Effect of supraspinal Nocistatin on Nociceptin/Orphanin FQ antagonism of selective opioid analgesia

Antinociceptive profile of LP1, a non-peptide multitarget opioid ligand

AIMS

Opioid drugs are the principal treatment option for moderate to severe pain and exert their biological effects through interactions with opioid receptors that are widely distributed throughout the CNS and peripheral tissues. Ligands capable of simultaneously targeting different receptors could be successful candidates for the treatment of chronic pain. Enhanced antinociception coupled with a low incidence of side effects has been demonstrated for ligands possessing mixed mu-opioid receptor (MOR) and delta-opioid receptor (DOR) activity. We previously reported that 3-[(2R,6R,11R)-8-hydroxy-6,11-dimethyl-1,4,5,6-tetrahydro-2,6-methano-3-benzazocin-3(2H)-yl]-N-phenylpropanamide (LP1) acted as a MOR-DOR ligand in in vitro functional assays and moreover this drug produced a valid antinociception that was longer lasting than that of morphine. The aim of this work was to determine whether the antinociceptive effect produced by LP1 was central or peripheral and to assess which opioid receptor subtypes are involved in its effects.

MAIN METHODS

We explored the effects of naloxone methiodide (NX-M), a quaternary opioid antagonist, administered either intracerebroventricularly (i.c.v.) or subcutaneously (s.c.), on LP1-mediated antinociception in male Sprague-Dawley rats. In addition, we administered s.c. selective antagonists for MOR, DOR and kappa-opioid receptor (KOR) to investigate the effects of LP1. To characterise this drug's DOR profile better, we also investigated the effects of LP1 on DPDPE, a selective DOR agonist.

KEY FINDINGS

Data obtained by tail flick test showed that LP1 induced predominantly MOR-mediated supraspinal antinociception and was able to counteract DPDPE analgesia.

SIGNIFICANCE

LP1, a multitarget opioid ligand, is a supraspinal acting antinociceptive agent that is useful for the treatment of chronic pain.

Supraspinal injection of Substance P attenuates allodynia and hyperalgesia in a rat model of inflammatory pain

The neuropeptide Substance P (SP), that has a high affinity for the neurokinin 1 (NK1) receptor, is involved in modulation of pain transmission. Although SP is thought to have excitatory actions and promote nociception in the spinal cord, the peptide induces analgesia at the supraspinal level. The aim of this study was to evaluate the role of supraspinal SP and the NK1 receptor in inflammatory pain induced by injection of carrageenan in the hind paw of the rat. There are two nociceptive behavioral responses associated with this pain state: mechanical allodynia and heat hyperalgesia. Because the NK1 receptor colocalizes with the MOP receptor in supraspinal sites involved in pain modulation, we also decided to study the possible involvement of the opioid system on SP-induced analgesia. We found that treatment with SP, at doses of 3.5, 5 and 7 μg/5 μl/rat i.c.v., clearly showed inhibition of allodynia and hyperalgesia. Pretreatment with the selective NK1 antagonist L-733,060 (10mg/kg i.p.) blocked the SP-induced analgesia, suggesting the involvement of the NK1 receptor. This SP-induced analgesia was significantly reduced by administration of the opioid antagonist naloxone (3mg/kg s.c.). This reduction occurred when SP was administered either before or after the carrageenan injection. These results suggest a significant antinociceptive role for SP and the NK1 receptor in inflammatory pain at the supraspinal level, possibly through the release of endogenous opioids.

Effects of intraplantar nocistatin and (±)-J 113397 injections on nociceptive behavior in a rat model of inflammation

Nocistatin (NST) and Nociceptin/Orphanin FQ (N/OFQ) are derived from the same precursor protein, pre-proN/OFQ, and exert opposite effects on the modulation of pain signals. However, the role of the peripheral N/OFQ and the NOP receptor, which is located at the endings of sensory nerves, in inflammatory pain was not ascertained. NST administered intrathecally (i.t.) prevented the nociceptive effects induced by i.t. N/OFQ and PGE₂. Moreover an up regulation of N/OFQ was shown in the rat in response to peripheral inflammation. Here, we investigated the effects of intraplantar (i.pl.) administration of functional N/OFQ and NOP receptor antagonists in a rat model of inflammatory pain. Our findings showed that i.pl. injection of (±)-J 113397, a selective antagonist of the NOP receptor, and NST, the functional N/OFQ antagonist, prior to carrageenan significantly reduced the paw allodynic and thermal hyperalgesic threshold induced by the inflammatory agent. The resulting antiallodynic and antihyperalgesic effects by co-administering NST and (±)-J 113397 prior to carrageenan were markedly enhanced, and the basal latencies were restored. Thus, it is likely that the peripheral N/OFQ/NOP receptor system contributes to the abnormal pain sensitivity in an inflammatory state.

