Molecular Interactions between Dietary Lipids and Bone Tissue during Aging.

Age-related bone disorders such as osteoporosis or osteoarthritis are a major public health problem due to the functional disability for millions of people worldwide. Furthermore, fractures are associated with a higher degree of morbidity and mortality in the long term, which generates greater financial and health costs. As the world population becomes older, the incidence of this type of disease increases and this effect seems notably greater in those countries that present a more westernized lifestyle. Thus, increased efforts are directed toward reducing risks that need to focus not only on the prevention of bone diseases, but also on the treatment of persons already afflicted. Evidence is accumulating that dietary lipids play an important role in bone health which results relevant to develop effective interventions for prevent bone diseases or alterations, especially in the elderly segment of the population. This review focuses on evidence about the effects of dietary lipids on bone health and describes possible mechanisms to explain how lipids act on bone metabolism during aging. Little work, however, has been accomplished in humans, so this is a challenge for future research.

New perspectives on traumatic bone infections.

In this paper, we review the results of previous studies and summarize the effects of various factors on the regulation of bone metabolism in traumatic bone infections. Infection-related bone destruction incorporates pathogens and iatrogenic factors in the process of bone resorption dominated by the skeletal and immune systems. The development of bone immunology has established a bridge of communication between the skeletal system and the immune system. Exploring the effects of pathogens, skeletal systems, immune systems, and antibacterials on bone repair in infectious conditions can help improve the treatment of these diseases.

Role of Galectin-3 in Bone Cell Differentiation, Bone Pathophysiology and Vascular Osteogenesis.

Galectin-3 is expressed in various tissues, including the bone, where it is considered a marker of chondrogenic and osteogenic cell lineages. Galectin-3 protein was found to be increased in the differentiated chondrocytes of the metaphyseal plate cartilage, where it favors chondrocyte survival and cartilage matrix mineralization. It was also shown to be highly expressed in differentiating osteoblasts and osteoclasts, in concomitance with expression of osteogenic markers and Runt-related transcription factor 2 and with the appearance of a mature phenotype. Galectin-3 is expressed also by osteocytes, though its function in these cells has not been fully elucidated. The effects of galectin-3 on bone cells were also investigated in galectin-3 null mice, further supporting its role in all stages of bone biology, from development to remodeling. Galectin-3 was also shown to act as a receptor for advanced glycation endproducts, which have been implicated in age-dependent and diabetes-associated bone fragility. Moreover, its regulatory role in inflammatory bone and joint disorders entitles galectin-3 as a possible therapeutic target. Finally, galectin-3 capacity to commit mesenchymal stem cells to the osteoblastic lineage and to favor transdifferentiation of vascular smooth muscle cells into an osteoblast-like phenotype open a new area of interest in bone and vascular pathologies.

Osteitis and chronic rhinosinusitis: a review of the current literature.

Chronic rhinosinusitis is a common debilitating condition characterized by inflammation of the nose and paranasal sinuses. Osteitis is an associated finding but it is not clear whether it is cause or effect. This review will report on studies that have examined the role of osteitis in CRS, with the ultimate aim of clarifying the definition, pathogenesis and clinical implications of this relatively new clinical entity. Literature searches of Medline, EMBASE and CENTRAL using the search terms osteitis, rhinosinusitis, sinusitis, rhinitis, chronic disease, and recurrence were performed. 21 articles were identified and reviewed. The papers highlighted key pathological features including periosteal thickening, new woven bone formation, bone resorption, fibrosis and inflammatory cell infiltration. Radiological grading systems and basic science research into the role of matrix metalloproteinases and P-glycoprotein were also identified and reviewed.

Increased neutrophil infiltration, IL-1 production and a SAPHO syndrome-like phenotype in PSTPIP2-deficient mice.

