Efficacy of the selective extrasynaptic GABAA agonist, gaboxadol, in a model of transient insomnia: A randomized, controlled clinical trial

Novel neuropharmacological activity of citrus lime (Citrus aurantifolia): A standardized lime peel supplement enhances non-rapid eye movement sleep by activating the GABA type A receptor

Polyphenols have been well-established to exert sedative-hypnotic effects in psychopharmacology. Lime (Citrus aurantifolia) peel is rich in biologically active polyphenols; however, the effects of lime peel extract on sleep have not yet been demonstrated. A comparison was conducted in mice, between the sleep-promoting effects of a standardized lime peel supplement (SLPS) and a well-known hypnotic drug, zolpidem, and its hypnotic mechanism was investigated using in vivo and in vitro assays. The effects of SLPS on sleep were assessed using a pentobarbital-induced sleep test and sleep architecture analysis based on recording electroencephalograms and electromyograms. Additionally, a GABAA receptor binding assay, electrophysiological measurements, and in vivo animal models were used to elucidate the hypnotic mechanism. SLPS (200 and 400 mg/kg) was found to significantly decrease sleep latency and increase the amount of non-rapid eye movement sleep without altering delta activity. The hypnotic effects of SLPS were attributed to its flavonoid-rich ethyl acetate fraction. SLPS had a binding affinity to the GABA-binding site of the GABAA receptor and directly activated the GABAA receptors. The hypnotic effects and GABAA receptor activity of SLPS were completely blocked by bicuculline, a competitive antagonist of the GABAA receptor, in both in vitro and in vivo assays. To the best of our knowledge, this study is the first to demonstrate the hypnotic effects of SLPS, which acts via the GABA-binding site of the GABAA receptor. Our results suggest that lime peel, a by-product abundantly generated during juice processing, can potentially be used as a novel sedative-hypnotic.

Extra-synaptic modulation of GABAA and efficacy in bipolar disorder

BACKGROUND

Bipolar disorder type I is a severe psychiatric condition that leads to significant morbidity and mortality and whose treatment remains suboptimal. Its pathophysiology involves disturbance in the control of ionic fluxes so that when patients are either manic or depressed, the resting membrane potential of neurons is more depolarized than normal. Available mood stabilizers have a shared mechanism of normalizing ion flux by compensating for ionic abnormalities, and normalizing membrane potential.

HYPOTHESIS

Agents that significantly potentiate extrasynaptic GABA_A receptors are expected to be particularly effective in hyperpolarizing resting membrane potential in bipolar patients, thereby normalizing their membrane potential.

DISCUSSION

New neuroactive steroid-like agents are being tested in humans for depression and insomnia. These agents include brexanolone, ganaxolone, and gaboxadol. Brexanolone has been approved for the treatment of postpartum depression, ganaxolone is being studied for treatment-resistant depression, and gaboxadol development for the treatment of insomnia has been abandoned due to narrow therapeutic index. In addition to the current studies, these agents are expected to have particular efficacy in acute and prophylactic management of bipolar I disorder by hyperpolarizing the resting potential of neurons and antagonizing one of the most reproducible demonstrated biologic abnormalities of this illness.

EEG spectral analysis of NREM sleep in a large sample of patients with insomnia and good sleepers: effects of age, sex and part of the night

Previous studies of the differences between patients with insomnia and good sleepers with regard to quantitative electroencephalographic measures have mostly utilized small samples and consequently had limited ability to account for potentially important confounding factors of age, sex and part of the night. We conducted a power spectral analysis using a large database of sleep electroencephalographic recordings to evaluate differences between patients with insomnia (N = 803) and good sleepers (N = 811), while simultaneously accounting for these factors and their interaction. Comparisons of power as a function of age and part of the night were made between cohorts (patients with insomnia versus good sleepers) by sex. Absolute power in the delta, theta and sigma bands declined with age for both females and males. Females had significantly greater power than males at all ages, and for each band, cohort and part of the night. These sex differences were much greater than differences between patients with insomnia and good sleepers. Compared with good sleepers, patients with insomnia under age 40-45 years had reduced delta band power during Part 1 of the night. Females with insomnia over age 45 years had increased delta and theta band power in Parts 2 and 3 of the night, and males with insomnia under age 40 years had reduced theta power in Part 1. Females with insomnia had increased beta2 power in all parts of the night, and males with insomnia had reduced alpha power during all parts of the night. Relative power (the proportion that an individual frequency band contributes to the total power) decreased in the delta band and increased in all other bands with age for both cohorts, sexes and all parts of the night. This analysis provides a unique resource for quantitative information on the differences in power spectra between patients with insomnia and good sleepers accounting for age, sex and part of the night.

