title: Physical presence of nor-binaltorphimine in mouse brain over 21 days after a single administration corresponds to its long-lasting antagonistic effect on κ-opioid receptors.
abstract: In the mouse 55°C warm-water tail-withdrawal assay, a single administration of nor-binaltorphimine (nor-BNI; 10 mg/kg i.p.) antagonized κ-opioid receptor (KOR) agonist-induced antinociception up to 14 days, whereas naloxone (10 mg/kg i.p.)-mediated antagonism lasted less than 1 day. In saturation binding experiments, mouse brain membranes isolated and washed 1 or 7 (but not 14) days after nor-BNI administration demonstrated a significant time-dependent decrease in maximal KOR agonist [(3)H]U69,593 binding. To determine whether brain concentrations of nor-BNI were sufficient to explain the antagonism of KOR-mediated antinociception, mouse blood and perfused brain were harvested at time points ranging from 30 minutes to 21 days after a single administration and analyzed for the presence of nor-BNI using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). Nor-BNI was detected in the perfused brain homogenate up to 21 days after administration (30 nmol i.c.v. or 10 mg/kg i.p.). Subsequent experiments in which nor-BNI was administered at doses estimated from the amounts detected in the brain homogenates isolated from pretreated mice over time demonstrated significant antagonism of U50,488 antinociception in a manner consistent with the magnitude of observed KOR antagonism. The dose (1.4 nmol) approximating the lowest amount of nor-BNI detected in brain on day 14 did not antagonize U50,488-induced antinociception, consistent with the absence of U50,488 antagonism observed in vivo at this time point after pretreatment. Overall, the physical presence of nor-BNI in the mouse brain paralleled its in vivo pharmacological profile, suggesting physicochemical and pharmacokinetic properties of nor-BNI may contribute to the prolonged KOR antagonism.
authors.affiliation: Torrey Pines Institute for Molecular Studies, Port St Lucie, Florida 34987, USA.
authors.forename: Kshitij A
authors.initials: KA
authors.lastname: Patkar
authors.forename: Jinhua
authors.initials: J
authors.lastname: Wu
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Ganno
authors.forename: Harminder D
authors.initials: HD
authors.lastname: Singh
authors.forename: Nicolette C
authors.initials: NC
authors.lastname: Ross
authors.forename: Khampaseuth
authors.initials: K
authors.lastname: Rasakham
authors.forename: Lawrence
authors.initials: L
authors.lastname: Toll
authors.forename: Jay P
authors.initials: JP
authors.lastname: McLaughlin
mesh_terms: D000700:Analgesics / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D044482:Benzeneacetamides / Q000378:metabolism / Q000494:pharmacology; D001921:Brain / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D006358:Hot Temperature; D007276:Injections, Intraventricular; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009270:Naloxone / Q000493:pharmacokinetics / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000493:pharmacokinetics / Q000494:pharmacology*; D010147:Pain Measurement / Q000187:drug effects; D011759:Pyrrolidines / Q000378:metabolism / Q000494:pharmacology; D017473:Receptors, Opioid, kappa / Q000037:antagonists & inhibitors*; D012015:Reference Standards; D053719:Tandem Mass Spectrometry; D013997:Time Factors
chemical_list: D000700:Analgesics; D044482:Benzeneacetamides; D009292:Narcotic Antagonists; D011759:Pyrrolidines; D017473:Receptors, Opioid, kappa; D009270:Naloxone; C051844:norbinaltorphimine; D009271:Naltrexone; C045444:U 69593