Acetyl-11-keto-β-boswellic acid attenuates titanium particle-induced osteogenic inhibition via activation of the GSK-3β/β-catenin signaling pathway

Periprosthetic osteolysis: Mechanisms and potential treatment strategies

Periprosthetic osteolysis is a common bone-related disorder that often occurs after total hip arthroplasty. The implants can cause damage to bone and bone-related cells due to mechanical stress and micromotions, resulting in the generation of a large number of wear particles. These wear particles trigger inflammation and oxidative stress in the surrounding tissues, disrupting the delicate balance maintained by osteoblasts and osteoclasts, ultimately leading to bone loss around the implant. Clinical investigations have demonstrated that Epimedium prenylflavonoids, miR-19a-3p, stem cell-derived exosomes, and certain non-PPO category pharmaceuticals have regulatory effects on bone homeostasis through distinct molecular pathways. Notably, this phenomenon reflects inherent biological rationality rather than stochastic occurrence. Extensive research has revealed that multiple natural compounds, non-coding RNAs, exosomes, and non-PPO therapeutics not only exert modulatory influences on critical pathophysiological processes including inflammatory cascades, oxidative stress responses, and tissue regeneration mechanisms, but also effectively regulate bone-related cellular functions to inhibit PPO progression. Therefore, this review comprehensively and systematically summarizes the main pathogenic mechanisms of periprosthetic osteolysis. Furthermore, it delves deeper into the research progress on the applications of currently reported natural products, ncRNAs, exosomes, and non-PPO medications in the treatment of periprosthetic osteolysis. Based on this, we hope that this paper can provide new perspectives and references for the future development of drugs targeting periprosthetic osteolysis.

Unphosphorylated STAT1 binds to the BST2 transcription promoter, promoting increased AKBA anchoring on HPMECs to alleviate ARDS

Although the drug therapeutic targets of acute respiratory distress syndrome (ARDS) are still unclear and no specific drugs for ARDS treatment have been found, some breakthroughs have been gradually made in the biological target pathways such as endothelial injury. The Traditional Chinese Medicine Systems Pharmacology (TCMSP) database suggests that Acetyl-11-keto-β-boswellic acid (AKBA), a processed product of boswellic acid, may be an effective intervention for ARDS. After preliminary in vitro and in vivo verification of the protective role of AKBA on ARDS, in order to explore the mechanism of AKBA in ARDS, we used transcriptomic and proteomic methods to explore its main targets, and used molecular docking and cell thermal shift assay (CETSA) to further reveal the potential value of bone marrow stromal cell antigen 2 (BST2) as a target. We subsequently examined the effect of AKBA targeting BST2 on tubule formation, cell proliferation (Colony formation and EdU assay), migration (transwell and scratch assays), apoptosis and autophagy levels both in vitro and in vivo, and protein changes (analyzed by Western blotting analysis). Our results show that the unphosphorylated signal transducers and transcription activation factors (U-STAT1) bins to the BST2 transcription promoter to encourage more AKBA anchoring the human pulmonary microvascular endothelial cells (HPMECs), thus inhibiting apoptosis and autophagy, promoting migration and tube formation, and restraining the cecal ligation and puncture (CLP) induced lung tissue damage in mice. In conclusion, AKBA treatment may be a potential strategy in the intervention of ARDS. Alternatively, BST2 may contribute to the anchoring of AKBA to HPMECs, and STAT1 as a transcription factor promoting BST2 expression may bind to its promoter.

Injectable Nano-Micron AKBA Delivery Platform for Treatment of Tendinopathy in a Rat Model

Tendinopathy is a disorder characterized by pain and reduced function due to a series of changes in injured or diseased tendons. Inflammation and collagen degeneration are key contributors to the onset and chronic nature of tendinopathy. Acetyl-11-keto-β-boswellic acid (AKBA) is an effective anti-inflammatory agent widely used in chronic inflammatory disorders and holds potential for tendinopathy treatment; however, its therapeutic efficacy is limited by poor aqueous solubility. Here, we fabricated AKBA-encapsulated cationic liposome-gelatin methacrylamide (GelMA) microspheres (GM-Lipo-AKBA) using thin-film hydration and microfluidic technology for drug delivery therapy. GM-Lipo-AKBA exhibited high encapsulation efficiency, extended AKBA release for over 4 weeks, and prolonged degradation. In vitro and in vivo experiments demonstrated its effectiveness in improving inflammation and ECM remodeling in tendinopathy. In summary, the injectable nano-micron drug delivery platform provides a promising strategy for the sustained and localized delivery of AKBA for tendinopathy treatment.

Acetyl-11-keto-β-boswellia acid attenuates Ti particle-induced osteoblastic oxidative stress and osteolysis through the Foxo3 signaling pathway