The sleep effects of lurasidone: a placebo-controlled cross-over study using a 4-h phase-advance model of transient insomnia

BACKGROUND

Lurasidone, an atypical antipsychotic, is a potent 5-HT7 antagonist and D2 , 5-HT2A antagonist, and 5-HT1A partial agonist. As such, lurasidone would be expected to modulate sleep and circadian function but there have been no human studies of the sleep effects of a 5-HT7 antagonist. The purpose of this study was to assess effects of lurasidone on sleep.

METHODS

This was a cross-over, polysomnographic study involving 54 healthy volunteers who underwent two treatment periods (order randomized) each consisting of two nights in the laboratory: Night 1-lights out at usual bedtime; Night 2-4-h advance of sleep phase and randomization to either lurasidone 40 mg or placebo. The next morning impairment testing was carried out.

RESULTS

Lurasidone significantly (p < 0.05) increased total sleep time by an average of 28.4 min versus placebo, decreased wake time after sleep onset and wake time after the final awakening, and increased sleep efficiency. No other effects were found.

CONCLUSIONS

Lurasidone had a sleep maintenance effect without effects on sleep onset, rapid eye movement, or slow-wave sleep. Lurasidone is likely to be beneficial to patients with disturbed sleep, particularly those with sleep maintenance problems. Copyright © 2016 John Wiley & Sons, Ltd.

A randomized, double-blind, placebo-controlled, multicenter, 28-day, polysomnographic study of gabapentin in transient insomnia induced by sleep phase advance

STUDY OBJECTIVE

To evaluate multiple doses of gabapentin 250 mg on polysomnography (PSG) and participant-reported sleep assessments in a 5-h phase advance insomnia model.

METHODS

Adults reporting occasional disturbed sleep received gabapentin 250 mg (n = 128) or placebo (n = 128). On Days 1 and 28, participants received medication 30 min before bedtime and were in bed from 17:00 to 01:00, ∼5 h before their habitual bedtime. Sleep was assessed by PSG, a post sleep questionnaire, and the Karolinska Sleep Diary. Next-day residual effects and tolerability were evaluated. On Days 2-27, participants took medication at home 30 min before their habitual bedtime.

RESULTS

Treatment-group demographics were comparable. Gabapentin resulted in significantly less PSG wake after sleep onset (WASO) compared with placebo on Day 1 (primary endpoint, mean: 107.0 versus 149.1 min, p ≤ 0.001) and Day 28 (113.6 versus 152.3 min, p = 0.002), and significantly greater total sleep time (TST; Day 1: 347.6 versus 283.9 min; Day 28: 335.3 versus 289.1 min) (p ≤ 0.001). Participant-reported WASO and TST also showed significant treatment effects on both days. Gabapentin was associated with less %stage1 on Day 1, and greater %REM on Day 28, versus placebo. During home use, gabapentin resulted in significantly less participant-reported WASO and higher ratings of sleep quality. Gabapentin was well tolerated (most common adverse events: headache, somnolence) with no evidence of next-day impairment.

CONCLUSION

Gabapentin 250 mg resulted in greater PSG and participant-reported sleep duration following a 5-h phase advance on Day 1 and Day 28 of use without evidence of next-day impairment, and greater sleep duration during at-home use.

