Obstructive sleep apnea decreases central nervous system-derived proteins in the cerebrospinal fluid

Obstructive Sleep Apnea is Associated With Early but Possibly Modifiable Alzheimer's Disease Biomarkers Changes

Study Objectives

Obstructive sleep apnea (OSA) is a common sleep disorder. The, literature lacks studies examining sleep, cognition, and Alzheimer's Disease (AD) cerebrospinal fluid (CSF) biomarkers in OSA patients. Therefore, we first studied cognitive performances, polysomnographic sleep, and CSF β-amyloid42, tau proteins, and lactate levels in patients affected by subjective cognitive impairment (SCI) divided in three groups: OSA patients (showing an Apnea-Hypopnea Index [AHI] ≥15/hr), controls (showing an AHI < 15/hr), and patients with OSA treated by continuous positive airway pressure (CPAP).

Methods

We compared results among 25 OSA, 10 OSA-CPAP, and 15 controls who underwent a protocol counting neuropsychological testing in the morning, 48-hr polysomnography followed by CSF analysis.

Results

OSA patients showed lower CSF Aβ42 concentrations, higher CSF lactate levels, and higher t-tau/Aβ42 ratio compared to controls and OSA-CPAP patients. OSA patients also showed reduced sleep quality and continuity and lower performances at memory, intelligence, and executive tests than controls and OSA-CPAP patients. We found significant relationships among higher CSF tau proteins levels, sleep impairment, and increased CSF lactate levels in the OSA group. Moreover, lower CSF Aβ42 levels correlate with memory impairment and nocturnal oxygen saturation parameters in OSA patients.

Conclusions

We hypothesize that OSA reducing sleep quality and producing intermittent hypoxia lowers CSF Aβ42 levels, increases CSF lactate levels, and alters cognitive performances in SCI patients, thus inducing early AD clinical and neuropathological biomarkers changes. Notably, controls as well as OSA-CPAP SCI patients did not show clinical and biochemical AD markers. Therefore, OSA may induce early but possibly CPAP-modifiable AD biomarkers changes.

Slow wave sleep disruption increases cerebrospinal fluid amyloid-β levels

See Mander et al. (doi:10.1093/awx174) for a scientific commentary on this article.Sleep deprivation increases amyloid-β, suggesting that chronically disrupted sleep may promote amyloid plaques and other downstream Alzheimer's disease pathologies including tauopathy or inflammation. To date, studies have not examined which aspect of sleep modulates amyloid-β or other Alzheimer's disease biomarkers. Seventeen healthy adults (age 35-65 years) without sleep disorders underwent 5-14 days of actigraphy, followed by slow wave activity disruption during polysomnogram, and cerebrospinal fluid collection the following morning for measurement of amyloid-β, tau, total protein, YKL-40, and hypocretin. Data were compared to an identical protocol, with a sham condition during polysomnogram. Specific disruption of slow wave activity correlated with an increase in amyloid-β40 (r = 0.610, P = 0.009). This effect was specific for slow wave activity, and not for sleep duration or efficiency. This effect was also specific to amyloid-β, and not total protein, tau, YKL-40, or hypocretin. Additionally, worse home sleep quality, as measured by sleep efficiency by actigraphy in the six nights preceding lumbar punctures, was associated with higher tau (r = 0.543, P = 0.045). Slow wave activity disruption increases amyloid-β levels acutely, and poorer sleep quality over several days increases tau. These effects are specific to neuronally-derived proteins, which suggests they are likely driven by changes in neuronal activity during disrupted sleep.

Neuropsychiatric signs and symptoms of Alzheimer's disease: New treatment paradigms

Neuropsychiatric symptoms (NPSs) are hallmarks of Alzheimer's disease (AD), causing substantial distress for both people with dementia and their caregivers, and contributing to early institutionalization. They are among the earliest signs and symptoms of neurocognitive disorders and incipient cognitive decline, yet are under-recognized and often challenging to treat. With this in mind, the Alzheimer's Association convened a Research Roundtable in May 2016, bringing together experts from academia, industry, and regulatory agencies to discuss the latest understanding of NPSs and review the development of therapeutics and biomarkers of NPSs in AD. This review will explore the neurobiology of NPSs in AD and specific symptoms common in AD such as psychosis, agitation, apathy, depression, and sleep disturbances. In addition, clinical trial designs for NPSs in AD and regulatory considerations will be discussed.

