Decrease in sleep depth is associated with higher cerebrospinal fluid neurofilament light levels in patients with Alzheimer's disease

Sleep abnormalities are associated with greater cognitive deficits and disease activity in Huntington's disease: a 12-year polysomnographic study

Increasing evidence suggests that the sleep pathology associated with neurodegenerative diseases can in turn exacerbate both the cognitive deficits and underlying pathobiology of these conditions. Treating sleep may therefore bear significant, even disease-modifying, potential for these conditions, but how best and when to do so remains undetermined. Huntington's disease, by virtue of being an autosomal dominant neurodegenerative disease presenting in mid-life, presents a key 'model' condition through which to advance this field. To date, however, there has been no clinical longitudinal study of sleep abnormalities in Huntington's disease and no robust interrogation of their association with disease onset, cognitive deficits and markers of disease activity. Here, we present the first such study. Huntington's disease gene carriers (n = 28) and age- and sex-matched controls (n = 21) were studied at baseline and 10- and 12-year follow-up. All Huntington's disease gene carriers were premanifest at baseline and were stratified at follow-up into 'prodromal/manifest' versus 'premanifest' groups. Objective sleep abnormalities were assessed through two-night inpatient polysomnography and 2-week domiciliary actigraphy, and their association was explored against Montreal Cognitive Assessment, Trail A/B task, Symbol Digit Modalities Task (SDMT), Hopkins Verbal Learning Task (HVLT) and Montgomery-Asberg Depression Rating Scale (MADRS) scores, plus serum neurofilament light levels. Statistical analysis incorporated cross-sectional ANOVA, longitudinal repeated measures linear models and regressions adjusted for multiple confounders including disease stage. Fifteen Huntington's disease gene carriers phenoconverted to prodromal/early manifest Huntington's disease by study completion. At follow-up, these gene carriers showed more frequent sleep stage changes (P ≤ 0.001, ηp 2 = 0.62) and higher levels of sleep maintenance insomnia (defined by wake after sleep onset, P = 0.002, ηp 2 = 0.52). The latter finding was corroborated by nocturnal motor activity patterns on follow-up actigraphy (P = 0.004, ηp 2 = 0.32). Greater sleep maintenance insomnia was associated with greater cognitive deficits (Trail A P ≤ 0.001, R 2 = 0.78; SDMT P = 0.008, R 2 = 0.63; Trail B P = 0.013, R 2 = 0.60) and higher levels of neurofilament light (P = 0.015, R 2 = 0.39). Longitudinal modelling suggested that sleep stage instability accrues from the early premanifest phase, whereas sleep maintenance insomnia emerges closer to phenoconversion. Baseline sleep stage instability was able to discriminate those who phenoconverted within the study period from those who remained premanifest (area under curve = 0.81, P = 0.024). These results demonstrate that the key sleep abnormalities of premanifest/early Huntington's disease are sleep stage instability and sleep maintenance insomnia and suggest that the former bears value in predicting disease onset, while the latter is associated with greater disease activity and cognitive deficits. Intervention studies to interrogate causation within this association could not only benefit patients with Huntington's disease but also help provide fundamental proof-of-concept findings for the wider sleep-neurodegeneration field.

Sleep spindles and slow oscillations predict cognition and biomarkers of neurodegeneration in mild to moderate Alzheimer's disease

INTRODUCTION

Changes in sleep physiology can predate cognitive symptoms by decades in persons with Alzheimer's disease (AD), but it remains unclear which sleep characteristics predict cognitive and neurodegenerative changes after AD onset.

METHODS

Using data from a prospective cohort of mild to moderate AD (n = 60), we analyzed non-rapid eye movement sleep spindles and slow oscillations (SOs) at baseline and their associations with baseline amyloid beta (Aβ) and tau and with cognition from baseline to 3-year follow-up.

