Targeting SAT1 prevents osteoporosis through promoting osteoclast apoptosis.

Osteoporosis is a systemic bone disease characterized by decreased bone mass that is tightly regulated by the coordinated actions of osteoclasts and osteoblasts. Apoptosis as a precise programmed cell death involves a cascade of gene expression events which are mechanistically linked to the regulation of bone metabolism. Nevertheless, the critical biomolecules involved in regulating cell apoptosis in osteoporosis remain unknown. To gain a deeper insight into the relationship between apoptosis and osteoporosis, this study integrated the sequencing results of human samples and using a machine learning workflow to overcome the limitations of a single study. Among all immune cell populations, we assessed the apoptotic level and portrayed the distinct subtypes and lineage differentiation of monocytic cells in osteoporotic tissues. Osteoclasts expressed a higher level of Spermidine/spermine-N1-Acetyltransferase1 (SAT1) during osteoclastogenesis which prevented osteoclasts apoptosis and facilitate osteoporosis progression. In addition, Berenil, one potent SAT1 inhibitor, increased osteoclast apoptosis and reversed the bone loss in the femurs of a murine ovariectomy model. In summary, Berenil promotes osteoclast apoptosis, inhibits the bone resorption and improves the abnormal bone structure in vitro and in vivo models by targeting SAT1, demonstrating its potential as a precise therapeutic strategy for clinical osteoporosis treatment.

6-O-angeloylplenolin inhibits osteoclastogenesis in vitro via suppressing c-Src/NF-κB/NFATc1 pathways and ameliorates bone resorption in collagen-induced arthritis mouse model.

One of the effective therapeutic strategies to treat rheumatoid arthritis (RA)-related bone resorption is to target excessive activation of osteoclasts. We discovered that 6-O-angeloylplenolin (6-OAP), a pseudoguaianolide from Euphorbia thymifolia Linn widely used for the treatment of RA in traditional Chinese medicine, could inhibit RANKL-induced osteoclastogenesis and bone resorption in both RAW264.7 cells and BMMs from 1 µM and protect a collagen-induced arthritis (CIA) mouse model from bone destruction in vivo. The severity of arthritis and bone erosion observed in paw joints and the femurs of the CIA model were attenuated by 6-OAP administered at both dosages (1 or 5 mg/kg, i.g.). BMD, Tb.N and BV/TV were also improved by 6-OAP treatment. Histological analysis and TRAP staining of femurs further confirmed the protective effects of 6-OAP on bone erosion, which is mainly due to reduced osteoclasts. Molecular docking indicated that c-Src might be a target of 6-OAP and phosphorylation of c-Src was suppressed by 6-OAP treatment. CETSA and SPR assay further confirmed the potential interaction between 6-OAP and c-Src. Three signaling molecules downstream of c-Src that are vital to the differentiation and function of osteoclasts, NF-κB, c-Fos and NFATc1, were also suppressed by 6-OAP in vitro. In summary, the results demonstrated that the function of c-Src was disrupted by 6-OAP, which led to the suppression of downstream signaling vital to osteoclast differentiation and function. In conclusion, 6-OAP has the potential to be further developed for the treatment of RA-related bone erosion.

Isobavachin attenuates osteoclastogenesis and periodontitis-induced bone loss by inhibiting cellular iron accumulation and mitochondrial biogenesis.

