Elevated Aortic Pulse Wave Velocity Relates to Longitudinal Gray and White Matter Changes.

OBJECTIVE: To determine whether baseline aortic stiffness, measured by aortic pulse wave velocity (PWV), relates to longitudinal cerebral gray or white matter changes among older adults. Baseline cardiac magnetic resonance imaging will be used to assess aortic PWV while brain magnetic resonance imaging will be used to assess gray matter and white matter hyperintensity (WMH) volumes at baseline, 18 months, 3 years, 5 years, and 7 years. Approach and Results: Aortic PWV (m/s) was quantified from cardiac magnetic resonance. Multimodal 3T brain magnetic resonance imaging included T1-weighted imaging for quantifying gray matter volumes and T2-weighted fluid-attenuated inversion recovery imaging for quantifying WMHs. Mixed-effects regression models related baseline aortic PWV to longitudinal gray matter volumes (total, frontal, parietal, temporal, occipital, hippocampal, and inferior lateral ventricle) and WMH volumes (total, frontal, parietal, temporal, and occipital) adjusting for age, sex, race/ethnicity, education, cognitive diagnosis, Framingham stroke risk profile, APOE (apolipoprotein E)-ε4 carrier status, and intracranial volume. Two hundred seventy-eight participants (73±7 years, 58% male, 87% self-identified as non-Hispanic White, 159 with normal cognition, and 119 with mild cognitive impairment) from the Vanderbilt Memory & Aging Project (n=335) were followed on average for 4.9±1.6 years with PWV measurements occurring from September 2012 to November 2014 and longitudinal brain magnetic resonance imaging measurements occurring from September 2012 to June 2021. Higher baseline aortic PWV was related to greater decrease in hippocampal (ß=-3.6 [mm3/y]/[m/s]; [95% CI, -7.2 to -0.02] P=0.049) and occipital lobe (ß=-34.2 [mm3/y]/[m/s]; [95% CI, -67.8 to -0.55] P=0.046) gray matter volume over time. Higher baseline aortic PWV was related to greater increase in WMH volume over time in the temporal lobe (ß=17.0 [mm3/y]/[m/s]; [95% CI, 7.2-26.9] P<0.001). All associations may be driven by outliers. CONCLUSIONS: In older adults, higher baseline aortic PWV related to greater decrease in gray matter volume and greater increase in WMHs over time. Because of unmet cerebral metabolic demands and microvascular remodeling, arterial stiffening may preferentially affect certain highly active brain regions like the temporal lobes. These same regions are affected early in the course of Alzheimer disease.

Perivascular space burden interacts with APOE-ε4 status on cognition in older adults.

Enlarged perivascular spaces (ePVS) may adversely affect cognition. Little is known about how basal ganglia ePVS interact with apolipoprotein (APOE)-ε4 status. Vanderbilt Memory and Aging Project participants (n = 326, 73 ± 7, 59% male) underwent 3 T brain MRI at baseline to assess ePVS and longitudinal neuropsychological assessments. The interaction between ePVS volume and APOE-ε4 carrier status was related to baseline outcomes using ordinary least squares regressions and longitudinal cognition using linear mixed-effects regressions. ePVS volume interacted with APOE-ε4 status on cross-sectional naming performance (ß = -0.002, p = 0.002), and executive function excluding outliers (ß = 0.001, p = 0.009). There were no significant longitudinal interactions (p-values>0.10) except for Coding excluding outliers (ß = 0.002, p = 0.05). While cross-sectional models stratified by APOE-ε4 status indicated greater ePVS related to worse cognition mostly in APOE-ε4 carriers, longitudinal models stratified by APOE-ε4 status showed greater ePVS volume related to worse cognition among APOE-ε4 non-carriers only. Results indicated that greater ePVS volume interacts with APOE-ε4 status on cognition cross-sectionally. Longitudinally, the association of greater ePVS volume and worse cognition appears stronger in APOE-ε4 non-carriers, possibly due to the deleterious effects of APOE-ε4 on cognition across the lifespan.

Enlarged perivascular space burden associations with arterial stiffness and cognition.

