White matter hyperintensity topography in Alzheimer's disease and links to cognition

Characterization of brain morphology associated with metabolic dysfunction-associated steatotic liver disease in the UK Biobank

BACKGROUND

Emerging evidence has linked metabolic dysfunction-associated steatotic liver disease (MASLD) with accelerated cognitive decline and dementia. We aimed to investigate the associations of MASLD with volumes of total brain tissue and subcortical grey matter, and white matter microstructures in the UK Biobank.

METHODS

This cross-sectional study included 29,195 individuals (aged 45-82 years) from the UK Biobank who undertook a magnetic resonance imaging (MRI) sub-study between 2014 and 2022. The brain MRI covers three modalities (T1, T2 FLAIR, and diffusion). Volumes of grey matter, subcortical grey matter structures, and regional cortex were derived from T1-weighted images. Fractional anisotropy (FA) and mean diffusivity (MD) were derived from diffusion tensor imaging (DTI) to assess global and tract-specific microstructure. MASLD was defined as the MRI-derived proton density fat fraction (MRI-PDFF) ≥5% and the presence of at least one cardiometabolic criterion. Data were analysed using multiple linear regression models.

RESULTS

MASLD was significantly associated with smaller volumes of total grey matter and subcortical grey matter (p < 0.05) and reduced Alzheimer's disease (AD)-signature cortical thickness (multivariable-adjusted β = -0.04; 95% confidence interval [CI]: -0.07, -0.01). Having MASLD was associated with higher total white matter hyperintensity (WMH) volume (multivariable-adjusted β = 0.12; 95% CI: 0.10, 0.15). For white matter microstructure, MASLD was associated with increased global FA (multivariable-adjusted β = 0.05; 95% CI: 0.03, 0.08) and reduced global MD (multivariable-adjusted β = -0.04; 95% CI: -0.07, -0.01).

CONCLUSIONS

Brain morphology associated with MASLD is characterized by smaller subcortical grey matter volume and higher coherence but lower magnitudes of white matter microstructure.

Identifying the mediating role of brain atrophy on the relationship between DNA damage repair pathway and Alzheimer's disease: A Mendelian randomization analysis and mediation analysis

BackgroundDNA damage and repair (DDR) and structural atrophies in different brain regions were recognized as critical factors in the onset of Alzheimer's disease (AD).ObjectiveWe utilized Mendelian randomization (MR) to examine the causal effects of the DDR-related molecular traits on AD and the potential mediating roles of different brain region volumes.MethodsIn primary analysis, we utilized public genome-wide association studies of AD and summary data from existing molecular traits datasets, including gene expression, DNA methylation, and protein levels quantitative trait loci (eQTL, mQTL, and pQTL) in both blood and brain to examine their causal associations by summary-data-based MR analysis and additional five two-sample MR methods. Subsequently, mediation analysis explored the potential mediate roles of 13 imaging-derived brain volume phenotypes in the associations between the DDR pathways and AD through a network MR design.ResultsWe found that the volumes of the right thalamus proper and global cerebral white matter mediated the causal pathways from EGFR to AD and relatively weak mediation effects of the right lateral ventricle volume in the causal pathways involving CHRNE, DNTT, and AD.ConclusionsWe identified causal relationships among DDR pathways, specific brain region volumes, and AD. Monitoring the molecular traits of these DDR-related genes and developing targeted drugs may help detect and interrupt the early progression of AD.

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.

Risk factors and clinical significance of neurodegenerative co-pathologies in symptomatic cerebral small vessel disease

BACKGROUND

Cerebral small vessel disease (CSVD) often coexists with neurodegenerative pathologies, yet their role remains underexplored. This study aims to determine their prevalence, risk factors, and cognitive effects in patients with deep perforator arteriopathy (DPA) or cerebral amyloid angiopathy (CAA) using the biomarker-based ATN classification.

METHODS

In this cross-sectional study 186 patients (median age 75 years, 41% females, 111 with probable CAA, 75 with DPA) underwent MRI for analysis of CSVD severity and etiology, and lumbar puncture for analysis of cerebrospinal fluid amyloid-β 42/40 ratio, phosphorylated-tau, total-tau and neurofilament light. ATN profiles were related to clinical characteristics, MRI markers and cognitive performance in multivariate regression models.

RESULTS

Among CSVD patients, 30% had normal biomarkers (A-T-N-), 33% were within the AD pathology continuum (A + T ± N ± : 47% in CAA vs. 13% in DPA, p < .001), and 37% showed non-AD pathological changes (A-T ± N + : 53% in DPA vs. 25% in CAA, p < .001). The AD pathology continuum was associated with a severe lobar hemorrhagic phenotype and cognitive impairment, while non-AD pathological change was related to CSVD severity, history of stroke and similarly cognitive impairment. Both pathological ATN profiles were further related to lower MMSE scores (A + T ± N ± : B = - 3.3, p = .006; A-T ± N + : B = - 2.7, p = .021).

CONCLUSIONS

Using biomarkers, this study confirms in vivo that CSVD frequently co-occurs with neurodegenerative pathologies, exerting detrimental effects on cognitive health.

Does white matter and vascular injury from repetitive head impacts lead to a novel pattern on T2 FLAIR MRI? A hypothesis proposal and call for research

The goal of this paper is to introduce the hypothesis that white matter (WM) and vascular injury are long-term consequences of repetitive head impacts (RHI) that result in a novel T2 fluid attenuated inversion recovery (FLAIR) magnetic resonance imaging pattern. A non-systematic literature review of autopsy and FLAIR studies of RHI-exposed adults was first conducted as a foundation for our hypothesis. A case series of RHI-exposed participants is presented to illustrate the unique FLAIR WM hyperintensities (WMH) pattern. Current literature shows a direct link between RHI and later-life WM/vascular neuropathologies, and that FLAIR WMH are associated with RHI, independent of modifiable vascular risk factors. Initial observations suggest a distinctive pattern of WMH in RHI-exposed participants, termed RHI-associated WMH (RHI-WMH). RHI-WMH defining features are as follows: (1) small, punctate, non-confluent, (2) spherical, and (3) proximal to the gray matter. Our hypothesis serves as a call for research to empirically validate RHI-WMH and clarify their biological and clinical correlates. HIGHLIGHTS: Repetitive head impacts (RHI) have been associated with later-life white matter (WM) and vascular neuropathologies. T2 FLAIR MRI of RHI-exposed participants reveals a potentially unique WM hyperintensity (WMH) pattern that is termed RHI-associated WMH (RHI-WMH). RHI-WMH are characterized as (1) small, punctate, and non-confluent, (2) spherical, and (3) proximal to the gray matter at an area anatomically susceptible to impact injury, such as the depths of the cortical sulci.

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.

Microstructural white matter injury contributes to cognitive decline: Besides amyloid and tau

BACKGROUND

Cognitive decline and the progression to Alzheimer's disease (AD) are traditionally associated with amyloid-beta (Aβ) and tau pathologies. This study aims to evaluate the relationships between microstructural white matter injury, cognitive decline and AD core biomarkers.

METHODS

We conducted a longitudinal study of 566 participants using peak width of skeletonized mean diffusivity (PSMD) to quantify microstructural white matter injury. The associations of PSMD with changes in cognitive functions, AD pathologies (Aβ, tau, and neurodegeneration), and volumes of AD-signature regions of interest (ROI) or hippocampus were estimated. The associations between PSMD and the incidences of clinical progression were also tested. Covariates included age, sex, education, apolipoprotein E4 status, smoking, and hypertension.

RESULTS

Higher PSMD was associated with greater cognitive decline (β=-0.012, P < 0.001 for Mini-Mental State Examination score; β<0, P < 0.05 for four cognitive domains) and a higher risk of clinical progression from normal cognition to mild cognitive impairment (MCI) or AD (Hazard ratio=2.11 [1.38-3.23], P < 0.001). These associations persisted independently of amyloid status. PSMD did not predict changes in Aβ or tau levels, but predicted changes in volumes of AD-signature ROI (β=-0.003, P < 0.001) or hippocampus (β=-0.002, P = 0.010). Besides, the whole-brain PSMD could predict cognitive decline better than regional PSMDs.

CONCLUSIONS

PSMD may be a valuable biomarker for predicting cognitive decline and clinical progression to MCI and AD, providing insights besides traditional Aβ and tau pathways. Further research could elucidate its role in clinical assessments and therapeutic strategies.

Urinary formic acid is associated with cerebral amyloid deposition and glucose metabolism in memory clinic patients

BACKGROUND

Urinary formic acid (FA) has been reported to be a biomarker for Alzheimer's disease (AD). However, the association between FA and pathological changes in memory clinic patients is currently unclear.

OBJECTIVE

This study aims to investigate associations between FA and pathological changes across different cognitive statuses in memory clinic patients.

METHODS

A cohort of patients with mild cognitive impairment (MCI-Aβ- n = 37, MCI-Aβ+ n = 33), AD dementia (n = 39), and cognitively normal subjects (CN-Aβ- n = 98, CN-Aβ+ n = 50) were included. Comprehensive neuropsychological assessment, urinary FA, AD-related plasma biomarkers, MRI scans, [18F]-flurbetapir and [18F]-FDG PET scan data were collected from all participants.

