How Do Modifiable Risk Factors Affect Alzheimer's Disease Pathology or Mitigate Its Effect on Clinical Symptom Expression?

Amyloid and Tau Pathology in Cognitively Unimpaired Individuals With a Parental History of Alzheimer Disease: Role of Sex and Parent's Sex

BACKGROUND AND OBJECTIVES

Female sex and a parental history of Alzheimer disease (AD), especially maternal, confer increased risk of AD. Associations between sex, or affected AD parent's sex, and biomarkers of AD are less clear. We examined whether sex or affected AD parent's sex influences (1) β-amyloid (Aβ) and tau burden/accumulation, (2) the association between Aβ and tau burden, and (3) brain and cognitive resilience to Aβ and tau burden.

METHODS

The sample included 243 participants from the Presymptomatic Evaluation of Experimental or Novel Treatments for AD cohort in Canada. All participants with [18F]-NAV4694 and [18F]-AV1451 PET and MRI were included. We examined (1) sex or affected AD parent's sex differences on regional Aβ and tau burden/accumulation; (2) 2-way interactions between sex, or affected AD parent's sex, and Aβ on tau burden; and (3) 3-way interactions between time, sex or affected AD parent's sex, and Aβ or tau deposition on hippocampal volume (brain resilience) and cognition (cognitive resilience) over time.

RESULTS

Participants (69.4% female) were aged 68.3 ± 5.1 years at their first PET scans. All were cognitively unimpaired at baseline. Longitudinal cognitive data were available for 242 participants (follow-up, 6.72 ± 2.38 years), including 238 (6.53 ± 2.48 years of follow-up) with MRI follow-ups and 115 (4.4 ± 0.6 years of follow-up) with PET follow-ups, and 71 developed mild cognitive impairment. Women showed greater tau deposition (standardized β = 0.13 ± 0.3) and showed a stronger association between global Aβ and tau deposition than men (standardized β = 0.79 ± 0.1). Individuals with an affected AD father showed stronger association between global Aβ and tau deposition than those with an affected AD mother (standardized β = 0.65 ± 0.1). Women showed less Aβ-associated hippocampal atrophy over time (standardized β = 0.24 ± 0.1).

DISCUSSION

Women and, surprisingly, individuals with a paternal history of AD seemed more vulnerable to the Aβ-related spread of tau, whereas women showed greater brain resilience to Aβ. Understanding sex-specific risk and resilience could allow more clinical trial precision and personalization. A major limitation included the reduced sample for the affected AD parent's sex analyses.

Mental health and psychological processes associated with cognitive aging and dementia

PURPOSE OF REVIEW

This review focuses on the role of psychological factors in cognitive aging and dementia, an area that has received less attention compared to other modifiable factors (e.g. sleep, physical activity, and so on) or reduction of disease risk.

RECENT FINDINGS

A range of mental health and psychological aspects, including clinical symptoms, stable personality traits, and more specific constructs or processes (e.g. repetitive negative thinking, purpose in life), are associated with cognitive aging and dementia risk. Psychological factors can either serve as protective or risk elements, influencing brain health through general mechanisms, including stress regulation and impact on several biological systems, as well as modulate brain resistance and cognitive resilience to Alzheimer's disease and age-related brain changes. Protective psychological traits are linked to healthier lifestyle habits, while risk factors are associated with negative behaviors, and may impact cognitive function across the lifespan, suggesting benefits for psychological education from early life.

SUMMARY

The review emphasizes the need for greater focus on optimizing psychological well being, particularly in at-risk populations, and suggests that interventions should be tailored to individuals' values and life purposes. Additionally, further research is needed to explore the neurobiological mechanisms through which psychologically focused interventions may influence cognitive decline and dementia.

Loneliness and Biomarkers of Alzheimer's Disease, Axonal Damage, and Astrogliosis: A Coordinated Analysis of Two Longitudinal Cohorts

OBJECTIVES

Loneliness is associated with an elevated risk of dementia. There is mixed evidence from imaging studies on whether loneliness is associated with neuropathology in dementia-free adults. This study tests whether loneliness is associated with plasma neurobiomarkers of amyloid (Aβ42/Aβ40), phosphorylated tau 181 (pTau181), neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP) and imaging measures of amyloid and tau.

