Phosphorylated tau-Aβ42 ratio as a continuous trait for biomarker discovery for early-stage Alzheimer's disease in multiplex immunoassay panels of cerebrospinal fluid

Neuronal fatty acid-binding protein enhances autophagy and suppresses amyloid-β pathology in a Drosophila model of Alzheimer's disease

Fatty acid-binding proteins (FABPs) are small cytoplasmic proteins involved in intracellular lipid transport and bind free fatty acids, cholesterol, and retinoids. FABP3, the major neuronal FABP in the adult brain, is upregulated in the CSF of patients with Alzheimer's disease (AD). However, the precise role of neuronal FABPs in AD pathogenesis remains unclear. This study investigates the contribution of fabp, the Drosophila homolog of FABP3 and FABP7, to amyloid β (Aβ) pathology using a Drosophila model. Neuronal knockdown of fabp shortened the lifespan of flies and increased age-related protein aggregates in the brain. In an AD model, fabp knockdown in neurons increased Aβ accumulation and Aβ-induced neurodegeneration, whereas fabp overexpression ameliorated Aβ pathology. Notably, fabp overexpression stimulated autophagy, which was inhibited by the knockdown of Eip75B, the Drosophila homolog of the peroxisome proliferator-activated receptor (PPAR). The PPAR activator rosiglitazone restored autophagy impaired by fabp knockdown and reduced fabp knockdown-induced increased Aβ aggregation and cell death. Furthermore, knockdown of either fabp or Eip75B in the wing imaginal disc or adult fly brain reduced the expression of Atg6 and Atg8a. Additionally, treatment of the fabp knockdown AD model flies with polyunsaturated fatty acids, such as docosahexaenoic acid or linoleic acid, partially alleviated cell death in the developing eye, restored impaired autophagy flux, reduced Aβ aggregation, and attenuated Aβ-induced cell death. Our results suggest that Drosophila fabp plays an important role in maintaining protein homeostasis during aging and protects neurons from Aβ-induced cell death by enhancing autophagy through the PPAR pathway. These findings highlight the potential importance of neuronal FABP function in AD pathogenesis.

Exploring the Dynamic Changes of Brain Lipids, Lipid Rafts, and Lipid Droplets in Aging and Alzheimer's Disease

Aging induces complex changes in the lipid profiles across different areas of the brain. These changes can affect the function of brain cells and may contribute to neurodegenerative diseases such as Alzheimer's disease. Research shows that while the overall lipid profile in the human brain remains quite steady throughout adulthood, specific changes occur with age, especially after the age of 50. These changes include a slow decline in total lipid content and shifts in the composition of fatty acids, particularly in glycerophospholipids and cholesterol levels, which can vary depending on the brain region. Lipid rafts play a crucial role in maintaining membrane integrity and facilitating cellular signaling. In the context of Alzheimer's disease, changes in the composition of lipid rafts have been associated with the development of the disease. For example, alterations in lipid raft composition can lead to increased accumulation of amyloid β (Aβ) peptides, contributing to neurotoxic effects. Lipid droplets store neutral lipids and are key for cellular energy metabolism. As organisms age, the dynamics of lipid droplets in the brain change, with evidence suggesting a decline in metabolic activity over time. This reduced activity may lead to an imbalance in lipid synthesis and mobilization, contributing to neurodegenerative processes. In model organisms like Drosophila, studies have shown that lipid metabolism in the brain can be influenced by diet and insulin signaling pathways, crucial for maintaining metabolic balance. The interplay between lipid metabolism, oxidative stress, and inflammation is critical in the context of aging and Alzheimer's disease. Lipid peroxidation, a consequence of oxidative stress, can lead to the formation of reactive aldehydes that further damage neurons. Inflammatory processes can also disrupt lipid metabolism, contributing to the pathology of AD. Consequently, the accumulation of oxidized lipids can affect lipid raft integrity, influencing signaling pathways involved in neuronal survival and function.

Cognivue Clarity characterizes mild cognitive impairment and Alzheimer's disease in biomarker confirmed cohorts in the Bio-Hermes Study

The Bio-Hermes Study was a cross-sectional observational study designed to develop a database of blood-based and digital biomarkers to improve detection of Alzheimer's disease (AD) and mild cognitive impairment (MCI). We examined the ability of Cognivue Clarity to (a) detect MCI and AD in clinical diagnostics groups, (b) determine the presence of amyloid, and (c) distinguish between biomarker-confirmed groups. Bio-Hermes enrolled 887 participants who completed both Cognivue Clarity and amyloid PET scans (388 Cognitively Normal, 282 MCI, 217 Probable AD). Cognivue Clarity differentiated between Cognitively Normal, MCI, and probable AD in clinical cohorts, amyloid positive from amyloid negative individuals, and True Controls from MCI due to AD and AD in biomarker-confirmed cohorts (all p < 0.001) with large effect sizes. Cognivue Clarity correlated with amyloid PET and plasma amyloid and pTau (all p < 0.001). In biomarker confirmed groups, Cognivue Clarity had a positive likelihood ratio of 2.17, a negative likelihood ratio of 0.29, and a diagnostic odds ratio of 7.48. Cognivue Clarity detected cognitive impairment and differentiated between both clinically and biomarker defined MCI and AD groups. The use of Cognivue Clarity could assist with identification of MCI-AD or AD for inclusion into current treatment protocols or for enriching recruitment into clinical trials. Trial registration ClinicalTrials.gov (NCT04733989).

Misfolded alpha synuclein co-occurrence with Alzheimer's disease proteinopathy

INTRODUCTION

Multi-etiology dementia necessitates in-vivo markers of copathologies including misfolded α -synuclein (syn). We measured misfolded syn aggregates (syn-seeds) via qualitative seed amplifcation assays (synSAA) and examined relationships with markers of Alzheimer's disease (AD).

METHODS

Cerebrospinal fluid (CSF) was obtained from 420 participants in two Wisconsin AD risk cohorts (35% male; 91% cognitively unimpaired; mean (SD) age, 65.42 (7.78) years; education, 16.17 (2.23) years). synSAA results were compared to phosphorylated tau (T), beta amyloid (A), and clinical outcomes. Longitudinal cognition was modeled with mixed effects.

RESULTS

Syn positivity (synSAA+) co-occurred with T (in synSAA+ vs synSAA-, 36% vs 20% T+; p=0.011) and with cognitive impairment (10% vs 7% MCI; 10% vs 0% dementia; p=0.00050). synSAA+ participants' cognitive performance declined ∼40% faster than synSAA-for Digit Symbol, but not other tests.

DISCUSSION

Findings support prevalent syn copathology in a mostly-unimpaired AD risk cohort. Future work will explore relationships with disease progression.

Elevated CSF angiopoietin-2 correlates with blood-brain barrier leakiness and markers of neuronal injury in early Alzheimer's disease

Breakdown of the neurovascular unit is associated with blood-brain barrier (BBB) leakiness contributing to cognitive decline and disease pathology in the early stages of Alzheimer's disease (AD). Vascular stability depends on angiopoietin-1 (ANGPT-1) signalling, antagonised by angiopoietin-2 (ANGPT-2) expressed upon endothelial injury. We examined the relationship between CSF ANGPT-2 and CSF markers of BBB leakiness and core AD biomarkers across three independent cohorts: (i) 31 AD patients and 33 healthy controls grouped according to their biomarker profile (i.e., AD cases t-tau > 400 pg/mL, p-tau > 60 pg/mL and Aβ42 < 550 pg/mL); (ii) 121 participants in the Wisconsin Registry for Alzheimer's Prevention or Wisconsin Alzheimer's Disease Research study (84 participants cognitively unimpaired (CU) enriched for a parental history of AD, 20 participants with mild cognitive impairment (MCI), and 17 with AD); (iii) a neurologically normal cohort aged 23-78 years with paired CSF and serum samples. CSF ANGPT-2, sPDGFRβ, albumin and fibrinogen levels were measured by sandwich ELISA. In cohort (i), CSF ANGPT-2 was elevated in AD and correlated with CSF t-tau and p-tau181 but not Aβ42. ANGPT-2 also correlated positively with CSF sPDGFRβ and fibrinogen - markers of pericyte injury and BBB leakiness. In cohort (ii), CSF ANGPT-2 was highest in MCI and correlated with CSF albumin in the CU and MCI cohorts but not in AD. CSF ANGPT-2 also correlated with CSF t-tau and p-tau and with markers of neuronal injury (neurogranin and α-synuclein) and neuroinflammation (GFAP and YKL-40). In cohort (iii), CSF ANGPT-2 correlated strongly with the CSF/serum albumin ratio. Serum ANGPT-2 showed non-significant positive associations with CSF ANGPT-2 and the CSF/serum albumin ratio. Together, these data indicate that CSF and possibly serum ANGPT-2 is associated with BBB leakiness in early AD and is closely related to tau pathology and neuronal injury. The utility of serum ANGPT-2 as a biomarker of BBB damage in AD requires further study.

Cerebrospinal fluid biomarker profiling of diverse pathophysiological domains in Alzheimer's disease

INTRODUCTION

While Alzheimer's disease (AD) is defined by amyloid-β plaques and tau tangles in the brain, it is evident that many other pathophysiological processes such as inflammation, neurovascular dysfunction, oxidative stress, and metabolic derangements also contribute to the disease process and that varying contributions of these pathways may reflect the heterogeneity of AD. Here, we used a previously validated panel of cerebrospinal fluid (CSF) biomarkers to explore the degree to which different pathophysiological domains are dysregulated in AD and how they relate to each other.

