Apolipoprotein E genotypes and plasma levels in mild cognitive impairment conversion to Alzheimer's disease: A follow-up study

Monoclonal antibodies and aptamers: The future therapeutics for Alzheimer's disease

Alzheimer's disease (AD) is considered the most common and prevalent form of dementia of adult-onset with characteristic progressive impairment in cognition and memory. The cure for AD has not been found yet and the treatments available until recently were only symptomatic. Regardless of multidisciplinary approaches and efforts made by pharmaceutical companies, it was only in the past two years that new drugs were approved for the treatment of the disease. Amyloid beta (Aβ) immunotherapy is at the core of this therapy, which is one of the most innovative approaches looking to change the course of AD. This technology is based on synthetic peptides or monoclonal antibodies (mAb) to reduce Aβ levels in the brain and slow down the advance of neurodegeneration. Hence, this article reviews the state of the art about AD neuropathogenesis, the traditional pharmacologic treatment, as well as the modern active and passive immunization describing approved drugs, and drug prototypes currently under investigation in different clinical trials. In addition, future perspectives on immunotherapeutic strategies for AD and the rise of the aptamer technology as a non-immunogenic alternative to curb the disease progression are discussed.

Influence of gut microbiota on the development of most prevalent neurodegenerative dementias and the potential effect of probiotics in elderly: A scoping review

Dementia is one of today's greatest public health challenges. Its high socio-economic impact and difficulties in diagnosis and treatment are of increasing concern to an aging world population. In recent years, the study of the relationship between gut microbiota and different neurocognitive disorders has gained a considerable interest. Several studies have reported associations between gut microbiota dysbiosis and some types of dementia. Probiotics have been suggested to restore dysbiosis and to improve neurocognitive symptomatology in these dementias. Based on these previous findings, the available scientific evidence on the gut microbiota in humans affected by the most prevalent dementias, as well as the probiotic trials conducted in these patients in recent years, have been here reviewed. Decreased concentrations of short-chain fatty acids (SCFA) and other bacterial metabolites appear to play a major role in the onset of neurocognitive symptoms in Alzheimer disease (AD) and Parkinson disease dementia (PDD). Increased abundance of proinflammatory taxa could be closely related to the more severe clinical symptoms in both, as well as in Lewy Bodies dementia. Important lack of information was noted in Frontotemporal dementia behavioral variant. Moreover, geographical differences in the composition of the gut microbiota have been reported in AD. Some potential beneficial effects of probiotics in AD and PDD have been reported. However, due to the controversial results further investigations are clearly necessary.

Role of estrogen in women's Alzheimer's disease risk as modified by APOE

Alzheimer's disease (AD) is characterized by numerous sexual dimorphisms that impact the development, progression, and probably the strategies to prevent and treat the most common form of dementia. In this review, we consider this topic from a female perspective with a specific focus on how women's vulnerability to the disease is affected by the individual and interactive effects of estrogens and apolipoprotein E (APOE) genotype. Importantly, APOE appears to modulate systemic and neural outcomes of both menopause and estrogen-based hormone therapy. In the brain, dementia risk is greater in APOE4 carriers, and the impacts of hormone therapy on cognitive decline and dementia risk vary according to both outcome measure and APOE genotype. Beyond the CNS, estrogen and APOE genotype affect vulnerability to menopause-associated bone loss, dyslipidemia and cardiovascular disease risk. An emerging concept that may link these relationships is the possibility that the effects of APOE in women interact with estrogen status by mechanisms that may include modulation of estrogen responsiveness. This review highlights the need to consider the key AD risk factors of advancing age in a sex-specific manner to optimize development of therapeutic approaches for AD, a view aligned with the principle of personalized medicine.

The Relationship Between Low-Density Lipoprotein Cholesterol and Progression of Mild Cognitive Impairment: The Influence of rs6859 in PVRL2

