LPS-induced Osteoclast Formation Research Articles

Triterpenoids from Potentilla chinensis inhibit RANKL-induced osteoclastogenesis in vitro and lipopolysaccharide-induced osteolytic bone loss in vivo.

In this study, a phytochemical investigation on the methanol extract of Potentilla chinensis led to the isolation of eleven triterpenoids including ursolic acid (1), pomolic acid (2), tormentic acid (3), 2-epi-corosolic acid (4), 3-epi-corosolic acid (ECA, 5), 3β-hydroxyurs-11-en-13β(28)-olide (6), euscaphic acid (7), 2-epi-tormentic acid (8), corosolic acid (9), uvaol (10), and 3-O-acetylpomolic acid (11). Among them, ECA (5) showed potential anti-osteoclastogenic activity. To the best of our knowledge, this represents the first isolation of ECA (5) from P. chinensis as well as the first investigation of its effects on osteoclast formation. Further study revealed that ECA inhibited RANKL-induced mature osteoclast formation in vitro without compromising cell viability. Mechanistically, ECA attenuated RANKL-induced mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB) activation, leading to the inhibition of c-Fos and nuclear factor of activated T cells cytoplasmic 1 (NFATc1) activation. Moreover, ECA protected against LPS-induced inflammatory bone loss and osteoclast formation in a mouse model. However, ECA did not inhibit LPS-induced inflammatory responses in macrophages. Our findings suggest that ECA mitigates LPS-induced inflammatory bone loss in mice by inhibiting RANKL-induced activation of key osteoclastogenic transcription factors, including c-Fos and NFATc1, and may be a potential natural triterpenoid for preventing or treating osteolytic diseases.

Iris Koreana NAKAI Inhibits Osteoclast Formation via p38-Mediated Nuclear Factor of Activated T Cells 1 Signaling Pathway.

Iris Koreana NAKAI (IKN) is a flowering perennial plant that belongs to the Iridaceae family. In this study, we aimed to demonstrate the effects of IKN on osteoclast differentiation in vitro and in vivo. We also sought to verify the molecular mechanisms underlying its anti-osteoclastogenic effects. Osteoclasts were formed by culturing mouse bone marrow macrophage (BMM) cells with macrophage colony-stimulating factor and receptor activator of nuclear factor-κB ligand (RANKL). Bone resorption assays were performed on dentin slices. mRNA expression levels were analyzed by quantitative polymerase chain reaction. Western blotting was performed to detect protein expression or activation. Lipopolysaccharide (LPS)-induced osteoclast formation was performed using a mouse calvarial model. In BMM cultures, an ethanol extract of the root part of IKN suppressed RANKL-induced osteoclast formation and bone resorptive activity. In contrast, an ethanol extract of the aerial parts of IKN had a minor effect on RANKL-induced osteoclast formation. Mechanistically, the root part of IKN suppressed RANKL-induced p38 mitogen-activated protein kinase (MAPK) activation, effectively abrogating the induction of c-Fos and nuclear factor of activated T cells 1 (NFATc1) expression. IKN administration decreased LPS-induced osteoclast formation in a calvarial osteolysis model in vivo. Our study suggested that the ethanol extract of the root part of IKN suppressed osteoclast differentiation and function partly by downregulating the p38 MAPK/c-Fos/NFATc1 signaling pathways. Thus, the root part.

Fermented Rice Bran Supplementation Inhibits LPS-Induced Osteoclast Formation and Bone Resorption in Mice.

Fermented rice bran (FRB) is known to have numerous beneficial bioactivities, amongst which is its anti-inflammatory properties when used as a supplement. To determine its effects, we examined osteoclastogenesis and bone resorption caused by injections of lipopolysaccharide (LPS), using mice with and without FRB supplementation. The results were favorable: those that received FRB showed reduced osteoclast numbers and bone resorption compared to those with the control diet. Notably, receptor activator of NF-κB ligand (RANKL) and tumor necrosis factor-α (TNF-α) mRNA levels were shown to be lower in the LPS-treated animals with FRB supplementation. FRB's inhibitory effect on RANKL- and TNF-α-induced osteoclastogenesis was further confirmed in vitro. In culture, macrophages exhibited decreased TNF-α mRNA levels when treated with FRB extract and LPS versus treatment with LPS alone, but there was no significant change in RANKL levels in osteoblasts. We can conclude that FRB supplementation dampens the effect of LPS-induced osteoclastogenesis and bone resorption by controlling TNF-α expression in macrophages and the direct inhibition of osteoclast formation.

