The missing link between sleep disorders and age-related dementia: recent evidence and plausible mechanisms

Chronic Sleep Disturbances Alters Sleep Structure and Tau Phosphorylation in AβPP/PS1 AD Mice and Their Wild-Type Littermates

Background: Emerging evidence indicates that sleep disorders are the common non-cognitive symptoms of Alzheimer’s disease (AD), and they may contribute to the pathogenesis of this disease. Objective: In this study, we aim to investigate the effect of chronic sleep deprivation (CSD) on AD-related pathologies with a focus on tau phosphorylation and the underlying DNA methylation regulation. Methods: AβPPswe/PS1ΔE9 AD mice and their wild-type (WT) littermates were subjected to a two-month CSD followed by electroencephalography and electromyography recording. The mice were examined for learning and memory evaluation, then pathological, biochemical, and epigenetic assessments including western blotting, immunofluorescence, dot blotting, and bisulfite sequencing. Results: The results show that CSD caused sleep disorders shown as sleep pattern change, poor sleep maintenance, and increased sleep fragmentation. CSD increased tau phosphorylation at different sites and increased the level of tau kinases in AD and WT mice. The increased expression of cyclin-dependent kinase 5 (CDK5) may result from decreased DNA methylation of CpG sites in the promoter region of CDK5 gene, which might be associated with the downregulation of DNA methyltransferase 3A and 3B. Conclusion: CSD altered AD-related tau phosphorylation through epigenetic modification of tau kinase gene. The findings in this study may give insights into the mechanisms underlying the effects of sleep disorders on AD pathology and provide new therapeutic targets for the treatment of this disease.

Brain Photobiomodulation Improves Sleep Quality in Subjective Cognitive Decline: A Randomized, Sham-Controlled Study

Background: Sleep appears to be a sensitive biomarker that facilitates early detection and effective intervention for Alzheimer’s disease, while subjective cognitive decline (SCD) is a risk factor for Alzheimer’s disease. Prefrontal cortex atrophy is associated with both sleep disruption and cognitive decline. Transcranial brain photobiomodulation (PBM) therapy can enhance frontal cortex oxygen consumption, increasing frontal cortex mediated memory function. Objective: This study aimed to test whether PBM therapy targeting the frontal cortex could improve sleep and cognitive function in SCD. Methods: Fifty-eight SCDs were divided into the PBM group (N = 32) in which real light therapy was administered and a sham light therapy group (N = 26). All the participants received either real light or sham light therapy for 6 days consecutively, while the sleep data were recorded. The n-back task was employed to measure each participant’s working memory. Results: We found no differences in sleep efficiency change (F = 211, p = 0.279), REM stage percent change (F = 420, p = 0.91), and wake-up time (F = 212, p = 0.277) between the two groups. The sleep efficiency and REM were improved within the true light group on the fifth day. The true light group perform better than the control group in the n-back test, the accuracy was higher in the 2-back test (88.6% versus 79.6%, p = 0.001), and the reaction time in 1-back was shorter (544.80±202.00 versus 592.87±222.05, p = 0.003). Conclusion: After five days of PBM therapy targeting the prefrontal cortex, sleep efficiency and N-back cognitive performance were improved on the fifth day.

Sleep deprivation impairs cognitive performance, alters task-associated cerebral blood flow and decreases cortical neurovascular coupling-related hemodynamic responses