Oxidative stress injury in osteoblasts is one of the leading causes of periprosthetic osteolysis (PPOL). Acetyl-11-keto-β-boswellia acid (AKBA) has been used as an antioxidant in the treatment of various diseases, but its antioxidant mechanism in osteolysis has yet to be elucidated. In this study, a mouse cranial osteolysis model was constructed, and MC3T3-E1 cells and bone marrow mesenchymal stem cells (BMSCs) were cultured in vitro. Western blotting and immunofluorescence staining revealed that titanium (Ti) particles aggravated osteoblast oxidative stress injury and apoptosis. Ti particles and hydrogen peroxide reduced the osteogenic ability of BMSCs. At a certain concentration, AKBA alleviated the oxidative stress injury of MC3T3-E1 cells induced by Ti particles and enhanced the osteogenic ability of BMSCs, and the expression of Forkhead box O3 (Foxo3) increased with increasing AKBA concentration. To verify the antioxidant mechanism of AKBA, we designed and synthesized Foxo3-targeting siRNAs. We found that after Foxo3 expression was inhibited, the protective effect of AKBA on osteoblasts decreased significantly. Moreover, AKBA treatment suppressed bone mass loss in the skull mediated by Ti particles in mice. Therefore, we suggest that AKBA alleviates the oxidative stress injury in osteoblasts induced by Ti particles, at least in part, by regulating the expression of Foxo3. In this study, the mechanism and biosafety of AKBA in treating PPOL were demonstrated to some extent.

Role of immune dysregulation in peri-implantitis

Peri-implantitis, a complex condition that can lead to dental implant failure, is characterized by inflammatory destruction resulting from immune dysregulation. Oral microbial dysbiosis and foreign body stimulation are the main factors contributing to such dysregulation, impairing immune cell function and triggering an inflammatory response. Immune dysregulation plays a critical role in the pathophysiology of peri-implantitis, impacting the balance of T cell subsets, the production of inflammatory factors, and immune-related molecular signaling pathways. Understanding the relationship between immune dysregulation and peri-implantitis is crucial for developing targeted strategies for clinical diagnosis and individualized treatment planning. This review explores the similarities and differences in the immune microenvironment of oral bacterial infections and foreign body rejection, analyzes the relevant molecular signaling pathways, and identifies new key targets for developing innovative immunotherapeutic drugs and effective and personalized treatment modalities for peri-implantitis. Additionally, it addresses the challenges and potential directions for translating immunotherapy into clinical practice for peri-implantitis, offering insights that bridge the gaps in current literature and pave the way for future research.

Anti-osteoporotic effects of Boswellia serrata gum resin extract in vitro and in vivo

BACKGROUND/OBJECTIVES

This study evaluated the beneficial effects of an ethanol extract of Boswellia serrata gum resin (FJH-UBS) in osteoporosis.

MATERIALS/METHODS

MC3T3-E1 osteoblastic cells and RAW 264.7 osteoclastic cells were treated with FJH-UBS. The alkaline phosphatase (ALP) activity, mineralization, collagen synthesis, osteocalcin content, and Runt-related transcription factor 2 (RUNX2) and Osterix expression were measured in MC3T3-E1 cells. The actin ring structures, tartrate-resistant acid phosphatase (TRAP) activity, and the nuclear factor of activator T-cells, cytoplasm 1 (NFATc1) expression were evaluated in RAW 264.7 cells. Ovariectomized ICR mice were orally administered FJH-UBS for eight weeks. The bone mineral density (BMD) and the serum levels of osteocalcin, procollagen 1 N-terminal propeptide (P1NP), osteoprotegerin, and TRAP 5b were analyzed.

RESULTS

FJH-UBS increased the ALP activity, collagen, osteocalcin, mineralization, and RUNX2 and osterix expression in MC3T3-E1 osteoblastic cells, whereas it decreased the TRAP activity, actin ring structures, and NFATc1 expression in RAW 264.7 osteoclastic cells. In ovariectomy-induced osteoporosis mice, FJH-UBS positively restored all of the changes in the bone metabolism biomarkers (BMD, osteocalcin, P1NP, osteoprotegerin, and TRAP 5b) caused by the ovariectomy.

CONCLUSION

FJH-UBS has anti-osteoporotic activity by promoting osteoblast activity and inhibiting osteoclast activity in vitro and in vivo, suggesting that FJH-UBS is a potential functional food ingredient for osteoporosis.

Mettl3‑mediated m6A RNA methylation regulates osteolysis induced by titanium particles

Peri‑prosthetic osteolysis (PPO) induced by wear particles is considered the primary cause of titanium prosthesis failure and revision surgery. The specific molecular mechanisms involve titanium particles inducing multiple intracellular pathways, which impact disease prevention and the targeted therapy of PPO. Notably, N6‑methyladenosine (m6A) serves critical roles in epigenetic regulation, particularly in bone metabolism and inflammatory responses. Thus, the present study aimed to determine the role of RNA methylation in titanium particle‑induced osteolysis. Results of reverse transcription‑quantitative PCR (RT‑qPCR), western blotting, ELISA and RNA dot blot assays revealed that titanium particles induced osteogenic inhibition and proinflammatory responses, accompanied by the reduced expression of methyltransferase‑like (Mettl) 3, a key component of m6A methyltransferase. Specific lentiviruses vectors were employed for Mettl3 knockdown and overexpression experiments. RT‑qPCR, western blotting and ELISA revealed that the knockdown of Mettl3 induced osteogenic inhibition and proinflammatory responses comparable with that induced by titanium particle, while Mettl3 overexpression attenuated titanium particle‑induced cellular reactions. Methylated RNA immunoprecipitation‑qPCR results revealed that titanium particles mediated the methylation of two inhibitory molecules, namely Smad7 and SMAD specific E3 ubiquitin protein ligase 1, via Mettl3 in bone morphogenetic protein signaling, leading to osteogenic inhibition. Furthermore, titanium particles induced activation of the nucleotide binding oligomerization domain 1 signaling pathway through methylation regulation, and the subsequent activation of the MAPK and NF‑κB pathways. Collectively, the results of the present study indicated that titanium particles utilized Mettl3 as an upstream regulatory molecule to induce osteogenic inhibition and inflammatory responses. Thus, the present study may provide novel insights into potential therapeutic targets for aseptic loosening in titanium prostheses.

