Inhibition of Orexin Signaling Promotes Sleep Yet Preserves Salient Arousability in Monkeys

Effects of methamphetamine on actigraphy-based sleep parameters in female rhesus monkeys: Orexin receptor mechanisms

BACKGROUND

The orexin system has been implicated as a mechanism underlying insomnia and methamphetamine-induced sleep disruptions, with a potential role for OX2 receptors in the sleep-modulating effects of orexin. The aim of the present study was to investigate the extent to which orexin receptors mediate the effects of acute methamphetamine administration on actigraphy-based sleep in female rhesus monkeys.

METHODS

Actigraphy-based sleep measures were obtained in female rhesus monkeys (n=5) under baseline and acute test conditions. First, morning (10h) i.m. injections of methamphetamine (0.03 - 0.56mg/kg) were administered to determine the effects of methamphetamine alone. Then, saline or methamphetamine (0.3mg/kg) were administered at 10h, and evening (17h30) oral treatments with vehicle, the non-selective orexin receptor antagonist suvorexant (1 - 10mg/kg, p.o.), or the OX2-selective orexin receptor antagonist MK-1064 (1 - 10mg/kg, p.o.) were given. The ability of suvorexant and MK-1064 (10mg/kg, p.o.) to improve actigraphy-based sleep was also assessed in a group of female monkeys quantitatively identified with "short-duration sleep" (n=4).

RESULTS

Methamphetamine dose-dependently disrupted actigraphy-based sleep parameters. Treatment with either suvorexant or MK-1064 dose-dependently improved actigraphy-based sleep in monkeys treated with methamphetamine. Additionally, both suvorexant and MK-1064 promoted actigraphy-based sleep in a group of monkeys with baseline short actigraphy-based sleep.

CONCLUSIONS

These findings suggest that orexin-mediated mechanisms play a role in the effects of methamphetamine on actigraphy-based sleep in female monkeys. Targeting the orexin system, in particular OX2 receptors, could be an effective option for treating sleep disruptions observed in individuals with methamphetamine use disorder.

Emerging and upcoming therapies in insomnia

Insomnia, commonly treated with benzodiazepine (BZD) receptor agonists, presents challenges due to associated serious side effects such as abuse and dependence. To address these concerns, many researches have been conducted to develop and advance both pharmacological and non-pharmacological interventions. Dual orexin receptor antagonists (DORAs), which include suvorexant, daridorexant and lemborexant, have recently been approved by United States Food and Drug Administration (US FDA) as a novel pharmacotherapeutic alternative. Unlike BZD receptor agonists that act as positive allosteric modulators of the gamma-aminobutyric acid type A subunit alpha 1 receptor, DORAs function by binding to both orexin receptor types 1 and 2, and inhibiting the action of the wake-promoting orexin neuropeptide. These drugs induce normal sleep without sleep stage change, do not impair attention and memory performance, and facilitate easier awakening. However, more real-world safety information is needed. Selective orexin-2 receptor antagonists (2-SORAs) is under clinical developments. This review provides an overview of the mechanism of action in relation to insomnia, pharmacokinetics, efficacy and safety information of DORAs and SORA. According to insomnia management guidelines, the first-line treatment for chronic insomnia is cognitive behavioral therapy for insomnia (CBT-I). Although it has proven effective in improving sleep-related quality of life, it has several restrictions limitations due to a face-to-face format. Recently, prescription digital therapy such as Somryst® was approved by US FDA. Somryst®, a smartphone app-based CBT-I, demonstrated meaningful responses in patients. However, digital limitations may impact scalability. Overall, these developments offer promising alternatives for insomnia treatment, emphasizing safety, efficacy, and accessibility.

Orexin Receptor Antagonism: Normalizing Sleep Architecture in Old Age and Disease

Sleep is essential for human well-being, yet the quality and quantity of sleep reduce as age advances. Older persons (>65 years old) are more at risk of disorders accompanied and/or exacerbated by poor sleep. Furthermore, evidence supports a bidirectional relationship between disrupted sleep and Alzheimer's disease (AD) or related dementias. Orexin/hypocretin neuropeptides stabilize wakefulness, and several orexin receptor antagonists (ORAs) are approved for the treatment of insomnia in adults. Dysregulation of the orexin system occurs in aging and AD, positioning ORAs as advantageous for these populations. Indeed, several clinical studies indicate that ORAs are efficacious hypnotics in older persons and dementia patients and, as in adults, are generally well tolerated. ORAs are likely to be more effective when administered early in sleep/wake dysregulation to reestablish good sleep/wake-related behaviors and reduce the accumulation of dementia-associated proteinopathic substrates. Improving sleep in aging and dementia represents a tremendous opportunity to benefit patients, caregivers, and health systems.

The orexin story and orexin receptor antagonists for the treatment of insomnia

Insomnia is present in up to one third of the adult population worldwide, and it can present independently or with other medical conditions such as mental, metabolic, or cardiovascular diseases, which highlights the importance of treating this multifaceted disorder. Insomnia is associated with an abnormal state of hyperarousal (increased somatic, cognitive, and cortical activation) and orexin has been identified as a key promotor of arousal and vigilance. The current standards of care for the treatment of insomnia recommend non-pharmacological interventions (cognitive behavioural therapy) as first-line treatment and, if behavioural interventions are not effective or available, pharmacotherapy. In contrast to most sleep medications used for decades (benzodiazepines and 'Z-drugs'), the new orexin receptor antagonists do not modulate the activity of γ-aminobutyric acid receptors, the main inhibitory mechanism of the central nervous system. Instead, they temporarily block the orexin pathway, causing a different pattern of effects, e.g., less morning or next-day effects, motor dyscoordination, and cognitive impairment. The pharmacokinetic/pharmacodynamic properties of these drugs are the basis of the different characteristics explained in the package inserts, including the recommended starting dose. Orexin receptor antagonists seem to be devoid of any dependence and tolerance-inducing effects, rendering them a viable option for longer-term treatment. Safety studies did not show exacerbation of existing respiratory problems, but more real-world safety and pharmacovigilance experience is needed. This review provides an overview of the orexin history, the mechanism of action, the relation to insomnia, and key features of available drugs mediating orexin signalling.

