Serum apolipoprotein E is associated with long-term risk of Alzheimer's disease: The Rotterdam Study

Lipids, lipoproteins, and apolipoproteins: Associations with cognition and dementia

Due to increasing lifespan and aging populations globally there has been a steep rise in late-life dementia, which is now the second most common cause of death in high-income countries. In general, dementia can be divided into two major groups: Alzheimer's disease (AD) and vascular-related dementia (VD). AD is pathologically characterised by senile plaques containing amyloid-β and neurofibrillary tangles composed of hyperphosphorylated tau, whereas VD is dominated by vascular pathology such as cerebral small vessel disease, major strokes, and white matter lesions. Recently, the importance of vascular components in AD is increasingly recognized and it is estimated that up to 45 % of all dementia cases can be prevented by preventing or treating midlife cardiovascular risk factors such as physical inactivity, diabetes, and hypertension. Even though the brain contains approximately 25 % of the total body cholesterol pool, and several genetic variants related to the lipid metabolism have been identified in genome-wide associations studies of AD, the role of lipids, lipoproteins, and apolipoproteins in dementia risk is less well-known. In this review, we go through the current literature on lipids, lipoproteins, and apolipoproteins and risk of dementia. We conclude that the evidence is primarily insufficient or conflicting, possibly due to nonoptimal study designs. The future calls for large, prospective studies of midlife measurements of lipids, lipoproteins, and apolipoproteins and one-sample, individual level data Mendelian randomization studies to overcome survival bias. However, the current literature suggests that it is safe to say that what is good for the heart is good for the brain.

Deciphering Proteomic Expression in Inflammatory Disorders: A Mass Spectrometry Exploration Comparing Infectious, Noninfectious, and Traumatic Brain Injuries in Human Cerebrospinal Fluid

The central nervous system (CNS) evokes a complex inflammatory response to injury. Inflammatory cascades are present in traumatic, infectious, and noninfectious disorders affecting the brain. It contains a mixture of pro- and anti-inflammatory reactions involving well-known proteins, but also numerous proteins less explored in these processes. The aim of this study was to explore the distinct inflammatory response in traumatic brain injury (TBI) compared with other CNS injuries by utilization of mass-spectrometry. In total, 56 patients had their cerebrospinal fluid (CSF) analyzed with the use of mass-spectrometry. Among these, CSF was collected via an external ventricular drain (EVD) from n = 21 patients with acute TBI. The resulting protein findings were then compared with CSF obtained by lumbar puncture from n = 14 patients with noninfectious CNS disorders comprising relapsing-remitting multiple sclerosis, anti-N-methyl-d-aspartate-receptor encephalitis, acute disseminated encephalomyelitis, and n = 14 patients with progressive multifocal leukoencephalopathy, herpes simplex encephalitis, and other types of viral meningitis. We also utilized n = 7 healthy controls (HCs). In the comparison between TBI and noninfectious inflammatory CNS disorders, concentrations of 55 proteins significantly differed between the groups. Among them, 23 and 32 proteins were up- and downregulated, respectively, in the TBI group. No proteins were uniquely identified in either group. In the comparison of TBI and HC, 51 proteins were significantly different, with 24 and 27 proteins being up- and downregulated, respectively, in TBI. Two proteins (fibrinogen gamma chain and transketolase) were uniquely identified in all samples of the TBI group. Also in the last comparison, TBI versus infectious inflammatory CNS disorders, 51 proteins differed between the two groups, with 19 and 32 proteins being up- and downregulated, respectively, in TBI, and no unique proteins being identified. Due to large discrepancies between the groups compared, the following proteins were selected for further deeper analysis among those being differentially regulated: APOE, CFB, CHGA, CHI3L1, C3, FCGBP, FGA, GSN, IGFBP7, LRG1, SERPINA3, SOD3, and TTR. We found distinct proteomic profiles in the CSF of TBI patients compared with HC and different disease controls, indicating a specific interplay between inflammatory factors, metabolic response, and cell integrity. In relation to primarily infectious or inflammatory disorders, unique inflammatory pathways seem to be engaged, and could potentially serve as future treatment targets.

The vascular contribution of apolipoprotein E to Alzheimer's disease

Alzheimer's disease, the most prevalent form of dementia, imposes a substantial societal burden. The persistent inadequacy of disease-modifying drugs targeting amyloid plaques and neurofibrillary tangles suggests the contribution of alternative pathogenic mechanisms. A frequently overlooked aspect is cerebrovascular dysfunction, which may manifest early in the progression of Alzheimer's disease pathology. Mounting evidence underscores the pivotal role of the apolipoprotein E gene, particularly the apolipoprotein ε4 allele as the strongest genetic risk factor for late-onset Alzheimer's disease, in the cerebrovascular pathology associated with Alzheimer's disease. In this review, we examine the evidence elucidating the cerebrovascular impact of both central and peripheral apolipoprotein E on the pathogenesis of Alzheimer's disease. We present a novel three-hit hypothesis, outlining potential mechanisms that shed light on the intricate relationship among different pathogenic events. Finally, we discuss prospective therapeutics targeting the cerebrovascular pathology associated with apolipoprotein E and explore their implications for future research endeavours.

