Cerebrovascular Dysfunction Research Articles

Abstract WP227: Endothelin Receptor A (eta) Inhibition By Intranasal Administration Of Bq-123 In Hypoperfused Diabetic Rats Exerts Different Effects In Various Domains Of Cognition

Cerebrovascular dysfunction leading to brain hypoperfusion is an early event in vascular cognitive impairment & dementia ( VCID ). Postmortem brain levels of endothelin (ET)-1, the most potent vasoconstrictor, closely correlate with blood barrier breakdown and hypoperfusion in individuals with VCID. The prevalence of diabetes in people with dementia is as high as 39%. We have reported that there is upregulation of circulating and brain ET-1 in diabetic male rats that later develop cognitive impairment and all the cell types of the neurovascular unit express ETA receptors. We hypothesized that inhibition of brain ETA receptors can prevent cognitive decline in diabetes. Methods: Experimental design is depicted in Fig 1. The impact of unilateral common carotid occlusion (UCCAO) on ETA receptor expression and brain hypoxia was assessed by immunohistochemistry. A battery of cognitive tests was performed. Results: Bioavailability of drug in brain post intranasal delivery was confirmed by LCMS. UCCAO increased the expression of HIF1a and ETA receptors in most of the cell types of NVU. Mobility of diabetic animals was significantly reduced (1522±272.8cm control vs 1051±61.17cm diabetic; p<0.05) without affecting the velocity. Other behavior outcomes are summarized in Fig 1. Conclusions: While hypoxic conditions increased the ETA receptor expression in the brain, in contrast to our hypothesis, ETA inhibition worsened recognition memory and promoted anxiety with no effect on short-term learning and spatial memory. The intranasal drug delivery approach may offer a novel approach to further investigate the complex role of the ET system without systemic side effects of ETA inhibition.

Abstract 111: Cerebrovascular Effects Of Pre/post-losartan Treatment In Humanized ACE2 Knock-in Mice After SARS-CoV-2 Spike Protein Injection

SARS-CoV-2 has killed millions of people globally and has left many with devastating health problems, including neurological deficits. SARS-CoV-2 invades endothelial cells via binding its Spike-protein with angiotensin-converting enzyme 2 (ACE2) receptors. Losartan, an angiotensin receptor blocker, upregulates ACE2 expression. We hypothesize that pre-treatment with losartan could increase the cerebrovascular dysfunction associated with SARS-CoV-2 spike-protein, while post-SARS-CoV-2 losartan would provide potential protective effects. Methods: Recombinant SARS-CoV-2 spike-protein was injected intravenously in transgenic hACE2 mice, humanized ACE2 receptors knock-in mice. Treatment with losartan was started either two weeks before or right after spike-protein injection. Cognitive function was assessed using Y-Maze. Vascular density and cerebral blood flow were evaluated in the hACE2 mice with/out spike protein injection. Western blot and RT-PCR analysis were used to measure protein/gene expression. Results: Spike-protein injection decreased cerebral vascular density and cerebral blood flow in hACE2 brains compared to control (*P<0.05), which was associated with increased cognitive dysfunction in h ACE2 mice (*P<0.05). Pre-losartan treatment exacerbated spike protein-induced cognitive dysfunction, while post-losartan treatment helped restore cognitive function (*P<0.05). Spike-protein decreased ACE2 expression and increased endothelial cell inflammation and apoptosis, as shown by the increased expression of TNF- α ; and caspase-3 (*P<0.05), which were prevented by post-losartan treatment. Conclusion: Spike-protein decreased vascular density, cerebral blood flow, and cognitive function via increasing brain endothelial cell apoptosis. Pre-losartan treatment exacerbated the detrimental effects of spike-protein, while post-losartan treatment restored ACE2 expression and decreased SARS-CoV-2 spike-protein damaging effects.