Daridorexant, an Orexin Receptor Antagonist for the Management of Insomnia

BACKGROUND

Insomnia is a common sleep disorder that is diagnosed primarily by patients' subjective reported symptoms. Daridorexant is a new dual orexin receptor antagonist that was recently approved by Food and Drug Administration for insomnia characterized by difficulty falling asleep and/or maintaining sleep.

MECHANISM OF ACTION, PHARMACODYNAMICS, AND PHARMACOKINETICS

The orexin neuropeptide signaling system plays a role in wakefulness, and blocking the wake-promoting neuropeptides results in diminished wake signaling, thus exerting a sedative effect using an entirely different mechanism of action than the classical sleep promoting agents. The drug has quick onset of action, high volume of distribution, and high protein binding. Pharmacokinetics and pharmacodynamic parameters were similar in patients of different sex and age and were not significantly affected by race, body size, or mild-to-moderate kidney impairment. Dose limitation to 25 mg in moderate liver impairment and no use in severe liver impairment are recommended. The drug undergoes hepatic CYP3A4 metabolism; thus, caution with strong CYP3A4 inhibitors and inducers is warranted.

CLINICAL TRIALS

The drug was approved based on phase 3 trials involving study 1 and study 2. Study 1 noted daridorexant at doses of 25 and 50 mg demonstrated a statistically significant improvement in wake time after sleep onset, latency to persistent sleep, and self-reported total sleep time against placebo at months 1 and 3. Similarly in study 2, compared with placebo, the 25 mg dose demonstrated statistically significant improvement in wake time after sleep onset, latency to persistent sleep, and self-reported total sleep time at months 1 and 3. Treatment-emergent adverse events were similar for daridorexant and placebo, with nasopharyngitis and headache most frequently reported.

THERAPEUTIC ADVANCE

Daridorexant is a novel agent with demonstrated efficacy in sleep onset and maintenance and decrease in daytime sedation. Preliminary results from a 1-year extension study note similar incidences of mild-to-moderate side effects as noted in previous trials. Further studies are needed to establish its place in the pharmacological treatment of insomnia.

Regulatory effect of orexin system on various diseases through mTOR signaling pathway

Orexin (OX)A and OXB are a pair of neuropeptides secreted by orexin-producing neurons in the lateral hypothalamus. The orexin system can regulate many physiological processes through these two receptor pathways, such as feeding behavior, sleep/wake state, energy homeostasis, reward, and the coordination of emotion. Mammalian target of rapamycin (mTOR) can coordinate upstream signals with downstream effectors, thereby regulating fundamental cellular processes and also plays an essential role in the signaling network downstream of the orexin system. In turn, the orexin system can activate mTOR. Here, we review the association of the orexin system with the mTOR signaling pathway mainly by discussing that drugs in various diseases exert their effects on the orexin system, indirectly affecting the mTOR signaling pathway.

Daridorexant for the Treatment of Insomnia

Purpose of Review

Insomnia is a complex sleeping disorder that affects the lives of many individuals worldwide. Insomnia often occurs in the presence of coexisting comorbidities making it a complex disorder that requires a multifactorial approach to therapy. First-line therapy is cognitive-behavioral therapy for insomnia (CBT-I). Pharmacotherapy for insomnia falls into four classes based on mechanism of action: benzodiazepine receptor agonists (BZRAs), histamine receptor antagonists, melatonin receptor agonists, and dual orexin receptor antagonists (DORAs).

Recent Findings

Daridorexant is a dual orexin type 1 and types 2 (OX₁ and OX₂) receptor antagonist that was recently approved by the US FDA for the treatment of adults suffering from insomnia. It was shown to be effective in reducing insomnia symptoms, increasing daytime functioning, and improving the overall quality of sleep. Daridorexant offers patients relief from insomnia while avoiding the severe side effects and dependency issues of traditional treatments like benzodiazepines and sedatives.

Summary

In this article, we review the most recent data on insomnia treatments and summarize the safety and efficacy of daridorexant in treating insomnia.