Neurocognitive trajectory and proteomic signature of inherited risk for Alzheimer's disease

For Alzheimer's disease-a leading cause of dementia and global morbidity-improved identification of presymptomatic high-risk individuals and identification of new circulating biomarkers are key public health needs. Here, we tested the hypothesis that a polygenic predictor of risk for Alzheimer's disease would identify a subset of the population with increased risk of clinically diagnosed dementia, subclinical neurocognitive dysfunction, and a differing circulating proteomic profile. Using summary association statistics from a recent genome-wide association study, we first developed a polygenic predictor of Alzheimer's disease comprised of 7.1 million common DNA variants. We noted a 7.3-fold (95% CI 4.8 to 11.0; p < 0.001) gradient in risk across deciles of the score among 288,289 middle-aged participants of the UK Biobank study. In cross-sectional analyses stratified by age, minimal differences in risk of Alzheimer's disease and performance on a digit recall test were present according to polygenic score decile at age 50 years, but significant gradients emerged by age 65. Similarly, among 30,541 participants of the Mass General Brigham Biobank, we again noted no significant differences in Alzheimer's disease diagnosis at younger ages across deciles of the score, but for those over 65 years we noted an odds ratio of 2.0 (95% CI 1.3 to 3.2; p = 0.002) in the top versus bottom decile of the polygenic score. To understand the proteomic signature of inherited risk, we performed aptamer-based profiling in 636 blood donors (mean age 43 years) with very high or low polygenic scores. In addition to the well-known apolipoprotein E biomarker, this analysis identified 27 additional proteins, several of which have known roles related to disease pathogenesis. Differences in protein concentrations were consistent even among the youngest subset of blood donors (mean age 33 years). Of these 28 proteins, 7 of the 8 proteins with concentrations available were similarly associated with the polygenic score in participants of the Multi-Ethnic Study of Atherosclerosis. These data highlight the potential for a DNA-based score to identify high-risk individuals during the prolonged presymptomatic phase of Alzheimer's disease and to enable biomarker discovery based on profiling of young individuals in the extremes of the score distribution.

Plasma apolipoprotein E levels in longitudinally followed patients with mild cognitive impairment and Alzheimer’s disease

Background

Low levels of plasma apolipoprotein E (apoE) and presence of the APOE ε4 allele are associated with an increased risk of Alzheimer’s disease (AD). Although the increased risk of AD in APOE ε4-carriers is well-established, the protein levels have received limited attention.

Methods

We here report the total plasma apoE and apoE isoform levels at baseline from a longitudinally (24 months) followed cohort including controls (n = 39), patients with stable amnestic mild cognitive impairment during 24 months follow up (MCI-MCI, n = 30), patients with amnestic MCI (aMCI) that during follow-up were clinically diagnosed with AD with dementia (ADD) (MCI-ADD, n = 28), and patients with AD with dementia (ADD) at baseline (ADD, n = 28). We furthermore assessed associations between plasma apoE levels with cerebrospinal fluid (CSF) AD biomarkers and α-synuclein, as well as both CSF and plasma neurofilament light chain (NfL), YKL-40 and kallikrein 6.

Results

Irrespective of clinical diagnosis, the highest versus the lowest apoE levels were found in APOE ε2/ε3 versus APOE ε4/ε4 subjects, with the most prominent differences exhibited in females. Total plasma apoE levels were 32% and 21% higher in the controls versus MCI-ADD and ADD patients, respectively. Interestingly, MCI-ADD patients exhibited a 30% reduction in plasma apoE compared to MCI-MCI patients. This decrease appeared to be associated with brain amyloid-β (Aβ42) pathology regardless of disease status as assessed using the Amyloid, Tau, and Neurodegeneration (A/T/N) classification. In addition to the association between low plasma apoE and low levels of CSF Aβ42, lower apoE levels were also related to higher levels of CSF total tau (t-tau) and tau phosphorylated at Threonine 181 residue (p-tau) and NfL as well as a worse performance on the mini-mental-state-examination. In MCI-ADD patients, low levels of plasma apoE were associated with higher levels of CSF α-synuclein and kallikrein 6. No significant correlations between plasma apoE and the astrocytic inflammatory marker YKL40 were observed.

Conclusions

Our results demonstrate important associations between low plasma apoE levels, Aβ pathology, and progression from aMCI to a clinical ADD diagnosis.