OBJECTIVE: Proline-serine-threonine-phosphatase-interacting protein 2 (PSTPIP2) is involved in macrophage activation, neutrophil motility and osteoclast differentiation. However, the role of PSTPIP2 in inflammation and autoinflammatory diseases is still not clear. In this study, we generated PSTPIP2 knockout (Pstpip2(-/-)) mice to investigate its phenotype and role in autoinflammatory diseases. METHODS: We constructed a Pstpip2-targeting vector and generated Pstpip2(-/-) mice. The phenotype and immunopathology of Pstpip2(-/-) mice were analysed. RESULTS: All Pstpip2(-/-) mice developed paw swelling, synovitis, hyperostosis and osteitis, resembling SAPHO syndrome, an inflammatory disorder of the bone, skin and joints. Multifocal osteomyelitis was found in inflamed paws, with increased macrophage and marked neutrophil infiltrations in the bone, joint and skin. Profound osteolytic lesions with markedly decreased bone volume density developed in paws and limbs. Neutrophil-attracting chemokines and IL-1ß were markedly elevated in inflamed tissues. CONCLUSION: Our study suggests that PSTPIP2 could play a role in innate immunity and development of autoinflammatory bone disorders, and may be associated with the pathogenesis of human SAPHO syndrome.

Osteitis and synovitis, but not bone erosion, is associated with proteoglycan loss and microstructure damage in the cartilage of patients with rheumatoid arthritis.

OBJECTIVES: To investigate the relation between anatomic changes of the synovium, the bone, the bone marrow and the cartilage to biochemical properties of the cartilage in patients with rheumatoid arthritis (RA). METHODS: 33 patients with RA received 3-T MRI scans of the metacarpophalangeal joints. Two independent methods, (A) the delayed gadolinium enhanced MRI of the cartilage (dGEMRIC, T2-mapping), which was used to assess the biochemical properties of the cartilage; (B) synovitis, osteitis and bone erosions were quantified according to the RA MRI scoring (RAMRIS) method and cartilage thickness (CT), interbone joint space (IBJS, distance between proximal and distal bone surface) and intercartilage joint space (ICJS, distance between proximal and distal cartilage surface) were measured. RESULTS: Biochemical changes of the cartilage, corresponding to low dGEMRIC and high T2 values, were more likely to be seen in joints with decreased IBJS and ICJS as well as decreased CT. For instance, dGEMRIC was directly correlated to the IBJS (p=0.001) and ICJS (p=0.001), whereas T2 mapping was inversely correlated to IBJS and ICJS (both p=0.017). Moreover, the degree of osteitis, and to some extent synovitis, was correlated to biochemical cartilage changes as measured by dGEMRIC (p=0.003) or the T2 mapping (p=0.013). By contrast, bone erosions did not correlate to the degree of biochemical cartilage changes. DISCUSSION: These data support the concept that synovitis and osteitis may be two main triggers for cartilage damage. Thus, the actual inflammatory state of a joint, but not so much the degree of bone erosion, appears to influence cartilage properties in RA.

TNF-α induces matrix metalloproteinase-9-dependent soluble intercellular adhesion molecule-1 release via TRAF2-mediated MAPKs and NF-κB activation in osteoblast-like MC3T3-E1 cells.

