Plasma apolipoprotein levels are associated with cognitive status and decline in a community cohort of older individuals

Divergent Roles of APOAI and APOM in the Identification of Alcohol Use Disorder and Their Association With Inflammation and Cognitive Decline: A Pilot Study

BACKGROUND

Alcohol use disorder (AUD) courses with inflammation and cognitive decline. Apolipoproteins have emerged as novel target compounds related to inflammatory processes and cognition.

METHODS

A cross-sectional study was performed on abstinent AUD patients with at least 1 month of abstinence (n  = 33; 72.7% men) and healthy controls (n  = 34; 47.1% men). A battery of plasma apolipoproteins (APOAI, APOAII, APOB, APOCII, APOE, APOJ, and APOM), plasma inflammatory markers (LPS, LBP), and their influence on cognition and presence of the disorder were investigated.

RESULTS

Higher levels of plasma APOAI, APOB, APOE, and APOJ, as well as the proinflammatory LPS, were observed in the AUD group, irrespective of sex, whereas APOM levels were lower vs controls. Hierarchical logistic regression analyses, adjusting for covariates (age, sex, education), associated APOM with the absence of cognitive impairment in AUD and identified APOAI and APOM as strong predictors of the presence or absence of the disorder, respectively. APOAI and APOM did not correlate with alcohol abuse variables or liver status markers, but they showed an opposite profile in their associations with LPS (positive for APOAI; negative for APOM) and cognition (negative for APOAI; positive for APOM) in the entire sample.

CONCLUSIONS

The HDL constituents APOAI and APOM were differentially regulated in the plasma of AUD patients compared with controls, playing divergent roles in the disorder identification and associations with inflammation and cognitive decline.

Plasma and CSF biomarkers of aging and cognitive decline in Caribbean vervets

INTRODUCTION

Vervets are non-human primates that share high genetic homology with humans and develop amyloid beta (Aβ) pathology with aging. We expand current knowledge by examining Aβ pathology, aging, cognition, and biomarker proteomics.

METHODS

Amyloid immunoreactivity in the frontal cortex and temporal cortex/hippocampal regions from archived vervet brain samples ranging from young adulthood to old age was quantified. We also obtained cognitive scores, plasma samples, and cerebrospinal fluid (CSF) samples in additional animals. Plasma and CSF proteins were quantified with platforms utilizing human antibodies.

RESULTS

We found age-related increases in Aβ deposition in both brain regions. Bioinformatic analyses assessed associations between biomarkers and age, sex, cognition, and CSF Aβ levels, revealing changes in proteins related to immune-related inflammation, metabolism, and cellular processes.

DISCUSSION

Vervets are an effective model of aging and early-stage Alzheimer's disease, and we provide translational biomarker data that both align with previous results in humans and provide a basis for future investigations.

HIGHLIGHTS

We found changes in immune and metabolic plasma biomarkers associated with age and cognition. Cerebrospinal fluid (CSF) biomarkers revealed changes in cell signaling indicative of adaptative processes. TNFRSF19 (TROY) and Artemin co-localize with Alzheimer's disease pathology. Vervets are a relevant model for translational studies of early-stage Alzheimer's disease.

Alzheimer's disease early screening and staged detection with plasma proteome using machine learning and convolutional neural network

Alzheimer's disease (AD) stands as the prevalent progressive neurodegenerative disease, precipitating cognitive impairment and even memory loss. Amyloid biomarkers have been extensively used in the diagnosis of AD. However, amyloid proteins offer limited information about the disease process and accurate diagnosis depends on the presence of a substantial accumulation of amyloid deposition which significantly impedes the early screening of AD. In this study, we have combined plasma proteomics with an ensemble learning model (CatBoost) to develop a cost-effective and non-invasive diagnostic method for AD. A longitudinal panel has been identified that can serve as reliable biomarkers across the entire progression of AD. Simultaneously, we have developed a neural network algorithm that utilizes plasma proteins to detect stages of Alzheimer's disease. Based on the developed longitudinal panel, the CatBoost model achieved an area under the operating curve of at least 0.90 in distinguishing mild cognitive impairment from cognitively normal. The neural network model was utilized for the detection of three stages of AD, and the results demonstrated that the neural network model exhibited an accuracy as high as 0.83, surpassing that of the traditional machine learning model.

APOE Genotype, ApoE Plasma Levels, Lipid Metabolism, and Cognition in Monozygotic Twins with, at Risk of, and without Affective Disorders

Background: Lipids influence brain function and mental health. Understanding the role of apolipoproteins in affective disorders could provide valuable insights and potentially pave the way for novel therapeutic approaches. Methods: We examined the apolipoprotein E genotype and ApoE-levels, lipid profiles, and the correlation with cognition in 204 monozygotic (MZ) twins with unipolar or bipolar disorder in remission or partial remission (affected, AT), their unaffected co-twins (high-risk, HR), and twins with no personal or family history of affective disorder (low-risk, LR). Results: The APOE genotype was not associated with affective disorders. No significant group differences in ApoE levels were found between the three risk groups. Post hoc analysis group-wise comparisons showed higher ApoE levels in the AT than HR twins and in the concordant AT twin pairs relative to the discordant twin pairs. Within the discordant twin pairs, higher ApoE levels were observed in the affected twins (AT = 39.4 mg/L vs. HR = 36.8 mg/L, p = 0.037). Limitations: The present study could benefit from a larger sample size. We did not assess dietary habits. Conclusions: The results did not support our main hypothesis. However, exploratory post hoc analysis suggests a role for plasma ApoE and triglycerides in affective disorders. Future research is needed.

Multiomics Blood-Based Biomarkers Predict Alzheimer's Predementia with High Specificity in a Multicentric Cohort Study

BACKGROUND

The primary criteria for diagnosing mild cognitive impairment (MCI) due to Alzheimer's Disease (AD) or probable mild AD dementia rely partly on cognitive assessments and the presence of amyloid plaques. Although these criteria exhibit high sensitivity in predicting AD among cognitively impaired patients, their specificity remains limited. Notably, up to 25% of non-demented patients with amyloid plaques may be misdiagnosed with MCI due to AD, when in fact they suffer from a different brain disorder. The introduction of anti-amyloid antibodies complicates this scenario. Physicians must prioritize which amyloid-positive MCI patients receive these treatments, as not all are suitable candidates. Specifically, those with non-AD amyloid pathologies are not primary targets for amyloid-modifying therapies. Consequently, there is an escalating medical necessity for highly specific blood biomarkers that can accurately detect pre-dementia AD, thus optimizing amyloid antibody prescription.

OBJECTIVES

The objective of this study was to evaluate a predictive model based on peripheral biomarkers to identify MCI and mild dementia patients who will develop AD dementia symptoms in cognitively impaired population with high specificity.

DESIGN

Peripheral biomarkers were identified in a gene transfer-based animal model of AD and then validated during a retrospective multi-center clinical study.

SETTING

Participants from 7 retrospective cohorts (US, EU and Australia).

PARTICIPANTS

This study followed 345 cognitively impaired individuals over up to 13 years, including 193 with MCI and 152 with mild dementia, starting from their initial visits. The final diagnoses, established during their last assessments, classified 249 participants as AD patients and 96 as having non-AD brain disorders, based on the specific diagnostic criteria for each disorder subtype. Amyloid status, assessed at baseline, was available for 82.9% of the participants, with 61.9% testing positive for amyloid. Both amyloid-positive and negative individuals were represented in each clinical group. Some of the AD patients had co-morbidities such as metabolic disorders, chronic diseases, or cardiovascular pathologies.

MEASUREMENTS

We developed targeted mass spectrometry assays for 81 blood-based biomarkers, encompassing 45 proteins and 36 metabolites previously identified in AAV-AD rats.

METHODS

We analyzed blood samples from study participants for the 81 biomarkers. The B-HEALED test, a machine learning-based diagnostic tool, was developed to differentiate AD patients, including 123 with Prodromal AD and 126 with mild AD dementia, from 96 individuals with non-AD brain disorders. The model was trained using 70% of the data, selecting relevant biomarkers, calibrating the algorithm, and establishing cutoff values. The remaining 30% served as an external test dataset for blind validation of the predictive accuracy.

RESULTS

Integrating a combination of 19 blood biomarkers and participant age, the B-HEALED model successfully distinguished participants that will develop AD dementia symptoms (82 with Prodromal AD and 83 with AD dementia) from non-AD subjects (71 individuals) with a specificity of 93.0% and sensitivity of 65.4% (AUROC=81.9%, p<0.001) during internal validation. When the amyloid status (derived from CSF or PET scans) and the B-HEALED model were applied in association, with individuals being categorized as AD if they tested positive in both tests, we achieved 100% specificity and 52.8% sensitivity. This performance was consistent in blind external validation, underscoring the model's reliability on independent datasets.

CONCLUSIONS

The B-HEALED test, utilizing multiomics blood-based biomarkers, demonstrates high predictive specificity in identifying AD patients within the cognitively impaired population, minimizing false positives. When used alongside amyloid screening, it effectively identifies a nearly pure prodromal AD cohort. These results bear significant implications for refining clinical trial inclusion criteria, facilitating drug development and validation, and accurately identifying patients who will benefit the most from disease-modifying AD treatments.

