Phase-shifts of 24-h rhythms of hormonal release and body temperature following early evening administration of the melatonin agonist agomelatine in healthy older men

Circadian rhythms and mood disorders: Time to see the light

The importance of time is ever prevalent in our world, and disruptions to the normal light/dark and sleep/wake cycle have now become the norm rather than the exception for a large part of it. All mood disorders, including seasonal affective disorder (SAD), major depressive disorder (MDD), and bipolar disorder (BD), are strongly associated with abnormal sleep and circadian rhythms in a variety of physiological processes. Environmental disruptions to normal sleep/wake patterns, light/dark changes, and seasonal changes can precipitate episodes. Moreover, treatments that target the circadian system have proven to be therapeutic in certain cases. This review will summarize much of our current knowledge of how these disorders associate with specific circadian phenotypes, as well as the neuronal mechanisms that link the circadian clock with mood regulation. We also discuss what has been learned from therapies that target circadian rhythms and how we may use current knowledge to develop more individually designed treatments.

Human circadian rhythm studies: Practical guidelines for inclusion/exclusion criteria and protocol

As interest in circadian rhythms and their effects continues to grow, there is an increasing need to perform circadian studies in humans. Although the constant routine is the gold standard for these studies, there are advantages to performing more naturalistic studies. Here, a review of protocols for such studies is provided along with sample inclusion and exclusion criteria. Sleep routines, drug use, shift work, and menstrual cycle are addressed as screening considerations. Regarding protocol, best practices for measuring melatonin, including light settings, posture, exercise, and dietary habits are described. The inclusion/exclusion recommendations and protocol guidelines are intended to reduce confounding variables in studies that do not involve the constant routine. Given practical limitations, a range of recommendations is provided from stringent to lenient. The scientific rationale behind these recommendations is discussed. However, where the science is equivocal, recommendations are based on empirical decisions made in previous studies. While not all of the recommendations listed may be practical in all research settings and with limited potential participants, the goal is to allow investigators to make well informed decisions about their screening procedures and protocol techniques and to improve rigor and reproducibility, in line with the objectives of the National Institutes of Health.

Drugs Used in Circadian Sleep-Wake Rhythm Disturbances

This article focuses on melatonin and other melatonin receptor agonists and summarizes their circadian phase shifting and sleep-enhancing properties, along with their associated possible safety concerns. The circadian system and circadian rhythm sleep-wake disorders are described, along with the latest American Academy of Sleep Medicine recommendations for the use of exogenous melatonin in treating them. In addition, the practical aspects of using exogenous melatonin obtainable over the counter in the United States, consideration of the effects of concomitant light exposure, and assessing treatment response are discussed.

Agomelatine: An astounding sui-generis antidepressant?

Major depressive disorder (MDD) is one of the foremost causes of disability and premature death worldwide. Although the available antidepressants are effective and well tolerated, they also have many limitations. Therapeutic advances in developing a new drug's ultimate relation between MDD and chronobiology, which targets the circadian rhythm, have led to a renewed focus on psychiatric disorders. In order to provide a critical analysis about antidepressant properties of agomelatine, a detailed PubMed (Medline), Scopus (Embase), Web of Science (Web of Knowledge), Cochrane Library, Google Scholar, and PsycInfo search was performed using the following keywords: melatonin analog, agomelatine, safety, efficacy, adverse effects, pharmacokinetics, pharmacodynamics, circadian rhythm, sleep disorders, neuroplasticity, MDD, bipolar disorder, anhedonia, anxiety, generalized anxiety disorder (GAD), and mood disorders. Agomelatine is a unique melatonin analog with antidepressant properties and a large therapeutic index that improves clinical safety. It is a melatonin receptor agonist (MT1 and MT2) and a 5-HT2C receptor antagonist. The effects on melatonin receptors enable the resynchronization of irregular circadian rhythms with beneficial effects on sleep architectures. In this way, agomelatine is accredited for its unique mode of action, which helps to exert antidepressant effects and resynchronize the sleep-wake cycle. To sum up, an agomelatine has not only antidepressant properties but also has anxiolytic effects.

Antidepressants and Circadian Rhythm: Exploring Their Bidirectional Interaction for the Treatment of Depression

Scientific evidence that circadian rhythms affect pharmacokinetics and pharmacodynamics has highlighted the importance of drug dosing-time. Circadian oscillations alter drug absorption, distribution, metabolism, and excretion (ADME) as well as intracellular signaling systems, target molecules (e.g., receptors, transporters, and enzymes), and gene transcription. Although several antidepressant drugs are clinically available, less than 50% of depressed patients respond to first-line pharmacological treatments. Chronotherapeutic approaches to enhance the effectiveness of antidepressants are not completely known. Even so, experimental results found until this day suggest a positive influence of drug dosing-time on the efficacy of depression therapy. On the other hand, antidepressants have also demonstrated to modulate circadian rhythmicity and sleep-wake cycles. This review aims to evidence the potential of chronotherapy to improve the efficacy and/or safety of antidepressants. It includes pre-clinical and clinical studies that demonstrate the relevance of determining the most appropriate time of administration for antidepressant drugs. In parallel, their positive influence on the resynchronization of disrupted circadian rhythms is also herein discussed. It is expected that this review will promote the investigation of chronotherapy for the treatment of depression, contribute to a better understanding of the relationship between antidepressants and circadian rhythms, and consequently promote the development of new therapeutics.

Molecular Link between Circadian Rhythmicity and Mood Disorders

BACKGROUND

The internal clock is driven by circadian genes [e.g., Clock, Bmal1, Per1-3, Cry1-2], hormones [e.g., melatonin, cortisol], as well as zeitgeber ['synchronisers']. Chronic disturbances in the circadian rhythm in patients diagnosed with mood disorders have been recognised for more than 50 years.

OBJECTIVES

The aim of this review is to summarise the current knowledge and literature regarding circadian rhythms in the context of mood disorders, focussing on the role of circadian genes, hormones, and neurotransmitters.

METHOD

The review presents the current knowledge and literature regarding circadian rhythms in mood disorders using the Pubmed database. Articles with a focus on circadian rhythms and mood disorders [n=123], particularly from 1973 to 2020, were included.

RESULTS

The article suggests a molecular link between disruptions in the circadian rhythm and mood disorders. Circadian disturbances, caused by the dysregulation of circadian genes, hormones, and neurotransmitters, often result in a clinical picture resembling depression.

CONCLUSION

Circadian rhythms are intrinsically linked to affective disorders, such as unipolar depression and bipolar disorder.

