induced molecular/cellular mechanisms that drive the increase or decrease in movement of the fluorescent tracer were correlated to BBB integrity and arterial vessel reactivity. We found that activation of endothelial nitric oxide synthase (eNOS) under low-dose ethanol conditions with a shift to activation of inducible NOS (iNOS) under chronic high ethanol exposure conditions, which appeared to regulate these contrasting effects. We validated these observations by qualitative and quantitative investigation of eNOS, iNOS, BBB integrity, and perivascular clearance of waste metabolites. We concluded that the effects of low-dose ethanol increased the diffusive movement of waste metabolites via eNOS-derived NO, which increased the arterial endothelial-smooth muscle cell dilative reactivity without affecting BBB integrity, whereas a prolonged induction of iNOS under chronic ethanol exposure conditions caused oxidative damage of the arterial endothelial-smooth muscle layers resulting in cerebral amyloid-like angiopathy. This led to dysfunction of the BBB, dilative reactivity, and impaired waste metabolites movement from the interstitial space or subarachnoid space (SAS) through perivascular clearance.

Cerebral amyloid angiopathy and related inflammatory disorders

Inflammatory cerebral amyloid angiopathy is a largely reversible inflammatory vasculopathy that develops in an acute or subacute fashion in reaction to amyloid protein deposition in the central nervous system blood vessels. There are two recognized pathologically characterized variants: cerebral amyloid angiopathy-related inflammation (CAAri) and A beta-related angiitis (ABRA). Both variants produce a clinical picture that resembles primary angiitis of the CNS but is distinguished by a characteristic radiologic appearance. Although originally defined as a clinicopathologic diagnosis, it can now often be diagnosed based on clinicoradiologic criteria, though confirmation with brain and meningeal biopsy is still required in some cases. This disorder typically responds to steroids but addition of other immune suppressants may be needed in some cases to control the disease.

Heterogenous deposition of β-amyloid in the brain of aged dogs

Dogs have been used as animal models for human diseases in which there is beta-amyloid (Aβ) deposition in the central nervous system (CNS), such as Alzheimer's and cerebral amyloid angiopathy (CAA). However, many aspects of Aβ deposition in the CNS of dogs still remain unknown. This study aimed to evaluate the deposition of Aβ in different areas of the CNS of aged dogs from different breeds. Aβ was detected in the brains of aged dogs, forming either senile plaques in the neuropil of cortical gray matter or within the walls of parenchymal or leptomeningeal blood vessels. There was a positive correlation between aging and senile plaques or CAA. In dogs older than 8 years, there was no correlation between the area of Aβ plaques and age, with frontal, temporal, and occipital cortices being affected with approximately equal frequency. There was a positive correlation between Aβ deposition in vessel walls and age. Importantly, CAA was associated with the occurrence of microperivascular hemorrhages in the brains of aged dogs. In conclusion, this study demonstrated that Aβ deposition as plaques or within vessel walls are extremely heterogenous in dogs from different breeds and sizes. Although many features of this disease in dogs are similar to those observed in humans, the choice of dog breed and size as a model for human disease will substantially affect the pattern of Aβ deposition.

Chronic Traumatic Encephalopathy and Neuropathological Comorbidities

With age, the presence of multiple neuropathologies in a single individual becomes increasingly common. Given that traumatic brain injury and the repetitive head impacts (RHIs) that occur in contact sports have been associated with the development of many neurodegenerative diseases, including chronic traumatic encephalopathy (CTE), Alzheimer's disease, Lewy body disease, and amyotrophic lateral sclerosis, it is becoming critical to understand the relationship and interactions between these pathologies. In fact, comorbid pathology is common in CTE and likely influenced by both age and the severity and type of exposure to RHI as well as underlying genetic predisposition. Here, we review the major comorbid pathologies seen with CTE and in former contact sports athletes and discuss what is known about the associations between RHI, age, and the development of neuropathologies. In addition, we examine the distinction between CTE and age-related pathology including primary age-related tauopathy and age-related tau astrogliopathy.

