Emodin regulates bone remodeling by inhibiting osteoclastogenesis and stimulating osteoblast formation

Hecogenin alleviates LPS-induced osteolysis via regulating pyroptosis and ROS involved Nrf2 activation

Reactive oxidative species (ROS) generation triggers pyroptosis and induces development of inflammatory osteolysis. Hecogenin (HG) has anti-inflammatory and antioxidative property, but its effects on inflammatory osteolysis remains unclear. In our study, we investigated the mechanism of HG on pyroptosis and its effect on inflammatory osteolysis in vitro and in vivo. The impact of HG on osteoclastogenesis was evaluated using cytotoxicity, TRAcP staining and bone resorption assays. The RNA-sequencing was employed to identify potential signaling pathways, and then RT-qPCR, western blot, immunofluorescence, and ELISA were used to verify. To determine the protective effect of HG in vivo, Lipopolysaccharide (LPS)-induced animal models were utilized, along with micro-CT and histological examination. HG suppressed RANKL-induced osteoclast differentiation, bone resorption, NFATc1 activity and downstream factors. RNA-sequencing results showed that HG inhibited osteoclastogenesis by modulating the inflammatory response and macrophage polarization. Furthermore, HG inhibited the NF-κB pathway, and deactivated the NLRP3 inflammasome. HG activated the expression of nuclear factor E2-related factor 2 (Nrf2) to eliminate ROS generation. Importantly, the inhibitory effect of HG on NLRP3 inflammasome could be reversed by treatment with the Nrf2 inhibitor ML385. In vivo, HG prevented the mice against LPS-induced osteolysis by suppressing osteoclastogenesis and inflammatory factors. In conclusion, HG could activate Nrf2 to eliminate ROS generation, inactivate NLRP3 inflammasome and inhibit pyroptosis, thereby suppressing osteoclastogenesis in vitro and alleviating inflammatory osteolysis in vivo, which indicating that HG might be a promising candidate to treat inflammatory osteolysis.

Germacrone alleviates breast cancer-associated osteolysis by inhibiting osteoclastogenesis via inhibition of MAPK/NF-κB signaling pathways

Bone is one of the most frequent sites for metastasis in breast cancer patients. Bone metastasis significantly reduces the survival time and the life quality of breast cancer patients. Germacrone (GM) can serve humans as an anti-cancer and anti-inflammation agent, but its effect on breast cancer-induced osteolysis remains unclear. This study aims to investigate the functions and mechanisms of GM in alleviating breast cancer-induced osteolysis. The effects of GM on osteoclast differentiation, bone resorption, F-actin ring formation, and gene expression were examined in vitro. RNA-sequencing and Western Blot were conducted to explore the regulatory mechanisms of GM on osteoclastogenesis. The effects of GM on breast cancer-induced osteoclastogenesis, and breast cancer cell malignant behaviors were also evaluated. The in vivo efficacy of GM in the ovariectomy model and breast cancer bone metastasis model with micro-CT and histomorphometry. GM inhibited osteoclastogenesis, bone resorption and F-actin ring formation in vitro. Meanwhile, GM inhibited the expression of osteoclast-related genes. RNA-seq analysis and Western Blot confirmed that GM inhibited osteoclastogenesis via inhibition of MAPK/NF-κB signaling pathways. The in vivo mouse osteoporosis model further confirmed that GM inhibited osteolysis. In addition, GM suppressed the capability of proliferation, migration, and invasion and promoted the apoptosis of MDA-MB-231 cells. Furthermore, GM could inhibit MDA-MB-231 cell-induced osteoclastogenesis in vitro and alleviate breast cancer-associated osteolysis in vivo human MDA-MB-231 breast cancer bone metastasis-bearing mouse models. Our findings identify that GM can be a promising therapeutic agent for patients with breast cancer osteolytic bone metastasis.

Protective effects of emodin on subchondral bone and articular cartilage in osteoporotic osteoarthritis rats: A preclinical study

BACKGROUND

Osteoporotic osteoarthritis (OP-OA) is a severe pathological form of OA, urgently requiring precise management strategies and more efficient interventions. Emodin (Emo), an effective ingredient found in the traditional Chinese medicine rhubarb, has been dEmonstrated to promote osteogenesis and inhibit extracellular matrix degradation. In this study, we aimed to investigate the interventional effects of Emo on the subchondral bone and cartilage of the knee joints in OP-OA model rats.

METHODS

Thirty-two SD rats were randomly and equally divided into sham, OP-OA, Emo low-dose, and Emo high-dose groups. Micro-CT scanning was conducted to examine the bone microstructure of the rat knee joints. H&E and Safranin O and Fast Green staining (SO&FG) were performed for the pathomorphological evaluation of the rat cartilage tissues. ELISA was used to estimate the rat serum expression levels of inflammatory factors, including interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). Additionally, the CCK-8 assay was utilized for determining the viability of Emo-treated BMSCs. Western blot and real-time PCR analyses were also employed to measure the bone formation indexes and cartilage synthesis and decomposition indexes. Lastly, the osteogenic and chondrogenic differentiation efficiency of the BMSCs was investigated via Alizarin Red and Alcian Blue staining.

RESULTS

Emo intervention alleviated the bone microstructural disruption of the subchondral bone and articular cartilage in the OP-OA rats and up-regulated the expression of bone and cartilage anabolic metabolism indicators, decreased the expression of cartilage catabolism indicators, and diminished the expression of inflammatory factors in the rat serum (P<0.05). Furthermore, Emo reversed the decline in the osteogenic and chondrogenic differentiation ability of the BMSCs (P<0.05).

CONCLUSION

Emo intervention mitigates bone loss and cartilage damage in OP-OA rats and promotes the osteogenic and chondrogenic differentiation of BMSCs.

Emodin suppresses adipogenesis of bone marrow derived mesenchymal stem cells from aplastic anemia via increasing TRIB3 expression

BACKGROUND

Increasing evidence indicate that enhanced adipogenic differentiation of bone marrow mesenchymal stem cells (BM-MSCs) could contribute to the adiposity alteration in marrow microenvironment of aplastic anemia (AA). Identifying small molecule drugs with role in inhibiting adipogenesis of BM-MSCs may represent a novel direction in AA therapy by improving BM-MSCs mediated marrow microenvironment.

METHODS

For the purpose, we isolated AA BM-MSCs through whole bone marrow cell culture, evaluated a series of small molecule drugs using the in vitro adipogenic differentiation model of BM-MSCs, and finally focused on emodin, a natural anthraquinone derivative. Subsequently, we systematically investigated the molecular mechanism of emodin in attenuating adipogenic process by means of microarray profiling, bioinformatics analysis and lentivirus-mediated functional studies and rescue assay.

RESULTS

We found that emodin presented significantly suppressive effect on the in vitro adipogenic differentiation of AA BM-MSCs. Further mechanistic investigation revealed that emodin could increase the expression of Tribbles homolog 3 (TRIB3) which exhibited remarkably decreased expression in AA BM-MSCs compared with the normal counterparts and was subsequently demonstrated as a negative regulator in adipogenesis of AA BM-MSCs. Besides, TRIB3 depletion alleviated the suppressive effect of emodin on the adipogenic differentiation of AA BM-MSCs.

CONCLUSION

Our findings propose that emodin mediated TRIB3 up-regulation alleviates the adipogenic capacity of AA BM-MSCs, and emodin could serve as a potential therapeutic regimen for AA therapy.

Advances in the pharmacological effects and molecular mechanisms of emodin in the treatment of metabolic diseases

Rhubarb palmatum L., Polygonum multijiorum Thunb., and Polygonum cuspidatum Sieb. Et Zucc. are traditional Chinese medicines that have been used for thousands of years. They are formulated into various preparations and are widely used. Emodin is a traditional Chinese medicine monomer and the main active ingredient in Rhubarb palmatum L., Polygonum multijiorum Thunb., and Polygonum cuspidatum Sieb. Et Zucc. Modern research shows that it has a variety of pharmacological effects, including promoting lipid and glucose metabolism, osteogenesis, and anti-inflammatory and anti-autophagy effects. Research on the toxicity and pharmacokinetics of emodin can promote its clinical application. This review aims to provide a basis for further development and clinical research of emodin in the treatment of metabolic diseases. We performed a comprehensive summary of the pharmacology and molecular mechanisms of emodin in treating metabolic diseases by searching databases such as Web of Science, PubMed, ScienceDirect, and CNKI up to 2023. In addition, this review also analyzes the toxicity and pharmacokinetics of emodin. The results show that emodin mainly regulates AMPK, PPAR, and inflammation-related signaling pathways, and has a good therapeutic effect on obesity, hyperlipidemia, non-alcoholic fatty liver disease, diabetes and its complications, and osteoporosis. In addition, controlling toxic factors and improving bioavailability are of great significance for its clinical application.