Background: Genome-wide association studies have identified many Alzheimer's disease (AD) genetic-risk single nucleotide polymorphisms (SNPs) and indicated the important role of the cholesterol/lipid metabolism pathway in AD pathogenesis. This study aims to investigate the effects of cholesterol and genetic risk factors on progression of mild cognitive impairment (MCI) to AD. Methods: We prospectively followed 316 MCI participants aged ≥50 years with a baseline cholesterol profile and SNP genotyping data for 4.5 years on average in a sub-cohort of the Shanghai Aging Study. Total cholesterol, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol in serum were measured at baseline. SNP genotyping was performed using a MassARRAY system. At follow-up, consensus diagnosis of incident dementia and AD were established based on medical, neurological, and neuropsychological examinations. Cox regression models were used to assess the association of cholesterol and SNP with incident AD. Results: The AG/AA genotypes of PVRL2 rs6859 were significantly associated with increased incident AD in MCI participants, compared with GG genotype (adjusted hazard ratio [HR] 2.75, 95% confidence interval [CI] 1.32-5.76, p = .007, false discovery rate-adjusted p = .030). In PVRL2 rs6859 AG/AA carriers, each-1 mmol/L higher level of LDL-C was significantly associated with a 48% decreased risk of AD (adjusted HR 0.52, 95%CI 0.33-0.84, p = .007). Consistent results were obtained when using LDL-C as the categorical variable (P for trend = 0.016). Conclusion: The relationship between LDL-C and progression of MCI may be influenced by genetic variants.

Effect of APOEε4 on Functional Brain Network in Patients with Subjective Cognitive Decline: A Resting State Functional MRI Study

PURPOSE

Subjective cognitive decline (SCD) is the earliest symptom stage of Alzheimer's disease (AD), and the APOEε4 allele is the strongest genetic risk factor for sporadic AD. Based on graph theory, the resting state functional connectivity (rsFC) in SCD patients with APOEε4 was studied to explore the effect of APOEε4 on the rsFC network properties of SCD patients.

PATIENTS AND METHODS

This cross-sectional study included MRI image data from 19 SCD patients with APOEε4 (SCD+), 29 SCD patients without APOEε4 (SCD-), and 30 normal control (NC-) individuals without APOEε4. We generated a binary matrix based on anatomical automatic labeling (AAL) 90 atlas to construct the functional network. We then calculated the whole brain network characteristics and intracerebral node characteristics by graph theory.

RESULTS

For the whole brain network characteristics, all three groups showed small-worldness. The SCD+ group had increased compensatory information transfer speed and enhanced integration capability. This group also had high heterogeneity for intracerebral node characteristics, mainly in the default mode network, left superior occipital gyrus, and bilateral putamen.

CONCLUSION

APOEε4 effects the functional brain network in patients with SCD and may be a potential indicator for the identification of SCD.

Apolipoprotein E4-driven effects on inflammatory and neurotrophic factors in peripheral extracellular vesicles from cognitively impaired, no dementia participants who converted to Alzheimer's disease

INTRODUCTION

In brain, extracellular vesicles (EVs) play an essential role in the neuron-glia interface and ensure the crosstalk between the brain and the periphery. Some studies now link the pathway dysfunction of the EVs to apolipoprotein E gene variant (APOE ε4) and the risk of progression to Alzheimer's disease (AD). To better understand the role of APOE ε4 in pre-clinical AD, we have determined levels of pathogenic, neurotrophic and inflammatory proteins in peripheral EVs (pEVs) and in plasma from cognitively impaired, no dementia (CIND) participants stratified upon the absence (APOE ε4-) or the presence (APOE ε4+ ) of the ε4 allele of APOE.

METHODS

Levels of 15 neurodegenerative, neurotrophic and neuroinflammatory proteins were quantified in pEVs and compared to their plasma levels from cognitively normal and CIND participants.

RESULTS

Levels of neurotrophic and inflammatory markers were reduced in pEVs from APOE ε4+. The pentraxin-2/α-synuclein ratio measured in pEVs was able to predict AD 5 years before the onset among APOE ε4+-CIND individuals.

DISCUSSION

Our findings suggest an alteration of the endosomal pathway in APOE ε4+ and that pEVs pentraxin-2/α-synuclein ratio could serve as a useful early biomarker for AD susceptibility.