Disturbed balance in the expression of MMP9 and TIMP3 in cerebral amyloid angiopathy-related intracerebral haemorrhage

Cerebral amyloid angiopathy (CAA) is characterized by the deposition of the amyloid β (Aβ) protein in the cerebral vasculature and poses a major risk factor for the development of intracerebral haemorrhages (ICH). However, only a minority of patients with CAA develops ICH (CAA-ICH), and to date it is unclear which mechanisms determine why some patients with CAA are more susceptible to haemorrhage than others. We hypothesized that an imbalance between matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) contributes to vessel wall weakening. MMP9 plays a role in the degradation of various components of the extracellular matrix as well as of Aβ and increased MMP9 expression has been previously associated with CAA. TIMP3 is an inhibitor of MMP9 and increased TIMP3 expression in cerebral vessels has also been associated with CAA. In this study, we investigated the expression of MMP9 and TIMP3 in occipital brain tissue of CAA-ICH cases (n = 11) by immunohistochemistry and compared this to the expression in brain tissue of CAA cases without ICH (CAA-non-haemorrhagic, CAA-NH, n = 18). We showed that MMP9 expression is increased in CAA-ICH cases compared to CAA-NH cases. Furthermore, we showed that TIMP3 expression is increased in CAA cases compared to controls without CAA, and that TIMP3 expression is reduced in a subset of CAA-ICH cases compared to CAA-NH cases. In conclusion, in patients with CAA, a disbalance in cerebrovascular MMP9 and TIMP3 expression is associated with CAA-related ICH.

Location-Specific Association Between Cerebral Microbleeds and Arterial Pulsatility

Objective: Increased arterial pulsatility index (API), usually representative of distal vascular resistance, have been linked to cerebral small vessel disease. However, their relationship with cerebral microbleeds (CMBs) is less well-studied. The present study aimed to evaluate the relationship between CMBs and API.

Methods: We cross-sectionally evaluated participants from a non-clinical stroke, non-demented community-based population. APIs of cervical internal carotid and vertebral arteries were measured by ultrasonography. CMBs were assessed by susceptibility-weighted-imaging on 3T magnetic resonance imaging (MRI). Subjects were classified according to CMB locations: deep/infratentorial (DI) or strictly lobar (SL) CMB groups. DI-CMB group also included subjects with simultaneous lobar CMBs.

Results: Of the 681 subjects [62.2 (8.4) years, 43.5% men] included, CMBs were found in 92 (13.5%) subjects: 57 (8.4%) with DI-CMB and 35 (5.1%) with SL-CMB. The results showed that CMB location influenced their association with API. DI-CMB was significantly associated with elevated API of internal carotid arteries (β = 0.031; 95% confidence interval = 0.002–0.059; P = 0.03), while SL-CMB was significantly associated with elevated API of vertebral arteries (β = 0.050; 95% confidence interval = 0.006–0.094; P = 0.025) in multivariate analyses adjusting for age, sex, cardiovascular risk factors, white matter hyperintensities (WMH), and lacunes.

Conclusion: Our study again emphasizes (1) the association between API and cerebral small vessel disease and (2) the pathogenic differences between DI- and SL-CMBs. Our results lead to the postulation that in the presence of CMBs without clinical dysfunction yet, insidious small vascular disorders might already occur with corresponding topography.

