The effect of melatonergic and non-melatonergic antidepressants on sleep: weighing the alternatives

Agomelatine for the treatment of generalized anxiety disorder: focus on its distinctive mechanism of action

Generalized anxiety disorder (GAD), the most frequently diagnosed form of anxiety, is usually treated by cognitive-behavioural approaches or medication; in particular, benzodiazepines (acutely) and serotonin or serotonin/noradrenaline reuptake inhibitors (long term). Efficacy, compliance, and acceptability are, however, far from ideal, reinforcing interest in alternative options. Agomelatine, clinically employed in the treatment of major depression, expresses anxiolytic properties in rodents and was effective in the treatment of GAD (including severely ill patients) in several double-blind, short-term (12 weeks) and relapse-prevention (6 months) studies. At active doses, the incidence of adverse effects was no higher than for placebo. Agomelatine possesses a unique binding profile, behaving as a melatonin (MT₁/MT₂) receptor agonist and 5-HT_2C receptor antagonist, yet recognizing neither monoamine transporters nor GABA_A receptors. Extensive evidence supports a role for 5-HT_2C receptors in the induction of anxious states, and their blockade likely plays a primary role in mediating the anxiolytic actions of agomelatine, including populations in the amygdala and bed nucleus of stria terminalis, as well as the hippocampus. Recruitment of MT receptors in the suprachiasmatic nucleus, thalamic reticular nucleus, and hippocampus appears to fulfil a complimentary role. Downstream of 5-HT_2C and MT receptors, modulation of stress-sensitive glutamatergic circuits and altered release of the anxiogenic neuropeptides, corticotrophin-releasing factor, and vasopressin, may be implicated in the actions of agomelatine. To summarize, agomelatine exerts its anxiolytic actions by mechanisms clearly distinct from those of other agents currently employed for the management of GAD.

PLAIN LANGUAGE SUMMARY

How agomelatine helps in the treatment of anxiety disorders.

INTRODUCTION

• Anxiety disorders have a significant negative impact on quality of life.• The most common type of anxiety disorder, called generalized anxiety disorder (GAD), is associated with nervousness and excessive worry.• These symptoms can lead to additional symptoms like tiredness, sleeplessness, irritability, and poor attention.• GAD is generally treated through either cognitive-behavioural therapy or medication. However, widely used drugs like benzodiazepines and serotonin reuptake inhibitors have adverse effects.• Agomelatine, a well-established antidepressant drug, has shown anxiety-lowering ('anxiolytic') properties in rats and has been shown to effectively treat GAD with minimal side effects.• However, exactly how it acts on the brain to manage GAD is not yet clear.• Thus, this review aims to shed light on agomelatine's mechanism of action in treating GAD.

METHODS

• The authors reviewed studies on how agomelatine treats anxiety in animals.• They also looked at clinical studies on the effects of agomelatine in people with GAD.

RESULTS

• The study showed that agomelatine 'blocks' a receptor in nerve cells, which plays a role in causing anxiety, called the 5-HT_2C receptor.• Blocking this receptor, especially in specific brain regions such as nerve cells of the amygdala, bed nucleus of stria terminalis, and hippocampus, produced the anxiety reduction seen during agomelatine treatment.• Agomelatine also activates the melatonin (MT) receptor, which is known to keep anxiety in check, promote sleep, and maintain the sleep cycle.• Agomelatine should thus tackle sleep disturbances commonly seen in patients with GAD.• Beyond 5-HT_2C and MT receptors, signalling molecules in nerve cells that are known to be involved in anxiety disorders (called 'neurotransmitters' and 'neuropeptides') are also affected by agomelatine.

CONCLUSION

• Agomelatine's anxiolytic effects are caused by mechanisms that are distinct from those of other medications currently used to treat GAD.• This explains its therapeutic success and minimal adverse side effects.

Effects of agomelatine and mirtazapine on sleep disturbances in major depressive disorder: evidence from polysomnographic and resting-state functional connectivity analyses

