Biomarkers.

The 42 amino acid form of amyloid-β (Aβ42) plays a key role in the pathogenesis of Alzheimer's disease (AD) and is a core biomarker for the diagnosis of AD. Numerous studies have shown that cerebrospinal fluid (CSF) Aβ42 concentrations are decreased in AD, when measured by enzyme-linked immunosorbent assay (ELISA) and other conventional immunoassays. While most studies report no change in plasma Aβ42, independent studies using the immunomagnetic reduction (IMR) technique report an increase in plasma Aβ42 levels in AD. To confirm the opposite changes of Aβ42 levels in CSF and plasma for AD, we assayed the levels of Aβ42 in plasma of subjects with known CSF Aβ42 levels. In total 43 controls and 63 AD patients were selected at two sites: the VU University Medical Center (n = 55) and Sahlgrenska University Hospital (n = 51). IMR and ELISA were applied to assay Aβ42 in plasma and CSF, respectively. We found a moderately negative correlation between plasma and CSF Aβ42 levels in AD patients (r = -0.352), and a weakly positive correlation in controls (r = 0.186). These findings further corroborate that there are opposite changes of Aβ42 levels in CSF and plasma in AD. The possible causes for the negative correlation are discussed by taken assay technologies, Aβ42 transport from brain to peripheral blood, and sample matrix into account.

Recent studies show that fibrinogen plays a role in the pathogenesis of Alzheimer’s disease (AD), which may be crucial to neurovascular damage and cognitive impairment. However, there are few clinical studies on the relationship between fibrinogen and AD. 59 11C-PiB-PET diagnosed AD patients and 76 age- and gender-matched cognitively normal controls were included to analyze the correlation between plasma β-amyloid (Aβ) and tau levels with fibrinogen levels. 35 AD patients and 76 controls with cerebrospinal fluid (CSF) samples were included to further analyze the correlation between CSF Aβ and tau levels with fibrinogen levels. In AD patients, plasma fibrinogen levels were positively correlated with plasma Aβ40 and Aβ42 levels, and negatively correlated with CSF Aβ42 levels. Besides, fibrinogen levels were positively correlated with CSF total tau (t-tau), and phosphorylated tau-181 (p-tau) levels and positively correlated with the indicators of Aβ deposition in the brain, such as t-tau/Aβ42, p-tau/Aβ42 levels. In normal people, fibrinogen levels lack correlation with Aβ and tau levels in plasma and CSF. This study suggests that plasma fibrinogen levels are positively correlated with Aβ levels in the plasma and brain in AD patients. Fibrinogen may be involved in the pathogenesis of AD.

Amyloid-β42 (Aβ42) is associated with plaque formation in the brain of patients with Alzheimer's disease (AD). Studies have suggested the potential utility of plasma Aβ42 levels in the diagnosis, and in longitudinal study of AD pathology. Conventional ELISAs are used to measure Aβ42 levels in plasma but are not sensitive enough to quantitate low levels. Although ultrasensitive assays like single molecule array or immunoprecipitation-mass spectrometry have been developed to quantitate plasma Aβ42 levels, the high cost of instruments and reagents limit their use. We hypothesized that a sensitive and cost-effective chemiluminescence (CL) immunoassay could be developed to detect low Aβ42 levels in human plasma. We developed a sandwich ELISA using high affinity rabbit monoclonal antibody specific to Aβ42. The sensitivity of the assay was increased using CL substrate to quantitate low levels of Aβ42 in plasma. We examined the levels in plasma from 13 AD, 25 Down syndrome (DS), and 50 elderly controls. The measurement range of the assay was 0.25 to 500 pg/ml. The limit of detection was 1 pg/ml. All AD, DS, and 45 of 50 control plasma showed measurable Aβ42 levels. This assay detects low levels of Aβ42 in plasma and does not need any expensive equipment or reagents. It offers a preferred alternative to ultrasensitive assays. Since the antibodies, peptide, and substrate are commercially available, the assay is well suited for academic or diagnostic laboratories, and has a potential for the diagnosis of AD or in clinical trials.

