Nociceptin

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Nociceptin
Nociceptin.png
Names
Other names
Orphanin FQ
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
MeSH nociceptin
PubChem CID
UNII
  • InChI=1S/C79H129N27O22/c1-41(2)33-54(72(122)95-44(5)66(116)103-56(36-59(84)110)73(123)102-53(77(127)128)27-28-58(83)109)104-70(120)49(23-13-15-29-80)100-69(119)52(26-18-32-90-79(87)88)99-65(115)43(4)96-75(125)57(40-107)105-71(121)50(24-14-16-30-81)101-68(118)51(25-17-31-89-78(85)86)98-64(114)42(3)94-61(112)39-93-76(126)63(45(6)108)106-74(124)55(35-47-21-11-8-12-22-47)97-62(113)38-91-60(111)37-92-67(117)48(82)34-46-19-9-7-10-20-46/h7-12,19-22,41-45,48-57,63,107-108H,13-18,23-40,80-82H2,1-6H3,(H2,83,109)(H2,84,110)(H,91,111)(H,92,117)(H,93,126)(H,94,112)(H,95,122)(H,96,125)(H,97,113)(H,98,114)(H,99,115)(H,100,119)(H,101,118)(H,102,123)(H,103,116)(H,104,120)(H,105,121)(H,106,124)(H,127,128)(H4,85,86,89)(H4,87,88,90)/t42-,43-,44-,45+,48-,49-,50-,51-,52-,53-,54-,55-,56-,57-,63-/m0/s1 X mark.svgN
    Key: PULGYDLMFSFVBL-SMFNREODSA-N X mark.svgN
  • C[C@H]([C@@H](C(=O)NCC(=O)N[C@@H](C)C(=O)N[C@@H](CCCNC(=N)N)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CO)C(=O)N[C@@H](C)C(=O)N[C@@H](CCCNC(=N)N)C(=O)N[C@@H](CCCCN)C(=O)N[C@@H](CC(C)C)C(=O)N[C@@H](C)C(=O)N[C@@H](CC(=O)N)C(=O)N[C@@H](CCC(=O)N)C(=O)O)NC(=O)[C@H](Cc1ccccc1)NC(=O)CNC(=O)CNC(=O)[C@H](Cc2ccccc2)N)O
Properties
C79H129N27O22
Molar mass 1809.04
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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prepronociceptin
Identifiers
SymbolPNOC
NCBI gene 5368
HGNC 9163
OMIM 601459
RefSeq NM_006228
UniProt Q13519
Other data
Locus Chr. 8 p21
Search for
Structures Swiss-model
Domains InterPro

Nociceptin/orphanin FQ (N/OFQ), a 17-amino acid neuropeptide, is the endogenous ligand for the nociceptin receptor (NOP, ORL-1). Nociceptin acts as a potent anti-analgesic, effectively counteracting the effect of pain-relievers; its activation is associated with brain functions such as pain sensation and fear learning.

Contents

The gene coding for prepronociceptin is located on Ch8p21 in humans. [1] Nociceptin is derived from the prepronociceptin protein, as are a further two peptides, nocistatin and NocII, both of which inhibit N/OFQ receptor function. [2] Nociceptin is the first example of reverse pharmacology; the NOP receptor was discovered before the endogenous ligand which was discovered by two separate groups in 1995. [3] [4]

Roles of nociceptin

Since its discovery, nociceptin has been of great interest to researchers. Nociceptin is a peptide related to the kappa opioid receptor ligand dynorphin A, [5] but it does not act at the classic opioid receptors (namely, mu, kappa, and delta opioid receptors) which typically act as pain relievers. Nociceptin is widely distributed in the CNS; it is found in the hypothalamus, brainstem, and forebrain, as well as in the ventral and dorsal horns of the spinal cord. The NOP receptor is also widely distributed throughout areas of the brain, including the cortex, anterior olfactory nucleus, lateral septum, hypothalamus, hippocampus, amygdala, central gray, pontine nuclei, interpeduncular nucleus, substantia nigra, raphe complex, locus coeruleus, and spinal cord. [6]

