Nociceptin

Nociceptin, a heptadecapeptide, is the endogenous ligand of the nociceptin receptor, acting as a potent anti-analgesic. Sequence: Phe-Gly-Gly-Phe-Thr-Gly-Ala-Arg-Lys-Ser-Ala-Arg-Lys-Leu-Ala-Asn-Gln.

In Vitro:Nociceptin (1 μg/mL) significantly prevents LPS (10 ng/mL)-stimulated cell migration whereas it is ineffective when added alone. Nociceptin (1 nM-10 μM) elicits a concentration-dependent blockade of LPS-mediated cell migration, with a maximal effect at 1 and 10 μM. Nociceptin counteracts LPS-induced elevation of IL-1β mRNA levels. Nociceptin (1 μM) and NNC 55-0396 induce apoptotic cell death in U87 cells. Nociceptin (1 μM) counteracts LPS-induced [Ca2+]i increase in U87 cells via β-arrestin 2. Nociceptin counteracts the LPS-induced phosphorylation of PKC and ERK in U87 cells. Nociceptin inhibits the LPS-mediated transcriptional activation of NF-kB and AP-1 reporter genes[1].

References:
[1]. Bedini A, et al. Nociceptin/orphanin FQ antagonizes lipopolysaccharide-stimulated proliferation, migration and inflammatory signaling in human glioblastoma U87 cells. Biochem Pharmacol. 2017 Sep 15;140:89-104.

Respiratory Effects of the Nociceptin/Orphanin FQ Peptide and Opioid Receptor Agonist, Cebranopadol, in Healthy Human Volunteers.[Pubmed:28291085]

Anesthesiology. 2017 Apr;126(4):697-707.

BACKGROUND: Cebranopadol is a novel strong analgesic that coactivates the Nociceptin/orphanin FQ receptor and classical opioid receptors. There are indications that activation of the Nociceptin/orphanin FQ receptor is related to ceiling in respiratory depression. In this phase 1 clinical trial, we performed a pharmacokinetic-pharmacodynamic study to quantify cebranopadol's respiratory effects. METHODS: Twelve healthy male volunteers received 600 mug oral cebranopadol as a single dose. The following main endpoints were obtained at regular time intervals for 10 to 11 h after drug intake: ventilation at an elevated clamped end-tidal pressure of carbon dioxide, pain threshold and tolerance to a transcutaneous electrical stimulus train, and plasma cebranopadol concentrations. The data were analyzed using sigmoid Emax (respiration) and power (antinociception) models. RESULTS: Cebranopadol displayed typical opioid-like effects including miosis, analgesia, and respiratory depression. The blood-effect-site equilibration half-life for respiratory depression and analgesia was 1.2 +/- 0.4 h (median +/- standard error of the estimate) and 8.1 +/- 2.5 h, respectively. The effect-site concentration causing 50% respiratory depression was 62 +/- 4 pg/ml; the effect-site concentration causing 25% increase in currents to obtain pain threshold and tolerance was 97 +/- 29 pg/ml. The model estimate for minimum ventilation was greater than zero at 4.9 +/- 0.7 l/min (95% CI, 3.5 to 6.6 l/min). CONCLUSIONS: At the dose tested, cebranopadol produced respiratory depression with an estimate for minimum ventilation greater than 0 l/min. This is a major advantage over full mu-opioid receptor agonists that will produce apnea at high concentrations. Further clinical studies are needed to assess whether such behavior persists at higher doses.

Opioid-type Respiratory Depressant Side Effects of Cebranopadol in Rats Are Limited by Its Nociceptin/Orphanin FQ Peptide Receptor Agonist Activity.[Pubmed:28291086]

Anesthesiology. 2017 Apr;126(4):708-715.

BACKGROUND: Cebranopadol is a first-in-class analgesic with agonist activity at classic opioid peptide receptors and the Nociceptin/orphanin FQ peptide receptor. The authors compared the antinociceptive and respiratory depressant effects of cebranopadol and the classic opioid fentanyl and used selective antagonists to provide the first mechanistic evidence of the contributions of the Nociceptin/orphanin FQ peptide and mu-opioid peptide receptors to cebranopadol's respiratory side-effect profile. METHODS: Antinociception was assessed in male Sprague-Dawley rats using the low-intensity tail-flick model (n = 10 per group). Arterial blood gas tensions (PaCO2 and PaO2) were measured over time in samples from unrestrained, conscious rats after intravenous administration of cebranopadol or fentanyl (n = 6 per group). RESULTS: The ED50 for peak antinociceptive effect in the tail-flick model was 7.4 mug/kg for cebranopadol (95% CI, 6.6 to 8.2 mug/kg) and 10.7 mug/kg for fentanyl citrate (9 to 12.7 mug/kg). Fentanyl citrate increased PaCO2 levels to 45 mmHg (upper limit of normal range) at 17.6 mug/kg (95% CI, 7.6 to 40.8 mug/kg) and to greater than 50 mmHg at doses producing maximal antinociception. In contrast, with cebranopadol, PaCO2 levels remained less than 35 mmHg up to doses producing maximal antinociception. The Nociceptin/orphanin FQ peptide receptor antagonist J-113397 potentiated the respiratory depressant effects of cebranopadol; these changes in PaCO2 and PaO2 were fully reversible with the mu-opioid peptide receptor antagonist naloxone. CONCLUSIONS: The therapeutic window between antinociception and respiratory depression in rats is larger for cebranopadol than that for fentanyl because the Nociceptin/orphanin FQ peptide receptor agonist action of cebranopadol counteracts side effects resulting from its mu-opioid peptide receptor agonist action.