Kaempferol attenuates wear particle-induced inflammatory osteolysis via JNK and p38-MAPK signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Wear particle-induced inflammatory osteoclast activation is a master contributor to periprosthetic osteolysis, which can cause pathological bone loss and destruction. Hence, inhibiting inflammation and osteoclastogenesis is an important strategy for preventing wear particle-induced osteolysis. To date, there are no FDA-approved non-surgical pharmacotherapies for arresting periprosthetic osteolysis. Kaempferol (KAE), a natural flavonol abundant in many traditional Chinese herbal medicines, has been shown to have protective effects against inflammatory bone diseases such as rheumatoid arthritis, but no previous study has evaluated the effects of KAE on wear particle-induced osteolysis.

AIM OF THE STUDY

The study aimed to investigate the effects of KAE on wear particle-induced inflammatory osteolysis and osteoclast activation, and further explore the underlying mechanisms.

MATERIALS AND METHODS

TiAl6V4 metal particles (TiPs) were retrieved from the prosthesis of patients who underwent revision hip arthroplasty due to aseptic loosening. A mouse calvarial osteolysis model was used to investigate the effects of KAE on wear particle-induced inflammatory osteolysis in vivo. Primary bone marrow-derived macrophages (BMMs) were used to explore the effects of KAE on osteoclast differentiation and bone-resorbing activity as well as the underlying mechanisms in vitro.

RESULTS

In the present study, we found that KAE alleviated wear particle-induced inflammatory bone loss in vivo and inhibited osteoclast differentiation and function in vitro. Furthermore, we revealed that KAE exerted anti-osteoclastogenic effects by downregulating JNK and p38-MAPK signaling as well as the downstream NFATc1 expression.

CONCLUSIONS

KAE is an alternative therapeutic agent for preventing and treating periprosthetic osteolysis and aseptic loosening.

The age-related characteristics in bone microarchitecture, osteoclast distribution pattern, functional and transcriptomic alterations of BMSCs in mice

Deteriorated age-related bone loss is the hallmarks of skeletal aging. However, how the aging of bone marrow mesenchymal stem cells (BMSCs) and osteoclasts are linked to the bone microstructure degeneration is not yet very clear. In this study, the characteristics of age-related bone loss, distribution patterns of osteoclasts, functional and transcriptomic alterations of BMSCs, hub genes responsible for BMSCs senescence, were analyzed. Our study revealed an age-related declined trends in trabecular and cortical bones of femur, tibia and lumbar vertebra in mice, which was accompanied by a shift from the trabecular to cortical bones in osteoclasts. Additionally, middle-aged or aged mice exhibited remarkably reduced dynamic bone formation capacities, along with reversed osteogenic-adipogenic differentiation potentials in BMSCs. Finally, transcriptomic analysis indicated that aging-related signaling pathways were significantly activated in BMSCs from aged mice (e.g., cellular senescence, p53 signaling pathway, etc.). Also, weighted correlation network analysis (WGCNA) and venn diagram analysis based on our RNA-Seq data and GSE35956 dataset revealed the critical role of PTPN1 in BMSCs senescence. Targeted inhibition of PTP1B with AAV-Ptpn1-RNAi dramatically postponed age-related bone loss in middle-aged mice. Collectively, our study has uncovered the age-dependent cellular characteristics in BMSCs and osteoclasts underlying progressive bone loss with advancing age.

Titanium particles in peri-implantitis: distribution, pathogenesis and prospects

Peri-implantitis is one of the most important biological complications in the field of oral implantology. Identifying the causative factors of peri-implant inflammation and osteolysis is crucial for the disease's prevention and treatment. The underlying risk factors and detailed pathogenesis of peri-implantitis remain to be elucidated. Titanium-based implants as the most widely used implant inevitably release titanium particles into the surrounding tissue. Notably, the concentration of titanium particles increases significantly at peri-implantitis sites, suggesting titanium particles as a potential risk factor for the condition. Previous studies have indicated that titanium particles can induce peripheral osteolysis and foster the development of aseptic osteoarthritis in orthopedic joint replacement. However, it remains unconfirmed whether this phenomenon also triggers inflammation and bone resorption in peri-implant tissues. This review summarizes the distribution of titanium particles around the implant, the potential roles in peri-implantitis and the prevalent prevention strategies, which expects to provide new directions for the study of the pathogenesis and treatment of peri-implantitis.