RESULTS

Higher spindle and SO activity predicted significant changes in Aβ and tau at baseline, lower Alzheimer's Disease Assessment Scale Cognitive Subscale (better cognitive performance) score, and higher Mini-Mental State Examination score from baseline to 36 months. Spindles and SOs mediated the effect of phosphorylated tau 181 (pTau181)/Aβ42 on cognition, while pTau181/aβ42 moderated the effect of spindles and SOs on cognition.

DISCUSSION

Our findings demonstrate that spindle and SO activity during sleep constitute predictive and non-invasive biomarkers of neurodegeneration and cognition in AD patients.

HIGHLIGHTS

Sleep spindles predict long-term cognitive performance in AD. Sleep spindle and SOs can be predictive, non-invasive biomarkers for AD. Sleep may be one of the most important modifiable risk factors for AD progression. Sleep microarchitecture is a novel therapeutic target for preserving brain heath. Sleep physiology can provide novel therapeutic targets to slow AD progression.

Sleep structure of short-term insomnia disorder with mild cognitive impairment in older adults and their correlation with cognitive function: a case-control study

Objectives

This study seeks to delineate the sleep architecture characteristics in older adults with short-term insomnia and mild cognitive impairment (MCI) and to explore their association with cognitive performance.

Methods

Ninety elderly individuals with short-term insomnia were enrolled and stratified into two cohorts based on their Montreal Cognitive Assessment (MoCA) scores: the Short-Term Insomnia Group (STID) comprising 35 participants and the Short-Term Insomnia with Cognitive Impairment Group (STID-MCI) with 55 participants. Demographic data, Pittsburgh Sleep Quality Index (PSQI), MoCA, Hamilton Depression Rating Scale (HAMD-17), Hamilton Anxiety Rating Scale (HAMA), and polysomnography (PSG) parameters were compared between groups. Correlations between MoCA scores and PSG metrics were also analyzed.

Results

No significant disparities were noted between groups in terms of HAMD-17, HAMA, and PSQI scores (p > 0.05). However, marked differences were identified in MoCA scores and its subdomains (p < 0.05). Significant variations were also observed in the duration and proportion of slow-wave sleep (N3) between groups (p < 0.05). In STID-MCI patients, memory scores correlated positively with N3 duration and percentage (p < 0.05), while verbal functions and attention were positively associated with rapid eye movement (REM) sleep duration.

Conclusion

This study highlights the potential of PSG in the clinical assessment of cognitive function and underscores the need for targeted interventions to improve sleep quality in this vulnerable population.

Effects of obstructive sleep apnea treatment on neurodegenerative biomarker neurofilament light chain and cognitive performance

Obstructive sleep apnea is associated with cognitive impairment and increased risk for neurodegenerative diseases. Obstructive sleep apnea treatment with positive airway pressure therapy helps to improve cognitive symptoms and reduces long-term dementia risk. To test whether these treatment effects are due to a reduction in neuronal damage, we examined longitudinal changes in the neurodegenerative serum neurofilament light chain and cognitive performance of patients with obstructive sleep apnea. In this study, 17 patients with obstructive sleep apnea completed baseline and follow-up (9 month after starting PAP treatment) investigation of sleep, daytime symptoms, cognitive testing and serum neurofilament light chain measurements. Depending on treatment adherence and efficacy, participants were assigned either to the effective treatment (n = 10) or non-effective treatment group (n = 7). As results at baseline lower mean oxygen saturation during sleep was associated with higher serum neurofilament light chain. Patients in the non-effective treatment group showed a significant increase of age-adjusted percentile of serum neurofilament light chain levels at follow-up, whereas serum neurofilament light chain values remained constant in the effective treatment group. At a functional level, effective treatment leads to an improvement in processing speed, which was not the case in the non-effective treatment group. Longitudinal changes of age-adjusted serum neurofilament light chain levels were associated with changes in cognitive performance. To conclude, this longitudinal observational study showed that effective obstructive sleep apnea treatment positively affects the amount of neuronal damage as well as working memory performance. As cognitive symptoms might not only be attributed to obstructive sleep apnea-related sleep deficiency, but also neurodegeneration, our results underline the importance of treatment adherence and efficacy for the prevention of neuronal damage and cognitive consequences.