To investigate effects of agomelatine and mirtazapine on sleep disturbances in patients with major depressive disorder. A total of 30 depressed patients with sleep disturbances, 27 of which completed the study, took agomelatine or mirtazapine for 8 weeks. Subjective scales were administered, and polysomnography was performed at baseline and at the end of week 1 and 8. Functional magnetic resonance imaging was performed at baseline and at the end of week 8. Compared with baseline, scores on the Hamilton Depression Scale, Hamilton Anxiety Scale, Pittsburgh Sleep Quality Index, Sleep Dysfunction Rating Scale, and Insomnia Severity Index after 8 weeks of treatment significantly decreased in both groups, with no significant differences between groups, accompanied by significant increases in total sleep time, sleep efficiency, and rapid eye movement (REM) sleep and significant decrease in wake after sleep onset. Mirtazapine treatment increased N3 sleep at week 1 compared with agomelatine treatment, but this difference disappeared at week 8. The increases in the percentage and duration of N3 sleep were positively correlated with increases in connectivity between right dorsal lateral prefrontal cortex (dlPFC) and right precuneus and between left posterior cingulate cortex and right precuneus in both groups, respectively. Functional connectivity (FC) between right dlPFC and left precuneus in mirtazapine group was higher compared with agomelatine group after 8 weeks of treatment. These findings indicated that both agomelatine and mirtazapine improved sleep in depressed patients, and the effect of mirtazapine was greater than agomelatine with regard to rapidly increasing N3 sleep and gradually improving FC in the brain.

Depressive disorders: Processes leading to neurogeneration and potential novel treatments

Mood disorders are wide spread with estimates that one in seven of the population are affected at some time in their life (Kessler et al., 2012). Many of those affected with severe depressive disorders have cognitive deficits which may progress to frank neurodegeneration. There are several peripheral markers shown by patients who have cognitive deficits that could represent causative factors and could potentially serve as guides to the prevention or even treatment of neurodegeneration. Circadian rhythm misalignment, immune dysfunction and oxidative stress are key pathologic processes implicated in neurodegeneration and cognitive dysfunction in depressive disorders. Novel treatments targeting these pathways may therefore potentially improve patient outcomes whereby the primary mechanism of action is outside of the monoaminergic system. Moreover, targeting immune dysfunction, oxidative stress and circadian rhythm misalignment (rather than primarily the monoaminergic system) may hold promise for truly disease modifying treatments that may prevent neurodegeneration rather than simply alleviating symptoms with no curative intent. Further research is required to more comprehensively understand the contributions of these pathways to the pathophysiology of depressive disorders to allow for disease modifying treatments to be discovered.

Zolpidem's use for insomnia

Zolpidem is a short-acting non-benzodiazepine hypnotic drug that belongs to the imidazopyridine class. In addition to immediate-release (IR) and extended-release (ER) formulations, the new delivery forms including two sublingual tablets [standard dose (SD) and low dose (LD)], and an oral spray form have been recently developed which bypass the gastrointestinal tract. So far, Zolpidem has been studied in several clinical populations: cases poor sleepers, transient insomnia, elderly and non-elderly patients with chronic primary insomnia, and in comorbid insomnia. Peak plasma concentration (Tmax) of zolpidem-IR occurs in 45 to 60min, with the terminal elimination half-life (t½) equating to 2.4h. The extended-release formulation results in a higher concentration over a period of more than 6h. Peak plasma concentration is somewhat shorter for the sublingual forms and the oral spray, while their t½ is comparable to that of zolpidem-IR. Zolpidem-IR reduces sleep latency (SL) at recommended doses of 5mg and 10mg in elderly and non-elderly patients, respectively. Zolpidem-ER at doses of 6.25mg and 12.5mg, improves sleep maintenance in elderly and non-elderly patients, respectively, 4h after its administration. Sublingual zolpidem-LD (5mg) and zolpidem oral spray are indicated for middle-of-the-night (MOTN) wakefulness and difficulty returning to sleep, while sublingual zolpidem-SD (10mg) is marketed for difficulty falling asleep. With their array of therapeutic uses and their popularity among physicians and patients; this review describes the clinical pharmacology, indications and uses, identifying withdrawal symptoms, abuse and dependence potentials, and adverse drug reactions are discussed.

Therapeutic strategies for circadian rhythm and sleep disturbances in Huntington disease

Aside from the well-known motor, cognitive and psychiatric signs and symptoms, Huntington disease (HD) is also frequently complicated by circadian rhythm and sleep disturbances. Despite the observation that these disturbances often precede motor onset and have a high prevalence, no studies are available in HD patients which assess potential treatments. In this review, we will briefly outline the nature of circadian rhythm and sleep disturbances in HD and subsequently focus on potential treatments based on findings in other neurodegenerative diseases with similarities to HD, such as Parkinson and Alzheimer disease. The most promising treatment options to date for circadian rhythm and sleep disruption in HD include melatonin (agonists) and bright light therapy, although further corroboration in clinical trials is warranted.