Particle-induced osteolysis is mediated by endoplasmic reticulum stress-associated osteoblast apoptosis

Osteoblast dysfunction plays a crucial role in periprosthetic osteolysis and aseptic loosening, and endoplasmic reticulum (ER) stress is recognized as an important causal factor of wear particle-induced osteolysis. However, the influence of ER stress on osteoblast activity during osteolysis and its underlying mechanisms remain elusive. This study aims to investigate whether ER stress is involved in the detrimental effects of wear particles on osteoblasts. Through our investigation, we observed elevated expression levels of ER stress and apoptosis markers in particle-stimulated bone specimens and osteoblasts. To probe further, we employed the ER stress inhibitor, 4-PBA, to treat particle-stimulated osteoblasts. The results revealed that 4-PBA effectively alleviated particle-induced osteoblast apoptosis and mitigated osteogenic reduction. Furthermore, our study revealed that wear particle-induced ER stress in osteoblasts coincided with mitochondrial damage, calcium overload, and oxidative stress, all of which were effectively alleviated by 4-PBA treatment. Encouragingly, 4-PBA administration also improved bone formation and attenuated osteolysis in a mouse calvarial model. In conclusion, our results demonstrate that ER stress plays a crucial role in mediating wear particle-induced osteoblast apoptosis and impaired osteogenic function. These findings underscore the critical involvement of ER stress in wear particle-induced osteolysis and highlight ER stress as a potential therapeutic target for ameliorating wear particle-induced osteogenic reduction and bone destruction.

Osteocytes Exposed to Titanium Particles Inhibit Osteoblastic Cell Differentiation via Connexin 43

Periprosthetic osteolysis (PPO) induced by wear particles is the most severe complication of total joint replacement; however, the mechanism behind PPO remains elusive. Previous studies have shown that osteocytes play important roles in wear-particle-induced osteolysis. In this study, we investigated the effects of connexin 43 (Cx43) on the regulation of osteocyte-to-osteoblast differentiation. We established an in vivo murine model of calvarial osteolysis induced by titanium (Ti) particles. The osteolysis characteristic and osteogenesis markers in the osteocyte-selective Cx43 (CKO)-deficient and wild-type (WT) mice were observed. The calvarial osteolysis induced by Ti particles was partially attenuated in CKO mice. The expression of β-catenin and osteogenesis markers increased significantly in CKO mice. In vitro, the osteocytic cell line MLO-Y4 was treated with Ti particles. The co-culturing of MLO-Y4 cells with MC3T3-E1 osteoblastic cells was used to observe the effects of Ti-treated osteocytes on osteoblast differentiation. When Cx43 of MLO-Y4 cells was silenced or overexpressed, β-catenin was detected. Additionally, co-immunoprecipitation detection of Cx43 and β-catenin binding in MLO-Y4 cells and MC3T3-E1 cells was performed. Finally, β-catenin expression in MC3T3-E1 cells and osteoblast differentiation were evaluated after 18α-glycyrrhetinic acid (18α-GA) was used to block the intercellular communication of Cx43 between MLO-Y4 and MC3T3-E1 cells. Ti particles increased Cx43 expression and decreased β-catenin expression in MLO-Y4 cells. The silencing of Cx43 increased the β-catenin expression, and the over-expression of Cx43 decreased the β-catenin expression. In the co-culture model, Ti treatment of MLO-Y4 cells inhibited the osteoblastic differentiation of MC3T3-E1 cells and Cx43 silencing in MLO-Y4 cells attenuated the inhibitory effects on osteoblastic differentiation. With Cx43 silencing in the MLO-Y4 cells, the MC3T3-E1 cells, co-cultured alongside MLO-Y4, displayed decreased Cx43 expression, increased β-catenin expression, activation of Runx2, and promotion of osteoblastic differentiation in vitro co-culture. Finally, Cx43 expression was found to be negatively correlated to the activity of the Wnt signaling pathway, mostly through the Cx43 binding of β-catenin from its translocation to the nucleus. The results of our study suggest that Ti particles increased Cx43 expression in osteocytes and that osteocytes may participate in the regulation of osteoblast function via the Cx43 during PPO.

The Dopamine D1 Receptor Attenuates Titanium Particle-Induced Inhibition of Osteogenesis by Activating the Wnt Signaling Pathway

Periprosthetic osteolysis (PPO), caused by wear particles, has become a major cause of joint replacement failure. Secondary surgery after joint replacement poses a serious threat to public health worldwide. Therefore, determining how to effectively inhibit wear particle-induced PPO has become an urgent issue. Recently, the interaction between osteogenic inhibition and wear particles at the biological interface of the implant has been found to be an important factor in the pathological process. Previous studies have found that the central nervous system plays an important role in the regulation of bone formation and bone remodeling. Dopamine (DA), an important catecholamine neurotransmitter, plays an integral role in the physiological and pathological processes of various tissues through its corresponding receptors. Our current study found that upregulation of dopamine first receptors could be achieved by activating the Wnt/β-catenin pathway, improving osteogenesis in vivo and in vitro, and significantly reducing the inhibition of titanium particle-induced osteogenesis. Overall, these findings suggest that dopamine first receptor (D1R) may be a plausible target to promote osteoblast function and resist wear particle-induced PPO.

Boswellic acids ameliorate neurodegeneration induced by AlCl3: the implication of Wnt/β-catenin pathway

