A clinical-stage Nrf2 activator suppresses osteoclast differentiation via the iron-ornithine axis.

Activating Nrf2 by small molecules is a promising strategy to treat postmenopausal osteoporosis. However, there is currently no Nrf2 activator approved for treating chronic diseases, and the downstream mechanism underlying the regulation of Nrf2 on osteoclast differentiation remains unclear. Here, we found that bitopertin, a clinical-stage glycine uptake inhibitor, suppresses osteoclast differentiation and ameliorates ovariectomy-induced bone loss by activating Nrf2. Mechanistically, bitopertin interacts with the Keap1 Kelch domain and decreases Keap1-Nrf2 binding, leading to reduced Nrf2 ubiquitination and degradation. Bitopertin is associated with less adverse events than clinically approved Nrf2 activators in both mice and human subjects. Furthermore, Nrf2 transcriptionally activates ferroportin-coding gene Slc40a1 to reduce intracellular iron levels in osteoclasts. Loss of Nrf2 or iron supplementation upregulates ornithine-metabolizing enzyme Odc1, which decreases ornithine levels and thereby promotes osteoclast differentiation. Collectively, our findings identify a novel clinical-stage Nrf2 activator and propose a novel Nrf2-iron-ornithine metabolic axis in osteoclasts.

Gadolinium-Based Contrast Agents and Free Gadolinium Inhibit Differentiation and Activity of Bone Cell Lineages.

OBJECTIVES: Administration of gadolinium-based contrast agents (GBCA) in magnetic resonance imaging results in the long-term retention of gadolinium (Gd) in tissues and organs, including the bone, and may affect their function and metabolism. This study aims to investigate the effects of Gd and GBCA on the proliferation/survival, differentiation, and function of bone cell lineages. MATERIALS AND METHODS: Primary murine osteoblasts (OB) and osteoclast progenitor cells (OPC) isolated from C57BL/6J mice were used to test the effects of Gd 3+ (12.5-100 µM) and GBCA (100-2000 µM). Cultures were supplemented with the nonionic linear Gd-DTPA-BMA (gadodiamide), ionic linear Gd-DTPA (gadopentetic acid), and macrocyclic Gd-DOTA (gadoteric acid). Cell viability and differentiation were analyzed on days 4-6 of the culture. To assess the resorptive activity of osteoclasts, the cells were grown in OPC cultures and were seeded onto layers of amorphous calcium phosphate with incorporated Gd. RESULTS: Gd 3+ did not affect OB viability, but differentiation was reduced dose-dependently up to 72.4% ± 6.2%-73.0% ± 13.2% (average ± SD) at 100 µM Gd 3+ on days 4-6 of culture as compared with unexposed controls ( P < 0.001). Exposure to GBCA had minor effects on OB viability with a dose-dependent reduction up to 23.3% ± 10.2% for Gd-DTPA-BMA at 2000 µM on day 5 ( P < 0.001). In contrast, all 3 GBCA caused a dose-dependent reduction of differentiation up to 88.3% ± 5.2% for Gd-DTPA-BMA, 49.8% ± 16.0% for Gd-DTPA, and 23.1% ± 8.7% for Gd-DOTA at 2000 µM on day 5 ( P < 0.001). In cultures of OPC, cell viability was not affected by Gd 3+ , whereas differentiation was decreased by 45.3% ± 9.8%-48.5% ± 15.8% at 100 µM Gd 3+ on days 4-6 ( P < 0.05). Exposure of OPC to GBCA resulted in a dose-dependent increase in cell viability of up to 34.1% ± 11.4% at 2000 µM on day 5 of culture ( P < 0.001). However, differentiation of OPC cultures was reduced on day 5 by 24.2% ± 9.4% for Gd-DTPA-BMA, 47.1% ± 14.0% for Gd-DTPA, and 38.2% ± 10.0% for Gd-DOTA ( P < 0.001). The dissolution of amorphous calcium phosphate by mature osteoclasts was reduced by 36.3% ± 5.3% upon incorporation of 4.3% Gd/Ca wt/wt ( P < 0.001). CONCLUSIONS: Gadolinium and GBCA inhibit differentiation and activity of bone cell lineages in vitro. Thus, Gd retention in bone tissue could potentially impair the physiological regulation of bone turnover on a cellular level, leading to pathological changes in bone metabolism.

Zanthoxylum bungeanum seed oil inhibits RANKL-induced osteoclastogenesis by suppressing ERK/c-JUN/NFATc1 pathway and regulating cell cycle arrest in RAW264.7 cells.

