Asperpyrone A attenuates RANKL-induced osteoclast formation through inhibiting NFATc1, Ca2+ signalling and oxidative stress

RANKL promotes MT2 degradation and ROS production in osteoclast precursors through Beclin1-dependent autophagy

ROS produced under oxidative stress are crucial for osteoclast differentiation. Metallothionein (MT) is a ROS-scavenging molecule. As a member of MT family, MT2 can clear ROS in osteoclast precursors (OCPs) and contributes to osteoclast differentiation. RANKL can promote OCP autophagy. Given the molecular-degrading effect of autophagy, the relationship between RANKL-dependent autophagy, MT2 and ROS during osteoclast differentiation is worth exploring. We depended in vitro RANKL administration and RANKL-overexpressing (Tg-RANKL) mice to observe the effects of RANKL on ROS production, MT2 protein expression, Beclin1 expression and autophagic activity in OCPs. Spautin1 was used to investigate the relationship between Beclin1-dependent autophagy and RANKL-regulated MT2 expression. Osteoclast-targeting MT2-cDNA-AAVs were applied to assess the therapeutic effect of MT2 on Tg-RANKL-related bone loss. The results showed that RANKL promoted ROS production but reduced MT2 protein expression in OCPs. RANKL also enhanced Beclin1 expression and LC3-puncta abundance. Decreased Beclin1 expression with spautin1 blocked RANKL-increased ROS production and osteoclast differentiation and recovered RANKL-decreased MT2 expression. MT2 selective overexpression with CD11b-promoter-MT2-cDNA-AAVs attenuated ROS production and osteoclastogenesis in Tg-RANKL mice and improved bone loss. Overall, RANKL can reduce MT2 protein expression through Beclin1-dependent autophagy, thereby promoting ROS production and osteoclast differentiation; this suggests that MT2-overexpressing small molecule drugs have the potential to treat RANKL-related bone loss.

Experimental study of radial extracorporeal shock wave therapy for periprosthetic osteolysis induced by wear particles

Radial Extracorporeal Shock Wave Therapy (rESWT) is applied as a conservative treatment modality in orthopedics, yet its effectiveness in addressing aseptic loosening of cementless joint prostheses remains unclear. Through animal experimentation, we have revealed that in a titanium particle-induced osteolysis rat model, rESWT intervention significantly increased periprosthetic bone density compared to untreated controls, concurrently reducing osteolytic lesion area and lowering serum IL-1β levels. Histological analyses demonstrated a relative decrease in osteoclast counts within the treatment group versus non-treated controls. These findings indicate that rESWT, through mechanisms involving anti-inflammatory actions and suppression of osteoclastogenesis, may serve as a non-invasive therapeutic strategy for preventing and managing periprosthetic bone loss, demonstrating clinical potential to delay or eliminate the necessity for revision surgeries.

Anti‑osteoclastogenic effect of fermented mealworm extract by inhibiting RANKL‑induced NFATc1 action

Augmented osteoclast activity and differentiation can lead to destructive bone diseases, such as arthritis and osteoporosis. Therefore, modulating osteoclastogenesis and differentiation may serve to be a possible strategy for treating such diseases. Tenebrio molitor larvae, also known as mealworms, are considered a good source of protein with nutritional value, digestibility, flavor and functional properties, such as antioxidant, anti-diabetic and anti-obesity effects. However, the role of mealworms in osteoclastogenesis remains poorly understood. The present study therefore investigated the effects of fermented mealworm extract (FME) on receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclastogenesis in bone marrow-derived macrophages (BMMs) whilst also attempting to understand the underlying mechanism, if any. The cells treated with RANKL were used as the negative control. To prepare FME, defatted mealworm powder was fermented with a Saccharomyces cerevisiae strain, and then extracted with fermented alcohol. Cell viability of BMMs isolated from 5-week-old Institute of Cancer Research mice was measured using Cell Counting Kit-8 assay. Subsequently, the effects of FME on osteoclast differentiation were measured using tartrate-resistant acid phosphatase (TRAP) staining. In addition, expression of markers associated with osteoclast differentiation was assessed by reverse transcription-quantitative PCR. Expression of nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) was assessed by western blotting. TRAP staining revealed that FME inhibited osteoclast differentiation in a dose-dependent manner (10-100 µg/ml) without causing cytotoxicity. Specifically, the formation of osteoclasts appear to have been suppressed by FME as indicated by the reduction in the number of TRAP-positive multinucleated cells observed. Furthermore, FME treatment significantly decreased the mRNA expression of c-Fos, whilst also significantly decreasing the expression of NFATc1 on both protein and mRNA levels. c-Fos and NFATc1 are transcription factors that can regulate osteoclast differentiation. FME treatment also reduced the expression of genes associated with osteoclast differentiation and function, including dendritic cell-specific transmembrane protein, osteoclast associated Ig-like receptor, Cathepsin K and TRAP, compared with that in the control group. Subsequently, FME was found to effectively suppress RANKL-induced osteoclast differentiation compared with that by the non-fermented mealworm extract. These findings suggest that FME may confer anti-osteoclastogenic effects, providing insights into its potential application in treatment of osteoporosis.