Aquaporin-4 polymorphisms predict amyloid burden and clinical outcome in the Alzheimer's disease spectrum

Clearance of amyloid-β (Aβ) from the brain is hypothesized to be mediated by the glymphatic system through aquaporin-4 (AQP4) water channels. Genetic variation of AQP4 may impact water channel function, Aβ clearance, and clinical outcomes. We examined whether single-nucleotide polymorphisms (SNPs) of the AQP4 gene were related to Aβ neuropathology on [¹⁸F]Florbetapir PET in 100 Aβ positive late mild cognitive impairment (LMCI) or Alzheimer's disease (AD) patients and were predictive of clinical outcome in prodromal AD patients. AQP4 SNP rs72878794 was associated with decreased Aβ uptake, whereas rs151244 was associated with increased Aβ uptake, increased risk of conversion from MCI and LMCI to AD, and an increased 4-year rate of cognitive decline in LMCI. AQP4 genetic variation was associated with Aβ accumulation, disease stage progression, and cognitive decline. This variation may correspond to changes in glymphatic system functioning and brain Aβ clearance and could be a useful biomarker in predicting disease burden for those on the dementia spectrum.

Subjective Cognitive Decline and APOE ɛ4: A Systematic Review

Individuals with subjective cognitive decline (SCD) report self-perceived declines in cognitive function but perform within normal limits on standardized tests. However, for some, these self-perceived changes may herald eventual decline to Alzheimer's disease (AD). In light of this, the relationship between SCD and APOE ɛ4, a known genetic risk factor for AD, has garnered interest; however, no systematic review of this literature exists. The current review (n = 36 articles) examined the prevalence of APOE ɛ4 in SCD samples relative to healthy and objectively impaired samples, and summarized APOE ɛ4-related risk of conversion from SCD to AD. Univariate ANOVA indicated that APOE ɛ4 frequency was comparable between healthy control and SCD samples, yet significantly higher in objectively impaired samples (i.e., MCI, AD) relative to either of these groups. Narrative review provided mixed evidence linking coincident APOE ɛ4-positive genotype and SCD to structural neuropathology. Though there was little evidence to suggest that APOE ɛ4 predisposes individuals to developing SCD, both APOE ɛ4 and SCD were found to confer individual and multiplicative risk of conversion to objective cognitive impairment. Combined, it is likely that a relationship between APOE ɛ4, SCD, and AD exists, though its exact nature remains undetermined. A clearer understanding of these relationships is hindered by a lack of standardization in SCD classification and a dearth of longitudinal outcome research. Wide-scale adoption of genetic screening for dementia risk in persons with SCD is considered premature at this time. Ethical considerations and clinical implications of genetic testing for dementia risk are discussed.

The effect of ApoE ε4 on longitudinal brain region-specific glucose metabolism in patients with mild cognitive impairment: a FDG-PET study

While the ApoE ε4 allele is a known risk factor for mild cognitive impairment (MCI) and Alzheimer's disease, brain region specific effects remain elusive. In this study, we investigate whether the ApoE ε4 allele exhibits brain region specific effects in longitudinal glucose uptake among patients with MCI from the Alzheimer's Disease Neuroimaging Initiative (ADNI). Preprocessed FDG PET images, MRIs, and demographic information were downloaded from the ADNI database. An iterative reblurred Van Cittertiteration method was used for partial volume correction (PVC) on all PET images. Structural MRIs were used for PET spatial normalization and region of interest (ROI) definition in standard space. Longitudinal changes in ROI FDG standardized uptake value ratio (SUVR) relative to cerebellum in 24 ApoE ε4 carriers and 24 age-matched ApoE ε4 non-carriers were measured for up to 84-months (median 72 months, SD = 11.2 months) and compared using a generalized linear mixed effects model controlling for gender, education, baseline age, and follow-up period. Additionally, voxelwise analysis was performed by implementing a paired t-test comparing matched baseline and 72 month FDG SUVR images in ApoE carriers and non-carriers separately. Results with PVC were compared with ones from non-PVC based analysis. After applying PVC, the superior fontal, parietal, lateral temporal, medial temporal, caudate, thalamus, and post-cingulate, and amygdala regions had greater longitudinal decreases in FDG uptake in ApoE ε4 carriers with MCI compared to non-carriers with MCI. Similar forebrain and limbic clusters were found through voxelwise analysis. Compared to the PVC based analysis, fewer significant ApoE-associated regions and clusters were found in the non-PVC based PET analysis. Our findings suggest that the ApoE ε4 genotype is associated with a longitudinal decline in glucose uptake in 8 forebrain and limbic brain regions in the context of MCI. In conclusion, this 84-months longitudinal FDG PET study demonstrates a novel ApoE ε4-associated brain-region specific glucose metabolism pattern in patients with MCI. Partial volume correction improved FDG PET quantification.

