Vascular burden and cognition: Mediating roles of neurodegeneration and amyloid PET

Vascular cognitive impairment: Advances in clinical research and management

ABSTRACT

Vascular cognitive impairment (VCI) encompasses a wide spectrum of cognitive disorders, ranging from mild cognitive impairment to vascular dementia. Its diagnosis relies on thorough clinical evaluations and neuroimaging. VCI predominately arises from vascular risk factors (VRFs) and cerebrovascular disease, either independently or in conjunction with neurodegeneration. Growing evidence underscores the prevalence of VRFs, highlighting their potential for early prediction of cognitive impairment and dementia in later life. The precise mechanisms linking vascular pathologies to cognitive deficits remain elusive. Chronic cerebrovascular pathology is the most common neuropathological feature of VCI, often interacting synergistically with neurodegenerative processes. Current research efforts are focused on developing and validating reliable biomarkers to unravel the etiology of vascular brain changes in VCI. The collaborative integration of these biomarkers into clinical practice, alongside routine incorporation into neuropathological assessments, presents a promising strategy for predicting and stratifying VCI. The cornerstone of VCI prevention remains the control of VRFs, which includes multi-domain lifestyle modifications. Identifying appropriate pharmacological approaches is also of paramount importance. In this review, we synthesize recent advancements in the field of VCI, including its definition, determinants of vascular risk, pathophysiology, neuroimaging and fluid-correlated biomarkers, predictive methodologies, and current intervention strategies. Increasingly evident is the notion that more rigorous research for VCI, which arises from a complex interplay of physiological events, is still needed to pave the way for better clinical outcomes and enhanced quality of life for affected individuals.

Association of amyloid and cardiovascular risk with cognition: Findings from KBASE

BACKGROUND

Limited research has explored the effect of cardiovascular risk and amyloid interplay on cognitive decline in East Asians.

METHODS

Vascular burden was quantified using Framingham's General Cardiovascular Risk Score (FRS) in 526 Korean Brain Aging Study (KBASE) participants. Cognitive differences in groups stratified by FRS and amyloid positivity were assessed at baseline and longitudinally.

RESULTS

Baseline analyses revealed that amyloid-negative (Aβ-) cognitively normal (CN) individuals with high FRS had lower cognition compared to Aβ- CN individuals with low FRS (p < 0.0001). Longitudinally, amyloid pathology predominantly drove cognitive decline, while FRS alone had negligible effects on cognition in CN and mild cognitive impairment (MCI) groups.

CONCLUSION

Our findings indicate that managing vascular risk may be crucial in preserving cognition in Aβ- individuals early on and before the clinical manifestation of dementia. Within the CN and MCI groups, irrespective of FRS status, amyloid-positive individuals had worse cognitive performance than Aβ- individuals.

HIGHLIGHTS

Vascular risk significantly affects cognition in amyloid-negative older Koreans. Amyloid-negative CN older adults with high vascular risk had lower baseline cognition. Amyloid pathology drives cognitive decline in CN and MCI, regardless of vascular risk. The study underscores the impact of vascular health on the AD disease spectrum.

Associations of neurocognitive and neuropsychiatric patterns with brain structural biomarkers and dementia risk: A latent class analysis

BACKGROUND

Neurocognitive and neuropsychiatric symptoms are essential clinical manifestations of age-related cognitive impairment, yet their patterns of co-existence remain unclear through the cognitive continuum.

OBJECTIVE

To examine the associations of person-centered cluster-derived patterns, based on a comprehensive collection of domain-specific cognitive and neuropsychiatric assessments, with neuroimaging markers and dementia risk.

METHODS

641 participants were included in the analysis from memory clinics in Singapore. Latent class analysis was applied to define clusters of individuals with different clinical patterns. The associations between identified clinical groups with neuroimaging markers of cerebrovascular diseases and neurodegeneration were analyzed using logistic regression models. Cox proportional hazard models were applied for incident dementia.

RESULTS

Three latent classes differing in neurocognitive and neuropsychiatric impairment were identified (Class 1 "memory impairment only"; Class 2 "global cognitive impairment"; Class 3 "global cognitive and neuropsychiatric impairment"). Compared with Class 1, Class 2 and 3 were associated with smaller brain volumes, moderate-to-severe cortical atrophy and medial temporal lobe atrophy, and the presence of all cerebrovascular lesions. Moreover, compared with Class 2, Class 3 had smaller brain volumes, moderate-to-severe cortical atrophy and presence of intracranial stenosis. Additionally, compared to Class 1, Class 2 (hazard ratio [HR] = 3.84, 95%CI 2.11-7.00), and Class 3 (HR = 6.92, 95%CI 2.84-16.83) showed an increased risk of incident dementia.

