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      Association of Extracellular Vesicle Biomarkers With Alzheimer Disease in the Baltimore Longitudinal Study of Aging

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          This case-control study examines neuronal-enriched extracellular vesicles as predictors of Alzheimer disease. Can blood extracellular vesicle biomarkers diagnose Alzheimer disease at the preclinical and clinical stages? In a large case-control study examining 887 longitudinal samples from 128 Baltimore Longitudinal Study of Aging participants (split into training and test sets), combining extracellular vesicle biomarkers predicted Alzheimer disease with high discrimination accuracy and specificity about 4 years before symptom onset; individual biomarkers were associated with cognitive performance. Biomarkers were further validated in a case-control cohort from Johns Hopkins. Further development of extracellular vesicle biomarkers may establish them as a blood test for Alzheimer disease. Blood biomarkers able to diagnose Alzheimer disease (AD) at the preclinical stage would enable trial enrollment when the disease is potentially reversible. Plasma neuronal-enriched extracellular vesicles (nEVs) of patients with AD were reported to exhibit elevated levels of phosphorylated (p) tau, Aβ42, and phosphorylated insulin receptor substrate 1 (IRS-1). To validate nEV biomarkers as AD predictors. This case-control study included longitudinal plasma samples from cognitively normal participants in the Baltimore Longitudinal Study of Aging (BLSA) cohort who developed AD up to January 2015 and age- and sex-matched controls who remained cognitively normal over a similar length of follow-up. Repeated samples were blindly analyzed over 1 year from participants with clinical AD and controls from the Johns Hopkins Alzheimer Disease Research Center (JHADRC). Data were collected from September 2016 to January 2018. Analyses were conducted in March 2019. Neuronal-enriched extracellular vesicles were immunoprecipitated; tau, Aβ42, and IRS-1 biomarkers were quantified by immunoassays; and nEV concentration and diameter were determined by nanoparticle tracking analysis. Levels and longitudinal trajectories of nEV biomarkers between participants with future AD and control participants were compared. Overall, 887 longitudinal plasma samples from 128 BLSA participants who eventually developed AD and 222 age and sex-matched controls who remained cognitively normal were analyzed. Participants were followed up (from earliest sample to AD symptom onset) for a mean (SD) of 3.5 (2.31) years (range, 0-9.73 years). Overall, 161 participants were included in the training set, and 80 were in the test set. Participants in the BLSA cohort with future AD (mean [SD] age, 79.09 [7.02] years; 68 women [53.13%]) had longitudinally higher p-tau181, p-tau231, pSer312-IRS-1, pY-IRS-1, and nEV diameter than controls (mean [SD] age, 76.2 [7.36] years; 110 women [50.45%]) but had similar Aβ42, total tau, TSG101, and nEV concentration. In the training BLSA set, a model combining preclinical longitudinal data achieved 89.6% area under curve (AUC), 81.8% sensitivity, and 85.8% specificity for predicting AD. The model was validated in the test BLSA set (80% AUC, 55.6% sensitivity, 88.7% specificity). Preclinical levels of nEV biomarkers were associated with cognitive performance. In addition, 128 repeated samples over 1 year from 64 JHADRC participants with clinical AD and controls were analyzed. In the JHADRC cohort (35 participants with AD: mean [SD] age, 74.03 [8.73] years; 18 women [51.43%] and 29 controls: mean [SD] age, 72.14 [7.86] years; 23 women [79.31%]), nEV biomarkers achieved discrimination with 98.9% AUC, 100% sensitivity, and 94.7% specificity in the training set and 76.7% AUC, 91.7% sensitivity, and 60% specificity in the test set. We validated nEV biomarker candidates and further demonstrated that their preclinical longitudinal trajectories can predict AD diagnosis. These findings motivate further development of nEV biomarkers toward a clinical blood test for AD.

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          Brain and blood metabolite signatures of pathology and progression in Alzheimer disease: A targeted metabolomics study

