Targeting the orexin/hypocretin system for the treatment of neuropsychiatric and neurodegenerative diseases: from animal to clinical studies

The Flavonoids and Monoterpenes from Citrus unshiu Peel Contained in Ninjinyoeito Synergistically Activate Orexin 1 Receptor: A Possible Mechanism of the Orexigenic Effects of Ninjinyoeito

Cancer cachexia, often observed in patients with advanced-stage cancer, is characterized by the loss of body weight and appetite. The Japanese herbal medicine Ninjinyoeito (NYT), which is composed of 12 crude herbal components, has been used as a therapeutic in Japan to improve anorexia and fatigue, which are commonly observed in cancer patients with cachexia. We have previously reported that Citrus unshiu peel (CUP) contained in NYT can enhance food intake by activating the orexin 1 receptor (OX1R). Using the CellKey™ system, which offers detection of OXR activity in intracellular impedance changes, NYT and CUP were found to activate OX1R, which in turn was inhibited by SB-674042, a selective OX1R antagonist. Among the flavonoids contained in CUP, nobiletin and hesperidin, but not naringin, activated OX1R. Furthermore, some monoterpenes contained in CUP, including limonene and linalool, but not terpineol, activated OX1R. In addition, nobiletin and limonene synergistically activated OX1R when added simultaneously. However, neither NYT nor CUP induced OX2R activity. The results collectively suggested that the CUP contained in NYT activates OX1R, but not OX2R, and that flavonoids and monoterpenes in CUP can synergistically activate OX1R. These findings could provide evidence supporting the therapeutic potential of NYT in cancer patients with cachexia.

Exploring the Toxicity and Therapeutic Potential of A. dahurica and A. pubescens in Zebrafish Larvae: Insights into Anxiety Treatment Mechanisms

This study assessed the toxicity and therapeutic potential of Angelica dahurica and Angelica pubescens using Danio rerio (zebrafish) larvae. Toxicity was evaluated through mortality, malformations, and gene expression changes related to stress and the HPA axis. A. dahurica demonstrated low toxicity (LD50 (50% lethal dose) >200 µg/mL), with no significant malformations at 15-30 µg/mL, although higher doses caused edemas and heart defects. A. pubescens exhibited higher toxicity, with 100% mortality at 200 µg/mL and severe malformations. Both species showed potential cardiotoxicity, slowing heart rates after prolonged exposure. Gene expression studies suggested A. dahurica had stress-protective effects, increasing nr3c1 expression, while A. pubescens had dose-dependent effects, with lower concentrations having anxiolytic properties and higher concentrations increasing stress. Interestingly, diazepam showed unexpected gene expression changes, highlighting the influence of environmental and dosage factors. In conclusion, both species show therapeutic potential for anxiety, with A. dahurica showing promising effects at lower concentrations. However, A. pubescens requires careful dosage management due to its higher toxicity risks. Further studies are needed to optimize therapeutic applications and fully understand mechanisms of action.

Efficacy And Safety of Dual Orexin Receptor Antagonist (DORA) For Sleep Disturbance in Patients With Alzheimer's Disease Dementia. A Review Article

INTRODUCTION

The rising prevalence of Alzheimer's disease (AD) and related dementia worldwide underscores the urgent need for effective interventions, particularly for managing neuropsychiatric symptoms (NPS) such as sleep disturbance. This review explores the emerging role of Dual Orexin Receptor Antagonists (DORA) in addressing sleep disturbance in patients with Alzheimer's disease dementia.

METHODS

A comprehensive literature search identified four relevant publications between 2014 and 2024, detailing the use of DORA medications, including suvorexant and lemborexant, in patients with Alzheimer's disease.