CONCLUSIONS

Participants characterized by multi-domain cognitive impairment and co-occurrence of cognitive and neuropsychiatric impairment showed the highest risk of incident dementia, which may be attributed to both neurodegenerative and cerebrovascular pathologies.

Retinal vascular alterations are associated with cognitive function and neuroimaging in white matter hyperintensities

AIM

To reveal alterations in retinal structure, vessels, and function, and their association with cognitive function and neuroimaging in white matter hyperintensities (WMH).

METHODS

This study enlisted WMH and age-matched healthy controls (HC). All participants underwent six different tests: magnetic resonance imaging (MRI) of the brain, the Mini-Mental State Examination (MMSE), the Montreal Cognitive Assessment (MoCA), fundus photography, optical coherence tomography (OCT), and visual field testing. Visual field can reflect the function of optic nerve and retina. The peripapillary retinal nerve fiber layer (p-RNFL) was analyzed using OCT. Image J software was employed to measure retinal vascular caliber in fundus photographs and to compute the central retinal artery equivalent (CRAE), central retinal venous equivalent (CRVE) and arteriole-to-venule ratio (AVR).

RESULTS

A total of 90 WMH patients and 93 HC participants. In comparison with the HC, the WMH group exhibited reduced cognitive function scores (MoCA: P < 0.001; MMSE: P < 0.001), narrower retinal arteries (P < 0.001), smaller AVR (P < 0.001) and thinner p-RNFL thickness (total: P = 0.026; temporal: P = 0.006). About visual field, both univariate and multivariate analysis showed that mean sensitivity decreased, and mean defect increased in WMH group (P < 0.05). Additionally, correlation analysis indicated a positive correlation between CRAE and AVR with MMSE and MoCA score (r = 0.424-0.57, P < 0.001) and a negative correlation with Fazekas score (CRAE: r = -0.515, P < 0.001; AVR: r = -0.554, P < 0.001), and p-RNFL was negatively correlated with Fazekas score (total p-RNFL: r = -0.192, P = 0.009; temporal p-RNFL: r = -0.217, P = 0.003). Notably, no significant correlation was found between cognitive function and p-RNFL.

CONCLUSION

WMH group exhibit narrower retinal arteries, smaller arteriole-to-venule ratio, damaged p-RNFL and visual function. These alterations in retinal vessels are associate with both neuroimaging and cognitive function. Our results suggest that retinal imaging could serve as a valuable instrument for evaluating WMH and provides some new approaches to study the characteristic markers of WMH.

Systolic blood pressure variability in late-life predicts cognitive trajectory and risk of Alzheimer's disease

Background

The relationship of systolic blood pressure variability (SBPV) with Alzheimer's disease (AD) remains controversial. We aimed to explore the roles of SBPV in predicting AD incidence and to test the pathways that mediated the relationship of SBPV with cognitive functions.

Methods

Longitudinal data across 96 months (T0 to T4) were derived from the Alzheimer's disease Neuroimaging Initiative cohort. SBPV for each participant was calculated based on the four measurements of SBP across 24 months (T0 to T3). At T3, logistic regression models were used to test the SBPV difference between 86 new-onset AD and 743 controls. Linear regression models were used to test the associations of SBPV with cognition and AD imaging endophenotypes for 743 non-demented participants (median age = 77.0, female = 42%). Causal mediation analyses were conducted to explore the effects of imaging endophenotypes in mediating the relationships of SBPV with cognitive function. Finally, Cox proportional hazard model was utilized to explore the association of SBPV with incident risk of AD (T3 to T4, mean follow-up = 3.5 years).

Results

Participants with new-onset AD at T3 had significantly higher SBPV compared to their controls (p = 0.018). Higher SBPV was associated with lower scores of cognitive function (p = 0.005 for general cognition, p = 0.029 for memory, and p = 0.016 for executive function), higher cerebral burden of amyloid deposition by AV45 PET (p = 0.044), lower brain metabolism by FDG PET (p = 0.052), and higher burden of white matter hyperintensities (WMH) (p = 0.012). Amyloid pathology, brain metabolism, and WMH partially (ranging from 17.44% to 36.10%) mediated the associations of SBPV with cognition. Higher SBPV was significantly associated with elevated risk of developing AD (hazard ratio = 1.29, 95% confidence interval = 1.07 to 1.57, p = 0.008).