RESULTS

Urinary FA levels were higher in patients with MCI and AD than in CN subjects and higher in Aβ+ (CN- Aβ+, MCI-Aβ+, AD dementia) subjects than in Aβ-subjects (CN- Aβ-, MCI-Aβ-). Urinary FA was positively associated with cerebral Aβ deposition and negatively associated with glucose metabolism, both at the global level and in multiple regions of interest cortical regions in participants with different cognitive statuses. Additionally, urinary FA levels were positively correlated with the severity of white matter hyperintensities and hippocampal atrophy. Urinary FA combined with age, Mini-Mental State Examination, plasma p-tau181, and neurofilament light chain could be used to predict Aβ deposition in the brain.

CONCLUSIONS

Urinary FA is associated with brain pathological changes in memory clinic patients, including cerebral Aβ deposition, glucose metabolism, white matter hyperintensities, and hippocampal atrophy. It could be used as a biomarker for the early diagnosis of AD and predicting Aβ deposition.

Quantitative assessments of white matter hyperintensities and plasma biomarkers can predict cognitive impairment and cerebral microbleeds in cerebral small vessel disease patients

The objective of this study is to examine the efficacy of magnetic resonance imaging (MRI) features and peripheral blood biomarkers in assessing cognitive function in patients with cerebral small vessel disease (CSVD). A total of 58 CSVD patients were recruited. Six features of white matter hyperintensities (WMHs) were derived from MRI scans. Additionally, five neurodegenerative biomarkers (Aβ40, Aβ42, t-tau, p-tau181, NfL) and 13 serum inflammatory cytokines (VILIP-1, CCL2, IL-6, IL-18, TNF-α, CX3CL, sTREM-1/2, VEGF, s-RAGE, BNDF, TGF-β1, β-NGF) were quantified. Cognitive assessments were conducted using standardized neuropsychological scales. Spearman analysis revealed that the volumetric characteristics (absolute area, upper area, bottom area, absolute area percentage, upper percentage, and bottom percentage) of WMHs were negatively correlated with performance on all cognitive scale measures except the verbal fluency test (VFT) (r < -0.3, p > 0.05), while they were positively correlated with plasma neurofilament light (NFL) levels (r > 0.4, p < 0.05). Additionally, serum tumor necrosis factor-α (TNF-α) and soluble receptor for advanced glycation end-products (s-RAGE) showed significant correlations with scales of speech function. An integrated model incorporating WMHs features, neurodegenerative biomarkers, and neuroinflammatory markers was developed, demonstrating high predictive accuracy for cognitive impairment with an area under the curve (AUC) of 0.95 (accuracy 0.88, sensitivity 0.87, specificity 0.89). Another integrated model that includes features of WMHs and inflammatory cytokines for predicting cerebral microbleeds (CMBs) achieved an AUC of 0.95 (accuracy 0.88, sensitivity 0.82, specificity 0.92). Our findings suggest that these markers have the potential to be used for the early detection of cognitive decline and CMBs in patients with CSVD.

Cross-sectional and prognostic associations of baseline [18F]GTP1 tau PET signal and white matter lesion volumes for cognitive and functional decline in prodromal-to-mild Alzheimer's disease

BACKGROUND

In Alzheimer's disease (AD), tau and white matter lesion pathology are associated with clinical severity and subsequent decline, but their relative relationships with clinical assessments remain uncertain.

OBJECTIVE

To examine cross-sectional and prognostic associations between baseline [18F]GTP1 tau positron emission tomography (PET) standardized uptake value ratio (SUVRs) and T1 white matter hypointensity (WMHypo) volumes with clinical indices.

METHODS

We analyzed participants with biomarker-confirmed prodromal (n = 127) or mild (n = 233) AD with baseline [18F]GTP1 tau PET and MRI and longitudinal Clinical Dementia Rating-Sum of Boxes (CDR-SB), 13-item version of the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog13), Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), Mini-Mental Status Examination (MMSE), and Alzheimer's Disease Cooperative Study-Activities of Daily Living (ADCS-ADL) data.

RESULTS

Higher baseline [18F]GTP1 SUVRs were independently associated with poorer baseline performance and faster rates of subsequent decline on all five clinical outcome measures. Higher baseline WMHypo volumes were independently associated with poorer baseline performance on the CDR-SB, ADAS-Cog13, RBANS, and MMSE and faster rates of subsequent decline on the CDR-SB and ADCS-ADL.

CONCLUSIONS

The independent associations of tau and white matter lesion pathology with clinical decline in AD suggest future prognostic models should include both imaging modalities.

Tract-Specific White Matter Hyperintensities Disrupt Brain Networks and Associated With Cognitive Impairment in Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is considered to initiate cerebrovascular pathology, involving in the development of multiple forms of neurodegeneration. However, it is unknown the relationships between imaging marker of cerebrovascular injury (white matter hyperintensity, WMH), its load on white matter tract and disrupted brain dynamics with cognitive function in mild TBI (mTBI). MRI data and neuropsychological assessments were collected from 85 mTBI patients and 52 healthy controls. Between-group difference was conducted for the tract-specific WMH volumes, white matter integrity, and dynamic brain connectivity (i.e., fractional occupancies [%], dwell times [seconds], and state transitions). Regression analysis was used to examine associations between white matter damage, brain dynamics, and cognitive function. Increased WMH volumes induced by mTBI within the thalamic radiation and corpus callosum were highest among all tract fibers, and related with altered fractional anisotropy (FA) within the same tracts. Clustering identified two brain states, segregated state characterized by the sparse inter-independent component connections, and default mode network (DMN)-centered integrated state with strongly internetwork connections between DMN and other networks. In mTBI, higher WMH loads contributed to the longer dwell time and larger fractional occupancies in DMN-centered integrated state. Every 1 mL increase in WMH volume within the left thalamic radiation was associated with a 47% increase fractional occupancies, and contributed to 65.6 s delay in completion of cognitive processing speed test. Our study provided the first evidence for the structural determinants (i.e., small vessel lesions) that mediate the spatiotemporal brain dynamics to cognitive impairments in mTBI.

Myelin Lipid Alterations in Neurodegenerative Diseases: Landscape and Pathogenic Implications

Significance: Lipids, which constitute the highest portion (over 50%) of brain dry mass, are crucial for brain integrity, energy homeostasis, and signaling regulation. Emerging evidence revealed that lipid profile alterations and abnormal lipid metabolism occur during normal aging and in different forms of neurodegenerative diseases. Moreover, increasing genome-wide association studies have validated new targets on lipid-associated pathways involved in disease development. Myelin, the protective sheath surrounding axons, is crucial for efficient neural signaling transduction. As the primary site enriched with lipids, impairments of myelin are increasingly recognized as playing significant and complex roles in various neurodegenerative diseases, beyond simply being secondary effects of neuronal loss. Recent Advances: With advances in the lipidomics field, myelin lipid alterations and their roles in contributing to or reflecting the progression of diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, multiple sclerosis, and others, have recently caught great attention. Critical Issues: This review summarizes recent findings of myelin lipid alterations in the five most common neurodegenerative diseases and discusses their implications in disease pathogenesis. Future Directions: By highlighting myelin lipid abnormalities in neurodegenerative diseases, this review aims to encourage further research focused on lipids and the development of new lipid-oriented therapeutic approaches in this area. Antioxid. Redox Signal. 00, 000-000.

Association between fibrinogen and white matter lesions and cerebral atrophy in patients with acute ischemic stroke

BACKGROUND

Inflammation is a potential mechanism underlying the development of white matter lesions (WMLs) and cerebral atrophy. We aimed to investigate the relationship of fibrinogen levels with WMLs and cerebral atrophy in patients with acute ischemic stroke (AIS).

METHODS

A total of 701 AIS patients were enrolled. Participants were divided into four groups according to the quartiles of fibrinogen levels: Q1 < 2.58 g/L, Q2: 2.58-3.12 g/L, Q3: 3.12-3.67 g/L, Q4: ≥ 3.67 g/L. White matter hyperintensity (WMH), periventricular hyperintensity (PVH) and deep white matter hyperintensity (DWMH) were defined according to the Fazekas scale. Cerebral atrophy was defined according to global cortical atrophy scores. Univariate and multivariate logistic regression were used to explore the relationship of fibrinogen levels and WMHs, PVH, DWMH and cerebral atrophy.

RESULTS

Among 701 AIS patients, 498 (71.0 %), 425 (60.6 %), 442 (63.1 %), and 560 (79.9 %) had WMHs, PVH, DWMH and cerebral atrophy, respectively. After adjustment for potential covariates, the highest fibrinogen quartiles were significantly associated with increased risk of WMHs (odds ratio [OR] 1.97, 95 % confidence intervals [CI] 1.10-3.50), PVH (OR 1.85, 95 % CI 1.08-3.16) and cerebral atrophy (OR 2.53, 95 % CI 1.19-5.40) but not DWMH (OR 1.37 95 % CI 0.81-2.31) compared with the lowest fibrinogen quartile. Moreover, the association between elevated fibrinogen levels and the risk of WMLs and cerebral atrophy remained significant as continuous variables.