Clinical Accuracy of Serum Neurofilament Light to Differentiate Frontotemporal Dementia from Primary Psychiatric Disorders is Age-Dependent

BACKGROUND

Symptoms of behavioral variant frontotemporal dementia (bvFTD) overlap with primary psychiatric disorders (PPD) making diagnosis challenging. Serum neurofilament light (sNfL) is a candidate biomarker to distinguish bvFTD from PPD, but large-scale studies in PPD are lacking.

OBJECTIVE

Determine factors that influence sNfL from a large database of PPD patients, and test its diagnostic accuracy.

DESIGN, SETTINGS, SUBJECTS, MEASUREMENTS

Clinical data of people aged 40-81 were obtained from healthy subjects (n = 69), and patients with PPD (n = 848) or bvFTD (n = 82). sNfL was measured using Simoa technology on an HD-X instrument. Data were analyzed using general linear models, and Receiver Operating Characteristic (ROC) curve analyses to determine global and age-specific sNfL cutoffs to distinguish bvFTD from PPD, using the Youden Index.

RESULTS

sNfL increased with age, while sex, BMI and diabetes status were modestly associated with sNfL. sNfL was slightly higher in PPD than healthy subjects (14.1 versus 11.7 pg/mL), when controlling for covariates. sNfL was markedly lower in PPD than bvFTD (14.1 versus 44.1 pg/mL). sNfL could differentiate PPD from bvFTD with an AUC = 0.868, but the effect was driven by the younger subjects between age 40-60 years at a cutoff of 16.0 pg/mL. No valid cutoff was detected over age 60, however, values of sNfL above 38.5 pg/mL, or below 13.9 pg/mL, provided 90% diagnostic certainty of bvFTD or PPD, respectively.

CONCLUSION

PPD have mildly elevated sNfL compared to healthy subjects but much lower than bvFTD. Results support the use of sNfL as a biomarker to differentiate PPD from bvFTD at age 60 or below, but accuracy decreases in older ages.

Associations between Sleep Quality and Serum Levels of Neurofilament Light in Individuals with Premanifest Huntington Disease

Objectives  To evaluate the associations between sleep quality and serum levels of neurofilament light (NfL) protein in individuals with premanifest Huntington disease (HD). Materials and Methods  We recruited 28 individuals with premanifest HD from a pre-existing database (of the Huntington's Environmental Research Optimisation Scheme, HEROs). The participants filled out the Pittsburgh Sleep Quality Index (PSQI), a subjective measure of sleep quality, and blood was collected via routine venepuncture to measure peripheral NfL levels. Results  The PSQI scores (median: 5.0; interquartile range: 4.0-7.5) indicated poor sleep quality. General linear modelling revealed no significant ( p  = 0.242) association between PSQI scores and NfL levels. No significant differences were found between individuals with good and poor sleep quality for any demographic variable collected. Discussion  Contrary to studies on other neurological conditions, there was no association between sleep quality and NfL levels in individuals with premanifest HD. This was unexpected, given the influence of environmental factors (such as social network size) on neurodegeneration in individuals with premanifest HD.

Sleep disorders and Alzheimer's disease pathophysiology: The role of the Glymphatic System. A scoping review

BACKGROUND

Alzheimer's disease (AD) is highly intertwined with sleep disturbances throughout its whole natural history. Sleep consists of a major compound of the functionality of the glymphatic system, as the synchronized slow-wave activity during NREM facilitates cerebrospinal and interstitial long-distance mixing.

OBJECTIVE

The present study undertakes a scoping review of research on the involvement of the glymphatic system in AD-related sleep disturbances.

DESIGN

we searched Medline, Embase, PsychInfo and HEAL-link databases, without limitations on date and language, along with reference lists of relevant reviews and all included studies. We included in vivo, in vitro and post-mortem studies examining glymphatic implications of sleep disturbances in human populations with AD spectrum pathology. A thematic synthesis of evidence based on the extracted content was applied and presented in a narrative way.