Initial and ongoing tobacco smoking elicits vascular damage and distinct inflammatory response linked to neurodegeneration

Tobacco smoking is strongly linked to vascular damage contributing to the development of hypertension, atherosclerosis, as well as increasing the risk for neurodegeneration. Still, the involvement of the innate immune system in the development of vascular damage upon chronic tobacco use before the onset of clinical symptoms is not fully characterized. Our data provide evidence that a single acute exposure to tobacco elicits the secretion of extracellular vesicles expressing CD105 and CD49e from endothelial cells, granting further recognition of early preclinical biomarkers of vascular damage. Furthermore, we investigated the effects of smoking on the immune system of healthy asymptomatic chronic smokers compared to never-smokers, focusing on the innate immune system. Our data reveal a distinct immune landscape representative for early stages of vascular damage in clinically asymptomatic chronic smokers, before tobacco smoking related diseases develop. These results indicate a dysregulated immuno-vascular axis in chronic tobacco smokers that are otherwise considered as healthy individuals. The distinct alterations are characterized by increased CD36 expression by the blood monocyte subsets, neutrophilia and increased plasma IL-18 and reduced levels of IL-33, IL-10 and IL-8. Additionally, reduced levels of circulating BDNF and elevated sTREM2, which are associated with neurodegeneration, suggest a considerable impact of tobacco smoking on CNS function in clinically healthy individuals. These findings provide profound insight into the initial and ongoing effects of tobacco smoking and the potential vascular damage contributing to neurodegenerative disorders, specifically cerebrovascular dysfunction and dementia.

Cerebroprotective actions of hydrogen sulfide in the epileptic brain in newborn pigs.

Neonatal epileptic seizures cause postictal dysregulation of cerebral blood flow. Hydrogen sulfide (H2S), a mediator with vasodilator and antioxidant properties, is produced in the brain by astrocyte cystathionine β-synthase (CBS). This study investigated whether H2S improves the cerebral vascular outcome of seizures. Epileptic seizures were induced in newborn pigs using bicuculline. The effects of the CBS inhibitor aminooxyacetate (AOA) and the H2S donor NaHS on cerebral vascular outcome of seizures were examined in live pigs, cerebral endothelial cells, and cortical astrocytes. Brain H2S was elevated during seizures. AOA blocked H2S and reduced functional hyperemia in the epileptic brain. The endothelium- and astrocyte-dependent vasodilation of pial arterioles was impaired 48 h after seizures suggesting cerebral vascular dysfunction. Systemic NaHS elevated brain H2S and blocked reactive oxygen species in the epileptic brain and in primary endothelial cells and astrocytes during inflammatory and excitotoxic conditions. Postictal cerebrovascular dysfunction was exaggerated in H2S-inhibited pigs and minimized in NaHS-treated pigs. H2S elevation in the epileptic brain via activation of CBS contributes to functional hyperemia and exhibits cerebroprotective properties. The H2S donor NaHS enhances brain antioxidant defense and provides a therapeutic approach for preventing adverse cerebral vascular outcome of neonatal epileptic seizures. Epileptic seizures in neonates lead to prolonged postictal cerebral vascular dysregulation. The role of hydrogen sulfide (H2S), a mediator with vasodilator and antioxidant properties, in the epileptic brain has been explored. Astrocytes are major sites of enzymatic H2S production in the epileptic brain. Postictal cerebral vascular dysfunction is exaggerated when astrocyte H2S production is pharmacologically inhibited during seizures. Postictal cerebral vascular dysfunction is minimized when the brain H2S is elevated by systemic administration of NaHS during seizures. NaHS provides a therapeutic approach for improving cerebrovascular outcome of epileptic seizures via a mechanism that involves the antioxidant potential of H2S.

The Association between Electronegative Low-Density Lipoprotein Cholesterol L5 and Cognitive Functions in Patients with Mild Cognitive Impairment

L5, the most electronegative subfraction of low-density lipoprotein cholesterol (LDL-C), may play a role in the pathogenesis of cerebrovascular dysfunction and neurodegeneration. We hypothesized that serum L5 is associated with cognitive impairment and investigated the association between serum L5 levels and cognitive performance in patients with mild cognitive impairment (MCI). This cross-sectional study conducted in Taiwan included 22 patients with MCI and 40 older people with normal cognition (healthy controls). All participants were assessed with the Cognitive Abilities Screening Instrument (CASI) and a CASI-estimated Mini-Mental State Examination (MMSE-CE). We compared the serum total cholesterol (TC), LDL-C, and L5 levels between the MCI and control groups and examined the association between lipid profiles and cognitive performance in these groups. The serum L5 concentration and total CASI scores were significantly negatively correlated in the MCI group. Serum L5% was negatively correlated with MMSE-CE and total CASI scores, particularly in the orientation and language subdomains. No significant correlation between the serum L5 level and cognitive performance was noted in the control group. Conclusions: Serum L5, instead of TC or total LDL-C, could be associated with cognitive impairment through a disease stage-dependent mode that occurs during neurodegeneration.

