Differential effects of the APOE genotype on brain function across the lifespan

Increasing age and carrying an APOE ε4 allele are well established risk factors for Alzheimer's disease (AD). The earlier age of onset of AD observed in ε4-carriers may reflect an accelerated aging process. We recently reported that APOE genotype modulates brain function decades before the appearance of any cognitive or clinical symptoms. Here we test the hypothesis that APOE influences brain aging by comparing healthy ε4-carriers and non-carriers, using the same imaging protocol in distinct groups of younger and older healthy volunteers. A cross-sectional factorial design was used to examine the effects of age and APOE genotype, and their interaction, on fMRI activation during an encoding memory task. The younger (N=36; age range 20-35; 18 ε4-carriers) and older (35 middle-age/elderly; age range 50-78 years; 15 ε4-carriers) healthy volunteers taking part in the study were cognitively normal. We found a significant interaction between age and ε4-status in the hippocampi, frontal pole, subcortical nuclei, middle temporal gyri and cerebellum, such that aging was associated with decreased activity in e4-carriers and increased activity in non-carriers. Reduced cerebral blood flow was found in the older ε4-carriers relative to older non-carriers despite preserved grey matter volume. Overactivity of brain function in young ε4-carriers is disproportionately reduced with advancing age even before the onset of measurable memory impairment. The APOE genotype determines age-related changes in brain function that may reflect the increased vulnerability of ε4-carriers to late-life pathology or cognitive decline.

The effect of borderline diabetes on the risk of dementia and Alzheimer's disease

To verify the hypothesis that borderline diabetes may increase the risk of dementia and Alzheimer's disease, a community-based cohort of 1,173 dementia- and diabetes-free individuals aged >or=75 years was longitudinally examined three times to detect patients with dementia and Alzheimer's disease (Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition criteria). Borderline diabetes was defined as a random plasma glucose level of 7.8-11.0 mmol/l. Data were analyzed using Cox proportional hazards models. During the 9-year follow-up, 397 subjects developed dementia, including 307 Alzheimer's cases. At baseline, 47 subjects were identified with borderline diabetes. Borderline diabetes was associated with adjusted hazard ratios (95% CIs) of 1.67 (1.04-2.67) for dementia and 1.77 (1.06-2.97) for Alzheimer's disease; the significant associations were present after additional adjustment for future development of diabetes. Stratified analysis suggested a significant association between borderline diabetes and Alzheimer's disease only among noncarriers of APOE epsilon4 allele. There was an interaction between borderline diabetes and severe systolic hypertension on the risk of Alzheimer's disease (P = 0.04). We conclude that borderline diabetes is associated with increased risks of dementia and Alzheimer's disease; the risk effect is independent of the future development of diabetes. Borderline diabetes may interact with severe systolic hypertension to multiply the risk of Alzheimer's disease.

Effect of quercetin on traits of the metabolic syndrome, endothelial function and inflammation in men with different APOE isoforms

BACKGROUND AND AIMS

The polyphenol quercetin may prevent cardiovascular diseases due to its vasorelaxant and anti-oxidative properties. We investigated the effects of quercetin on risk factors of atherosclerosis, biomarkers of inflammation and oxidative stress, depending on the apolipoprotein E (APOE) genotype.

METHODS AND RESULTS

In a double-blind crossover study 49 healthy male subjects with APOE genotype 3/3 (n = 19), 3/4 (n = 22) and 4/4 (n = 8) consumed 150 mg/d quercetin or placebo for 8 weeks each, intermitted by a three-week washout phase. After each intervention, endothelial function, anthropometry, metabolic and inflammatory parameters were measured in the fasting and postprandial state following a standardized lipid-rich meal. Endothelial function was not changed. In all subjects combined, quercetin significantly decreased waist circumference (P = 0.004) and postprandial systolic blood pressure (P = 0.044). Postprandial triacylglycerol concentrations were significantly decreased and HDL-cholesterol concentrations increased after quercetin as compared to placebo consumption (P = 0.025). Quercetin also moderately increased levels of TNFα (P = 0.024). There was a significant gene-diet interaction for waist circumference and for body mass index (BMI).

CONCLUSIONS

Quercetin supplementation improved some risk factors of cardiovascular disease, yet exerted slightly pro-inflammatory effects. Genotype-dependent effects were seen only on waist circumference and BMI.