Effect of the ABCA1 agonist CS-6253 on amyloid-β and lipoprotein metabolism in cynomolgus monkeys

BACKGROUND

Inducing brain ATP-binding cassette 1 (ABCA1) activity in Alzheimer's disease (AD) mouse models is associated with improvement in AD pathology. The purpose of this study was to investigate the effects of the ABCA1 agonist peptide CS-6253 on amyloid-β peptides (Aβ) and lipoproteins in plasma and cerebrospinal fluid (CSF) of cynomolgus monkeys, a species with amyloid and lipoprotein metabolism similar to humans.

METHODS

CS-6253 peptide was injected intravenously into cynomolgus monkeys at various doses in three different studies. Plasma and CSF samples were collected at several time points before and after treatment. Levels of cholesterol, triglyceride (TG), lipoprotein particles, apolipoproteins, and Aβ were measured using ELISA, ion-mobility analysis, and asymmetric-flow field-flow fractionation (AF4). The relationship between the change in levels of these biomarkers was analyzed using multiple linear regression models and linear mixed-effects models.

RESULTS

Following CS-6253 intravenous injection, within minutes, small plasma high-density lipoprotein (HDL) particles were increased. In two independent experiments, plasma TG, apolipoprotein E (apoE), and Aβ42/40 ratio were transiently increased following CS-6253 intravenous injection. This change was associated with a non-significant decrease in CSF Aβ42. Both plasma total cholesterol and HDL-cholesterol levels were reduced following treatment. AF4 fractionation revealed that CS-6253 treatment displaced apoE from HDL to intermediate-density- and low density-lipoprotein (IDL/LDL)-sized particles in plasma. In contrast to plasma, CS-6253 had no effect on the assessed CSF apolipoproteins or lipids.

CONCLUSIONS

Treatment with the ABCA1 agonist CS-6253 appears to favor Aβ clearance from the brain.

Endogenous Human Proteins Interfering with Amyloid Formation

Amyloid formation is a pathological process associated with a wide range of degenerative disorders, including Alzheimer’s disease, Parkinson’s disease, and diabetes mellitus type 2. During disease progression, abnormal accumulation and deposition of proteinaceous material are accompanied by tissue degradation, inflammation, and dysfunction. Agents that can interfere with the process of amyloid formation or target already formed amyloid assemblies are consequently of therapeutic interest. In this context, a few endogenous proteins have been associated with an anti-amyloidogenic activity. Here, we review the properties of transthyretin, apolipoprotein E, clusterin, and BRICHOS protein domain which all effectively interfere with amyloid in vitro, as well as displaying a clinical impact in humans or animal models. Their involvement in the amyloid formation process is discussed, which may aid and inspire new strategies for therapeutic interventions.

Whole Blood Transcriptome Characterization of 3xTg-AD Mouse and Its Modulation by Transcranial Direct Current Stimulation (tDCS)

The 3xTg-AD mouse is a widely used model in the study of Alzheimer’s Disease (AD). It has been extensively characterized from both the anatomical and behavioral point of view, but poorly studied at the transcriptomic level. For the first time, we characterize the whole blood transcriptome of the 3xTg-AD mouse at three and six months of age and evaluate how its gene expression is modulated by transcranial direct current stimulation (tDCS). RNA-seq analysis revealed 183 differentially expressed genes (DEGs) that represent a direct signature of the genetic background of the mouse. Moreover, in the 6-month-old 3xTg-AD mice, we observed a high number of DEGs that could represent good peripheral biomarkers of AD symptomatology onset. Finally, tDCS was associated with gene expression changes in the 3xTg-AD, but not in the control mice. In conclusion, this study provides an in-depth molecular characterization of the 3xTg-AD mouse and suggests that blood gene expression can be used to identify new biomarkers of AD progression and treatment effects.

Impact of metabolic dysfunction on cognition in humans

PURPOSE OF REVIEW

The current review evaluates the recent literature on the impact of metabolic dysfunction in human cognition, focusing on epidemiological studies and meta-analyses of these.

RECENT FINDINGS

Worldwide around 50 million people live with dementia, a number projected to triple by 2050. Recent reports from the Lancet Commission suggest that 40% of dementia cases may be preventable primarily by focusing on well established metabolic dysfunction components and cardiovascular risk factors.

SUMMARY

There is robust evidence that type 2 diabetes and midlife hypertension increase risk of dementia in late life. Obesity and elevated levels of LDL cholesterol in midlife probably increase risk of dementia, but further research is needed in these areas. Physical activity, diet, alcohol, and smoking might also influence the risk of dementia through their effect on metabolic dysfunction. A key recommendation is to be ambitious about prevention, focusing on interventions to promote healthier lifestyles combating metabolic dysfunction. Only comprehensive multidomain and staff-requiring interventions are however efficient to maintain or improve cognition in at-risk individuals and will be unrealistic economic burdens for most societies to implement. Therefore, a risk score that identifies high-risk individuals will enable a targeted early intensive intervention toward those high-risk individuals that will benefit the most from a prevention against cardiovascular risk factors and metabolic dysfunction.