CONCLUSIONS

Increased baseline fibrinogen levels were independently associated with WMHs, PVH and cerebral atrophy in patients with ischemic stroke. Fibrinogen could be the potential blood biomarker of WMLs and cerebral atrophy.

Longitudinal evidence for a mutually reinforcing relationship between white matter hyperintensities and cortical thickness in cognitively unimpaired older adults

BACKGROUND

For over three decades, the concomitance of cortical neurodegeneration and white matter hyperintensities (WMH) has sparked discussions about their coupled temporal dynamics. Longitudinal studies supporting this hypothesis nonetheless remain scarce.

METHODS

We applied global and regional bivariate latent growth curve modelling to determine the extent to which WMH and cortical thickness were interrelated over a four-year period. For this purpose, we leveraged longitudinal MRI data from 451 cognitively unimpaired participants (DELCODE; median age 69.71 [IQR 65.51, 75.50] years; 52.32% female). Participants underwent MRI sessions annually over a four-year period (1815 sessions in total, with roughly four MRI sessions per participant). We adjusted all models for demographics and cardiovascular risk.

RESULTS

Our findings were three-fold. First, larger WMH volumes were linked to lower cortical thickness (σ = -0.165, SE = 0.047, Z = -3.515, P < 0.001). Second, individuals with higher WMH volumes experienced more rapid cortical thinning (σ = -0.226, SE = 0.093, Z = -2.443, P = 0.007), particularly in temporal, cingulate, and insular regions. Similarly, those with lower initial cortical thickness had faster WMH progression (σ = -0.141, SE = 0.060, Z = -2.336, P = 0.009), with this effect being most pronounced in temporal, cingulate, and insular cortices. Third, faster WMH progression was associated with accelerated cortical thinning (σ = -0.239, SE = 0.139, Z = -1.710, P = 0.044), particularly in frontal, occipital, and insular cortical regions.

CONCLUSIONS

Our study suggests that cortical thinning and WMH progression could be mutually reinforcing rather than parallel, unrelated processes, which become entangled before cognitive deficits are detectable.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS00007966, 04/05/2015).

Deep medullary vein abnormalities impact white matter hyperintensity volume through increases in interstitial free water

BACKGROUND

Our intent was to explore the mediating role of interstitial free water (FW) linking deep medullary vein (DMV) score to white matter hyperintensity (WMH) volume.

METHODS

Our research team conducted a forward-looking analysis of initial clinical and imaging information gathered from 125 patients with cerebral small vessel disease. We identified six anatomic DMV regions on susceptibility weighted imaging (SWI) studies. Each region earned a score of 0-3, determined by the visual conditions of vessels, summing all six to generate a DMV score. We utilized fluid-attenuated inversion recovery (FLAIR) sequences to measure the volume of WMH. Additionally, we employed diffusion tensor imaging (DTI) to assess FW value.

RESULTS

DMV score significantly positively correlated with FW value and with WMH volume (p < 0.05), and value of FW positively correlated with WMH volume (p < 0.05). The indirect effect of DMV score on WMH volume was mediated by FW (β = 0.281, 95% confidence interval [CI]: 0.178-0.388), whether adjusted for age and gender (β = 0.142, 95% CI: 0.058-0.240) or for age, gender and vascular risk factors (β = 0.141, 95% CI: 0.054-0.249).

CONCLUSION

DMV score correlate with WMH volume by virtue of FW increases in white matter.

Associations of cerebrovascular disease and Alzheimer's disease pathology with cognitive decline: Analysis of the National Alzheimer's Coordinating Center Uniform Data Set

Cerebrovascular disease (CVD) and Alzheimer's disease (AD) often co-occur and may impact specific cognitive domains. This study's goal was to determine effects of CVD and AD burden on cross-sectional and longitudinal executive function (EF) and memory in older adults. Longitudinally followed participants from the National Alzheimer Coordinating Center database (n = 3342) were included. Cognitive outcomes were EF and memory composite scores. Baseline CVD presence was defined by moderate-to-severe white matter hyperintensities or lacunar infarct on MRI. Baseline AD pathology was defined by amyloid positivity via PET or CSF. Linear mixed models examined effects of CVD, AD, and time on cognitive outcomes, controlling for sex, education, baseline age, MoCA score, and total number of study visits. At baseline, CVD associated with lower EF (p < 0.001), while AD associated with lower EF and memory (ps < 0.001). Longitudinally only AD associated with faster declines in memory and EF (ps < 0.001). These results extend our understanding of CVD and AD pathology, highlighting that CVD does not necessarily indicate accelerated decline.

Correspondence between white matter hyperintensities and regional grey matter volumes in Alzheimer's disease

Objective

White matter hyperintensities (WMH) are the most common neuroimaging manifestation of cerebral small vessel disease, and is frequently observed in Alzheimer's disease (AD). This study aimed to investigate the relationship between WMH and cognition and to verify the mediation of grey matter atrophy in this relationship.

Methods

The diffusion tensor imaging (DTI) technique analyses white matter fiber tract to assess white matter integrity. Voxel-based morphometry was applied to measure the grey matter volume (GMV). A linear regression model was applied to examine the associations between WMH and GMV, and mediation analyses was performed to determine the mediating role of regional GMV in the effect of WMH on cognitive function.

Results

Compared to the HC group, AD group have 8 fiber tract fractional anisotropy (FA) decreased and 16 fiber tract mean diffusivity (MD) increased. Compared to AD without WMH, AD with high WMH had 9 fiber tracts FA decreased and 13 fiber tracts MD increased. High WMH volume was negatively correlated with GMV in the frontal-parietal region. Low WMH volume was also negatively correlated with GMV except for the three regions (right angular gyrus, right superior frontal gyrus and right middle/inferior parietal gyrus), where GMV was positively correlated. Mediation analysis showed that the association between WMH and executive function or episodic memory were mediated by GMV in the frontal-parietal region.

Conclusion

Damage to white matter integrity was more severe in AD with WMH. Differential changes in DTI metrics may be caused by progressive myelin and axonal damage. There was a negative correlation between WMH and grey matter atrophy in frontal-parietal regions in a volume-dependent manner. This study indicates the correspondence between WMH volume and GMV in cognition, and GMV being a key modulator between WMH and cognition in AD. This result will contribute to understanding the progression of the disease process and applying targeted therapeutic intervention in the earlier stage to delay neurodegenerative changes in frontal-parietal regions to achieve better treatment outcomes and affordability.

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.

Characterization of white matter hyperintensities in Down syndrome

INTRODUCTION

In Down syndrome (DS), white matter hyperintensities (WMHs) are highly prevalent, yet their topography and association with sociodemographic data and Alzheimer's disease (AD) biomarkers remain largely unexplored.

METHODS

In 261 DS adults and 131 euploid controls, fluid-attenuated inversion recovery magnetic resonance imaging scans were segmented and WMHs were extracted in concentric white matter layers and lobar regions. We tested associations with AD clinical stages, sociodemographic data, cerebrospinal fluid (CSF) AD biomarkers, and gray matter (GM) volume.

RESULTS

In DS, total WMHs arose at age 43 and showed stronger associations with age than in controls. WMH volume increased along the AD continuum, particularly in periventricular regions, and frontal, parietal, and occipital lobes. Associations were found with CSF biomarkers and temporo-parietal GM volumes.

DISCUSSION

WMHs increase 10 years before AD symptom onset in DS and are closely linked with AD biomarkers and neurodegeneration. This suggests a direct connection to AD pathophysiology, independent of vascular risks.

HIGHLIGHTS

White matter hyperintensities (WMHs) increased 10 years before Alzheimer's disease symptom onset in Down syndrome (DS). WMHs were strongly associated in DS with the neurofilament light chain biomarker. WMHs were more associated in DS with gray matter volume in parieto-temporal areas.

Inflammatory aspects of Alzheimer's disease

Alzheimer´s disease (AD) stands out as the most common chronic neurodegenerative disorder. AD is characterized by progressive cognitive decline and memory loss, with neurodegeneration as its primary pathological feature. The role of neuroinflammation in the disease course has become a focus of intense research. While microglia, the brain's resident macrophages, have been pivotal to study central immune inflammation, recent evidence underscores the contributions of other cellular entities to the neuroinflammatory process. In this article, we review the inflammatory role of microglia and astrocytes, focusing on their interactions with AD's core pathologies, amyloid beta deposition, and tau tangle formation. Additionally, we also discuss how different modes of regulated cell death in AD may impact the chronic neuroinflammatory environment. This review aims to highlight the evolving landscape of neuroinflammatory research in AD and underscores the importance of considering multiple cellular contributors when developing new therapeutic strategies.

Navigating oligodendrocyte precursor cell aging in brain health

Oligodendrocyte precursor cells (OPCs) comprise 5-8 % of the adult glial cell population and stand out as the most proliferative cell type in the central nervous system (CNS). OPCs are responsible for generating oligodendrocytes (OLs), the myelinating cells of the CNS. However, OPC functions decline as we age, resulting in impaired differentiation and inadequate remyelination. This review explores the cellular and molecular changes associated with OPC aging, and their impact on OPC differentiation and functionality. Furthermore, it examines the impact of OPC aging within the context of multiple sclerosis and Alzheimer's disease, both neurodegenerative conditions wherein aged OPCs exacerbate disease progression by impeding remyelination. Moreover, various pharmacological interventions targeting pathways related to senescence and differentiation are discussed as potential strategies to rejuvenate aged OPCs. Enhancing our understanding of OPC aging mechanisms holds promise for developing new therapies to improve remyelination and repair in age-related neurodegenerative disorders.