METHODS

Twenty-five CSF biomarkers were analyzed in individuals with a clinical diagnosis of AD verified by positive CSF AD biomarkers (AD, n = 54) and cognitively unimpaired controls negative for CSF AD biomarkers (CU-N, n = 26) using commercial single- and multi-plex immunoassays.

RESULTS

We noted that while AD was associated with increased levels of only three biomarkers (MMP-10, FABP3, and 8OHdG) on a group level, half of all AD participants had increased levels of biomarkers belonging to at least two pathophysiological domains reflecting the diversity in AD. LASSO modeling showed that a panel of FABP3, 24OHC, MMP-10, MMP-2, and 8OHdG constituted the most relevant and minimally correlated set of variables differentiating AD from CU-N. Interestingly, factor analysis showed that two markers of metabolism and oxidative stress (24OHC and 8OHdG) contributed independent information separate from MMP-10 and FABP3 suggestive of two independent pathophysiological pathways in AD, one reflecting neurodegeneration and vascular pathology, and the other associated with metabolism and oxidative stress.

DISCUSSION

Better understanding of the heterogeneity among individuals with AD and the different contributions of pathophysiological processes besides amyloid-β and tau will be crucial for optimizing personalized treatment strategies.

Highlights

A panel of 25 highly validated biomarker assays were measured in CSF.MMP10, FABP3, and 8OHdG were increased in AD in univariate analysis.Many individuals with AD had increased levels of more than one biomarker.Markers of metabolism and oxidative stress contributed to an AD multianalyte profile.Assessing multiple biomarker domains is important to understand disease heterogeneity.

Neuropathology-based APOE genetic risk score better quantifies Alzheimer's risk

INTRODUCTION

Apolipoprotein E (APOE) ε4-carrier status or ε4 allele count are included in analyses to account for the APOE genetic effect on Alzheimer's disease (AD); however, this does not account for protective effects of APOE ε2 or heterogeneous effect of ε2, ε3, and ε4 haplotypes.

METHODS

We leveraged results from an autopsy-confirmed AD study to generate a weighted risk score for APOE (APOE-npscore). We regressed cerebrospinal fluid (CSF) amyloid and tau biomarkers on APOE variables from the Wisconsin Registry for Alzheimer's Prevention (WRAP), Wisconsin Alzheimer's Disease Research Center (WADRC), and Alzheimer's Disease Neuroimaging Initiative (ADNI).

RESULTS

The APOE-npscore explained more variance and provided a better model fit for all three CSF measures than APOE ε4-carrier status and ε4 allele count. These findings were replicated in ADNI and observed in subsets of cognitively unimpaired (CU) participants.

DISCUSSION

The APOE-npscore reflects the genetic effect on neuropathology and provides an improved method to account for APOE in AD-related analyses.

Charting the Next Road Map for CSF Biomarkers in Alzheimer's Disease and Related Dementias

Clinical prediction of underlying pathologic substrates in people with Alzheimer's disease (AD) dementia or related dementia syndromes (ADRD) has limited accuracy. Etiologic biomarkers - including cerebrospinal fluid (CSF) levels of AD proteins and cerebral amyloid PET imaging - have greatly modernized disease-modifying clinical trials in AD, but their integration into medical practice has been slow. Beyond core CSF AD biomarkers (including beta-amyloid 1-42, total tau, and tau phosphorylated at threonine 181), novel biomarkers have been interrogated in single- and multi-centered studies with uneven rigor. Here, we review early expectations for ideal AD/ADRD biomarkers, assess these goals' future applicability, and propose study designs and performance thresholds for meeting these ideals with a focus on CSF biomarkers. We further propose three new characteristics: equity (oversampling of diverse populations in the design and testing of biomarkers), access (reasonable availability to 80% of people at risk for disease, along with pre- and post-biomarker processes), and reliability (thorough evaluation of pre-analytical and analytical factors influencing measurements and performance). Finally, we urge biomarker scientists to balance the desire and evidence for a biomarker to reflect its namesake function, indulge data- as well as theory-driven associations, re-visit the subset of rigorously measured CSF biomarkers in large datasets (such as Alzheimer's disease neuroimaging initiative), and resist the temptation to favor ease over fail-safe in the development phase. This shift from discovery to application, and from suspended disbelief to cogent ingenuity, should allow the AD/ADRD biomarker field to live up to its billing during the next phase of neurodegenerative disease research.

Vascular endothelial growth factor isoforms differentially protect neurons against neurotoxic events associated with Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia, the chronic and progressive deterioration of memory and cognitive abilities. AD can be pathologically characterised by neuritic plaques and neurofibrillary tangles, formed by the aberrant aggregation of β-amyloid and tau proteins, respectively. We tested the hypothesis that VEGF isoforms VEGF-A₁₆₅a and VEGF-A₁₆₅b, produced by differential splice site selection in exon 8, could differentially protect neurons from neurotoxicities induced by β-amyloid and tau proteins, and that controlling expression of splicing factor kinase activity could have protective effects on AD-related neurotoxicity in vitro. Using oxidative stress, β-amyloid, and tau hyperphosphorylation models, we investigated the effect of VEGF-A splicing isoforms, previously established to be neurotrophic agents, as well as small molecule kinase inhibitors, which selectively inhibit SRPK1, the major regulator of VEGF splicing. While both VEGF-A₁₆₅a and VEGF-A₁₆₅b isoforms were protective against AD-related neurotoxicity, measured by increased metabolic activity and neurite outgrowth, VEGF-A₁₆₅a was able to enhance neurite outgrowth but VEGF-A₁₆₅b did not. In contrast, VEGF-A₁₆₅b was more effective than VEGF-A₁₆₅a in preventing neurite "dieback" in a tau hyperphosphorylation model. SRPK1 inhibition was found to significantly protect against neurite "dieback" through shifting AS of VEGFA towards the VEGF-A₁₆₅b isoform. These results indicate that controlling the activities of the two different isoforms could have therapeutic potential in Alzheimer's disease, but their effect may depend on the predominant mechanism of the neurotoxicity-tau or β-amyloid.

Resting heart rate (variability) and cognition relationships reveal cognitively healthy individuals with pathological amyloid/tau ratio

Introduction

Resting heart rate (HR) and heart rate variability (HRV) have been linked with cognition in the general population and in older individuals. The knowledge of this aspect of heart-brain relationship is relatively absent in older individuals with early Alzheimer's disease (AD) pathology. This study explores relationships of the HR, HRV, and cognition in cognitively healthy individuals with pathological amyloid/tau ratio (CH-PATs) in cerebral spinal fluid (CSF) compared to those with normal ratio (CH-NATs).

Methods

We examined therelationshipsbetween1) resting HR and Mini-Mental State Examination (MMSE); 2) resting HR and brain processing during Stroop interference; and 3) resting vagally mediated HRV (vmHRV) and task switching performance.

Results

Our studies showed that compared to CH-NATs, those CH-PATs with higher resting HR presented with lower MMSE, and less brain activation during interference processing. In addition, resting vmHRV was significantly correlated with task switching accuracy in CH-NATs, but not in CH-PATs.

Discussion

Thesethreedifferenttestsindicatedysfunctionalheart-brainconnections in CH-PATs, suggesting a potential cardio-cerebral dysfunctional integration.

CSF Biomarkers in the Early Diagnosis of Mild Cognitive Impairment and Alzheimer's Disease

Alzheimer's disease (AD) is a rapidly growing disease that affects millions of people worldwide, therefore there is an urgent need for its early diagnosis and treatment. A huge amount of research studies are performed on possible accurate and reliable diagnostic biomarkers of AD. Due to its direct contact with extracellular space of the brain, cerebrospinal fluid (CSF) is the most useful biological fluid reflecting molecular events in the brain. Proteins and molecules that reflect the pathogenesis of the disease, e.g., neurodegeneration, accumulation of Abeta, hyperphosphorylation of tau protein and apoptosis may be used as biomarkers. The aim of the current manuscript is to present the most commonly used CSF biomarkers for AD as well as novel biomarkers. Three CSF biomarkers, namely total tau, phospho-tau and Abeta42, are believed to have the highest diagnostic accuracy for early AD diagnosis and the ability to predict AD development in mild cognitive impairment (MCI) patients. Moreover, other biomarkers such as soluble amyloid precursor protein (APP), apoptotic proteins, secretases and inflammatory and oxidation markers are believed to have increased future prospects.

Plasma p-tau181/Aβ1-42 ratio predicts Aβ-PET status and correlates with CSF-p-tau181/Aβ1-42 and future cognitive decline

Background

In Alzheimer's disease (AD), plasma amyloid beta (Aβ)1-42 and phosphorylated tau (p-tau) predict high amyloid status from Aβ positron emission tomography (PET); however, the extent to which combination of these plasma assays can predict remains unknown.

Methods

Prototype Simoa assays were used to measure plasma samples from participants who were either cognitively normal (CN) or had mild cognitive impairment (MCI)/AD in the Australian Imaging, Biomarkers and Lifestyle (AIBL) study.