Plasma levels of apolipoprotein E, APOE genotype, and all-cause and cause-specific mortality in 105 949 individuals from a white general population cohort

Aims

To determine whether plasma apoE levels and APOE genotype are associated with all-cause and cause-specific mortality.

Methods and results

Using a prospective cohort design with 105 949 white individuals from the general population, we tested the association between plasma apoE at study enrolment and death during follow-up, and whether this was independent of APOE genotype. We confirmed the well-known association between APOE genotypes and mortality. For all-cause, cardiovascular, and cancer mortality, high levels of apoE were associated with increased risk, while for dementia-associated mortality low levels were associated with increased risk. For the highest vs. the fifth septile of plasma apoE, hazard ratios (HRs) were 1.20 (95% confidence interval 1.12–1.28) for all-cause mortality, 1.28 (1.13–1.44) for cardiovascular mortality, and 1.18 (1.05–1.32) for cancer mortality. Conversely, for the lowest vs. the fifth septile the HR was 1.44 (1.01–2.05) for dementia-associated mortality. Results were similar in analyses restricted to APOE ɛ33 carriers. Examining genetically determined plasma apoE, a 1 mg/dL increase conferred risk ratios of 0.97 (0.92–1.03) for cardiovascular mortality and 1.01 (0.95–1.06) for cancer mortality, while a 1 mg/dL decrease conferred a risk ratio of 1.70 (1.36–2.12) for dementia-associated mortality.

Conclusion

High plasma levels of apoE were associated with increased all-cause, cardiovascular, and cancer mortality, however of a non-causal nature, while low levels were causally associated with increased dementia-associated mortality.

APOE and dementia - resequencing and genotyping in 105,597 individuals

Introduction

The mechanism behind the strong association between the ɛ2/ɛ3/ɛ4 apolipoprotein E gene (APOE) polymorphism and Alzheimer's disease is not well‐characterized. Because low plasma levels of apoE associate with risk of dementia, genetic variants altering apoE levels in general may also associate with dementia.

Methods

The APOE gene was sequenced in 10,369 individuals, and nine amino acid–changing variants with frequencies ≥2/10,000 were further genotyped in 95,228 individuals. Plasma apoE levels were measured directly.

Results

Risk of all dementia and Alzheimer's disease (AD) increased with decreasing genetically determined apoE levels (P = 5 × 10⁻⁴ and P = 1 × 10⁻⁴ after APOE ɛ2/ɛ3/ɛ4 adjustment). Hazard ratios (95% confidence intervals) for all dementia and AD were 2.76 (1.39 to 5.47) and 4.92 (2.36 to 10.29) for the group with the genetically lowest apoE versus ɛ33.

Discussion

We found that genetically low apoE levels increase and genetically high levels decrease risk, beyond ɛ2/ɛ3/ɛ4. This underscores that dementia risk more likely relates to variants affecting levels of apoE.

Work Hours and Cognitive Function: The Multi-Ethnic Study of Atherosclerosis

Background

Cognitive impairment is a public health burden. Our objective was to investigate associations between work hours and cognitive function.

Methods

Multi-Ethnic Study of Atherosclerosis (MESA) participants (n = 2,497; 50.7% men; age range 44–84 years) reported hours per week worked in all jobs in Exams 1 (2000–2002), 2 (2002–2004), 3 (2004–2005), and 5 (2010–2011). Cognitive function was assessed (Exam 5) using the Cognitive Abilities Screening Instrument (version 2), a measure of global cognitive functioning; the Digit Symbol Coding, a measure of processing speed; and the Digit Span test, a measure of attention and working memory. We used a prospective approach and linear regression to assess associations for every 10 hours of work.

Results

Among all participants, associations of hours worked with cognitive function of any type were not statistically significant. In occupation-stratified analyses (interaction p = 0.051), longer work hours were associated with poorer global cognitive function among Sales/Office and blue-collar workers, after adjustment for age, sex, physical activity, body mass index, race/ethnicity, educational level, annual income, history of heart attack, diabetes, apolipoprotein E-epsilon 4 allele (ApoE4) status, birth-place, number of years in the United States, language spoken at MESA Exam 1, and work hours at Exam 5 (β = –0.55, 95% CI = –0.99, –0.09) and (β = –0.80, –1.51, –0.09), respectively. In occupation-stratified analyses (interaction p = 0.040), we also observed an inverse association with processing speed among blue-collar workers (adjusted β = –0.80, –1.52, –0.07). Sex, race/ethnicity, and ApoE4 did not significantly modify associations between work hours and cognitive function.