Alzheimer's disease (AD) is a neurodegenerative disease (ND) that represents the principal cause of dementia. Effective treatment is still lacking. Without prevention, Alzheimer's disease (AD) incidence is expected to triple within 30 years. The risk increases in highly polluted areas and is positively linked to chronic aluminum (Al) exposure. Canonical Wingless-Int (Wnt)/β-catenin pathway has been found to play a considerable role in ND pathogenesis. Resins of Boswellia serrata (frankincense) have been used traditionally for their psychoactive activity, in addition to their memory-boosting effects. Boswellic acids (BA) are pentacyclic triterpenes. They have antioxidant, anti-inflammatory, antinociceptive, and immunomodulatory activities. This study aimed to elucidate the role of the Wnt/β-catenin pathway in BA protective activity against aluminum-induced Alzheimer's disease. For 6 weeks, rats were treated daily with AlCl3 (100 mg/kg/i.p.) either alone or with BA (125 or 250 mg/kg PO). Results indicated that BA significantly improved learning and memory impairments induced by AlCl3 treatment. Moreover, BA treatment significantly decreased acetylcholinesterase levels and reduced amyloid-beta (Aβ) expression. In addition, BA ameliorated the increased expression of tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β), inhibited lipid peroxidation, and increased total antioxidants in the brain. Indeed, BA significantly suppressed AlCl3-induced decrease of brain-derived neurotrophic factor, pGSK-3β (Ser 9), and β-catenin. BA (250 mg/kg) showed a significant protective effect compared to a lower dose. The results conclude that BA administration modulated the expression of Wnt/β-catenin pathway-related parameters, contributing to BA's role against Al-induced Alzheimer's disease. Effect of Boswellic acids on AlCl3-induced neurodegenerative changes. ChE cholinesterase, Ach acetylcholine, BDNF brain-derived neurotrophic factor, IL-1β interleukin-1β, TNF-α tumor necrosis factor-α.

Boswellic Acids, Pentacyclic Triterpenes, Attenuate Oxidative Stress, and Bladder Tissue Damage in Cyclophosphamide-Induced Cystitis

Boswellic acids, derived from the Boswellia serrata plant, have been demonstrated to have anti-inflammatory properties in experimental animal models. The present study was aimed to evaluate the uro-protective effect of boswellic acids in rats with cyclophosphamide-induced cystitis. Interstitial cystitis was induced by cyclophosphamide (CYP). In order to analyze the reduction of the urothelial damage, the bladder weight, the nociception response, and the Evans blue dye extravasation from the bladder were evaluated. To investigate the involvement of lipid peroxidation and enzymatic antioxidants CAT, SOD, and GPX and MPO and NO were evaluated. IL-6 and TNF-α were measured by the ELISA immunoassay technique. The results showed that pretreatment with boswellic acids significantly reduced urothelial damage which was accompanied by a decrease in the activity of MDA, CPO, and NO levels and prevention of the depletion of CAT, SOD, and GPX. The levels of IL-6 and TNF-α were dramatically reduced by boswellic acids. Histopathological findings revealed a considerable reduction in cellular infiltration, edema, epithelial denudation, and bleeding. Our findings showed that boswellic acids, by their antioxidant and anti-inflammatory properties, negate the detrimental effects of cyclophosphamide on the bladder, suggesting boswellic acids as promising therapeutic alternatives for cystitis.

The Biological Activity of 3-O-Acetyl-11-keto-β-Boswellic Acid in Nervous System Diseases

Frankincense is a hard gelatinous resin exuded by Boswellia serrata. It contains a complex array of components, of which acetyl-11-keto-beta-boswellic acid (AKBA), a pentacyclic triterpenoid of the resin class, is the main active component. AKBA has a variety of physiological actions, including anti-infection, anti-tumor, and antioxidant effects. The use of AKBA for the treatment of mental diseases has been documented as early as ancient Greece. Recent studies have found that AKBA has anti-aging and other neurological effects, suggesting its potential for the treatment of neurological diseases. This review focuses on nervous system-related diseases, summarizes the functions and mechanisms of AKBA in promoting nerve repair and regeneration after injury, protecting against ischemic brain injury and aging, inhibiting neuroinflammation, ameliorating memory deficits, and alleviating neurotoxicity, as well as having anti-glioma effects and relieving brain edema. The mechanisms by which AKBA functions in different diseases and the relationships between dosage and biological effects are discussed in depth with the aim of increasing understanding of AKBA and guiding its use for the treatment of nervous system diseases.

Effect of Dietary Polyphenols on Osteoarthritis-Molecular Mechanisms

Osteoarthritis is a common crippling and degenerative disease resulting in irreversible functional changes due to damage of the cartilage and other tissues of the joint. With limited safe and effective pharmaceutical treatments, the demand and use for alternative therapeutic approaches with symptomatic relief for OA patients have increased. Clinical, pre-clinical, and in vitro studies have demonstrated that polyphenols can exert pain-relieving symptoms coupled with increased functional capacity in OA models. This review will highlight studies carried out in the last five years to define the efficacies and underlying mechanisms in polyphenols such as quercetin, resveratrol, curcumin, epigallocatechin-3-gallate, rosmarinic acid, genistein, ginger, berries, silver fir, pine bark, and Boswellia. Most of these studies indicate that polyphenols exhibit their beneficial roles through regulating changes at the biochemical and molecular levels, inducing or inhibiting various signaling pathways related to inflammation and oxidative stress. Polyphenols have also been implicated in modulating microRNA at the posttranscriptional level to counteract OA pathogenesis.