Results

The p-tau181/Aβ1-42 ratio showed the best prediction of Aβ-PET across all participants (area under the curve [AUC] = 0.905, 95% confidence interval [CI]: 0.86-0.95) and in CN (AUC = 0.873; 0.80-0.94), and symptomatic (AUC = 0.908; 0.82-1.00) adults. Plasma p-tau181/Aβ1-42 ratio correlated with cerebrospinal fluid (CSF) p-tau181 (Elecsys, Spearman's ρ = 0.74, P < 0.0001) and predicted abnormal CSF Aβ (AUC = 0.816; 0.74-0.89). The p-tau181/Aβ1-42 ratio also predicted future rates of cognitive decline assessed by AIBL Preclinical Alzheimer Cognitive Composite or Clinical Dementia Rating Sum of Boxes (P < 0.0001).

Discussion

Plasma p-tau181/Aβ1-42 ratio predicted both Aβ-PET status and cognitive decline, demonstrating potential as both a diagnostic aid and as a screening and prognostic assay for preclinical AD trials.

Association between air pollution and CSF sTREM2 in cognitively normal older adults: The CABLE study

Objectives

Ambient air pollution aggravates the process of Alzheimer's disease (AD) pathology. Currently, the exact inflammatory mechanisms underlying these links from clinical research remain largely unclear.

Methods

This study included 1,131 cognitively intact individuals from the Chinese Alzheimer's Biomarker and LifestylE database with data provided on cerebrospinal fluid (CSF) AD biomarkers (amyloid beta‐peptide 42 [Aβ42], total tau [t‐tau], and phosphorylated tau [p‐tau]), neuroinflammatory (CSF sTREM2), and systemic inflammatory markers (high sensitivity C‐reactive protein and peripheral immune cells). The 2‐year averaged levels of ambient fine particulate matter with diameter <2.5 μm (PM_2.5), nitrogen dioxide (NO₂), and ozone (O₃) were estimated at each participant's residence. Multiple‐adjusted models were approached to detect associations of air pollution with inflammatory markers and AD‐related proteins.

Results

Ambient 2‐year averaged exposure of PM_2.5 was associated with changes of neuroinflammatory markers, that is, CSF sTREM2 (β = −0.116, p = 0.0002). Similar results were found for O₃ exposure among the elderly (β = −0.111, p = 0.0280) or urban population (β = −0.090, p = 0.0144). No significant evidence supported NO₂ related to CSF sTREM2. For potentially causal associations with accumulated AD pathologies, the total effects of PM_2.5 on CSF amyloid‐related protein (CSF Aβ42 and p‐tau/Aβ42) were partly mediated by CSF sTREM2, with proportions of 14.22% and 47.15%, respectively. Additional analyses found inverse associations between peripheral inflammatory markers with PM_2.5 and NO₂, but a positive correlation with O₃.

Interpretation

These findings demonstrated a strong link between PM_2.5 exposure and microglial dysfunction. Furthermore, CSF sTREM2 as a key mediator modulated the influences of PM_2.5 exposure on AD amyloid pathologies.

Posttraumatic stress disorder symptom severity is associated with reduced Montreal Cognitive Assessment scores in a sample of Vietnam War Veterans

The goal of the present study was to examine associations between posttraumatic stress disorder (PTSD) symptom severity, the number of stressors experienced, and cognitive outcomes in a sample of U.S. Vietnam War Veterans (N = 274). Adults between 60 and 85 years of age completed a Vietnam Veterans Alzheimer's Disease Neuroimaging Initiative Project visit. A modified version of the Life Stressor Checklist-Revised (LSC-R) was used to assess the number of stressful experiences participants experienced, current PTSD severity scores were measured via the Clinician-Administered PTSD Scale for DSM-IV (CAPS-IV), and cognition was assessed using the Montreal Cognitive Assessment (MoCA). Linear regressions were conducted to examine the effect of CAPS-IV and LSC-R scores on cognitive performance. Higher CAPS-IV scores were associated with worse cognitive outcomes on the MoCA, ΔF(1, 264) = 12.686, p < .001, R² = .142. In contrast, the number of reported stressful experiences was not associated with cognitive outcomes. After accounting for multiple comparisons, findings indicated that CAPS-IV severity scores were significantly associated with the MoCA memory index. In a sample of older Veterans, PTSD symptom severity, but not the number of reported stressors, was associated with poorer performance on a well-established cognitive function screening tool. Analyses of specific MoCA domains indicated that memory may be driving this association. These findings suggest that highly arousing stressors characteristic of PTSD, rather than stressful experiences more broadly, contribute to this association. Future work can use these findings to explore whether treating PTSD symptoms may help maintain cognitive function during the aging process.

Association of Long-term Exposure to Ambient Air Pollution With Cognitive Decline and Alzheimer's Disease-Related Amyloidosis

BACKGROUND

Air pollution induces neurotoxic reactions and may exert adverse effects on cognitive health. We aimed to investigate whether air pollutants accelerate cognitive decline and affect neurobiological signatures of Alzheimer's disease (AD).

METHODS

We used a population-based cohort from the Chinese Longitudinal Healthy Longevity Survey with 31,573 participants and a 10-year follow-up (5878 cognitively unimpaired individuals in Chinese Longitudinal Healthy Longevity Survey followed for 5.95 ± 2.87 years), and biomarker-based data from the Chinese Alzheimer's Biomarker and Lifestyle study including 1131 participants who underwent cerebrospinal fluid measurements of AD-related amyloid-β (Aβ) and tau proteins. Cognitive impairment was determined by education-corrected performance on the China-Modified Mini-Mental State Examination. Annual exposures to fine particulate matter (PM_2.5), ground-level ozone (O₃), and nitrogen dioxide (NO₂) were estimated at areas of residence. Exposures were aggregated as 2-year averages preceding enrollments using Cox proportional hazards or linear models.

RESULTS

Long-term exposure to PM_2.5 (per 20 μg/m³) increased the risk of cognitive impairment (hazard ratio, 1.100; 95% CI: 1.026-1.180), and similar associations were observed from separate cross-sectional analyses. Exposures to O₃ and NO₂ yielded elevated risk but with nonsignificant estimates. Individuals exposed to high PM_2.5 manifested increased amyloid burdens as reflected by cerebrospinal fluid-AD biomarkers. Moreover, PM_2.5 exposure-associated decline in global cognition was partly explained by amyloid pathology as measured by cerebrospinal fluid-Aβ₄₂/Aβ₄₀, P-tau/Aβ₄₂, and T-tau/Aβ₄₂, with mediation proportions ranging from 16.95% to 21.64%.

CONCLUSIONS

Long-term exposure to PM_2.5 contributed to the development of cognitive decline, which may be partly explained by brain amyloid accumulation indicative of increased AD risk.

The Correlations of Plasma Liver-Type Fatty Acid-Binding Protein with Amyloid-β and Tau Levels in Patients with Alzheimer’s Disease

Background: The dysregulation of lipid metabolism plays an important role in the pathogenesis of Alzheimer’s disease (AD). Liver-type fatty acid-binding protein (L-FABP, also known as FABP1) is critical for fatty acid transport and may be involved in AD. Objective: To investigate whether the FABP1 level is altered in patients with AD, and its associations with levels of amyloid-β (Aβ) and tau in the plasma and cerebrospinal fluid (CSF). Methods: A cross-sectional study was conducted in a Chinese cohort consisting of 39 cognitively normal controls and 47 patients with AD. The levels of FABP1 in plasma, and Aβ and tau in CSF, were measured by enzyme-linked immunosorbent assay (ELISA). A single-molecule array (SIMOA) was used to detect plasma Aβ levels. Results: The level of plasma FABP1 was significantly elevated in the AD group (p = 0.0109). Further analysis showed a positive correlation of FABP1 with CSF total tau (t-tau) and phosphorylated tau (p-tau) levels. Besides, plasma FABP1/Aβ 42 (AUC = 0.6794, p = 0.0071) and FABP1/t-tau (AUC = 0.7168, p = 0.0011) showed fair diagnostic efficacy for AD. When combined with other common AD biomarkers including plasma Aβ 42, Aβ 40, and t-tau, both FABP1/Aβ 42 and FABP1/t-tau showed better diagnostic efficacy than using these biomarkers alone. Among all AUC analyses, the combination of plasma FABP1/t-tau and Aβ 42 had the highest diagnostic value (AUC = 0.8075, p <  0.0001). Conclusion: These findings indicate that FABP1 may play a role in AD pathogenesis and be worthy of further investigation in the future.

sTREM2 mediates the associations of minimal depressive symptoms with amyloid pathology in prodromal Alzheimer's disease: The CABLE study

The effects of microglial activation on the associations between depression and Alzheimer's disease (AD) are still unclear. TREM2 gene plays a pivotal role in microglial activation, has been identified as a risk factor for AD. In this work, we aimed to assess the interrelationships of soluble TREM2 (sTREM2) level in cerebrospinal fluid (CSF), minimal depressive symptoms (MDSs), and CSF amyloid markers. The linear regression analyses were conducted on 796 cognitively unimpaired participants from the CABLE (Chinese Alzheimer's Biomarker and LifestylE) study. Causal mediation analyses with 10,000 bootstrapped iterations were used to test the mediation effects. In addition, similar statistical analyses were performed in subgroups stratified by sex, age, and APOE ε4 carrier status. In total subjects, MDSs were associated with lower CSF sTREM2 levels (p < 0.0001), lower CSF amyloid markers (p < 0.0001), and poorer cognitive performance (MMSE, p = 0.0014). The influence of MDSs on CSF amyloid markers was partially mediated by CSF sTREM2 (proportion from 2.91 to 32.58%, p < 0.0001). And we found that the sTREM2-amyloid pathway partially mediated the effects of MDSs on cognition. Of note, exploratory subgroup analyses showed that the above influences of CSF sTREM2 were pronounced in the APOE ε4 (-) group. These results suggest that early depression is associated with amyloid pathology, which might be partly mediated by microglial activation, especially in the absence of APOE ε4.