Conclusion

These findings supported that maintaining stable SBP in late life helped lower the risk of AD, partially by modulating amyloid pathology, cerebral metabolism, and cerebrovascular health.

Assessing cognitive impairment and disability in older adults through the lens of whole brain white matter patterns

INTRODUCTION

This study aimed to explore the potential of whole brain white matter patterns as novel neuroimaging biomarkers for assessing cognitive impairment and disability in older adults.

METHODS

We conducted an in-depth analysis of magnetic resonance imaging (MRI) and amyloid positron emission tomography (PET) scans in 454 participants, focusing on white matter patterns and white matter inter-subject variability (WM-ISV).

RESULTS

The white matter pattern ensemble model, combining MRI and amyloid PET, demonstrated a significantly higher classification performance for cognitive impairment and disability. Participants with Alzheimer's disease (AD) exhibited higher WM-ISV than participants with subjective cognitive decline, mild cognitive impairment, and vascular dementia. Furthermore, WM-ISV correlated significantly with blood-based biomarkers (such as glial fibrillary acidic protein and phosphorylated tau-217 [p-tau217]), and cognitive function and disability scores.

DISCUSSION

Our results suggest that white matter pattern analysis has significant potential as an adjunct neuroimaging biomarker for clinical decision-making and determining cognitive impairment and disability.

HIGHLIGHTS

The ensemble model combined both magnetic resonance imaging (MRI) and amyloid positron emission tomography (PET) and demonstrated a significantly higher classification performance for cognitive impairment and disability. Alzheimer's disease (AD) revealed a notably higher heterogeneity compared to that in subjective cognitive decline, mild cognitive impairment, or vascular dementia. White matter inter-subject variability (WM-ISV) was significantly correlated with blood-based biomarkers (glial fibrillary acidic protein and phosphorylated tau-217 [p-tau217]) and with the polygenic risk score for AD. White matter pattern analysis has significant potential as an adjunct neuroimaging biomarker for clinical decision-making processes and determining cognitive impairment and disability.

Perivascular spaces, plasma GFAP, and speeded executive function in neurodegenerative diseases

INTRODUCTION

We investigated the effect of perivascular spaces (PVS) volume on speeded executive function (sEF), as mediated by white matter hyperintensities (WMH) volume and plasma glial fibrillary acidic protein (GFAP) in neurodegenerative diseases.

METHODS

A mediation analysis was performed to assess the relationship between neuroimaging markers and plasma biomarkers on sEF in 333 participants clinically diagnosed with Alzheimer's disease/mild cognitive impairment, frontotemporal dementia, or cerebrovascular disease from the Ontario Neurodegenerative Disease Research Initiative.

RESULTS

PVS was significantly associated with sEF (c = -0.125 ± 0.054, 95% bootstrap confidence interval [CI] [-0.2309, -0.0189], p = 0.021). This effect was mediated by both GFAP and WMH.

DISCUSSION

In this unique clinical cohort of neurodegenerative diseases, we demonstrated that the effect of PVS on sEF was mediated by the presence of elevated plasma GFAP and white matter disease. These findings highlight the potential utility of imaging and plasma biomarkers in the current landscape of therapeutics targeting dementia.

HIGHLIGHTS

Perivascular spaces (PVS) and white matter hyperintensities (WMH) are imaging markers of small vessel disease. Plasma glial fibrillary protein acidic protein (GFAP) is a biomarker of astroglial injury. PVS, WMH, and GFAP are relevant in executive dysfunction from neurodegeneration. PVS's effect on executive function was mediated by GFAP and white matter disease.

Premenopausal bilateral oophorectomy and brain white matter brain integrity in later-life

INTRODUCTION

Premenopausal bilateral oophorectomy (PBO) is associated with later-life cognition, but the underlying brain changes remain unclear. We assessed the impact of PBO and PBO age on white matter integrity.

METHODS

Female participants with regional diffusion tensor imaging (DTI) metrics of fractional anisotropy (FA) and mean diffusivity (MD) were included (22 with PBO < 40 years; 43 with PBO 40-45 years; 39 with PBO 46-49 years; 907 referents without PBO < 50 years). Linear regression models adjusted for age and apolipoprotein E (APOE) genotype.

