Circadian activity rhythms and risk of incident dementia and mild cognitive impairment in older women

Systems-Level G Protein-Coupled Receptor Therapy Across a Neurodegenerative Continuum by the GLP-1 Receptor System

With our increasing appreciation of the true complexity of diseases and pathophysiologies, it is clear that this knowledge needs to inform the future development of pharmacotherapeutics. For many disorders, the disease mechanism itself is a complex process spanning multiple signaling networks, tissues, and organ systems. Identifying the precise nature and locations of the pathophysiology is crucial for the creation of systemically effective drugs. Diseases once considered constrained to a limited range of organ systems, e.g., central neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington' disease (HD), the role of multiple central and peripheral organ systems in the etiology of such diseases is now widely accepted. With this knowledge, it is increasingly clear that these seemingly distinct neurodegenerative disorders (AD, PD, and HD) possess multiple pathophysiological similarities thereby demonstrating an inter-related continuum of disease-related molecular alterations. With this systems-level appreciation of neurodegenerative diseases, it is now imperative to consider that pharmacotherapeutics should be developed specifically to address the systemic imbalances that create the disorders. Identification of potential systems-level signaling axes may facilitate the generation of therapeutic agents with synergistic remedial activity across multiple tissues, organ systems, and even diseases. Here, we discuss the potentially therapeutic systems-level interaction of the glucagon-like peptide 1 (GLP-1) ligand-receptor axis with multiple aspects of the AD, PD, and HD neurodegenerative continuum.

Circadian clock proteins regulate neuronal redox homeostasis and neurodegeneration

Brain aging is associated with diminished circadian clock output and decreased expression of the core clock proteins, which regulate many aspects of cellular biochemistry and metabolism. The genes encoding clock proteins are expressed throughout the brain, though it is unknown whether these proteins modulate brain homeostasis. We observed that deletion of circadian clock transcriptional activators aryl hydrocarbon receptor nuclear translocator-like (Bmal1) alone, or circadian locomotor output cycles kaput (Clock) in combination with neuronal PAS domain protein 2 (Npas2), induced severe age-dependent astrogliosis in the cortex and hippocampus. Mice lacking the clock gene repressors period circadian clock 1 (Per1) and period circadian clock 2 (Per2) had no observed astrogliosis. Bmal1 deletion caused the degeneration of synaptic terminals and impaired cortical functional connectivity, as well as neuronal oxidative damage and impaired expression of several redox defense genes. Targeted deletion of Bmal1 in neurons and glia caused similar neuropathology, despite the retention of intact circadian behavioral and sleep-wake rhythms. Reduction of Bmal1 expression promoted neuronal death in primary cultures and in mice treated with a chemical inducer of oxidative injury and striatal neurodegeneration. Our findings indicate that BMAL1 in a complex with CLOCK or NPAS2 regulates cerebral redox homeostasis and connects impaired clock gene function to neurodegeneration.

Aging, circadian rhythms and depressive disorders: a review

INTRODUCTION

Aging is typically associated with impairing behavioral patterns that are frequently and inappropriately seen as normal. Circadian rhythm changes and depressive disorders have been increasingly proposed as the two main overlapping and interpenetrating changes that take place in older age. This study aims to review the state of the art on the subject concerning epidemiology, pathophysiological mechanism, clinical findings and relevance, as well as available treatment options.

MATERIALS AND METHODS

A nonsystematic review of all English language PubMed articles published between 1995 and December 2012 using the terms "circadian rhythms", "mood disorders", "depression", "age", "aging", "elderly" and "sleep".