Reduced neuroinflammation and enhanced neurogenesis following chronic agomelatine treatment in rats undergoing chronic constant light

Experimental studies have revealed the involvement of neuroinflammation mediated by activated microglia in the pathophysiology of depression, suggesting a novel target for treatment. The atypical antidepressant Agomelatine (Ago) has an advantage compared to the classical antidepressants due to its chronobiotic activity and unique pharmacological profile as a selective agonist at the melatonin receptors and an antagonist at the 5HT_2C receptors. We have recently revealed that Ago can exert a potent antidepressant effect in rats exposed to a chronic constant light (CCL). In the present study, we hypothesized that the anti-inflammatory activity of this melatonin analog on activated neuroglia in specific brain structures might contribute to its antidepressant effect in this model. Chronic Ago treatment (40 mg/kg, i.p. for 21 days) was executed during the last 3 weeks of a 6-week period of CCL exposure in rats. The CCL-vehicle-treated rats showed a profound neuroinflammation characterized by microgliosis and astrogliosis in the hippocampus, basolateral amygdala (BL) and partly in the piriform cortex (Pir) confirmed by immunohistochemistry. With the exception of the Pir, the CCL regime was accompanied by neuronal damage, identified by Nissl staining, in the hippocampus and basolateral amygdala and impaired neurogenesis with reduced dendritic complexity of hippocampal neuroprogenitor cells detected by doublecortin-positive cells in the dentate gyrus (DG) subgranular zone compared to the control group. Ago reversed the gliosis in a region-specific manner and partially restored the suppressed DG neurogenesis. Ago failed to produce neuroprotection in CCL exposed rats. The present results suggest that the beneficial effects of Ago represent an important mechanism underlying its antidepressant effect in models characterized by impaired circadian rhythms.

Circadian depression: A mood disorder phenotype

Major mood syndromes are among the most common and disabling mental disorders. However, a lack of clear delineation of their underlying pathophysiological mechanisms is a major barrier to prevention and optimised treatments. Dysfunction of the 24-h circadian system is a candidate mechanism that has genetic, behavioural, and neurobiological links to mood syndromes. Here, we outline evidence for a new clinical phenotype, which we have called 'circadian depression'. We propose that key clinical characteristics of circadian depression include disrupted 24-h sleep-wake cycles, reduced motor activity, low subjective energy, and weight gain. The illness course includes early age-of-onset, phenomena suggestive of bipolarity (defined by bidirectional associations between objective motor and subjective energy/mood states), poor response to conventional antidepressant medications, and concurrent cardiometabolic and inflammatory disturbances. Identifying this phenotype could be clinically valuable, as circadian-targeted strategies show promise for reducing depressive symptoms and stabilising illness course. Further investigation of underlying circadian disturbances in mood syndromes is needed to evaluate the clinical utility of this phenotype and guide the optimal use of circadian-targeted interventions.

Dreams, Sleep, and Psychotropic Drugs

Over the past 60 years, the impact of psychotropic drugs on dream recall and content has been scarcely explored. A review of the few existing experimental results on the topic leads us to the following conclusions. For antidepressant drugs, in the great majority, they reduce dream recall frequency (DRF), and the improvement of depressive symptoms is associated with an increase of positive emotion in dream content. For sedative psychotropic drugs, their improvement of sleep quality is associated with a reduction of DRF, but the effect on dream content is less clear. Few occurrences of nightmare frequency increase have been reported, with intake of molecules disturbing sleep or with the withdrawal of some psychotropic drugs. Importantly, the impact of psychotropic drugs on rapid eye movement (REM) sleep does not explain DRF modulations. The reduction of intra-sleep awakenings seems to be the parameter explaining best the modulation of DRF by psychotropic drugs. Indeed, molecules that improve sleep continuity by reducing intra-sleep awakenings also reduce the frequency of dream recall, which is coherent with the “arousal-retrieval model” stating that nighttime awakenings enable dreams to be encoded into long-term memory and therefore facilitate dream recall. DRF is nonetheless influenced by several other factors (e.g., interest in dreams, the method of awakening, and personality traits), which may explain a large part of the variability of results observed and cited in this article.

Drugs Used in Circadian Sleep-Wake Rhythm Disturbances

This article focuses on melatonin and other melatonin receptor agonists, and specifically their circadian phase shifting and sleep-enhancing properties. The circadian system and circadian rhythm sleep-wake disorders are briefly reviewed, followed by a summary of the circadian phase shifting, sleep-enhancing properties, and possible safety concerns associated with melatonin and other melatonin receptor agonists. The recommended use of melatonin, including dose and timing, in the latest American Academy of Sleep Medicine Clinical Practice Guidelines for the treatment of intrinsic circadian rhythm disorders is also reviewed. Lastly, the practical aspects of treatment and consideration of clinical treatment outcomes are discussed.

The Changes of Expression and Methylation of Genes Involved in Oxidative Stress in Course of Chronic Mild Stress and Antidepressant Therapy with Agomelatine

Preclinical studies conducted so far suggest that oxidative stress processes may be associated with the mechanism of depression development. This study shows the effects of chronic administration of agomelatine on expression and the methylation status of Sod1, Sod2, Gpx1, Gpx4, Cat, Nos1, and Nos2 in the brain stricture and blood in the chronic mild stress (CMS) animal model of depression. The animals were exposed to the CMS procedure and treatment with agomelatine (10 mg/kg/day, IP) for five weeks and then were sacrificed. TaqMan Gene Expression Assay, Western blot, and methylation-sensitive high-resolution melting techniques were used to evaluate mRNA and protein expression of the genes, and the methylation status of their promoters. Gpx1, Gpx4, and Sod2 expression in the PBMCs and Sod1 and Sod2 expression in the brain were reduced in the stressed group after agomelatine administration. CMS caused an increase in the methylation of the third Gpx4 promoter in peripheral blood mononuclear cells and Gpx1 promoter in the cerebral cortex. Additionally, stressed rats treated with agomelatine displayed a significantly lower Gpx4 level in the hypothalamus. The results confirm the hypothesis that the CMS procedure and agomelatine administration change the expression level and methylation status of the promoter region of genes involved in oxidative and nitrosative stress.

