Apolipoprotein E epsilon4 and the risk of dementia with stroke. A population-based investigation

Cholesterol, Atherosclerosis, and APOE in Vascular Contributions to Cognitive Impairment and Dementia (VCID): Potential Mechanisms and Therapy

Vascular contributions to cognitive impairment and dementia (VCID) are a common cause of cognitive decline, yet limited therapies exist. This cerebrovascular disease results in neurodegeneration via acute, chronic, local, and systemic mechanisms. The etiology of VCID is complex, with a significant impact from atherosclerosis. Risk factors including hypercholesterolemia and hypertension promote intracranial atherosclerotic disease and carotid artery stenosis (CAS), which disrupt cerebral blood flow and trigger ischemic strokes and VCID. Apolipoprotein E (APOE) is a cholesterol and phospholipid carrier present in plasma and various tissues. APOE is implicated in dyslipidemia and Alzheimer disease (AD); however, its connection with VCID is less understood. Few experimental models for VCID exist, so much of the present information has been drawn from clinical studies. Here, we review the literature with a focus on the clinical aspects of atherosclerotic cerebrovascular disease and build a working model for the pathogenesis of VCID. We describe potential intermediate steps in this model, linking cholesterol, atherosclerosis, and APOE with VCID. APOE4 is a minor isoform of APOE that promotes lipid dyshomeostasis in astrocytes and microglia, leading to chronic neuroinflammation. APOE4 disturbs lipid homeostasis in macrophages and smooth muscle cells, thus exacerbating systemic inflammation and promoting atherosclerotic plaque formation. Additionally, APOE4 may contribute to stromal activation of endothelial cells and pericytes that disturb the blood-brain barrier (BBB). These and other risk factors together lead to chronic inflammation, atherosclerosis, VCID, and neurodegeneration. Finally, we discuss potential cholesterol metabolism based approaches for future VCID treatment.

Potential role of exosome in post-stroke reorganization and/or neurodegeneration

Currently, stroke is a common and devastating condition, which is sometimes associated with permanent cerebral damages. Although in early time after stroke, the related treatments are mainly focused on the restoration of cerebral blood flow (CBF), at the same time, some changes are commencing that continue for a long time and need to be specially noticed. Previous studies have proposed several molecular mechanisms in these post-stroke events. Exosomes are a type of vesicle, which are formed and secreted by most cells as a mean to transfer cellular constituents such as proteins, DNA and/or RNA to distant cells. Therefore, they are considered as a novel mechanism of cellular communication. Herein, we reviewed the current knowledge on cascades, which are activated after stroke and consequently lead to the reorganization and/or continuance of tissue damage and development of other disorders such as Neurodegenerative diseases (ND). Thereafter, we summarized the latest proofs about the possible participation of exosomes in transferring some components such as proteins and micro-RNAs (miRs), from the affected areas to other parts of the brain and eventually cause the above-mentioned post-stroke events.

Delirium Post-Stroke-Influence on Post-Stroke Dementia (Research Study-Part of the PROPOLIS Study)

BACKGROUND

Previous research confirmed association between delirium and subsequent dementia in different clinical settings, but the impact of post-stroke delirium on cognitive functioning is still under-investigated. Therefore, we aimed to assess the risk of dementia among patients with stroke and in-hospital delirium.

METHODS

A total of 750 consecutive patients admitted to the stroke unit with acute stroke or transient ischemic attacks were screened for delirium, during the first seven days after admission. At the three- and twelve-month follow-up, patients underwent cognitive evaluation. The DSM-5 definition for dementia was used. Cases with pre-stroke dementia were excluded from the analysis.

RESULTS

Out of 691 included cases, 423 (61.22%) and 451 (65.27%) underwent cognitive evaluation, three and twelve months after stroke; 121 (28.61%) and 151 (33.48%) patients were diagnosed with dementia, respectively. Six (4.96%) patients with dementia, three months post-stroke did not meet the diagnostic criteria for dementia nine months later. After twelve months, 37 (24.50%) patients were diagnosed with dementia, first time after stroke. Delirium in hospital was an independent risk factor for dementia after three months (OR = 7.267, 95%CI 2.182-24.207, p = 0.001) but not twelve months after the stroke.

CONCLUSIONS

Patients with stroke complicated by in-hospital delirium are at a higher risk for dementia at three but not twelve months post-stroke.

APOE-ε4 Genotype and Dementia Before and After Transient Ischemic Attack and Stroke: Population-Based Cohort Study

Background and Purpose- APOE-ε4 genotype is a risk factor for sporadic Alzheimer disease and reduced recovery from brain injury. Since data on APOE genotype and dementia associated with transient ischemic attack/stroke are sparse, we determined the associations in a longitudinal population-based cohort. Methods- All patients with transient ischemic attack or stroke (2002-2012) in a defined population of 92 728 OxVASC (Oxford Vascular Study) had follow-up to 5-years. Pre-event and incident postevent dementia were ascertained through direct patient assessment and follow-up, supplemented by review of hospital/primary care records. Associations between pre- and post-event dementia and APOE genotype (ε4/ε4-homozygous and ε4/ε3-heterozygous versus ε3/ε3) were examined using logistic regression and Cox regression models, respectively, adjusted for age, sex, education, cerebrovascular burden (stroke severity, prior stroke, white matter disease), diabetes mellitus, and dysphasia. Results- Among 1767 genotyped patients (mean/SD age, 73.0/13.0 years, 901 [51%] male, 602 [34%] transient ischemic attack), 1058 (59.9%) were APOE-ε3/ε3, 403 (22.8%) were ε4/ε3 and 30 (1.7%) were ε4-homozygous. Homozygosity was associated with both pre-event (adjusted odds ratio, 5.81 [95% CI, 1.93-17.48]; P=0.002) and postevent dementia (adjusted hazard ratio, 3.64 [95% CI, 1.90-7.00]; P<0.0001). Association with postevent dementia was maintained after further adjustment for baseline cognitive impairment (hazard ratio, 2.41 [95% CI, 1.19-4.89]; P=0.01). There were no associations overall between ε4/ε3 and pre-event dementia (adjusted odds ratio, 1.47 [95% CI, 0.88-2.45]; P=0.14) or postevent dementia (hazard ratio, 1.11 [95% CI, 0.84-1.48]; P=0.47). Conclusions- In patients with transient ischemic attack and stroke, APOE-ε4 homozygosity was associated with both pre- and post-event dementia. Associations were independent of cerebrovascular burden and may be mediated through increased neurodegenerative pathology or vulnerability to injury.

HIV-1 Tat: Role in Bystander Toxicity

HIV Tat protein is a critical protein that plays multiple roles in HIV pathogenesis. While its role as the transactivator of HIV transcription is well-established, other non-viral replication-associated functions have been described in several HIV-comorbidities even in the current antiretroviral therapy (ART) era. HIV Tat protein is produced and released into the extracellular space from cells with active HIV replication or from latently HIV-infected cells into neighboring uninfected cells even in the absence of active HIV replication and viral production due to effective ART. Neighboring uninfected and HIV-infected cells can take up the released Tat resulting in the upregulation of inflammatory genes and activation of pathways that leads to cytotoxicity observed in several comorbidities such as HIV associated neurocognitive disorder (HAND), HIV associated cardiovascular impairment, and accelerated aging. Thus, understanding how Tat modulates host and viral response is important in designing novel therapeutic approaches to target the chronic inflammatory effects of soluble viral proteins in HIV infection.