Aβ43 in human Alzheimer's disease: effects of active Aβ42 immunization

Neuropathological follow-up of patients with Alzheimer’s disease (AD) who participated in the first clinical trial of Amyloid-β 42 (Aβ42) immunization (AN1792, Elan Pharmaceuticals) has shown that immunization can induce removal of Aβ42 and Aβ40 from plaques, whereas analysis of the cerebral vessels has shown increased levels of these Aβ peptides in cerebral amyloid angiopathy (CAA). Aβ43 has been less frequently studied in AD, but its aggregation propensity and neurotoxic properties suggest it may have an important pathogenic role. In the current study we show by using immunohistochemistry that in unimmunized AD patients Aβ43 is a frequent constituent of plaques (6.0% immunostained area), similar to Aβ42 (3.9% immunostained area). Aβ43 immunostained area was significantly higher than that of Aβ40 (2.3%, p = 0.006). In addition, we show that Aβ43 is only a minor component of CAA in both parenchymal vessels (1.5 Aβ43-positive vessels per cm² cortex vs. 5.3 Aβ42-positive vessels, p = 0.03, and 6.2 Aβ40-positive vessels, p = 0.045) and leptomeningeal vessels (5.6% Aβ43-positive vessels vs. 17.3% Aβ42-positive vessels, p = 0.007, and 27.4% Aβ40-positive vessels, p = 0.003). Furthermore, we have shown that Aβ43 is cleared from plaques after Aβ immunotherapy, similar to Aβ42 and Aβ40. Cerebrovascular Aβ43 levels did not change after immunotherapy.

Contact sport participation and chronic traumatic encephalopathy are associated with altered severity and distribution of cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) consists of beta-amyloid deposition in the walls of the cerebrovasculature and is commonly associated with Alzheimer's disease (AD). However, the association of CAA with repetitive head impacts (RHI) and with chronic traumatic encephalopathy (CTE) is unknown. We evaluated the relationship between RHI from contact sport participation, CTE, and CAA within a group of deceased contact sport athletes (n = 357), a community-based cohort (n = 209), and an AD cohort from Boston University AD Center (n = 241). Unsupervised hierarchal cluster analysis demonstrated a unique cluster (n = 11) with increased CAA in the leptomeningeal vessels compared to the intracortical vessels (p < 0.001) comprised of participants with significantly greater frequencies of CTE (7/11) and history of RHI. Overall, participants with CTE (n = 251) had more prevalent (p < 0.001) and severe (p = 0.010) CAA within the frontal leptomeningeal vessels compared to intracortical vessels. Compared to those with AD, participants with CTE had more severe CAA in frontal than parietal lobes (p < 0.001) and more severe CAA in leptomeningeal than intracortical vessels (p = 0.002). The overall frequency of CAA in participants with CTE was low, and there was no significant association between contact sport participation and the presence of CAA. However, in those with CAA, a history of contact sports was associated with increased CAA severity in the frontal leptomeningeal vessels (OR = 4.01, 95% CI 2.52-6.38, p < 0.001) adjusting for AD, APOE ε4 status, and age. Participants with CAA had increased levels of sulcal tau pathology and decreased levels of the synaptic marker PSD-95 (p's < 0.05), and CAA was a predictor of dementia (OR = 1.75, 95% CI 1.02-2.99, p = 0.043) adjusting for age, sex, and comorbid pathology. Overall, contact sport participation and CTE were associated with more severe frontal and leptomeningeal CAA, and CAA was independently associated with worse pathological and clinical outcomes.

The Gut-Brain Axis in Neurodegenerative Diseases and Relevance of the Canine Model: A Review

Identifying appropriate animal models is critical in developing translatable in vitro and in vivo systems for therapeutic drug development and investigating disease pathophysiology. These animal models should have direct biological and translational relevance to the underlying disease they are supposed to mimic. Aging dogs not only naturally develop a cognitive decline in many aspects including learning and memory deficits, but they also exhibit human-like individual variability in the aging process. Neurodegenerative processes that can be observed in both human and canine brains include the progressive accumulation of β-amyloid (Aβ) found as diffuse plaques in the prefrontal cortex (PFC), including the gyrus proreus (i.e., medial orbital PFC), as well as the hippocampus and the cerebral vasculature. Tau pathology, a marker of neurodegeneration and dementia progression, was also found in canine hippocampal synapses. Various epidemiological data show that human patients with neurodegenerative diseases have concurrent intestinal lesions, and histopathological changes in the gastrointestinal (GI) tract occurs decades before neurodegenerative changes. Gut microbiome alterations have also been reported in many neurodegenerative diseases including Alzheimer's (AD) and Parkinson's diseases, as well as inflammatory central nervous system (CNS) diseases. Interestingly, the dog gut microbiome more closely resembles human gut microbiome in composition and functional overlap compared to rodent models. This article reviews the physiology of the gut-brain axis (GBA) and its involvement with neurodegenerative diseases in humans. Additionally, we outline the advantages and weaknesses of current in vitro and in vivo models and discuss future research directions investigating major human neurodegenerative diseases such as AD and Parkinson's diseases using dogs.