Circadian Regulation of Apolipoproteins in the Brain: Implications in Lipid Metabolism and Disease

The circadian rhythm is a 24 h internal clock within the body that regulates various factors, including sleep, body temperature, and hormone secretion. Circadian rhythm disruption is an important risk factor for many diseases including neurodegenerative illnesses. The central and peripheral oscillators' circadian clock network controls the circadian rhythm in mammals. The clock genes govern the central clock in the suprachiasmatic nucleus (SCN) of the brain. One function of the circadian clock is regulating lipid metabolism. However, investigations of the circadian regulation of lipid metabolism-associated apolipoprotein genes in the brain are lacking. This review summarizes the rhythmic expression of clock genes and lipid metabolism-associated apolipoprotein genes within the SCN in Mus musculus. Nine of the twenty apolipoprotein genes identified from searching the published database (SCNseq and CircaDB) are highly expressed in the SCN. Most apolipoprotein genes (ApoE, ApoC1, apoA1, ApoH, ApoM, and Cln) show rhythmic expression in the brain in mice and thus might be regulated by the master clock. Therefore, this review summarizes studies on lipid-associated apolipoprotein genes in the SCN and other brain locations, to understand how apolipoproteins associated with perturbed cerebral lipid metabolism cause multiple brain diseases and disorders. This review describes recent advancements in research, explores current questions, and identifies directions for future research.

Lipids and lipoproteins may play a role in the neuropathology of Alzheimer's disease

Alzheimer's disease (AD) and other classes of dementia are important public health problems with overwhelming social, physical, and financial effects for patients, society, and their families and caregivers. The pathophysiology of AD is poorly understood despite the extensive number of clinical and experimental studies. The brain's lipid-rich composition is linked to disturbances in lipid homeostasis, often associated with glucose and lipid abnormalities in various neurodegenerative diseases, including AD. Moreover, elevated low-density lipoprotein (LDL) cholesterol levels may be related to a higher probability of AD. Here, we hypothesize that lipids, and electronegative LDL (L5) in particular, may be involved in the pathophysiology of AD. Although changes in cholesterol, triglyceride, LDL, and glucose levels are seen in AD, the cause remains unknown. We believe that L5-the most electronegative subfraction of LDL-may be a crucial factor in understanding the involvement of lipids in AD pathology. LDL and L5 are internalized by cells through different receptors and mechanisms that trigger separate intracellular pathways. One of the receptors involved in L5 internalization, LOX-1, triggers apoptotic pathways. Aging is associated with dysregulation of lipid homeostasis, and it is believed that alterations in lipid metabolism contribute to the pathogenesis of AD. Proposed mechanisms of lipid dysregulation in AD include mitochondrial dysfunction, blood-brain barrier disease, neuronal signaling, inflammation, and oxidative stress, all of which lead ultimately to memory loss through deficiency of synaptic integration. Several lipid species and their receptors have essential functions in AD pathogenesis and may be potential biomarkers.

Associations between circulating cardiovascular disease risk factors and cognitive performance in cognitively healthy older adults from the NuAge study

Introduction

Cardiovascular disease risk factors (CVRFs) contribute to the development of cognitive impairment and dementia.

Methods

This study examined the associations between circulating CVRF biomarkers and cognition in 386 cognitively healthy older adults (mean age = 78 ± 4 years, 53% females) selected from the Quebec Longitudinal Study on Nutrition and Successful Aging (NuAge). Memory, executive function, and processing speed were assessed at baseline and 2-year follow-up. CVRF biomarkers included total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein-cholesterol (LDL-C), triglycerides, glucose, insulin, high sensitivity C-reactive protein (hs-CRP), homocysteine, protein carbonyls, and cortisol. Linear mixed models were used to determine associations between individual CVRF biomarkers and cognition at both time points.

Results

HDL-C was most consistently associated with cognition with higher values related to better performance across several domains. Overall, stronger and more consistent relationships between CVRF biomarkers and cognition were observed in females relative to males.

Discussion

Findings suggest that increases in the majority of circulating CVRFs are not associated with worse cognition in cognitively healthy older adults.

Apolipoproteins and Suicide: A Potential Psychiatric Biomarker

Every year around 800,000 people commit suicide, this represents one death every 40 s. In the search for possible biological biomarkers associated with suicide and/or psychiatric disorders, serum cholesterol levels have been extensively explored. Several studies indicate that cholesterol and associated proteins, especially apolipoproteins (Apos), may play an important role in the diagnosis, prognosis, and susceptibility of suicidal behavior. Here, we describe the current knowledge and findings in the relationship between apolipoproteins and suicide.HIGHLIGHTSThis is the first systematic review of Apos in relation to suicidal behavior.Dysregulations of Apos expression has been observed in patients with suicidal behavior.Apos seem to be associated with cognitive dysfunction in suicide attempters.ApoE is a potential biomarker regarding suicidal behavior.

A plasma protein signature associated with cognitive function in men without severe cognitive impairment

BACKGROUND

A minimally invasive blood-based assessment of cognitive function could be a promising screening strategy to identify high-risk groups for the incidence of Alzheimer's disease.

METHODS

The study included 448 cognitively unimpaired men (mean age 64.1 years) drawn from the Geelong Osteoporosis Study. A targeted mass spectrometry-based proteomic assay was performed to measure the abundance levels of 269 plasma proteins followed by linear regression analyses adjusted for age and APOE ε4 carrier status to identify the biomarkers related to overall cognitive function. Furthermore, two-way interactions were conducted to see whether Alzheimer's disease-linked genetic variants or health conditions modify the association between biomarkers and cognitive function.

RESULTS

Ten plasma proteins showed an association with overall cognitive function. This association was modified by allelic variants in genes ABCA7, CLU, BDNF and MS4A6A that have been previously linked to Alzheimer's disease. Modifiable health conditions such as mood disorders and poor bone health, which are postulated to be risk factors for Alzheimer's disease, also impacted the relationship observed between protein marker levels and cognition. In addition to the univariate analyses, an 11-feature multianalyte model was created using the least absolute shrinkage and selection operator regression that identified 10 protein features and age associated with cognitive function.

CONCLUSIONS

Overall, the present study revealed plasma protein candidates that may contribute to the development of a blood-based screening test for identifying early cognitive changes. This study also highlights the importance of considering other risk factors in elucidating the relationship between biomarkers and cognition, an area that remains largely unexplored.

Identification of Plasma Proteins as Biomarkers for Mild Cognitive Impairment and Alzheimer's Disease Using Liquid Chromatography-Tandem Mass Spectrometry

Blood proteins can be used for biomarkers to monitor the progression of cognitive decline, even in the early stages of disease. In this study, we developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based blood test to identify plasma proteins that can be used to detect mild cognitive impairment (MCI) and Alzheimer's disease (AD). Using this system, we quantified plasma proteins using isotope-labeled synthetic peptides. A total of 192 patients, including 63 with AD, 71 with MCI, and 58 non-demented controls (NDCs), were analyzed. Multinomial regression and receiver operating characteristic (ROC) analyses were performed to identify specific combinations of plasma protein panels that could differentiate among NDCs, those with MCI, and those with AD. We identified eight plasma protein biomarker candidates that can be used to distinguish between MCI and AD. These biomarkers were associated with coagulation pathways, innate immunity, lipid metabolism, and nutrition. The clinical potential to differentiate cognitive impairment from NDC was assessed using area under the curve values from ROC analysis, which yielded values of 0.83 for males and 0.71 for females. This LC-MS-based plasma protein panel allows the pathophysiology of AD to be followed through detection of cognitive decline and disease progression markers.

Alzheimer's disease-associated complement gene variants influence plasma complement protein levels

BACKGROUND

Alzheimer's disease (AD) has been associated with immune dysregulation in biomarker and genome-wide association studies (GWAS). GWAS hits include the genes encoding complement regulators clusterin (CLU) and complement receptor 1 (CR1), recognised as key players in AD pathology, and complement proteins have been proposed as biomarkers.

MAIN BODY

To address whether changes in plasma complement protein levels in AD relate to AD-associated complement gene variants we first measured relevant plasma complement proteins (clusterin, C1q, C1s, CR1, factor H) in a large cohort comprising early onset AD (EOAD; n = 912), late onset AD (LOAD; n = 492) and control (n = 504) donors. Clusterin and C1q were significantly increased (p < 0.001) and sCR1 and factor H reduced (p < 0.01) in AD plasma versus controls. ROC analyses were performed to assess utility of the measured complement biomarkers, alone or in combination with amyloid beta, in predicting AD. C1q was the most predictive single complement biomarker (AUC 0.655 LOAD, 0.601 EOAD); combining C1q with other complement or neurodegeneration makers through stepAIC-informed models improved predictive values slightly. Effects of GWS SNPs (rs6656401, rs6691117 in CR1; rs11136000, rs9331888 in CLU; rs3919533 in C1S) on protein concentrations were assessed by comparing protein levels in carriers of the minor vs major allele. To identify new associations between SNPs and changes in plasma protein levels, we performed a GWAS combining genotyping data in the cohort with complement protein levels as endophenotype. SNPs in CR1 (rs6656401), C1S (rs3919533) and CFH (rs6664877) reached significance and influenced plasma levels of the corresponding protein, whereas SNPs in CLU did not influence clusterin levels.

CONCLUSION

Complement dysregulation is evident in AD and may contribute to pathology. AD-associated SNPs in CR1, C1S and CFH impact plasma levels of the encoded proteins, suggesting a mechanism for impact on disease risk.