BACKGROUND: Matrix metalloproteinase-9 (MMP-9) has been shown to be induced by cytokines including TNF-α and may contribute to bone inflammatory diseases. However, the mechanisms underlying MMP-9 expression induced by TNF-α in MC3T3-E1 cells remain unclear. RESULTS: We applied gelatin zymography, Western blot, RT-PCR, real-time PCR, selective pharmacological inhibitors of transcription (actinomycin D, Act.D), translation (cycloheximide, CHI), c-Src (PP1), MEK1/2 (U0126), p38 MAPK (SB202190), JNK1/2 (SP600125), and NF-κB (Bay11-7082), respective siRNAs transfection, promoter assay, immunofluorescence staining, and ELISA to investigate the MMP-9 expression and soluble ICAM-1 (sICAM-1) release induced by TNF-α in MC3T3-E1 cells. Here we demonstrated that TNF-α-induced MMP-9 expression was attenuated by Act.D, CHI, PP1, U0126, SB202190, SP600125, and Bay11-7082, and by the transfection with siRNAs for ERK2, p38 MAPK, and JNK2. TNF-α-stimulated TNFR1, TRAF2, and c-Src complex formation was revealed by immunoprecipitation and Western blot. Furthermore, TNF-α-stimulated NF-κB phosphorylation and translocation were blocked by Bay11-7082, but not by PP1, U0126, SB202190, or SP600125. TNF-α time-dependently induced MMP-9 promoter activity which was also inhibited by PP1, U0126, SB202190, SP600125, or Bay11-7082. Up-regulation of MMP-9 was associated with the release of sICAM-1 into the cultured medium, which was attenuated by the pretreatment with MMP-2/9i, an MMP-9 inhibitor. CONCLUSIONS: In this study, we demonstrated that TNF-α up-regulates MMP-9 expression via c-Src, MAPKs, and NF-κB pathways. In addition, TNF-α-induced MMP-9 expression may contribute to the production of sICAM-1 by MC3T3-E1 cells. The interplay between MMP-9 expression and sICAM-1 release may exert an important role in the regulation of bone inflammatory diseases.

Th17 and Treg cells in bone related diseases.

Bone-related diseases share the process of immune response that targets bone tissue and bone marrow and then induce adverse effects on structure and function. In recent years, reciprocal relationship between immune cells and bone systems has been uncovered gradually. Regulatory T (Treg) and T helper 17 (Th17) cells are newly identified subsets of CD4+ T cells, and the balance between them is particularly essential for maintaining immune homeostasis. Accumulated data have demonstrated quantitative or functional imbalance between Th17 and Treg in bone related diseases, suggesting that Th17 and Treg cells are involved in these bone diseases. Understanding the molecular mechanisms regulating Th17 and Treg cells will create opportunities for the development of therapeutic approaches. This review will present the role of Th17 and Treg cells in the inflammatory bone diseases and bone marrow malignancies and find the potential therapeutic target for immunotherapy.

Nordihydroguaiaretic acid inhibition of NFATc1 suppresses osteoclastogenesis and arthritis bone destruction in rats.

Nordihydroguaiaretic acid (NDGA) is known to have prominent anticancer activity against several cancers, and is also known to be an inhibitor of 5-lipoxygenase (5-LO). In this study, we investigated the regulatory function of NDGA on inflammatory bone destruction mediated by osteoclasts. NDGA markedly inhibited receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-induced formation of osteoclasts in cultures of murine osteoclast precursor cell line RAW-D cells and primary bone marrow-derived macrophages culture systems. The inhibitory effect of NDGA on osteoclastogenesis did not arise from the inhibition of 5-LO activity. NDGA did not affect MAPKs, such as p38, JNK, and NF-κB, but significantly inhibited the induction of NFATc1, a key transcription factor for osteoclastogenesis. NDGA also suppressed activation of ERK in osteoclast precursors. RANKL-induced calcium oscillation observed in osteoclast precursors was completely diminished by the addition of NDGA. In mature osteoclasts, RANKL-induced nuclear translocation of NFATc1 was clearly inhibited by NDGA treatment. Finally, in vivo studies demonstrated that administration of NDGA significantly reduced severe bone destruction and osteoclast recruitment in the ankle joint of rats with adjuvant-induced arthritis. These results indicate the potential utility of NDGA as a therapeutic agent for ameliorating inflammatory bone destruction in rheumatoid arthritis.

[Investigation of the role of Zn2+ and zinc-containing proteins in the pathogenesis of bone inflammmation (the case of periodontitis)].

