Therapeutic targeting of osteoclast function and pathways

Oroxylin A suppresses breast cancer-induced osteoclastogenesis and osteolysis as a natural RON inhibitor

BACKGROUND

Malignant breast cancer cells trigger the over-activation of osteoclast precursor cells, leading to bone loss and severe pain. Targeted inhibition of osteoclast differentiation has emerged as an important strategy for treating bone syndromes induced by breast cancer.

PURPOSE

The objective is to discover natural osteoclast inhibitor to treat osteoclastogenesis and bone destruction induced by breast cancer, and clarify the specific mechanisms.

METHODS

Recepteur d'origine Nantais (RON) protein was employed to search the natural osteoclast inhibitor for breast cancer-induced osteoclastogenesis by molecular docking, molecular dynamics simulation and cellular thermal shift assay (CETSA). In the in vitro experiment, breast cancer MDA-MB-231 cell-conditioned medium (MDA-MB-231 CM) was used to induce osteoclastogenesis in murine bone marrow-derived macrophages (BMMs), aiming to elucidate the effects and mechanisms of the natural osteoclast inhibitor. In the in vivo model, MDA-MB-231 cells was injected into the mouse tibia to evaluate the therapeutic effect of drug on breast cancer-induced bone destruction.

RESULTS

We discovered a significant increase in the expression of RON during MDA-MB-231 CM-induced osteoclast differentiation in vitro. Molecular docking analysis found that oroxylin A (OA), a flavonoid derived from the Chinese medicine Scutellaria baicalensis Georgi, showed binding ability with RON, while its impact and mechanism on breast cancer-induced osteoclastogenesis and osteolysis remains unclear. Molecular dynamics simulation and CETSA further revealed that OA bound directly to the RON protein, and it also decreased RON expression in breast cancer CM-induced osteoclastogenesis. Correspondingly, OA suppressed the MDA-MB-231 CM-induced osteoclastogenesis and bone resorption in vitro. The downstream signals of RON including Src and NFATc1, as well as the osteoclast-specific genes, were downregulated by OA. Of interesting, the suppressive effect of OA on osteoclastogenesis induced by MDA-MB-231 CM was abolished after RON was knocked down by the specific RON-siRNA, this further confirmed that OA showed inhibitory effects on osteoclasts through targeting RON. In addition, we found that OA attenuated MDA-MB-231 cell-induced osteolysis and reduced the number of osteoclasts in vivo.

CONCLUSION

Our results indicate that OA acts as a natural RON inhibitor to suppress breast cancer-induced osteoclastogenesis and osteolysis. This provides new strategy for treating breast cancer-induced bone destruction and related syndromes.

Targeting Sclerostin and Dkk1 at Optimized Proportions of Low-Dose Antibody Achieves Similar Skeletal Benefits to Higher-Dose Sclerostin Targeting in the Mature Adult and Aged Skeleton

Age-associated low bone mass disease is a growing problem in the US. Development of osteoanabolic therapies for treating skeletal fragility has lagged behind anti-catabolic therapies, but several bone-building molecules are clinically available. We reported previously that antibody-based neutralization of the Lrp5/Lrp6 inhibitor Dkk1 has minimal effects on bone gain, but can potentiate the already potent osteoanabolic effects of sclerostin inhibition (another Lrp5/Lrp6 inhibitor highly expressed by osteocytes). In this communication, we test whether an optimized ratio of sclerostin and Dkk1 antibodies (Scl-mAb and Dkk1-mAb, respectively), administered at low doses, can maintain the same bone-building effects as higher dose Scl-mAb, in adult (6 months of age) and aged (20 months of age) wild-type mice. A 3:1 dose of Scl-mAb:Dkk1-mAb at 12.5 mg/kg was equally efficacious as 25 mg/kg of Scl-mAb in both age groups, using radiographic (DXA, µCT), biomechanical, (3-point bending tests), and histological (fluorochrome-based bone formation parameters) outcome measures. For some bone properties, including trabecular thickness and bone mineral density in the spine, and endocortical bone formation rates in the femur, the 3:1 treatment was associated with significantly improved skeletal properties compared to twice the dose of Scl-mAb. Cortical porosity in aged mice was also reduced by both Scl-mAb and low-dose 3:1 treatment. Overall, both treatments were efficacious in the mature adult (6 mo.) and aged (20 mo.) skeletons, suggesting Wnt targeting is a viable strategy for improving skeletal fragility in the very old. Further, the data suggest that low dose of combination therapy can be at least equally efficacious as higher doses of Scl-mAb monotherapy.

A Vitronectin-Derived Peptide Restores Ovariectomy-Induced Bone Loss by Dual Regulation of Bone Remodeling

BACKGROUND

Bone remodeling is tightly regulated through bone resorption and bone formation; imbalances in bone remodeling can cause various pathological conditions such as osteoporosis. Antiresorptive agents commonly used for treating osteoporosis do not substantially reverse osteoporotic bone loss.

METHODS

We evaluated the effects of the RVYFFKGKQYWE motif (residues 270-281; VnP-16) of human vitronectin on the osteogenic differentiation of human mesenchymal stem cells (hMSCs) and osteoclastogenesis of bone marrow-derived macrophages. The effects of VnP-16 were also assessed in a mouse model of estrogen deficiency-induced osteoporosis (ovariectomized female C57BL/6 mice). To assay whether VnP-16 can reverse ovariectomy-induced bone loss, synthetic peptides or vehicle were subcutaneously injected into ovariectomized mice once a week for 4 weeks (n = 10/group). To evaluate the bone restorative effects of VnP-16, in-vivo micro-computed tomography analysis and histological staining were performed.

RESULTS

VnP-16 induced osteogenic differentiation of hMSCs and inhibited the RANKL-RANK-TRAF6 axis in the osteoclastogenesis signaling pathway. Furthermore, systemic administration of VnP-16 reversed ovariectomy-induced bone loss in the femoral neck, distal femur and lumbar spine by increasing osteoblast differentiation and promoting bone formation, and concomitantly decreasing osteoclastogenesis and inhibiting bone resorption. The bone restorative effect of VnP-16 was observed one week after subcutaneous administration, and although the timing of the effect differed according to bone location, it persisted for at least 3 weeks.

CONCLUSION

Our findings suggest that VnP-16 is a potential therapeutic agent for treating osteoporosis that mediates its effects through dual regulation of bone remodeling.

