title: A new potent analgesic agent with reduced liability to produce morphine tolerance.
abstract: The therapeutic use of opioids is limited by the development of tolerance to the analgesic effect and the cellular and molecular mechanisms underlying this phenomenon are still not completely understood. For this reason the search for new analgesic derivatives, endowed with lower tolerance, is always an active field. The newly synthesized 14-O-Methylmorphine-6-sulfate (14-O-MeM6SU) shows high efficacy in in vitro assays and a strong analgesic action in the rat tail flick test. The aim of present work was to investigate: the analgesic effect of 14-O-MeM6SU in mouse tail-flick test; the tolerance to analgesic effect of 14-O-MeM6SU compared to morphine in mice, the effects of test compounds on glutamatergic neurotransmission by measuring spontaneous excitatory postsynaptic currents (sEPSCs) of layer V pyramidal cells from rat prefrontal cortices; and the effect of acute and chronic 14-O-MeM6SU treatments on opioid receptor gene expression in SH-SY5Y neuroblastoma cells expressing μ-opioid (MOP) and nociceptin/opioid receptor-like 1 (NOP) receptors. 14-O-MeM6SU was 17 times more potent than morphine in analgesia and had long duration of action in analgesic dose equipotent to morphine. Mice were treated subcutaneously (s.c.) either with 200 μmol/kg morphine or with 14-O-MeM6SU (12 μmol/kg) twice daily for three days. The magnitude of tolerance or cross-tolerance indicated by the shift in antinociceptive ED50 measured was greater for morphine compared to 14-O-MeM6SU. Subsequent to behavioral testing, patch-clamp experiments in layer V pyramidal neurons of rat prefrontal cortical slices in the presence of bicuculline were performed. Both 14-O-MeM6SU (0.1 μM) and morphine (1 μM) decreased the frequency of sEPSCs, indicating reduction of glutamate release. The effect of the novel compound was reversed by the opioid receptor antagonist naloxone, indicating an opioid mediated action. In contrast, the amplitude was not affected. Finally, gene expression data showed a dose dependent down-regulation of MOP receptor after 24h and 48 h exposure to 14-O-MeM6SU. Interestingly, no changes were detected for NOP receptor gene expression. The specific lack of this effect could be related to the lower tolerance development to analgesic effect of 14-O-MeM6SU. Furthermore, 14-O-MeM6SU displayed high intrinsic efficacy possibly an important factor in the observed effects. Further, the observed inhibition of glutamatergic signaling might be attributed also to the reduction of opioid tolerance. Based on our results the development of a new clinically important, safe analgesic agent might be possible.
authors.affiliation: Department of Pharmacology and Pharmacotherapy, Semmelweis University, Nagyvárad tér 4, H-1089 Budapest, Hungary.
authors.forename: Kornel
authors.initials: K
authors.lastname: Kiraly
authors.affiliation: Department of Pharmacy and Biotechnology (FaBiT), Alma Mater Studiorum, University of Bologna, Via Irnerio 48, Bologna 40126, Italy.
authors.forename: Francesca Felicia
authors.initials: FF
authors.lastname: Caputi
authors.affiliation: Department of Pharmacology and Pharmacotherapy, Semmelweis University, Nagyvárad tér 4, H-1089 Budapest, Hungary.
authors.forename: Adrienn
authors.initials: A
authors.lastname: Hanuska
authors.affiliation: Department of Pharmacology and Pharmacotherapy, Semmelweis University, Nagyvárad tér 4, H-1089 Budapest, Hungary.
authors.forename: Erzsébet
authors.initials: E
authors.lastname: Kató
authors.affiliation: Department of Pharmacology and Pharmacotherapy, Semmelweis University, Nagyvárad tér 4, H-1089 Budapest, Hungary.
authors.forename: Mihaly
authors.initials: M
authors.lastname: Balogh
authors.affiliation: Department of Pharmacology and Pharmacotherapy, Semmelweis University, Nagyvárad tér 4, H-1089 Budapest, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Köles
authors.affiliation: Department of Pharmacy and Biotechnology (FaBiT), Alma Mater Studiorum, University of Bologna, Via Irnerio 48, Bologna 40126, Italy.
authors.forename: Martina
authors.initials: M
authors.lastname: Palmisano
authors.affiliation: Department of Pharmacology and Pharmacotherapy, Semmelweis University, Nagyvárad tér 4, H-1089 Budapest, Hungary.
authors.forename: Pal
authors.initials: P
authors.lastname: Riba
authors.affiliation: Department of Pharmaceutical Chemistry, Semmelweis University, Hőgyes Endre u., 9. H-1092 Budapest, Hungary.
authors.forename: Sándor
authors.initials: S
authors.lastname: Hosztafi
authors.affiliation: Department of Pharmacy and Biotechnology (FaBiT), Alma Mater Studiorum, University of Bologna, Via Irnerio 48, Bologna 40126, Italy.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Romualdi
authors.affiliation: Department of Pharmacy and Biotechnology (FaBiT), Alma Mater Studiorum, University of Bologna, Via Irnerio 48, Bologna 40126, Italy.
authors.forename: Sanzio
authors.initials: S
authors.lastname: Candeletti
authors.affiliation: Department of Pharmacology and Pharmacotherapy, Semmelweis University, Nagyvárad tér 4, H-1089 Budapest, Hungary.
authors.forename: Péter
authors.initials: P
authors.lastname: Ferdinandy
authors.affiliation: Department of Pharmacology and Pharmacotherapy, Semmelweis University, Nagyvárad tér 4, H-1089 Budapest, Hungary.
authors.forename: Susanna
authors.initials: S
authors.lastname: Fürst
authors.affiliation: Department of Pharmacology and Pharmacotherapy, Semmelweis University, Nagyvárad tér 4, H-1089 Budapest, Hungary. Electronic address: al-khrasani.mahmoud@med.semmelweis-univ.hu.
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Al-Khrasani
mesh_terms: D000701:Analgesics, Opioid / Q000009:adverse effects / Q000494:pharmacology*; D000818:Animals; D045744:Cell Line, Tumor; D003061:Codeine / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D004361:Drug Tolerance; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D018698:Glutamic Acid / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D009020:Morphine / Q000009:adverse effects / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D059226:Nociceptive Pain / Q000188:drug therapy; D017397:Prefrontal Cortex / Q000187:drug effects / Q000502:physiology; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000235:genetics / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000235:genetics / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D046509:Tissue Culture Techniques; D000094942:Nociceptin Receptor
chemical_list: C579042:14-O-methylmorphine-6-O-sulfate; D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; D009270:Naloxone; D018698:Glutamic Acid; D009020:Morphine; D003061:Codeine; D000094942:Nociceptin Receptor
keywords: 14-O-Methylmorphine-6-sulfate; Analgesia; Glutamatergic transmission; MOP receptor down-regulation; Tolerance