Older adults at greater risk for Alzheimer's disease show stronger associations between sleep apnea severity and verbal memory

Background

Obstructive sleep apnea (OSA) increases risk for cognitive decline and Alzheimer's disease (AD). While the underlying mechanisms remain unclear, hypoxemia during OSA has been implicated in cognitive impairment. OSA during rapid eye movement (REM) sleep is usually more severe than in non-rapid eye movement (NREM) sleep, but the relative effect of oxyhemoglobin desaturation during REM versus NREM sleep on memory is not completely characterized. Here, we examined the impact of OSA, as well as the moderating effects of AD risk factors, on verbal memory in a sample of middle-aged and older adults with heightened AD risk.

Methods

Eighty-one adults (mean age:61.7±6.0 years, 62% females, 32% apolipoprotein E ε4 allele (APOE4) carriers, and 70% with parental history of AD) underwent clinical polysomnography including assessment of OSA. OSA features were derived in total, NREM, and REM sleep. REM-NREM ratios of OSA features were also calculated. Verbal memory was assessed with the Rey Auditory Verbal Learning Test (RAVLT). Multiple regression models evaluated the relationships between OSA features and RAVLT scores while adjusting for sex, age, time between assessments, education years, body mass index (BMI), and APOE4 status or parental history of AD. The significant main effects of OSA features on RAVLT performance and the moderating effects of AD risk factors (i.e., sex, age, APOE4 status, and parental history of AD) were examined.

Results

Apnea-hypopnea index (AHI), respiratory disturbance index (RDI), and oxyhemoglobin desaturation index (ODI) during REM sleep were negatively associated with RAVLT total learning and long-delay recall. Further, greater REM-NREM ratios of AHI, RDI, and ODI (i.e., more events in REM than NREM) were related to worse total learning and recall. We found specifically that the negative association between REM ODI and total learning was driven by adults 60+ years old. In addition, the negative relationships between REM-NREM ODI ratio and total learning and REM-NREM RDI ratio and long-delay recall were driven by APOE4 carriers.

Conclusion

Greater OSA severity, particularly during REM sleep, negatively affects verbal memory, especially for people with greater AD risk. These findings underscore the potential importance of proactive screening and treatment of REM OSA even if overall AHI appears low.

Whole-body modelling reveals microbiome and genomic interactions on reduced urine formate levels in Alzheimer's disease

In this study, we aimed to understand the potential role of the gut microbiome in the development of Alzheimer's disease (AD). We took a multi-faceted approach to investigate this relationship. Urine metabolomics were examined in individuals with AD and controls, revealing decreased formate and fumarate concentrations in AD. Additionally, we utilized whole-genome sequencing (WGS) data obtained from a separate group of individuals with AD and controls. This information allowed us to create and investigate host-microbiome personalized models. Notably, AD individuals displayed diminished formate microbial secretion in these models. Additionally, we identified specific reactions responsible for the production of formate in the host, and interestingly, these reactions were linked to genes that have correlations with AD. This study suggests formate as a possible early AD marker and highlights genetic and microbiome contributions to its production. The reduced formate secretion and its genetic associations point to a complex connection between gut microbiota and AD. This holistic understanding might pave the way for novel diagnostic and therapeutic avenues in AD management.

Inflammation, tau pathology, and synaptic integrity associated with sleep spindles and memory prior to β-amyloid positivity

STUDY OBJECTIVES

Fast frequency sleep spindles are reduced in aging and Alzheimer's disease (AD), but the mechanisms and functional relevance of these deficits remain unclear. The study objective was to identify AD biomarkers associated with fast sleep spindle deficits in cognitively unimpaired older adults at risk for AD.

METHODS

Fifty-eight cognitively unimpaired, β-amyloid-negative, older adults (mean ± SD; 61.4 ± 6.3 years, 38 female) enriched with parental history of AD (77.6%) and apolipoprotein E (APOE) ε4 positivity (25.9%) completed the study. Cerebrospinal fluid (CSF) biomarkers of central nervous system inflammation, β-amyloid and tau proteins, and neurodegeneration were combined with polysomnography (PSG) using high-density electroencephalography and assessment of overnight memory retention. Parallelized serial mediation models were used to assess indirect effects of age on fast frequency (13 to <16Hz) sleep spindle measures through these AD biomarkers.

RESULTS

Glial activation was associated with prefrontal fast frequency sleep spindle expression deficits. While adjusting for sex, APOE ε4 genotype, apnea-hypopnea index, and time between CSF sampling and sleep study, serial mediation models detected indirect effects of age on fast sleep spindle expression through microglial activation markers and then tau phosphorylation and synaptic degeneration markers. Sleep spindle expression at these electrodes was also associated with overnight memory retention in multiple regression models adjusting for covariates.

CONCLUSIONS

These findings point toward microglia dysfunction as associated with tau phosphorylation, synaptic loss, sleep spindle deficits, and memory impairment even prior to β-amyloid positivity, thus offering a promising candidate therapeutic target to arrest cognitive decline associated with aging and AD.

053 REM Sleep Apnea Severity Contributes to Poor Verbal Memory in Cognitively Asymptomatic Older Adults

Introduction

The prevalence of obstructive sleep apnea (OSA) rises with age, leading to increased dementia risk and memory decline. However, it remains unclear which OSA features drive this relationship. Here, we examine associations between verbal memory and multiple OSA features in healthy older adults.

Methods

58 cognitively asymptomatic adults (61.4±6.3 years; 38 females) underwent polysomnography (PSG) and the Rey Auditory Verbal Learning Test (RAVLT; 0.2±0.5 years between assessments). OSA measures included apnea-hypopnea index (AHI), respiratory disturbance index (RDI), and desaturation index in both NREM and REM sleep. RAVLT measures included total learning (sum of trials 1–5), short-delayed recall, and long-delayed recall. Pearson correlations with FDR correction were calculated between OSA-related measures and RAVLT. Multiple regression was then used to adjust for OSA features in other sleep stages (i.e., REM versus NREM), age, sex, time between PSG and neuropsychological assessments, years of education, and APOE4 status. We also explored whether age moderated these relationships.

Results

REM RDI is negatively associated with RAVLT total learning (r=-0.31, p&lt;0.01 with age moderating the effect at 1SD above mean: B=-0.22, t(49)=-2.88, p=0.01) and RAVLT long-delayed recall (r=-0.36, p&lt;0.001; with age moderating the effect at mean: B=-0.05, t(49)=-2.38, p=0.02; and moderating at 1SD above mean: B=-0.09, t(49)=-3.91, p&lt;0.01). REM desaturation index was also associated with RAVLT total learning (r=-0.21, p&lt;0.01) and RAVLT long-delayed recall (r=-0.34, p&lt;0.01). REM AHI was negatively correlated to RAVLT long-delayed recall (r=-0.34, p&lt;0.01; with age significantly moderating the effect at the mean: B=-0.06, t(49)=-2.87, p=0.01; and moderating at 1SD above the mean: B=-0.11, t(49)=-4.23, p&lt;0.01). Of note, NREM OSA features were not significantly correlated to RAVLT measures when REM OSA features were included in the model.

Conclusion

These findings demonstrate that REM OSA features in particular contribute to poor verbal memory encoding and retrieval, especially at older ages. Verbal memory decline has been predictive of conversion to Alzheimer’s disease (AD). Future studies including brain imaging, AD biomarkers, REM sleep oscillations, and comprehensive neuropsychological testing may elucidate the underlying mechanisms linking REM OSA features to memory decline and dementia risk.

Support (if any)

This research was supported by R56 AG052698 and P50AG033514.