Ex Vivo Model to Evaluate the Antibacterial and Anti-Inflammatory Effects of Gelatin-Tricalcium Phosphate Composite Incorporated with Emodin and Lumbrokinase for Bone Regeneration

Tricalcium phosphate (TCP) has gained attention due to its interconnected porous structures which promote fibrovascular invasion and bony replacement. Moreover, when gelatin is added and crosslinked with genipin (GGT), TCP exhibits robust biocompatibility and stability, making it an excellent bone substitute. In this study, we incorporated emodin and lumbrokinase (LK) into GGT to develop an antibacterial biomaterial. Emodin, derived from various plants, possesses antibacterial and anti-inflammatory properties. LK comprises proteolytic enzymes extracted from the earthworm Lumbricus rubellus and exhibits fibrinolytic activity, enabling it to dissolve biofilms. Additionally, LK stimulates osteoblast activity while inhibiting osteoclast differentiation. GGT was combined with emodin and lumbrokinase to produce the GGTELK composite. The biomedical effects of GGTELK were assessed through in vitro assays and an ex vivo bone defect model. The GGTELK composite demonstrated antibacterial properties, inhibiting the growth of S. aureus and reducing biofilm formation. Moreover, it exhibited anti-inflammatory effects by reducing the secretion of IL-6 in both in vivo cell experiments and the ex vivo model. Therefore, the GGTELK composite, with its stability, efficient degradation, biocompatibility, and anti-inflammatory function, is expected to serve as an ideal bone substitute.

Emodin protects against apoptosis and inflammation by regulating reactive oxygen species-mediated NF-κB signaling in interleukin-1β-stimulated human nucleus pulposus cells

Intervertebral disc degeneration (IDD) is a complex degradative disorder associated with inflammation. Emodin, an anthraquinone derivative, possesses strong anti-inflammatory activity. This study focused on the in vitro therapeutic action of emodin in a cellular model of IDD. Human nucleus pulposus cells (NPCs) were stimulated with interleukin-1β (IL-1β) to induce inflammation. Cell Counting Kit-8 and terminal deoxynucleotidyl transferase dUTP nick end labeling staining assays were performed to evaluate the viability and apoptosis of NPCs, respectively. Caspase-3 activity was measured to indirectly assess cell apoptosis. Western blot analysis was performed to detect protein expression levels. Reverse transcription-polymerase chain reaction was performed for the detection of relative mRNA levels of tumor necrosis factor-α (TNF-α) and IL-6. Enzyme-linked immunosorbent assay was performed to analyze TNF-α and IL-6 secretion. Our results showed that emodin treatment mitigated IL-1β-induced reduction of cell viability in NPCs. Moreover, the increase in reactive oxygen species (ROS) production, apoptotic rate, and caspase-3 activity in IL-1β-stimulated NPCs was reduced by emodin treatment. Treatment with emodin also abolished IL-1β-induced inflammation in NPCs, as indicated by reduced secretion of IL-6 and TNF-α. Besides, the increase in expression levels of phosphorylated p65 and nuclear p65 in IL-1β-stimulated NPCs was suppressed by emodin treatment. Furthermore, inhibition of nuclear factor kappa B (NF-κB) activation with pyrrolidine dithiocarbamate aggravated the protective effects of emodin. These results suggested that emodin protected NPCs against IL-1β-induced apoptosis and inflammation via inhibiting ROS-mediated activation of NF-κB.

Lipopolysaccharide-Induced Bone Loss in Rodent Models: A Systematic Review and Meta-Analysis

Osteoporosis has traditionally been characterized by underlying endocrine mechanisms, though evidence indicates a role of inflammation in its pathophysiology. Lipopolysaccharide (LPS), a component of gram-negative bacteria that reside in the intestines, can be released into circulation and stimulate the immune system, upregulating bone resorption. Exogenous LPS is used in rodent models to study the effect of systemic inflammation on bone, and to date a variety of different doses, routes, and durations of LPS administration have been used. The study objective was to determine whether systemic administration of LPS induced inflammatory bone loss in rodent models. A systematic search of Medline and four other databases resulted in a total of 110 studies that met the inclusion criteria. Pooled standardized mean differences (SMDs) and corresponding 95% confidence intervals (CI) with a random-effects meta-analyses were used for bone volume fraction (BV/TV) and volumetric bone mineral density (vBMD). Heterogeneity was quantified using the I² statistic. Shorter-term (<2 weeks) and longer-term (>2 weeks) LPS interventions were analyzed separately because of intractable study design differences. BV/TV was significantly reduced in both shorter-term (SMD = -3.79%, 95% CI [-4.20, -3.38], I² 62%; p < 0.01) and longer-term (SMD = -1.50%, 95% CI [-2.00, -1.00], I² 78%; p < 0.01) studies. vBMD was also reduced in both shorter-term (SMD = -3.11%, 95% CI [-3.78, -2.44]; I² 72%; p < 0.01) and longer-term (SMD = -3.49%, 95% CI [-4.94, -2.04], I² 82%; p < 0.01) studies. In both groups, regardless of duration, LPS negatively impacted trabecular bone structure but not cortical bone structure, and an upregulation in bone resorption demonstrated by bone cell staining and serum biomarkers was reported. This suggests systemically delivered exogenous LPS in rodents is a viable model for studying inflammatory bone loss, particularly in trabecular bone. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

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.

Efficacy of Oregano Essential Oil Extract in the Inhibition of Bacterial Lipopolysaccharide (LPS)-Induced Osteoclastogenesis Using RAW 264.7 Murine Macrophage Cell Line—An In-Vitro Study

Gram-negative, anaerobic bacterias are predominate in periapical infections. The bacterial lipopolysaccharide (LPS) initiates the process of inflammation and periapical bone resorption. Usage of various medicaments retards or inactivates the bacterial endotoxin (LPS). However, the results are not highly effective. In recent years, owing to antimicrobial resistance, the shift from conventional agents to herbal agents has been increased tremendously in research. Keeping this in mind, the present study was formulated to evaluate the efficacy of oregano essential oil in inhibiting bacterial LPS- induced osteoclastogenesis. Four different concentrations (0 ng/mL, 25 ng/mL, 50 ng/mL, and 100 ng/mL) of oregano essential oil extract were added into 96-well culture plate. Under light microscope, quantification of osteoclast cells was performed. One-way ANOVA with post-hoc Tukey test was carried out on SPSS v21. A significant reduction (p < 0.001) in the osteoclast was observed in the experimental groups compared to no oregano essential oil extract (control). A dose-dependent significant reduction (p < 0.001) in osteoclast formation was observed among the experimental groups, with lesser osteoclast seen in group IV with 100 ng/mL of oregano essential oil extract. Thus, it can be concluded that oregano essential oil extract can be utilized as a therapeutic agent that can target bacterial LPS-induced osteoclastogenesis. However, randomized controlled studies should be conducted to assess the potential use of this extract in the periapical bone resorption of endodontic origin.

Anti-Osteoporosis Effects of the Eleutherococcus senticosus, Achyranthes japonica, and Atractylodes japonica Mixed Extract Fermented with Nuruk

Vigeo is a mixture of fermented extracts of Eleutherococcus senticosus Maxim (ESM), Achyranthes japonica (Miq.) Nakai (AJN), and Atractylodes japonica Koidzumi (AJK) manufactured using the traditional Korean nuruk fermentation method. Although the bioactive effects of ESM, AJN, and AJK have already been reported, the pharmacological effects of Vigeo have not been proven. Therefore, in this study, we investigated whether Vigeo had inhivitory effects on lipopolysaccharide (LPS)-induced inflammatory bone loss in vivo and receptor activator of nuclear factor-B ligand (RANKL)-induced osteoclastogenesis and the related mechanism in vitro. Vigeo administration conferred effective protection against bone loss induced by excessive inflammatory response and activity of osteoclasts in LPS-induced inflammatory osteoporosis mouse model. In addition, Vigeo significantly suppressed the formation of tartrate-resistant acid phosphatase-positive osteoclasts induced by RANKL and inhibited F-actin formation and bone resorbing activity without any cytotoxicity. Moreover, Vigeo significantly inhibited RANKL-induced phosphorylation of p38, ERK, JNK, IκB, and AKT and degradation of IkB. Additionally, Vigeo strongly inhibited the mRNA and protein expression of c-FOS and NFATc1 and subsequently attenuated the expression of osteoclast specific marker genes induced by RANKL. We demonstrated for the first time the anti-osteoporosis effect of Vigeo, suggesting that it could be a potential therapeutic candidate for the treatment of osteoclast-mediated inflammatory bone diseases.

7,8-Dihydroxyflavone modulates bone formation and resorption and ameliorates ovariectomy-induced osteoporosis

Imbalances in bone formation and resorption cause osteoporosis. Mounting evidence supports that brain-derived neurotrophic factor (BDNF) implicates in this process. 7,8-Dihydroxyflavone (7,8-DHF), a plant-derived small molecular TrkB agonist, mimics the functions of BDNF. We show that both BDNF and 7,8-DHF promoted the proliferation, osteogenic differentiation, and mineralization of MC3T3-E1 cells. These effects might be attributed to the activation of the Wnt/β-catenin signaling pathway as the expression of cyclin D1, phosphorylated-glycogen synthase kinase-3β (p-GSK3β), β-catenin, Runx2, Osterix, and osteoprotegerin (OPG) was all significantly up-regulated. Knockdown of β-catenin restrained the up-regulation of Runx2 and Osterix stimulated by 7,8-DHF. In particular, blocking TrkB by its specific inhibitor K252a suppressed 7,8-DHF-induced osteoblastic proliferation, differentiation, and expression of osteoblastogenic genes. Moreover, BDNF and 7,8-DHF repressed osteoclastic differentiation of RAW264.7 cells. The transcription factor c-fos and osteoclastic genes such as tartrate-resistant acid phosphatase (TRAP), matrix metalloprotein-9 (MMP-9), Adamts5 were inhibited by 7,8-DHF. More importantly, 7,8-DHF attenuated bone loss, improved trabecular microarchitecture, tibial biomechanical properties, and bone biochemical indexes in an ovariectomy (OVX) rat model. The current work highlights the dual regulatory effects that 7,8-DHF exerts on bone remodeling.