Metabolic syndrome biomarkers relate to rate of cognitive decline in MCI and dementia stages of Alzheimer's disease

BACKGROUND

The relationship between biomarkers of metabolic syndrome and insulin resistance, plasma triglyceride/HDL cholesterol (TG/HDL-C) ratio, on the rate of cognitive decline in mild cognitive impairment (MCI) and dementia stages of Alzheimer's disease (AD) is unknown. The role of peripheral and cerebrospinal fluid (CSF) levels of Apolipoprotein A1 (ApoA1), a key functional component of HDL, on cognitive decline also remains unclear among them. Here we evaluate baseline plasma TG/HDL-C ratio and CSF and plasma ApoA1 levels and their relation with cognitive decline in the MCI and Dementia stages of AD.

PATIENTS AND METHODS

A retrospective longitudinal study (156 participants; 106 MCI, 50 AD dementia) from the Alzheimer's Disease Neuroimaging Initiative, with an average of 4.0 (SD 2.8) years follow-up. Baseline plasma TG/HDL-C, plasma, and CSF ApoA1 and their relationship to inflammation and blood-brain barrier (BBB) biomarkers and longitudinal cognitive outcomes were evaluated. Multivariable linear mixed effect models were used to assess the effect of baseline analytes with longitudinal changes in Mini-Mental State Exam (MMSE), Clinical Dementia Rating-Sum of Boxes (CDR-SB), and Logical Memory delayed recall (LM) score after controlling for well-known covariates.

RESULTS

A total of 156 participants included 98 women, 63%; mean age was 74.9 (SD 7.3) years. At baseline, MCI and dementia groups did not differ significantly in TG/HDL-C (Wilcoxon W statistic = 0.39, p = 0.39) and CSF ApoA1 levels (W = 3642, p = 0.29), but the dementia group had higher plasma ApoA1 than the MCI group (W = 4615, p = 0.01). Higher TG/HDL-C ratio was associated with faster decline in CDR-SB among MCI and dementia groups. Higher plasma ApoA1 was associated with faster decline in MMSE and LM among MCI, while in contrast higher CSF ApoA1 levels related to slower cognitive decline in MMSE among MCI. CSF and plasma ApoA1 also show opposite directional correlations with biomarkers of BBB integrity. CSF but not plasma levels of ApoA1 positively correlated to inflammation analytes in the AGE-RAGE signaling pathway in diabetic complications (KEGG ID:KO04933).

CONCLUSIONS

Biomarkers of metabolic syndrome relate to rate of cognitive decline among MCI and dementia individuals. Elevated plasma TG/HDL-C ratio and plasma ApoA1 are associated with worse cognitive outcomes in MCI and dementia participants. CSF ApoA1 and plasma ApoA1 likely have different roles in AD progression in MCI stage.

Alternations of Lipoprotein Profiles in the Plasma as Biomarkers of Huntington's Disease

Alterations in lipid composition and disturbed lipoprotein metabolism are involved in the pathomechanism of Huntington's disease (HD). Here, we measured 112 lipoprotein subfractions and components in the plasma of 20 normal controls, 24 symptomatic (sympHD) and 9 presymptomatic (preHD) HD patients. Significant changes were found in 30 lipoprotein subfractions and components in all HD patients. Plasma levels of total cholesterol (CH), apolipoprotein (Apo)B, ApoB-particle number (PN), and components of low-density lipoprotein (LDL) were lower in preHD and sympHD patients. Components of LDL4, LDL5, LDL6 and high-density lipoprotein (HDL)4 demonstrated lower levels in preHD and sympHD patients compared with controls. Components in LDL3 displayed lower levels in sympHD compared with the controls, whereas components in very low-density lipoprotein (VLDL)5 were higher in sympHD patients compared to the controls. The levels of components in HDL4 and VLDL5 demonstrated correlation with the scores of motor assessment, independence scale or functional capacity of Unified Huntington's Disease Rating Scale. These findings indicate the potential of components of VLDL5, LDL3, LDL4, LDL5 and HDL4 to serve as the biomarkers for HD diagnosis and disease progression, and demonstrate substantial evidence of the involvement of lipids and apolipoproteins in HD pathogenesis.

Serum lipid traits and the risk of dementia: A cohort study of 254,575 women and 214,891 men in the UK Biobank

Background

Serum lipid traits are associated with cardiovascular disease, but uncertainty remains regarding their associations with dementia.

Methods

From 2006 to 2010, 254,575 women and 214,891 men were included from the UK Biobank. Cox regression estimated overall and sex-specific hazard ratios (HRs) for apolipoprotein A (ApoA), apolipoprotein B (ApoB), HDL, LDL, total cholesterol, triglycerides, lipoprotein A, and various lipid ratios, by quarters and standard deviation (SD) higher, associated with all-cause dementia, Alzheimer's disease (AD) and vascular dementia (VaD). Subgroup analyses by age and social deprivation were conducted.

Findings

Over 11·8 years (median), 3734 all-cause dementia (1,716 women), 1231 AD and 929 VaD were recorded. Compared to respective lowest quarters, highest quarter of ApoA was associated with lower dementia risk (HR, [95% confidence interval (95% CI)]: 0·77 [0·69, 0·86]) while the highest quarter of ApoB was associated with greater risk (HR, 1·12 [1·01, 1·24]). Higher HDL/ApoA and ApoB/ApoA, were associated with greater risk of dementia (HR, 1·12 [1·00, 1·25], per standard deviation (SD), 1.23 [1·11, 1·37], per SD, respectively), LDL/ApoB was inversely associated (HR, 0·85 [0·76, 0·94], per SD. Higher triglycerides was associated with higher dementia risk in <60 years, but the inverse was observed for ≥60 years. Similar associations were observed for VaD and AD.

Interpretation

Apolipoproteins, and their ratios, were associated with the risk of dementia. It may be prudent to consider apolipoproteins, along with circulating cholesterol, when assessing dementia risk.

Funding

University of New South Wales, UK Medical Research Council, and the Australian National Health and Medical Research Council.

Serum levels of apolipoprotein A-I and E are associated with postoperative delirium: A post hoc analysis

Postoperative delirium is a common complication for elderly patients. Detection of phosphorylated neurofilament heavy subunit in the serum reflects axonal damage with postoperative delirium. Although it has been implicated that serum apolipoprotein levels might be associated with senile cognitive disorder, its role in the development of delirium has not been fully investigated. This study examined the association of apolipoproteins with delirium after surgery. This was a post hoc analysis of 117 patients who participated in a prospective observational study of delirium in patients undergoing cancer surgery. Patients were clinically assessed for delirium within the first 5 days of surgery. Serum levels of apolipoprotein A-I, B, and E were measured on postoperative day 3. Forty-one patients (35%) were clinically diagnosed with postoperative delirium. Serum levels of apolipoprotein A-I and B were increased in patients with delirium whereas those of apolipoprotein E were decreased. These changes in apolipoprotein A-I and E levels were associated with the presence of phosphorylated neurofilament heavy subunit in the serum, and were significantly associated with delirium (A-I: adjusted odds ratio [aOR], 6.238; 95% confidence interval [CI], 2.766-20.68; P < .0001; E: aOR, 0.253; 95% CI, 0.066-0.810; P = .0193). A combination of apolipoprotein A-I and E offers significant discrimination between delirium and nondelirium with high accuracy (area under the curve, 0.8899). Serum apolipoprotein A-I and E levels were associated with delirium and the presence of phosphorylated neurofilament heavy subunit in serum. Therefore, apolipoproteins might be useful biomarkers of postoperative delirium.

Comparison of cognitive impairments with lipid profiles and inflammatory biomarkers in unipolar and bipolar depression

Cognitive impairments is one of important accompanied symptom in Unipolar depressive disorder (UD) and bipolar disorder (BD) that was hard to distinguish, as their diagnosis is based on behavioural observations and subjective symptoms. In this study, we could highlight the difference of cognitive ability in UD and BD by testing lipid profiles and inflammatory biomarkers in major depressive episodes (MDE). 207 subjects (96 unipolar and 111 bipolar depressed patients) were included in this study. We applied Montreal Cognitive Assessment (MoCA) to test cognitive ability. The 24-item Hamilton Depression Rating Scale was used for assessment at the beginning of treatment. A series of clinical variables and lipid profiles were collected from clinic record. We detected pro-inflammatory biomarkers Interleukin-1β (IL-1β), Interleukin-6 (IL-6), C-reaction protein (CRP) levels and brain-derived neurotrophic factor (BDNF) by enzyme linked immunosorbent assay. From the results, cognitive impairments were more popular in BD than UD, most obviously in severe cognitive impairments (MoCA score<23). And UD showed better cognitive ability than BD in MoCA, particularly in language domain. Compared lipid profiles like total cholesterol (TC), triglycerides (TG), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), apolipoprotein A1 (ApoA1), Apolipoprotein B (ApoB) and lipoprotein α (Lpα), we found that ApoB was higher in BD than UD that maybe a risk factor in cognition. There was no obviously difference in TC, TG, HDL-C, LDL-C, ApoA1, or Lpα. Also, we found CRP level in BD was higher than UD, and showed no significant difference in IL-1β and IL-6 levels. Furthermore, BDNF level which was neurotrophic biomarker for cognition and mood was significantly declined in BD compared with UD. Correlation analysis showed that ApoB and CRP was negative closed associated with MoCA scores. And BDNF level was positive related with cognitive ability in MDE patients. From our results mentioned that quantitative lipid profiles and inflammatory biomarkers analysis might help to objectively identify between these disorders and up our understanding of their pathophysiology. And ApoB, CRP and BDNF could be as potential peripheral candidates in cognitive evaluation to distinguish UD and BD.