Neurodegenerative Diseases and Ageing

This chapter describes the main neuropathological features of the most common age associated neurodegenerative diseases including Alzheimer's disease, Lewy body diseases, vascular dementia and the various types of frontotemporal lobar degeneration. In addition, the more recent concepts of primary age-related tauopathy and ageing-related tau astrogliopathy as well as chronic traumatic encephalopathy are briefly described. One section is dedicated to cerebral multi-morbidity as it is becoming increasingly clear that the old brain is characterised by the presence of multiple pathologies (to varying extent) rather than by one single, disease specific pathology alone. The main aim of this chapter is to inform the reader about the neuropathological basics of age associated neurodegenerative diseases as we feel this is crucial to meaningfully interpret the vast literature that is published in the broad field of dementia research.

Cerebral Amyloid Angiopathy: Similarity in African-Americans and Caucasians with Alzheimer's Disease

Cerebral amyloid angiopathy (CAA) of the Aβ type is variably present in the brains of patients with Alzheimer's disease (AD). CAA contributes to cognitive decline and increases the risk of lobar hemorrhage; because both AD-typical dementia and lobar hemorrhage are more common in African-Americans than in Caucasians, we postulated that African-Americans with AD might be particularly susceptible to CAA. To test this hypothesis, we analyzed CAA histopathologically in the large vessels and capillaries of autopsy-derived frontal, temporal, parietal, and occipital cortical samples from African-Americans (n = 18) and Caucasians (n = 19) with end-stage AD. In the combined cohort of 37 subjects, 22% of the subjects had severe CAA in large vessels, and 11% had severe CAA in capillaries. However, the prevalence and histopathologic characteristics of CAA were similar in the African-Americans and Caucasians. This conclusion was substantiated in an independent sample from the National Alzheimer's Coordinating Center database, in which the degree of CAA was comparable in 1,554 Caucasians and 68 African-Americans with end-stage AD. These findings support a growing consensus that the fundamental histopathologic features of AD are largely impartial to the race of the afflicted.

Contributions of Drug Transporters to Blood-Brain Barriers

Blood-brain interfaces comprise the cerebral microvessel endothelium forming the blood-brain barrier (BBB) and the epithelium of the choroid plexuses forming the blood-cerebrospinal fluid barrier (BCSFB). Their main functions are to impede free diffusion between brain fluids and blood; to provide transport processes for essential nutrients, ions, and metabolic waste products; and to regulate the homeostasis of central nervous system (CNS), all of which are attributed to absent fenestrations, high expression of tight junction proteins at cell-cell contacts, and expression of multiple transporters, receptors, and enzymes. Existence of BBB is an important reason that systemic drug administration is not suitable for the treatment of CNS diseases. Some diseases, such epilepsy, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and diabetes, alter BBB function via affecting tight junction proteins or altering expression and function of these transporters. This chapter will illustrate function of BBB, expression of transporters, as well as their alterations under disease status.

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.

Pathologically Confirmed Cerebral Amyloid Angiopathy with No Radiological Sign in a Patient with Early Onset Alzheimer's Disease

Cerebral amyloid angiopathy (CAA) is associated with perivascular disruption, which is caused by progressive amyloid-beta (Aβ) deposition in vessels. Previous autopsy studies have shown that the prevalence of CAA in Alzheimer's disease (AD) is 70% to 90%. CAA is principally characterized by restricted lobar microbleeds (MBs), which can be detected by gradient-echo T2* (GRE) and susceptibility-weighted imaging (SWI). We herein report on a 62-year-old man who presented with 8 years of memory impairment. The apolipoprotein E (APOE) genotype was ε4/ε4, and a brain GRE performed 28 months before death revealed mild atrophy and no MBs. At autopsy, the patient scored "A3, B3, C3" according to the National Institute on Aging-Alzheimer's Association guidelines; the patient thus exhibited a high level of AD neuropathological changes. Furthermore, immunohistochemical staining for Aβ showed antibody accumulation and severe cerebral amyloid angiopathic changes in numerous vessels with amyloid deposits. Our case suggests that radiological CAA markers, such as cerebral microbleed (CMB) or cerebral superficial siderosis, may not suffice to detect amyloid angiopathy in cerebral vessels. CAA should therefore be considered as a combined pathology in APOE ε4 homozygotes with AD, even if such patients do not exhibit CMB on MRI.