ETHNOPHARMACOLOGICAL RELEVANCE: Zanthoxylum bungeanum Maxim (ZBM), a traditional Chinese medicine, is traditionally used for osteoporosis treatment recorded in ancient Chinese medicine work Benjingshuzheng and reported to have the anti-bone loss activity in recent studies. However, the anti-osteoporotic activities of the seed of ZBM have not been elucidated yet. Our previous study found that Zanthoxylum bungeanum Maxim seed oil (ZBSO) was rich in polyunsaturated fatty acids (PUFAs), which were reported to prevent bone loss. Thus, we propose a hypothesis that ZBSO could be a potential natural resource for anti-bone loss. AIM OF THE STUDY: To investigate whether ZBSO could prevent bone loss by targeting osteoclastogenesis and investigate the potential mechanisms in receptor-activator of nuclear factor κB ligand (RANKL)-induced RAW264.7 cells. MATERIALS AND METHODS: RAW264.7 cells were treated with RANKL in the presence or absence of ZBSO. The effect of ZBSO on osteoclast differentiation and bone resorption activity of RAW264.7 cells were evaluated by tartrate-resistant acid phosphatase (TRAP) staining, F-actin ring staining, and bone resorption assay. Differentially expression genes (DEGs) and relevant pathways of different cell groups were obtained from RNA sequencing and protein-protein interaction (PPI) network analysis followed by KEGG pathway enrichment analysis. The effect of ZBSO on the RANKL-induced cell cycle change was analyzed by flow cytometry assay, and the expression of genes and proteins related to the selected pathways was further verified by RT-qPCR and western blot analysis. RESULTS: The inhibitory effects of ZBSO on osteoclast differentiation and bone resorption activity in a dose-dependent manner were demonstrated by TRAP staining, F-actin ring staining, and bone resorption assay in RANKL-induced RAW264.7 cells. Osteoclast differentiation and cell cycle pathways were the most enriched pathways based on DEGs enrichment analysis among different cell groups. The reversion effect of ZBSO on the RANKL-induced RAW264.7 cell cycle arrest at the G1 phase was observed by flow cytometry assay. Western blot results showed that ZBSO markedly decreased RANKL-induced activation of ERK, as well as the phosphorylation of c-JUN and NFATc1 expression, and subsequently suppressed osteoclast-specific genes, such as Ctsk, Trap, and Dc-stamp. CONCLUSIONS: ZBSO exhibited an inhibitory effect on osteoclastogenesis via suppressing the ERK/c-JUN/NFATc1 pathway and regulating cell cycle arrest induced by RANKL, suggesting that ZBSO may serve as a promising agent for anti-bone loss.

D(-)-salicin inhibits RANKL-induced osteoclast differentiation and function in vitro.

Osteoporosis is a disease, which causes huge economic and social burden. Using natural compound to treat such disease is beneficial for the fewer side effects and effectiveness. D-(-)-salicin (DSA) is a component extracted from the bark of Populus and Salix species. In our research, we discovered that DSA suppressed RANKL-induced differentiation of osteoclast in vitro in a dose-dependent manner. It was also found that the mineral resorbing activity by osteoclasts was depressed via DSA. For the mechanism, we confirmed the inhibitory effect, by which DSA suppressed osteoclast formation and function, was through the inhibition of ROS signaling, MAPK and NF-κB cascades. DSA also suppressed the expression and activity of NFATc1. Therefore, by inhibiting the ROS production, MAPK and NF-κB signal cascade, DSA inhibited the osteoclast differentiation and function in vitro.

Butyrate Inhibits Osteoclast Activity In Vitro and Regulates Systemic Inflammation and Bone Healing in a Murine Osteotomy Model Compared to Antibiotic-Treated Mice.

Short-chain fatty acids (SCFAs) produced by the gut microbiota have previously been demonstrated to play a role in numerous chronic inflammatory diseases and to be key mediators in the gut-bone signaling axis. However, the role of SCFAs in bone fracture healing and its impact on systemic inflammation during the regeneration process has not been extensively investigated yet. The aim of this study was to first determine the effects of the SCFA butyrate on key cells involved in fracture healing in vitro, namely, osteoclasts and mesenchymal stromal cells (MSCs), and second, to assess if butyrate supplementation or antibiotic therapy impacts bone healing, systemic immune status, and inflammation levels in a murine osteotomy model. Butyrate significantly reduced osteoclast formation and resorption activity in a dose-dependent manner and displayed a trend for increased calcium deposits in MSC cultures. Numerous genes associated with osteoclast differentiation were differentially expressed in osteoclast precursor cells upon butyrate exposure. In vivo, antibiotic-treated mice showed reduced SCFA levels in the cecum, as well as a distinct gut microbiome composition. Furthermore, circulating proinflammatory TNFα, IL-17a, and IL-17f levels, and bone preserving osteoprotegerin (OPG), were increased in antibiotic-treated mice compared to controls. Antibiotic-treated mice also displayed a trend towards delayed bone healing as revealed by reduced mineral apposition at the defect site and higher circulating levels of the bone turnover marker PINP. Butyrate supplementation resulted in a lower abundance of monocyte/macrophages in the bone marrow, as well as reduced circulating proinflammatory IL-6 levels compared to antibiotic- and control-treated mice. In conclusion, this study supports our hypothesis that SCFAs, in particular butyrate, are important contributors to successful bone healing by modulating key cells involved in fracture healing as well as systemic inflammation and immune responses.