Effects of traditional Chinese exercise on vascular function in patients with Alzheimer's disease: A protocol for systematic review and network meta-analysis of randomized controlled trials.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with an insidious onset, usually characterized by memory impairment, visual-spatial skill impairment, executive dysfunction and personality behavioral changes. Studies have confirmed that vascular dysfunction may precede AD pathological changes and can present as vascular malformations, atherosclerosis, and impaired self-regulation, and can affect oxidative stress and amyloidosis. Therefore, it is important to improve or prevent vascular dysfunction in AD patients. Regular exercise can effectively inhibit the production of reactive oxygen species during the occurrence of AD and can improve the reduction of cerebral blood flow due to AD. Previous studies have shown that exercise can achieve superior clinical results in improving vascular function in AD patients. Therefore, we hypothesize that traditional Chinese exercises (TCEs) may have a good clinical effect in improving vascular function in patients with AD. We will search "PubMed," "the Cochrane Library," "Embase," "Web of Science," "CINAHL," "ProQuest Dissertations and Theses," and "ProQuest-Health & Medical Collection," "CNKI," "SinoMed," "VIP," and "Wanfang Data" to find randomized controlled trials of the effects of TCEs on AD vascular function from the creation of the database to the present, including at least 1 indicator in carotid intima-media thickness (cIMT), middle cerebral artery mean flow velocity (MFV), blood indicators [Heme Oxidase-1 (HO-1), angiopoietin I (Ang I), vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor, matrix metalloproteinase-9 (MMP-9)], and arterial stiffness [(Ankle Brachial Index (ABI), pulse wave velocity (PWV)]. For the included literature, Excel 2019 will be used for data extraction and collection. For the indicators that can be netted for network meta-analysis, Surface Under the Cumulative Ranking for each exercise modality will be calculated with the help of Stata 16.0 and rank, where the higher the SUCRA score, the higher the ranking. For the indicators that cannot be netted, Review Manager 5.4 will be used for meta-analysis will be performed to evaluate the improvement effect of TCEs on AD patients. This meta-analysis will further determine the efficacy and safety of TCEs on vascular function in AD patients. In this study, randomized controlled trials of the effects of TCEs on vascular function in AD patients will be selected to provide evidence-based medical evidence for promoting the application of TCEs by observing the order of advantages and disadvantages of various exercise modalities through network meta-analysis.

Xanthine oxidase mediates chronic stress-induced cerebrovascular dysfunction and cognitive impairment

Xanthine oxidase (XO) mediates vascular function. Chronic stress impairs cerebrovascular function and increases the risk of stroke and cognitive decline. Our study determined the role of XO on stress-induced cerebrovascular dysfunction and cognitive decline. We measured middle cerebral artery (MCA) function, free radical formation, and working memory in 6-month-old C57BL/6 mice who underwent 8 weeks of control conditions or unpredictable chronic mild stress (UCMS) with or without febuxostat (50 mg/L), a XO inhibitor. UCMS mice had an impaired MCA dilation to acetylcholine vs. controls (p < 0.0001), and increased total free radical formation, XOR protein levels, and hydrogen peroxide production in the liver compared to controls. UCMS increased hydrogen peroxide production in the brain and cerebrovasculature compared to controls. Working memory, using the y-maze test, was impaired (p < 0.05) in UCMS mice compared to control mice. However, blocking XO using febuxostat prevented the UCMS-induced impaired MCA response, while free radical production and hydrogen peroxide levels were similar to controls in the liver and brain of UCMS mice treated with febuxostat. Further, UCMS + Feb mice did not have a significant reduction in working memory. These data suggest that the cerebrovascular dysfunction associated with chronic stress may be driven by XO, which leads to a reduction in working memory.

Comparison of peripheral and cerebral vascular function between premenopausal, early and late postmenopausal females.