DISCUSSION AND CONCLUSION

Sleep disorders, mainly insomnia, and depression have been demonstrated to be highly co-prevalent and mutually precipitating conditions in the elderly population. There is extensive research on the pathophysiological mechanisms through which age conditions circadian disruption, being the disruption of the Melatonin system one of the main changes. However, research linking clearly and unequivocally circadian disruption and mood disorders is still lacking. Nonetheless, there are consistently described molecular changes on shared genes and also several proposed pathophysiological models linking depression and sleep disruption, with clinical studies also suggesting a bi-directional relationship between these pathologies. In spite of this suggested relation, clinical evaluation of these conditions in elderly patients consistently reveals itself rather complicated due to the frequently co-existing co-morbidities, some of them having been demonstrated to alter sleep and mood patters. This is the case of strokes, forms of dementia such as Alzheimer and Parkinson, several neurodegenerative disorders, among others. Although there are to the present no specific treatment guidelines, available treatment options generally base themselves on the premise that depression and sleep disturbances share a bidirectional relationship and so, the adoption of measures that address specifically one of the conditions will reciprocally benefit the other. Treatment options range from Cognitive Behavioral Therapy, Chronotherapy, and Light therapy, to drugs such as Melatonin/Melatonin agonists, antidepressants and sedatives.

Causes and consequences of age-related steroid hormone changes: insights gained from nonhuman primates

Similar to humans, rhesus macaques (Macaca mulatta) are large, long-lived diurnal primates, and show similar age-related changes in the secretion of many steroid hormones, including oestradiol, testosterone, cortisol and dehydroepiandrosterone (DHEA). Consequently, they represent a pragmatic animal model in which to examine the mechanisms by which these steroidal changes contribute to perturbed sleep-wake cycles and cognitive decline in the elderly. Using remote serial blood sampling, we have found the circulating levels of DHEA sulphate, as well as oestradiol and testosterone, decline markedly in old monkeys. Furthermore, using the real-time polymerase chain reaction, we have shown that the genes for the enzymes associated with the conversion of DHEA to oestradiol and testosterone (3β-hydroxysteroid dehydrogenase, 17β-hydroxysteroid dehydrogenase, and aromatase) are highly expressed in brain areas associated with cognition and behaviour, including the hippocampus, prefrontal cortex and amygdala. Taken together, these findings suggest that the administration of supplementary DHEA in the elderly may have therapeutic potential for cognitive and behavioural disorders, although with fewer negative side effects outside of the central nervous system. To test this, we have developed a novel steroid supplementation paradigm for use in old animals; this involves the oral administration of DHEA and testosterone at physiologically relevant times of the day to mimic the circadian hormone patterns observed in young adults. We are currently evaluating the efficacy of this steroid supplementation paradigm with respect to reversing age-associated disorders, including perturbed sleep-wake cycles and cognitive decline, as well as an impaired immune response.

Shift work and cognition in the Nurses' Health Study

Rotating night-shift work, which can disrupt circadian rhythm, may adversely affect long-term health. Experimental studies indicate that circadian rhythm disruption might specifically accelerate brain aging; thus, we prospectively examined shift-work history at midlife as associated with cognitive function among older women in the Nurses' Health Study. Women reported their history of rotating night-shift work in 1988 and participated in telephone-based cognitive interviews between 1995 and 2001; interviews included 6 cognitive tests that were subsequently repeated 3 times, at 2-year intervals. We focused on shift work through midlife (here, ages 58-68 years) because cognitive decline is thought to begin during this period. Using multivariable-adjusted linear regression, we evaluated mean differences in both "average cognitive status" at older age (averaging cognitive scores from all 4 interviews) and rates of cognitive decline over time across categories of shift-work duration at midlife (none, 1-9, 10-19, or ≥20 years). There was little association between shift work and average cognition in later life or between shift work and cognitive decline. Overall, this study does not clearly support the hypothesis that shift-work history in midlife has long-term effects on cognition in older adults.

Midlife sleep characteristics associated with late life cognitive function

STUDY OBJECTIVES

Previous studies with limited follow-up times have suggested that sleep-related traits are associated with an increased risk of incident dementia or cognitive decline. We investigated the association between midlife sleep characteristics and late life cognitive function.

DESIGN

A follow-up study with a median follow-up time of 22.5 (range 15.8-25.7) years assessing the association between midlife sleep characteristics and later cognitive function.

SETTING

Questionnaire data from 1981 were used in the assessment of sleep characteristics, use of hypnotics, and covariates at baseline. Between 1999 and 2007, participants were assigned a linear cognitive score with a maximum score of 51 based on a telephone interview (mean score 38.3, SD 6.1). Linear regression analyses were controlled for age, sex, education, ApoE genotype, and follow-up time.