A Nitrobenzoyl Sesquiterpenoid Insulicolide A Prevents Osteoclast Formation via Suppressing c-Fos-NFATc1 Signaling Pathway

It is a viable strategy to inhibit osteoclast differentiation for the treatment of osteolytic diseases such as osteoporosis, rheumatoid arthritis and tumor bone metastases. Here we assessed the effects of insulicolide A, a natural nitrobenzoyl sesquiterpenoid derived from marine fungus, on receptor activator of nuclear factor-κB ligand (RANKL)-stimulated osteoclastogenesis in vitro and its protective effects on LPS-induced osteolysis mice model in vivo. The results demonstrated that insulicolide A inhibited osteoclastogenesis from 1 μM in vitro. Insulicolide A could prevent c-Fos and nuclear factor of activated T-cell cytoplasmic 1 (NFATc1) nuclear translocation and attenuate the expression levels of osteoclast-related genes and DC-STAMP during RANKL-stimulated osteoclastogenesis but have no effects on NF-κB and MAPKs. Insulicolide A can also protect the mice from LPS-induced osteolysis. Our research provides the first evidence that insulicolide A may inhibit osteoclastogenesis both in vitro and in vivo, and indicates that it may have potential for the treatment of osteoclast-related diseases.

Interferon-induced protein with tetratricopeptide repeats 1 (IFIT1) accelerates osteoclast formation by regulating signal transducer and activator of transcription 3 (STAT3) signalling

Osteoclasts (OCs), the main cause of bone resorption irregularities, may ultimately cause various bone diseases, including osteoarthritis. The objective of this study was to investigate the effect of interferon-induced protein with tetratricopeptide repeats 1 (IFIT1) on OC formation induced by receptor activator of nuclear factor κB (NF-κB) ligand (RANKL) and to further explore its underlying mechanism. IFIT1 expression in Raw264.7 cells treated with macrophage colony-stimulating factor (M-CSF) and RANKL was determined by qRT-PCR. OC formation was detected using tartrate-resistant acid phosphatase (TRAP) staining. The effect of IFIT1 on STAT3 activation was detected using Western blotting. Additionally, Western blotting was used to measure the change in the expression of OC-specific proteins. IFIT1 was highly expressed in Raw264.7 cells after stimulation with M-CSF and RANKL. IFIT1 overexpression accelerated the formation of OCs, as evidenced by the increased number and size of multinuclear cells, and the upregulation of OC-specific proteins, and activated the STAT3 pathway, by inducing phosphorylation of JAK1 and STAT3. However, silencing of IFIT1 inhibited the formation of OCs and a STAT3 inhibitor Stattic weakened the effects of IFIT1. In conclusion, IFIT1 accelerates the formation of OCs, which is caused by RANKL by STAT3 pathway regulation. This study provides a potential basis for further research and for development of drugs for treating bone resorption-related diseases.

Benefits and mechanisms of polysaccharides from Chinese medicinal herbs for anti-osteoporosis therapy: A review

Osteoporosis is a systemic metabolic bone disease with an increasing incidence rate. Chinese medicinal herbs have a long history of treating bone diseases. Polysaccharides are an important category of phytochemicals in Chinese medicinal herbs, and their health benefits have increased the interest of the public. Numerous studies have indicated that polysaccharides exhibit anti-osteoporosis effects by balancing bone resorption and bone formation, but the detailed effects and mechanism have not been systematically summarized. We performed a comprehensive review of the literature to consolidate studies for the period 2000-2021 by conducting electronic searches on the PubMed, CNKI, VIP, and Wanfang databases. In total, polysaccharides from 19 kinds of Chinese medicinal herbs in 54 studies have shown bone homeostasis protective properties. In vivo and in vitro experiments have demonstrated that polysaccharides present properties in the treatment of postmenopausal osteoporosis, senile osteoporosis, and glucocorticoid-induced secondary osteoporosis, especially postmenopausal osteoporosis. Moreover, a number of signalling pathways, such as the Wnt/β-catenin signalling pathway, BMP/SMAD/RUNX2 signalling pathway, OPG/RANKL/RANK signalling pathway, apoptosis pathway, and transcription factors, are regulated by polysaccharides and participate in improving bone homeostasis. This review will provide a better understanding of the anti-osteoporotic effects of polysaccharides and the concomitant modulations of signalling pathways.

Kirenol inhibits RANKL-induced osteoclastogenesis and prevents ovariectomized-induced osteoporosis via suppressing the Ca2+-NFATc1 and Cav-1 signaling pathways

BACKGROUND

Osteoporosis is a threat to aged people who have excessive osteoclast activation and bone resorption, subsequently causing fracture and even disability. Inhibiting osteoclast differentiation and absorptive functions has become an efficient approach to treat osteoporosis, but osteoclast-targeting inhibitors available clinically remain rare. Kirenol (Kir), a bioactive diterpenoid derived from an antirheumatic Chinese herbal medicine Herba Siegesbeckiae, can treat collagen-induced arthritis in vivo and promote osteoblast differentiation in vitro, while the effects of Kir on osteoclasts are still unclear.

PURPOSE

We explore the role of Kir on RANKL-induced osteoclastogenesis in vitro and bone loss in vivo.

METHODS

The in vitro effects of Kir on osteoclast differentiation, bone resorption and the underlying mechanisms were evaluated with bone marrow-derived macrophages (BMMs). In vivo experiments were performed using an ovariectomy (OVX)-induced osteoporosis model.

RESULTS

We found that Kir remarkably inhibited osteoclast generation and bone resorption in vitro. Mechanistically, Kir significantly inhibited F-actinring formation and repressed RANKL-induced NF-κB p65 activation and p-p38, p-ERK and c-Fos expression. Moreover, Kir inhibited both the expression and nuclear translocation of NFATc1. Ca2+ oscillation and caveolin-1 (Cav-1) were also reduced by Kir during osteoclastogenesis in vitro. Consistent with these findings, 2-10 mg/kg Kir attenuated OVX-induced osteoporosis in vivo as evidenced by decreased osteoclast numbers and downregulated Cav-1 and NFATc1 expression.

CONCLUSIONS

Kir suppresses osteoclastogenesis and the Cav-1/NFATc1 signaling pathway both in vitro and in vivo and protects against OVX-induced osteoporosis. Our findings reveal Kir as a potential safe oral treatment for osteoporosis.

Linarin and its aglycone acacetin abrogate actin ring formation and focal contact to bone matrix of bone-resorbing osteoclasts through inhibition of αvβ3 integrin and core-linked CD44

BACKGROUND

Since enhanced bone resorption due to osteoclast differentiation and activation cause skeletal diseases, there is a growing need in therapeutics for combating bone-resorbing osteoclasts. Botanical antioxidants are being increasingly investigated for their health-promoting effects on bone. Edible Cirsium setidens contains various polyphenols of linarin, pectolinarin, and apigenin with antioxidant and hepatoprotective effects.

PURPOSE

This study aimed to determine whether linarin present in Cirsium setidens water extracts (CSE) and its aglycone acacetin inhibited osteoclastogenesis of RANKL-exposed RAW 264.7 murine macrophages for 5 days.