A reinforcing circuit action of extrasynaptic GABAA receptor modulators on cerebellar granule cell inhibition

GABA_A receptors (GABARs) are the targets of a wide variety of modulatory drugs which enhance chloride flux through GABAR ion channels. Certain GABAR modulators appear to acutely enhance the function of δ subunit-containing GABAR subtypes responsible for tonic forms of inhibition. Here we identify a reinforcing circuit mechanism by which these drugs, in addition to directly enhancing GABAR function, also increase GABA release. Electrophysiological recordings in cerebellar slices from rats homozygous for the ethanol-hypersensitive (α6100Q) allele show that modulators and agonists selective for δ-containing GABARs such as THDOC, ethanol and THIP (gaboxadol) increased the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) in granule cells. Ethanol fails to augment granule cell sIPSC frequency in the presence of glutamate receptor antagonists, indicating that circuit mechanisms involving granule cell output contribute to ethanol-enhancement of synaptic inhibition. Additionally, GABAR antagonists decrease ethanol-induced enhancement of Golgi cell firing. Consistent with a role for glutamatergic inputs, THIP-induced increases in Golgi cell firing are abolished by glutamate receptor antagonists. Moreover, THIP enhances the frequency of spontaneous excitatory postsynaptic currents in Golgi cells. Analyses of knockout mice indicate that δ subunit-containing GABARs are required for enhancing GABA release in the presence of ethanol and THIP. The limited expression of the GABAR δ subunit protein within the cerebellar cortex suggests that an indirect, circuit mechanism is responsible for stimulating Golgi cell GABA release by drugs selective for extrasynaptic isoforms of GABARs. Such circuit effects reinforce direct actions of these positive modulators on tonic GABAergic inhibition and are likely to contribute to the potent effect of these compounds as nervous system depressants.

About sleep's role in memory

Over more than a century of research has established the fact that sleep benefits the retention of memory. In this review we aim to comprehensively cover the field of "sleep and memory" research by providing a historical perspective on concepts and a discussion of more recent key findings. Whereas initial theories posed a passive role for sleep enhancing memories by protecting them from interfering stimuli, current theories highlight an active role for sleep in which memories undergo a process of system consolidation during sleep. Whereas older research concentrated on the role of rapid-eye-movement (REM) sleep, recent work has revealed the importance of slow-wave sleep (SWS) for memory consolidation and also enlightened some of the underlying electrophysiological, neurochemical, and genetic mechanisms, as well as developmental aspects in these processes. Specifically, newer findings characterize sleep as a brain state optimizing memory consolidation, in opposition to the waking brain being optimized for encoding of memories. Consolidation originates from reactivation of recently encoded neuronal memory representations, which occur during SWS and transform respective representations for integration into long-term memory. Ensuing REM sleep may stabilize transformed memories. While elaborated with respect to hippocampus-dependent memories, the concept of an active redistribution of memory representations from networks serving as temporary store into long-term stores might hold also for non-hippocampus-dependent memory, and even for nonneuronal, i.e., immunological memories, giving rise to the idea that the offline consolidation of memory during sleep represents a principle of long-term memory formation established in quite different physiological systems.

GABA site agonist gaboxadol induces addiction-predicting persistent changes in ventral tegmental area dopamine neurons but is not rewarding in mice or baboons

Dopamine neurons of the ventral tegmental area (VTA) are involved at early phases of drug addiction. Even the first in vivo dose of various abused drugs induces glutamate receptor plasticity at the excitatory synapses of these neurons. Benzodiazepines that suppress the inhibitory GABAergic interneurons in the VTA via facilitation of synaptic GABA(A) receptors have induced neuroplasticity in dopamine neurons due to this disinhibitory mechanism. Here, we have tested a non-benzodiazepine direct GABA site agonist 4,5,6,7-tetrahydroisoxazolol[4,5-c]pyridine-3-ol (THIP) (also known as gaboxadol) that acts preferentially via high-affinity extrasynaptic GABA(A) receptors. A single sedative dose of THIP (6 mg/kg) to mice induced glutamate receptor plasticity for at least 6 d after administration. Increased AMPA/NMDA receptor current ratio and increased frequency, amplitude, and rectification of AMPA receptor responses suggested persistent targeting of GluA2-lacking AMPA receptors in excitatory synapses of VTA dopamine neurons ex vivo after THIP administration. This effect was abolished in GABA(A) receptor δ(-/-) mice, which have a loss of extrasynaptic GABA(A) receptors. In behavioral experiments, we found neither acute reinforcement in intravenous self-administration sessions with THIP at relevant doses using a yoked control paradigm in mice nor in baboons using a standard paradigm for assessing drug abuse liability; nor was any place preference found after conditioning sessions with various doses of THIP but rather a persistent aversion in 6 mg/kg THIP-conditioned mice. In summary, we found that activation of extrasynaptic δ-subunit-containing GABA(A) receptors leads to glutamate receptor plasticity of VTA dopamine neurons, but is not rewarding, and, instead, induces aversion.