Plasma amyloid-β oligomers level is a biomarker for Alzheimer’s disease diagnosis

Selective Reductions in Plasma Aβ 1-42 in Healthy Elderly Subjects During Longitudinal Follow-Up: A Preliminary Report

Alzheimer disease (AD) diagnosis is confirmed using a medley of modalities, such as the detection of amyloid-β (Aβ) neuritic plaques and neurofibrillary tangles with positron electron tomography (PET) or the appraisal of irregularities in cognitive function with examinations. Although these methods have been efficient in confirming AD pathology, the rising demand for earlier intervention during pathogenesis has led researchers to explore the diagnostic potential of fluid biomarkers in cerebrospinal fluid (CSF) and plasma. Since CSF sample collection is invasive and limited in quantity, biomarker detection in plasma has become more attractive and modern advancements in technology has permitted more efficient and accurate analysis of plasma biomolecules. In this study, we found that a composite of standard factors, Aβ40 and total tau levels in plasma, divided by the variation factor, plasma Aβ42 level, provide better correlation with amyloid neuroimaging and neuropsychological test results than a level comparison between total tau and Aβ42 in plasma. We collected EDTA-treated blood plasma samples of 53 subjects, of randomly selected 27 AD patients and 26 normal cognition (NC) individuals, who received amyloid-PET scans for plaque quantification, and measured plasma levels of Aβ40, Aβ42, and total tau with digital enzyme-linked immunosorbent assay (ELISA) in a blinded manner. There was difficulty distinguishing AD patients from controls when analyzing biomarkers independently. However, significant differentiation was observed between the two groups when comparing individual ratios of total-tau×Aβ40/Aβ42. Our results indicate that collectively comparing fluctuations of these fluid biomarkers could aid in monitoring AD pathogenesis.

To explore the neuroimage change in Parkinson's disease (PD) patients with cognitive impairments, this study investigated the correlation between plasma biomarkers and morphological brain changes in patients with normal cognition and mild cognitive impairment. The objective was to identify the potential target deposition regions of the plasma biomarkers and to search for the relevant early neuroimaging biomarkers on the basis of different cognitive domains. Structural brain MRI and diffusion weighted images were analyzed from 49 eligible PD participants (male/female: 27/22; mean age: 73.4 ± 8.5years) from a retrospective analysis. Plasma levels of α-synuclein, amyloid beta peptide, and total tau were collected. A comprehensive neuropsychological assessment of the general and specific cognitive domains was performed. Difference between PD patients with normal cognition and impairment was examined. Regression analysis was performed to evaluate the correlation between image-derived index and plasma biomarkers or neuropsychological assessments. Significant correlation was found between plasma Aβ-42 level and fractional anisotropy of the middle occipital, angular, and middle temporal gyri of the left brain, as well as plasma T-tau level and the surface area of the isthmus or the average thickness of the posterior part of right cingulate gyrus. Visuospatial and executive function is positively correlated with axial diffusivity in bilateral cingulate gyri. In nondemented PD patients, the target regions for plasma deposition might be located in the cingulate, middle occipital, angular, and middle temporal gyri. Changes from multiple brain regions can be correlated to the performance of different cognitive domains. Cognitive impairment in Parkinson's disease is primarily linked to biomarkers associated with Alzheimer's disease rather than those related to Parkinson's disease and resembles the frontal variant of Alzheimer's disease, which may guide management strategies for cognitive impairment in Parkinson's disease. • Fractional anisotropy, surface area, and thickness in the cingulate, middle occipital, angular, and middle temporal gyri can be significantly correlated with plasma Aβ-42 and T-tau level. • Axial diffusivity in the cingulate gyri was correlated with visuospatial and executive function. • The pattern of cognitive impairment in Parkinson's disease can be similar to the frontal variant than typical Alzheimer's disease.

Purpose Recent study shows that blood-derived amyloid-beta (Aβ) can induce cerebral amyloidosis and is involved in the pathogenesis of Alzheimer's disease (AD). The vast majority of blood Aβ is generated from platelet. Whether blood Aβ levels are associated with the count of platelets remains unknown. Methods 58 clinically diagnosed AD patients, 18 11C-PIB-PET diagnosed AD patients, and 61 age- and gender-matched cognitively normal controls were included to analyze the correlation of plasma Aβ levels with platelet count. 13 AD patients and 40 controls with cerebrospinal fluid (CSF) samples were included to further analyze the correlation of CSF Aβ levels with platelet count. Aβ40 and Aβ42 levels in plasma and CSF were measured by ELISA kits. Results The plasma Aβ42 level was positively correlated with platelet count in both AD patients and control group, especially in AD patients with positive PIB-PET, while there was no correlation as to Aβ40. The CSF Aβ levels also had no significant correlation with platelet count. Conclusion It suggests that platelets may be involved in the pathogenesis of AD and become a potential peripheral biomarker for AD.