Identification of Novel Cannabinoid CB2 Receptor Agonists from Botanical Compounds and Preliminary Evaluation of Their Anti-Osteoporotic Effects

As cannabinoid CB2 receptors (CB2R) possess various pharmacological effects—including anti-epilepsy, analgesia, anti-inflammation, anti-fibrosis, and regulation of bone metabolism—without the psychoactive side effects induced by cannabinoid CB1R activation, they have become the focus of research and development of new target drugs in recent years. The present study was intended to (1) establish a double luciferase screening system for a CB2R modulator; (2) validate the agonistic activities of the screened compounds on CB2R by determining cAMP accumulation using HEK293 cells that are stably expressing CB2R; (3) predict the binding affinity between ligands and CB2 receptors and characterize the binding modes using molecular docking; (4) analyze the CB2 receptors–ligand complex stability, conformational behavior, and interaction using molecular dynamics; and (5) evaluate the regulatory effects of the screened compounds on bone metabolism in osteoblasts and osteoclasts. The results demonstrated that the screening system had good stability and was able to screen cannabinoid CB2R modulators from botanical compounds. Altogether, nine CB2R agonists were identified by screening from 69 botanical compounds, and these CB2R agonists exhibited remarkable inhibitory effects on cAMP accumulation and good affinity to CB2R, as evidenced by the molecular docking and molecular dynamics. Five of the nine CB2R agonists could stimulate osteoblastic bone formation and inhibit osteoclastic bone resorption. All these findings may provide useful clues for the development of novel anti-osteoporotic drugs and help elucidate the mechanism underlying the biological activities of CB2R agonists identified from the botanical materials.

Curculigoside Protects against Titanium Particle-Induced Osteolysis through the Enhancement of Osteoblast Differentiation and Reduction of Osteoclast Formation

Wear particle-induced periprosthetic osteolysis is mainly responsible for joint replacement failure and revision surgery. Curculigoside is reported to have bone-protective potential, but whether curculigoside attenuates wear particle-induced osteolysis remains unclear. In this study, titanium particles (Ti) were used to stimulate osteoblastic MC3T3-E1 cells in the presence or absence of curculigoside, to determine their effect on osteoblast differentiation. Rat osteoclastic bone marrow stromal cells (BMSCs) were cocultured with Ti in the presence or absence of curculigoside, to evaluate its effect on osteoclast formation in vitro. Ti was also used to stimulate mouse calvaria to induce an osteolysis model, and curculigoside was administrated to evaluate its effect in the osteolysis model by micro-CT imaging and histopathological analyses. As the results indicated, in MC3T3-E1 cells, curculigoside treatment attenuated the Ti-induced inhibition on cell differentiation and apoptosis, increased alkaline phosphatase activity (ALP) and cell mineralization, and inhibited TNF-α, IL-1β, and IL-6 production and ROS generation. In BMSCs, curculigoside treatment suppressed the Ti-induced cell formation and suppressed the TNF-α, IL-1β, and IL-6 production and F-actin ring formation. In vivo, curculigoside attenuated Ti-induced bone loss and histological damage in murine calvaria. Curculigoside treatment also reversed the RANK/RANKL/OPG and NF-κB signaling pathways, by suppressing the RANKL and NF-κB expression, while activating the OPG expression. Our study demonstrated that curculigoside treatment was able to attenuate wear particle-induced periprosthetic osteolysis in in vivo and in vitro experiments, promoted osteoblastic MC3T3-E1 cell differentiation, and inhibited osteoclast BMSC formation. It suggests that curculigoside may be a potential pharmaceutical agent for wear particle-stimulated osteolysis therapy.

Harmine Alleviates Titanium Particle-Induced Inflammatory Bone Destruction by Immunomodulatory Effect on the Macrophage Polarization and Subsequent Osteogenic Differentiation

Peri-prosthetic osteolysis (PPO) and following aseptic loosening are regarded as the prime reasons for implant failure after joint replacement. Increasing evidence indicated that wear-debris-irritated inflammatory response and macrophage polarization state play essential roles in this osteolytic process. Harmine, a β-carboline alkaloid primitively extracted from the Peganum harmala seeds, has been reported to have various pharmacological effects on monoamine oxidase action, insulin intake, vasodilatation and central nervous systems. However, the impact of harmine on debris-induced osteolysis has not been demonstrated, and whether harmine participates in regulating macrophage polarization and subsequent osteogenic differentiation in particle-irritated osteolysis remains unknown. In the present study, we investigated the effect of harmine on titanium (Ti) particle-induced osteolysis in vivo and in vitro. The results suggested harmine notably alleviated Ti particle-induced bone resorption in a murine PPO model. Harmine was also found to suppress the particle-induced inflammatory response and shift the polarization of macrophages from M1 phenotypes to M2 phenotypes in vivo and in vitro, which improved anti-inflammatory and bone-related cytokines levels. In the conditioned medium from Ti particle-stimulated murine macrophage RAW264.7 cells treated with harmine, the osteoblast differentiation ability of mouse pre-osteoblastic MC3T3-E1 cells was greatly increased. And we also provided evidences that the immunomodulatory capacity of harmine might be attributed to the inhibition of the c-Jun N-terminal kinase (JNK) in wear particle-treated macrophages. All the results strongly show that harmine might be a promising therapeutic agent to treat PPO.