Unveiling the potential of Butylphthalide: inhibiting osteoclastogenesis and preventing bone loss

Osteoporosis, resulting from overactive osteoclasts and leading to elevated fracture risk, has emerged as a global public health concern due to the aging population. Therefore, inhibiting osteoclastogenesis and bone resorption function represents a crucial approach for preventing and treating osteoporosis. The purpose of this study was to examine the effects and molecular mechanisms of Butylphthalide (NBP) on the differentiation and function of osteoclasts induced by RANKL. Osteoclastogenesis was assessed through TRAP staining and bone slice assay. An animal model that underwent ovariectomy, simulating postmenopausal women's physiological characteristics, was established to investigate the impact of Butylphthalide on ovariectomy-induced bone loss. To delve deeper into the specific mechanisms, we employed Western blot, PCR, immunofluorescence, and immunohistochemical staining to detect the expression of proteins that are associated with the osteoclast signaling pathway. In this study, we found that Butylphthalide not only suppressed osteoclastogenesis and bone resorption in vitro but also significantly decreased TRAcP-positive osteoclasts and prevented bone loss in vivo. Further mechanistic experiments revealed that Butylphthalide reduces intracellular ROS in osteoclasts, inhibits the MAPK and NFATc1 signaling pathways, and downregulates the key genes and proteins of osteoclasts. This inhibits osteoclast formation and function. The reduction in ROS in osteoclasts is intricately linked to the activity of Butylphthalide-modulated antioxidant enzymes. Overall, NBP may offer a alternative treatment option with fewer side effects for skeletal diseases such as osteoporosis.

CGK733 alleviates ovariectomy-induced bone loss through blocking RANKL-mediated Ca2+ oscillations and NF-κB/MAPK signaling pathways

Osteoporosis is a prevalent systemic metabolic disease in modern society, in which patients often suffer from bone loss due to over-activation of osteoclasts. Currently, amelioration of bone loss through modulation of osteoclast activity is a major therapeutic strategy. Ataxia telangiectasia mutated (ATM) inhibitor CGK733 (CG) was reported to have a sensitizing impact in treating malignancies. However, its effect on osteoporosis remains unclear. In this study, we investigated the effects of CG on osteoclast differentiation and function, as well as the therapeutic effects of CG on osteoporosis. Our study found that CG inhibits osteoclast differentiation and function. We further found that CG inhibits the activation of NFATc1 and ultimately osteoclast formation by inhibiting RANKL-mediated Ca2+ oscillation and the NF-κB/MAPK signaling pathway. Next, we constructed an ovariectomized mouse model and demonstrated that CG improved bone loss in ovariectomized mice. Therefore, CG may be a potential drug for the prevention and treatment of osteoporosis.

MT2 INHIBITS OSTEOCLASTOGENESIS BY SCAVENGING ROS

Context and objective

Reactive oxygen species (ROS) produced under oxidative stress is important for osteoclastogenesis. As a major member of the metallothionein (MT) family, metallothionein2 (MT2) can scavenge ROS in osteoblasts. However, the role of MT2 in osteoclastogenesis and ROS production in osteoclast precursors (OCPs) is unknown.

