Parental history of Alzheimer disease associated with lower plasma apolipoprotein E levels

Association Between Cardiovascular Risk Factors and Stress Hormones With Cognitive Performance in Mexican Adolescents

Objective

The objective of this study was to determine whether cardiovascular disease (CVD) risk factors and stress hormones are associated with cognitive performance in Mexican adolescents.

Methods

This was a cross-sectional study including 139 Mexican adolescents 10-14 years old. Participants were divided into three categories: 0, 1-2, and ≥3 CVD risk factors. These factors included: high-density lipoprotein-cholesterol (HDL-C) <40 mg/dl; waist circumference (WC) ≥90th percentile for age and sex, systolic or diastolic blood pressure ≥90th percentile for age, sex, and height; and triacylglycerols (TGs) ≥110 mg/dl. Low-density lipoprotein-cholesterol (LDL-C), very low-density lipoprotein-cholesterol (VLDL-C), total cholesterol, cortisol, and plasma catecholamines were measured as well. Furthermore, attention, memory, and executive functions were evaluated using a validated test for Spanish-speaking individuals (Neuropsi).

Results

Adolescents in the three risk categories did not show significant differences in Neuropsi test performance tasks; however, they presented different lipid and plasma norepinephrine concentrations. TG and VLDL-C were inversely associated with memory (r = -0.19, **p < .01). Multivariate regression analysis showed consistently that TG/HDL-C ratio was inversely related to attention-memory general score (standardized β = -0.99, t = -2.30, p = .023), memory (standardized β = -0.83, t = -2.08, p = .039), and attention-executive functions (standardized β = -1.02, t = -2.42, p = .017). Plasma epinephrine levels presented an inverse and weak relation to the attention-executive functions score (standardized β = -0.18, t = -2.19, p = .030).

Conclusions

Cognitive performance is not completely dependent on the accumulation of risk factors, but instead on the combination of strong predictors of CVD like waist to height ratio, TG/HDL-C, and VLDL-C. Plasma norepinephrine and epinephrine have a stronger association with cognition and CVD risk than dopamine and cortisol.

Update on the laboratory investigation of dyslipidemias

The role of the clinical laboratory is evolving to provide more information to clinicians to assess cardiovascular disease (CVD) risk and target therapy more effectively. Current routine methods to measure LDL-cholesterol (LDL-C), the Friedewald calculation, ultracentrifugation, electrophoresis and homogeneous direct methods have established limitations. Studies suggest that LDL and HDL size or particle concentration are alternative methods to predict future CVD risk. At this time there is no consensus role for lipoprotein particle or subclasses in CVD risk assessment. LDL and HDL particle concentration are measured by several methods, namely gradient gel electrophoresis, ultracentrifugation-vertical auto profile, nuclear magnetic resonance and ion mobility. It has been suggested that HDL functional assays may be better predictors of CVD risk. To assess the issue of lipoprotein subclasses/particles and HDL function as potential CVD risk markers robust, simple, validated analytical methods are required. In patients with small dense LDL particles, even a perfect measure of LDL-C will not reflect LDL particle concentration. Non-HDL-C is an alternative measurement and includes VLDL and CM remnant cholesterol and LDL-C. However, apolipoprotein B measurement may more accurately reflect LDL particle numbers. Non-fasting lipid measurements have many practical advantages. Defining thresholds for treatment with new measurements of CVD risk remain a challenge. In families with genetic variants, ApoCIII and lipoprotein (a) may be additional risk factors. Recognition of familial causes of dyslipidemias and diagnosis in childhood will result in early treatment. This review discusses the limitations in current laboratory technologies to predict CVD risk and reviews the evidence for emergent approaches using newer biomarkers in clinical practice.

The benefit of docosahexaenoic acid for the adult brain in aging and dementia

A brief overview of the evidence for omega-3 fatty acids and, in particular, of docosahexaenoic acid (DHA), involvement in cognition and in dementia is given. Two studies are presented in this regard in which the key intervention is a DHA supplement. The fist, the MIDAS Study demonstrated that DHA can be of benefit for episodic memory in healthy adults with a mild memory complaint. The second, the ADCS AD trial found no benefit of DHA in the primary outcomes but found an intriguing benefit for cognitive score in ApoE4 negative allele patients. This leads to a consideration of the mechanisms of action and role of ApoE and its modulation by DHA. Given the fundamental role of ApoE in cellular lipid transport and metabolism in the brain and periphery, it is no surprise that ApoE affects n-3 PUFA brain function as well. It remains to be seen to what extent ApoE4 deleterious effect in AD is associated with n-3 PUFA-related cellular mechanisms in the brain and, more specifically, whether ApoE4 directly impairs the transport of DHA into the brain, as has been suggested.

