Naturally occurring 2′-hydroxyl-substituted flavonoids as high-affinity benzodiazepine site ligands

• Published in: Biochemical pharmacology Vol. 66; no. 12; pp. 2397 - 2407
• Main Authors: Huen, Michael S.Y., Hui, Kwok-Min, Leung, Justin W.C., Sigel, Erwin, Baur, Roland, Wong, J.Tze-Fei, Xue, Hong
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 15-12-2003; Elsevier Science
• Subjects: Allosteric Regulation; Animals; Anxiolytics; Benzodiazepine receptor; Benzodiazepines; Benzodiazepines - metabolism; Biological and medical sciences; Disease Models, Animal; Flavonoids; Flavonoids - pharmacology; Flavonoids - therapeutic use; GABA Modulators - pharmacology; GABA-A Receptor Agonists; Ligands; Male; Maze Learning - drug effects; Medical sciences; Mice; Mice, Inbred ICR; Pain - drug therapy; Pain Measurement - drug effects; Pharmacology. Drug treatments; Radioligand Assay; Receptors, GABA - metabolism; Receptors, GABA-A - metabolism; Recombinant Proteins - drug effects; Recombinant Proteins - metabolism; Scutellaria baicalensis Georgi; Structure–activity relationship; Flavonoids; Scutellaria baicalensis Georgi; BDZR; SAR; GABA; BDZ; Benzodiazepine receptor; Benzodiazepines; Structure–activity relationship; Anxiolytics; K36; Structure-activity relationship; Anxiolotics; Benzodiazepine derivatives; Pharmacology; Flavonoid
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/j.bcp.2003.08.016

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 [
3
H
]flunitrazepam binding to native BDZR with a
K
i
value of 6.05
nM. In electrophysiological experiments K36 potentiated currents mediated by rat recombinant α
1β
2γ
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
μM 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.