Conclusion

Weak inverse associations were observed between work hours and cognitive function among Sales/Office and blue-collar workers.

Association of Apolipoprotein E in Lipoprotein Subspecies With Risk of Dementia

Importance

The ε4 allele of the apolipoprotein E (APOE) gene and lower apolipoprotein E (apoE) protein levels in plasma are risk factors for Alzheimer disease, but the underlying biological mechanisms are not fully understood. Half of plasma apoE circulates on high-density lipoproteins (HDLs). Higher apoE levels in plasma HDL were previously found to be associated with lower coronary heart disease risk, but the coexistence of another apolipoprotein, apoC3, modified this lower risk.

Objective

To investigate associations between the presence of apoE in different lipoproteins with cognitive function, particularly the risk of dementia.

Design, Setting, and Participants

This prospective case-cohort study embedded in the Ginkgo Evaluation of Memory Study (2000-2008) analyzed data from 1351 community-dwelling participants 74 years and older. Of this group, 995 participants were free of dementia at baseline (recruited from September 2000 to June 2002) and 521 participants were diagnosed with incident dementia during follow-up until 2008. Data analysis was performed from January 2018 to December 2019.

Exposures

Enzyme-linked immunosorbent assay-measured concentration of apoE in whole plasma, HDL-depleted plasma (non-HDL), HDL, and HDL subspecies that contain or lack apoC3 or apoJ.

Main Outcomes and Measures

Adjusted hazard ratios for risk of dementia and Alzheimer disease during follow-up and adjusted differences (β coefficients) in Alzheimer Disease Assessment-Cognitive Subscale (ADAS-cog) and Modified Mini-Mental State Examination scores at baseline.

Results

Among 1351 participants, the median (interquartile range) age was 78 (76-81) years; 639 (47.3%) were women. The median (interquartile range) follow-up time was 5.9 (3.7-6.5) years. Higher whole plasma apoE levels and higher apoE levels in HDL were associated with better cognitive function assessed by ADAS-cog (whole plasma, β coefficient, -0.15; 95% CI, -0.24 to -0.06; HDL, β coefficient, -0.20; 95% CI, -0.30 to -0.10) but were unassociated with dementia or Alzheimer disease risk. When separated by apoC3, a higher apoE level in HDL that lacks apoC3 was associated with better cognitive function (ADAS-cog per SD: β coefficient, 0.17; 95% CI, -0.27 to -0.07; Modified Mini-Mental State Examination score per SD: β coefficient, 0.25; 95% CI, 0.07 to 0.42) and lower risk of dementia (hazard ratio per SD, 0.86; 95% CI, 0.76 to 0.99). In contrast, apoE levels in HDL that contains apoC3 were unassociated with any of these outcomes.

Conclusions and Relevance

In a prospective cohort of older adults with rigorous follow-up of dementia, the apoE level in HDL that lacked apoC3 was associated with better cognitive function and lower dementia risk. This finding suggests that the cardioprotective associations of this novel lipoprotein extend to dementia.

Physical Exercise May Increase Plasma Concentration of High-Density Lipoprotein-Cholesterol in Patients With Alzheimer's Disease

Lifestyle factors have been shown to increase the risk of developing Alzheimer's disease (AD) later in life. Specifically, an unfavorable cholesterol profile, and insulin resistance are associated with increased risk of developing AD. One way to non-pharmacologically affect the levels of plasma lipids is by exercise, which has been shown to be beneficial in cognitively healthy individuals. In this randomized controlled trial y, we therefore aimed to clarify the effect of physical exercise on the lipid profile, insulin and glucose in patients with AD. In addition, we investigated the effect of apolipoproteinE genotype on total cholesterol, high-density lipoprotein-cholesterol (HDL-C), low-density lipoprotein-cholesterol (LDL-C), and triglycerides (TG) in plasma from patients with AD. Plasma samples from 172 patients who underwent 16 weeks of moderate-to-high intensity exercise (n = 90) or treatment as usual (n = 82) were analyzed change from baseline for the levels of total cholesterol, LDL-C, HDL-C, TG, glucose, and insulin. In addition, we analyzed those from the exercise group who adhered to the protocol with an attendance of 2/3 or more of the exercise session and who followed the protocol of an intensity of 70% of the maximum heart rate. We found a significant increase in plasma HDL-C levels between the "high exercise sub-group" compared to control group. After intervention HDL-C was increased by 4.3% in the high-exercise group, and decreased by 0.7% in the control group, after adjustment for statin use. In conclusion, short term physical activity may be beneficial on the cholesterol profile in patients with AD.