Neurobiology, pathophysiology, and treatment of melatonin deficiency and dysfunction

Melatonin is a highly pleiotropic signaling molecule, which is released as a hormone of the pineal gland predominantly during night. Melatonin secretion decreases during aging. Reduced melatonin levels are also observed in various diseases, such as types of dementia, some mood disorders, severe pain, cancer, and diabetes type 2. Melatonin dysfunction is frequently related to deviations in amplitudes, phasing, and coupling of circadian rhythms. Gene polymorphisms of melatonin receptors and circadian oscillator proteins bear risks for several of the diseases mentioned. A common symptom of insufficient melatonin signaling is sleep disturbances. It is necessary to distinguish between symptoms that are curable by short melatonergic actions and others that require extended actions during night. Melatonin immediate release is already effective, at moderate doses, for reducing difficulties of falling asleep or improving symptoms associated with poorly coupled circadian rhythms, including seasonal affective and bipolar disorders. For purposes of a replacement therapy based on longer-lasting melatonergic actions, melatonin prolonged release and synthetic agonists have been developed. Therapies with melatonin or synthetic melatonergic drugs have to consider that these agents do not only act on the SCN, but also on numerous organs and cells in which melatonin receptors are also expressed.

Melatonin, the circadian multioscillator system and health: the need for detailed analyses of peripheral melatonin signaling

Evidence is accumulating regarding the importance of circadian core oscillators, several associated factors, and melatonin signaling in the maintenance of health. Dysfunction of endogenous clocks, melatonin receptor polymorphisms, age- and disease-associated declines of melatonin likely contribute to numerous diseases including cancer, metabolic syndrome, diabetes type 2, hypertension, and several mood and cognitive disorders. Consequences of gene silencing, overexpression, gene polymorphisms, and deviant expression levels in diseases are summarized. The circadian system is a complex network of central and peripheral oscillators, some of them being relatively independent of the pacemaker, the suprachiasmatic nucleus. Actions of melatonin on peripheral oscillators are poorly understood. Various lines of evidence indicate that these clocks are also influenced or phase-reset by melatonin. This includes phase differences of core oscillator gene expression under impaired melatonin signaling, effects of melatonin and melatonin receptor knockouts on oscillator mRNAs or proteins. Cross-connections between melatonin signaling pathways and oscillator proteins, including associated factors, are discussed in this review. The high complexity of the multioscillator system comprises alternate or parallel oscillators based on orthologs and paralogs of the core components and a high number of associated factors with varying tissue-specific importance, which offers numerous possibilities for interactions with melatonin. It is an aim of this review to stimulate research on melatonin signaling in peripheral tissues. This should not be restricted to primary signal molecules but rather include various secondarily connected pathways and discriminate between direct effects of the pineal indoleamine at the target organ and others mediated by modulation of oscillators.

Sedative antidepressants and insomnia

OBJECTIVE: The present review addresses the relationship between sleep and depression and how serotonergic transmission is implicated in both conditions. METHOD: Literature searches were performed in the PubMed and MedLine databases up to March 2010. The terms searched were "insomnia", "depression", "sedative antidepressants" and "serotonin". In order to pinpoint the sedative antidepressants most used to treat insomnia, 34 ISI articles, mainly reviews and placebo-controlled clinical trials, were selected from 317 articles found in our primary search. RESULTS: Sleep problems may appear months before the diagnosis of clinical depression and persist after the resolution of depression. Treatment of insomnia symptoms may improve this comorbid disease. Some antidepressant drugs can also result in insomnia or daytime sleepiness. Serotonin (5-HT) demonstrates a complex pattern with respect to sleep and wakefulness that is related to the array of 5-HT receptor subtypes involved in different physiological functions. It is now believed that 5HT2 receptor stimulation is subjacent to insomnia and changes in sleep organization related to the use of some antidepressants. CONCLUSION: Some drugs commonly prescribed for the treatment of depression may worsen insomnia and impair full recovery from depression. 5-HT2 receptor antagonists are promising drugs for treatment strategies since they can improve comorbid insomnia and depression.

Strategies to enhance the therapeutic efficacy of antidepressants: targeting residual symptoms

Major depressive disorder (MDD) is an illness of great morbidity that affects many people across the world. The current goal for treatment of MDD is to achieve remission (i.e., no depressive symptoms). However, despite scientific advances in the treatment for MDD, antidepressants as first-line agents yield only modest remission rates. In fact, a recent study indicated that only one out of three subjects who received a standard, first-line antidepressant attained remission. Not achieving remission from depressive symptoms increases the risk of a more chronic and debilitating course of illness with frequent recurrences. Although a number of reasons contribute to these modest outcomes, the presence of residual symptoms is a major problem. Residual symptoms are defined as symptoms that linger despite an adequate dose and duration of an antidepressant medication. This article reviews the prevalence and clinical impact of common residual symptoms and discusses the utility of aggressively addressing residual symptoms to enhance the efficacy of antidepressant medications.