Role of APOE and Age at Enrollment in the Alzheimer's Disease Anti-Inflammatory Prevention Trial (ADAPT)

Clinical Application of APOE in Alzheimer's Prevention: A Precision Medicine Approach

Population-attributable risk models estimate that up to one-third of Alzheimer's disease (AD) cases may be preventable through risk factor modification. The field of AD prevention has largely focused on addressing these factors through universal risk reduction strategies for the general population. However, targeting these strategies in a clinical precision medicine fashion, including the use of genetic risk factors, allows for potentially greater impact on AD risk reduction. Apolipoprotein E (APOE), and specifically the APOE ε4 variant, is one of the most well-established genetic influencers on late-onset AD risk. In this review, we evaluate the impact of APOE ε4 carrier status on AD prevention interventions, including lifestyle, nutrigenomic, pharmacogenomic, AD comorbidities, and other biological and behavioral considerations. Using a clinical precision medicine strategy that incorporates APOE ε4 carrier status may provide a highly targeted and distinct approach to AD prevention with greater potential for success.

Effect of the Apolipoprotein E Genotype on Cognitive Change During a Multidomain Lifestyle Intervention: A Subgroup Analysis of a Randomized Clinical Trial

Importance

The role of the apolipoprotein E (APOE) ε4 allele as an effect modifier in lifestyle interventions to prevent cognitive impairment is still unclear.

Objective

To examine whether the APOE ε4 allele modifies the previously reported significant cognitive benefits of a multidomain lifestyle intervention (prespecified subgroup analysis).

Design, Setting, and Participants

The Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) was a randomized clinical trial in 6 centers across Finland (screening and randomization performed from September 7, 2009, through November 24, 2011; intervention duration, 2 years). Data analysis was performed from August 1, 2015, to March 31, 2016. The study population was at-risk older individuals from the general population. Inclusion criteria were age of 60 to 77 years; Cardiovascular Risk Factors, Aging, and Dementia risk score of at least 6 points; and cognition at a mean level or slightly lower than expected for age. Individuals with dementia or substantial cognitive impairment and conditions that prevented cooperation or safe engagement in the intervention were excluded. APOE genotype data were available for 1175 of the 1260 participants.

Interventions

Participants were randomly assigned in a 1:1 ratio to a multidomain intervention group (diet, exercise, cognitive training, and vascular risk management) or a control group (general health advice). Group allocation was not actively disclosed to participants, and outcome assessors were masked to group allocation.

Main Outcomes and Measures

Primary outcome was change in cognition measured through a comprehensive neuropsychological test battery. Analysis was based on modified intention to treat (participants with at least 1 postbaseline assessment).

Results

A total of 1109 participants (mean [SD] age, 69.3 [4.7] years; 514 [46.3%] female) were included in the analysis: 362 APOE ε4 allele carriers (173 intervention and 189 control) and 747 noncarriers (380 intervention and 367 control). The APOE ε4 carriers and noncarriers were not significantly different at baseline (except for serum cholesterol level). The difference between the intervention and control groups in annual neuropsychological test battery total score change was 0.037 (95% CI, 0.001 to 0.073) among carriers and 0.014 (95% CI, -0.011 to 0.039) among noncarriers. Intervention effect was not significantly different between carriers and noncarriers (0.023; 95% CI, -0.021 to 0.067).

Conclusions and Relevance

Healthy lifestyle changes may be beneficial for cognition in older at-risk individuals even in the presence of APOE-related genetic susceptibility to dementia. Whether such benefits are more pronounced in APOE ε4 carriers compared with noncarriers should be further investigated. The findings also emphasize the importance of early prevention strategies that target multiple modifiable risk factors simultaneously.

Trial Registration

ClinicalTrials.gov Identifier: NCT01041989.

Application of Chitosan, Chitooligosaccharide, and Their Derivatives in the Treatment of Alzheimer's Disease

Classic hypotheses of Alzheimer's disease (AD) include cholinergic neuron death, acetylcholine (ACh) deficiency, metal ion dynamic equilibrium disorder, and deposition of amyloid and tau. Increased evidence suggests neuroinflammation and oxidative stress may cause AD. However, none of these factors induces AD independently, but they are all associated with the formation of Aβ and tau proteins. Current clinical treatments based on ACh deficiency can only temporarily relieve symptoms, accompanied with many side-effects. Hence, searching for natural neuroprotective agents, which can significantly improve the major symptoms and reverse disease progress, have received great attention. Currently, several bioactive marine products have shown neuroprotective activities, immunomodulatory and anti-inflammatory effects with low toxicity and mild side effects in laboratory studies. Recently, chitosan (CTS), chitooligosaccharide (COS) and their derivatives from exoskeletons of crustaceans and cell walls of fungi have shown neuroprotective and antioxidative effects, matrix metalloproteinase inhibition, anti-HIV and anti-inflammatory properties. With regards to the hypotheses of AD, the neuroprotective effect of CTS, COS, and their derivatives on AD-like changes in several models have been reported. CTS and COS exert beneficial effects on cognitive impairments via inhibiting oxidative stress and neuroinflammation. They are also a new type of non-toxic β-secretase and AChE inhibitor. As neuroprotective agents, they could reduce the cell membrane damage caused by copper ions and decrease the content of reactive oxygen species. This review will focus on their anti-neuroinflammation, antioxidants and their inhibition of β-amyloid, acetylcholinesterase and copper ions adsorption. Finally, the limitations and future work will be discussed.