The levels of Ag, Al, Bi, Co, Cr, Fe, Mo, Si in osseous tissue of periodontium of domestic cats decreased in case of periodontitis in comparision with those of a healthy animals. At the same time the level of Zn increased dramatically. The level of tagged [14C] glycine in protein of bones of periodontium increased twofold and [35S] methionine 1,54 times which is explained by the fact of predominance of I type collagen in which one third of amino acids is represented by glycine while sulfur-containing amino acids are virtually absent. The latter are contained in non-collagenous proteins of bones of periodontium contributing for its metabolism. The difference in tagged aminoacids inclusion in bones of periodontium is mainly provoked by redistribution of the collagen and non-collagenous proteins.

Receptor activator of nuclear factor κB ligand is a biomarker for osteitis of chronic rhinosinusitis.

BACKGROUND: Evidence of osteitis is frequently observed in patients with chronic rhinosinusitis (CRS), especially in recalcitrant cases. However, studies focusing on biological markers of osteitis are limited and it remains unclear whether osteitis is associated with different phenotypes of CRS. This study aimed to analyze the expression and assess the roles of receptor activator of nuclear factor κB ligand (RANKL) in patients with CRS and osteitis. METHODS: CRS patients with nasal polyps (CRSwNP, n = 63), CRS patients without nasal polyps (CRSsNP, n = 8), and control subjects (n = 12) were enrolled. Histologic phenotypes, clinical information, and computed tomography (CT) scores were investigated. The Global Osteitis Scoring Scale (GOSS) and RANKL, a molecular marker of bone remodeling, were analyzed in each type of CRS. CRS mouse models were treated with anti-RANKL. RESULTS: GOSS values were significantly higher in all CRS patients than in the control group. The GOSS value in non-eosinophilic CRSwNP was higher than in eosinophilic CRSwNP. RANKL was upregulated whereas decoy receptor osteoprotegerin (OPG) was downregulated in CRS. RANKL messenger RNA (mRNA) and protein levels were positively correlated with GOSS. RANKL/OPG was increased in recurrent cases compared with primary cases. Multiple inflammatory mediators were positively correlated with the protein level of RANKL in CRS tissues. In the mouse CRSwNP model, anti-RANKL treatment abrogated mucosal inflammation and bone remodeling. CONCLUSION: RANKL expression is associated with clinical osteitis and disease severity in CRSwNP. These findings shed light on the importance of RANKL as a potential biomarker of CRS and a key player in CRS pathogenesis.

Cellular characterisation of magnetic resonance imaging bone oedema in rheumatoid arthritis; implications for pathogenesis of erosive disease.

OBJECTIVES: Magnetic resonance imaging (MRI) bone oedema is an important predictor of bone erosion in rheumatoid arthritis (RA). This study aimed to determine the cellular components of MRI bone oedema, and clarify the relationship between bone erosion and MRI bone oedema. METHODS: Twenty-eight bones from 11 patients with RA undergoing orthopaedic surgery were analysed by quantitative and semi-quantitative immunohistochemistry. Pre-operative contrast-enhanced MRI scans were analysed for bone oedema. RESULTS: The density of osteoclasts was higher in those samples with MRI bone oedema than those without MRI bone oedema (p = 0.01). Other cells identified within bone marrow included macrophages and plasma cells, and these were more numerous in samples with MRI bone oedema (p = 0.02 and 0.05 respectively). B cells were present in lower numbers, but B cell aggregates were identified in some samples with MRI bone oedema. There was a trend to increased RANKL expression in samples with MRI bone oedema (p = 0.09). Expression of RANKL correlated with the number of osteoclasts (r = 0.592, p = 0.004). CONCLUSIONS: The increased number of osteoclasts and RANKL expression in samples with MRI bone oedema supports the hypothesis that bone erosion in RA occurs through activation of local bone resorption mechanisms within subchondral bone as well as through synovial invasion into bone.

Rheumatoid arthritis and ankylosing spondylitis - pathology of acute inflammation.

