Orexin/hypocretin receptor, Orx1, gene variants are associated with major depressive disorder

Unraveling the function and structure impact of deleterious missense SNPs in the human OX1R receptor by computational analysis

The orexin/hypocretin receptor type 1 (OX1R) plays a crucial role in regulating various physiological functions, especially feeding behavior, addiction, and reward. Genetic variations in the OX1R have been associated with several neurological disorders. In this study, we utilized a combination of sequence and structure-based computational tools to identify the most deleterious missense single nucleotide polymorphisms (SNPs) in the OX1R gene. Our findings revealed four highly conserved and structurally destabilizing missense SNPs, namely R144C, I148N, S172W, and A297D, located in the GTP-binding domain. Molecular dynamics simulations analysis demonstrated that all four most detrimental mutant proteins altered the overall structural flexibility and dynamics of OX1R protein, resulting in significant changes in the structural organization and motion of the protein. These findings provide valuable insights into the impact of missense SNPs on OX1R function loss and their potential contribution to the development of neurological disorders, thereby guiding future research in this field.

Characteristics of Seltorexant-Innovative Agent Targeting Orexin System for the Treatment of Depression and Anxiety

Twenty-five years have passed since the discovery of the orexin system, during which time we have learned more and more about it. A number of studies have been conducted showing the role of the orexin system in insomnia, as well as its potential use in the treatment of obesity and depression. In this review, we present the role of the orexin system in the development of depressive illness and show the characteristics of seltorexant, a potential drug for the treatment of depression. This review describes the structure and synthesis of the compound as well as its pharmacodynamics and pharmacokinetics. Pre-clinical and clinical studies are also described, including side effects. There is evidence that the use of seltorexant is considered safe, with no clear or major clinically significant side effects, which makes it a promising candidate for the treatment of depression and anxiety disorders.

Use of experimental medicine approaches for the development of novel psychiatric treatments based on orexin receptor modulation

Despite progress in understanding the pathological mechanisms underlying psychiatric disorders, translation from animal models into clinical use remains a significant bottleneck. Preclinical studies have implicated the orexin neuropeptide system as a potential target for psychiatric disorders through its role in regulating emotional, cognitive, and behavioral processes. Clinical studies are investigating orexin modulation in addiction and mood disorders. Here we review performance-outcome measures (POMs) arising from experimental medicine research methods which may show promise as markers of efficacy of orexin receptor modulators in humans. POMs provide objective measures of brain function, complementing patient-reported or clinician-observed symptom evaluation, and aid the translation from preclinical to clinical research. Significant challenges include the development, validation, and operationalization of these measures. We suggest that collaborative networks comprising clinical practitioners, academics, individuals working in the pharmaceutical industry, drug regulators, patients, patient advocacy groups, and other relevant stakeholders may provide infrastructure to facilitate validation of experimental medicine approaches in translational research and in the implementation of these approaches in real-world clinical practice.

Orexin Receptor Antagonists in the Treatment of Depression: A Leading Article Summarising Pre-clinical and Clinical Studies

The orexin (hypocretin) system comprises two neuropeptides (orexin-A and orexin-B) and two G-protein coupled receptors (the orexin type 1 and the orexin type 2 receptor). The system regulates several biological functions including appetite, the sleep-wake cycle, the stress response, and motivation and reward processing. Dysfunction of the orexin system has been implicated in the pathophysiology of depression in human and animal studies, although the exact nature of this dysfunction remains unclear. Orexin receptor antagonists (ORAs) are a class of compounds developed for the treatment of insomnia and have demonstrated efficacy in this area. Three dual orexin receptor antagonists (DORAs) have received licences for treatment of primary insomnia and some ORAs have since been investigated as potential treatments for major depressive disorder (MDD). In this leading article, we summarise the existing literature on use of ORAs in depression, in pre-clinical and clinical studies. In rodent models of depression, investigated ORAs have included the DORA almorexant and TCS1102, the selective orexin 1 receptor antagonists SB334867 and SB674042 and the selective orexin 2 receptor antagonists LSN2424100, MK-1064 and TCS-OX2-29. These pre-clinical studies suggest a possible antidepressant effect of systemic DORA treatment, however the evidence from selective ORAs is conflicting. To date, four published RCTs (one with the DORA filorexant and three with the selective orexin 2 receptor antagonist seltorexant), have compared an ORA with placebo in the treatment of MDD. Only one of these demonstrated a statistically significant difference relative to placebo.

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.

Orexin a levels of adolescents with major depressive disorder

OBJECTIVE

This study examines orexin A levels in adolescents with major depressive disorder (MDD).

METHODS

Serum orexin A levels of adolescents with MDD (n = 40) were compared to healthy controls (n = 38) using ANCOVA test. In addition, the relationship between orexin A levels and MDD symptom severity (i.e., child depression inventory) was investigated in the MDD group using correlation and linear regression analyses.

RESULTS

Orexin A levels of the subjects with MDD were similar to controls while controlling for age, gender, body mass index, and anxiety levels of the subjects. In addition, correlation and regression analyses did not reveal any relationship between orexin A and MDD symptoms.

DISCUSSION

Adolescent MDD is not associated with orexin A according to the findings of this study. Future studies considering the effect of stress on this relationship would improve our understanding of this issue.Key PointsAdult studies exploring the relationship between orexin A and major depressive disorder reported contradictory findings.This study showed no relationship between serum orexin A levels and depressive symptom severity among adolescents with major depressive disorder.Orexin A levels of the subjects with major depressive disorder are not significantly different from healthy adolescents.

