title: Micromolar concentrations of rimonabant directly inhibits delta opioid receptor specific ligand binding and agonist-induced G-protein activity.
abstract: BACKGROUND
  There is a growing number of evidence showing, that the cannabinoid receptor 1 (CB1) antagonist rimonabant has many non-cannabimimetic actions, such as affecting the opioid system. The direct effect of rimonabant on opioid receptors has been studied so far mainly on μ-opioid receptors. However recently the δ-opioid receptor (DOR) receives much more attention as before, due to its potential therapeutic applications, such as nociception or treatment for psychiatric disorders.
  
  
  OBJECTIVE
  To investigate the direct effect of rimonabant on DOR specific ligand binding and on the DOR mediated G-protein activation.
  
  
  RESULTS
  Micromolar concentrations of rimonabant directly inhibited the DOR specific agonist binding in radioligand competition binding experiments using Chinese hamster ovary cells stably transfected with mouse DOR (CHO-mDOR). However the inhibition occurred also in the subnanomolar range during DOR specific antagonist binding in similar experimental conditions. In functional [(35)S]GTPγS binding assays rimonabant significantly decreased the basal receptor activity in CHO-mDOR but also in parental CHO cell membranes. During DOR agonist stimulation, micromolar concentration of rimonabant attenuated the DOR G-protein activation and the potency of the activator ligand in [(35)S]GTPγS binding assays performed in CHO-mDOR, in wild type and also in CB1/CB2 double knock-out mouse forebrain membranes. Yet again this inhibitory action was DOR specific, since it did not occur during other specific GPCR agonist mediated G-protein activation.
  
  
  CONCLUSIONS
  Rimonabant directly inhibited DOR function in the micromolar concentrations. The inhibitory actions indicate an antagonistic behavior towards DOR which was established by the followings: (i) rimonabant inhibited DOR antagonist binding more effectively than agonist binding, (ii) the inverse agonistic, agonistic effect of the compound can be excluded, and (iii) additionally according to previous findings the allosteric mechanism can also be foreclosed.
authors: Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary. Electronic address: zador.ferenc@gmail.com.
authors: Ferenc
authors: F
authors: Zádor
authors: Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary.
authors: Dóra
authors: D
authors: Kocsis
authors: Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary.
authors: Anna
authors: A
authors: Borsodi
authors: Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary.
authors: Sándor
authors: S
authors: Benyhe
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D008024:Ligands; D051379:Mice; D010880:Piperidines / Q000494:pharmacology*; D011485:Protein Binding; D011720:Pyrazoles / Q000494:pharmacology*; D043884:Receptor, Cannabinoid, CB1 / Q000235:genetics; D043885:Receptor, Cannabinoid, CB2 / Q000235:genetics; D017465:Receptors, Opioid, delta / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000077285:Rimonabant
chemical_list: D008024:Ligands; D010880:Piperidines; D011720:Pyrazoles; D043884:Receptor, Cannabinoid, CB1; D043885:Receptor, Cannabinoid, CB2; D017465:Receptors, Opioid, delta; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins; D000077285:Rimonabant
keywords: Cannabinoid receptor; Delta opioid receptor; G-protein; Radioligand binding; Rimonabant; [(35)S]GTPγS binding