suvorexant and Narcolepsy

Although sleep is a ubiquitous behavior in animal species with well-developed central nervous systems, many aspects in the neurobiology of sleep remain mysterious. Our discovery of orexin, a hypothalamic neuropeptide involved in the maintenance of wakefulness, has triggered an intensive research examining the exact role of the orexinergic and other neural pathways in the regulation of sleep/wakefulness. The orexin receptor antagonist suvorexant, which specifically block the endogenous waking system, has been approved as a new drug to treat insomnia. Also, since the sleep disorder narcolepsy-cataplexy is caused by orexin deficiency, orexin receptor agonists are expected to provide mechanistic therapy for narcolepsy; they will likely be also useful for treating excessive sleepiness due to other etiologies.Despite the fact that the executive neurocircuitry and neurochemistry for sleep/wake switching has been increasingly revealed in recent years, the mechanism for homeostatic regulation of sleep, as well as the neural substrate for "sleepiness" (sleep need), remains unknown. To crack open this black box, we have initiated a large-scale forward genetic screen of sleep/wake phenotype in mice based on true somnographic (EEG/EMG) measurements. We have so far screened >8,000 heterozygous ENU-mutagenized founders and established a number of pedigrees exhibiting heritable and specific sleep/wake abnormalities. By combining linkage analysis and the next-generation whole exome sequencing, we have molecularly identified and verified the causal mutation in several of these pedigrees. Biochemical and neurophysiological analyses of these mutations are underway. Since these dominant mutations cause strong phenotypic traits, we expect that the mutated genes will provide new insights into the elusive pathway regulating sleep/wakefulness. Indeed, through a systematic cross-comparison of the Sleepy mutants and sleep-deprived mice, we have recently found that the cumulative phosphorylation state of a specific set of mostly synaptic proteins may be the molecular substrate of sleep need.

Topics: Animals; Azepines; Cataplexy; Humans; Hypothalamus; Mice; Mice, Transgenic; Mutation; Narcolepsy; Nerve Tissue Proteins; Orexin Receptor Antagonists; Orexin Receptors; Orexins; Polysomnography; Sleep; Sleep Aids, Pharmaceutical; Sleep Initiation and Maintenance Disorders; Synapses; Triazoles; Wakefulness

Since its discovery in 1998, the orexin system, composed of two G-protein coupled receptors, orexins 1 and 2, and two neuropeptide agonists, orexins A and B, has captured the attention of the scientific community as a potential therapeutic target for the treatment of obesity, anxiety, and sleep/wake disorders. Genetic evidence in rodents, dogs, and humans was revealed between 1999 and 2000, demonstrating a causal link between dysfunction or deletion of the orexin system and narcolepsy, a disorder characterized by hypersomnolence during normal wakefulness. These findings encouraged efforts to discover agonists to treat narcolepsy and, alternatively, antagonists to treat insomnia. This perspective will focus on the discovery and development of structurally diverse orexin antagonists suitable for preclinical pharmacology studies and human clinical trials. The work described herein culminated in the 2014 FDA approval of suvorexant as a first-in-class dual orexin receptor antagonist for the treatment of insomnia.

Topics: Animals; Dogs; Humans; Hypnotics and Sedatives; Mice; Models, Molecular; Narcolepsy; Orexin Receptor Antagonists; Orexin Receptors; Rats; Sleep Initiation and Maintenance Disorders

INTRODUCTION. Recent research has reported the existence of a new class of neuropeptides, called orexins or hypocretins, which are produced by a small group of neurons in the hypothalamus and whose actions are mediated by two types of receptors: OX1R and OX2R. More specifically, the orexinergic neurons have been located exclusively in cells in the lateral, dorsomedial and perifornical areas of the hypothalamus. Despite this highly specific anatomical origin, the orexinergic neurons are projected widely into a number of brainstem, cortical and limbic regions. DEVELOPMENT. This fuzzy pattern of distribution of the orexinergic fibres would be indicating the involvement of this peptidic system in a wide range of functions; indeed, it has been related with the mechanisms that enable regulation of the sleep-wake cycle, the ingestion of food and drink, and some particular types of learning, such as learning certain preferences regarding tastes. It has also been suggested that upsets in the functioning of the orexinergic system would explain the appearance of certain clinical disorders like narcolepsy, obesity or addiction to drug of abuse. CONCLUSIONS. Further research will help to determine the functioning of orexinergic neurons and the interaction between the systems that regulate emotion, energetic homeostasis and the reward mechanisms, on the one hand, and the systems that regulate the sleep-wake cycle on the other. That knowledge would almost certainly make it possible to develop new drugs that, by acting upon the orexinergic system, would be effective in the treatment of sleep disorders such as insomnia or narcolepsy, eating disorders or drug addiction.. Orexina: implicaciones clinicas y terapeuticas.. Introduccion. Se ha descrito recientemente una nueva clase de neuropeptidos, las orexinas, tambien llamadas hipocretinas, producidos por un reducido grupo de neuronas hipotalamicas y cuyas acciones son mediadas por dos tipos de receptores, OX1R y OX2R. En concreto, las neuronas orexinergicas se han localizado en exclusiva en celulas de areas del hipotalamo lateral, dorsomedial y perifornical. A pesar de este origen anatomico tan localizado, las neuronas orexinergicas se proyectan ampliamente a numerosas regiones troncoencefalicas, corticales y limbicas. Desarrollo. Este patron difuso de distribucion de las fibras orexinergicas estaria indicando la intervencion de este sistema peptidico en una amplia variedad de funciones y, de hecho, se ha relacionado con los mecanismos que permiten la regulacion del ciclo sueño-vigilia, la ingesta de comida y de bebida y determinados aprendizajes como el aprendizaje de preferencias gustativas. Se ha sugerido tambien que la alteracion en el funcionamiento del sistema orexinergico explicaria la aparicion de determinados trastornos clinicos como la narcolepsia, la obesidad o la adiccion a drogas de abuso. Conclusiones. Nuevas investigaciones ayudaran a conocer el funcionamiento de las neuronas orexinergicas y la interaccion entre los sistemas que regulan la emocion, la homeostasis energetica y los mecanismos de recompensa con los sistemas que regulan el ciclo de sueño-vigilia. Se confia en que ese conocimiento permita desarrollar nuevos farmacos que, actuando sobre el sistema orexinergico, sean eficaces en el tratamiento de las alteraciones del sueño como el insomnio o la narcolepsia, de los trastornos de la alimentacion o de la drogadiccion.

Topics: Animals; Arousal; Azepines; Benzoxazoles; Disease Models, Animal; Drug Evaluation, Preclinical; Feeding and Eating Disorders; Feeding Behavior; Humans; Intracellular Signaling Peptides and Proteins; Mice; Mice, Knockout; Mice, Transgenic; Motor Activity; Naphthyridines; Narcolepsy; Neuropeptides; Obesity; Orexin Receptor Antagonists; Orexin Receptors; Orexins; Sleep Disorders, Circadian Rhythm; Sleep Disorders, Intrinsic; Substance-Related Disorders; Triazoles; Urea