The low density lipoprotein receptor-related protein 1 (LRP1 gene) is a candidate gene for Alzheimer's disease (AD), because it is a ligand for proteins involved in AD pathogenesis, such as apolipoprotein E (APOE), alpha2-macroglobulin (A2M), amyloid precursor protein (APP), and is located on chromosome 12, within a region linked with AD. An association between a silent polymorphism (C/T) in exon 3 and late onset AD has been reported, with an increased frequency of the C allele, although with conflicting results. We examined this polymorphism in a cohort of 166 sporadic AD patients and 225 sex- and age-matched nondemented controls from Southern Italy. No statistically significant differences were found in LRP1 genotype and allele frequencies between the whole AD sample and controls, nor in early- and late-onset subsets of AD patients. No statistically significant differences in frequencies between LRP1 alleles and AD among APOE allele, age, or gender strata were found. Finally, comparing our results with the findings from other European populations, the LRP1 C allele frequency showed a statistically significant decreasing trend from Northern to Southern regions of Europe, with a concomitant increase in LRP1 T allele frequency, but in AD patients only. Finally, in the AD sample, a decreasing geographical trend from North to South of Europe was found for LRP1 CC genotype, and an inverse trend for LRP1 CT genotype frequency. We suggest that these regional variations in LRP1 genotype and allele frequencies in AD could be related to the different patterns of association between this polymorphism and the disease in various European studies.

Introduction We determined whether slow wave sleep is associated with plasma levels of Aβ40, Aβ42, Aβ42/Aβ40, Tau, tau/Aβ42 and NfL and whether this relationship differed between Blacks/African-Americans and non-Hispanic Whites. Methods This was a cross-sectional analysis of baseline data from 171 community-dwelling cognitively normal older-adults, participating in ongoing NYU studies on memory, sleep and aging. Non-rapid eye movement sleep (NREM) slow wave sleep (SWS) duration was calculated from 2 nights of in-lab NPSGs. Plasma Aβ40, Aβ42, Tau and NfL were determined using single molecule array (SIMOA). Associations of NREM SWS duration and plasma AD biomarker levels were assessed using adjusted generalized linear models and Pearson correlation analysis after data normalization. Analyses were adjusted for age, sex, BMI, race, and education. Results Of the 171 subjects (128 non-Hispanic Whites and 43 Blacks/African-Americans), 112 (65.5%) were females, and mean (SD) age was 68.6 (6.6) years, BMI was 27.6 (6.1) kg/m**2, and education was 16.9 (2.1). There were no racial differences in age, sex, BMI, NREM SWS and AHI4%. Compared to non-Hispanic Whites, Blacks/African-Americans had significantly lower years of education (14.2 vs. 17.2, p <.01), plasma Aβ40 (248.3 vs. 262.5 pg/ml) and NfL levels (11.4 vs. 15.2 pg/ml) p<.05 for both. There were no significant racial differences in levels of plasma Aβ42, Aβ42/Aβ40, Tau, Tau/Aβ40 and Tau/Aβ42 (p>.05 for all). NREM SWS duration was not associated with plasma Aβ42, Aβ40 or tau in the overall sample (p>.05 for all). However, in non-Hispanic Whites, NREM SWS negatively correlated with plasma Aβ42 (r=-0.28, p<=0.05), plasma Aβ40 (r=-0.087, p=0.72), though not significant, and plasma Tau (r=-0.153, p=0.27), though not significant. In Black/African-Americans, NREM SWS positively correlated with plasma Aβ42 (r=0.48, p=0.05), plasma Aβ40 levels (r=0.32, p=0.04), and plasma Tau levels (r=0.52, p=0.04). NREM SWS was not associated with plasma tau/Aβ42, plasma tau/Aβ40 or plasma NfL in the overall sample and across racial subgroups. Conclusion Race-specific divergent associations between NREM SWS and plasma Aβ42, Aβ40 & Tau may suggest differences in SDOH factors and mechanisms that could influence sleep and AD-risk in older-adults. Support (if any) AASMBTS#231-BS-20, NIAK23AG068534A, AARG-D- 21-848397, BFFA2022033S