Meta-analysis of peripheral blood apolipoprotein E levels in Alzheimer's disease

Background

Peripheral blood Apolipoprotein E (ApoE) levels have been proposed as biomarkers of Alzheimer’s disease (AD), but previous studies on levels of ApoE in blood remain inconsistent. This meta-analysis was designed to re-examine the potential role of peripheral ApoE in AD diagnosis and its potential value as a candidate biomarker.

Methods

We conducted a systematic literature search of MEDLINE, EMBASE, the Cochrane library, and BIOSIS previews for case-control studies measuring ApoE levels in serum or plasma from AD subjects and healthy controls. The pooled weighted mean difference (WMD) and 95% confidence interval (CI) were used to estimate the association between ApoE levels and AD risk.

Results

Eight studies with a total of 2250 controls and 1498 AD cases were identified and analyzed. The pooled WMD from a random-effect model of AD participants compared with the healthy controls was −5.59 mg/l (95% CI: [−8.12, −3.06]). The overall pattern in WMD was not varied by characteristics of study, including age, country, assay method, publication year, and sample type.

Conclusions

Our meta-analysis supports a lowered level of blood ApoE in AD patients, and indicates its potential value as an important risk factor for AD. Further investigation employing standardized assay for ApoE measurement are still warranted to uncover the precise role of ApoE in the pathophysiology of AD.

Insulin-like growth factor-1 and risk of late-onset Alzheimer's disease: findings from a family study

Insulin-like growth factor-1 (IGF-1), part of an evolutionary conserved signaling pathway in both mammalian and non-mammalian species, is inferred in neurodegenerative disorders including Alzheimer's disease (AD). A murine model for AD shows that reduced IGF-1 signaling prevents AD-like characteristics. However, variation in serum levels of IGF-1 and risk of AD in humans has yet to be determined. We used a proven family design, comparing middle-aged offspring with and without a parental history of AD. The offspring under study carry an increased risk of AD but do not yet experience cognitive impairment. A total of 206 offspring from 92 families with a parental history of AD were compared with 200 offspring from 97 families without a parental history of AD. Apolipoprotein-E (APOE) genotypes and serum IGF-1 levels were compared in subjects with and without a parental history of AD using linear regression, adjusted for APOE genotype and other possible demographic and clinical confounders. Offspring with a parental history of AD were more likely to be an APOE ε4 allele carrier (46.5% vs. 21%, p = 0.001) than were offspring without such a parental history. Offspring with a parental history of AD had higher IGF-1 levels than subjects without such a history, in both unadjusted and adjusted analyses (18.3 mmol/L vs. 16.7 mmol/L, p = 0.001). In conclusion, higher serum IGF-1 levels in middle age are associated with risk of AD disease in older age, independent of APOE genotype.

Plasma signaling proteins in persons at genetic risk for Alzheimer disease: influence of APOE genotype

OBJECTIVE

To study the effect of familial Alzheimer disease (FAD) mutations and APOE genotype on plasma signaling protein levels.

DESIGN

Cross-sectional comparison of plasma levels of 77 proteins measured using multiplex immune assays.

SETTING

A tertiary referral dementia research center.

PARTICIPANTS

Thirty-three persons from families harboring PSEN1 or APP mutations, aged 19 to 59 years.

MAIN OUTCOME MEASURES

Protein levels were compared between FAD mutation carriers (MCs) and noncarriers (NCs) and among APOE genotype groups, using multiple linear regression models.

RESULTS

Twenty-one participants were FAD MCs and 12 were NCs. Six had the APOE ε2/3, 6 had the ε3/4, and 21 had the ε3/3 genotype. Levels of 17 proteins differed among APOE genotype groups, and there were significant interactions between age and APOE genotype for 12 proteins. Plasma levels of apolipoprotein E and superoxide dismutase 1 were highest in the ε2 carriers, lowest in ε4 carriers, and intermediate in the ε3 carriers. Levels of multiple interleukins showed the opposite pattern and, among the ε4 carriers, demonstrated significant negative correlations with age. Although there were no significant differences between FAD MCs and NCs, there were interactions between mutation status and APOE genotype for 13 proteins.

