title: Identification of kaempferol as a monoamine oxidase inhibitor and potential Neuroprotectant in extracts of Ginkgo biloba leaves.
abstract: The effects of Ginkgo biloba leaf extract on rat brain or livermonoamine oxidase (MAO)-A and -B activity, biogenic amine concentration in nervous tissue, N-methyl-D-aspartate (NMDA)- and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4)-induced neurotoxicity and antioxidant activity was investigated to determine the effects of the extract on monoamine catabolism and neuroprotection. Ginkgo biloba leaf extract was shown to produce in-vitro inhibition of rat brain MAO-A and -B. The Ginkgo biloba extract was chromatographed on a reverse-phase HPLC system and two of the components isolated were shown to be MAO inhibitors (MAOIs). These MAOIs were identified by high-resolution mass spectrometry as kaempferol and isorhamnetin. Pure kaempferol and a number of related flavonoids were examined as MAOIs in-vitro. Kaempferol, apigenin and chrysin proved to be potent MAOIs, but produced more pronounced inhibition of MAO-A than MAO-B. IC50 (50% inhibition concentration) values for the ability of these three flavones to inhibit MAO-A were 7 x 10(-7), 1 x 10(-6) and 2 x 10(-6) M, respectively. Ginkgo biloba leaf extract and kaempferol were found to have no effect ex-vivo on rat or mouse brain MAO or on concentrations of dopamine, noradrenaline, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid. Kaempferol was shown to protect against NMDA-induced neuronal toxicity in-vitro in rat cortical cultures, but did not prevent DSP-4-induced noradrenergic neurotoxicity in an in-vivo model. Both Ginkgo biloba extract and kaempferol were demonstrated to be antioxidants in a lipid-peroxidation assay. This data indicates that the MAO-inhibiting activity of Ginkgo biloba extract is primarily due to the presence of kaempferol. Ginkgo biloba extract has properties indicative of potential neuroprotective ability.
authors.affiliation: CV Technologies, Edmonton, Alberta, Canada.
authors.forename: B D
authors.initials: BD
authors.lastname: Sloley
authors.forename: L J
authors.initials: LJ
authors.lastname: Urichuk
authors.forename: P
authors.initials: P
authors.lastname: Morley
authors.forename: J
authors.initials: J
authors.lastname: Durkin
authors.forename: J J
authors.initials: JJ
authors.lastname: Shan
authors.forename: P K
authors.initials: PK
authors.lastname: Pang
authors.forename: R T
authors.initials: RT
authors.lastname: Coutts
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000284:Administration, Oral; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004298:Dopamine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005419:Flavonoids; D020441:Ginkgo biloba / Q000737:chemistry*; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D044949:Kaempferols; D015227:Lipid Peroxidation / Q000187:drug effects; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008297:Male; D051379:Mice; D008995:Monoamine Oxidase / Q000187:drug effects / Q000378:metabolism; D008996:Monoamine Oxidase Inhibitors / Q000032:analysis* / Q000494:pharmacology; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000187:drug effects; D018696:Neuroprotective Agents / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*; D018515:Plant Leaves / Q000737:chemistry*; D010946:Plants, Medicinal; D011794:Quercetin / Q000031:analogs & derivatives* / Q000032:analysis / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
chemical_list: D005419:Flavonoids; D044949:Kaempferols; D008996:Monoamine Oxidase Inhibitors; D018696:Neuroprotective Agents; D010936:Plant Extracts; D015102:3,4-Dihydroxyphenylacetic Acid; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D016202:N-Methylaspartate; C006552:kaempferol; D011794:Quercetin; D008995:Monoamine Oxidase; D004298:Dopamine; D009638:Norepinephrine