Association of plasma apolipoproteins and levels of inflammation-related factors with different stages of Alzheimer's disease: a cross-sectional study

OBJECTIVE

Blood-based biomarkers for the early diagnosis of Alzheimer's disease (AD) are a 'Holy Grail' of AD research. Growing evidence shows that levels of apolipoproteins and various inflammation-related factors are altered in the peripheral blood of patients with AD. The purpose of this study was to clear and definite whether these biomarkers are differentially expressed at the early stages of AD, and could be a biomarker as an early diagnosis of the disease.

DESIGN

Observation study.

SETTING

This study was a part of the Sino Longitudinal Study on Cognitive Decline, an ongoing prospective cohort study (ClinicalTrials.gov identifier: NCT03370744) that centres on Xuanwu Hospital (Beijing, China) in cooperation with an alliance of 94 hospitals from 50 cities across China.

PARTICIPANTS

In the present study, 416 right-handed Chinese Han subjects were recruited through standardised public advertisements from 2014 to 2019.

OUTCOME MEASURES

Concentrations of plasma apolipoprotein A1, apolipoprotein CIII (ApoCIII), apolipoprotein E (ApoE), A-2-macroglobulin (A2M), complement C3 (C3) and complement factor H (FH) were determined using a commercial multiplex Luminex-based panel in normal controls (NC), subjective cognitive decline (SCD), mild cognitive impairment and AD groups.

RESULTS

For individual analysis, pairwise comparisons showed that: (1) For SCD versus NC, no biomarker showed significant difference; (2) For amnestic mild cognitive impairment (aMCI) versus NC, levels of ApoCIII, ApoE, A2M, C3 and FH increased significantly; and (3) For AD versus NC, amounts of C3 increased. For models differentiating clinical groups, discriminant analysis was performed by including all protein markers, age, sex, genotype and education level in the model. This approach could distinguish between patients with aMCI (area under the curve (AUC): 0.743) and AD (AUC: 0.837) from NC.

CONCLUSION

Our results suggest that concentrations of certain apolipoproteins and inflammation-related factors are altered at the early stage of AD, and could be useful biomarkers for early diagnosis.

TRIAL REGISTRATION NUMBER

NCT03370744.

Cerebrospinal Fluid Proteome Alterations Associated with Neuropsychiatric Symptoms in Cognitive Decline and Alzheimer's Disease

Although neuropsychiatric symptoms (NPS) are common and severely affect older people with cognitive decline, little is known about their underlying molecular mechanisms and relationships with Alzheimer’s disease (AD). The aim of this study was to identify and characterize cerebrospinal fluid (CSF) proteome alterations related to NPS. In a longitudinally followed-up cohort of subjects with normal cognition and patients with cognitive impairment (MCI and mild dementia) from a memory clinic setting, we quantified a panel of 790 proteins in CSF using an untargeted shotgun proteomic workflow. Regression models and pathway enrichment analysis were used to investigate protein alterations related to NPS, and to explore relationships with AD pathology and cognitive decline at follow-up visits. Regression analysis selected 27 CSF proteins associated with NPS. These associations were independent of the presence of cerebral AD pathology (defined as CSF p-tau181/Aβ1−42 > 0.0779, center cutoff). Gene ontology enrichment showed abundance alterations of proteins related to cell adhesion, immune response, and lipid metabolism, among others, in relation to NPS. Out of the selected proteins, three were associated with accelerated cognitive decline at follow-up visits after controlling for possible confounders. Specific CSF proteome alterations underlying NPS may both represent pathophysiological processes independent from AD and accelerate clinical disease progression.

Novel Exosome Biomarker Candidates for Alzheimer's Disease Unravelled Through Mass Spectrometry Analysis

Exosomes are small extracellular vesicles (EVs) present in human biofluids that can transport specific disease-associated molecules. Consequently blood-derived exosomes have emerged as important peripheral biomarker sources for a wide range of diseases, among them Alzheimer’s disease (AD). Although there is no effective cure for AD, an accurate diagnosis, relying on easily accessible peripheral biofluids, is still necessary to discriminate this disease from other dementias, test potential therapies and even monitor rate of disease progression. The ultimate goal is to produce a cost-effective and widely available alternative, which can also be employed as a first clinical screen. In this study, EVs with exosome-like characteristics were isolated from serum of Controls and AD cases through precipitation- and column-based methods, followed by mass spectrometry analysis. The resulting proteomes were characterized by Gene Ontology (GO) and multivariate analyses. Although GO terms were similar for exosomes’ proteomes of Controls and ADs, using both methodologies, a clear segregation of disease cases was obtained when using the precipitation-based method. Nine significantly different abundant proteins were identified between Controls and AD cases, representing putative biomarker candidate targets. Among them are AACT and C4BPα, two Aβ-binding proteins, whose exosome levels were further validated in individuals from independent cohorts using antibody-based approaches. The findings discussed represent an important contribution to the identification of novel exosomal biomarker candidates useful as potential blood-based tools for AD diagnosis.

Isotopic N,N-dimethyl leucine tags for absolute quantification of clusterin and apolipoprotein E in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia and one of the leading causes of death in the United States. In the past decades, extensive efforts have been devoted to biomarker discovery for early diagnosis and treatment of AD. Herein, this study aims to quantify clusterin (CLU) and apolipoprotein E (APOE) in blood samples from AD patients and evaluate these two proteins as potential biomarkers in AD diagnosis. In-house synthesized 5-plex isotopic N,N-dimethyl leucine (iDiLeu) tags were used to label target peptide standards at different concentrations to construct standard curves. Our study revealed that the levels of CLU and APOE exhibited clear differences in male vs. female AD groups but not in male vs. female non-AD groups. In contrast, the levels of serum CLU and APOE did not show statistically significant differences in the AD groups and non-AD groups. Principal component analysis (PCA) with CLU and APOE showed some separation between the AD and non-AD participants. Significance: Dissecting CLU and APOE heterogeneity in AD pathogenesis may therefore facilitate delineating the pathological relevance for sex-related pathways, leading to personalized medicine in the future. Collectively, this study introduces a cost-effective absolute quantitative proteomics strategy for target protein quantitation and lays the foundation for future investigation of CLU and APOE as potential biomarkers for AD. SIGNIFICANCE STATEMENT: As blood-based biomarkers for AD diagnosis are cost-effective and introduce less invasiveness, discovery and validation of biomarkers in the blood samples of AD patients have become a hot topic in Alzheimer's and dementia research. Thus far, amyloid β (Aβ), total-tau and phosphorylated tau (p-tau) in blood show great accuracy and specificity in diagnosis of AD. However, the underlying mechanism of AD pathology remains to be elusive and complex. Besides these well studied proteins, many other proteins, such as clusterin (CLU) and apolipoprotein E (APOE) have also been found to be related to AD development. It has been implicated that these two proteins are involved in Aβ clearance and deposition. In this study, we measure the absolute concentrations of these two proteins in blood and shed some light on the potential roles of CLU and APOE in AD pathology. Dissecting CLU and APOE heterogeneity in AD pathogenesis may therefore facilitate delineating the pathological relevance for specific pathways between different genders, leading to personalized medicine in the future. Collectively, this study introduces a cost-effective absolute quantitative proteomics strategy for target protein quantitation and lays the foundation for future investigation of CLU and APOE as potential biomarkers for AD.

Investigating Causal Relations Between Circulating Metabolites and Alzheimer's Disease: A Mendelian Randomization Study

BACKGROUND

Metabolomics is a promising approach that can be used to understand pathophysiological pathways of Alzheimer's disease (AD). However, the causal relationships between metabolism and AD are poorly understood.

OBJECTIVE

We aimed to investigate the causal association between circulating metabolites and risk of AD through two-sample Mendelian randomization (MR) approach.

METHODS

Genetic associations with 123 circulating metabolic traits were utilized as exposures. Summary statistics data from International Genomics of Alzheimer's Project was used in primary analysis, including 21,982 AD cases and 41,944 controls. Validation was performed using family history of AD data from UK Biobank (27,696 cases of maternal AD, 14,338 cases of paternal AD, and 272,244 controls). We utilized inverse-variance weighted method as primary method.

RESULTS

We found significantly increased risks of developing AD per standard deviation increase in the levels of circulating ApoB (odd ratio[OR] = 3.18; 95% confidence interval[CI]: 1.52-6.66, p = 0.0022), glycoprotein acetyls (OR = 1.21; 95% CI: 1.05-1.39, p = 0.0093), total cholesterol (OR = 2.73; 95% CI: 1.41-5.30, p = 0.0030), and low-density lipoprotein (LDL) cholesterol (OR = 2.34; 95% CI: 1.53-3.57, p = 0.0001). Whereas glutamine (OR = 0.81; 95% CI: 0.71-0.92, p = 0.0011) were significantly associated with lower risk of AD. We also detected causal effects of several different composition of LDL fractions on increased AD risk, which has been verified in validation. However, we found no association between circulating high-density lipoprotein cholesterol and AD.

CONCLUSION

Our findings suggest causal effects of circulating glycoprotein acetyls, ApoB, LDL cholesterol, and serum total cholesterol on higher risk of AD, whereas glutamine showed the protective effect.