As bone-resorbing cells rich in mitochondria, osteoclasts require high iron uptake to promote mitochondrial biogenesis and maintain a high-energy metabolic state for active bone resorption. Given that abnormal osteoclast formation and activation leads to imbalanced bone remodeling and osteolytic bone loss, osteoclasts may be crucial targets for treating osteolytic diseases such as periodontitis. Isobavachin (IBA), a natural flavonoid compound, has been confirmed to be an inhibitor of receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast differentiation from bone marrow-derived macrophages (BMMs). However, its effects on periodontitis-induced bone loss and the potential mechanism of its anti-osteoclastogenesis effect remain unclear. Our study demonstrated that IBA suppressed RANKL-induced osteoclastogenesis in BMMs and RAW264.7 cells and inhibited osteoclast-mediated bone resorption in vitro. Transcriptomic analysis indicated that iron homeostasis and reactive oxygen species (ROS) metabolic process were enriched among the differentially expressed genes following IBA treatment. IBA exerted its anti-osteoclastogenesis effect by inhibiting iron accumulation in osteoclasts. Mechanistically, IBA attenuated iron accumulation in RANKL-induced osteoclasts by inhibiting the mitogen-activated protein kinase (MAPK) pathway to upregulate ferroportin1 (Fpn1) expression and promote Fpn1-mediated intracellular iron efflux. We also found that IBA inhibited mitochondrial biogenesis and function, and reduced RANKL-induced ROS generation in osteoclasts. Furthermore, IBA attenuated periodontitis-induced bone loss by reducing osteoclastogenesis in vivo. Overall, these results suggest that IBA may serve as a promising therapeutic strategy for bone diseases characterized by osteoclastic bone resorption.

The novel small molecule E0924G dually regulates bone formation and bone resorption through activating the PPARδ signaling pathway to prevent bone loss in ovariectomized rats and senile mice.

Osteoporosis is particularly prevalent among postmenopausal women and the elderly. In the present study, we investigated the effect of the novel small molecule E0924G (N-(4-methoxy-pyridine-2-yl)-5-methylfuran-2-formamide) on osteoporosis. E0924G significantly increased the protein expression levels of osteoprotegerin (OPG) and runt-related transcription factor 2 (RUNX2), and thus significantly promoted osteogenesis in MC3T3-E1 cells. E0924G also significantly decreased osteoclast differentiation and inhibited bone resorption and F-actin ring formation in receptor activator of NF-κB ligand (RANKL)-induced osteoclasts from RAW264.7 macrophages. Importantly, oral administration of E0924G in both ovariectomized (OVX) rats and SAMP6 senile mice significantly increased bone mineral density and decreased bone loss compared to OVX controls or SAMR1 mice. Further mechanistic studies showed that E0924G could bind to and then activate peroxisome proliferator-activated receptor delta (PPARδ), and the pro-osteoblast effect and the inhibition of osteoclast differentiation induced by E0924G were significantly abolished when PPARδ was knocked down or inhibited. In conclusion, these data strongly suggest that E0924G has the potential to prevent OVX-induced and age-related osteoporosis by dual regulation of bone formation and bone resorption through activation of the PPARδ signaling pathway.

Antrodia cinnamomea prevents ovariectomized-promoted bone loss by inhibiting osteoclast formation.

Osteoporosis is a common bone disease in aging populations, particularly in postmenopausal women. Anti-resorptive and anabolic drugs have been applied to prevent and cure osteoporosis and are linked with a variety of adverse effects. Antrodia cinnamomea extracts (ACE) are highly renowned for their anticancer, antioxidative, and anti-inflammatory properties. However, whether ACE-enriched anti-osteoporosis functions are largely unknown. In a preclinical animal model, we found that ovariectomy significantly decreased bone volume in the ovariectomized (OVX) rats. Administration of ACE antagonized OVX-induced bone loss. In addition, ACE reversed OVX-reduced biomechanical properties. The serum osteoclast marker also showed improvement in the ACE-treated group. In the cellular model, it was indicated that ACE inhibits RANKL-induced osteoclast formation. Taken together, ACE seems to be a hopeful candidate for the development of novel anti-osteoporosis treatment.

Cichoric acid targets RANKL to inhibit osteoclastogenesis and prevent ovariectomy-induced bone loss.