CONCLUSIONS

We found different patterns of inflammatory markers in young and middle-aged persons among APOE genotype groups. The APOE ε4 carriers had the lowest levels of apolipoprotein E. Young ε4 carriers have increased inflammatory markers that diminish with age. We demonstrated altered inflammatory responses in young and middle adulthood in ε4 carriers that may relate to AD risk later in life.

Machine learning amplifies the effect of parental family history of Alzheimer's disease on list learning strategy

Identification of preclinical Alzheimer's disease (AD) is an essential first step in developing interventions to prevent or delay disease onset. In this study, we examine the hypothesis that deeper analyses of traditional cognitive tests may be useful in identifying subtle but potentially important learning and memory differences in asymptomatic populations that differ in risk for developing Alzheimer's disease. Subjects included 879 asymptomatic higher-risk persons (middle-aged children of parents with AD) and 355 asymptotic lower-risk persons (middle-aged children of parents without AD). All were administered the Rey Auditory Verbal Learning Test at baseline. Using machine learning approaches, we constructed a new measure that exploited finer differences in memory strategy than previous work focused on serial position and subjective organization. The new measure, based on stochastic gradient descent, provides a greater degree of statistical separation (p = 1.44 × 10-5) than previously observed for asymptomatic family history and non-family history groups, while controlling for apolipoprotein epsilon 4, age, gender, and education level. The results of our machine learning approach support analyzing memory strategy in detail to probe potential disease onset. Such distinct differences may be exploited in asymptomatic middle-aged persons as a potential risk factor for AD.

Gene dose of apolipoprotein E and age-related hearing loss

Next to outer hair cell dysfunction, age-related hearing loss may be explained by apolipoprotein E (APOE) genotype. In the Leiden 85-plus Study, a population-based study, the participants were 85 years old. We measured hearing loss by pure-tone audiometry in 435 participants in relation to APOE. Results demonstrated that those with the APOE-ε4/ε4 genotype had the highest levels of hearing loss (n = 6; 56.1 dB), those with the APOE-ε3/ε4 or ε2/ε4 genotype (n = 89) had intermediate levels of hearing loss (51.0 dB), and those without the APOE-ε4 allele (n = 340) had the lowest levels of hearing loss (48.9 dB), p for trend = 0.02. Eighty percent of participants had hearing loss of 35 dB and more, that is, hearing impairment. The APOE-ε4 allele was associated with a 2.0-fold increased risk of hearing impairment (confidence interval [CI 95%], 1.0-4.0), compared with those without the APOE-ε4 allele. The risk for hearing impairment in subjects with the APOE-ε4 allele remained similar after adjustment for cardiovascular disease, stroke, and cognitive impairment. Our results suggest that the APOE-ε4 allele contributes to age-related hearing loss.

Butyrylcholinesterase genotype and gender influence Alzheimer's disease phenotype

Retrospective data are presented to support a spectrum of early Alzheimer's disease (AD) along a continuum defined by gender and genotype. The putative neurodegenerative mechanisms driving distinct phenotypes at each end of the spectrum are glial hypoactivity associated with early failure of synaptic cholinergic neurotransmission and glial overactivation associated with loss of neural network connectivity due to accelerated age-related breakdown of myelin. In early AD, male butyrylcholinesterase K-variant carriers with one or two apolipoprotein ɛ4 alleles have prominent medial temporal atrophy, synaptic failure, cognitive decline, and accumulation of aggregated beta-amyloid peptide. Increasing synaptic acetylcholine in damaged but still functional cholinergic synapses improves cognitive symptoms, whereas increasing the ability of glia to support synapses and to clear beta-amyloid peptide might be disease-modifying. Conversely, chronic glial overactivation can also drive degenerative processes and in butyrylcholinesterase K-variant negative females generalized glial overactivation may be the main driver from mild cognitive impairment to AD. Females are more likely than males to have accelerated age-related myelin breakdown, more widespread white matter loss, loss of neural network connectivity, whole brain atrophy, and functional decline. Increasing extracellular acetylcholine levels blocks glial activation, reduces myelin loss and damage to neural network connectivity, and is disease-modifying. Between extremes characterized by gender, genotype, and age, pathophysiology may be mixed and this spectrum may explain much of the heterogeneity of amnestic mild cognitive impairment. Preservation of the functional integrity of the neural network may be an important component of strengthening cognitive reserve and significantly delaying the onset and progression of dementia, particularly in females. Prospective confirmation of these hypotheses is required. Implications for future research and therapeutic opportunities are discussed.