EEG power spectra response to a 4-h phase advance and gaboxadol treatment in 822 men and women

STUDY OBJECTIVE

To explore the effect of gaboxadol on NREM EEG in transient insomnia using power spectral analysis and evaluate the response between men and women.

METHODS

This was a randomized, double-blind, 3-way, parallel-group transient insomnia study in 22 sleep laboratories. After a baseline night (N1), subjects underwent a 4-h phase-advance of their habitual sleep time the following night (N2). Healthy subjects aged 18-64 y were given single-blind placebo on N1 followed by double-blind treatment on N2 (gaboxadol 10 mg [n = 271], 15 mg [n = 274], or placebo [n = 277])

RESULTS

At baseline, women showed significantly greater values in low frequency activity (< 10 Hz) and in high spindle/low beta frequency activity (14-18 Hz) compared to men. During the phase advance (placebo N2-baseline N1), there was a significant increase in power within the high spindle/low beta frequency range (15-17 Hz) and a significant reduction in beta activity (20-32 Hz), which was greater in women than men. Gaboxadol induced a significant (dose-related) increase in low frequencies (< 8 Hz) and a significant (dose-related) decrease within the alpha/spindle range (11-12 Hz). The effect was dependent upon sex, with a greater magnitude of effect observed in women than men.

CONCLUSION

Gaboxadol shows a characteristic NREM EEG spectral profile in a model of transient insomnia. Men and women show clear differences in NREM EEG activity at baseline, to gaboxadol treatment and to phase-shifts in habitual sleep/wake times. The exact mechanisms underlying the sex differences remain unclear, but sex is an important variable in studies evaluating sleep and gaboxadol. TRIAL REGISTRY INFORMATION:

TRIAL REGISTRY

www.clinicaltrials.gov, study identifier: NCT00102167.

Insomnia pharmacology

Insomnia is not only the most common sleep disorder in the population, it is a frequent complaint heard overall by primary care physicians and specialists alike. Given the high prevalence of this disorder, its tendency to persist, and the frequency with which patients complain of symptoms in practice, it is imperative to have an understanding of basic sleep-wake mechanisms and the evolving field of pharmacologic approaches to enhance sleep. Currently, pharmacologic approaches are among the most widely used therapies for insomnia. This article reviews sleep-wake mechanisms, the neuroanatomic targets for sleep and wake-promoting agents, and discusses currently used agents to promote sleep and investigational hypnotics.

Emerging drugs for insomnia: new frontiers for old and novel targets

BACKGROUND

Insomnia is the most prevalent sleep disorder, with up to 50% of the US adult population reporting symptoms of insomnia on a weekly basis and approximately 12% with insomnia disorder. Comorbid conditions such as depression and anxiety are frequent. Insomnia is more common with older age, female gender and socioeconomic status. Traditionally, therapy has focused on GABA(A) receptor agonists, and off-label antidepressant and antihistamine use.

OBJECTIVE

With increased understanding of complex neural networks involved in sleep and wake, hypnotics are being developed to target a broader variety of receptors with increasing selectivity. This review summarizes promising compounds in Phase II and III trials with evidence supporting efficacy for treatment of insomnia.

METHODS

5-HT(2A) and 5-HT(2C) antagonists, melatonergic (MT1/MT2) agonists, orexin receptor (OX1/OX2) antagonists, as well as GABA(A) receptor agonists are reviewed and summarized. Data are collected from PubMed and Pharmaprojects database searches, company websites, recent scientific meeting presentations and abstracts.

RESULTS/CONCLUSIONS

A variety of drugs targeting several pathways, including GABA(A) agonism, MT1/MT2 agonism, 5-HT(2A) antagonism, OX1/OX2 antagonism and others, are in Phase II and III trials. More work should be done to understand the impact of these drugs in certain populations and in the context of comorbid conditions.