Sialic Acid Ameliorates Cognitive Deficits by Reducing Amyloid Deposition, Nerve Fiber Production, and Neuronal Apoptosis in a Mice Model of Alzheimer’s Disease

(1) Background: As a natural carbohydrate, sialic acid (SA) is helpful for brain development, cognitive ability, and the nervous system, but there are few reports about the effect of SA on Alzheimer’s disease (AD). (2) Method: The present study evaluated the effect of SA on cognitive ability, neuronal activity, Aβ formation, and tau hyperphosphorylation in a double transgenic AD (2×Tg-AD) mice model. The 2×Tg-AD mice were randomly divided into four groups: the AD control group, 17 mg/kg SA-treated AD group, 84 mg/kg SA-treated AD group, and 420 mg/kg SA-treated AD group. Mice from all four groups were fed to 7 months of age for the behavioral test and to 9 months of age for the pathological factors investigation. (3) Results: In the Morris water maze, the escape latency significantly decreased on the fifth day in the SA-treated groups. The number of rearing and crossing times in the open field test also increased significantly, compared with the control group. SA treatment significantly reduced amyloid β-peptide (Aβ) and nerve fibers and increased the number of Nissl bodies in the brain of AD mice. (4) Conclusions: SA reduced the neuron damage by reducing Aβ and inhibited tau protein hyperphosphorylation, which improved the cognitive ability and mobility of AD mice.

Association between clinical symptoms and apolipoprotein A1 or apolipoprotein B levels is regulated by apolipoprotein E variant rs429358 in patients with chronic schizophrenia

BACKGROUND

The apolipoprotein E (ApoE) gene polymorphisms are correlated with blood lipid levels and several neuropsychiatric symptoms. Therefore, this study aimed to examine whether the ApoE rs429358 affected the development and clinical symptoms of schizophrenia and to explore the relationship between apolipoproteins levels and clinical symptoms.

METHODS

The ApoE rs429358 was genotyped using a case-control design. The Positive and Negative Syndrome Scale (PANSS) was employed to evaluate the psychopathology of all patients.

RESULTS

A total of 637 patients with schizophrenia and 467 healthy controls were recruited. We found no significant differences in the genotype and allele distribution between the patient and control groups. A significant correlation between PANSS negative symptoms and ApoA1 levels (p = 0.048) or ApoB levels (p = 0.001) was found in patients with schizophrenia, which was also confirmed by linear regression analyses (p = 0.048 vs. p = 0.001). Interestingly, only in the T homozygote group, ApoA1 and ApoB levels were predictors of the PANSS negative symptom score (p = 0.008 vs. p = 0.012), while in the C allele carrier group, no correlation was observed.

CONCLUSIONS

This study found that the levels of ApoA1 and ApoB were negatively associated with negative symptoms of patients with schizophrenia. Furthermore, the association between ApoA1 or ApoB levels and psychopathology of schizophrenia was regulated by ApoE rs429358.

Sex Differences in the Association between Different Obesity Parameters and Cognitive Function in Older Adults: A Cross-Sectional Study in Rural China

BACKGROUND

Early identification of risk factors for cognition decline may contribute to the interventions for Alzheimer's disease. Obesity is a common modifiable risk factor for chronic diseases. The association between obesity and cognition in older adults is limited, and sex differences in this area have not been well recognized.

OBJECTIVE

The aim of the study was to observe the sex differences in the relationship between obesity and cognition in a rural community-dwelling older population of Guizhou, China.

METHODS

Data were gathered from the baseline survey of a cohort study of older people in rural areas of Guizhou, China. Demographic and behavioral data (sex, age, education, household income, smoking history, drinking history, history of head injury, diet, and level of physical exercise time) were collected. The Mini-Mental State Examination (MMSE) was used to assess cognitive function. Body mass index (BMI), waist circumference (WC), hip circumference (HC), and waist-to-hip ratio (WHR) were used as different measures of obesity. Comparisons between the groups were made by the Wilcoxon rank-sum test or Kruskal-Wallis H test. Restricted cubic spline regression was used to examine a dose-response relationship between obesity indicators and cognitive function. Linear relationships were performed by the multivariable linear regression model.

RESULTS

A total of 1,654 participants including 964 women and 690 men were enrolled in this study. After adjustment, BMI showed a nonlinear relationship with MMSE scores in women. There was a significant trend toward increasing MMSE scores at the low end of BMI (13.52-20.10 kg/m2, p = 0.014). The multivariable linear regression model showed that MMSE increased by 0.631 (p < 0.001) for every one standard deviation increase in HC in women. No association was found between obesity parameters and cognitive function in men.

CONCLUSION

Our results suggest that there are significant sex differences in some obesity parameters and cognition in an older Chinese population. BMI and HC are positively associated with cognitive function in women. No association was found between obesity measures and cognitive function in men.

Plasmalogens improve swimming performance by modulating the expression of genes involved in amino acid and lipid metabolism, oxidative stress, and ferroptosis in an Alzheimer's disease zebrafish model

Plasmalogens (PLs) are critical to human health. Studies have reported a link between the downregulation of PLs levels and cognitive impairments in patients with Alzheimer's disease (AD). However, the underlying mechanisms remain to be clarified. In the present study, an AlCl₃-induced AD zebrafish model was established, and the model was used to elucidate the neuroprotective effects of PLs on AD by analysing the transcriptional profiles of zebrafish in the control, AD model, AD_PL, and PL groups. Chronic AlCl₃ exposure caused swimming performance impairments in the zebrafish, yet PLs supplementation could improve the dyskinesia recovery rate in the AD zebrafish model. Through transcriptional profiling, a total of 5413 statistically significant differentially expressed genes (DEGs) were identified among the groups. In addition to the DEGs involved in amino acid metabolism, we found that the genes related to iron homeostasis, lipid peroxidation, and oxidative stress, all of which contribute to ferroptosis, were dramatically altered among different groups. These results suggest that seafood-derived PLs, in addition to their role in eliminating oxidative stress, can improve the swimming performance in AlCl₃-exposed zebrafish partly by suppressing neuronal ferroptosis and accelerating synaptic transmission at the transcriptional level. This study provides evidence for PLs to be developed as a functional food supplement to relieve AD symptoms.

Plasma High Density Lipoprotein Small Subclass is Reduced in Alzheimer's Disease Patients and Correlates with Cognitive Performance

Background:

The link between cholesterol and Alzheimer’s disease (AD) has received much attention, as evidence suggests high levels of cholesterol might be an AD risk factor. The carriage of cholesterol and lipids through the body is mediated via lipoproteins, some of which, particularly apolipoprotein E (ApoE), are intimately linked with AD. In humans, high density lipoprotein (HDL) is regarded as a “good” lipid complex due to its ability to enable clearance of excess cholesterol via ‘cholesterol reverse transport’, although its activities in the pathogenesis of AD are poorly understood. There are several subclasses of HDL; these range from the newly formed small HDL, to much larger HDL.

Objective:

We examined the major subclasses of HDL in healthy controls, mild cognitively impaired, and AD patients who were not taking statins to determine whether there were HDL profile differences between the groups, and whether HDL subclass levels correlated with plasma amyloid-β (Aβ) levels or brain Aβ deposition.

Methods:

Samples from AIBL cohort were used in this study. HDL subclass levels were assessed by Lipoprint while Aβ_1–42 levels were assessed by ELISA. Brain Aβ deposition was assessed by PET scan. Statistical analysis was performed using parametric and non-parametric tests.

Results:

We found that small HDL subclass is reduced in AD patients and it correlates with cognitive performance while plasma Aβ concentrations do not correlate with lipid profile or HDL subfraction levels.

Conclusion:

Our data indicate that AD patients exhibit altered plasma HDL profile and that HDL subclasses correlate with cognitive performances.

Discovery of Novel Markers for Identifying Cognitive Decline Using Neuron-Derived Exosomes

Alzheimer's disease (AD), the predominant cause of late-life dementia, has a multifactorial etiology. Since there are few therapeutic options for symptomatic AD, research is increasingly focused on the identification of pre-symptomatic biomarkers. Recently, evaluation of neuron-derived exosomal markers has emerged as a promising novel approach for determining neuronal dysfunction. We aimed to identify novel neuron-derived exosomal markers that signify a transition from normal aging to Mild Cognitive Impairment (MCI) and then to clinically established AD, a sequence we refer to as AD progression. By using a Tandem Mass Tag-based quantitative proteomic approach, we identified a total of 360 neuron-derived exosomal proteins. Subsequent fuzzy c-means clustering revealed two clusters of proteins displaying trends of gradually increasing/decreasing expression over the period of AD progression (normal to MCI to AD), both of which were mainly involved in immune response-associated pathways, proteins within these clusters were defined as bridge proteins. Several differentially expressed proteins (DEPs) were identified in the progression of AD. The intersections of bridge proteins and DEPs were defined as key proteins, including C7 (Complement component 7), FERMT3 (Fermitin Family Member 3), CAP1 (Adenylyl cyclase-associated protein 1), ENO1 (Enolase 1), and ZYX (Zyxin), among which the expression patterns of C7 and ZYX were almost consistent with the proteomic results. Collectively, we propose that C7 and ZYX might be two novel neuron-derived exosomal protein markers, expression of which might be used to evaluate cognitive decline before a clinical diagnosis of AD is warranted.