Selective inhibition of the NOP receptor in the ventrolateral periaqueductal gray attenuates the development and the expression of tolerance to morphine-induced antinociception in rats

The ventrolateral periaqueductal gray (vlPAG) is a major site of opioid analgesic action and a key locus for the development of morphine tolerance. Previous experimental evidence supports the hypothesis that the brain synthesizes and secretes neuropeptides, which act as a part of the homeostatic system to attenuate the effects of morphine and endogenous opioid peptides. Among the known antiopioid peptides, nociceptin/orphanin FQ (N/OFQ) has been shown to inhibit various opioid effects, especially analgesia. The present study investigated the effect of NOP receptor blockade on the tolerance to morphine antinociception in the vlPAG. Systemic morphine (10mg/kg s.c. twice per day) induced an antinociceptive effect that diminished significantly on the third day when tolerance developed, as quantified by the tail flick and the hot plate tests. Intra vlPAG (i.vlPAG) administration of the NOP receptor antagonist (+/-)-J 113397 restored the opioid's analgesic effect. When (+/-)-J 113397 was administered beginning the first day preceding each morphine administration, tolerance did not develop, but it appeared if the NOP antagonist had been suspended. These data suggest that the N/OFQ in the vlPAG may play a key role in opioid-induced antinociceptive tolerance.

Nocistatin and nociceptin given centrally induce opioid-mediated gastric mucosal protection

Nociceptin (N/OFQ) and nocistatin (NST) are two endogenous neuropeptides derived from the same precursor protein, preproN/OFQ. The aim of the present work was to study the effect of NST on the ethanol-induced mucosal damage compared with that of N/OFQ following intracerebroventricular (i.c.v.) administration in the rat and to analyze the mechanism of the gastroprotective action. It was found that both NST and N/OFQ reduced the mucosal lesions in the same dose range (0.2-1 nmol i.c.v.), but in higher doses (2-5 nmol i.c.v.) the gastroprotective effect of both peptides was highly diminished. The gastroprotective effect of N/OFQ (1 nmol), but not that of NST (1 nmol), was reduced by the selective nociceptin receptor antagonist J-113397 (69 nmol i.c.v.). Similarly, decrease of the gastroprotective effect was observed after the combination of NST (1 nmol) with N/OFQ (0.6 or 1 nmol). However, addition of the gastroprotective effects was observed, when lower dose (0.2 nmol) of NST was given prior to N/OFQ (0.6 nmol). The gastroprotective effect of both N/OFQ and NST was antagonized by naloxone (27 nmol), beta-funaltrexamine (20 nmol), naltrindole (5 nmol) and norbinaltorphimine (14 nmol), the mu-, delta- and kappa-opioid receptor antagonists, respectively, given i.c.v. The mucosal protection was significantly decreased after bilateral cervical vagotomy. The present findings suggest that NST similar to N/OFQ, may also induce gastric mucosal protective action initiated centrally in a vagal-dependent mechanism. Opioid component is likely to be involved in the gastroprotective effect of both NST and N/OFQ.

Blockade of the nociceptin/orphanin FQ/NOP receptor system in the rat ventrolateral periaqueductal gray potentiates DAMGO analgesia

Nociceptin/orphanin FQ (N/OFQ) and its receptor (NOP) are involved in various biological functions including pain. High density of NOP receptor has been found in the ventrolateral periaqueductal gray (vlPAG), the main output pathway involved in descending pain-control system. The aim of our work was to evaluate the involvement of the N/OFQ/NOP system in the modulation of MOP analgesia in the rat vlPAG using UFP-101, a selective NOP antagonist. N/OFQ significantly blocked DAMGO (a selective MOP agonist) analgesia, while UFP-101 enhanced the effect of the opioid given at a subanalgesic dose. These results confirm our hypothesis of an antiopioid role for N/OFQ in the vlPAG.

Levels of neuropeptides nocistatin, nociceptin/orphanin FQ and their precursor protein in a rat neuropathic pain model

Neuropeptides nociceptin/orphanin FQ (N/OFQ) and nocistatin (NST) are related to pain modulation. The amounts of these peptides and their precursor protein, prepronociceptin (ppN/OFQ) in the brain, spinal cord and serum samples of rats with partial sciatic nerve ligation (PSNL) were compared with those in naïve rats using radioimmunoassay (RIA). There was a significant rise in the levels of ppN/OFQ, N/OFQ and NST in the brains of PSNL rats. Their spinal cords showed significantly increased ppN/OFQ and NST levels but no change in N/OFQ levels. The PSNL rats also had increased serum NST (statistically significant) and N/OFQ (statistically insignificant) with decreased ppN/OFQ suggesting important roles of these peptides in neuropathic pain mechanism.

