Amyloid deposition after cerebral hypoperfusion: Evidenced on [18F]AV-45 positron emission tomography

Cerebral amyloid-β deposition in patients with heart disease or carotid occlusive disease: A systematic review and meta-analysis

BACKGROUND

Cardiovascular disease is an important contributor to cognitive impairment. This likely involves prototypical vascular disease mechanisms like ischemia, but cardiovascular disease might also impact the brain by accelerating cerebral amyloid-β accumulation. We aimed to determine whether there is an association between heart disease or carotid occlusive disease (COD) and cerebral amyloid-β burden.

METHODS

We conducted a systematic review of studies investigating cerebral amyloid-β burden, measured with positron emission tomography, in adults with and without heart disease or COD. Where possible, we obtained standardized mean differences (SMD) of amyloid-β standardized uptake volume ratios (SUVr) for meta-analysis.

RESULTS

Eight cross-sectional studies were identified (1478 participants, aged 60-81 years, 51% female). Three studies on heart disease (two on atrial fibrillation (AF) only, one on AF, coronary artery disease and heart failure) did not find a difference in amyloid-β burden between patients and controls. The pooled difference for 746 participants with and without AF did not reach significance (SMD SUVr 0.14, 95%CI -0.06-0.34). Of the five studies on COD (one on differences between participants with and without COD, four on differences between hemispheres in unilateral COD), four did not find a difference in amyloid-β between participants or hemispheres. The pooled difference in amyloid-β load between hemispheres in 24 patients with unilateral COD was not significant (SMD SUVr -0.13, 95%CI -0.70-0.43).

CONCLUSION

Based on current studies, although limited and heterogeneous, there is insufficient evidence to support the hypothesis that heart disease or COD are associated with increased cerebral amyloid-β burden.

Intracranial artery stenosis is associated with cortical thinning in stroke-free individuals of two longitudinal cohorts

BACKGROUND

We examined the association between asymptomatic intracranial artery stenosis (aICAS) and cortical thickness using brain magnetic resonance morphometry in two cohorts.

METHODS

This cross-sectional study included stroke-free participants from the Northern Manhattan Study (NOMAS) and the National Alzheimer's Coordinating Center (NACC). We represented the predictor aICAS in NOMAS as a continuous global stenosis score reflecting an overall burden of stenosis (possible range 0-44) assessed by magnetic resonance angiography and in NACC as a dichotomous autopsy-determined Circle of Willis (CoW) atherosclerosis (none-mild vs moderate-severe). The primary outcome of interest was total cortical thickness. We analyzed each dataset separately using multivariable linear regression.

RESULTS

The analysis included 1209 NOMAS (46% had any stenosis, 5% had ≥70% stenosis of at least one vessel; stenosis score range 0-11) and 392 NACC (36% moderate-severe CoW atherosclerosis) participants. We found an inverse relationship between stenosis score and total cortical thickness (β-estimate [95% confidence interval (CI)]: -2.98 [-5.85, -0.11]) in adjusted models. We replicated these results in NACC (β-estimate [95% CI]: -0.06 [-0.11, -0.003]). Post-hoc, we segregated stenosis scores by location and only posterior circulation stenosis score was associated with total cortical thickness (anterior β-estimate [95% CI]: -0.90 [-5.16, 3.36], posterior β-estimate [95% CI]: -7.25 [-14.30, -0.20]).

CONCLUSION

We found both radiographically and neuropathologically determined aICAS to be associated with global cortical thinning. Interestingly, posterior circulation stenoses appeared to drive this association with global cortical thinning, raising the possibility of pathophysiologic mechanisms for cortical thinning other than impaired hemodynamics.

Association of small vessel disease with tau pathology

Emerging evidence suggests that small vessel disease (SVD) is a risk factor for clinical dementia and may contribute to AD neuropathological changes. Watershed brain regions are located at the most distal areas between arterial territories, making them vulnerable to SVD-related changes. We examined the association of pathologic markers of SVD, specifically arteriolosclerosis in watershed brain regions, with AD pathologic changes. Participants (N = 982; mean age-at-death = 90; 69% women) were enrolled as part of one of two cohort studies of aging and dementia. At autopsy, neuropathological evaluation included semi-quantitative grading of arteriolosclerosis pathology from 2 cortical watershed regions: the anterior watershed (AWS) and posterior watershed (PWS), densities for cortical β-amyloid and tau-tangle pathology, and other common age-related pathologies. Linear regression models examined the association of watershed arteriolosclerosis pathology with β-amyloid and tau-tangle burden. In follow-up analyses, available ex-vivo MRI and proteomics data in a subset of decedents were leveraged to examine the association of whole brain measure of WMH, as a presumed MRI marker of SVD, with β-amyloid and tau-tangle burden, as well as to examine the association of watershed arteriolosclerosis with proteomic tau. Watershed arteriolosclerosis was common, with 45% of older persons having moderate-to-severe arteriolosclerosis pathology in the AWS region, and 35% in the PWS. In fully adjusted models that controlled for demographics and common age-related pathologies, an increase in severity of PWS arteriolosclerosis was associated with a higher burden of tau-tangle burden, specifically neocortical tau burden, but not with β-amyloid. AWS arteriolosclerosis was not associated with β-amyloid or tau pathology. Ex-vivo WMH was associated with greater tau-tangle pathology burden but not β-amyloid. Furthermore, PWS arteriolosclerosis was associated with higher abundance of tau phosphopeptides, that promote formation of tau aggregates. These data provide compelling evidence that SVD, specifically posterior watershed arteriolosclerosis pathology, is linked with tau pathological changes in the aging brain.