β-Boswellic Acid Inhibits RANKL-Induced Osteoclast Differentiation and Function by Attenuating NF-κB and Btk-PLCγ2 Signaling Pathways

Osteoporosis is a systemic metabolic bone disorder that is caused by an imbalance in the functions of osteoclasts and osteoblasts and is characterized by excessive bone resorption by osteoclasts. Targeting osteoclast differentiation and bone resorption is considered a good fundamental solution for overcoming bone diseases. β-boswellic acid (βBA) is a natural compound found in Boswellia serrata, which is an active ingredient with anti-inflammatory, anti-rheumatic, and anti-cancer effects. Here, we explored the anti-resorptive effect of βBA on osteoclastogenesis. βBA significantly inhibited the formation of tartrate-resistant acid phosphatase-positive osteoclasts induced by receptor activator of nuclear factor-B ligand (RANKL) and suppressed bone resorption without any cytotoxicity. Interestingly, βBA significantly inhibited the phosphorylation of IκB, Btk, and PLCγ2 and the degradation of IκB. Additionally, βBA strongly inhibited the mRNA and protein expression of c-Fos and NFATc1 induced by RANKL and subsequently attenuated the expression of osteoclast marker genes, such as OC-STAMP, DC-STAMP, β3-integrin, MMP9, ATP6v0d2, and CtsK. These results suggest that βBA is a potential therapeutic candidate for the treatment of excessive osteoclast-induced bone diseases such as osteoporosis.

Citrate-Stabilized Gold Nanorods-Directed Osteogenic Differentiation of Multiple Cells

Objective

Gold nanorods (AuNRs) show great potential for versatile biomedical applications, such as stem cell therapy and bone tissue engineering. However, as an indispensable shape-directing agent for the growth of AuNRs, cetyltrimethylammonium bromide (CTAB) is not optimal for biological studies because it forms a cytotoxic bilayer on the AuNR surface, which interferes with the interactions with biological cells.

Methods

Citrate-stabilized AuNRs with various aspect-ratios (Cit-NRI, Cit-NRII, and Cit-NRIII) were prepared by the combination of end-selective etching and poly(sodium 4-styrenesulfonate)-assisted ligand exchange method. Their effects on osteogenic differentiation of the pre-osteoblastic cell line (MC3T3-E1), rat bone marrow mesenchymal stem cells (rBMSCs), and human periodontal ligament progenitor cells (PDLPs) have been investigated. Potential signaling pathway of citrate-stabilized AuNRs-induced osteogenic effects was also investigated.

Results

The experimental results showed that citrate-stabilized AuNRs have superior biocompatibility and undergo aspect-ratio-dependent osteogenic differentiation via expression of osteogenic marker genes, alkaline phosphatase (ALP) activity and formation of mineralized nodule. Furthermore, Wnt/β-catenin signaling pathway might provide a potential explanation for the citrate-stabilized AuNRs-mediated osteogenic differentiation.

Conclusion

These findings revealed that citrate-stabilized AuNRs with great biocompatibility could regulate the osteogenic differentiation of multiple cell types through Wnt/β-catenin signaling pathway, which promote innovative AuNRs in the field of tissue engineering and other biomedical applications.

Inhibitory effect of acetyl-11-keto-β-boswellic acid on titanium particle-induced bone loss by abrogating osteoclast formation and downregulating the ERK signaling pathway

Wear debris-induced osteoclast accumulation around implants plays a crucial role during the progression of periprosthetic osteolysis (PPO). We have confirmed that acetyl-11-keto-β-boswellic acid (AKBA) promotes bone formation and protects against particle-induced bone destruction in vivo. However, the effect of AKBA on titanium-induced bone resorption is unknown. In this study, we detected the inhibitory effect of AKBA on titanium-induced bone erosion in vivo and used RAW264.7 cells and bone marrow macrophages (BMMs) to investigate the effect and underlying mechanism of AKBA on the differentiation and resorptive function of osteoclasts. Our findings revealed that AKBA inhibited particle-induced bone loss and osteoclast formation in vivo. Furthermore, AKBA exerted inhibitory effects on RANKL-induced osteoclastogenesis, osteoclastic ring-dependent resorption and the expression of osteoclast marker genes via the ERK signaling pathway in vitro. Our data further established the protective effect of AKBA on titanium particle-induced bone erosion from a new perspective of bone erosion prevention, strongly confirming that AKBA is an appropriate agent for protection against PPO.

The Beneficial Effect of Boswellic Acid on Bone Metabolism and Possible Mechanisms of Action in Experimental Osteoporosis

Estrogen is instrumental in the pathological process of osteoporosis because a deficiency of this hormone increases the release of bone-resorbing cytokines. Acetyl-11-keto-β-boswellic acid (AKBA), a constituent from Boswellia serrata, has an anti-inflammatory effect by inhibiting tumor necrosis factor-α (TNF-α) expression, which leads to a decline in receptor activator of nuclear factor-kappa B (NF-κB) ligand, and consequently, a reduction in osteoclast activity. Hence, AKBA may be beneficial against bone loss during osteoporosis. Therefore, the current study intended to evaluate the beneficial effects of AKBA in ovariectomy-induced osteoporosis and to investigate its mechanism of action. Sham-operation or ovariectomy female Sprague Dawley rats were used for evaluating the antiosteoporotic effect of AKBA in this study. AKBA (35 mg/kg, p.o.) and estradiol (0.05 mg/kg, i.m.) were administered for 42 days. At the end of the experiment, body and uterus weights, serum and urine calcium and phosphorus, serum alkaline phosphatase, and urinary creatinine levels, besides serum levels of NF-κB and TNF-α were determined. Weight, length, thickness, hardness, calcium content, as well as the bone mineral density of femur bone and lumbar vertebra were measured. A histopathological examination was also carried out. AKBA ameliorated all tested parameters and restored a normal histological structure. Thus, AKBA showed good antiosteoporotic activity, which may be mediated through its suppression of the NF-κB-induced TNF-α signaling pathway.