Fermented rice bran supplementation inhibits LPS-induced osteoclast formation and bone resorption in mice

Fermented rice bran supplementation inhibits LPS-induced osteoclast formation and bone resorption in mice

Marein Prevented LPS-Induced Osteoclastogenesis by Regulating the NF-κB Pathway In Vitro.

Many bone diseases such as osteolysis, osteomyelitis, and septic arthritis are caused by gram-negative bacterial infection, and lipopolysaccharide (LPS), a bacterial product, plays an essential role in this process. Drugs that inhibit LPS-induced osteoclastogenesis are urgently needed to prevent bone destruction in infective bone diseases. Marein, a major bioactive compound of Coreopsis tinctoria, possesses anti-oxidative, anti-inflammatory, anti-hypertensive, anti-hyperlipidemic, and anti-diabetic effects. In this study, we measured the effect of marein on RAW264.7 cells by CCK-8 assay and used TRAP staining to determine osteoclastogenesis. The levels of osteoclast-related genes and NF-κB-related proteins were then analyzed by western blot, and the levels of pro-inflammatory cytokines were quantified by ELISA. Our results showed that marein inhibited LPS-induced osteoclast formation by osteoclast precursor RAW264.7 cells. The effect of marein was related to its inhibitory function on expressions of pro-inflammatory cytokines and osteoclast-related genes containing RANK, TRAF6, MMP-9, CK, and CAII. Additionally, marein leads to markedly inhibited NF-κB signaling pathway activation in LPS-induced RAW264.7 cells. Concurrently, when the NF-κB signaling pathway was inhibited, osteoclast formation and pro-inflammatory cytokine expression were decreased. Collectively, marein could inhibit LPS-induced osteoclast formation in RAW264.7 cells via regulating the NF-κB signaling pathway. Our data demonstrate that marein might be a potential drug for bacteria-induced bone destruction disease. Our findings provide new insights into LPS-induced bone disease.

Egg-Derived Tripeptide IRW Attenuates LPS-Induced Osteoclastogenesis in RAW 264.7 Macrophages via Inhibition of Inflammatory Responses and NF-κB/MAPK Activation.

Excessive bone resorption, because of increased osteoclastic activity, is a key underlying cause of osteolytic disorders. Lipopolysaccharide (LPS) is a potent factor to stimulate osteoclastic activity by inducing inflammatory stress. An egg-derived tripeptide IRW (Ile-Arg-Trp) was previously shown to exert anti-inflammatory activity. The overall objective of this study was to investigate the effect of IRW on inhibiting LPS-induced osteoclastogenesis and inflammatory bone resorption in the mouse macrophage RAW 264.7 cells. IRW (25 and 50 μM) significantly inhibited the LPS-induced osteoclast formation and resorptive activity. Meanwhile, IRW significantly suppressed the LPS-induced expression of TNF-α, IL-6, iNOS, COXII, NO, and PGE2. Furthermore, IRW regulated a group of osteoclastogenesis-associated factors (TRAF6, c-Fos, NFATc1, and cathepsin K) because of the inhibition of LPS-activated NF-κB and MAPK pathways. In conclusion, our study suggested the ability of IRW to prevent LPS-induced inflammatory bone resorption activity via the inhibition of inflammatory responses and the activation of osteoclastogenesis-associated signaling pathways.

Artesunate attenuates LPS-induced osteoclastogenesis by suppressing TLR4/TRAF6 and PLCγ1-Ca2+-NFATc1 signaling pathway.