A temporal study on musculoskeletal morphology and metabolism in hibernating Daurian ground squirrels (Spermophilus dauricus)

Hibernators provide a natural model to study the mechanisms underlying the prevention of disuse-induced musculoskeletal deterioration. Currently, however, these mechanisms remain poorly understood. Here, we investigated changes in morphology and metabolic indices in the hindlimb skeletal muscle and bone of Daurian ground squirrels (Spermophilus dauricus) during different periods of hibernation, and further explored the possible mechanisms involved in the musculoskeletal maintenance of hibernators after prolonged inactivity. Results showed that, compared with levels in the summer active group (SA), almost all morphological indices of skeletal muscle and bone, including muscle mass, muscle fiber cross-sectional area, bone mass, bone length, and bone mechanical properties, were unchanged in the different periods of hibernation. Only a few microstructural parameters of bone showed deterioration in the post-hibernation group (POST), including increased specific bone surface (+71%), decreased trabecular thickness (-43%), and decreased average cortical thickness (-51%) in the tibia, and increased trabecular separation (+60%) in the femur. Furthermore, most examined metabolic indices involved in muscle protein turnover and bone remodeling were unchanged, except for several indices in the inter-bout arousal group (IBA), i.e., increase in the phosphorylation of eukaryotic initiation factor 4E binding protein 1 (4E-BP1) (IBA vs. SA, +80%) in the vastus medialis muscle, increase in chymotrypsin-like activity (IBA vs. SA, +62%) in the tibialis anterior muscle, increase in osteoblast number (IBA vs. SA, +110%; IBA vs. torpor (TOR), +68%) and osteoclast number (IBA vs. TOR, +105%) per bone surface in the tibia, and increase in osteoclast surface per bone surface (IBA vs. TOR, +128%) in the femur. The above evidence demonstrates that the musculoskeletal morphology of squirrels was largely preserved, and musculoskeletal metabolism was generally maintained after prolonged hibernation inactivity. These findings suggest that the well-maintained musculoskeletal metabolism may be a vital mechanism underlying the preservation of the musculoskeletal system during hibernation. The coincident up-regulation of several metabolic indicators during IBA indicates that musculoskeletal metabolism may be relatively active during this period; however, its role in musculoskeletal maintenance during hibernation needs further clarification.

Eudebeiolide B Inhibits Osteoclastogenesis and Prevents Ovariectomy-Induced Bone Loss by Regulating RANKL-Induced NF-κB, c-Fos and Calcium Signaling

Eudebeiolide B is a eudesmane-type sesquiterpenoid compound isolated from Salvia plebeia R. Br., and little is known about its biological activity. In this study, we investigated the effects of eudebeiolide B on osteoblast differentiation, receptor activator nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis in vitro and ovariectomy-induced bone loss in vivo. Eudebeiolide B induced the expression of alkaline phosphatase (ALP) and calcium accumulation during MC3T3-E1 osteoblast differentiation. In mouse bone marrow macrophages (BMMs), eudebeiolide B suppressed RANKL-induced osteoclast differentiation of BMMs and bone resorption. Eudebeiolide B downregulated the expression of nuclear factor of activated T-cells 1 (NFATc1) and c-fos, transcription factors induced by RANKL. Moreover, eudebeiolide B attenuated the RANKL-induced expression of osteoclastogenesis-related genes, including cathepsin K (Ctsk), matrix metalloproteinase 9 (MMP9) and dendrocyte expressed seven transmembrane protein (DC-STAMP). Regarding the molecular mechanism, eudebeiolide B inhibited the phosphorylation of Akt and NF-κB p65. In addition, it downregulated the expression of cAMP response element-binding protein (CREB), Bruton's tyrosine kinase (Btk) and phospholipase Cγ2 (PLCγ2) in RANKL-induced calcium signaling. In an ovariectomized (OVX) mouse model, intragastric injection of eudebeiolide B prevented OVX-induced bone loss, as shown by bone mineral density and contents, microarchitecture parameters and serum levels of bone turnover markers. Eudebeiolide B not only promoted osteoblast differentiation but inhibited RANKL-induced osteoclastogenesis through calcium signaling and prevented OVX-induced bone loss. Therefore, eudebeiolide B may be a new therapeutic agent for osteoclast-related diseases, including osteoporosis, rheumatoid arthritis and periodontitis.

Effects of emodin on inflammatory bowel disease-related osteoporosis

Inflammatory bowel diseases (IBD) are related to bone loss. Emodin can influence the activity and differentiation of osteoblasts and osteoclasts. However, few studies have shown the effects of emodin on IBD-induced bone damage. The aim of the present study was to investigate the role of emodin in IBD-induced osteoporosis in an animal model. An IBD model in Sprague Dawley male rats was established by administering 2.5% dextran sulfate sodium (DSS) in the drinking water. Emodin was administered orally (30 mg/kg body weight) every other day starting in the third week for 9 weeks. Blood, colon and bone samples were obtained for biomarker assays and histological analysis. Bone biomechanical properties, microCT, metabolic biomarkers and bone histological changes were analyzed. The bone mass was significantly decreased, and the bone biomechanical properties and bone microstructure parameters of IBD rats were significantly worse than those of control rats (P<0.05). Tartrate resistant acid phosphatase staining also showed that the number of osteoclasts in bone in IBD rats were larger than that in bone in control rats. Emodin intervention abolished the changes in bone microstructure and biomechanical properties (P<0.05) induced by IBD. Osteoclast formation and serum C-terminal cross-linked peptide (CTX) and tumor necrosis factor α (TNF-α) were also inhibited by emodin (P<0.05). Emodin significantly abolished IBD-enhanced Traf6, NFATC1 and c-fos expression. Our data demonstrated that emodin suppresses IBD-induced osteoporosis by inhibiting osteoclast formation.

The pharmacology, toxicology and therapeutic potential of anthraquinone derivative emodin

Emodin (1, 3, 8-trihydroxy-6-methylanthraquinone) is a derived anthraquinone compound extracted from roots and barks of pharmaceutical plants, including Rheum palmatum, Aloe vera, Giant knotweed, Polygonum multiflorum and Polygonum cuspidatum. The review aims to provide a scientific summary of emodin in pharmacological activities and toxicity in order to identify the therapeutic potential for its use in human specific organs as a new medicine. Based on the fundamental properties, such as anticancer, anti-inflammatory, antioxidant, antibacterial, antivirs, anti-diabetes, immunosuppressive and osteogenesis promotion, emodin is expected to become an effective preventive and therapeutic drug of cancer, myocardial infarction, atherosclerosis, diabetes, acute pancreatitis, asthma, periodontitis, fatty livers and neurodegenerative diseases. This article intends to provide a novel insight for further development of emodin, hoping to reveal the potential of emodin and necessity of further studies in this field.

Integrative Analysis of Regulatory Module Reveals Associations of Microgravity with Dysfunctions of Multi-body Systems and Tumorigenesis

Previous studies have demonstrated that microgravity could lead to health risks. The investigation of the molecular mechanisms from the aspect of systems biology has not been performed yet. Here, we integratively analyzed transcriptional and post-transcriptional regulations based on gene and miRNA expression profiles in human peripheral blood lymphocytes cultured in modeled microgravity. Two hundred and thirty dysregulated TF-miRNA (transcription factor and microRNA) feed-forward loops (FFLs) were identified in microgravity. The immune, cardiovascular, endocrine, nervous and skeletal system subnetworks were constructed according to the functions of dysregulated FFLs. Taking the skeletal system as an example, most of genes and miRNAs in the subnetwork were involved in bone loss. In addition, several drugs have been predicted to have potential to reduce bone loss, such as traditional Chinese medicines Emodin and Ginsenoside Rh2. Furthermore, we investigated the relationships between microgravity and 20 cancer types, and found that most of cancers might be promoted by microgravity. For example, rectum adenocarcinoma (READ) might be induced by microgravity through reducing antigen presentation and suppressing IgA-antibody-secreting cells' migration. Collectively, TF-miRNA FFL might provide a novel mechanism to elucidate the changes induced by microgravity, serve as drug targets to relieve microgravity effects, and give new insights to explore the relationships between microgravity and cancers.

Oridonin promotes osteogenesis through Wnt/β-catenin pathway and inhibits RANKL-induced osteoclastogenesis in vitro

AIMS

To study the molecular mechanism of oridonin (ORI) on osteoblast differentiation and osteoclast formation in vitro.

MAIN METHODS

Rat bone marrow mesenchymal stem cells (BMSCs) were treated with different concentrations of ORI in osteogenic medium (OM). CCK-8 assay and were used to detect the effect on BMSCs viability. Alizarin red staining and ALP activity were used to illuminate the effect of ORI on osteogenic differentiation. Expressions of osteogenic differentiation related genes were detected by real-time quantitative PCR (qRT-PCR), and expressions of osteogenic related proteins were detected by Western blot (WB) and immunofluorescence. Similarly, bone marrow mononuclear cells (BMMs) were treated with different concentrations of ORI. CCK-8 assay and Live/Dead staining were used to detect the effect of ORI on BMMs activity. TRAP staining was used to detect its effect on osteoclast differentiation. Expressions of osteoclast-related genes were detected by qRT-PCR, and expressions of osteoclast-related proteins were detected by WB and immunofluorescence.