Redefining transcriptional regulation of the APOE gene and its association with Alzheimer's disease

The apolipoprotein E gene (APOE) is the strongest genetic risk factor for late-onset Alzheimer's disease (AD), yet the expression of APOE is not clearly understood. For example, it is unclear whether AD patients have elevated or decreased APOE expression or why the correlation levels of APOE RNA and the ApoE protein differ across studies. Likewise, APOE has a single CpG island (CGI) that overlaps with its 3'-exon, and this CGI's effect is unknown. We previously reported that the APOE CGI is highly methylated in human postmortem brain (PMB) and that this methylation is altered in AD frontal lobe. In this study, we comprehensively characterized APOE RNA transcripts and correlated levels of RNA expression with DNA methylation levels across the APOE CGI. We discovered the presence of APOE circular RNA (circRNA) and found that circRNA and full-length mRNA each constitute approximately one third of the total APOE RNA, with truncated mRNAs likely constituting some of the missing fraction. All APOE RNA species demonstrated significantly higher expression in AD frontal lobe than in control frontal lobe. Furthermore, we observed a negative correlation between the levels of total APOE RNA and DNA methylation at the APOE CGI in the frontal lobe. When stratified by disease status, this correlation was strengthened in controls but not in AD. Our findings suggest a possible modified mechanism of gene action for APOE in AD that involves not only the protein isoforms but also an epigenetically regulated transcriptional program driven by DNA methylation in the APOE CGI.

Plasma Apolipoprotein E Monomer and Dimer Profile and Relevance to Alzheimer's Disease

The APOEɛ4 gene variant is the strongest genetic risk factor for Alzheimer's disease (AD), whereas APOEɛ3 conventionally is considered as 'risk neutral' although APOEɛ3-carriers also develop AD. Previous studies have shown that the apolipoprotein E3 (apoE3) isoform occurs as monomers, homodimers and heterodimers with apolipoprotein A-II in human body fluids and brain tissue, but the relevance of a plasma apoE3 monomer/dimer profile to AD is unknown. Here we assessed the distribution of monomers, homodimers and heterodimers in plasma from control subjects and patients with mild cognitive impairment (MCI) and AD with either a homozygous APOEɛ3 (n = 31 control subjects, and n = 14 MCI versus n = 5 AD patients) or APOEɛ4 genotype (n = 1 control subject, n = 21 MCI and n = 7 AD patients). Total plasma apoE levels were lower in APOEɛ4-carriers and overall correlated significantly to CSF Aβ42, p(Thr181)-tau and t-tau levels. Apolipoprotein E dimers were only observed in the APOEɛ3-carriers and associated with total plasma apoE levels, negatively correlated to apoE monomers, but were unrelated to plasma homocysteine levels. Importantly, the APOEɛ3-carrying AD patients versus controls exhibited a significant decrease in apoE homodimers (17.8±9.6% versus 26.7±6.3%, p = 0.025) paralleled by an increase in apoE monomers (67.8±18.3% versus 48.5±11.2%, p = 0.008). In the controls, apoE monomers and heterodimers were significantly associated with plasma triglycerides; the apoE heterodimers were also associated with levels of high-density lipoprotein cholesterol. The physiological relevance of apoE dimer formation needs to be further investigated, though the distribution of apoE in monomers and dimers appears to be of relevance to AD in APOEɛ3 subjects.

Peripheral versus central nervous system APOE in Alzheimer's disease: Interplay across the blood-brain barrier

The apolipoprotein E (APOE) ε4 allele has been demonstrated as the preeminent genetic risk factor for late onset Alzheimer's disease (AD), which comprises greater than 90% of all AD cases. The discovery of the connection between different APOE genotypes and AD risk in the early 1990s spurred three decades of intense and comprehensive research into the function of APOE in the normal and diseased brain. The importance of APOE in the periphery has been well established, due to its pivotal role in maintaining cholesterol homeostasis and cardiovascular health. The influence of vascular factors on brain function and AD risk has been extensively studied in recent years. As a major apolipoprotein regulating multiple molecular pathways beyond its canonical lipid-related functions in the periphery and the central nervous system, APOE represents a critical link between the two compartments, and may influence AD risk from both sides of the blood-brain barrier. This review discusses recent advances in understanding the different functions of APOE in the periphery and in the brain, and highlights several promising APOE-targeted therapeutic strategies for AD.