Toxic Effects of Indoxyl Sulfate on Osteoclastogenesis and Osteoblastogenesis.

Uremic toxins, such as indoxyl sulfate (IS) and kynurenine, accumulate in the blood in the event of kidney failure and contribute to further bone damage. To maintain the homeostasis of the skeletal system, bone remodeling is a persistent process of bone formation and bone resorption that depends on a dynamic balance of osteoblasts and osteoclasts. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that regulates the toxic effects of uremic toxins. IS is an endogenous AhR ligand and is metabolized from tryptophan. In osteoclastogenesis, IS affects the expression of the osteoclast precursor nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) through AhR signaling. It is possible to increase osteoclast differentiation with short-term and low-dose IS exposure and to decrease differentiation with long-term and/or high-dose IS exposure. Coincidentally, during osteoblastogenesis, through the AhR signaling pathway, IS inhibits the phosphorylation of ERK, and p38 reduces the expression of the transcription factor 2 (Runx2), disturbing osteoblastogenesis. The AhR antagonist resveratrol has a protective effect on the IS/AhR pathway. Therefore, it is necessary to understand the multifaceted role of AhR in CKD, as knowledge of these transcription signals could provide a safe and effective method to prevent and treat CKD mineral bone disease.

Melatonin Inhibits Osteoclastogenesis and Osteolytic Bone Metastasis: Implications for Osteoporosis.

Osteoblasts and osteoclasts are major cellular components in the bone microenvironment and they play a key role in the bone turnover cycle. Many risk factors interfere with this cycle and contribute to bone-wasting diseases that progressively destroy bone and markedly reduce quality of life. Melatonin (N-acetyl-5-methoxy-tryptamine) has demonstrated intriguing therapeutic potential in the bone microenvironment, with reported effects that include the regulation of bone metabolism, acceleration of osteoblastogenesis, inhibition of osteoclastogenesis and the induction of apoptosis in mature osteoclasts, as well as the suppression of osteolytic bone metastasis. This review aims to shed light on molecular and clinical evidence that points to possibilities of melatonin for the treatment of both osteoporosis and osteolytic bone metastasis. It appears that the therapeutic qualities of melatonin supplementation may enable existing antiresorptive osteoporotic drugs to treat osteolytic metastasis.

Apoptotic mesenchymal stromal cells support osteoclastogenesis while inhibiting multinucleated giant cells formation in vitro.

In bone regeneration induced by the combination of mesenchymal stromal cells (MSCs) and calcium-phosphate (CaP) materials, osteoclasts emerge as a pivotal cell linking inflammation and bone formation. Favorable outcomes are observed despite short-term engraftments of implanted MSCs, highlighting their major paracrine function and the possible implication of cell death in modulating their secretions. In this work, we focused on the communication from MSCs towards osteoclasts-like cells in vitro. MSCs seeded on a CaP biomaterial or undergoing induced apoptosis produced a conditioned media favoring the development of osteoclasts from human CD14+ monocytes. On the contrary, MSCs' apoptotic secretion inhibited the development of inflammatory multinucleated giant cells formed after IL-4 stimulation. Components of MSCs' secretome before and after apoptotic stress were compared using mass spectrometry-based quantitative proteomics and a complementary immunoassay for major cytokines. CXCR-1 and CXCR-2 ligands, primarily IL-8/CXCL-8 but also the growth-regulated proteins CXCL-1, -2 or -3, were suggested as the major players of MSCs' pro-osteoclastic effect. These findings support the hypothesis that osteoclasts are key players in bone regeneration and suggest that apoptosis plays an important role in MSCs' effectiveness.

Solanum nigrum Line inhibits osteoclast differentiation and suppresses bone mineral density reduction in the ovariectomy­induced osteoporosis model.