RESULTS

Females with PBO < 40 years, compared to referents, had lower FA and higher MD in the anterior corona radiata, genu of the corpus collosum, inferior fronto-occipital fasciculus, superior occipital, and superior temporal white matter. Females who underwent PBO between 45 and 49 also had some changes in white matter integrity.

DISCUSSION

Females who underwent PBO < 40 years had reduced white matter integrity across multiple regions in later-life. These results are important for females considering PBO for noncancerous conditions.

HIGHLIGHTS

Females with premenopausal bilateral oophorectomy (PBO) < 40 years had lower FA versus referents. Females with PBO < 40 years had higher MD in many regions versus referents. Adjusting for estrogen replacement therapy use did not attenuate results. Females with PBO 45-49 years also had some white matter changes versus referents.

Distinct spatial contributions of amyloid pathology and cerebral small vessel disease to hippocampal morphology

INTRODUCTION

Cerebral small vessel disease (SVD) and amyloid beta (Aβ) pathology frequently co-exist. The impact of concurrent pathology on the pattern of hippocampal atrophy, a key substrate of memory impacted early and extensively in dementia, remains poorly understood.

METHODS

In a unique cohort of mixed Alzheimer's disease and moderate-severe SVD, we examined whether total and regional neuroimaging measures of SVD, white matter hyperintensities (WMH), and Aβ, as assessed by 18F-AV45 positron emission tomography, exert additive or synergistic effects on hippocampal volume and shape.

RESULTS

Frontal WMH, occipital WMH, and Aβ were independently associated with smaller hippocampal volume. Frontal WMH had a spatially distinct impact on hippocampal shape relative to Aβ. In contrast, hippocampal shape alterations associated with occipital WMH spatially overlapped with Aβ-vulnerable subregions.

DISCUSSION

Hippocampal degeneration is differentially sensitive to SVD and Aβ pathology. The pattern of hippocampal atrophy could serve as a disease-specific biomarker, and thus guide clinical diagnosis and individualized treatment strategies for mixed dementia.

Presenilin-1 mutation position influences amyloidosis, small vessel disease, and dementia with disease stage

INTRODUCTION

Amyloidosis, including cerebral amyloid angiopathy, and markers of small vessel disease (SVD) vary across dominantly inherited Alzheimer's disease (DIAD) presenilin-1 (PSEN1) mutation carriers. We investigated how mutation position relative to codon 200 (pre-/postcodon 200) influences these pathologic features and dementia at different stages.

METHODS

Individuals from families with known PSEN1 mutations (n = 393) underwent neuroimaging and clinical assessments. We cross-sectionally evaluated regional Pittsburgh compound B-positron emission tomography uptake, magnetic resonance imaging markers of SVD (diffusion tensor imaging-based white matter injury, white matter hyperintensity volumes, and microhemorrhages), and cognition.

RESULTS

Postcodon 200 carriers had lower amyloid burden in all regions but worse markers of SVD and worse Clinical Dementia Rating® scores compared to precodon 200 carriers as a function of estimated years to symptom onset. Markers of SVD partially mediated the mutation position effects on clinical measures.

DISCUSSION

We demonstrated the genotypic variability behind spatiotemporal amyloidosis, SVD, and clinical presentation in DIAD, which may inform patient prognosis and clinical trials.

HIGHLIGHTS

Mutation position influences Aβ burden, SVD, and dementia. PSEN1 pre-200 group had stronger associations between Aβ burden and disease stage. PSEN1 post-200 group had stronger associations between SVD markers and disease stage. PSEN1 post-200 group had worse dementia score than pre-200 in late disease stage. Diffusion tensor imaging-based SVD markers mediated mutation position effects on dementia in the late stage.

Investigating the impact of hypertension with and without diabetes on Alzheimer's disease risk: A clinico-pathological study

INTRODUCTION

Hypertension and diabetes are common cardiovascular risk factors that increase Alzheimer's disease (AD) risk. However, it is unclear whether AD risk differs in hypertensive individuals with and without diabetes.

METHODS

Cognitively normal individuals (N = 11,074) from the National Alzheimer's Coordinating Center (NACC) were categorized as having (1) hypertension with diabetes (HTN+/DM+), (2) hypertension without diabetes (HTN+/DM-), or (3) neither (HTN-/DM-). AD risk in HTN+/DM+ and HTN+/DM- was compared to HTN-/DM-. This risk was then investigated in those with AD neuropathology (ADNP), cerebral amyloid angiopathy (CAA), cerebrovascular neuropathology (CVNP), arteriolosclerosis, and atherosclerosis. Finally, AD risk in HTN-/DM+ was compared to HTN-/DM-.