Effects of exercise training on stroke risk factors, homocysteine concentration, and cognitive function according the APOE genotype in stroke patients

The apolipoprotein E (APOE) gene has been suggested to be associated with stroke and dementia. However, the effects of exercise training on dementia according to the APOE genotype are not consistent to those reported by previous studies. Therefore, we examined the effects of exercise training on stroke risk factors including blood pressure, lipid profiles, homocysteine (Hcy) concentrations, and cognitive function according to the APOE genotype in stroke patients. We examined the stroke risk factors, Hcy, and cognitive function in 28 ischemic stroke patients before and after 6 months of exercise training. After exercise training, body weight, body mass index (BMI), and percent body fat decreased significantly in both APOE groups. According to the APOE genotype, the changes in BMI in the APOE ɛ4 group higher than those in APOE ɛ3 group significantly. Total cholesterol (TC), low-density lipoprotein (LDL)-C, triglyceride (TG), and Hcy decreased and high-density lipoprotein (HDL)-C increased significantly in the both groups. According to the APOE genotype, systolic blood pressure in the APOE ɛ4 group decreased, but in the APOE ɛ3 group increased after exercise training. TC, LDL-C, and TG in the APOE ɛ4 group decreased more extensively than those in the APOE ɛ3 group after exercise training. VO_2max (maximal oxygen consumption) and cognition increased significantly in both groups. Folate acid intake also increased significantly in both groups. The APOE genotype affects variations in the risk factors of stroke after exercise training. However, the Hcy and cognitive function did not differ based on the APOE genotype.

Post-stroke dementia - a comprehensive review

Post-stroke dementia (PSD) or post-stroke cognitive impairment (PSCI) may affect up to one third of stroke survivors. Various definitions of PSCI and PSD have been described. We propose PSD as a label for any dementia following stroke in temporal relation. Various tools are available to screen and assess cognition, with few PSD-specific instruments. Choice will depend on purpose of assessment, with differing instruments needed for brief screening (e.g., Montreal Cognitive Assessment) or diagnostic formulation (e.g., NINDS VCI battery). A comprehensive evaluation should include assessment of pre-stroke cognition (e.g., using Informant Questionnaire for Cognitive Decline in the Elderly), mood (e.g., using Hospital Anxiety and Depression Scale), and functional consequences of cognitive impairments (e.g., using modified Rankin Scale). A large number of biomarkers for PSD, including indicators for genetic polymorphisms, biomarkers in the cerebrospinal fluid and in the serum, inflammatory mediators, and peripheral microRNA profiles have been proposed. Currently, no specific biomarkers have been proven to robustly discriminate vulnerable patients ('at risk brains') from those with better prognosis or to discriminate Alzheimer's disease dementia from PSD. Further, neuroimaging is an important diagnostic tool in PSD. The role of computerized tomography is limited to demonstrating type and location of the underlying primary lesion and indicating atrophy and severe white matter changes. Magnetic resonance imaging is the key neuroimaging modality and has high sensitivity and specificity for detecting pathological changes, including small vessel disease. Advanced multi-modal imaging includes diffusion tensor imaging for fiber tracking, by which changes in networks can be detected. Quantitative imaging of cerebral blood flow and metabolism by positron emission tomography can differentiate between vascular dementia and degenerative dementia and show the interaction between vascular and metabolic changes. Additionally, inflammatory changes after ischemia in the brain can be detected, which may play a role together with amyloid deposition in the development of PSD. Prevention of PSD can be achieved by prevention of stroke. As treatment strategies to inhibit the development and mitigate the course of PSD, lowering of blood pressure, statins, neuroprotective drugs, and anti-inflammatory agents have all been studied without convincing evidence of efficacy. Lifestyle interventions, physical activity, and cognitive training have been recently tested, but large controlled trials are still missing.

Stroke injury, cognitive impairment and vascular dementia

The global burden of ischaemic strokes is almost 4-fold greater than haemorrhagic strokes. Current evidence suggests that 25–30% of ischaemic stroke survivors develop immediate or delayed vascular cognitive impairment (VCI) or vascular dementia (VaD). Dementia after stroke injury may encompass all types of cognitive disorders. States of cognitive dysfunction before the index stroke are described under the umbrella of pre-stroke dementia, which may entail vascular changes as well as insidious neurodegenerative processes. Risk factors for cognitive impairment and dementia after stroke are multifactorial including older age, family history, genetic variants, low educational status, vascular comorbidities, prior transient ischaemic attack or recurrent stroke and depressive illness. Neuroimaging determinants of dementia after stroke comprise silent brain infarcts, white matter changes, lacunar infarcts and medial temporal lobe atrophy. Until recently, the neuropathology of dementia after stroke was poorly defined. Most of post-stroke dementia is consistent with VaD involving multiple substrates. Microinfarction, microvascular changes related to blood–brain barrier damage, focal neuronal atrophy and low burden of co-existing neurodegenerative pathology appear key substrates of dementia after stroke injury. The elucidation of mechanisms of dementia after stroke injury will enable establishment of effective strategy for symptomatic relief and prevention. Controlling vascular disease risk factors is essential to reduce the burden of cognitive dysfunction after stroke. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

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Ischaemic injury is common among long-term stroke survivors

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About 25% stroke survivors develop dementia with a much greater proportion developing cognitive impairment

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Risk factors of dementia after stroke include older age, vascular comorbidities, prior stroke and pre-stroke impairment

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Current imaging and pathological studies suggest 70% of dementia after stroke is vascular dementia

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Severe white matter changes and medial temporal lobe atrophy as sequelae after ischaemic injury are substrates of dementia

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Controlling vascular risk factors and prevention strategies related to lifestyle factors would reduce dementia after stroke

Apolipoprotein E: structure and function in lipid metabolism, neurobiology, and Alzheimer's diseases

Apolipoprotein (apo) E is a multifunctional protein with central roles in lipid metabolism, neurobiology, and neurodegenerative diseases. It has three major isoforms (apoE2, apoE3, and apoE4) with different effects on lipid and neuronal homeostasis. A major function of apoE is to mediate the binding of lipoproteins or lipid complexes in the plasma or interstitial fluids to specific cell-surface receptors. These receptors internalize apoE-containing lipoprotein particles; thus, apoE participates in the distribution/redistribution of lipids among various tissues and cells of the body. In addition, intracellular apoE may modulate various cellular processes physiologically or pathophysiologically, including cytoskeletal assembly and stability, mitochondrial integrity and function, and dendritic morphology and function. Elucidation of the functional domains within this protein and of the three-dimensional structure of the major isoforms of apoE has contributed significantly to our understanding of its physiological and pathophysiological roles at a molecular level. It is likely that apoE, with its multiple cellular origins and multiple structural and biophysical properties, is involved widely in processes of lipid metabolism and neurobiology, possibly encompassing a variety of disorders of neuronal repair, remodeling, and degeneration by interacting with different factors through various pathways.

Apolipoprotein E and lipid homeostasis in the etiology and treatment of sporadic Alzheimer's disease

The discovery that the apolipoprotein E (apoE) ε4 allele is genetically linked to both sporadic and familial late-onset Alzheimer's disease (AD) raises the possibility that a dysfunction of the lipid transport system could seriously affect lipid homeostasis in the brain of AD subjects. The presence of the ε4 allele has been associated with lower levels of apoE in both serum and brain tissues of normal and AD subjects. In an attempt to reverse the apoE deficit in AD, we identified and characterized several apoE inducer agents using a low-throughput in vitro screening assay. The most promising of these compounds is called probucol. Administration of probucol, an old cholesterol-lowering drug, in a pilot trial in mild-to-moderate sporadic AD led to a significant increase in cerebrospinal fluid (CSF) apoE levels and a decrease in CSF in both phosphorylated tau 181 and beta-amyloid 1-42 concentrations without significant modifications of lipid hydroperoxide levels.

Stem cell derived basal forebrain cholinergic neurons from Alzheimer's disease patients are more susceptible to cell death

An early substantial loss of basal forebrain cholinergic neurons (BFCNs) is a constant feature of Alzheimer’s disease (AD) and is associated with deficits in spatial learning and memory. Induced pluripotent stem cells (iPSCs) derived from patients with AD as well as from normal controls could be efficiently differentiated into neurons with characteristics of BFCNs. We used BFCNs derived from iPSCs to model sporadic AD with a focus on patients with ApoE3/E4 genotypes (AD-E3/E4). BFCNs derived from AD-E3/E4 patients showed typical AD biochemical features evidenced by increased Aβ42/Aβ40 ratios. AD-E3/E4 neurons also exhibited altered responses to treatment with γ-secretase inhibitors compared to control BFCNs or neurons derived from patients with familial AD. BFCNs from patients with AD-E3/E4 also exhibited increased vulnerability to glutamate-mediated cell death which correlated with increased intracellular free calcium upon glutamate exposure. The ability to generate BFCNs with an AD phenotype is a significant step both for understanding disease mechanisms and for facilitating screening for agents that promote synaptic integrity and neuronal survival.