RESULTS

Findings suggest that suvorexant may improve total sleep time (TST), wakefulness after sleep onset (WASO), and sleep efficiency (SE) in Alzheimer's patients with insomnia. Lemborexant demonstrated potential in improving circadian rhythm parameters, particularly in patients with irregular sleep-wake rhythm disorder (ISWRD). Safety profiles of DORA medications appeared favorable, with mild to moderate adverse events reported. However, concerns over potential adverse events, such as falls, underscore the need for careful monitoring.

CONCLUSION

While the evidence suggests promise for DORA medications in addressing sleep disturbance in Alzheimer's disease, limitations in study populations and duration highlight the need for further investigation. Future clinical trials should aim for broader inclusion criteria, encompassing diverse dementia subtypes and severity levels, to enhance generalizability. Additionally, longer-term trials are essential to assess the sustained efficacy and safety of DORA interventions in this vulnerable population.

The Aggravating Role of Failing Neuropeptide Networks in the Development of Sporadic Alzheimer's Disease

Alzheimer's disease imposes an increasing burden on aging Western societies. The disorder most frequently appears in its sporadic form, which can be caused by environmental and polygenic factors or monogenic conditions of incomplete penetrance. According to the authors, in the majority of cases, Alzheimer's disease represents an aggravated form of the natural aging of the central nervous system. It can be characterized by the decreased elimination of amyloid β1-42 and the concomitant accumulation of degradation-resistant amyloid plaques. In the present paper, the dysfunction of neuropeptide regulators, which contributes to the pathophysiologic acceleration of senile dementia, is reviewed. However, in the present review, exclusively those neuropeptides or neuropeptide families are scrutinized, and the authors' investigations into their physiologic and pathophysiologic activities have made significant contributions to the literature. Therefore, the pathophysiologic role of orexins, neuromedins, RFamides, corticotrope-releasing hormone family, growth hormone-releasing hormone, gonadotropin-releasing hormone, ghrelin, apelin, and natriuretic peptides are discussed in detail. Finally, the therapeutic potential of neuropeptide antagonists and agonists in the inhibition of disease progression is discussed here.

Analysis of the finasteride treatment and its withdrawal in the rat hypothalamus and hippocampus at whole-transcriptome level

PURPOSE

As reported in patients treated for androgenetic alopecia with finasteride (i.e., a blocker of the enzyme 5 alpha-reductase) and in an animal model, side effects affecting sexual, psychiatric, neurological, and physical domains, may occur during the treatment and persist with drug suspension. The etiopathogenesis of these side effects has been poorly explored. Therefore, we performed a genome-wide analysis of finasteride effects in the brain of adult male rat.

METHODS

Animals were treated (i.e., for 20 days) with finasteride (1mg/rat/day). 24 h after the last treatment and 1 month after drug suspension, RNA sequencing analysis was performed in hypothalamus and hippocampus. Data were analyzed by differential expression analysis and Gene-Set Enrichment Analyses (GSEA).

RESULTS

Data obtained after finasteride treatment showed that 186 genes (i.e., 171 up- and 15 downregulated) and 19 (i.e., 17 up- and 2 downregulated) were differentially expressed in the hypothalamus and hippocampus, respectively. Differential expression analysis at the drug withdrawal failed to identify dysregulated genes. Several gene-sets were enriched in these brain areas at both time points.

CONCLUSION

Some of the genes reported to be differentially expressed (i.e., TTR, DIO2, CLDN1, CLDN2, SLC4A5, KCNE2, CROT, HCRT, MARCKSL1, VGF, IRF2BPL) and GSEA, suggest a potential link with specific side effects previously observed in patients and in the animal model, such as depression, anxiety, disturbance in memory and attention, and sleep disturbance. These data may provide an important background for future experiments aimed at confirming the pathological role of these genes.