METHODS

This study assessed the osteoprotective effects of CSE, linarin and acacetin on RANKL-induced differentiation and activation of osteoclasts by using MTT assay, TRAP staining, Western blot analysis, bone resorption assay actin ring staining, adhesion assay and immunocytochemical assay. This study explored the underlying mechanisms of their osteoprotection, and identified major components present in CSE by HPLC analysis.

RESULTS

Linarin and pectolinarin were identified as major components of CSE. Nontoxic linarin and acacetin as well as CSE, but not pectolinarin attenuated the RANKL-induced macrophage differentiation into multinucleated osteoclasts, and curtailed osteoclastic bone resorption through reducing lacunar acidification and bone matrix degradation in the osteoclast-bone interface. Linarin and acacetin in CSE reduced the transmigration and focal contact of osteoclasts to bone matrix-mimicking RGD peptide. Such reduction was accomplished by inhibiting the induction of integrins, integrin-associated proteins of paxillin and gelsolin, cdc42 and CD44 involved in the formation of actin rings. The inhibition of integrin-mediated actin ring formation by linarin and acacetin entailed the disruption of TRAF6-c-Src-PI3K signaling of bone-resorbing osteoclasts. The functional inhibition of c-Src was involved in the loss of F-actin-enriched podosome core protein cortactin-mediated actin assembly due to linarin and acacetin.

CONCLUSION

These observations demonstrate that CSE, linarin and acacetin were effective in retarding osteoclast function of focal adhesion to bone matrix and active bone resorption via inhibition of diffuse cloud-associated αvβ3 integrin and core-linked CD44.

A marine fungus-derived nitrobenzoyl sesquiterpenoid suppresses receptor activator of NF-κB ligand-induced osteoclastogenesis and inflammatory bone destruction

BACKGROUND AND PURPOSE

Osteoclasts are unique cells to absorb bone. Targeting osteoclast differentiation is a therapeutic strategy for osteolytic diseases. Natural marine products have already become important sources of new drugs. The naturally occurring nitrobenzoyl sesquiterpenoids first identified from marine fungi in 1998 are bioactive compounds with a special structure, but their pharmacological functions are largely unknown. Here, we investigated six marine fungus-derived nitrobenzoyl sesquiterpenoids on osteoclastogenesis and elucidated the mechanisms.

EXPERIMENTAL APPROACH

Compounds were first tested by RANKL-induced NF-κB luciferase activity and osteoclastic TRAP assay, followed by molecular docking to characterize the structure-activity relationship. The effects and mechanisms of the most potent nitrobenzoyl sesquiterpenoid on RANKL-induced osteoclastogenesis and bone resorption were further evaluated in vitro. Micro-CT and histology analysis were used to assess the prevention of bone destruction by nitrobenzoyl sesquiterpenoids in vivo.

KEY RESULTS

Nitrobenzoyl sesquiterpenoid 4, with a nitrobenzoyl moiety at C-14 and a hydroxyl group at C-9, was the most active compound on NF-κB activity and osteoclastogenesis. Consequently, nitrobenzoyl sesquiterpenoid 4 exhibited suppression of RANKL-induced osteoclastogenesis and bone resorption from 0.5 μM. It blocked RANKL-induced IκBa phosphorylation, NF-κB p65 and RelB nuclear translocation, NFATc1 activation, reduced DC-STAMP but not c-Fos expression during osteoclastogenesis in vitro. Nitrobenzoyl sesquiterpenoid 4 also ameliorated LPS-induced osteolysis in vivo.

CONCLUSION AND IMPLICATIONS

These results highlighted nitrobenzoyl sesquiterpenoid 4 as a novel inhibitor of osteoclast differentiation. This marine-derived sesquiterpenoid is a promising lead compound for the treatment of osteolytic diseases.

Pharmacological evaluation of imidazole-derived bisphosphonates on receptor activator of nuclear factor-κB ligand-induced osteoclast differentiation and function

Bisphosphonates (BPs) have been commonly used in the treatment of osteolytic bone lesions, such as osteoporosis and osteogenesis imperfecta. However, serious side-effects can occur during the therapy. To search for novel potent BPs with lower side-effects, a series of imidazole-containing BPs (zoledronic acid [ZOL]; ZOL derivatives by substitution of the hydrogen at the 2-position on the imidazole ring with a methyl [MIDP], ethyl [EIDP], n-propyl [PIDP], or n-butyl group [BIDP]) were developed and the effects on receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation were investigated using the murine macrophage RAW 264.7 cells at the protein, gene, and morphological and functional levels. Influences of these BPs on the cell growth and proliferation of RAW 264.7 were also studied in order to determine cytotoxicity. The results showed that PIDP significantly inhibited the RANKL-induced osteoclast formation in a dose-dependent fashion without inducing cytotoxicity under the concentration of 12.5 μM. It exerted remarkable suppressive effects on the development of actin rings, the bone resorption, and the expressions of osteoclastogenesis-related gene and protein markers. The down-regulation of c-Jun N-terminal kinase (JNK), protein kinase B (Akt), and inhibitor of nuclear factor kappa-B (IκB) phosphorylation in the early signaling event and subsequent inhibition of the expression of c-Fos and nuclear factor of activated T cells (NFATc1) might be involved in these effects. All these results indicated that PIDP might be a promising drug to treat bone-related disorders.

Osthole inhibits osteoclasts formation and bone resorption by regulating NF-κB signaling and NFATc1 activations stimulated by RANKL

Chinese herbal medicine Fructus Cnidii has an outstanding effect on chronic lumbar pain and impotence, also has been used against osteoporosis with high frequency. Yet, the mechanisms of osthole, a derivative of Fructus Cnidii, on osteoclasts remains barely known. In this study, it was found out that osthole (10^-6 mol/L, 10^-5 mol/L) had the influence of inhibiting osteoclast formation and bone resorptive activities induced by receptor activator of nuclear factor κB ligand (RANKL), rather than affecting the viability of osteoclast-like cells. Furthermore, osthole could also inhibit the messenger RNA expressions of c-Src, tartrate-resistant acid phosphatase, β3-Integrin, matrix metallopeptidase 9, and cathepsin K. The results of the mechanistic study indicated that osthole regulated the nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) and nuclear factor-κB (NF-κB) activations following the RANKL stimulation. These findings suggested that the inhibitory effects of osthole were associated with restraining the activations of NFATc1 and NF-κB induced by RANKL. Thus osthole can be used as a potential treatment for abnormal bone-resorption related diseases.