PARTICIPANTS

2,336 members of the Finnish Twin cohort who were at least 65 years of age.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Baseline short (< 7 h/day) and long (> 8 h/day) sleepers had lower cognitive scores than participants sleeping 7-8 h/ day (β = -0.84, P = 0.014 and β = -1.66, P < 0.001, respectively). As compared to good sleep quality, poor or rather poor sleep quality was associated with a lower cognitive score (β = -1.00, P = 0.011). Also, the use of hypnotics ≥ 60 days per year was associated with poorer cognitive function (β = -1.92, P = 0.002).

CONCLUSIONS

This is the first study indicating that midlife sleep length, sleep quality, and use of hypnotics are associated with late life cognitive function. Further confirmation is needed, but sleep-related characteristics may emerge as new risk factors for cognitive impairment.

The circadian system in Alzheimer's disease: disturbances, mechanisms, and opportunities

Alzheimer's disease (AD) is a devastating neurodegenerative condition associated with severe cognitive and behavioral impairments. Circadian rhythms are recurring cycles that display periods of approximately 24 hours and are driven by an endogenous circadian timekeeping system centered on the suprachiasmatic nucleus of the hypothalamus. We review the compelling evidence that circadian rhythms are significantly disturbed in AD and that such disturbance is of significant clinical importance in terms of behavioral symptoms. We also detail findings from neuropathological studies of brain areas associated with the circadian system in postmortem studies, the use of animal models of AD in the investigation of circadian processes, and the evidence that chronotherapeutic approaches aimed at bolstering weakened circadian rhythms in AD produce beneficial outcomes. We argue that further investigation in such areas is warranted and highlight areas for future research that might prove fruitful in ultimately providing new treatment options for this most serious and intractable of conditions.

Delirium: a disturbance of circadian integrity?

Delirium is a serious neuropsychiatric syndrome of acute onset that occurs in approximately one in five general hospital patients and is associated with serious adverse outcomes that include loss of adaptive function, persistent cognitive problems and increased mortality. Recent studies indicate a three-domain model for delirium that includes generalised cognitive impairment, disturbed executive cognition, and disruption of behaviours that are under circadian control such as sleep-wake cycle and motor activity levels. As a consequence, attention has focused upon the possible role of the circadian timing system (CTS) in the pathophysiology of delirium. We explored this possibility by reviewing evidence that (1) many symptoms that occur in delirium are influenced by circadian rhythms, (2) many features of recognised circadian rhythm disorders are similar to characteristic features of delirium, (3) common risk factors for delirium are known to disrupt circadian systems, (4) physiological disturbances of circadian systems have been noted in delirious patients, and (5) positive effects in the treatment of delirium have been demonstrated for melatonin and related agents that influence the circadian timing system. A programme of future studies that can help to clarify the relevance of circadian integrity to delirium is described. Such work can provide a better understanding of the pathophysiology of delirium while also identifying opportunities for more targeted therapeutic efforts.

Persistent impairments in hippocampal function following a brief series of photoperiod shifts in rats

The impact of an acute circadian disruption on learning and memory in male and female rats was examined. Circadian disruption was elicited using a brief series of photoperiod shifts. Previous research using male rats showed that acute circadian disruption during acquisition of a spatial navigation task impaired long-term retention and that chronic circadian disruption impaired acquisition of the same task. However, the long-term effects of acute circadian disruption following circadian re-entrainment and whether sex differences in response to circadian disruption exist are still unknown. For the present study, rats were trained on the standard, spatial version of the Morris water task (MWT) and a visual discrimination task developed for the eight-arm radial maze. After reaching asymptotic performance, behavioural training was terminated and the experimental group experienced a series of photoperiod shifts followed by circadian re-entrainment. Following circadian re-entrainment, the subjects were given retention tests on the MWT and visual discrimination task. Following retention testing, an extra-dimensional shift using the eight-arm radial maze was also performed. An acute episode of circadian disruption elicited via photoperiod shifts negatively impacted retention of spatial memory in male and female rats. Retention of the visual discrimination task and the ability to detect extra-dimensional shifts were not impaired. The observed impairments on the MWT indicate that hippocampal representations are susceptible to a small number of photoperiod shifts even if the association is acquired prior to rhythm manipulation and retention is assessed following rhythm stabilization. Effects were limited to a hippocampus-dependent task, indicating that impairments are specific, not global.