Material and methods

In this study, we first investigated MT2 expression level in osteoporotic model mice. Next, we explored the roles of MT2 in osteoclastic differentiation and ROS production in OCPs. Ultimately, via rescue assays based on hydrogen peroxide (H2O2), the significance of ROS in MT-2-regulated osteoclastic differentiation was further elucidated.

Results

Compared with sham operated (Sham) mice, ovariectomized (OVX) mice displayed bone marrow primary OCPs (Ly6C+CD11b-) having higher ROS levels and lower MT2 expression. MT2 overexpression inhibited the formation of mature osteoclasts, while MT2 knockdown was contrary. Moreover, MT2 overexpression inhibited ROS production in OCPs, while MT2 knockdown exhibited the opposite effects. Notably, the inhibitory effect of MT2 overexpression on osteoclastogenesis and ROS production was blocked by the addition of H2O2.

Conclusion

MT2 inhibits osteoclastogenesis through repressing ROS production in OCPs, which indicates that the strategy of upregulating MT2 in OCPs may be applied to the clinical treatment of osteoclastic bone loss.

Effects of Piper sarmentosum on Bone Health and Fracture Healing: A Scoping Review

BACKGROUND

Piper sarmentosum (PS) is a traditional herb used by Southeast Asian communities to treat various illnesses. Recent pharmacological studies have discovered that PS possesses antioxidant and anti-inflammatory activities. Since oxidative stress and inflammation are two important processes driving the pathogenesis of bone loss, PS may have potential therapeutic effects against osteoporosis.

OBJECTIVE

This review systematically summarised the therapeutic effects of PS on preventing osteoporosis and promoting fracture healing.

METHODS

A systematic literature search was performed in November 2021 using 4 electronic databases and the search string "Piper sarmentosum" AND (bone OR osteoporosis OR osteoblasts OR osteoclasts OR osteocytes).

RESULTS

Nine unique articles were identified from the literature. The efficacy of PS has been studied in animal models of osteoporosis induced by ovariectomy and glucocorticoids, as well as bone fracture models. PS prevented deterioration of bone histomorphometric indices, improved fracture healing and restored the biomechanical properties of healed bone in ovariectomised rats. PS also prevented osteoblast/osteocyte apoptosis, increased bone formation and mineralisation and subsequently improved trabecular bone microstructures and strength of rats with osteoporosis induced by glucocorticoids. Apart from its antioxidant and anti-inflammatory activity, PS also suppressed circulating and skeletal expression of corticosterone and skeletal expression of 11β hydroxysteroid dehydrogenase type 1 but increased the enzyme activity in the glucocorticoid osteoporosis model. This review also identified several research gaps about the skeletal effects of PS and suggested future studies to bridge these gaps.

CONCLUSION

PS may be of therapeutic benefit to bone health. However, further research is required to validate this claim.

Receptor activator of nuclear factor-κB ligand-mediated osteoclastogenesis signaling pathway and related therapeutic natural compounds

Osteoclast is a hematopoietic precursor cell derived from the mononuclear macrophage cell line, which is the only cell with bone resorption function. Its abnormal activation can cause serious osteolysis related diseases such as rheumatoid arthritis, Paget's disease and osteoporosis. In recent years, the adverse effects caused by anabolic anti-osteolytic drugs have increased the interest of researchers in the potential therapeutic and preventive effects of natural plant derivatives and natural compounds against osteolytic diseases caused by osteoclasts. Natural plant derivatives and natural compounds have become major research hotspots for the treatment of osteolysis-related diseases due to their good safety profile and ability to improve bone. This paper provides an overview of recent advances in the molecular mechanisms of RANKL and downstream signaling pathways in osteoclast differentiation, and briefly outlines potential natural compounds with antiosteoclast activity and molecular mechanisms.