What is the central question of this study? We sought to investigate whether peripheral and cerebrovascular function are impaired in early and late postmenopausal females compared with premenopausal females, while also accounting for nitric oxide and estradiol levels. What is the main finding and its importance? We observed no differences in peripheral vascular and cerebrovascular function between healthy and physically active premenopausal females and early and late postmenopausal females. Our findings contradict previous cross-sectional observations of vascular and cerebrovascular dysfunction across menopause. Longitudinal studies assessing vascular and cerebrovascular outcomes across the menopausal transition are warranted. The risk of cardiovascular and cerebrovascular disease increases in ageing females, coinciding with the onset of menopause. Differences in peripheral and cerebrovascular function across menopausal stages, however, are poorly characterized. The aim of this study was to compare peripheral and cerebrovascular function between healthy premenopausal (PRE), early (1-6 years after final menstrual period; E-POST) and late (>6 years after final menstrual period; L-POST) postmenopausal females. We also explored the association between reproductive hormones, NO bioavailability and cerebrovascular function. In 39 females (40-65 years of age), we measured arterial stiffness, brachial artery flow-mediated dilatation, and cerebrovascular reactivity (CVR) to hypercapnia in the middle (MCAv) and internal (ICA) carotid arteries. Follicle-stimulating hormone, estradiol, progesterone and plasma nitrate and nitrite concentrations were also measured. Years since final menstrual period (PRE, 0±0 years; E-POST, 3±1 years; L-POST, 11±4 years; P<0.001) and estradiol levels (PRE, 145.5±65.6 pgml-1 ; E-POSTm 30.2±81.2 pgml-1 ; L-POST, 7.7±11.3 pgml-1 ; P<0.001) were different between groups. All groups exceeded the guidelines for recommended physical activity. There were no group differences in blood pressure (P=0.382), arterial stiffness (P=0.129), flow-mediated dilatation (P=0.696) or MCAv CVR (P=0.442). The ICA CVR blood flow response was lower in PRE compared with L-POST (26.5±19.2vs. 47.8±12.6%; P=0.010), but after adjusting for age these differences were no longer present. Flow-mediated dilatation (r=0.313, P=0.105) and ICA CVR (r=-0.154, P=0.495) were not associated with the estradiol concentration. There were no associations between the estradiol concentration and NO bioavailability. These results suggest that in healthy, physically active early and late postmenopausal females, vascular and cerebrovascular function is generally well preserved.

Age and APOE affect L-carnitine system metabolites in the brain in the APOE-TR model.

With age the apolipoprotein E (APOE) E4 allele (involved in lipid homeostasis) is associated with perturbation of bioenergetics pathways in Alzheimer's disease (AD). We therefore hypothesized that in aging mice APOE genotype would affect the L-carnitine system (central to lipid bioenergetics), in the brain and in the periphery. Using liquid chromatography-mass spectrometry, levels of L-carnitine and associated metabolites: γ-butyrobetaine (GBB), crotonobetaine, as well as acylcarnitines, were evaluated at 10-, 25-, and 50-weeks, in the brain and the periphery, in a targeted replacement mouse model of human APOE (APOE-TR). Aged APOE-TR mice were also orally administered 125 mg/kg of L-carnitine daily for 7 days followed by evaluation of brain, liver, and plasma L-carnitine system metabolites. Compared to E4-TR, an age-dependent increase among E2- and E3-TR mice was detected for medium- and long-chain acylcarnitines (MCA and LCA, respectively) within the cerebrovasculature and brain parenchyma. While following L-carnitine oral challenge, E4-TR mice had higher increases in the L-carnitine metabolites, GBB and crotonobetaine in the brain and a reduction of plasma to brain total acylcarnitine ratios compared to other genotypes. These studies suggest that with aging, the presence of the E4 allele may contribute to alterations in the L-carnitine bioenergetic system and to the generation of L-carnitine metabolites that could have detrimental effects on the vascular system. Collectively the E4 allele and aging may therefore contribute to AD pathogenesis through aging-related lipid bioenergetics as well as cerebrovascular dysfunctions.

Arterial Aging and Cerebrovascular Function: Impact of Aerobic Exercise Training in Older Adults.

Advanced age is the major risk factor for dementia including Alzheimer's disease. The clinical effects of recently developed anti-amyloid therapy for Alzheimer's disease were modest and the long-term outcome is unknown. Thus, an in-depth understanding of the mechanisms of brain aging is essential to develop preventive interventions to maintain cognitive health in late life. Mounting evidence suggests that arterial aging manifested as increases in central arterial stiffness is associated closely with cerebrovascular dysfunction and brain aging while improvement of cerebrovascular function with aerobic exercise training contributes to brain health in older adults. We summarized evidence in this brief review that 1) increases in central arterial stiffness and arterial pulsation with age are associated with increases in cerebrovascular resistance, reduction in cerebral blood flow, and cerebrovascular dysfunction, 2) aerobic exercise training improves cerebral blood flow by modifying arterial aging as indicated by reductions in cerebrovascular resistance, central arterial stiffness, arterial pulsation, and improvement in cerebrovascular function, and 3) improvement in cerebral blood flow and cerebrovascular function with aerobic exercise training may lead to improvement in cognitive function. These findings highlight the associations between arterial aging and cerebrovascular function and the importance of aerobic exercise in maintaining brain health in older adults.

