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.

Diabetes Medication Metformin Inhibits Osteoclast Formation and Activity in In Vitro Models for Periodontitis

Diabetes and periodontitis are comorbidities and may share common pathways. Several reports indicate that diabetes medication metformin may be beneficial for the periodontal status of periodontitis patients. Further research using appropriate cell systems of the periodontium, the tissue that surrounds teeth may reveal the possible mechanism. Periodontal ligament fibroblasts anchor teeth in bone and play a role in the onset of both alveolar bone formation and degradation, the latter by inducing osteoclast formation from adherent precursor cells. Therefore, a cell model including this type of cells is ideal to study the influence of metformin on both processes. We hypothesize that metformin will enhance bone formation, as described for osteoblasts, whereas the effects of metformin on osteoclast formation is yet undetermined. Periodontal ligament fibroblasts were cultured in the presence of osteogenic medium and 0.2 or 1 mM metformin. The influence of metformin on osteoclast formation was first studied in PDLF cultures supplemented with peripheral blood leukocytes, containing osteoclast precursors. Finally, the effect of metformin on osteoclast precursors was studied in cultures of CD14+ monocytes that were stimulated with M-CSF and receptor activator of Nf-κB ligand (RANKL). No effects of metformin were observed on osteogenesis: not on alkaline phosphatase activity, Alizarin red deposition, nor on the expression of osteogenic markers RUNX-2, Collagen I and Osteonectin. Metformin inhibited osteoclast formation and accordingly downregulated the genes involved in osteoclastogenesis: RANKL, macrophage colony stimulating factor (M-CSF) and osteoclast fusion gene DC-STAMP. Osteoclast formation on both plastic and bone as well as bone resorption was inhibited by metformin in M-CSF and RANKL stimulated monocyte cultures, probably by reduction of RANK expression. The present study unraveling the positive effect of metformin in periodontitis patients at the cellular level, indicates that metformin inhibits osteoclast formation and activity, both when orchestrated by periodontal ligament fibroblasts and in cytokine driven osteoclast formation assays. The results indicate that metformin could have a systemic beneficiary effect on bone by inhibiting osteoclast formation and activity.

Vindoline Attenuates Osteoarthritis Progression Through Suppressing the NF-κB and ERK Pathways in Both Chondrocytes and Subchondral Osteoclasts

Disruption of extracellular matrix (ECM) homeostasis and subchondral bone remodeling play significant roles in osteoarthritis (OA) pathogenesis. Vindoline (Vin), an indole alkaloid extracted from the medicinal plant Catharanthus roseus, possesses anti-inflammatory properties. According to previous studies, inflammation is closely associated with osteoclast differentiation and the disorders of the homeostasis between ECM. Although Vin has demonstrated effective anti-inflammatory properties, its effects on the progression of OA remain unclear. We hypothesized that Vin may suppress the progress of OA by suppressing osteoclastogenesis and stabilizing ECM of articular cartilage. Therefore, we investigated the effects and molecular mechanisms of Vin as a treatment for OA in vitro and in vivo. In the present study, we found that Vin significantly suppressed RANKL-induced osteoclast formation and obviously stabilized the disorders of the ECM homeostasis stimulated by IL-1β in a dose-dependent manner. The mRNA expressions of osteoclast-specific genes were inhibited by Vin treatment. Vin also suppressed IL-1β-induced mRNA expressions of catabolism and protected the mRNA expressions of anabolism. Moreover, Vin notably inhibited the activation of RANKL-induced and IL-1β-induced NF-κB and ERK pathways. In vivo, Vin played a protective role by inhibiting osteoclast formation and stabilizing cartilage ECM in destabilization of the medial meniscus (DMM)-induced OA mice. Collectively, our observations provide a molecular-level basis for Vin’s potential in the treatment of OA.