BACKGROUND AND AIM: Osteoporosis, a systemic metabolic bone disease, is characterized by the decline of bone mass and quality due to excessive osteoclast activity. Currently, drug-targeting osteoclasts show promising therapy for osteoporosis. In this study, we investigated the effect of cichoric acid (CA) on receptor activator of nuclear kappa-B ligand (RANKL)-induced osteoclastogenesis and the bone loss induced by ovariectomy in mice. EXPERIMENTAL PROCEDURE: Molecular docking technologies were employed to examine the interaction between CA and RANKL. CCK8 assay was used to evaluate the cell viability under CA treatment. TRAcP staining, podosome belt staining, and bone resorption assays were used to test the effect of CA on osteoclastogenesis and osteoclast function. Further, an OVX-induced osteoporosis mice model was employed to identify the effect of CA on bone loss using micro-CT scanning and histological examination. To investigate underlying mechanisms, network pharmacology was applied to predict the downstream signaling pathways, which were verified by Western blot and immunofluorescence staining. KEY RESULTS: The molecular docking analysis revealed that CA exhibited a specific binding affinity to RANKL, engaging multiple binding sites. CA inhibited RANKL-induced osteoclastogenesis and bone resorption without cytotoxic effects. Mechanistically, CA suppressed RANKL-induced intracellular reactive oxygen species, nuclear factor-kappa B, and mitogen-activated protein kinase pathways, followed by abrogated nuclear factor activated T-cells 1 activity. Consistent with this finding, CA attenuated post-ovariectomy-induced osteoporosis by ameliorating osteoclastogenesis. CONCLUSIONS AND IMPLICATIONS: CA inhibited osteoclast activity and bone loss by targeting RANKL. CA might represent a promising candidate for treating osteoclast-related diseases, such as osteoporosis.

Phillygenin prevents osteoclast differentiation and bone loss by targeting RhoA.

Forsythia suspensa tea is a popular traditional Chinese medicine decoction for its healthy and therapeutic benefits. However, its effects in bone metabolism were not clear. In recent study, we uncovered anti-osteoclastogenesis property of Phillygenin (Phi), a compound abundant in Forsythia suspensa leaves, and aimed to investigate the effect and mechanism of Phi on bone metabolism in vivo and in vitro. Lipopolysaccharides-induced murine calvaria osteolysis and ovariectomy-induced bone loss animal models were used to identify the bone-protective effect of Phi in vivo and micro-CT, pQCT, and TRAP staining were applied. We used CCK8, TUNEL, BrdU, and TRAP staining to evaluate the efficacy of Phi on the proliferation and formation of OCs in primary mBMMs. RNA sequence, activity-based protein profiling, molecular docking, G-LISA, and WB were used to inspect the target and underlying mechanism of Phi's actions in mBMMs. We found Phi significantly inhibited bone resorption in vivo and inhibited mBMMs osteoclastogenesis in vitro. Ras homolog gene family member A (RhoA) was identified as the direct target of Phi. It counteracted the effects of RhoA activator and acted as a RhoA inhibitor. By targeting RhoA, Phi modulated Rho-associated coiled-coil containing protein kinase 1 (ROCK1) activity and regulated its downstream NF-κB/NFATc1/c-fos pathway. Furthermore, Phi depressed the disassembling of F-actin ring through cofilin and myosin1a. Our findings provided Phi as a potential option for treating bone loss diseases by targeting RhoA and highlighted the importance of F. suspensa as a preventive approach in bone disorders.

Piperlongumine, a Piper longum-derived amide alkaloid, protects mice from ovariectomy-induced osteoporosis by inhibiting osteoclastogenesis via suppression of p38 and JNK signaling.