Hypocretins (orexins): The ultimate translational neuropeptides

The hypocretins (Hcrts), also known as orexins, are two neuropeptides produced exclusively in the lateral hypothalamus. They act on two specific receptors that are widely distributed across the brain and involved in a myriad of neurophysiological functions that include sleep, arousal, feeding, reward, fear, anxiety and cognition. Hcrt cell loss in humans leads to narcolepsy with cataplexy (narcolepsy type 1), a disorder characterized by intrusions of sleep into wakefulness, demonstrating that the Hcrt system is nonredundant and essential for sleep/wake stability. The causal link between Hcrts and arousal/wakefulness stabilisation has led to the development of a new class of drugs, Hcrt receptor antagonists to treat insomnia, based on the assumption that blocking orexin-induced arousal will facilitate sleep. This has been clinically validated: currently, two Hcrt receptor antagonists are approved to treat insomnia (suvorexant and lemborexant), with a New Drug Application recently submitted to the US Food and Drug Administration for a third drug (daridorexant). Other therapeutic applications under investigation include reduction of cravings in substance-use disorders and prevention of neurodegenerative disorders such as Alzheimer's disease, given the apparent bidirectional relationship between poor sleep and worsening of the disease. Circuit neuroscience findings suggest that the Hcrt system is a hub that integrates diverse inputs modulating arousal (e.g., circadian rhythms, metabolic status, positive and negative emotions) and conveys this information to multiple output regions. This neuronal architecture explains the wealth of physiological functions associated with Hcrts and highlights the potential of the Hcrt system as a therapeutic target for a number of disorders. We discuss present and future possible applications of drugs targeting the Hcrt system for the treatment of circuit-related neuropsychiatric and neurodegenerative conditions.

Alprazolam-induced EEG spectral power changes in rhesus monkeys: a translational model for the evaluation of the behavioral effects of benzodiazepines

RATIONALE

Benzodiazepines induce electroencephalography (EEG) changes in rodents and humans that are associated with distinct behavioral effects and have been proposed as quantitative biomarkers for GABA_A receptor modulation. Specifically, central EEG beta and occipital EEG delta activity have been associated with anxiolysis and sedation, respectively. The extent to which nonhuman primates show the same dose- and topography-dependent effects remained unknown.

OBJECTIVES

We aimed at establishing a nonhuman primate model for the evaluation of benzodiazepine EEG pharmacology.

METHODS

Four adult male rhesus monkeys were prepared with fully implantable telemetry devices that monitored activity, peripheral body temperature, and contained two EEG (central and occipital), one electromyography (EMG), and one electrooculography channel. We investigated daytime alprazolam-induced changes in EEG spectral power, sleep-wake states, EMG activity, locomotor activity, and body temperature. Alprazolam (0.01-1.8 mg/kg, i.m.) or vehicle was administered acutely, and telemetry recording was conducted for 1 h.

RESULTS

Daytime alprazolam dose-dependently increased central EEG power (including beta activity), increased occipital EEG delta power, and decreased occipital EEG alpha, theta, and sigma power. There was an ~8-fold difference in the potency of alprazolam to increase central EEG beta vs. occipital EEG delta activity (based on relative EEG power). The highest dose, which increased both central EEG beta and occipital EEG delta relative power, induced sedative effects (increased time spent in N1 and N2 sleep stages) and decreased peripheral body temperature and locomotor activity.

CONCLUSIONS

Alprazolam induces dose- and topography-dependent EEG changes in rhesus monkeys and provides a valuable model for studying benzodiazepine pharmacology.

Suvorexant improves intractable nocturnal enuresis by altering sleep architecture

Little is known about sleep-based approaches to the treatment of nocturnal enuresis (NE). This report is the first to describe the successful use of suvorexant, an orexin receptor antagonist, in a 12-year-old boy with intractable NE. With suvorexant, the frequency of NE gradually decreased from 14 of 14 days (100%) to 5 of 14 days (35.7%). Sleep polysomnography indicated that rapid eye movement (REM) sleep increased from 101.5 min (19.9%) before suvorexant to 122.1 min (24.9%) with suvorexant. Furthermore, N2 increased from 233 min (45.6%) to 287.5 min (58.7%) during non-REM sleep. In contrast, N3 decreased from 160 min (31.3%) to 65 min (13.3%) during non-REM sleep. Suvorexant appeared to lighten the depth of sleep and alter sleep architecture. Although the application of an insomnia medication for treating NE seems paradoxical, suvorexant reduced the frequency of NE in patients with severe intractable NE. Thus, this treatment strategy warrants further examination.

The Dual Orexin Receptor Antagonist DORA-22 Improves Mild Stress-induced Sleep Disruption During the Natural Sleep Phase of Nocturnal Rats

Dual orexinergic antagonists (DORAs) have been recently developed as a pharmacotherapy alternative to established hypnotics. Hypnotics are largely evaluated in preclinical rodent models in the dark/active period yet should be ideally evaluated in the light/inactive period, analogous to when sleep disruption occurs in humans. We describe here the hypnotic efficacy of DORA-22 in rodent models of sleep disturbance produced by cage changes in the light/inactive period. Rats were administered DORA-22 or the GABA receptor-targeting hypnotic eszopiclone early in the light period, then exposed to six hourly clean cage changes with measurements of NREM sleep onset latency. Both compounds initially promoted sleep (hours 1 and 2), with DORA-22 exhibiting a more rapid hypnotic onset; and exhibited extended efficacy, evident six hours after administration in a sleep latencies test. A common complaint concerning hypnotic use is lingering hypersomnolence, and this is a concern in pharmacotherapy of the elderly. A second study was designed to determine a minimal dose of DORA-22 which would initially promote sleep but exhibit minimal extended hypnotic effect.Animals were administered DORA-22, then exposed for six hours to a single cage previously dirtied by a conspecific, followed by return to home cage. EEG measures indicated that all DORA-22 doses largely promoted sleep in the first hour. The lowest dose (1 mg/kg) did not decrease sleep onset latency at the six-hour timepoint, suggesting no residual hypersomnolence. We described here DORA-22 hypnotic efficacy during the normal sleep period of nocturnal rats, and demonstrate that well-chosen (low) hypnotic doses of DORA-22 may be hypnotically effective yet have minimal lingering effects.