Alpha desynchronization during Stroop test unmasks cognitively healthy individuals with abnormal CSF Amyloid/Tau

Synaptic dysfunctions precede cognitive decline in Alzheimer's disease by decades, affect executive functions, and can be detected by quantitative electroencephalography (qEEG). We used quantitative electroencephalography combined with Stroop testing to identify changes of inhibitory controls in cognitively healthy individuals with an abnormal versus normal ratio of cerebrospinal fluid (CSF) amyloid/total-tau. We studied two groups of participants (60-94 years) with either normal (CH-NAT or controls, n = 20) or abnormal (CH-PAT, n = 21) CSF amyloid/tau ratio. We compared: alpha event-related desynchronization (ERD), alpha spectral entropy (SE), and their relationships with estimated cognitive reserve. CH-PATs had more negative occipital alpha ERD, and higher frontal and occipital alpha SE during low load congruent trials, indicating hyperactivity. CH-PATs demonstrated fewer frontal SE changes with higher load, incongruent Stroop testing. Correlations of alpha ERD with estimated cognitive reserve were significant in CH-PATs but not in CH-NATs. These results suggested compensatory hyperactivity in CH-PATs compared to CH-NATs. We did not find differences in alpha ERD comparisons with individual CSF amyloid(A), p-tau(T), total-tau(N) biomarkers.

Alzheimer's disease: a step closer to understanding type 3 diabetes in African Americans

Alzheimer's disease (AD) is the fourth leading cause of death in the United States and the most common cause of adult-onset dementia. Recent results suggest an increased prevalence and severity in African Americans compared to Caucasians. Our understanding of the potential mechanism(s) underlying this ethnicity difference is limited. We previously described ethnicity-related differences in levels of neurodegenerative proteins and cytokines/chemokines in the BA21 region of African Americans and Caucasians with AD. Here, similar multiplex assays were used to examine those endpoints in patient postmortem cerebrospinal fluid (CSF). Additionally, we measured levels of C-peptide, ghrelin, gastric inhibitory polypeptide (GIP), glucagon-like peptide-1 (GLP-1), glucagon, insulin, leptin, PAI-1, resistin, and visfatin using a human diabetes 10-plex assay. The cytokine and chemokine assays revealed that levels of 26 chemokines or cytokines differed significantly with ethnicity, and three of those were significantly associated with gender. The neurodegenerative disease panel indicated that levels of soluble RAGE were significantly elevated in African Americans compared to Caucasians. All measures in the diabetes disease panel assay were significantly elevated in African Americans: ghrelin, GIP, GLP-1, glucagon, insulin, and visfatin. Through peripheral sample analysis, these results provide further evidence that ethnicity is critically involved in the manifestation of AD.

Associations of Green Tea Consumption and Cerebrospinal Fluid Biomarkers of Alzheimer's Disease Pathology in Cognitively Intact Older Adults: The CABLE Study

BACKGROUND

Green tea has been widely recognized in ameliorating cognitive impairment and Alzheimer's disease (AD), especially the progression of cognitive dysfunction. But the underlying mechanism is still unclear.

OBJECTIVE

This study was designed to determine the role of green tea consumption in the association with cerebrospinal fluid (CSF) biomarkers of AD pathology and to ascertain whether specific population backgrounds showed the differences toward these relationships.

METHODS

Multivariate linear models analyzed the available data on CSF biomarkers and frequency of green tea consumption of 722 cognitively intact participants from the Chinese Alzheimer's Biomarker and LifestylE (CABLE) database, and we additionally detected the interaction effects of tea consumption with APOEɛ4 status and gender using a two-way analysis of covariance.

RESULTS

Frequent green tea consumption was associated with a decreased level of CSF total-tau protein (t-tau) (p = 0.041) but not with the levels of CSF amyloid-β 42 (Aβ42) and CSF phosphorylated tau. The more pronounced associations of green tea consumption with CSF t-tau (p = 0.007) and CSF t-tau/Aβ42 (p = 0.039) were observed in individuals aged 65 years or younger. Additionally, males with frequent green tea consumption had a significantly low level of CSF t-tau/Aβ42 and a modest trend toward decreased CSF t-tau. There were no interaction effects of green tea consumption with APOEɛ4 and gender.

CONCLUSION

Collectively, our findings consolidated the favorable effects of green tea on the mitigation of AD risk. The constituents of green tea may improve abnormal tau metabolism and are promising targets in interventions and drug therapies.

Serum Uric Acid May Aggravate Alzheimer's Disease Risk by Affecting Amyloidosis in Cognitively Intact Older Adults: The CABLE Study

BACKGROUND

Serum uric acid (SUA) affects the reaction of oxidative stress and free radicals in the neurodegenerative processes. However, whether SUA impacts Alzheimer's disease (AD) pathology remains unclear.

OBJECTIVE

We aimed to explore whether high SUA levels can aggravate the neurobiological changes of AD in preclinical AD.

METHODS

We analyzed cognitively intact participants (n = 839, age 62.16 years) who received SUA and cerebrospinal fluid (CSF) biomarkers (amyloid-β [Aβ], total tau [t-Tau], and phosphorylated tau [p-Tau]) measurements from the Chinese Alzheimer's Biomarker and LifestylE (CABLE) database using multivariable-adjusted linear models.

RESULTS

Levels of SUA in the preclinical AD elevated compared with the healthy controls (p = 0.007) and subjects with amyloid pathology had higher concentration of SUA than controls (p = 0.017). Roughly, equivalent levels of SUA displayed among cognitively intact individuals with or without tau pathology and neurodegeneration. CSF Aβ1 - 42 (p = 0.019) and Aβ1 - 42/Aβ1 - 40 (p = 0.027) were decreased and CSF p-Tau/Aβ1 - 42 (p = 0.009) and t-Tau/Aβ1 - 42 (p = 0.043) were increased with the highest (> 75th percentile) SUA when compared to lowest SUA, implying a high burden of cerebral amyloidosis in individuals with high SUA. Sensitivity analyses using the usual threshold to define hyperuricemia and precluding drug effects yielded robust associations. Nevertheless, the quadratic model did not show any U-shaped relationships between them.

CONCLUSION

SUA may aggravate brain amyloid deposition in preclinical AD, which corroborated the detrimental role of SUA.

Social Networks and Cerebrospinal Fluid Biomarkers of Alzheimer's Disease Pathology in Cognitively Intact Older Adults: The CABLE Study

BACKGROUND

Although social networks are deemed as moderators of incident Alzheimer's disease (AD), few data are available on the mechanism relevant to AD pathology.

OBJECTIVE

We aimed to investigate whether social networks affect metabolism of cerebrospinal fluid (CSF) AD biomarkers during early stage and identify modification effects of genetic factor and subjective cognitive decline (SCD).

METHODS

We studied participants from the Chinese Alzheimer's disease Biomarker and Lifestyle (CABLE) database who received cognition assessments and CSF amyloid-β (Aβ1-42 and Aβ1-40) and tau proteins (total-tau [T-tau] and phosphorylated-tau [P-tau]) measurements. The social networks were measured using self-reported questionnaires about social ties. Linear regression models were used.

RESULTS

Data were analyzed from 886 cognitively intact individuals aged 61.91 years (SD = 10.51), including 295 preclinical AD participants and 591 healthy controls. Social networks were mostly associated with CSF indicators of AD multi-pathologies (low P-tau/Aβ1-42 and T-tau/Aβ1-42 and high Aβ1-42/Aβ1-40). Significant differences of genetic and cognitive status were observed for CSF indicators, in which associations of social network scores with CSF P-tau and indicators of multi-pathologies appeared stronger in APOE 4 carriers (versus non-carriers) and participants with SCD (versus controls), respectively. Alternatively, more pronounced associations for CSF T-tau (β= -0.005, p < 0.001), Aβ1-42/Aβ1-40 (β= 0.481, p = 0.001), and T-tau/Aβ1-42 (β= -0.047, p < 0.001) were noted in preclinical AD stage than controls.

CONCLUSION

These findings consolidated strong links between social networks and AD risks. Social networks as a modifiable lifestyle probably affected metabolisms of multiple AD pathologies, especially among at-risk populations.

Amyloid Pathologies Modulate the Associations of Minimal Depressive Symptoms With Cognitive Impairments in Older Adults Without Dementia

BACKGROUND

The relationship between depression and Alzheimer's disease (AD) is complex and still not well understood. We aimed to examine the roles of the AD core pathologies in modulating the associations of minimal depressive symptoms (MDSs) with cognitive impairments.