Impaired Glymphatic Function and Pulsation Alterations in a Mouse Model of Vascular Cognitive Impairment

Large vessel disease and carotid stenosis are key mechanisms contributing to vascular cognitive impairment (VCI) and dementia. Our previous work, and that of others, using rodent models, demonstrated that bilateral common carotid stenosis (BCAS) leads to cognitive impairment via gradual deterioration of the neuro-glial-vascular unit and accumulation of amyloid-β (Aβ) protein. Since brain-wide drainage pathways (glymphatic) for waste clearance, including Aβ removal, have been implicated in the pathophysiology of VCI via glial mechanisms, we hypothesized that glymphatic function would be impaired in a BCAS model and exacerbated in the presence of Aβ. Male wild-type and Tg-SwDI (model of microvascular amyloid) mice were subjected to BCAS or sham surgery which led to a reduction in cerebral perfusion and impaired spatial learning acquisition and cognitive flexibility. After 3 months survival, glymphatic function was evaluated by cerebrospinal fluid (CSF) fluorescent tracer influx. We demonstrated that BCAS caused a marked regional reduction of CSF tracer influx in the dorsolateral cortex and CA1-DG molecular layer. In parallel to these changes increased reactive astrogliosis was observed post-BCAS. To further investigate the mechanisms that may lead to these changes, we measured the pulsation of cortical vessels. BCAS impaired vascular pulsation in pial arteries in WT and Tg-SwDI mice. Our findings show that BCAS influences VCI and that this is paralleled by impaired glymphatic drainage and reduced vascular pulsation. We propose that these additional targets need to be considered when treating VCI.

The Worldwide Alzheimer's Disease Neuroimaging Initiative: ADNI-3 updates and global perspectives

The Worldwide Alzheimer's Disease Neuroimaging Initiative (WW-ADNI) is a collaborative effort to investigate imaging and biofluid markers that can inform Alzheimer's disease treatment trials. It is a public-private partnership that spans North America, Argentina, Australia, Canada, China, Japan, Korea, Mexico, and Taiwan. In 2004, ADNI researchers began a naturalistic, longitudinal study that continues today around the globe. Through several successive phases (ADNI-1, ADNI-GO, ADNI-2, and ADNI-3), the study has fueled amyloid and tau phenotyping and refined neuroimaging methodologies. WW-ADNI researchers have successfully standardized analyses and openly share data without embargo, providing a rich data set for other investigators. On August 26, 2020, the Alzheimer's Association convened WW-ADNI researchers who shared updates from ADNI-3 and their vision for ADNI-4.

The biological pathways of Alzheimer disease: a review

Alzheimer disease is a progressive neurodegenerative disorder, mainly affecting older people, which severely impairs patients' quality of life. In the recent years, the number of affected individuals has seen a rapid increase. It is estimated that up to 107 million subjects will be affected by 2050 worldwide. Research in this area has revealed a lot about the biological and environmental underpinnings of Alzheimer, especially its correlation with β-Amyloid and Tau related mechanics; however, the precise molecular events and biological pathways behind the disease are yet to be discovered. In this review, we focus our attention on the biological mechanics that may lie behind Alzheimer development. In particular, we briefly describe the genetic elements and discuss about specific biological processes potentially associated with the disease.

Association of carotid and intracranial stenosis with Alzheimer's disease biomarkers

Background

To clarify whether atherosclerosis of the carotid and intracranial arteries is related to Alzheimer’s disease (AD) pathology in vivo, we investigated the associations of carotid and intracranial artery stenosis with cerebral beta-amyloid (Aβ) deposition and neurodegeneration in middle- and old-aged individuals. Given different variations of the pathologies between cognitive groups, we focused separately on cognitively normal (CN) and cognitively impaired (CI) groups.