RESULTS

In total, 70 original research articles were included and were grouped as following: a) Protein aggregation and toxicity, after sleep deprivation, along with its effects on sleep architecture, b) Glymphatic Sequalae in SDB, yielding potential glymphatic markers c) Circadian Dysregulation, d) Possible Interventions.

CONCLUSIONS

this review sought to provide insight into the role of sleep disturbances in AD pathogenesis, in the context of the glymphatic disruption.

Sleep and APOE-ε4 have a synergistic effect on plasma biomarkers and longitudinal cognitive decline in older adults

BACKGROUND

Sleep disorders are prevalent among patients with Alzheimer's disease (AD), and the APOE ε4 genotype is a key genetic risk factor for sporadic AD. However, the combined effect of the genotype and sleep disorders on cognitive decline remains uncertain.

METHODS

A total of 972 participants were drawn from the SILCODE cohort, comprising 655 without the ε4 allele (APOE-) and 317 with ε4 allele (APOE+). Data were collected, including neuropsychological assessments, sleep measurements, plasma biomarkers, and PET imaging. A Sleep Composite Index (SCI) was created, categorizing participants into high risk (Sleep+) and low risk (Sleep-).

RESULTS

Significant predictions of dementia risk associated with plasma p-tau181, neurofilament light chain (NfL), and SCI. Individuals with both Sleep+ and APOE+ had a higher risk of dementia compared to those with Sleep-. The Sleep+/APOE+ group had higher plasma NfL levels than the Sleep-/APOE- group. Similar trends emerged in plasma NfL levels among the Aβ PET-positive subgroup. Plasma NfL levels explained 23% of the relationship between SCI and cognitive impairment.

CONCLUSION

Our study highlights sleep disorder was associated with cognitive decline, with plasma NfL playing a partial mediating role. These findings explain how sleep disorders affect cognitive function and emphasize the importance of healthy sleep for older adults.

Predicting neurodegeneration from sleep related biofluid changes

Sleep-wake disturbances are common in neurodegenerative diseases and may occur years before the clinical diagnosis, potentially either representing an early stage of the disease itself or acting as a pathophysiological driver. Therefore, discovering biomarkers that identify individuals with sleep-wake disturbances who are at risk of developing neurodegenerative diseases will allow early diagnosis and intervention. Given the association between sleep and neurodegeneration, the most frequently analyzed fluid biomarkers in people with sleep-wake disturbances to date include those directly associated with neurodegeneration itself, such as neurofilament light chain, phosphorylated tau, amyloid-beta and alpha-synuclein. Abnormalities in these biomarkers in patients with sleep-wake disturbances are considered as evidence of an underlying neurodegenerative process. Levels of hormonal sleep-related biomarkers such as melatonin, cortisol and orexin are often abnormal in patients with clinical neurodegenerative diseases, but their relationships with the more standard neurodegenerative biomarkers remain unclear. Similarly, it is unclear whether other chronobiological/circadian biomarkers, such as disrupted clock gene expression, are causal factors or a consequence of neurodegeneration. Current data would suggest that a combination of fluid biomarkers may identify sleep-wake disturbances that are most predictive for the risk of developing neurodegenerative disease with more optimal sensitivity and specificity.

Shedding light on neurofilament involvement in cognitive decline in obstructive sleep apnea and its possible role as a biomarker