A Review on the Molecular Mechanisms of Action of Natural Products in Preventing Bone Diseases

The drugs used for treating bone diseases (BDs), at present, elicit hazardous side effects that include certain types of cancers and strokes, hence the ongoing quest for the discovery of alternatives with little or no side effects. Natural products (NPs), mainly of plant origin, have shown compelling promise in the treatments of BDs, with little or no side effects. However, the paucity in knowledge of the mechanisms behind their activities on bone remodeling has remained a hindrance to NPs’ adoption. This review discusses the pathological development of some BDs, the NP-targeted components, and the actions exerted on bone remodeling signaling pathways (e.g., Receptor Activator of Nuclear Factor κ B-ligand (RANKL)/monocyte/macrophage colony-stimulating factor (M-CSF)/osteoprotegerin (OPG), mitogen-activated protein kinase (MAPK)s/c-Jun N-terminal kinase (JNK)/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), Kelch-like ECH-associated protein 1 (Keap-1)/nuclear factor erythroid 2–related factor 2 (Nrf2)/Heme Oxygenase-1 (HO-1), Bone Morphogenetic Protein 2 (BMP2)-Wnt/β-catenin, PhosphatidylInositol 3-Kinase (PI3K)/protein kinase B (Akt)/Glycogen Synthase Kinase 3 Beta (GSK3β), and other signaling pathways). Although majority of the studies on the osteoprotective properties of NPs against BDs were conducted ex vivo and mostly on animals, the use of NPs for treating human BDs and the prospects for future development remain promising.

Dendrobine attenuates osteoclast differentiation through modulating ROS/NFATc1/ MMP9 pathway and prevents inflammatory bone destruction

BACKGROUND

Osteolytic diseases share symptoms such as bone loss, fracture and pain, which are caused by over-activated osteoclasts. Targeting osteoclast differentiation has emerged as a therapeutic strategy clinically. Dendrobine is an alkaloid isolated from Chinese herb Dendrobium nobile, with knowing effects of analgesia and anti-inflammation. The roles of dendrobine on osteoclasts and osteolysis remain unclear.

PURPOSE

Herein, the possible roles of dendrobine in osteoclastogenesis, inflammatory osteolysis and the underlying mechanism were explored.

METHODS

Bone marrow-derived macrophages (BMMs) and RAW264.7 cells were employed to evaluate the roles of dendrobine on osteoclastogenesis, bone absorption and the underlying mechanism in vitro. LPS injection was used to cause inflammatory osteolysis in vivo.

RESULTS

Dendrobine repressed osteoclastogenesis, bone resorption induced by receptor activator of nuclear factor kappa B ligand (RANKL) in vitro. Mechanistically, dendrobine inhibited RANKL-upregulated intracellular (ROS), p-p38, c-Fos expression and nuclear factor of activated T cells (NFATc1) nuclear translocation. Osteoclastic genes were reduced, and among them matrix metalloproteinase 9 (MMP9) mRNA was dramatically blocked by dendrobine. Moreover, it substantially suppressed MMP9 protein expression during osteoclastogenesis in vitro. Accordingly, oral 20 mg/kg/day dendrobine was capable of preventing LPS-induced osteolysis with decreased osteoclasts in vivo.

CONCLUSION

Taken together, dendrobine suppresses osteoclastogenesis through restraining ROS, p38-c-Fos and NFATc1-MMP9 in vitro, thus attenuates inflammatory osteolysis in vivo. This finding supports the discover of dendrobine as a novel osteoclast inhibitor for impeding bone erosion in the future.

Inhibitory Effects of Rhaponticin on Osteoclast Formation and Resorption by Targeting RANKL-Induced NFATc1 and ROS Activity