Circadian rhythm as a therapeutic target

The circadian clock evolved in diverse organisms to integrate external environmental changes and internal physiology. The clock endows the host with temporal precision and robust adaptation to the surrounding environment. When circadian rhythms are perturbed or misaligned, as a result of jet lag, shiftwork or other lifestyle factors, adverse health consequences arise, and the risks of diseases such as cancer, cardiovascular diseases or metabolic disorders increase. Although the negative impact of circadian rhythm disruption is now well established, it remains underappreciated how to take advantage of biological timing, or correct it, for health benefits. In this Review, we provide an updated account of the circadian system and highlight several key disease areas with altered circadian signalling. We discuss environmental and lifestyle modifications of circadian rhythm and clock-based therapeutic strategies, including chronotherapy, in which dosing time is deliberately optimized for maximum therapeutic index, and pharmacological agents that target core clock components and proximal regulators. Promising progress in research, disease models and clinical applications should encourage a concerted effort towards a new era of circadian medicine.

Nonclinical pharmacology of daridorexant: a new dual orexin receptor antagonist for the treatment of insomnia

Dual orexin receptor antagonists (DORAs) represent a novel type of sleep medication that provide an alternative to the traditionally used positive allosteric gamma-aminobutyric acid (GABA)-A receptor modulators. Daridorexant is a new DORA that exhibited in phase 3 trials in insomnia not only a beneficial effect on sleep variables, measured objectively and assessed subjectively, but also an improvement in daytime functioning. Daridorexant was discovered through a tailored research program aimed at identifying an optimized sleep-promoting molecule with pharmacokinetic properties appropriate for covering the whole night while avoiding next-morning residual activity at efficacious doses. By specific binding to both orexin receptors, daridorexant inhibits the actions of the wake-promoting orexin (also called hypocretin) neuropeptides. This mechanism avoids a more widespread inhibition of neuronal pathways and associated side effects that are intrinsic to positive allosteric GABA-A receptor modulators. Here, we review the general pharmacology of daridorexant, based on nonclinical pharmacology studies of daridorexant, unpublished or already described, or based on work with other DORAs. Some unique features of daridorexant will be highlighted, such as the promotion of natural and surmountable sleep, the preservation of memory and cognition, the absence of tolerance development or risk of physical dependence, and how it can benefit daytime functioning.

Pharmacological Interactions between the Dual Orexin Receptor Antagonist Daridorexant and Ethanol in a Double-Blind, Randomized, Placebo-Controlled, Double-Dummy, Four-Way Crossover Phase I Study in Healthy Subjects

BACKGROUND

Daridorexant (ACT-541468) is a potent dual orexin receptor antagonist under development for the treatment of sleep disorders. Concomitant intake of ethanol and hypnotics has been shown to result in additive/supra-additive depression of the central nervous system, resulting in pronounced sedation.

OBJECTIVE

The aim of this study was to evaluate the pharmacokinetic (PK) and pharmacodynamic (PD) interactions between ethanol and daridorexant.

METHOD

This was a single-center, double-blind, placebo-controlled, randomized, four-way crossover study conducted in 19 healthy male/female subjects. Subjects received the following four treatments: ethanol with daridorexant, daridorexant alone, ethanol alone, and placebo. Daridorexant 50 mg and the matching placebo were administered as single oral tablets. Ethanol was infused intravenously and clamped at a level of 0.6 g/L for 5 h. The PK of ethanol and daridorexant were assessed and a battery of PD tests performed.

RESULTS

Concomitant administration of ethanol prolonged the time to reach maximum plasma concentrations (t_max) of daridorexant (median difference 1.25 h). No other relevant PK interactions were observed. Coadministration with ethanol produced a numerically greater impairment on saccadic peak velocity, body sway, visual analog scale (VAS) alertness, VAS alcohol intoxication, smooth pursuit, and adaptive tracking compared with daridorexant alone. All treatments were generally well tolerated without serious adverse events (AEs). The most commonly reported treatment-emergent AEs following coadministration of daridorexant and ethanol included somnolence, headache, fatigue, sudden onset of sleep, and dizziness.

CONCLUSIONS

Apart from a shift in t_max, no relevant changes in PK parameters were observed following coadministration of daridorexant and ethanol. The coadministration led to reinforced drug actions that were, at most, indicative of infra-additive effects on certain PD markers. Patients will be advised not to consume ethanol with daridorexant.

CLINICAL TRIALS REGISTRATION NUMBER

NCT03609775 (ClinicalTrials.gov Identifier).

Acute cognitive effects of the hypocretin receptor antagonist almorexant relative to zolpidem and placebo: a randomized clinical trial

STUDY OBJECTIVES

Hypnotic medications can adversely affect behavior during unanticipated awakenings during the night. Animals treated with the hypocretin (Hcrt) receptor antagonist almorexant (ALM) have less acute cognitive impairment compared to the GABAA receptor modulator zolpidem (ZOL). This study aimed to determine whether ALM produces less acute cognitive impairment than ZOL in human subjects.

METHODS

Healthy, young adult, unmedicated male and female subjects participated in a controlled trial of a single dose of ALM 100 mg (N = 48), ALM 200 mg (N = 53), ZOL 10 mg (N = 49), and placebo (PBO, N = 52).

