Sh-I-048A, an in vitro non-selective super-agonist at the benzodiazepine site of GABAA receptors: the approximated activation of receptor subtypes may explain behavioral effects.
Enormous progress in understanding the role of four populations of benzodiazepine-sensitive GABAA receptors was paralleled by the puzzling findings suggesting that substantial separation of behavioral effects may be accomplished by apparently non-selective modulators. We report on SH-I-048A, a newly synthesized chiral positive modulator of GABAA receptors characterized by exceptional subnanomolar affinity, high efficacy and non-selectivity. Its influence on behavior was assessed in Wistar rats and contrasted to that obtained with 2mg/kg diazepam. SH-I-048A reached micromolar concentrations in brain tissue, while the unbound fraction in brain homogenate was around 1.5%. The approximated electrophysiological responses, which estimated free concentrations of SH-I-048A or diazepam are able to elicit, suggested a similarity between the 10mg/kg dose of the novel ligand and 2mg/kg diazepam; however, SH-I-048A was relatively more active at α1- and α5-containing GABAA receptors. Behaviorally, SH-I-048A induced sedative, muscle relaxant and ataxic effects, reversed mechanical hyperalgesia 24h after injury, while it was devoid of clear anxiolytic actions and did not affect water-maze performance. While lack of clear anxiolytic actions may be connected with an enhanced potentiation at α1-containing GABAA receptors, the observed behavior in the rotarod, water maze and peripheral nerve injury tests was possibly affected by its prominent action at receptors containing the α5 subunit. The current results encourage further innovative approaches aimed at linking in vitro and in vivo data in order to help define fine-tuning mechanisms at four sensitive receptor populations that underlie subtle differences in behavioral profiles of benzodiazepine site ligands.
Department of Physiology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia.
Aleksandar Lj
ALj
Obradović
Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia.
Srđan
S
Joksimović
Department of Chemistry and Biochemistry, University of Wisconsin - Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA.
Michael M
MM
Poe
Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Vienna, Austria.
Joachim
J
Ramerstorfer
Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Vienna, Austria.
Zdravko
Z
Varagic
Department of Chemistry and Biochemistry, University of Wisconsin - Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA.
Ojas
O
Namjoshi
Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia.
Bojan
B
Batinić
Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia.
Tamara
T
Radulović
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia.
Bojan
B
Marković
Department of Pharmacology, University of North Carolina Chapel Hill Medical School, Chapel Hill, NC 27514, USA; Division of Chemical Biology and Medicinal Chemistry, University of North Carolina Chapel Hill Medical School, Chapel Hill, NC 27514, USA.
Brian L
BL
Roth
Department of Biochemistry and Molecular Biology, Center for Brain Research, Medical University Vienna, Vienna, Austria.
Werner
W
Sieghart
Department of Chemistry and Biochemistry, University of Wisconsin - Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA.
James M
JM
Cook
Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11221 Belgrade, Serbia. Electronic address: miroslav@pharmacy.bg.ac.rs.
Miroslav M
MM
Savić
D000818:Animals; D001569:Benzodiazepines / Q000493:pharmacokinetics / Q000494:pharmacology; D001570:Benzodiazepinones / Q000494:pharmacology*; D001665:Binding Sites; D001921:Brain / Q000187:drug effects; D003975:Diazepam / Q000493:pharmacokinetics / Q000494:pharmacology; D018757:GABA Modulators / Q000493:pharmacokinetics / Q000494:pharmacology; D058785:GABA-A Receptor Agonists / Q000493:pharmacokinetics / Q000494:pharmacology*; D057809:HEK293 Cells; D006801:Humans; D006930:Hyperalgesia / Q000188:drug therapy; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D051379:Mice; D009043:Motor Activity / Q000187:drug effects; D053580:Muscle Strength / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000378:metabolism*; D014982:Xenopus laevis
C000593251:7-bromo-5-(2-fluorophenyl)-3-methyl-1H-benzo(e)(1,4)diazepin-2(3H)-one; D001570:Benzodiazepinones; D018757:GABA Modulators; D058785:GABA-A Receptor Agonists; C546242:Gabra1 protein, rat; C511535:Gabra5 protein, rat; D011963:Receptors, GABA-A; D001569:Benzodiazepines; D003975:Diazepam
Diazepam; Equilibrium dialysis; Free brain concentration; Rat