Postmenopausal osteoporosis (PMOP) is a metabolic bone disease that results from overproduction and hyperactivation of osteoclasts caused by insufficient estrogen in women after menopause. Current therapeutic strategies are mainly focused on treating PMOP patients who have already developed severe bone loss or even osteoporotic fractures. Obviously, a better strategy is to prevent PMOP from occurring in the first place. However, such reagents are largely lacking. Piperlongumine (PLM), an amide alkaloid extracted from long pepper Piper longum, exhibits the anti-osteoclastogenic effect in normal bone marrow macrophages (BMMs) and the protective effect against osteolysis induced by titanium particles in mice. This study examined the preventive effect of PLM on PMOP and explored the potential mechanism of this effect using both ovariectomized mice and their primary cells. The result showed that PLM (5 and 10 mg kg-1) administered daily for 6 weeks ameliorated ovariectomy-induced bone loss and osteoclast formation in mice. Further cell experiments showed that PLM directly suppressed osteoclast formation, F-actin ring formation, and osteoclastic resorption pit formation in BMMs derived from osteoporotic mice, but did not obviously affect osteogenic differentiation of bone marrow stromal cells (BMSCs) from these mice. Western blot analysis revealed that PLM attenuated maximal activation of p38 and JNK pathways by RANKL stimulation without affecting acute activation of NF-κB, AKT, and ERK signaling. Furthermore, PLM inhibited expression of key osteoclastogenic transcription factors NFATc1/c-Fos and their target genes (Dcstamp, Atp6v0d2, Acp5, and Oscar). Taken together, our findings suggest that PLM inhibits osteoclast formation and function by suppressing RANKL-induced activation of the p38/JNK-cFos/NFATc1 signaling cascade, thereby preventing ovariectomy-induced osteoporosis in mice. Thus, PLM can potentially be used as an anti-resorption drug or dietary supplement for the prevention of PMOP.

Effect of vitamin D supplementation or fortification on bone turnover markers in women: a systematic review and meta-analysis.

Vitamin D is a vital indicator of musculoskeletal health, as it plays an important role through the regulation of bone and mineral metabolism. This meta-analysis was performed to investigate the effects of vitamin D supplementation/fortification on bone turnover markers in women. All human randomised clinical trials reported changes in bone resorption markers (serum C-terminal telopeptide of type-I collagen (sCTX) and urinary type I collagen cross-linked N-telopeptide (uNTX)) or bone formation factors (osteocalcin (OC), bone alkaline phosphatase (BALP) and procollagen type-1 intact N-terminal propeptide (P1NP)) following vitamin D administration in women (aged ≥ 18 years) were considered. Mean differences (MD) and their respective 95 % CI were calculated based on fixed or random effects models according to the heterogeneity status. Subgroup analyses, meta-regression models, sensitivity analysis, risk of bias, publication bias and the quality of the included studies were also evaluated. We found that vitamin D supplementation had considerable effect on sCTX (MD: -0·038, n 22) and OC (MD: -0·610, n 24) with high heterogeneity and uNTX (MD: -8·188, n 6) without heterogeneity. Our results showed that age, sample size, dose, duration, baseline vitamin D level, study region and quality of studies might be sources of heterogeneity in this meta-analysis. Subgroup analysis also revealed significant reductions in P1NP level in dose less than 600 µg/d and larger study sample size (>100 participants). Moreover, no significant change was found in BALP level. Vitamin D supplementation/fortification significantly reduced bone resorption markers in women. However, results were inconsistent for bone formation markers.

Sucrosephenylpropanoid esters and isoflavonoids isolated from Belamcanda chinensis roots and their potential anti-osteoclastogenic activity.

Repeated chromatography of the CH2Cl2 and EtOAc soluble fractions from the methanol extract of Belamcanda chinensis root yielded six new sucrosephenylpropanoid esters (1-6) and twenty-one known compounds (7-27). The structures of 1-6 were elucidated using diverse nuclear magnetic resonance (NMR) techniques and high-resolution mass spectrometry (HRMS) data analysis, together with chemical methods. All the twenty-seven isolated compounds were evaluated for their anti-osteoclastogenic activities. Preliminary screening results revealed that compounds 1 and 19 exhibited strong effects against RANKL-induced osteoclast formation in RAW264.7 cells. In addition, the treatment of mouse bone marrow macrophages (BMMs) with compounds 1 and 19 significantly decreased RANKL-induced TRAP-positive multinucleated osteoclast formation in a concentration-dependent manner without affecting cell viability. Further bioassay investigation showed that compounds 1 and 19 inhibited the expression of some osteoclast-specific marker genes and the transcription factor nuclear factor of activated T cells cytoplasmic 1 (NFATc1) in response to RANKL. To the best of our knowledge, this is the first investigation of anti-osteoclastogenic activity for compounds isolated from B. chinensis.