In chronic infectious diseases caused by gram-negative bacteria, such as osteomyelitis, septic arthritis, and periodontitis, osteoclastic activity is enhanced with elevated inflammation, which disturbs the bone homeostasis and results in osteolysis. Lipopolysaccharide (LPS), as a bacteria product, plays an important role in this process. Recent evidence shows that an antimalarial drug artesunate attenuates LPS-induced osteolysis independent of RANKL. In this study we evaluated the effects of artesunate on LPS-induced osteoclastogenesis in vitro and femur osteolysis in vivo, and explored the mechanisms underlying the effects of artesunate on LPS-induced osteoclast differentiation independent of RANKL. In preosteoclastic RAW264.7 cells, we found that artesunate (1.56−12.5 μM) dose dependently inhibited LPS-induced osteoclast formation accompanied by suppressing LPS-stimulated osteoclast-related gene expression (Fra-2, TRAP, Cathepsin K, β3-integrin, DC-STAMP, and Atp6v0d2). We showed that artesunate (3.125−12.5 µM) inhibited LPS-stimulated nuclear factor of activated T cells c1 (NFATc1) but not NF-κB transcriptional activity; artesunate (6.25, 12.5 μM) significantly inhibited LPS-stimulated NFATc1 protein expression. Furthermore, artesunate treatment markedly suppressed LPS-induced Ca2+ influx, and decreased the expression of PP2B-Aα (calcineurin) and pPLCγ1 in the cells. In addition, artesunate treatment significantly decreased the expression of upstream signals TLR4 and TRAF6 during LPS-induced osteoclastogenesis. Administration of artesunate (10 mg/kg, ip) for 8 days effectively inhibited serum TNF-α levels and ameliorated LPS (5 mg/kg, ip)-induced inflammatory bone loss in vivo. Taken together, artesunate attenuates LPS-induced inflammatory osteoclastogenesis by inhibiting the expression of TLR4/TRAF6 and the downstream PLCγ1-Ca2+-NFATc1 signaling pathway. Artesunate is a valuable choice to treat bone loss induced by gram-negative bacteria infection or inflammation in RANKL-independent pathway.

Ethanol extract of Polyscias fruticosa leaves suppresses RANKL-mediated osteoclastogenesis in vitro and LPS-induced bone loss in vivo

BackgroundMany bone-related diseases such as osteoporosis and rheumatoid arthritis are commonly associated with the excessive activity of osteoclasts. Polyscias fruticosa has been used as traditional medicine for the treatment of ischemia and inflammation and also eaten as a salad. However, its effect on the bone related diseases has not been investigated yet. PurposeThis study aimed to investigate the effect of ethanol extract of P. fruticosa on RANKL-induced osteoclastogenesis in vitro and LPS-induced bone loss in mouse, and evaluate anti-osteoclastogenic activities of its major constituents. MethodsBMMs or RAW264.7 cells were treated with ethanol extract from P. fruticose leaves (EEPL), followed by an evaluation of cell viability, RANKL-induced osteoclast differentiation, actin-ring formation, and resorption pits activity. Effects of EEPL on RANKL-induced phosphorylation of MAPKs were evaluated by Western blotting. The expression levels of NFATc1 and c-Fos were evaluated by Western blotting or immunofluorescence assay. The expression levels of osteoclast-specific marker genes were evaluated by Western blotting and reverse transcription-qPCR analysis. A LPS-induced murine bone loss model was used to evaluate the protective effect of EEPL on inflammation-induced bone loss. HPLC analysis was performed to identify the major constituents of EEPL. ResultsEEPL significantly inhibited RANKL-induced osteoclast differentiation by decreasing the number of osteoclasts, osteoclast actin-ring formation, and bone resorption. EEPL suppressed RANKL-induced phosphorylation of p38 and JNK MAPKs, as well as the expression of c-Fos and NFATc1. EEPL decreased the expression levels of osteoclast marker genes, including MMP-9, TRAP and CtsK. Mice treated with EEPL significantly protected the mice from LPS-induced osteoclast formation and bone destruction as indicated by micro-CT and histological analysis of femurs. We also identified 3-O-[β-d-glucopyranosyl-(1→4)-β-d-glucuronopyranosyl] oleanolic acid 28-O-β-d-glucopyranosyl ester (1) and quercitrin (3) as the active constituents in EEPL for inhibiting RANKL-induced osteoclast differentiation. ConclusionThe results showed that EEPL exerted anti-osteoclastogenic activity in vitro and in vivo by inhibiting RANKL-induced osteoclast differentiation and function, and suggested that EEPL could have beneficial applications for preventing or inhibiting osteoclast-mediated bone diseases.

Docosahexaenoic Acid Inhibits Inflammation-Induced Osteoclast Formation and Bone Resorption in vivo Through GPR120 by Inhibiting TNF-α Production in Macrophages and Directly Inhibiting Osteoclast Formation.