Western-type diet modulates inflammatory responses and impairs functional outcome following permanent middle cerebral artery occlusion in aged mice expressing the human apolipoprotein E4 allele

Background

Numerous clinical trials in stroke have failed, most probably partially due to preclinical studies using young, healthy male rodents with little relevance to the heterogenic conditions of human stroke. Co-morbid conditions such as atherosclerosis and infections coupled with advanced age are known to contribute to increased risk of cerebrovascular diseases. Clinical and preclinical studies have shown that the E4 allele of human apolipoprotein (ApoE4) is linked to poorer outcome in various conditions of brain injury and neurodegeneration, including cerebral ischemia. Since ApoE is a known regulator of lipid homeostasis, we studied the impact of a high-cholesterol diet in aged mice in the context of relevant human ApoE isoforms on the outcome of focal brain ischemia.

Methods

Aged mice expressing human E3 and E4 isoforms of ApoE in C57BL/6J background and C57BL/6J mice fed on either a high-fat diet or a normal diet underwent permanent middle cerebral artery occlusion. The impact of a high-cholesterol diet was assessed by measuring the serum cholesterol level and the infarction volume was determined by magnetic resonance imaging. Sensorimotor deficits were assessed using an adhesive removal test and the findings were correlated with inflammatory markers.

Results

We show that expression of human ApoE4 renders aged mice fed with a western-type diet more susceptible to sensorimotor deficits upon stroke. These deficits are not associated with atherosclerosis but are accompanied with altered astroglial activation, neurogenesis, cyclooxygenase-2 immunoreactivity and increased plasma IL-6.

Conclusions

Our results support the hypothesis that ApoE alleles modify the inflammatory responses in the brain and the periphery, thus contributing to altered functional outcome following stroke.

Effects of type 2 diabetes on 12-year cognitive change: results from the Maastricht Aging Study

OBJECTIVE

To examine the effects of baseline and incident diabetes on change in cognitive function over 12 years.

RESEARCH DESIGN AND METHODS

A sample of 1,290 individuals aged ≥ 40 years at baseline, participating in the Maastricht Aging Study, were cognitively tested at baseline, after 6 years, and after 12 years. Of these, 68 participants had type 2 diabetes at baseline, and 54 and 57 had incident diabetes at the 6- and 12-year follow-up, respectively. Changes in performance on tests of information-processing speed, executive function, and verbal memory from baseline to 6- and 12-year follow-up were compared between groups using linear mixed models. Effects of diabetes on cognitive decline were adjusted for demographic variables, history of smoking, alcohol intake, and comorbid conditions, including hypertension, cardiovascular disease, BMI, and depression.

RESULTS

Participants with baseline diabetes showed larger decline in information-processing speed (estimate -7.64; P < 0.01), executive function (21.82; P < 0.01), and delayed word recall (-1.35; P < 0.05) over the 12-year follow-up compared with control subjects. No significant difference in decline was observed for immediate word recall. Compared with control subjects, participants with incident diabetes showed subtle early decline in information-processing speed only. Interestingly, they did not show larger decline in any other cognitive domain.

CONCLUSIONS

Individuals with baseline type 2 diabetes show accelerated cognitive decline, particularly in information-processing speed and executive function, compared with individuals without diabetes. In incident diabetes, decline in speed becomes detectable first, and cognitive decline seems to increase with increasing exposure time.

Apolipoprotein e sets the stage: response to injury triggers neuropathology

Apolipoprotein (apo) E4 is the major genetic risk factor for Alzheimer's disease and is associated with poor clinical outcome following traumatic brain injury and other neuropathological disorders. Protein instability and an isoform-specific apoE property called domain interaction are responsible for these neuropathological effects. ApoE4 is the most neurotoxic isoform and can induce neuropathology through various cellular pathways. Neuronal damage or stress induces apoE synthesis as part of the repair response; however, when apoE4 is expressed in neurons, its unique conformation makes it susceptible to proteolysis, resulting in the generation of neurotoxic fragments. These fragments cause pathological mitochondrial dysfunction and cytoskeletal alterations. Here, we review data supporting the hypothesis that apoE4 (> apoE3 > apoE2) has direct neurotoxic effects and highlight studies showing that blocking domain interaction reverses these detrimental effects.

Small-molecule structure correctors target abnormal protein structure and function: structure corrector rescue of apolipoprotein E4-associated neuropathology

An attractive strategy to treat proteinopathies (diseases caused by malformed or misfolded proteins) is to restore protein function by inducing proper three-dimensional structure. We hypothesized that this approach would be effective in reversing the detrimental effects of apolipoprotein (apo) E4, the major allele that significantly increases the risk of developing Alzheimer's disease and other neurodegenerative disorders. ApoE4's detrimental effects result from its altered protein conformation ("domain interaction"), making it highly susceptible to proteolytic cleavage and the generation of neurotoxic fragments. Here, we review apoE structure and function and how apoE4 causes neurotoxicity, and describe the identification of potent small-molecule-based "structure correctors" that induce proper apoE4 folding. SAR studies identified a series of small molecules that significantly reduced apoE4's neurotoxic effects in cultured neurons and a series that reduced apoE4 fragment levels in vivo, providing proof-of-concept for our approach. Structure-corrector-based therapies could prove to be highly effective for the treatment of many protein-misfolding diseases.

Neuropathologic substrates of Parkinson disease dementia

OBJECTIVE

A study was undertaken to examine the neuropathological substrates of cognitive dysfunction and dementia in Parkinson disease (PD).

METHODS

One hundred forty patients with a clinical diagnosis of PD and either normal cognition or onset of dementia 2 or more years after motor symptoms (PDD) were studied. Patients with a clinical diagnosis of dementia with Lewy bodies were excluded. Autopsy records of genetic data and semiquantitative scores for the burden of neurofibrillary tangles, senile plaques, Lewy bodies (LBs), and Lewy neurites (LNs) and other pathologies were used to develop a multivariate logistic regression model to determine the independent association of these variables with dementia. Correlates of comorbid Alzheimer disease (AD) were also examined.

RESULTS

Niney-two PD patients developed dementia, and 48 remained cognitively normal. Severity of cortical LB (CLB)/LN pathology was positively associated with dementia (p < 0.001), with an odds ratio (OR) of 4.06 (95% confidence interval [CI], 1.87-8.81), as was apolipoprotein E4 (APOE4) genotype (p = 0.018; OR, 4.19; 95% CI, 1.28-13.75). A total of 28.6% of all PD cases had sufficient pathology for comorbid AD, of whom 89.5% were demented. The neuropathological diagnosis of PDD+AD correlated with an older age of PD onset (p = 0.001; OR, 1.12; 95% CI, 1.04-1.21), higher CLB/LN burden (p = 0.037; OR, 2.48; 95% CI, 1.06-5.82), and cerebral amyloid angiopathy severity (p = 0.032; OR, 4.16; 95% CI, 1.13-15.30).

INTERPRETATION

CLB/LN pathology is the most significant correlate of dementia in PD. Additionally, APOE4 genotype may independently influence the risk of dementia in PD. AD pathology was abundant in a subset of patients, and may modify the clinical phenotype. Thus, therapies that target α-synuclein, tau, or amyloid β could potentially improve cognitive performance in PD.