RESULTS

ZOL and both doses of ALM produced similar levels of subjective sleepiness and impaired the ability of subjects to remain awake in a dark, low-stimulus setting relative to PBO. For most cognitive measures, performance under ZOL was significantly worse than ALM or PBO. For tasks involving verbal memory or visual-motor coordination, ZOL impaired performance, whereas the two doses of ALM were no different than PBO. For tasks involving higher-order executive function, ZOL produced impairment in processing speed and inhibitory control, whereas the two doses of ALM were no different than PBO. Performance decrements for ALM were less than ZOL but greater than PBO for some reaction time measures.

CONCLUSIONS

The data provide support for the hypothesis that Hcrt receptor antagonists produce less functional impairment than a benzodiazepine receptor agonist (BzRA). These observations are particularly relevant to patients treated with sedative-hypnotics who are at elevated risk for falls and other untoward events during the intended hours for sleep.

Distinct effects of orexin receptor antagonist and GABAA agonist on sleep and physical/cognitive functions after forced awakening

The majority of patients with insomnia are treated with hypnotic agents. In the present study, we evaluated the side-effect profile of an orexin receptor antagonist and γ-aminobutyric acid A (GABA_A) receptor agonist on physical/cognitive functions upon forced awakening. This double-blind, randomized, placebo-controlled, cross-over study was conducted on 30 healthy male subjects. Fifteen minutes before bedtime, the subjects took a pill of suvorexant (20 mg), brotizolam (0.25 mg), or placebo and were forced awake 90 min thereafter. Physical- and cognitive-function tests were performed before taking the pill, after forced awakening, and the next morning. Polysomnographic recordings revealed that the efficacies of the hypnotic agents in prolonging total sleep time (∼30 min) and increasing sleep efficiency (∼6%) were comparable. When the subjects were allowed to go back to sleep after the forced awakening, the sleep latency was shorter under the influence of hypnotic agents (∼2 min) compared to the placebo trial (24 min), and the rapid eye movement latency was significantly shorter under suvorexant (98.8, 81.7, and 48.8 min for placebo, brotizolam, and suvorexant, respectively). Although brotizolam significantly impaired the overall physical/cognitive performance (sum of z score) compared with placebo upon forced awakening, there was no significant difference in the total z score of performance between suvorexant and placebo. Notably, the score for static balance with the eyes open was higher under suvorexant compared to brotizolam administration. The energy expenditure was lower under suvorexant and brotizolam compared with the placebo. The effect size of brotizolam (d = 0.24) to reduce the energy expenditure was larger than that of suvorexant (d < 0.01).

Can the Orexin Antagonist Suvorexant Preserve the Ability to Awaken to Auditory Stimuli While Improving Sleep?

STUDY OBJECTIVES

The safety profile of the dual orexin receptor antagonists (DORAs) are currently unknown with regard to nocturnal responsivity among people with insomnia. We compared the auditory awakening thresholds (AATs) of the DORA suvorexant (10 and 20 mg) versus placebo in 12 individuals with DSM-5 insomnia.

METHODS

The study used a double-blind, placebo-controlled, three-way crossover design. Participants were randomly assigned to a treatment sequence that included placebo, suvorexant 10 mg, and suvorexant 20 mg. At the time of maximum drug concentration, auditory tones were played during stable stage N2 sleep. Tones increased by 5-decibel (db) increments until the participant awakened. The db at awakening was recorded as the AAT and compared between conditions. The proportion of awakenings higher than 85 db was also compared between conditions. Finally, sensitivity analyses were also conducted using surrounding thresholds (80 db and 90 db).

RESULTS

The mean AAT did not differ significantly between either dose of suvorexant compared to placebo. Moreover, the proportions of individuals who remained asleep at the AAT 85 db cutoff did not differ across conditions. In addition, wake after sleep onset decreased and total sleep time increased in the suvorexant 20 mg condition compared to placebo.

CONCLUSIONS

Suvorexant (10 and 20 mg) preserved the ability to respond to nocturnal stimuli, whereas the 20-mg dose improved the sleep of people with insomnia. This suggests that DORAs such as suvorexant can effectively treat insomnia while allowing patients to awaken to nocturnal stimuli in the environment.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov; Title: A Phase IV 3-Way Double-blind, Randomized, Crossover Study to Compare the Awakening Threshold Effects (Responsivity) of Belsomra 10 mg and 20 mg to Placebo in Non-elderly Insomniacs; Identifier NCT03312517; URL: https://clinicaltrials.gov/ct2/show/NCT03312517.

CITATION

Drake CL, Kalmbach DA, Cheng P, Roth T, Tran KM, Cuamatzi-Castelan A, Atkinson R, SinghM, Tonnu CV, Fellman-Couture C. Can the orexin antagonist suvorexant preserve the ability to awaken to auditory stimuli while improving sleep? J Clin Sleep Med. 2019;15(9):1285-1291.

Trace amine-associated receptor 1 agonism promotes wakefulness without impairment of cognition in Cynomolgus macaques