The relationship of vascular complications with cerebrovascular reactivity and endothelial dysfunction in patients with obstructive sleep apnea

To assess the relationship of vascular complications with cerebrovascular reactivity (CVR) and endothelial dysfunction in patients with obstructive sleep apnea (OSA). One hundred and twelve patients were examined. The patients were stratified into the main group with moderate and severe OSA and the control group without apnea. All patients underwent anthropometry, polysomnography, transcranial dopplerography and duplex scanning of the brachial artery. Patients with OSA showed a more frequent decrease in post-occlusive vascular dilatation. The CVR indices in the hypercapnic test in the main group were in the range of 0.91-0.97 and significantly lower after 1 minute on the left, after 5 minutes on both sides and after 10 minutes on the left. A positive correlation during a hypercapnic test between the CVR on the left after 10 minutes and the desaturation index (r=0.287, p=0.021), between the CVR on the left after 5 and 10 minutes and acute cerebrovascular accident (r=0.248, p=0.048 and r=0.285, p=0.022, respectively), as well as a negative correlation between the indicators of the middle cerebral artery and chronic cerebral ischemia were established in patients with apnea. Timely assessment of pathological changes in central and peripheral hemodynamics in patients with OSA will allow diagnosing early signs of vascular complications, which will further improve the personalized strategy for the prevention of stroke and chronic cerebral ischemia.

Cerebrovascular pulsatility index is higher in chronic kidney disease.

Patients with chronic kidney disease (CKD) are more likely to die of cardiovascular diseases, including cerebrovascular disease, than to progress to end-stage kidney disease. Cerebrovascular dysfunction, characterized by reduced cerebrovascular reactivity, cerebral hypoperfusion, and increased pulsatile flow within the brain, precedes the onset of dementia and is linked to cognitive dysfunction. However, whether impaired cerebrovascular function is present in non-dialysis dependent CKD is largely unknown. Using transcranial Doppler, we compared middle cerebral artery (MCA) blood velocity response to hypercapnia (normalized for blood pressure and end-tidal CO2 ; a measure of cerebrovascular reactivity) and MCA pulsatility index (PI; a measure of cerebrovascular stiffness) in patients with stage 3-4 CKD vs. age-matched healthy controls. We also administered the NIH cognitive toolbox (cognitive function), measured carotid-femoral pulse-wave velocity (PWV; aortic stiffness), and assessed ex vivo nitric oxide (NO) and reactive oxygen species (ROS) production from human brain endothelial cells incubated with serum obtained from study participants. MCA PI was higher in patients with CKD vs. controls; however, normalized MCA blood velocity response to hypercapnia did not differ between groups. Similar results were observed in a validation cohort of midlife and older adults divided by the median estimated glomerular filtration rate (eGFR). MCA PI was associated with greater large-elastic artery stiffness (carotid-femoral PWV), worse executive function (trails B time), lower eGFR, and higher ex vivo ROS production. These data suggest that impaired kidney function is associated with greater cerebrovascular stiffness, which may contribute to the known increased risk for cognitive impairment in patients with CKD.

Short-term blood pressure variability is inversely related to regional amplitude of low frequency fluctuations in older and younger adults

Blood pressure variability (BPV), independent of mean blood pressure levels, is associated with cerebrovascular disease burden on MRI and postmortem evaluation. However, less is known about relationships with markers of cerebrovascular dysfunction, such as diminished spontaneous brain activity as measured by the amplitude of low frequency fluctuations (ALFF), especially in brain regions with vascular and neuronal vulnerability in aging. We investigated the relationship between short-term BPV and concurrent regional ALFF from resting state fMRI in a sample of community-dwelling older adults (n = 44) and healthy younger adults (n = 49). In older adults, elevated systolic BPV was associated with lower ALFF in widespread medial temporal regions and the anterior cingulate cortex. Higher systolic BPV in younger adults was also related to lower ALFF in the medial temporal lobe, albeit in fewer subregions, and the amygdala. There were no significant associations between systolic BPV and ALFF across the right/left whole brain or in the insular cortex in either group. Findings suggest a possible regional vulnerability to cerebrovascular dysfunction and short-term fluctuations in blood pressure. BPV may be an understudied risk factor for cerebrovascular changes in aging.