Pathway for the Management of Sleep Apnea in the Cardiac Patient

Sleep-disordered breathing is a highly prevalent medical condition, which if undiagnosed leads to increased morbidity and mortality, particularly related to increased incidence of cardiovascular events. It is therefore imperative that we identify patient population at high risk for sleep apnea and refer them to the appropriate therapy as early as possible. Up-to-date there is no management guideline specifically geared towards cardiac patients. Thus, we propose a (SAP) Sleep Apnea Pathway to correctly identify and triage these patients to the appropriate therapy.

Sleep Disturbance, Cognitive Decline, and Dementia: A Review

Approximately half of older people report sleep disturbances, which are associated with various health conditions, including neurodegenerative disease and dementia. Indeed, 60 to 70% of people with cognitive impairment or dementia have sleep disturbances, which are linked to poorer disease prognosis. Sleep disturbances in people with dementia have long been recognized and studied; however, in the past 10 years, researchers have begun to study disturbed sleep, including sleep fragmentation, abnormal sleep duration, and sleep disorders, as risk factors for dementia. In this review the authors summarize evidence linking sleep disturbance and dementia. They describe how specific aspects of sleep (e.g., quality, duration) and the prevalence of clinical sleep disorders (e.g., sleep-disordered breathing, rapid eye movement sleep behavior disorder) change with age; how sleep parameters and sleep disorders are associated with the risk of dementia; how sleep can be disturbed in dementia; and how disturbed sleep affects dementia prognosis. These findings highlight the potential importance of identifying and treating sleep problems and disorders in middle-aged and older adults as a strategy to prevent cognitive decline and dementia. The authors also review recent evidence linking sleep disturbances to the pathophysiology underlying dementing conditions, and briefly summarize available treatments for sleep disorders in people with dementia.

Perivascular spaces, glymphatic dysfunction, and small vessel disease

Cerebral small vessel diseases (SVDs) range broadly in etiology but share remarkably overlapping pathology. Features of SVD including enlarged perivascular spaces (EPVS) and formation of abluminal protein deposits cannot be completely explained by the putative pathophysiology. The recently discovered glymphatic system provides a new perspective to potentially address these gaps. This work provides a comprehensive review of the known factors that regulate glymphatic function and the disease mechanisms underlying glymphatic impairment emphasizing the role that aquaporin-4 (AQP4)-lined perivascular spaces (PVSs), cerebrovascular pulsatility, and metabolite clearance play in normal CNS physiology. This review also discusses the implications that glymphatic impairment may have on SVD inception and progression with the aim of exploring novel therapeutic targets and highlighting the key questions that remain to be answered.

Poor sleep is associated with CSF biomarkers of amyloid pathology in cognitively normal adults

OBJECTIVE

To determine the relationship between sleep quality and CSF markers of Alzheimer disease (AD) pathology in late midlife.

METHODS

We investigated the relationship between sleep quality and CSF AD biomarkers in a cohort enriched for parental history of sporadic AD, the Wisconsin Registry for Alzheimer's Prevention. A total of 101 participants (mean age 62.9 ± 6.2 years, 65.3% female) completed sleep assessments and CSF collection and were cognitively normal. Sleep quality was measured with the Medical Outcomes Study Sleep Scale. CSF was assayed for biomarkers of amyloid metabolism and plaques (β-amyloid 42 [Aβ42]), tau pathology (phosphorylated tau [p-tau] 181), neuronal/axonal degeneration (total tau [t-tau], neurofilament light [NFL]), neuroinflammation/astroglial activation (monocyte chemoattractant protein-1 [MCP-1], chitinase-3-like protein 1 [YKL-40]), and synaptic dysfunction/degeneration (neurogranin). To adjust for individual differences in total amyloid production, Aβ42 was expressed relative to Aβ40. To assess cumulative pathology, CSF biomarkers were expressed in ratio to Aβ42. Relationships among sleep scores and CSF biomarkers were assessed with multiple regression, controlling for age, sex, time between sleep and CSF measurements, and CSF assay batch.

RESULTS

Worse subjective sleep quality, more sleep problems, and daytime somnolence were associated with greater AD pathology, indicated by lower CSF Aβ42/Aβ40 and higher t-tau/Aβ42, p-tau/Aβ42, MCP-1/Aβ42, and YKL-40/Aβ42. There were no significant associations between sleep and NFL or neurogranin.