Obstructive sleep apnea is one of the most common sleep disorders with a high estimated global prevalence and a large number of associated comorbidities in general as well as specific neuropsychiatric complications such as cognitive impairment. The complex pathogenesis and effects of the disorder including chronic intermittent hypoxia and sleep fragmentation may lead to enhanced neuronal damage, thereby contributing to neuropsychiatric pathologies. Obstructive sleep apnea has been described as an independent risk factor for several neurodegenerative diseases, including Alzheimer's disease and all-cause dementia. The influence of obstructive sleep apnea on cognitive deficits is still a topic of recent debate, and several mechanisms, including neurodegeneration and depression-related cognitive dysfunction, underlying this correlation are taken into consideration. The differentiation between both pathomechanisms of cognitive impairment in obstructive sleep apnea is a complex clinical issue, requiring the use of multiple and costly diagnostic methods. The studies conducted on neuroprotection biomarkers, such as brain-derived neurotrophic factors and neurofilaments, are recently gaining ground in the topic of cognition assessment in obstructive sleep apnea patients. Neurofilaments as neuron-specific cytoskeletal proteins could be useful non-invasive indicators of brain conditions and neurodegeneration, which already are observed in many neurological diseases leading to cognitive deficits. Additionally, neurofilaments play an important role as a biomarker in other sleep disorders such as insomnia. Thus, this review summarizes the current knowledge on the involvement of neurofilaments in cognitive decline and neurodegeneration in obstructive sleep apnea patients as well as discusses its possible role as a biomarker of these changes.

Understanding the Episodic Memory and Executive Functioning Axis Impairment in MCI Patients: A Multicenter Study in Comparison with CSF Biomarkers

BACKGROUND

This study aimed to explore the association between a verbal learning task that evaluates the potential mutual dependency between memory and executive functions (i.e., the Test of Memory Strategies, TMS) and cerebrospinal fluid (CSF) Alzheimer's Disease (AD) biomarkers.

METHODS

A sample of 47 mild cognitive impairment (MCI) participants from Poland and Spain were classified according to the Erlangen Score Diagnostic Algorithm (ESA) into CSF- (n = 16) and CSF+ (n = 31) groups. Correlation analyses between TMS word-list conditions and CSF biomarkers were conducted. Additionally, an analysis of covariance was performed to define the effect on ESA classification in the sample, using as a covariable the country of origin of the participants.

RESULTS

Significant associations between the TMS-3 condition and Aβ42, t-tau, and p-tau were observed for the whole sample. In addition, the CSF- participants obtained higher cognitive performance in TMS-3 compared to the CSF+ group. This outcome persisted if the groups were based on Aβ42 scores, but not t-tau or p-tau values.

CONCLUSIONS

These findings could indicate that poor performance on verbal learning tests may be affected by executive dysfunctions. Therefore, future intervention plans focused on training executive functions would be of interest to improve the ability of MCI patients to encode and organize information.

Association between serum neurofilament light chain levels and sleep disorders in patients with Parkinson's disease

OBJECTIVES

This study aimed to investigate the levels of serum neurofilament light chain (NFL) and glial fibrillary acidic protein (GFAP) in patients with Parkinson's disease (PD) and PD patients with sleep disorders (PD-SD), as well as the relationship between these proteins and sleep disorders in PD patients.

METHODS

A total of 96 PD patients and 38 healthy controls (HC) were included in this study, of which 70 PD patients experienced sleep disorders. Both motor symptoms and sleep conditions were assessed in all PD patients. The ultrasensitive single molecule array (SIMOA) technique was used to quantify NFL and GFAP in the serum. All data were statistically analyzed using SPSS 23.0.

RESULTS

Serum NFL and GFAP levels were significantly higher in PD patients than in HC. Similarly, PD-SD patients exhibited higher levels of these two proteins than PD patients without sleep disorders (PD-NSD). In addition, both serum GFAP and NFL were significantly associated with sleep-related scales in PD patients. After covariate-adjusted binary logistic regression analysis, NFL remained statistically significant in PD patients with or without sleep disorders, unlike GFAP.

CONCLUSIONS

Our findings substantiate that serum NFL and GFAP levels are elevated in PD and PD-SD, suggesting neurological axon damage in PD patients, which may be more severe in PD-SD than in PD-NSD. These findings may affect disease diagnosis and provide the foothold for future studies on the underlying mechanisms.

