Quercetin, a flavonoid, inhibits the proliferation, differentiation, and mineralization of osteoblasts in vitro

The flavonoid quercetin induces apoptosis and inhibits migration through a MAPK-dependent mechanism in osteoblasts

The present study was undertaken to evaluate effects of quercetin, a major dietary flavonoid occurring in foods of plant origin, on cell viability and migration of osteoblastic cells. Quercetin inhibited cell viability, which was largely attributed to apoptosis, in a dose-and time-dependent manner in osteoblastic cells. Similar cytotoxicity of quercetin was observed in adipose tissue-derived stromal cells. Quercetin exerted a protective effect against H(2)O(2)-induced cell death, whereas it increased TNF-alpha-induced cell death. Western blot analysis showed that quercetin induced activation of ERK and p38, but not JNK. Quercetin-induced cell death was prevented by the ERK inhibitor PD98059, but not by inhibitors of p38 and JNK. Quercetin increased Bax expression and caused depolarization of mitochondrial membrane potential, which were inhibited by PD98059. Quercetin induced caspase-3 activation, and the quercetininduced cell death was prevented by caspase inhibitors. Quercetin inhibited cell migration, and its effect was prevented by inhibitors of ERK and p38. Taken together, these findings suggest that quercetin induces apoptosis through a mitochondria-dependent mechanism involving ERK activation and inhibits migration through activation of ERK and p38 pathways. Quercetin may exert both protective and deleterious effects in bone repair.

Simultaneous analysis of glycyrrhizin, paeoniflorin, quercetin, ferulic acid, liquiritin, formononetin, benzoic acid and isoliquiritigenin in the Chinese proprietary medicine Xiao Yao Wan by HPLC

A high performance liquid chromatography coupled with photodiode-array detection method was developed for simultaneous determination of glycyrrhizin, paeoniflorin, benzoic acid, quercetin, ferulic acid, formononetin, liquiritin and isoliquiritigenin in the Chinese proprietary medicine "Xiao Yao Wan" (XYW). The analysis was performed by reverse phase gradient elution, using an aqueous mobile phase (containing 0.1% phosphoric acid) modified by acetonitrile and detection made simultaneously at four wavelengths. The method was validated for accuracy, precision and limits of detection and quantification. Ten batches of XYW obtained from different pharmaceutical companies were analyzed and found to contain different amounts of the eight bioactive markers. This method could be used for quality assessment of this herbal medicine.

Role of Sandhika: A Polyherbal Formulation on MC3T3-E1 Osteoblast-like Cells

Sandhika is a polyherbal formulation, (water soluble fraction of Commiphora mukul, Boswellia serrata, Semecarpus anacardium and Strychnos nux vomica), which has been in clinical use in India for last 20 years. Its modified formulation BHUx has shown specific inhibition of cyclooxygenase (COX)-2 and lipoxygenase (LOX)-15 and has prevented diet-induced atherosclerosis in rabbits. In order to explore the possibility of the use of Sandhika for the management of osteoporosis, we have examined its influence on MC3T3-E1 osteoblast-like cells in presence of lipopolysaccharide (1 microg/ml) in terms of calcium nodule formation and alkaline phosphatase activity. MC3T3-E1 osteoblast-like cells (80% confluence in 6-well plates) were treated with water extract of Sandhika, for 10 days, in the concentration range of 0.5 to 16 mg/ml final concentration, in presence of LPS. Media was changed on every third day and culture supernatant was collected after every change to assess the alkaline phosphatase activity and on the tenth day, cells were washed and stained with "Alizarin S" for visualization of calcium nodules by using Meta Morph software (Universal Imaging, Downingtown, PA). The results showed significant enhancement in calcium nodule formation in the dose dependent manner up to 2 mg/ml, followed by gradual decrease at higher concentrations. This change was accompanied with the increase in the alkaline phosphatase activity in these plates, indicating a potential anabolic effect of this polyherbal formulation on osteoblast-like cells under inflammatory conditions induced by LPS.