Pain

The N/OFQ-NOP system is found in central and peripheral nervous tissue, where it is well placed to modulate nociception, or the body's sensation of pain. [1] Unlike morphine and other opioids that are used to alleviate pain, nociceptin's role in nociception is not straightforward. Administration of N/OFQ in the brain causes increased sensations of pain (hyperalgesia). [3] This makes it unique from classic opioid peptides, which typically act as analgesics (pain relievers), as it means that nociceptin can even counteract analgesia, thus acting as an antiopioid. Additionally, blocking the nociceptin receptor can lead to an increased pain threshold and a decreased tolerance development to analgesic opioids. As such, nociceptin has a lower risk of addiction than many pain relievers that are currently used. [7] Recent studies have proposed that this anti-analgesic function of nociceptin stems from the inhibition of the periaqueductal grey, which controls pain modulation from the central nervous system. This effect of nociceptin may lead to its future use as a method to reduce morphine dosage and decrease the development of tolerance and dependence. [6] When administered to the spinal cord, nociceptin produces similar analgesic effects to classical opioids. [8]

Mood disorders

There are various studies on animals that suggest that the N/OFQ-NOP system has a part to play in both anxiety and depression. [9] It appears that nociceptin is an anxiolytic (anxiety inhibitor) but also seems to perpetuate depression, since preventing N/OFQ from binding to NOP seems to improve depression. [10] [11]

Drug abuse medications

The NOP receptor has shown potential as a target for medications designed to alleviate the effects of substance abuse disorders. Areas in the hypothalamus and amygdala that correlate to the reward process of drug abuse have been found to contain NOP receptors. Nociceptin has also been found to inhibit dopamine production related to the reward process. Specifically, nociceptin acts to inhibit neural rewards induced by drugs such as amphetamines, morphine, cocaine, and especially alcohol in animal models, though the exact mechanism of this has not yet been proven. Additionally, nociceptin may have lower tolerance development than drugs such as morphine. This was shown when nociceptin compounds were used as a pain medication substitution for morphine. Nociceptin also has therapeutic capabilities for addictions to multiple drugs, potentially playing a role in compounds that have decreased withdrawal tendencies (such as muscle aches, anxiety, and restlessness). [7]

Learning and memory

In animal studies, the N/OFQ-NOP receptor pathway has also been found to play both positive and negative roles in both learning and memory. For example, malfunctions in this pathway are linked to altered fear learning in brain disorders such as post-traumatic stress disorder (PTSD). As such, the receptor pathway maintains homeostatic responses to fear and stressful situations. [12] Nociceptin could also play an inhibitory role in memory function, as some studies show that it impairs spatial learning in vivo, while inhibiting long term potentiation and synaptic transmission in vitro. [6]

Cardiovascular system

The N/OFQ-NOP system has also been implicated in control of the cardiovascular system, as nociceptin administration has led to high blood pressure and bradycardia. Nociceptin has significant effects on cardiovascular parameters such as blood pressure and heart rate that vary by species, as it is excitatory for rodents yet inhibitory for sheep. [6]

Renal system

In the renal system, nociceptin plays a role in water balance, electrolyte balance, and arterial blood pressure regulation. It has also shown potential as a diuretic treatment for alleviating water-retaining diseases. [6]

Immune system

Additional research suggests that nociceptin may be involved in the immune system and sepsis. [13] A study at the University of Leicester looked at patients who were critically ill with sepsis and found that blood N/OFQ levels were significantly higher in patients who died within thirty days in comparison to survivors. [14]

Digestive system

In the gut, nociceptin has been found to have varying effects on stomach and intestinal contractility while also stimulating the increased consumption of food. Additional studies have shown that nociceptin may have an effect as an anti-epileptic drug component. [6]

See also

Related Research Articles

<span class="mw-page-title-main">Opioid receptor</span> Group of biological receptors

Opioid receptors are a group of inhibitory G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatostatin receptors (SSTRs). Opioid receptors are distributed widely in the brain, in the spinal cord, on peripheral neurons, and digestive tract.

<span class="mw-page-title-main">Hyperalgesia</span> Abnormally increased sensitivity to pain

Hyperalgesia is an abnormally increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves and can cause hypersensitivity to stimulus. Prostaglandins E and F are largely responsible for sensitizing the nociceptors. Temporary increased sensitivity to pain also occurs as part of sickness behavior, the evolved response to infection.

