Alzheimer’s Disease Biomarkers Interactively Influence Physical Activity, Mobility, and Cognition Associations in a Non-Demented Aging Population

Increased frequency of light physical activity during midlife and old age buffers against cognitive declines

Although it is well established that moderate-to-vigorous physical activity (MVPA) buffers against declines in cognitive health, less is known about the benefits of light physical activity (LPA). Research on the role of LPA is crucial to advancing behavioral interventions to improve late life health outcomes, including cognitive functioning, because this form of physical activity remains more feasible and amenable to change in old age. Our study examined the extent to which increases in LPA frequency protected against longitudinal declines in cognitive functioning and whether such a relationship becomes pronounced in old age when opportunities for MVPA are typically reduced. We analyzed 9-year data from the national Midlife in the United States Study (n = 2,229; Mage = 56 years, range = 33-83; 56% female) using autoregressive models that assessed whether change in LPA frequency predicted corresponding changes in episodic memory and executive functioning in middle and later adulthood. Increases in LPA frequency predicted less decline in episodic memory (β = 0.06, p = .004) and executive functioning (β = 0.14, p < .001) over the 9-year follow-up period, even when controlling for moderate and vigorous physical activity. Effect sizes for moderate and vigorous physical activity were less than half that observed for LPA. Moderation models showed that, for episodic memory, the benefits of increases in LPA frequency were more pronounced at older ages. Findings suggest that increases in LPA over extended periods of time may help slow age-related cognitive declines, particularly in later life when opportunities for MVPA are often diminished.

Association of Physical Activity and APOE Genotype With Longitudinal Cognitive Change in Early Parkinson Disease

OBJECTIVE

To determine whether greater physical activity could modify the negative association of APOE ε4 with longitudinal cognitive changes in early Parkinson disease (PD) and to uncover the disease-specific mechanism for explaining such benefits of physical activity.

METHODS

We used data from the Parkinson's Progression Markers Initiative cohort. Because self-reported physical activity, measured by the Physical Activity Scale of the Elderly, was initiated at 2 years after enrollment, this longitudinal analysis was based on assessments performed at years 2, 3, and 4. Cognitive function was measured annually with the Montreal Cognitive Assessment (MoCA). Dopamine transporter (DAT) imaging was performed at years 2 and 4. We assessed the interactive associations between physical activity and the APOE ε4 allele on the longitudinal changes in MoCA scores and striatal DAT activities.

RESULTS

A total of 173 patients with early PD (age 63.3 ± 10.0 years, 27% APOE ε4 carriers) were included. The APOE ε4 allele showed a steeper rate of cognitive decline than the non-APOE ε4 allele (estimate -1.33, 95% confidence interval [CI] -2.12 to -0.47, p = 0.002). However, there was a significant interaction between physical activity and APOE ε4 such that higher physical activity was related to slower APOE ε4-related cognitive decline (estimate 0.007, 95% CI 0.003-0.011, p = 0.001). No significant interaction was found between physical activity and the APOE ε4 allele regarding the change in striatal DAT activities.

CONCLUSION

Increased physical activity attenuated APOE ε4-related vulnerability to early cognitive decline in patients with PD. This protective effect did not appear to be mediated by striatal dopaminergic function.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov Identifier: NCT01141023.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that increased physical activity was associated with decreased APOE ε4-related early cognitive decline in patients with PD.

Integrating Three Characteristics of Executive Function in Non-Demented Aging: Trajectories, Classification, and Biomarker Predictors

OBJECTIVE

With longitudinal executive function (EF) data from the Victoria Longitudinal Study, we investigated three research goals pertaining to key characteristics of EF in non-demented aging: (a) examining variability in EF longitudinal trajectories, (b) establishing trajectory classes, and (c) identifying biomarker predictors discriminating these classes.

METHOD

We used a trajectory analyses sample (n = 781; M age = 71.42) for the first and second goals and a prediction analyses sample (n = 570; M age = 70.10) for the third goal. Eight neuropsychological EF measures were used as indicators of three EF dimensions: inhibition, updating, and shifting. Data-driven classification analyses were applied to the full trajectory distribution. Machine learning prediction analyses tested 15 predictors from genetic, functional, lifestyle, mobility, and demographic risk domains.

RESULTS

First, we observed: (a) significant variability in EF trajectories over a 40-year band of aging and (b) significantly variable patterns of EF decline. Second, a four-class EF trajectory model was observed, characterized with classes differentiated by an algorithm of level and slope information. Third, the highest group class was discriminated from lowest by several prediction factors: more education, more novel cognitive activity, lower pulse pressure, younger age, faster gait, lower body mass index, and better balance.

CONCLUSION

First, with longitudinal variability in EF aging, the data-driven approach showed that long-term trajectories can be differentiated into separable classes. Second, prediction analyses discriminated class membership by a combination of multiple biomarkers from demographic, lifestyle, functional, and mobility domains of risk for brain and cognitive aging decline.