Methods

A total of 281 CN and 199 CI (mild cognitive impairment and AD dementia) subjects underwent comprehensive clinical assessment, [¹¹C] Pittsburgh compound B-positron emission tomography, and magnetic resonance (MR) imaging including MR angiography. We evaluated extracranial carotid and intracranial arteries for the overall presence, severity (i.e., number and degree of narrowing), and location of stenosis.

Results

We found no associations between carotid and intracranial artery stenosis and cerebral Aβ burden in either the CN or the CI group. In terms of neurodegeneration, exploratory univariable analyses showed associations between the presence and severity of stenosis and regional neurodegeneration biomarkers (i.e., reduced hippocampal volume [HV] and cortical thickness in the AD-signature regions) in both the CN and CI groups. In confirmatory multivariable analyses controlling for demographic covariates and diagnosis, the association between number of stenotic intracranial arteries ≥ 2 and reduced HV in the CI group remained significant.

Conclusions

Neither carotid nor intracranial artery stenosis appears to be associated with brain Aβ burden, while intracranial artery stenosis is related to amyloid-independent neurodegeneration, particularly hippocampal atrophy.

Astrocyte dysfunction and neurovascular impairment in neurological disorders: Correlation or causation?

The neurovascular unit, consisting of neurons, astrocytes, and vascular cells, has become the focus of much discussion in the last two decades and emerging literature now suggests an association between neurovascular dysfunction and neurological disorders. In this review, we synthesize the known and suspected contributions of astrocytes to neurovascular dysfunction in disease. Throughout the brain, astrocytes are centrally positioned to dynamically mediate interactions between neurons and the cerebral vasculature, and play key roles in blood-brain barrier maintenance and neurovascular coupling. It is increasingly apparent that the changes in astrocytes in response to a variety of insults to brain tissue -collectively referred to as "reactive astrogliosis" - are not just an epiphenomenon restricted to morphological alterations, but comprise functional changes in astrocytes that contribute to the phenotype of neurological diseases with both beneficial and detrimental effects. In the context of the neurovascular unit, astrocyte dysfunction accompanies, and may contribute to, blood-brain barrier impairment and neurovascular dysregulation, highlighting the need to determine the exact nature of the relationship between astrocyte dysfunction and neurovascular impairments. Targeting astrocytes may represent a new strategy in combinatorial therapeutics for preventing the mismatch of energy supply and demand that often accompanies neurological disorders.

Relationship of Area of Soft Drusen in Retina with Cerebral Amyloid-β Accumulation and Blood Amyloid-β Level in the Elderly

BACKGROUND

Histopathological studies have confirmed that soft drusen contains amyloid-β (Aβ).

OBJECTIVE

To examine the relationship between the area of soft drusen in the macular area and cerebral Aβ accumulation or plasma Aβ level in elderly persons without dementia.

METHODS

Fourteen consecutive patients (18 eyes) aged ≥50 years with macular soft drusen were studied prospectively. From color fundus photographs, the area of soft drusen (pixel) within a 6,000 μm diameter with the macula as center was measured. Standard uptake value ratio (SUVR) was obtained from positron emission tomography using florbetapir, which indicates the ratio of cerebral cortical-to-cerebellar Aβ accumulation. Ratio of plasma Aβ1-42 to Aβ1-40 level was calculated.

RESULTS

Mean age was 73.3±7.6 years. The soft drusen area was 4.32±2.42 mm2. The SUVR was 1.08±0.15. Plasma Aβ1-42/Aβ1-40 ratio was 0.17±0.08. When SUVR ≥1.10 was defined as positive and <1.10 as negative, the soft drusen area in SUVR-positive patients (6.19±1.14 mm2) was significantly (p = 0.0043) larger than that in SUVR-negative patients (3.13±2.27 mm2). Multivariate regression analysis showed that SUVR positivity correlated with soft drusen area (p = 0.0484) and with Voxel-based Specific Regional Analysis System for Alzheimer's Disease score (p = 0.0360). However, there was no correlation with gender (p = 0.1921), age (p = 0.2361), Alzheimer's Disease Assessment Scale score (p = 0.6310), Mini-Mental State Examination score (p = 0.4246), or plasma Aβ1-42/Aβ1-40 ratio (p = 0.8398).

CONCLUSION

Among elderly persons without dementia, the area of soft drusen was larger in those with more extensive cerebral Aβ accumulation. The area of soft drusen may be a biomarker of cerebral Aβ accumulation.