Effect of Earthing Mats on Sleep Quality in Rats

Grounding, a therapeutic technique involving direct contact with the earth, has been proposed by various studies to potentially have beneficial effects on pressure, sleep quality, stress, inflammation, and mood. However, the scientific evidence supporting its sedative effects remains incomplete. This study examined the sedative effectiveness of an earthing mat on sleep quality and investigated the underlying neural mechanisms using electroencephalography (EEG) analysis in rodents, focusing on orexin and superoxide dismutase (SOD) levels in the brain. Rats were randomly assigned to four groups: the naïve normal group (Nor), the group exposed to an earthing mat for 7 days (A-7D), the group exposed to an earthing mat for 21 days (A-21D), and the group exposed to an electronic blanket for 21 days (EM). EEG results revealed that the A-21D group exhibited significantly reduced wake time and increased rapid eye movement (REM), non-rapid eye movement (NREM), and total sleep time compared to the Nor group (p < 0.05). Moreover, the A-21D group demonstrated a significant increase in NREM sleep (p < 0.001), REM sleep (p < 0.01), and total sleep time (p < 0.001), along with a decrease in wake time compared to the EM group (p < 0.001). The orexin level in the A-21D group was significantly lower compared to the Nor group (p < 0.01), while SOD1 expression was markedly elevated in the A-21D group compared to the Nor group (p < 0.001). These results suggest that the earthing mat may represent a promising new method for promoting sleep quality and could serve as an effective therapeutic technique.

Heteroaryl derivatives of suvorexant as OX1R selective PET ligand candidates: Cu-mediated 18F-fluorination of boroxines, in vitro and initial in vivo evaluation

BACKGROUND

The orexin receptor (OXR) plays a role in drug addiction and is aberrantly expressed in colorectal tumors. Subtype-selective OXR PET ligands suitable for in vivo use have not yet been reported. This work reports the development of 18F-labeled OXR PET ligand candidates derived from the OXR antagonist suvorexant and the OX1R-selective antagonist JH112.

RESULTS

Computational analysis predicted that fluorine substitution (1e) and introduction of the fluorobenzothiazole scaffold (1f) would be suitable for maintaining high OX1R affinity. After multi-step synthesis of 1a-1f, in vitro OXR binding studies confirmed the molecular dynamics calculations and revealed single-digit nanomolar OX1R affinities for 1a-f, ranging from 0.69 to 2.5 nM. The benzothiazole 1f showed high OX1R affinity (Ki = 0.69 nM), along with 77-fold subtype selectivity over OX2R. Cu-mediated 18F-fluorination of boroxine precursors allowed for a shortened reaction time of 5 min to provide the non-selective OXR ligand [18F]1c and its selective OX1R congener [18F]1f in activity yields of 14% and 22%, respectively, within a total synthesis time of 52-76 min. [18F]1c and [18F]1f were stable in plasma and serum in vitro, with logD7.4 of 2.28 ([18F]1c) and 2.37 ([18F]1f), and high plasma protein binding of 66% and 77%, respectively. Dynamic PET imaging in rats showed similar brain uptake of [18F]1c (0.17%ID/g) and [18F]1f (0.15%ID/g). However, preinjection of suvorexant did not significantly block [18F]1c or [18F]1f uptake in the rat brain. Pretreatment with cyclosporine A to study the role of P-glycoprotein (P-gp) in limiting brain accumulation moderately increased brain uptake of [18F]1c and [18F]1f. Accordingly, in vitro experiments demonstrated that the P-gp inhibitor zosuquidar only moderately inhibited polarized, basal to apical transport of 1c (p < 0.05) and had no effect on the transport of 1f, indicating that P-gp does not play a relevant role in brain accumulation of [18F]1c and [18F]1f in vivo.

CONCLUSIONS

The in vitro and in vivo results of [18F]1c and [18F]1f provide a solid basis for further development of suitable OXR PET ligands for brain imaging.