Brain structure, amyloid, and behavioral features for predicting clinical progression in subjective cognitive decline

As a potential preclinical stage of Alzheimer's dementia, subjective cognitive decline (SCD) reveals a higher risk of future cognitive decline and conversion to dementia. However, it has not been clear whether SCD status increases the clinical progression of older adults in the context of amyloid deposition, cerebrovascular disease (CeVD), and psychiatric symptoms. We identified 99 normal controls (NC), 15 SCD individuals who developed mild cognitive impairment in the next 2 years (P-SCD), and 54 SCD individuals who did not (S-SCD) from ADNI database with both baseline and 2-year follow-up data. Total white matter hyperintensity (WMH), WMH in deep (DWMH) and periventricular (PWMH) regions, and voxel-wise grey matter volumes were compared among groups. Furthermore, using structural equation modelling method, we constructed path models to explore SCD-related brain changes longitudinally and to determine whether baseline SCD status, age, and depressive symptoms affect participants' clinical outcomes. Both SCD groups showed higher baseline amyloid PET SUVR, baseline PWMH volumes, and larger increase of PWMH volumes over time than NC. In contrast, only P-SCD had higher baseline DWMH volumes and larger increase of DWMH volumes over time than NC. No longitudinal differences in grey matter volume and amyloid was observed among NC, S-SCD, and P-SCD. Our path models demonstrated that SCD status contributed to future WMH progression. Further, baseline SCD status increases the risk of future cognitive decline, mediated by PWMH; baseline depressive symptoms directly contribute to clinical outcomes. In conclusion, both S-SCD and P-SCD exhibited more severe CeVD than NC. The CeVD burden increase was more pronounced in P-SCD. In contrast with the direct association of depressive symptoms with dementia severity progression, the effects of SCD status on future cognitive decline may manifest via CeVD pathologies. Our work highlights the importance of multi-modal longitudinal designs in understanding the SCD trajectory heterogeneity, paving the way for stratification and early intervention in the preclinical stage. PRACTITIONER POINTS: Both S-SCD and P-SCD exhibited more severe CeVD at baseline and a larger increase of CeVD burden compared to NC, while the burden was more pronounced in P-SCD. Baseline SCD status increases the risk of future PWMH and DWMH volume accumulation, mediated by baseline PWMH and DWMH volumes, respectively. Baseline SCD status increases the risk of future cognitive decline, mediated by baseline PWMH, while baseline depression status directly contributes to clinical outcome.

Can white matter hyperintensities based Fazekas visual assessment scales inform about Alzheimer's disease pathology in the population?

BACKGROUND

White matter hyperintensities (WMH) are considered hallmark features of cerebral small vessel disease and have recently been linked to Alzheimer's disease (AD) pathology. Their distinct spatial distributions, namely periventricular versus deep WMH, may differ by underlying age-related and pathobiological processes contributing to cognitive decline. We aimed to identify the spatial patterns of WMH using the 4-scale Fazekas visual assessment and explore their differential association with age, vascular health, AD imaging markers, namely amyloid and tau burden, and cognition. Because our study consisted of scans from GE and Siemens scanners with different resolutions, we also investigated inter-scanner reproducibility and combinability of WMH measurements on imaging.

METHODS

We identified 1144 participants from the Mayo Clinic Study of Aging consisting of a population-based sample from Olmsted County, Minnesota with available structural magnetic resonance imaging (MRI), amyloid, and tau positron emission tomography (PET). WMH distribution patterns were assessed on FLAIR-MRI, both 2D axial and 3D, using Fazekas ratings of periventricular and deep WMH severity. We compared the association of periventricular and deep WMH scales with vascular risk factors, amyloid-PET, and tau-PET standardized uptake value ratio, automated WMH volume, and cognition using Pearson partial correlation after adjusting for age. We also evaluated vendor compatibility and reproducibility of the Fazekas scales using intraclass correlations (ICC).

RESULTS

Periventricular and deep WMH measurements showed similar correlations with age, cardiometabolic conditions score (vascular risk), and cognition, (p < 0.001). Both periventricular WMH and deep WMH showed weak associations with amyloidosis (R = 0.07, p = < 0.001), and none with tau burden. We found substantial agreement between data from the two scanners for Fazekas measurements (ICC = 0.82 and 0.74). The automated WMH volume had high discriminating power for identifying participants with Fazekas ≥ 2 (area under curve = 0.97) and showed poor correlation with amyloid and tau PET markers similar to the visual grading.

CONCLUSION

Our study investigated risk factors underlying WMH spatial patterns and their impact on global cognition, with no discernible differences between periventricular and deep WMH. We observed minimal impact of amyloidosis on WMH severity. These findings, coupled with enhanced inter-scanner reproducibility of WMH data, suggest the combinability of inter-scanner data assessed by harmonized protocols in the context of vascular contributions to cognitive impairment and dementia biomarker research.

Prolonged ventricular repolarization associated with mild cognitive impairment and white matter hyperintensities: a cross-sectional study

Prolonged ventricular repolarization has been associated with cardiovascular disease. We sought to investigate the association of prolonged ventricular repolarization with mild cognitive impairment (MCI) and the potential underlying neuropathological mechanisms in older adults. This cross-sectional study included 4328 dementia-free participants (age ≥ 65 years; 56.8% female) in the baseline examination of the Multidomain INterventions to delay dementia and Disability in rural China; of these, 989 undertook structural brain magnetic resonance imaging (MRI) scans. QT, QTc, JT, JTc, and QRS intervals were derived from 12-lead electrocardiograph. MCI, amnestic MCI (aMCI), and non-amnestic MCI (naMCI) were defined following the Petersen's criteria. Volumes of gray matter (GM), white matter, cerebrospinal fluid, total white matter hyperintensities (WMH), periventricular WMH (PWMH), and deep WMH (DWMH) were automatically estimated. Data were analyzed using logistic and general linear regression models. Prolonged QT, QTc, JT, and JTc intervals were significantly associated with an increased likelihood of MCI and aMCI, but not naMCI (p < 0.05). In the MRI subsample, QT, QTc, JT, and JTc intervals were significantly associated with larger total WMH and PWMH volumes (p < 0.05), but not with DWMH volume. Statistical interactions were detected, such that prolonged QT and JT intervals were significantly associated with reduced GM volume only among participants with coronary heart disease or without APOE ε4 allele (p < 0.05). Prolonged ventricular repolarization is associated with MCI and cerebral microvascular lesions in a general population of older adults. This underlies the importance of cognitive assessments and brain MRI examination among older adults with prolonged QT interval.

Older adults with reduced cerebrovascular reactivity exhibit high white matter hyperintensity burden

Cerebrovascular reactivity (CVR) deficits may contribute to small vessel disease, such as white matter hyperintensities (WMH). Moreover, apolipoprotein-e4 (APOE4) carriers at genetic risk for Alzheimer's disease exhibit cerebrovascular dysfunction relative to non-carriers. We examined whether older adults, and APOE4 carriers specifically, with diminished CVR would exhibit higher WMH burden. Independently living older adults (N = 125, mean age = 69.2 years; SD = 7.6; 31.2% male) free of dementia or clinical stroke underwent brain MRI to quantify cerebral perfusion during CVR to hypercapnia and hypocapnia and determine WMH volume. Adjusting for age, sex and intracranial volume, hierarchical regression analysis revealed a significant association between whole brain CVR to hypercapnia and WMH overall [B = -.02, 95% CI (-.04, -.008), p =.003] and in APOE4 carriers [B = -.03, 95% CI (-.06, -.009), p =.009]. Findings suggest deficits in cerebral vasodilatory capacity are associated with WMH burden in older adults and future studies are warranted to further delineate the effect of APOE4 on precipitating WMH.

Associations between accelerometer-derived sedentary behavior and physical activity with white matter hyperintensities in middle-aged to older adults

INTRODUCTION

We examined the relationship between sedentary behavior (SB), moderate-to-vigorous physical activity (MVPA), and white matter hyperintensity (WMH) volumes, a common magnetic resonance imaging (MRI) marker associated with risk of neurodegenerative disease in middle-aged to older adults.

METHODS

We used data from the UK Biobank (n = 14,415; 45 to 81 years) that included accelerometer-derived measures of SB and MVPA, and WMH volumes from MRI.

RESULTS

Both MVPA and SB were associated with WMH volumes (βMVPA = -0.03 [-0.04, -0.01], p < 0.001; βSB = 0.02 [0.01, 0.03], p = 0.007). There was a significant interaction between SB and MVPA on WMH volumes (βSB×MVPA = -0.015 [-0.028, -0.001], p SB×MVPA = 0.03) where SB was positively associated with WMHs at low MVPA, and MVPA was negatively associated with WMHs at high SB.