Bone homeostasis is maintained by osteoclasts that absorb bone and osteoblasts that form bone tissue. Menopausal osteoporosis is a disease associated with aging and hormonal changes due to menopause causing abnormal activation of osteoclasts, resulting in a decrease in bone density. Existing treatments for osteoporosis have been reported to have serious side effects, such as jawbone necrosis and breast and uterine cancer; therefore, their use by patients is decreasing, whilst studies focusing on alternative treatments are increasingly popular. Solanum nigrum Line (SL) has been used as a medicinal plant that possesses several pharmacological effects, such as anti­inflammatory and hepatotoxic protective effects. To the best of our knowledge, however, its effects on osteoporosis and osteoclasts have not been demonstrated previously. In the present study, the anti­osteoporotic effect of SL was investigated using a postmenopausal model of osteoporosis in which Sprague­Dawley rat ovaries were extracted. In addition, the inhibitory effects on osteoclast differentiation and function of SL was confirmed using an osteoclast model treated with receptor activator of NF­κB ligand (RANKL) on murine RAW 264.7 macrophages. In vivo experiments showed that SL reduced the decrease in bone mineral density and improved changes in the morphological index of bone microstructure, such as trabecular number and separation. In addition, the number of tartrate resistant acid phosphatase­positive cells in the femur and the expression levels of nuclear factor of activated T­cells cytoplasmic 1 (NFATc1) and cathepsin K protein were inhibited. In vitro, SL suppressed RANKL­induced osteoclast differentiation and bone resorption ability; this was mediated by NFATc1/c­Fos, a key transcription factor involved in osteoclast differentiation, ultimately inhibiting expression of various osteoclast­associated genes. These experimental results show that SL may be an alternative treatment for osteoporosis caused by abnormal activation of osteoclasts in the future.

Nanohydroxyapatite (nHAp) Doped with Iron Oxide Nanoparticles (IO), miR-21 and miR-124 Under Magnetic Field Conditions Modulates Osteoblast Viability, Reduces Inflammation and Inhibits the Growth of Osteoclast - A Novel Concept for Osteoporosis Treatment: Part 1.

PURPOSE: Osteoporosis results in a severe decrease in the life quality of many people worldwide. The latest data shows that the number of osteoporotic fractures is becoming an increasing international health service problem. Therefore, a new kind of controllable treatment methods for osteoporotic fractures is extensively desired. For that reason, we have manufactured and evaluated nanohydroxyapatite (nHAp)-based composite co-doped with iron oxide (IO) nanoparticles. The biomaterial was used as a matrix for the controlled delivery of miR-21-5p and miR-124-3p, which have a proven impact on bone cell metabolism. METHODS: The nanocomposite Ca5(PO4)3OH/Fe3O4 (later called nHAp/IO) was obtained by the wet chemistry method and functionalised with microRNAs (nHAp/IO@miR-21/124). Its physicochemical characterization was performed using XRPD, FT-IR, SEM-EDS and HRTEM and SAED methods. The modulatory effect of the composite was tested in vitro using murine pre-osteoblasts MC3T3-E1 and pre-osteoclasts 4B12. Moreover, the anti-inflammatory effects of biomaterial were analysed using a model of LPS-treated murine macrophages RAW 264.7. We have analysed the cells' viability, mitochondria membrane potential and oxidative stress under magnetic field (MF+) and without (MF-). Moreover, the results were supplemented with RT-qPCR and Western blot assays to evaluate the expression profile for master regulators of bone metabolism. RESULTS: The results indicated pro-osteogenic effects of nHAp/IO@miR-21/124 composite enhanced by exposure to MF. The enhanced osteogenesis guided by nHAp/IO@miR-21/124 presence was associated with increased metabolism of progenitor cells and activation of osteogenic markers (Runx-2, Opn, Coll-1). Simultaneously, nanocomposite decreased metabolism and differentiation of pre-osteoclastic 4B12 cells accompanied by reduced expression of CaII and Ctsk. Obtained composite regulated viability of bone progenitor cells and showed immunomodulatory properties inhibiting the expression of inflammatory markers, ie, TNF-α, iNOs or IL-1ß, in LPS-stimulated RAW 264.7 cells. CONCLUSION: We have described for the first time a new concept of osteoporosis treatment based on nHAp/IO@miR-21/124 application. Obtained results indicated that fabricated nanocomposite might impact proper regeneration of osteoporotic bone, restoring the balance between osteoblasts and osteoclast.

Plastrum testudinis extract suppresses osteoclast differentiation via the NF-κB signaling pathway and ameliorates senile osteoporosis.

