Neuroendocrine and sympathetic responses to an orexin receptor antagonist, SB-649868, and alprazolam following insulin-induced hypoglycemia in humans

Orexin, Sleep, Sympathetic Neural Activity, and Cardiovascular Function

Inadequate sleep duration and quality are associated with reduced cardiovascular health and increased mortality. Experimental evidence points to the sympathetic nervous system as a key mediator in the observed relationship between poor sleep and cardiovascular dysfunction. However, brain mechanisms underpinning the impaired sympathetic function associated with poor sleep remain unclear. Recent evidence suggests the central orexin system, particularly orexins A and B and their receptors, have a key regulatory role for sleep in animal and human models. While orexin system activity has been observed to significantly impact sympathetic regulation in animals, the extension of these findings to humans has been difficult due to an inability to directly assess orexin system activity in humans. However, direct measures of sympathetic activity in populations with narcolepsy and chronic insomnia, 2 sleep disorders associated with deficient and excessive orexin neural activity, have allowed indirect assessment of the relationships between orexin, sleep, and sympathetic regulation. Further, the recent pharmaceutical development of dual orexin receptor antagonists for use in clinical insomnia populations offers an unprecedented opportunity to examine the mechanistic role of orexin in sleep and cardiovascular health in humans. The current review assesses the role of orexin in both sleep and sympathetic regulation from a translational perspective, spanning animal and human studies. The review concludes with future research directions necessary to fully elucidate the mechanistic role for orexin in sleep and sympathetic regulation in humans.

Exploring the Role of Orexinergic Neurons in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disease affecting about 2% of the population. A neuropeptide, orexin, is linked with sleep abnormalities in the parkinsonian patient. This study aimed to review the changes in the orexinergic system in parkinsonian subjects and the effects of orexin. A number of search techniques were used and presumed during the search, including cloud databank searches of PubMed and Medline using title words, keywords, and MeSH terms. PD is characterised by motor dysfunctions (postural instability, rigidity, tremor) and cognitive disorders, sleep-wake abnormalities grouped under non-motor disorders. The Orexinergic system found in the hypothalamus is linked with autonomic function, neuroprotection, learning and memory, and the sleep-wake cycle. Prepro-orexin, a precursor peptide (130 amino acids), gives rise to orexins (Orx-A and Orx-B). Serum orexin level measurement is vital for evaluating several neurological disorders (Alzheimer's disease, Huntington's disease, and PD). Orexinergic neurons are activated by hypoglycemia and ghrelin, while they are restrained by food consumption and leptin. Orexinergic system dysfunctioning was found to be linked with non-motor symptoms (sleep abnormalities) in PD. Orexinergic neuron's behaviour may be either inhibitory or excitatory depending on the environment in which they are present. As well, orexin antagonists are found to improve the abnormal sleep pattern. Since the orexinergic system plays a role in several psychological and neurological disorders, therefore, these disorders can be managed by targeting this system.

Involvement of orexinergic system in psychiatric and neurodegenerative disorders: A scoping review

Orexin is a neuropeptide secreted from lateral hypothalamus and pre-frontal cortex concerned in the wakefulness and excitement. This study aimed to review the possible neurobiological effect of orexin. A diversity of search strategies was adopted and assumed which included electronic database searches of Medline and PubMed using MeSH terms, keywords, and title words during the search. Orexin plays a vital role in activation of learning, memory acquisition, and consolidation through activation of monoaminergic system, which affect cognitive flexibility and cognitive function. Orexin stimulates adrenocorticotropin and corticosteroid secretions via activation of central corticotropin-releasing hormone. Cerebrospinal fluid (CSF) and serum orexin serum levels are reduced in depression, schizophrenia, and narcolepsy. However, high orexin serum levels are revealed in drug addictions. Regarding neurodegenerative brain diseases, CSF and serum orexin serum levels are reduced Parkinson disease, Alzheimer dementia, Huntington's disease, amyotrphic lateral sclerosis, and multiple sclerosis. Orexin antagonist leads to significant reduction of sympathetic over-activity during withdrawal syndrome. As well, orexin antagonist improves sleep pattern. Orexinergic system is involved in the different psychiatric and neurological disorders; therefore, targeting of this system could be possible novel pathway in the management of these disorders. In addition, measurement of CSF and serum orexin levels might predict the relapse and withdrawal of addict patients.

Orexin A in adolescents with anxiety disorders

Objectives: The relationships between orexins and stress-related conditions have been well documented in animal studies. However, human studies confirming this relationship are limited. The aim of this study was to investigate the association between orexin-A and anxiety disorders in adolescents. Additionally, we aimed to examine the relationship between orexin-A and cortisol levels in those with anxiety disorders.Methods: A total of 56 medication-free adolescents diagnosed with any anxiety disorder, except for specific phobias, and 32 healthy controls were included in this study. Depression, state and trait anxiety levels of the participants were measured using self-report scales. Orexin-A and cortisol levels were measured by an enzyme-linked immunosorbent assay (ELISA).Results: Analysis of covariance (ANCOVA) indicated that serum orexin-A levels were significantly higher in the anxiety disorder group than in the control group while controlling for age, sex and depression levels. After controlling for age and sex, orexin-A levels were positively and negatively correlated to depression and cortisol levels, respectively. In addition, a positive correlation trend between trait anxiety and orexin-A was found.Conclusions: Orexin-A levels are higher in adolescents with anxiety disorder; however, depressive symptoms should be considered when investigating this relationship.