A blood-based diagnostic test incorporating plasma Aβ42/40 ratio, ApoE proteotype, and age accurately identifies brain amyloid status: findings from a multi cohort validity analysis

BACKGROUND

The development of blood-based biomarker tests that are accurate and robust for Alzheimer's disease (AD) pathology have the potential to aid clinical diagnosis and facilitate enrollment in AD drug trials. We developed a high-resolution mass spectrometry (MS)-based test that quantifies plasma Aβ42 and Aβ40 concentrations and identifies the ApoE proteotype. We evaluated robustness, clinical performance, and commercial viability of this MS biomarker assay for distinguishing brain amyloid status.

METHODS

We used the novel MS assay to analyze 414 plasma samples that were collected, processed, and stored using site-specific protocols, from six independent US cohorts. We used receiver operating characteristic curve (ROC) analyses to assess assay performance and accuracy for predicting amyloid status (positive, negative, and standard uptake value ratio; SUVR). After plasma analysis, sites shared brain amyloid status, defined using diverse, site-specific methods and cutoff values; amyloid PET imaging using various tracers or CSF Aβ42/40 ratio.

RESULTS

Plasma Aβ42/40 ratio was significantly (p < 0.001) lower in the amyloid positive vs. negative participants in each cohort. The area under the ROC curve (AUC-ROC) was 0.81 (95% CI = 0.77-0.85) and the percent agreement between plasma Aβ42/40 and amyloid positivity was 75% at the optimal (Youden index) cutoff value. The AUC-ROC (0.86; 95% CI = 0.82-0.90) and accuracy (81%) for the plasma Aβ42/40 ratio improved after controlling for cohort heterogeneity. The AUC-ROC (0.90; 95% CI = 0.87-0.93) and accuracy (86%) improved further when Aβ42/40, ApoE4 copy number and participant age were included in the model.

CONCLUSIONS

This mass spectrometry-based plasma biomarker test: has strong diagnostic performance; can accurately distinguish brain amyloid positive from amyloid negative individuals; may aid in the diagnostic evaluation process for Alzheimer's disease; and may enhance the efficiency of enrolling participants into Alzheimer's disease drug trials.

Total apolipoprotein E levels and specific isoform composition in cerebrospinal fluid and plasma from Alzheimer's disease patients and controls

The apolipoprotein E (ApoE) ε4 allele is the strongest risk factor of sporadic Alzheimer's disease (AD), however, the fluid concentrations of ApoE and its different isoforms (ApoE2, ApoE3 and ApoE4) in AD patients and among APOE genotypes (APOE ε2, ε3, ε4) remain controversial. Using a novel mass spectrometry-based method, we quantified total ApoE and specific ApoE isoform concentrations and potential associations with age, cognitive status, cholesterol levels and established AD biomarkers in cerebrospinal fluid (CSF) from AD patients versus non-AD individuals with different APOE genotypes. We also investigated plasma total ApoE and ApoE isoform composition in a subset of these individuals. In total n = 43 AD and n = 43 non-AD subjects were included. We found that CSF and plasma total ApoE levels did not correlate with age or cognitive status and did not differ between AD and non-AD subjects deeming ApoE as an unfit diagnostic marker for AD. Also, whereas CSF ApoE levels did not vary between APOE genotypes APOE ε4 carriers exhibited significantly decreased plasma ApoE levels attributed to a specific decrease in the ApoE4 isoform concentrations. CSF total ApoE concentrations were positively associated with CSF, total tau, tau phosphorylated at Thr181 and Aβ1-42 of which the latter association was weaker and only present in APOE ε4 carriers indicating a differential involvement of ApoE in tau versus Aβ-linked neuropathological processes. Future studies need to elucidate whether the observed plasma ApoE4 deficiency is a life-long condition in APOE ɛ4 carriers and whether this decrease in plasma ApoE predisposes APOE ɛ4 carriers to AD.

Interactive effects of physical activity and APOE-ε4 on BOLD semantic memory activation in healthy elders

Evidence suggests that physical activity (PA) is associated with the maintenance of cognitive function across the lifespan. In contrast, the apolipoproteinE-ε4 (APOE-ε4) allele, a genetic risk factor for Alzheimer's disease (AD), is associated with impaired cognitive function. The objective of this study was to examine the interactive effects of PA and APOE-ε4 on brain activation during memory processing in older (ages 65-85) cognitively intact adults. A cross-sectional design was used with four groups (n=17 each): (1) Low Risk/Low PA; (2) Low Risk/High PA; (3) High Risk/Low PA; and (4) High Risk/High PA. PA level was based on self-reported frequency and intensity. AD risk was based on presence or absence of an APOE-ε4 allele. Brain activation was measured using event-related functional magnetic resonance imaging (fMRI) while participants performed a famous name discrimination task. Brain activation subserving semantic memory processing occurred in 15 functional regions of interest. High PA and High Risk were associated with significantly greater semantic memory activation (famous>unfamiliar) in 6 and 3 of the 15 regions, respectively. Significant interactions of PA and Risk were evident in 9 of 15 brain regions, with the High PA/High Risk group demonstrating greater semantic memory activation than the remaining three groups. These findings suggest that PA selectively increases memory-related brain activation in cognitively intact but genetically at-risk elders. Longitudinal studies are required to determine whether increased semantic memory processing in physically active at-risk individuals is protective against future cognitive decline.