Misery perfusion and amyloid deposition in atherosclerotic major cerebral artery disease

Although experimental studies have shown that global cerebral hypoperfusion leads to amyloid deposition in the hemisphere with carotid artery occlusion in rodents, the results of such occurrence are controversial in humans. Hence, we aim to determine whether global cerebral hypoperfusion leading to decreased blood flow relative to metabolic demand [increased oxygen extraction fraction (OEF), misery perfusion] is associated with increases in amyloid deposition in the hemisphere with atherosclerotic major cerebral artery disease in patients. We evaluated the distribution of β-amyloid plaques using positron emission tomography and a [18F]-pyridylbenzofuran derivative (¹⁸F-FPYBF-2) in 13 patients with unilateral atherosclerotic disease of the internal carotid artery (ICA) or middle cerebral artery (MCA) disease and no cortical infarction. The distribution volume ratio (DVR) of ¹⁸F- FPYBF-2 was calculated using dynamic data and Logan graphical analysis with reference tissue and was correlated with the cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO₂), and OEF, obtained from ¹⁵O-gas PET. The mean cortical value was calculated as the mean value within the frontal, posterior cingulate, precuneus, parietal, and lateral temporal cortical regions. Significant reductions in CBF and CMRO₂ and increases in OEF were found in the hemisphere ipsilateral to the arterial lesion compared with the contralateral hemisphere. There was no significant difference for ¹⁸F-FPYBF-2 DVR between hemispheres. The ipsilateral to contralateral ratio of the ¹⁸F- FPYBF-2 DVR was increased in 3 patients, while the ipsilateral to contralateral OEF ratio was increased in 4 patients. The incidence of an increased hemispheric DVR ratio was significantly higher in patients with an increased hemispheric OEF ratio (3/4) than in patients without (0/9) (p < 0.02). Although the ¹⁸F- FPYBF-2 DVR in the ipsilateral hemisphere was positively correlated with OEF after adjustment for the ¹⁸F- FPYBF-2 DVR in the contralateral hemisphere using multiple regression analysis (p < 0.05), the contribution rate of OEF was small (R² = 5.5%). Only one of the 4 patients with an increased hemispheric OEF ratio showed amyloid positivity based on the DVR value. In atherosclerotic major cerebral artery disease, misery perfusion accompanied only small increases of amyloid deposition at best. Misery perfusion was not associated with amyloid positivity.

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Misery perfusion accompanied only small increases of amyloid deposition at best.

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Relative oxygen extraction fraction correlated with relative amyloid deposition.

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Misery perfusion was not associated with amyloid positivity.

Plasma β-Amyloids and Tau Proteins in Patients with Vascular Cognitive Impairment

Increases in plasma of β-amyloids (Aβ) and tau proteins have been noted in patients with Alzheimer's dementia (AD). Our study investigated the associations of plasma Aβ and tau proteins with dementia in stroke patients. This cross-sectional study recruited 24 controls (mean age: 67.4 ± 7.5 years, 33.3% male), 27 stroke patients without dementia (mean age: 70.7 ± 6.9 years, 60.7% male), 34 stroke patients with dementia (mean age: 78.3 ± 5.3 years, 45.5% male, Clinical Dementia Ranking (CDR): 1.46 ± 0.63), and 21 AD patients (mean age: 77.1 ± 9.1 years, 42.9% male, CDR: 1.43 ± 0.60) from a medical center. Dementia was defined as a CDR scale score of ≥ 1. The plasma levels of Aβ-40, Aβ-42, and tau were analyzed using immunomagnetic reduction. One-way analysis of variance was used to compare the differences in measured protein levels between the groups. The results indicated that plasma levels of tau and Aβ-42, but not Aβ-40, in stroke patients were significantly higher than in the controls. After adjustment for age, sex, diabetes mellitus, hypertension, and hyperlipidemia, only plasma level of Aβ-42 remained significantly higher in stroke patients with dementia than in those without dementia (OR 1.85, 1.25-2.75, p = 0.002). In summary, our results suggest that plasma Aβ-42 is a potential biomarker for dementia in stroke patients.

The correlation of asymmetrical functional connectivity with cognition and reperfusion in carotid stenosis patients

Objective

Neural disruption and cognitive impairment have been reported in patients with carotid stenosis (CS), but carotid artery stenting (CAS) may not contribute to the cognitive recovery. Although functional hyper-connectivity is one of the physiological over-compensation phenomena in neurological diseases, the literature on the cognitive influence of functional hyper-connectivity in CS patients is limited. We aimed to investigate the longitudinal changes of hyper-connectivity after CAS and its association with cognition in CS patients.

Methods

Thirteen patients with unilateral CS and 17 controls without CS were included. Cognitive function was evaluated at baseline, and resting-state functional MRI was performed 1 week before and 1 month and 1 year after CAS. Comparisons of functional connectivity (FC) between CS patients and controls in multiple brain networks were performed.