Docosahexaenoic acid (DHA) is an n-3 fatty acid that is an important structural component of the cell membrane. DHA exerts potent anti-inflammatory effects through G protein-coupled receptor 120 (GPR120), which is a functional receptor for n-3 fatty acids. DHA also regulates osteoclast formation and function. However, no studies have investigated the effect of DHA on inflammation-induced osteoclast formation in vivo. In the present study, we investigated whether DHA influences osteoclast formation, bone resorption and the expression of osteoclast-associated cytokines during lipopolysaccharide (LPS)-induced inflammation in vivo, and then we elucidated the underlying mechanisms by using in vitro experiments. In vitro experiments revealed both receptor activator of NF-kB ligand (RANKL)- and tumor necrosis factor-α (TNF-α)-induced osteoclast formation was inhibited by DHA. Supracalvarial administration of LPS with or without DHA was carried out for 5 days and then the number of osteoclasts, ratio of bone resorption pits and the level of type I collagen C-terminal cross-linked telopeptide were measured. All measurements were significantly lower in LPS+DHA-co-administered mice than LPS-administered mice. However, this DHA-induced inhibition was not observed in LPS-, DHA-, and selective GPR120 antagonist AH7614-co-administered mice. Furthermore, the expression of RANKL and TNF-α mRNAs was lower in the LPS+DHA-co-administered group than in the LPS-administered group in vivo. TNF-α mRNA levels were decreased in macrophages co-treated with LPS+DHA compared with cells treated with LPS in vitro. In contrast, RANKL mRNA expression levels from osteoblasts co-treated with DHA and LPS in vitro were equal to that in cells treated with LPS alone. Finally, the inhibitory effects of DHA on osteoclast formation in vitro were not observed by using osteoclast precursors from GPR120-deficient mice, and inhibition of LPS-induced osteoclast formation and bone resorption by DHA in vivo was not observed in GPR120-deficient mice. These results suggest that DHA inhibits LPS-induced osteoclast formation and bone resorption in vivo via GPR120 by inhibiting LPS-induced TNF-α production in macrophages along with direct inhibition of osteoclast formation.

DPP-4 inhibitor impedes lipopolysaccharide-induced osteoclast formation and bone resorption in vivo

ObjectivesDipeptidyl peptidase 4 (DPP-4) inhibition is a new therapeutic strategy for type 2 diabetic patients. DPP-4 has been reported to enhance inflammation. However, the effect of DPP-4 inhibition on inflammation remains unknown. Lipopolysaccharide (LPS) is a strong inducer of inflammation and osteoclast formation. In this study, we investigated in vivo effects of DPP-4 inhibition on LPS-induced osteoclast formation and bone resorption, as well as in vitro effects of DPP-4 inhibition on RANKL-induced osteoclastogenesis and TNF-α-induced osteoclastogenesis. MethodsLPS with or without a DPP-4 inhibitor was subcutaneously injected into mouse calvaria for 5 days. Histological sections of calvaria were stained for tartrate-resistant acid phosphatase, and osteoclast numbers were determined. The ratio of calvaria bone resorption was evaluated via microfocal computed tomography reconstruction images. ResultsOsteoclast number and bone resorption were significantly lower in mice that underwent LPS and DPP-4 inhibitor co-administration than in those that underwent LPS administration alone. Moreover, RANKL, TNF-α, and M-CSF expression was reduced in the LPS and DPP-4 inhibitor co-administration group. In vitro, there were no direct effects of DPP-4 inhibitor or DPP-4 on RANKL- and TNF-α-induced osteoclastogenesis, or on LPS-induced RANKL expression in stromal cells. Nevertheless, macrophages from LPS and DPP-4 inhibitor co-administered mice exhibited lower TNF-α expression than macrophages from LPS-only mice. Notably, TNF-α expression was not reduced in LPS and DPP-4 inhibitor co-treated macrophages in vitro, compared with macrophages treated with LPS alone.

Magnesium Lithospermate B Protects against Lipopolysaccharide-Induced Bone Loss by Inhibiting RANKL/RANK Pathway.

