Nociceptin/Orphanin FQ and Urinary Bladder

Voiding and storage symptoms in depression/anxiety

We here described the frequency and nature of voiding and storage bladder symptoms in depression/anxiety, for which we propose the name "bladder somatic symptom disorder (SSD)" because such symptoms most probably have brain mechanisms. SSD was formerly called as various terms including "somatoform disorder", "medically unexplained physical symptoms", "functional somatic syndrome" and "hysterical neurosis/hysteria". Bladder SSD has the following specific features that are distinguishable from "true" neurologic/organic bladder dysfunction: 1) situation-dependence (close association with life event in some), 2) urodynamically increased bladder sensation/hypersensitivity and 3) absence of neurologic/organic diseases, in addition to 4) other stress symptoms (insomnia, etc.), are key clues to the possibility of bladder SSD. Urodynamics in these patients showed, to a lesser extent, underactive bladder without post-void residual. These findings might reflect the biological changes of the depressive brain; e.g., decreases in serotonin and GABA, and possible increases in CRH. Treatment of bladder SSD can follow that of general depression/anxiety, with the potential addition of anticholinergic or selective beta3 bladder drugs.

The NOP Receptor System in Neurological and Psychiatric Disorders: Discrepancies, Peculiarities and Clinical Progress in Developing Targeted Therapies

The nociceptin opioid peptide (NOP) receptor and its endogenous ligand nociceptin/orphanin FQ (N/OFQ) are the fourth members of the opioid receptor and opioid peptide families. Although they have considerable sequence homology to the other family members, they are not considered opioid per se because they do not have pharmacological profiles similar to the other family members. The number of NOP receptors in the brain is higher than the other family members, and NOP receptors can be found throughout the brain. Because of the widespread distribution of NOP receptors, N/OFQ and other peptide and small molecule agonists and antagonists have extensive CNS activities. Originally thought to be anti-opioid, NOP receptor agonists block some opioid activities, potentiate others, and modulate other activities not affected by traditional opiates. Because the effect of receptor activation can be dependent upon site of administration, state of the animal, and other variables, the study of NOP receptors has been fraught with contradictions and inconsistencies. In this article, the actions and controversies pertaining to NOP receptor activation and inhibition are discussed with respect to CNS disorders including pain (acute, chronic, and migraine), drug abuse, anxiety and depression. In addition, progress towards clinical use of NOP receptor-directed compounds is discussed.

Functional Selectivity Does Not Predict Antinociceptive/Locomotor Impairing Potencies of NOP Receptor Agonists

Nociceptin/orphanin FQ controls several functions, including pain transmission, via stimulation of the N/OFQ peptide (NOP) receptor. Here we tested the hypothesis that NOP biased agonism may be instrumental for identifying innovative analgesics. In vitro experiments were performed with the dynamic mass redistribution label free assay and the NOP non-peptide agonists Ro 65-6570, AT-403 and MCOPPB. In vivo studies were performed in wild type and β-arrestin 2 knockout mice using the formalin, rotarod and locomotor activity tests. In vitro all compounds mimicked the effects of N/OFQ behaving as potent NOP full agonists. In vivo Ro 65-6570 demonstrated a slightly higher therapeutic index (antinociceptive vs. motor impairment effects) in knockout mice. However, all NOP agonists displayed very similar therapeutic index in normal mice despite significant differences in G protein biased agonism. In conclusion the different ability of inducing G protein vs. β-arrestin 2 recruitment of a NOP agonist cannot be applied to predict its antinociceptive vs. motor impairment properties.

Biased Agonism at Nociceptin/Orphanin FQ Receptors: A Structure Activity Study on N/OFQ(1-13)-NH2

Nociceptin/orphanin FQ (N/OFQ) controls different biological functions via selective stimulation of the N/OFQ peptide (NOP) receptor. The pleiotropic actions of N/OFQ may limit the development of NOP ligands as innovative drugs in different therapeutic areas. The pharmacological concept of functional selectivity (aka biased agonism) might be useful for amplifying beneficial actions and/or counteracting side effects. Thus, molecules with large bias factors toward G protein or β arrestin are required for investigating the translational value of NOP biased modulation. Herein, the biased behavior of a heterogeneous library of NOP-targeting peptide derivatives was evaluated in vitro with the aim to provide possible insights into the structural determinants that govern the selective activation of G protein versus β-arrestin. Our results demonstrate that lipidation of N/OFQ(1-13)-NH2 is a useful strategy for obtaining G protein biased agonists for the NOP receptor.

Crosstalk between Opioid and Anti-Opioid Systems: An Overview and Its Possible Therapeutic Significance

Opioid peptides and receptors are broadly expressed throughout peripheral and central nervous systems and have been the subject of intense long-term investigations. Such studies indicate that some endogenous neuropeptides, called anti-opioids, participate in a homeostatic system that tends to reduce the effects of endogenous and exogenous opioids. Anti-opioid properties have been attributed to various peptides, including melanocyte inhibiting factor (MIF)-related peptides, cholecystokinin (CCK), nociceptin/orphanin FQ (N/OFQ), and neuropeptide FF (NPFF). These peptides counteract some of the acute effects of opioids, and therefore, they are involved in the development of opioid tolerance and addiction. In this work, the anti-opioid profile of endogenous peptides was described, mainly taking into account their inhibitory influence on opioid-induced effects. However, the anti-opioid peptides demonstrated complex properties and could show opioid-like as well as anti-opioid effects. The aim of this review is to detail the phenomenon of crosstalk taking place between opioid and anti-opioid systems at the in vivo pharmacological level and to propose a cellular and molecular basis for these interactions. A better knowledge of these mechanisms has potential therapeutic interest for the control of opioid functions, notably for alleviating pain and/or for the treatment of opioid abuse.

Detailed In Vitro Pharmacological Characterization of the Clinically Viable Nociceptin/Orphanin FQ Peptide Receptor Antagonist BTRX-246040

The peptide nociceptin/orphanin FQ (N/OFQ) is the natural ligand of the N/OFQ receptor (NOP), which is widely expressed in the central and peripheral nervous system. Selective NOP antagonists are worthy of testing as innovative drugs to treat depression, Parkinson disease, and drug abuse. The aim of this study was to perform a detailed in vitro characterization of BTRX-246040 (also known as LY2940094, [2-[4-[(2-chloro-4,4-difluoro-spiro[5H-thieno[2,3-c]pyran-7,4'-piperidine]-1'-yl)methyl]-3-methyl-pyrazol-1-yl]-3-pyridyl]methanol), a novel NOP antagonist that has been already studied in humans. BTRX-246040 has been tested in vitro in the following assays: calcium mobilization in cells expressing NOP and classic opioid receptors and chimeric G proteins, bioluminescence resonance energy transfer assay measuring NOP interaction with G proteins and β-arrestins, the label-free dynamic mass redistribution assay, and the electrically stimulated mouse vas deferens. BTRX-246040 was systematically compared with the standard NOP antagonist SB-612111. In all assays, BTRX-246040 behaves as a pure and selective antagonist at human recombinant and murine native NOP receptors displaying 3-10-fold higher potency than the standard antagonist SB-612111. BTRX-246040 is an essential pharmacological tool to further investigate the therapeutic potential of NOP antagonists in preclinical and clinical studies. SIGNIFICANCE STATEMENT: NOP antagonists may be innovative antidepressant drugs. In this research, the novel clinically viable NOP antagonist BTRX-246040 has been deeply characterized in vitro in a panel of assays. BTRX-246040 resulted a pure, potent, and selective NOP antagonist.