Agomelatine: A novel mechanism of antidepressant action involving the melatonergic and the serotonergic system

The clinical finding that depressive disorders are often associated with desynchronization of internal rhythms has encouraged the idea that resetting normal circadian rhythms may have antidepressant potential. Agomelatine, a naphthalene analog of melatonin, is both an agonist of human cloned melatonergic MT1 and MT2 receptors and a serotonin 5-HT2C receptor antagonist. Agomelatine combines zeitgeber (synchroniser of the circadian system) activity with neurotransmitter augmentation properties (enhances the levels of dopamine and noradrenaline in frontal cortex). The efficacy of agomelatine in treating depression has been shown in three short-term, pivotal, randomized, placebo–controlled studies. These studies have demonstrated agomelatine to be efficacious in Major Depressive Disorder at the standard dose of 25 mg/day, with the possibility of increasing doses to 50 mg/day in those patients with insufficient improvement. The number of adverse events during the treatment period was comparable to placebo. Four studies have shown the positive effect of agomelatine on sleep continuity and quality and shortening of sleep latency. Despite these promising data, further studies are needed to examine agomelatine's efficacy over a longer treatment period.

Agomelatine treatment corrects impaired sleep-wake cycle and sleep architecture and increases MT1 receptor as well as BDNF expression in the hippocampus during the subjective light phase of rats exposed to chronic constant light

RATIONALE

Exposure to chronic constant light (CCL) has a detrimental impact on circadian rhythms of motor activity and sleep/wake cycles. Agomelatine is an atypical antidepressant showing a chronotropic activity.

OBJECTIVES

In this study, we explored the role of melatonin (MT) receptors and brain-derived neurotrophic factor (BDNF) in the brain in the mechanism underlying the effects of agomelatine on diurnal variations of motor activity, sleep/wake cycle, and sleep architecture in a rat model of CCL.

METHODS

In Experiment #1, home cage activity was monitored automatically with cameras for a period of 24 h. The diurnal rhythm of MT_1, MT₂ receptors, and BDNF expression in the hippocampus and frontal cortex (FC), was tested using the ELISA test. In Experiment #2, rats were equipped with electroencephalographic (EEG) and electromyographic (EMG) electrodes and recordings were made under basal conditions (12:12 LD cycle + vehicle), LL + vehicle and LL + agomelatine (40 mg/kg/day for 21 days).

RESULTS

The rats exposed to CCL showed an impaired diurnal rhythm of motor activity and sleep/wake cycle with reduced NREM sleep and delta power and increased REM sleep and theta power. The duration and number of episodes of the wake were diminished during the subjective dark phase in this group. The circadian rhythm of MT₁ and MT₂ receptors and their expression did not change in the hippocampus and FC under CCL exposure, while the BDNF levels in the hippocampus decreased during the subjective light phase. Agomelatine restored the diurnal rhythm of motor activity, disturbed sleep/wake cycle, and sleep architecture, which effect was accompanied by an increase in MT₁ receptor and BDNF expression in the hippocampus at 10:00 in CCL rats.

CONCLUSIONS

These findings support the value of agomelatine as an antidepressant that can adjust circadian homeostasis of motor activity and sleep/wake cycle in a CCL model.

Circadian rhythm disruption and mental health

Circadian rhythms are internal manifestations of the solar day that permit adaptations to predictable environmental temporal changes. These ~24-h rhythms are controlled by molecular clockworks within the brain that are reset daily to precisely 24 h by exposure to the light-dark cycle. Information from the master clock in the mammalian hypothalamus conveys temporal information to the entire body via humoral and neural communication. A bidirectional relationship exists between mood disorders and circadian rhythms. Mood disorders are often associated with disrupted circadian clock-controlled responses, such as sleep and cortisol secretion, whereas disruption of circadian rhythms via jet lag, night-shift work, or exposure to artificial light at night, can precipitate or exacerbate affective symptoms in susceptible individuals. Evidence suggests strong associations between circadian rhythms and mental health, but only recently have studies begun to discover the direct interactions between the circadian system and mood regulation. This review provides an overview of disrupted circadian rhythms and the relationship to behavioral health and psychiatry. The focus of this review is delineating the role of disruption of circadian rhythms on mood disorders using human night shift studies, as well as jet lag studies to identify links. We also review animal models of disrupted circadian rhythms on affective responses. Lastly, we propose low-cost behavioral and lifestyle changes to improve circadian rhythms and presumably behavioral health.

Evaluation of agomelatine for the treatment of sleep problems in adults with autism spectrum disorder and co-morbid intellectual disability

PURPOSE

Intellectual disability (ID) and autism spectrum disorder (ASD) are common, co-occurring developmental disorders and are frequently associated with sleep problems. This study aimed to assess the effectiveness and tolerability of agomelatine as a pharmacotherapy for sleep problems in ASD adults with ID.

METHOD

A randomised, crossover, triple-blind, placebo-controlled clinical trial, with two three-month periods of treatment starting with either agomelatine or placebo and a washout period of two weeks. Ambulatory circadian monitoring (24 hours/7 days) evaluated total sleep time (TST) as the primary outcome variable.

RESULTS

Participants (N=23; 35±12 years old; 83% male) had a median of three (interquartile range (IQR) 1-4) co-morbidities and were taking a median of five (IQR 2-7) prescribed drugs. Before agomelatine or placebo treatment, all subjects presented with insomnia symptoms, including sleep latency (100% abnormal, 55±23 minutes) or TST (55% abnormal, 449±177 minutes), and 66% had circadian rhythm sleep-wake abnormalities with rhythm phase advancements according to the M5 sleep phase marker values. During the three-month agomelatine treatment, night TST significantly increased by a mean of 83 minutes (16% abnormal, 532±121 minutes), together with a phase correction (M5 1:45±2:28 hours vs. 3:15±2:20 hours), improving sleep stability in wrist temperature rhythm (0.43±0.29 vs. 0.52±0.18 AU). Adverse events were mild and transient.

CONCLUSIONS

Agomelatine was effective and well tolerated for treating insomnia and circadian rhythm sleep problems present in adults with ASD and ID.

Significant role of gene-gene interactions of clock genes in mood disorder

BACKGROUND

The genetic interactions in the circadian rhythm biological system are promising as a source of pathophysiology in mood disorder. We examined the role of the gene-gene interactions of clock genes in mood disorder.

METHODS

We included 413 patients with mood disorder and 1294 controls. The clock genes investigated were BHLHB2, CLOCK, CSNK1E, NR1D1, PER2, PER3, and TIMELESS. Allele, genotype, and haplotype associations were tested. Gene--gene interactions were analyzed using the non-parametric model-free multifactor-dimensionality reduction (MDR) method.