A study on the prevention and treatment of murine calvarial inflammatory osteolysis induced by ultra-high-molecular-weight polyethylene particles with neomangiferin

The present study aimed to examine the influence of neomangiferin on murine calvarial inflammatory osteolysis induced by ultra-high-molecular-weight polyethylene (UHMWPE) particles. Eight-week-old male C57BL/J6 mice served as an inflammatory osteolysis model, in which UHMWPE particles were implanted into the calvarial subperiosteal space. The mice were randomly distributed into four groups and treated with different interventions; namely, a sham group [phosphate-buffered saline (PBS) injection and no UHMWPE particles], model group (PBS injection and implantation of UHMWPE particles), low-dose neomangiferin group (UHMWPE particles +2.5 mg/kg neomangiferin), and high-dose neomangiferin group (UHMWPE particles +5 mg/kg neomangiferin). Following 3 weeks of feeding according to the above regimens, celiac artery blood samples were collected for an enzyme-linked immunosorbent assay (ELISA) to determine the expression of receptor activator of nuclear factor-κB ligand (RANKL), osteoclast-related receptor (OSCAR), cross-linked C-telopeptide of type I collagen (CTX-1); osteoprotegerin (OPG), tumor necrosis factor (TNF)-α, and interleukin (IL)-1β. Subsequently, the mice were sacrificed by cervical dislocation following ether-inhalation anesthesia, and the skull was separated for osteolysis analysis by micro-computed tomography (micro-CT). Following hematoxylin and eosin staining, tartrate-resistant acid phosphatase (TRAP) staining was performed to observe the dissolution and destruction of the skull. The micro-CT results suggested that neomangiferin significantly inhibited the murine calvarial osteolysis and bone resorption induced by UHMWPE particles. In addition, the ELISA results showed that neomangiferin decreased the expression levels of osteoclast markers RANKL, OSCAR, CTX-1, TNF-α and IL-1β. By contrast, the levels of OPG increased with the neomangiferin dose. Histopathological examination revealed that the TRAP-positive cell count was significantly reduced in the neomangiferin-treated animals compared with that in the positive control group, and the degree of bone resorption was also markedly reduced. Neomangiferin was found to have significant anti-inflammatory effects and to inhibit osteoclastogenesis. Therefore, it has the potential to prevent the aseptic loosening of a prosthesis following artificial joint replacement.

Identification of N-(5-(phenoxymethyl)-1,3,4-thiadiazol-2-yl)acetamide derivatives as novel protein tyrosine phosphatase epsilon inhibitors exhibiting anti-osteoclastic activity

Cytosolic protein tyrosine phosphatase epsilon (cyt-PTPε) plays a central role in controlling differentiation and function of osteoclasts, whose overactivation causes osteoporosis. Based on our previous study reporting a number of cyt-PTPε inhibitory chemical compounds, we carried out a further and extended analysis of our compounds to examine their effects on cyt-PTPε-mediated dephosphorylation and on osteoclast organization and differentiation. Among five compounds showing target selectivity to cyt-PTPε over three other phosphatases in vitro, two compounds exhibited an inhibitory effect against the dephosphorylation of cellular Src protein, the cyt-PTPε substrate. Moreover, these two compounds caused destabilization of the podosome structure that is necessary for the bone-resorbing activity of osteoclasts, and also attenuated cellular differentiation of monocytes into osteoclasts, without affecting cell viability. Therefore, these findings not only verified anti-osteoclastic effects of our cyt-PTPε inhibitory compounds, but also showed that cyt-PTPε expressed in osteoclasts could be a putative therapeutic target worth considering.

T63 inhibits osteoclast differentiation through regulating MAPKs and Akt signaling pathways

Inhibition of excessive osteoclast differentiation and activity is a valid approach for the treatment of osteoporosis. T63 is a small-molecule compound identified from a high throughput screening based on RUNX2 transcriptional activity, and has been reported to stimulate osteoblast formation. However, whether the compound has any effect on osteoclast differentiation remains unknown. Here, we examined the in vitro effect of T63 on osteoclastogenesis. T63 was found to inhibit the number of TRAP-positive cells in an osteoblast-osteoclast co-culture system, and inhibited Rankl expression in the preosteoblast MC3T3-E1 cells. The compound also directly suppressed RANKL-induced osteoclast differentiation in both dose- and time-dependent manner, as evidenced by the decrease of TRAP activity, F-actin formation and osteoclastogenesis-related genes expression in RAW264.7 cells. Moreover, pretreatment with T63 markedly decreased the activation of mitogen-activated protein kinases and Akt, both of which are positively involved in the regulation of osteoclastogenesis. Collectively, our findings suggest T63 has a protective effect against bone loss by inhibiting bone resorption. Its regulatory effect on bone metabolism makes the compound a more promising candidate for the potential application in the treatment of osteoporosis.

A vitronectin-derived peptide reverses ovariectomy-induced bone loss via regulation of osteoblast and osteoclast differentiation

Osteoporosis affects millions of people worldwide by promoting bone resorption and impairing bone formation. Bisphosphonates, commonly used agents to treat osteoporosis, cannot reverse the substantial bone loss that has already occurred by the time of diagnosis. Moreover, their undesirable side-effects, including osteonecrosis of the jaw, have been reported. Here, we demonstrated that a new bioactive core vitronectin-derived peptide (VnP-16) promoted bone formation by accelerating osteoblast differentiation and activity through direct interaction with β1 integrin followed by FAK activation. Concomitantly, VnP-16 inhibited bone resorption by restraining JNK-c-Fos-NFATc1-induced osteoclast differentiation and αvβ3 integrin-c-Src-PYK2-mediated resorptive function. Moreover, VnP-16 decreased the bone resorbing activity of pre-existing mature osteoclasts without changing their survival rate. Furthermore, VnP-16 had a strong anabolic effect on bone regeneration by stimulating osteoblast differentiation and increasing osteoblast number, and significantly alleviated proinflammatory cytokine-induced bone resorption by restraining osteoclast differentiation and function in murine models. Moreover, VnP-16 could reverse ovariectomy-induced bone loss by both inhibiting bone resorption and promoting bone formation. Given its dual role in promoting bone formation and inhibiting bone resorption, our results suggest that VnP-16 could be an attractive therapeutic agent for treating osteoporosis.

