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AnimalWakefulness neuropeptide driving arousal and cognition

Orexin B

Also indexed as Hypocretin-2, OXB, Orexin-2

Orexin B (also known as Hypocretin-2) is a neuropeptide produced in the lateral hypothalamus that plays a central role in regulating wakefulness, arousal, appetite, and energy homeostasis. It acts primarily through the OX2 receptor (orexin receptor type 2) to promote and maintain wakefulness and modulate feeding behavior. Research into orexin B is largely preclinical, but it has significant implications for understanding narcolepsy, sleep disorders, and metabolic regulation.

Overview

Exogenously administered Orexin B faces significant pharmacokinetic barriers. As a peptide, it is rapidly degraded by serum proteases (t½ ~10–20 min systemic) and has poor blood-brain barrier (BBB) penetrance due to its molecular weight (~2.16 kDa) and hydrophilicity. Intranasal delivery has been explored as a non-invasive CNS delivery route, leveraging olfactory/trigeminal nerve pathways to bypass the BBB; studies in rodents (Dhuria et al., 2010, J Pharm Sci) show modest CNS delivery efficiency (~0.1–1% of dose). Intracerebroventricular (ICV) administration in animal models achieves direct CNS exposure and represents the primary research delivery method. Peripheral administration primarily affects cardiovascular and metabolic endpoints via peripheral OX receptors in the adrenal glands, pancreas, and gastrointestinal tract.

Proposed mechanism

Orexin B binds with approximately equal affinity to both OX1R and OX2R G-protein-coupled receptors, though it shows a slight preference for OX2R. Upon receptor activation, downstream signaling involves Gq/11-mediated phospholipase C activation, IP3-driven intracellular calcium release, and activation of PKC pathways, as well as Gs-mediated cAMP elevation. These cascades increase the excitability of wake-promoting neurons in the locus coeruleus, dorsal raphe, and tuberomammillary nucleus, sustaining arousal and suppressing transitions into REM sleep.

What the evidence supports

Most data comes from preclinical animal studies. Human clinical trial evidence is limited or absent.

Graded Animal

Evidence drawn from in vivo animal models or in vitro systems. Mechanistically informative; translation to humans is unproven.

Key citations

Representative primary sources, including results that did not favour the compound.

  1. [1]

    Orexins and orexin receptors: a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behavior

    · Cell. 92(4):573-585. Sakurai T et al. PMID: 9491897 · 1998

  2. [2]

    The hypocretins: hypothalamus-specific peptides with neuroexcitatory activity

    · PNAS. 95(1):322-327. de Lecea L et al. PMID: 9390374 · 1998

  3. [3]

    Intranasal delivery to the central nervous system: Mechanisms and experimental considerations

    · J Pharm Sci. 99(4):1654-1673. Dhuria SV et al. PMID: 19697349 · 2010

  4. [4]

    Orexin receptor antagonism, a new sleep-enabling paradigm: a proof-of-concept clinical trial

    · Sci Transl Med. 4(129):129ra43. Bettica P et al. PMID: 22491949 · 2012

  5. [5]

    The role of orexin in regulating the sleep-wake cycle and its implications for narcolepsy

    · Sleep Med Rev. 35:1-13. Kornum BR et al. PMID: 27816503 · 2017

Citation records in this build are illustrative placeholders for the design.

Reference information for research purposes. Not medical advice, and not a recommendation to use any compound. Many entries describe substances that are not approved for human use.

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