Mild cognitive impairment: associations with sleep disturbance, apolipoprotein e4, and sleep medications

OBJECTIVE

Mild cognitive impairment (MCI) is associated with increased memory problems although the ability to complete daily life activities remains relatively intact. This study examined: (1) if sleep disturbance increased the hazard of MCI; (2) if APOE e4 carriers with sleep disturbance experience an increased risk of MCI; and, (3) if prescription sleep medications provide a protective effect against MCI. We hypothesized that sleep disturbance increases the hazard of MCI, this relationship is stronger among APOE e4 carriers reporting a sleep disturbance. Furthermore, we hypothesized that sleep medications decrease the hazard of MCI.

METHODS

To determine whether sleep medication mediates the risk of developing MCI for individuals with sleep disturbance and/or APOE e4, we analyzed the National Alzheimer's Coordinating Center Uniform Data Set. We selected participants with normal cognition at baseline (n = 6798), and conduced survival analyses.

RESULTS

Our main findings indicated that the hazard of MCI was significantly associated with sleep disturbance. The hazard remained among those who did not use sleep medication. Trazodone and zolpidem users did not have a significant hazard of MCI, but the significant hazard remained for those who did not use these medications. APOE e4 carriers had a significantly higher hazard of MCI. Among e4 carriers who used trazodone or zolpidem, there was not a statistically significant risk of MCI.

CONCLUSION

This study demonstrated the potential utilization of trazodone and zolpidem in the treatment of sleep disturbance while potentially mitigating the risk of MCI. While trazodone and zolpidem have been shown to positively impact sleep disturbance in individuals with normal cognition, further research should explore these findings given that these medications are potentially inappropriate for older adults.

Apolipoprotein E DNA methylation and posttraumatic stress disorder are associated with plasma ApoE level: A preliminary study

Mild traumatic brain injury (mTBI) occurred in 15-30% of Veterans returning from Iraq and Afghanistan. We examined whether DNA methylation of the apolipoprotein E (APOE) gene promoter region or plasma ApoE protein levels are altered in mTBI. APOE promoter region DNA methylation, APOE genotype, and plasma ApoE concentration were determined in 87 Veterans with or without mTBI who were recruited from 2010-2014. Plasma ApoE concentration was found to be associated with Posttraumatic Stress Disorder (PTSD) symptom severity ratings by hierarchical linear regression (p = .013) and ANCOVA (p = .007). Hierarchical linear regression revealed that plasma ApoE concentration was associated with APOE-ε4 genotype status (p=.022). Higher ApoE plasma levels were found in ε3/ε3 Veterans than in APOE-ε4 carriers (p = .031). Furthermore, plasma ApoE concentration was associated experiment-wise with DNA methylation at CpG sites -877 (p = .021), and -775 (p = .014). The interaction between APOE-ε4 genotype and having a PTSD diagnosis was associated with DNA methylation at CpG site -675 (p = .009).

Increased expression of TREM2 in peripheral cells from mild cognitive impairment patients who progress into Alzheimer's disease

BACKGROUND AND PURPOSE

Neuroinflammation plays a role in the aetiopathogenesis of Alzheimer's disease (AD). Triggering receptor expressed on myeloid cells 2 (TREM2), a cell surface receptor of the immunoglobulin superfamily, seems to have protective anti-inflammatory activity in AD.

METHODS

Triggering receptor expressed on myeloid cells 2 expression was analysed in peripheral blood mononuclear cells from healthy subjects (CT) and from patients with either AD or mild cognitive impairment (MCI). MCI patients were re-evaluated at a 2-year follow-up to investigate their progression to AD (MCI-AD) or lack thereof (MCI-MCI).

RESULTS

Triggering receptor expressed on myeloid cells 2 gene expression was higher in AD than CT patients, but was highest in MCI. At recruitment TREM2 levels were higher in MCI-AD than in MCI-MCI, and in MCI-AD were higher initially than at follow-up. TREM2 displayed a moderate degree of sensitivity and specificity for identifying MCI-AD in all MCI patients. Our data showed higher TREM2 levels in allele ε4 of apolipoprotein E (ApoE ε4) carriers than non-carriers in MCI and particularly in MCI-AD.

CONCLUSIONS

These data seem to confirm the protective role of TREM2 in the pre-clinical stage of AD. Upregulation of TREM2 in MCI-AD could be a mechanism to counteract the activation of neuroinflammatory processes. It is possible that TREM2 and ApoE ε4 interact synergistically in the pre-clinical stage of AD. Therefore, TREM2 may be useful as an early peripheral biomarker for the development of AD.