METHODS

A total of 721 participants who had measures of cognition, depressive symptoms, and cerebrospinal fluid AD biomarkers were included from the CABLE (Chinese Alzheimer's Biomarker and LifestylE) study. Causal mediation analyses with 10,000 bootstrapped iterations were conducted to explore the mediation effects of AD pathologies on cognition. The ADNI (Alzheimer's Disease Neuroimaging Initiative) was used 1) to replicate the mediation effects and 2) to examine the longitudinal relationships of MDSs with amyloid pathology and incident AD risk.

RESULTS

In CABLE, MDSs were associated with poorer global cognition (p = .006) and higher amyloid burden as indicated by cerebrospinal fluid amyloid markers (p < .0001). The influence of MDSs on cognition was partially mediated by amyloid pathology (a maximum of 85%). The mediation effects were replicated in 725 elderly persons without dementia (age, mean ± SD = 73.5 ± 6.9 years; 301 female subjects [42%]) in ADNI, such that the mediation percentage varied from 10% to 30% for general cognition, memory, and executive functions. Longitudinal analyses revealed a bidirectional relationship between MDSs and amyloid pathology (p = .01). MDSs were associated with 83% increased risk of developing AD dementia (hazard ratio = 1.83, p < .01).

CONCLUSIONS

Overall, amyloid pathology might partially mediate and magnify the influences of MDSs on cognitive impairments and AD risk.

Cerebrospinal Fluid Biomarkers of Alzheimer's Disease: Current Evidence and Future Perspectives

Alzheimer's disease is a progressive, clinically heterogeneous, and particularly complex neurodegenerative disease characterized by a decline in cognition. Over the last two decades, there has been significant growth in the investigation of cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease. This review presents current evidence from many clinical neurochemical studies, with findings that attest to the efficacy of existing core CSF biomarkers such as total tau, phosphorylated tau, and amyloid-β (Aβ42), which diagnose Alzheimer's disease in the early and dementia stages of the disorder. The heterogeneity of the pathophysiology of the late-onset disease warrants the growth of the Alzheimer's disease CSF biomarker toolbox; more biomarkers showing other aspects of the disease mechanism are needed. This review focuses on new biomarkers that track Alzheimer's disease pathology, such as those that assess neuronal injury (VILIP-1 and neurofilament light), neuroinflammation (sTREM2, YKL-40, osteopontin, GFAP, progranulin, and MCP-1), synaptic dysfunction (SNAP-25 and GAP-43), vascular dysregulation (hFABP), as well as CSF α-synuclein levels and TDP-43 pathology. Some of these biomarkers are promising candidates as they are specific and predict future rates of cognitive decline. Findings from the combinations of subclasses of new Alzheimer's disease biomarkers that improve their diagnostic efficacy in detecting associated pathological changes are also presented.

Quantitative endophenotypes as an alternative approach to understanding genetic risk in neurodegenerative diseases

Endophenotypes, as measurable intermediate features of human diseases, reflect underlying molecular mechanisms. The use of quantitative endophenotypes in genetic studies has improved our understanding of pathophysiological changes associated with diseases. The main advantage of the quantitative endophenotypes approach to study human diseases over a classic case-control study design is the inferred biological context that can enable the development of effective disease-modifying treatments. Here, we summarize recent progress on biomarkers for neurodegenerative diseases, including cerebrospinal fluid and blood-based, neuroimaging, neuropathological, and clinical studies. This review focuses on how endophenotypic studies have successfully linked genetic modifiers to disease risk, disease onset, or progression rate and provided biological context to genes identified in genome-wide association studies. Finally, we review critical methodological considerations for implementing this approach and future directions.

Association of Alzheimer's disease risk variants on the PICALM gene with PICALM expression, core biomarkers, and feature neurodegeneration

It is still unclear how PICALM mutations influence the risk of Alzheimer's disease (AD). We tested the association of AD risk variants on the PICALM gene with PICALM expression and AD feature endophenotypes. Bioinformatic methods were used to annotate the functionalities and to select the tag single nucleotide polymorphisms (SNPs). Multiple regressions were used to examine the cross-sectional and longitudinal influences of tag SNPs on cerebrospinal fluid (CSF) AD biomarkers and neurodegenerations. A total of 59 SNPs, among which 75% were reported in Caucasians, were associated with AD risk. Of these, 73% were linked to PICALM expression in the whole blood (p < 0.0001) and/or brain regions (p < 0.05). Eleven SNPs were selected as tag SNPs in Caucasians. rs510566 (T allele) was associated with decreased CSF ptau and ptau/abeta42 ratio. The G allele of rs1237999 and rs510566 was linked with greater reserve capacities of the hippocampus, parahippocampus, middle temporal lobe, posterior cingulate, and precuneus. The longitudinal analyses revealed four loci that could predict dynamic changes of CSF ptau and ptau/abeta42 ratio (rs10501610, p = 0.0001) or AD feature neurodegeneration (rs3851179, rs592297, and rs7480193, p < 0.005). Overall, the genetic, bioinformatic, and association studies tagged four SNPs (rs3851179, rs7480193, rs510566, and rs1237999) as the most prominent PICALM loci contributing to AD in Caucasians.

Interrelations of Alzheimer´s disease candidate biomarkers neurogranin, fatty acid-binding protein 3 and ferritin to neurodegeneration and neuroinflammation

There is growing evidence that promising biomarkers of inflammation in Alzheimer´s disease (AD) and other neurodegenerative diseases correlate strongest to levels of tau or neurofilament, indicating an inflammatory response to neuronal damage or death. To test this hypothesis, we investigated three AD candidate markers (ferritin, fatty acid binding protein 3 (FABP-3), and neurogranin) in interrelation to established AD and inflammatory protein markers. We further aimed to determine if such interrelations would be evident in pathological subjects only or also under non-pathological circumstances. Cerebrospinal fluid levels of the three proteins were quantified in samples from the University Clinic of Bonn (UKB) Department of Neurodegenerative Diseases & Geriatric Psychiatry, Germany. Data were analyzed based on clinical or biomarker-defined stratification of subjects with adjustment for covariates age, sex, and APOE status. Levels of ferritin, FABP-3 and neurogranin were elevated in subjects with pathological levels of t-tau independent of beta-amyloid status. The three markers correlated with each other, tau isoforms, age, and those inflammatory markers previously described as related to neurodegeneration, predominantly sTREM2, macrophage migration inhibitory factor, soluble vascular endothelial growth factor receptor, soluble vascular cell adhesion molecule 1 (sVCAM-1), and C1q. These interrelations existed in subjects with pathological and sub-pathological tau levels, in particular for FABP-3 and neurogranin. Relations to ferritin were independent of absolute levels of tau, too, but showed differing trajectories between pathological and non-pathological subjects. A specific set of inflammatory markers is highly related to markers of neuronal damage such as tau, neurogranin, or FABP-3. These proteins could be used as readouts of the inflammatory response during the neurodegeneration phase of AD.

Anterolateral entorhinal cortex thickness as a new biomarker for early detection of Alzheimer's disease

INTRODUCTION

Loss of entorhinal cortex (EC) layer II neurons represents the earliest Alzheimer's disease (AD) lesion in the brain. Research suggests differing functional roles between two EC subregions, the anterolateral EC (aLEC) and the posteromedial EC (pMEC).

METHODS

We use joint label fusion to obtain aLEC and pMEC cortical thickness measurements from serial magnetic resonance imaging scans of 775 ADNI-1 participants (219 healthy; 380 mild cognitive impairment; 176 AD) and use linear mixed-effects models to analyze longitudinal associations among cortical thickness, disease status, and cognitive measures.

RESULTS

Group status is reliably predicted by aLEC thickness, which also exhibits greater associations with cognitive outcomes than does pMEC thickness. Change in aLEC thickness is also associated with cerebrospinal fluid amyloid and tau levels.

DISCUSSION

Thinning of aLEC is a sensitive structural biomarker that changes over short durations in the course of AD and tracks disease severity-it is a strong candidate biomarker for detection of early AD.

Sleep characteristics and cerebrospinal fluid biomarkers of Alzheimer's disease pathology in cognitively intact older adults: The CABLE study

INTRODUCTION

This study tested the self-reported sleep characteristics associated with cerebrospinal fluid (CSF) Alzheimer's disease (AD) biomarkers in cognitively intact older adults.

METHODS

The linear and non-linear regression analyses were conducted in 736 cognitively normal participants (mean [standard deviation; SD] age, 62.3 [10.5] years, range 40 to 88 years, 59% female) who had measurements of cerebrospinal fluid (CSF) amyloid beta (Aβ) and tTau proteins and sleep characteristics, after adjusting for age, gender, education, apolipoprotein E gene (APOE) ε4 status, and general cognition.

RESULTS

Greater daytime sleepiness was associated with higher CSF indicators of amyloid deposition in female patients. No significant associations were revealed for CSF tTau proteins after Bonferroni correction. A U-shaped relationship was revealed for nocturnal sleep habits, such that those with insufficient or excessive nocturnal sleep duration had greater CSF biomarkers of amyloid deposition (the reflection range: bedtime: around 10:00 p.m. and sleep duration: 6.0 to 6.5 hours).

DISCUSSION

These findings consolidated the close relationship between sleep and AD.