RESULTS

Seven percent (N = 830) of individuals developed AD. HTN+/DM+ (hazard ratio [HR] = 1.31 [1.19-1.44]) and HTN+/DM- (HR = 1.24 [1.17-1.32]) increased AD risk compared to HTN-/DM-. AD risk was greater in HTN+/DM+ with ADNP (HR = 2.10 [1.16-3.79]) and CAA (HR = 1.52 [1.09-2.12]), and in HTN+/DM- with CVNP (HR = 1.54 [1.17-2.03]). HTN-/DM+ also increased AD risk (HR = 1.88 [1.30-2.72]) compared to HTN-/DM-.

DISCUSSION

HTN+/DM+ and HTN+/DM- increased AD risk compared to HTN-/DM-, but pathological differences between groups suggest targeted therapies may be warranted based on cardiovascular risk profiles.

HIGHLIGHTS

AD risk was studied in hypertensive (HTN+) individuals with/without diabetes (DM+/-). HTN+/DM+ and HTN+/DM- both had an increased risk of AD compared to HTN-/DM-. Post mortem analysis identified neuropathological differences between HTN+/DM+ and HTN+/DM-. In HTN+/DM+, AD risk was greater in those with AD neuropathology and CAA. In HTN+/DM-, AD risk was greater in those with cerebrovascular neuropathology.

White matter hyperintensity patterns: associations with comorbidities, amyloid, and cognition

BACKGROUND

White matter hyperintensities (WMHs) are often measured globally, but spatial patterns of WMHs could underlie different risk factors and neuropathological and clinical correlates. We investigated the spatial heterogeneity of WMHs and their association with comorbidities, Alzheimer's disease (AD) risk factors, and cognition.

METHODS

In this cross-sectional study, we studied 171 cognitively unimpaired (CU; median age: 65 years, range: 50 to 89) and 51 mildly cognitively impaired (MCI; median age: 72, range: 53 to 89) individuals with available amyloid (18F-flutementamol) PET and FLAIR-weighted images. Comorbidities were assessed using the Cumulative Illness Rating Scale (CIRS). Each participant's white matter was segmented into 38 parcels, and WMH volume was calculated in each parcel. Correlated principal component analysis was applied to the parceled WMH data to determine patterns of WMH covariation. Adjusted and unadjusted linear regression models were used to investigate associations of component scores with comorbidities and AD-related factors. Using multiple linear regression, we tested whether WMH component scores predicted cognitive performance.

RESULTS

Principal component analysis identified four WMH components that broadly describe FLAIR signal hyperintensities in posterior, periventricular, and deep white matter regions, as well as basal ganglia and thalamic structures. In CU individuals, hypertension was associated with all patterns except the periventricular component. MCI individuals showed more diverse associations. The posterior and deep components were associated with renal disorders, the periventricular component was associated with increased amyloid, and the subcortical gray matter structures was associated with sleep disorders, endocrine/metabolic disorders, and increased amyloid. In the combined sample (CU + MCI), the main effects of WMH components were not associated with cognition but predicted poorer episodic memory performance in the presence of increased amyloid. No interaction between hypertension and the number of comorbidities on component scores was observed.

CONCLUSION

Our study underscores the significance of understanding the regional distribution patterns of WMHs and the valuable insights that risk factors can offer regarding their underlying causes. Moreover, patterns of hyperintensities in periventricular regions and deep gray matter structures may have more pronounced cognitive implications, especially when amyloid pathology is also present.

Contributions of amyloid beta and cerebral small vessel disease in clinical decline

INTRODUCTION

We assessed whether co-morbid small vessel disease (SVD) has clinical predictive value in preclinical or prodromal Alzheimer's disease.

METHODS

In 1090 non-demented participants (65.4 ± 10.7 years) SVD was assessed with magnetic resonance imaging and amyloid beta (Aβ) with lumbar puncture and/or positron emission tomography scan (mean follow-up for cognitive function 3.1 ± 2.4 years).