DISCUSSION

While this study cannot establish causality, the results highlight the potential importance of considering both MVPA and SB in strategies aimed at reducing the accumulation of WMH volumes in middle-aged to older adults.

Highlights

SB is associated with greater WMH volumes and MVPA is associated with lower WMH volumes.Relationships between SB and WMH are strongest at low levels of MVPA.Associations between MVPA and WMH are strongest at high levels of SB.Considering both SB and MVPA may be effective strategies for reducing WMHs.

Association analyses of apolipoprotein E genotypes and cognitive performance in patients with Parkinson's disease

BACKGROUND

Cognitive impairment is a common non-motor symptom of Parkinson's disease (PD). The apolipoprotein E (APOE) ε4 genotype increases the risk of Alzheimer's disease (AD). However, the effect of APOEε4 on cognitive function of PD patients remains unclear. In this study, we aimed to understand whether and how carrying APOEε4 affects cognitive performance in patients with early-stage and advanced PD.

METHODS

A total of 119 Chinese early-stage PD patients were recruited. Movement Disorder Society Unified Parkinson's Disease Rating Scale, Hamilton anxiety scale, Hamilton depression scale, non-motor symptoms scale, Mini-mental State Examination, Montreal Cognitive Assessment, and Fazekas scale were evaluated. APOE genotypes were determined by polymerase chain reactions and direct sequencing. Demographic and clinical information of 521 early-stage and 262 advanced PD patients were obtained from Parkinson's Progression Marker Initiative (PPMI).

RESULTS

No significant difference in cognitive performance was found between ApoEε4 carriers and non-carriers in early-stage PD patients from our cohort and PPMI. The cerebrospinal fluid (CSF) Amyloid Beta 42 (Aβ42) level was significantly lower in ApoEε4 carrier than non-carriers in early-stage PD patients from PPMI. In advanced PD patients from PPMI, the BJLOT, HVLT retention and SDMT scores seem to be lower in ApoEε4 carriers without reach the statistical significance.

CONCLUSIONS

APOEε4 carriage does not affect the cognitive performance of early-stage PD patients. However, it may promote the decline of CSF Aβ42 level and the associated amyloidopathy, which is likely to further contribute to the cognitive dysfunction of PD patients in the advanced stage.

Linking white matter hyperintensities to regional cortical thinning, amyloid deposition, and synaptic density loss in Alzheimer's disease

INTRODUCTION

We investigated the association between white matter hyperintensities (WMH) and regional cortical thickness, amyloid and tau deposition, and synaptic density in the WMH-connected cortex using multimodal images.

METHODS

We included 107 participants (59 with Alzheimer's disease [AD]; 27 with mild cognitive impairment; 21 cognitively normal controls) with amyloid beta (Aβ) positivity on amyloid positron emission tomography (PET). The cortex connected to WMH was identified using probabilistic tractography.

RESULTS

We found that WMH connected to the cortex with more severe regional degeneration as measured by cortical thickness, Aβ and tau deposition, and synaptic vesicle glycoprotein 2 A (SV2A) density using 18F-SynVesT-1 PET. In addition, higher ratios of Aβ in the deep WMH-connected versus WMH-unconnected cortex were significantly related to lower cognitive scores. Last, the cortical thickness of WMH-connected cortex reduced more than WMH-unconnected cortex over 12 months.

DISCUSSION

Our results suggest that WMH may be associated with AD-intrinsic processes of degeneration, in addition to vascular mechanisms.

HIGHLIGHTS

We studied white matter hyperintensities (WMHs) and WMH-connected cortical changes. WMHs are associated with more severe regional cortical degeneration. Findings suggest WMHs may be associated with Alzheimer's disease-intrinsic processes of degeneration.

White matter hyperintensities and the surrounding normal appearing white matter are associated with water channel disruption in the oldest old

INTRODUCTION

Age-related magnetic resonance imaging (MRI) T2 white matter hyperintensities (WMHs) are common and associated with neurological decline. We investigated the histopathological underpinnings of MRI WMH and surrounding normal appearing white matter (NAWM), with a focus on astroglial phenotypes.

METHODS

Brain samples from 51 oldest old Oregon Alzheimer's Disease Research Center participants who came to autopsy underwent post mortem (PM) 7 tesla MRI with targeted histopathological sampling of WMHs and NAWM. Stained slides were digitized and quantified. Mixed-effects models determined differences in molecular characteristics between WMHs and the NAWM and across NAWM.

RESULTS

PM MRI-targeted WMHs are characterized by demyelination, microglial activation, and prominent astrocytic alterations, including disrupted aquaporin (AQP) expression. Similar changes occur within the surrounding NAWM in a pattern of decreasing severity with increased distance from WMHs.

DISCUSSION

Decreased AQP expression within WMH and proximal NAWM suggest an overwhelmed system wherein water homeostasis is no longer maintained, contributing to WM damage in older individuals.

HIGHLIGHTS

Post mortem magnetic resonance imaging (MRI) was used to characterize the pathology of white matter hyperintensities (WMHs) and surrounding normal appearing white matter (NAWM). Stained immunohistochemical (IHC) slides from targeted WMH and NAWM samples were digitized and quantified. WMHs and NAWM were associated with inflammation, demyelination, and gliosis. WMHs and NAWM astrocytic changes included decreased AQP1 and AQP4 expression. Abnormal NAWM pathology diminished in severity with increasing distance from WMH.

Cardiometabolic risk factors and neurodegeneration: a review of the mechanisms underlying diabetes, obesity and hypertension in Alzheimer's disease

A growing body of evidence suggests that cardiometabolic risk factors play a significant role in Alzheimer's disease (AD). Diabetes, obesity and hypertension are highly prevalent and can accelerate neurodegeneration and perpetuate the burden of AD. Insulin resistance and enzymes including insulin degrading enzymes are implicated in AD where breakdown of insulin is prioritised over amyloid-β. Leptin resistance and inflammation demonstrated by higher plasma and central nervous system levels of interleukin-6 (IL-6), IL-1β and tumour necrosis factor-α, are mechanisms connecting obesity and diabetes with AD. Leptin has been shown to ameliorate AD pathology and enhance long-term potentiation and hippocampal-dependent cognitive function. The renin-aldosterone angiotensin system, involved in hypertension, has been associated with AD pathology and neurotoxic reactive oxygen species, where angiotensin binds to specific angiotensin-1 receptors in the hippocampus and cerebral cortex. This review aims to consolidate the evidence behind putative processes stimulated by obesity, diabetes and hypertension, which leads to increased AD risk. We focus on how novel knowledge can be applied clinically to facilitate recognition of efficacious treatment strategies for AD.

Structural white matter properties and cognitive resilience to tau pathology

INTRODUCTION

We assessed whether macro- and/or micro-structural white matter properties are associated with cognitive resilience to Alzheimer's disease pathology years prior to clinical onset.

METHODS

We examined whether global efficiency, an indicator of communication efficiency in brain networks, and diffusion measurements within the limbic network and default mode network moderate the association between amyloid-β/tau pathology and cognitive decline. We also investigated whether demographic and health/risk factors are associated with white matter properties.

RESULTS

Higher global efficiency of the limbic network, as well as free-water corrected diffusion measures within the tracts of both networks, attenuated the impact of tau pathology on memory decline. Education, age, sex, white matter hyperintensities, and vascular risk factors were associated with white matter properties of both networks.

DISCUSSION

White matter can influence cognitive resilience against tau pathology, and promoting education and vascular health may enhance optimal white matter properties.

HIGHLIGHTS

Aβ and tau were associated with longitudinal memory change over ∼7.5 years. White matter properties attenuated the impact of tau pathology on memory change. Health/risk factors were associated with white matter properties.

Effect of cerebral small vessel disease on the integrity of cholinergic system in mild cognitive impairment patients: a longitudinal study

We aimed to investigate the effect of cerebral small vessel disease (SVD) on cholinergic system integrity in mild cognitive impairment (MCI) patients. Nucleus basalis of Meynert (NBM) volume and cholinergic pathways integrity was evaluated at baseline, 1-, 2-, and 4-year follow-ups in 40 cognitively unimpaired (CU) participants, 29 MCI patients without SVD, and 23 MCI patients with SVD. We compared cholinergic markers among three groups and examined their associations with SVD burden in MCI patients. We used linear mixed models to assess longitudinal changes in cholinergic markers over time among groups. Mediation analysis was employed to investigate the mediating role of cholinergic system degeneration between SVD and cognitive impairment. Increased mean diffusivity (MD) in medial and lateral pathways was observed in MCI patients with SVD compared to those without SVD and CU participants. Both MCI groups showed decreased NBM volume compared to CU participants, while there was no significant difference between the two MCI groups. Longitudinally, compared to CU participants, MCI patients with SVD displayed a more rapid change in MD in both pathways, but not in NBM volume. Furthermore, SVD burden was associated with cholinergic pathway disruption and its faster rate of change in MCI patients. However, mediation analyses showed that cholinergic pathways did not mediate significant indirect effects of SVD burden on cognitive impairment. Our findings suggest that SVD could accelerate the degeneration of cholinergic pathways in MCI patients. However, they do not provide evidence to support that SVD could contribute to cognitive impairment through cholinergic system injury.