Marein prevented LPS-induced osteoclastogenesis by regulating the NF-κB pathway in vitro

Gram-negative bacterial infection causes many bone diseases such as osteolysis, osteomyelitis and septic arthritis. Lipopolysaccharide (LPS), a bacteria product, played an important role in this process. Drugs that inhibited LPS-induced osteoclastogenesis were urgently needed for the prevention of bone destruction in infective bone diseases. Marein, a major bioactive compound of Coreopsis.tinctoria, which possesses anti-oxidative, anti-inflammatory, anti-hypertensive, anti-hyperlipidemic and anti-diabetic effects. In this study, the effect of marein on RAW264.7 cells was measured by CCK-8 assay; TRAP staining was used to determine osteoclastogenesis; the levels of osteoclast-related genes and NF-κB-related proteins were analyzed by WB; the levels of pro-inflammatory cytokines were quantified by ELISA. Our results showed that marein inhibited LPS-induced osteoclast formation from osteoclast precursor RAW264.7 cells. The effect of marein was related to its inhibitory function on expressions of pro-inflammatory cytokines and osteoclast-related genes including RANK, TRAF6, MMP-9, CK and CAⅡ. Besides, marein treatment could inhibit LPS-induced activation of NF-κB signaling pathway in RAW264.7 cells. Meanwhile, inhibition of NF-κB signaling pathway decreased the formation of osteoclasts and expression of pro-inflammatory cytokines which were LPS-induced. Collectively, marein could prevent LPS-induced osteoclast formation in vitro by regulating NF-κB signaling pathway. These findings provided evidence that marein might be beneficial as a valuable choice for the prevention and treatment of bacteria-induced bone destruction disease, and gave new insights for understanding its possible mechanism.

α-Mangostin Inhibits LPS-Induced Bone Resorption by Restricting Osteoclastogenesis Via NF-κB and MAPK Signaling

Background: Excessive activation of osteoclasts is an important cause of imbalance in bone remodeling, which further leads to pathological bone destruction. This is a clear feature of many osteolytic diseases, such as rheumatoid arthritis, osteoporosis, and osteolysis around the prosthesis. Based on the fact that many natural compounds have therapeutic potential for treating these diseases by suppressing osteoclast formation and function, we proved that α-mangostin, a natural compound isolated from mango, might be a promising choice. α-mangostin was described had anti‐inflammatory, anticancer and cardioprotective effects. Methods: We evaluated the therapeutic effect of α-mangostin in the process of osteoclast formation and bone resorption. The receptor activator of NF-κB ligand (RANKL) induces the formation of osteoclasts in vitro, and the potential pathways of α-mangostin to inhibit the differentiation and function of osteoclasts were explored. A mouse model of LPS‐induced calvarial osteolysis was establish. Subsequently, micro-CT, histology, etc. were used to evaluate the effect of α-mangostin in preventing inflammatory osteolysis.Results: In our study, we found that α-mangostin could inhibit RANKL-induced osteoclastogenesis and reduced osteoclast‐related gene expression in vitro. Besides, F-actin ring immunofluorescence and resorption pit assay indicated that α-mangostin can also destroy the function of osteoclast. Furthermore, α-mangostin achieved these effects by disrupting the activation of NF-κB/MAPKs signaling pathways. In vivo, our data revealed that α-mangostin could protect mouse calvarial from osteolysis. Conclusions: Together, our study demonstrates that α-mangostin exhibit the ability of inhibiting steoclastogenesis both in vitro and in vivo, and may be a potential option for treating osteoclast‐related diseases.

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.

Inhibition of Human Osteoclast Differentiation by Kynurenine through the Aryl-Hydrocarbon Receptor Pathway

Aryl-hydrocarbon receptor (AhR) is a ligand-activated transcription factor and regulates differentiation and function of various immune cells such as dendritic cells, Th17, and regulatory T cells. In recent studies, it was reported that AhR is involved in bone remodeling through regulating both osteoblasts and osteoclasts. However, the roles and mechanisms of AhR activation in human osteoclasts remain unknown. Here we show that AhR is involved in human osteoclast differentiation. We found that AhR expressed highly in the early stage of osteoclastogenesis and decreased in mature osteoclasts. Kynurenine (Kyn), formylindolo[3,4-b] carbazole (FICZ), and benzopyrene (BaP), which are AhR agonists, inhibited osteoclast formation and Kyn suppressed osteoclast differentiation at an early stage. Furthermore, blockade of AhR signaling through CH223191, an AhR antagonist, and knockdown of AhR expression reversed Kyn-induced inhibition of osteoclast differentiation. Overall, our study is the first report that AhR negatively regulates human osteoclast differentiation and suggests that AhR could be good therapeutic molecule to prevent bone destruction in chronic inflammatory diseases such as rheumatoid arthritis (RA).