International Union of Basic and Clinical Pharmacology CXIV: Orexin Receptor Function, Nomenclature and Pharmacology

The orexin system consists of the peptide transmitters orexin-A and -B and the G protein-coupled orexin receptors OX1 and OX2 Orexin receptors are capable of coupling to all four families of heterotrimeric G proteins, and there are also other complex features of the orexin receptor signaling. The system was discovered 25 years ago and was immediately identified as a central regulator of sleep and wakefulness; this is exemplified by the symptomatology of the disorder narcolepsy with cataplexy, in which orexinergic neurons degenerate. Subsequent translation of these findings into drug discovery and development has resulted to date in three clinically used orexin receptor antagonists to treat insomnia. In addition to sleep and wakefulness, the orexin system appears to be a central player at least in addiction and reward, and has a role in depression, anxiety and pain gating. Additional antagonists and agonists are in development to treat, for instance, insomnia, narcolepsy with or without cataplexy and other disorders with excessive daytime sleepiness, depression with insomnia, anxiety, schizophrenia, as well as eating and substance use disorders. The orexin system has thus proved an important regulator of numerous neural functions and a valuable drug target. Orexin prepro-peptide and orexin receptors are also expressed outside the central nervous system, but their potential physiological roles there remain unknown. SIGNIFICANCE STATEMENT: The orexin system was discovered 25 years ago and immediately emerged as an essential sleep-wakefulness regulator. This discovery has tremendously increased the understanding of these processes and has thus far resulted in the market approval of three orexin receptor antagonists, which promote more physiological aspects of sleep than previous hypnotics. Further, orexin receptor agonists and antagonists with different pharmacodynamic properties are in development since research has revealed additional potential therapeutic indications. Orexin receptor signaling is complex and may represent novel features.

Hypocretin-1/orexin-A, sleep and excessive daytime sleepiness in patients with nonconvulsive status epilepticus: A cross-sectional cohort study

BACKGROUND AND OBJECTIVES

Nonconvulsive status epilepticus (NCSE) manifests as a change in mental status without a coma (NCSE proper) or comatose NCSE. Hypocretin-1/orexin-A (H/O) is involved in alertness and sleep maintenance. Sleep impairment and excessive daytime sleepiness (EDS) have a negative impact on cognitive functions and activities of daily living (ADL).

METHODS

Patients meeting the NCSE criteria underwent cerebrospinal fluid and brain magnetic resonance imaging examinations, polysomnographies (PSG), multiple latency sleep tests (MSLT), and completed Epworth Sleepiness Scale (ESS). Montreal Cognitive Assessment was used to evaluate cognitive functions, and the Barthel Index was used to assess ADL in the acute phase (V1) and three months follow-up (V2).

RESULTS

From May 2020 to May 2023, we enrolled 15 patients, eight (53.3 %) women, with a median age of 69 (14) years. The median H/O CSF concentration was 250 (63.6) pg/ml; however, only three CSF samples (20 %) decreased below the borderline concentration of 200 pg/ml. Fourteen out of 15 patients (93.3 %) completed the PSG study. The median of wakefulness after sleep onset was 167 (173.5) min, sleep efficiency (SE) was 62.9 (63) %, sleep latency (SL) was 6 (32) min, REM sleep was 2.85 (7.2) %, and REM first episode latency was 210.5 (196.5) minutes. The medians of the stages N1 NREM were 4.65 (15) %, N2 NREM 68.4 (29.9) %, and N3 NREM 21.8 (35.5) %. MSLT mean latency was 7.7 (12.6) minutes. A significant negative correlation exists between H/O CSF concentrations and the stage N1 NREM (rs = -0.612, p = 0.02), and the proportion of cumulative sleep time with oxygen saturation below 90 % in total sleep time (TST) t90 (rs = -0.57, p = 0.03). MSLT had significant negative correlation with TST (rs = -0.5369, p = 0.0478), with SE (rs = -0.5897, p = 0.0265), with apnea-hypopnea index (rs = -0.7631, p = 0.0002) and with deoxygenation index (rs = -0.8009, p = 0.0006). A positive correlation exists between MSLT and SL (rs = 0.6284, p = 0.0161) and between ESS and t90 (rs = 0.9014, p = 0.0004). The correlation between H/O CSF concentrations and EDS, cognitive performance, and ADL was not proved.

