title: Inhibitory effects of flavonoids from Hypericum perforatum on nitric oxide synthase.
abstract: The inhibitory effects of six flavonoids from Hypericum perforatum were assessed spectrophotometrically using nitric oxide synthase (NOS) in blood and cerebral homogenate of rats. Of the assayed compounds, quercetin and hyperoside showed concentration-dependent enzyme inhibitory actions. The IC50 values of quercetin for inhibiting NOS in rat cerebral homogenate and blood were 63.06 and 57.54 microM, and those of hyperoside 56.23 and 158.49 microM, respectively. The competitive patterns were discerned with the inhibition of the two flavonoids on NOS in serum and cerebral homogenate (except a mixed type inhibition was observed with quercetin in inhibiting cerebral NOS). Furthermore, similar inhibitions were found for quercetin upon NOS in cerebral homogenate and blood. However, a stronger inhibitory effect of hyperoside on the enzyme was discerned in cerebrum than in blood. These results suggested that the galactose moiety in hyperoside may be associated with the selectivity of the NOS inhibition.
authors.affiliation: Institute of Functional Biomolecules, State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210093, PR China.
authors.forename: L
authors.initials: L
authors.lastname: Luo
authors.forename: Q
authors.initials: Q
authors.lastname: Sun
authors.forename: Y Y
authors.initials: YY
authors.lastname: Mao
authors.forename: Y H
authors.initials: YH
authors.lastname: Lu
authors.forename: R X
authors.initials: RX
authors.lastname: Tan
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000201:enzymology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D005419:Flavonoids / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D020902:Hypericum; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000097:blood / Q000187:drug effects* / Q000378:metabolism; D008517:Phytotherapy; D010936:Plant Extracts / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D018547:Plant Stems; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D010936:Plant Extracts; D019001:Nitric Oxide Synthase