Preferential interactions between ApoE-containing lipoproteins and Aβ revealed by a detection method that combines size exclusion chromatography with non-reducing gel-shift

The association between apolipoprotein E (apoE) and amyloid-β peptide (Aβ) may significantly impact the function of both proteins, thus affecting the etiology of Alzheimer's disease (AD). However, apoE/Aβ interactions remain fundamentally defined by the stringency of the detection method. Here we use size exclusion chromatography (SEC) as a non-stringent approach to the detection of apoE/Aβ interactions in solution, specifically apoE and both endogenous and exogenous Aβ from plasma, CSF and astrocyte conditioned media. By SEC analysis, Aβ association with plasma and CNS lipoproteins is apoE-dependent. While endogenous Aβ elutes to specific human plasma lipoproteins distinct from those containing apoE, it is the apoE-containing lipoproteins that absorb excess amounts of exogenous Aβ40. In human CSF, apoE, endogenous Aβ and phospholipid elute in an almost identical profile, as do apoE, exogenous Aβ and phospholipid from astrocyte conditioned media. Combining SEC fractionation with subsequent analysis for SDS-stable apoE/Aβ complex reveals that apoE-containing astrocyte lipoproteins exhibit the most robust interactions with Aβ. Thus, standardization of the methods for detecting apoE/Aβ complex is necessary to determine its functional significance in the neuropathology characteristic of AD. Importantly, a systematic understanding of the role of apoE-containing plasma and CNS lipoproteins in Aβ homeostasis could potentially contribute to identifying a plasma biomarker currently over-looked because it has multiple components.

ApoE gene polymorphism and vascular dementia in Chinese population: a meta-analysis

Vascular dementia is the second common cause of dementia, only second to Alzheimer's disease in later life. The Apolipoprotein E (ApoE) gene polymorphism as a risk factor in vascular dementia has been suggested, but direct evidence from genetic association studies remains inconclusive even in Chinese population. Therefore, we performed this meta-analysis in order to evaluate the relationship between ApoE gene polymorphism and susceptibility to vascular dementia in Chinese population by pooling data from all relevant case-control studies published domestically and abroad from January 1990 to May 2011. 18 case-control studies were selected. Meta-analysis results showed that the pooled OR value of vascular dementia subjects in Chinese population with ε4 allele carriers was 2.07 [95% CI (1.69, 2.53)], and the pooled OR value of vascular dementia subjects with E4/E4 genotype was 3.34 [95% CI (1.89, 5.88)]. These results suggest that ApoE polymorphism is significantly associated with susceptibility to vascular dementia in Chinese population. The subject with at least one ε4 allele or E4/E4 genotype has higher risk suffering from vascular dementia than others.

Apolipoprotein E genotypes and the risk of Parkinson disease

We examined apolipoprotein E (ApoE) genotypes in relation to Parkinson's disease (PD) among 786 cases and 1537 controls, all non-Hispanic Caucasians. Odds ratios (ORs) and 95% confidence intervals (CIs) were derived from multivariate logistic regression models, adjusting for year of birth, sex, smoking status, daily caffeine intake, and family history of PD. Compared with participants with ApoE ε33, ε4 carriers (ε34/ε44) had significantly lower odds for having PD (OR, 0.75; 95% CI, 0.59-0.94; p = 0.01), whereas ε2 carriers (ε23/ε22) did not (OR, 0.95; 95% CI, 0.73-1.24; p = 0.71). Subgroup analyses showed similar results. In addition, we conducted a meta-analysis which confirmed our primary findings (ε34/ε44 vs. ε33: OR, 0.90; 95% CI, 0.81-0.99; p = 0.024 and ε23/ε22 vs. ε33: OR, 1.10; 95% CI, 0.97-1.23; p = 0.13). In PD patients, the prevalence of dementia appeared to be higher among ε4 carriers (compared with ε33: OR, 1.59; 95% CI, 0.98-2.58; p = 0.06), but lower among ε2 carriers (OR, 0.75; 95% CI, 0.40-1.42; p = 0.38), although neither test was statistically significant. Our study suggested that the ApoE ε4 allele may be associated with a lower PD risk among non-Hispanic Caucasians.

Apolipoproteins in the brain: implications for neurological and psychiatric disorders

The brain is the most lipid-rich organ in the body and, owing to the impermeable nature of the blood-brain barrier, lipid and lipoprotein metabolism within this organ is distinct from the rest of the body. Apolipoproteins play a well-established role in the transport and metabolism of lipids within the CNS; however, evidence is emerging that they also fulfill a number of functions that extend beyond lipid transport and are critical for healthy brain function. The importance of apolipoproteins in brain physiology is highlighted by genetic studies, where apolipoprotein gene polymorphisms have been identified as risk factors for several neurological diseases. Furthermore, the expression of brain apolipoproteins is significantly altered in several brain disorders. The purpose of this article is to provide an up-to-date assessment of the major apolipoproteins found in the brain (ApoE, ApoJ, ApoD and ApoA-I), covering their proposed roles and the factors influencing their level of expression. Particular emphasis is placed on associations with neurological and psychiatric disorders.

Cellular source of apolipoprotein E4 determines neuronal susceptibility to excitotoxic injury in transgenic mice

The lipid transport protein apolipoprotein E (apoE) is abundantly expressed in the brain. Its main isoforms in humans are apoE2, apoE3, and apoE4. ApoE4 is the major known genetic risk factor for Alzheimer's disease and also contributes to the pathogenesis of various other neurological conditions. In the central nervous system, apoE is synthesized by glial cells and neurons, but it is unclear whether the cellular source affects its biological activities. To address this issue, we induced excitotoxic injury by systemic kainic acid injection in transgenic Apoe knockout mice expressing human apoE isoforms in astrocytes or neurons. Regardless of its cellular source, apoE3 expression protected neuronal synapses and dendrites against the excitotoxicity seen in apoE-deficient mice. Astrocyte-derived apoE4, which has previously been shown to have detrimental effects in vitro, was as excitoprotective as apoE3 in vivo. In contrast, neuronal expression of apoE4 was not protective and resulted in loss of cortical neurons after excitotoxic challenge, indicating that neuronal apoE4 promotes excitotoxic cell death. Thus, an imbalance between astrocytic (excitoprotective) and neuronal (neurotoxic) apoE4 expression may increase susceptibility to diverse neurological diseases involving excitotoxic mechanisms.

Vascular health, diabetes, APOE and dementia: the Aging, Demographics, and Memory Study

INTRODUCTION

Evidence from clinical samples and geographically limited population studies suggests that vascular health, diabetes and apolipoprotein epsilon4 (APOE) are associated with dementia.

METHODS

A population-based sample of 856 individuals aged 71 years or older from all contiguous regions of the United States received an extensive in-home clinical and neuropsychological assessment in 2001-2003. The relation of hypertension, diabetes, heart disease, stroke, medication usage, and APOE epsilon4 to dementia was modelled using adjusted multivariable logistic regression.

RESULTS

Treated stroke (odds ratio [OR] 3.8, 95% confidence interval [CI] 2.0, 7.2), untreated stroke (OR 3.5, 95% CI 1.7, 7.3), and APOE epsilon4 (OR 2.8, 95% CI 1.7, 4.5) all increased the odds of dementia. Treated hypertension was associated with lower odds of dementia (OR 0.5, 95% CI 0.3, 1.0). Diabetes and heart disease were not significantly associated with dementia. A significant interaction was observed between APOE epsilon4 and stroke (P = 0.001).

CONCLUSIONS

Data from the first dementia study that is representative of the United States population suggest that stroke, the APOE epsilon4 allele and their interaction are strongly associated with dementia.

Abeta-independent roles of apolipoprotein E4 in the pathogenesis of Alzheimer's disease

Human apolipoprotein (APO) E has three common isoforms that differentially affect lipid and neuronal homeostasis. APOE4, the major known genetic risk factor for Alzheimer's disease (AD), increases the occurrence and lowers the age of onset of AD. APOE4 carriers account for 65-80% of all AD cases, highlighting the importance of APOE4 in AD pathogenesis. Emerging data suggest that APOE4 contributes to AD through various pathways, some of which are dependent on amyloid-beta (Abeta). Although these Abeta-dependent roles of APOE4 have been widely studied, APOE4 has detrimental effects on neurons independent of Abeta: aberrant proteolysis of APOE4 generates neurotoxic fragments, stimulates Tau phosphorylation, which disrupts the cytoskeleton, and impairs mitochondrial function.