CONCLUSIONS

Self-report of poor sleep was associated with greater AD-related pathology in cognitively healthy adults at risk for AD. Effective strategies exist for improving sleep; therefore sleep health may be a tractable target for early intervention to attenuate AD pathogenesis.

Functional reorganization in obstructive sleep apnoea and insomnia: A systematic review of the resting-state fMRI

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Resting state functional MRI studies is a promising non-invasive tool for better understanding of the pathophysiology of sleep disorders.

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The salience network is involved in hyperarousal and affective symptoms in insomnia.

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The posterior default mode network appears to underlie cognitive and depressive symptoms of obstructive sleep apnoea.

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Disruption of intrinsic networks have been demonstrated in major depression, which is a common co-morbidity of sleep disorders.

Functional neuroimaging techniques have accelerated progress in the study of sleep disorders. Considering the striking prevalence of these disorders in the general population, however, as well as their strong bidirectional relationship with major neuropsychiatric disorders, including major depressive disorder, their numbers are still surprisingly low. This review examines the contribution of resting state functional MRI to current understanding of two major sleep disorders, insomnia disorder and obstructive sleep apnoea. An attempt is made to learn from parallels of previous resting state functional neuroimaging findings in major depressive disorder. Moreover, shared connectivity biomarkers are suggested for each of the sleep disorders. Taken together, despite some inconsistencies, the synthesis of findings to date highlights the importance of the salience network in hyperarousal and affective symptoms in insomnia. Conversely, dysfunctional connectivity of the posterior default mode network appears to underlie cognitive and depressive symptoms of obstructive sleep apnoea.

Reduced Slow-Wave Sleep Is Associated with High Cerebrospinal Fluid Aβ42 Levels in Cognitively Normal Elderly

STUDY OBJECTIVES

Emerging evidence suggests a role for sleep in contributing to the progression of Alzheimer disease (AD). Slow wave sleep (SWS) is the stage during which synaptic activity is minimal and clearance of neuronal metabolites is high, making it an ideal state to regulate levels of amyloid beta (Aβ). We thus aimed to examine relationships between concentrations of Aβ42 in the cerebrospinal fluid (CSF) and measures of SWS in cognitively normal elderly subjects.

METHODS

Thirty-six subjects underwent a clinical and cognitive assessment, a structural MRI, a morning to early afternoon lumbar puncture, and nocturnal polysomnography. Correlations and linear regression analyses were used to assess for associations between CSF Aβ42 levels and measures of SWS controlling for potential confounders. Resulting models were compared to each other using ordinary least squared linear regression analysis. Additionally, the participant sample was dichotomized into "high" and "low" Aβ42 groups to compare SWS bout length using survival analyses.

RESULTS

A significant inverse correlation was found between CSF Aβ42 levels, SWS duration and other SWS characteristics. Collectively, total SWA in the frontal lead was the best predictor of reduced CSF Aβ42 levels when controlling for age and ApoE status. Total sleep time, time spent in NREM1, NREM2, or REM sleep were not correlated with CSF Aβ42.

CONCLUSIONS

In cognitively normal elderly, reduced and fragmented SWS is associated with increases in CSF Aβ42, suggesting that disturbed sleep might drive an increase in soluble brain Aβ levels prior to amyloid deposition.

Exploring the bi-directional relationship between sleep and beta-amyloid

PURPOSE OF REVIEW

Suboptimal sleep has been reported as both a comorbidity and risk factor for the development of Alzheimer's disease. Previous research suggests that beta-amyloid (Aβ) may be central to this association, with reports indicating a bi-directional relationship between sleep and Aβ. Here, we review recent animal and human studies investigating the relationship between sleep and measures of Aβ, and explore the potential mechanisms underlying this association.

RECENT FINDINGS

Two recent animal studies have provided further support for a bi-directional relationship between sleep and Aβ. In addition, five recent human studies support the notion that higher brain Aβ is linked to poor sleep in cognitively healthy individuals. One of the recent human studies utilized polysomnography to link brain Aβ to a disruption in slow wave activity during sleep, which in turn was associated with decreased hippocampal-dependent memory.

SUMMARY

Recent findings indicate that poor sleep is a risk factor for brain Aβ deposition, and Aβ deposition contributes to sleep disruption. Through the conduct of more mechanistic studies, and both longitudinal and intervention human studies, we can further elucidate the clearly complex nature of the relationship between sleep and Aβ.