A longitudinal study using latent curve models of groups with mild cognitive impairment and Alzheimer's disease

BACKGROUND

This study explores how mild cognitive impairment (MCI) and Alzheimer's disease (AD) develop over time. NEW METHOD: this study involves a new application of latent curve models (LCM) to examine the development trajectory of a healthy, MCI, and AD groups on a series of clinical and neural measures. Multiple-group latent curve models were used to compare the parameters of the trajectories across groups.

RESULTS

LCM results showed that a linear functional form of growth was adequate for all the clinical and neural measures. Positive and significant differences in initial levels were seen across groups on all of the clinical and neural measures. In all groups, the following measures increased slightly, or considerably, over time: Clinical Dementia Rating, Alzheimer's disease Cognitive Assessment, and Montreal Assessment Test for Dementia. In contrast, a slight or a greatly decreasing trajectory was observed on the following measures: Fluorodeoxyglucose, Mini-Mental State Exam, Rey Auditory Verbal Learning Test as well as Hippocampus, Fusiform and Entorhinal Cortex volume measures. However, a constant mean trajectory was seen on Cognition Self Report Memory and languages scores. COMPARISION WITH EXISTING METHODS: there are no prior studies that applied LCM on large AD datasets.

CONCLUSIONS

cognitive decline occurs in the cognitively normal (CN), MCI, and AD groups but at different rates. Further, some important cognitive, neural, and clinical variables that (a) best differentiate between CN, MCI, and AD as well as (b) differentially change over time in MCI and AD, which may explain disease progression.

The relationship between physical activity, apolipoprotein E ε4 carriage, and brain health

BACKGROUND

Neuronal hyperexcitability and hypersynchrony have been described as key features of neurophysiological dysfunctions in the Alzheimer's disease (AD) continuum. Conversely, physical activity (PA) has been associated with improved brain health and reduced AD risk. However, there is controversy regarding whether AD genetic risk (in terms of APOE ε4 carriage) modulates these relationships. The utilization of multiple outcome measures within one sample may strengthen our understanding of this complex phenomenon.

METHOD

The relationship between PA and functional connectivity (FC) was examined in a sample of 107 healthy older adults using magnetoencephalography. Additionally, we explored whether ε4 carriage modulates this association. The correlation between FC and brain structural integrity, cognition, and mood was also investigated.

RESULTS

A relationship between higher PA and decreased FC (hyposynchrony) in the left temporal lobe was observed among all individuals (across the whole sample, in ε4 carriers, and in ε4 non-carriers), but its effects manifest differently according to genetic risk. In ε4 carriers, we report an association between this region-specific FC profile and preserved brain structure (greater gray matter volumes and higher integrity of white matter tracts). In this group, decreased FC also correlated with reduced anxiety levels. In ε4 non-carriers, this profile is associated with improved cognition (working and episodic memory).

CONCLUSIONS

PA could mitigate the increase in FC (hypersynchronization) that characterizes preclinical AD, being beneficial for all individuals, especially ε4 carriers.

ABCA7 Genotype Moderates the Effect of Aerobic Exercise Intervention on Generalization of Prior Learning in Healthy Older African Americans

African Americans are at elevated risk for age-related cognitive decline, with double the prevalence of Alzheimer's disease (AD) compared to Caucasians Americans. Various behavioral, biological, and lifestyle factors may underlie this health disparity, but little is known about the relative importance and interactions among these different risk factors in African Americans. While the neuroprotective effects of aerobic exercise on biomarkers are well established, few studies have examined the differential benefits of exercise based on genetic risk for AD. Furthermore, evidence is limited regarding the potential moderating effects of ABCA7, a gene known to confer significantly greater AD risk in African Americans. In a case-control matched sample of 56 healthy older African Americans, we investigated the effect of an aerobic exercise intervention on a hippocampus-related assessment of generalization following rule learning, in individuals who were carriers of the ABCA7 rs3764650 non-risk (TT) or high-risk (GG) genotype. Following the exercise-intervention, the non-risk group made significantly fewer generalization errors, while there was no improvement in generalization for the high-risk group. For the controls, no changes in generalization scores were observed regardless of genotype status. Our results indicate that the ongoing adverse effects of ABCA7 high-risk genotype may diminish the benefits associated with aerobic exercise. As such, the potential disease-modifying effects of aerobic exercise on AD-related neuropathology may be limited to carriers of the ABCA7 rs3764650 non-risk genotype.

Frailty effects on non-demented cognitive trajectories are moderated by sex and Alzheimer's genetic risk

BACKGROUND

Age-related frailty reflects cumulative multisystem physiological and health decline. Frailty increases the risk of adverse brain and cognitive outcomes, including differential decline and dementia. In a longitudinal sample of non-demented older adults, we examine whether (a) the level and/or change in frailty predicts trajectories across three cognitive domains (memory, speed, and executive function (EF)) and (b) prediction patterns are modified by sex or Alzheimer's genetic risk (Apolipoprotein E (APOE)).