Role of vascular risk factors and vascular dysfunction in Alzheimer's disease

Recent findings indicate that vascular risk factors and neurovascular dysfunction play integral roles in the pathogenesis of Alzheimer's disease. In addition to aging, the most common risk factors for Alzheimer's disease are apolipoprotein e4 allele, hypertension, hypotension, diabetes, and hypercholesterolemia. All of these can be characterized by vascular pathology attributed to conditions such as cerebral amyloid angiopathy and subsequent blood-brain barrier dysfunction. Many epidemiological, clinical, and pharmacotherapeutic studies have assessed the associations between such risk factors and Alzheimer's disease and have found positive associations between hypertension, hypotension, and diabetes mellitus. However, there are still many conflicting results from these population-based studies, and they should be interpreted carefully. Recognition of these factors and the mechanisms by which they contribute to Alzheimer's disease will be beneficial in the current treatment regimens for Alzheimer's disease and in the development of future therapies. Here we discuss vascular factors with respect to Alzheimer's disease and dementia and review the factors that give rise to vascular dysfunction and contribute to Alzheimer's disease.

Association between APOE epsilon4 allele and vascular dementia: The Cache County study

BACKGROUND

The APOE epsilon4 allele is an established risk factor for Alzheimer's disease, but reports of its association with vascular dementia (VaD) have been inconsistent. We examined the relationship between APOE epsilon4 allele and the risk of incident VaD in a large, population-based cohort of elderly adults with up to 10 years of follow-up between 1995 and 2005.

METHODS

A total of 3,424 elderly men and women free of dementia were genotyped at the baseline assessment. Incident VaD was identified through standardized procedures administered at 3 follow-up assessments. Cox proportional hazards models were used to evaluate the risk of VaD associated with APOE epsilon4.

RESULTS

The adjusted hazard ratio was 1.6 for the participants with 1 APOE epsilon4 allele (95% CI: 0.9-2.7; p = 0.083) and 4.4 for those with 2 APOE epsilon4 alleles (95% CI: 1.6-12.5; p = 0.005). The increased risk did not appear to be mediated by vascular risk factors.

CONCLUSIONS

The APOE epsilon4 allele is associated with an increased risk of VaD in a dose-dependent fashion and accounts for almost 20% of VaD in the population.

Novel mechanisms of central nervous system damage in HIV infection

Human immunodeficiency virus-1 infection of the central nervous system is an early event after primary infection, resulting in motor and cognitive defects in a significant number of individuals despite successful antiretroviral therapy. The pathology of the infected brain is characterized by enhanced leukocyte infiltration, microglial activation and nodules, aberrant expression of inflammatory factors, neuronal dysregulation and loss, and blood–brain barrier disruption. Months to years following the primary infection, these central nervous system insults result in a spectrum of motor and cognitive dysfunction, ranging from mild impairment to frank dementia. The mechanisms that mediate impairment are still not fully defined. In this review we discuss the cellular and molecular mechanisms that facilitate impairment and new data that implicate intercellular communication systems, gap junctions and tunneling nanotubes, as mediators of human immunodeficiency virus-1 toxicity and infection within the central nervous system. These data suggest potential targets for novel therapeutics.

Observation of the density and size of cells in hippocampus and vascular lesion in thalamus of GFAP-apoE transgenic mice

OBJECTIVE

Apolipoprotein E (apoE) is associated with increased risk of age-related diseases, such as Alzheimer's disease (AD) and cerebrovascular disease (CVD). The present study aims to investigate the age-related general morphological changes of the brain in GFAP-apoE transgenic mice, especially the alterations in number and size of hippocampal pyramidal cells and the microvascular lesions in the thalamus.

METHODS

Nine female apoE4/4 mice were divided into 3 groups (n=3 in each group): 3-4 months (young group), 9-10 months (middle-aged group) and 20-21 months (old group). Age-matched apoE3/3 mice were employed as control group (n=3 in each group). The paraffin sections of brain tissue were stained by 2 conventional staining methods, thionin staining and hematoxylin-esion(HE) staining, the former of which was to observe the hippocampal cells, while the latter was used to examine the brain microvasculature.

RESULTS

There was no apparent difference in the cortical layer between apoE3/3 and apoE4/4 mice, neither any significant difference in the number of cells in hippocampal CA1-CA3 subfields between apoE3/3 and apoE4/4 mice at various age points (P>0.05). However, the mean size of pyramidal cells in CA1 subfield in apoE3/3 and apoE4/4 mice decreased as mice were getting older (P<0.001). At the age of 20-21 months, this cellular atrophy in apoE4/4 mice was more severe than that in old apoE3/3 mice (P<0.05). Furthermore, microvascular lesion in the thalamus was detected in all the 3 old apoE4/4 mice, at varying degrees (5.24%, 1.41% and 3.97%, respectively), while only one apoE3/3 mouse exhibited microvascular lesion in the thalamus, at a low level (0.85%).

CONCLUSION

The current study suggests that the cell size in hippocampal CA1 subfield decreases with aging, irrespective of apoE genotype. Cellular atrophy in CA1 subfield and the microvascular lesion in the thalamus are both more severe in old apoE4/4 mice as compared with those in age-matched apoE3/3 mice. Doubts still exist on whether the decreased cell size in hippocampal CA1 subfield in old apoE4/4 mice is associated with dysfunction in learning and memory and whether the microvascular lesions indicate a higher risk of stroke in human apoE4 allele mice. To clarify these issues, further investigations are needed.

Risk factors for age-related maculopathy

Age-related maculopathy (ARM) is the leading cause of blindness in the elderly. Although beneficial therapeutic strategies have recently begun to emerge, much remains unclear regarding the etiopathogenesis of this disorder. Epidemiologic studies have enhanced our understanding of ARM, but the data, often conflicting, has led to difficulties with drawing firm conclusions with respect to risk for this condition. As a consequence, we saw a need to assimilate the published findings with respect to risk factors for ARM, through a review of the literature appraising results from published cross-sectional studies, prospective cohort studies, case series, and case control studies investigating risk for this condition. Our review shows that, to date, and across a spectrum of epidemiologic study designs, only age, cigarette smoking, and family history of ARM have been consistently demonstrated to represent risk for this condition. In addition, genetic studies have recently implicated many genes in the pathogenesis of age-related maculopathy, including Complement Factor H, PLEKHA 1, and LOC387715/HTRA1, demonstrating that environmental and genetic factors are important for the development of ARM suggesting that gene-environment interaction plays an important role in the pathogenesis of this condition.

Significance of apolipoprotein E in subarachnoid hemorrhage: neuronal injury, repair, and therapeutic perspectives--a review

Subarachnoid hemorrhage (SAH) strikes individuals at a young age with devastating neurologic consequences. Classic formulations that correlate complications and outcome with clinical variables do not explain all the heterogeneity that is usually found in clinical practice. The role of genetic predisposition has recently been investigated. Particular attention has been paid to the apolipoprotein E (APOE) genotype that encodes for a polymorphic protein existing as 3 isoforms (apoE2, apoE3, apoE4), products of alleles E2, E3, and E4 at a single gene locus. ApoE is produced by astrocytes and exerts complex neuroprotective functions that make it a hub of the biochemical network of SAH. The neuroprotective effectiveness of the apoE4 isoform is reduced with respect to the others and this has made the E4 allele a risk factor candidate. Recently published observational studies and meta-analyses suggested that the APOE genotype may strongly improve the usual predictive model with the possibility of optimizing clinical decisions according to the individual's needs. Furthermore, the clinical results, together with new biological insights, suggest that SAH may be a possible candidate for the ongoing research on apoE-based neuroprotective therapy. This article reviews the clinical studies, analyzes their methodology, and surveys the biological links between the physiopathology of SAH and apoE and the possible prospects.

