Orphanin FQ (1-11)

Quantitative study of [Tyr10]nociceptin/orphanin FQ (1-11) at NOP receptors in rat periaqueductal gray and expressed NOP receptors in HEK293 cells.[Pubmed:22213115]

Life Sci. 2012 Feb 13;90(7-8):306-12.

AIM: The nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor was reported to be functionally heterogeneous. We investigated if [Tyr(10)]N/OFQ(1-11), a peptide ligand reported to selectively bind to the high affinity site of (125)I-[Tyr(14)]N/OFQ in rodent brains, can be a tool for revealing the NOP receptor heterogeneity. We have previously founded an NOP receptor subset insensitive to Ro 64-6198 and (+)-5a Compound, two non-peptide NOP agonists, in rat ventrolateral periaqueductal gray (vlPAG) neurons. Here, we examined if [Tyr(10)]N/OFQ(1-11) differentiated (+)-5a Compound-sensitive and -insensitive vlPAG neurons. Certain mu-opioid (MOP) receptor ligands highly competing with [Tyr(10)]N/OFQ(1-11) in binding studies also showed high affinity at expressed heteromeric NOP-MOP receptors. We also examined if [Tyr(10)]N/OFQ(1-11) distinguished heteromeric NOP-MOP receptors from homomeric NOP receptors. MAIN METHODS: The NOP receptor activity was evaluated by G-protein coupled inwardly rectifying potassium (GIRK) currents in rat vlPAG slices, and by inhibition of cAMP accumulation in HEK293 cells expressing NOP receptors or co-expressing NOP and MOP receptors. KEY FINDINGS: In vlPAG neurons, [Tyr(10)]N/OFQ(1-11), like N/OFQ, induced GIRK currents through NOP receptors. It was less potent (EC(50): 8.98muM) but equi-efficacious as N/OFQ. [Tyr(10)]N/OFQ(1-11) displayed different pharmacological profiles as (+)-5a Compound, and was effective in both (+)-5a Compound-sensitive and -insensitive neurons. In NOP-expressing HEK293 cells and NOP- and MOP-co-expressing cells, [Tyr(10)]N/OFQ(1-11) displayed similar concentration-response curves in decreasing cAMP accumulation. SIGNIFICANCE: [Tyr(10)]N/OFQ(1-11) is an NOP full agonist and less potent than N/OFQ. However, it can neither reveal the functional heterogeneity of NOP receptors in vlPAG neurons nor differentiate heteromeric NOP-MOP and homomeric NOP receptors.

Identification of a high-affinity orphanin FQ/nociceptin(1-11) binding site in mouse brain.[Pubmed:10523755]

Synapse. 1999 Dec;34(3):181-6.

The presence of pairs of basic amino acids within the orphanin FQ/Nociceptin (OFQ/N) sequence has raised the possibility that truncated versions of the peptide might be physiologically important. OFQ/N(1-11) is pharmacologically active in mice, despite its poor affinity in binding assays (K(i) > 250 nM) for the OFQ/N receptor. Using an analog of OFQ/N(1-11), [(125)I][Tyr(10)]OFQ/N(1-11), we identified a high-affinity binding site (K(D) 234 pM; B(max) 43 fmol/mg protein) with a selectivity profile distinct from the OFQ/N receptor and all the traditional opioid receptors. This site had very high affinity for OFQ/N and its related peptides. The most striking differences between the new site and the OFQ/N receptor previously observed in brain were seen with traditional opioids. Dynorphin A analogs and alpha-neoendorphin competed with [(125)I][Tyr(10)]OFQ/N(1-11) binding in mouse brain with K(i) values below 10 nM, while naloxone benzoylhydrazone (K(i) 3.9 nM) labeled the [(125)I][Tyr(10)]OFQ/N(1-11) binding site as potently as many traditional opioid receptors. Several other opioids, including fentanyl, (-)cyclazocine, levallorphan, naltrindole, and diprenorphine, also displayed moderate affinities for this site. Finally, the [(125)I][Tyr(10)]OFQ/N(1-11) site had a unique regional distribution consistent with a distinct receptor. Thus, [(125)I][Tyr(10)]OFQ/N(1-11) labels a novel site in brain with a selectivity profile intermediate between that of either opioid or OFQ/N receptors.