CONCLUSIONS

Patients after NCSE exhibited sleep impairment and excessive daytime sleepiness. Hypocretin-1/orexin-A concentrations decreased only in 20 % of these cases.

Orexin B protects dopaminergic neurons from 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurotoxicity associated with reduced extracellular signal-regulated kinase phosphorylation

BACKGROUND

The loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) is a major pathological hallmark of Parkinson's disease (PD). Orexin B (OXB) has been reported to promote the growth of DA neurons. However, the roles of OXB in the degeneration of DA neurons still remained not fully clear.

METHODS

An in vivo PD model was constructed by administrating 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice. Pole test was performed to investigate the motor function of mice and the number of DA neurons was detected by immunofluorescence (IF). A PD cell model was established by treating SH-SY5Y cells with 1-methyl-4-phenylpyridinium (MPP+). OXB was added to the culture medium 2 h after MPP + treatment. Microscopic analysis was carried out to investigate the function of OXB in the cell model of PD 24 h after MPP + challenge. RNA-Seq analysis of the PD cell model was performed to explore the possible mechanisms. Western blot was used to detect the phosphorylation levels of extracellular signal-regulated kinase (ERK).

RESULTS

OXB significantly decreased the DA neurons death caused by MPTP, alleviated MPP+-induced neurotoxicity in SH-SY5Y cells, and robustly enhanced the weight and motor ability of PD mice. Besides, RNA-Seq analysis demonstrated that the mitogen-activated protein kinase (MAPK) pathway was involved in the pathology of PD. Furthermore, MPP + led to increased levels of phosphorylation of ERK (p-ERK), OXB treatment significantly decreased the levels of p-ERK in MPP+-treated SH-SY5Y cells.

CONCLUSIONS

This study demonstrated that OXB exerts a neuroprotective role associated with reduced ERK phosphorylation in the PD model. This suggests that OXB may have therapeutic potential for treatment of PD.

Discovery and first-time disclosure of CVN766, an exquisitely selective orexin 1 receptor antagonist

Modulators of orexin receptors are being developed for neurological illnesses such as sleep disorders, addictive behaviours and other psychiatric diseases. We herein describe the discovery of CVN766, a potent orexin 1 receptor antagonist that has greater than 1000-fold selectivity for the orexin 1 receptor over the orexin 2 receptor and demonstrates low off target hits in a diversity screen. In agreement with its in vitro ADME data, CVN766 demonstrated moderate in vivo clearance in rodents and displayed good brain permeability and target occupancy. This drug candidate is currently being investigated in clinical trials for schizophrenia and related psychiatric conditions.

The Orexin/Hypocretin System, the Peptidergic Regulator of Vigilance, Orchestrates Adaptation to Stress

The orexin/hypocretin neuropeptide family has emerged as a focal point of neuroscientific research following the discovery that this family plays a crucial role in a variety of physiological and behavioral processes. These neuropeptides serve as powerful neuromodulators, intricately shaping autonomic, endocrine, and behavioral responses across species. Notably, they serve as master regulators of vigilance and stress responses; however, their roles in food intake, metabolism, and thermoregulation appear complementary and warrant further investigation. This narrative review provides a journey through the evolution of our understanding of the orexin system, from its initial discovery to the promising progress made in developing orexin derivatives. It goes beyond conventional boundaries, striving to synthesize the multifaceted activities of orexins. Special emphasis is placed on domains such as stress response, fear, anxiety, and learning, in which the authors have contributed to the literature with original publications. This paper also overviews the advancement of orexin pharmacology, which has already yielded some promising successes, particularly in the treatment of sleep disorders.

