Anti-RANKL therapy for inflammatory bone disorders: Mechanisms and potential clinical applications

Role of Polyphenols in the Metabolism of the Skeletal System in Humans and Animals – A Review

Polyphenols are a group of compounds arousing enormous interest due to their multiple effects on both human and animal health and omnipresence in plants. A number of in vitro and animal model studies have shown that all polyphenols exhibit anti-inflammatory and antioxidant activities, and play a significant role against oxidative stress-related pathologies. They also exert gut promotory effects and prevent chronic degenerative diseases. However, less attention has been paid to the potential influence of polyphenols on bone properties and metabolism. It is well known that proper growth and functioning of the organism depend largely on bone growth and health. Therefore, understanding the action of substances (including polyphenols) that may improve the health and functioning of the skeletal system and bone metabolism is extremely important for the health of the present and future generations of both humans and farm animals. This review provides a comprehensive summary of literature related to causes of bone loss during ageing of the organism (in both humans and animals) and possible effects of dietary polyphenols preventing bone loss and diseases. In particular, the underlying cellular and molecular mechanisms that can modulate skeletal homeostasis and influence the bone modeling and remodeling processes are presented.

Drug Delivery to the Bone Microenvironment Mediated by Exosomes: An Axiom or Enigma

The increasing incidence of bone-related disorders is causing a burden on the clinical scenario. Even though bone is one of the tissues that possess tremendous regenerative potential, certain bone anomalies need therapeutic intervention through appropriate delivery of a drug. Among several nanosystems and biologics that offer the potential to contribute towards bone healing, the exosomes from the class of extracellular vesicles are outstanding. Exosomes are extracellular nanovesicles that, apart from the various advantages, are standing out of the crowd for their ability to conduct cellular communication. The internal cargo of the exosomes is leading to its potential use in therapeutics. Exosomes are being unraveled in terms of the mechanism as well as application in targeting various diseases and tissues. Through this review, we have tried to understand and review all that is already established and the gap areas that still exist in utilizing them as drug delivery vehicles targeting the bone. The review highlights the potential of the exosomes towards their contribution to the drug delivery scenario in the bone microenvironment. A comparison of the pros and cons of exosomes with other prevalent drug delivery systems is also done. A section on the patents that have been generated so far from this field is included.

Association Between Marginal Jawbone Loss and Onset of Rheumatoid Arthritis and Relationship to Plasma Levels of RANKL

OBJECTIVE

To investigate whether periodontitis, characterized by marginal jawbone loss, precedes the onset of symptoms of rheumatoid arthritis (RA), and to analyze plasma levels of RANKL (a cytokine that is crucial for bone resorption) and anti-citrullinated peptide antibodies (ACPAs) in presymptomatic individuals compared with matched referent controls.

METHODS

Marginal jawbone loss was measured on dental radiographs of the premolar/molar regions in the jaws in 176 subjects, 93 of whom subsequently developed RA. Among these participating subjects, 46 had documented radiographs predating symptom onset, and 45 cases could be matched to controls, according to sex, age, and smoking status. Plasma RANKL concentrations were analyzed using enzyme-linked immunosorbent assay. A receiver operating characteristic curve was used to define the cutoff value for RANKL positivity.

RESULTS

Bone loss was significantly greater in presymptomatic subjects classified as never smokers compared with that in controls, and increasing levels of bone loss were associated with a higher risk of the subsequent development of RA (hazard ratio 1.03, 95% confidence interval 1.01-1.05). No association between jawbone loss and RA was observed in smokers. A significantly greater extent of marginal jawbone loss was detected in RANKL-positive presymptomatic subjects, and even more pronounced jawbone loss was observed in those who were positive for both RANKL and ACPA.

CONCLUSION

Marginal jawbone loss preceded the clinical onset of RA symptoms, but this was observed only in nonsmokers. Moreover, marginal jawbone loss was significantly greater in RANKL-positive presymptomatic subjects compared with RANKL-negative presymptomatic subjects and was highest in presymptomatic subjects positive for both ACPA and RANKL.