Adenosine and Metabotropic Glutamate Receptors Are Present in Blood Serum and Exosomes from SAMP8 Mice: Modulation by Aging and Resveratrol

Adenosine (ARs) and metabotropic glutamate receptors (mGluRs) are G-protein coupled receptors (GPCRs) that are modulated in the brain of SAMP8 mice, an animal model of Alzheimer's disease (AD). In the present work, it is shown the presence of ARs and mGluRs in blood serum and derived exosomes from SAMP8 mice as well as its possible modulation by aging and resveratrol (RSV) consumption. In blood serum, adenosine A₁ and A_2A receptors remained unaltered from 5 to 7 months of age. However, an age-related decrease in adenosine level was observed, while 5'-Nucleotidase activity was not modulated. Regarding the glutamatergic system, it was observed a decrease in mGluR₅ density and glutamate levels in older mice. In addition, dietary RSV supplementation caused an age-dependent modulation in both adenosinergic and glutamatergic systems. These GPCRs were also found in blood serum-derived exosomes, which might suggest that these receptors could be released into circulation via exosomes. Interestingly, changes elicited by age and RSV supplementation on mGluR₅ density, and adenosine and glutamate levels were similar to that detected in whole-brain. Therefore, we might suggest that the quantification of these receptors, and their corresponding endogenous ligands, in blood serum could have predictive value for early diagnosis in combination with other distinctive hallmarks of AD.

Biomarker profiling beyond amyloid and tau: cerebrospinal fluid markers, hippocampal atrophy, and memory change in cognitively unimpaired older adults

Brain changes occurring in aging can be indexed by biomarkers. We used cluster analysis to identify subgroups of cognitively unimpaired individuals (n = 99, 64-93 years) with different profiles of the cerebrospinal fluid biomarkers beta amyloid 1-42 (Aβ42), phosphorylated tau (P-tau), total tau, chitinase-3-like protein 1 (YKL-40), fatty acid binding protein 3 (FABP3), and neurofilament light (NFL). Hippocampal volume and memory were assessed across multiple follow-up examinations covering up to 6.8 years. Clustering revealed one group (39%) with more pathological concentrations of all biomarkers, which could further be divided into one group (20%) characterized by tauopathy and high FABP3 and one (19%) by brain β-amyloidosis, high NFL, and slightly higher YKL-40. The clustering approach clearly outperformed classification based on Aβ42 and P-tau alone in prediction of memory decline, with the individuals with most tauopathy and FABP3 showing more memory decline, but not more hippocampal volume change. The results demonstrate that older adults can be classified based on biomarkers beyond amyloid and tau, with improved prediction of memory decline.

CCL23: A Chemokine Associated with Progression from Mild Cognitive Impairment to Alzheimer's Disease

CCL23 is a chemokine implicated in inflammation and host defense responses. It has been recently associated with acquired brain damage and stroke outcomes. In this study, we reported the role of CCL23 in Alzheimer's disease (AD). We evaluated the levels of CCL23 in 659 individuals: cognitively normal, mild cognitive impaired (MCI), and AD patients. Two cross-sectional (study 1, n = 53; study 2, n = 200) and two longitudinal (study 3, n = 74; study 4, n = 332) studies were analyzed separately. CCL23 levels in the blood and/or cerebrospinal fluid (CSF) of each study were measured by immunoassays. Globally, our results suggest a predictive role of CCL23 protein levels both in the plasma in study 3 (hazard ratio (HR) = 2.5 (confidence interval (CI) 95% : 1.2-5.3), p = 0.02) and in the CSF in study 4 (HR = 3.05 (CI 95% : 1.02-5), p = 0.04) in cases of MCI that progress to AD. Moreover, we observed that the APOEɛ4 allele was associated with higher levels of CCL23 in study 2 (470.33 pg/mL (interquartile range (IQR): 303.33-597.76) versus 377.94 pg/mL (IQR: 267.16-529.19), p = 0.01) (APOE genotypes were available in studies 2 and 4). Together, these findings support the role of CCL23 in neuroinflammation in the early stages of AD, suggesting that CCL23 might be a candidate blood biomarker for MCI to AD progression.

Increased inflammation in BA21 brain tissue from African Americans with Alzheimer's disease

Chronic neuroinflammation is strongly associated with AD and altered peripheral and central levels of chemokines and cytokines have been frequently described in those with AD. Given the increasing evidence of ethnicity-related differences in AD, it was of interest to determine if those altered chemokine and cytokine levels are ethnicity-related. Because African Americans exhibit a higher incidence of AD and increased symptom severity, we explored chemokine and cytokine concentrations in post-mortem brain tissue from the BA21 region of African Americans and Caucasians with AD using multiplex assays. IL-1β, MIG, TRAIL, and FADD levels were significantly increased in African Americans while levels of IL-3 and IL-8 were significantly decreased. Those effects did not interact with gender; however, overall levels of CCL25, CCL26 and CX3CL1 were significantly decreased in women. The NLRP3 inflammasome is thought to be critically involved in AD. Increased activation of this inflammasome in African Americans is consistent with the current results.

The TMEM106B FTLD-protective variant, rs1990621, is also associated with increased neuronal proportion

Apart from amyloid β deposition and tau neurofibrillary tangles, Alzheimer's disease (AD) is a neurodegenerative disorder characterized by neuronal loss and astrocytosis in the cerebral cortex. The goal of this study is to investigate genetic factors associated with the neuronal proportion in health and disease. To identify cell-autonomous genetic variants associated with neuronal proportion in cortical tissues, we inferred cellular population structure from bulk RNA-Seq derived from 1536 individuals. We identified the variant rs1990621 located in the TMEM106B gene region as significantly associated with neuronal proportion (p value = 6.40 × 10-07) and replicated this finding in an independent dataset (p value = 7.41 × 10-04) surpassing the genome-wide threshold in the meta-analysis (p value = 9.42 × 10-09). This variant is in high LD with the TMEM106B non-synonymous variant p.T185S (rs3173615; r2 = 0.98) which was previously identified as a protective variant for frontotemporal lobar degeneration (FTLD). We stratified the samples by disease status, and discovered that this variant modulates neuronal proportion not only in AD cases, but also several neurodegenerative diseases and in elderly cognitively healthy controls. Furthermore, we did not find a significant association in younger controls or schizophrenia patients, suggesting that this variant might increase neuronal survival or confer resilience to the neurodegenerative process. The single variant and gene-based analyses also identified an overall genetic association between neuronal proportion, AD and FTLD risk. These results suggest that common pathways are implicated in these neurodegenerative diseases, that implicate neuronal survival. In summary, we identified a protective variant in the TMEM106B gene that may have a neuronal protection effect against general aging, independent of disease status, which could help elucidate the relationship between aging and neuronal survival in the presence or absence of neurodegenerative disorders. Our findings suggest that TMEM106B could be a potential target for neuronal protection therapies to ameliorate cognitive and functional deficits.

Examination of the Effect of Rare Variants in TREM2, ABI3, and PLCG2 in LOAD Through Multiple Phenotypes

BACKGROUND

Rare variants in PLCG2 (p.P522R), ABI3 (p.S209F), and TREM2 (p.R47H, p.R62H) have been associated with late onset Alzheimer's disease (LOAD) risk in Caucasians. After the initial report, several studies have found positive results in cohorts of different ethnic background and with different phenotype.

OBJECTIVE

In this study, we aim to evaluate the association of rare coding variants in PLCG2, ABI3, and TREM2 with LOAD risk and their effect at different time points of the disease.

METHODS

We used a European American cohort to assess the association of the variants prior onset (using CSF Aβ42, tau, and pTau levels, and amyloid imaging as endophenotypes) and after onset (measured as rate of memory decline).

RESULTS

We confirm the association with LOAD risk of TREM2 p.R47H, p.R62H and ABI3 p.S209F variants, and the protective effect of PLCG2 p.P522R. In addition, ABI3 and TREM2 gene-sets showed significant association with LOAD risk. TREM2 p.R47H and PLCG2 p.P522R variants were also statistically associated with increase of amyloid imaging and AD progression, respectively. We did not observe any association of ABI3 p.S209F with any of the other AD endophenotypes.

CONCLUSION

The results of this study highlight the importance of including biomarkers and alternative phenotypes to better understand the role of novel candidate genes with the disease.

Macrophage Migration Inhibitory Factor Alters Functional Properties of CA1 Hippocampal Neurons in Mouse Brain Slices

Neuroinflammation is implicated in a host of neurological insults, such as traumatic brain injury (TBI), ischemic stroke, Alzheimer's disease, Parkinson's disease, and epilepsy. The immune response to central nervous system (CNS) injury involves sequelae including the release of numerous cytokines and chemokines. Macrophage migration inhibitory factor (MIF), is one such cytokine that is elevated following CNS injury, and is associated with the prognosis of TBI, and ischemic stroke. MIF has been identified in astrocytes and neurons, and some of the trophic actions of MIF have been related to its direct and indirect actions on astrocytes. However, the potential modulation of CNS neuronal function by MIF has not yet been explored. This study tests the hypothesis that MIF can directly influence hippocampal neuronal function. MIF was microinjected into the hippocampus and the genetically encoded calcium indicator, GCaMP6f, was used to measure Ca²⁺ events in acute adult mouse brain hippocampal slices. Results demonstrated that a single injection of 200 ng MIF into the hippocampus significantly increased baseline calcium signals in CA1 pyramidal neuron somata, and altered calcium responses to N-methyl-d-aspartate (NMDA) + D-serine in pyramidal cell apical dendrites located in the stratum radiatum. These data are the first to show direct effects of MIF on hippocampal neurons and on NMDA receptor function. Considering that MIF is elevated after brain insults such as TBI, the data suggest that, in addition to the previously described role of MIF in astrocyte reactivity, elevated MIF can have significant effects on neuronal function in the hippocampus.