Trace amine-associated receptor 1 (TAAR1) is a G-protein coupled receptor with affinity for the trace amines. TAAR1 agonists have pro-cognitive, antidepressant-, and antipsychotic-like properties in both rodents and non-human primates (NHPs). TAAR1 agonism also increases wakefulness and suppresses rapid-eye movement (REM) sleep in mice and rats and reduces cataplexy in two mouse models of narcolepsy. We investigated the effects of TAAR1 agonism in Cynomolgus macaques, a diurnal species that exhibits consolidated night-time sleep, and evaluated the effects of TAAR1 agonists on cognition using a working memory (WM) paradigm in this species. Adult male Cynomolgus macaques (n = 6) were surgically implanted to record the electroencephalogram (EEG), electromyogram, and locomotor activity (LMA) and the efficacy of the TAAR1 partial agonist RO5263397 (0.1,1,10 mg/kg, p.o.) on sleep/wake, EEG spectra, and LMA was determined. In a second experiment, the acute effects of RO5263397 (0.1,1,10 mg/kg, p.o.) were assessed on a delayed-match-to-sample test of WM in adult male macaques (n = 7). RO5263397 (10 mg/kg) administered at lights off, when sleep pressure was high, promoted wakefulness and reduced both REM and non-REM sleep without inducing hyperlocomotion. RO5263397 (10 mg/kg) also increased delta/theta activity during all vigilance states. RO5263397 had no effect on WM at either short (2 sec) or long (10 sec) delay intervals. The wake-enhancing and REM-suppressing effects of R05263397 shown here in a diurnal primate are consistent with previous results in nocturnal rodents. These effects and the associated alterations in EEG spectra occurred without inducing hyperlocomotion or affecting WM, encouraging further study of TAAR1 agonists as potential narcolepsy therapeutics.

Hypocretin Mediates Sleep and Wake Disturbances in a Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is a major cause of disability worldwide. Post-TBI sleep and wake disturbances are extremely common and difficult for patients to manage. Sleep and wake disturbances contribute to poor functional and emotional outcomes from TBI, yet effective therapies remain elusive. A more comprehensive understanding of mechanisms underlying post-TBI sleep and wake disturbance will facilitate development of effective pharmacotherapies. Previous research in human patients and animal models indicates that altered hypocretinergic function may be a major contributor to sleep-wake disturbance after TBI. In this study, we further elucidate the role of hypocretin by determining the impact of TBI on sleep-wake behavior of hypocretin knockout (HCRT KO) mice. Adult male C57BL/6J and HCRT KO mice were implanted with electroencephalography recording electrodes, and pre-injury baseline recordings were obtained. Mice were then subjected to either moderate TBI or sham surgery. Additional recordings were obtained and sleep-wake behavior determined at 3, 7, 15, and 30 days after TBI or sham procedures. At baseline, HCRT KO mice had a significantly different sleep-wake phenotype than control C57BL/6J mice. Post-TBI sleep-wake behavior was altered in a genotype-dependent manner: sleep of HCRT KO mice was not altered by TBI, whereas C57BL/6J mice had more non-rapid eye movement sleep, less wakefulness, and more short wake bouts and fewer long wake bouts. Numbers of hypocretin-positive cells were reduced in C57BL/6J mice by TBI. Collectively, these data indicate that the hypocretinergic system is involved in the alterations in sleep-wake behavior that develop after TBI in this model, and suggest potential therapeutic interventions.

Orexin Receptor Blockade-Induced Sleep Preserves the Ability to Wake in the Presence of Threat in Mice

Retention of the ability to wake from sleep in response to dangerous situations is an ideal characteristic of safe hypnotics. We studied the effects of a dual orexin receptor antagonist-22 (DORA-22) and the GABA-A receptor modulator, triazolam, on the ability to wake in response to aversive stimuli. We examined four modalities of sensory inputs, namely, auditory (ultrasonic sound), vestibular (trembling), olfactory (predator odor), and autonomic (hypoxia) stimuli. When the mice fell asleep, one of the four stimuli was applied for 30 s. In the case of auditory stimulation, latency to arousal following vehicle, DORA-22, and triazolam administration was 3.0 (2.0–3.8), 3.5 (2.0–6.5), and 161 (117–267) s (median and 25–75 percentile in the parentheses, n = 8), respectively. Latency to return to sleep after arousal was 148 (95–183), 70 (43–98), and 60 (52–69) s, respectively. Similar results were obtained for vestibular and olfactory stimulation. During the hypoxic stimulation, latencies for arousal and returning to sleep were not significantly different among the groups. The findings of this study are consistent with the distinct mechanisms of these sleep promoting therapies; GABA-A receptor activation by triazolam is thought to induce widespread central nervous system (CNS) suppression while DORA-22 more specifically targets sleep/wake pathways through orexin receptor antagonism. These data support the notion that DORA-22 preserves the ability to wake in response to aversive and consciousness-inducing sensory stimuli, regardless of modality, while remaining effective in the absence of threat. This study provides a unique and important safety evaluation of the potential for certain hypnotics.

Palatable food self-administration and reinstatement are not affected by dual orexin receptor antagonism

The orexins are widely regarded potential therapeutic targets for a range of disorders of appetitive motivation, including obesity. The motivational activator theory, the first coherent account of the orexin system's role in appetitive motivation, predicts that orexin release motivates appetitive behaviour when the reinforcer is highly salient, available under a high unit-cost or when reward seeking is cue-driven. The present study tested the effect of intracerebroventricular (i.c.v.) administration of the highly potent and commercially available dual orexin receptor antagonist, TCS 1102, on self-administration and reinstatement of palatable food seeking in hungry and sated rats. TCS 1102 was also tested on FR1, FR5, FR10 and PR schedules. Orexin neuron activation was measured by c-Fos/orexin-A immunohistochemistry after cue-induced reinstatement, an extinction test, or a home-cage control. No effect of i.c.v. TCS 1102 was observed on self-administration at any fixed or progressive ratio schedule of reinforcement or reinstatement in hungry or sated rats. Although there was robust recruitment of orexin neurons during behavioural testing conditions, there was no specific activation of these neurons during cue-induced reinstatement when compared to extinction testing conditions. These results suggest that orexin antagonism may not be a useful therapeutic target for obesity as it does not appear to regulate food-seeking, and that the conditions determining orexin involvement as a motivational activator may be less clear than currently understood.