METHODS

Participants (n = 632; M age = 70.7, range 53-95; 3 waves) were from the Victoria Longitudinal Study. After computing a frailty index, we used latent growth modeling and path analysis to test the frailty effects on level and change in three latent variables of cognition. We tested two potential moderators by stratifying by sex and APOE risk (ε4+, ε4-).

RESULTS

First, frailty levels predicted speed and EF performance (level) and differential memory change slopes. Second, change in frailty predicted the rate of decline for both speed and EF. Third, sex moderation analyses showed that females were selectively sensitive to (a) frailty effects on memory change and (b) frailty change effects on speed change. In contrast, the frailty effects on EF change were stronger in males. Fourth, genetic moderation analyses showed that APOE risk (e4+) carriers were selectively sensitive to frailty effects on memory change.

CONCLUSION

In non-demented older adults, increasing frailty is strongly associated with the differential decline in cognitive trajectories. For example, higher (worse) frailty was associated with more rapid memory decline than was lower (better) frailty. These effects, however, are moderated by both genetic risk and sex.

Physical Activity and Mobility Differentially Predict Nondemented Executive Function Trajectories: Do Sex and APOE Moderate These Associations?

BACKGROUND

In nondemented aging, higher levels of everyday physical activity (EPA) and mobility performance are associated with better executive function (EF) trajectories. However, these associations may be moderated by both sex and Alzheimer's disease (AD) genetic risk.

OBJECTIVES

In a longitudinal study, we investigate sex differences in (a) EPA and mobility effects on EF performance (level) and change (slope) and (b) AD genetic risk moderation of these associations.

METHODS

The longitudinal design included nondemented adults (n = 532, mean age = 70.4 years, range 53-95) from the Victoria Longitudinal Study. Using structural equation analyses on an EF latent variable, we tested (a) sex moderation and (b) interactive effects of sex and APOE on observed EPA-EF and mobility-EF performance and change relationships.

RESULTS

First, we observed independent sex effects for the EPA-EF and mobility-EF predictions. Whereas EPA had a significant effect on EF performance and change only for females, mobility had a significant effect for both sexes. Notably, males with lower mobility levels experienced steeper EF decline than females with lower mobility levels. Second, we observed significant sex × APOE interaction effects. The combination of lower genetic risk and higher EPA benefitted females but not males. In contrast, lower genetic risk and higher mobility benefited both sexes, although male APOE no-risk carriers with lower mobility levels had EF decline patterns that were similar to APOE risk carriers.

CONCLUSIONS

Longitudinal analyses across a broad band of aging show that sex moderates the effects of both EPA and mobility on EF performance and change. Notably, this moderation occurs differentially across the AD genetic risk status. These results point to a precision health approach to observational and interventional research in which effects of physical activity and mobility on EF trajectories and dementia are examined in the personalized and interactive context of sex and AD risk.

Alzheimer's Biomarkers From Multiple Modalities Selectively Discriminate Clinical Status: Relative Importance of Salivary Metabolomics Panels, Genetic, Lifestyle, Cognitive, Functional Health and Demographic Risk Markers

Background: Among the neurodegenerative diseases of aging, sporadic Alzheimer’s disease (AD) is the most prevalent and perhaps the most feared. With virtually no success at finding pharmaceutical therapeutics for altering progressive AD after diagnosis, research attention is increasingly directed at discovering biological and other markers that detect AD risk in the long asymptomatic phase. Both early detection and precision preclinical intervention require systematic investigation of multiple modalities and combinations of AD-related biomarkers and risk factors. We extend recent unbiased metabolomics research that produced a set of metabolite biomarker panels tailored to the discrimination of cognitively normal (CN), cognitively impaired and AD patients. Specifically, we compare the prediction importance of these panels with five other sets of modifiable and non-modifiable AD risk factors (genetic, lifestyle, cognitive, functional health and bio-demographic) in three clinical groups.

Method: The three groups were: CN (n = 35), mild cognitive impairment (MCI; n = 25), and AD (n = 22). In a series of three pairwise comparisons, we used machine learning technology random forest analysis (RFA) to test relative predictive importance of up to 19 risk biomarkers from the six AD risk domains.

Results: The three RFA multimodal prediction analyses produced significant discriminating risk factors. First, discriminating AD from CN was the AD metabolite panel and two cognitive markers. Second, discriminating AD from MCI was the AD/MCI metabolite panel and two cognitive markers. Third, discriminating MCI from CN was the MCI metabolite panel and seven markers from four other risk modalities: genetic, lifestyle, cognition and functional health.

Conclusions: Salivary metabolomics biomarker panels, supplemented by other risk markers, were robust predictors of: (1) clinical differences in impairment and dementia and even; (2) subtle differences between CN and MCI. For the latter, the metabolite panel was supplemented by biomarkers that were both modifiable (e.g., functional) and non-modifiable (e.g., genetic). Comparing, integrating and identifying important multi-modal predictors may lead to novel combinations of complex risk profiles potentially indicative of neuropathological changes in asymptomatic or preclinical AD.