Sleep deprivation (SD) is a common condition and an important health concern. In addition to metabolic and cardiovascular risks, SD associates with decreases in cognitive performance. Neurovascular coupling (NVC, "functional hyperemia") is a critical homeostatic mechanism, which maintains adequate blood supply to the brain during periods of intensive neuronal activity. To determine whether SD alters NVC responses and cognitive performance, cognitive and hemodynamic NVC assessments were conducted prior to and 24 h post-SD in healthy young male individuals (n = 10, 27 ± 3 years old). Cognition was evaluated with a battery of tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB). Hemodynamic components of NVC were measured by transcranial Doppler sonography (TCD) during cognitive stimulation, dynamic retinal vessel analysis (DVA) during flicker light stimulation, and functional near infrared spectroscopy (fNIRS) during finger tapping motor task. Cognitive assessments revealed impairments in reaction time and sustained attention after 24 h of SD. Functional NIRS analysis revealed that SD significantly altered hemodynamic responses in the prefrontal cortex and somatosensory cortex during a motor task. NVC-related vascular responses measured by DVA and TCD did not change significantly. Interestingly, TCD detected decreased task-associated cerebral blood flow (CBF) in the right middle cerebral artery in sleep deprived participants. Our results demonstrate that 24 h of SD lead to impairments in cognitive performance together with altered CBF and hemodynamic components of cortical NVC responses.

New therapeutics beyond amyloid-β and tau for the treatment of Alzheimer's disease

As the population ages, Alzheimer's disease (AD), the most common neurodegenerative disease in elderly people, will impose social and economic burdens to the world. Currently approved drugs for the treatment of AD including cholinesterase inhibitors (donepezil, rivastigmine, and galantamine) and an N-methyl-D-aspartic acid receptor antagonist (memantine) are symptomatic but poorly affect the progression of the disease. In recent decades, the concept of amyloid-β (Aβ) cascade and tau hyperphosphorylation leading to AD has dominated AD drug development. However, pharmacotherapies targeting Aβ and tau have limited success. It is generally believed that AD is caused by multiple pathological processes resulting from Aβ abnormality, tau phosphorylation, neuroinflammation, neurotransmitter dysregulation, and oxidative stress. In this review we updated the recent development of new therapeutics that regulate neurotransmitters, inflammation, lipid metabolism, autophagy, microbiota, circadian rhythm, and disease-modified genes for AD in preclinical research and clinical trials. It is to emphasize the importance of early diagnosis and multiple-target intervention, which may provide a promising outcome for AD treatment.

Non-benzodiazepine hypnotic use for sleep disturbance in people aged over 55 years living with dementia: a series of cohort studies

BACKGROUND

Sleep disturbance affects around 60% of people living with dementia and can negatively affect their quality of life and that of their carers. Hypnotic Z-drugs (zolpidem, zopiclone and zaleplon) are commonly used to treat insomnia, but their safety and efficacy have not been evaluated for people living with dementia.

OBJECTIVES

To estimate the benefits and harms of Z-drugs in people living with dementia with sleep disturbance.

DESIGN

A series of observational cohort studies using existing data from (1) primary care linked to hospital admission data and (2) clinical cohort studies of people living with dementia.

DATA SOURCES

Primary care study - Clinical Practice Research Datalink linked to Hospital Episode Statistics and Office for National Statistics mortality data. Clinical cohort studies - the Resource Use and Disease Course in Dementia - Nursing Homes (REDIC) study, National Alzheimer's Coordinating Centre (NACC) clinical data set and the Improving Well-being and Health for People with Dementia (WHELD) in nursing homes randomised controlled trial.

SETTING

Primary care study - 371 primary care practices in England. Clinical cohort studies - 47 nursing homes in Norway, 34 Alzheimer's disease centres in the USA and 69 care homes in England.

PARTICIPANTS

Primary care study - NHS England primary care patients diagnosed with dementia and aged > 55 years, with sleep disturbance or prescribed Z-drugs or low-dose tricyclic antidepressants, followed over 2 years. Clinical cohort studies - people living with dementia consenting to participate, followed over 3 years, 12 years and 9 months, for REDIC, NACC and WHELD, respectively.

INTERVENTIONS

The primary exposure was prescription or use of Z-drugs. Secondary exposures included prescription or use of benzodiazepines, low-dose tricyclic antidepressants and antipsychotics.

MAIN OUTCOME MEASURES

Falls, fractures, infection, stroke, venous thromboembolism, mortality, cognitive function and quality of life. There were insufficient data to investigate sleep disturbance.