The protective effect of berberine hydrochloride on LPS‑induced osteoclastogenesis through inhibiting TRAF6‑Ca2+‑calcineurin‑NFATcl signaling pathway

The present study investigated the protective effect of berberine hydrochloride on lipopolysaccharide (LPS) ‑induced acute bone destruction through inhibition of the TNF receptor associated factor 6 (TRAF6)‑Ca2+‑calcineurin‑nuclear factor of activated T‑cell 1 (NFATc1) signaling pathway. An osteoclast culture system of RAW264.7 cells induced by LPS in vitro was established. A polymerase chain reaction (PCR) assay was applied to determine the effect of berberine hydrochloride on the mRNA expression levels of fos‑related antigen 2 (Fra‑2), tartrate‑resistant acid phosphatase (TRAP), β3‑integrin, cathepsin K, dendritic cell‑specific transmembrane protein (DC‑STAMP), V‑type proton ATPase subunit d 2 (Atp6v0d2) and NFATcl. An ELISA assay was performed to measure the release of tumor necrosis factor‑α (TNF‑α). Western blot analysis was used to measure the effect of berberine hydrochloride on the expression of calcineurin in the LPS‑induced NFATc1 signaling pathway, as well as the expression levels of phosphoinositide phospholipase C‑γl (PLC‑γ1), toll like receptor 4 (TLR4) and TRAF6. The effect of berberine hydrochloride on Ca2+ concentration was detected using a confocal technique with a Flou‑3/acetoxymethyl ester Ca2+ probe. The PCR results demonstrated that berberine hydrochloride inhibited the mRNA expression levels of Fra‑2, TRAP, β3‑integrin, cathepsin K, DC‑STAMP, Atp6v0d2 and NFATc1. Furthermore, the ELISA results demonstrated that TNF‑α expression was decreased. The western blot analysis revelead that berberine hydrochloride treatment results in decreased expression levels of PLC‑γ1, TLR4 and TRAF6, and inhibition of Ca2+ influx. In conclusion, the results of the present study suggest that berberine hydrochloride targets TRAF6 and NFATc1, thus inhibiting osteoclastogenesis and bone destruction via inhibition of the TRAF6‑Ca2+‑calcineurin‑NFATcl signaling pathway.

Ferulic acid impairs osteoclast fusion and exacerbates survival of mature osteoclasts

Elevated bone loss induced by osteoclasts is a critical and most commonly observed pathological complication during osteolytic diseases such as osteoporosis. Hence, attenuation of osteoclast formation or function is a classical therapeutic approach to regulate bone loss. In this study, we found that ferulic acid (FA), a natural compound potently inhibited osteoclast formation in human CD14+ peripheral blood monocytes ex vivo with an IC50 of 39 µM. Moreover, due to impaired differentiation of osteoclast progenitors, actin ring formation and bone resorption activity were also perturbed. Investigation of underlying molecular mechanisms revealed that FA inhibited the RANKL-induced expression of dendritic cell-specific transmembrane protein (DC-STAMP), a critical regulator of osteoclast fusion. In addition, expression of matrix metalloproteinase-9 (MMP-9) and cathepsin K, the key osteoclast specific lysosomal proteases involved in bone matrix resorption were severely aggravated by FA. A significant reduction in mature osteoclast numbers was detected in the presence of FA accompanied by increased caspase-3 activity and DNA-fragmentation, a characteristic hallmark of apoptosis. Collectively, these results suggested that FA inhibited osteoclast fusion by suppressing the expression of DC-STAMP and induced apoptosis in mature osteoclasts by the caspase-3 pathway.

A novel pyrazole derivative protects from ovariectomy-induced osteoporosis through the inhibition of NADPH oxidase

Osteoclast cells (OCs) are differentiated from bone marrow-derived macrophages (BMMs) by activation of receptor activator of nuclear factor κB (NF-κB) ligand (RANKL). Activation of NADPH oxidase (Nox) isozymes is involved in RANKL-dependent OC differentiation, implicating Nox isozymes as therapeutic targets for treatment of osteoporosis. Here, we show that a novel pyrazole derivative, Ewha-18278 has high inhibitory potency on Nox isozymes. Blocking the activity of Nox with Ewha-18278 inhibited the responses of BMMs to RANKL, including reactive oxygen species (ROS) generation, activation of mitogen-activated protein (MAP) kinases and NF-κB, and OC differentiation. To evaluate the anti-osteoporotic function of Ewha-18278, the derivative was applied to estrogen-deficient ovariectomized (OVX) ddY mice. Oral administration of Ewha-18278 (10 mg/kg/daily, 4 weeks) into the mice recovered bone mineral density, trabecular bone volume, trabecular bone length, number and thickness, compared to control OVX ddY mice. Moreover, treatment of OVX ddY mice with Ewha-18278 increased bone strength by increasing cortical bone thickness. We provide that Ewha-18278 displayed Nox inhibition and blocked the RANKL-dependent cell signaling cascade leading to reduced differentiation of OCs. Our results implicate Ewha-18278 as a novel therapeutic agent for the treatment of osteoporosis.

Aconine inhibits RANKL-induced osteoclast differentiation in RAW264.7 cells by suppressing NF-κB and NFATc1 activation and DC-STAMP expression

AIM

Aconiti Lateralis Radix Preparata is a traditional Chinese medicine used to treat chronic arthritis and is highly effective against rheumatoid arthritis. However, the effects of aconine, a derivative of aconitum alkaloids, on osteoclasts, which can absorb bone, remain unknown. Here, we investigated the effects of aconine on osteoclast differentiation and bone resorption in vitro.

METHODS

The viability of mouse leukemic monocyte/macrophage cell line RAW264.7 was measured using CCK-8 assays. Osteoclast differentiation was induced by incubation of RAW264.7 cells in the presence of RANKL, and assessed with TRAP staining assay. Bone resorption was examined with bone resorption pits assay. The expression of relevant genes and proteins was analyzed using RT-PCR and Western blots. The activation of NF-κB and nuclear factor of activated T-cells (NFAT) was examined using stable NF-κB and NFATc1 luciferase reporter gene systems, RT-PCR and Western blot analysis.

RESULTS

Aconine (0.125, 0.25 μmol/L) did not affect the viability of RAW264.7 cells, but dose-dependently inhibited RANKL-induced osteoclast formation and bone resorptive activity. Furthermore, aconine dose-dependently inhibited the RANKL-induced activation of NF-κB and NFATc1 in RAW264.7 cells, and subsequently reduced the expression of osteoclast-specific genes (c-Src, β3-Integrin, cathepsin K and MMP-9) and the expression of dendritic cell-specific transmembrane protein (DC-STAMP), which played an important role in cell-cell fusion.

CONCLUSION

These findings suggest that aconine inhibits RANKL-induced osteoclast differentiation in RAW264.7 cells by suppressing the activation of NF-κB and NFATc1 and the expression of the cell-cell fusion molecule DC-STAMP.

