Neuropsychiatric Symptoms, Endophenotypes, and Syndromes in Late-Onset Alzheimer's Disease: Focus on APOE Gene

Nasal Microbiota, Olfactory Health, Neurological Disorders and Aging—A Review

The nasal region is one of the distinct environments for the survival of various microbiota. The human microbial niche begins to inhabit the human body right from birth, and the microbiota survive as commensals or opportunistic pathogens throughout the life of humans in their bodies in various habitats. These microbial communities help to maintain a healthy microenvironment by preventing the attack of pathogens and being involved in immune regulation. Any dysbiosis of microbiota residing in the mucosal surfaces, such as the nasal passages, guts, and genital regions, causes immune modulation and severe infections. The coexistence of microorganisms in the mucosal layers of respiratory passage, resulting in infections due to their co-abundance and interactions, and the background molecular mechanisms responsible for such interactions, need to be considered for investigation. Additional clinical evaluations can explain the interactions among the nasal microbiota, nasal dysbiosis and neurodegenerative diseases (NDs). The respiratory airways usually act as a substratum place for the microbes and can act as the base for respiratory tract infections. The microbial metabolites and the microbes can cross the blood–brain barrier and may cause NDs, such as Parkinson’s disease (PD), Alzheimer’s disease (AD), and multiple sclerosis (MS). The scientific investigations on the potential role of the nasal microbiota in olfactory functions and the relationship between their dysfunction and neurological diseases are limited. Recently, the consequences of the severe acute respiratory syndrome coronavirus (SARS-CoV-2) in patients with neurological diseases are under exploration. The crosstalk between the gut and the nasal microbiota is highly influential, because their mucosal regions are the prominent microbial niche and are connected to the olfaction, immune regulation, and homeostasis of the central nervous system. Diet is one of the major factors, which strongly influences the mucosal membranes of the airways, gut, and lung. Unhealthy diet practices cause dysbiosis in gut microbiota and the mucosal barrier. The current review summarizes the interrelationship between the nasal microbiota dysbiosis, resulting olfactory dysfunctions, and the progression of NDs during aging and the involvement of coronavirus disease 2019 in provoking the NDs.

Association between clinical symptoms and apolipoprotein A1 or apolipoprotein B levels is regulated by apolipoprotein E variant rs429358 in patients with chronic schizophrenia

BACKGROUND

The apolipoprotein E (ApoE) gene polymorphisms are correlated with blood lipid levels and several neuropsychiatric symptoms. Therefore, this study aimed to examine whether the ApoE rs429358 affected the development and clinical symptoms of schizophrenia and to explore the relationship between apolipoproteins levels and clinical symptoms.

METHODS

The ApoE rs429358 was genotyped using a case-control design. The Positive and Negative Syndrome Scale (PANSS) was employed to evaluate the psychopathology of all patients.

RESULTS

A total of 637 patients with schizophrenia and 467 healthy controls were recruited. We found no significant differences in the genotype and allele distribution between the patient and control groups. A significant correlation between PANSS negative symptoms and ApoA1 levels (p = 0.048) or ApoB levels (p = 0.001) was found in patients with schizophrenia, which was also confirmed by linear regression analyses (p = 0.048 vs. p = 0.001). Interestingly, only in the T homozygote group, ApoA1 and ApoB levels were predictors of the PANSS negative symptom score (p = 0.008 vs. p = 0.012), while in the C allele carrier group, no correlation was observed.

CONCLUSIONS

This study found that the levels of ApoA1 and ApoB were negatively associated with negative symptoms of patients with schizophrenia. Furthermore, the association between ApoA1 or ApoB levels and psychopathology of schizophrenia was regulated by ApoE rs429358.