<span class="mw-page-title-main">Enkephalin</span> Pentapeptide

An enkephalin is a pentapeptide involved in regulating nociception in the body. The enkephalins are termed endogenous ligands, as they are internally derived and bind to the body's opioid receptors. Discovered in 1975, two forms of enkephalin have been found, one containing leucine ("leu"), and the other containing methionine ("met"). Both are products of the proenkephalin gene.

β-Endorphin Peptide hormone in humans

β-Endorphin (beta-endorphin) is an endogenous opioid neuropeptide and peptide hormone that is produced in certain neurons within the central nervous system and peripheral nervous system. It is one of three endorphins that are produced in humans, the others of which include α-endorphin and γ-endorphin.

<span class="mw-page-title-main">Opioid peptide</span> Class of peptides that bind to opioid receptors

Opioid peptides or opiate peptides are peptides that bind to opioid receptors in the brain; opiates and opioids mimic the effect of these peptides. Such peptides may be produced by the body itself, for example endorphins. The effects of these peptides vary, but they all resemble those of opiates. Brain opioid peptide systems are known to play an important role in motivation, emotion, attachment behaviour, the response to stress and pain, control of food intake, and the rewarding effects of alcohol and nicotine.

<span class="mw-page-title-main">Endomorphin</span> Chemical compound

Endomorphins are considered to be natural opioid neuropeptides central to pain relief. The two known endomorphins, endomorphin-1 and endomorphin-2, are tetrapeptides, consisting of Tyr-Pro-Trp-Phe and Tyr-Pro-Phe-Phe amino acid sequences respectively. These sequences fold into tertiary structures with high specificity and affinity for the μ-opioid receptor, binding it exclusively and strongly. Bound μ-opioid receptors typically induce inhibitory effects on neuronal activity. Endomorphin-like immunoreactivity exists within the central and peripheral nervous systems, where endomorphin-1 appears to be concentrated in the brain and upper brainstem, and endomorphin-2 in the spinal cord and lower brainstem. Because endomorphins activate the μ-opioid receptor, which is the target receptor of morphine and its derivatives, endomorphins possess significant potential as analgesics with reduced side effects and risk of addiction.

<span class="mw-page-title-main">Opiorphin</span> Endogenous chemical compound first isolated from human saliva

Opiorphin is an endogenous chemical compound first isolated from human saliva. Initial research with mice shows the compound has a painkilling effect greater than that of morphine. It works by stopping the normal breakup of enkephalins, natural pain-killing opioids in the spinal cord. It is a relatively simple molecule consisting of a five-amino acid polypeptide, Gln-Arg-Phe-Ser-Arg (QRFSR).

<span class="mw-page-title-main">Nociceptin receptor</span> Protein-coding gene in the species Homo sapiens

The nociceptin opioid peptide receptor (NOP), also known as the nociceptin/orphanin FQ (N/OFQ) receptor or kappa-type 3 opioid receptor, is a protein that in humans is encoded by the OPRL1 gene. The nociceptin receptor is a member of the opioid subfamily of G protein-coupled receptors whose natural ligand is the 17 amino acid neuropeptide known as nociceptin (N/OFQ). This receptor is involved in the regulation of numerous brain activities, particularly instinctive and emotional behaviors. Antagonists targeting NOP are under investigation for their role as treatments for depression and Parkinson's disease, whereas NOP agonists have been shown to act as powerful, non-addictive painkillers in non-human primates.

The neuropeptide FF receptors are members of the G-protein coupled receptor superfamily of integral membrane proteins which bind the pain modulatory neuropeptides AF and FF. The Neuropeptide FF receptor family is a member of the G protein-coupled receptor superfamily containing two subtypes, NPFF1 and NPFF2, which exhibit a high affinity for Neuropeptide FF (NPFF) peptides. NPFF1 is broadly distributed in the central nervous system with the highest levels found in the limbic system and the hypothalamus. NPFF2 is present in high density, particularly in mammals in the superficial layers of the spinal cord where it is involved in nociception and modulation of opioid functions. These receptors participate to the modulation of opioid receptor function in the brain and spinal cord, and can either reduce or increase opioid receptor function depending which tissue they are released in, reflecting a complex role for neuropeptide FF in pain responses.

<span class="mw-page-title-main">JTC-801</span> Chemical compound

JTC-801 is an opioid analgesic drug used in scientific research.