KEY FINDINGS

(1) ORI (2 μM) promoted the ALP activity of BMSCs differentiation into osteoblasts and increased the number of calcium nodules. (2) ORI stimulated the expressions of wnt1, β-catenin and Runx2, but with no significantly effect on p-GSK-3β and GSK-3β. (3) ORI promoted the expression of OPG and inhibited the expression of RANKL. (4) ORI directly/indirectly inhibited the osteoclast formation and expressions of osteoclast-related genes TRAP, NFATc1 and c-Fos.

SIGNIFICANCE

ORI may promote BMSCs differentiate into osteoblasts through the Wnt/β-catenin signaling pathway. At the same time, it may also inhibit the formation of osteoclasts mediated by RANKL.

Guided bone regeneration with a gelatin layer and adenoviral delivery of c-myb enhances bone healing in rat tibia

Aim: Bone healing becomes problematic during certain states, such as trauma. This study verifies whether the application of c-myb with gelatin promotes bone healing during bone injuries. Materials & methods: A biodegradable membrane was modified with adenoviral vector c-myb (Ad/c-myb) and gelatin and applied in the bone injury site of rat tibia. Results: c-myb enhanced osteogenic differentiation and mineralization in bone marrow stromal cells after induction with osteogenic media. In vivo examination of rat tibia after application of the biodegradable membrane with Ad/c-myb and a gelatin layer demonstrated increased bone volume, bone mineral density, new bone formation and osteogenic molecules, compared with Ad/LacZ. Conclusion: c-myb has the potential to assist bone healing and may be applicable to the treatment of bone during injury.

Macrolactin A protects against LPS-induced bone loss by regulation of bone remodeling

An imbalance between bone resorption and bone formation leads to several kinds of bone diseases such as rheumatoid arthritis, osteoporosis and Paget's disease. The imbalance between bone formations relative to bone resorption is responsible in bone remodeling. Several studies have suggested that macrolactin A (MA) has potent anti-inflammatory, anti-cancer and anti-angiogenic effects in various cell types. We investigate whether macrolactin A (MA) could inhibit bone loss and enhance bone formation. We used bone marrow monocytes/macrophages (BMMs) cells to study osteoclast activity and MC3T3-E1 cells to study osteoblast activity. MA suppressed tartrate resistant acid phosphatase (TRAP) positive multinucleated cells in a concentration-dependent manner, as well as at a specific time point. MA markedly reduced bone resorption activity and F-actin ring formation. Moreover, MA markedly suppressed receptor activator of nuclear factor k-B ligand (RANKL)-induced osteoclastogenic marker genes and transcription factors in-vitro. MA repressed osteoclast differentiation via activation of the phosphoinositide kinase-3/Akt, extracellular signal-regulated kinase 1/2 (ERK 1/2), c-Jun N-terminal kinase (JNK), nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) and c-Fos signaling pathways. MA enhanced pre-osteoblast cell differentiation on mineralization activity, alkaline phosphatase (ALP) activity, and the expression of osteoblastogenic markers including osterix, RUNX-2, SMAD4, BMP-2, and ALP. Importantly, MA repressed lipopolysaccharide (LPS)-induced inflammatory bone loss in mice as shown by TRAP staining of femurs and μCT analysis. Therefore, MA could be a promising candidate for the inhibition and management of osteoporosis, arthritis, and bone lytic diseases.

BMP9 Reduces Bone Loss in Ovariectomized Mice by Dual Regulation of Bone Remodeling

Bone remodeling is dynamic and is tightly regulated through bone resorption dominated by osteoclasts and bone formation dominated by osteoblasts. Imbalances in this process can cause various pathological conditions, such as osteoporosis. Bone morphogenetic protein 9 (BMP9), a biomolecule produced and secreted by the liver, has many pharmacological effects, including anti-liver fibrosis, antitumor, anti-heart failure, and antidiabetic activities. However, the effects of BMP9 on the regulation of osteoblast and osteoclast functions and the underlying molecular mechanism(s) have not yet been investigated. In this study, BMP9 increased the expression of osteoblastogenic gene markers, such as ALP, Cola1, OCN, RUNX2, and OSX, and ALP activity in MC3T3-E1 cells by upregulating LGR6 and activating the Wnt/β-catenin pathway. BMP9 also suppressed receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-induced osteoclast differentiation of bone marrow macrophages (BMMs) by inhibiting the Akt-NF-κB-NFATc1 pathway. More importantly, in an ovariectomy (OVX) mouse model, BMP9 attenuated bone loss and improved bone biomechanical properties in vivo by increasing bone-forming activity and suppressing bone resorption activity. Accordingly, our current work highlights the dual regulatory effects that BMP9 exerts on bone remodeling by promoting bone anabolic activity and inhibiting osteoclast differentiation in OVX mice. © 2020 American Society for Bone and Mineral Research.

Synthesis and biological activities of drugs for the treatment of osteoporosis

Osteoporosis is an asymptomatic progressive disease. With the improvement of people's living standard and the aging of population, osteoporosis and its fracture have become one of the main diseases threatening the aging society. The serious medical and social burden caused by this has aroused wide public concern. Osteoporosis is listed as one of the three major diseases of the elderly. At present, the drugs for osteoporosis include bone resorption inhibitors and bone formation promoters. The purpose of these anti-osteoporosis drugs is to balance osteoblast bone formation and osteoclast bone resorption. With the development of anti-osteoporosis drugs, new anti osteoporosis drugs have been designed and synthesized. There are many kinds of new compounds with anti osteoporosis activity, but most of them are concentrated on the original drugs with anti osteoporosis activity, or the natural products with anti-osteoporosis activity are extracted from the natural products for structural modification to obtain the corresponding derivatives or analogues. These target compounds showed good ALP activity in vitro and in vivo, promoted osteoblast differentiation and mineralization, or had anti TRAP activity, inhibited osteoclast absorption. This work attempts to systematically review the studies on the synthesis and bioactivity of anti-osteoporosis drugs in the past 10 years. The structure-activity relationship was discussed, which provided a reasonable idea for the design and development of new anti-osteoporosis drugs.

Sweroside promotes osteoblastic differentiation and mineralization via interaction of membrane estrogen receptor-α and GPR30 mediated p38 signalling pathway on MC3T3-E1 cells

BACKGROUND

Dipsaci Radix has been clinically used for thousands of years in China for strengthening muscles and bones. Sweroside is the major active iridoid glycoside isolated from Dipsaci Radix. It has been reported that sweroside can promote alkaline phosphatase (ALP) activity in both the human osteosarcoma cell line MG-63 and rat osteoblasts. However, the underlying mechanism involved in these osteoblastic processes is poorly understood.

PURPOSE

This study aimed to characterize the bone protective effects of sweroside and to investigate the signaling pathway that is involved in its actions in MC3T3-E1 cells.

METHODS

Cell proliferation, differentiation and mineralization were evaluated by the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay, ALP test and Alizarin Red S staining, respectively. The concentration of sweroside in intracellular and extracellular fluids was determined by ultra-performance liquid chromatography coupled to triple quadrupole xevo-mass spectrometry (UPLC/TQ-XS-MS). Proteins associated with the osteoblastic signaling pathway were analysed by western blot and immunofluorescence methods.

RESULTS

Sweroside did not obviously affect the proliferation but significantly promoted the ALP activity and mineralization of MC3T3-E1 cells. The maximal absorption amount 0.465 ng/ml (1.3 × 10^-9 M) of sweroside was extremely lower than the tested concentration of 358.340 ng/ml (10^-6 M), indicating an extremely low absorption rate by MC3T3-E1 cells. Moreover, the ALP activity, the protein expression of ER-α and G protein-coupled receptor 30 (GPR30) induced by sweroside were markedly blocked by both the ER antagonist ICI 182780 and the GPR30 antagonist G15. In addition, sweroside also activated the phosphorylation of p38 kinase (p-p38), while the phosphorylation effects together with ALP and mineralization activities were completely blocked by a p38 antagonist, SB203580. Additionally, the phosphorylation of p38 induced by sweroside were markedly blocked by both the ER antagonist ICI 182780 and the GPR30 antagonist G15.

CONCLUSIONS

The present study indicated that sweroside, as a potential agent in treatment of osteoporosis, might exert beneficial effects on MC3T3-E1 cells by interaction with the membrane estrogen receptor-α and GPR30 that then activates the p38 signaling pathway. This is the first study to report the specific mechanism of the effects of sweroside on osteoblastic differentiation and mineralization of MC3T3-E1 cells.