RESULTS

Thirty-nine percent had neither Aβ nor SVD (A-V-), 21% had SVD only (A-V+), 23% Aβ only (A+V-), and 17% had both (A+V+). Pooled cohort linear mixed model analyses demonstrated that compared to A-V- (reference), A+V- had a faster rate of cognitive decline. Co-morbid SVD (A+V+) did not further increase rate of decline. Cox regression showed that dementia risk was modestly increased in A-V+ (hazard ratio [95% confidence interval: 1.8 [1.0-3.2]) and most strongly in A+ groups. Also, mortality risk was increased in A+ groups.

DISCUSSION

In non-demented persons Aβ was predictive of cognitive decline, dementia, and mortality. SVD modestly predicts dementia in A-, but did not increase deleterious effects in A+.

HIGHLIGHTS

Amyloid beta (Aβ; A) was predictive for cognitive decline, dementia, and mortality. Small vessel disease (SVD) had no additional deleterious effects in A+. SVD modestly predicted dementia in A-. Aβ should be assessed even when magnetic resonance imaging indicates vascular cognitive impairment.

CD163-Mediated Small-Vessel Injury in Alzheimer's Disease: An Exploration from Neuroimaging to Transcriptomics

Patients with Alzheimer's disease (AD) often present with imaging features indicative of small-vessel injury, among which, white-matter hyperintensities (WMHs) are the most prevalent. However, the underlying mechanism of the association between AD and small-vessel injury is still obscure. The aim of this study is to investigate the mechanism of small-vessel injury in AD. Differential gene expression analyses were conducted to identify the genes related to WMHs separately in mild cognitive impairment (MCI) and cognitively normal (CN) subjects from the ADNI database. The WMH-related genes identified in patients with MCI were considered to be associated with small-vessel injury in early AD. Functional enrichment analyses and a protein-protein interaction (PPI) network were performed to explore the pathway and hub genes related to the mechanism of small-vessel injury in MCI. Subsequently, the Boruta algorithm and support vector machine recursive feature elimination (SVM-RFE) algorithm were performed to identify feature-selection genes. Finally, the mechanism of small-vessel injury was analyzed in MCI from the immunological perspectives; the relationship of feature-selection genes with various immune cells and neuroimaging indices were also explored. Furthermore, 5×FAD mice were used to demonstrate the genes related to small-vessel injury. The results of the logistic regression analyses suggested that WMHs significantly contributed to MCI, the early stage of AD. A total of 276 genes were determined as WMH-related genes in patients with MCI, while 203 WMH-related genes were obtained in CN patients. Among them, only 15 genes overlapped and were thus identified as the crosstalk genes. By employing the Boruta and SVM-RFE algorithms, CD163, ALDH3B1, MIR22HG, DTX2, FOLR2, ALDH2, and ZNF23 were recognized as the feature-selection genes linked to small-vessel injury in MCI. After considering the results from the PPI network, CD163 was finally determined as the critical WMH-related gene in MCI. The expression of CD163 was correlated with fractional anisotropy (FA) values in regions that are vulnerable to small-vessel injury in AD. The immunostaining and RT-qPCR results from the verifying experiments demonstrated that the indicators of small-vessel injury presented in the cortical tissue of 5×FAD mice and related to the upregulation of CD163 expression. CD163 may be the most pivotal candidates related to small-vessel injury in early AD.

A Closer Look at Practice Effects in Mild Cognitive Impairment and Alzheimer's Disease

Practice effects have become a potentially important variable regarding the diagnosis, prognosis, and treatment recommendations in mild cognitive impairment (MCI) and Alzheimer's disease (AD). However, the understanding of these short-term changes in test scores remains unclear. The current observational study sought to examine variables that influence the magnitude of short-term practice effects in MCI and AD, including demographic information, cognitive performance, daily functioning, and medical comorbidities. One hundred sixty-six older adults classified as cognitively intact, amnestic MCI, or mild AD were tested twice across 1 week with a brief battery of neuropsychological tests. Correlational and regression analyses examined the relationship of practice effects with demographic and clinical variables. Results indicated that practice effects were minimally related to demographic variables and medical comorbidities, but they were significantly related to cognitive variables, depressive symptoms, and daily functioning. These findings expand our understanding of practice effects in MCI and AD, and they may allow a better appreciation of how they could affect clinical care and research.

