title: Characterization of a new synthetic isoflavonoid with inverse agonist activity at the central benzodiazepine receptor.
abstract: Research aimed at developing selective drugs acting on gamma-aminobutyric acid (GABA)A receptors introduced compounds from diverse chemical classes unrelated to the 1,4-benzodiazepines, including flavonoids. These studies also revealed the potential use of inverse agonists as cognition-enhancing agents. Here we report pharmacological properties of the novel synthetic isoflavonoid 2-methoxy-3,8,9-trihydroxy coumestan (PCALC36). PCALC36 displaced [3H]flunitrazepam binding to rat brain synaptosomes with an IC50 of 13.8 microM. Scatchard analysis of the effect of PCALC36 showed a concentration-dependent reduction of the Bmax of [3H]flunitrazepam, without a marked change in Kd. This effect could be reversed by diluting and washing the preparation. Addition of 20-microM GABA shifted to the right the inhibition curve of PCALC36 on [3H]flunitrazepam binding (IC50 ratio of 0.68), which is characteristic for inverse agonists. PCALC36 produced little change in the GABAergic tonic currents recorded by whole-cell patch clamp in cultured rat hippocampal neurones, but it caused a 20% reduction in miniature inhibitory postsynaptic current amplitude and completely antagonised the full (direct) agonist midazolam in a quickly reversible manner. The data suggest that the coumestan backbone can be useful for developing novel ligands at the GABAA receptor.
authors.affiliation: Departamento de Farmacologia Básica e Clínica, Instituto de Ciências Biomédicas, Bloco J, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha Do Fundao, 21941-590 Rio de Janeiro, Brazil.
authors.forename: Daniele V S
authors.initials: DV
authors.lastname: Lopes
authors.forename: Rodrigo R B
authors.initials: RR
authors.lastname: Caruso
authors.forename: Newton G
authors.initials: NG
authors.lastname: Castro
authors.forename: Paulo R R
authors.initials: PR
authors.lastname: Costa
authors.forename: Alcides J M
authors.initials: AJ
authors.lastname: da Silva
authors.forename: François
authors.initials: F
authors.lastname: Noël
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D001921:Brain / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D005419:Flavonoids / Q000138:chemical synthesis / Q000494:pharmacology*; D005445:Flunitrazepam / Q000378:metabolism; D018755:GABA Agonists / Q000138:chemical synthesis / Q000494:pharmacology*; D018757:GABA Modulators / Q000494:pharmacology; D058785:GABA-A Receptor Agonists; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D007529:Isoflavones / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008874:Midazolam / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000502:physiology; D013574:Synaptosomes / Q000378:metabolism; D013997:Time Factors; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: C495408:2-methoxy-3,8,9-trihydroxy coumestan; D005419:Flavonoids; D018755:GABA Agonists; D018757:GABA Modulators; D058785:GABA-A Receptor Agonists; D007529:Isoflavones; D011963:Receptors, GABA-A; D014316:Tritium; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam; D008874:Midazolam; D001640:Bicuculline