APOE and cytokines as biological markers for recovery of prevalent delirium in elderly medical inpatients

BACKGROUND

Delirium frequently occurs in the context of infection and other inflammatory conditions associated with elevated levels of cytokines. Cytokines used therapeutically can induce symptoms of delirium as an adverse effect. We hypothesized that a causal relationship might exist between delirium and cytokine production during illness. Further, we speculated that the APOE genotype of patients might influence their rate of recovery from delirium given that APOE is associated with amyloid deposition, increased susceptibility to exogenous neurotoxins, and can affect the immune response.

METHODS

A cohort of 164 acutely ill patients, 70 years or older, admitted to an elderly medical unit were studied within 3 days of hospital admission and re-assessed twice weekly until their discharge, to identify and follow the clinical course of delirium. The APOE genotype and the level of circulating cytokines were determined for 116 and 60 patients respectively.

RESULTS

Prevalent delirium was significantly (p < 0.05) associated with a previous history of dementia, age, illness severity, disability and low levels of circulating IGF-I. Recovery was significantly associated (p < 0.05) with lack of APOE 4 allele and higher initial IFN-gamma. A model incorporating gender, APOE epsilon 4 status and IGF-I levels predicted recovery or not from delirium in 76.5% of cases, with a sensitivity 0.77 and specificity 0.75.

CONCLUSIONS

A relationship between delirium with APOE genotype, IFN-gamma, and IGF-I, but not with IL-6, IL-1, TNF-alpha, and LIF was found. A predictive model of recovery was derived from gender, APOE status, and IGF-I levels. This model needs replication with further studies.

EFAD transgenic mice as a human APOE relevant preclinical model of Alzheimer's disease

Identified in 1993, APOE4 is the greatest genetic risk factor for sporadic Alzheimer's disease (AD), increasing risk up to 15-fold compared with APOE3, with APOE2 decreasing AD risk. However, the functional effects of APOE4 on AD pathology remain unclear and, in some cases, controversial. In vivo progress to understand how the human (h)-APOE genotypes affect AD pathology has been limited by the lack of a tractable familial AD-transgenic (FAD-Tg) mouse model expressing h-APOE rather than mouse (m)-APOE. The disparity between m- and h-apoE is relevant for virtually every AD-relevant pathway, including amyloid-β (Aβ) deposition and clearance, neuroinflammation, tau pathology, neural plasticity and cerebrovascular deficits. EFAD mice were designed as a temporally useful preclinical FAD-Tg-mouse model expressing the h-APOE genotypes for identifying mechanisms underlying APOE-modulated symptoms of AD pathology. From their first description in 2012, EFAD mice have enabled critical basic and therapeutic research. Here we review insights gleaned from the EFAD mice and summarize future directions.

Methylation analysis of multiple genes in blood DNA of Alzheimer's disease and healthy individuals

We collected blood DNA from 120 late-onset Alzheimer's disease (AD) patients and 115 healthy matched controls and analysed the methylation levels of genes involved in amyloid-beta peptide production (PSEN1 and BACE1), in DNA methylation (DNMT1, DNMT3A and DNMT3B), and in one-carbon metabolism (MTHFR), searching for correlation with age and gender, with biomarkers of one-carbon metabolism (plasma homocysteine, and serum folate and vitamin B12 levels), and with disease status (being healthy or having AD). We also evaluated the contribution of the APOE ϵ4 allele, the major late-onset AD genetic risk factor, to the studied gene methylation levels. All the genes showed low mean methylation levels (<5%) in both AD and control DNA, no difference between groups, and no correlation with the studied biomarkers, except for MTHFR that showed methylation levels ranging from 5% to 75%, and correlation with circulating biomarkers of one-carbon metabolism. However, mean MTHFR methylation levels were similar between groups (31.1% in AD and 30.7% in controls, P=0.58). Overall, present data suggest that none of the studied regions is differently methylated in blood DNA between AD and control subjects.