RESULTS

TIMELESS rs4630333 and CSNK1E rs135745 were significantly associated with both major depressive disorder and bipolar disorder. The CLOCK haplotype was also strongly associated. The genetic roles of these SNPs were consistent from the allele and genotypic associations to the MDR interaction results. In MDR analysis, the combination of TIMELESS rs4630333 and CSNK1E rs135745 exhibited the most significant association with mood disorders in the two-locus model. BHLHB2 rs2137947 for major depressive disorder and CLOCK rs12649507 for bipolar disorder were the most significant third loci in the three-locus combination model. The four-locus SNP combination model showed the best balanced accuracy (BA), but its cross-validation consistency (CVC) was unsatisfactory.

LIMITATIONS

We included only 17 SNPs for seven circadian genes due to our limited resources; all subjects were ethnically Korean.

CONCLUSIONS

Our results suggest significant single-gene associations and gene-gene interactions of circadian genes with mood disorder. Gene-gene interactions play a crucial role in mood disorder, even when individual clock genes do not have significant roles.

Advanced melatonin onset relative to sleep in women with unmedicated major depressive disorder

Studies on circadian timing in depression have produced variable results, with some investigations suggesting phase advances and others phase delays. This variability may be attributable to differences in participant diagnosis, medication use, and methodology between studies. This study examined circadian timing in a sample of unmedicated women with and without unipolar major depressive disorder. Participants were aged 18-28 years, had no comorbid medical conditions, and were not taking medications. Eight women were experiencing a major depressive episode, nine had previously experienced an episode, and 31 were control participants with no history of mental illness. Following at least one week of actigraphic sleep monitoring, timing of salivary dim light melatonin onset (DLMO) was assessed in light of <1 lux. In currently depressed participants, melatonin onset occurred significantly earlier relative to sleep than in controls, with a large effect size. Earlier melatonin onset relative to sleep was also correlated with poorer mood for all participants. Our results indicate that during a unipolar major depressive episode, endogenous circadian phase is advanced relative to sleep time. This is consistent with the early-morning awakenings often seen in depression. Circadian misalignment may represent a precipitating or perpetuating factor that could be targeted for personalized treatment of major depression.

Social isolation rearing-induced anxiety and response to agomelatine in male and female rats: Role of corticosterone, oxytocin, and vasopressin

BACKGROUND

The chronobiotic antidepressant, agomelatine, acts via re-entrainment of circadian rhythms. Earlier work has demonstrated late-life anxiety and reduced corticosterone in post-weaning social isolation reared (SIR) rats. Agomelatine was anxiolytic in this model but did not reverse hypocortisolemia. Reduced corticosterone or cortisol (in humans) is well-described in anxiety states, although the anxiolytic-like actions of agomelatine may involve targeting another mechanism. Central oxytocin and vasopressin exert anxiolytic and anxiogenic effects, respectively, and are subject to circadian fluctuation, while also showing sex-dependent differences in response to various challenges.

AIMS AND METHODS

If corticosterone is less involved in the anxiolytic-like actions of agomelatine in SIR rats, we wondered whether effects on vasopressin and oxytocin may mediate these actions, and whether sex-dependent effects are evident. Anxiety as assessed in the elevated plus maze, as well as plasma vasopressin, oxytocin, and corticosterone were analyzed in social vs SIR animals receiving sub-chronic treatment with vehicle or agomelatine (40 mg/kg/day intraperitoneally at 16:00) for 16 days.

RESULTS

Social isolation rearing induced significant anxiety together with increased plasma vasopressin levels, but decreased corticosterone and oxytocin. While corticosterone displayed sex-dependent changes, vasopressin, and oxytocin changes were independent of sex. Agomelatine suppressed anxiety as well as reversed elevated vasopressin in both male and female rats and partially reversed reduced oxytocin in female but not male rats.

CONCLUSION

SIR-associated anxiety later in life involves reduced corticosterone and oxytocin, and elevated vasopressin. The anxiolytic-like effects of agomelatine in SIR rats predominantly involve targeting of elevated vasopressin.

Prospects for circadian treatment of mood disorders

Disruption of circadian clocks is strongly associated with mood disorders. Chronotherapies targeting circadian rhythms have been shown to be very effective treatments of mood disorders, but still are not widely used in clinical practice. The mechanisms by which circadian disruption leads to mood disorders are poorly characterized and, therefore, may not convince clinicians to apply chronotherapies. Hence, in this review, we describe specific potential mechanisms, in order to make this connection more credible to clinicians. We believe that four major features of disrupted clocks may contribute to the development of mood disorders: (1) loss of synchronization to environmental 24-h rhythms, (2) internal desynchronization among body clocks, (3) low rhythm amplitude, and (4) changes in sleep architecture. Discussing these attributes and giving plausible examples, we will discuss prospects for relatively simple chronotherapies addressing these features that are easy to implement in clinical practice. Key messages In this review, we describe specific potential mechanisms by which disrupted clocks may contribute to the development of mood disorders: (1) loss of synchronization to environmental 24-h rhythms, (2) internal desynchronization among body clocks, (3) low rhythm amplitude, and (4) changes in sleep architecture. We provide prospects for relatively simple chronotherapies addressing these features that are easy to implement in clinical practice.

Circadian rhythms and psychiatric profiles in young adults with unipolar depressive disorders

Abnormalities in circadian rhythms have been reported in people with mood disorders, but these abnormalities are marked by considerable inter-individual variability. This study aimed to identify pathophysiological subgroups on the basis of circadian markers and evaluate how these subgroups relate to psychiatric profiles. Thirty-five young adults (18-31 years old) receiving clinical care for unipolar depressive disorders and 15 healthy controls took part to this study. The Hamilton Rating Scale for Depression and the Young Mania rating scale were used to evaluate the severity of mood symptoms in participants with depressive disorders. All participant underwent ambulatory sleep monitoring with actigraphy for about 12 days before attending a laboratory-based chronobiological assessment which included repeated salivary samples to determine dim light melatonin onset (DLMO) and continuous core body temperature (CBT) monitoring using an ingestible temperature sensor. Cluster analyses were conducted across all participants to identify subgroups with consistent circadian timing profiles based on DLMO and the nocturnal minima of CBT. Two clusters were identified: 'delayed' and 'conventional timing' circadian phase. Descriptive analyses showed that the delayed cluster was characterised by abnormal time relationships between circadian phase markers and the sleep-wake cycle. Importantly, individuals from the delayed cluster had worse depression severity (t(28) = -2.7, p = 0.011) and hypomanic symptoms (Z = -2.2, p = 0.041) than their peers with conventional circadian timing. These findings suggest that delayed and disorganised circadian rhythms may be linked to worse psychiatric profiles in young people with depressive disorders.