Antinociceptive analogs of orphanin FQ/nociceptin(1-11).[Pubmed:9747901]

Life Sci. 1998;63(11):PL 161-6.

The presence of pairs of basic amino acids within the sequence of orphanin FQ/nociceptin (OFQ/N) peptide, the endogenous ligand for the ORL1/KOR-3 receptor, has raised the possibility that processing might generate pharmacologically important truncated peptides, including OFQ/N(1-11). OFQ/N(1-11) is pharmacologically active in vivo with a potency comparable to OFQ/N. Several tyrosine-containing analogs of OFQ/N(1-11) have been synthesized and examined for antinociceptive activity. Like OFQ/N(1-11), [Tyr1]OFQ/N(1-11), [Tyr10]OFQ/N(1-11) and [IodoTyr10]OFQ/N(1-11) given supraspinally in mice were antinociceptive in the tailflick assay in mice. The tyrosine analogs showed similar potencies as OFQ/N(1-11) but longer durations of action. This response was readily reversed by the opioid antagonist naloxone despite poor affinities for these analogs at opioid receptors. Another compound, [Tyr11]OFQ/N(1-11) was highly epileptogenic, inducing naloxone-sensitive seizures in greater than 50% of the mice tested at doses comparable to those examined with the other analogs. These results indicate that it is possible to make analgesic OFQ/N(1-11) analogs. The activity of [IodoTyr10]OFQ/N(1-11) suggests that it may prove useful as a radioligand in exploring potential OFQ/N(1-11) binding sites.

Autoradiographic localization of (125)I[Tyr(14)]orphanin FQ/nociceptin and (125)I[Tyr(10)]orphanin FQ/nociceptin(1-11) binding sites in rat brain.[Pubmed:10867661]

J Comp Neurol. 2000 Jul 24;423(2):319-29.

The endogenous ligand for the orphan opioid receptor, orphanin FQ/nociceptin (OFQ), has recently been characterized. The OFQ peptide sequence contains paired basic amino acids, suggesting the possibility of posttranslational processing to a peptide containing the first 11 amino acids of the OFQ peptide. This peptide has been reported in the brain and it has a unique pharmacology. In the present study, we compared the autoradiographic distribution of (125)I[Tyr(14)]OFQ and (125)I[Tyr(10)]OFQ(1-11) in coronal rat brain sections. Nonspecific binding was defined with unlabeled OFQ or OFQ(1-11), respectively. Both radioligands demonstrated high levels of specific binding (>95% of total binding), with no appreciable binding in white matter areas with either ligand. (125)I[Tyr(14)]OFQ binding was widely distributed throughout the rat brain. In contrast, (125)I[Tyr(10)]OFQ(1-11) binding was more restricted. The highest (125)I[Tyr(14)]OFQ binding levels measured in this study were found in the locus coeruleus, an area which contained very low (125)I[Tyr(10)]OFQ(1-11) binding. Both ligands labeled the cortex, hippocampus and amygdala. In the thalamus, (125)I[Tyr(14)]OFQ binding was prominent in most nuclei, whereas (125)I[Tyr(10)]OFQ(1-11) binding was restricted to the midline thalamus. (125)I[Tyr(14)]OFQ binding was heavy in the suprachiasmatic hypothalamus, and moderate in other hypothalamic nuclei. (125)I[Tyr(10)]OFQ(1-11) binding in the hypothalamus, however, was present mainly in the ventromedial hypothalamic nucleus. Lower binding levels of both ligands were found in the caudate putamen. The distinct autoradiographic patterns of these two ligands are consistent with different binding sites, which might help explain their different functional activities.

Orphanin FQ/nociceptin analgesia in the rat.[Pubmed:9593974]

Brain Res. 1998 May 11;792(2):327-30.