Synthesis and Characterization of a New Carbon-11 Labeled Positron Emission Tomography Radiotracer for Orexin 2 Receptors Neuroimaging

Purpose

Orexin receptors (OXRs) play a crucial role in modulating various physiological and neuropsychiatric functions within the central nervous system (CNS). Despite their significance, the precise role of OXRs in the brain remains elusive. Positron emission tomography (PET) imaging is instrumental in unraveling CNS functions, and the development of specific PET tracers for OXRs is a current research focus.

Methods

The study investigated MDK-5220, an OX2R-selective agonist with promising binding properties (EC50 on OX2R: 0.023 μM, Ki on hOX2R: 0.14 μM). Synthesized and characterized as an OX2R PET probe, [11C]MDK-5220 was evaluated for its potential as a tracer. Biodistribution studies in mice were conducted to assess OX2R binding selectivity, with particular attention to its interaction with P-glycoprotein (P-gp) on the blood-brain barrier.

Results

[11C]MDK-5220 exhibited promising attributes as an OX2R PET probe, demonstrating robust OX2R binding selectivity in biodistribution studies. However, an observed interaction with P-gp impacted its brain uptake. Despite this limitation, [11C]MDK-5220 presents itself as a potential candidate for further development.

Discussion

The study provides insights into the functionality of the OX system and the potential of [11C]MDK-5220 as an OX2R PET probe. The observed interaction with P-gp highlights a consideration for future modifications to enhance brain uptake. The findings pave the way for innovative tracer development and propel ongoing research on OX systems, contributing to a deeper understanding of their role in the CNS.

Conclusion

[11C]MDK-5220 emerges as a promising OX2R PET probe, despite challenges related to P-gp interaction. This study lays the foundation for further exploration and development of PET probes targeting OXRs, opening avenues for advancing our understanding of OX system functionality within the brain.

Sulfonamide Compounds as Orexin Receptor Agonists for Treating Sleep Disorders, Namely, Narcolepsy and Hypersomnia

Provided herein are novel sulfonamide compounds as orexin receptor agonists, their pharmaceutical compositions, the use of such compounds in treating sleep disorders, namely, narcolepsy and hypersomnia, and processes for preparing such compounds.

Structure and function of neocortical layer 6b

Cortical layer 6b is considered by many to be a remnant of the subplate that forms during early stages of neocortical development, but its role in the adult is not well understood. Its neuronal complement has only recently become the subject of systematic studies, and its axonal projections and synaptic input structures have remained largely unexplored despite decades of research into neocortical function. In recent years, however, layer 6b (L6b) has attracted increasing attention and its functional role is beginning to be elucidated. In this review, I will attempt to provide an overview of what is currently known about the excitatory and inhibitory neurons in this layer, their pre- and postsynaptic connectivity, and their functional implications. Similarities and differences between different cortical areas will be highlighted. Finally, layer 6b neurons are highly responsive to several neuropeptides such as orexin/hypocretin, neurotensin and cholecystokinin, in some cases exclusively. They are also strongly controlled by neurotransmitters such as acetylcholine and norepinephrine. The interaction of these neuromodulators with L6b microcircuitry and its functional consequences will also be discussed.

Rethinking the Role of Orexin in the Regulation of REM Sleep and Appetite

Orexin plays a significant role in the modulation of REM sleep, as well as in the regulation of appetite and feeding. This review explores, first, the current evidence on the role of orexin in the modulation of sleep and wakefulness and highlights that orexin should be considered essentially as a neurotransmitter inhibiting REM sleep and, to a much lesser extent, a wake promoting agent. Subsequently, the relationship between orexin, REM sleep, and appetite regulation is examined in detail, shedding light on their interconnected nature in both physiological conditions and diseases (such as narcolepsy, sleep-related eating disorder, idiopathic hypersomnia, and night eating syndrome). Understanding the intricate relationship between orexin, REM sleep, and appetite regulation is vital for unraveling the complex mechanisms underlying sleep-wake patterns and metabolic control. Further research in this field is encouraged in order to pave the way for novel therapeutic approaches to sleep disorders and metabolic conditions associated with orexin dysregulation.

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.