BackgroundWe studied whether plasma levels of Aβ40, Aβ42, Aβ42/Aβ40, Tau, tau/Aβ42 and NfL are associated with slow wave sleep, and if this association varied within non‐Hispanic Whites and Blacks/African‐Americans.MethodThis was a cross‐sectional analysis of baseline data from 171 cognitively normal older‐adults, volunteering in active NYU studies on memory and sleep. Plasma Aβ40, Aβ42, Tau and NfL were measured using single molecule array (SIMOA). Non‐rapid eye movement sleep (NREM) slow wave sleep (SWS) duration was assessed from 2 nights of in‐lab NPSGs. Associations of NREM SWS duration and plasma AD biomarker levels were examined by applying adjusted generalized linear models and Pearson correlation analysis after data normalization. Analyses were adjusted for age, sex, BMI, race, and education.ResultOf the 171 subjects (128 Whites and 43 Blacks), 112 (65.5%) were females, and mean (SD) age was 68.6 (6.6) years, BMI was 27.6 (6.1) kg/m**2, and education was 16.9 (2.1). There were no racial differences in age, sex, and BMI, SWS and AHI4%. In comparison to whites, blacks had significantly lower years of education (14.2 vs. 17.2, p <.01). Black/African‐American subjects had significantly lower plasma Aβ40 (248.3 vs. 262.5 pg/ml) and NfL levels (11.4 vs. 15.2 pg/ml). p<.05 for both. There were no significant racial differences in levels of plasma Aβ42, Aβ42/Aβ40, Tau, Tau/Aβ40 and Tau/Aβ42. NREM SWS duration was not associated with plasma Aβ42, Aβ40 or tau in the overall sample. However, in Whites, SWS negatively correlated with plasma Aβ42 (r = ‐0.28, p< = 0.05). In Black/African‐Americans, SWS positively correlated with plasma Aβ42 (r = 0.48, p = 0.05). In Whites, SWS negatively correlated with plasma Aβ40 (r = ‐0.087, p = 0.72), though not significant. In Black/African‐Americans, SWS positively correlated with plasma Aβ40 levels (r = 0.32, p = 0.04). In Whites, SWS negatively correlated with plasma Tau (r = ‐0.153, p = 0.27), though not significant. In Black/African‐Americans, SWS positively correlated with plasma Tau levels (r = 0.52, p = 0.04). NREM SWS was not associated with plasma tau/Aβ42, plasma tau/Aβ40 or plasma NfL in the overall sample and across racial‐subgroups.ConclusionRace‐specific relationships between NREM SWS and plasma Aβ42, Aβ40 & Tau might propose differences in SDOH mechanisms that may affect sleep and AD‐risk in older‐adults.

BackgroundAggregatable amyloid β-peptide (Aβ) and non-aggregatable p3-Alcα are metabolic products of the γ-secretase cleavage of amyloid β-protein precursor (APP) and Alcadeinα (Alcα), respectively. Familial AD (FAD) -linked mutations in the presenilin 1 or 2 (PS1 or PS2) component of γ-secretase can cause alternative intramembranous processing of APP and Alcα, leading to a coordinated generation of variants of both Aβ and p3-Alcα. Variant Alcα peptides have been observed in the cerebrospinal fluid (CSF) of patients with mild cognitive impairment and sporadic Alzheimer's disease (AD). Since, like APP, Alcα is largely expressed in brain, one might predict that alternative processing of Alcα would be reflected in body fluids of some AD patients. These patients with misprocessing of multiple γ-secretase substrates might define an endophenotype of p3-Alcα, in whom AD is due either to dysfunction of γ-secretase or to a disorder of the clearance of hydrophobic peptides such as those derived from transmembrane domains.ResultsWe developed a simple procedure for extraction of p3-Alcα from plasma and for analyzing this extract in a sensitive, p3-Alcα-specific sandwich enzyme-linked immunosorbent assay (ELISA) system. Plasma p3-Alcα levels and Aβ40 levels were examined in sporadic AD subjects from two independent Japanese cohorts. In some of these patients, levels of plasma p3-Alcα were significantly higher, and were accompanied by parallel changes in Aβ40 levels. This AD-related difference was more marked in female subjects, but this phenomenon was not observed in subjects with frontotemporal lobar degeneration (FTLD).ConclusionReagents and procedures have been established that enable extraction of p3-Alcα from plasma and for quantification of plasma p3-Alcα levels by ELISA. Some populations of AD subjects apparently show increased levels of both p3-Alcα and Aβ40. Quantification of p3-Alcα level may be useful as a readily accessible biomarker for a population of sporadic AD patients in which disease pathogenesis is associated with either dysfunction of γ-secretase or with a disorder of the clearance of transmembrane domain-derived peptides.