High-density lipoprotein in Alzheimer's disease: From potential biomarkers to therapeutics

The inverse correlation between high-density lipoprotein (HDL) levels in vivo and the risk of Alzheimer's disease (AD) has become an inspiration for HDL-inspired AD therapy, including plain HDL and various intelligent HDL-based drug delivery systems. In this review, we will focus on the two endogenous HDL subtypes in the central nervous system (CNS), apolipoprotein E-based HDL (apoE-HDL) and apolipoprotein A-I-based HDL (apoA-I-HDL), especially their influence on AD pathophysiology to reveal HDL's potential as biomarkers for risk prediction, and summarize the relevant therapeutic mechanisms to propose possible treatment strategies. We will emphasize the latest advances of HDL as therapeutics (plain HDL and HDL-based drug delivery systems) to discuss the potential for AD therapy and review innovative techniques in the preparation of HDL-based nanoplatforms to provide a basis for the rational design and future development of anti-AD drugs.

Elevated Plasma Free Fatty Acid Susceptible to Early Cognitive Impairment in Type 2 Diabetes Mellitus

BACKGROUND

Elevated free fatty acid (FFA) induces lipotoxicity, attributed to diabetes and cognitive decline. Sterol regulatory element-binding protein-1c (SREBP-1c) regulates lipid metabolism.

OBJECTIVE

We investigated the roles of FFA in mild cognitive impairment (MCI) of type 2 diabetes mellitus (T2DM) patients and determine its association with rs11868035 polymorphism.

METHODS

We recruited 191 Chinese T2DM patients into two groups through Montreal Cognitive Assessment. Demographic and clinical data were collected, multiple domain cognitive functions were tested, plasma FFA levels were measured through ELISA, and SREBP-1c rs11868035 genotype was detected using the Seqnome method.

RESULTS

In comparison with the healthy-cognition group (n = 128), the MCI group (n = 63) displayed lower glucose control (p = 0.012) and higher plasma FFA level (p = 0.021), which were independent risk factors of MCI in T2DM patients in multivariate regression analysis (OR = 1.270, p = 0.003; OR = 1.005, p = 0.036). Additionally, the plasma FFA levels of MCI patients were positively correlated with Stroop color word test-C time scores (r = 0.303, p = 0.021) and negatively related to apolipoprotein A1 levels (r = -0.311, p = 0.017), which are associated positively with verbal fluency test scores (r = 0.281, p = 0.033). Both scores reflected attention ability and executive function. Moreover, the G allele carriers of rs11868035 showed higher digit span test scores than non-carriers in T2DM patients (p = 0.019) but without correlation with plasma FFA levels.

CONCLUSION

In T2DM, elevated plasma level of FFA, when combined with lower apolipoprotein A1 level portends abnormal cholesterol transport, were susceptible to early cognitive impairment, especially for attention and execution deficits. The G allele of SREBP-1c rs11868035 may be a protective factor for memory.

Biomarkers for the Clinical Diagnosis of Alzheimer's Disease: Metabolomics Analysis of Brain Tissue and Blood

With an increase in aging populations worldwide, age-related diseases such as Alzheimer's disease (AD) have become a global concern. At present, a cure for neurodegenerative disease is lacking. There is an urgent need for a biomarker that can facilitate the diagnosis, classification, prognosis, and treatment response of AD. The recent emergence of highly sensitive mass-spectrometry platforms and high-throughput technology can be employed to discover and catalog vast datasets of small metabolites, which respond to changed status in the body. Metabolomics analysis provides hope for a better understanding of AD as well as the subsequent identification and analysis of metabolites. Here, we review the state-of-the-art emerging candidate biomarkers for AD.

Mendelian Randomization of Dyslipidemia on Cognitive Impairment Among Older Americans

Background: Altered lipid metabolism may be a risk factor for dementia, and blood cholesterol level has a strong genetic component. We tested the hypothesis that dyslipidemia (either low levels of high-density lipoprotein cholesterol (HDL-C) or high total cholesterol) is associated with cognitive status and domains, and assessed causality using genetic predisposition to dyslipidemia as an instrumental variable. Methods: Using data from European and African genetic ancestry participants in the Health and Retirement Study, we selected observations at the first non-missing biomarker assessment (waves 2006-2012). Cognition domains were assessed using episodic memory, mental status, and vocabulary tests. Overall cognitive status was categorized in three levels (normal, cognitive impairment non-dementia, dementia). Based on 2018 clinical guidelines, we compared low HDL-C or high total cholesterol to normal levels. Polygenic scores for dyslipidemia were used as instrumental variables in a Mendelian randomization framework. Multivariable logistic regressions and Wald-type ratio estimators were used to examine associations. Results: Among European ancestry participants (n = 8,781), at risk HDL-C levels were associated with higher odds of cognitive impairment (OR = 1.20, 95% CI: 1.03, 1.40) and worse episodic memory, specifically. Using cumulative genetic risk for HDL-C levels as a valid instrumental variable, a significant causal estimate was observed between at risk low HDL-C levels and higher odds of dementia (OR = 2.15, 95% CI: 1.16, 3.99). No significant associations were observed between total cholesterol levels and cognitive status. No significant associations were observed in the African ancestry sample (n = 2,101). Conclusion: Our study demonstrates low blood HDL-C is a potential causal risk factor for impaired cognition during aging in non-Hispanic whites of European ancestry. Dyslipidemia can be modified by changing diets, health behaviors, and therapeutic strategies, which can improve cognitive aging. Studies on low density lipoprotein cholesterol, the timing of cholesterol effects on cognition, and larger studies in non-European ancestries are needed.

Association between cognitive impairment and apolipoprotein A1 or apolipoprotein B levels is regulated by apolipoprotein E variant rs429358 in patients with chronic schizophrenia

ApoE gene polymorphism may be involved in the change in blood lipid profile and cognitive impairment of the general population. However, few studies explored the effects of ApoE gene polymorphism on blood lipid levels and cognition in schizophrenia. The Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) was employed to evaluate the cognition and the SNPStats was used to investigate the association of ApoE rs429358 with schizophrenia. The models of analysis of covariance and multivariate analysis were conducted to investigate the effect of ApoE rs429358 on cognition in schizophrenia. Altogether, 637 patients with schizophrenia and 467 healthy controls were recruited in this study. The findings in the case group found that both the ApoA1 and ApoB levels were predictors for RBANS total score (p < 0.001 vs. p = 0.011), immediate memory (p < 0.001 vs. p = 0.019), language (p < 0.001 vs. p = 0.013), attention (p < 0.001 vs. p < 0.001), except ApoA1 level only was a predictor for visuospatial/constructional (p = 0.014) and delayed memory (p < 0.001). When the association was examined in different ApoE rs429358 genotype subgroups, the association between ApoA1 level and RBANS scores (except for the language score) or between ApoB level and RBANS scores (except for the attention score) was regulated by ApoE rs429358. Our results suggest that patients with schizophrenia have broad cognitive impairment compared with healthy controls. For patients with schizophrenia, both ApoA1 and ApoB levels were positively associated with cognition. There was a significant association between ApoA1 or ApoB levels and cognition in schizophrenia, which was regulated by the ApoE rs429358.

Exosomal Aβ-Binding Proteins Identified by "In Silico" Analysis Represent Putative Blood-Derived Biomarker Candidates for Alzheimer´s Disease

The potential of exosomes as biomarker resources for diagnostics and even for therapeutics has intensified research in the field, including in the context of Alzheimer´s disease (AD). The search for disease biomarkers in peripheral biofluids is advancing mainly due to the easy access it offers. In the study presented here, emphasis was given to the bioinformatic identification of putative exosomal candidates for AD. The exosomal proteomes of cerebrospinal fluid (CSF), serum and plasma, were obtained from three databases (ExoCarta, EVpedia and Vesiclepedia), and complemented with additional exosomal proteins already associated with AD but not found in the databases. The final biofluids’ proteomes were submitted to gene ontology (GO) enrichment analysis and the exosomal Aβ-binding proteins that can constitute putative candidates were identified. Among these candidates, gelsolin, a protein known to be involved in inhibiting Abeta fibril formation, was identified, and it was tested in human samples. The levels of this Aβ-binding protein, with anti-amyloidogenic properties, were assessed in serum-derived exosomes isolated from controls and individuals with dementia, including AD cases, and revealed altered expression patterns. Identification of potential peripheral biomarker candidates for AD may be useful, not only for early disease diagnosis but also in drug trials and to monitor disease progression, allowing for a timely therapeutic intervention, which will positively impact the patient’s quality of life.

Paraoxonase-1 and Other HDL Accessory Proteins in Neurological Diseases

The burden of neurological diseases continues to increase as they still are the leading cause of disability and the second-leading cause of death worldwide [...].

Change in the plasma proteome associated with canine cognitive dysfunction syndrome (CCDS) in Thailand

BACKGROUND

Canine cognitive dysfunction syndrome (CCDS) is a progressive neurodegenerative disorder found in senior dogs. Due to the lack of biological markers, CCDS is commonly underdiagnosed. The aim of this study was to identify potential plasma biomarkers using proteomics techniques and to increase our understanding of the pathogenic mechanism of the disease. Plasma amyloid beta 42 (Aβ₄₂) has been seen to be a controversial biomarker for CCDS. Proteomics analysis was performed for protein identification and quantification.