RESULTS

The primary care study and combined clinical cohort studies included 6809 and 18,659 people living with dementia, with 3089 and 914 taking Z-drugs, respectively. New Z-drug use was associated with a greater risk of fractures (hazard ratio 1.40, 95% confidence interval 1.01 to 1.94), with risk increasing with greater cumulative dose (p = 0.002). The hazard ratio for Z-drug use and hip fracture was 1.59 (95% confidence interval 1.00 to 2.53) and for mortality was 1.34 (95% confidence interval 1.10 to 1.64). No excess risks of falls, infections, stroke or venous thromboembolism were detected. Z-drug use also did not have an impact on cognition, neuropsychiatric symptoms, disability or quality of life.

LIMITATIONS

Primary care study - possible residual confounding because of difficulties in identifying patients with sleep disturbance and by dementia severity. Clinical cohort studies - the small numbers of people living with dementia taking Z-drugs and outcomes not necessarily being measured before Z-drug initiation restricted analyses.

CONCLUSIONS

We observed a dose-dependent increase in fracture risk, but no other harms, with Z-drug use in dementia. However, multiple outcomes were examined, increasing the risk of false-positive findings. The mortality association was unlikely to be causal. Further research is needed to confirm the increased fracture risk. Decisions to prescribe Z-drugs may need to consider the risk of fractures, balanced against the impact of improved sleep for people living with dementia and that of their carers. Our findings suggest that when Z-drugs are prescribed, falls prevention strategies may be needed, and that the prescription should be regularly reviewed.

FUTURE WORK

More research is needed on safe and effective management strategies for sleep disturbance in people living with dementia.

STUDY REGISTRATION

This study is registered as European Union electronic Register of Post-Authorisation Studies (EU PAS) 18006.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 25, No. 1. See the NIHR Journals Library website for further project information.

Characteristics of Sleep Structure Assessed by Objective Measurements in Patients With Amnestic Mild Cognitive Impairment: A Meta-Analysis

Objectives: This study aims to explore the differences of sleep structure between patients with amnestic mild cognitive impairment (aMCI) and elderly people with normal cognition, which will help to provide evidence for the relationship between sleep disturbances and cognitive impairment.

Methods: A systematic review and meta-analysis were conducted on the literature on sleep parameters obtained by polysomnography or actigraphy in patients with aMCI. The PubMed and EMBASE databases were searched up to April 2020. Inclusion and exclusion criteria were established according to evidence-based medicine methods, and data of all eligible studies were meta-analyzed using the Review Manager 5.3 software.

Results: Among the 1,171 literature articles on sleep structure of patients with MCI, eight case-control studies met the inclusion criteria and were included in this meta-analysis. A total of 278 subjects were included, of which 103 were patients with aMCI and 175 were elderly people with normal cognition. The results showed that sleep efficiency (SE) and slow wave sleep (SWS) of patients with aMCI were significantly lower than those of healthy elderly people. Compared with the control group, the percentage of stage 1 of non-rapid eye movement (N1%) in the aMCI patients group increased, and the percentage of stage 2 of non-rapid eye movement (N2%) decreased.

Conclusions: Patients with aMCI may experience more severe sleep disturbances than normal cognitive elderly people. There were specific changes, especially in SE and SWS, in the sleep structure of patients with aMCI when compared to those with normal cognition.

Treadmill exercise ameliorates chronic REM sleep deprivation-induced anxiety-like behavior and cognitive impairment in C57BL/6J mice