The extravagant osteoclast formation and resorption is the main cause of osteoporosis. Inhibiting the hyperactive osteoclastic resorption is considered as an efficient treatment for osteoporosis. Rhaponticin (RH) is a small molecule that has been reported to possess anti-inflammatory, anti-allergic, anti-fibrotic, and anti-diabetic activities. However, the influence of RH on osteoclasts differentiation and function is still unclear. To this end, an array of assays including receptor activator of nuclear factor kappa-Β (NF-κB) ligand (RANKL) induced osteoclastogenesis, tartrate-resistant acidic phosphatase (TRAcP) staining, immunofluorescence, and hydroxyapatite resorption were performed in this study. It was found that RH had significant anti-catabolic effects by inhibiting osteoclastogenesis and bone resorption without cytotoxicity. Mechanistically, the expression of NADPH oxidase 1 (Nox1) was found to be suppressed and antioxidant enzymes including catalase, superoxide dismutase 2 (SOD-2), and heme oxygenase-1(HO-1) were enhanced following RH treatment, suggesting RH exhibited antioxidant activity by reducing the generation of reactive oxygen species (ROS) as well as enhancing the depletion of ROS. In addition, MAPKs, NF-κB, and intracellular Ca2+ oscillation pathways were significantly inhibited by RH. These changes led to the deactivation of osteoclast master transcriptional factor-nuclear factor of activated T cells 1 (NFATc1), as examined by qPCR and Western blot assay, which led to the decreased expression of downstream integrin β3, c-Fos, cathepsin K, and Atp6v0d2. These results suggested that RH could effectively suppress RANKL-regulated osteoclast formation and bone resorption. Therefore, we propose that RH can represent a novel natural small molecule for the treatment of osteoporosis by inhibiting excessive osteoclast activity.

Briarane-type diterpenoids suppress osteoclastogenisis by regulation of Nrf2 and MAPK/NF-kB signaling pathway

Excess osteoclastic activity leads to an imbalance in bone remodeling and causes most adult skeletal diseases. Natural products are a promising source to attenuate the osteoporosis and relevant diseases of bone loss. Herein, a bioassay-guided detection of gorgonian corals resulted in junceellolide D (JD), a briarane-type diterpenoid from gorgonian Dichotella gemmacea, showing significant inhibition against the receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast differentiation in bone marrow macrophages (BMMs) in vitro. To extend the investigation for structure-activity relationship (SAR), a total of 39 briarane-type analogues were isolated including 28 new compounds, and their structures were determined by extensive analyses of spectroscopic data. The SAR data indicated that JD is the most active to inhibit osteoclast development due to the decreased number of multinucleated tartrate-resistance acid phosphatase positive cells, suppression of the actin ring formation, blockage of bone resorption, and downregulation of osteoclast-specific marker genes. Mechanistically, JD increased the protein stability of nuclear factor (erythroid-derived 2)-related factor-2 (Nrf2) and promoted Nrf2 nuclear translocation followed by activation its downstream antioxidant enzymes, which strongly abolished RANKL-induced generation of reactive oxygen species (ROS). Furthermore, JD inhibits the RANKL-stimulated activation of NF-κB and MAPK signaling pathways. Hence, JD is considered as a promising lead compound for anti-osteoclastogenesis via activating Nrf2 and suppressing NF-κB and MAPK signaling pathways to prevent osteoclast-mediated bone destructive diseases.

Peiminine Suppresses RANKL-Induced Osteoclastogenesis by Inhibiting the NFATc1, ERK, and NF-κB Signaling Pathways

Osteoclasts (OCs) play an important role in osteoporosis, a disease that is mainly characterized by bone loss. In our research, we aimed to identify novel approach for regulating osteoclastogenesis and thereby treating osteoporosis. Previous studies have set a precedent for screening traditional Chinese herbal extracts for effective inhibitors. Peiminine is an alkaloid extracted from the bulb of Fritillaria thunbergii Miq that reportedly has anticancer and anti-inflammatory effects. Thus, the potential inhibitory effect of peiminine on OC differentiation was investigated via a series of experiments. According to the results, peiminine downregulated the levels of specific genes and proteins in vitro and consequently suppressed OC differentiation and function. Based on these findings, we further investigated the underlying molecular mechanisms and identified the NF-κB and ERK1/2 signaling pathways as potential targets of peiminine. In vivo, peiminine alleviated bone loss in an ovariectomized mouse model.

