Flavonoid quercetin decreases osteoclastic differentiation induced by RANKL via a mechanism involving NFκB and AP‐1

Abstract

Flavonoids are micronutrients widely present in food of plant origin. They have been attributed pharmacological properties such as anticancer and prevention of age-related pathologies. It has been recently hypothesized that flavonoids increase bone mass and prevent osteoporosis. However, little is known about the in vitro effects of flavonoids on osteoclast activities. We investigated the effects of quercetin, one of the most commonly occurring flavonoids, on osteoclast differentiation which is a critical determinant step of in vivo bone resorption. Two in vitro models of osteoclast differentiation were used in this study: a murine one, involving the culture of RAW 264.7 cells in presence of receptor activator of NF kappa B ligand (RANKL), and a human model consisting of differentiating peripheral blood monocytic cells (PBMC) isolated from peripheral blood in presence of RANKL and macrophage-colony stimulating factor (M-CSF). Osteoclastogenesis was assessed by osteoclast-like number, tartrate resistant acid phosphatase (TRAP) activity, and bone resorbing activity. We showed that quercetin (0.1-10 microM) decreased osteoclastogenesis in a dose dependent manner in both models with significant effects observed at low concentrations, from 1 to 5 microM. The IC(50) value was about 1 microM. Analysis of protein-DNA interaction by electrophoretic mobility shift assay (EMSA) performed on RAW cells showed that a pre-treatment with quercetin inhibited RANKL-induced nuclear factor kB (NF kappa B) and activator protein 1 (AP-1) activation. NF kappa B and AP-1 are transcription factors highly involved in osteoclastic differentiation and their inhibition could play an important role in the decrease of osteoclastogenesis observed in the presence of quercetin. In conclusion, the present results demonstrate for the first time that quercetin, a flavonoid characterized by antioxidant activities, is a potent inhibitor of in vitro osteoclastic differentiation, via a mechanism involving NF kappa B and AP-1.

Habitual flavonoid intakes are positively associated with bone mineral density in women

“…(7,(10)(11)(12)33,34) In another study, the flavanone glycoside, naringin, protected against ovariectomy-induced bone loss, potentially mediated through ligand-independent activation of estrogen receptors in osteoblastic cells. (10) Mechanistic support also exists for a beneficial effect of higher flavonol intake on BMD; quercetin and kampferol have been found to inhibit bone loss in ovariectomized mice (8) via a range of potential mechanisms including effects on osteoclast differentiation involving NF-kB and AP-1 induction by RANKL, (13,15) stimulating alkaline phosphatase activity, promoting osteoblast activity, and upregulating bone sialoprotein gene promoter. (16,18) We found an association between a higher flavonol intake and higher BMD at the spine, similar to findings from a previous study, which had only included intakes of a few flavonols.…”

“…(5,6) Flavonoids have the potential to affect bone health; certain classes of flavonoid compounds have been shown to prevent bone loss in ovariectomized animal models (7)(8)(9)(10) and to improve bone quality and strength in orchidectomized rats. (11,12) A number of potential mechanisms have been proposed, including effects on osteoclast differentiation via mechanisms involving NF-kB and AP-1 induced by receptor activator of NF-kB ligand (RANKL) in vitro, (13)(14)(15) stimulating alkaline phosphatase activity or promoting osteoblast activity and upregulating bone sialoprotein gene promoter. (16)(17)(18) Most previous research examining flavonoids and bone health, including randomized controlled trials (RCTs), have focused on the isoflavone subclass with equivocal results.…”

In vivo quercitrin anti‐inflammatory effect involves release of quercetin, which inhibits inflammation through down‐regulation of the NF‐κB pathway

“…In vitro studies have clearly shown that quercetin acts as a potent pleiotropic modulator in several physiological functions, showing different activities such as anti-proliferative effect in numerous cell lines [6,7], pro-apoptotic effect in lung carcinoma cell lines [8], and inhibitory effect of osteoclastic differentiation [9]. It is important to note that when the glycosylated forms of quercetin are assayed, there is usually a loss of activity in these effects in comparison with those obtained with the aglycone, due to the presence of the sugar moiety in the flavonoid structure [10].…”

<i>In-vitro</i> anti-inflammatory activities of 3-methoxy quercetin isolated from Nigerian mistletoe parasitic on <i>Garcinia kola</i> Heckel, Clusiaceae

“…Quercetin as a naturally occurring flavonoid protects cells against oxidative stress [7,8]. Several studies have shown that quercetin in its free or glycosylated form modulates certain physiological functions with potent antiproliferative effects in numerous cell lines [9,10], pro-apoptotic effect in lung carcinoma cell lines [11], and inhibitory effect of bone metabolism [12].…”