Lipopolysaccharide (LPS) can induce bone loss by stimulating bone resorption. Natural compounds have great potential for the treatment of osteolytic bone diseases. Magnesium lithospermate B (MLB) plays an important role in protecting against oxidative damage and also has potential anti-inflammatory pharmacological properties. However, its role in LPS-induced bone loss is still unknown. In the present study, we observed the effects of MLB on LPS-induced bone damage and investigated the possible mechanisms. The bone loss models were established by LPS administration in male Sprague–Dawley rats. MLB (200 mg/kg body weight) was given by subcutaneous injection. MicroCT analysis, biomarker assay, histological examination and immunohistochemical staining were performed at the 8th weeks. In addition, RAW264.7 cells were treated with LPS in the presence or absence of MLB. The osteoclast formation, resorption activity and differentiation-related genes [(receptor activator of nuclear factor kappa-B (RANK), Traf6, Fra-1, and c-src)] expression were evaluated. LPS induced bone loss shown as the decrease in bone volume fraction and trabecular number, and increase in trabecular separation. LPS also markedly enhanced the osteoclast formation and resorption activity compared with the control. MLB significantly abolished the LPS-induced bone microstructure damage (p < 0.05) and osteoclast formation. MLB also inhibited the increases of serum tartrate-resistant acid phosphatase 5b, RANK ligand (RANKL) and TNF-α level enhanced by LPS (p < 0.05). Immunohistochemical staining indicated that MLB attenuated the high expression of RANKL and RANK stimulated by LPS. In addition, MLB significantly abolished the LPS-enhanced osteoclast formation, resorption activity, RANK, Traf6, Fra-1, and c-src expression in vitro. Our data demonstrate that MLB can suppress LPS-induced bone loss via inhibiting RANKL/RANK related osteoclast formation.

The Glucagon-Like Peptide-1 Receptor Agonist Exendin-4 Inhibits Lipopolysaccharide-Induced Osteoclast Formation and Bone Resorption via Inhibition of TNF-α Expression in Macrophages.

Glucagon-like peptide-1 (GLP-1) receptor agonists are an effective treatment approach for type 2 diabetes. Recently, anti-inflammatory effects of GLP-1 receptor agonists have also been reported. Lipopolysaccharide (LPS) induces inflammation and osteoclast formation. In this study, we investigated the effect of exendin-4, a widely used GLP-1 receptor agonist, in LPS-induced osteoclast formation and bone resorption. LPS with or without exendin-4 was administered on mouse calvariae by daily subcutaneous injection. The number of osteoclasts, the ratio of bone resorption pits, and the level of C-terminal cross-linked telopeptide of type I collagen (CTX) were significantly lower in LPS- and exendin-4-coadministered mice than in mice administered with LPS alone. RANKL and TNF-α mRNA expression levels were lower in the exendin-4- and LPS-coadministered group than in the LPS-administered group. Our in vitro results showed no direct effects of exendin-4 on RANKL-induced osteoclast formation, TNF-α-induced osteoclast formation, or LPS-induced RANKL expression in stromal cells. Conversely, TNF-α mRNA expression was inhibited in the exendin-4- and LPS-cotreated macrophages compared with cells treated with LPS alone. These results indicate that the GLP-1 receptor agonist exendin-4 may inhibit LPS-induced osteoclast formation and bone resorption by inhibiting LPS-induced TNF-α production in macrophages.

Anti-mouse RANKL Antibodies Inhibit Alveolar Bone Destruction in Periodontitis Model Mice.

Denosumab is an anti-bone resorptive drug consisting of complete human monoclonal antibodies that targets receptor activator of nuclear factor κB ligand (RANKL), which is responsible for osteoclast formation. The drug has been adapted for bone diseases, such as osteoporosis and bone metastasis related to cancer, but is not used for alveolar bone destruction related to periodontitis. In the present study, we aimed to clarify whether denosumab prevents bone destruction associated with lipopolysaccharide (LPS)-induced calvaria inflammation and experimental periodontitis in model mice. Denosumab does not bind to mouse RANKL, thus we used anti-mouse monoclonal RANKL antibodies. We also examined the inhibitory effects toward bone destruction of another anti-bone resorptive drug zoledronate, a nitrogen-containing bisphosphonate. Local administration of anti- RANKL antibodies into the calvaria area inhibited LPS-induced osteoclast formation and bone destruction, while zoledronate inhibited bone destruction but not osteoclast formation due to its different action mechanism. In periodontitis model mice, in which the second molars were ligated with a silk suture to induce inflammation, intraperitoneal administration of anti-RANKL antibodies significantly inhibited alveolar bone destruction and tooth root exposure. On the other hand, zoledronate only weakly repressed alveolar bone destruction and failed to inhibit root exposure. These results suggest that denosumab is a promising candidate to prevent alveolar bone destruction associated with periodontitis.

