Spotlight on nociceptin/orphanin FQ receptor in the treatment of pain

In our society today, pain has become a main source of strain on most individuals. It is crucial to develop novel treatments against pain while focusing on decreasing their adverse effects. Throughout the extent of development for new pain therapies, the nociceptin/orphanin FQ receptor (NOP receptor) has appeared to be an encouraging focal point. Concentrating on NOP receptor to treat chronic pain with limited range of unwanted effects serves as a suitable alternative to prototypical opioid morphine that could potentially lead to life-threatening effects caused by respiratory depression in overdose, as well as generate abuse and addiction. In addition to these harmful effects, the uprising opioid epidemic is responsible for becoming one of the most disastrous public health issues in the US. In this article, the contributing molecular and cellular structure in controlling the cellular trafficking of NOP receptor and studies that support the role of NOP receptor and its ligands in pain management are reviewed

Biochemistry of opioid (morphine) receptors : binding, structure and molecular modelling

Morphine is the most widely used compound among narcotic analgesics and remains the gold standard when the effects of other analgetic drugs are compared. The most characteristic effect of morphine is the modulation of pain perception resulting in an increase in the threshold of noxious stimuli. Antinociception induced by morphine is mediated via opioid receptors, namely the μ-type opioid receptor. Apart from the μ-opioid receptor, two other classical opioid receptors κ- and δ- and one non-classical opioid receptor, the nociceptin receptor was discovered and cloned so far. At the same time endogenous opioids were also discovered, such as enkephalins, endorphins, and dynorphins. The opioid receptors together with the endogenous opioids form the so called endogenous opioid system, which is highly distributed throughout the body and apart from analgesia it has several other important physiological functions. In this article we will review the historical milestones of opioid research − in detail with morphine. The review will also cover the upmost knowledge in the molecular structure and physiological effects of opioid receptors and endogenous opioids and we will discuss opioid receptor modelling − a rapidly evolving field in opioid receptor research

Nociceptin/orphanin FQ – NOP receptor system: novel genetic and pharmacological tools

The neuropeptide nociceptin/orphanin FQ (N/OFQ) selectively binds and activates the N/OFQ peptide (NOP) receptor. In cells expressing the NOP receptor N/OFQ inhibits cAMP accumulation and Ca2+ conductance and stimulates K+ currents. Via these mechanisms N/OFQ regulates several biological functions in the central nervous system (pain, locomotion, memory, emotional responses, food intake), as well as in the periphery (airways, cardiovascular, genitourinary and gastrointestinal systems). Several research tools including knockout mice and NOP selective agonists and antagonists have been developed in the past and used to investigate the role played by this peptidergic system in pathophysiology and to identify possible therapeutic indications of NOP receptor ligands. The aim of the present study was to make available to the scientific community novel genetic and pharmacological tools to speed up the process of target validation of the NOP receptor. Knockout rats for the NOP receptor gene (NOP(-/-)) have been recently generated. These animals were used in the present study to investigate their emotional (open field, elevated plus maze, and forced swimming test), locomotor (drag and rotarod test), and nociceptive (plantar and formalin test) phenotype in comparison to NOP(+/+) littermates. The results were in line with previous findings obtained with selective NOP receptor antagonists in mice and rats and with mouse knockout studies and indicated that the blockage of N/OFQergic signalling elicits antidepressant and motor stimulant effects. A detailed pharmacological characterization of novel NOP receptor non peptide ligands has been performed. The compound GF-4 displayed high affinity and potency at recombinant human NOP receptor associated with pure antagonist properties. This profile was confirmed in N/OFQ sensitive animal tissues. In vivo GF-4 elicited, similar to other NOP antagonists, beneficial effects in animal models of Parkinson disease. The NOP non-peptide agonists Ro 65-6570, SCH 221510 and compound 6d were characterized in vitro using a calcium mobilization assay and electrically stimulated mouse and rat vas deferens tissues. The results of these studies demonstrated that Ro 65-6570 and SCH-221510 behaved as full agonists showing however some level of NOP selectivity in rat, but not mouse, tissues. Compound 6d did not display NOP selectivity. Finally, mixed NOP/MOP receptor agonists were generated. [Dmt1]N/OFQ(1-13)NH2 was selected as the most potent compound. The mixed NOP/MOP full agonist activity and high affinity of [Dmt1]N/OFQ(1- 13)NH2 was confirmed at human recombinant receptors in receptor and [35S]GTPgS binding studies, at rat spinal cord receptors in [35S]GTPgS binding experiments, and at guinea pig receptors inhibiting neurogenic contractions in the ileum. In vivo in the mouse tail withdrawal assay in mice [Dmt1]N/OFQ(1-13)NH2 was also able to elicit a robust antinociceptive effect being more potent than N/OFQ (by 30 fold) and morphine (by 3 fold). The antinociceptive properties of spinal [Dmt1]N/OFQ(1-13)NH2 were confirmed in non human primate studies. Collectively these results demonstrate that [Dmt1]N/OFQ(1-13)NH2 behaves as mixed NOP/MOP agonist and susbtantiate the suggestion that such mixed ligands are worthy of development as innovative spinal analgesics