Breathing cessation events that compose the apnea-hypopnea index are distinctively associated with the adverse outcomes in Alzheimer's disease

BACKGROUND

Previous studies challenge the impact of obstructive sleep apnea (OSA) once patients are diagnosed with Alzheimer's disease (AD). Nevertheless, OSA recognizably disrupts sleep, and relevant associations between sleep, AD pathological markers, and cognition have been demonstrated. We aimed to further explore this, evaluating the associations between each breathing cessation event that compose the apnea-hypopnea index (AHI) and the sleep structure to finally investigate whether this was related to increased levels of AD markers and higher cognitive decline.

METHODS

Observational, prospective study, including consecutive patients diagnosed with mild-moderate AD. The participants were submitted to overnight polysomnography followed by a cerebrospinal fluid collection for AD pathological markers levels determination. Neuropsychological assessment was performed at baseline and after 12 months of follow-up.

RESULTS

The cohort was composed of 116 patients (55.2% females) with a median [p25;p75] age of 76.0 [72.0;80.0] years and an AHI of 25.9 [15.1;48.5], which was mainly defined by the presence of hypopneas and obstructive apneas. These were distinctively associated with the sleep structure, with obstructive apneas being related to arousals and sleep lightening and hypopneas being related to an increased number of arousals only. Despite having a lower frequency, mixed and central apneas also presented associations with the sleep structure, particularly increasing the time spent in the lighter sleep stages. In relation to AD pathological markers, obstructive and mixed apneas were related to an augment in neurofilament light levels while hypopneas were associated with a higher phosphorylated-tau/amyloid-beta protein ratio. Hypopneas were the most important event for an increased cognitive decline at the 12-month follow-up.

CONCLUSIONS

Our findings highlight the importance of a patient-centered approach, with a comprehensive and detailed analysis of the AHI to effectively predict the different outcomes and tailor the appropriate therapeutic strategies.

Disentangling the impact of cerebrospinal fluid formation and neuronal activity on solute clearance from the brain

BACKGROUND

Despite recent attention, pathways and mechanisms of fluid transposition in the brain are still a matter of intense discussion and driving forces underlying waste clearance in the brain remain elusive. Consensus exists that net solute transport is a prerequisite for efficient clearance. The individual impact of neuronal activity and cerebrospinal fluid (CSF) formation, which both vary with brain state and anesthesia, remain unclear.

METHODS

To separate conditions with high and low neuronal activity and high and low CSF formation, different anesthetic regimens in naive rat were established, using Isoflurane (ISO), Medetomidine (MED), acetazolamide or combinations thereof. With dynamic contrast-enhanced MRI, after application of low molecular weight contrast agent (CA) Gadobutrol to cisterna magna, tracer distribution was monitored as surrogate for solute clearance. Simultaneous fiber-based Ca²⁺-recordings informed about the state of neuronal activity under different anesthetic regimen. T2-weighted MRI and diffusion-weighted MRI (DWI) provided size of subarachnoidal space and aqueductal flow as surrogates for CSF formation. Finally, a pathway and mechanism-independent two-compartment model was introduced to provide a measure of efficiency for solute clearance from the brain.

RESULTS

Anatomical imaging, DWI and Ca²⁺-recordings confirmed that conditions with distinct levels of neuronal activity and CSF formation were achieved. A sleep-resembling condition, with reduced neuronal activity and enhanced CSF formation was achieved using ISO+MED and an awake-like condition with high neuronal activity using MED alone. CA distribution in the brain correlated with the rate of CSF formation. The cortical brain state had major influence on tracer diffusion. Under conditions with low neuronal activity, higher diffusivity suggested enlargement of extracellular space, facilitating a deeper permeation of solutes into brain parenchyma. Under conditions with high neuronal activity, diffusion of solutes into parenchyma was hindered and clearance along paravascular pathways facilitated. Exclusively based on the measured time signal curves, the two-compartment model provided net exchange ratios, which were significantly larger for the sleep-resembling condition than for the awake-like condition.

CONCLUSIONS

Efficiency of solute clearance in brain changes with alterations in both state of neuronal activity and CSF formation. Our clearance pathway and mechanism agnostic kinetic model informs about net solute transport, solely based on the measured time signal curves. This rather simplifying approach largely accords with preclinical and clinical findings.