Social defeat disrupts reward learning and potentiates striatal nociceptin/orphanin FQ mRNA in rats.[Pubmed:28280884]

Psychopharmacology (Berl). 2017 May;234(9-10):1603-1614.

RATIONALE: Mood disorders can be triggered by stress and are characterized by deficits in reward processing, including disrupted reward learning (the ability to modulate behavior according to past rewards). Reward learning is regulated by the anterior cingulate cortex (ACC) and striatal circuits, both of which are implicated in the pathophysiology of mood disorders. OBJECTIVES: Here, we assessed in rats the effects of a potent stressor (social defeat) on reward learning and gene expression in the ACC, ventral tegmental area (VTA), and striatum. METHODS: Adult male Wistar rats were trained on an operant probabilistic reward task (PRT) and then exposed to 3 days of social defeat before assessment of reward learning. After testing, the ACC, VTA, and striatum were dissected, and expression of genes previously implicated in stress was assessed. RESULT: Social defeat blunted reward learning (manifested as reduced response bias toward a more frequently rewarded stimulus) and was associated with increased Nociceptin/orphanin FQ (N/OFQ) peptide mRNA levels in the striatum and decreased Fos mRNA levels in the VTA. Moreover, N/OFQ peptide and Nociceptin receptor mRNA levels in the ACC, VTA and striatum were inversely related to reward learning. CONCLUSIONS: The behavioral findings parallel previous data in humans, suggesting that stress similarly disrupts reward learning in both species. Increased striatal N/OFQ mRNA in stressed rats characterized by impaired reward learning is consistent with accumulating evidence that antagonism of Nociceptin receptors, which bind N/OFQ, has antidepressant-like effects. These results raise the possibility that Nociceptin systems represent a molecular substrate through which stress produces reward learning deficits in mood disorders.

Bifunctional opioid/nociceptin hybrid KGNOP1 effectively attenuates pain-related behaviour in a rat model of neuropathy.[Pubmed:28347772]

Eur J Pharm Sci. 2017 Jun 15;104:221-229.

A bifunctional peptide containing an opioid and Nociceptin receptor-binding pharmacophore, H-Dmt-D-Arg-Aba-beta-Ala-Arg-Tyr-Tyr-Arg-Ile-Lys-NH2 (KGNOP1), was tested for its analgesic properties when administered intrathecally in naive and chronic constriction injury (CCI)-exposed rats with neuropathy-like symptoms. KGNOP1 significantly increased the acute pain threshold, as measured by the tail-flick test, and also increased the threshold of a painful reaction to mechanical and thermal stimuli in CCI-exposed rats. Both of the effects could be blocked by pre-administration of [Nphe1]-Nociceptin (1-13)-NH2 (NPhe) or naloxone, antagonists for Nociceptin and opioid receptors, respectively. This led us to conclude that KGNOP1 acts as a dual opioid and Nociceptin receptor agonist in vivo. The analgesic effect of KGNOP1 proved to be more powerful than clinical drugs such as morphine and buprenorphine. Repeated daily intrathecal injections of KGNOP1 led to the development of analgesic tolerance, with the antiallodynic action being completely abolished on day 6. Nevertheless, the development of tolerance to the antihyperalgesic effect was delayed in comparison to morphine, which lost its efficacy as measured by the cold plate test after 3days of daily intrathecal administration, whereas KGNOP1 was efficient up to day 6. A single intrathecal injection of morphine to KGNOP1-tolerant rats did not raise the pain threshold in any of the behavioural tests; in contrast, a single intrathecal dose of KGNOP1 significantly suppressed allodynia and hyperalgesia in morphine-tolerant rats.

Structure-activity relationships of nociceptin and related peptides: comparison with dynorphin A.[Pubmed:10998526]

Peptides. 2000 Jul;21(7):923-33.