METHODS

Participants were cognitively unimpaired older adults from the Baltimore Longitudinal Study on Aging (BLSA; N = 1,028 individuals and up to 2,277 neurobiomarker measurements; Baseline mean age = 66, SD = 15 years) and the UK Biobank (N = 1,263 individuals and up to 2,526 neurobiomarker measurements; Baseline mean age = 60, SD = 7 years). Single-item measures of loneliness and the Quanterix Single Molecule Array assays were used in both samples. In a subset of BLSA participants, positron emission tomography (PET) was used to assess cerebral amyloid burden (n = 220) and tau in the entorhinal cortex (n = 102).

RESULTS

In both samples and meta-analyses, loneliness was unrelated to plasma measures of Aβ42/Aβ40, pTau181, NfL, and GFAP. Changes in loneliness were also unrelated to changes in the plasma neurobiomarkers, and no consistent evidence of moderation by age, sex, or APOE ε4 allele was found. Loneliness was also unrelated to PET-based measures of amyloid and tau.

DISCUSSION

This study found no associations between loneliness and measures of Alzheimer's disease pathology, axonal damage, or astrogliosis.

World no-tobacco: effects of second-hand smoke (SHS) and vapors on the developing and adult brain

The goal of this review is to highlight the role of second-hand smoke (SHS) or environmental tobacco smoke (ETS) and e-cigarette (EC) vapors on brain integrity and function during development and adulthood, including how it relates to increasing the risk for age-related neurodegenerative disorders. A systematic review of the literature of the effect of SHS or ETS and e-cigarette vapors on the brain revealed a total of 284 or 372 publications and 312 publications, respectively. After taking into account duplicate publications or publications focused on policy, surveys or other organs than brain, there are limited studies on the effects of SHS, ETS or EC vapors on brain structure and function. In this review, we examine the major constituents in SHS or EC vapors and their effects on brain health, mechanisms by which SHS or vapors alters brain integrity and function, including behavioral and cognitive performance. We hope that this review will encourage investigators to explore further the short-as well long-term effects of SHS or vapor exposure on the developing and adult brain to better understand its role in neurodevelopmental disorders and neurodegenerative diseases and ultimately to develop therapeutic modalities to reduce or even prevent the short- and long-term detrimental effects on brain health.

Trends in modifiable risk factors for dementia among midlife adults in the United States: The National Health and nutrition examination survey 1999-2018

OBJECTIVE

Dementia has a large public health burden, and modifiable risk factors, particularly in midlife, may provide an opportunity for early prevention. We aimed to examine trends in age-adjusted prevalence of modifiable risk factors for dementia and the number of modifiable risk factors among midlife adults from 1999 to 2018.

METHODS

A total of 14,851 participants aged 40 to 64 years without a history of cardiovascular disease in the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2018 were included in the analysis. The age-adjusted prevalence of six modifiable risk factors consistently measured across all surveys, including hypertension, diabetes, hyperlipidemia, obesity, smoking, and heavy drinking, as well as the average number of these modifiable risk factors, were estimated and compared across survey periods. Subgroup analyses were conducted by sex, race/ethnicity, education, and family income.

RESULTS

The age-adjusted prevalence of diabetes (p for linear trend <0.0001) and obesity (p for linear trend = 0.0001) showed increasing trends from 1999 to 2018 among midlife adults in the U.S. and in virtually all subgroups, while smoking showed a decreasing trend (p for linear trend <0.0001). The average number of modifiable risk factors remained around two (p for linear trend = 0.84).

CONCLUSION

The prevalence of diabetes and obesity increased in this large, nationally representative U.S. study population, while the prevalence of smoking decreased. More effective public health interventions are needed to mitigate the impact of these risk factors and ultimately reduce the burden of dementia in aging populations.

Decoding meditation mechanisms underlying brain preservation and psycho-affective health in older expert meditators and older meditation-naive participants

Meditation is a mental training approach that can improve mental health and well-being in aging. Yet the underlying mechanisms remain unknown. The Medit-Ageing model stipulates that three mechanisms - attentional, constructive, and deconstructive - upregulate positive psycho-affective factors and downregulate negative ones. To test this hypothesis, we measured brain structural MRI and perfusion, negative and positive psycho-affective composite scores, and meditation mechanisms in 27 older expert meditators and 135 meditation-naive older controls. We identified brain and psycho-affective differences and performed mediation analyses to assess whether and which meditation mechanisms mediate their links.Meditators showed significantly higher volume in fronto-parietal areas and perfusion in temporo-occipito-parietal areas. They also had higher positive and lower negative psycho-affective scores. Attentional and constructive mechanisms both mediated the links between brain differences and the positive psycho-affective score whereas the deconstructive mechanism mediated the links between brain differences and the negative psycho-affective score.Our results corroborate the Medit-Ageing model, indicating that, in aging, meditation leads to brain changes that decrease negative psycho-affective factors and increase positive ones through relatively specific mechanisms. Shedding light on the neurobiological and psycho-affective mechanisms of meditation in aging, these findings provide insights to refine future interventions.