Blood-based biomarkers for Alzheimer's disease: plasma Aβ40 and Aβ42, and genetic variants

Identifying a biomarker for Alzheimer's disease that can be obtained from a blood sample has been a goal of researchers for many years. Over the past few years a number of investigators have studied several plasma biomarkers but most frequently plasma amyloid beta (Aβ)40 and Aβ42 while others have explored the use of genetic variants as biomarkers for diagnosis or risk. This review considers the cross-sectional and longitudinal data regarding plasma Aβ40 and Aβ42 as diagnostic biomarkers as well as risk biomarkers. Review of recent genome-wide association studies indicates as many as 10 genetic variants have been associated with susceptibility to Alzheimer's disease (AD). Further analysis suggests that these factors have modest effects on risk and are thus not helpful, as yet, in the diagnosis of disease. Until the function of these genes is understood, their role in risk and diagnosis will remain uncertain. Thus, there are several types of peripheral biomarkers under investigation, but more work is required before they can be deemed clinically useful.

The effect of TOMM40 poly-T length on gray matter volume and cognition in middle-aged persons with APOE ε3/ε3 genotype

OBJECTIVE

Apolipoprotein E (APOE) genotypes are associated with variable risk of developing late-onset Alzheimer's disease (LOAD), with APOE epsilon 4 (APOE ε4) having higher risk. A variable poly-T length polymorphism at rs10524523, within intron 6 of the translocase of the outer mitochondrial membrane (TOMM40) gene, has been shown to influence age of onset in LOAD, with very long (VL) poly-T length associated with earlier disease onset, and short poly-T length associated with later onset. In this study, we tested the hypothesis that brain and cognitive changes suggestive of presymptomatic LOAD may be associated with this TOMM40 polymorphism.

METHODS

Among healthy APOE ε3 homozygous adults (N = 117; mean age, 55 years), we compared those who were homozygous for VL/VL (n = 35) TOMM40 poly-T lengths (who were presumably at higher risk) with those homozygous for short (S/S; n = 38) poly-T lengths, as well as those with heterozygous (S/VL; n = 44) poly-T length polymorphisms, on measures of learning and memory and on structural brain imaging.

RESULTS

The VL/VL group showed lower performance than the S/S TOMM40 group on primacy retrieval from a verbal list learning task, a finding which is also seen in early Alzheimer's disease. A dose-dependent increase in the VL TOMM40 polymorphism (from no VL alleles, to S/VL heterozygous, to VL/VL homozygous) was associated with decreasing gray matter volume in the ventral posterior cingulate and medial ventral precuneus, a region of the brain affected early in LOAD.

CONCLUSIONS

These findings among APOE ε3/ε3 late middle-aged adults suggest that a subgroup with VL TOMM40 poly-T lengths may be experiencing incipient LOAD-related cognitive and brain changes.

Apolipoproteins: metabolic role and clinical biochemistry applications

Lipoprotein metabolism is dependent on apolipoproteins, multifunctional proteins that serve as templates for the assembly of lipoprotein particles, maintain their structure and direct their metabolism through binding to membrane receptors and regulation of enzyme activity. The three principal functions of lipoproteins are contribution to interorgan fuel (triglyceride) distribution (by means of the fuel transport pathway), to the maintenance of the extracellular cholesterol pool (by means of the overflow pathway) and reverse cholesterol transport. The most important clinical application of apolipoprotein measurements in the plasma is in the assessment of cardiovascular risk. Concentrations of apolipoprotein B and apolipoprotein AI (and their ratio) seem to be better markers of cardiovascular risk than conventional markers such as total cholesterol and LDL-cholesterol. Apolipoprotein measurements are also better standardized than the conventional tests. We suggest that measurements of apolipoprotein AI and apolipoprotein B are included as a part of the specialist lipid profile. We also suggest that lipoprotein (a) should be measured as part of the initial assessment of dyslipidaemias because of its consistent association with cardiovascular risk. Genotyping of apolipoprotein E isoforms remains useful in the investigation of mixed dyslipidaemias. Lastly, the role of postprandial metabolism is increasingly recognized in the context of atherogenesis, obesity and diabetes. This requires better markers of chylomicrons, very-low-density lipoproteins and remnant particles. Measurements of apolipoprotein B48 and remnant lipoprotein cholesterol are currently the key tests in this emerging field.