Results

In patients before CAS, FC in the cerebral hemispheres ipsilateral and contralateral to CS was mainly decreased and increased, respectively, compared with normal controls. Part of the FC alterations gradually recovered to the normal condition after CAS. The stronger FC abnormality (both hypo- and hyper-connectivity compared with normal controls) was associated with poorer cognitive performances, especially in memory and executive functions.

Conclusion

The study demonstrated the lateralization of hyper-connectivity and hypo-connectivity in patients with unilateral CS in contrast to the FC in normal controls. These FC alterations were associated with poor cognitive performances and tended to recover after CAS, implying that hyper-connectivity is served as a compensation for neural challenge.

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Cerebral hypoconnectivity on functional MRI is lateralized to carotid stenosis side.

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Cerebral hyperconnectivity is in regions contralateral to carotid stenosis side.

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Abnormal connectivity gradually returns back to normal after carotid stenting.

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Hypo- and hyper-connectivity associate with poor cognitive performances.

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Hyperconnectivity could be served as a compensation for neural challenge.

Cognitive impairment and intracranial atherosclerotic stenosis in general population

OBJECTIVE

To investigate the association between asymptomatic intracranial atherosclerosis and cognitive impairment in the Atherosclerosis Risk in Communities (ARIC) cohort.

METHODS

ARIC participants underwent high-resolution 3T magnetic resonance angiography and a neuropsychology battery and neurologic examination adjudicated by an expert panel to detect mild cognitive impairment (MCI) and dementia. We adjusted for demographic and vascular risk factors in weighted logistic regression analysis, accounting for stratified sampling design and attrition, to determine the association of intracranial atherosclerotic stenosis (ICAS) with cognitive impairment.

RESULTS

In 1,701 participants (mean age 76 ± 5.3, 41% men, 71% whites, 29% blacks) with adequate imaging quality and no history of stroke, MCI was identified in 578 (34%) and dementia in 79 (4.6%). In white participants, after adjustment for demographic and vascular risk factors, ICAS ≥50% (vs no ICAS) was strongly associated with dementia (odds ratio [OR] 4.1, 95% confidence interval [CI] 1.7-10.0) and with any cognitive impairment (OR 1.7, 95% CI 1.1-2.8). In contrast, no association was found between ICAS ≥50% and MCI or dementia in blacks, although the sample size was limited and estimates were imprecise.

CONCLUSION

Our results suggest that asymptomatic ICAS is independently associated with cognitive impairment and dementia in whites.

The Role of Cerebrovascular Disease in Amyloid Deposition

BACKGROUND

Some patients clinically diagnosed with subcortical vascular cognitive impairment (SVCI) have co-morbidity with AD pathology.

OBJECTIVE

We investigated topographical differences in amyloid burden between SVCI and Alzheimer's disease type cognitive impairment (ADCI) using [11C] Pittsburgh compound B (PiB) positron emission tomography (PET). The purpose of this study was to investigate the role of cerebrovascular disease (CVD) in amyloid deposition.

METHODS

We recruited 44 patients with SVCI and 44 patients with ADCI (amnestic mild cognitive impairment or Alzheimer's disease) with absent or minimal white matter hyperintensities, all with PiB-positive PET scans [PiB+]. As controls, we included 13 participants with normal cognition and PiB-negative scans. We divided the SVCI and ADCI patients into three groups according to global PiB retention ratio of SVCI, and then compared the tertiles in terms of the distribution of PiB retention using statistical parametric mapping analyses. Lobar to global PiB retention ratio and asymmetry indices were also compared between SVCI and ADCI groupsResults: Compared to PiB+ ADCI patients, PiB+ SVCI patients exhibited: 1) increased left-right asymmetry, and increased anterior-posterior difference; and 2) increased PiB retention in the parietal cortex, the occipital cortex and the precuneus-posterior cingulate cortex. In contrast, ADCI patients showed increased PiB retention in the striatum. When stratified by level of PiB retention, each group showed different characteristics.

CONCLUSION

Our results showed that the distribution of amyloid deposition differed between patients with PiB+ SVCI and ADCI. These suggest that CVD contribute to and alter the known progression pattern in amyloid deposition in Alzheimer's disease.

Orthostatic hypotension associated with executive dysfunction in mild cognitive impairment

INTRODUCTION

Midlife hypertension is associated with dementia in longitudinal studies while chronic hypotension in the elderly is associated with dementia onset. Orthostatic hypotension could influence cognitive performance in the elderly. The objective of this study was to assess the relationship between orthostatic hypotension and cognitive functions.