Myricetin induces human osteoblast differentiation through bone morphogenetic protein-2/p38 mitogen-activated protein kinase pathway

Myricetin (3,3',4',5,5',7-hexahydroxyflavone), a flavonoid compound, is present in vegetables and fruits. By means of alkaline phosphatase (ALP) activity, osteocalcin, and type I collagen enzyme-linked immunosorbent assay (ELISA), we have shown that myricetin exhibits a significant induction of differentiation in MG-63 and hFOB human osteoblasts. Alkaline phosphatase and osteocalcin are phenotypic markers for early-stage differentiated osteoblasts and terminally differentiated osteoblasts, respectively. Our results indicate that myricetin stimulates osteoblast differentiation at various stages, from maturation to terminally differentiated osteoblasts. Induction of differentiation by myricetin is associated with increased bone morphogenetic protein-2 (BMP-2) production. The BMP-2 antagonist noggin blocked myricetin-mediated ALP activity and osteocalcin secretion enhancement, indicating that BMP-2 production is required in myricetin-mediated osteoblast maturation and differentiation. Induction of differentiation by myricetin is associated with increased activation of SMAD1/5/8 and p38 mitogen-activated protein kinases. Cotreatment of p38 inhibitor SB203580 inhibited myricetin-mediated ALP upregulation and osteocalcin production. In conclusion, myricetin increased BMP-2 synthesis, and subsequently activated SMAD1/5/8 and p38 MAPK, and this effect may contribute to its action on the induction of osteoblast maturation and differentiation, followed by an increase of bone mass.

Quercetin, a flavonoid, inhibits proliferation and increases osteogenic differentiation in human adipose stromal cells

Flavonoids, which have been detected in a variety of foods, have been repeatedly reported to affect bone metabolism. However, the effects of flavonoids on osteoblastogenesis remain a matter of some controversy. In this study, the effects of quercetin on the differentiation and proliferation of human adipose tissue-derived stromal cells (hADSC) were determined. Quercetin was found to increase osteogenic differentiation in a dose-dependent manner. Other flavonoids, chrysin and kaempferol, were also shown to increase the osteogenic differentiation of hADSC, but this stimulatory effect was weaker than that associated with quercetin. Quercetin pretreatment administered prior to the induction of differentiation also exerted stimulatory effects on the osteogenic differentiation of hADSC. RT-PCR and real time PCR analysis showed that quercetin treatment induced an increase in the expression of osteopontin, BMP2, alkaline phosphatase and Runx2. Quercetin inhibited the proliferation of hADSC, but did not affect their survival. The pretreatment of quercetin increased ERK phosphorylation during osteogenic differentiation, although it did not increase ERK activity in control culture condition. ICI182780, an specific estrogen receptor antagonist, failed to inhibit the effects of quercetin on osteogenic differentiation. Quercetin-pretreated hADSC showed better bone regenerating ability in skull defect model of nude mice than naive cells. Our findings indicate that quercetin enhances osteogenic differentiation via an independent mechanism from estrogen receptor (ER) activation, and prove useful for in vivo bone engineering, using human mesencymal stem cells (hMSC).

Curcumin inhibits the proliferation and mineralization of cultured osteoblasts

The effects of curcumin, which is an important constituent of rhizomes of the plant Curcuma longa Linn, on the metabolism of osteoblasts were examined in cultures of rat calvarial osteoblastic cells (ROB cells). The proliferation of cells was markedly inhibited upon exposure of cells to curcumin at 5x10(-6) to 1x10(-5) M. Curcumin at 1x10(-5) M did not induce apoptosis in ROB cells but arrested cells at the G1 phase of the cell cycle. In addition, curcumin stimulated the expression of mRNA for p21(WAF1/CIP1), which inhibits the activity of cyclin-dependent kinases, and inhibited the phosphorylation of histone H1. Furthermore, curcumin reduced the rate of deposition of calcium and the formation of mineralized nodules. Our results indicate that curcumin might inhibit the proliferation and mineralization of osteoblastic cells through the expression of p21(WAF1/CIP1).

Grape-seed derived procyanidins interfere with adipogenesis of 3T3-L1 cells at the onset of differentiation

OBJECTIVE

Our group's previous results on the effects of a grape seed procyanidin extract (GSPE) on adipose metabolism showed that peroxisome proliferator-activated receptor-gamma (PPARgamma) plays a central role in the lipolytic effects of GSPE on adipocytes. Since PPARgamma2 is a main regulator of the differentiation process of adipocytes, we investigated whether GSPE affects the adipogenesis of 3T3-L1 cells.