Drugs Used in Circadian Sleep-Wake Rhythm Disturbances

This article focuses on melatonin and other melatonin receptor agonists, and specifically their circadian phase shifting and sleep-enhancing properties. The circadian system and circadian rhythm sleep-wake disorders are briefly reviewed, followed by a summary of the circadian phase shifting, sleep-enhancing properties, and possible safety concerns associated with melatonin and other melatonin receptor agonists. The recommended use of melatonin, including dose and timing, in the latest American Academy of Sleep Medicine Clinical Practice Guidelines for the treatment of intrinsic circadian rhythm disorders is also reviewed. Lastly, the practical aspects of treatment and consideration of clinical treatment outcomes are discussed.

Circadian rhythm in bipolar disorder: A review of the literature

Sleep disturbances and circadian rhythm dysfunction have been widely demonstrated in patients with bipolar disorder (BD). Irregularity of the sleep-wake rhythm, eveningness chronotype, abnormality of melatonin secretion, vulnerability of clock genes, and the irregularity of social time cues have also been well-documented in BD. Circadian rhythm dysfunction is prominent in BD compared with that in major depressive disorders, implying that circadian rhythm dysfunction is a trait marker of BD. In the clinical course of BD, the circadian rhythm dysfunctions may act as predictors for the first onset of BD and the relapse of mood episodes. Treatments focusing on sleep disturbances and circadian rhythm dysfunction in combination with pharmacological, psychosocial, and chronobiological treatments are believed to be useful for relapse prevention. Further studies are therefore warranted to clarify the relation between circadian rhythm dysfunction and the pathophysiology of BD to develop treatment strategies for achieving recovery in BD patients.

[A profile of antidepressive effects of agomelatine and a current view on the mechanism of its action]

Agomelatine is one of the latest antidepressants (melatoninergic agonists) with a new mechanism of action. From the positions of classical monoaminoergic theory, tts mechanism of action is difficult to understand, because the drug increases the levels of monoamines and neurotrophic factors, while not affecting their reuptake and negative feedback, which control neurotransmission level. Besides the effect on suprachiasmatic nucleus, a relevant role in the mechanism of action of agomelatine plays its special functionally selective (with regard to intracellular signaling pathways) interaction with heteromeric complexes of serotonin 5-НТ2С and melatonin MT2 receptors in the hippocampus and cerebral cortex. Agomelatine is competitive to other modern antidepressants in the efficacy assessed by the percentage of complete responders and superior in the total frequency of remissions. Compared to other SSRI antidepressants, agomelatine is more effective for anhedonia. In these cases, agomelatine increases the level of brain-derived neurotrophic factor (BDNF) in the blood of responders.

Drug information update: agomelatine

Agomelatine is a new antidepressant, licensed for the treatment of unipolar major depression, with a mode of action that combines activation of melatonin receptors with blockade of 5-HT2C receptors. Agomelatine is notable for its short duration of action in the body and modest side-effect burden; however, a number of theoretical and practical challenges have limited its adoption into mainstream treatment in the UK. Current meta-analyses show marginal clinical benefits of agomelatine relative to placebo and an association with occasional increases in liver transaminases. Theoretically it is not clear whether agomelatine does block brain 5-HT2C receptors in humans at therapeutic doses and the optimum daily timing of administration in depression has not been clearly established. However, agomelatine's novel mode of action justifies further study, perhaps with the eventual aim of matching its use in depression to patients with specific disturbances in circadian rhythm.

Parallel Changes in Mood and Melatonin Rhythm Following an Adjunctive Multimodal Chronobiological Intervention With Agomelatine in People With Depression: A Proof of Concept Open Label Study

Background: Agomelatine is a melatonin agonist and 5HT antagonist developed for the treatment of major depressive disorder which also has some effects on the circadian system. Since circadian dysfunctions are thought to play a role in the pathophysiology of depression, some of the mechanism of action of this drug may relate to improvements in circadian rhythms. Objective: This proof of concept open-label study sought to determine if improvements in depressive symptoms following an adjunctive multimodal intervention including agomelatine intake are associated with the magnitude of circadian realignment. This was investigated in young people with depression, a subgroup known to have high rates of delayed circadian rhythms. Methods: Young people with depression received a psychoeducation session about sleep and circadian rhythms, were asked to progressively phase advance their wake up time, and completed an 8 weeks course of agomelatine (25-50 mg). Participants underwent semi-structured psychological assessments, ambulatory sleep-wake monitoring and measurement of melatonin circadian phase before and after the intervention. Results: Twenty-four young adults with depression (17-28 years old; 58% females) completed the study. After the intervention, depressive symptoms were significantly reduced [t ₍₂₃₎ = 6.9, p < 0.001] and, on average, the timing of dim light melatonin onset (DLMO) shifted 3.6 h earlier [t ₍₁₈₎ = 4.4, p < 0.001]. On average, sleep onset was phase shifted 28 min earlier [t ₍₁₉₎ = 2.1, p = 0.047] and total sleep time increased by 24 min [t ₍₁₉₎ = -2.6, p = 0.018]. There was no significant change in wake-up times. A strong correlation (r = 0.69, p = 0.001) was found between the relative improvements in depression severity and the degree of phase shift in DLMO. Conclusion: Although this needs to be replicated in larger randomized controlled trials, these findings suggest that the degree of antidepressant response to a multimodal intervention including psychoeducation and agomelatine intake may be associated with the degree of change in evening melatonin release in young people with depression. This offers promising avenues for targeted treatment based on the prior identification of objective individual characteristics.

Clock-Enhancing Small Molecules and Potential Applications in Chronic Diseases and Aging

Normal physiological functions require a robust biological timer called the circadian clock. When clocks are dysregulated, misaligned, or dampened, pathological consequences ensue, leading to chronic diseases and accelerated aging. An emerging research area is the development of clock-targeting compounds that may serve as drug candidates to correct dysregulated rhythms and hence mitigate disease symptoms and age-related decline. In this review, we first present a concise view of the circadian oscillator, physiological networks, and regulatory mechanisms of circadian amplitude. Given a close association of circadian amplitude dampening and disease progression, clock-enhancing small molecules (CEMs) are of particular interest as candidate chronotherapeutics. A recent proof-of-principle study illustrated that the natural polymethoxylated flavonoid nobiletin directly targets the circadian oscillator and elicits robust metabolic improvements in mice. We describe mood disorders and aging as potential therapeutic targets of CEMs. Future studies of CEMs will shed important insight into the regulation and disease relevance of circadian clocks.