Polymorphism of CLOCK gene rs 4580704 C > G is associated with susceptibility of Alzheimer's disease in a Chinese population

BACKGROUND AND AIMS

The association of polymorphism of circadian locomotor output cycle kaput (CLOCK) gene rs 4580704 C/G with susceptibility of Alzheimer's disease (AD) was examined in the present study.

METHODS

This was a case/control study and investigated the association of polymorphism of CLOCK gene rs 4580704 C/G with susceptibility of AD. Genotypes of apolipoprotein E (APOE) and CLOCK gene rs 4580704 C/G were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) detection method.

RESULTS

This study was comprised of 296 unrelated AD patients and 423 controls. We performed an analysis the association of polymorphism of CLOCK gene rs 4580704 C/G with susceptibility of AD. In the whole sample or APOEε4 noncarriers, prevalence of C carriers in CLOCK gene rs 4580704 in AD patients was significantly higher than in controls (in the whole sample: χ(2) = 13.773, p <0.0001; in APOEε4 noncarriers: χ(2) = 51.588, p <0.0001). However, among APOEε4 carriers, prevalence of C carriers in CLOCK gene rs 4580704 between patients and controls was not statistically significant (χ(2) = 0.753, p = 0.386).

CONCLUSIONS

Among APOEε4 noncarriers, C carriers in CLOCK gene rs 4580704 were associated with a high susceptibility of AD; however, among APOEε4 carriers the functional polymorphism of clock gene rs 4580704 C/G was not associated with AD susceptibility.

Sleep loss as risk factor for neurologic disorders: a review

Sleep loss refers to sleep of shorter duration than the average baseline need of seven to eight hours per night. Sleep loss and sleep deprivation have severe effects on human health. In this article, we review the main aspects of sleep loss, taking into account its effects on the central nervous system. The neurocognitive and behavioral effects of sleep loss are well known. However, there is an increasing amount of research pointing to sleep deprivation as a risk factor for neurologic diseases, namely stroke, multiple sclerosis, Alzheimer's disease, headache, epilepsy, pain, and somnambulism. Conversely, sleep loss has been reported to be a potential protective factor against Parkinson's disease. The pathophysiology involved in this relationship is multiple, comprising immune, neuroendocrine, autonomic, and vascular mechanisms. It is extremely important to identify the individuals at risk, since recognition and adequate treatment of their sleep problems may reduce the risk of certain neurologic disorders.

Poor Sleep as a Precursor to Cognitive Decline in Down Syndrome : A Hypothesis

We propose that sleep disruption is a lever arm that influences how cognition emerges in development and then declines in response to Alzheimer disease in people with Down syndrome. Addressing sleep disruptions might be an overlooked way to improve cognitive outcomes in this population. This article is a contribution to a Special Issue on Down Syndrome curated by the editors of the Journal of Alzheimer’s Disease & Parkinsonism.

Therapeutic application of melatonin in mild cognitive impairment

Mild cognitive impairment (MCI) is an etiologically heterogeneous syndrome defined by cognitive impairment in advance of dementia. We previously reported in a retrospective analysis that daily 3 - 9 mg of a fast-release melatonin preparation given p. o. at bedtime for up to 3 years significantly improved cognitive and emotional performance and daily sleep/wake cycle in MCI patients. In a follow up of that study we now report data from another series of 96 MCI outpatients, 61 of who had received daily 3 - 24 mg of a fast-release melatonin preparation p. o. at bedtime for 15 to 60 months. Melatonin was given in addition to the standard medication prescribed by the attending psychiatrist. Patients treated with melatonin exhibited significantly better performance in Mini-Mental State Examination and the cognitive subscale of the Alzheimer's disease Assessment Scale. After application of a neuropsychological battery comprising a Mattis´ test, Digit-symbol test, Trail A and B tasks and the Rey´s verbal test, better performance was found in melatonin-treated patients for every parameter tested. Abnormally high Beck Depression Inventory scores decreased in melatonin-treated patients, concomitantly with the improvement in the quality of sleep and wakefulness. The comparison of the medication profile in both groups of MCI patients indicated that 9.8% in the melatonin group received benzodiazepines vs. 62.8% in the non-melatonin group. The results further support that melatonin can be a useful add-on drug for treating MCI in a clinic environment.

