A novel, orally available orexin 2 receptor-selective agonist, tak-994, ameliorates narcolepsy-like symptoms in narcolepsy mouse models

Evaluation of the efficacy of the hypocretin/orexin receptor agonists TAK-925 and ARN-776 in narcoleptic orexin/tTA; TetO-DTA mice

The sleep disorder narcolepsy, a hypocretin deficiency disorder thought to be due to degeneration of hypothalamic hypocretin/orexin neurons, is currently treated symptomatically. We evaluated the efficacy of two small molecule hypocretin/orexin receptor-2 (HCRTR2) agonists in narcoleptic male orexin/tTA; TetO-DTA mice. TAK-925 (1-10 mg/kg, s.c.) and ARN-776 (1-10 mg/kg, i.p.) were injected 15 min before dark onset in a repeated measures design. EEG, EMG, subcutaneous temperature (T_sc ) and activity were recorded by telemetry; recordings for the first 6 h of the dark period were scored for sleep/wake and cataplexy. At all doses tested, TAK-925 and ARN-776 caused continuous wakefulness and eliminated sleep for the first hour. Both TAK-925 and ARN-776 caused dose-related delays in NREM sleep onset. All doses of TAK-925 and all but the lowest dose of ARN-776 eliminated cataplexy during the first hour after treatment; the anti-cataplectic effect of TAK-925 persisted into the second hour for the highest dose. TAK-925 and ARN-776 also reduced the cumulative amount of cataplexy during the 6 h post-dosing period. The acute increase in wakefulness produced by both HCRTR2 agonists was characterised by increased spectral power in the gamma EEG band. Although neither compound provoked a NREM sleep rebound, both compounds affected NREM EEG during the second hour post-dosing. TAK-925 and ARN-776 also increased gross motor activity, running wheel activity, and T_sc , suggesting that the wake-promoting and sleep-suppressing activities of these compounds could be a consequence of hyperactivity. Nonetheless, the anti-cataplectic activity of TAK-925 and ARN-776 is encouraging for the development of HCRTR2 agonists.

Pharmacologic Management of Excessive Daytime Sleepiness

Excessive daytime sleepiness (EDS) is defined as "irresistible sleepiness in a situation when an individual would be expected to be awake, and alert." EDS has been a big concern not only from a medical but also from a public health point of view. Patients with EDS have the possibility of falling asleep even when they should wake up and concentrate, for example, when they drive, play sports, or walk outside. In this article, clinical characteristics of common hypersomnia and pharmacologic treatments of each hypersomnia are described.

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.

Hypocretin (Orexin) Replacement Therapies

Twenty-two years after their discovery, the hypocretins (Hcrts), also known as orexins, are two of the most studied peptidergic systems, involved in myriad physiological systems that range from sleep, arousal, motivation, homeostatic regulation, fear, anxiety and learning. A causal relationship between activity of Hcrt and arousal stability was established shortly after their discovery and have led to the development of a new class of drugs to treat insomnia. In this review we discuss the many faces of the Hcrt system and examine recent findings that implicate decreased Hcrt function in the pathogenesis of a number of neuropsychiatric conditions. We also discuss future therapeutic strategies to replace or enhance Hcrt function as a treatment option for these neuropsychiatric conditions.

Living with Narcolepsy: Current Management Strategies, Future Prospects, and Overlooked Real-Life Concerns

Narcolepsy is a neurological disorder of the sleep-wake cycle characterized by excessive daytime sleepiness (EDS), cataplexy, nighttime sleep disturbances, and REM-sleep-related phenomena (sleep paralysis, hallucinations) that intrude into wakefulness. Dysfunction of the hypocretin/orexin system has been implicated as the underlying cause of narcolepsy with cataplexy. In most people with narcolepsy, symptom onset occurs between the ages of 10 and 35 years, but because the disorder is underrecognized and testing is complex, delays in diagnosis and treatment are common. Narcolepsy is treated with a combination of lifestyle modifications and medications that promote wakefulness and suppress cataplexy. Treatments are often effective in improving daytime functioning for individuals with narcolepsy, but side effects and/or lack of efficacy can result in suboptimal management of symptoms and, in many cases, significant residual impairment. Additionally, the psychosocial ramifications of narcolepsy are often neglected. Recently two new pharmacologic treatment options, solriamfetol and pitolisant, have been approved for adults, and the indication for sodium oxybate in narcolepsy has been expanded to include children. In recent years, there has been an uptick in patient-centered research, and promising new diagnostic and therapeutic options are in development. This paper summarizes current and prospective pharmacological therapies for treating both EDS and cataplexy, discusses concerns specific to children and reproductive-age women with narcolepsy, and reviews the negative impact of health-related stigma and efforts to address narcolepsy stigma.

Recently Approved and Upcoming Treatments for Narcolepsy

Narcolepsy is a chronic, disabling neurologic disorder characterised by excessive daytime sleepiness (EDS) and, in up to 60% of patients, cataplexy. Treatments for narcolepsy are aimed at improving wakefulness (e.g. modafinil, armodafinil, stimulants), reducing cataplexy attacks (e.g. sodium oxybate, venlafaxine), and treating the symptoms of disturbed nocturnal sleep, sleep paralysis and sleep-related hallucinations (e.g. sodium oxybate). In general, medications that increase the release, or inhibit the reuptake, of norepinephrine or dopamine have wake-promoting effects and are useful in managing EDS, whereas medications that inhibit serotonin or norepinephrine reuptake have anticataplectic effects. Modulation of γ-aminobutyric acid B (GABAB) receptors or histamine H3 receptors (H3Rs) has effects on both EDS and cataplexy. Pitolisant, an H3R antagonist, and solriamfetol, a dopamine and norepinephrine reuptake inhibitor, are the most recently approved treatments for EDS associated with narcolepsy in the European Union (pitolisant) and the USA (pitolisant and solriamfetol). Several new agents are being developed and tested as potential treatments for EDS and cataplexy associated with narcolepsy; these agents include novel oxybate formulations (once-nightly [FT218]; low sodium [JZP-258]), a selective norepinephrine reuptake inhibitor (AXS-12), and a product combining modafinil and an astroglial connexin inhibitor (THN102). This review summarises the mechanisms of action, pharmacokinetics, efficacy, and safety/tolerability of recently approved and emerging treatments for narcolepsy.