Associations of sleep duration with open angle glaucoma in the Korea national health and nutrition examination survey

The aim of this study is to investigate the relationship between sleep duration and glaucoma, stratified by obesity status.This study was conducted using data from the Korean National Health and Nutrition Examination Survey V 2010 to 2012. Open-angle glaucoma was diagnosed according to the International Society of Geographical and Epidemiological Ophthalmology criteria. Subjects were divided into subgroups based on those who were overweight (body mass index ≥25 kg/m or <25 kg/m) or with abdominal obesity (based on waist circumference). Multiple logistic regression analysis was done to estimate the magnitude of the association between sleep duration (<7 h, 7-<9, or ≥9 hours) and prevalence of glaucoma in the total population and in the subgroups.Individuals who slept <5 hours per night had the highest prevalence of glaucoma (5.55 ± 1.09%), followed by those who slept ≥9 hours per night (4.56 ± 0.10%), and then by those who slept 5 to <6 hours per night (4.15 ± 0.68%), which revealed a U-shaped pattern (P for trend = 0.072). Among overweight individuals, subjects who slept <7 hours and those who slept ≥9 hours were significantly more likely to have glaucoma compared with subjects who slept 7 to <9 hours after adjusting for survey year, age, sex, smoking, drinking, exercise, education level, household income, hypertension, intraocular pressure, stress, and depression (odds ratio, 2.41; 95% confidence interval, 1.14-5.03). Unlike for overweight individuals, sleep duration in nonoverweight individuals was not statistically significantly associated with glaucoma.Our results reveal a U-shaped association between sleep duration and the prevalence of glaucoma. An effect of sleep duration on glaucoma was present in the subgroup of overweight patients.

MT1 and MT2 Melatonin Receptors: A Therapeutic Perspective

Melatonin, or 5-methoxy-N-acetyltryptamine, is synthesized and released by the pineal gland and locally in the retina following a circadian rhythm, with low levels during the day and elevated levels at night. Melatonin activates two high-affinity G protein-coupled receptors, termed MT1 and MT2, to exert beneficial actions in sleep and circadian abnormality, mood disorders, learning and memory, neuroprotection, drug abuse, and cancer. Progress in understanding the role of melatonin receptors in the modulation of sleep and circadian rhythms has led to the discovery of a novel class of melatonin agonists for treating insomnia, circadian rhythms, mood disorders, and cancer. This review describes the pharmacological properties of a slow-release melatonin preparation (i.e., Circadin®) and synthetic ligands (i.e., agomelatine, ramelteon, tasimelteon), with emphasis on identifying specific therapeutic effects mediated through MT1 and MT2 receptor activation. Discovery of selective ligands targeting the MT1 or the MT2 melatonin receptors may promote the development of novel and more efficacious therapeutic agents.

Does melatonin treatment change emotional processing? Implications for understanding the antidepressant mechanism of agomelatine

The antidepressant, agomelatine, has a novel pharmacological profile, with agonist properties at M1 and M2 receptors and antagonist properties at 5HT2C receptors. Whether the antidepressant effects of this treatment are mediated by the drug's effects at the M1 and M2 receptors or the 5HT2C receptor or a synergy between these actions remains unclear. In the present study, a healthy volunteer model of emotional processing, which discriminates between effective and non-effective antidepressant compounds, was used to assess the contribution of melatonin agonism to the efficacy of agomelatine. Fifty-eight healthy volunteers were randomised to receive 7 days of once daily treatment with either 1 mg melatonin, 3 mg melatonin or placebo. Seven days treatment with 3 mg melatonin resulted in earlier bedtimes consistent with a phase advance in circadian rhythm. Some marginal effects of melatonin were observed on emotional processing; however, these were neither consistent with nor comparable to those seen following conventional antidepressant treatment or with agomelatine itself. These data suggest that the antidepressant action of agomelatine cannot be accounted for solely by its action at the M1 and M2 receptors.

The bipolarity of light and dark: A review on Bipolar Disorder and circadian cycles

BACKGROUND

Bipolar Disorder is characterized by episodes running the full mood spectrum, from mania to depression. Between mood episodes, residual symptoms remain, as sleep alterations, circadian cycle disturbances, emotional deregulation, cognitive impairment and increased risk for comorbidities. The present review intends to reflect about the most recent and relevant information concerning the biunivocal relation between bipolar disorder and circadian cycles.

METHODS

It was conducted a literature search on PubMed database using the search terms "bipolar", "circadian", "melatonin", "cortisol", "body temperature", "Clock gene", "Bmal1 gene", "Per gene", "Cry gene", "GSK3β", "chronotype", "light therapy", "dark therapy", "sleep deprivation", "lithum" and "agomelatine". Search results were manually reviewed, and pertinent studies were selected for inclusion as appropriate.

RESULTS

Several studies support the relationship between bipolar disorder and circadian cycles, discussing alterations in melatonin, body temperature and cortisol rhythms; disruption of sleep/wake cycle; variations of clock genes; and chronotype. Some therapeutics for bipolar disorder directed to the circadian cycles disturbances are also discussed, including lithium carbonate, agomelatine, light therapy, dark therapy, sleep deprivation and interpersonal and social rhythm therapy.

LIMITATIONS

This review provides a summary of an extensive research for the relevant literature on this theme, not a patient-wise meta-analysis.

CONCLUSIONS

In the future, it is essential to achieve a better understanding of the relation between bipolar disorder and the circadian system. It is required to establish new treatment protocols, combining psychotherapy, therapies targeting the circadian rhythms and the latest drugs, in order to reduce the risk of relapse and improve affective behaviour.

Agomelatine beyond borders: current evidences of its efficacy in disorders other than major depression

Agomelatine, a melatonergic antidepressant with a rapid onset of action, is one of the most recent drugs in the antidepressant category. Agomelatine's antidepressant actions are attributed to its sleep-promoting and chronobiotic actions mediated by MT1 and MT2 receptors present in the suprachiasmatic nucleus, as well as to its effects on the blockade of 5-HT2c receptors. Blockade of 5-HT2c receptors causes release of both noradrenaline and dopamine at the fronto-cortical dopaminergic and noradrenergic pathways. The combined actions of agomelatine on MT1/MT2 and 5-HT2c receptors facilitate the resynchronization of altered circadian rhythms and abnormal sleep patterns. Agomelatine appeared to be effective in treating major depression. Moreover, evidence exists that points out a possible efficacy of such drug in the treatment of bipolar depression, anxiety disorders, alcohol dependence, migraines etc. Thus, the aim of this narrative review was to elucidate current evidences on the role of agomelatine in disorders other than major depression.