Total Saponin from Anemone flaccida Fr. Schmidt Prevents Bone Destruction in Experimental Rheumatoid Arthritis via Inhibiting Osteoclastogenesis

Anemone flaccida Fr. Schmidt is used in the clinical compound prescription for the treatment of rheumatoid arthritis (RA) in China and has the traditional use of draining dampness, diminishing swelling, and relieving pain. Total saponins (TS) are the characteristic components and also the main active ingredients of A. flaccida. Previous reports indicated that TS possess anti-inflammatory and immunoregulatory properties; however, the effects of TS on bone destruction of RA have not been evaluated. In this study, our data first showed the therapeutic effects of TS on severity of arthritis and arthritis progression in collagen-induced arthritis (CIA) rats. Then, by microfocal computed tomography (CT) quantification, TS significantly increased bone mineral density, bone volume fraction, and trabecular thickness and decreased trabecular separation of inflamed joints both at peri-articular and extra-articular locations. TS also diminished the level of the bone resorption marker CTX-I and simultaneously increased the bone formation marker osteocalcin in sera of CIA rats. Interestingly, TS prevented bone destruction by reducing the number of osteoclasts in inflamed joints, reducing the expression of receptor activator of nuclear factor-κF (RANK) ligand (RANKL) and RANK, increasing the expression of osteoprotegerin (OPG), at both mRNA and protein levels, and decreasing the ratio of RANKL to OPG in inflamed joints and sera of CIA rats. This was further confirmed in the co-culture system of human fibroblast-like synovial and peripheral blood mononuclear cells. In addition, TS inhibited the levels of pro-inflammatory cytokines implicated in bone resorption, such as interleukin-1β (IL-1β), tumor necrosis factor-α (TNFα), IL-6, IL-17, and IL-23 in sera and joints. These findings offer convincing evidence that TS attenuate RA partially by preventing both focal bone destruction and systemic bone loss. This anti-erosive effect results in part from inhibiting osteoclastogenesis by regulating the RANKL/RANK/OPG signaling pathway. The suppression of systemic and local pro-osteoclastogenic cytokines by TS was also highly effective.

Total saponin from Anemone flaccida Fr. Schmidt abrogates osteoclast differentiation and bone resorption via the inhibition of RANKL-induced NF-κB, JNK and p38 MAPKs activation

Osteoclasts, bone-specialized multinucleated cells, are responsible for bone destructive diseases such as rheumatoid arthritis and osteoporosis. Natural plant-derived products have received substantial attention given their potential therapeutic and preventive activities against bone destructive diseases. In the present study, we investigated the effects of total saponin (TS) from Anemone flaccida Fr. Schmidt, on receptor activator of nuclear factor-κB ligand (RANKL)-induced in vitro osteoclast differentiation. We observed that TS concentration-dependently inhibited RANKL-induced osteoclast formation from RAW 264.7 cell and bone marrow-derived macrophages (BMMs), as well as decreased extent of actin ring formation and lacunar resorption. The RANKL-stimulated expression of osteoclast-related transcription factors were also diminished by TS. Moreover, TS blocked the RANKL-triggered TRAF6 expression, phosphorylation of mitogen-activated protein kinases (MAPKs) and IκB-α, and inhibited NF-κB p65 DNA binding activity. Furthermore, TS almost abrogated the nuclear factor of activated T cells (NFATc1) and c-Fos expression. Taken together, our results demonstrated that TS suppresses RANKL-induced osteoclast differentiation and inflammatory bone loss via the down-regulation of TRAF6 level, suppression of JNK and p38 MAPKs and NF-κB activation, and subsequent decreased expression of c-Fos and NFATc1. Therefore, TS may be a potential agent and needs to be more evaluated in vivo or in clinical trials to become a therapeutic for lytic bone diseases.

Urokinase receptor mediates osteoclastogenesis via M-CSF release from osteoblasts and the c-Fms/PI3K/Akt/NF-κB pathway in osteoclasts

Bone remodeling is a dynamic process based on a fine-tuned balance between formation and degradation of bone. Osteoblasts (OBLs) are responsible for bone formation and bone resorption is mediated by osteoclasts (OCLs). The mechanisms regulating the OBL-OCL balance are critical in health and disease; however, they are still far from being understood. We reported recently that the multifunctional urokinase receptor (uPAR) mediates osteogenic differentiation of mesenchymal stem cells (MSCs) to OBLs and vascular calcification in atherosclerosis. Here, we address the question of whether uPAR may also be engaged in regulation of osteoclastogenesis. We show that uPAR mediates this process in a dual fashion. Thus, uPAR affected OBL-OCL interplay. We observed that osteoclastogenesis was significantly impaired in co-culture of monocyte-derived OCLs and in OBLs derived from MSCs lacking uPAR. We show that expression and release, from OBLs, of macrophage colony-stimulating factor (M-CSF), which is indispensable for OCL differentiation, was inhibited by uPAR loss. We further found that uPAR, on the other hand, controlled formation, differentiation, and functional properties of macrophage-derived OCLs. Expression of osteoclastogenic markers, such as tartrate-resistant acid phosphatase (TRAP) and cathepsin K, was impaired in OCLs derived from uPAR-deficient macrophages. The requirement of uPAR for osteoclastogenesis was further confirmed by immunocytochemistry and in bone resorption assay. We provide evidence that the underlying signaling mechanisms involve uPAR association with the M-CSF binding receptor c-Fms followed by c-Fms phosphorylation and activation of the PI3K/Akt/NF-κB pathway in OCLs. We further show that uPAR uses this pathway to regulate a balance between OCL differentiation, apoptosis, and cell proliferation. Our study identified uPAR as an important and multifaceted regulator of OBL-OCL molecular interplay that may serve as an attractive target in bone disease and ectopic calcification.

Baicalein induces human osteosarcoma cell line MG-63 apoptosis via ROS-induced BNIP3 expression

Baicalein, a flavonoid compound, is one of the active constituents of the root of Scutellariae Radix. Its antitumor effects have attracted widespread attention worldwide. One of its major functions is to induce the apoptosis of tumor cells, but the antitumor mechanism is currently unclear. In the present study, we found that baicalein increased MG-63 cell mortality in a dose-dependent manner. Meanwhile, baicalein activated apoptosis through induced intracellular reactive oxygen species (ROS) generation, and that ROS scavenger N-acetyl-cysteine (NAC), glutathione (GSH), and superoxide dismutase (SOD) apparently inhibited intracellular ROS production, consequently attenuating the baicalein-induced apoptosis. Baicalein also induce the mitochondrial fragmentation which precedes the cell apoptosis. This morphological alteration is accompanied by an increase in the expression of the protein BNIP3 as well as Mul1 and Drp1. Furthermore, we show that the inhibition of BNIP3 expression can inhibit cell apoptosis by baicalein treatment. Taken together, our results bring the evidence of a mechanism that links apoptosis and ROS-induced BNIP3 expression in MG-63 cells with bacalein treatment and suggest that baicalein has a good potential as an anti-osteosarcoma drug.