ETHNOPHARMACOLOGICAL RELEVANCE: Plastrum testudinis (PT) is a kind of single traditional Chinese medicine that can tonify kidney and strengthen bone. Plastrum testudinis extract (PTE) has been approved to promote the osteogenic differentiation of bone marrow-derived mesenchymal stem cells in vitro. However, the mechanism by which PTE reduces osteoclast differentiation has not yet been reported. AIM OF THE STUDY: To explore the potential of PTE as a therapeutic treatment for bone loss caused by senile osteoporosis (SOP). MATERIALS AND METHODS: We evaluated whether PTE could inhibit RANKL-induced osteoclast differentiation both in vitro and in vivo, and investigated PTE-induced phenotypes of human peripheral blood monocytes. RESULTS: We found that PTE inhibited osteoclast differentiation and bone resorption in vitro in a concentration-dependent manner and that PTE treatment is most effective during the early stages of osteoclastogenesis. Moreover, we found that PTE could block the NF-κB signaling pathway in vitro, leading to the down-regulation of osteoclast-specific genes including C-FOS and NFATC1. The results from our in vivo mouse study suggest that PTE treatment suppresses osteoclast formation and mitigates bone loss caused by SOP. Notably, we also found that PTE inhibited RANKL-induced osteoclast differentiation in human peripheral blood monocytes. CONCLUSION: Our results suggest that PTE treatment suppresses osteoclastogenesis and ameliorates bone loss caused by SOP by selectively blocking the nuclear translocation of NF-κB/p50.

Nitrogen-Doped Multiwalled Carbon Nanotubes Enhance Bone Remodeling through Immunomodulatory Functions.

It has been reported that multiwalled carbon nanotubes (MWCNTs) can reportedly positively affect growth and differentiation of bone-related cells and therefore offer great potential in biomedical applications. To overcome negative immune responses that limit their application, specific doping and functionalization can improve their biocompatibility. Here, we demonstrated that nitrogen-doped carboxylate-functionalized MWCNTs (N-MWCNTs) enhance bone remodeling both in vitro and in vivo with excellent biocompatibility, via stimulation of both bone resorption and formation. We revealed that 0.2 µg/mL N-MWCNTs not only increase the transcription of osteoblastogenic and osteoclastogenic genes but also up-regulate the activities of both TRAP and AKP in the differentiation of bone marrow stromal cells (BMSCs). Additionally, intramuscular administration of N-MWCNTs at a dosage of 1.0 mg/kg body weight enhances bone mineral density and bone mass content in mice, as well as induces potentiated degree of TRAP- and ARS-positive staining in the femur. The positive regulation of N-MWCNTs on bone remodeling is initiated by macrophage phagocytosis, which induces altered production of inflammatory cytokines by immune response pathways, and consequently up-regulates IL1α, IL10, and IL16. These cytokines collectively regulate the central osteoclastogenic transcription factor NFATc1 and osteoblastogenic BMP signaling, the suppression of which confirmed that these factors respectively participate in N-MWCNT-mediated regulation of osteoclastic and osteoblastic bone marrow stem cell activities. These results suggest that N-MWCNTs can be readily generalized for use as biomaterials in bone tissue engineering for metabolic bone disorders.

Biological Evaluation and Transcriptomic Analysis of Corylin as an Inhibitor of Osteoclast Differentiation.

Corylin, a flavonoid isolated from the fruit of Psoralea corylifolia, has an osteogenic effect on osteoblasts in vitro and bone micromass ex vivo. However, the effect and mechanism of corylin in regulating osteoclastogenesis remain unknown. By using murine bone marrow macrophages as the osteoclast precursor, corylin was found to inhibit the receptor activator of nuclear factor (NF) κB ligand (RANKL)-induced osteoclast differentiation via down-regulating osteoclastic marker genes. In parallel, F-actin formation and osteoclast migration were diminished in corylin-treated cultured osteoclasts, and subsequently the expressions of osteoclastic proteins were suppressed: the suppression of protein expression was further illustrated by transcriptomic analysis. Furthermore, corylin inhibited the nuclear translocation of p65, giving rise to a restraint in osteoclastic differentiation through the attenuation of transcription factors nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and nuclear factor of activated T cells c1 (NFATc1). There was no obvious change in apoptosis when the RANKL-induce osteoclasts were cultured in the presence of corylin. The finding supports the potential development of corylin as an osteoclast inhibitor against osteoporosis.

Human osteoclastogenesis in Epstein-Barr virus-induced erosive arthritis in humanized NOD/Shi-scid/IL-2Rγnull mice.