Koumine inhibits RANKL-induced ubiquitination and NF-κB activation to prevent ovariectomy and aging-induced bone loss.

Osteoporosis (OP) is a bone remodeling disease characterized by an imbalance between bone resorption and formation. Osteoclasts are the primary therapeutic targets for treating bone destruction. Koumine (KM), the most bioactive component in Gelsemium alkaloids, exhibits antitumor, immunosuppressive, anti-inflammatory, and analgesic properties. However, the effects of bone loss have not been well studied. This study conducted in vitro and in vivo verification experiments on KM. The results showed that KM inhibited bone resorption and tartrate-resistant acid phosphatase positive (TRAP+) osteoclasts development by mature osteoclasts in a dose-dependent manner. Moreover, KM prevented OVX-induced OP in vivo and potentially inhibited ubiquitination, a process closely related to various biological activities, including protein interaction, transcription, and transmembrane signal transduction regulation, especially within the nuclear factor-κB (NF-κB) pathway. Previous studies have demonstrated that several proteins ubiquitination promotes osteoclastogenesis, our study indicated that KM inhibits early NF-κB activation and receptor activator of NF-κB ligand induced ubiquitination, a critical factor in osteoclast differentiation. In conclusion, our research suggests that KM holds potential as an effective therapeutic agent for OP.

Activating transcriptional coactivator with PDZ-binding motif by (R)-PFI-2 attenuates osteoclastogenesis and prevents ovariectomized-induced osteoporosis.

Excessive osteoclast activation is a leading cause of osteoporosis. Therefore, identifying molecular targets and relevant pharmaceuticals that inhibit osteoclastogenesis is of substantial clinical importance. Prior research has indicated that transcriptional coactivator with PDZ-binding motif (TAZ) impedes the process of osteoclastogenesis by engaging the nuclear factor (NF)-κB signaling pathway, thereby suggesting TAZ activation as a potential therapeutic approach to treat osteoporosis. (R)-PFI-2 is a novel selective inhibitor of SETD7 methyltransferase activity, which prevents the nuclear translocation of YAP, a homolog of TAZ. Therefore, we hypothesized that (R)-PFI-2 could be an effective therapeutic agent in the treatment of osteoporosis. To test this hypothesis and explore the underlying mechanism, we first examined the impact of (R)-PFI-2 on osteoclastogenesis in bone marrow macrophages (BMMs) in vitro. (R)-PFI-2 treatment inhibited TAZ phosphorylation induced by NF-κB, thereby enhancing its nuclear localization, protein expression, and activation in BMMs. Moreover, (R)-PFI-2-induced TAZ activation inhibited osteoclast formation in a dose-dependent manner, which involved inhibition of osteoclastogenesis through the TAZ and downstream NF-κB pathways. Furthermore, (R)-PFI-2 inhibited osteoclastogenesis and prevented ovariectomy-induced bone loss in vivo in a mouse model. Overall, our findings suggest that TAZ activation by (R)-PFI-2 inhibits osteoclastogenesis and prevents osteoporosis, indicating an effective strategy for treating osteoclast-induced osteoporosis.

Yunnan Baiyao Inhibits Periodontitis by Suppressing the Autophagic Flux.