DESIGN

We performed a time point screening by treating 3T3-L1 cells with GSPE during the differentiation process for 24 h.

MEASUREMENTS

Differentiation markers and differential gene expression due to GSPE treatment (using the microarray technique).

RESULTS

Twenty four hour-GSPE treatment at the onset of differentiation reduces adipose-specific markers and maintains the expression of preadipocyte marker preadipocyte factor-1 (Pref-1) significantly elevated. These effects were not found in other time points. Microarray analysis of gene expression after GSPE treatment at the early stage of differentiation showed a modified gene expression profile in which cell cycle and growth-related genes were downregulated by GSPE.

CONCLUSION

These results suggest that GSPE affects adipogenesis, mainly at the induction of differentiation, and that procyanidins may have a new role in which they impede the formation of adipose cells.

Ellagic acid potentiates the effect of quercetin on p21waf1/cip1, p53, and MAP-kinases without affecting intracellular generation of reactive oxygen species in vitro

Anticarcinogenic effects attributed to polyphenols in fruits may be based on synergistic, additive, or antagonistic interactions of many compounds. In a previous study, it was demonstrated that quercetin and ellagic acid interacted synergistically in the induction of apoptosis in the human leukemia cell line, MOLT-4. To investigate possible cellular mechanisms, this study evaluated whether synergistic effects might be detectable within proapoptotic or antiproliferative signal transduction pathways. We found that quercetin and combinations of quercetin and ellagic acid nonsynergistically increased p53 protein levels. In contrast, ellagic acid potentiated the effects of quercetin for p21(cip1/waf1) protein levels and p53 phosphorylation at serine 15, possibly explaining the synergistic effect observed in apoptosis induction. Phosphorylation of the mitogen-activated protein (MAP) kinases, c-jun N-terminal (JNK)1,2 and p38, was also increased by the combination of ellagic acid and quercetin, whereas quercetin alone induced only p38. We further evaluated whether the generation of reactive oxygen species (ROS) and/or quercetin stability were influenced by interactions of ellagic acid with quercetin. Quercetin increased the generation of ROS, which was neither potentiated nor inhibited by ellagic acid. The stability of intracellular and extracellular quercetin was not influenced by the presence of ellagic acid. In summary, quercetin and ellagic acid combined increase the activation of p53 and p21(cip1/waf1) and the MAP kinases, JNK1,2 and p38, in a more than additive manner, suggesting a mechanism by which quercetin and ellagic acid synergistically induce apoptosis in cancer cells.

Inhibition of ossification in vivo and differentiation of osteoblasts in vitro by tributyltin

Tributyltin is ubiquitous in the environment and an endocrine disruptor for many wildlife species. However, minimal information is available regarding the effect of this chemical on bone formation. When tributyltin chloride (TBT) (1mg/kg body weight) was administered subcutaneously to pregnant mice at 10, 12, and 14 days post coitus (dpc), fetuses at 17.5 days post coitus revealed the inhibition of calcification of supraoccipital bone. In contrast, 1mg/kg body weight monobutyltin trichloride (MBT) did not affect the fetal skeleton. Therefore, we examined the effects of TBT and its metabolites (dibutyltin dichloride, DBT, and MBT) on bone metabolism using rat calvarial osteoblast-like cells (ROB cells). The viability of ROB cells was not affected by the exposure of the cells to 10(-10) to 10(-7)M TBT. However, TBT reduced the activity of alkaline phosphatase (ALPase) and the rate of deposition of calcium of ROB cells. In addition, the expression levels of mRNA for ALPase and osteocalcin, which are markers of osteoblastic differentiation, were depressed by the treatment with TBT. TBT inhibited ALPase activity and the deposition of calcium to a greater extent than did DBT. MBT had no effect on the osteoblast differentiation of ROB cells. Tributyltin is known to inhibit the activity of aromatase. However, the aromatase inhibitor aminoglutethimide did not reproduce the inhibitory effects of TBT on osteoblast differentiation. Our findings indicate that TBT might have critical effects on the formation of bone both in vivo and in vitro although its action mechanism is not clarified.