Chronic Rhinosinusitis and Alzheimer's Disease-A Possible Role for the Nasal Microbiome in Causing Neurodegeneration in the Elderly

Among millions of sufferers of chronic rhinosinusitis (CRS), the challenge is not only constantly coping with CRS-related symptoms, such as congested nose, sinus pain, and headaches, but also various complications, such as attention difficulties and possible depression. These complications suggest that neural activity in the central nervous system may be altered in those patients, leading to unexpected conditions, such as neurodegeneration in elderly patients. Recently, some studies linked the presence of CRS and cognitive impairments that could further develop into Alzheimer’s disease (AD). AD is the leading cause of dementia in the elderly and is characterised by progressive memory loss, cognitive behavioural deficits, and significant personality changes. The microbiome, especially those in the gut, has been recognised as a human organ and plays an important role in the development of various conditions, including AD. However, less attention has been paid to the microbiome in the nasal cavity. Increased nasal inflammatory responses due to CRS may be an initial event that changes local microbiome homeostasis, which may further affect neuronal integrity in the central nervous system resulting in AD. Evidence suggests a potential of β-amyloid deposition starting in olfactory neurons, which is then expanded from the nasal cavity to the central nervous system. In this paper, we reviewed currently available evidence that suggests this potential mechanism to advise the need to investigate the link between these two conditions.

Scope of β-Secretase (BACE1)-Targeted Therapy in Alzheimer's Disease: Emphasizing the Flavonoid Based Natural Scaffold for BACE1 Inhibition

Alzheimer's disease (AD) is a progressive neurodegenerative disease and the most common form of dementia in the world. Studies report the presence of extracellular amyloid plaques consisting of β-amyloid peptide and intracellular tangles consisting of hyperphosphorylated tau proteins as the histopathological indicators of AD. The process of β-amyloid peptide generation by sequential cleavage of amyloid precursor protein by β-secretase (BACE1) and γ-secretase, followed by its aggregation to form amyloid plaques, is the mechanistic basis of the amyloid hypothesis. Other popular hypotheses related to the pathogenesis of AD include the tau hypothesis and the oxidative stress hypothesis. Various targets of the amyloid cascade are now in prime focus to develop drugs for AD. Many BACE1 inhibitors, β-amyloid aggregation inhibitors, and Aβ clearance strategies using monoclonal antibodies are in various stages of clinical trials. This review provides an in-depth evaluation of the role of BACE1 in disease pathogenesis and also highlights the therapeutic approaches developed to find more potent but less toxic inhibitors for BACE1, particularly emphasizing the natural scaffold as a nontoxic lead for BACE1 inhibition. Cellular targets and signaling cascades involving BACE1 have been highlighted to understand the physiological role of BACE1. This knowledge is extremely crucial to understand the toxicity evaluations for BACE1-targeted therapy. We have particularly highlighted the scope of flavonoids as a new generation of nontoxic BACE1 inhibitory scaffolds. The structure-activity relationship of BACE1 inhibition for this group of compounds has been highlighted to provide a guideline to design more selective highly potent inhibitors. The review aims to provide a holistic overview of BACE1-targeted therapy for AD that paves the way for future drug development.

Neuropsychiatric symptoms in cognitively normal older persons, and the association with Alzheimer's and non-Alzheimer's dementia

Background

Neuropsychiatric symptoms (NPS) have been reported to be useful in predicting incident dementia among cognitively normal older persons. However, the literature has not been conclusive on the differential utilities of the various NPS in predicting the subtypes of dementia. This study compared the risks of Alzheimer’s and non-Alzheimer’s dementia associated with the various NPS, among cognitively normal older persons.

Methods

This cohort study included 12,452 participants from the Alzheimer’s Disease Centers across USA, who were ≥ 60 years and had normal cognition at baseline. Participants completed the Neuropsychiatric Inventory-Questionnaire at baseline and were followed up almost annually for incident dementia (median follow-up = 4.7 years). Symptom clusters of NPS—as identified from exploratory and confirmatory factor-analyses—were included in the Cox regression to investigate their associations with incident dementia.

Results

The various NPS showed independent yet differential associations with incident dementia. Although psychotic symptoms were rarely endorsed by the participants, they predicted much higher risk of dementia (HR 3.6, 95% CI 2.0–6.4) than affective symptoms (HR 1.5, 95% CI 1.2–1.8) or agitation symptoms (HR 1.6, 95% CI 1.3–2.1). Psychotic symptoms predicted all dementia subtypes, while affective and agitation symptoms differentially predicted some subtypes. Across dementia subtypes, psychotic symptoms had relatively higher risk estimates than affective or agitation symptoms, with the risk estimates being particularly high in non-Alzheimer’s dementia.