Midlife cardiovascular risk factors and late cognitive impairment

Cardiovascular risk factors increase the risk of dementia in later life. The aims of the current study were to assess the effect of multiple midlife cardiovascular risk factors on the risk of cognitive impairment in later life, and to assess the validity of the previously suggested CAIDE Study risk score predicting dementia risk 20 years later. A total of 2,165 Finnish twins were followed and at the end of the follow-up their cognitive status was assessed with a validated telephone interview. The assessment of the risk factors at baseline was based on a self-report questionnaire. Relative risk ratios (RR) were calculated and receiver operating characteristic analyses performed. Midlife obesity (RR 2.42, 95 % CI 1.47-3.98), hypertension (RR 1.38, 95 % CI 1.01-1.88) and low leisure time physical activity (RR 2.52, 95 % CI 1.10-5.76) increased the risk of cognitive impairment after a mean follow-up of 22.6 ± 2.3 years. Hypercholesterolemia did not significantly increase the risk (RR 1.52, 95 % CI 0.92-2.51). Overweight individuals who gained more than 10 % weight between 1981 and 1990 had an increased risk of cognitive impairment (RR 4.27, 95 % CI 1.62-11.2). The CAIDE Study risk score combining various individual risk factors had an area-under-curve of 0.74 (95 % CI 0.69-0.79, n = 591), and there was a strong association between an increasing risk score and the risk of cognitive impairment. The results indicate that multiple midlife cardiovascular risk factors increase the risk of cognitive impairment in later life. Also, a risk score including easily measurable midlife factors predicts an individual's cognitive impairment risk well.

Current evidence for the clinical use of long-chain polyunsaturated n-3 fatty acids to prevent age-related cognitive decline and Alzheimer's disease

An NIH State of the Science Conference panel concluded in 2010 that insufficient evidence is available to recommend the use of any primary prevention therapy for Alzheimer's disease or cognitive decline with age. Despite the insufficient evidence, candidate therapies with varying levels of evidence for safety and efficacy are taken by the public and discussed in the media. One example is the long-chain n-3 (omega-3) polyunsaturated fatty acids (n-3 LC-PUFA), DHA and EPA, found in some fish and dietary supplements. With this report, we seek to provide a practical overview and rating of the level and type of available evidence that n-3 LC-PUFA supplements are safe and protective against cognitive aging and Alzheimer's disease, with additional discussion of the evidence for effects on quality of life, vascular aging, and the rate of aging. We discuss available sources, dose, bioavailability, and variables that may impact the response to n-3 LC-PUFA treatment such as baseline n-3 LC-PUFA status, APOE ε4 genotype, depression, and background diet. Lastly, we list ongoing clinical trials and propose next research steps to validate these fatty acids for primary prevention of cognitive aging and dementia. Of particular relevance, epidemiology indicates a higher risk of cognitive decline in people in the lower quartile of n-3 LC-PUFA intake or blood levels but these populations have not been specifically targeted by RCTs.

Apolipoprotein E gene polymorphism and the risk of cardiovascular disease and type 2 diabetes

BACKGROUND

The role of apolipoprotein E gene (APOE) in lipid metabolism has been well established, and APOE is associated with the risk of cardiovascular disease (CVD) and diabetes mellitus (DM). However, the relationship between APOE polymorphisms and type 2 diabetes (T2DM) with or without CVD remains unclear.

METHODS

In this cross-sectional study, a total of 924 participants including 211 controls (CVD-T2DM-), 247 T2DM patients with CVD (CVD-T2DM+), 232 CVD patients without T2DM (CVD + T2DM-) and 234 T2DM patients with CVD (CVD + T2DM+), were genotyped using chip platform. The association between APOE polymorphisms and T2DM patients with or without CVD was analyzed by univariable and multivariable logistic analysis.

RESULTS

The present study showed that the frequency of E3/E4 increased in T2DM patients with CVD (p < 0.01). The ε4 allele was higher in CVD patients without T2DM (p < 0.01) and T2DM patients with CVD (p < 0.01) as compared with the controls.

CONCLUSIONS

The subjects carrying ε4 allele have increased risk of CVD and T2DM, and exhibit higher level of lipid profiles.

APOE interacts with tau PET to influence memory independently of amyloid PET in older adults without dementia

INTRODUCTION

Apolipoprotein E (APOE) interacts with Alzheimer's disease pathology to promote disease progression. We investigated the moderating effect of APOE on independent associations of amyloid and tau positron emission tomography (PET) with cognition.

METHODS

For 297 nondemented older adults from the Alzheimer's Disease Neuroimaging Initiative, regression equations modeled associations between cognition and (1) cortical amyloid beta (Aβ) PET levels adjusting for tau and (2) medial temporal lobe (MTL) tau PET levels adjusting for Aβ, including interactions with APOE ε4-carrier status.

