Degradation of nociceptin (orphanin FQ) by mouse spinal cord synaptic membranes is triggered by endopeptidase-24.11: an in vitro and in vivo study

• Published in: Biochemical pharmacology 2002-10, Vol.64 (8), p.1293-1303
• Main Authors: Sakurada, Chikai, Sakurada, Shinobu, Orito, Tohru, Tan-No, Koichi, Sakurada, Tsukasa
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Behavior, Animal - drug effects; Biological and medical sciences; Intrathecal injection; Male; Medical sciences; Metabolic pathway; Mice; Molecular Sequence Data; Neprilysin; Neprilysin - metabolism; Neuropharmacology; Neurotransmitters. Neurotransmission. Receptors; Neutral endopeptidase; Nociceptin; Nociceptin-induced behavioral response; Opioid Peptides - metabolism; Opioid Peptides - pharmacology; Peptidergic system (neuropeptide, opioid peptide, opiates...). Adenosinergic and purinergic systems; Pharmacology. Drug treatments; Protease Inhibitors - pharmacology; Spinal Cord - cytology; Synaptic membranes; Synaptic Membranes - enzymology; Synaptic Membranes - metabolism; Vasodilator Agents - metabolism
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/S0006-2952(02)01295-9

We analyzed spinal metabolic pathway of nociceptin/orphanin FQ related to pain-transmission or modulation in the both in vitro and in vivo experiments. Nociceptin was degraded by spinal synaptic membranes. Major metabolites of nociceptin were free phenylalanine, nociceptin (1–13) and nociceptin (14–17). Both the degradation of nociceptin and the accumulation of the major cleavage metabolites, nociceptin (1–13) and nociceptin (14–17), were strongly inhibited by a metal chelator and also by specific inhibitors of endopeptidase-24.11, thiorphan and phosphoramidon. Furthermore, purified endopeptidase-24.11 hydrolyzed nociceptin at the cleavage site (Lys 13–Leu 14 bond) identical to that by spinal synaptic membranes. Recently, we have found that nociceptin, injected intrathecally at small doses (fmol order) elicits a behavioral response consisting of scratching, biting and licking in mice. In the present study, we have examined the effect of peptidase inhibitors on the behavioral response elicited by intrathecal injection of nociceptin in mice. Phosphoramidon simultaneously injected with nociceptin additively enhanced nociceptin-induced behavioral response, whereas the nociceptin-induced behavioral response was unaffected by either bestatin, an aminopeptidase inhibitor or captopril, an angiotensin-converting enzyme inhibitor. However, the nociceptin effect was potentiated by combined injection of phosphoramidon and bestatin, indicating that inhibition of aminopeptidase may also contribute to inducing the behavioral response to nociceptin. These data suggest that endopeptidase-24.11 plays a major role in initial stage of nociceptin metabolism at the spinal cord level in mice.