Antimicrobial Peptide Combined with BMP2-Modified Mesenchymal Stem Cells Promotes Calvarial Repair in an Osteolytic Model.

Repair and regeneration of inflammation-induced bone loss remains a clinical challenge. LL37, an antimicrobial peptide, plays critical roles in cell migration, cytokine production, apoptosis, and angiogenesis. Migration of stem cells to the affected site and promotion of vascularization are essential for tissue engineering therapy, including bone regeneration. However, it is largely unknown whether LL37 affects mesenchymal stem cell (MSC) behavior and bone morphogenetic protein 2 (BMP2)-mediated bone repair during the bone pathologic remodeling process. By performing invitro and invivo studies with MSCs and a lipopolysaccharide (LPS)-induced mouse calvarial osteolytic bone defect model, we found that LL37 significantly promotes cell differentiation, migration, and proliferation in both unmodified MSCs and BMP2 gene-modified MSCs. Additionally, LL37 inhibited LPS-induced osteoclast formation and bacterial activity invitro. Furthermore, the combination of LL37 and BMP2 markedly promoted MSC-mediated angiogenesis and bone repair and regeneration in LPS-induced osteolytic defects in mouse calvaria. These findings demonstrate for the first time that LL37 can be a potential candidate drug for promoting osteogenesis and for inhibiting bacterial growth and osteoclastogenesis, and that the combination of BMP2 and LL37 is ideal for MSC-mediated bone regeneration, especially for inflammation-induced bone loss.

Inhibition of lipopolysaccharide-induced osteoclast formation and bone resorption in vitro and in vivo by cysteine proteinase inhibitors.

Inflammation-induced bone destruction is a major treatment target in many inflammatory skeletal diseases. The aim of this study was to investigate if the cysteine proteinase inhibitors cystatin C, fungal cysteine proteinase inhibitor (E-64), and N-benzyloxycarbonyl-arginyl-leucyl-valyl-glycyl-diazomethane acetate (Z-RLVG-CHN2) can inhibit LPS-induced osteoclast formation. Mouse bone marrow macrophages (BMMs) were isolated and primed with receptor activator of NF-κB ligand (RANKL) for 24 h, followed by stimulation with LPS, with and without inhibitors. Adult mice were injected locally with LPS and then treated with E-64 and osteoclast formation assessed by the number of cathepsin K+ multinucleated cells. Cystatin C inhibited LPS-induced osteoclast formation time and concentration dependently (IC50 = 0.3 μM). The effect was associated with decreased mRNA and protein expression of tartrate-resistant acid phosphatase (TRAP) and cathepsin K and of the osteoclastogenic transcription factors c-Fos and NFATc1. LPS-induced osteoclast formation on bone slices was also inhibited by cystatin C, resulting in decreased pit formation and release of bone matrix proteins. Similar data were obtained with E-64 and Z-RLVG-CHN2 Cystatin C was internalized in BMMs stimulated by LPS but not in unstimulated BMMs. Osteoclast formation induced by LPS was dependent on TNF-α, and the 3 inhibitors abolished LPS-induced TNF superfamily 2 (gene encoding TNF-α; Tnfsf2) mRNA expression without affecting Il1b, Il6, or oncostatin M (Osm) expression. Formation of osteoclasts in the skull bones after local LPS stimulation was inhibited by E-64. It is concluded that cysteine proteinase inhibitors effectively inhibit LPS-induced osteoclast formation in vivo and in vitro by inhibition of TNF-α expression. The targeting of cysteine proteinases might represent a novel treatment modality for prevention of inflammatory bone loss.