Histomorphological analysis of inflammatory lesions in rheumatoid arthritis (RA) and ankylosing spondylitis (AS) display similarities but also major differences. Ankylosing spondylitis is characterised by two key pathological findings: sacroiliac joint and spinal inflammation and new bone formation with the possible consequence of bone fusion, usually in the axial skeleton. In AS the primary site of inflammation is located at the enthesis or subchondral bone marrow with bone marrow oedema, lymphocytic infiltrates, increased osteoclast density and increased microvessel density are typical findings in acute inflammation. In RA joint inflammation has its origin in the synovial membrane of peripheral joints. Osteitis in the subchondral bone marrow reveals similar findings compared to AS and it is suggested to occur secondary to inflammation in the synovial membrane. Structural damage defines the outcome in both diseases. However, in AS it is defined by new bone formation and in RA by the destruction of cortical bone.

Omnipresence of inflammasome activities in inflammatory bone diseases.

The inflammasomes are intracellular protein complexes that are assembled in response to a variety of perturbations including infections and injuries. Failure of the inflammasomes to rapidly clear the insults or restore tissue homeostasis can result in chronic inflammation. Recurring inflammation is also provoked by mutations that cause the constitutive assembly of the components of these protein platforms. Evidence suggests that chronic inflammation is a shared mechanism in bone loss associated with aging, dysregulated metabolism, autoinflammatory, and autoimmune diseases. Mechanistically, inflammatory mediators promote bone resorption while suppressing bone formation, an imbalance which over time leads to bone loss and increased fracture risk. Thus, while acute inflammation is important for the maintenance of bone integrity, its chronic state damages this tissue. In this review, we discuss the role of the inflammasomes in inflammation-induced osteolysis.

The role of bone cells in immune regulation during the course of infection.

Bone homeostasis depends on a balance between osteoclastic bone resorption and osteoblastic bone formation. Bone cells are regulated by a variety of biochemical factors, such as hormones and cytokines, as well as various types of physical stress. The immune system affects bone, since such factors are dysregulated under pathologic conditions, including infection. The bone marrow, one of the primary lymphoid organs, provides a special microenvironment that supports the function and differentiation of immune cells and hematopoietic stem cells (HSCs). Thus, bone cells contribute to immune regulation by modulating immune cell differentiation and/or function through the maintenance of the bone marrow microenvironment. Although osteoblasts were first reported as the population that supports HSCs, the role of osteoblast-lineage cells in hematopoiesis has been shown to be more limited than previously expected. Osteoblasts are specifically involved in the differentiation of lymphoid cells under physiological and pathological conditions. It is of critical importance how bone cells are modified during inflammation and/or infection and how such modification affects the immune system.

Osteitis is associated with dysregulated pro-osteoblastic activity in patients with nasal polyps.

OBJECTIVES/HYPOTHESIS: The overlying inflammatory mucosa plays a crucial role in the initiation of osteitis; however, the molecular mechanism is unclear. The objective of this study was to explore the bone morphogenetic protein (BMP) pathway and to correlate the expression of key signaling molecules with the degree of osteitis in patients with chronic rhinosinusitis with nasal polyps (CRSwNP). STUDY DESIGN: Prospective experimental analysis. METHODS: This was an institutional review board-approved study in which mucosal samples were obtained from sites of osteitis in CRSwNP and compared to nonosteitic healthy controls (n = 10/group). Protein expression of key BMP pathway was quantified by aptamer-based protein array and confirmed by a set of selected mRNA analyses. Degree of osteitis was assessed using both Kennedy Osteitis Score and Global Osteitis Score (GOS). RESULTS: Pro-osteoblastic expression of BMP7 (fold change [FC] = -1.18, P = .017) and BMP9 (FC = -1.32, P = .023), their receptors, BMP receptor type-1A (BMPR1A) (FC = -2.56, P = .005) and BMP receptor type-2 (FC = -1.28, P = .022), and two enhancers of BMP signaling pathway, the repulsive guidance molecule domain family member B (FC = -1.13, P = .008) and the chordin-like protein 1 (FC = -1.18, P = .027), were all significantly downregulated in CRSwNP. Conversely, the pro-osteoclastic factor, tartrate-resistant acid phosphatase type 5 (ACP5) (FC = 2.36, P = .001), was significantly increased in CRSwNP. GOS was inversely correlated with levels of BMP7 (r = -0.684, P = .005) and BMPR1A (r = -0.864, P = .005) and positively correlated with levels of ACP5 (r = 0.815, P = .004). The FCs among the proteins studied significantly and positively correlated with the FCs of their mRNA expression (r = 0.908, P = .002). CONCLUSIONS: Downregulated pro-osteoblastic mucosal BMP signaling is strongly and significantly associated with increased osteitis in CRSwNP. LEVEL OF EVIDENCE: NA Laryngoscope, 129:E102-E109, 2019.