METHODS

Consecutive participants with complete neuropsychological evaluation from a Memory Clinic were included. Orthostatic hypotension (OH) was defined by a fall≥20/10mmHg systolic/diastolic pressure. Participants were classified into one of 3 groups: 1) subjective cognitive impairment (SCI), 2) mild cognitive impairment (MCI), and 3) dementia. Neuropsychological tests were analyzed for patients with and without OH.

RESULTS

One hundred and twenty participants were included, of which 16 (13%) were classified as SCI, 42 (35%) as MCI, and 63 (52%) with dementia. Prevalence of OH was 0% for the SCI group, 26% (n=11) for the MCI group, and 38% (n=24) for the dementia group. Age, sex, education, and brief cognitive test scores (MMSE & MoCA) were not different between groups with or without OH. In the MCI group, OH was associated with lower cognitive performance in several executive functions tests: visual working memory (p<0.001), processing speed (p=0.006), Stroop flexibility (p=0.030) and Trail-Making Test part B (p=0.024). There was no difference in episodic memory performance. OH was associated with a diagnosis of hypertension and the use of antihypertensive medication. No differences were observed in vascular brain injury between groups with and without OH.

CONCLUSIONS

This study found that orthostatic hypotension prevalence is correlated to severity of cognitive deficits in a Memory Clinic. In MCI, OH is associated with lower performance in executive functions. OH could represent an under-recognized correlate of cognitive performance.

Astrocyte dysfunction in Alzheimer disease

Astrocytes are glial cells that are distributed throughout the central nervous system in an arrangement optimal for chemical and physical interaction with neuronal synapses and brain blood supply vessels. Neurotransmission modulates astrocytic excitability by activating an array of cell surface receptors and transporter proteins, resulting in dynamic changes in intracellular Ca²⁺ or Na⁺ . Ionic and electrogenic astrocytic changes, in turn, drive vital cell nonautonomous effects supporting brain function, including regulation of synaptic activity, neuronal metabolism, and regional blood supply. Alzheimer disease (AD) is associated with aberrant oligomeric amyloid β generation, which leads to extensive proliferation of astrocytes with a reactive phenotype and abnormal regulation of these processes. Astrocytic morphology, Ca²⁺ responses, extracellular K⁺ removal, glutamate transport, amyloid clearance, and energy metabolism are all affected in AD, resulting in a deleterious set of effects that includes glutamate excitotoxicity, impaired synaptic plasticity, reduced carbon delivery to neurons for oxidative phosphorylation, and dysregulated linkages between neuronal energy demand and regional blood supply. This review summarizes how astrocytes are affected in AD and describes how these changes are likely to influence brain function. © 2017 Wiley Periodicals, Inc.

Dual-phase 18F-florbetapir positron emission tomography in patients with primary progressive aphasia, Alzheimer's disease, and healthy controls: A preliminary study

BACKGROUND/PURPOSE

To determine whether dual-phase ¹⁸F-florbetapir positron emission tomography imaging with perfusion-like and amyloid deposition information can distinguish among primary progressive aphasia (PPA), Alzheimer's disease (AD), and healthy controls (HCs).

METHODS

Patients diagnosed with PPA, including four semantic dementia (SD) and two progressive nonfluent aphasia (PNFA), as well as one logopenic variant (LV) of PPA, were studied. All PPA patients, and age-/sex-matched patients with probable AD (n=8) and HCs (n=8) were subjected to dual-phase ¹⁸F-florbetapir imaging. Atlas-based quantitative volumes of interest (VOIs) analysis for six cortical areas and whole cerebellum was performed. The standardized uptake value ratios were calculated by normalizing the dual-phase-integrated activities of the six VOIs to whole cerebellum counts.

RESULTS

Early phase ¹⁸F-florbetapir image showed significantly lower global perfusion index in six PPA patients as compared with HCs. According to VOI analysis, the hypoperfusion lesions were identified in the frontal, anterior cingulate, parietal, precuneus, and temporal regions. Similar findings were confirmed by voxel-base image comparison. ¹⁸F-florbetapir late-phase image showed significantly increased amyloid burden in the global cortex index and all six brain regions of eight AD and LV patients when compared with the other six PPA patients and eight HCs. There was no apparent uptake of amyloid tracer in both six PPA patients and eight HCs.

CONCLUSION

Dual-phase ¹⁸F-florbetapir images of six PPA (SD and PNFA) patients showed hypoperfusion in the frontotemporal cortex, and little global amyloid uptake, which may be a distinct image pattern for differentiation among HC, AD, and PPA patients.

Associations between amyloid β and white matter hyperintensities: A systematic review

INTRODUCTION

This systematic review synthesizes current evidence for associations between cortical amyloid β, visualized on amyloid positron emission tomography imaging, and white matter hyperintensity (WMH) burden on magnetic resonance imaging in healthy elderly adults and individuals with cognitive impairment and dementia.