Finely-Tuned Calcium Oscillations in Osteoclast Differentiation and Bone Resorption

Calcium (Ca²⁺) plays an important role in regulating the differentiation and function of osteoclasts. Calcium oscillations (Ca oscillations) are well-known phenomena in receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclastogenesis and bone resorption via calcineurin. Many modifiers are involved in the fine-tuning of Ca oscillations in osteoclasts. In addition to macrophage colony-stimulating factors (M-CSF; CSF-1) and RANKL, costimulatory signaling by immunoreceptor tyrosine-based activation motif-harboring adaptors is important for Ca oscillation generation and osteoclast differentiation. DNAX-activating protein of 12 kD is always necessary for osteoclastogenesis. In contrast, Fc receptor gamma (FcRγ) works as a key controller of osteoclastogenesis especially in inflammatory situation. FcRγ has a cofactor in fine-tuning of Ca oscillations. Some calcium channels and transporters are also necessary for Ca oscillations. Transient receptor potential (TRP) channels are well-known environmental sensors, and TRP vanilloid channels play an important role in osteoclastogenesis. Lysosomes, mitochondria, and endoplasmic reticulum (ER) are typical organelles for intracellular Ca²⁺ storage. Ryanodine receptor, inositol trisphosphate receptor, and sarco/endoplasmic reticulum Ca²⁺ ATPase on the ER modulate Ca oscillations. Research on Ca oscillations in osteoclasts has still many problems. Surprisingly, there is no objective definition of Ca oscillations. Causality between Ca oscillations and osteoclast differentiation and/or function remains to be examined.

Imperatorin promotes osteogenesis and suppresses osteoclast by activating AKT/GSK3 β/β-catenin pathways

Osteoporosis is caused by disturbance in the dynamic balance of bone remodelling, a physiological process, vital for maintenance of healthy bone tissue in adult humans. In this process, a new bone is formed by osteoblasts and the pre‐existing bone matrix is resorbed by osteoclasts. Imperatorin, a widely available and inexpensive plant extract with antioxidative and apoptotic effects, is reported to treat osteoporosis. However, the underlying mechanism and specific effects on bone metabolism have not been elucidated. In this study, we used rat bone marrow‐derived mesenchymal stem cells and found that imperatorin can activate RUNX2, COL1A1 and osteocalcin by promoting the Ser9 phosphorylation of GSK3β and entry of β‐catenin into the nucleus. Imperatorin also enhanced the production of phospho‐AKT (Ser473), an upstream factor that promotes the Ser9 phosphorylation of GSK3β. We used ipatasertib, a pan‐AKT inhibitor, to inhibit the osteogenic effect of imperatorin, and found that imperatorin promotes osteogenesis via AKT/GSK3β/β‐catenin pathway. Next, we used rat bone marrow‐derived monocytes, to check whether imperatorin inhibits osteoclast differentiation via AKT/GSK3β/β‐catenin pathway. Further, we removed the bilateral ovaries of rats to establish an osteoporotic model. Intragastric administration of imperatorin promoted osteogenesis and inhibited osteoclast in vivo. Our experiments showed that imperatorin is a potential drug for osteoporosis treatment.

Asperpyrone A attenuates RANKL-induced osteoclast formation through inhibiting NFATc1, Ca2+ signalling and oxidative stress

Imbalance of osteoblast and osteoclast in adult leads to a variety of bone-related diseases, including osteoporosis. Thus, suppressing the activity of osteoclastic bone resorption becomes the main therapeutic strategy for osteoporosis. Asperpyrone A is a natural compound isolated from Aspergillus niger with various biological activities of antitumour, antimicrobial and antioxidant. The present study was designed to investigate the effects of Asperpyrone A on osteoclastogenesis and to explore its underlining mechanism. We found that Asperpyrone A inhibited RANKL-induced osteoclastogenesis in a dose-dependent manner when the concentration reached 1 µm, and with no cytotoxicity until the concentration reached to 10 µm. In addition, Asperpyrone A down-regulated the mRNA and protein expression of NFATc1, c-fos and V-ATPase-d2, as well as the mRNA expression of TRAcP and Ctsk. Furthermore, Asperpyrone A strongly attenuated the RNAKL-induced intracellular Ca2+ oscillations and ROS (reactive oxygen species) production in the process of osteoclastogenesis and suppressed the activation of MAPK and NF-κB signalling pathways. Collectively, Asperpyrone A attenuates RANKL-induced osteoclast formation via suppressing NFATc1, Ca2+ signalling and oxidative stress, as well as MAPK and NF-κB signalling pathways, indicating that this compound may become a potential candidate drug for the prevention or treatment of osteoporosis.