Lateral hypothalamus orexinergic inputs to lateral habenula modulate maladaptation after social defeat stress

Social stress, a common stressor, causes multiple forms of physical and mental dysfunction. Prolonged exposure to social stress is associated with a higher risk of psychological disorders, including anxiety disorders and major depressive disorder (MDD). The orexinergic system is involved in the regulation of multiple motivated behaviors. The current study examined the regulatory effect of orexinergic projections from the lateral hypothalamic area (LHA) to the lateral habenula (LHb) in depression- and anxiety-like behaviors after chronic social defeat stress. When mice were defeated during social interaction, both orexinergic neurons in the LHA and glutamatergic neurons in the LHb were strongly activated, as indicated by the FosTRAP strategy. Infusion of orexin in the LHb significantly alleviated social avoidance and depression-like behaviors induced by chronic social defeat stress. Administration of an orexin receptor 2 antagonist in the LHb further aggravated the depressive phenotype. Photoactivation of orexinergic cell bodies in the LHA or terminals in the LHb relieved anxiety-like behaviors induced by chronic social defeat stress. Collectively, we identified the antidepressant and anxiolytic effects of the circuit from LHA orexinergic neurons to the LHb in response to chronic social stress, providing new evidence of the antidepressant properties of LHA orexin circuits.

Orexin-A potentiates glycine currents by activating OX1R and IP3/Ca2+/PKC signaling pathways in spinal cord ventral horn neurons

Orexin-A/B modulates multiple physical functions by activating their receptors (OX₁R and OX₂R), but its effects in the spinal cord motor control remain unknown. Using acute separation (by digestive enzyme) of cells and patch-clamp recordings, we aimed to investigate the effect and mechanisms of orexin-A on the glycine receptors in the spinal cord ventral horn neurons. Orexin-A potentiated the glycine currents by activating OX₁R. In Ca²⁺-free extracellular solution, orexin-A still increased the glycine currents. While, the orexin-A-induced potentiation was blocked when Ca²⁺ was chelated by internal infusion of BAPTA, and the orexin-A effect was abolished by the IP₃ receptor antagonists heparin and Xe-C. The PKC inhibitor Bis-IV nullified the orexin-A effect. In addition, orexin-A did not cause a further enhancement of the glycine currents after bath application of the PKC activator PMA. In conclusion, after OX₁R is activated, a distinct IP₃/Ca²⁺-dependent PKC signaling pathway, is likely responsible for the orexin-A potentiation on glycine currents in the spinal cord ventral horn neurons.

Orexin Receptor Antagonists as Emerging Treatments for Psychiatric Disorders

Orexins comprise two neuropeptides produced by orexin neurons in the lateral hypothalamus and are released by extensive projections of these neurons throughout the central nervous system. Orexins bind and activate their associated G protein-coupled orexin type 1 receptors (OX1Rs) and OX2Rs and act on numerous physiological processes, such as sleep-wake regulation, feeding, reward, emotion, and motivation. Research on the development of orexin receptor antagonists has dramatically increased with the approval of suvorexant for the treatment of primary insomnia. In the present review, we discuss recent findings on the involvement of the orexin system in the pathophysiology of psychiatric disorders, including sleep disorders, depression, anxiety, and drug addiction. We discuss the actions of orexin receptor antagonists, including selective OX1R antagonists (SORA1s), selective OX2R antagonists (SORA2s), and dual OX1/2R antagonists (DORAs), in the treatment of these disorders based on both preclinical and clinical evidence. SORA2s and DORAs have more pronounced efficacy in the treatment of sleep disorders, whereas SORA1s may be promising for the treatment of anxiety and drug addiction. We also discuss potential challenges and opportunities for the application of orexin receptor antagonists to clinical interventions.

Orexin/Hypocretin Type 2 Receptor (HCRTR2) Gene as a Candidate Gene in Sertraline-Associated Insomnia in Depressed Patients

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) are considered as first-line drugs for treating depressive disorders. Among the adverse effects reported with sertraline is sleep disturbances; however, the etiology lying beneath is obscure. Orexin, the most recently discovered neurotransmitter, is involved in the sleep cycle. It exerts its physiological actions through orexin or hypocretin type 1 and 2 receptors (HCRTR1 and HCRTR2). Dysfunction of the orexin system contributes to various psychiatric, neurologic and neuropsychiatric disorders. Thus, our study aimed to assess the possible association of genetic variation of HCRTR2 G1246A with hypersomnia reported with sertraline in a group of major depressive disorder (MDD) patients.

PATIENTS AND METHODS

Ninety-six newly diagnosed MDD patients were enrolled in our cohort study. MDD was assessed using DSM-V criteria. Insomnia Severity Index (ISI) was used to assess insomnia at baseline (week 0) and week 4. Blood samples were collected for further genotyping of HCRTR2 G1246A (rs2653349) using polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

A significant association between G1264A polymorphism of HCRTR2 and insomnia was observed. Insomnia with sertraline happens by 2.5-fold (P=0.022; odds ratio (OR)=2.5; 95% confidence interval (CI): 1.1-5.7) in patients having GG genotype. Patients with G allele experience insomnia by 2.1-fold more than A allele carriers (P=0.022; OR=2.1; 95% CI= 1.1-4.0). Subgroup analysis showed a significant association between GG genotype as well as the G allele and insomnia only in female MDD patients (P=0.011; OR=4.0; 95% CI=1.3-12.0 and P=0.033; OR=2.4; 95% CI=1.02-5.7, respectively).

CONCLUSION

In conclusion, the G1246A variant might be a predictor for insomnia in MDD patients treated with sertraline. Our findings support the idea that some variants of the HCRTR might contribute to inter-individual variability in the sleep pattern of patients receiving antidepressants.