Progress and Challenges in the Diagnosis of Dementia: A Critical Review

Longer life expectancies have led to an increased number of neurodegenerative disease cases globally. Accurate diagnosis of this devastating disorder is of crucial importance but is still feasible only by a brain biopsy after death. An enormous amount of attention and research has been in place over the years toward the better understanding of the mechanisms, as well as the early diagnosis, of neurodegeneration. However, numerous studies have been contradictory from time to time, while new diagnostic methods are constantly developed in a tireless effort to tackle the disease. Nonetheless, there is not yet a conclusive report covering a broader range of techniques for the diagnosis of different types of dementia. In this paper, we critically review current knowledge on the different hypotheses about the pathogenesis of distinct types of dementia, as well as risk factors and current diagnostic approaches in a clinical setting, including neuroimaging, cerebrospinal (CSF), and blood tests. Encouraging research results for the diagnosis and investigation of neurodegenerative disorders are also reported. Particular attention is given to the field of spectroscopy as an emerging tool to detect dementias, follow-up patients, and potentially monitor the patients' response to a therapeutic approach. Spectroscopic techniques, such as infrared and Raman spectroscopy, have facilitated numerous disease-related studies, including neurodegenerative disorders, and are currently undergoing trials for clinical implementation. This review constitutes a comprehensive report with an in-depth focus on promising imaging, molecular biomarker and spectroscopic tests in the field of dementive diseases.

Apolipoprotein E DNA methylation and late-life disease

Background

This study aims to investigate if DNA methylation of the apolipoprotein E (APOE) locus affects the risks of dementia, Alzheimeŕs disease (AD) or cardiovascular disease (CVD).

Methods

DNA methylation across theAPOE gene has previously been categorized into three distinct regions: a hypermethylated region in the promoter, a hypomethylated region in the first two introns and exons and a hypermethylated region in the 3′exon that also harbours theAPOE ε2 and ε4 alleles. DNA methylation levels in leukocytes were measured using the Illumina 450K array in 447 Swedish twins (mean age 78.1 years). We used logistic regression to investigate whether methylation levels in those regions affect the odds of disease.

Results

We found that methylation levels in the promoter region were associated with dementia and AD after adjusting for sex, age at blood draw, education, smoking and relatedness among twins [odds ratio (OR) 1.32 per standard deviation increase in methylation levels, 95% confidence interval (CI) 1.08–1.62 for dementia; OR 1.38, 95% CI 1.07–1.78 for AD). We did not detect any difference in methylation levels between CVD cases and controls. Results were similar when comparing within discordant twin pairs, and did not differ as a function ofAPOE genotype.

Conclusions

We found that higher DNA methylation levels in the promoter region ofAPOE increase the odds of dementia and AD, but not CVD. The effect was independent ofAPOE genotype, indicating that allelic variation and methylation variation inAPOE may act independently to increase the risk of dementia.

Association between polymorphisms in the promoter region of the apolipoprotein E (APOE) gene and Alzheimer's disease: A meta-analysis

Several studies have evaluated the role of polymorphisms in the promoter region of APOE gene that encodes apolipoprotein E (APOE) and the susceptibility to Alzheimer's disease (AD). The aim of this literature review and meta-analysis was to investigate the relationship between the APOE promoter region single nucleotide polymorphisms (SNPs) (rs449647, -491A/T; rs769446, -427T/C and rs405509 -219T/G) and the risk of developing AD. Eligible controlled studies published up to November 2016 were retrieved from main online scientific and medical databases. Odds ratio (OR) and 95 % confidence interval (CI) were used to calculate the strength of the relationship. A total of 23 publications (19 for rs449647, ten for rs769446 and ten for rs405509) were retrieved that included 5,703 patients with AD and 5,692 controls. The C allele of the rs769446 variant of the promoter region of APOE gene was significantly associated with an increase of risk of AD (OR = 1.271, 95 % CI = 1.114-1.449, P < 0.0001), while other genetic models of this variant were not related with susceptibility to AD. Rs449647 and rs405509 polymorphisms of APOE gene were not associated with an increase of risk of AD. The findings of this literature review and meta-analysis have shown that rs769446 polymorphism in the promoter region of APOE gene could be a risk factor for AD. Future large-scale studies on the role of polymorphisms in the promoter region of APOE gene in AD are still awaited.

CSF ApoE predicts clinical progression in nondemented APOEε4 carriers

Possible associations between cerebrospinal fluid (CSF) and plasma apolipoprotein E (ApoE) concentration and early clinical and pathophysiological manifestation of Alzheimer's disease were studied in a large and well-defined population of nondemented patients. CSF and plasma ApoE concentrations were related to CSF Aβ42, Tau and pTau levels and clinical characteristics in patients with subjective cognitive decline (n = 207) or mild cognitive impairment (n = 213) aged 64.2 ± 9.0 years, with a 2.5 ± 1.5 years follow-up. A 1 standard deviation increase in log-transformed CSF ApoE concentrations increased the risk of clinical progression in APOEε4 carriers 1.5 times (hazard ratio [95% confidence interval] 1.5 [1.1-2.0]), while this was not the case in APOEε4 noncarriers (hazard ratio [95% confidence interval] 1.0 [0.8-1.2]). Plasma ApoE did not predict clinical progression. Using linear regression models, strong associations between CSF ApoE levels and CSF Tau (β 0.51 [0.38-0.65]) and pTau (β 0.53 [0.40-0.60]) values were observed in APOEε4 carriers. We hypothesize CSF ApoE4 increases risk of clinical progression through its association with CSF Tau in APOEε4 carriers. Development of Alzheimer's disease in APOEε4 noncarriers may be unrelated to ApoE concentration.