Electrophysiological characterization of sleep/wake, activity and the response to caffeine in adult cynomolgus macaques

Most preclinical sleep studies are conducted in nocturnal rodents that have fragmented sleep in comparison to humans who are primarily diurnal, typically with a consolidated sleep period. Consequently, we sought to define basal sleep characteristics, sleep/wake architecture and electroencephalographic (EEG) activity in a diurnal non-human primate (NHP) to evaluate the utility of this species for pharmacological manipulation of the sleep/wake cycle. Adult, 9–11 y.o. male cynomolgus macaques (n = 6) were implanted with telemetry transmitters to record EEG and electromyogram (EMG) activity and Acticals to assess locomotor activity under baseline conditions and following injections either with vehicle or the caffeine (CAF; 10 mg/kg, i.m.) prior to the 12 h dark phase. EEG/EMG recordings (12–36 h in duration) were analyzed for sleep/wake states and EEG spectral composition. Macaques exhibited a sleep state distribution and architecture similar to previous NHP and human sleep studies. Acute administration of CAF prior to light offset enhanced wakefulness nearly 4-fold during the dark phase with consequent reductions in both NREM and REM sleep, decreased slow wave activity during wakefulness, and increased higher EEG frequency activity during NREM sleep. Despite the large increase in wakefulness and profound reduction in sleep during the dark phase, no sleep rebound was observed during the 24 h light and dark phases following caffeine administration. Cynomolgus macaques show sleep characteristics, EEG spectral structure, and respond to CAF in a similar manner to humans. Consequently, monitoring EEG/EMG by telemetry in this species may be useful both for basic sleep/wake studies and for pre-clinical assessments of drug-induced effects on sleep/wake.

•

Cynomolgus macaques show diurnal sleep/wake architecture similar to humans.

•

Caffeine enhanced wakefulness with consequent reductions in both NREM and REM sleep.

•

Caffeine decreased slow wave activity during wakefulness.

•

Caffeine increased higher EEG frequency activity during NREM sleep.

•

No sleep rebound was observed during the subsequent 24 h light and dark phases after CAF treatment.

Pharmacological validation of a novel nonhuman primate measure of thermal responsivity with utility for predicting analgesic effects

Introduction

The development of novel analgesics to treat acute or chronic pain has been a challenge due to a lack of translatable measurements. Preclinical end points with improved translatability are necessary to more accurately inform clinical testing paradigms, which may help guide selection of viable drug candidates.

Methods

In this study, a nonhuman primate biomarker which is sensitive to standard analgesics at clinically relevant plasma concentrations, can differentiate analgesia from sedation and utilizes a protocol very similar to that which can be employed in human clinical studies is described. Specifically, acute heat stimuli were delivered to the volar forearm using a contact heat thermode in the same manner as the clinical setting.

Results

Clinically efficacious exposures of morphine, fentanyl, and tramadol produced robust analgesic effects, whereas doses of diazepam that produce sedation had no effect.

Conclusion

We propose that this assay has predictive utility that can help improve the probability of success for developing novel analgesics.

The Discovery of Suvorexant, the First Orexin Receptor Drug for Insomnia

Historically, pharmacological therapies have used mechanisms such as γ-aminobutyric acid A (GABA_A) receptor potentiation to drive sleep through broad suppression of central nervous system activity. With the discovery of orexin signaling loss as the etiology underlying narcolepsy, a disorder associated with hypersomnolence, orexin antagonism emerged as an alternative approach to attenuate orexin-induced wakefulness more selectively. Dual orexin receptor antagonists (DORAs) block the activity of orexin 1 and 2 receptors to both reduce the threshold to transition into sleep and attenuate orexin-mediated arousal. Among DORAs evaluated clinically, suvorexant has pharmacokinetic properties engineered for a plasma half-life appropriate for rapid sleep onset and maintenance at low to moderate doses. Unlike GABA_A receptor modulators, DORAs promote both non-rapid eye movement (NREM) and REM sleep, do not disrupt sleep stage-specific quantitative electroencephalogram spectral profiles, and allow somnolence indistinct from normal sleep. The preservation of cognitive performance and the ability to arouse to salient stimuli after DORA administration suggest further advantages over historical therapies.

Arousability and Fall Risk During Forced Awakenings From Nocturnal Sleep Among Healthy Males Following Administration of Zolpidem 10 mg and Doxepin 6 mg: A Randomized, Placebo-Controlled, Four-Way Crossover Trial

Study Objectives

To examine and compare the arousability threshold and fall risk upon awakening of doxepin (6 mg) versus zolpidem (10 mg).

Methods

A total of 52 healthy adult males were included in a double-blind, placebo-controlled, four-way crossover study. The experimental procedure included four nights with polysomnography in the lab (zolpidem, doxepin, and their respective placebo conditions). Arousability was measured using an auditory awakening threshold delivered at the peak-plasma concentration for the active hypnotics and at matched times for the respective placebo conditions. Fall risk during the night was measured following awakening using the Berg Balance Scale and the Tandem Walk Task.

Results

Both arousability and fall risk were lower in the doxepin condition compared to the zolpidem condition. Furthermore, arousability and fall risk for doxepin did not differ significantly from the placebo conditions. A significantly greater proportion of participants in the zolpidem condition (63.5%) did not wake until receiving the loudest tone (110 dB) as compared to the doxepin (17.6%) and placebo conditions (17.3%, 5.8%).