Amyloid Angiopathy in Brain Hemorrhage: A Postmortem Neuropathological-Magnetic Resonance Imaging Study

Background: Risk factors for intracerebral hemorrhage (ICH) include hypertension and cerebral amyloid angiopathy (CAA). The objective of this study was to determine the autopsy prevalence of CAA and the potential overlap with other risk factors among patients who died from ICH and also the correlation of CAA with cerebral microbleeds. Methods: We analyzed 81 consecutive autopsy brains from patients with ICH. Staining for CAA detection was performed. We used an age- and sex-matched control group of routine brain autopsies of nonneurological patients to determine the frequencies of CAA and hypertension. Postmortem 3D T2-weighted gradient-echo magnetic resonance imaging (MRI) with a 1.5-T magnet was performed in 11 brains with ICH (5 with CAA and 6 without) and histological correlation was performed when microbleeds were detected. Results: Hypertension and CAA were found in 69.1 and 24.7% of cases respectively. Among patients with CAA, 65.0% also had hypertension. The prevalence of CAA was similar among non-hypertensive cases and controls (33.3 and 23.1%; p = 0.54), whereas a significant difference was found between hypertensive cases vs. controls (28.9% vs. 0; p = 0.01). MRI documented 48 microbleeds and all 5 brains with CAA had ≥1 microbleed, compared to 3/6 brains without CAA. Among 48 microbleeds on MRI, 45 corresponded histologically to microbleeds surrounding microvessels (23 <200 µm in diameter, 19 between 200 µm and 2 mm, 3 were hemosiderin granules). Conclusions: Both hypertension and CAA frequently coexist in patients with ICH. MRI-detected microbleeds, proven by histological analysis, were twice as common in patients with CAA as in those with hypertensive ICH.

Cerebral microbleeds and CSF Alzheimer biomarkers in primary progressive aphasias

OBJECTIVE

To reveal the prevalence and localization of cerebral microbleeds (CMBs) in the 3 main variants of primary progressive aphasia (PPA) (logopenic, semantic, and nonfluent/agrammatic), to identify the relationship with underlying Alzheimer pathology, and to explore whether CMBs contribute to language breakdown.

METHODS

We used a cross-sectional design in a multicenter cohort of 82 patients with PPA and 19 similarly aged healthy controls. MRI allowed for rating CMBs (2-dimensional gradient recalled echo T2*, susceptibility weighted imaging sequences) and white matter hyperintensities. CSF Alzheimer disease biomarker analyses available in 63 of the 82 patients provided the stratification of PPA into subgroups with patients who had or did not have probable underlying Alzheimer pathology.

RESULTS

The prevalence of CMBs was higher in patients with PPA (28%) than in controls (16%). They were more prevalent in logopenic PPA (50%) than in semantic PPA (18%) and nonfluent/agrammatic PPA (17%). The localization of CMBs was mainly lobar (81%) with no difference between the PPA variants. CMBs were more frequent in PPA patients with positive than with negative CSF Alzheimer disease biomarkers (67% vs 20%). Patients with and without lobar CMBs had similar volumes of white matter hyperintensities. Language and general cognitive impairment in PPA was unrelated to CMB rates.

CONCLUSIONS

CMB prevalence in PPA is higher than in healthy controls. CMBs were most prevalent in the logopenic variant, were related to underlying Alzheimer pathology, and did not affect the language/cognitive impairment. Our findings also suggest that CMB detection with MRI contributes to PPA variant diagnosis, especially of logopenic PPA, and provides an estimator of the underlying neuropathology.