Conclusions

Among cognitively normal individuals, the presence of NPS may warrant greater clinical vigilance as precursors to dementia and its subtypes. The findings highlight the need for further research to enrich our understanding on the neurobiological links between various NPS and dementia subtypes. They may also change the clinical approach in managing late-life psychotic symptoms, requiring a greater emphasis on dementia surveillance in the diagnostic criteria of late-life psychotic disorders.

Influence of APOE and RNF219 on Behavioral and Cognitive Features of Female Patients Affected by Mild Cognitive Impairment or Alzheimer's Disease

The risk for Alzheimer’s disease (AD) is associated with the presence of the 𝜀4 allele of Apolipoprotein E (APOE) gene and, recently, with a novel genetic variant of the RNF219 gene. This study aimed at evaluating interactions between APOE-𝜀4 and RNF219/G variants in the modulation of behavioral and cognitive features of two cohorts of patients suffering from mild cognitive impairment (MCI) or AD. We enrolled a total of 173 female MCI or AD patients (83 MCI; 90 AD). Subjects were screened with a comprehensive set of neuropsychological evaluations and genotyped for the APOE and RNF219 polymorphic variants. Analysis of covariance was performed to assess the main and interaction effects of APOE and RNF219 genotypes on the cognitive and behavioral scores. The analysis revealed that the simultaneous presence of APOE-𝜀4 and RNF219/G variants results in significant effects on specific neuropsychiatric scores in MCI and AD patients. In MCI patients, RNF219 and APOE variants worked together to impact the levels of anxiety negatively. Similarly, in AD patients, the RNF219 variants were found to be associated with increased anxiety levels. Our data indicate a novel synergistic activity APOE and RNF219 in the modulation of behavioral traits of female MCI and AD patients.

Olfactory Dysfunction as a Global Biomarker for Sniffing out Alzheimer's Disease: A Meta-Analysis

Cases of Alzheimer’s disease (AD) are rising exponentially due to increasing global life expectancy. There are approximately 50 million sufferers worldwide, with prevalence rising most rapidly in low-income countries such as Africa and Asia. There is currently no definite diagnosis of AD until after death, thus an early biomarker for AD is urgently required in order to administer timelier and more effective interventions. Olfactory dysfunction (problems with the sense of smell) is one of the earliest, preclinical symptoms observed in AD. Olfaction is a promising early biomarker for use worldwide as it is easy, cheap to measure, and not reliant on specialist clinicians or laboratory analysis. We carried out a meta-analysis to determine the credibility of olfaction in diagnosing AD in the preclinical stages, by comparing olfaction in healthy controls against AD patients and patients with mild cognitive impairment (MCI). Data from 10 articles were subjected to two comparative meta-analyses. In the case of AD, the results illustrated that the overall magnitude of effect size was more apparent, d = −1.63, 95% CI [−1.95, −1.31], in comparison to that of MCI, d = −0.81, 95% CI [−1.08, −0.55]. This shows that olfaction worsens progressively as patients progress from MCI to AD, highlighting the potential for olfactory dysfunction to identify AD in the preclinical stages prior to MCI.

A depressive endophenotype of poorer cognition among cognitively healthy community-dwelling adults: results from the Western Australia memory study

OBJECTIVE

The objective was to evaluate in a cognitively normal population the utility of an endophenotype of the depression-cognition link previously shown to be related to cognitive functioning in mild cognitive impairment and Alzheimer's disease.

METHODS

The data of 460 cognitively normal adults aged 32-92 years (M = 63.5, standard deviation = 9.24) from the Western Australian Memory Study with the Cross-national comparisons of the Cambridge Cognitive Examination-revised (CAMCOG-R) scores and 30-item Geriatric Depression Scale (GDS) scores were analyzed to determine the relationship between the five-item depressive endophenotype (DepE) scale drawn from the GDS and level of performance on a measure of cognitive functioning.