Apolipoprotein E4 Allele and Gait Performance in Mild Cognitive Impairment: Results From the Gait and Brain Study

Background

The apolipoprotein E polymorphism ε4 allele (ApoE4) and gait impairment are both known risk factors for developing cognitive decline and dementia. However, it is unclear the interrelationship between these factors, particularly among older adults with mild cognitive impairment (MCI) who are considered as prodromal for Alzheimer's disease. This study aimed to determine whether ApoE4 carrier individuals with MCI may experience greater impairment in gait performance.

Methods

Fifty-six older adults with MCI from the "Gait and Brain Study" who were identified as either ApoE4 carriers (n = 20) or non-ApoE4 carriers (n = 36) with 1 year of follow-up were included. Gait variability, the main outcome variable, was assessed as stride time variability with an electronic walkway. Additional gait variables and cognitive performance (mini-mental state examination [MMSE] and Montreal Cognitive Assessment [MoCA]) were also recorded. Covariates included age, sex, education level, body mass index, and number of comorbidities.

Results

Baseline characteristics were similar for both groups. Repeated measures analysis of covariance showed that gait stride time and stride length variabilities significantly increased in ApoE4 carriers but was maintained in the non-ApoE4 carriers. Similarly, ApoE4 carriers showed greater decrease in MMSE score at follow-up.

Conclusions

In this sample of older adults with MCI, the presence of at least one copy of ApoE4 was associated with the development of both increased gait variability and cognitive decline during 1 year of follow-up. ApoE4 genotype might be considered as a potential mediator of decline in mobility function in MCI; future studies with larger samples are needed to confirm our preliminary findings.

APOE ε4 specific imbalance of arachidonic acid and docosahexaenoic acid in serum phospholipids identifies individuals with preclinical Mild Cognitive Impairment/Alzheimer's Disease

This study was designed to explore the influence of apolipoprotein E (APOE) on blood phospholipids (PL) in predicting preclinical Alzheimer's disease (AD). Lipidomic analyses were also performed on blood from an AD mouse model expressing human APOE isoforms (EFAD) and five AD mutations and from 195 cognitively normal participants, 23 of who converted to mild cognitive impairment (MCI)/AD within 3 years. APOE ε4-carriers converting to MCI/AD had high arachidonic acid (AA)/docosahexaenoic acid (DHA) ratios in PL compared to cognitively normal ε4 and non-ε4 carriers. Arachidonic acid and DHA containing PL species, ε4-status and Aβ42/Aβ40 ratios provided 91% accuracy in detecting MCI/AD. Fish oil/omega-3 fatty acid consumption was associated with lower AA/DHA ratios even among ε4 carriers. High plasma AA/DHA ratios were observed in E4FAD compared to EFAD mice with other isoforms. In particular, alterations in plasma AA and DHA containing PL species were also observed in the brains of E4FAD mice compared to E3FAD mice. Despite the small sample size and a short follow-up, these results suggest that blood PL could potentially serve as biomarkers of preclinical MCI/AD.

Leukocyte telomere length in mild cognitive impairment and Alzheimer's disease patients

Numerous studies have reported an association between shortened leukocyte telomere length (LTL) and increased risk of Alzheimer's disease (AD). In this study we investigated the relationship between LTL and AD development, including in the analysis patients with amnestic mild cognitive impairment (aMCI), a clinical entity considered prodromal of AD. LTL (T/S ratio) was measured in patients with AD (n=61) or aMCI (n=46), and compared with LTL of age-matched controls (n=56). Significant LTL differences were observed between controls, aMCI and AD patients (p<0.0001), with mean LTL values (±s.d) in the order: AD patients (0.70±0.15)<aMCI patients (0.80±0.14)<controls (0.88±0.15). A positive relationship (linear regression p=0.004) was observed between LTL and cognitive performance (measured by Mini Mental State Examination score). LTL did not differ by APOE genotype. The shortened LTL observed in AD patients appears to stem from progressive telomere erosion possibly correlated with the cognitive decline characterizing conversion from aMCI to AD. LTL reduction, indicating active cell proliferation, may reflect immune system involvement in AD pathogenesis.

CSF ApoE predicts clinical progression in nondemented APOEε4 carriers

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