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.

The interaction between insulin resistance and Alzheimer's disease: a review article

Insulin serves multiple functions as a growth-promoting hormone in peripheral tissues. It manages glucose metabolism by promoting glucose uptake into cells and curbing the production of glucose in the liver. Beyond this, insulin fosters cell growth, drives differentiation, aids protein synthesis, and deters degradative processes like glycolysis, lipolysis, and proteolysis. Receptors for insulin and insulin-like growth factor-1 are widely expressed in the central nervous system. Their widespread presence in the brain underscores the varied and critical functions of insulin signaling there. Insulin aids in bolstering cognition, promoting neuron extension, adjusting the release and absorption of catecholamines, and controlling the expression and positioning of gamma-aminobutyric acid (GABA). Importantly, insulin can effortlessly traverse the blood-brain barrier. Furthermore, insulin resistance (IR)-induced alterations in insulin signaling might hasten brain aging, impacting its plasticity and potentially leading to neurodegeneration. Two primary pathways are responsible for insulin signal transmission: the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway, which oversees metabolic responses, and the mitogen-activated protein kinase (MAPK) pathway, which guides cell growth, survival, and gene transcription. This review aimed to explore the potential shared metabolic traits between Alzheimer's disease (AD) and IR disorders. It delves into the relationship between AD and IR disorders, their overlapping genetic markers, and shared metabolic indicators. Additionally, it addresses existing therapeutic interventions targeting these intersecting pathways.

Amyloid pathology and vascular risk are associated with distinct patterns of cerebral white matter hyperintensities: A multicenter study in 3132 memory clinic patients

INTRODUCTION

White matter hyperintensities (WMH) are associated with key dementia etiologies, in particular arteriolosclerosis and amyloid pathology. We aimed to identify WMH locations associated with vascular risk or cerebral amyloid-β1-42 (Aβ42)-positive status.

METHODS

Individual patient data (n = 3,132; mean age 71.5 ± 9 years; 49.3% female) from 11 memory clinic cohorts were harmonized. WMH volumes in 28 regions were related to a vascular risk compound score (VRCS) and Aß42 status (based on cerebrospinal fluid or amyloid positron emission tomography), correcting for age, sex, study site, and total WMH volume.

RESULTS

VRCS was associated with WMH in anterior/superior corona radiata (B = 0.034/0.038, p < 0.001), external capsule (B = 0.052, p < 0.001), and middle cerebellar peduncle (B = 0.067, p < 0.001), and Aß42-positive status with WMH in posterior thalamic radiation (B = 0.097, p < 0.001) and splenium (B = 0.103, p < 0.001).

DISCUSSION

Vascular risk factors and Aß42 pathology have distinct signature WMH patterns. This regional vulnerability may incite future studies into how arteriolosclerosis and Aß42 pathology affect the brain's white matter.

HIGHLIGHTS

Key dementia etiologies may be associated with specific patterns of white matter hyperintensities (WMH). We related WMH locations to vascular risk and cerebral Aβ42 status in 11 memory clinic cohorts. Aβ42 positive status was associated with posterior WMH in splenium and posterior thalamic radiation. Vascular risk was associated with anterior and infratentorial WMH. Amyloid pathology and vascular risk have distinct signature WMH patterns.

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.

Association between white matter hyperintensity and anxiety/depression

Although previous studies have explored the associations of white matter hyperintensity with psychiatric disorders, the sample size is small and the conclusions are inconsistent. The present study aimed to further systematically explore the association in a larger sample. All data were extracted from the UK Biobank. First, general linear regression models and logistic regression models were used to assess the association between white matter hyperintensity volume and anxiety/depression. White matter hyperintensity has been classified into periventricular white matter hyperintensity and deep white matter hyperintensity. Anxiety was determined by General Anxiety Disorder-7 score (n = 17,221) and self-reported anxiety (n = 15,333), depression was determined by Patient Health Questionnaire-9 score (n = 17,175), and self-reported depression (n = 14,519). Moreover, we employed Cox proportional hazard models to explore the association between white matter hyperintensity volume and anxiety/depression. The covariates included in fully adjusted model are age, gender, body mass index, Townsend deprivation index, healthy physical activity, cigarette consumption, alcohol consumption, educational attainment, diabetes, hypertension, and coronary heart disease. The results of the fully adjusted model showed that white matter hyperintensity volume was significantly associated with General Anxiety Disorder-7 score (periventricular white matter hyperintensity: β = 0.152, deep white matter hyperintensity: β = 0.094) and Patient Health Questionnaire-9 score (periventricular white matter hyperintensity: β = 0.168). Logistic regression analysis results indicated that periventricular white matter hyperintensity volume (odds ratio = 1.153) was significantly associated with self-reported anxiety. After applying the Cox proportional hazard models, we found that larger white matter hyperintensity volume was associated with increased risk of depression (periventricular white matter hyperintensity: hazard ratio = 1.589, deep white matter hyperintensity: hazard ratio = 1.200), but not anxiety. In summary, our findings support a positive association between white matter hyperintensity volume and depression.

Can white matter hyperintensities based Fazekas visual assessment scales inform about Alzheimer's disease pathology in the population?

Background

White matter hyperintensities (WMH) are considered hallmark features of cerebral small vessel disease and have recently been linked to Alzheimer's disease pathology. Their distinct spatial distributions, namely periventricular versus deep WMH, may differ by underlying age-related and pathobiological processes contributing to cognitive decline. We aimed to identify the spatial patterns of WMH using the 4-scale Fazekas visual assessment and explore their differential association with age, vascular health, Alzheimer's imaging markers, namely amyloid and tau burden, and cognition. Because our study consisted of scans from GE and Siemens scanners with different resolutions, we also investigated inter-scanner reproducibility and combinability of WMH measurements on imaging.

Methods

We identified 1144 participants from the Mayo Clinic Study of Aging consisting of older adults from Olmsted County, Minnesota with available structural magnetic resonance imaging (MRI), amyloid, and tau positron emission tomography (PET). WMH distribution patterns were assessed on FLAIR-MRI, both 2D axial and 3D, using Fazekas ratings of periventricular and deep WMH severity. We compared the association of periventricular and deep WMH scales with vascular risk factors, amyloid-PET and tau-PET standardized uptake value ratio, WMH volume, and cognition using Pearson partial correlation after adjusting for age. We also evaluated vendor compatibility and reproducibility of the Fazekas scales using intraclass correlations (ICC).

Results

Periventricular and deep WMH measurements showed similar correlations with age, cardiometabolic conditions score (vascular risk), and cognition, (p < 0.001). Both periventricular WMH and deep WMH showed weak associations with amyloidosis (R = 0.07, p = < 0.001), and none with tau burden. We found substantial agreement between data from the two scanners for Fazekas measurements (ICC = 0.78). The automated WMH volume had high discriminating power for identifying participants with Fazekas ≥ 2 (area under curve = 0.97).

Conclusion

Our study investigates risk factors underlying WMH spatial patterns and their impact on global cognition, with no discernible differences between periventricular and deep WMH. We observed minimal impact of amyloidosis on WMH severity. These findings, coupled with enhanced inter-scanner reproducibility of WMH data, suggest the combinability of inter-scanner data assessed by harmonized protocols in the context of vascular contributions to cognitive impairment and dementia biomarker research.

Association between brain amyloid deposition and longitudinal changes of white matter hyperintensities

BACKGROUND

Growing evidence suggests that not only cerebrovascular disease but also Alzheimer's disease (AD) pathological process itself cause cerebral white matter degeneration, resulting in white matter hyperintensities (WMHs). Some preclinical evidence also indicates that white matter degeneration may precede or affect the development of AD pathology. This study aimed to clarify the direction of influence between in vivo AD pathologies, particularly beta-amyloid (Aβ) and tau deposition, and WMHs through longitudinal approach.

METHODS

Total 282 older adults including cognitively normal and cognitively impaired individuals were recruited from the Korean Brain Aging Study for the Early Diagnosis and Prediction of Alzheimer's Disease (KBASE) cohort. The participants underwent comprehensive clinical and neuropsychological assessment, [11C] Pittsburgh Compound B PET for measuring Aβ deposition, [18F] AV-1451 PET for measuring tau deposition, and MRI scans with fluid-attenuated inversion recovery image for measuring WMH volume. The relationships between Aβ or tau deposition and WMH volume were examined using multiple linear regression analysis. In this analysis, baseline Aβ or tau were used as independent variables, and change of WMH volume over 2 years was used as dependent variable to examine the effect of AD pathology on increase of WMH volume. Additionally, we set baseline WMH volume as independent variable and longitudinal change of Aβ or tau deposition for 2 years as dependent variables to investigate whether WMH volume could precede AD pathologies.

RESULTS

Baseline Aβ deposition, but not tau deposition, had significant positive association with longitudinal change of WMH volume over 2 years. Baseline WMH volume was not related with any of longitudinal change of Aβ or tau deposition for 2 years. We also found a significant interaction effect between baseline Aβ deposition and sex on longitudinal change of WMH volume. Subsequent subgroup analyses showed that high baseline Aβ deposition was associated with increase of WMH volume over 2 years in female, but not in male.