Enlarged perivascular spaces (ePVS) are difficult to quantify, and their etiologies and consequences are poorly understood. Vanderbilt Memory and Aging Project participants (n = 327, 73 ± 7 years) completed 3T brain MRI to quantify ePVS volume and count, longitudinal neuropsychological assessment, and cardiac MRI to quantify aortic stiffness. Linear regressions related (1) PWV to ePVS burden and (2) ePVS burden to cross-sectional and longitudinal neuropsychological performance adjusting for key demographic and medical factors. Higher aortic stiffness related to greater basal ganglia ePVS volume (ß = 7.0×10-5, p = 0.04). Higher baseline ePVS volume was associated with worse baseline information processing (ß = -974, p = 0.003), executive function (ß = -81.9, p < 0.001), and visuospatial performances (ß = -192, p = 0.02) and worse longitudinal language (ß = -54.9, p = 0.05), information processing (ß = -147, p = 0.03), executive function (ß = -10.9, p = 0.03), and episodic memory performances (ß = -10.6, p = 0.02). Results were similar for ePVS count. Greater arterial stiffness relates to worse basal ganglia ePVS burden, suggesting cardiovascular aging as an etiology. ePVS burden is associated with adverse cognitive trajectory, emphasizing the clinical relevance of ePVS.

Physiology and Clinical Relevance of Enlarged Perivascular Spaces in the Aging Brain.

Perivascular spaces (PVS) are fluid-filled compartments that are part of the cerebral blood vessel wall and represent the conduit for fluid transport in and out of the brain. PVS are considered pathologic when sufficiently enlarged to be visible on MRI. Recent studies have demonstrated that enlarged PVS (ePVS) may have clinical consequences related to cognition. Emerging literature points to arterial stiffening and abnormal protein aggregation in vessel walls as 2 possible mechanisms that drive ePVS formation. We describe the clinical consequences, anatomy, fluid dynamics, physiology, risk factors, and in vivo quantification methods of ePVS. Given competing views of PVS physiology, we detail the 2 most prominent theoretical views and review ePVS associations with other common small vessel disease markers. Because ePVS are a marker of small vessel disease and ePVS burden is higher in Alzheimer disease, a comprehensive understanding about ePVS is essential in developing prevention and treatment strategies.

Lower cardiac output is associated with neurodegeneration among older adults with normal cognition but not mild cognitive impairment.

Subclinical cardiac dysfunction is associated with smaller total brain volume on magnetic resonance imaging (MRI). To study whether cardiac output relates to regional measurements of grey and white matter structure, older adults (n = 326) underwent echocardiogram to quantify cardiac output (L/min) and brain MRI. Linear regressions related cardiac output to grey matter volumes measured on T1 and white matter hyperintensities assessed on T2-FLAIR. Voxelwise analyses related cardiac output to diffusion tensor imaging adjusting for demographic, genetic, and vascular risk factors. Follow-up models assessed a cardiac output x diagnosis interaction with stratification (normal cognition, mild cognitive impairment). Cardiac output interacted with diagnosis, such that lower cardiac output related to smaller total grey matter (p = 0.01), frontal lobe (p = 0.01), and occipital lobe volumes (p = 0.01) among participants with normal cognition. When excluding participants with cardiovascular disease and atrial fibrillation, associations emerged with smaller parietal lobe (p = 0.005) and hippocampal volume (p = 0.05). Subtle age-related cardiac changes may disrupt neuronal homeostasis and impact grey matter integrity prior to cognitive impairment.

Lower Cardiac Output Relates to Longitudinal Cognitive Decline in Aging Adults.

BACKGROUND: Subclinical reductions in cardiac output correspond to lower cerebral blood flow (CBF), placing the brain at risk for functional changes. OBJECTIVES: This study aims to establish the consequences of reduced cardiac output on longitudinal cognitive outcomes in aging adults. METHODS: Vanderbilt Memory and Aging Project participants free of clinical dementia and heart failure (n = 306, 73 ± 7, 58% male) underwent baseline echocardiography to assess cardiac output (L/min) and longitudinal neuropsychological assessment at baseline, 18 months, 3 and 5 years. Linear mixed-effects regressions related cardiac output to trajectory for each longitudinal neuropsychological outcome, adjusting for age, sex, race/ethnicity, education, body surface area, Framingham Stroke Risk Profile score, apolipoprotein E (APOE) ε4 status and follow-up time. Models were repeated, testing interactions with cognitive diagnosis and APOE-ε4 status. RESULTS: Lower baseline cardiac output related to faster declines in language (ß = 0.11, p = 0.01), information processing speed (ß = 0.31, p = 0.006), visuospatial skills (ß = 0.09, p = 0.03), and episodic memory (ß = 0.02, p = 0.001). No cardiac output x cognitive diagnosis interactions were observed (p > 0.26). APOE-ε4 status modified the association between cardiac output and longitudinal episodic memory (ß = 0.03, p = 0.047) and information processing speed outcomes (ß = 0.55, p = 0.02) with associations stronger in APOE-ε4 carriers. CONCLUSION: The present study provides evidence that even subtle reductions in cardiac output may be associated with more adverse longitudinal cognitive health, including worse language, information processing speed, visuospatial skills, and episodic memory performances. Preservation of healthy cardiac functioning is important for maintaining optimal brain aging among older adults.