IL-37 inhibits lipopolysaccharide-induced osteoclast formation and bone resorption in vivo

IL-37 is a newly defined member of the IL-1 cytokine family. It has been reported that IL-37 inhibited innate immunity and inflammatory responses in autoimmune diseases and tumors. IL-37 also inhibited Lipopolysaccharide (LPS)-induced immunological reaction. LPS is a bacterial cell wall component that is capable of inducing osteoclast formation and pathological bone resorption. However, there is no study to investigate the effect of IL-37 on LPS-induced osteoclast formation and bone resorption. The purpose of this study is to investigate the effect of IL-37 in LPS-induced osteoclast formation and bone resorption.LPS was administrated with or without IL-37 by subcutaneous injection on mice calvariae. The number of osteoclasts, the level of tartrate-resistant acid phosphatase (TRAP) and cathepsin K mRNA, the ratio of the bone resorption pits and the level of C-terminal telopeptide fragments of type I collagen cross-Links as a marker of bone resorption in mice administrated both LPS and IL-37 were lower than that in mice administrated LPS alone.Real-time RT-PCR was performed to analyze osteoclast related cytokines RANKL, TNF-α and IL-1β mRNA levels in vivo. RANKL, TNF-α and IL-1β mRNAs were increased in the LPS alone administrated mice as compared with PBS administrated groups. On the other hand, RANKL, TNF-α and IL-1β mRNAs were inhibited in the IL-37 and LPS administrated mice as compared with LPS alone administrated group.In vitro analysis, there was no effect of IL-37 in RANKL-induced osteoclast formation, TNF-α-induced osteoclast formation and cell viability from bone marrow macrophages as osteoclast precursor and LPS-induced RANKL expression from stromal cells.These results indicated that IL-37 inhibited LPS-induced osteoclast formation and bone resorption via inhibition of LPS-induced osteoclast related cytokines, but might not directly inhibit osteoclast formation on osteoclast precursor and RANKL expression on stromal cells.

Sinomenine down-regulates TLR4/TRAF6 expression and attenuates lipopolysaccharide-induced osteoclastogenesis and osteolysis

Sinomenine (SIN) is an anti-inflammatory and anti-arthritic alkaloid derived from Sinomenioum acutum. Effects of SIN on lipopolysaccharide (LPS)-induced osteolysis have not been reported. Here, we found that SIN reduced LPS-induced erosion of skull bones in C57BL/6 mice significantly. LPS can induce bone-absorbing osteoclast formation independent of RANKL in pre-osteoclastic RAW264.7 cells in vitro. Here, SIN suppressed LPS-induced osteoclast formation and osteoclast survival in RAW264.7 cells. Expression of osteoclastic-specific marker genes was also inhibited by SIN during osteoclast differentiation and osteoclast survival stimulated with LPS. SIN showed much stronger inhibitory effects on expression of Fra-1 and MMP-9 mRNA in osteoclast differentiation rather than osteoclast survival. SIN dramatically inhibited LPS-induced TNF-α production in vitro and in vivo. Further signaling studies revealed that SIN suppressed the activation and relative gene expression of three notable nuclear factors (NF-κB, AP-1, NFAT), reduced intracellular levels of Ca2+, and down-regulated phosphorylation of MAPK p38 (but not JNK) in LPS-induced osteoclastogenesis. Focusing on upstream signals after LPS stimulation, SIN decreased expression of TLR4 and TRAF6 during osteoclast differentiation, and reduced expression of TLR4 (but not TRAF6) in osteoclast survival. These data suggest that SIN might be a potential agent for the treatment of osteolysis caused by Gram-negative bacteria infection or inflammation due to its inhibition of osteoclastogenesis through reduction of TLR4/TRAF6 expression and downstream signal transduction.

Puerarin Prevents LPS-Induced Osteoclast Formation and Bone Loss via Inhibition of Akt Activation.

Osteolysis induced by chronic Gram-negative bacterial infection underlies many bone diseases such as osteomyelitis, septic arthritis, and periodontitis. Drugs that inhibit lipopolysaccharide (LPS)-induced osteolysis are critically needed for the prevention of bone destruction in infective bone diseases. In this study, we assessed the effect of puerarin, a natural isoflavone isolated from Pueraria lobata OHWI root, on LPS-induced osteoclastogenesis and bone loss. Our in vitro study showed that puerarin significantly inhibited LPS-induced osteoclast differentiation from osteoclast precursor RAW264.7 cells. The inhibition occurred through suppressing the production of osteoclast activating factor tumor necrosis factor (TNF)-α, interleukin (IL)-1β and prostaglandin E2 (PGE2), which led to down-regulating mRNA expression of osteoclastogenic genes including tartrate-resistant acid phosphatase (TRAP), cathepsin K and matrix metalloprotein 9 (MMP-9). Furthermore, LPS triggered activation of Akt in osteoclast precursor RAW264.7 cells, which was inhibited by puerarin treatment. In vivo, puerarin attenuated LPS-induced bone loss in a murine calvarial osteolysis model. Collectively, puerarin prevents LPS-induced osteoclast formation, function and bone loss, where the inhibition of Akt activation plays an important role. These findings provide evidences that puerarin might be beneficial as a promising candidate drug for the prevention and treatment of bacteria-induced bone destruction disease, and give new insights for understanding its possible mechanism.

