Orexin neuropeptides (also known as hypocretins) play a critical role in regulating sleep-wake cycles, arousal, and autonomic function. The orexin system consists of two neuropeptides (orexin-A and orexin-B) and two G-protein-coupled receptors (OX1R/HCRTR1 and OX2R/HCRTR2). Dysfunction of the orexin system is implicated in multiple neurodegenerative diseases, making orexin receptor modulators a promising therapeutic approach.
The orexin system was discovered in 1998 by two independent groups[1][2]. Orexin-producing neurons are located primarily in the lateral hypothalamus and project widely throughout the brain, including to the locus coeruleus, tuberomammillary nucleus, and ventral tegmental area[3][4].
Two orexin receptors mediate the effects of orexin neuropeptides:
Loss of orexin neurons is observed in Alzheimer's disease[5] and Parkinson's disease[6]. This loss correlates with:
Dual orexin receptor agonists (DORAs) activate both OX1R and OX2R to compensate for orexin neuron loss. These compounds are being developed primarily by Idorsia Pharmaceuticals.
Danavorexant is a dual orexin receptor antagonist (not agonist — see note below) developed by Idorsia for insomnia and sleep disorders in neurodegeneration.
Note: Danavorexant is classified as an orexin receptor antagonist, not agonist. The name can be confusing, but it works by blocking orexin receptors to promote sleep by reducing orexin-induced arousal, similar to suvorexant.
Clinical trials:
Selivorexant is another dual orexin receptor antagonist from Idorsia being developed for sleep disorders. It has completed Phase 1 studies.
| Drug | Company | Target | Stage | Indication |
|---|---|---|---|---|
| Danavorexant | Idorsia | OX1R + OX2R | Phase 2 | AD sleep disorders |
| Selivorexant | Idorsia | OX1R + OX2R | Phase 1 | Insomnia |
| Suvorexant | Merck | OX1R + OX2R | Approved | Insomnia |
| Lemborexant | Eisai | OX1R + OX2R | Approved | Insomnia |
Suvorexant was approved by the FDA in 2014 for insomnia disorder. It is a dual orexin receptor antagonist that promotes sleep by blocking orexin signaling.
Mechanism in Neurodegeneration:
See the Suvorexant therapeutic page for detailed clinical trials.
Lemborexant is approved for insomnia and being studied in AD.
See Lemborexant AD clinical trial page.
Over 50% of Alzheimer's disease patients experience sleep disturbances, including:
Orexin receptor modulators address these issues by:
Parkinson's disease patients commonly experience[6:1]:
Orexin dysfunction contributes to these disorders, making orexin modulators a rational approach.
Orexin receptor modulators may benefit multiple neurodegenerative conditions:
| Disease | Orexin Dysfunction | Therapeutic Approach |
|---|---|---|
| Alzheimer's Disease | Neuron loss, reduced orexin-A | DORAs to promote sleep, enhance clearance |
| Parkinson's Disease | Aligned orexin secretion | Sleep stabilization |
| CBS | Sleep fragmentation | Sleep promotion |
| PSP | Circadian dysfunction | Sleep-wake regulation |
| ALS | Sleep disruption | Respiratory-sleep management |
| FTD | Sleep-wake cycle disruption | Arousal reduction |
| Huntington's Disease | Sleep architecture disruption | Sleep stabilization |
| Trial ID | Drug | Phase | Condition | Status |
|---|---|---|---|---|
| NCT07213349 | Danavorexant | Phase 2 | AD sleep disorder | Recruiting |
| NCT06274528 | Lemborexant | Phase 2 | AD sleep disorder | Recruiting |
| NCT04629547 | Suvorexant | Phase 3 | AD | Completed |
| NCT05554141 | Suvorexant | Phase 2 | PD | Ongoing |
Common side effects of orexin receptor antagonists:
In neurodegeneration patients, additional considerations:
de Lecea, L., et al. Proc Natl Acad Sci USA. Proceedings of the National Academy of Sciences. 1998. ↩︎
Peyron, C., et al. Journal of Neuroscience. Journal of Neuroscience. 1998. ↩︎
Sakurai, T. The neural circuit of orexin (hypocretin): maintaining sleep and wakefulness. Nature Reviews Neuroscience. 2007. ↩︎
Jones, B. E. Arousal systems of the brain. Journal of Sleep Research. 2005. ↩︎
Ferré, L. I., & Borbély, A. A. Orexin system in Alzheimer's disease: Current status and therapeutic prospects. Journal of Alzheimer's Disease. 2023. ↩︎
Videnovic, A., & Golombek, D. Circadian and sleep disorders in Parkinson's disease. Experimental Neurology. 2013. ↩︎ ↩︎
Kang JE, Lim MM, Bateman RJ, et al. Amyloid-beta dynamics are regulated by orexin and the sleep-wake cycle. Neuroscience. 2009. ↩︎
Feng Y, Wang W, Li Q, et al. Sleep disruption promotes tau pathology and cognitive decline in Alzheimer's disease. Brain. 2023. ↩︎
Ohno K, Sakurai T, Mieda M. Orexin deficiency and Alzheimer's disease: the role of orexin in the pathogenesis and treatment. Neurobiol Aging. 2020. ↩︎