Apolipoprotein E Genotype Modifies the Association Between Cardiac Output and Cognition in Older Adults.

Background Subtle reductions in cardiac output relate to lower cerebral blood flow, especially in regions where Alzheimer's disease pathology first develops. Apolipoprotein E (APOE)-ε4 is a genetic susceptibility risk factor for Alzheimer's disease that also moderates vascular damage. This study investigated whether APOE-ε4 carrier status modifies the cross-sectional association between cardiac output and cognition. Methods and Results Vanderbilt Memory & Aging Project participants free of clinical stroke and dementia (n=306, 73±7 years, 42% female) underwent echocardiography to determine cardiac output (L/min), comprehensive neuropsychological assessment, and venous blood draw to determine APOE genotype and ε4 carrier status. Linear regressions related cardiac output to neuropsychological test performance, adjusting for age, sex, education, race/ethnicity, body surface area, cognitive diagnosis, Framingham Stroke Risk Profile, and APOE-ε4 status. Main effect models were null (P>0.19). With identical covariates, models were repeated testing a cardiac output×APOE-ε4 status interaction and again stratified by ε4 carrier status. Cardiac output×APOE-ε4 status related to naming (ß=0.91, P=0.0009), category fluency (ß=1.2, P=0.01), information processing speed (ß=-5.4, P=0.001), visuospatial skill (ß=0.85, P=0.003), and executive function performances (ß=0.22, P=0.002). Stratified models suggested that lower cardiac output was associated with worse neuropsychological performances among APOE-ε4 carriers. Conclusions APOE-ε4 carrier status appears to modify the cross-sectional association between cardiac output and neuropsychological performance such that lower cardiac output relates to poorer performances among carriers of the ε4 allele. These findings add to increasing evidence that APOE-ε4 carrier status has important implications for associations between vascular and brain health in aging adults.

Cerebrospinal fluid and plasma neurofilament light relate to abnormal cognition.

INTRODUCTION: Neuroaxonal damage may contribute to cognitive changes preceding clinical dementia. Accessible biomarkers are critical for detecting such damage. METHODS: Plasma and cerebrospinal fluid (CSF) neurofilament light (NFL) were related to neuropsychological performance among Vanderbilt Memory & Aging Project participants (plasma n = 333, 73 ± 7 years; CSF n = 149, 72 ± 6 years) ranging from normal cognition (NC) to mild cognitive impairment (MCI). Models adjusted for age, sex, race/ethnicity, education, apolipoprotein E ε4 carriership, and Framingham Stroke Risk Profile. RESULTS: Plasma NFL was related to all domains (P values ≤ .008) except processing speed (P values ≥ .09). CSF NFL was related to memory and language (P values ≤ .04). Interactions with cognitive diagnosis revealed widespread plasma associations, particularly in MCI participants, which were further supported in head-to-head comparison models. DISCUSSION: Plasma and CSF NFL (reflecting neuroaxonal injury) relate to cognition among non-demented older adults albeit with small to medium effects. Plasma NFL shows particular promise as an accessible biomarker with relevance to cognition in MCI.

Altered glutamate clearance in ascorbate deficient mice increases seizure susceptibility and contributes to cognitive impairment in APP/PSEN1 mice.

Ascorbate (vitamin C) is critical as a first line of defense antioxidant within the brain, and specifically within the synapse. Ascorbate is released by astrocytes during glutamate clearance and disruption of this exchange mechanism may be critical in mediating glutamate toxicity within the synapse. This is likely even more critical in neurodegenerative disorders with associated excitotoxicity and seizures, in particular Alzheimer's disease, in which ascorbate levels are often low. Using Gulo-/- mice that are dependent on dietary ascorbate, we established that low brain ascorbate increased sensitivity to kainic acid as measured via behavioral observations, electroencephalography (EEG) measurements, and altered regulation of several glutamatergic system genes. Kainic acid-induced immobility was improved in wild-type mice following treatment with ceftriaxone, which upregulates glutamate transporter GLT-1. The same effect was not observed in ascorbate-deficient mice in which sufficient ascorbate is not available for release. A single, mild seizure event was sufficient to disrupt performance in the water maze in low-ascorbate mice and in APPSWE/PSEN1dE9 mice. Together, the data support the critical role of brain ascorbate in maintaining protection during glutamatergic hyperexcitation events, including seizures. The study further supports a role for mild, subclinical seizures in cognitive decline in Alzheimer's disease.