Effect of Wenhua Juanbi Recipe () on expression of receptor activator of nuclear factor kappa B ligand, osteoprotegerin, and tumor necrosis factor receptor superfamily member 14 in rats with collagen-induced arthritis

OBJECTIVES

To study the effect of Wenhua Juanbi Recipe (, WJR) on expression of receptor activator of nuclear factor kappa B ligand (RANKL), osteoprotegerin (OPG), and tumor necrosis factor receptor superfamily member 14 (TNFRSF14, also known as LIGHT) in rats with collagen-induced arthritis (CIA).

METHODS

CIA rats were generated by subcutaneous injection of bovine collagen type-II at the tail base. Sixty CIA rats were randomly assigned (10 animals/group) to: model, methotrexate (MTX)-treated (0.78 mg/kg body weight), and WJR-treated (22.9 g/kg) groups. Healthy normal rats (n=10) were used as the normal control. Treatments or saline were administered once daily by oral gavage. Rats were sacrifificed at day 28 post-treatment and knee synovium and peripheral blood serum were collected. Toe swelling degree and expression of RANKL, OPG, and LIGHT were determined by Western blot and immunohistochemistry.

RESULTS

Compared with the normal group, toe swelling degree was signifificantly increased in the model group (P<0.01). After treatment, toe swelling degree decreased signifificantly in the WJR and MTX groups compared with the model group (P<0.01). Compared with the normal group, expression of RANKL and LIGHT were signifificantly increased and OPG signifificantly decreased in peripheral blood and synovium of the model group (P<0.01). Conversely, RANKL and LIGHT expression were signifificantly reduced and OPG increased in the WJR and MTX groups compared with the model group (P<0.01). No statistically significant difference existed between WJR and MTX groups.

CONCLUSION

WJR likely acts by reducing RANKL expression and increasing OPG expression, thus inhibiting RANKL/RANK interaction and reducing LIGHT expression, thereby inhibiting osteoclast formation/activation to block bone erosion.

RANK/RANKL Expression Is Induced by Cardiac Surgical Operation

Background: Cardiac surgery provokes a systemic inflammatory response in any patient. This complex body reaction involves also RANK/RANKL molecules which have been recently identified as principal regulators of bone metabolism. Aims: To follow the changes in the expression of RANK/RANKL molecules on innate immune cells of cardiac surgical patients. Patients and Methods: Twenty-six patients undergoing cardiac surgical were assigned to undergo coronary artery bypass grafting using either cardiopulmonary bypass (“on-pump”) or modified “miniinvasive on-pump”. The expression of RANK/RANKL was performed by flow cytometry. Results: Significantly increased expression of RANK on monocytes of “miniinvasive on-pump” patients was found at the 1st, the 3nd, and 7th postoperative days. The similar pattern was found also for monocyte RANKL expression. In addition, RANKL expression was significantly increased at the 3rd postoperative day in “on-pump” patient. No significant differences between “miniinvasive on-pump” and “on-pump” cardiac surgical patients were found. Conclusion: The expression of both RANK and RANKL molecules is significantly enhanced on monocytes of “miniinvasive on-pump” cardiac surgical patients.

Optimization of roasting conditions through antioxidant and anti-inflammatory activities of Yak-kong (Rhynchosia nulubilis)