CONCLUSIONS

Our findings suggest that Aβ deposition accelerates cerebral WMHs, particularly in female, whereas white matter degeneration appears not influence on longitudinal Aβ increase. The results also did not support any direction of influence between tau deposition and WMHs.

Unhealthy white matter connectivity, cognition, and racialization in older adults

INTRODUCTION

White matter hyperintensities (WMH) may promote clinical Alzheimer's disease (AD) disparities between Black American (BA) and non-Hispanic White (nHW) populations. Using a novel measurement, unhealthy white matter connectivity (UWMC), we interrogated racialized group differences in associations between WMH in AD pathology-affected regions and cognition.

METHODS

UWMC is the proportion of white matter fibers that pass through WMH for every pair of brain regions. Individual regression models tested associations of UWMC in beta-amyloid (Aβ) or tau pathology-affected regions with cognition overall, stratified by racialized group, and with a racialized group interaction.

RESULTS

In 201 older adults ranging from cognitively unimpaired to AD, BA participants exhibited greater UWMC and worse cognition than nHW participants. UWMC was negatively associated with cognition in 17 and 5 Aβ- and tau-affected regions, respectively. Racialization did not modify these relationships.

DISCUSSION

Differential UWMC burden, not differential UWMC-and-cognition associations, may drive clinical AD disparities between racialized groups.

HIGHLIGHTS

Unhealthy white matter connectivity (UWMC) in Alzheimer's disease (AD) pathology-affected brain regions is associated with cognition. Relationships between UWMC and cognition are similar between Black American (BA) and non-Hispanic White (nHW) individuals. More UWMC may partially drive higher clinical AD burden in BA versus nHW populations. UWMC risk factors, particularly social and environmental, should be identified.

Florbetapir PET-assessed demyelination is associated with faster tau accumulation in an APOE ε4-dependent manner

PURPOSE

The main objectives were to test whether (1) a decrease in myelin is associated with enhanced rate of fibrillar tau accumulation and cognitive decline in Alzheimer's disease, and (2) whether apolipoprotein E (APOE) ε4 genotype is associated with worse myelin decrease and thus tau accumulation.

METHODS

To address our objectives, we repurposed florbetapir-PET as a marker of myelin in the white matter (WM) based on previous validation studies showing that beta-amyloid (Aβ) PET tracers bind to WM myelin. We assessed 43 Aβ-biomarker negative (Aβ-) cognitively normal participants and 108 Aβ+ participants within the AD spectrum with florbetapir-PET at baseline and longitudinal flortaucipir-PET as a measure of fibrillar tau (tau-PET) over ~ 2 years. In linear regression analyses, we tested florbetapir-PET in the whole WM and major fiber tracts as predictors of tau-PET accumulation in a priori defined regions of interest (ROIs) and fiber-tract projection areas. In mediation analyses we tested whether tau-PET accumulation mediates the effect of florbetapir-PET in the whole WM on cognition. Finally, we assessed the role of myelin alteration on the association between APOE and tau-PET accumulation.

RESULTS

Lower florbetapir-PET in the whole WM or at a given fiber tract was predictive of faster tau-PET accumulation in Braak stages or the connected grey matter areas in Aβ+ participants. Faster tau-PET accumulation in higher cortical brain areas mediated the association between a decrease in florbetapir-PET in the WM and a faster rate of decline in global cognition and episodic memory. APOE ε4 genotype was associated with a worse decrease in the whole WM florbetapir-PET and thus enhanced tau-PET accumulation.

CONCLUSION

Myelin alterations are associated in an APOE ε4 dependent manner with faster tau progression and cognitive decline, and may therefore play a role in the etiology of AD.

Small vessel cerebrovascular disease is associated with cognition in prospective Alzheimer's clinical trial participants

BACKGROUND

Secondary prevention clinical trials for Alzheimer's disease (AD) target amyloid accumulation in asymptomatic, amyloid-positive individuals, but it is unclear to what extent other pathophysiological processes, such as small vessel cerebrovascular disease, account for participant performance on the primary cognitive outcomes in those trials. White matter hyperintensities are areas of increased signal on T2-weighted magnetic resonance imaging (MRI) that reflect small vessel cerebrovascular disease. They are associated with cognitive functioning in older adults and with clinical presentation and course of AD, particularly when distributed in posterior brain regions. The purpose of this study was to examine to what degree regional WMH volume is associated with performance on the primary cognitive outcome measure in the Anti-Amyloid Treatment in Asymptomatic Alzheimer's Disease (A4) study, a secondary prevention trial.

METHODS

Data from 1791 participants (59.5% women, mean age (SD) 71.6 (4.74)) in the A4 study and the Longitudinal Evaluation of Amyloid Risk and Neurodegeneration (LEARN) companion study at the screening visit were used to quantify WMH volumes on T2-weighted fluid-attenuated inversion recovery (FLAIR) MR images. Cognition was assessed with the preclinical Alzheimer cognitive composite (PACC). We tested the association of total and regional WMH volumes with PACC performance, adjusting for age, education, and amyloid positivity status, with general linear models. We also considered interactions between WMH and amyloid positivity status.

RESULTS

Increased frontal and parietal lobe WMH volume was associated with poorer performance on the PACC. While amyloid positivity was also associated with lower cognitive test scores, WMH volumes did not interact with amyloid positivity status.

CONCLUSION

These results highlight the potential of small vessel cerebrovascular disease to drive AD-related cognitive profiles. Measures of small vessel cerebrovascular disease should be considered when evaluating outcome in trials, both as potential effect modifiers and as a possible target for intervention or prevention.

Genetic Predisposition for White Matter Hyperintensities and Risk of Mild Cognitive Impairment and Alzheimer's Disease: Results from the HELIAD Study

The present study investigated the association of genetic predisposition for white matter hyperintensities (WMHs) with incident amnestic mild cognitive impairment (aMCI) or Alzheimer's disease (AD), as well as whether such an association was influenced by age, sex, and cognitive reserve. Overall, 537 individuals without aMCI or dementia at baseline were included. Among them, 62 individuals developed aMCI/AD at follow up. Genetic propensity to WMH was estimated using a polygenic risk score for WMHs (PRS WMH). The association of PRS WMH with aMCI/AD incidence was examined using COX models. A higher PRS WMH was associated with a 47.2% higher aMCI/AD incidence (p = 0.015) in the fully adjusted model. Subgroup analyses showed significant results in the older age group, in which individuals with a higher genetic predisposition for WMHs had a 3.4-fold higher risk for developing aMCI/AD at follow up (p < 0.001), as well as in the lower cognitive reserve (CR, proxied by education years) group, in which individuals with a higher genetic predisposition for WMHs had an over 2-fold higher risk (p = 0.013). Genetic predisposition for WMHs was associated with aMCI/AD incidence, particularly in the group of participants with a low CR. Thus, CR might be a modifier in the relationship between genetic predisposition for WMHs and incident aMCI/AD.

Bridging Reduced Grip Strength and Altered Executive Function: Specific Brain White Matter Structural Changes in Patients with Alzheimer's Disease

Objective

To investigate the correlation between specific fiber tracts and grip strength and cognitive function in patients with Alzheimer's disease (AD) by fixel-based analysis (FBA).

Methods

AD patients were divided into AD with low grip strength (AD-LGS, n=29) and AD without low grip strength (AD-nLGS, n=25), along with 31 normal controls (NC). General data, neuropsychological tests, grip strength and cranial magnetic resonance imaging (MRI) scans were collected. FBA evaluated white matter (WM) fiber metrics, including fiber density (FD), fiber cross-sectional (FC), and fiber density and cross-sectional area (FDC). The mean fiber indicators of the fiber tracts of interest (TOI) were extracted in cerebral region of significant statistical differences in FBA to further compare the differences between groups and analyze the correlation between fiber properties and neuropsychological test scores.

Results

Compared to AD-nLGS group, AD-LGS group showed significant reductions in FDC in several cerebral regions. In AD patients, FDC values of bilateral uncinate fasciculus and left superior longitudinal fasciculus were positively correlated with Clock Drawing Test scores, while FDC of splenium of corpus callosum, bilateral anterior cingulate tracts, forceps major, and bilateral inferior longitudinal fasciculus were positively correlated with the Executive Factor Score of Memory and Executive Screening scale scores.

Conclusion

Reduced grip strength in AD patients is associated with extensive impairment of WM structural integrity. Changes in FDC of specific WM fiber tracts related to executive function play a significant mediating role in the reduction of grip strength in AD patients.

Interpretation of Neurodegenerative GWAS Risk Alleles in Microglia and their Interplay with Other Cell Types

Microglia have been implicated in numerous neurodegenerative and neuroinflammatory disorders; however, the causal contribution of this immune cell type is frequently debated. Genetic studies offer a unique vantage point in that they infer causality over a secondary consequence. Genome-wide association studies (GWASs) have identified hundreds of loci in the genome that are associated with susceptibility to neurodegenerative disorders. GWAS studies implicate microglia in the pathogenesis of Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), and to a lesser degree suggest a role for microglia in vascular dementia (VaD), frontotemporal dementia (FTD), and amyotrophic lateral sclerosis (ALS), and other neurodegenerative and neuropsychiatric disorders. The contribution and function of GWAS risk loci on disease progression is an ongoing field of study, in which large genomic datasets, and an extensive framework of computational tools, have proven to be crucial. Several GWAS risk loci are shared between disorders, pointing towards common pleiotropic mechanisms. In this chapter, we introduce key concepts in GWAS and post-GWAS interpretation of neurodegenerative disorders, with a focus on GWAS risk genes implicated in microglia, their interplay with other cell types and shared convergence of GWAS risk loci on microglia.