Lipid and Lipid Raft Alteration in Aging and Neurodegenerative Diseases: A Window for the Development of New Biomarkers

Lipids in the brain are major components playing structural functions as well as physiological roles in nerve cells, such as neural communication, neurogenesis, synaptic transmission, signal transduction, membrane compartmentalization, and regulation of gene expression. Determination of brain lipid composition may provide not only essential information about normal brain functioning, but also about changes with aging and diseases. Indeed, deregulations of specific lipid classes and lipid homeostasis have been demonstrated in neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). Furthermore, recent studies have shown that membrane microdomains, named lipid rafts, may change their composition in correlation with neuronal impairment. Lipid rafts are key factors for signaling processes for cellular responses. Lipid alteration in these signaling platforms may correlate with abnormal protein distribution and aggregation, toxic cell signaling, and other neuropathological events related with these diseases. This review highlights the manner lipid changes in lipid rafts may participate in the modulation of neuropathological events related to AD and PD. Understanding and characterizing these changes may contribute to the development of novel and specific diagnostic and prognostic biomarkers in routinely clinical practice.

Age-related hearing loss accelerates cerebrospinal fluid tau levels and brain atrophy: a longitudinal study

Age-related hearing loss (ARHL) has been considered as a promising modifiable risk factor for cognitive impairment and dementia. Nonetheless, it is still unclear whether age-related hearing loss associates with neurodegenerative biomarkers of Alzheimer's disease (AD). Participants with ARHL were selected from the established Alzheimer's Disease Neuroimaging Initiative (ADNI) database. In multivariable models, the cross-sectional and longitudinal associations of ARHL with CSF β-amyloid (Aβ) and tau measurements, brain Aβ load, and cortical structural measures were explored. ARHL was associated with higher CSF levels of tau (p < 0.001) or ptau181 (p < 0.05) at baseline as well as faster elevation rates of these two types of biomarkers (p < 0.05). Although the baseline volume/thickness of hippocampus (p < 0.05) and entorhinal cortex (p < 0.0005) were higher in individuals with ARHL, these two regions (p < 0.01 for hippocampus, p < 0.05 for entorhinal cortex) displayed significantly accelerated atrophy in individuals with ARHL. No association of ARHL with CSF or brain Aβ levels was found. Subgroup analyses indicated that the above effects of ARHL were more significant in non-demented stage. Age-related hearing loss was associated with elevated cerebrospinal fluid tau levels and atrophy of entorhinal cortex.

Development of FABP3 ligands that inhibit arachidonic acid-induced α-synuclein oligomerization

In Parkinson's disease (PD), α-synuclein (αSyn) accumulation and inclusion triggers dopamine neuronal death and synapse dysfunction in vivo. We previously reported that fatty acid-binding protein 3 (FABP3) is highly expressed in the brain and accelerates αSyn oligomerization when cells are exposed to 1-Methyl-1,2,3,6-tetrahydropiridine (MPTP). Here, we demonstrate that αSyn oligomerization was markedly enhanced by co-overexpressing FABP3 in neuro-2A cells when cells were treated with arachidonic acid (AA). We developed FABP3 ligands, which bind to the fatty acid binding domain of FABP3, using an 8-Anilinonaphthalene-1-sulfonic acid (ANS) assay with a recombinant FABP3 protein. The prototype for the FABP4 ligand, BMS309403, has no affinity for FABP3. We developed more FABP3-specific ligands derived from the chemical structure of BMS309403. Like AA, ligands 1, 7, and 8 had a relatively high affinity for FAPB3 in the ANS assay. Then, we evaluated the inhibition of αSyn oligomerization in neuro-2A cells co-overexpressing FABP3 and αSyn. Importantly, AA treatments markedly enhanced αSyn oligomerization in the co-expressing cells. Ligands 1, 7, and 8 significantly reduced AA-induced αSyn oligomerization in neuro-2A cells. Taken together, our results indicate that FABP3 ligands that target FABP3 may be used as potential therapeutics that inhibit αSyn aggregation in vivo.

Role of FABP3 as biomarker in Alzheimer's disease and synucleinopathies

Lipids are fundamental components of brain cells as they are involved in several essential processes like remodeling of plasma membrane, synaptic function and receptor–ligand interactions. Systemic and brain alterations in lipid metabolism have been linked to the pathogenesis of neurodegenerative disorders like dementia and parkinsonisms. Intracellular transport of lipids is regulated by fatty acid-binding proteins. Recently, a member of this family, the fatty acid-binding protein 3 has been proposed as a potential biomarker across a range of neurodegenerative diseases, including Alzheimer's disease and dementia with Lewy bodies. In this special report, we describe recent progresses in characterizing the role of fatty acid-binding protein 3 in neurodegeneration and its putative role as biomarker measurable in biological fluids.

Non-beta-amyloid/tau cerebrospinal fluid markers inform staging and progression in Alzheimer's disease

Background

Alzheimer’s disease (AD) is a complex neurodegenerative disorder characterized by neuropathologic changes involving beta-amyloid (Aβ), tau, neuronal loss, and other associated biological events. While levels of cerebrospinal fluid (CSF) Aβ and tau peptides have enhanced the antemortem detection of AD-specific changes, these two markers poorly reflect the severity of cognitive and functional deficits in people with altered Aβ and tau levels. While multiple previous studies identified non-Aβ, non-tau proteins as candidate neurodegenerative markers to inform the A/T/N biomarker scheme of AD, few have advanced beyond association with clinical AD diagnosis. Here we analyzed nine promising neurodegenerative markers in a three-centered cohort using independent assays to identify candidates most likely to complement Aβ and tau in the A/T/N framework.

Methods

CSF samples from 125 subjects recruited at the three centers were exchanged such that each of the nine previously identified biomarkers can be measured at one of the three centers. Subjects were classified according to cognitive status and CSF AD biomarker profiles as having normal cognition and normal CSF (n = 31), normal cognition and CSF consistent with AD (n = 13), mild cognitive impairment and normal CSF (n = 13), mild cognitive impairment with CSF consistent with AD (n = 23), AD dementia (n = 32; CSF consistent with AD), and other non-AD dementia (n = 13; CSF not consistent with AD).

Results

Three biomarkers were identified to differ among the AD stages, including neurofilament light chain (NfL; p < 0.001), fatty acid binding protein 3 (Fabp3; p < 0.001), and interleukin (IL)-10 (p = 0.033). Increased NfL levels were most strongly associated with the dementia stage of AD, but increased Fabp3 levels were more sensitive to milder AD stages and correlated with both CSF tau markers. IL-10 levels did not correlate with tau biomarkers, but were associated with rates of longitudinal cognitive decline in mild cognitive impairment due to AD (p = 0.006). Prefreezing centrifugation did not influence measured CSF biomarker levels.

Conclusion

CSF proteins associated with AD clinical stages and progression can complement Aβ and tau markers to inform neurodegeneration. A validated panel inclusive of multiple biomarker features (etiology, stage, progression) can improve AD phenotyping along the A/T/N framework.

Concordance Between Cerebrospinal Fluid Biomarkers with Alzheimer's Disease Pathology Between Three Independent Assay Platforms

BACKGROUND

To enhance the accuracy of clinical diagnosis for Alzheimer's disease (AD), pre-mortem biomarkers have become increasingly important for diagnosis and for participant recruitment in disease-specific treatment trials. Cerebrospinal fluid (CSF) biomarkers provide a low-cost alternative to positron emission tomography (PET) imaging for in vivo quantification of different AD pathological hallmarks in the brains of affected subjects; however, consensus around the best platform, most informative biomarker and correlations across different methodologies are controversial.

OBJECTIVE

Assessing levels of Aβ-amyloid and tau species determined using three different versions of immunoassays, the current study explored the ability of CSF biomarkers to predict PET Aβ-amyloid (32 Aβ-amyloid-and 45 Aβ-amyloid+), as well as concordance between CSF biomarker levels and PET Aβ-amyloid imaging.

METHODS

Prediction and concordance analyses were performed using a sub-cohort of 77 individuals (48 healthy controls, 15 with mild cognitive impairment, and 14 with AD) from the Australian Imaging Biomarker and Lifestyle study of aging.

RESULTS

Across all three platforms, the T-tau/Aβ42 ratio biomarker had modestly higher correlation with SUVR/BeCKeT (ρ= 0.69-0.8) as compared with Aβ42 alone (ρ= 0.66-0.75). Differences in CSF biomarker levels between the PET Aβ-amyloid-and Aβ-amyloid+ groups were strongest for the Aβ42/Aβ40 and T-tau/Aβ42 ratios (p < 0.0001); however, comparison of predictive models for PET Aβ-amyloid showed no difference between Aβ42 alone and the T-tau/Aβ42 ratio.

CONCLUSION

This study confirms strong concordance between CSF biomarkers and PET Aβ-amyloid status is independent of immunoassay platform, supporting their utility as biomarkers in clinical practice for the diagnosis of AD and for participant enrichment in clinical trials.