Structural white matter properties and cognitive resilience to tau pathology

INTRODUCTION

We assessed whether macro- and/or micro-structural white matter properties are associated with cognitive resilience to Alzheimer's disease pathology years prior to clinical onset.

METHODS

We examined whether global efficiency, an indicator of communication efficiency in brain networks, and diffusion measurements within the limbic network and default mode network moderate the association between amyloid-β/tau pathology and cognitive decline. We also investigated whether demographic and health/risk factors are associated with white matter properties.

RESULTS

Higher global efficiency of the limbic network, as well as free-water corrected diffusion measures within the tracts of both networks, attenuated the impact of tau pathology on memory decline. Education, age, sex, white matter hyperintensities, and vascular risk factors were associated with white matter properties of both networks.

DISCUSSION

White matter can influence cognitive resilience against tau pathology, and promoting education and vascular health may enhance optimal white matter properties.

HIGHLIGHTS

Aβ and tau were associated with longitudinal memory change over ∼7.5 years. White matter properties attenuated the impact of tau pathology on memory change. Health/risk factors were associated with white matter properties.

Biomarker-based staging of Alzheimer disease: rationale and clinical applications

Disease staging, whereby the spatial extent and load of brain pathology are used to estimate the severity of Alzheimer disease (AD), is pivotal to the gold-standard neuropathological diagnosis of AD. Current in vivo diagnostic frameworks for AD are based on abnormal concentrations of amyloid-β and tau in the cerebrospinal fluid or on PET scans, and breakthroughs in molecular imaging have opened up the possibility of in vivo staging of AD. Focusing on the key principles of disease staging shared across several areas of medicine, this Review highlights the potential for in vivo staging of AD to transform our understanding of preclinical AD, refine enrolment criteria for trials of disease-modifying therapies and aid clinical decision-making in the era of anti-amyloid therapeutics. We provide a state-of-the-art review of recent biomarker-based AD staging systems and highlight their contributions to the understanding of the natural history of AD. Furthermore, we outline hypothetical frameworks to stage AD severity using more accessible fluid biomarkers. In addition, by applying amyloid PET-based staging to recently published anti-amyloid therapeutic trials, we highlight how biomarker-based disease staging frameworks could illustrate the numerous pathological changes that have already taken place in individuals with mildly symptomatic AD. Finally, we discuss challenges related to the validation and standardization of disease staging and provide a forward-looking perspective on potential clinical applications.

Apathy Associated with Alzheimer's Disease

INTRODUCTION/OBJECTIVE

Apathy is a multidimensional and complex disease that is the primary neuropsychiatric symptom among those diagnosed with Alzheimer's disease (AD). Yet, apathy in AD is sometimes underestimated.

METHODS

A systematic literature review was conducted using databases such as PubMed, Scopus, and Web of Science. The search utilized specific keywords related to apathy and Alzheimer's disease (e.g., "apathy," "Alzheimer's disease," "neuropsychiatric symptoms," "front-striatal circuitry"). The studies were selected based on pre-defined criteria, including publication date (within the last 10 years), peer-reviewed status, and relevance to neurobiological, neurochemical, and behavioral aspects of apathy in AD. The articles were screened through title and abstract reviews, followed by full-text evaluations to ensure they met the inclusion criteria, such as relevance to apathy in Alzheimer's patients, study design rigor, and methodological quality.

RESULTS

Some research on the behavioral and neurobiological characteristics of apathy in AD points to the role of the front-striatal circuitry, particularly the anterior cingulate cortex (ACC). In addition, we reviewed the neurochemical, neuropsychological, and neuropathological characteristics believed to be associated with apathy symptoms.

CONCLUSION

The findings indicate that understanding the intricate neurobiological underpinnings of apathy in AD is crucial for developing targeted interventions. Our analysis suggests that a multimodal approach, incorporating both pharmacological and personalized non-pharmacological strategies, could enhance therapeutic efficacy and improve patient outcomes. This highlights the need for future research to explore these combined treatment modalities and their potential to alleviate apathy in AD patients.