Intermittent fasting and Alzheimer's disease-Targeting ketone bodies as a potential strategy for brain energy rescue

Alzheimer's disease (AD) lacks effective clinical treatments. As the disease progresses, the cerebral glucose hypometabolism that appears in the preclinical phase of AD gradually worsens, leading to increasingly severe brain energy disorders. This review analyzes the brain energy deficit in AD and its etiology, brain energy rescue strategies based on ketone intervention, the effects and mechanisms of IF, the differences in efficacy between IF and ketogenic diet and the duality of IF. The evidence suggests that brain energy deficits lead to the development and progression of AD pathology. IF, which improves brain energy impairments by promoting ketone metabolism, thus has good therapeutic potential for AD.

Incident Dementia After Spontaneous Intracerebral Hemorrhage

 Post-stroke cognitive impairment and dementia (PSCID) is a complication that affects long-term functional outcomes after stroke. Studies on dementia after long-term follow-up in stroke have focused predominantly on ischemic stroke, which may be different from the development of dementia after spontaneous intracerebral hemorrhage (ICH). In this review, we summarize the existing data and hypotheses on the development of dementia after spontaneous ICH, review the management of post-ICH dementia, and suggest areas for future research. Dementia after spontaneous ICH has a cumulative incidence of up to 32.0-37.4% at 5 years post-ICH. Although the pathophysiology of post-ICH dementia has not been fully understood, two main theoretical frameworks can be considered: 1) the triggering role of ICH (both primary and secondary brain injury) in precipitating cognitive decline and dementia; and 2) the contributory role of pre-existing brain pathology (including small vessel disease and neurodegenerative pathology), reduced cognitive reserve, and genetic factors predisposing to cognitive dysfunction. These pathophysiological pathways may have synergistic effects that converge on dysfunction of the neurovascular unit and disruptions in functional connectivity leading to dementia post-ICH. Management of post-ICH dementia may include screening and monitoring, cognitive therapy, and pharmacotherapy. Non-invasive brain stimulation is an emerging therapeutic modality under investigation for safety and efficacy. Our review highlights that there remains a paucity of data and standardized reporting on incident dementia after spontaneous ICH. Further research is imperative for determining the incidence, risk factors, and pathophysiology of post-ICH dementia, in order to identify new therapies for the treatment of this debilitating condition.

Associations between white matter hyperintensities, lacunes, entorhinal cortex thickness, declarative memory and leisure activity in cognitively healthy older adults: A 7-year study

INTRODUCTION

Cerebral small vessel disease (cSVD) is a growing epidemic that affects brain health and cognition. Therefore, a more profound understanding of the interplay between cSVD, brain atrophy, and cognition in healthy aging is of great importance. In this study, we examined the association between white matter hyperintensities (WMH) volume, number of lacunes, entorhinal cortex (EC) thickness, and declarative memory in cognitively healthy older adults over a seven-year period, controlling for possible confounding factors. Because there is no cure for cSVD to date, the neuroprotective potential of an active lifestyle has been suggested. Supporting evidence, however, is scarce. Therefore, a second objective of this study is to examine the relationship between leisure activities, cSVD, EC thickness, and declarative memory.

METHODS

We used a longitudinal dataset, which consisted of five measurement time points of structural MRI and psychometric cognitive ability and survey data, collected from a sample of healthy older adults (baseline N = 231, age range: 64-87 years, age M = 70.8 years), to investigate associations between cSVD MRI markers, EC thickness and verbal and figural memory performance. Further, we computed physical, social, and cognitive leisure activity scores from survey-based assessments and examined their associations with brain structure and declarative memory. To provide more accurate estimates of the trajectories and cross-domain correlations, we applied latent growth curve models controlling for potential confounders.

RESULTS

Less age-related thinning of the right (β = 0.92, p<.05) and left EC (β = 0.82, p<.05) was related to less declarative memory decline; and a thicker EC at baseline predicted less declarative memory loss (β = 0.54, p<.05). Higher baseline levels of physical (β = 0.24, p<.05), and social leisure activity (β = 0.27, p<.01) predicted less thinning of right EC. No relation was found between WMH or lacunes and declarative memory or between leisure activity and declarative memory. Higher education was initially related to more physical activity (β = 0.16, p<.05) and better declarative memory (β = 0.23, p<.001), which, however, declined steeper in participants with higher education (β = -.35, p<.05). Obese participants were less physically (β = -.18, p<.01) and socially active (β = -.13, p<.05) and had thinner left EC (β = -.14, p<.05) at baseline. Antihypertensive medication use (β = -.26, p<.05), and light-to-moderate alcohol consumption (β = -.40, p<.001) were associated with a smaller increase in the number of lacunes whereas a larger increase in the number of lacunes was observed in current smokers (β = 0.30, p<.05).

CONCLUSIONS

Our results suggest complex relationships between cSVD MRI markers (total WMH, number of lacunes, right and left EC thickness), declarative memory, and confounding factors such as antihypertensive medication, obesity, and leisure activitiy. Thus, leisure activities and having good cognitive reserve counteracting this neurodegeneration. Several confounding factors seem to contribute to the extent or progression/decline of cSVD, which needs further investigation in the future. Since there is still no cure for cSVD, modifiable confounding factors should be studied more intensively in the future to maintain or promote brain health and thus cognitive abilities in older adults.

Disentangling in-vivo microstructural changes of white and gray matter in mild cognitive impairment and Alzheimer's disease: a systematic review and meta-analysis

The microstructural characteristics of white and gray matter in mild cognitive impairment (MCI) and the early-stage of Alzheimer's disease (AD) remain unclear. This study aimed to systematically identify the microstructural damages of MCI/AD in studies using neurite orientation dispersion and density imaging (NODDI), and explore their correlations with cognitive performance. Multiple databases were searched for eligible studies. The 10 eligible NODDI studies were finally included. Patients with MCI/AD showed overall significant reductions in neurite density index (NDI) of specific white matter structures in bilateral hemispheres (left hemisphere: -0.40 [-0.53, -0.27], P < 0.001; right: -0.33 [-0.47, -0.19], P < 0.001), involving the bilateral superior longitudinal fasciculus (SLF), uncinate fasciculus (UF), the left posterior thalamic radiation (PTR), and the left cingulum. White matter regions exhibited significant increased orientation dispersion index (ODI) (left: 0.25 [0.02, 0.48], P < 0.05; right: 0.27 [0.07, 0.46], P < 0.05), including the left cingulum, the right UF, and the bilateral parahippocampal cingulum (PHC), and PTR. Additionally, the ODI of gray matter showed significant reduction in bilateral hippocampi (left: -0.97 [-1.42, -0.51], P < 0.001; right: -0.90 [-1.35, -0.45], P < 0.001). The cognitive performance in MCI/AD was significantly associated with NDI (r = 0.50, P < 0.001). Our findings highlight the microstructural changes in MCI/AD were characterized by decreased fiber orientation dispersion in the hippocampus, and decreased neurite density and increased fiber orientation dispersion in specific white matter tracts, including the cingulum, UF, and PTR. Moreover, the decreased NDI may indicate the declined cognitive level of MCI/AD patients.

Retinal ganglion cell-inner plexiform layer, white matter hyperintensities, and their interaction with cognition in older adults

Purpose

We explored the interaction of optical coherence tomography (OCT) parameters and white matter hyperintensities with cognitive measures in our older adult cohort.

Methods

This observational study enrolled participants who underwent a comprehensive neuropsychological battery, structural 3-T brain magnetic resonance imaging (MRI), visual acuity examination, and OCT imaging. Cerebral small vessel disease (CSVD) markers were read on MR images; lacune, cerebral microbleeds (CMB), white matter hyperintensities (WMH), and enlarged perivascular spaces (EPVS), were defined according to the STRIVE standards. Retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GCIPL) thicknesses (μm) were measured on the OCT tool.

Results

Older adults with cognitive impairment (CI) showed lower RNFL (p = 0.001), GCIPL (p = 0.009) thicknesses, and lower hippocampal volume (p = 0.004) when compared to non-cognitively impaired (NCI). RNFL (p = 0.006) and GCIPL thicknesses (p = 0.032) correlated with MoCA scores. GCIPL thickness (p = 0.037), total WMH (p = 0.003), PWMH (p = 0.041), and DWMH (p = 0.001) correlated with hippocampal volume in our older adults after adjusting for covariates. With hippocampal volume as the outcome, a significant interaction (p < 0.05) between GCIPL and PWMH and total WMH was observed in our older adults.

Conclusion

Both GCIPL thinning and higher WMH burden (especially PWMH) are associated with hippocampal volume and older adults with both pathologies are more susceptible to subclinical cognitive decline.