Natural polyamines inhibit the migration of preosteoclasts by attenuating Ca2+-PYK2-Src-NFATc1 signaling pathways

Natural polyamines have numerous biological activities. Several studies have reported their beneficial role in bone metabolism, but their mode of action is not fully understood. Bone diseases such as osteoporosis, which is characterized by impaired bone structure and low bone mass, are caused by an increased number of osteoclasts and/or overactivation of osteoclastogenesis. Osteoclast differentiation is a multi-complex procedure involving the following sequential steps: differentiation-migration-fusion-resorption. In this study, we found that putrescine, spermidine or spermine inhibited the RANKL-mediated migration of preosteoclasts. Furthermore, the RANKL-mediated activation of the Src-PYK2 signaling axis and of transcription factors such as NF-κB and NFATc1 was prevented by each polyamine. Anti-osteoclastogenic and anti-migration activities of polyamines were confirmed by evaluating their potential to downregulate the mRNA expression levels of osteoclastogenesis-related genes such as OSCAR, TRAP, cathepsin K and c-Src, and genes related to fusion and/or migration of preosteoclasts. Moreover, ATP-mediated elevation of cytosolic free Ca(2+) concentration ([Ca(2+)]i) was strongly inhibited by each polyamine, indicating the involvement of [Ca(2+)]i in the anti-fusion activities of polyamines. In conclusion, polyamines could exhibit anti-osteoclastogenic activity by inhibiting the migration of preosteoclasts via the Ca(2+)-PYK2-Src-NFATc1 signaling axis.

The study of mechanisms of protective effect of Rg1 against arthritis by inhibiting osteoclast differentiation and maturation in CIA mice

Ginsenoside Rg1 is a natural product extracted from Panax ginseng C.A. Although Rg1 protects tissue structure and functions by inhibiting local inflammatory reaction, the mechanism remains poorly understood. In vitro, Rg1 dose-dependently inhibited TRAP activity in receptor activator of nuclear factor-κB ligand- (RANKL-) induced osteoclasts and decreased the number of osteoclasts and osteoclast resorption area. Rg1 also significantly inhibited the RANK signaling pathway, including suppressing the expression of Trap, cathepsin K, matrix metalloproteinase 9 (MMP9), and calcitonin receptor (CTR). In vivo, Rg1 dramatically decreased arthritis scores in CIA mice and effectively controlled symptoms of inflammatory arthritis. Pathologic analysis demonstrated that Rg1 significantly attenuated pathological changes in CIA mice. Pronounced reduction in synovial hyperplasia and inflammatory cell invasion were observed in CIA mice after Rg1 therapy. Alcian blue staining results illustrated that mice treated with Rg1 had significantly reduced destruction in the articular cartilage. TRAP and cathepsin K staining results demonstrated a significant reduction of numbers of OCs in the articular cartilage in proximal interphalangeal joints and ankle joints in Rg1-treated mice. In summary, this study revealed that Rg1 reduced the inflammatory destruction of periarticular bone by inhibiting differentiation and maturation of osteoclasts in CIA mice.

Establishing an osteosarcoma associated protein-protein interaction network to explore the pathogenesis of osteosarcoma

Background

The aim of this study was to establish an osteosarcoma (OS) associated protein-protein interaction network and explore the pathogenesis of osteosarcoma.

Methods

The gene expression profile GSE9508 was downloaded from the Gene Expression Omnibus database, including five samples of non-malignant bone (the control), seven samples for non-metastatic patients (six of which were analyzed in duplicate), and 11 samples for metastatic patients (10 of which were analyzed in duplicate). Differentially expressed genes (DEGs) between osteosarcoma and control samples were identified by packages in R with the threshold of |logFC (fold change)| > 1 and false discovery rate < 0.05. Osprey software was used to construct the interaction network of DEGs, and genes at protein-protein interaction (PPI) nodes with high degrees were identified. The Database for Annotation, Visualization and Integrated Discovery and WebGestalt software were then used to perform functional annotation and pathway enrichment analyses for PPI networks, in which P < 0.05 was considered statistically significant.

Results

Compared to the control samples, the expressions of 42 and 341 genes were altered in non-metastatic OS and metastatic OS samples, respectively. A total of 15 significantly enriched functions were obtained with Gene Ontology analysis (P < 0.05). The DEGs were classified and significantly enriched in three pathways, including the tricarboxylic acid cycle, lysosome and axon guidance. Genes such as HRAS, IDH3A, ATP6ap1, ATP6V0D2, SEMA3F and SEMA3A were involved in the enriched pathways.

Conclusions

The hub genes from metastatic OS samples are not only bio-markers of OS, but also help to improve therapies for OS.

Norisoboldine suppresses osteoclast differentiation through preventing the accumulation of TRAF6-TAK1 complexes and activation of MAPKs/NF-κB/c-Fos/NFATc1 Pathways

Norisoboldine (NOR) is the main alkaloid constituent in the dry root of Lindera aggregata (Sims) Kosterm. (L. strychnifolia Vill.). As reported previously, orally administered NOR displayed a robust inhibition of joint bone destruction present in both mouse collagen-induced arthritis and rat adjuvant-induced arthritis with lower efficacious doses than that required for ameliorating systemic inflammation. This attracted us to assess the effects of NOR on differentiation and function of osteoclasts, primary effector cells for inflammatory bone destruction, to get insight into its anti-rheumatoid arthritis mechanisms. Both RAW264.7 cells and mouse bone marrow-derived macrophages (BMMs) were stimulated with RANKL (100 ng/mL) to establish osteoclast differentiation models. ELISA, RT-PCR, gelatin zymography, western blotting, immunoprecipitation and EMSA were used to reveal related signalling pathways. NOR (10 and 30 µM), without significant cytotoxicity, showed significant reduction of the number of osteoclasts and the resorption pit areas, and it targeted osteoclast differentiation at the early stage. In conjunction with the anti-resorption effect of NOR, mRNA levels of cathepsin K and MMP-9 were decreased, and the activity of MMP-9 was attenuated. Furthermore, our mechanistic studies indicated that NOR obviously suppressed the ubiquitination of TRAF6, the accumulation of TRAF6-TAK1 complexes and the activation of ERK and p38 MAPK, and reduced the nuclear translocation of NF-κB-p65 and DNA-binding activity of NF-κB. However, NOR had little effect on expressions of TRAF6 or the phosphorylation and degradation of IκBα. Moreover, NOR markedly inhibited expressions of transcription factor NFATc1, but not c-Fos. Intriguingly, the subsequent nuclear translocations of c-Fos and NFATc1 were substantially down-regulated. Hence, we demonstrated for the first time that preventing the differentiation and function of osteoclasts at the early stage was an important anti-bone destruction mechanism of NOR, which might be attributed to inhibition of ubiquitination of TRAF6, the accumulation of TRAF6-TAK1 complexes and the activation of MAPKs/NF-κB/c-Fos/NFATc1 pathways.