The Alzheimer's Disease Neuroimaging Initiative in the era of Alzheimer's disease treatment: A review of ADNI studies from 2021 to 2022

The Alzheimer's Disease Neuroimaging Initiative (ADNI) aims to improve Alzheimer's disease (AD) clinical trials. Since 2006, ADNI has shared clinical, neuroimaging, and cognitive data, and biofluid samples. We used conventional search methods to identify 1459 publications from 2021 to 2022 using ADNI data/samples and reviewed 291 impactful studies. This review details how ADNI studies improved disease progression understanding and clinical trial efficiency. Advances in subject selection, detection of treatment effects, harmonization, and modeling improved clinical trials and plasma biomarkers like phosphorylated tau showed promise for clinical use. Biomarkers of amyloid beta, tau, neurodegeneration, inflammation, and others were prognostic with individualized prediction algorithms available online. Studies supported the amyloid cascade, emphasized the importance of neuroinflammation, and detailed widespread heterogeneity in disease, linked to genetic and vascular risk, co-pathologies, sex, and resilience. Biological subtypes were consistently observed. Generalizability of ADNI results is limited by lack of cohort diversity, an issue ADNI-4 aims to address by enrolling a diverse cohort.

Association of Cumulative Lifetime Exposure to Female Hormones With Cerebral Small Vessel Disease in Postmenopausal Women in the UK Biobank

BACKGROUND AND OBJECTIVES

Rates of cerebrovascular disease increase after menopause, which is often attributed to the absence of hormones. It remains unknown whether the cumulative exposure to hormones across a female person's premenopausal life extends the window of cerebrovascular protection to the postmenopausal period. To investigate this, we examined the relationship between lifetime hormone exposure (LHE) and cerebral small vessel disease in more than 9,000 postmenopausal women in the UK-Biobank.

METHODS

The cohort consisted of women (aged 40-69 years) who attended one of 22 research centers across the United Kingdom between 2006 and 2010. Women were excluded if they were premenopausal when scanned, had missing reproductive history data, self-reported neurologic disorders, brain cancer, cerebral vascular incidents, head or neurologic injury, and nervous system infection. Endogenous LHE (LHEEndo) was estimated by summing the number of years pregnant (LHEParity) with the duration of the reproductive period (LHECycle = age menopause - age menarche). Exogenous LHE (LHEExo) was estimated by summing the number of years on oral contraceptives and hormone replacement therapy. Cerebral small vessel disease was determined by estimating white matter hyperintensity volume (WMHV) from T2-fluid-attenuated inversion recovery brain MRI (acquired between 2014 and 2021), normalized to intracranial volume and log-transformed. Multiple linear regressions were used to assess the relationship between LHEEndo on WMHV adjusted for age, cardiovascular risk factors, sociodemographics, and LHEExo.

RESULTS

A total of 9,163 postmenopausal women (age 64.21 ± 6.81 years) were retained for analysis. Average LHEEndo was 39.77 ± 3.59 years. Women with higher LHEEndo showed smaller WMHV (adj-R 2 = 0.307, LHEEndo β = -0.007 [-0.012 to -0.002], p < 0.01). LHEParity and LHECycle were independent contributors to WMHV (adj-R 2 = 0.308, p << 0.001; LHEParity β = -0.022 [-0.042 to -0.002], p < 0.05; LHECycle β = -0.006 [-0.011 to -0.001], p < 0.05). LHEExo was not significantly related to WMHV (LHEExo β = 0.001 [-0.001 to 0.002], p > 0.05).

DISCUSSION

Women with more prolonged exposure to endogenous hormones show relatively smaller burden of cerebral small vessel disease independent of the history of oral contraceptive use or hormone replacement therapy. Our results highlight the critical role endogenous hormones play in female brain health and provide real-world evidence of the protective effects premenopausal endogenous hormone exposure plays on postmenopausal cerebrovascular health.

Alzheimer's disease: an axonal injury disease?

Alzheimer's disease (AD) is the primary cause of dementia and is anticipated to impose a substantial economic burden in the future. Over a significant period, the widely accepted amyloid cascade hypothesis has guided research efforts, and the recent FDA approval of an anti- amyloid-beta (Aβ) protofibrils antibody, believed to decelerate AD progression, has further solidified its significance. However, the excessive emphasis placed on the amyloid cascade hypothesis has overshadowed the physiological nature of Aβ and tau proteins within axons. Axons, specialized neuronal structures, sustain damage during the early stages of AD, exerting a pivotal influence on disease progression. In this review, we present a comprehensive summary of the relationship between axonal damage and AD pathology, amalgamating the physiological roles of Aβ and tau proteins, along with the impact of AD risk genes such as APOE and TREM2. Furthermore, we underscore the exceptional significance of axonal damage in the context of AD.