Agomelatine in the treatment of major depressive disorder: an assessment of benefits and risks

Agomelatine (AGM) was approved for the treatment of major depressive disorder (MDD) in adults by the European Medicines Agency (EMA) in February 2009. It is an analogue of melatonin and features a unique pharmacodynamic profile with agonism on both types of melatonergic receptors (MT1/MT2) and antagonism at serotonergic 5-HT2C receptors. There is, however, an ongoing debate regarding the efficacy and safety of this novel antidepressant agent, originally evoked by claims of a significant publication bias underlying the assessment of AGM being an effective antidepressant. Indeed, two recent comprehensive metaanalyses of published and unpublished clinical trials found evidence for a relevant publication bias. However, due to its statistically significant advantage over placebo based on the results of these metaanalyses AGM must be referred to as an effective antidepressant agent in the acute phase of MDD. However, the effect sizes of AGM in the treatment of MDD were evaluated as being small in comparison to other antidepressant agents. In addition, there is insufficient evidence for the efficacy of AGM in relapse prevention of MDD. Apart from efficacy issues, AGM appears to have the potential to exhibit severe hepatotoxicity (the EMA has identified AGM-associated “hepatotoxic reactions” as a new safety concern in September 2013) that is currently poorly understood. Considering these aspects, it seems inappropriate to evaluate AGM as an antidepressant agent of first choice. Nevertheless, its unique mechanism of action with particular sleep modulating effects may represent a specific treatment strategy for patients with particular characteristics; further studies with thorough characterization of patients are needed to test this hypothesis.

Plasma melatonin is reduced in Huntington's disease

This study was undertaken to determine whether the production of melatonin, a hormone regulating sleep in relation to the light/dark cycle, is altered in Huntington's disease. We analyzed the circadian rhythm of melatonin in a 24-hour study of cohorts of control, premanifest, and stage II/III Huntington's disease subjects. The mean and acrophase melatonin concentrations were significantly reduced in stage II/III Huntington's disease subjects compared with controls. We also observed a nonsignificant trend toward reduced mean and acrophase melatonin in premanifest Huntington's disease subjects. Onset of melatonin rise was significantly more temporally spread in both premanifest and stage II/III Huntington's disease subjects compared with controls. A nonsignificant trend also was seen for reduced pulsatile secretion of melatonin. Melatonin concentrations are reduced in Huntington's disease. Altered melatonin patterns may provide an explanation for disrupted sleep and circadian behavior in Huntington's disease, and represent a biomarker for disease state. Melatonin therapy may help the sleep disorders seen in Huntington's disease.

Agomelatine: mechanism of action and pharmacological profile in relation to antidepressant properties

Agomelatine behaves both as a potent agonist at melatonin MT1 and MT2 receptors and as a neutral antagonist at 5-HT2C receptors. Accumulating evidence in a broad range of experimental procedures supports the notion that the psychotropic effects of agomelatine are due to the synergy between its melatonergic and 5-hydroxytryptaminergic effects. The recent demonstration of the existence of heteromeric complexes of MT1 and MT2 with 5-HT2C receptors at the cellular level may explain how these two properties of agomelatine translate into a synergistic action that, for example, leads to increases in hippocampal proliferation, maturation and survival through modulation of multiple cellular pathways (increase in trophic factors, synaptic remodelling, glutamate signalling) and key targets (early genes, kinases). The present review focuses on the pharmacological properties of this novel antidepressant. Its mechanism of action, strikingly different from that of conventional classes of antidepressants, opens perspectives towards a better understanding of the physiopathological bases underlying depression.

Agomelatine in the tree shrew model of depression: effects on stress-induced nocturnal hyperthermia and hormonal status

The antidepressive drug agomelatine combines the properties of an agonist of melatonergic receptors 1 and 2 with an antagonist of the 5-HT2C receptor. We analyzed the effects of agomelatine in psychosocially stressed male tree shrews, an established preclinical model of depression. Tree shrews experienced daily social stress for a period of 5 weeks and were concomitantly treated with different drugs daily for 4 weeks. The effects of agomelatine (40 mg/kg/day) were compared with those of the agonist melatonin (40 mg/kg/day), the inverse 5-HT2C antagonist S32006 (10mg/kg/day), and the SSRI fluoxetine (15 mg/kg/day). Nocturnal core body temperature (CBT) was recorded by telemetry, and urinary norepinephrine and cortisol concentrations were measured. Chronic social stress induced nocturnal hyperthermia. Agomelatine normalized the CBT in the fourth week of the treatment (T4), whereas the other drugs did not significantly counteract the stress-induced hyperthermia. Agomelatine also reversed the stress-induced reduction in locomotor activity. Norepinephrine concentration was elevated by the stress indicating sympathetic hyperactivity, and was normalized in the stressed animals treated with agomelatine or fluoxetine but not in those treated with melatonin or S32006. Cortisol concentration was elevated by stress but returned to basal levels by T4 in all animals, irrespective of the treatment. These observations show that agomelatine has positive effects to counteract stress-induced physiological processes and to restore the normal rhythm of nocturnal CBT. The data underpin the antidepressant properties of agomelatine and are consistent with a distinctive profile compared to its constituent pharmacological components and other conventional agents.

A functional polymorphism in the 5HTR2C gene associated with stress responses also predicts incident cardiovascular events

Previously we have shown that a functional nonsynonymous single nucleotide polymorphism (rs6318) of the 5HTR2C gene located on the X-chromosome is associated with hypothalamic-pituitary-adrenal axis response to a stress recall task, and with endophenotypes associated with cardiovascular disease (CVD). These findings suggest that individuals carrying the rs6318 Ser23 C allele will be at higher risk for CVD compared to Cys23 G allele carriers. The present study examined allelic variation in rs6318 as a predictor of coronary artery disease (CAD) severity and a composite endpoint of all-cause mortality or myocardial infarction (MI) among Caucasian participants consecutively recruited through the cardiac catheterization laboratory at Duke University Hospital (Durham, NC) as part of the CATHGEN biorepository. Study population consisted of 6,126 Caucasian participants (4,036 [65.9%] males and 2,090 [34.1%] females). A total of 1,769 events occurred (1,544 deaths and 225 MIs; median follow-up time =  5.3 years, interquartile range  = 3.3–8.2). Unadjusted Cox time-to-event regression models showed, compared to Cys23 G carriers, males hemizygous for Ser23 C and females homozygous for Ser23C were at increased risk for the composite endpoint of all-cause death or MI: Hazard Ratio (HR)  = 1.47, 95% confidence interval (CI)  = 1.17, 1.84, p  = .0008. Adjusting for age, rs6318 genotype was not related to body mass index, diabetes, hypertension, dyslipidemia, smoking history, number of diseased coronary arteries, or left ventricular ejection fraction in either males or females. After adjustment for these covariates the estimate for the two Ser23 C groups was modestly attenuated, but remained statistically significant: HR  = 1.38, 95% CI = 1.10, 1.73, p = .005. These findings suggest that this functional polymorphism of the 5HTR2C gene is associated with increased risk for CVD mortality and morbidity, but this association is apparently not explained by the association of rs6318 with traditional risk factors or conventional markers of atherosclerotic disease.