Glycogen synthase kinase-3β: a promising candidate in the fight against fibrosis

Fibrosis exists in almost all organs/tissues of the human body, plays an important role in the occurrence and development of diseases and is also a hallmark of the aging process. However, there is no effective prevention or therapeutic method for fibrogenesis. As a serine/threonine (Ser/Thr)-protein kinase, glycogen synthase kinase-3β (GSK-3β) is a vital signaling mediator that participates in a variety of biological events and can inhibit extracellular matrix (ECM) accumulation and the epithelial-mesenchymal transition (EMT) process, thereby exerting its protective role against the fibrosis of various organs/tissues, including the heart, lung, liver, and kidney. Moreover, we further present the upstream regulators and downstream effectors of the GSK-3β pathway during fibrosis and comprehensively summarize the roles of GSK-3β in the regulation of fibrosis and provide several potential targets for research. Collectively, the information reviewed here highlights recent advances vital for experimental research and clinical development, illuminating the possibility of GSK-3β as a novel therapeutic target for the management of tissue fibrosis in the future.

Punicalagin ameliorates wear-particle-induced inflammatory bone destruction by bi-directional regulation of osteoblastic formation and osteoclastic resorption

Periprosthetic osteolysis (PPO) and subsequent aseptic loosening are the main causes of implant failure and revision surgery. Emerging evidence has suggested that wear-particle-induced chronic inflammation, osteoblast inhibition and osteoclast formation at the biointerface of implant materials are responsible for PPO. Punicalagin (PCG), a polyphenolic compound molecularly extracted from pomegranate rinds, plays a critical role in antioxidant, anticancer and anti-inflammatory activities. However, whether PCG could attenuate chronic inflammation and bone destruction at sites of titanium (Ti)-particle-induced osteolysis remains to be determined. In this study, we explored the effect of PCG on Ti-particle-induced osteolysis in vivo and osteoblast and osteoclast differentiation in vitro. We found that PCG could relieve wear-particle-induced bone destruction in a murine calvarial osteolysis model by increasing bone formation activity and suppressing bone resorption activity. PCG treatment also reduced the Ti-particle-induced inflammatory response in vivo and vitro. In addition, we also observed that PCG promotes osteogenic differentiation of MC3T3-E1 cells under inflammatory conditions and inhibits RANKL-induced osteoclast formation of bone marrow-derived macrophages (BMMs). Meanwhile, the induction of the RANKL to OPG ratio was reversed by PCG treatment in vivo and in vitro, which demonstrated that PCG could also indirectly inhibit osteoclastogenesis. Collectively, our findings suggest that PCG represents a potential approach for the treatment of wear-particle-induced inflammatory osteolysis.

Genetic and pharmacological activation of Hedgehog signaling inhibits osteoclastogenesis and attenuates titanium particle-induced osteolysis partly through suppressing the JNK/c-Fos-NFATc1 cascade

Rationale: Wear particle-induced periprosthetic osteolysis (PPO) is a common long-term complication of total joint arthroplasty, and represents the major cause of aseptic loosening and subsequent implant failure. Previous studies have identified the central role of osteoclast-mediated bone resorption in the pathogenesis of PPO. Thus, therapeutic approaches of inhibiting osteoclast formation and activity are considered to be of great potential to prevent and treat this osteolytic disease. Hedgehog (Hh) signaling has been shown to play an important role in promoting osteoblast differentiation and bone formation. While Hh signaling is also implicated in regulating osteoclastogenesis, whether it can directly inhibit osteoclast differentiation and bone resorption remains controversial. Moreover, its potential therapeutic effects on PPO have never been assessed. In this study, we explored the cell-autonomous role of Hh signaling in regulating osteoclastogenesis and its therapeutic potential in preventing wear particle-induced osteolysis. Methods: Hh signaling was activated in macrophages by genetically ablating Sufu in these cells using LysM-Cre or by treating them with purmorphamine (PM), a pharmacological activator of Smoothened (Smo). In vitro cell-autonomous effects of Hh pathway activation on RANKL-induced osteoclast differentiation and activity were evaluated by TRAP staining, phalloidin staining, qPCR analyses, and bone resorption assays. In vivo evaluation of its therapeutic efficacy against PPO was performed in a murine calvarial model of titanium particle-induced osteolysis by μCT and histological analyses. Mechanistic details were explored in RANKL-treated macrophages through Western blot analyses. Results: We found that Sufu deletion or PM treatment potently activated Hh signaling in macrophages, and strongly inhibited RANKL-induced TRAP+ osteoclast production, F-actin ring formation, osteoclast-specific gene expression, and osteoclast activity in vitro. Furthermore, we found that Sufu deletion or PM administration significantly attenuated titanium particle-induced osteoclast formation and bone loss in vivo. Our mechanistic study revealed that activation of Hh signaling suppressed RANKL-induced activation of JNK pathway and downregulated protein levels of two key osteoclastic transcriptional factors, c-Fos and its downstream target NFATc1. Conclusions: Both genetic and pharmacological activation of Hh signaling can cell-autonomously inhibit RANKL-induced osteoclast differentiation and activity in vitro and protect against titanium particle-induced osteolysis in vivo. Mechanistically, Hh signaling hinders osteoclastogenesis partly through suppressing the JNK/c-Fos-NFATc1 cascade. Thus, Hh signaling may serve as a promising therapeutic target for the prevention and treatment of PPO and other osteolytic diseases.