BACKGROUND: Yunnan Baiyao (YNBY), a traditional Chinese medicine, is renowned for its anti-inflammatory properties. Recent studies have suggested that YNBY plays a significant role in inhibiting osteoclast differentiation and autophagy, which are essential processes in inflammation and bone resorption associated with periodontitis. However, the precise relationship between autophagy and the mechanism by which YNBY inhibits osteoclastogenesis remains unexplored.The primary objective of this study was to investigate the inhibitory effects of YNBY on the process of osteoclastogenesis and its potential in preventing inflammatory bone loss. METHODS: The animals were subjected to sacrifice at intervals of 2, 4, and 6 weeks postintervention whilst under deep anaesthesia, and specimens were subsequently collected. The specimens were subjected to hematoxylin and eosin (HE) staining, in addition to tartrate-resistant acid phosphatase (TRAP) staining and subsequently imaged employing a digital scanner. The confirmation of osteoclast (OC) differentiation and autophagic flux was achieved through various techniques, including western blotting, transmission electron microscopy (TEM), TRAP staining, pit formation assay, and immunofluorescence. RESULTS: The microcomputed tomography images provided evidence of the effective inhibition of alveolar bone absorption at 2, 4, and 6 weeks following YNBY treatment. Additionally, the histomorphometric evaluations of tissue segments stained with HE and TRAP, which involved measuring the distance between the alveolar bone crest (ABC) and cementoenamel junction (CEJ) and quantifying TRAP-positive OCs, yielded comparable results to those obtained through computed tomography analysis. YNBY treatment resulted in a decrease in the CEJ-ABC distance and inhibition of OC differentiation. Furthermore, in vitro studies showed that the autophagy modulators rapamycin (RAP) and 3-methyladenine (3-MA) significantly affected OC differentiation and function. YNBY attenuated the impact of RAP on the differentiation of OCs, autophagy-related factor activation, and bone resorption. CONCLUSIONS: We hypothesise that YNBY suppresses the differentiation of OC and bone resorption by blocking autophagy. This study reveals that targeting autophagy might be a new alternative treatment methodology for periodontitis treatment.

Lactate dehydrogenase A inhibition prevents RANKL-induced osteoclastogenesis by reducing enhanced glycolysis.

Osteoclasts are multinucleated, specializes bone-resorbing cells that are derived from the monocyte/macrophage lineage. Excessive resorbing activities of osteoclasts are involved in destructive bone diseases. The detailed mechanism of acidification at the bone adhesion surface during the bone resorption process of osteoclasts remains to be defined. During glycolysis, pyruvate proceeds to the tricarboxylic cycle under aerobic conditions and pyruvate is converted to lactate via lactate dehydrogenase A (LDHA) under anaerobic conditions. However, tumor cells produce ATP during aerobic glycolysis and large amounts of pyruvate are converted to lactate and H+ by LDHA. Lactate and H+ are excreted outside the cell, whereby they are involved in invasion of tumor cells due to the pH drop around the cell. In this study, we focused on aerobic glycolysis and investigated the production of lactate by LDHA in osteoclasts. Expression of LDHA and monocarboxylate transporter 4 (MCT4) was upregulated during osteoclast differentiation. Intracellular and extracellular lactate levels increased with upregulation of LDHA and MCT4, respectively. FX11 (an LDHA inhibitor) inhibited osteoclast differentiation and suppressed the bone-resorbing activity of osteoclasts. We propose that inhibition of LDHA may represent a novel therapeutic strategy for controlling excessive bone resorption in osteoporosis and rheumatoid arthritis.

Anti-Osteoporotic Potential of Water Extract of Anethum graveolens L. Seeds.