Human APOE isoform-dependent effects on brain beta-amyloid levels in PDAPP transgenic mice

To investigate the role of human apolipoprotein E (apoE) on Abeta deposition in vivo, we crossed PDAPP mice lacking mouse Apoe to targeted replacement mice expressing human apoE (PDAPP/TRE2, PDAPP/TRE3, or PDAPP/TRE4). We then measured the levels of apoE protein and Abeta peptides in plasma, CSF, and brain homogenates in these mice at different ages. We also quantified the amount of brain Abeta and amyloid burden in 18-month-old mice. In young PDAPP/TRE4 mice that were analyzed at an age before brain Abeta deposition, we observed a significant decrease in the levels of apoE in CSF and brain when compared with age-matched mice expressing either human E2 or E3. The brain levels of Abeta42 in PDAPP/TRE4 mice were substantially elevated even at this very early time point. In older PDAPP/TRE4 mice, the levels of insoluble apoE protein increased in parallel to the dramatic rise in brain Abeta burden, and the majority of apoE was associated with Abeta. In TRE4 only mice, we also observed a significant decrease in the level of apoE in brain homogenates. Since the relative level of apoE mRNA was equivalent in PDAPP/TRE and TRE only mice, it appears that post-translational mechanisms influence the levels of apoE protein in brain (E4 < E3 << E2), resulting in early and dramatic apoE isoform-dependent effects on brain Abeta levels (E4 >> E3 > E2) that increase with age. Therapeutic strategies aimed at increasing the soluble levels of apoE protein, regardless of isoform, may effectively prevent and (or) treat Alzheimer's disease.

Human apolipoprotein E4 targeted replacement mice show increased prevalence of intracerebral hemorrhage associated with vascular amyloid deposition

Previous studies show that APOE *4 carriers are at increased risk for ischemic stroke and intracerebral hemorrhage (ICH). The APOE *4 gene is also linked to increased incidence of cerebral amyloid angiopathy. It has been suggested that apolipoprotein E4 expression leads to increased vascular amyloid deposition, which may explain the increased incidence of ICH in APOE *4 carriers. Here we show a significant increase in ICH in apoE4 targeted replacement mice compared with apoE3 mice. In all, 89% of the vessels in the apoE4 mice that showed evidence for hemorrhage contained fibrillar amyloid beta based on thioflavine-S staining. Aged apoE4 mice contained predominantly vascular amyloid deposits in the frontal cortex and hippocampus, but also showed evidence for parenchymal amyloid deposits. Most of the parenchymal amyloid appeared diffuse in nature; however, a small fraction was thioflavine-S positive, indicating presence of fibrillar amyloid. Electron microscopy further revealed evidence for fibrillar deposits in the vessel walls of apoE4 mice, but not apoE3 mice. The apoE4 targeted replacement mice do not harbor any mutation in the amyloid precursor protein gene and, therefore, are similar to the majority of humans susceptible to cerebral amyloid angiopathy and ICH, where the APOE genetic polymorphism is the only known genetic risk factor.

Intron-3 retention/splicing controls neuronal expression of apolipoprotein E in the CNS

Neuronal expression of apolipoprotein (apo) E4 may contribute to the pathogenesis of Alzheimer's disease (AD). In studying how apoE expression is regulated in neurons, we identified a splicing variant of apoE mRNA with intron-3 retention (apoE-I3). ApoE-I3 mRNA was detected in neuronal cell lines and primary neurons, but not in astrocytic cell lines or primary astrocytes, from humans and mice by reverse transcription (RT)-PCR. In both wild-type and human apoE knock-in mice, apoE-I3 was found predominantly in cortical and hippocampal neurons by in situ hybridization. Cell fractionation and quantitative RT-PCR revealed that over 98% of the apoE-I3 mRNA was retained in the nucleus without protein translation. In transfected primary neurons, apoE expression increased dramatically when intron-3 was deleted from a genomic DNA construct and decreased markedly when intron-3 was inserted into a cDNA construct, suggesting that intron-3 retention/splicing controls apoE expression in neurons. In response to excitotoxic challenge, the apoE-I3 mRNA was markedly increased in morphologically normal hippocampal neurons but reduced in degenerating hippocampal neurons in mice; apoE mRNA showed the opposite pattern. This apparent precursor-product relationship between apoE-I3 and apoE mRNA was supported by a transcriptional inhibition study. Thus, neuronal expression of apoE is controlled by transcription of apoE-I3 under normal conditions and by processing of apoE-I3 into mature apoE mRNA in response to injury.

Apolipoprotein E genotypes in hospitalized elderly patients with vascular dementia

BACKGROUND

Polymorphism in the apolipoprotein E (APOE) gene is the major genetic risk factor associated with late-onset Alzheimer's Disease (AD). However, it is still unclear if a relationship exists between the APOE epsilon4 allele and vascular dementia (VaD) in elderly subjects.

OBJECTIVES

To evaluate the prevalence of APOE alleles in elderly patients with VaD compared to AD patients and to control subjects with no cognitive impairment (NoCI).

PATIENTS AND METHODS

We evaluated 396 consecutive patients aged > or =65 years with definite or suspected cognitive impairment with a clinical (Mini-Mental State Examination, Clinical Dementia Rating, Geriatric Depression Scale), functional (Activities of Daily Living, Instrumental Activities of Daily Living), comorbidity (Cumulative Illness Rating Scale) and instrumental (CT scan, NMR) assessment. Diagnosis of dementia was made according to NINCDS-ADRDA and NINDS-AIREN Work Group and the DSM-IV. APOE genotypes were analyzed by a recently described method resulting in positive/negative chain reaction products for each APOE genotype. Statistical analysis was carried out using the Pearson chi(2), the Kruskal-Wallis test and the ANOVA post hoc comparisons.

RESULTS

A total of 287 elderly patients (males = 138, females = 149, mean age = 77.8 +/- 6.9 years, range = 65-98) with diagnoses of VaD (n = 97), AD (n = 82) or NoCI (n = 108) were included in the study. A significantly higher APOE epsilon4 allele frequency was observed in AD patients compared to VaD and/or NoCI subjects, while no differences were found between VaD patients and subjects with NoCI (AD = 24.3%, VaD = 10.3, NoCI = 8.7, p < 0.05). Furthermore, a significantly lower APOE epsilon3 allele frequency was observed in AD patients compared to VaD and/or NoCI subjects but not between VaD and NoCI patients (AD = 71.3%, VaD = 80.9, NoCI = 83.4, p < 0.05). No significant differences were observed in the APOE epsilon2 allele (VaD = 8.8%, AD = 4.4, NoCI = 7.9, p = n.s.) among the 3 groups.

CONCLUSIONS

In this population, the frequency of the APOE epsilon4 allele is lower in VaD than in AD.

Apolipoprotein E epsilon4 allele frequency and age at onset of Alzheimer's disease

The age distribution of the epsilon4 allelic form of the apolipoprotein E gene (APOE) was investigated in 630 patients with Alzheimer's disease (AD) with onset age ranging from 35 to 90 years. Overall, mean age at onset in APOE epsilon4 allele bearers was significantly later than that in nonbearers. However, when stratified into early onset AD (EOAD) and late onset (LOAD) groups, mean age at onset in EOAD cases bearing APOE epsilon4 allele was later than that in those EOAD cases without epsilon4 allele, whereas in LOAD mean age at onset in cases bearing APOE epsilon4 allele was earlier than in those without epsilon4 allele. When analysed by decade, it was observed that 37% of the total number of APOE epsilon4 allele bearers, and 43% of total number of cases with APOE epsilon4/epsilon4 genotype fell into the 60-69 years age class. Hence, APOE epsilon4 allele frequency, at 0.44, was highest in the 60-69 years age class, progressively decreasing either side of this age group. APOE epsilon4 allele therefore has its maximum impact between onset ages of between 60 and 70 years.

Cognitive impact of subcortical vascular and Alzheimer's disease pathology

OBJECTIVE

To assess the interactions among three types of pathology (ie, cerebrovascular disease, hippocampal sclerosis [HS], and Alzheimer's disease [AD]), cognitive status, and apolipoprotein E genotype.

