Quercetin reversed lipopolysaccharide-induced inhibition of osteoblast differentiation through the mitogen­activated protein kinase pathway in MC3T3-E1 cells.

Quercetin, a flavonoid found in onions and other vegetables, has potential inhibitory effects on bone resorption in vivo and in vitro. In our previous study it was identified that quercetin triggered the apoptosis of lipopolysaccharide (LPS)­induced osteoclasts and inhibited bone resorption. Currently, little information is available detailing the effect of quercetin on osteoblast differentiation and bone formation in bacteria­induced inflammatory diseases. The present study aimed to investigate the effect of quercetin on osteoblast differentiation in MC3T3­E1 osteoblasts stimulated with LPS. LPS significantly downregulated the mRNA expression of osteoblast­related genes in the MC3T3­E1 cells. By contrast, quercetin significantly restored the LPS­suppressed mRNA expression of osteoblast­related genes in a dose­dependent manner. Quercetin also restored the protein expression of Osterix in MC3T3­E1 cells suppressed by LPS. Furthermore, quercetin selectively triggered the activation of the mitogen­activated protein kinase (MAPK) pathway by enhancing the expression of extracellular signal-regulated kinase and reducing the expression of c­Jun N­terminal kinase. These data suggest that quercetin reversed the inhibition of osteoblast differentiation induced by LPS through MAPK signaling. These findings suggest that quercetin may be of potential use as a therapeutic agent to restore osteoblast function in bacteria­induced bone diseases.