RESULTS

Adjusting for tau PET, Aβ was not associated with cognition and did not interact with APOE. In contrast, adjusting for Aβ PET, MTL tau was associated with all cognitive domains. Further, there was a stronger moderating effect of APOE on MTL tau and memory associations in ε4-carriers, even among Aβ-negative individuals.

DISCUSSION

Findings suggest that APOE may interact with tau independently of Aβ and that elevated MTL tau confers negative cognitive consequences in Aβ-negative ε4 carriers.

Apolipoprotein E genotype influences presence and severity of delusions and aggressive behavior in Alzheimer disease

AIM

We investigated differences in the prevalence and severity of 10 neuropsychiatric and behavioral symptoms according to apolipoprotein E (APOE) genotype and dementia severity in Alzheimer disease (AD).

METHODS

Neuropsychiatric and behavioral symptoms of 110 AD patients were assessed using the Neuropsychatric Inventory. Dementia severity was assessed using the Mini Mental State Examination (MMSE).

RESULTS

There were 27 APOE-epsilon4-negative patients, 65 heterozygous patients and 18 homozygous patients. There was a significant association between the number of APOE epsilon4 alleles and prevalence and severity of neuropsychiatric and behavioral symptoms that was mainly attributable to delusions and agitation/aggression, which were more common and severer among homozygous APOE epsilon4 carriers. In addition, the presence of hallucinations, anxiety, apathy and aberrant motor behavior increased with deteriorating MMSE score, independently of APOE epsilon4 status.

CONCLUSIONS

The present study showed that the APOE epsilon4 genotype modifies neuropsychiatric and behavioral phenotype in AD. In particular, it was shown that delusions and agitation/aggression were more common and severer among homozygous APOE epsilon4 carriers than among heterozygous or APOE-epsilon4-negative patients.

Apolipoprotein E4 genotype does not increase risk of HIV-associated neurocognitive disorders

This is a cross-sectional, observational study to evaluate the hypothesis that HIV-seropositive (HIV+) apolipoprotein E4 (APOE4) carriers are at increased risk for HIV-associated neurocognitive disorders (HAND) compared to APOE4 noncarriers with HIV in the CNS HIV Antiretroviral Therapy Effects Research (CHARTER) Group sample. APOE genotype was determined in 466 CHARTER participants with varying disease stages and histories of antiretroviral treatment who did not have severe psychiatric or medical comorbid conditions that preclude diagnosis of HAND. HAND diagnoses were based on results of comprehensive neurobehavioral evaluation and use of current neuroAIDS diagnostic criteria. HAND status consists of two levels: neuropsychologically normal status (i.e., no HAND) and any HAND diagnosis (i.e., asymptomatic neurocognitive impairment, minor neurocognitive disorder, HIV-associated dementia). Logistic regression analyses revealed no association between APOE4 carrier status and HAND, and there were no interactions between APOE4 carrier status and ethnicity, age, substance use disorders, duration of infection, or nadir CD4. Results did not differ when analysis was restricted to symptomatic HAND, and no APOE4 gene dose-dependent relationship to HAND emerged. APOE4 status was not associated with concurrent HAND in this large, well-characterized sample. This does not preclude emergence of an association between APOE4 status and HAND as this population ages. Prospective, longitudinal studies are needed to examine APOE4 as a risk factor for neurocognitive decline, incident HAND at older ages, and potential associations with cerebrospinal fluid amyloid.

Metabolic response to a ketogenic breakfast in the healthy elderly

OBJECTIVE

To determine whether the metabolism of glucose or ketones differs in the healthy elderly compared to young or middle-aged adults during mild, short-term ketosis induced by a ketogenic breakfast.

DESIGN AND PARTICIPANTS

Healthy subjects in three age groups (23 +/- 1, 50 +/- 1 and 76 +/- 2 y old) were given a ketogenic meal and plasma beta -hydroxybutyrate, glucose, insulin, triacylglycerols, total cholesterol, non-esterified fatty acids and breath acetone were measured over the subsequent 6 h. Each subject completed the protocol twice in order to determine the oxidation of a tracer dose of both carbon-13 (13C) glucose and 13C-beta-hydroxybutyrate. The tracers were given separately in random order. Apolipoprotein E genotype was also determined in all subjects.