Conclusions

Results suggest that zolpidem has greater risks for balance and awakening threshold compared with low-dose doxepin. Future prospective studies should extend results to clinical samples with population-level risk of injury and arousability.

Excitation of GABAergic Neurons in the Bed Nucleus of the Stria Terminalis Triggers Immediate Transition from Non-Rapid Eye Movement Sleep to Wakefulness in Mice

Emotionally salient situations usually trigger arousal along with autonomic and neuroendocrine reactions. To determine whether the extended amygdala plays a role in sleep-wakefulness regulation, we examined the effects of optogenetic and pharmacogenetic excitation of GABAergic neurons in the bed nucleus of the stria terminalis (GABA^BNST neurons). Acute optogenetic excitation of these cells during nonrapid eye movement (NREM) sleep resulted in an immediate state transition to wakefulness, whereas stimulation during REM sleep showed no effect on sleep-wakefulness states in male mice. An anterograde tracing study suggested GABA^BNST neurons send axonal projections to several brain regions implicated in arousal, including the preoptic area, lateral hypothalamus, periaqueductal gray, deep mesencephalic nucleus, and parabrachial nucleus. A dual orexin receptor antagonist, DORA-22, did not affect the optogenetic transition from NREM sleep to wakefulness. Chemogenetic excitation of GABA^BNST neurons evoked a sustained wakefulness state, but this arousal effect was markedly attenuated by DORA-22. These observations suggest that GABA^BNST neurons play an important role in transition from NREM sleep to wakefulness without the function of orexin neurons, but prolonged excitation of these cells mobilizes the orexin system to sustain wakefulness.SIGNIFICANCE STATEMENT We examined the role of the bed nucleus of the stria terminalis (BNST) in the regulation of wakefulness. Optogenetic excitation of GABAergic neurons in the BNST (GABA^BNST neurons) during nonrapid eye movement (NREM) sleep in mice resulted in immediate transition to a wakefulness state without function of orexins. Prolonged excitation of GABA^BNST neurons by a chemogenetic method evoked a longer-lasting, sustained wakefulness state, which was abolished by preadministration of a dual orexin receptor antagonist, DORA-22. This study revealed a role of the BNST GABAergic system in sleep-wakefulness control, especially in shifting animals' behavioral states from NREM sleep to wakefulness, and provides an important insight into the pathophysiology of insomnia and the role of orexin in arousal regulation.

Orexin 2 receptor regulation of the hypothalamic-pituitary-adrenal (HPA) response to acute and repeated stress

Orexins are hypothalamic neuropeptides that have a documented role in mediating the acute stress response. However, their role in habituation to repeated stress, and the role of orexin receptors (OX₁R and OX₂R) in the stress response, has yet to be defined. Orexin neuronal activation and levels in the cerebrospinal fluid (CSF) were found to be stimulated with acute restraint, but were significantly reduced by day five of repeated restraint. As certain disease states such as panic disorder are associated with increased central orexin levels and failure to habituate to repeated stress, the effect of activating orexin signaling via Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) on the hypothalamic-pituitary-adrenal (HPA) response was evaluated after repeated restraint. While vehicle-treated rats displayed habituation of Adrenocorticotropic Hormone (ACTH) from day 1 to day 5 of restraint, stimulating orexins did not further increase ACTH beyond vehicle levels for either acute or repeated restraint. We delineated the roles of orexin receptors in acute and repeated stress using a selective OX₂R antagonist (MK-1064). Pretreatment with MK-1064 reduced day 1 ACTH levels, but did not allow further habituation on day 5 compared with vehicle-treated rats, indicating that endogenous OX₂R activity plays a role in acute stress, but not in habituation to repeated stress. However, in restrained rats with further stimulated orexins by DREADDs, MK-1064 decreased ACTH levels on day 5. Collectively, these results indicate that the OX₂R plays a role in acute stress, and can prevent habituation to repeated stress under conditions of high orexin release.

Development of a Functional Observational Battery in the Minipig for Regulatory Neurotoxicity Assessments

A functional observational battery (FOB) is recommended as the first-tier neurotoxicity screening in the preclinical safety pharmacology testing guidelines. Minipigs have increasingly been used in regulatory toxicology studies; however, no current FOB protocol is available for neurotoxicity testing in these species. Hence, a minipig FOB instrument was developed. A complete crossover study with Sinclair minipigs was performed to evaluate physiologic, neurologic, and behavioral effects of amphetamine, ketamine, and diazepam. The treated minipigs were first observed in their home cage, were video-recorded for 10 minutes in an open field, and then went through a complete neurologic examination. Both ketamine and diazepam were shown to reduce the freezing and behavior shifts of treated minipigs, while increasing their exploratory behaviors. Both drugs also caused muscular and gait impairment. The effects of ketamine and diazepam were consistent with their roles as central nervous system (CNS) suppressants. Unique effects were also observed with ketamine and diazepam treatments, which may reflect their unique mechanisms of action. Consistent with its role as a CNS stimulant, amphetamine caused the treated minipigs to be hyperactive and to display increased freezing and behavior shifts and reduced exploring activities. These effects of amphetamine were opposite to those observed with ketamine and diazepam. Amphetamine also increased locomotion in the treated minipigs. The present effects of amphetamine, ketamine, and diazepam are in agreement with observations by others. In conclusion, the minipig is a suitable species for FOB evaluation of pharmaceuticals in preclinical safety pharmacology testing.