Arabidopsis thaliana extracts optimized for polyphenols production as potential therapeutics for the APOE-modulated neuroinflammation characteristic of Alzheimer's disease in vitro

Although the cause of Alzheimer's disease (AD) is unknown, glial-induced neuroinflammation is an early symptom. Familial AD is caused by increases in amyloid-beta (Aβ) peptide, particularly soluble oligomeric (oAβ), considered a proximal neurotoxin and neuroinflammatory stimuli. APOE4, a naturally occurring genotype of APOE, is the greatest genetic risk factor for AD; increasing risk up to 12-fold compared to APOE3 and APOE2. oAβ-induced neuroinflammation is greater with APOE4 compared to APOE3 and APOE2. As sinapates and flavonoids have anti-inflammatory properties, a protocol was developed for optimizing polyphenol production in seedlings of Arabidopsis thaliana (A. thaliana). Three mutants (cop1, prn1, xpf3) were identified, and the extracts treated with liver microsomes to mimic physiological metabolism, with HPLC and MS performed on the resulting metabolites for peak identification. These extracts were used to treat primary glial cells isolated from human APOE-targeted-replacement (APOE-TR) and APOE-knock-out (KO) mice, with neuroinflammation induced by lipopolysaccharide (LPS) or oAβ. The dose-response data for TNFα secretion demonstrate the followed the order: APOE-KO > APOE4 > APOE3 > APOE2, with xpf3 the most effective anti-neuroinflammatory across APOE genotypes. Thus, the plant-based approach described herein may be particularly valuable in treating the APOE4-induced neuroinflammatory component of AD risk.

APOE-modulated Aβ-induced neuroinflammation in Alzheimer's disease: current landscape, novel data, and future perspective

Chronic glial activation and neuroinflammation induced by the amyloid-β peptide (Aβ) contribute to Alzheimer's disease (AD) pathology. APOE4 is the greatest AD-genetic risk factor; increasing risk up to 12-fold compared to APOE3, with APOE4-specific neuroinflammation an important component of this risk. This editorial review discusses the role of APOE in inflammation and AD, via a literature review, presentation of novel data on Aβ-induced neuroinflammation, and discussion of future research directions. The complexity of chronic neuroinflammation, including multiple detrimental and beneficial effects occurring in a temporal and cell-specific manner, has resulted in conflicting functional data for virtually every inflammatory mediator. Defining a neuroinflammatory phenotype (NIP) is one way to address this issue, focusing on profiling the changes in inflammatory mediator expression during disease progression. Although many studies have shown that APOE4 induces a detrimental NIP in peripheral inflammation and Aβ-independent neuroinflammation, data for APOE-modulated Aβ-induced neuroinflammation are surprisingly limited. We present data supporting the hypothesis that impaired apoE4 function modulates Aβ-induced effects on inflammatory receptor signaling, including amplification of detrimental (toll-like receptor 4-p38α) and suppression of beneficial (IL-4R-nuclear receptor) pathways. To ultimately develop APOE genotype-specific therapeutics, it is critical that future studies define the dynamic NIP profile and pathways that underlie APOE-modulated chronic neuroinflammation. In this editorial review, we present data supporting the hypothesis that impaired apoE4 function modulates Aβ-induced effects on inflammatory receptor signaling, including amplification of detrimental (TLR4-p38α) and suppression of beneficial (IL-4R-nuclear receptor) pathways, resulting in an adverse NIP that causes neuronal dysfunction. NIP, Neuroinflammatory phenotype; P.I., pro-inflammatory; A.I., anti-inflammatory.

Differential effects of duration and age on the consequences of neuroinflammation in the hippocampus

The current study investigated the hypothesis that the duration of the proinflammatory environment plays a critical role in the brain's response that results in negative consequences on cognition, biochemistry, and pathology. Lipopolysaccharide or artificial cerebrospinal fluid was slowly (250 ηg/h) infused into the fourth ventricle of young (3-month-old), adult (9-month-old), or aged (23-month-old) male F-344 rats for 21 or 56 days. The rats were then tested in the water pool task and endogenous hippocampal levels of pro- and anti-inflammatory proteins and genes and indicators of glutamatergic function were determined. The duration of the lipopolysaccharide infusion, compared with the age of the rat, had the greatest effect on (1) spatial working memory; (2) the density and distribution of activated microglia within the hippocampus; and (3) the cytokine protein and gene expression profiles within the hippocampus. The duration- and age-dependent consequences of neuroinflammation might explain why human adults respond positively to anti-inflammatory therapies and aged humans do not.