Mild Traumatic Brain Injury Induces Time- and Sex-Dependent Cerebrovascular Dysfunction and Stroke Vulnerability.

Mild traumatic brain injury (mTBI) produces subtle cerebrovascular impairments that persist over time and promote increased ischemic stroke vulnerability. We recently established a role for vascular impairments in exacerbating stroke outcomes 1 week after TBI, but there is a lack of research regarding long-term impacts of mTBI-induced vascular dysfunction, as well as a significant need to understand how mTBI promotes stroke vulnerability in both males and females. Here, we present data using a mild closed head TBI model and an experimental stroke occurring either 7 or 28 days later in both male and female mice. We report that mTBI induces larger stroke volumes 7 days after injury, however, this increased vulnerability to stroke persists out to 28 days in female but not male mice. Importantly, mTBI-induced changes in blood-brain barrier permeability, intravascular coagulation, angiogenic factors, total vascular area, and glial expression were differentially altered across time and by sex. Taken together, these data suggest that mTBI can result in persistent cerebrovascular dysfunction and increased susceptibility to worsened ischemic outcomes, although these dysfunctions occur differently in male and female mice.

Impact of impaired cerebral blood flow autoregulation on cognitive impairment.

Although the causes of cognitive impairment are multifactorial, emerging evidence indicates that cerebrovascular dysfunction plays an essential role in dementia. One of the most critical aspects of cerebrovascular dysfunction is autoregulation of cerebral blood flow (CBF), mainly mediated by the myogenic response, which is often impaired in dementia individuals with comorbidities, such as diabetes and hypertension. However, many unsolved questions remain. How do cerebrovascular networks coordinately modulate CBF autoregulation in health and disease? Does poor CBF autoregulation have an impact on cognitive impairment, and what are the underlying mechanisms? This review summarizes the cerebral vascular structure and myogenic (a three-phase model), metabolic (O2, CO2, adenosine, and H+), and endothelial (shear stress) factors in the regulation of CBF; and the consequences of CBF dysautoregulation. Other factors contributing to cerebrovascular dysfunction, such as impaired functional hyperemia and capillary abnormalities, are included as well. Moreover, this review highlights recent studies from our lab in terms of novel mechanisms involved in CBF autoregulation and addresses a hypothesis that there is a three-line of defense for CBF autoregulation in the cerebral vasculature.

Multi‐parametric Neuroimaging in a Non‐Human Primate Model of Sporadic Cerebral Amyloid Angiopathy (Saimiri boliviensis boliviensis)

AbstractBackgroundSquirrel monkeys (SQMs) are a unique non‐human primate model (NHP), which unlike other NHPs, develops extensive age‐associated cerebral amyloid angiopathy (CAA). The growing recognition of CAA contribution to clinical decline and CAA‐related complications in current clinical trials underscore the utility of the SQM model for studying CAA pathology development. Neuroimaging can play a key role in noninvasively detecting and monitoring disease progression in conjunction with histological methods. We have previously shown the utility of quantitative R2 * to map age‐related differences in SQM neuropathology cross‐sectionally and longitudinally. Here we aim to complement our protocol with advanced MRI approaches sensitive to brain microstructure to enable early and specific detection of alteration in tissue integrity. Our overarching goals aim to establish the in vivo and ex vivo MRI metrics profile of young and geriatric SQM cohorts.Method2D T2‐w (a) Turbo‐spin‐echo (TSE) and (b) FLAIR MRIs were acquired in vivo and ex vivo, while (c) multi‐shell diffusion‐weighted MRI (DWI) was limited to ex vivo imaging. Diffusion tensor imaging (DTI) and Diffusion kurtosis imaging (DKI) metrics were derived from comprehensive DWI datasets. Immunohistochemistry was subsequently performed to characterize the microstructural underpinnings of MRI abnormalities.ResultBothin vivo and ex vivo T2‐w TSE and FLAIR helped identify spontaneous asymmetric hyperintensities (ARIA‐E) in geriatric SQMs (21‐23yrs), predominantly in the parieto‐occipital WM, not seen in the young cohort (5‐yrs). Importantly, DKI‐derived mean kurtosis proved to be the most sensitive of DWI metrics for detecting lesions in the parieto‐occipital region. Widely adopted DTI metrics were far less sensitive in identifying microstructural changes. Histological assessment of region‐matched sections revealed Iba1 microgliosis, as well as immunoreactivity for both extravascular fibrinogen and decreased MBP when compared to the contralateral side. Aß immunohistochemistry (6E10/4G8) confirmed presence of CAA in the affected regions.ConclusionAdvanced DWI models are sensitive and specific neuroimaging tools for identifying abnormalities associated with tissue integrity that are potentially linked to age‐associated cerebrovascular dysfunction. Ex vivo conventional MRI detected similar abnormalities observed in vivo and proved to be a useful step to validate the performance of advanced imaging strategies, which can help bridge the gap between in vivo MRI and histology.