Many human viruses, including Epstein-Barr virus (EBV), do not infect mice, which is challenging for biomedical research. We have previously reported that EBV infection induces erosive arthritis, which histologically resembles rheumatoid arthritis, in humanized NOD/Shi-scid/IL-2Rγnull (hu-NOG) mice; however, the underlying mechanisms are not known. Osteoclast-like multinucleated cells were observed during bone erosion in this mouse model, and therefore, we aimed to determine whether the human or mouse immune system activated bone erosion and analyzed the characteristics and origin of the multinucleated cells in hu-NOG mice. Sections of the mice knee joint tissues were immunostained with anti-human antibodies against certain osteoclast markers, including cathepsin K and matrix metalloproteinase-9 (MMP-9). Multinucleated cells observed during bone erosion stained positively for human cathepsin K and MMP-9. These results indicate that human osteoclasts primarily induce erosive arthritis during EBV infections. Human osteoclast development from hematopoietic stem cells transplanted in hu-NOG mice remains unclear. To confirm their differentiation potential into human osteoclasts, we cultured bone marrow cells of EBV-infected hu-NOG mice and analyzed their characteristics. Multinucleated cells cultured from the bone marrow cells stained positive for human cathepsin K and human MMP-9, indicating that bone marrow cells of hu-NOG mice could differentiate from human osteoclast progenitor cells into human osteoclasts. These results indicate that the human immune response to EBV infection may induce human osteoclast activation and cause erosive arthritis in this mouse model. Moreover, this study is the first, to our knowledge, to demonstrate human osteoclastogenesis in humanized mice. We consider that this model is useful for studying associations of EBV infections with rheumatoid arthritis and human bone metabolism.

Vitamin D receptor expression in mature osteoclasts reduces bone loss due to low dietary calcium intake in male mice.

Mature osteoclasts express the vitamin D receptor (VDR) and are able to respond to active vitamin D (1α, 25-dihydroxyvitamin D3; 1,25(OH)2D3) by regulating cell maturation and activity. However, the in vivo consequences of vitamin D signalling directly within functionally mature osteoclasts is only partially understood. To investigate the in vivo role of VDR in mature osteoclasts, conditional deletion of the VDR under control of the cathepsin K promoter (CtskCre/Vdr-/-), was assessed in 6 and 12-week-old mice, either under normal dietary conditions (NormCaP) or when fed a low calcium (0.03 %), low phosphorous (0.08 %) diet (LowCaP). Splenocytes from CtskCre/Vdr-/- mice were co-cultured with MLO-Y4 osteocyte-like cells to assess the effect on osteoclastogenesis. Six-week-old CtskCre/Vdr-/- mice demonstrated a 10 % decrease in vertebral bone volume (p < 0.05), which was associated with increased osteoclast size (p < 0.05) when compared to Vdrfl/fl control mice. Control mice fed a LowCaP diet exhibited extensive trabecular bone loss associated with increased osteoclast surface, number and size (p < 0.0001). Interestingly, CtskCre/Vdr-/- mice fed a LowCaP diet showed exacerbated loss of bone volume fraction (BV/TV%) and trabecular number (Tb.N), by a further 22 % and 21 %, respectively (p < 0.05), suggesting increased osteoclastic bone resorption activity with the loss of VDR in mature osteoclasts under these conditions. Co-culture of CtskCre/Vdr-/- splenocytes with MLO-Y4 cells increased resulting osteoclast numbers 2.5-fold, which were greater in nuclei density and exhibited increased resorption of dentine compared to osteoclasts derived from Vdrfl/fl splenocyte cultures. These data suggest that in addition to RANKL-mediated osteoclastogenesis, intact VDR signalling is required for the direct regulation of the differentiation and activity of osteoclasts in both in vivo and ex vivo settings.

Guizhi-Shaoyao-Zhimu decoction attenuates bone erosion in rats that have collagen-induced arthritis via modulating NF-κB signalling to suppress osteoclastogenesis.