Norisoboldine alleviates joint destruction in rats with adjuvant-induced arthritis by reducing RANKL, IL-6, PGE(2), and MMP-13 expression

AIM

To explore the effects of norisoboldine (NOR), a major isoquinoline alkaloid in Radix Linderae, on joint destruction in rats with adjuvant-induced arthritis (AIA) and its underlying mechanisms.

METHODS

AIA was induced in adult male SD rats by intradermal injection of Mycobacterium butyricum in Freund's complete adjuvant at the base of the right hind paw and tail. From d 14 after immunization, the rats were orally given NOR (7.5, 15, or 30 mg/kg) or dexamethasone (0.5 mg/kg) daily for 10 consecutive days. Joint destruction was evaluated with radiological scanning and H&E staining. Fibroblast-like synoviocytes (FLS) were prepared from fresh synovial tissues in the AIA rats. The expression of related proteins and mRNAs were detected by ELISA, Western blotting and RT-PCR.

RESULTS

In AIA rats, NOR (15 and 30 mg/kg) significantly decreased the swelling of paws and arthritis index scores, and elevated the mean body weight. NOR (30 mg/kg) prevented both the infiltration of inflammatory cells and destruction of bone and cartilage in joints. However, NOR (15 mg/kg) only suppressed the destruction of bone and cartilage, but did not obviously ameliorate synovial inflammation. NOR (15 and 30 mg/kg) significantly decreased the serum levels of receptor activator of nuclear factor κB ligand (RANKL), IL-6, PGE2, and MMP-13, but not the osteoprotegerin and MMP-1 levels. The mRNA levels of RANKL, IL-6, COX-2, and MMP-13 in synovium were also suppressed. Dexamethasone produced similar effects in AIA rats as NOR did, but without elevating the mean body weight. In the cultured FLS, treatment with NOR (10 and 30 mmol/L) significantly decreased the secretion of RANKL, IL-6, PGE2, and MMP-13 proteins. Furthermore, the treatment selectively prevented the activation of MAPKs, AKT and transcription factor AP-1 component c-Jun, but not the recruitment of TRAF6 or the activation of JAK2/STAT3. Treatment of the cultured FLS with the specific inhibitors of p38, ERK, AKT, and AP-1 significantly decreased the secretion of RANKL, IL-6, PGE2, and MMP-13 proteins.

CONCLUSION

NOR can alleviate joint destruction in AIA rats by reducing RANKL, IL-6, PGE2, and MMP-13 expression via the p38/ERK/AKT/AP-1 pathway.

Giant-cell tumor of bone, anti-RANKL therapy

Giant-cell tumor of bone (GCTB) is a rare osteolytic tumor of the bone. Although classified as a benign tumor, GCTB is characterized by local aggressiveness and risk of local recurrence. In addition, GTCB can in some cases lead to the development of so-called 'benign' chest metastases. Surgical resection by intralesional curettage with high-speed burring and polymethylmethacrylate cement is the standard treatment for resectable tumors. In cases of metastatic or unresectable disease (when planned surgical procedure is impossible or would result in severe morbidity), medical treatments such as cytotoxic chemotherapy or interferon-α have limited efficacy. Bisphosphonates have been proposed as a therapeutic option to reduce osteoclast activity. In bone, various pathological states may result from an imbalance in the RANK (receptor activator of nuclear factor kappa-B)/RANKL (receptor activator of nuclear factor kappa-B ligand)/OPG (osteoprotegerin) pathway. Involvement of the RANKL pathway in pathogenesis of GCTB was first proposed in 2000. Denosumab is a fully human monoclonal antibody that binds and inhibits RANKL, thereby preventing the activation of the RANK pathway. As it showed the possibility to counteract osteoclast activation in GCTB and prevent the known physiopathological role of RANKL, denosumab has been under evaluation in the clinic as a treatment for GCTB since 2005. Results of a first Phase II trial demonstrate the therapeutic potential of denosumab to inhibit progressive bone destruction and metastatic progression in patients with unsalvageable giant-cell tumor (GCT), and have also provided key insights into the biology of GCT. Denosumab is currently a therapeutic option for patients with unresectable GCTB but its place in the global therapeutic strategy has not yet been defined.

Tartrate-Resistant Acid Phosphatase 5b is a Useful Serum Marker for Diagnosis and Recurrence Detection of Giant Cell Tumor of Bone

Serum tartrate-resistant acid phosphatase (TRACP) 5b was investigated for use as a marker for diagnosis of giant cell tumor (GCT) of bone and for detection of its recurrence.

Four patients with GCT of bone who were initially referred to our hospital were classified as a primary group. Three patients who had local recurrence following curettage were classified as a local recurrence group. Five with no recurrence were classified as a no-recurrence group. Eighteen patients with primary and metastatic malignant bone tumors were also enrolled in the study as a control group. Serum TRACP 5b was measured before the biopsy in all patients and was measured periodically after the operation in patients with GCT of bone. Student t-tests were used for statistical analyses.

TRACP 5b was greater than 1500 Um/dL in all primary group patients. Mean TRACP 5b values decreased gradually with post-operative time, showing lower values until local recurrence. The mean value of TRACP 5b of the local recurrence group (753 ± 68.7 mU/dL) was significantly higher than that of the no-recurrence group (340.6 ± 78.3 mU/dL). The mean value of TRACP 5b of the control group (466.9 ± 130.3 mU/dL) was much lower than that of the primary group and markedly lower than that of the local recurrence group. However, no significant difference was found between the no-recurrence group and the control group.

Serum TRACP 5b is a useful and convenient marker for diagnosing GCT of bone and for predicting its recurrence.

V-ATPases in osteoclasts: structure, function and potential inhibitors of bone resorption

The vacuolar-type H(+)-ATPase (V-ATPase) proton pump is a macromolecular complex composed of at least 14 subunits organized into two functional domains, V(1) and V(0). The complex is located on the ruffled border plasma membrane of bone-resorbing osteoclasts, mediating extracellular acidification for bone demineralization during bone resorption. Genetic studies from mice to man implicate a critical role for V-ATPase subunits in osteoclast-related diseases including osteopetrosis and osteoporosis. Thus, the V-ATPase complex is a potential molecular target for the development of novel anti-resorptive agents useful for the treatment of osteolytic diseases. Here, we review the current structure and function of V-ATPase subunits, emphasizing their exquisite roles in osteoclastic function. In addition, we compare several distinct classes of V-ATPase inhibitors with specific inhibitory effects on osteoclasts. Understanding the structure-function relationship of the osteoclast V-ATPase may lead to the development of osteoclast-specific V-ATPase inhibitors that may serve as alternative therapies for the treatment of osteolytic diseases.