A butanolic fraction from the standardized stem extract of Cassia occidentalis L delivered by a self-emulsifying drug delivery system protects rats from glucocorticoid-induced osteopenia and muscle atrophy

We recently reported that a butanol soluble fraction from the stem of Cassia occidentalis (CSE-Bu) consisting of osteogenic compounds mitigated methylprednisone (MP)-induced osteopenia in rats, albeit failed to afford complete protection thus leaving a substantial scope for further improvement. To this aim, we prepared an oral formulation that was a lipid-based self-nano emulsifying drug delivery system (CSE-BuF). The globule size of CSE-BuF was in the range of 100–180 nm of diluted emulsion and the zeta potential was −28 mV. CSE-BuF enhanced the circulating levels of five osteogenic compounds compared to CSE-Bu. CSE-BuF (50 mg/kg) promoted bone regeneration at the osteotomy site and completely prevented MP-induced loss of bone mass and strength by concomitant osteogenic and anti-resorptive mechanisms. The MP-induced downregulations of miR29a (the positive regulator of the osteoblast transcription factor, Runx2) and miR17 and miR20a (the negative regulators of the osteoclastogenic cytokine RANKL) in bone was prevented by CSE-BuF. In addition, CSE-BuF protected rats from the MP-induced sarcopenia and/or muscle atrophy by downregulating the skeletal muscle atrogenes, adverse changes in body weight and composition. CSE-BuF did not impact the anti-inflammatory effect of MP. Our preclinical study established CSE-BuF as a prophylactic agent against MP-induced osteopenia and muscle atrophy.

MicroRNA-135a-5p is involved in osteoporosis progression through regulation of osteogenic differentiation by targeting RUNX2

A number of microRNAs (miRs) have been revealed to be involved in the development of osteoporosis, including postmenopausal osteoporosis. The aim of the present study was to investigate miR-135a-5p expression and the cellular function of miR-135a-5p and its underlying mechanism in postmenopausal osteoporosis. miR-135a-5p expression levels in the femoral neck trabecular bone tissue fragments from postmenopausal women with or without osteoporosis were detected by reverse transcription-quantitative polymerase chain reaction and western blot analysis. The role of miR-135a-5p during osteogenic differentiation was examined by performing gain- and loss-of-function experiments using miR-135a-5p mimic or inhibitor. TargetScan bioinformatics analysis was sued to predict targets of miR-135a-5p, which were confirmed using luciferase reporter assays. miR-135a-5p expression was significantly upregulated in femoral neck trabecular bone tissue fragments from postmenopausal women with osteoporosis compared with postmenopausal women without osteoporosis. In addition, miR-135a-5p expression levels significantly decreased during osteogenic differentiation in the C2C12 cell model. miR-135a-5p overexpression decreased the osteogenic potential of C2C12 cells, as miR-135a-5p overexpression significantly reduced the expression levels of several key osteoblast markers, whilst miR-135a-5p knockdown had the opposite effect. Furthermore, the current study demonstrated that RUNX2 was a direct target of miR-135a-5p. Rescue experiments indicated that RUNX2 overexpression significantly reversed the effect of miR-135a-5p mimic on the osteogenic potential of C2C12 cells, indicating that miR-135a-5p mediates osteogenic differentiation via direct targeting of RUNX2. Taken together, these results suggest that miR-135a-5p may serve a role in osteoporosis progression by regulating osteogenic differentiation via RUNX2.

Leonurus sibiricus L. ethanol extract promotes osteoblast differentiation and inhibits osteoclast formation

Leonurus sibiricus L. (LS) is a medicinal plant used in East Asia, Europe and the USA. LS is primarily used in the treatment of gynecological diseases, and recent studies have demonstrated that it exerts anti-inflammatory and antioxidant effects. To the best of our knowledge, the present study demonstrated for the first time that LS may promote osteoblast differentiation and suppress osteoclast differentiation in vitro, and that it inhibited lipopolysaccharide (LPS)-induced bone loss in a mouse model. LS was observed to promote the osteoblast differentiation of MC3T3-E1 cells and upregulate the expression of runt-related transcription factor 2 (RUNX2), a key gene involved in osteoblast differentiation. This resulted in the induction of the expression of various osteogenic genes, including alkaline phosphatase (ALP), osteonectin (OSN), osteopontin (OPN), type I collagen (COL1) and bone sialoprotein (BSP). LS was also observed to inhibit osteoclast differentiation and bone resorption. The expression levels of nuclear factor of activated T-cells 1 (NFATc1) and c-Fos were inhibited following LS treatment. NFATc1 and c-Fos are key markers of osteoclast differentiation that inhibit receptor activator of nuclear factor-κB ligand (RANKL)-induced mitogen-activated protein kinase (MAPKs) and nuclear factor (NF)-κB. As a result, LS suppressed the expression of osteoclast-associated genes, such as matrix metallopeptidase-9 (MMP-9), cathepsin K (Ctsk), tartrate-resistant acid phosphatase (TRAP), osteoclast-associated immunoglobulin-like receptor (OSCAR), c-src, c-myc, osteoclast stimulatory transmembrane protein (OC-STAMP) and ATPase H+ transporting V0 subunit d2 (ATP6v0d2). Consistent with the in vitro results, LS inhibited the reduction in bone mineral density and the bone volume/total volume ratio in a mouse model of LPS-induced osteoporosis. These results suggest that LS may be a valuable agent for the treatment of osteoporosis and additional bone metabolic diseases.

Piceatannol-3-O-β-D-glucopyranoside (PG) exhibits in vitro anti-metastatic and anti-angiogenic activities in HT1080 malignant fibrosarcoma cells

BACKGROUND

Several components isolated from rhubarb, the root of Rheum undulatum L., including emodin, rhein, rhaponticin, and piceatannol, have been reported to induce cell death and inhibit metastasis in various types of cancer. Recently, piceatannol-3-O-β-D-glucopyranoside (PG) isolated from rhubarb was demonstrated to improve vascular dysfunction by inhibiting arginase activity.

PURPOSE

In this study, we examined the anti-cancer activities of PG, including effects on the proliferation, metastasis, and angiogenesis of endothelial and malignant cancer cells.

RESULTS

We found that PG did not affect the proliferation of human fibrosarcoma (HT1080) and human umbilical vein endothelial cells (HUVECs) at treatments up to 100  μM. However, PG efficiently suppressed the metastatic ability of HT1080 cells, as determined by scratch wound migration, transwell migration/invasion assay, and three-dimensional (3D) spheroid invasion assay. PG significantly suppressed the phorbol 12-myristate 13-acetate (PMA)-induced increase of matrix metalloproteinase (MMP)-9 expression as well as gelatinolytic MMP-9 activity, which are essential for cancer metastasis. In addition, PG treatment reduced the production of proangiogenic factors in HT1080 cells under normoxic and hypoxic conditions and suppressed hypoxia-induced activation of the hypoxia-inducible factor (HIF)-1α pathway. We also found that HUVEC angiogenic activity, including migration and tubular structure formation, were significantly reduced by PG treatment. Moreover, in an in ovo chick chorioallantoic membrane assay, spontaneous and vascular endothelial growth factor (VEGF)-induced vessel formation were significantly inhibited by PG treatment.

CONCLUSION

These results collectively indicate that PG has potent anti-metastatic and anti-angiogenic activities with no cytotoxicity. Thus, PG may be useful to limit the hyperplasia of malignant tumors and the spread of cancer to distant secondary organs.

A Novel Rhein Derivative Modulates Bone Formation and Resorption and Ameliorates Estrogen-Dependent Bone Loss

Osteoporosis, an osteolytic disease that affects millions of people worldwide, features a bone remodeling imbalance between bone resorption by osteoclasts and bone formation by osteoblasts. Identifying dual target-directed agents that inhibit excessive bone resorption and increase bone formation is considered an efficient strategy for developing new osteoporosis treatments. Rhein, a natural anthraquinone, can be isolated from various Asian herbal medicines. Rhein and its derivatives have been reported to have various beneficial pharmacological effects, especially their bone-targeting ability and anti-osteoclastogenesis activity. Moreover, hydrogen sulfide (H₂ S) was reported to prevent ovariectomy- (OVX-) induced bone loss by enhancing bone formation, and sulfur replacement therapy has been considered a novel and plausible therapeutic option. Based on this information, we synthesized a rhein-derived thioamide (RT) and investigated its effects on bone resorption and bone formation in vitro and in vivo. It has been found that the RT-inhibited receptor activator of the nuclear factor-κB (NF-κB) ligand- (RANKL-) induced osteoclastogenesis and bone resorption in a dose-dependent manner. The expression of osteoclast marker genes was also suppressed by RT treatment. Furthermore, exploration of signal transduction pathways indicated that RT markedly blocked RANKL-induced osteoclastogenesis by attenuating MAPK pathways. However, RT treatment in an osteoblastic cell line, MC3TE-E1, indicated that RT led to an increase in the deposition of minerals and the expression of osteoblast marker genes, as demonstrated by Alizarin Red staining and alkaline phosphatase activity. Importantly, an OVX mouse model showed that RT could attenuate the bone loss in estrogen deficiency-induced osteoporosis in vivo with a smart H₂ S-releasing property and that there was a considerable improvement in the biomechanical properties of bone. Accordingly, our current work highlights the dual regulation of bone remodeling by the rhein-derived molecule RT. This may be a highly promising approach for a new type of anti-osteoporosis agent. © 2018 American Society for Bone and Mineral Research.