CONTEXT: Guizhi-Shaoyao-Zhimu decoction (GSZD) is commonly used to treat rheumatoid arthritis (RA), but its mechanism is unclear. OBJECTIVE: To investigate the effect of GSZD on bone erosion in type II collagen (CII)-induced arthritis (CIA) in rats and to identify the underlying mechanism. MATERIALS AND METHODS: The CIA model was prepared in male Wistar rats by two subcutaneous injections of CII, 1 mg/mL. Fifty CIA rats were randomized equally into the control group given saline daily, the positive group given saline daily and methotrexate 0.75 mg/kg once a week, and three GSZD-treated groups gavaged daily with 800, 1600 and 3200 mg/kg of GSZD for 21 days. GSZD effects were assessed by paw volume, arthritic severity index and histopathology. Cytokine levels were determined by ELISA. The effects of GSZD on RAW264.7 cells were evaluated by receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis and bone resorption assay. Expression of IκB-α and p65 was measured by Western blotting. Major components of GSZD were identified by HPLC. RESULTS: Arthritis index score, paw volume and bone destruction score showed that GSZD improved inflammatory symptoms and reduced joint tissue erosion (p < 0.01). GSZD decreased RANKL, and the number of osteoclasts (OCs) in joint tissues (p < 0.01) and increased osteoprotegerin levels (p < 0.01). GSZD inhibited RANKL-induced RAW264.7 differentiation and reduced bone resorption by OCs. GSZD upregulated IκB (p < 0.01) and p65 (p < 0.01) in the cytoplasm and downregulated p65 (p < 0.01) in the cell nucleus. CONCLUSIONS: Guizhi-Shaoyao-Zhimu decoction has an anti-RA effect, suggesting its possible use as a supplement and alternative drug therapy for RA.

Anti-perimenopausal osteoporosis effects of Erzhi formula via regulation of bone resorption through osteoclast differentiation: A network pharmacology-integrated experimental study.

ETHNOPHARMACOLOGICAL RELEVANCE: Erzhi formula (EZF) consists of Ecliptae herba (EH) and Fructus Ligustri Lucidi (FLL) at a ratio 1:1, and constitutes a well-known formula in China that is commonly used for treating menopausal diseases. AIM OF THE STUDY: In this study, we explored the pharmacologic actions and potential molecular mechanisms underlying EZF's action in preventing and treating osteoporosis. MATERIALS AND METHODS: The active components and related targets of EZF's anti-osteoporotic effects were predicted by network pharmacology, and functional enrichment analysis was also performed. We then used an osteoporosis model of ovariectomized (OVX) mice to detect the effects of EZF on osteoporosis. RESULTS: The results from network pharmacology identified a total of 10 active ingredients from EH and 13 active ingredients from FLL that might affect 65 potential therapeutic targets. GO enrichment analysis revealed that EZF affected bone tissue primarily via hormone (particularly estradiol)-related pathways and bone resorption by osteoclast differentiation. KEGG analysis demonstrated that bone-related factors such as Runt-related transcription factor 2 (Runx2), Ca2, estrogen receptor1 (ESR1), androgen receptors (AR), and TNFα served as the primary targets during osteoclastic differentiation. In vivo experiments showed that the formula significantly improved the diminution in estrogen and the subsequent uterine atrophy induced by ovariectomy (P < 0.01 or 0.05), implying that the EZF exerted its actions via regulation of estradiol and the nourishing effects of the uterus in OVX mice. Dual-energy X-ray absorptiometry and micro-CT showed that EZF significantly inhibited bone loss and improved bone micro-architecture by statistically increasing the number of bone trabeculae and decreasing the separation of bone trabeculae in OVX mice (P < 0.01 or 0.05); EZF also inhibited bone loss and enhanced bone-fracture load. Furthermore, we confirmed that EZF reduced the calcium concentrations, augmented protein and mRNA levels for Runx2 in the bone marrow, and reduced PPARγ levels. RANKL-a key downstream regulatory protein of many targets that was referred to in our results of network pharmacology as being involved in the regulation of osteoclastogenesis-was significantly diminished by EZF; it also elevated OPG content. In addition, we used monocytes of bone-marrow origin to detect the effects of the potential components of EZF on osteoclast differentiation and found that wedelolactone, oleanolic acid, echinocystic acid, luteolin, and luteolin-7-o-glucoside significantly inhibited osteoclast differentiation from monocytes induced by 25 ng/mL MCSF and 50 ng/mL RANKL (P < 0.01 or 0.05). CONCLUSIONS: Our present study indicated that EZF significantly inhibited the bone loss induced by OVX in mice by its regulation of estradiol combined with the nourishing effect of the uterus, and that it also attenuated bone resorption by decreasing the RANKL/OPG ratio so as to inhibit osteoclast maturation.

Flavonoids from the peels of Citrus unshiu Markov. and their inhibitory effects on RANKL-induced osteoclastogenesis through the downregulation of c-Fos signaling in vitro.

