N-Desmethylclozapine, a major clozapine metabolite, acts as a selective and efficacious delta-opioid agonist at recombinant and native receptors.
The present study examined the effects of N-desmethylclozapine (NDMC), a biologically active metabolite of the atypical antipsychotic clozapine, at cloned human opioid receptors stably expressed in Chinese hamster ovary (CHO) cells and at native opioid receptors present in NG108-15 cells and rat brain. In CHO cells expressing the delta-opioid receptor (CHO/DOR), NDMC behaved as a full agonist both in stimulating [(35)S]GTPgammaS binding (pEC(50)=7.24) and in inhibiting cyclic AMP formation (pEC(50)=6.40). NDMC inhibited [(3)H]naltrindole binding to CHO/DOR membranes with competition curves that were modulated by guanine nucleotides in an agonist-like manner. Determination of intrinsic efficacies by taking into consideration both the maximal [(35)S]GTPgammaS binding stimulation and the extent of receptor occupancy at which half-maximal effect occurred indicated that NDMC had an efficacy value equal to 82% of that of the full delta-opioid receptor agonist DPDPE, whereas clozapine and the other clozapine metabolite clozapine N-oxide displayed much lower levels of agonist efficacy. NDMC exhibited poor agonist activity and lower affinity at the kappa-opioid receptor and was inactive at mu-opioid and NOP receptors. In NG108-15 cells, NDMC inhibited cyclic AMP formation and stimulated the phosphorylation of extracellular signal-regulated kinase 1/2 by activating the endogenously expressed delta-opioid receptor. Moreover, in membranes of different brain regions, NDMC stimulated [(35)S]GTPgammaS binding and regulated adenylyl cyclase activity and the effects were potently antagonized by naltrindole. These data demonstrate for the first time that NDMC acts as a selective and efficacious delta-opioid receptor agonist and suggest that this unique property may contribute, at least in part, to the clinical actions of the atypical antipsychotic clozapine.
Onali
Pierluigi
P
Department of Neurosciences, Section of Biochemical Pharmacology, University of Cagliari, Cagliari, Italy. onali@unica.it
Olianas
Maria C
MC
D000262:Adenylyl Cyclases / Q000378:metabolism; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D014150:Antipsychotic Agents / Q000494:pharmacology; D016466:CHO Cells; D003024:Clozapine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005455:Fluorescent Antibody Technique / Q000379:methods; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D009447:Neuroblastoma; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D017465:Receptors, Opioid, delta / Q000187:drug effects* / Q000378:metabolism; D011994:Recombinant Proteins
D000701:Analgesics, Opioid; D014150:Antipsychotic Agents; D017465:Receptors, Opioid, delta; D011994:Recombinant Proteins; C058272:norclozapine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D003024:Clozapine