Anethum graveolens L., known as European dill, is a versatile herb widely used in both traditional medicine and culinary practices. Despite its long-standing history, the potential impact of the water extract of A. graveolens seeds (WEAG) on bone health remains unexplored. In this study, we investigated the influence of WEAG on osteoclast differentiation and assessed its potential as an anti-osteoporotic agent. WEAG hindered osteoclast differentiation through the suppression of receptor activator of nuclear factor-κB ligand (RANKL) expression in osteoclast-supporting cells and by directly targeting osteoclast precursor cells. WEAG significantly reduced the expression of key osteoclastogenic transcription factors, namely c-Fos and NFATc1, typically induced by RANKL in osteoclast precursors. This reduction was attributed to the suppression of both MAPKs and NF-κB pathways in response to RANKL. In vivo experiments further revealed that WEAG administration effectively reduces trabecular bone loss and weight gain triggered by ovariectomy, mimicking postmenopausal osteoporosis. Furthermore, our comprehensive phytochemical analysis of WEAG identified a range of phytochemical constituents, associated with bone health and weight regulation. Notably, we discovered a specific compound, isorhamnetin-3-O-glucuronide, within WEAG that exhibits anti-osteoclastogenic potential. Overall, this research elucidated the beneficial effects and mechanistic basis of WEAG on osteoclast differentiation and bone loss, indicating its potential as a viable alternative to address bone loss in conditions like postmenopause.

Micheliolide prevents estrogen deficiency-induced bone loss via inhibiting osteoclast bone resorption.

Osteoporosis is one of the major health problems characterized by decreased bone density and increased risk of fractures. Nowadays, the treating strategies against osteoporosis are efficient, but still have some drawbacks. Micheliolide, a guaianolide sesquiterpene lactone isolated from Michelia compressa and Michelia champac, has been reported to have anti-inflammatory effects. Here, our data suggest that Micheliolide could protect mice from ovariectomy induced bone loss. According to the Micro-CT scan and histomorphometry quantification data, Micheliolide treatment inhibits excessive osteoclast bone resorption without affecting bone formation in estrogen deficiency mice. Consistently, our data suggest that Micheliolide could inhibit osteoclastogenesis in vitro. Additionally, we confirmed that Micheliolide inhibits osteoclasts formation via inhibiting P38 MAPK signaling pathway, and P79350 (a P38 agonist) could rescue this effect. In summary, our data suggest that Micheliolide could ameliorate estrogen deficiency-induced bone loss via attenuating osteoclastogenesis. Hence, Micheliolide could be used as a novel anti-resorptive agent against osteoporosis.

Inhibition of KIF11 ameliorates osteoclastogenesis via regulating mTORC1-mediated NF-κB signaling.

Osteoporosis, characterized by over-production and activation of osteoclasts, has become a major health problem especially in elderly women. In our study, we first tested the effect of Caudatin (Cau) in osteoclastogenesis, which is separated from Cynanchum auriculatum as a species of C-21 steroidal glyosides. The results indicated that Cau suppressed osteoclastogenesis in a time- and dose-dependent manner in vitro. Mechanistically, Cau was identified to inhibit NF-κB signaling pathway via modulation of KIF11-mediated mTORC1 activity. In vivo, by establishing an ovariectomized (OVX) mouse model to mimic osteoporosis, we confirmed that Cau treatment prevented OVX-induced bone loss in mice. In conclusion, we demonstrated that Cau inhibited NF-κB signaling pathway via modulation of KIF11-mediated mTORC1 activity to suppress osteoclast differentiation in vitro as well as OVX-induced bone loss in vivo. This provides the possibility of a novel prospective drug for osteoporosis remedies.

Interleukin-21 knockout reduces bone loss in ovariectomized mice by inhibiting osteoclastogenesis.

Estrogen deficiency accelerates osteoporosis in elderly women. However, the role of IL-21 in postmenopausal osteoporosis remains unclear. Female wild-type (WT) C57BL/6 and IL-21 knockout (KO) mice were used for ovariectomy (OVX). Here, IL-21 levels were significantly increased in the serum and bone tissues of WT-OVX mice. The trabecular bone space of the femur was significantly increased, and the bone mass was reduced in OVX mice, accompanied by a significant decrease in the maximum load, energy absorption, and elastic modulus indices. In contrast, IL-21 knockout effectively alleviated the effects of OVX on bone mass. Serum TRACP-5b and receptor activator of nuclear factor kappa B ligand (RANKL) levels and osteoclastogenesis were significantly higher in OVX mice than in sham mice, while serum TRACP-5b and RANKL levels and osteoclastogenesis were significantly decreased in IL-21 KO + OVX mice compared to WT + OVX mice. IL-21 knockdown reduces TRACP-5b, RANKL, and osteoclastogenesis, effectively preventing bone resorption and alleviating the progression of OVX-induced osteoporosis.