<span class="mw-page-title-main">RB-101</span> Chemical compound

RB-101 is a drug that acts as an enkephalinase inhibitor, which is used in scientific research.

<span class="mw-page-title-main">J-113,397</span> Chemical compound

J-113,397 is an opioid drug which was the first compound found to be a highly selective antagonist for the nociceptin receptor, also known as the ORL-1 receptor. It is several hundred times selective for the ORL-1 receptor over other opioid receptors, and its effects in animals include preventing the development of tolerance to morphine, the prevention of hyperalgesia induced by intracerebroventricular administration of nociceptin, as well as the stimulation of dopamine release in the striatum, which increases the rewarding effects of cocaine, but may have clinical application in the treatment of Parkinson's disease.

<span class="mw-page-title-main">SB-612,111</span> Chemical compound

SB-612,111 is an opioid receptor ligand which is a potent and selective antagonist for the nociceptin receptor (ORL-1), several times more potent than the older drug J-113,397. It does not have analgesic effects in its own right, but prevents the development of hyperalgesia, and also shows antidepressant effects in animal studies.

<span class="mw-page-title-main">Ro64-6198</span> Chemical compound

Ro64-6198 is an opioid drug used in scientific research. It acts as a potent and selective agonist for the nociceptin receptor, also known as the ORL-1 receptor, with over 100x selectivity over the other opioid receptors. It produces anxiolytic effects in animal studies equivalent to those of benzodiazepine drugs, but has no anticonvulsant effects and does not produce any overt effects on behaviour. However it does impair short-term memory, and counteracts stress-induced anorexia. It also has antitussive effects, and reduces the rewarding and analgesic effects of morphine, although it did not prevent the development of dependence. It has been shown to reduce alcohol self-administration in animals and suppressed relapses in animal models of alcoholism, and ORL-1 agonists may have application in the treatment of alcoholism.

<span class="mw-page-title-main">(+)-Naloxone</span> Drug

(+)-Naloxone (dextro-naloxone) is a drug which is the opposite enantiomer of the opioid antagonist drug (−)-naloxone. Unlike (−)-naloxone, (+)-naloxone has no significant affinity for opioid receptors, but instead has been discovered to act as a selective antagonist of Toll-like receptor 4. This receptor is involved in immune system responses, and activation of TLR4 induces glial activation and release of inflammatory mediators such as TNF-α and Interleukin-1.

<span class="mw-page-title-main">MCOPPB</span> Chemical compound

MCOPPB is a drug which acts as a potent and selective agonist for the nociceptin receptor, with a pKi of 10.07 and much weaker activity at other opioid receptors. It has only moderate affinity for the mu opioid receptor, weak affinity for the kappa opioid receptor and negligible binding at the delta opioid receptor. In animal studies, MCOPPB produces potent anxiolytic effects, with no inhibition of memory or motor function, and only slight sedative side effects which do not appear until much higher doses than the effective anxiolytic dose range.

<span class="mw-page-title-main">Cebranopadol</span> Opioid analgesic drug

Cebranopadol is an opioid analgesic of the benzenoid class which is currently under development internationally by Grünenthal, a German pharmaceutical company, and its partner Depomed, a pharmaceutical company in the United States, for the treatment of a variety of different acute and chronic pain states. As of November 2014, it is in phase III clinical trials.

<span class="mw-page-title-main">Olivier Civelli</span> Molecular biologist

Olivier Civelli is a molecular biologist, a researcher in the field of neuropharmacology and an educator. He is the Eric L. and Lila D. Nelson Professor of Neuropharmacology at University of California, Irvine. He is also a Professor in the Department of Developmental and Cell Biology at University of California, Irvine. He is most known for his work in advancing understanding of neurotransmission and his impact on drug discovery.

<span class="mw-page-title-main">SR-16435</span> Drug

SR-16435 is a drug which acts as a potent partial agonist at both the μ-opioid receptor and nociceptin receptor. In animal studies it was found to be a potent analgesic, with results suggestive of reduced development of tolerance and increased activity against neuropathic pain compared to classic μ-selective agonists.

<span class="mw-page-title-main">Ro65-6570</span> Nociceptin receptor agonist

Ro65-6570 is an opioid drug. It has a potential use in preventing the addiction to other opioids.

References

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