Effect of antibiotic infused calcium sulfate/hydroxyapatite (CAS/HA) insets on implant-associated osteitis in a femur fracture model in mice.

Cerament (Bonesupport Holding, Lund, Sweden) is a bioresorbable synthetic bone substitute consisting of calcium sulfate and hydroxyapatite which is successfully used as a bone graft in bone defects or in delayed and non-unions after fractures. Besides, calcium sulfate/ hydroxyapatite (CAS/HA) could have, attributed to its composition and osteoinductive properties, have great importance in the treatment of bone infections with critical size defects (CSD). Aim of the study was to evaluate the effects of antibiotic infused CAS/HA on inflammation and bone healing in an implant-associated osteitis mice model. In a standardized murine model, the left femur of 72 BALB/c mice were osteotomized, generating a CSD (2,5 mm) with stabilization through a 6-hole titanium locking plate. Osteitis has been induced through inoculation of Staphylococcus aureus (SA) into the fracture gap. To analyze the effect of CAS/HA, following groups were generated with either CAS/HA, CAS/HA with gentamycin (CAS/ HA-G) or CAS/HA with vancomycin (CAS/HA-V) insets placed into the osteotomy. Debridément and lavages were progressed on day 7 and 42 to determine the local bacterial growth and the immune reaction. Fracture healing was quantified on day 7 and 42 by x-ray and bone healing markers from blood samples. Progression of infection was assessed by estimation of colony-forming units (CFU) and immune response was analyzed by determination of Interleukin (IL)- 6 and polymorphonuclear neutrophils (PMN) in lavage samples. Osteitis induced higher IL-6 and PMN-levels in the lavage samples on day 7. Both parameters showed a reduction in all groups on day 42. CAS/HA-V revealed a significant reduction of CFU and PMNs in lavage samples on day 42. A positive effect on bone healing could only be shown in non-infected mice. Whereas, application of mere CAS/HA in infected mice did show tendencies of bone destruction and lysis, independent of impregnation with antibiotics or not. Thus, application of CAS/HA in acute implant-associated infections is not recommended. In non-infectious environments or after infect-convalescence CAS/HA could albeit serve as a suggestive tool in trauma and orthopedic surgery.

A Jack of All Trades: Impact of Glucocorticoids on Cellular Cross-Talk in Osteoimmunology.

Glucocorticoids (GCs) are known to have a strong impact on the immune system, metabolism, and bone homeostasis. While these functions have been long investigated separately in immunology, metabolism, or bone biology, the understanding of how GCs regulate the cellular cross-talk between innate immune cells, mesenchymal cells, and other stromal cells has been garnering attention rather recently. Here we review the recent findings of GC action in osteoporosis, inflammatory bone diseases (rheumatoid and osteoarthritis), and bone regeneration during fracture healing. We focus on studies of pre-clinical animal models that enable dissecting the role of GC actions in innate immune cells, stromal cells, and bone cells using conditional and function-selective mutant mice of the GC receptor (GR), or mice with impaired GC signaling. Importantly, GCs do not only directly affect cellular functions, but also influence the cross-talk between mesenchymal and immune cells, contributing to both beneficial and adverse effects of GCs. Given the importance of endogenous GCs as stress hormones and the wide prescription of pharmaceutical GCs, an improved understanding of GC action is decisive for tackling inflammatory bone diseases, osteoporosis, and aging.