Dihydrotanshinone I attenuates estrogen-deficiency bone loss through RANKL-stimulated NF-κB, ERK and NFATc1 signaling pathways.

Postmenopausal osteoporosis, a chronic condition that predominantly affects postmenopausal women, presents a significant impediment to their overall well-being. The condition arises from estrogen deficiency, leading to enhanced osteoclast activity. Salvia miltiorrhiza, a well-established Chinese herbal medicine with a history of clinical use for osteoporosis treatment, contains diverse active constituents that have shown inhibitory effects on osteoclast formation and bone loss. Dihydrotanshinone I (DTI), a phenanthrenonequinone compound derived from the root of Salvia miltiorrhiza, has been identified as a potential therapeutic agent, although its mechanism of action on osteoclasts remains elusive. In this study, we aimed to elucidate the inhibitory potential of DTI on RANKL-induced osteoclastogenesis. We observed the ability of DTI to effectively impede the expression of key osteoclast-specific genes and proteins, as assessed by Real-time PCR and Western Blotting analyses. Mechanistically, DTI exerted its inhibitory effects on osteoclast formation by modulating critical signaling pathways including NF-κB, ERK, and calcium ion signaling. Notably, DTI intervention disrupted the nuclear translocation and subsequent transcriptional activity of the NFATc1, thus providing mechanistic insights into its inhibitory role in osteoclastogenesis. To further assess the therapeutic potential of DTI, we employed an ovariectomized osteoporosis animal model to examine its impact on bone loss. Encouragingly, DTI demonstrated efficacy in mitigating bone loss induced by estrogen deficiency. In conclusion, our investigation elucidates the ability of DTI to regulate multiple signaling pathways activated by RANKL, leading to the inhibition of osteoclast formation and prevention of estrogen-deficiency osteoporosis. Consequently, DTI emerges as a promising candidate for the treatment of osteoporosis.

HIV patients' bone loss before and after antiretroviral treatment and its possible mechanisms.

HIV infection has been reported to cause bone loss and a higher risk of fracture. Under normal conditions, bone metabolism is regulated by mesenchymal cells, osteoclasts differentiated from mononuclear macrophages, osteoblasts, and their expression of regulatory factors, such as receptor activator of nuclear factor-kappa B ligand (RANKL), M-SCF, and transforming growth factor-beta. The balance between bone resorption and osteogenesis depends on the balance between osteoclasts and osteoblasts. In addition, some immune cells, such as B-cells, T-cells, and other non-immune cells expressing RANKL, can contribute to osteoporosis under inflammatory conditions. HIV proteins consist of three types: regulatory proteins, accessory proteins, and structural proteins, which contribute to HIV-mediated bone loss partly by upregulating NF-κB expression, tumor necrosis factor alpha content, and release of inflammatory cytokines. Even worse, although antiretroviral therapy has reduced HIV infection mortality and successfully transformed acquired immunodeficiency syndrome into a chronic disease, its impact on bone loss should not be overlooked, especially when the drug contains tenofovir. This review analyzes some reports focusing on the overall osteolytic situation due to imbalances in osteogenesis and bone resorption due to HIV infection and antiviral therapy. The intrinsic mechanism of bone loss provides a reference for researchers to analyze the risk factors for HIV patients complicated with bone loss and helps clinicians to provide ideas for the intervention and prevention of bone loss during clinical treatment and chronic disease management of HIV patients.