Psychosocial Stress‐Accelerates Alzheimer’s Disease Progression via the Xanthine Oxidase Pathway

AbstractBackgroundVascular contributions to cognitive impairment and dementia are a key pathology associated with Alzheimer’s disease (AD). We have shown that chronic stress induces cerebrovascular dysfunction due to a pro‐oxidative environment, a phenotype similar to that noted with AD. Epidemiological studies also suggest a link between chronic stress and dementia. We tested the hypothesis that chronic stress accelerates the AD pathology via the xanthine oxidase (XO) pathway.MethodsWild type (WT) and Triple transgenic (AD) mice were separated into 1) WT control, 2) WT+UCMS, 3) AD control, 4) AD control+Feb, 5) AD+UCMS, 6) AD+UCMS+Feb. At 4 months‐of‐age, dependent upon group, the unpredicted chronic mild stress (UCMS) model with or without Febuxostat (Feb) treated water (50mg/L) began for 8 weeks. Mice were either euthanized at 6 or 9 months‐of‐age. The middle cerebral artery (MCA) was removed for pressure myography. Brains were homogenized to extract soluble and insoluble fractions of tau proteins using Western blot normalized to GAPDH or B‐actin.ResultsAt 6 months‐of‐age, AD mice displayed a 72% impaired MCA dilation to acetylcholine compared to WT control mice (p&lt;0.05). WT and AD mice that underwent UCMS displayed similar MCA dysfunction compared to AD control mice. UCMS accelerated total and phosphorylated tau protein expression by 83% (p&lt;0.05) and 350% (p&lt;0.001), respectively, compared to AD controls. Treatment with Feb prevented MCA dysfunction in AD control mice, WT UCMS mice, and AD UCMS mice. Feb prevented the increased expression of phosphorylated tau and lowered the total tau protein expression in the AD‐UCMS group. However, total tau protein expression remained higher compared to AD control levels. At 9 months‐of‐age, the majority of these trends persisted with the one exception being a significant impairment in the AD UCMS group compared to both AD control or WT UCMS mice. Tau levels have yet to be processed for 9‐months.ConclusionOverall, these data suggest that chronic stress accelerates cerebrovascular pathology with AD and via a pro‐oxidative state driven by activation of the XO pathway. We will further explore Aβ1‐42 and XO in 3xTg brain homogenates at 6 and 9 months‐of‐age, to better understand how stress accelerates AD pathology.

Diabetes is related to cognition but not plasma amyloid‐β 42/40 in an African American cohort

AbstractBackgroundThe prevalence of clinical Alzheimer’s disease (AD) and type 2 diabetes is higher in African Americans (AA) relative to non‐Hispanic White Americans. Although diabetes is a risk factor for Alzheimer’s clinical syndrome, it is unclear whether diabetes associates with amyloid‐β, a pathological hallmark of AD. We investigated whether diabetic status was associated with age‐related decline in plasma amyloid‐β (Aβ) 42/40 ratio and cognition in a predominantly dementia‐free AA cohort.MethodParticipants (N=314) were middle‐aged and older adults (Table 1) enrolled in the African Americans Fighting Alzheimer’s in Midlife cohort. EDTA plasma was collected at 1‐8 visits for Aβ 42/40 quantification using immunoprecipitation mass spectrometry (C2N Diagnostics, St. Louis, MO). 52% had &gt;1 plasma Aβ 42/40 measurements over an average interval of 4.9 years (SD=3). Recall (immediate and delayed) and executive functioning were assessed using Rey’s Auditory Verbal Learning Test and Trails B, respectively. Diabetic status was determined from clinician‐report, self‐report, self‐report of antidiabetic medication use or fasting glucose ≥126 mg/dL. Cognitive data from the first of 1‐6 visits and diabetic status were obtained at the same visit as baseline plasma Aβ 42/40 for 96% of participants. Linear mixed‐effects models tested diabetic status as a moderator of age‐related decline in plasma Aβ 42/40 ratio and cognition. If age x diabetic status was not significant, diabetic status was tested without the interaction. Covariates included APOE4 carrier status and sex, and education was included when cognition was the outcome.ResultsDiabetic status did not significantly moderate age‐related decline in plasma Aβ 42/40 (β=0.0001, p=.21) or predict average plasma Aβ 42/40 ratio (β=‐0.001, p=.22). Diabetes was also not significantly related to aging‐associated decline in cognition but was a significant predictor of worse average Trails B scores (Table 2). Results from a cognitively unimpaired subsample (n=261) revealed a similar pattern.ConclusionIn a predominantly dementia‐free AA cohort, diabetes was unrelated to plasma Aβ 42/40 but was related to worse Trails B performance. Poor Trails B performance has been linked in previous studies to cerebrovascular dysfunction. Determining mechanisms, vascular and AD pathological pathways, that link diabetes to increased dementia risk in AAs warrants further investigation.