METHODS

We report clinicopathological correlations from 79 autopsy cases derived from a prospective longitudinal study of subcortical ischemic vascular disease and AD.

RESULTS

Thirty percent of the cases had significant cerebrovascular parenchymal pathology scores (CVDPS), 54% had significant AD pathology, and 18% had HS. In an ordinal logistic regression analysis that included interaction terms to assess the effects of each pathological variable when the other variables are interpolated to zero, each of the three pathology variables contributed independently to cognitive status: Braak and Braak stage odds ratio (OR) = 2.84 (95% confidence interval, 1.81-4.45), HS score OR = 2.43 (95% confidence interval, 1.01-5.85), and CVDPS OR = 1.02 (95% confidence interval, 1.00-1.04). Only Braak and Braak stage contributed to a global neuropsychological measure of cognitive impairment. Apolipoprotein E4 genotype was associated with Braak and Braak stage (OR, 1.31 [95% confidence interval, 1.03-1.68]), but not CVDPS or HS scores.

INTERPRETATION

In this convenience sample enriched for subcortical ischemic vascular disease, HS was a common unsuspected neuropathological finding. Apolipoprotein E4 genotype was associated with cerebral amyloid angiopathy, but not HS or arteriosclerosis. When Braak and Braak stage was interpolated to zero, both CVDPS and HS contributed to cognitive impairment. However, advancing stages of AD pathology overwhelmed the effects of CVDPS and HS, to become the major determinant of dementia.

Cerebrovascular disease, APOE epsilon4 allele and cognitive decline in a cognitively normal population

OBJECTIVES

To investigate whether cerebrovascular disease (CVD) and apolipoprotein E (APOE) epsilon4 allele were associated with cognitive decline and whether the relationship between CVD and cognitive decline varied by APOE epsilon4 status.

METHODS

A total of 809 cognitively normal community-dwelling residents aged >75 years were followed to detect subjects with cognitive decline, defined as follow-up. Mini-mental state examination (MMSE) score was >10% decease of the baseline score. Logistic and multinomial logistic models were developed to estimate odds ratio (OR) and 95% confidence interval (CI) of cognitive decline related to a history of CVD and APOE epsilon4 by taking into account major potential confounders including baseline MMSE score.

RESULTS

During the mean 3.5 years of follow-up, 190 subjects experienced cognitive decline. Multi-adjusted ORs (95% CIs) of overall cognitive decline were 2.27 (1.23-4.17) for CVD and 1.69 (1.13-2.54) for APOE epsilon4, but no interaction was detected. Multinomial logistic analysis led to the CVD-related ORs of 1.42 (0.75-2.67) for cognitive decline without progression to dementia and 3.41 (1.55-7.55) for the decline progressing to dementia; similar analysis from a separate model led to adjusted OR of 2.28 (0.88-5.87; p=0.09) for the decline progressing to Alzheimer's disease. The risk effects of CVD on cognitive decline with progression to dementias were statistically significant mainly among individuals without APOE epsilon4 allele.

CONCLUSIONS

CVD is a major risk factor for cognitive decline associated with progression to dementia and Alzheimer's disease. There appears no interaction between CVD and APOE epsilon4 on cognitive decline in very old people.

Apolipoprotein E epsilon4 allele frequency in vascular dementia

AIM

The aim of the study was to investigate whether possession of the epsilon4 allelic form of the apolipoprotein E (APOE) gene increases the risk of developing vascular dementia (VaD).

METHODS

APOE allele and genotype frequencies were determined by PCR in 89 patients with possible and probable VaD and compared with those in 97 patients with possible and probable Alzheimer's disease (AD) of similar age of disease onset and ethnic background, and with 766 control subjects drawn from the same geographical region.

RESULTS

The APOE epsilon4 allele frequency in all 97 patients with possible and probable AD was significantly higher (p < 0.001) than that in control subjects. However, the APOE epsilon4 allele frequency in all 89 patients with possible and probable VaD was also significantly higher (p < 0.001) than that in control subjects, but not significantly different from that in AD. The APOE epsilon4 allele frequency was similarly, and still significantly (p < 0.001), increased when only those patients with probable AD or probable VaD were considered.

CONCLUSION

Possession of APOE epsilon4 allele increases the risk of VaD.

Microvascular injury and blood-brain barrier leakage in Alzheimer's disease

Thinning and discontinuities within the vascular basement membrane (VBM) are associated with leakage of the plasma protein prothrombin across the blood-brain barrier (BBB) in Alzheimer's disease (AD). Prothrombin immunohistochemistry and ELISA assays were performed on prefrontal cortex. In severe AD, prothrombin was localized within the wall and neuropil surrounding microvessels. Factor VIII staining in severe AD patients indicated that prothrombin leakage was associated with shrinkage of endothelial cells. ELISA revealed elevated prothrombin levels in prefrontal cortex AD cases that increased with the Braak stage (Control=1.39, I-II=1.76, III-IV=2.28, and V-VI=3.11 ng prothrombin/mg total protein). Comparing these four groups, there was a significant difference between control and Braak V-VI (p=0.0095) and also between Braak stages I-II and V-VI (p=0.0048). There was no significant difference in mean prothrombin levels when cases with versus without cerebral amyloid angiopathy (CAA) were compared (p-value=0.3627). When comparing AD patients by APOE genotype (ApoE3,3=2.00, ApoE3,4=2.49, and ApoE4,4=2.96 ng prothrombin/mg total protein) an analysis of variance indicated a difference between genotypes at the 10% significance level (p=0.0705). Tukey's test indicated a difference between the 3,3 and 4,4 groups (p=0.0607). These studies provide evidence that in advanced AD (Braak stage V-VI), plasma proteins like prothrombin can be found within the microvessel wall and surrounding neuropil, and that leakage of the blood-brain barrier may be more common in patients with at least one APOE4 allele.

Familial Alzheimer disease in Latinos: interaction between APOE, stroke, and estrogen replacement

BACKGROUND

Factors that modify risk related to APOE variants have been examined primarily in unrelated patients and controls, but seldom in family-based studies. Stroke, vascular risk factors, estrogen replacement therapy (ERT), head injury (HI), and smoking have been reported to influence risk of sporadic but not familial Alzheimer disease (AD).

OBJECTIVES

To examine the potential relationship between these risk factors and APOE, the authors used a family study design in a population in which the APOE-epsilon4 variant is strongly associated with risk of AD.

METHODS

Latino families primarily from the Caribbean Islands in which two or more living relatives had dementia were identified in the New York City metropolitan area, the Dominican Republic, and Puerto Rico. A total of 1,498 participants from 350 families underwent a clinical interview, medical and neurologic examinations, neuropsychological testing, and APOE genotyping. Diagnosis was made by consensus using research criteria for AD.

RESULTS

APOE-epsilon4 was associated with a nearly twofold increased risk of AD. A history of stroke was also associated with a fourfold increased risk. A statistical interaction between APOE-epsilon4 and stroke was observed. Women with an APOE-epsilon4 who took ERT did not have an increased risk of AD, but in women with a history of stroke ERT was a deleterious effect modifier.

CONCLUSIONS

APOE-epsilon4 and stroke independently increase risk of familial Alzheimer disease (AD) among Latinos, and may interact to further increase AD risk. Among women, the risk of AD associated with APOE-epsilon4 may be attenuated by a history of ERT.