Deep gray matters iron deposition is positively associated with white matter hyperintensity in hypertension

The association and underlying mechanisms between iron deposition and white matter hyperintensity (WMH) remain unclear. In this study, quantitative susceptibility mapping (QSM) was used to quantify deep gray matters iron deposition and to explore the association from both global and regional perspectives. A total of 84 patients with hypertension and 26 healthy controls underwent a strategically acquired gradient echo (STAGE) protocol, and the multi-echo data were used to reconstruct QSM images. The susceptibilities were used to describe iron content. Global region (RI) susceptibilities were measured in regions of interest, and age-related thresholds were used to determine high-iron content region (RII) susceptibilities. Compared with healthy controls, hypertension had higher total WMH scores and regional scores (all p = .001) and higher susceptibilities using the RI or RII analysis (all p < .05). In healthy controls, there was no significant association between susceptibilities and WMH scores. In hypertension, the susceptibilities of deep gray matters were positively correlated with WMH scores (RI analysis: right putamen; RII analysis: bilateral caudate nucleus head, putamen, red nucleus, substantia nigra, and dentate nucleus; age and education corrected p < .05). These findings suggest that iron deposition in deep gray matters was positively associated with WMH in hypertension, especially using the RII analysis.

Amyloid-PET of the white matter: Relationship to free water, fiber integrity, and cognition in patients with dementia and small vessel disease

White matter (WM) injury is frequently observed along with dementia. Positron emission tomography with amyloid-ligands (Aβ-PET) recently gained interest for detecting WM injury. Yet, little is understood about the origin of the altered Aβ-PET signal in WM regions. Here, we investigated the relative contributions of diffusion MRI-based microstructural alterations, including free water and tissue-specific properties, to Aβ-PET in WM and to cognition. We included a unique cohort of 115 participants covering the spectrum of low-to-severe white matter hyperintensity (WMH) burden and cognitively normal to dementia. We applied a bi-tensor diffusion-MRI model that differentiates between (i) the extracellular WM compartment (represented via free water), and (ii) the fiber-specific compartment (via free water-adjusted fractional anisotropy [FA]). We observed that, in regions of WMH, a decrease in Aβ-PET related most closely to higher free water and higher WMH volume. In contrast, in normal-appearing WM, an increase in Aβ-PET related more closely to higher cortical Aβ (together with lower free water-adjusted FA). In relation to cognitive impairment, we observed a closer relationship with higher free water than with either free water-adjusted FA or WM PET. Our findings support free water and Aβ-PET as markers of WM abnormalities in patients with mixed dementia, and contribute to a better understanding of processes giving rise to the WM PET signal.

APOEɛ4 Status and Plasma p-tau181 Levels May Influence Memory and Executive Function Decline in Older Adults Without Dementia

BACKGROUND

Elevated tau phosphorylation has been linked to the Apolipoprotein E (APOE) ɛ4 allele, which is considered one of the most significant genes related to Alzheimer's disease (AD). However, it is uncertain whether the impact of increased plasma tau phosphorylated at threonine 181 (p-tau181) on memory and executive function decline would be greater among APOEɛ4 carriers.

OBJECTIVE

To investigate the effects of plasma p-tau181 and APOEɛ4 on memory and executive function.

METHODS

The longitudinal analysis included 608 older adults without dementia (aged 72±7 years; 47% female; follow-up period of 1.59±1.47 years) from the ADNI dataset, including 180 individuals with normal cognition and 429 individuals with mild cognitive impairment. Linear mixed-effects models were utilized to assess the contributions of APOEɛ4 status and plasma p-tau181 to longitudinal changes in memory composite score and executive function composite score.

RESULTS

At baseline, the APOEɛ4+/Tau+ group exhibited poorer performance in memory composite score and executive function composite score, and an elevated load of cerebrospinal fluid Aβ and tau pathologies. To further understand longitudinal changes, we compared groups directly based on plasma p-tau181 and APOEɛ4 status (four groups: APOEɛ4-/Tau-, APOEɛ4-/Tau+, APOEɛ4+/Tau-, APOEɛ4+/Tau+). Both the memory composite score and executive function composite score showed a significantly greater decline in the APOEɛ4+/Tau+ group than in all other groups.

CONCLUSIONS

Our findings indicate that there is an interaction between plasma p-tau181 levels and APOEɛ4 status, which contributes to the longitudinal changes of memory and executive function in older adults without dementia.