RESULTS

Within CCDS, ageing, and adult dogs, 87 proteins were identified specific to Canis spp. in the plasma samples. Of 87 proteins, 48 and 41 proteins were changed in the ageing and adult groups, respectively. Several distinctly expressed plasma proteins identified in CCDS were involved in complement and coagulation cascades and the apolipoprotein metabolism pathway. Plasma Aβ₄₂ levels considerably overlapped within the CCDS and ageing groups. In the adult group, the Aβ₄₂ level was low compared with that in the other groups. Nevertheless, plasma Aβ₄₂ did not show a correlation with the Canine Cognitive Dysfunction Rating scale (CCDR) score in the CCDS group (p = 0.131, R² = 0.261).

CONCLUSIONS

Our present findings suggest that plasma Aβ₄₂ does not show potential for use as a diagnostic biomarker in CCDS. The nano-LC-MS/MS data revealed that the predictive underlying mechanism of CCDS was the co-occurrence of inflammation-mediated acute phase response proteins and complement and coagulation cascades that partly functioned by apolipoproteins and lipid metabolism. Some of the differentially expressed proteins may serve as potential predictor biomarkers along with Aβ₄₂ in plasma for improved CCDS diagnosis. Further study in larger population-based cohort study is required in validation to define the correlation between protein expression and the pathogenesis of CCDS.

APOE Genotype Differentially Modulates Plasma Lipids in Healthy Older Individuals, with Relevance to Brain Health

Apolipoprotein E (APOE) genotype is an established genetic risk factor for sporadic Alzheimer's disease (AD) but the extent to which APOE genotype influences the plasma lipidome is unknown, even though lipids are potential diagnostic or prognostic biomarkers for AD. We quantified plasma lipids using untargeted liquid chromatography coupled mass spectrometry in a total of 152 non-demented participants aged 65-100 years carrying at least one ɛ2 or ɛ4 allele (ɛ2/ɛ2 or ɛ2/ɛ3, n = 38: ɛ4/ɛ3 or ɛ4/ɛ4, n = 38), who were roughly matched to an ɛ3/ɛ3 control by age, sex, and lipid-lowering medication (n = 76). Low density lipoprotein cholesterol levels were genotype dependent (ɛ4/ɛ4> ɛ4/ɛ3> ɛ3/ɛ3> ɛ2/ɛ3> ɛ2/ɛ2). The greatest variation in lipids was related to the ɛ2 isoform, where various lysophosphatidylcholines and all phosphatidylethanolamine (PE) subclasses were elevated relative to ɛ3/ɛ3 and ɛ4 carriers. APOEɛ4 carriers had reduced phosphatidylinositol relative to ɛ3/ɛ3 and ɛ2 carriers. Logistic regression revealed that ɛ2 carriers were at least 4 times higher odds of being in the highest tertile of PE lipid level relative to ɛ3/ɛ3. The elevation in PE and other phospholipids in ɛ2 carriers may indicate the protective effect of ɛ2 is linked to these phospholipids. Additionally, high baseline PE in cognitively normal participants predicted protection against cognitive decline six years later. Our data suggest substantial modulation of plasma lipids by APOE genotype and therefore indicates possible lipid targets and pathomechanisms involved in AD risk.

Cerebrovascular Changes and Neurodegeneration Related to Hyperlipidemia: Characteristics of the Human ApoB-100 Transgenic Mice

Serum lipid levels are closely related to the structure and function of blood vessels. Chronic hyperlipidemia may lead to damage in both the cardio- and the cerebrovascular systems. Vascular dysfunctions, including impairments of the blood-brain barrier, are known to be associated with neurodegenerative diseases. A growing number of evidence suggests that cardiovascular risk factors, such as hyperlipidemia, may increase the likelihood of developing dementia. Due to differences in lipoprotein metabolism, wild-type mice are protected against diet-induced hypercholesterolemia, and their serum lipid profile is different from that observed in humans. Therefore, several transgenic mouse models have been established to study the role of different apolipoproteins and their receptors in lipid metabolism, as well as the complications related to pathological lipoprotein levels. This mini-review focused on a transgenic mouse model overexpressing an apolipoprotein, the human ApoB-100. We discussed literature data and current advancements on the understanding of ApoB-100 induced cardio- and cerebrovascular lesions in order to demonstrate the involvement of this type of apolipoprotein in a wide range of pathologies, and a link between hyperlipidemia and neurodegeneration.

Novel Protein Biomarkers of Monoamine Metabolism Defects Correlate with Disease Severity

BACKGROUND

Genetic defects of monoamine neurotransmitters are rare neurological diseases amenable to treatment with variable response. They are major causes of early parkinsonism and other spectrum of movement disorders including dopa-responsive dystonia.

OBJECTIVES

The objective of this study was to conduct proteomic studies in cerebrospinal fluid (CSF) samples of patients with monoamine defects to detect biomarkers involved in pathophysiology, clinical phenotypes, and treatment response.

METHODS

A total of 90 patients from diverse centers of the International Working Group on Neurotransmitter Related Disorders were included in the study (37 untreated before CSF collection, 48 treated and 5 unknown at the collection time). Clinical and molecular metadata were related to the protein abundances in the CSF.

RESULTS

Concentrations of 4 proteins were significantly altered, detected by mass spectrometry, and confirmed by immunoassays. First, decreased levels of apolipoprotein D were found in severe cases of aromatic L-amino acid decarboxylase deficiency. Second, low levels of apolipoprotein H were observed in patients with the severe phenotype of tyrosine hydroxylase deficiency, whereas increased concentrations of oligodendrocyte myelin glycoprotein were found in the same subset of patients with tyrosine hydroxylase deficiency. Third, decreased levels of collagen6A3 were observed in treated patients with tetrahydrobiopterin deficiency.

CONCLUSION

This study with the largest cohort of patients with monoamine defects studied so far reports the proteomic characterization of CSF and identifies 4 novel biomarkers that bring new insights into the consequences of early dopaminergic deprivation in the developing brain. They open new possibilities to understand their role in the pathophysiology of these disorders, and they may serve as potential predictors of disease severity and therapies. © 2020 International Parkinson and Movement Disorder Society.

Interaction between high-density lipoproteins and inflammation: Function matters more than concentration!

High-density lipoprotein (HDL) plays an important role in lipid metabolism and especially contributes to the reverse cholesterol transport pathway. Over recent years it has become clear that the effect of HDL on immune-modulation is not only dependent on HDL concentration but also and perhaps even more so on HDL function. This review will provide a concise general introduction to HDL followed by an overview of post-translational modifications of HDL and a detailed overview of the role of HDL in inflammatory diseases. The clinical potential of HDL and its main apolipoprotein constituent, apoA-I, is also addressed in this context. Finally, some conclusions and remarks that are important for future HDL-based research and further development of HDL-focused therapies are discussed.

The Role of HDL and HDL Mimetic Peptides as Potential Therapeutics for Alzheimer's Disease

The role of high-density lipoproteins (HDL) in the cardiovascular system has been extensively studied and the cardioprotective effects of HDL are well established. As HDL particles are formed both in the systemic circulation and in the central nervous system, the role of HDL and its associated apolipoproteins in the brain has attracted much research interest in recent years. Alzheimer’s disease (AD) is the most prevalent neurodegenerative disorder and the leading cause of dementia worldwide, for which there currently exists no approved disease modifying treatment. Multiple lines of evidence, including a number of large-scale human clinical studies, have shown a robust connection between HDL levels and AD. Low levels of HDL are associated with increased risk and severity of AD, whereas high levels of HDL are correlated with superior cognitive function. Although the mechanisms underlying the protective effects of HDL in the brain are not fully understood, many of the functions of HDL, including reverse lipid/cholesterol transport, anti-inflammation/immune modulation, anti-oxidation, microvessel endothelial protection, and proteopathy modification, are thought to be critical for its beneficial effects. This review describes the current evidence for the role of HDL in AD and the potential of using small peptides mimicking HDL or its associated apolipoproteins (HDL-mimetic peptides) as therapeutics to treat AD.

Urinary Apolipoprotein C3 Is a Potential Biomarker for Alzheimer's Disease

INTRODUCTION

Biomarkers of Alzheimer's disease (AD) that can easily be measured in routine health checkups are desirable. Urine is a source of biomarkers that can be collected easily and noninvasively. We previously reported on the comprehensive profile of the urinary proteome of AD patients and identified proteins estimated to be significantly increased or decreased in AD patients by a label-free quantification method. The present study aimed to validate urinary levels of proteins that significantly differed between AD and control samples from our proteomics study (i.e., apolipoprotein C3 [ApoC3], insulin-like growth factor-binding protein 3 [Igfbp3], and apolipoprotein D [ApoD]).

METHODS

Enzyme-linked immunosorbent assays (ELISAs) were performed using urine samples from the same patient and control groups analyzed in the previous proteomics study (18 AD and 18 controls, set 1) and urine samples from an independent group of AD patients and controls (13 AD, 5 mild cognitive impairment [MCI], and 32 controls) from the National Center for Geriatrics and Gerontology Biobank (set 2).

RESULTS

In set 1, the crude urinary levels of ApoD, Igfbp3, and creatinine-adjusted ApoD were significantly higher in the AD group relative to the control group (p = 0.003, p = 0.002, and p = 0.019, respectively), consistent with our previous proteomics results. In set 2, however, the crude urinary levels of Igfbp3 were significantly lower in the AD+MCI group than in the control group (p = 0.028), and the levels of ApoD and ApoC3 did not differ significantly compared to the control group. Combined analysis of all samples revealed creatinine-adjusted ApoC3 levels to be significantly higher in the AD+MCI group (p = 0.015) and the AD-only group (p = 0.011) relative to the control group.

