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Objectives Brain white matter (WM) microstructural changes evaluated by diffusion MRI are well documented in patients with SLE. Yet, the conventional diffusion tensor imaging technique fails to differentiate WM changes that originate from tissue alterations from those due to increased extracellular free water (FW) related to neuroinflammation, microvascular disruption, atrophy, or other extracellular processes. Here, we sought to delineate changes in WM tissue microstructure and extracellular FW volume and examine their relationships with neurocognitive function in SLE patients. Methods Twenty SLE patients [16 females, aged 36.0 (10.6)] without clinically overt neuropsychiatric manifestation and 61 healthy controls (HCs) [29 females, aged 29.2 (9.4)] underwent diffusion MRI and computerized neuropsychological assessments cross-sectionally. The FW imaging method was applied to compare microstructural tissue changes and extracellular FW volume of the brain WM between SLE patients and HCs. Association between extracellular FW changes and neurocognitive performance was studied. Results SLE patients had higher WM extracellular FW compared with HCs (family-wise-error-corrected P  < 0.05), while no group difference was found in FW-corrected tissue compartment and structural connectivity metrics. Extracellular FW increases in SLE patients were associated with poorer neurocognitive performance that probed sustained attention (P  = 0.022) and higher cumulative glucocorticoid dose (P  = 0.0041). Such findings remained robust after controlling for age, gender, intelligence quotient, and total WM volume. Conclusion The association between WM extracellular FW increases and reduced neurocognitive performance suggest possible microvascular degradation and/or neuroinflammation in SLE patients with clinically inactive disease. The mechanistic impact of cumulative glucocorticoids on WM FW deserves further evaluation. [ABSTRACT FROM AUTHOR]

Background: Alzheimer's disease(AD) is associated with pathological deposition of amyloid‐beta(Aβ) plaques and neurofibrillary tau tangles which have been shown to be related to poorer white‐matter(WM) integrity using diffusion‐MRI(dMRI) [Vipin et al.,2019;Jacobs et al.,2018]. However, possible interactive effects between Aβ and tau on microstructural WM changes remain unclear. Additionally, partial volume artefacts impact dMRI sensitivity but can be corrected through free‐water(FW) correction to provide FW and FW‐corrected tissue measures(FAt)[Pasternak et al.,2009]. Thus, we examined additive and interactive effects of Aβ and tau burden on temporal progression of FW‐corrected WM changes in temporoparietal WM fibres at baseline and over‐time in cognitively normal elderly(CN) and mild cognitive impairment(MCI). We hypothesize that MCI subjects would show more widespread Aβ and tau‐related temporoparietal WM alterations than CN. Additionally, based on prior evidence, Aβ and tau interactive effects would be more prevalent for FW than tissue‐based measures. Method: We used dMRI data from 72 CN and 82 MCI subjects from the Alzheimer's Disease Neuroimaging Initiative followed over 2‐4 time‐points(55‐90 years). Aβ burden was quantified using AV‐45 PET standardized uptake value and tau burden was quantified using cerebrospinal fluid phosphorylated‐tau(Ptau) levels. We derived subject‐specific FW and FAt fibre maps using the longitudinal TRActs‐Constrained‐by‐UnderLying‐Anatomy method[Yendiki et al.,2016]. Result: CN with higher Aβ burden showed faster decline in RUNC FAt (uncorrected‐p=0.0055; Fig.1). However, in MCI, widespread Ptau effects were found(Fig.2) i.e. higher baseline Ptau burden was associated with lower fibre FAt in left superior longitudinal fasciculus parietal (SLFP; uncorrected‐p=0.039) and left(uncorrected‐p=0.0062) and right(uncorrected‐p=0.026) superior longitudinal fasciculus temporal(SLFT). Synergistic Aβ*Ptau effects were instead observed in right cingulum angular bundle(CAB) FW in CN at baseline and over‐time (FDR‐corrected:p<0.05; Fig.3). This effect was more widespread in MCI‐ higher Aβ combined with higher Ptau associated with higher FW in right CAB, SLFP, SLFT and uncinate fasciculus fibres at baseline(Fig.4). Conclusion: Our findings provide insights into stage‐dependent differences in additive and synergistic influences of Aβ and Ptau between tissue‐based and FW‐based WM metrics. Thus, together with Aβ and Ptau burden, FW‐corrected WM measures likely provide more detailed insight regarding the regions showing alterations related to the interaction between neuropathological hallmarks of AD to collectively inform regarding disease progression. [ABSTRACT FROM AUTHOR]

Alterations in parietal and temporal white matter microstructure derived from diffusion tensor imaging occur in preclinical and clinical Alzheimer's disease. Amyloid beta (Aβ) deposition and such white matter alterations are two pathological hallmarks of Alzheimer's disease. However, the relationship between these pathologies is not yet understood, partly since conventional diffusion MRI methods cannot distinguish between cellular and extracellular processes. Thus, we studied Aβ‐associated longitudinal diffusion MRI changes in Aβ‐positive (N = 21) and Aβ‐negative (N = 51) cognitively normal elderly obtained from the Alzheimer's Disease Neuroimaging Initiative dataset using linear mixed models. Aβ‐positivity was based on Alzheimer's Disease Neuroimaging Initiative amyloid‐PET recommendations using a standardized uptake value ratio cut‐off of 1.11. We used free‐water imaging to distinguish cellular and extracellular changes. We found that Aβ‐positive subjects had increased baseline right uncinate fasciculus free‐water fraction (FW), associated with worse baseline Alzheimer's disease assessment scale scores. Furthermore, Aβ‐positive subjects showed faster decrease in fractional anisotropy (FW‐corrected) in the right uncinate fasciculus and faster age‐dependent right inferior longitudinal fasciculus FW increases over time. Right inferior longitudinal fasciculus FW increases were associated with greater memory decline. Importantly, these results remained significant after controlling for gray and white matter volume and hippocampal volume. This is the first study to illustrate the influence of Aβ burden on early longitudinal (in addition to baseline) white matter changes in cognitively normal elderly individuals at‐risk of Alzheimer's disease, thus underscoring the importance of longitudinal studies in assessing microstructural alterations in individuals at risk of Alzheimer's disease prior to symptoms onset. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the influence of the apolipoprotein E‐ɛ4 allele (APOE‐ɛ4) on longitudinal age‐related changes in brain functional connectivity (FC) and cognition, in view of mixed cross‐sectional findings. One hundred and twenty‐two healthy older adults (aged 58–79; 25 APOE‐ɛ4 carriers) underwent task‐free fMRI scans at baseline. Seventy‐eight (16 carriers) had at least one follow‐up (every 2 years). Changes in intra‐ and internetwork FCs among the default mode (DMN), executive control (ECN), and salience (SN) networks, as well as cognition, were quantified using linear mixed models. Cross‐sectionally, APOE‐ɛ4 carriers had lower functional connectivity between the ECN and SN than noncarriers. Carriers also showed a stronger age‐dependent decrease in visuospatial memory performance. Longitudinally, carriers had steeper increase in inter‐ECN‐DMN FC, indicating loss of functional segregation. The longitudinal change in processing speed performance was not moderated by APOE‐ɛ4 genotype, but the brain–cognition association was. In younger elderly, faster loss of segregation was correlated with greater decline in processing speed regardless of genotype. In older elderly, such relation remained for noncarriers but reversed for carriers. APOE‐ɛ4 may alter aging by accelerating the change in segregation between high‐level cognitive systems. Its modulation on the longitudinal brain–cognition relationship was age‐dependent. [ABSTRACT FROM AUTHOR]