Moderate Changes in the Circadian System of Alzheimer's Disease Patients Detected in Their Home Environment

Abstract

Alzheimer's disease (AD) is a neurodegenerative disease often accompanied with disruption of sleep-wake cycle. The sleep-wake cycle is controlled by mechanisms involving internal timekeeping (circadian) regulation. The aim of our present pilot study was to assess the circadian system in patients with mild form of AD in their home environment. In the study, 13 elderly AD patients and 13 age-matched healthy control subjects (the patient's spouses) were enrolled. Sleep was recorded for 21 days by sleep diaries in all participants and checked by actigraphy in 4 of the AD patient/control couples. The samples of saliva and buccal mucosa were collected every 4 hours during the same 24 h-interval to detect melatonin and clock gene (PER1 and BMAL1) mRNA levels, respectively. The AD patients exhibited significantly longer inactivity interval during the 24 h and significantly higher number of daytime naps than controls. Daily profiles of melatonin levels exhibited circadian rhythms in both groups. Compared with controls, decline in amplitude of the melatonin rhythm in AD patients was not significant, however, in AD patients more melatonin profiles were dampened or had atypical waveforms. The clock genes PER1 and BMAL1 were expressed rhythmically with high amplitudes in both groups and no significant differences in phases between both groups were detected. Our results suggest moderate differences in functional state of the circadian system in patients with mild form of AD compared with healthy controls which are present in conditions of their home dwelling.

Fig 1. Protocol of the study.

The study began (day 1) with recording of sleep/wake schedule in diaries (all participants) together with Actiwatch monitoring (4 couples) for 21 days. During the monitored period, the subjects maintained their habitual sleep/wake regime. Thereafter, the samples were collected throughout the 24 h on the same day from all subjects. Time when saliva (blue arrows) and buccal mucosa samples (red arrows) were collected is depicted. The dark bar on the time scale corresponds to hours between the sunset and the sunrise on the sampling day. For more details, see Materials and Methods.

Fig 2. Analysis of sleep and activity rhythms of controls and AD patients.

(A) Total sleep duration of the 24-h period (in hours) was assessed by the diary data (mean ± SEM) collected during the 21 day recording period from 13 controls (black column) and 13 AD patients (red column). In AD patients, the mean total sleep duration was significantly longer compared to controls, ** P = 0.002; (B) The mean daily activity profiles of AD patients and controls. The activity was recorded by Actiwatch during 21 days and the cumulated activity levels (mean ± SEM) in 30 min bins throughout the day and night are depicted; for clarity, part of the day (00:00 to 06:00 h) was re-plotted. The activity levels in 4 controls (black columns) and 4 AD patients (red columns) are depicted. The blue and yellow areas on the graph background correspond with time of the environmental darkness and daylight, respectively, as occurred during the recording period. X axis represents clock time (hours). For more details, see Material and Methods.

Fig 3. Individual actigraphs of the control/AD patient couples.

Actigraphs from controls (A,C,E,G) and AD patients (B,D,F,H) are depicted, representing the AB, CD, EF and GH couples. The activity was recorded during 21 days (A-F) or 17 days (G,H). The record of activity (black area) from the Actiwatch analysis was completed with manual marking of nighttime sleep periods (blue area) and daytime naps (orange area) according to data from the individual sleep diaries. The green dashed areas represent intervals when the device was not operating.

Fig 4. Nighttime sleep parameters and naps of controls and AD patients.

(A) The nighttime sleep parameters (mean ± SEM), i.e., the length of the assumed sleep duration (hours), the number of awake episodes, the duration of awake episodes (hours), the real sleep duration (percent), the sleep efficiency (percent) and the fragmentation index (percent) were detected by Actiwatch analysis and compared between the group of 4 controls (black columns) and 4 AD patients (red columns); (B) The values of the sleep efficiencies and fragmentation indexes of the individual controls (left side) and AD patients (right side). For identification of the control/AD patients couples, the subjects of each couple are depicted with the same symbol (couple 1: yellow diamond, couple 2: black dot, couple 3: red triangle, couple 4: green square); (C) Mean number of daytime naps as detected by Actiwatch analysis (and confirmed by the sleep diaries records) for the control/AD patients couples. The symbols identifying the couples correspond to those depicting the nighttime sleep parameters in B). For more detail, see Material and Methods.

Fig 5. Daily profiles of melatonin levels in the saliva of controls and AD patients.

Melatonin levels were detected during the 24 h and expressed in pg/ml. (A) The daily melatonin profiles expressed as the means ± S.E.M. in controls (black circles and black lines, n = 13) and AD patients (red squares and red lines, n = 13); (B) The individual melatonin levels in controls (black circles) and AD patients (red squares) are depicted. Moreover, the mean cosine fits (black curve for controls and red curve for AD patients) were obtained by the cosinor analysis. X-axes represent the time of day in hours, the blue and yellow areas on the graphs backgrounds correspond with time of the outside darkness and daylight, respectively, as occurred during the recording period.

Fig 6. Daily profiles of clock gene expression in buccal cells of controls and AD patients.

PER1 (upper graph) and BMAL1 (lower graph) expression profiles were compared in controls (black circles, n = 13) and AD patients (red squares, n = 13). Data are expressed as % of maximal expression levels (means ± S.E.M.) and fitted with cosine curves (controls: black curves, AD patients: red curves). The X-axes represent the time of day in hours.