Role of orexins in the central and peripheral regulation of glucose homeostasis: Evidences & mechanisms

Orexins (A & B), neuropeptides of hypothalamic origin, act through G-protein coupled receptors, orexin 1 receptor (OX₁R) and orexin 2 receptor (OX₂R). The wide projection of orexin neurons in the hypothalamic region allows them to interact with the other neurons and regulate food intake, emotional status, sleep wake cycle and energy metabolism. The autonomic nervous system plays an important regulatory role in the energy metabolism as well as glucose homeostasis. Orexin neurons are also under the control of GABAergic neurons. Emerging preclinical as well as clinical research has reported the role of orexins in the glucose homeostasis since orexins are involved in hypothalamic metabolism circuitry and also rely on sensing peripheral metabolic signals such as gut, adipose derived and pancreatic peptides. Apart from the hypothalamic origin, integration and control in various physiological functions, peripheral origin in wide organs, raises the possibility of use of orexins as a therapeutic biomarker in the management of metabolic disorders. The present review focuses the central as well as peripheral roles of orexins in the glucose homeostasis.

Selective Inhibition of Orexin-2 Receptors Prevents Stress-Induced ACTH Release in Mice

Orexins peptides exert a prominent role in arousal-related processes including stress responding, by activating orexin-1 (OX1R) and orexin-2 (OX2R) receptors located widely throughout the brain. Stress or orexin administration stimulates hyperarousal, adrenocorticotropic hormone (ACTH) and corticosterone release, and selective OX1R blockade can attenuate several stress-induced behavioral and cardiovascular responses but not the hypothalamic-pituitary-adrenal (HPA) axis activation. As opposed to OX1R, OX2R are preferentially expressed in the paraventricular hypothalamic nucleus which is involved in the HPA axis regulation. In the present study, we investigated the effects of a psychological stress elicited by cage exchange (CE) on ACTH release in two murine models (genetic and pharmacological) of selective OX2R inhibition. CE-induced stress produced a significant increase in ACTH serum levels. Mice lacking the OX2R exhibited a blunted stress response. Stress-induced ACTH release was absent in mice pre-treated with the selective OX2R antagonist JNJ-42847922 (30 mg/kg po), whereas pre-treatment with the dual OX1/2R antagonist SB-649868 (30 mg/kg po) only partially attenuated the increase of ACTH. To assess whether the intrinsic and distinct sleep-promoting properties of each antagonist could account for the differential stress response, a separate group of mice implanted with electrodes for standard sleep recording were orally dosed with JNJ-42847922 or SB-649868 during the light phase. While both compounds reduced the latency to non-rapid eye movement (NREM) sleep without affecting its duration, a prevalent REM-sleep promoting effect was observed only in mice treated with the dual OX1/2R antagonist. These data indicate that in a psychological stress model, genetic or pharmacological inhibition of OX2R markedly attenuated stress-induced ACTH secretion, as a separately mediated effect from the NREM sleep induction of OX2R antagonism.

Neuroendocrine, Autonomic, and Metabolic Responses to an Orexin Antagonist, Suvorexant, in Psychiatric Patients with Insomnia

Aim: The aim of this study was to investigate the neuroendocrine, autonomic, and metabolic system responses to suvorexant in psychiatric subjects with insomnia. Design: This prospective study was conducted in Kusatsu Hospital in Hiroshima, Japan and included 40 psychiatric inpatients treated with suvorexant from December 2014 to April 2016. Methods: Questionnaire of Pittsburgh Sleep Quality Index (PSQI), Generalized Anxiety Disorder-7 (GAD-7), and Patient Health Questionnaire-9 (PHQ-9) scores were checked at baseline, Week 2, and Week 4, and fasting serum levels of prolactin, insulin, cortisol, noradrenaline, white blood cell count, and average pulse rate were measured at baseline and Week 4 and Week 8 after suvorexant initiation. Sequential change of the values were compared against baseline respectively. Results: Subjective sleep quality scores were significantly decreased at Weeks 2 and 4, and sleep duration, habitual sleep efficacy, and global scores were significantly decreased at Week 4 from baseline. Total scores on the Generalized Anxiety Disorder-7 and the Patient Health Questionnaire-9 significantly decreased at Week 4 from baseline. The levels of cortisol and white blood cell count were decreased, significantly at Week 8, and the levels of pulse rate were significantly decreased at Week 4 from baseline. The levels of noradrenaline decreased, although not significantly. The prolactin levels remained unchanged, and no trend was found in the insulin levels. Conclusion: Suvorexant treatment resulted in overall improvement in the quality of sleep and the severity of anxiety and depression. This dual orexin antagonist may be related to autonomic functions and neuroendocrine systems, especially in the hypothalamus-pituitary-adrenal axis in psychiatric subjects.