CONCLUSION

ApoC3 may be a potential biomarker for AD, as validated by ELISA. Further analysis of ApoC3 as a urinary biomarker for AD is warranted.

Genetic and environmental determinants of variation in the plasma lipidome of older Australian twins

The critical role of blood lipids in a broad range of health and disease states is well recognised but less explored is the interplay of genetics and environment within the broader blood lipidome. We examined heritability of the plasma lipidome among healthy older-aged twins (75 monozygotic/55 dizygotic pairs) enrolled in the Older Australian Twins Study (OATS) and explored corresponding gene expression and DNA methylation associations. 27/209 lipids (13.3%) detected by liquid chromatography-coupled mass spectrometry (LC-MS) were significantly heritable under the classical ACE twin model (h2 = 0.28-0.59), which included ceramides (Cer) and triglycerides (TG). Relative to non-significantly heritable TGs, heritable TGs had a greater number of associations with gene transcripts, not directly associated with lipid metabolism, but with immune function, signalling and transcriptional regulation. Genome-wide average DNA methylation (GWAM) levels accounted for variability in some non-heritable lipids. We reveal a complex interplay of genetic and environmental influences on the ageing plasma lipidome.

Alzheimer's disease in the gut-Major changes in the gut of 5xFAD model mice with ApoA1 as potential key player

Alzheimer's disease (AD) affects around 33 million people worldwide, which makes it the most prominent form of dementia. The main focus of AD research has been on the central nervous system (CNS) for long, but in recent years, the gut gained more attention. The intestinal tract is innervated by the enteric nervous system (ENS), built of numerous different types of neurons showing great similarity to neurons of the CNS. It already has been demonstrated that the amyloid precursor protein, which plays a major role in AD pathology, is also expressed in these cells. We analyzed gut tissue of AD model mice (5xFAD) and the respective wild-type littermates at different pathological stages: pre-pathological, early pathological and late pathological. Our results show significant difference in function of the intestine of 5xFAD mice as compared to wild-type mice. Using a pathway array detecting 84 AD-related gene products, we found ApoA1 expression significantly altered in colon tissue of 5xFAD mice. Furthermore, we unveil ApoA1's beneficial impact on cell viability and calcium homeostasis of cultured enteric neurons of 5xFAD animals. With this study, we demonstrate that the intestine is altered in AD-like pathology and that ApoA1 might be one key player within the gut.

Higher Apolipoprotein C-III Levels in Cerebrospinal Fluid are Associated with Slower Cognitive Decline in Mild Cognitive Impairment

BACKGROUND

Although a growing body of evidence shows an important role of apolipoproteins in the pathogenesis of Alzheimer's disease (AD), the association of apolipoprotein C-III (APOC-III) with cognitive decline is not clear.

OBJECTIVE

To examine whether higher cerebrospinal fluid (CSF) and plasma APOC-III levels were associated with better cognitive performance over time in the early stage of AD.

METHODS

Baseline CSF and plasma APOC-III levels were analyzed in relation to cross-sectionally and longitudinally cognitive performance over a 12-year period. Data were extracted from the Alzheimer's Disease Neuroimaging Initiative database, and 234 subjects (89 subjects with normal cognition (NC) and 145 subjects with mild cognitive impairment (MCI)) with CSF APOC-III measurements and 454 subjects (58 subjects with NC and 396 subjects with MCI) with plasma APOC-III measurements were included.

RESULTS

In the cross-sectional study, we did not find a significant relationship between CSF APOC-III and cognitive performance in pooled individuals with MCI and NC. However, longitudinal analysis found that higher baseline CSF APOC-III was significantly associated with slower cognitive decline over a 12-year period in individuals with MCI, but not the healthy controls, after controlling for several covariates and Alzheimer biomarkers. Plasma APOC-III levels showed a mild correlation with CSF APOC-III levels, but were not associated with longitudinal cognitive changes in the pooled sample or in diagnosis-stratified analyses.

CONCLUSIONS

Higher CSF APOC-III levels are significantly associated with slower cognitive decline over a 12-year period among individuals with MCI.

Arylesterase Activity of Paraoxonase-1 in Serum and Cerebrospinal Fluid of Patients with Alzheimer's Disease and Vascular Dementia

BACKGROUND

It has been suggested that circulating Paraoxonase-1 (PON1) and apolipoprotein A1 (APOA1), which closely interacts with the antioxidant enzyme, could be implicated in Alzheimer's disease (AD) and vascular dementia (VaD) development. This study aimed to evaluate PON1 changes in serum and cerebrospinal fluid (CSF) as evidence for its association with AD or VaD.

METHODS

Serum PON-arylesterase activity was measured in patients with AD, VaD, and CONTROLS distributed in two cohorts: Ferrara cohort (FC: n = 503, age = 74 years) and Amsterdam Dementia cohort (ADC: n = 71, age = 65 years). In the last cohort, CSF PON-arylesterase, CSF β-amyloid1-42, p-tau and t-tau, and imaging biomarkers were also measured.

RESULTS

AD and VaD patients of FC showed significantly lower levels of serum PON-arylesterase compared to CONTROLS, but this outcome was driven by older subjects (>71 years, p < 0.0001). In the younger ADC, a similar decreasing (but not significant) trend was observed in serum and CSF. Intriguingly, PON-arylesterase per APOA1 correlated with t-tau in AD group (r = -0.485, p = 0.002).

CONCLUSION

These results suggest that decreased peripheral PON-arylesterase might be a specific feature of older AD/VaD patients. Moreover, we showed that PON-arylesterase/APOA1 is inversely related to neurodegeneration in AD patients, suggesting a prognostic usefulness of this composite parameter.

Higher Plasma APOC-III Was Associated with a Slower Reduction of β-Amyloid Levels in Cerebrospinal Fluid Among Older Individuals Without Dementia

PURPOSE

Although emerging evidence has suggested that apolipoprotein C-III (APOC-III) is involved in the pathogenesis of Alzheimer's disease (AD), the association of APOC-III with longitudinal changes in cerebrospinal fluid (CSF) AD pathologies (β-amyloid (Aβ42) and tau proteins) is not clear. In the present study, we aimed to examine whether plasma APOC-III levels are associated with longitudinal changes in CSF Aβ42, total-tau (t-tau), and phosphorylated-tau (p-tau) levels among older individuals without dementia.

PATIENTS AND METHODS

Linear mixed models were fitted with plasma APOC-III used as a predictor for longitudinal changes in CSF AD biomarkers over a 7-year period. Data were obtained from the Alzheimer's Disease Neuroimaging Initiative database, and 195 older individuals without dementia (47 subjects with normal cognition (NC) and 148 subjects with mild cognitive impairment (MCI)) with baseline plasma APOC-III measurements were included.

RESULTS

Among older individuals without dementia, we found that the tertiles of plasma APOC-III were associated with changes in CSF Aβ42, but not t-tau or p-tau. Specifically, the CSF Aβ42 reduction for individuals in the highest plasma APOC-III tertile was significantly slower compared with those in the middle tertile, whereas no other pairwise difference was found to be statistically significant.

CONCLUSION

Among older individuals without dementia, higher plasma APOC-III levels were associated with slower declines in CSF Aβ42.

Associations Between APOE Variants, Tau and α-Synuclein

Neurodegenerative diseases are characterized by the aggregation and deposition of misfolded proteins in the brain, most prominently amyloid-β (Aβ), tau and α-synuclein (α-syn), and are thus referred to as proteinopathies. While tau is a hallmark of Alzheimer's disease (AD) and other non-AD tauopathies, and α-synuclein is the pathological feature of the spectrum of synucleinopathies including Parkinson's disease (PD), Parkinson's disease with dementia (PDD) and dementia with Lewy bodies (DLB), the presence of co-pathologies is very frequent in all these diseases. Positive and synergistic associations between the different types of protein deposits have been reported, leading to worse prognosis and cognitive decline. A large variation in phenotypic clinical presentation of these diseases, largely due to the frequent presence of co-pathologies, makes differential diagnosis challenging. The observed clinico-pathological overlaps suggest common underlying mechanisms, in part due to shared genetic risk factors. The ε4 allele of the apolipoprotein (APOE) gene is one of the major genetic risk factors for the sporadic forms of proteinopathies, but the biological mechanisms linking APOE, tau and α-syn are not fully understood. This chapter describes current experimental evidence on the relationships between APOE variants, tau and α-syn, from clinical studies on fluid biomarkers and positron emission tomography (PET) imaging, and from basic experimental studies in cellular/molecular biology and animal models. The chapter focuses on recent advances and identifies knowledge gaps. In particular, no PET tracer for assessment of brain α-syn deposits is yet available, although it is subject of intense research and development, therefore experimental evidence on in vivo α-syn levels is based on measures in the cerebrospinal fluid (CSF) and plasma. Moreover, tau PET imaging studies comparing the patterns of tracer retention in synucleinopathies versus in other proteinopathies are scarce and much is still unknown regarding the relationships between APOE variants and fluid and/or imaging biomarkers of tau and α-syn. Further research incorporating multimodal imaging, fluid biomarkers and genetic factors will help elucidate the biological mechanisms underlying these proteinopathies, and contribute to differential diagnosis and patient stratification for clinical trials.