Biochemical and pharmacological characterization of three opioid-nociceptin hybrid peptide ligands reveals substantially differing modes of their actions

In an attempt to design opioid-nociceptin hybrid peptides, three novel bivalent ligands, H-YGGFGGGRYYRIK-NH2, H-YGGFRYYRIK-NH2 and Ac-RYYRIKGGGYGGFL-OH were synthesized and studied by biochemical, pharmacological, biophysical and molecular modelling tools. These chimeric molecules consist of YGGF sequence, a crucial motif in the N-terminus of natural opioid peptides, and Ac-RYYRIK-NH2, which was isolated from a combinatorial peptide library as an antagonist or partial agonist that inhibits the biological activity of the endogenously occurring heptadecapeptide nociceptin. Solution structures for the peptides were studied by analysing their circular dichroism spectra. Receptor binding affinities were measured by equilibrium competition experiments using four highly selective radioligands. G-protein activating properties of the multitarget peptides were estimated in [35S]GTPγS binding tests. The three compounds were also measured in electrically stimulated mouse vas deferens (MVD) bioassay. H-YGGFGGGRYYRIK-NH2 (BA55), carrying N-terminal opioid and C-terminal nociceptin-like sequences interconnected with GGG tripeptide spacer displayed a tendency of having either unordered or β-sheet structures, was moderately potent in MVD and possessed a NOP/KOP receptor preference. A similar peptide without spacer H-YGGFRYYRIK-NH2 (BA62) exhibited the weakest effect in MVD, more α-helical periodicity was present in its structure and it exhibited the most efficacious agonist actions in the G-protein stimulation assays. The third hybrid peptide Ac-RYYRIKGGGYGGFL-OH (BA61) unexpectedly displayed opioid receptor affinities, because the opioid message motif is hidden within the C-terminus. The designed chimeric peptide ligands presented in this study accommodate well into a group of multitarget opioid compounds that include opioid-non-opioid peptide dimer analogues, dual non-peptide dimers and mixed peptide- non-peptide bifunctional ligands

Structure of the nociceptin/orphanin FQ receptor in complex with a peptide mimetic

Members of the Opioid Receptor (OR) family of G protein-coupled receptors (GPCRs) are found throughout the peripheral and central nervous system where they play key roles in nociception and analgesia. Unlike the classical ORs, δ–OR, κ–OR,1 and μ-OR,2 which were delineated by pharmacological criteria in the 1970’s and 1980’s, the nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP, aka ORL-1) was discovered relatively recently via molecular cloning and characterization of an orphan GPCR3. Despite its high sequence similarity (~60%) with ORs, NOP has a strikingly distinct pharmacology4,5. Despite high sequence similarity with classical opioid G protein-coupled receptor subtypes, the nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP) has a distinct biological and pharmacological role, featuring activation by the endogenous peptide N/OFQ, and unique selectivity for exogenous ligands. This study reports the crystal structure of human NOP solved in complex with the peptide mimetic antagonist Banyu Compound-24 (C-24), revealing atomic details of ligand-receptor recognition and selectivity. C-24 mimics the first four N-terminal residues of the NOP-selective peptide antagonist UFP-101, a close derivative of N/OFQ, and provides important clues to binding of these peptides. The X-ray structure also reveals substantial conformational differences in the pocket regions between NOP and the “classical” opioid receptors κ (Ref. 1) and μ (Ref. 2), which are likely due to a small number of residues that vary between the two receptors. The NOP/C-24 structure explains the divergent selectivity profile of NOP and provides a new structural template for the design of NOP ligands

El receptor tipo opioide ORL1 en los GASH/Sal: una nueva línea de hámsters sirios con epilepsia audiógena

[ES]Esta tesis doctoral presenta un estudio sobre la implicación del opioide ORL1 en las crisis epilépticas a partir de experimentos hechos en un modelo animal que presenta convulsiones audiógenas, el hámster GASH:Sal

The experimental power of FR900359 to study Gq-regulated biological processes.

Despite the discovery of heterotrimeric αβγ G proteins ∼25 years ago, their selective perturbation by cell-permeable inhibitors remains a fundamental challenge. Here we report that the plant-derived depsipeptide FR900359 (FR) is ideally suited to this task. Using a multifaceted approach we systematically characterize FR as a selective inhibitor of Gq/11/14 over all other mammalian Gα isoforms and elaborate its molecular mechanism of action. We also use FR to investigate whether inhibition of Gq proteins is an effective post-receptor strategy to target oncogenic signalling, using melanoma as a model system. FR suppresses many of the hallmark features that are central to the malignancy of melanoma cells, thereby providing new opportunities for therapeutic intervention. Just as pertussis toxin is used extensively to probe and inhibit the signalling of Gi/o proteins, we anticipate that FR will at least be its equivalent for investigating the biological relevance of Gq

Structure–activity relationships of opioid ligands

There are three different types of opioid receptor, namely mu, delta and kappa. Morphine and related clinically useful analgesics exert their actions through the mu opioid receptor. Such compounds represent a huge structural diversity, including both peptides and alkaloids. Nevertheless, there exists a common pharmacophore comprising two critical features, namely an amine nitrogen and an aromatic ring, usually with a hydroxyl substituent; the spatial relationship between them is also vital. [Continues.