          Background The metabolic basis of Alzheimer disease (AD) is poorly understood, and the relationships between systemic abnormalities in metabolism and AD pathogenesis are unclear. Understanding how global perturbations in metabolism are related to severity of AD neuropathology and the eventual expression of AD symptoms in at-risk individuals is critical to developing effective disease-modifying treatments. In this study, we undertook parallel metabolomics analyses in both the brain and blood to identify systemic correlates of neuropathology and their associations with prodromal and preclinical measures of AD progression. Methods and findings Quantitative and targeted metabolomics (Biocrates AbsoluteIDQ [identification and quantification] p180) assays were performed on brain tissue samples from the autopsy cohort of the Baltimore Longitudinal Study of Aging (BLSA) (N = 44, mean age = 81.33, % female = 36.36) from AD (N = 15), control (CN; N = 14), and “asymptomatic Alzheimer’s disease” (ASYMAD, i.e., individuals with significant AD pathology but no cognitive impairment during life; N = 15) participants. Using machine-learning methods, we identified a panel of 26 metabolites from two main classes—sphingolipids and glycerophospholipids—that discriminated AD and CN samples with accuracy, sensitivity, and specificity of 83.33%, 86.67%, and 80%, respectively. We then assayed these 26 metabolites in serum samples from two well-characterized longitudinal cohorts representing prodromal (Alzheimer’s Disease Neuroimaging Initiative [ADNI], N = 767, mean age = 75.19, % female = 42.63) and preclinical (BLSA) (N = 207, mean age = 78.68, % female = 42.63) AD, in which we tested their associations with magnetic resonance imaging (MRI) measures of AD-related brain atrophy, cerebrospinal fluid (CSF) biomarkers of AD pathology, risk of conversion to incident AD, and trajectories of cognitive performance. We developed an integrated blood and brain endophenotype score that summarized the relative importance of each metabolite to severity of AD pathology and disease progression (Endophenotype Association Score in Early Alzheimer’s Disease [EASE-AD]). Finally, we mapped the main metabolite classes emerging from our analyses to key biological pathways implicated in AD pathogenesis. We found that distinct sphingolipid species including sphingomyelin (SM) with acyl residue sums C16:0, C18:1, and C16:1 (SM C16:0, SM C18:1, SM C16:1) and hydroxysphingomyelin with acyl residue sum C14:1 (SM (OH) C14:1) were consistently associated with severity of AD pathology at autopsy and AD progression across prodromal and preclinical stages. Higher log-transformed blood concentrations of all four sphingolipids in cognitively normal individuals were significantly associated with increased risk of future conversion to incident AD: SM C16:0 (hazard ratio [HR] = 4.430, 95% confidence interval [CI] = 1.703–11.520, p = 0.002), SM C16:1 (HR = 3.455, 95% CI = 1.516–7.873, p = 0.003), SM (OH) C14:1 (HR = 3.539, 95% CI = 1.373–9.122, p = 0.009), and SM C18:1 (HR = 2.255, 95% CI = 1.047–4.855, p = 0.038). The sphingolipid species identified map to several biologically relevant pathways implicated in AD, including tau phosphorylation, amyloid-β (Aβ) metabolism, calcium homeostasis, acetylcholine biosynthesis, and apoptosis. Our study has limitations: the relatively small number of brain tissue samples may have limited our power to detect significant associations, control for heterogeneity between groups, and replicate our findings in independent, autopsy-derived brain samples. Conclusions We present a novel framework to identify biologically relevant brain and blood metabolites associated with disease pathology and progression during the prodromal and preclinical stages of AD. Our results show that perturbations in sphingolipid metabolism are consistently associated with endophenotypes across preclinical and prodromal AD, as well as with AD pathology at autopsy. Sphingolipids may be biologically relevant biomarkers for the early detection of AD, and correcting perturbations in sphingolipid metabolism may be a plausible and novel therapeutic strategy in AD.
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            Altered lysosomal proteins in neural-derived plasma exosomes in preclinical Alzheimer disease.

            Diverse autolysosomal proteins were quantified in neurally derived blood exosomes from patients with Alzheimer disease (AD) and controls to investigate disordered neuronal autophagy.
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              High complement levels in astrocyte-derived exosomes of Alzheimer disease

              Objective Astrocytes fulfill neuronal trophic roles normally, but are transformed in Alzheimer's disease (AD) into A1-type reactive astrocytes that may destroy neurons through unknown mechanisms. Methods To investigate astrocyte inflammatory mechanisms, astrocyte-derived exosomes (ADEs) were isolated immunochemically from plasmas of AD patients and matched controls for ELISA quantification of complement proteins. Results ADE levels of C1q, C4b, C3d, factor B, factor D, Bb, C3b and C5b-C9 terminal complement complex (TCC), but not mannose-binding lectin (MBL), normalized by the CD81 exosome marker were significantly higher for AD patients (n=28) than age- and gender-matched controls (all p<0.0001). ADE normalized levels of IL-6, TNF-α and IL-1β were significantly higher for AD patients than controls, but there was greater overlap between the two groups than for complement proteins. Mean ADE levels of complement proteins for AD patients in a longitudinal study were significantly higher (n=16, p<0.0001) at the AD2 stage of moderate dementia than at the AD1 preclinical stage five to 12 years earlier, which were the same as for controls. ADE levels of complement regulatory proteins CD59, CD46, decay-accelerating factor (DAF) and complement receptor type 1 (CR1), but not factor I, were significantly lower for AD patients than controls (p<0.0001 for CD59 and DAF), were diminished by the AD1 stage and were further decreased at the AD2 stage. Interpretation ADE complement effector proteins in AD are produced by dysregulated systems, attain higher levels than in controls, and may potentially damage neurons in the late inflammatory phase of AD.

                Author and article information

                JAMA Neurology
                JAMA Neurol
                American Medical Association (AMA)
                July 15 2019
                [1 ]Laboratory of Clinical Investigations, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
                [2 ]Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
                [3 ]Laboratory of Behavioral Neuroscience, Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland
                [4 ]Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland
                [5 ]Department of Medicine, University of California, San Francisco
                [6 ]Jewish Home of San Francisco, San Francisco, California
                © 2019


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