Influence of aging on Bmal1 and Per2 expression in extra-SCN oscillators in hamster brain

Deletion of the core clock gene, Bmal1, ablates circadian rhythms and accelerates aging, leading to cognitive deficits and tissue atrophy (e.g., skeletal muscle) (Kondratov et al., 2006, Kondratova et al., 2010). Although normal aging has been shown to attenuate Bmal1 expression in the master circadian pacemaker in the suprachiasmatic nucleus (SCN), relatively little is known about age-related changes in Bmal1 expression in other tissues, where Bmal1 may have multiple functions. This study tested the hypothesis that aging reduces Bmal1 expression in extra-SCN oscillators including brain substrates for memory and in skeletal muscle. Brains and gastrocnemius muscles were collected from young (3-5 months) and old hamsters (17-21 months) euthanized at four times of day. Bmal1 mRNA expression was determined by conducting in situ hybridization on brain sections or real-time PCR on muscle samples. The results showed age-related attenuation of Bmal1 expression in many brain regions, and included loss of diurnal rhythms in the hippocampal CA2 and CA3 subfields, but no change in muscle. In situ hybridization for Per2 mRNA was also conducted and showed age-related reduction of diurnal rhythm amplitude selectively in the hippocampal CA1 and DG subfields. In conclusion, aging has tissue-dependent effects on Bmal1 expression in extra-SCN oscillators. These finding on normal aging will provide a reference for comparing potential changes in Bmal1 and Per2 expression in age-related pathologies. In conjunction with previous reports, the results suggest the possibility that attenuation of clock gene expression in some brain regions (the hippocampus, cingulate cortex and SCN) may contribute to age-related cognitive deficits.

Disruption of the sleep-wake cycle and diurnal fluctuation of β-amyloid in mice with Alzheimer's disease pathology

Aggregation of β-amyloid (Aβ) in the brain begins to occur years before the clinical onset of Alzheimer's disease (AD). Before Aβ aggregation, concentrations of extracellular soluble Aβ in the interstitial fluid (ISF) space of the brain, which are regulated by neuronal activity and the sleep-wake cycle, correlate with the amount of Aβ deposition in the brain seen later. The amount and quality of sleep decline with normal aging and to a greater extent in AD patients. How sleep quality as well as the diurnal fluctuation in Aβ change with age and Aβ aggregation is not well understood. We report a normal sleep-wake cycle and diurnal fluctuation in ISF Aβ in the brain of the APPswe/PS1δE9 mouse model of AD before Aβ plaque formation. After plaque formation, the sleep-wake cycle markedly deteriorated and diurnal fluctuation of ISF Aβ dissipated. As in mice, diurnal fluctuation of cerebrospinal fluid Aβ in young adult humans with presenilin mutations was also markedly attenuated after Aβ plaque formation. Virtual elimination of Aβ deposits in the mouse brain by active immunization with Aβ(42) normalized the sleep-wake cycle and the diurnal fluctuation of ISF Aβ. These data suggest that Aβ aggregation disrupts the sleep-wake cycle and diurnal fluctuation of Aβ. Sleep-wake behavior and diurnal fluctuation of Aβ in the central nervous system may be functional and biochemical indicators, respectively, of Aβ-associated pathology.

Excessive sleepiness is predictive of cognitive decline in the elderly

STUDY OBJECTIVES

To examine the association of sleep complaints reported at baseline (insomnia complaints and excessive daytime sleepiness (EDS)) and medication, with cognitive decline in community-dwelling elderly.

DESIGN

An 8-yr longitudinal study.

SETTING

The French Three-City Study.

PARTICIPANTS

There were 4,894 patients without dementia recruited from 3 French cities and having a Mini-Mental Status Examination (MMSE) score ≥ 24 points at baseline.