Nociceptin and its receptor (OP(4)) share sequence homologies with the opioid peptide ligand dynorphin A and its receptor OP(2). Cationic residues in the C-terminal sequence of both peptides seem to be required for selective receptor occupation, but the number and the distribution of these basic residues are different and quite critical. Both receptors are presumably activated by the peptides N-terminal sequence (Xaa-Gly Gly-Phe, where Xaa = Phe or Tyr); however, although OP(4) requires Phe(4) as a determinant pharmacophore, OP(2) requires Tyr(1) as do the other opioid receptors. An extensive structure-activity analysis of the N-terminal tetrapeptide has led to conclude that the presence of aromatic residues in position one and four, preferably Phe, as well as the distance between Phe(1) and Phe(4) are extremely critical for occupation and activation of OP(4) in contrast with other opioid receptors (e.g. OP(1), OP(3), OP(2)). Modification of distance between the side chains of Phe(1) and Phe(4) (as obtained with Nphe(1) substitution in both NC and NC(1-13)-NH(2)) and/or conformational orientation of Phe(1) (as in Phe(1)psi(CH(2)-NH)-Gly(2)) has brought to discovery of pure antagonist ([Nphe(1)]-NC(1-13)-NH(2)) and a partial agonist ([Phe(1) psi(CH(2)-NH)-Gly(2)]-NC(1-13)-NH(2)), which have allowed us to characterize and classify the OP(4) receptor in several species. Thus, although antagonist activities at the OP(4) receptor are obtained by chemical modification of Phe(1)-Gly(2) peptide bond or by a shift of Phe(1) side chain of NC peptides, antagonism at the OP(2) receptor requires the diallylation of the N-terminal amino function, for instance, of dynorphin A. These considerations support the interpretation that the two systems Nociceptin/OP(4) and dynorphin A/OP(2) are distinct pharmacological entities that differs in both their active sites (Tyr(1) for Dyn A and Phe(4) for NC) and the number and position of cationic residues in the C-terminal portions of the molecules. The chemical features of novel OP(4) receptor ligands either pseudopeptides obtained by combinatorial library screening or molecules of nonpeptide structure are reported and discussed in comparison with NC and NC related peptides.

The orphan opioid receptor and its endogenous ligand--nociceptin/orphanin FQ.[Pubmed:9277133]

Trends Pharmacol Sci. 1997 Aug;18(8):293-300.

Following the elucidation of the amino acid sequences of the mu-, delta- and kappa-opioid receptors, a new 'orphan opioid receptor' was cloned with a high degree of homology to the 'classical' opioid receptors. The endogenous opioid peptides show little or no activity at this new receptor; however, a novel endogenous peptide for the orphan opioid receptor has been isolated and sequenced. Here, Graeme Henderson and Sandy McKnight review recent findings on this new receptor and its endogenous ligand, and address the contentious issue of whether activation of this receptor results in hyperalgesia or analgesia.

Isolation and structure of the endogenous agonist of opioid receptor-like ORL1 receptor.[Pubmed:7566152]

Nature. 1995 Oct 12;377(6549):532-5.

The ORL1 receptor, an orphan receptor whose human and murine complementary DNAs have recently been characterized, structurally resembles opioid receptors and is negatively coupled with adenylate cyclase. ORL1 transcripts are particularly abundant in the central nervous system. Here we report the isolation, on the basis of its ability to inhibit the cyclase in a stable recombinant CHO(ORL1+) cell line, of a neuropeptide that resembles dynorphin A9 and whose amino acid sequence is Phe-Gly-Gly-Phe-Thr-Gly-Ala-Arg-Lys-Ser-Ala-Arg-Lys-Leu-Ala-Asn-Gln. The rat-brain cDNA encodes the peptide flanked by Lys-Arg proteolytic cleavage motifs. The synthetic heptadecapeptide potently inhibits adenylate cyclase in CHO(ORL1+) cells in culture and induces hyperalgesia when administered intracerebroventricularly to mice. Taken together, these data indicate that the newly discovered heptadecapeptide is an endogenous agonist of the ORL1 receptor and that it may be endowed with pro-nociceptive properties.

Orphanin FQ: a neuropeptide that activates an opioidlike G protein-coupled receptor.[Pubmed:7481766]

Science. 1995 Nov 3;270(5237):792-4.

A heptadecapeptide was identified and purified from porcine brain tissue as a ligand for an orphan heterotrimeric GTP-binding protein (G protein)-coupled receptor (LC132) that is similar in sequence to opioid receptors. This peptide, orphanin FQ, has a primary structure reminiscent of that of opioid peptides. Nanomolar concentrations of orphanin FQ inhibited forskolin-stimulated adenylyl cyclase activity in cells transfected with LC132. This inhibitory activity was not affected by the addition of opioid ligands, nor did the peptide activate opioid receptors. Orphanin FQ bound to its receptor in a saturable manner and with high affinity. When injected intracerebroventricularly into mice, orphanin FQ caused a decrease in locomotor activity but did not induce analgesia in the hot-plate test. However, the peptide produced hyperalgesia in the tail-flick assay. Thus, orphanin FQ may act as a transmitter in the brain by modulating nociceptive and locomotor behavior.