Plasma neurodegeneration biomarker concentrations associate with glymphatic and meningeal lymphatic measures in neurological disorders

Clearance of neurotoxic brain proteins via cerebrospinal fluid (CSF) to blood has recently emerged to be crucial, and plasma biomarkers of neurodegeneration were newly introduced to predict neurological disease. This study examines in 106 individuals with neurological disorders associations between plasma biomarkers [40 and 42 amino acid-long amyloid-β (Aβ40 and Aβ42), total-tau, glial fibrillary acidic protein (GFAP), and neurofilament light (NfL)] and magnetic resonance imaging measures of CSF-mediated clearance from brain via extra-vascular pathways (proxy of glymphatic function) and CSF-to-blood clearance variables from pharmacokinetic modeling (proxy of meningeal lymphatic egress). We also examine how biomarkers vary during daytime and associate with subjective sleep quality. Plasma concentrations of neurodegeneration markers associate with indices of glymphatic and meningeal lymphatic functions in individual- and disease-specific manners, vary during daytime, but are unaffected by sleep quality. The results suggest that plasma concentrations of neurodegeneration biomarkers associate with measures of glymphatic and meningeal lymphatic function.

Cerebrospinal fluid neurofilament dynamic profiles predict cognitive progression in individuals with de novo Parkinson's disease

Background

Neurofilament light chain protein (NfL) in cerebrospinal fluid (CSF) reflects the severity of neurodegeneration, with its altered concentrations discovered in Parkinson's disease (PD) and Parkinson's disease dementia (PD-D).

Objective

To determine whether CSF NfL, a promising biomarker of neuronal/axonal damage, can be used to monitor cognitive progression in de novo Parkinson's disease and predict future cognitive decline.

Methods

A total of 259 people were recruited in this study, including 85 healthy controls (HC) and 174 neonatal PD patients from the Parkinson's Progression Markers Initiative (PPMI). Multiple linear regression and linear mixed effects models were used to examine the associations of baseline/longitudinal CSF NfL with cognitive decline and other CSF biomarkers. Kaplan-Meier analysis and log-rank test were used to compare the cumulative probability risk of cognition progression during the follow-up. Multivariate cox regression was used to detect cognitive progression in de novo PD.

Results

We found PD patients with mild cognitive impairment (PD-MCI) was higher than with normal cognition (PD-NC) in terms of CSF NfL baseline levels (p = 0.003) and longitudinal increase rate (p = 0.034). Both baseline CSF NfL and its rate of change predicted measurable cognitive decline in de novo PD (MoCA, β = -0.010, p = 0.011; β = -0.0002, p < 0.001, respectively). The predictive effects in de novo PD patients aged >65, male, ill-educated (<13 years) and without carrying Apolipoprotein E ε4 (APOE ε4) seemed to be more obvious and reflected in more domains investigated. We also observed that CSF NfL levels predicted progression in de novo PD patients with different cognitive diagnosis and amyloid status. After an average follow-up of 6.66 ± 2.54 years, higher concentration above the median of baseline CSF NfL was associated with a future high risk of PD with dementia (adjusted HR 2.82, 95% CI: 1.11-7.20, p = 0.030).

Conclusion

Our results indicated that CSF NfL is a promising prognostic predictor of PD, and its concentration and dynamics can monitor the severity and progression of cognitive decline in de novo PD patients.