Apolipoprotein E4: a causative factor and therapeutic target in neuropathology, including Alzheimer's disease

The premise of this review is that apolipoprotein (apo) E4 is much more than a contributing factor to neurodegeneration. ApoE has critical functions in redistributing lipids among CNS cells for normal lipid homeostasis, repairing injured neurons, maintaining synapto-dendritic connections, and scavenging toxins. In multiple pathways affecting neuropathology, including Alzheimer's disease, apoE acts directly or in concert with age, head injury, oxidative stress, ischemia, inflammation, and excess amyloid beta peptide production to cause neurological disorders, accelerating progression, altering prognosis, or lowering age of onset. We envision that unique structural features of apoE4 are responsible for apoE4-associated neuropathology. Although the structures of apoE2, apoE3, and apoE4 are in dynamic equilibrium, apoE4, which is detrimental in a variety of neurological disorders, is more likely to assume a pathological conformation. Importantly, apoE4 displays domain interaction (an interaction between the N- and C-terminal domains of the protein that results in a compact structure) and molten globule formation (the formation of stable, reactive intermediates with potentially pathological activities). In response to CNS stress or injury, neurons can synthesize apoE. ApoE4 uniquely undergoes neuron-specific proteolysis, resulting in bioactive toxic fragments that enter the cytosol, alter the cytoskeleton, disrupt mitochondrial energy balance, and cause cell death. Our findings suggest potential therapeutic strategies, including the use of "structure correctors" to convert apoE4 to an "apoE3-like" molecule, protease inhibitors to prevent the generation of toxic apoE4 fragments, and "mitochondrial protectors" to prevent cellular energy disruption.

Effect of domain interaction on apolipoprotein E levels in mouse brain

Apolipoprotein (apo) E4 is a risk factor for heart disease, Alzheimer's disease, and other forms of neurodegeneration, but the underlying mechanisms are unknown. Domain interaction, a structural property that distinguishes apoE4 from apoE2 and apoE3, results in more rapid turnover and lower plasma levels of apoE4. To determine whether domain interaction affects brain apoE levels, we analyzed brain homogenates from human apoE3 and apoE4 knock-in mice, wild-type mice, and Arg-61 apoE mice, in which domain interaction was introduced by gene targeting. As determined on Western blots, the hemibrain, cortex, hippocampus, and cerebellum of knock-in mice had 30-40% lower levels of apoE4 than apoE3, and Arg-61 mice had 25-50% lower apoE levels than wild-type mice. In the CSF, Arg-61 apoE level was 40% lower than the wild-type level. Arg-61 apoE mRNA levels were similar to or slightly higher than wild-type apoE mRNA levels. Thus, the lower Arg-61 apoE levels were not attributable to decreased mRNA levels. In culture medium from heterozygous Arg-61/wild-type and apoE4/apoE3 primary astrocytes, Arg-61 apoE and apoE4 levels were lower than wild-type apoE and apoE3, respectively, suggesting that primary astrocytes secrete lower amounts of Arg-61 apoE and apoE4. These results demonstrate that domain interaction is responsible for the lower levels of both human apoE4 and mouse Arg-61 apoE in mouse brain. Cells may recognize apoE4 and Arg-61 apoE as misfolded proteins and target them for degradation or accumulation. Thus, degradation/accumulation or lower levels of apoE4 may contribute to the association of apoE4 with Alzheimer's disease.

Apolipoprotein E, angiotensin-converting enzyme and kallikrein gene polymorphisms and the risk of Alzheimer's disease and vascular dementia

Lipoproteins and vascular factors may play roles in the development of Alzheimer's disease (AD) and/or vascular dementia (VaD). In this study, odd ratios (ORs) and 95% confidence intervals (CIs) for apolipoprotein E (APOE), angiotensin-converting enzyme (ACE), and kallikrein (KLK1) polymorphisms were computed to test their association with the disease by a case-control study. The risk of AD was significantly increased for individuals with APOE varepsilon4 allele (OR = 3.73, 95% CI = 2.38-5.98). The risk of AD was also significant for people with ACE DD genotype, D allele, or T-D haplotype [OR (95% CI) = 4.29 (1.96-10.23), 1.90 (1.35-2.70), or 2.91 (1.71-5.10), respectively]. The above association between ACE-VaD was also strong (p = 0.0012, 0.0050, 0.0007, respectively). Reporter constructs containing the -240 A or T allele displayed similar transcriptional activity in both HEK-293 and IMR-32 cells. Thus, another putative pathogenic marker that is linked with the Alu D allele might affect the risk of AD and VaD in Taiwan.

Cardiovascular damage in Alzheimer disease: autopsy findings from the Bryan ADRC

Autopsy information on cardiovascular damage was investigated for pathologically confirmed Alzheimer disease (AD) patients (n = 84) and non-AD control patients (n = 60). The 51 relevant items were entered into a grade-of-membership model to describe vascular damage in AD. Five latent groups were identified “I: early-onset AD,” “II: controls, cancer,” “III: controls, extensive atherosclerosis,” “IV: late-onset AD, male,” and “V: late-onset AD, female.” Expectedly, Groups IV and V had elevated APOE ϵ4 frequency. Unexpectedly, there was limited atherosclerosis and frequent myocardial valve and ventricular damage. The findings do not indicate a strong relationship between atherosclerosis and AD, although both are associated with the APOE ϵ4. Instead, autopsy findings of extensive atherosclerosis were associated with possible, not probable or definite AD, and premature death. They are consistent with the hypothesis that brain hypoperfusion contributes to dementia, possibly to AD pathogenesis, and raise the possibility that the APOE allele ϵ4 contributes directly to heart valve and myocardial damage.

Crystallization and preliminary X-ray diffraction analysis of apolipoprotein E-containing lipoprotein particles

High-resolution structural information is available for several soluble plasma apolipoproteins (apos) in a lipid-free state. However, this information provides limited insight into structure-function relationships, as this class of proteins primarily performs its functions of lipid transport and modulation of lipid metabolism in a lipid-bound state on lipoprotein particles. Here, the possibility of generating homogeneous lipoprotein particles that could be crystallized was explored, opening the possibility of obtaining high-resolution structural information by X-ray crystallography. To test this possibility, apoE4 complexed with the phospholipid dipalmitoylphosphatidylcholine was chosen. Uniform particles containing 50% lipid and 50% apoE4 were obtained and crystallized using the hanging-drop method. Two crystal forms diffract to beyond 8 A resolution.

Post-stroke dementia is associated with alpha(1)-antichymotrypsin polymorphism

BACKGROUND AND PURPOSE

Alpha-1-antichymotrypsin (ACT) is an acute phase protein involved in inflammatory reaction, promoting the assembly of beta amyloid protein into filaments and contributing to its resistance to proteolytic digestion. The aim of our study was to determine ACT signal peptide polymorphism (A/T) as a possible risk factor for post-stroke dementia (PSD).

METHODS

142 consecutive ischemic stroke patients and 188 controls were included in this study. Pre-stroke dementia (PRESD) was evaluated using the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE). The diagnosis of the post-stroke dementia (PSD) was established according to DSM-IV criteria. The ACT gene (A/T) polymorphism was determined by PCR-RFLR.

RESULTS

Both ACT-TT genotype and T-allele were significantly more prevalent in patients with PSD than in non-demented stroke patients, controls or patients with PRESD. After adjustment for age, gender, and vascular risk factors, both the ACT-TT genotype and T-allele remained independently associated with PSD.

CONCLUSION

Our findings suggest that ACT polymorphism (A/T) is a risk factor for PSD.

Apolipoprotein E e4 Allele and Neurobehavioral Status After On-Pump Coronary Artery Bypass Grafting

Abstract Background and Aim: The presence of apolipoprotein E epsilon4 allele is being considered as a risk factor for cognitive decline after cardiac surgery. We sought the effect of apolipoprotein E epsilon4 allele on neurobehavioral status after on-pump coronary artery bypass grafting.

METHODS

Prior to the operation, neurologic examination and neurobehavioral cognitive status test (COGNISTAT) were performed. Both procedures were repeated on the day of discharge and 3 months after surgery. Apolipoprotein E epsilon4 allele positive and apolipoprotein E epsilon4 allele negative patients' performance on COGNISTAT were compared.

RESULTS

There was no statistically significant demographic and operative data difference between two groups. No neurological impairment was observed on examinations. There was no statistically significant neurocognitive decline difference between two groups' postoperative performances.

CONCLUSIONS

It seems that apolipoprotein E epsilon4 allele may not affect neurobehavioral status in the intermediate period after on-pump coronary artery bypass grafting.