RESULTS

Plasma glucose decreased and beta-hydroxybutyrate, acetone and insulin increased similarly over 6 h in all three groups after the ketogenic meal. There was no significant change in cholesterol, triacylglycerols or non-esterified fatty acids over the 6 h. 13C-glucose and 13C-beta-hydroxybutyrate oxidation peaked at 2-3 h postdose for all age groups. Cumulative 13C-glucose oxidation over 24 h was significantly higher in the elderly but only versus the middle-aged group. There was no difference in cumulative 13C-beta-hydroxybutyrate oxidation between the three groups. Apolipoprotein E (epsilon 4) was associated with elevated fasting cholesterol but was unrelated to the other plasma metabolites.

CONCLUSION

Elderly people in relatively good health have a similar capacity to produce ketones and to oxidize 13C-beta-hydroxybutyrate as middle-aged or young adults, but oxidize 13C-glucose a little more rapidly than healthy middle-aged adults.

Phenotypic associations of tau and ApoE in Parkinson's disease

Overlaps in clinical, pathological and molecular features of Parkinson's disease (PD), dementing and motor tauopathies have prompted association studies in search of common genetic risk factors that may predispose or modify this spectrum of disorders. To explore possible phenotypic implications, we studied common tau and ApoE gene polymorphisms, associated with Alzheimer's disease (AD), progressive supranuclear palsy (PSP) and PD, in a clinically and pathologically characterized cohort of PD patients and aged control subjects. Our results reveal a novel association between PD-related hallucinations and H1H1 genotype. We also report an association between PDD and the presence of the ApoE epsilon4 allele. Better determination of subsets of PD patients based upon the presence of specific phenotypic features may improve the accuracy of association studies.

Emergence of a seizure phenotype in aged apolipoprotein epsilon 4 targeted replacement mice

The apolipoprotein ε4 allele is the strongest genetic risk factor for late-onset Alzheimer's disease (AD) and is associated with earlier age of onset. The incidence of spontaneous seizures has been reported to be increased in sporadic AD as well as in the early onset autosomal dominant forms of AD. We now report the emergence of a seizure phenotype in aged apolipoprotein E4 (apoE4) targeted replacement (TR) mice but not in age-matched apoE2 TR or apoE3 TR mice. Tonic-clonic seizures developed spontaneously after 5 months of age in apoE4 TR mice and are triggered by mild stress. Female mice had increased seizure penetrance compared to male mice, but had slightly reduced overall seizure severity. The majority of seizures were characterized by head and neck jerks, but 25% of aged apoE4 TR mice had more severe tonic-clonic seizures which occasionally progressed to tonic extension and death. Aged apoE4 TR mice progressed through pentylenetetrazol-induced seizure stages more rapidly than did apoE3 TR and apoE2 TR mice. Electroencephalographic (EEG) recordings revealed more frequent bursts of synchronous theta activity in the hippocampus of apoE4 TR mice than in apoE2 TR or apoE3 TR mice. Cortical EEG recordings also revealed sharp spikes and other abnormalities in apoE4 TR mice. Taken together, these findings demonstrate the emergence of an age-dependent seizure phenotype in old apoE4 TR mice in the absence of human amyloid-β peptide (Aβ) overexpression, suggesting increased central nervous system neural network excitability.

Influence of apolipoprotein E polymorphism on serum lipid and lipoprotein changes: a 21-year follow-up study from childhood to adulthood. The Cardiovascular Risk in Young Finns Study

BACKGROUND

We examined the influence of apolipoprotein E (apoE) polymorphism on longitudinal changes in serum lipids by following the subjects participating in The Cardiovascular Risk in Young Finns Study over a 21-year period.

METHODS

Serum lipids were determined in randomly selected Finnish children and adolescents in 1980 and the subjects were re-examined in 1983, 1986 and after 21 years in 2001. ApoE polymorphism was determined in 1736 participants, and serum lipid values and apoE phenotypes were available for 1233 subjects.

RESULTS

ApoE phenotype-related differences in serum total and low-density lipoprotein (LDL)-cholesterol were maintained throughout the 21-year follow-up from childhood to adulthood, i.e., the apoE epsilon2 allele was consistently associated with lower and the epsilon4 allele with higher total and LDL-cholesterol (p<0.001 for all). In adulthood, there was also a significant apoE phenotype-related difference in high-density lipoprotein (HDL)-cholesterol (p=0.007), and the epsilon2 allele was associated with higher and the epsilon4 allele with lower apoA-I and HDL-cholesterol. In addition, apoB increased in the phenotype order E3/2<E3/3<E4 (E4/3+E4/4) (p<0.001). The LDL-lowering effect of the epsilon2 allele was greater in adulthood than in childhood, i.e., there was a significant apoE phenotypextime interaction (p=0.039) with longitudinal change in LDL-cholesterol.