Plasma amyloid-β (Aβ) levels are increasingly studied as a potential, accessible marker of cognitive impairment and dementia. The most common plasma Aβ isoforms, i.e., Aβ1-40 and Aβ1-42 have been linked with risk of Alzheimer's disease. However, it remains under-explored whether plasma Aβ levels including novel Aβ1-38 relate to vascular brain disease and cognition in a preclinical-phase of dementiaObjective:To examine the association of plasma Aβ levels (i.e., Aβ1-38, Aβ1-40, and Aβ1-42) with markers of cerebral small vessel disease (SVD) and cognition in a large population-based setting. We analyzed plasma Aβ1 levels in 1201 subjects from two independent cohorts of the Rotterdam Study. Markers of SVD [lacunes, white matter hyperintensity (WMH) volume] were assessed on brain MRI (1.5T). Cognition was assessed by a detailed neuropsychological battery. In each cohort, the association of Aβ levels with SVD and cognition was performed using regression models. Estimates were then pooled across cohorts using inverse variance meta-analysis with fixed effects. Higher levels of plasma Aβ1-38, Aβ1-40, Aβ1-42, and Aβ1-40/ Aβ1-42 ratio were associated with increasing lacunar and microbleeds counts. Moreover, higher levels of Aβ1-40 and Aβ1-40/ Aβ1-42 were significantly associated with larger WMH volumes. With regard to cognition, a higher level of Aβ1-38 Aβ1-40 and Aβ1-40/ Aβ1-42 was related to worse performance on cognitive test specifically in memory domain. Higher plasma levels of Aβ levels are associated with subclinical markers of vascular disease and poorer memory. Plasma Aβ levels thus mark the presence of vascular brain pathology.

The potential similarity between the brain pathology of idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer disease (AD) is intriguing and thus further studies focusing on the underlying molecular mechanisms may offer valuable information for differential diagnostics and the development of treatments for iNPH. Here, we investigated β- and γ-secretase activities in relation to amyloid-β (Aβ) pathology in the brain tissue samples collected from iNPH and AD patients. β- and γ-secretase activities were measured from the frontal cortical biopsies of 26 patients with suspected iNPH as well as post-mortem tissue samples from the inferior temporal cortex of 74 AD patients and eight subjects without neurofibrillary pathology. In iNPH samples with detectable Aβ plaques, γ-secretase activity was significantly increased (∼1.6-fold) when compared to iNPH samples without Aβ plaques (p = 0.009). In the AD samples, statistically significant differences in the γ-secretase activity were not observed with respect to disease severity (mild, moderate and severe AD according to neurofibrillary pathology). Conversely, β-secretase activity was unaltered in iNPH samples with or without Aβ plaques, while it was significantly increased in relation to disease severity in the AD patients. These results show for the first time increased γ-secretase but not β-secretase activity in the biopsy samples from the frontal cortex of iNPH patients with AD-like Aβ pathology. Conversely, the opposite was observed in these secretase activities in AD patients with respect to neurofibrillary pathology. Despite the resemblances in the Aβ pathology, iNPH and AD patients appear to have marked differences in the cellular mechanisms responsible for the production of Aβ.

Oligomeric forms of amyloid-β (Aβ), tau, and TDP-43 play important roles in Alzheimer's disease (AD), and therefore are promising biomarkers. We previously generated single chain antibody fragments (scFvs) that selectively bind disease-related variants of these proteins including A4, C6T, and E1, which bind different oligomeric Aβ variants; D11C, which binds oligomeric tau; and AD-TDP1 and AD-TDP2, which bind disease related TDP-43 variants. To determine the utility of these disease-related variants as early biomarkers, we first analyzed 11 human sera samples obtained ∼2 years prior to an initial mild cognitive impairment (MCI) diagnosis. While the subsequent diagnoses for the cases covered several different conditions, all samples had elevated protein variant levels relative to the plasma controls although with different individual biomarker profiles. We then analyzed a set of longitudinal human plasma samples from four AD (encompassing time points prior to MCI diagnosis and continuing until after conversion to AD) and two control cases. Pre-MCI samples were characterized by high TDP-43 variant levels, MCI samples by high Aβ variant levels, and AD samples by high Aβ and tau variant levels. Sample time points ranged from ∼7 years pre-MCI to ∼9 years after AD conversion. Bivariate correlations showed a negative correlation with TDP-43 levels and positive correlations with cumulative Aβ and oligomeric tau levels indicating an increase in neurodegenerative processes with time in AD. Detection of disease related protein variants not only readily selects AD cases from controls, but also stages progression of AD and holds promise for a pre-symptomatic blood-based biomarker profile for AD.