Exploration of plasma biomarkers of neurodegeneration in OSA-related MCI
Exploratory groupwise comparisons between the two groups revealed that participants with OSA exhibited significantly elevated plasma levels of NfL in the MCI group compared to the NC group (p=0.004). Compared with the NC group, the MCI group had higher Epworth Sleepness Scale (ESS) scores (p=0.019). A significant negative relationship was observed between NfL and MoCA scores (r=-0.310, p=0.006), and associations were observed for NfL and the subdomains of the MoCA, including language and delayed recall (r=-0.234, p=0.039; r=-0.288, p=0.011, respectively). A negative correlation was observed between NfL and minimum SaO2 (r=-0.252, p=0.026), whereas a positive correlation was observed for AHI (r=0.224, p=0.049). Multiple regression analysis revealed that MoCA was significantly associated with NfL (β=-0.087, p=0.019).
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1. Polysomnography (PSG) The parameters investigated included respiratory airflow, electroencephalography (EEG) (C3/A2, C4/A1, O1/A2, and O2/A1), electrooculography (EOG), electrocardiography, (ECG) electromyography (EMG) (chin and leg muscles), thoracic and abdominal respiratory effort, snoring, body position, oxyhemoglobin saturation (SpO2), and pulse rate. Obstructive apnea was defined as cessation of air flow for at least 10 s, with effort to breathe during cessation. Obstructive hypopnea was defined as abnormal respiratory events with an at least 30% decrease compared to the baseline amplitude of nasal pressure for 10 s accompanied by <4% oxygen desaturation from the pre-event baseline OSA and was determined on the basis of the apnea-hypopnea index (AHI, calculated as the total number of apnea and hypopnea events per hour). The polysomnography system produced by Compumedics in Australia was used to collect signals, and all data were analyzed by trained technicians and sleep physicians with reference to the scoring standards of sleep and related events according to the 2007 American Academy of Sleep Medicine (AASM) alternate criteria as recommended by the AASM . 2. Epworth sleepiness scale (ESS) A validated Chinese version of the ESS questionnaire was used, and it consisted of eight items rated from 0 to 3, with higher numbers indicating a higher chance of dozing. It has been frequently used to quantify the degree of hypersomnia. The scores from the eight items were added together to provide a composite score ranging from 0 to 24. Higher scores reflected greater levels of sleepiness. Patients were considered to suffer from EDS if the ESS score was >10. 3. Montreal cognitive assessment (MoCA) The MoCA questionnaire is a fast and sensitive cognitive test developed to screen for mild cognitive dysfunction, and the Chinese version of the MoCA questionnaire (Beijing version) was used in this study for the cognitive function assessment by uniformly trained and qualified professionals. The MoCA is a 30-point test covering eight cognitive subdomains: (i) visuospatial and executive; (ii) naming; (iii) memory; (iv) attention; (v) language; (vi) abstraction; (vii) delayed recall; and (viii) orientation. A bonus point is given to individuals with ≤12 years of education for correction deviation. A total MoCA score ≤26 was considered an indicator of MCI. 4. Blood sampling and laboratory assays Blood samples were collected from the participants in the morning after overnight PSG by venipuncture of forearm veins using EDTA anticoagulant tubes. Then, the samples were centrifuged for 15 minutes at 1000 × g and 2-8 ℃ within 30 minutes of collection, and plasma samples were aliquoted and stored at −80°C until analysis. Plasma levels of NfL, Aβ-42, and Aβ-40 were measured using commercial ELISA kits (CUSABIO, China) in this study.