Strong binding active constituents of phytochemical to BMPR1A promote bone regeneration: In vitro, in silico docking, and in vivo studies

Two of the most problematic orthopedic and neurosurgeon visits are associated with spine and craniofacial fractures. Therefore, more attention needs to be paid to finding a medicine to repair these fractures. Amongst the most mysterious herbs, Aloe vera stands out. In the present study, the ameliorating function of A. vera on osteogenesis was studied in vitro and in vivo. Osteoblast-like cells were exposed to A. vera, followed by analysis of cell viability, lactate dehydrogenase release, and intracellular reactive oxygen species (ROS) production. The results showed an enhanced cell biocompatibility in a dose-dependent manner due to attenuated intracellular ROS production. Furthermore, a docking study indicated that the strong affinity of A. vera constituents to type I bone morphogenic protein receptor (BMPR1A) without the involvement of the BMPR1A chain B. The induction of osteogenesis prompts extracellular calcium deposition by osteoblasts, which affirms successful in vitro bone regeneration. However, injection of A. vera in rats with critical size calvarial defects induced Runx2, alkaline phosphatase (ALP), OCN, and BMP2 genes overexpression, which led to the formation of victorious bone with enhanced bone density and ALP activity. It is worthy to note that Aloin has the highest affinity to BMPR1A, whereas there are no reports regarding the impact of Aloenin, Aloesin, and γ-sitosterol on osteogenesis. Furthermore, some of them have antitumor potency, and it might be proposed that they are considered as a bone substitute in the osteotomy site of osteosarcoma with the aim of bone recovery and suppression of osteosarcoma. The whole consequences of this investigation manifests the plausibility of using A. vera as an antioxidant and osteoconductive substitute.

Rubiadin-1-methyl ether from Morinda officinalis How. Inhibits osteoclastogenesis through blocking RANKL-induced NF-κB pathway

Rubiadin-1-methyl ether (RBM) is a natural anthraquinone compound isolated from the root of Morinda officinalis How. In our previous study, RBM was found to have inhibitory effects on the TRAP activity of osteoclasts, which means that RBM may be a candidate for therapy of bone diseases characterized by enhanced bone resorption. However, the further effect of RBM on osteoclasts and the underlying mechanism remain unclear. In the present study, we investigated the effects of RBM isolated from Morinda officinalis How. on osteoclasts derived from bone marrow macrophages (BMMs) and the underlying mechanism in vitro. RBM at the dose that did not affect the viability of cells significantly inhibited RANKL-induced osteoclastogenesis and actin ring formation of osteoclast, while RBM performed a stronger effect at the early stage. In addition, RBM downregulated the expression of osteoclast-related proteins, including nuclear factor of activated T cells cytoplasmic 1 (NFATc1), cellular oncogene Fos (c-Fos), matrix metallopeptidase 9 (MMP-9) and cathepsin K (CtsK) as shown by Western blot. Furthermore, RBM inhibited the phosphorylation of NF-κB p65 and the degradation of IκBα as well as decreased the nuclear translocation of p65. Collectively, the results suggest that RBM inhibit osteoclastic bone resorption through blocking NF-κB pathway and may be a promising agent for the prevention and treatment of bone diseases characterized by excessive bone resorption.

Cordycepin Accelerates Osteoblast Mineralization and Attenuates Osteoclast Differentiation In Vitro

Bone homeostasis destruction is triggered by the uncontrolled activity of osteoblasts and osteoclasts. Targeting both the regulation of bone formation and resorption is a promising strategy for treating bone disorders. Cordycepin is a major component of Chinese caterpillar fungus Cordyceps militaris. It exerts a variety of biological actions in various cells and animal models. However, its function on bone metabolism remains unclear. In the present study, we discovered a dual-action function of cordycepin in murine MC3T3-E1 and RAW264.7 cells. MC3T3-E1 cells were cultured in an osteogenic medium in the presence of 1 μM cordycepin for up two weeks. Cordycepin was used for effects of osteoblast and osteoclast differentiation. Cell viability was measured using the MTT assay. Osteoblast differentiation was confirmed by alizarin red staining, ALP activity, western blot, and real-time PCR. Osteoclast differentiation and autophagic activity were confirmed via TRAP staining, pit formation assay, confocal microscopy, western blot, and real-time PCR. Cordycepin promoted osteoblast differentiation, matrix mineralization, and induction of osteoblast markers via BMP2/Runx2/Osterix pathway. On the other hand, RAW264.7 cells were differentiated into osteoclast by RANKL treatment for 72 h. 1 μM cordycepin significantly inhibited RANKL-induced osteoclast formation and resorption activity through disturbing the actin ring-formatted sealing zone and activating cathepsin K and MMP9. These findings indicate that cordycepin might be an innovative dual-action therapeutic agent for bone disease caused by an imbalance of osteoblasts and osteoclasts.

Thymol inhibits RANKL-induced osteoclastogenesis in RAW264.7 and BMM cells and LPS-induced bone loss in mice

Thymol was identified as one of key compounds contributing to the aroma of thyme leaves. We investigated the effects of thymol on receptor activator NF-κB ligand (RANKL)-induced osteoclastogenesis in murine macrophage RAW264.7 cells and bone marrow derived macrophage (BMMs) cells and lipopolysaccharide (LPS)-induced bone loss in vivo. Thymol markedly reduced RANKL-stimulated osteoclast formation and differentiation in RAW264.7 cells and BMMs cells without any cytotoxic effects. The in vitro and in vivo osteoclastogenesis inhibitory effect of thymol was assessed by calculating the quantity of TRAP (+) multinucleated cells and its inhibitory effects on the resorbing capacity were examined on calcium phosphate-coated plates. Moreover, the inhibitory effects of thymol resulted in a reduction of RANK, cathepsin K, matrix metalloproteinase-9 (MMP-9), dendritic cell-specific transmembrane protein (DC-STAMP), c-terminal myc kinase (C-MYC), C-terminal Src kinase (C-SRC), GRB2-associated-binding protein 2 (GAB2), microphthalmia-associated transcription factor (MITF), and carbonic anhydrase II genes. Similarly, activities of ERK, JNK and AKT and protein expressions of NFATc1, C-FOS, MMP-9 and cathepsin K were downregulated by thymol. More importantly, the application of thymol significantly reduced LPS-induced inflammatory bone loss in mice. In conclusion, these findings identified that thymol could be a useful therapeutic agent for the prevention of bone destructive diseases.

Inhibition effects of a natural inhibitor on RANKL downstream cellular signalling cascades cross-talking

Myricitrin is a natural occurring flavonoid glycoside that possesses effects on inhibiting nitric oxide (NO) transmission and preventing inflammatory reaction. Although previous study showed the myricitrin possesses antibone loss effects via reducing the expression of IL-6 and partially suppressing reactive oxygen species (ROS) production. However, the effects of myricitrin on nuclear factor-kappaB ligand (RANKL)-stimulated osteoclastogenesis have not yet been further investigated. The current study was aimed to demonstrating the inhibitory effects of myricitrin on RANKL-stimulated osteoclastogenesis and relevant mechanisms. We found myricitrin significantly suppressed osteoclastogenesis suggesting that it may acts on RANKL/RANK induced downstream signal cross cascading in osteoclast precursors. In that, our Western blotting results showed myricitrin significantly attenuated RNAKL/MAPKs (phosphorylation of p38, ERK, JNK) and AKT signal cascading. Complementing previous study, our results suggesting as a natural inhibitor, myricitrin possesses the potential therapeutic effects on inflammatory osteolysis.

A flavonoids compound inhibits osteoclast differentiation by attenuating RANKL induced NFATc-1/c-Fos induction

Function studies of pectolinarigenin demonstrated that, as a natural product, it possesses the regulatory effects on transcription factors (TFs) such as: signal transducer and activator of transcription 3 (STAT3). Herein, we aimed to identify the regulatroy effects of pectolinarigenin on the osteoclastogenesis TFs such as: NFATc1 and c-Fos, and further identify the relevant up-stream signals activity. We initially found pectolinarigenin inhibited receptor activator of nuclear factor-kappa B ligand (RANKL) induced osteoclast formation during the bone marrow-derived macrophages (BMMs) cultures, suggesting that this natural product could act on osteoclast precursors by inhibiting the down signaling cascades of RANKL signaling. Moreover, mechanistical investigation showed pectolinarigenin inhibits RANKL-mediated osteoclastogenesis by attenuating the nuclear factor of activated T cells cytoplasmic 1 (NFATc-1) and c-Fos following the Akt and mitogen activated protein kinases (MAPKs) signaling costimulatory. These findings identify that pectolinarigenin may act as an anti-resorption agent by blocking osteoclast activation.

Claudin 11 regulates bone homeostasis via bidirectional EphB4-EphrinB2 signaling

Claudins (Cldns) are well-established components of tight junctions (TJs) that play a pivotal role in the modulation of paracellular permeability. Several studies have explored the physiologic aspects of Cldn family members in bone metabolism. However, the effect of Cldn11, a major component of central nervous system myelin, on bone homeostasis has not been reported. In this study, we demonstrate that Cldn11 is a potential target for bone disease therapeutics as a dual modulator of osteogenesis enhancement and osteoclastogenesis inhibition. We found that Cldn11 played a negative role in the receptor activator of nuclear factor kappa B ligand-induced osteoclast (OC) differentiation and function by downregulating the phosphorylated form of extracellular signal-regulated kinase (ERK), Bruton's tyrosine kinase, and phospholipase C gamma 2, in turn impeding c-Fos and nuclear factor in activated T cell c1 expression. The enhancement of osteoblast (OB) differentiation by positive feedback of Cldn11 was achieved through the phosphorylation of Smad1/5/8, ERK, and c-Jun amino-terminal kinase. Importantly, this Cldn11-dependent dual event in bone metabolism arose from targeting EphrinB2 ligand reverse signaling in OC and EphB4 receptor forward signaling in OB. In agreement with these in vitro effects, subcutaneous injection of Cldn11 recombinant protein exerted anti-resorbing effects in a lipopolysaccharide-induced calvarial bone loss mouse model and increased osteogenic activity in a calvarial bone formation model. These findings suggest that Cldn11 is a novel regulator in bone homeostasis.