CONCLUSIONS

ApoE polymorphism is associated with lipid levels at different ages and affects the longitudinal change in LDL-cholesterol from childhood to adulthood.

APOE4 Genotype Exerts Greater Benefit in Lowering Plasma Cholesterol and Apolipoprotein B than Wild Type (E3/E3), after Replacement of Dietary Saturated Fats with Low Glycaemic Index Carbohydrates

We examined the impact of APOE genotype on plasma lipids and glucose in a secondary analysis of data from a five-arm, randomised controlled, parallel dietary intervention trial ('RISCK' study), to investigate the impact of replacing saturated fatty acids (SFA) with either monounsaturated fat (MUFA) or carbohydrate of high or low glycaemic index (GI) on CVD risk factors and insulin sensitivity. We tested the impact of APOE genotype (carriage of E2 and E4 alleles versus E3/E3), determined retrospectively, on plasma lipids, lipoproteins and glucose homeostasis at baseline (n = 469), and on the change in these variables after 24 weeks of dietary intervention (n = 389). At baseline, carriers of E2 (n = 70), E4 (n = 125) and E3/E3 (n = 274) expressed marked differences in total plasma cholesterol (TC, p = 0.001), low density lipoprotein cholesterol (LDL-C, p < 0.0001), apolipoprotein B (apo B, p < 0.0001) and total to high density lipoprotein cholesterol ratio (TC:HDL-C, p = 0.002), with plasma concentrations decreasing in the order E4 > E3/E3 > E2. Following intervention, there was evidence of a significant diet x genotype interaction with significantly greater decreases in TC (p = 0.02) and apo B (p = 0.006) among carriers of E4 when SFA was replaced with low GI carbohydrate on a lower fat diet (TC -0.28 mmol/L p = 0.03; apo B -0.1 g/L p = 0.02), and a relative increase in TC (in comparison to E3/E3) when SFA was replaced with MUFA and high GI carbohydrates (TC 0.3 mmol/L, p = 0.03). Among carriers of E2 (compared with E3/E3) there was an increase in triacylglycerol (TAG) when SFA was replaced with MUFA and low GI carbohydrates 0.46 mmol/L p = 0.001). There were no significant interactions between APOE genotype and diet for changes in indices of glucose homeostasis. In conclusion, variations in APOE genotype led to differential effects on the lipid response to the replacement of SFA with MUFA and low GI carbohydrates.

Peripheral apoE isoform levels in cognitively normal APOE ε3/ε4 individuals are associated with regional gray matter volume and cerebral glucose metabolism

BACKGROUND

Carriers of the APOE ε4 allele are at increased risk of developing Alzheimer's disease (AD), and have been shown to have reduced cerebral metabolic rate of glucose (CMRgl) in the same brain areas frequently affected in AD. These individuals also exhibit reduced plasma levels of apolipoprotein E (apoE) attributed to a specific decrease in the apoE4 isoform as determined by quantification of individual apoE isoforms in APOE ε4 heterozygotes. Whether low plasma apoE levels are associated with structural and functional brain measurements and cognitive performance remains to be investigated.

METHODS

Using quantitative mass spectrometry we quantified the plasma levels of total apoE and the individual apoE3 and apoE4 isoforms in 128 cognitively normal APOE ε3/ε4 individuals included in the Arizona APOE cohort. All included individuals had undergone extensive neuropsychological testing and 25 had in addition undergone FDG-PET and MRI to determine CMRgl and regional gray matter volume (GMV).

RESULTS

Our results demonstrated higher apoE4 levels in females versus males and an age-dependent increase in the apoE3 isoform levels in females only. Importantly, a higher relative ratio of apoE4 over apoE3 was associated with GMV loss in the right posterior cingulate and with reduced CMRgl bilaterally in the anterior cingulate and in the right hippocampal area. Additional exploratory analysis revealed several negative associations between total plasma apoE, individual apoE isoform levels, GMV and CMRgl predominantly in the frontal, occipital and temporal areas. Finally, our results indicated only weak associations between apoE plasma levels and cognitive performance which further appear to be affected by sex.

CONCLUSIONS

Our study proposes a sex-dependent and age-dependent variation in plasma apoE isoform levels and concludes that peripheral apoE levels are associated with GMV, CMRgl and possibly cognitive performance in cognitively healthy individuals with a genetic predisposition to AD.

Association of apolipoprotein E epsilon2 with white matter disease but not with microbleeds

BACKGROUND AND PURPOSE

Apolipoprotein E (apoE) alleles (epsilon2 and epsilon4) are associated with cerebral amyloid angiopathy, in which white matter disease and microbleeds are prominent features. The role of apoE in patients with microbleeds or white matter disease but no evidence of cerebral amyloid angiopathy has not been elucidated. We studied apoE alleles in relation to white matter disease and microbleeds in patients with transient ischemic attack or ischemic stroke.