Phytochemical investigation of Citrus unshiu peels led to the isolation of eight new flavonols (7-9, 11-15) and sixteen known compounds (1-6, 10, 16-24). Their structures were elucidated using spectroscopic analysis (1D, 2D NMR, and HR-MS). Besides, all isolated compounds (1-24) were evaluated for their inhibitory effects on receptor activator of RANKL-induced osteoclastogenesis in BMMs. Among them, dimethylmikanin (1), quercetogetin (2), 3,3',4',5,7,8-hexamethoxyflavone (3), 3-methoxynobiletin (4) showed a significant inhibitory effect on RANKL-induced osteoclast differentiation at a concentration of 10 µM. Moreover, 3-methoxynobiletin (4) suppressed RANKL-induced osteoclastogenesis by decreasing the number of osteoclasts and osteoclast actin-ring formation in a dose-dependent manner without causing any cytotoxic effects on BMMs. At the molecular level, 3-methoxynobiletin (4) inhibited RANKL-induced c-Fos expression and subsequently NFATc1 activation, as well as the expression of osteoclastogenesis-related marker genes c-Src and CtsK. These findings suggested that 3-methoxynobiletin (4) attenuated osteoclast differentiation by inhibiting RANKL-mediated c-Fos signaling and that it may have therapeutic potential for treating or preventing bone resorption-related diseases, such as osteoporosis.

Aqueous extract of Chrysanthemum morifolium Ramat. inhibits RANKL-induced osteoclast differentiation by suppressing the c-fos/NFATc1 pathway.

OBJECTIVE: The flower of chrysanthemum, used worldwide as a medicinal and edible product, has shown various bioactivities, such as anti-inflammatory, antioxidant, anti-tumorigenic, and hepatoprotective activities, as well as cardiovascular protection. However, the effect of Chrysanthemum morifolium Ramat. on the regulation of osteoclast differentiation has not yet been reported. In this study, we aimed to investigate the inhibitory effect of Chrysanthemum morifolium Ramat. water extract (CME) on RANKL-induced osteoclast differentiation in mouse bone marrow-derived macrophages (BMMs). STUDY DESIGN: Bone marrow-derived macrophages (BMMs) isolated from the C57BL/6 J mice. The viability of BMMs was detected with MTT assays. Inhibitory effects of CME on osteoclast differentiation and bone resorption was measured by TRAP staining and Pit assay. Osteoclast differentiation-associated gene expression were assessed by Real-time quantitative polymerase chain reaction. Intracellular signaling molecules was assessed by western blot. RESULTS: CME significantly inhibited osteoclast differentiation in BMMs without cytotoxicity, besides inhibiting MAPK/c-fos and PLCγ2/CREB activation. The inhibitory effects of CME on differentiation-related signaling molecules resulted in significant repression of NFATc1 expression, which is a key transcription factor in osteoclast differentiation, fusion, and activation. CONCLUSION: Our results confirmed the inhibition of RANKL-induced PLCγ2/CREB/c-fos/NFATc1 activation by CME during osteoclast differentiation. The findings collectively suggested CME as a traditional therapeutic agent for osteoporosis, RA, and periodontitis.

The dietary anthocyanin delphinidin prevents bone resorption by inhibiting Rankl-induced differentiation of osteoclasts in a medaka (Oryzias latipes) model of osteoporosis.

The anthocyanin delphinidin is a natural compound found as water-soluble pigment in coloured fruits and berries. Anthocyanin-rich diets have been proposed to have bone protective effects in humans and mice, but the underlying mechanisms remain unclear. In this study, we used a medaka (Oryzias latipes) osteoporosis model to test the effects of delphinidin on bone cells in vivo. In this model, inducible transgenic expression of receptor-activator of NF-kß ligand (Rankl) leads to ectopic formation of osteoclasts and excessive bone resorption, similar to the situation in human osteoporosis patients. Using live imaging in medaka bone reporter lines, we show that delphinidin significantly reduces the number of osteoclasts after Rankl induction and protects bone integrity in a dose-dependent manner. Our in vivo findings suggest that delphinidin primarily affects the de novo differentiation of macrophages into osteoclasts rather than the recruitment of macrophages to sites of bone resorption. For already existing osteoclasts, delphinidin treatment affected their morphology, leading to fewer protrusions and a more spherical shape. Apoptosis rates were not increased by delphinidin, suggesting that osteoclast numbers were reduced primarily by impaired differentiation from macrophage progenitors and reduced maintenance of pre-existing osteoclasts. Importantly, and in contrast to previously reported cell culture experiments, no effect of delphinidin on osteoblast differentiation and distribution was observed in medaka in vivo. Our study is the first report on the effects of delphinidin on bone cells in fish embryos, which are a unique model system for compound testing that is suitable for live imaging of bone cell behaviour in vivo.