Insomnia in patients with depression: some pathophysiological and treatment considerations

The almost ubiquitous sleep disturbances in patients with depression commonly, but not always, subside with the remission of depression. Evidence linking insomnia with the risk of relapses in recurrent depression, as well as suicide, makes optimization of the treatment of insomnia associated with depression a priority. However, most antidepressant agents do not adequately address the sleep complaints in depression: their effects on sleep range from sizeable improvement to equally significant worsening. One approach to the management of insomnia associated with depression is to choose a sedating antidepressant agent such as trazodone, mirtazapine or agomelatine. A second approach is to start with a non-sedating antidepressant (e.g. the selective serotonin reuptake inhibitors, bupropion, venlafaxine or duloxetine); those with a persistent or treatment-emergent insomnia can be switched to a more sedating antidepressant, or offered a hypnotic or cognitive-behavioural therapy as adjunctive treatment. The review discusses the advantages and disadvantages of all treatment options, pharmacological and otherwise.

A 2-week efficacy and safety study of gaboxadol and zolpidem using electronic diaries in primary insomnia outpatients

OBJECTIVES

To evaluate the efficacy and safety profile of gaboxadol, a selective extrasynaptic GABA(A) agonist (SEGA) previously in development for the treatment of insomnia.

METHODS

This was a randomised, double-blind, placebo-controlled, parallel-group, 2-week, Phase III study of gaboxadol 5, 10 and 15mg in outpatients meeting the DSM-IV criteria of primary insomnia (N=742). Zolpidem 10mg was used as active reference.

RESULTS

At weeks 1 and 2, significant improvement in total sleep time (sTST) compared to placebo was seen for all doses of gaboxadol (all p<0.05). In addition, gaboxadol 10 and 15mg decreased the number of awakenings (sNAW) (p<0.05) while only gaboxadol 15mg improved wakefulness after sleep onset (sWASO) (p<0.05). At week 1, all doses of gaboxadol significantly improved time-to-sleep onset (sTSO) (p<0.05). At week 2, a sustained effect on sTSO was observed for gaboxadol 15mg. Zolpidem also showed effect on all of these variables. Gaboxadol and zolpidem improved sleep quality, freshness after sleep, daytime function and energy at both weeks. Transient rebound insomnia was observed following discontinuation of treatment with zolpidem, but not gaboxadol.

CONCLUSIONS

Gaboxadol 15mg treatment for 2 weeks significantly improved sleep onset and maintenance variables as well as sleep quality and daytime function, as did zolpidem. Gaboxadol 5 and 10mg also showed benefits on most efficacy variables. Gaboxadol was generally safe and well tolerated, with no evidence of withdrawal symptoms or rebound insomnia after discontinuation of short-term treatment. For zolpidem, transient rebound insomnia was observed.

Next-day residual effects of gaboxadol and flurazepam administered at bedtime: a randomized double-blind study in healthy elderly subjects

OBJECTIVE

To evaluate the next-day residual effects of the novel hypnotic, gaboxadol, following bedtime dosing in healthy elderly subjects.

METHODS

Healthy women (N = 15) and men (N = 10) aged 65-79 years received a single bedtime (22:00 h) dose of gaboxadol 10 mg, flurazepam 30 mg (positive control), and placebo in a randomized, double-blind, crossover study. Measures of information processing and psychomotor performance (choice reaction time, critical flicker fusion, digit symbol substitution, compensatory tracking, body sway), memory (immediate and delayed word recall), and daytime sleepiness (Multiple Sleep Latency Test), as well as subjective ratings (line analog rating scales, Leeds Sleep Evaluation Questionnaire), were obtained starting at 07:00 h the following morning. Adverse events were recorded.

RESULTS

Gaboxadol did not show next-day impairments versus placebo on any pharmacodynamic measures whereas the positive control, flurazepam, did show impairments versus placebo on most measures. Gaboxadol showed improvements versus placebo on some measures including subjective rating of next-day alertness/clumsiness on the Leeds Sleep Evaluation Questionnaire. Gaboxadol was generally well-tolerated; there were no serious adverse experiences and no subjects discontinued due to an adverse experience.

CONCLUSIONS

A single oral bedtime dose of gaboxadol 10 mg did not have next-day residual effects in healthy elderly subjects, as measured by a range of pharmacodynamic assessments, in contrast to the clear impairments produced by flurazepam 30 mg.