RESULTS

For the entire sample, there was a nonsignificant trend toward a negative relationship between DepE and CAMCOG-R scores. When analyzed for those 65 years and older, there was a significant negative relationship between the two measures (p = 0.001) with DepE scores significantly increasing the risk for performing more poorly on the CAMCOG-R (odds ratio = 1.53). Analysis of data for those 70 years and older showed that DepE was the only predictor significantly related to poorer CAMCOG-R performance (p = 0.001). For the 70 years and older group, DepE scores significantly increased the risk of poorer CAMCOG-R scores (odds ratio = 2.23). Analysis of the entire sample on the basis of ApoEε4 carrier status revealed that DepE scores were significantly negatively related only to ApoEε4 noncarrier regardless of age.

CONCLUSIONS

Elevated DepE scores are associated with poor neuropsychological performance among cognitively normal older adults. Use of the DepE may allow for the identification of a subset of older adults where depression is a primary factor in cognitive decline and who may benefit from antidepressant therapies.

A depressive endophenotype of mild cognitive impairment and Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a devastating public health problem that affects over 5.4 million Americans. Depression increases the risk of Mild Cognitive Impairment (MCI) and AD. By understanding the influence of depression on cognition, the potential exists to identify subgroups of depressed elders at greater risk for cognitive decline and AD. The current study sought to: 1) clinically identify a sub group of geriatric patients who suffer from depression related cognitive impairment; 2) cross validate this depressive endophenotype of MCI/AD in an independent cohort.

METHODS AND FINDINGS

Data was analyzed from 519 participants of Project FRONTIER. Depression was assessed with the GDS30 and cognition was assessed using the EXIT 25 and RBANS. Five GDS items were used to create the Depressive endophenotype of MCI and AD (DepE). DepE was significantly negatively related to RBANS index scores of Immediate Memory (B=-2.22, SE=.37, p<0.001), visuospatial skills (B=-1.11, SE=0.26, p<0.001), Language (B=-1.03, SE=0.21, p<0.001), Attention (B=-2.56, SE=0.49, p<0.001), and Delayed Memory (B=-1.54, SE = 037, p<0.001), and higher DepE scores were related to poorer executive functioning (EXIT25; B=0.65, SE=0.19, p=0.001). DepE scores significantly increased risk for MCI diagnosis (odds ratio [OR] = 2.04; 95% CI=1.54-2.69). Data from 235 participants in the TARCC (Texas Alzheimer's Research & Care Consortium) were analyzed for cross-validation of findings in an independent cohort. The DepE was significantly related to poorer scores on all measures, and a significantly predicted of cognitive change over 12- and 24-months.

CONCLUSION

The current findings suggest that a depressive endophenotype of MCI and AD exists and can be clinically identified using the GDS-30. Higher scores increased risk for MCI and was cross-validated by predicting AD in the TARCC. A key purpose for the search for distinct subgroups of individuals at risk for AD and MCI is to identify novel treatment and preventative opportunities.

Anxiety and verbal memory performance in APOE-4 carriers and noncarriers aged 50 years and above

AIMS: The current study sought to explore the relationship between state and trait anxiety and delayed verbal memory performance in APOE-4 carriers and noncarriers who were aged 50 years and above. MATERIALS #ENTITYSTARTX00026; METHODS: The study was a retrospective analysis of 267 participants aged 50 years and above who had completed genetic testing for APOE status, the State-Trait Anxiety Inventory, and a comprehensive neuropsychological battery that included three delayed verbal memory measures (Wechsler Memory Scale - 3rd Edition, Logical Memory and Verbal Pairs subtests and the Buschke Selective Reminding Test). RESULTS: An inverse relationship was found between state anxiety and delayed verbal memory performance. No difference in level of anxiety was found between APOE-4 carriers versus noncarriers. CONCLUSION: State anxiety, but not trait anxiety, was found to have an inverse relationship with delayed verbal memory performance. For example, as self-reported state anxiety increased, delayed verbal memory scores decreased. This relationship did not appear to be influenced by the presence or absence of the APOE-4 allele.