Intranasal insulin in Alzheimer's disease: Food for thought

Accumulating evidence suggests that disrupted brain insulin signaling promotes the development and progression of Alzheimer's disease (AD), driving clinicians to target this circuitry. While both traditional and more modern antidiabetics show promise in combating insulin resistance, intranasal insulin appears to be the most efficient method of boosting brain insulin. Furthermore, intranasal delivery elegantly avoids adverse effects from peripheral insulin administration. However, there remain significant open questions regarding intranasal insulin's efficacy, safety, and potential as an adjunct or mono-therapy. Thus, this review aims to critically evaluate the present evidence and future potential of intranasal insulin as a meaningful treatment for AD. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Triggering receptor expressed on myeloid cells 2 (TREM2): a potential therapeutic target for Alzheimer disease?

INTRODUCTION

There are currently no effective therapeutics for Alzheimer disease (AD). Clinical trials targeting amyloid beta thus far have shown very little benefit and only in the earliest stages of disease. These limitations have driven research to identify alternative therapeutic targets, one of the most promising is the triggering receptor expressed on myeloid cells 2 (TREM2). Areas covered: Here, we review the literature to-date and discuss the potentials and pitfalls for targeting TREM2 as a potential therapeutic for AD. We focus on research in animal and cell models for AD and central nervous system injury models which may help in understanding the role of TREM2 in disease. Expert opinion: Studies suggest TREM2 plays a key role in AD pathology; however, results have been conflicting about whether TREM2 is beneficial or harmful. More research is necessary before designing TREM2-targeting therapies. Successful therapeutics will most likely be administered early in disease.

Longitudinal structural cerebral changes related to core CSF biomarkers in preclinical Alzheimer's disease: A study of two independent datasets

Alzheimer's disease (AD) is characterized by an accumulation of β-amyloid (Aβ₄₂) accompanied by brain atrophy and cognitive decline. Several recent studies have shown that Aβ₄₂ accumulation is associated with gray matter (GM) changes prior to the development of cognitive impairment, in the so-called preclinical stage of the AD (pre-AD). It also has been proved that the GM atrophy profile is not linear, both in normal ageing but, especially, on AD. However, several other factors may influence this association and may have an impact on the generalization of results from different samples. In this work, we estimate differences in rates of GM volume change in cognitively healthy elders in association with baseline core cerebrospinal fluid (CSF) AD biomarkers, and assess to what these differences are sample dependent. We report the dependence of atrophy rates, measured in a two-year interval, on Aβ₄₂, computed both over continuous and categorical values of Aβ₄₂, at voxel-level (p < 0.001; k < 100) and corrected for sex, age and education. Analyses were performed jointly and separately, on two samples. The first sample was formed of 31 individuals (22 Ctrl and 9 pre-AD), aged 60–80 and recruited at the Hospital Clinic of Barcelona. The second sample was a replica of the first one with subjects selected from the ADNI dataset. We also investigated the dependence of the GM atrophy rate on the basal levels of continuous p-tau and on the p-tau/Aβ₄₂ ratio. Correlation analyses on the whole sample showed a dependence of GM atrophy rates on Aβ₄₂ in medial and orbital frontal, precuneus, cingulate, medial temporal regions and cerebellum. Correlations with p-tau were located in the left hippocampus, parahippocampus and striatal nuclei whereas correlation with p-tau/Aβ₄₂ was mainly found in ventral and medial temporal areas. Regarding analyses performed separately, we found a substantial discrepancy of results between samples, illustrating the complexities of comparing two independent datasets even when using the same inclusion criteria. Such discrepancies may lead to significant differences in the sample size needed to detect a particular reduction on cerebral atrophy rates in prevention trials. Higher cognitive reserve and more advanced pathological progression in the ADNI sample could partially account for the observed discrepancies. Taken together, our findings in these two samples highlight the importance of comparing and merging independent datasets to draw more robust and generalizable conclusions on the structural changes in the preclinical stages of AD.

•

GM atrophy rates depends differently on values of CSF Aβ₄₂ than on CSF p-tau in the preclinical stage of AD.

•

Discrepant results were obtained. Although nominally equivalent, samples might reflect different time-windows in the AD continuum.

•

It is necessary a further effort to standardize CSF-biomarkers measures and thresholds to make different samples to be directly comparable.

A Systematic Review of Longitudinal Studies Which Measure Alzheimer's Disease Biomarkers

Alzheimer’s disease (AD) is a progressive and fatal neurodegenerative disease, with no effective treatment or cure. A gold standard therapy would be treatment to slow or halt disease progression; however, knowledge of causation in the early stages of AD is very limited. In order to determine effective endpoints for possible therapies, a number of quantitative surrogate markers of disease progression have been suggested, including biochemical and imaging biomarkers. The dynamics of these various surrogate markers over time, particularly in relation to disease development, are, however, not well characterized. We reviewed the literature for studies that measured cerebrospinal fluid or plasma amyloid-β and tau, or took magnetic resonance image or fluorodeoxyglucose/Pittsburgh compound B-positron electron tomography scans, in longitudinal cohort studies. We summarized the properties of the major cohort studies in various countries, commonly used diagnosis methods and study designs. We have concluded that additional studies with repeat measures over time in a representative population cohort are needed to address the gap in knowledge of AD progression. Based on our analysis, we suggest directions in which research could move in order to advance our understanding of this complex disease, including repeat biomarker measurements, standardization and increased sample sizes.

Characterization and clinical use of inflammatory cerebrospinal fluid protein markers in Alzheimer's disease

Background

Neuroinflammation has gained increasing attention as a potential contributing factor in Alzheimer’s disease (AD) pathology. A clinical cerebrospinal fluid biomarker capable of monitoring this process during the course of the disease has yet to emerge, chiefly owing to contradictory research findings. In this study, we sought to clarify the utility of inflammatory biomarkers in diagnostic procedures of AD in three steps: (1) to screen for proteins that are robustly detectable in cerebrospinal fluid; (2) based on this analysis, to explore any associations between the analytically robust markers and salient pathological features of AD; and (3) to determine the discriminative power of these markers in the clinical diagnosis of AD.

Methods

From a total of 46 proteins, 15 that were robustly detectable in cerebrospinal fluid were identified. A subsequent analysis of these markers in a cohort of 399 patients (nondemented subjects, patients with mild cognitive impairment [MCI], and patients with AD, supplemented by smaller cohorts of other diseases) was conducted. Fluid biomarker data were related to AD pathology and neuropsychological markers and adjusted for confounders such as age, sex, apolipoprotein E genotype, and biobank storage time.

Results

Cerebrospinal fluid levels of C-reactive protein and soluble TREM2 differed between nondemented subjects, patients with MCI, or patients with AD and were associated with amyloid and tau pathology. Several markers were associated with tau pathology only or with other neurodegenerative diseases. Correlations between neuropsychological performance and inflammatory markers were weak, but they were most prominent in AD and for the most challenging cognitive tests. All investigated covariates had significant influence, with varying effects across the markers. Still, none of the markers achieved discriminative power of more than 70% to distinguish between patient groups defined by clinical or neuropathological categories.

Conclusions

Basic analytical considerations proved indispensable for this type of study because only one-third of the tested markers were robustly detectable in cerebrospinal fluid. Detectable inflammatory protein markers were associated in multiple ways with AD pathology. Yet, even significantly associated markers were not powerful enough in terms of effect strength, sensitivity, and specificity, and hence they were not suited for direct use in clinical diagnostic practice. Targets other than those most commonly considered in this field of research might provide results with better clinical applicability.

Electronic supplementary material

The online version of this article (10.1186/s13195-018-0353-3) contains supplementary material, which is available to authorized users.

Effects of Regular and Long-Acting Insulin on Cognition and Alzheimer's Disease Biomarkers: A Pilot Clinical Trial

Background: Long acting insulin detemir administered intranasally for three weeks enhanced memory for adults with Alzheimer’s disease dementia (AD) or amnestic mild cognitive impairment (MCI). The investigation of longer-term administration is necessary to determine whether benefits persist, whether they are similar to benefits provided by regular insulin, and whether either form of insulin therapy affects AD biomarkers.

Objective: The present study aimed to determine whether four months of treatment with intranasal insulin detemir or regular insulin improves cognition, daily functioning, and AD biomarkers for adults with MCI or AD.

Methods: This randomized, double-blind, placebo-controlled trial included an intent-to-treat sample consisting of 36 adults diagnosed with MCI or mild to moderate AD. Participants received placebo (n = 12), 40 IU of insulin detemir (n = 12), or 40 IU of regular insulin (n = 12) daily for four months, administered with a nasal delivery device. A cognitive battery was administered at baseline and after two and four months of treatment. MRI was administered for all participants and lumbar puncture for a subset (n = 20) at baseline and four months. The primary outcome was change from baseline to four months on a memory composite (sum of Z scores for delayed list and story recall). Secondary outcomes included: global cognition (Alzheimer’s Disease Assessment Scale-Cognition), daily functioning (Dementia Severity Rating Scale), MRI volume changes in AD-related regions of interest, and cerebrospinal fluid AD markers.

Results: The regular insulin treated group had better memory after two and four months compared with placebo (p < 0.03). No significant effects were observed for the detemir-assigned group compared with the placebo group, or for daily functioning for either group. Regular insulin treatment was associated with preserved volume on MRI. Regular insulin treatment was also associated with reduction in the tau-P181/Aβ₄₂ ratio.

Conclusion: Future research is warranted to examine the mechanistic basis of treatment differences, and to further assess the efficacy and safety of intranasal insulin.