BDNF and proBDNF Serum Protein Levels in Obstructive Sleep Apnea Patients and Their Involvement in Insomnia and Depression Symptoms

Introduction: Obstructive sleep apnea (OSA) is a disorder that, apart from somatic sequelae, increases the risk of developing psychiatric conditions. Brain-derived neurotrophic factor (BDNF) signaling pathway is involved in the pathophysiology of depression and insomnia. Therefore, the study aimed to investigate differences in concentrations of BDNF and proBDNF in patients with OSA and healthy individuals, to evaluate diurnal changes of these proteins, and to assess the correlations with psychiatric symptoms. Methods: Sixty individuals following polysomnography (PSG) were divided into two groups based on the apnea-hypopnea index (AHI): OSA patients (AHI ≥ 30; n = 30) and control group (AHI < 5; n = 30). Participants filled out questionnaires: Beck Depression Inventory (BDI), Athens Insomnia Scale (AIS), and Pittsburgh Sleep Quality Index (PSQI). Peripheral blood was collected before and after PSG. Protein concentrations were measured using ELISA. OSA group was divided into subgroups: AIS (−)/AIS (+) (AIS > 5), PSQI (−)/PSQI (+) (PSQI > 5), and BDI (−)/BDI (+) (BDI > 19). Results: No differences in BDNF and proBDNF protein levels were observed between OSA and the control groups. However, BDNF and proBDNF evening protein concentrations were higher in the AIS (+) and PSQI (+) groups (p < 0.001 for all). The BDI (+) group was characterized by lower morning levels of both proteins (p = 0.047 and p = 0.003, respectively). Conclusions: BDNF signaling pathway might be involved in the pathophysiology of depression and insomnia in patients with OSA. BDNF and proBDNF protein levels might be useful in defining OSA phenotypes.

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.

Advances in brain barriers and brain fluids research in 2021: great progress in a time of adversity

This editorial highlights advances in brain barrier and brain fluid research in 2021. It covers research on components of the blood–brain barrier, neurovascular unit and brain fluid systems; how brain barriers and brain fluid systems are impacted by neurological disorders and their role in disease progression; and advances in strategies for treating such disorders.

The evaluation of serum brain-derived neurotrophic factor and neurofilament light chain levels in patients with obstructive sleep apnea syndrome

OBJECTIVES

This study aimed to compare serum levels of brain-derived neurotrophic factor (BDNF) and neurofilament light (NfL) chain in normal individuals and patients with mild and moderate-severe obstructive sleep apnea syndrome (OSAS).

METHODS

We enrolled 81 subjects referred to Otorhinolaryngology (Ear-Nose-Throat), Gazi University Faculty of Medicine, between 2017 and 2019. Based on the severity of OSAS, patients were divided into three groups: group 1 with mild OSAS (apnea-hypopnea index [AHI] 5-15; n = 26), group 2 with moderate-severe OSAS (AHI > 15; n = 32), and group 3 with normal individuals (AHI scores < 5; n = 23).

RESULTS

Serum NfL and BDNF levels were evaluated together with the clinical data for all subjects. Significant differences were seen in the oxygen desaturation index (ODI), apnea index, hypopnea index, sleep efficiency, and NfL levels (P < .05) between the three groups. In the moderate-severe group, NfL levels showed a significant positive correlation with apnea index (P < .05, r = .389), hypopnea index (P < .05, r = .455), and ODI (P = .04; r = .362).

CONCLUSIONS

Our findings clarify the pathophysiology of OSAS in cases of repetitive hypoxia and chronic neuronal damage. Based on our results, we recommend that in addition to BDNF, NfL should also be evaluated in different and larger patient cohorts.

Older Adults' Subjective Cognitive Decline Correlated with Subjective but Not Objective Sleep: A Mediator Role of Depression

This study examined the relationship between older adults' subjective versus objective sleep and subjective cognitive decline (SCD), and explored the role of depression on this association. One hundred and four community-dwelling older adults underwent a week of actigraphic sleep monitoring, and completed a series of neuropsychological screeners. Older adults'SCD score was positively correlated with subjective insomnia, but not with objective sleep parameters. Further mediation modeling revealed that older adults'depression mediated the association between subjective insomnia and SCD. Subjective sleep, rather than objective sleep, may be a more sensitive indicator for older adults' SCD, with depression symptoms appearing to account for most of the variance. These findings extend our perspective on the relationship between sleep disruption and cognitive decline, and highlight the necessity of early targeted interventions on sleep to reduce the risk of cognitive impairment in the elderly with SCD.

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.