METHODS

Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) systematic review guidelines, we systematically searched MEDLINE, Embase, Cochrane, and PsycINFO databases from January 2000 to September 2015.

RESULTS

Our search returned 492 articles, 34 of which met criteria for inclusion in the final selection. Most studies reported no significant relationships between amyloid β and WMH burden across diagnostic groups.

DISCUSSION

Findings of this systematic review suggest that amyloid accumulation and WMH are independent but additive processes. The limited number of independent cohorts, lack of longitudinal data, and exclusion of individuals with mixed dementia limit the generalizability of these findings. Further studies are required to elucidate the putative contributions of vascular processes to neurodegenerative pathology.

Vascular contributions to cognitive impairment, clinical Alzheimer's disease, and dementia in older persons

There is growing evidence suggesting that vascular pathologies and dysfunction play a critical role in cognitive impairment, clinical Alzheimer's disease, and dementia. Vascular pathologies such as macroinfarcts, microinfarcts, microbleeds, small and large vessel cerebrovascular disease, and white matter disease are common especially in the brains of older persons where they contribute to cognitive impairment and lower the dementia threshold. Vascular dysfunction resulting in decreased cerebral blood flow, and abnormalities in the blood brain barrier may also contribute to the Alzheimer's disease (AD) pathophysiologic process and AD dementia. This review provides a clinical-pathological perspective on the role of vessel disease, vascular brain injury, alterations of the neurovascular unit, and mixed pathologies in the Alzheimer's disease pathophysiologic process and Alzheimer's dementia. 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.

Positron Emission Tomographic Imaging in Stroke: Cross-Sectional and Follow-Up Assessment of Amyloid in Ischemic Stroke

Cardiovascular risk factors significantly increase the risk of developing Alzheimer disease. A possible mechanism may be via ischemic infarction–driving amyloid deposition. We conducted a study to determine the presence of β-amyloid in infarct, peri-infarct, and hemispheric areas after stroke. We hypothesized that an infarct would trigger β-amyloid deposition, with deposition over time.

White matter hyperintensities are associated with amyloid burden in APOE4 non-carriers

Previous preclinical studies have suggested a close relationship between cerebrovascular disease (CVD) and Alzheimer's disease. However, a direct correlation between CVD and amyloid burden has not yet been shown in humans. If there is a relationship between CVD and amyloid burden, it is possible that the apolipoprotein E4 (APOE4) genotype may have an effect on this relationship because APOE4 is a risk factor for the development of AD. We therefore evaluated the effects of APOE4 on the relationship between white matter hyperintensities (WMH), a marker of CVD, and amyloid burden, measured by 11C-Pittsburgh compound B (PiB) PET. We recruited 53 patients with subcortical vascular cognitive impairments, who had both WMH on MRI and amyloid deposition assessed by PiB PET. Twenty-two of these patients were APOE4 carriers (41.5%). In the APOE4 non-carriers, a significant positive correlation was shown between the volume of WMH and PiB retention (β = 7.0 × 10-3, p = 0.034) while no significant correlation was found in APOE4 carriers (β = -9.0 × 10-3, p = 0.085). Statistical parametric mapping analyses in APOE4 non-carriers showed that WMH were associated with PiB retention in the bilateral medial occipitotemporal gyrus, cuneus, and superior cerebellum. Our results suggested that WMH are correlated with amyloid burden especially in the posterior brain regions in APOE4 non-carriers. However, this correlation was not observed in APOE4 carriers, perhaps because in these subjects the influence of APOE4 overrides the effect of CVD.

Post-stroke cognitive decline: an update and perspectives for clinical research

The close relationship between stroke and dementia is an important health issue. Ischaemic stroke can facilitate the onset of vascular dementia as well as aggravate pre-existing cognitive decline. The onset of cognitive decline may become manifest immediately following the onset of ischaemic stroke, but often there is a delay in the development of cognitive decline after a stroke. This delay can be seen as a therapeutic time window allowing interventions to be applied to preserve cognition following stroke. Both neurodegenerative and vascular mechanisms are activated and probably result in overlapping processes within the neurovascular unit. This review focuses on the incidence and prevalence of cognitive decline following stroke, predisposing stroke aetiologies, pre-stroke decline, imaging factors and biomarkers. Outcomes are discussed in relation to timing of assessment and neuropsychological tests used for evaluation of cognitive decline in ischaemic stroke patients. Including such tests in routine evaluations of stroke patients after some weeks or months is recommended. Finally, an outlook on ongoing and planned intervention trials is added and some recommendations for future research are proposed.

