title: Potent inhibitory effect of naturally occurring flavonoids quercetin and kaempferol on in vitro osteoclastic bone resorption.
abstract: Several recent studies have suggested that flavonols, a class of phytochemicals with many biological activities, might exert a protective effect against post-menopausal bone loss. In the present study, we investigated the effects of quercetin and kaempferol, two of the major naturally occurring flavonols on the in vitro bone resorbing activity of osteoclasts. Our results indicate that both compounds, at concentrations ranging from 0.1 to 100 microM reduce bone resorption in a time and dose-dependent manner. Significant inhibitory effects were observed at concentrations as low as 0.1 microM especially with kaempferol. The IC(50)s, or concentration inhibitory of 50% of basal resorption, calculated for quercetin and kaempferol were 1.6 and 5.3 microM, respectively. Using highly purified rabbit osteoclasts, we showed that both flavonols directly induce apoptosis of mature osteoclasts in the same dose-range effective for inhibiting bone resorption. When osteoclasts were treated with 50 microM of quercetin and kaempferol, intracellular reactive oxygen species levels decreased significantly by 75 and 25%, respectively, indicating these molecules keep their antioxidant properties at this concentration. However, at concentrations below 50 microM, neither quercetin nor kaempferol exerted antiradical action, suggesting that antioxidant properties cannot fully explain the inhibitory effect on bone resorption. Finally, we report that kaempferol-, but not the quercetin-induced inhibition of bone resorption was partially abolished by the presence of the pure anti-estrogen ICI 182780 suggesting that kaempferol's estrogenic effect could be involved in the inhibition of bone resorption. The present study demonstrates that flavonols widely distributed in human diet such as quercetin and kaempferol, exert a potent inhibitory effect on in vitro bone resorption.
authors.affiliation: Clinical Pharmacy Laboratory, Université de Picardie Jules Verne, 1 rue des Louvels, 80000 Amiens, France.
authors.forename: Alice
authors.initials: A
authors.lastname: Wattel
authors.forename: Said
authors.initials: S
authors.lastname: Kamel
authors.forename: Romuald
authors.initials: R
authors.lastname: Mentaverri
authors.forename: Florence
authors.initials: F
authors.lastname: Lorget
authors.forename: Christophe
authors.initials: C
authors.lastname: Prouillet
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Petit
authors.forename: Patrice
authors.initials: P
authors.lastname: Fardelonne
authors.forename: Michel
authors.initials: M
authors.lastname: Brazier
mesh_terms: D000818:Animals; D017209:Apoptosis; D001862:Bone Resorption / Q000517:prevention & control*; D005419:Flavonoids / Q000627:therapeutic use*; D044949:Kaempferols; D023421:Models, Animal; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects; D011794:Quercetin / Q000627:therapeutic use*; D011817:Rabbits; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D005419:Flavonoids; D044949:Kaempferols; D017382:Reactive Oxygen Species; C006552:kaempferol; D011794:Quercetin