Various sleep disorders have deleterious effects on mental and cognitive performance. Exercise, as an alternative therapeutic strategy, exerts beneficial impacts on human health. In the present study, we aimed to evaluate the effects of 4 weeks treadmill exercise (4W-TE) on anxiety-like behavior and cognitive performance in mice exposed to 2 months REM sleep deprivation (2M-SD) (20 h per day). Behavioral performance of mice in elevated plus maze test (EPM), open field test (OFT), Y maze test (YM) and Morris water maze test (MWM) was recorded and analyzed 28 h after the last day of sleep deprivation. After behavioral tests, various neurotransmitters including norepinephrine (NE), dopamine (DA), serotonin (5-HT) and γ-aminobutyric acid (GABA) in mouse hippocampus were quantified using high performance liquid chromatography. The hippocampal levels of insulin-like growth factor-1 (IGF-1) and brain derived neurotrophic factor (BDNF) were further detected using ELISA. Behavioral data indicated that 2M-SD exposure induced anxiety-like behaviors and cognitive impairment, as evidenced by the decreased open-arm entries in EPM, reduced central area travels in OFT, declined spontaneous alteration in YM and prolonged escaping latency in MWM. In addition, 2M-SD exposure increased NE and DA, decreased 5-HT and GABA, and reduced IGF-1 and BDNF levels in mouse hippocampus. Interestingly, all these behavioral, neurochemical and neurobiological changes can be ameliorated by 4W-TE training. In summary, these findings confirm the beneficial impacts of exercise on health and provide further experimental evidence for future application of exercise as an alternative therapy against the mental and cognitive problems in patients with sleep disorders.

Rapid Eye Movement Sleep Behavior Disorder and Neurodegenerative Diseases: An Update

Rapid eye movement sleep behavior disorder (RBD) is a sleep behavior disorder characterized by abnormal behaviors and loss of muscle atonia during rapid eye movement (REM) sleep. RBD is generally considered to be associated with synucleinopathies, such as Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), and usually precedes years before the first symptom of these diseases. It is believed that RBD predicts the neurodegeneration in synucleinopathy. However, increasing evidences have shown that RBD is also found in non-synucleinopathy neurodegenerative diseases, including Alzheimer’s disease (AD), Huntington’s disease (HD), amyotrophic lateral sclerosis (ALS), etc. Sleep disturbance such as RBD may be an early sign of neurodegeneration in these diseases, and also serve as an assessment of cognitive impairments. In this review, we updated the clinical characteristics, diagnosis, and possible mechanisms of RBD in neurogenerative diseases. A better understanding of RBD in these neurogenerative diseases will provide biomarkers and novel therapeutics for the early diagnosis and treatment of the diseases.

Therapeutic Approaches for the Management of Sleep Disorders in Geriatric Population

OBJECTIVE

Aging is a natural biological phenomenon that occurs in human beings. With increasing of age, there is an appearance of deleterious changes related to progression onto pathological conditions, including hypertension, heart disease, diabetes, hearing and vision impairments, as well as sleep disorders. It is important to recognize that some sleep disturbances reported by aged subjects include insomnia, obstructive sleep apnea, restless legs syndrome, among others. Moreover, accumulating evidence indicates that coexistence of medical issues with sleep disorders constitutes clinical challenges for treatment of comorbidities in elderly. Here, we have attempted to review and summarize the available literature that assesses the sleep disturbances in aging. In addition, we highlight the management of sleep disorders associated with aging. Due to the particular health condition of aged adults, the development of effective pharmacological interventions for sleep disorders treatment in aging is warranted.

METHODS

Review of studies retrieved from the PubMed.

RESULTS

The sleep-wake cycle includes abnormalities classified as sleep disorders. Comorbidity between sleep disturbances and aging-related health issues will represent a public health challenge to be addressed in the near future. Moreover, this scenario will suggest an area that requires further drug investigation and design of new pharmacological and pharmaceutical strategies to treat sleep disorders in the elderly population.

CONCLUSION

The review highlights the sleep disturbances in aging. We focus on current knowledge in medicinal chemistry and further design of new treatments tools for managing sleep disturbances in the aged population.

Alteration in sleep architecture and electroencephalogram as an early sign of Alzheimer's disease preceding the disease pathology and cognitive decline

OBJECTIVE

The present work aims to evaluate the significance of sleep disturbance and electroencephalogram (EEG) alteration in the early stage of Alzheimer's disease (AD).

BACKGROUND AND RATIONALE

Sleep disturbance is common in patients with AD. It is not known if it can occur at the early stage of AD and if EEG recording may help identify the early sign of the disease.