Carvacrol Inhibits Osteoclastogenesis and Negatively Regulates the Survival of Mature Osteoclasts.

Bone is a dynamic tissue that undergoes continuous remodeling coupled with the action of osteoblasts and osteoclasts. Osteoclast activity is elevated during osteoporosis and periodontitis resulting in excessive loss of trabecular and alveolar bone. Osteoclasts are formed in an inflammatory response to cytokine production receptor activator of nuclear factor-kappaB (NF-κB) ligand (RANKL) and bacterial challenge lipopolysaccharide (LPS). Carvacrol, a monoterpenic phenol present in Origanum vulgare and Thymus vulgaris, is a natural compound with known medicinal properties. We investigated the effects of carvacrol on osteoclast formation induced by RANKL and LPS. Carvacrol suppressed RANKL-induced formation of tartrate resistant acid phosphatase (TRAP)-positive multinucleated cells in RAW264.7 macrophages and human CD14(+) monocytes. Furthermore, carvacrol inhibited LPS-induced osteoclast formation in RAW264.7 macrophages. Investigation of the underlying molecular mechanisms revealed that carvacrol downregulated RANKL-induced NF-κB activation in a dose-dependent manner. Furthermore, the suppression of NF-κB activation correlated with inhibition of inhibitor of kappaB (IκB) kinase (IKK) activation and attenuation of inhibitor of NF-κB (IκBa) degradation. Carvacrol potentiated apoptosis in mature osteoclasts by caspase-3 activation and DNA fragmentation. Moreover, carvacrol did not affect the viability of proliferating MC3T3-E1 osteoblast-like cells. Collectively, these results demonstrate that carvacrol mitigates osteoclastogenesis by impairing the NF-κB pathway and induction of apoptosis in mature osteoclasts.

Peroxiredoxin II negatively regulates lipopolysaccharide-induced osteoclast formation and bone loss via JNK and STAT3.

Lipopolysaccharide (LPS) is considered a prominent pathogenic factor in inflammatory bone diseases. LPS challenge contributes to the production of reactive oxygen species (ROS) in diverse inflammatory diseases. However, its mechanism remains to be clarified in bone. Thus, we investigated the critical mechanism of ROS in LPS-induced osteoclastogenesis and bone loss. Antioxidant prevented LPS-induced osteoclast formation via inhibition of nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) and c-Fos expression in preosteoclasts. Moreover, LPS-induced osteoclast formation via ROS was attenuated by treatment with c-Jun N-terminal protein kinase (JNK) inhibitor. Interestingly, LPS also activated signal transducer and activator of transcription 3 (STAT3), which is suppressed by antioxidants. We found that knockdown of STAT3 or use of a STAT3 inhibitor resulted in a significant reduction in interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and nitric oxide (NO) production, followed by decreased osteoclast formation by LPS. Peroxiredoxin II (PrxII) is a member of the antioxidant enzyme family, and it plays a protective role against oxidative damage caused by ROS. In our study, ROS production and osteoclast formation by LPS was significantly enhanced in PrxII(-/-) cells. Moreover, JNK-mediated c-Fos and NFATc1 expression was promoted in PrxII(-/-) cells. Furthermore, STAT3 activation and accompanying IL-1β, IL-6, and NO production was also increased in PrxII(-/-) cells. Consistent with the in vitro result, PrxII-deficient mice showed increased osteoclast formation and bone loss by LPS challenge compared with wild-type mice. For the first time, we showed that LPS-induced ROS signaling is dependent on the coordinated mechanism of JNK and STAT3 during osteoclastogenesis, which is negatively regulated by PrxII. We suggest that PrxII could be useful in the development of a novel target for inflammatory bone loss.