Nocistatin and its derivatives antagonize the impairment of short-term acquisition induced by nociceptin

We studied the effects of human nocistatin, a mature form of human nocistatin of 17 amino acid length (nocistatin 17), and the amide derivative of nocistain 17 (nocistatin amide), and nociceptin/orphanin FQ on short-term acquisition in mice using a multi trial passive avoidance protocol. Nociceptin 1 nmol administered by i.c.v. injection 15 min beforehand increased the number of trials required to achieve the learning objective and decreased the step through latency times in the first, second and third test trials. Nocistatin and nocistatin 17 on their own did not affect acquisition, but were able at doses of 4 nmol to antagonize the impairment caused by nociceptin 1 nmol. Nocistatin amide on its own also did not impair acquisition and at a lower dose of 1 nmol was able to completely antagonize nociceptin. [N-Phe(1)]-nociceptin (1-13) amide, a selective opioid receptor-like 1 (ORL1) receptor antagonist, could also antagonize the effect of nociceptin, confirming that nociceptin's effect is induced via the ORL1 receptor. The results support suggestions that both nocistatin and nociceptin have roles in learning and memory, with nocistatin working as a functional antagonist of nociceptin. The shorter mature human nocistatin peptide had similar activity to the larger peptide, and its amide derivative may be more potent.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).

Regulation of pancreatic secretion in vitro by nociceptin/orphanin FQ and opioid receptors: A comparative study

The effects of nociceptin/orphanin FQ (N/OFQ) on gastrointestinal functions resemble those of classic analgesic opioid agonists. In this study, we compared changes in amylase release from guinea pig isolated pancreatic acini and lobules induced by the N/OFQ analogue [Arg(14),Lys(15)]N/OFQ and by the delta-receptor opioid agonist deltorphin. Carbachol strongly stimulated amylase release from isolated acini. Both peptides left baseline and carbachol-stimulated amylase secretion from pancreatic acini unchanged. Co-incubation of KCl-stimulated lobules with [Arg(14),Lys(15)]N/OFQ or deltorphin inhibited KCl-induced amylase release in a concentration-dependent manner. Although maximal inhibition of amylase release by [Arg(14),Lys(15)]N/OFQ and deltorphin had similar amplitude, [Arg(14),Lys(15)]N/OFQ was 100-fold more potent than deltorphin on a molar basis. The selective NOP-receptor antagonist [Nphe(1),Arg(14),Lys(15)]N/OFQ-NH(2) (UFP-101) antagonized [Arg(14),Lys(15)]N/OFQ-induced inhibition but left deltorphin-induced inhibition unchanged. The selective delta opiate receptor antagonist naltrindole had no effect on [Arg(14),Lys(15)]N/OFQ inhibition but partly prevented the inhibition by deltorphin. [Arg(14),Lys(15)]N/OFQ and deltorphin combined had no influence on each other. These findings show that [Arg(14),Lys(15)]N/OFQ inhibits pancreatic enzyme secretion by suppressing cholinergic transmission in intralobular nerve fibers, as previously reported for opioid agents. They suggest that [Arg(14),Lys(15)]N/OFQ inhibition of amylase release is mediated through the NOP receptor and not through the delta opioid receptor. The N/OFQ-NOP receptor system, like the delta opioid system, plays an inhibitory role in regulating exocrine pancreatic secretion.

Supraspinal nocistatin and its amide derivative antagonize the hyperalgesic effects of nociceptin in mice

Nocistatin (NST) and nociceptin (NCP)/orphanin FQ are new neuropeptides derived from the same precursor molecule, and which are involved in pain transmission. Nocistatin has been shown to antagonize several effects of nociceptin by acting on a different receptor. We examined the effects of supraspinal nocistatin and nocistatin amide, and their interaction with nociceptin on nociceptive behavior in mice, using hotplate response times. We found that both nocistatin and nocistatin amide did not change the response time compared to control mice, whereas increasing doses of nociceptin caused progressive shortening of response times. Nocistatin and nocistatin amide were both able to antagonize the hyperalgesic effect of nociceptin. The effect of nocistatin amide was longer lasting and more potent, suggesting that the C-terminal free carboxyl group of nocistatin is not necessary for its biological activity, and that the amide derivative may be more biologically stable.