CypD-mPTP axis regulates mitochondrial functions contributing to osteogenic dysfunction of MC3T3-E1 cells in inflammation.

Bone is a dynamic organ, the bone-forming osteoblasts and bone-resorbing osteoclasts form the physiological basis of bone remodeling process. During pathological process of numerous inflammatory diseases, these two aspects are uncoupled and the balance is usually tipped in favor of bone destruction. Evidence suggests that the inflammatory destruction of bone is mainly attributed to oxidative stress and is closely related to mitochondrial dysfunction. The mechanisms underlying osteogenic dysfunction in inflammation still need further investigation. Reactive oxygen species (ROS) is associated with mitochondrial dysfunction and cellular damage. Here, we reported an unexplored role of cyclophilin D (CypD), the major modulator of mitochondrial permeability transition pore (mPTP), and the CypD-mPTP axis in inflammation-induced mitochondrial dysfunction and bone damage. And the protective effects of knocking down CypD by siRNA interference or the addition of cyclosporin A (CsA), an inhibitor of CypD, were evidenced by rescued mitochondrial function and osteogenic function of osteoblast under tumor necrosis factor-α (TNF-α) treatment. These findings provide new insights into the role of CypD-mPTP-dependent mitochondrial pathway in the inflammatory bone injury. The protective effect of CsA or other moleculars affecting the mPTP formation may hold promise as a potential novel therapeutic strategy for inflammation-induced bone damage via mitochondrial pathways.

The polymethoxy flavonoid sudachitin suppresses inflammatory bone destruction by directly inhibiting osteoclastogenesis due to reduced ROS production and MAPK activation in osteoclast precursors.

Inflammatory bone diseases, including rheumatoid arthritis, periodontitis and peri-implantitis, are associated not only with the production of inflammatory cytokines but also with local oxidative status, which is defined by intracellular reactive oxygen species (ROS). Osteoclast differentiation has been reported to be related to increased intracellular ROS levels in osteoclast lineage cells. Sudachitin, which is a polymethoxyflavone derived from Citrus sudachi, possesses antioxidant properties and regulates various functions in mammalian cells. However, the effects of sudachitin on inflammatory bone destruction and osteoclastogenesis remain unknown. In calvaria inflamed by a local lipopolysaccharide (LPS) injection, inflammation-induced bone destruction and the accompanying elevated expression of osteoclastogenesis-related genes were reduced by the co-administration of sudachitin and LPS. Moreover, sudachitin inhibited osteoclast formation in cultures of isolated osteoblasts and osteoclast precursors. However, sudachitin rather increased the expression of receptor activator of NF-κB ligand (RANKL), which is an important molecule triggering osteoclast differentiation, and the mRNA ratio of RANKL/osteoprotegerin that is a decoy receptor for RANKL, in the isolated osteoblasts, suggesting the presence of additional target cells. When osteoclast formation was induced from osteoclast precursors derived from bone marrow cells in the presence of soluble RANKL and macrophage colony-stimulating factor, sudachitin inhibited osteoclastogenesis without influencing cell viability. Consistently, the expression of osteoclast differentiation-related molecules including c-fos, NFATc1, cathepsin K and osteoclast fusion proteins such as DC-STAMP and Atp6v0d2 was reduced by sudachitin. In addition, sudachitin decreased activation of MAPKs such as Erk and JNK and the ROS production evoked by RANKL in osteoclast lineage cells. Our findings suggest that sudachitin is a useful agent for the treatment of anti-inflammatory bone destruction.