A Novel Diterpenoid Suppresses Osteoclastogenesis and Promotes Osteogenesis by Inhibiting Ifrd1-Mediated and IκBα-Mediated p65 Nuclear Translocation

Osteoporosis develops because of impaired bone formation and/or excessive bone resorption. Although the pharmacological treatment of osteoporosis has been extensively developed, alternative treatments are still needed. Here, we showed that oridonin (ORI), a diterpenoid isolated from Rabdosia rubescens, can suppress osteoclastogenesis and enhance osteogenesis. ORI inhibited the receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-induced osteoclast formation and bone resorption through the inhibition of p65 nuclear translocation. ORI-induced inhibition of this translocation led to an increase in osteoblast differentiation and mineralization through the promotion of Smad1/Smad5 phosphorylation. Further analyses demonstrated that the inhibition of p65 nuclear translocation is due to the suppression of IκBα phosphorylation and the induced proteasomal degradation of interferon-related development regulator 1 (Ifrd1), a transcriptional corepressor that is involved in the suppression of NF-κB nuclear translocation. Moreover, mice treated with ORI at catabolic and anabolic windows showed a considerable attenuation of ovariectomy (OVX)-induced osteoporosis. Taken together, our findings reveal that ORI protects against OVX-induced bone loss via inhibiting osteoclastic bone resorption but enhancing osteoblastic bone formation through abolishing both Ifrd1-mediating and IκBα-mediated p65 nuclear translocation. These results show the potential of ORI for treatment of osteoporosis and highlight Ifrd1 as a another novel promising target for anti-osteoporotic drugs. © 2017 American Society for Bone and Mineral Research.

Poligoni Multiflori Radix enhances osteoblast formation and reduces osteoclast differentiation

Poligoni Multiflori Radix (PMR) is a traditional Korean medicinal herb that is known to have various pharmacological effects, including antihyperlipidemic, anticancer, and anti-inflammatory effects. However, the effects of PMR on bone metabolism have not been elucidated to date. The present study aimed to investigate the in vitro and in vivo effect of PMR water extract on the regulation of osteoblast and osteoclast activity. Effects of PMR water extract on receptor activator of nuclear factor-kB ligand (RANKL)-induced osteoclast differentiation and survival of mouse bone marrow macrophages (BMMs) obtained from femurs were investigated by tartrate-acid resistant acid phosphatase (TRAP)-positive cells and XTT assay. Expression of osteoclast-related genes was assayed by western blot analysis and reverse transcription-quantitative polymerase chain reaction. Additionally, the effects of PMR water extract on osteoblastic proliferation and differentiation were investigated by alkaline phosphatase (ALP) activity assay, alizarin red staining, and levels of mRNA encoding known osteoblast markers. Furthermore, the effects of PMR water extract on lipopolysaccharide (LPS)-induced bone loss were examined in a mouse model. PMR inhibited RANKL-induced osteoclast differentiation of BMMs in a dose-dependent manner without significant cytotoxicity, and suppressed expression of the main osteoclast differentiation markers Fos proto-oncogene and nuclear factor of activated T-cell. In addition, PMR decreased the mRNA expression levels of NFATc1 target genes, including TRAP, osteoclast-associated receptor, ATPase H⁺ transporting, lysosomal 38 kDa V0 subunit d2, and Cathepsin K. These inhibitory effects were mediated by the p38 and extracellular signal-regulated kinase/nuclear factor-κB pathway. Simultaneously, PMR enhanced the differentiation of primary osteoblasts, and increased the mRNA expression of runt-related transcription factor 2, ALP, osterix, and osteocalcin. Notably, PMR improved LPS-induced trabecular bone loss in mice. Collectively, the present findings demonstrated that PMR may regulate bone remodeling by reducing osteoclast differentiation and stimulating osteoblast formation. These results suggest that PMR may be used for the treatment of bone diseases, such as osteoporosis and rheumatoid arthritis.

Sp1 Plays an Important Role in Vascular Calcification Both In Vivo and In Vitro

BACKGROUND

Vascular calcification and increased cardiovascular morbidity and mortality are closely related in patients with end-stage renal disease and diabetes mellitus. Specific protein 1 (Sp1) is a transactivation molecule that plays a crucial role in the regulation of apoptosis, fibrosis, angiogenesis, and other pathological disorders. There is evidence that specific protein 1 (Sp1) directly stimulates the transcription of bone morphogenetic protein 2 (BMP2) and that BMP2 plays a key role in the calcification process in the BMP2-expressing F9 cell model system. Here, we investigated whether Sp1 plays an important role in vascular calcification and its potential regulatory mechanism in vascular calcification.

METHODS AND RESULTS

In this study, vascular calcification was induced in male Wistar rats by administration of nicotine (25 mg/kg) and vitamin D3 (300 000 IU/kg). These rats were randomly selected for treatment with adenovirus harboring Sp1 knockdown gene or empty virus. The mechanism of Sp1 in vascular smooth muscle cells cultured in high phosphate medium was studied. Based on our findings, the Sp1 gene silencing or inhibition improved calcium deposition, which was partly achieved by inhibiting phenotype switch, apoptosis, and matrix vesicle release of vascular smooth muscle cells. Moreover, Sp1 can activate BMP2 transcription by binding to the Sp1-binding element of the BMP2 promoter.

CONCLUSIONS

Overall, elevated Sp1 exerts a pro-apoptotic effect, promoting BMP2 transcription and further accumulating vascular calcification. Proper and timely regulation of Sp1 expression may be a potential strategy for treatment of aging, end-stage renal disease, and diabetic-related macrovascular disease treatment.

Magnesium Lithospermate B Protects against Lipopolysaccharide-Induced Bone Loss by Inhibiting RANKL/RANK Pathway

Lipopolysaccharide (LPS) can induce bone loss by stimulating bone resorption. Natural compounds have great potential for the treatment of osteolytic bone diseases. Magnesium lithospermate B (MLB) plays an important role in protecting against oxidative damage and also has potential anti-inflammatory pharmacological properties. However, its role in LPS-induced bone loss is still unknown. In the present study, we observed the effects of MLB on LPS-induced bone damage and investigated the possible mechanisms. The bone loss models were established by LPS administration in male Sprague–Dawley rats. MLB (200 mg/kg body weight) was given by subcutaneous injection. MicroCT analysis, biomarker assay, histological examination and immunohistochemical staining were performed at the 8th weeks. In addition, RAW264.7 cells were treated with LPS in the presence or absence of MLB. The osteoclast formation, resorption activity and differentiation-related genes [(receptor activator of nuclear factor kappa-B (RANK), Traf6, Fra-1, and c-src)] expression were evaluated. LPS induced bone loss shown as the decrease in bone volume fraction and trabecular number, and increase in trabecular separation. LPS also markedly enhanced the osteoclast formation and resorption activity compared with the control. MLB significantly abolished the LPS-induced bone microstructure damage (p < 0.05) and osteoclast formation. MLB also inhibited the increases of serum tartrate-resistant acid phosphatase 5b, RANK ligand (RANKL) and TNF-α level enhanced by LPS (p < 0.05). Immunohistochemical staining indicated that MLB attenuated the high expression of RANKL and RANK stimulated by LPS. In addition, MLB significantly abolished the LPS-enhanced osteoclast formation, resorption activity, RANK, Traf6, Fra-1, and c-src expression in vitro. Our data demonstrate that MLB can suppress LPS-induced bone loss via inhibiting RANKL/RANK related osteoclast formation.

REV-ERB agonism suppresses osteoclastogenesis and prevents ovariectomy-induced bone loss partially via FABP4 upregulation

REV-ERBs (REV-ERBα and REV-ERBβ) are transcription repressors and circadian regulators. Previous investigations have shown that REV-ERBs repress the expression of target genes, including MMP9 and CX3CR1, in macrophages. Because MMP9 and CX3CR1 reportedly participate in receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis, we inferred that REV-ERBs might play a role in osteoclastogenesis. In the present study, we found that the REV-ERBα level decreased significantly during RANKL-induced osteoclast differentiation from primary bone marrow-derived macrophages (BMMs). REV-ERBα knockdown by small interfering RNA in BMMs resulted in the enhanced formation of osteoclasts, whereas REV-ERBβ knockdown showed no effect on osteoclast differentiation. Moreover, the REV-ERB agonist SR9009 inhibited osteoclast differentiation and bone resorption. Intraperitoneal SR9009 administration prevented ovariectomy-induced bone loss; this effect was accompanied by decreased serum RANKL and C-terminal telopeptide of type I collagen levels and increased osteoprotegerin levels. Further investigation revealed that NF-κB and MAPK activation and nuclear factor of activated T cells, cytoplasmic 1, and c-fos expression were suppressed by SR9009. The level of reactive oxygen species was also decreased by SR9009, with NADPH oxidase subunits also being down-regulated. In addition, an expression microarray showed that FABP4, an intracellular lipid-binding protein, was up-regulated by REV-ERB agonism. BMS309403, an inhibitor of FABP4, partially prevented the suppression of osteoclastogenesis by SR9009 through stabilizing phosphorylation of p65. To summarize, our results proved that the REV-ERB agonism inhibited osteoclastogenesis partially via FABP4 up-regulation.-Song, C., Tan, P., Zhang, Z., Wu, W., Dong, Y., Zhao, L., Liu, H., Guan, H., Li, F. REV-ERB agonism suppresses osteoclastogenesis and prevents ovariectomy-induced bone loss partially via FABP4 upregulation.