HISTORICAL EVOLUTION

Sleep disturbance in AD has generally been considered as late consequence of the neurodegenerative process. A growing body of evidence has suggested that the sleep disturbance may occur at the early stage of AD.

UPDATED HYPOTHESIS

Based on the previous epidemiologic studies and our recent findings, we propose that sleep disturbance may play an important role in the development of AD. Sleep EEG changes may serve as a valuable early sign for AD in the prepathological stage.

EARLY EXPERIMENTAL DATA

Our data suggested that AβPP^swe/PS1^ΔE9 transgenic AD mice at preplaque stage (3 and 4 months of age) exhibited different profile of sleep architecture and sleep EEG, which preceded the cognitive deficit and AD neuropathology.

FUTURE EXPERIMENTS AND VALIDATION STUDIES

Future experiments should focus on sleep EEG changes in patients with mild cognitive impairment and early stage of AD. Follow-up studies in high-risk population of the elderly are equally important. In addition, the exact molecular mechanism underlying the sleep disturbance should be thoroughly investigated.

MAJOR CHALLENGES FOR THE HYPOTHESIS

Studies on human participants with early stage of AD, especially the follow-up studies on the presymptomatic elderly in a large population, are difficult and time-consuming.

LINKAGE TO OTHER MAJOR THEORIES

Our hypothesis may link previous theories to establish a bidirectional relationship between sleep disorders and AD, which may finally form a new schematic mechanism to understand the disease pathogenesis and disease progression.

Advancing Research on Care Needs and Supportive Approaches for Persons With Dementia: Recommendations and Rationale

The first National Research Summit on Care, Services, and Supports for Persons with Dementia and Their Caregivers was held on October 16-17, 2017, at the National Institutes of Health. In this paper, participants from the Summit Session on Research on Care Needs and Supportive Approaches for Persons with Dementia summarize the state of the science, identify gaps in knowledge, and offer recommendations to improve science and practice in long-term care. Recommendations cover 4 areas focused on persons living with dementia: (1) symptoms (behavioral and psychological symptoms of dementia, function, cognition, and sleep); (2) dementia care settings (physical and social environments, home, and residential care); (3) living with dementia (living well with dementia, living alone with dementia, and living with dementia and intellectual and developmental disabilities); and (4) technology as a cross-cutting theme. The participants identify 10 of the most pressing research issues based on the findings from their collective papers. Final Summit recommendations included those presented by session participants and will be used to advise federal agencies and other organizations that fund research.

Non-amnestic mild cognitive impairment and sleep complaints: a bidirectional relationship?

BACKGROUND

Prior studies documented that several sleep disorders may coexist in patients affected by Mild Cognitive Impairment (MCI) and Alzheimer disease (AD), and have a strong bidirectional relationship with cognitive decline.

AIM

To assess the self-reported sleep quality and daytime sleepiness among subjects affected by MCI and AD at early-stage and healthy controls, and to verify if sleep disturbances might be an indicator of specific cognitive deficits.

METHODS

139 patients (102 MCI, 37 AD) underwent comprehensive neuropsychological, functional, and behavioral assessment, which also included Epworth Sleepiness Scale (ESS) and Pittsburgh Sleep Quality Index (PSQI). 80 healthy elderly subjects were used as controls. MCI patients have been divided into Good Sleepers and Bad Sleepers, depending on their reported sleep quality (PSQI global score ≤5/>5).

RESULTS

MCI patients experienced more subjective daytime sleepiness than AD matches. As for the subjective sleep quality among MCI patients, 54% of Bad Sleepers met diagnostic criteria for non-amnestic MCI; vice-versa, 73% of Good Sleepers were diagnosed with amnestic-MCI (p = 0.005), independently of depression and anxiety.

CONCLUSIONS

MCI patients complain of daytime sleepiness and dysfunction more than AD patients; among MCI patients, Bad Sleepers appear mainly characterized by a non-amnestic cognitive profile.