Melatonin and the theories of aging: a critical appraisal of melatonin's role in antiaging mechanisms

The classic theories of aging such as the free radical theory, including its mitochondria-related versions, have largely focused on a few specific processes of senescence. Meanwhile, numerous interconnections have become apparent between age-dependent changes previously thought to proceed more or less independently. Increased damage by free radicals is not only linked to impairments of mitochondrial function, but also to inflammaging as it occurs during immune remodeling and by release of proinflammatory cytokines from mitotically arrested, DNA-damaged cells that exhibit the senescence-associated secretory phenotype (SASP). Among other effects, SASP can cause mutations in stem cells that reduce the capacity for tissue regeneration or, in worst case, lead to cancer stem cells. Oxidative stress has also been shown to promote telomere attrition. Moreover, damage by free radicals is connected to impaired circadian rhythmicity. Another nexus exists between cellular oscillators and metabolic sensing, in particular to the aging-suppressor SIRT1, which acts as an accessory clock protein. Melatonin, being a highly pleiotropic regulator molecule, interacts directly or indirectly with all the processes mentioned. These influences are critically reviewed, with emphasis on data from aged organisms and senescence-accelerated animals. The sometimes-controversial findings obtained either in a nongerontological context or in comparisons of tumor with nontumor cells are discussed in light of evidence obtained in senescent organisms. Although, in mammals, lifetime extension by melatonin has been rarely documented in a fully conclusive way, a support of healthy aging has been observed in rodents and is highly likely in humans.

Major depressive disorder: a loss of circadian synchrony?

Circadian rhythms in the sleep/wake cycle, along with a range of physiological measures, are severely disrupted in individuals with major depressive disorder (MDD). Moreover, several central circadian genes have been implicated as potential genetic factors underlying the illness through candidate gene studies and some genome wide association studies. However, investigations into the molecular underpinnings of circadian disturbances in the human brain have been quite challenging. In their recent publication, Li and colleagues have used a novel approach to determine the rhythmic patterns of circadian gene expression in several regions of the human brain, and how these patterns are disrupted in MDD. Their findings demonstrate that in healthy subjects, several brain regions outside the suprachiasmatic nucleus (the master clock) exhibit diurnal gene expression patterns that are disrupted in the brains of MDD subjects. These findings will provide the foundation for future studies of gene-specific drug targets, and biomarkers for the disease.

The melatonergic system in mood and anxiety disorders and the role of agomelatine: implications for clinical practice

Melatonin exerts its actions through membrane MT1/MT2 melatonin receptors, which belong to the super family of G-protein-coupled receptors consisting of the typical seven transmembrane domains. MT1 and MT2 receptors are expressed in various tissues of the body either as single ones or together. A growing literature suggests that the melatonergic system may be involved in the pathophysiology of mood and anxiety disorders. In fact, some core symptoms of depression show disturbance of the circadian rhythm in their clinical expression, such as diurnal mood and other symptomatic variation, or are closely linked to circadian system functioning, such as sleep-wake cycle alterations. In addition, alterations have been described in the circadian rhythms of several biological markers in depressed patients. Therefore, there is interest in developing antidepressants that have a chronobiotic effect (i.e., treatment of circadian rhythm disorders). As melatonin produces chronobiotic effects, efforts have been aimed at developing agomelatine, an antidepressant with melatonin agonist activity. The present paper reviews the role of the melatonergic system in the pathophysiology of mood and anxiety disorders and the clinical characteristics of agomelatine. Implications of agomelatine in "real world" clinical practice will be also discussed.

Manipulating the sleep-wake cycle and circadian rhythms to improve clinical management of major depression

BACKGROUND

Clinical psychiatry has always been limited by the lack of objective tests to substantiate diagnoses and a lack of specific treatments that target underlying pathophysiology. One area in which these twin failures has been most frustrating is major depression. Due to very considerable progress in the basic and clinical neurosciences of sleep-wake cycles and underlying circadian systems this situation is now rapidly changing.

DISCUSSION

The development of specific behavioral or pharmacological strategies that target these basic regulatory systems is driving renewed clinical interest. Here, we explore the extent to which objective tests of sleep-wake cycles and circadian function - namely, those that measure timing or synchrony of circadian-dependent physiology as well as daytime activity and nighttime sleep patterns - can be used to identify a sub-class of patients with major depression who have disturbed circadian profiles.

SUMMARY

Once this unique pathophysiology is characterized, a highly personalized treatment plan can be proposed and monitored. New treatments will now be designed and old treatments re-evaluated on the basis of their effects on objective measures of sleep-wake cycles, circadian rhythms and related metabolic systems.

Pharmacotherapy of insomnia

INTRODUCTION

Insomnia is one of the most prevalent sleep disorders in developed countries, being surpassed only by chronic sleep deprivation. Patients with insomnia tend to have an altered quality of life, impaired daytime functioning and an increased risk of work accidents and motor vehicle crashes. Insomnia is commonly associated with chronic medical conditions, metabolic illnesses and mental disorders (such as depression and anxiety), with which there is a dual, reciprocal relationship.

AREAS COVERED

This paper focuses on current pharmacotherapy options for the treatment of insomnia, particularly benzodiazepine receptor agonists, which nowadays represent the mainstay of hypnotic therapy. The melatonin receptor antagonist, ramelteon, is reviewed (an alternative for some patients with only sleep-onset difficulty), as are sedating antidepressants, which are commonly used 'off-label' to treat insomnia, despite limited efficacy data and potential significant safety concerns. Orexin (OX) antagonists are also discussed, especially those that block OX2 or both OX1 and OX2 receptors, as these are the most promising new agents for the treatment of insomnia, with encouraging results in preliminary clinical trials.

EXPERT OPINION

Research to evaluate and formulate treatments for insomnia is often complicated by the fact that insomnia is usually of multifactorial etiology. Understanding the molecular and receptor mechanisms involved in promoting sleep in varied disorders could provide future approaches in new drug development. In the long term, more randomized controlled trials are needed to assess both short-term and long-term effects of these medications and their efficacy in comorbid diseases that affect sleep quality or quantity.