Cerebrovascular Dysfunction at the Intersection of Ischemia and Alzheimer’s Disease

AbstractBackgroundCerebrovascular dysregulation is one of the earliest detectable changes in Alzheimer’s disease (AD) etiology that precedes the descent into dementia1. Ischemic events such as stroke and silent infarcts trigger cerebrovascular dysfunction2,3, accelerate cognitive decline4 and increase dementia risk5. Further, the resulting decrease in cerebral blood flow (CBF) can induce the formation of amyloid β6. Thus, we examined cerebrovascular function at the intersection of ischemia and AD by measuring CO2‐evoked hyperemia and neurovascular coupling (NVC) after small strokes in wild type and Tg2576 model of AD‐related amyloidosis.MethodWe established a model of small ischemic strokes by performing a short 30‐minute middle cerebral artery occlusion, yielding a mild subcortical infarct (MSCI). We performed MSCI in 6‐month old Tg2576 and littermate wild‐type mice (WT) and compared them to naïve mice. We used arterial spin‐labeling (ASL) MRI to quantify CBF and CO2‐evoked hyperemia at 10 and 14 months of age and Laser Doppler flowmetry (LDF) to measure NVC at 14 months of age. We also quantified hippocampal volumes.ResultThere was no apparent change in hippocampal volume after MSCI in either genotype. There was a reduction in NVC in WT+MSCI mice in both hemispheres, with a trend towards greater reduction in Tg2576+MSCI mice. The CO2‐evoked hyperemia was also reduced in WT+MSCI and Tg2576+MSCI mice compared to WT naïves. Curiously, naïve Tg2576 mice showed the most severe impairment in CO2‐evoked hyperemia, which appeared improved in Tg2576+MSCI. We are re‐examining this finding.ConclusionUsing an innovative mixed model of mild ischemia and amyloidosis, here we report that the two pathologies can synergize to accelerate cerebrovascular impairments. Strikingly, we found that even a small one‐sided stroke can impair cerebrovascular function bilaterally. Future studies will determine the extent to which amyloid pathology and cognitive deficits are exacerbated by such impairments. Our findings suggest that targeting early cerebrovascular dysfunction after ischemia may prove useful in deterring the onset of dementia later in life.

Three-Dimensional Imaging of Fibrinogen and Neurovascular Alterations in Alzheimer's Disease.

Cerebrovascular dysfunction is a hallmark of Alzheimer's disease (AD) that is linked to cognitive decline. However, blood-brain barrier (BBB) disruption in AD is focal and requires sensitive methods to detect extravasated blood proteins and vasculature in large brain volumes. Fibrinogen, a blood coagulation factor, is deposited in AD brains at sites of BBB disruption and cerebrovascular damage. This chapter presents the methodology of fibrinogen immunolabeling-enabled three-dimensional (3D) imaging of solvent-cleared organs (iDISCO) which, when combined with immunolabeling of amyloid β (Aβ) and vasculature, enables sensitive detection of focal BBB vascular abnormalities, and reveals the spatial distribution of Aβ plaques and fibrin deposits, in large tissue volumes from cleared human brains. Overall, fibrinogen iDISCO enables the investigation of neurovascular and neuroimmune mechanisms driving neurodegeneration in disease.