METHODS

We obtained brain MRI scans and apoE genotypes in 334 transient ischemic attack or ischemic stroke patients. Microbleeds were scored on a gradient echo MRI and white matter disease was examined on fluid attenuated inversion recovery MRI using a semiquantitative rating scale.

RESULTS

Patients with moderate to severe white matter disease more frequently carried apoE epsilon2 alleles (25.2% versus 11.3%, P=0.001), but not apoE epsilon4 (26.6% in apoE epsilon4 carriers versus 25.9%; P=0.98). Adjustment for traditional risk factors did not modify this relationship (odds ratio, 2.9; 95% confidence interval, 1.5 to 5.3). There was no association between the presence of microbleeds and the apoE epsilon4 or apoE epsilon2 alleles.

CONCLUSIONS

ApoE alleles do not exert a major influence on the development of microbleeds, but apoE epsilon2 may be associated with development of moderate to severe white matter disease in transient ischemic attack and stroke patients.

Low plasma ApoE levels are associated with smaller hippocampal size in the Alzheimer's disease neuroimaging initiative cohort

Apolipoprotein E (APOE) genotype is the strongest known genetic risk factor for sporadic Alzheimer's disease (AD), but the utility of plasma ApoE levels for assessing the severity of underlying neurodegenerative changes remains uncertain. Here, we examined cross-sectional associations between plasma ApoE levels and volumetric magnetic resonance imaging indices of the hippocampus from 541 participants [57 with normal cognition (NC), 375 with mild cognitive impairment (MCI), and 109 with mild AD] who were enrolled in the Alzheimer's Disease Neuroimaging Initiative. Across the NC and MCI groups, lower plasma ApoE levels were significantly correlated with smaller hippocampal size, as measured by either hippocampal volume or hippocampal radial distance. These associations were driven primarily by findings from carriers of an APOE ε4 allele and are consistent with prior reports that lower plasma ApoE levels correlate with greater global cortical Pittsburgh Compound B retention. In this high-risk group, plasma ApoE levels may represent a peripheral marker of underlying AD neuropathology in nondemented elderly individuals.

Relation of plasma homocysteine to plasma amyloid beta levels

BACKGROUND

Elevated plasma homocysteine and amyloid beta (Abeta) have been associated with Alzheimer's disease (AD). We investigated the cross-sectional association between these biomarkers.

METHODS

We used linear regression to relate plasma homocysteine and Abeta adjusting for age, gender, creatinine, APOE-epsilon4, and ethnic group in 327 persons aged 78 +/- 6.6 years.

RESULTS

Plasma homocysteine correlated with age, serum creatinine, plasma Abeta40 and Abeta42, and was inversely correlated with serum vitamin B12, and folate. Abeta42, but not Abeta40, was related to later development of dementia. Homocysteine was related to higher Abeta40 levels (coefficient = 2.0; P < 0.0001) and this association was attenuated after adjustment for creatinine (coefficient = 1.0; P < 0.0001). The crude association between homocysteine and Abeta42 was weaker (coefficient = 0.5; P = 0.01) and became non-significant after adjustment for creatinine (coefficient = 0.4; P = 0.06). These associations were unrelated to ethnicity, the presence of APOE-epsilon4 or dementia. Analyses by quartiles of homocysteine showed that these association were driven primarily by the fourth quartile.

CONCLUSIONS

Plasma homocysteine is directly related to Abeta40. The association with Abeta42 is not significant. These results seem to indicate that homocysteine is related to aging but not specifically to AD.

Homocysteine and cognitive function in very elderly nondemented subjects

OBJECTIVES

To examine the association of homocysteine with cognitive functioning in very elderly community-dwelling individuals (80 years or older).

METHODS

Two hundred twenty-eight nondemented community-dwelling individuals were assessed with a broad neuropsychological battery. Bloods were drawn to measure homocysteine, serum vitamin B12, and folate levels and APOE genotype.

RESULTS

Higher homocysteine levels were associated with poorer executive-language functioning scores (r = -0.311). The association persisted when serum B12 and folate levels were controlled for (r = -0.308). Homocysteine levels were not associated with memory score (r = 0.120).

CONCLUSIONS

In very elderly, nondemented community dwellers, high homocysteine levels are associated with poorer executive-language functioning but not with memory. This possible differential effect of homocysteine on cognitive functions suggests that it may affect only specific brain regions or mechanisms underlying healthy executive functioning.