Water extract of Rumex crispus prevents bone loss by inhibiting osteoclastogenesis and inducing osteoblast mineralization

Background

Rumex crispus root has traditionally been used in Asian medicine for the treatment of hemorrhage and dermatolosis. The aim of this study was to explore the pharmaceutical effects of water extract of Rumex crispus (WERC) on osteoblast and osteoclast differentiation. We also studied the effect of WERC on the receptor activator of nuclear factor kappa-B ligand (RANKL)-induced trabecular bone destruction mice model.

Methods

High performance liquid chromatography analysis was used to identify three compounds (emodin, chrysophanol, and physcion) of WERC. The in vivo effect of WERC was examined using an administration of WERC or vehicle on the ICR mice with bone loss induced by intraperitoneal RANKL injection on day 0 and 1. All mice were sacrificed by cervical dislocation at day 7 and the femurs of mice were isolated for soft X-ray and Micro-CT analysis. The in vitro effect of WERC on osteoblast mineralization or osteoclast differentiation was examined by alizarin red S staining or by tartrate-resistant acid phosphatase staining and assay. To determine the transcription level of osteoblast or osteoclast-specific genes, real-time quantitative polymerase chain reaction was used. Western blot analysis was performed to study the effect of WERC on mitogen-activated protein kinases (MAPK) or nuclear factor-κB (NF-κB) signaling molecules.

Results

The presence of three compounds in WERC was determined. WERC significantly suppressed RANKL-induced trabecular bone loss by preventing microstructural deterioration. In vitro, WERC increased osteoblast mineralization by enhancing the transcription of runt-related transcription factor 2 and its transcriptional coactivators, and by stimulating extracellular signal–regulated kinase phosphorylation. Furthermore, WERC significantly inhibited osteoclast differentiation by suppressing the activation of the RANKL signalings (MAPK and NF-κB) and the increasing inhibitory factors of nuclear factor of activated T cells cytoplasmic 1.

Conclusion

This study showed that WERC could protect against osteoporosis and suggested that the possible mechanism of WERC might be related to increased osteoblast differentiation by activating Runx2 signaling and inhibition of osteoclast differentiation by suppression of RANKL signaling.

Electronic supplementary material

The online version of this article (10.1186/s12906-017-1986-7) contains supplementary material, which is available to authorized users.

Macrolactin F inhibits RANKL-mediated osteoclastogenesis by suppressing Akt, MAPK and NFATc1 pathways and promotes osteoblastogenesis through a BMP-2/smad/Akt/Runx2 signaling pathway

The balance between bone formation and bone resorption is maintained by osteoblasts and osteoclasts. In the current study, macrolactin F (MF) was investigated for novel biological activity on the receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-induced osteoclastogenesis in primary bone marrow-derived macrophages (BMMs). We found that RANKL-induced osteoclast formation and differentiation from BMMs was significantly inhibited by MF in a dose-dependent manner without cytotoxicity. RANKL-induced F-actin ring formation and bone resorption activity in BMMs which was attenuated by MF. In addition, MF suppressed the expression of osteoclast-related genes, including c-myc, RANK, tartrate-resistant acid phosphatase (TRAP), nuclear factor of activated T cells c1 (NFATc1), cathepsin K and matrix metalloproteinase 9 (MMP9). Furthermore, the protein expression NFATc1, c-Fos, MMP9, cathepsin K and phosphorylation of Jun N-terminal kinase (JNK), p38 and Akt were also down-regulated by MF treatment. Interestingly, MF promoted pre-osteoblast cell differentiation on Alizarin Red-mineralization activity, alkaline phosphatase (ALP) activity, and the expression of osteoblastogenic markers including Runx2, Osterix, Smad4, ALP, type I collagen alpha 1 (Col1α), osteopontin (OPN), and osteocalcin (OCN) via activation of the BMP-2/smad/Akt/Runx2 pathway on MC3T3-E1. Taken together, these results indicate that MF may be useful as a therapeutic agent to enhance bone health and treat osteoporosis.

Emodin suppresses cadmium-induced osteoporosis by inhibiting osteoclast formation

Environmental level of cadmium (Cd) exposure can induce bone loss. Emodin, a naturally compound found in Asian herbal medicines, could influence osteoblast/osteoclast differentiation. However, the effects of emodin on Cd-induced bone damage are not clarified. The aim of this study was to investigate the role of emodin on Cd-induced osteoporosis. Sprague-Dawley male rats were divided into three groups which were given 0mg/L, 50mg Cd/L and 50mg Cd/L plus emodin (50mg/kg body weight). Bone histological investigation, microCT analysis, metabolic biomarker determination and immunohistochemical staining were performed at the 12th week. The bone mass and bone microstructure index of rats treated with Cd were obviously lower than in control. Cd markedly enhanced the osteoclast formation compared with control. Emodin significantly abolished the Cd-induced bone microstructure damage (p<0.05), osteoclast formation and increase of tartrate-resistant acid phosphatase 5b level (p<0.05). Our data further showed that emodin attenuated the Cd-induced inhibition of osteoprotegerin expression and stimulation of receptor activator for nuclear factor-κ B ligand expression. Our data show that emodin suppresses the Cd-induced osteoporosis by inhibiting osteoclast formation.

Emerging Mycotoxins: Beyond Traditionally Determined Food Contaminants

Modern analytical techniques can determine a multitude of fungal metabolites contaminating food and feed. In addition to known mycotoxins, for which maximum levels in food are enforced, also currently unregulated, so-called "emerging mycotoxins" were shown to occur frequently in agricultural products. The aim of this review is to critically discuss the relevance of selected emerging mycotoxins to food and feed safety. Acute and chronic toxicity as well as occurrence data are presented for enniatins, beauvericin, moniliformin, fusaproliferin, fusaric acid, culmorin, butenolide, sterigmatocystin, emodin, mycophenolic acid, alternariol, alternariol monomethyl ether, and tenuazonic acid. By far not all of the detected compounds are toxicologically relevant at their naturally occurring levels and are therefore of little or no health concern to consumers. Still, gaps in knowledge have been identified for several compounds. These gaps should be closed by the scientific community in the coming years to allow a proper risk assessment.

Role of endoplasmic reticulum stress in disuse osteoporosis

Osteoporosis is a major skeletal disease with low bone mineral density, which leads to an increased risk of bone fracture. Salubrinal is a synthetic chemical that inhibits dephosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α) in response to endoplasmic reticulum (ER) stress. To understand possible linkage of osteoporosis to ER stress, we employed an unloading mouse model and examined the effects of salubrinal in the pathogenesis of disuse osteoporosis. The results presented several lines of evidence that osteoclastogenesis in the development of osteoporosis was associated with ER stress, and salubrinal suppressed unloading-induced bone loss. Compared to the age-matched control, unloaded mice reduced the trabecular bone area/total area (B.Ar/T.Ar) as well as the number of osteoblasts, and they increased the osteoclasts number on the trabecular bone surface in a time-dependent way. Unloading-induced disuse osteoporosis significantly increased the expression of Bip, p-eIF2α and ATF4 in short-term within 6h of tail suspension, but time-dependent decreased in HU2d to HU14d. Furthermore, a significant correlation of ER stress with the differentiation of osteoblasts and osteoclasts was observed. Administration of salubrinal suppressed the unloading-induced decrease in bone mineral density, B.Ar/T.Ar and mature osteoclast formation. Salubrinal also increased the colony-forming unit-fibroblasts and colony-forming unit-osteoblasts. It reduced the formation of mature osteoclasts, suppressed their migration and adhesion, and increased the expression of Bip, p-eIF2α and ATF4. Electron microscopy showed that rough endoplasmic reticulum expansion and a decreased number of ribosomes on ER membrane were observed in osteoblast of unloading mice, and the abnormal ER expansion was significantly improved by salubrinal treatment. A TUNEL assay together with CCAAT/enhancer binding protein homologous protein (CHOP) expression indicated that ER stress-induced osteoblast apoptosis was rescued by salubrinal. Collectively, the results support the notion that ER stress plays a key role in the pathogenesis of disuse osteoporosis, and salubrinal attenuates unloading-induced bone loss by altering proliferation and differentiation of osteoblasts and osteoclasts via eIF2α signaling.

Quercitrin attenuates osteoporosis in ovariectomized rats by regulating mitogen-activated protein kinase (MAPK) signaling pathways

MAPK signaling pathways are crucial in regulating osteogenesis, a genetic disorder affecting the bones. Quercitrin, a type of flavonoid, is widely distributed in nature and involved in many pharmacological activities. But its osteoprotective functions and mechanism in osteoporosis are far from being understood clearly. In this paper, the MAPK upregulation was observed in the ovariectomy-induced bone loss. Quercitrin was found to downregulate MAPK signaling pathways and prevent the ovariectomy-induced deterioration of bone mineral density (BMD), trabecular microstructure, and bone mechanical characteristics. In this study, quercitrin was seen to prevent the progression of the postmenopausal osteoporosis among the rats, which may be mediated by the downregulated MAPK signaling pathways.