Few serum proteins mediate APOE's association with dementia

The latent variable "δ" (for "dementia") appears to be uniquely responsible for the dementing aspects of cognitive impairment. Age, depression, gender and the apolipoprotein E (APOE) e4 allele are independently associated with δ. In this analysis, we explore serum proteins as potential mediators of APOE's specific association with δ in a large, ethnically diverse longitudinal cohort, the Texas Alzheimer's Research and Care Consortium (TARCC). APOE was associated only with C-Reactive Protein (CRP), Adiponectin (APN) and Amphiregulin (AREG), although the latter two's associations did not survive Bonferroni correction for multiple comparisons. All three proteins were associated with δ and had weak potential mediation effects on APOE's association with that construct. Our findings suggest that APOE's association with cognitive performance is specific to δ and partially mediated by serum inflammatory proteins. The majority of APOE's significant unadjusted effect on δ is unexplained. It may instead arise from direct central nervous system effects, possibly on native intelligence. If so, then APOE may exert a life-long influence over δ and therefore all-cause dementia risk.

Protective effects and mechanism of TPX2 on neurocyte apoptosis of rats in Alzheimer's disease model

We investigated the protective effects and mechanism of TPX2 on apoptosis of rat neurocytes. A total of 90 SD rats were randomly divided into the drug group, the control group and the blank group, with 30 rats in each group. The rats in the drug group and in the blank group were anesthetized with 10% chloral hydrate (at the dose of 0.5 ml/100 g) and Aβ_1-42, with the concentration of 5 µl (1 µg/µl), was injected in the exact position of bilateral hippocampal areas of rats to establish the model. The configured TPX2 inhibitors and edible benne oil were mixed and made into a suspension. After model establishment, the rats were given different treatment methods; the rats in the drug group were given gavage administration in the proportion of 75 mg/kg once a day. The rats in the control group were given intragastric administration with the same proportion of physiological saline once a day. The blank group was the normal healthy group and the rats in this group did not undergo any surgery or drug treatment. Brain tissue in rats were divided into two parts, one part was fixed, dehydrated, paraffin-embedded and made into slices of approximately 5 µm. TUNEL staining was used to examine the apoptosis of brain tissue, H&E staining was used to observe the brain tissue cells of each group, and western blotting for detecting the MAPK, Erk and expression levels of p38 and RT-polymerase chain reaction method was employed to examine mRNA expression levels of MAPK, Erk and p21. After one week, TUNEL staining showed that apoptosis of brain tissue in the drug group was significantly greater than those of the control and blank groups. The protein expression levels of MAPK, Erk and p38 were significantly higher than those of the control group and the normal healthy group; the differences were statistically significant (P<0.05). Western blotting showed that the protein expression levels of MAPK, Erk and p38 of the drug group were significantly lower than those of the control group but higher than those of the normal healthy group; the differences were statistically significant (P<0.05). TPX2 has a protective effect on the apoptosis of brain tissue processed by Aβ_1-42, which plays its role through the inhibition of the protein expression levels of MAPK, Erk and p38.

Relation between plasma and brain lipids

PURPOSE OF REVIEW

This article evaluates recent experimental and human evidence regarding the involvement of lipids, lipoproteins, and apolipoproteins in neurodegenerative diseases, and reviews the current literature of the effects of cholesterol-lowering treatment on cognition.

RECENT FINDINGS

Plasma levels of traditional lipids and lipoproteins are not consistently associated with risk of dementia even though low plasma levels of apolipoprotein E, through unknown mechanisms, robustly predict future dementia. Experimental evidence suggests neuroprotective roles of several brain and cerebrospinal fluid apolipoproteins. Whether plasma levels of apolipoprotein E, or any other apolipoprotein with possible central nervous system and/or blood-brain barrier functions (apolipoproteins J, A-I, A-II, A-IV, D, C-I, and C-III) may become accessible biomarker components that improve risk prediction for dementia together with genetic risk variants and cardiovascular risk factors remains to be determined.

SUMMARY

Apolipoproteins with well established functions in peripheral lipid metabolism may play important roles for brain vascular health and Alzheimer's disease pathophysiology. Experimental work on lipids, lipoproteins, and apolipoproteins in the central nervous system together with robust prospective human studies will help to substantiate the drug target potential of these lipid components.

Exploitation of nanoparticle–protein corona for emerging therapeutic and diagnostic applications

Exposure of nanoparticles (NPs) to biological fluids (e.g., plasma, interstitial fluid, and cytoplasm) leads to the absorption of proteins on the NP surface, forming a protein corona (PC) that drastically influences the NP physicochemical properties.