Overview of the development of personalized genomic medicine and surgery

Personalized genomic medicine and surgery (PGMS) represents a new approach to health care that customizes patients' medical treatment according to their own genetic information. This new approach is the result of increased knowledge of the human genome and ways this information can be applied by physicians in the medical and surgical management of their patients. A patient's genotype can yield important information concerning disease susceptibility and the effectiveness of medications, therefore guiding specific, targeted imaging and treatment therapies. This review summarizes major achievements of human genomic studies and applications of genomics in health care. Five years ago we developed a model for the development of PGMS in which genomic profile guides choice of therapy. In this article we discussed our progress, including an updating of the model, and a future vision of PGMS.

Proteome-based plasma markers of brain amyloid-β deposition in non-demented older individuals

Blood-based markers reflecting core pathological features of Alzheimer's disease (AD) in pre-symptomatic individuals are likely to accelerate the development of disease-modifying treatments. Our aim was to discover plasma proteins associated with brain amyloid-β (Aβ) burden in non-demented older individuals. We performed discovery-phase experiments using two dimensional gel electrophoresis (2DGE) and mass spectrometry-based proteomic analysis of plasma in combination with 11C-PiB PET imaging of the brain in samples collected 10 years prior to the PET scans. Confirmatory studies used ELISA assays in a separate set of blood samples obtained within a year of the PET scans. We observed that a panel of 18 2DGE plasma protein spots effectively discriminated between individuals with high and low brain Aβ. Mass spectrometry identified these proteins, many of which have established roles in Aβ clearance, including a strong signal from apolipoprotein-E (ApoE). In validation-phase studies, we observed a strong association between plasma ApoE concentration and Aβ burden in the medial temporal lobe. Targeted voxel-based analysis localized this association to the hippocampus and entorhinal cortex. APOE ε4 carriers also showed greater Aβ levels in several brain regions relative to ε4 non-carriers. These results suggest that both peripheral concentration of ApoE protein and APOE genotype are related to early neuropathological changes in brain regions vulnerable to AD pathology even in the non-demented elderly. Our strategy combining proteomics with in vivo brain amyloid imaging holds promise for the discovery of biologically relevant peripheral markers in those at risk for AD.

Cognitive function in elderly marathon runners: cross-sectional data from the marathon trial (APSOEM)

BACKGROUND

Cognitive impairment of the elderly contributes to morbidity, loss of quality of life, and impairment of work ability in aging western societies. Thus strategies to maintain cognitive function at an advanced age imply a great challenge to Occupational Medicine.

AIM

To study whether intensive endurance exercise training is associated with better cognitive performance and increases brain-derived neurotrophic factor (BDNF) and insulin-like growth factor (IGF).

METHODS

Active elderly marathon runners or bicyclists older than 60 years were recruited and matched with an inactive control group according to age, sex, and education years. After exclusion of various diseases according to the study protocol 56 athletes and 58 controls could be selected for follow-up studies. The influence of endurance training on cognitive function was assessed by the use of the Vienna Neuropsychological Test Battery and the CERAD test battery. Other relevant outcomes were the levels of BDNF, IGF-1, Apo e4 carrier state, and self-ratings.

RESULTS

The elderly marathon group performed better only in one specific cognitive task (the Five Point Test, p = 0.04) and almost significantly better in one additional test (the NAI Stroop Test, p = 0.08). Neither BDNF nor IGF-1 was related to the duration of daily exercise and no differences in the basal levels of these humoral growth factors in the exercise and the control cohort were found. Interestingly, we also found significantly decreased BDNF levels in subjects with Alzheimer's disease in the family in spite of the maintained normal cognitive performance (p = 0.01).

CONCLUSION

These results suggest that extensive endurance exercise training might be beneficial for maintaining cognitive function in elderly persons. Our data demonstrate that beneficial endurance training effects are not linked to the upregulation of the examined neurotrophins. Since we found reduced BDNF-levels in subjects with a positive family history of Alzheimer's disease, we speculate that BDNF-reduction might precede cognitive impairment.