MEASUREMENTS AND RESULTS

Questionnaires were used to evaluate insomnia complaints (poor sleep quality (SQ), difficulty in initiating sleep (DIS), difficulty in maintaining sleep (DMS), early morning awakening (EMA)), EDS, and sleep medication at baseline. Cognitive decline was defined as a 4-point reduction in MMSE score during follow-up at 2, 4, and 8 yr. Logistic regression models were adjusted for sociodemographic, behavioral, physical, and mental health variables, and apolipoprotein E genotype. EDS independently increased the risk of cognitive decline (odds ratio (OR) = 1.26, 95% confidence interval (CI) = 1.02-1.56), especially for those patients who also developed dementia during the follow-up period (OR = 1.39, 95% CI = 1.00-1.97). The number of insomnia complaints and DMS were negatively associated with MMSE cognitive decline (OR = 0.77, 95% CI = 0.60-0.98 for 3-4 complaints, OR = 0.81, 95% CI = 0.68-0.96, respectively). The 3 other components of insomnia (SQ, DIS, EMA) were not significantly associated with MMSE cognitive decline.

CONCLUSIONS

Our results suggest that EDS may be associated independently with the risk of cognitive decline in the elderly population. Such results could have important public health implications because EDS may be an early marker and potentially reversible risk factor of cognitive decline and onset of dementia.

Cognition in obstructive sleep apnea-hypopnea syndrome (OSAS): current clinical knowledge and the impact of treatment

Obstructive sleep apnea-hypopnea syndrome (OSAS) is characterized by the presence of disordered breathing events that occur during sleep, as well as symptoms such as sleepiness and snoring. OSAS is associated with a number of adverse health consequences, and a growing literature focuses on its cognitive correlates. Although research in this field is mixed, multiple studies indicate that OSAS patients show impairment in attention, memory, and executive function. Continuous positive airway pressure (CPAP) is the most effective and widely used treatment of OSAS, and supplemental medications may supplement CPAP treatment to ameliorate associated symptoms. Here, we review the literature on OSAS and cognition, including studies that have investigated the impact of CPAP and stimulant medication on cognitive performance in patients with OSAS. In general, no consistent effect of CPAP use on cognitive performance was evident. This may be due, in part, to variability in study design and sampling methodology across studies. Studies of stimulant medications generally reported positive effects on cognitive performance. We conclude with a discussion of the mechanisms that have been proposed to explain cognitive dysfunction in OSAS and directions for future research.

Sleep quality and 1-year incident cognitive impairment in community-dwelling older adults

STUDY OBJECTIVES

To examine in cognitively intact older men and women the associations between subjective sleep quality and 1-yr incident cognitive impairment.

DESIGN

Prospective cohort study.

SETTING

General community.

PARTICIPANTS

1,664 cognitively intact individuals age 65 to 96 years.

MEASUREMENTS AND RESULTS

Sleep quality at baseline was measured using the Pittsburgh Sleep Quality Index (PSQI). Cognitive functioning was assessed at baseline and 12 months later using the Mini-Mental State Examination (MMSE). Incident general cognitive impairment was defined according to a follow-up MMSE score below the 15(th) percentile according to normative data and of at least 2 points below baseline. General cognitive impairments were also separated into amnestic and nonamnestic subtypes according to MMSE delayed recall performance. Associations between sleep quality indicators at baseline and incident cognitive impairment were assessed by odds ratio (OR) adjusted for age, education, baseline MMSE score, psychotropic drug use, anxiety, depressive episodes, cardiovascular conditions, and chronic diseases. Results revealed that global PSQI score was significantly linked with incident cognitive impairment (OR 1.17, 95% confidence interval (CI) 1.05-1.30) in men, but not in women. In women, sleep disturbance score (OR 2.62, 95% CI 1.41-4.86) and long sleep duration (≥ 9 hr; OR 3.70, 95% CI 1.49-9.17) were associated with nonamnestic and amnestic incident cognitive impairment, respectively. In men, short sleep duration (≤ 5 hr; OR 4.95, 95% CI 1.72-14.27) and habitual sleep efficiency score (OR 1.94, 95% CI 1.42-2.66) were associated with amnestic and general incident cognitive impairment, respectively.

CONCLUSIONS

Sleep quality in older adults should receive particular attention by clinicians because poor sleep quality can be an early sign of cognitive decline.