Influence of cognitive impairment on the management of ischaemic stroke

BACKGROUND

Because of ageing of the population, it is more and more frequent to treat ischaemic stroke patients with pre-stroke cognitive impairment (PSCI). Currently, there is no specific recommendation on ischaemic stroke management in these patients, both at the acute stage and in secondary prevention. However, these patients are less likely to receive treatments proven effective in randomised controlled trials, even in the absence of contra-indication.

OBJECTIVE

To review the literature to assess efficacy and safety of validated therapies for acute ischaemic stroke and secondary prevention in PSCI patients.

RESULTS

Most randomised trials did not take into account the pre-stroke cognitive status. The few observational studies conducted at the acute stage or in secondary prevention, did not provide any information that the benefit could be either lost or replaced by harm in the presence of PSCI.

CONCLUSIONS

There is no reason not to treat ischaemic stroke patients with PSCI according to the currently available recommendations for acute management and secondary prevention. Further observational studies are needed and pre-stroke cognition should be taken into account in future stroke trials.

Is Alzheimer's disease a homogeneous disease entity?

The epidemic proportions of dementia in old age are a cause of great concern for the medical profession and the society at large. It is customary to consider Alzheimer's disease (AD) as the most common cause of dementia, and vascular dementia (VaD) as being the second. This dichotomous view of a primary neurodegenerative disease as opposed to a disorder where extrinsic factors cause brain damage led to separate lines of research in these two entities. New biomarkers, particularly the introduction of modern neuroimaging and cerebrospinal fluid changes, have, in recent years, helped to identify anatomical and chemical changes of VaD and of AD. Nevertheless, there is a substantial difference between the two entities. While it is clear that VaD is a heterogeneous entity, AD is supposed to be a single disorder. Nobody attempts to use CADASIL as a template to develops treatment for sporadic VaD. On the other hand, early-onset AD is used to develop therapy for sporadic AD. This paper will discuss the problems relating to this false concept and its consequences.

Amyloid-β probes: Review of structure-activity and brain-kinetics relationships

The number of people suffering from Alzheimer's disease (AD) is expected to increase dramatically in the coming years, placing a huge burden on society. Current treatments for AD leave much to be desired, and numerous research efforts around the globe are focused on developing improved therapeutics. In addition, current diagnostic tools for AD rely largely on subjective cognitive assessment rather than on identification of pathophysiological changes associated with disease onset and progression. These facts have led to numerous efforts to develop chemical probes to detect pathophysiological hallmarks of AD, such as amyloid-β plaques, for diagnosis and monitoring of therapeutic efficacy. This review provides a survey of chemical probes developed to date for AD with emphasis on synthetic methodologies and structure-activity relationships with regards to affinity for target and brain kinetics. Several probes discussed herein show particularly promising results and will be of immense value moving forward in the fight against AD.

Regional amyloid deposition in amnestic mild cognitive impairment and Alzheimer's disease evaluated by [18F]AV-45 positron emission tomography in Chinese population

Background

To compare the neocortical amyloid loads among cognitively normal (CN), amnestic mild cognitive impairment (aMCI), and Alzheimer's disease (AD) subjects with [¹⁸F]AV-45 positron emission tomography (PET).

Materials and Methods

[¹⁸F]AV-45 PET was performed in 11 CN, 13 aMCI, and 12 AD subjects to compare the cerebral cortex-to-whole cerebellum standard uptake value ratios (SUVRs) of global and individual volumes of interest (VOIs) cerebral cortex. The correlation between global cortical [¹⁸F]AV-45 SUVRs and Mini-Mental State Examination (MMSE) scores was analyzed.

Results

The global cortical [¹⁸F]AV-45 SUVRs were significantly different among the CN (1.08±0.08), aMCI (1.27±0.06), and AD groups (1.34±0.13) (p = 0.0003) with amyloidosis positivity rates of 9%, 62%, and 92% in the three groups respectively. Compared to CN subjects, AD subjects had higher SUVRs in the global cortical, precuneus, frontal, parietal, occipital, temporal, and posterior cingulate areas; while aMCI subjects had higher values in the global cortical, precuneus, frontal, occipital and posterior cingulate areas. There were negative correlations of MMSE scores with SUVRs in the global cortical, precuneus, frontal, parietal, occipital, temporal, posterior cingulate and anterior cingulate areas on a combined subject pool of the three groups after age and education attainment adjustment.

Conclusions

Amyloid deposition occurs relatively early in precuneus, frontal and posterior cingulate in aMCI subjects. Higher [¹⁸F]AV-45 accumulation is present in parietal, occipital and temporal gyri in AD subjects compared to the aMCI group. Significant correlation between MMSE scores and [¹⁸F]AV-45 SUVRs can be observed among CN, aMCI and AD subjects.