The heptadecapeptide orphanin FQ or nociceptin (OFQ/N), the endogenous ligand for the orphan opioid receptor, has a complex pharmacology in mice, eliciting either an anti-opioid/hyperalgesic action or analgesia depending upon the dose and testing paradigm. Unlike mice, orphanin FQ/nociceptin fails to elicit hyperalgesia in the rat following intracerebroventricular injection. Both OFQ/N and a truncated version, OFQ/N(1-11), produce a robust analgesic response. OFQ/N analgesia is readily antagonized by the opioid antagonists naloxone or diprenorphine, despite their very poor affinity for the cloned orphan opioid receptor. Antisense studies revealed that probes targeting the second and third coding exon of the orphan clone significantly attenuate OFQ/N analgesia, while the exon 1 probe was inactive. These results indicate that OFQ/N elicits a naloxone-sensitive analgesia in rats similar to that previously reported in mice.

Pharmacological characterization of orphanin FQ/nociceptin and its fragments.[Pubmed:9262352]

J Pharmacol Exp Ther. 1997 Aug;282(2):858-65.

The cloning of a fourth member of the opioid receptor family has led to the discovery of a new neuropeptide termed orphanin FQ or nociceptin (OFQ/N). Studies in CD-1 mice confirm the ability of OFQ/N to rapidly induce hyperalgesia within 15 min which is insensitive to opioid antagonists. This is followed in the next 30 min by loss of hyperalgesia and the appearance of analgesia in the tailflick assay which is readily reversed by opioid antagonists. However, the very poor affinity of OFQ/N for all the traditional opioid receptors and the insensitivity of OFQ/N analgesia to antisense oligodeoxynucleotides active against MOR-1, DOR-1 or KOR-1 sequences that selectively block mu, delta or kappa1 analgesia, respectively, make it unlikely that OFQ/N analgesia is mediated through typical opioid receptors. Blockade of the antiopioid sigma system by haloperidol enhances the analgesic potency of OFQ/N of more than 100-fold. This effect is pronounced in BALB-C and Swiss-Webster mice. Although OFQ/N alone has little analgesic activity in these mice, the blockade of sigma systems with haloperidol uncovers a robust analgesic response in both strains. Two shorter OFQ/N fragments, OFQ/N(1-7) and OFQ/N(1-11), also are analgesic in CD-1 mice and their actions are reversed by the opioid antagonist diprenorphine despite very poor affinities of both peptides against [125I]OFQ/N binding and all the opioid receptors. In antisense studies, a probe targeting the first coding exon of KOR-3 eliminates OFQ/N hyperalgesia, but not OFQ/N analgesia. Conversely, antisense probes based on the second and third coding exons are inactive against OFQ/N hyperalgesia but readily reverse kappa3 opioid analgesia. These results suggest that OFQ/N elicits both analgesia and hyperalgesia through pharmacologically distinct receptors that do not correspond to traditional opioid receptors.

Structure-activity relationship studies on the novel neuropeptide orphanin FQ.[Pubmed:8662940]

J Biol Chem. 1996 Jun 14;271(24):14163-8.

The heptadecapeptide orphanin FQ (OFQ) is an endogenous ligand to an opioid-like G protein-coupled receptor. Although the primary structure of OFQ exhibits some similarity to the opioid peptides, OFQ is not recognized by opioid receptors nor does the OFQ receptor bind opioid ligands. In order to investigate the structural determinants of this ligand/receptor selectivity, we conducted a systematic structure-activity study on OFQ to characterize which sites of the molecule are important for receptor activation. Alanine- and D-amino acid-scanning mutagenesis revealed several residues in the amino-terminal half of OFQ which participate in both receptor binding and activation. Most strikingly, the Phe1 position could be changed to a tyrosine without loss of biological activity. In addition, the OFQ receptor seemed to require recognition of the complete peptide molecule for activation. These results indicate that the mode of interaction of OFQ with its receptor may be different from that of the opioid peptides with their respective receptors and might therefore account for the observed selectivity.