title: Naturally occurring 2'-hydroxyl-substituted flavonoids as high-affinity benzodiazepine site ligands.
abstract: Screening of traditional medicines has proven invaluable to drug development and discovery. Utilizing activity-guided purification, we previously reported the isolation of a list of flavonoids from the medicinal herb Scutellaria baicalensis Georgi, one of which manifested an affinity for the benzodiazepine receptor (BDZR) comparable to that of the synthetic anxiolytic diazepam (K(i)=6.4 nM). In the present study, this high-affinity, naturally occurring flavonoid derivative, 5,7,2'-trihydroxy-6,8-dimethoxyflavone (K36), was chosen for further functional and behavioral characterization. K36 inhibited [3H]flunitrazepam binding to native BDZR with a K(i) value of 6.05 nM. In electrophysiological experiments K36 potentiated currents mediated by rat recombinant alpha(1)beta(2)gamma(2) GABA(A) receptors expressed in Xenopus oocytes. This potentiation was characterized by a threshold (1 nM) and half-maximal stimulation (24 nM) similar to diazepam. This enhancement was demonstrated to act via the BDZR, since co-application of 1 microM of the BDZR antagonist Ro15-1788 reversed the potentiation. Oral administration of K36 produced significant BDZR-mediated anxiolysis in the mice elevated plus-maze, which was abolished upon co-administration of Ro15-1788. Sedation, myorelaxation and motor incoordination were not observed in the chosen dosage regimen. Structure-activity relationships utilizing synthetic flavonoids with different 2' substituents on the flavone backbone supported that 2'-hydroxyl-substitution is a critical moiety on flavonoids with regard to BDZR affinities. These results further underlined the potential of flavonoids as therapeutics for the treatment of BDZR-associated syndromes.
authors.affiliation: Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
authors.forename: Michael S Y
authors.initials: MS
authors.lastname: Huen
authors.forename: Kwok-Min
authors.initials: KM
authors.lastname: Hui
authors.forename: Justin W C
authors.initials: JW
authors.lastname: Leung
authors.forename: Erwin
authors.initials: E
authors.lastname: Sigel
authors.forename: Roland
authors.initials: R
authors.lastname: Baur
authors.forename: J Tze-Fei
authors.initials: JT
authors.lastname: Wong
authors.forename: Hong
authors.initials: H
authors.lastname: Xue
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D001569:Benzodiazepines / Q000378:metabolism; D004195:Disease Models, Animal; D005419:Flavonoids / Q000494:pharmacology* / Q000627:therapeutic use; D018757:GABA Modulators / Q000494:pharmacology*; D058785:GABA-A Receptor Agonists; D008024:Ligands; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D051379:Mice; D008813:Mice, Inbred ICR; D010146:Pain / Q000188:drug therapy; D010147:Pain Measurement / Q000187:drug effects; D011869:Radioligand Assay; D018079:Receptors, GABA / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000378:metabolism*; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism
chemical_list: C471750:5,7,2'-trihydroxy-6,8-dimethoxyflavone; D005419:Flavonoids; D018757:GABA Modulators; D058785:GABA-A Receptor Agonists; D008024:Ligands; D018079:Receptors, GABA; D011963:Receptors, GABA-A; D011994:Recombinant Proteins; D001569:Benzodiazepines