The effects of roasting conditions on the antioxidant activities and anti-inflammatory activities of roasted yak-kong were investigated using a second-order central composite design. The optimum conditions for DPPH radical scavenging ability (IC₅₀), ABTS radical scavenging activity (IC₅₀), total phenolic content (TPC), and oxygen radical absorbance capacity (ORAC) were at 111.47°C for 20.45 min, with the best values (DPPH, IC₅₀; 2.143 mg/mL, ABTS, IC₅₀; 1.775 mg/mL, TPC; 51.39mg tannic acid (TAE)/g, and ORAC; 6.89 μmoL trolox equivalents (TE)/g). The optimum conditions of nitric oxide (NO) production, prostaglandin E2 (PGE2) production, and tumor necrosis factor-α (TNF-α) were at 110.24°C for 21.18 min, yielding the best values (NO; 14.484 μM, PGE2; 3.433 mg/mL, and TNF-α; 3.818 ng/mL). Superimposed contour plots with regard to 7 variables indicated that the optimum roasting temperature and time were 110.88°C and 20.86 min. This result suggested that the optimally roasted yak-kong could replace coffee beans to provide potential bone health benefits to heavy coffee drinkers.

The inhibitory effects of roasted black bean (Rhynchosia nulubilis) extracts on RANKL-mediated RAW264.7 cells differentiation

This study compared the inhibitory effects of roasted black bean (Rhynchosia nulubilis, seomoktae, RoS) extracts with raw seomoktae (RaS: control) extract on RANKL-mediated RAW264.7 cell differentiation after the determination of isoflavones content as well as antioxidant and antiinflammatory activities. The RoS extracts (RoS90-20, RoS100-20, RoS110-20, and RoS120-20) had significantly (p<0.05) higher isoflavones (genistein, daidzein, and glycitein) and better antioxidant activity than the RaS extract. Especially, RoS110-20, which was roasted at 110°C for 20 min, has the highest amounts of soy-derived compounds. The RoS110-20 extract significantly reduced LPS-induced nitric oxide (NO) and prostaglandin (PGE2) production compared to the RaS extract. The RoS110-20 extract showed a higher inhibitory effect on the expression of NFATc1 in RANKL-induced RAW 264.7 cells than the RaS extract without any evidence of cytotoxicity under western blotting and tartrateresistant acid phosphatase staining (TRAP). The results of this study suggest that roasting increased the concentration of soy-derived compounds and improved the antioxidant and anti-inflammatory activities of RoS110-20 extract compared with RaS. In addition, the differentiation of RANKL-mediated RAW264.7 cells was effectively inhibited by the RoS110-20 extract due to its enhanced antioxidant and anti-inflammatory activities caused by roasting, confirming its potential for ameliorating bone loss.

Side effects of bone-targeted therapies in advanced breast cancer

In up to 75% of cases, advanced breast cancer patients eventually develop bone metastases with often debilitating skeletal-related events (SREs). Osteoclast inhibitors are commonly used as therapeutic mainstay with clinical studies showing superiority of denosumab over bisphosphonates (e.g., zoledronate) for the prevention of SREs. The present review discusses the adverse event profile of these agents, and addresses the prevention and management of untoward side effects. Adverse events associated with osteoclast inhibitors comprise osteonecrosis of the jaw and hypocalcemia. Hypocalcemia is more common with denosumab, particularly in severe renal dysfunction. During therapy, the appropriate prevention of these adverse events includes close attention to dental health, avoidance of invasive dental procedures, supplementation with calcium and vitamin D unless patients are hypercalcemic, and regular monitoring of relevant serum values. Relating to the risk of nephrotoxicity, bisphosphonates but not denosumab have been incriminated. Therefore, serum creatinine levels should be checked prior to each dose of zoledronate, and in severe renal dysfunction (creatinine clearance < 30 ml/min) zoledronate is contraindicated anyway. Acute-phase reactions are particularly linked to bisphosphonates. Consequently, if these adverse events predominate, switching to denosumab is recommended.

Ageing and the border between health and disease

Ageing is associated with a progressive degeneration of the tissues, which has a negative impact on the structure and function of vital organs and is among the most important known risk factors for most chronic diseases. Since the proportion of the world's population aged >60 years will double in the next four decades, this will be accompanied by an increased incidence of chronic age-related diseases that will place a huge burden on healthcare resources. There is increasing evidence that many chronic inflammatory diseases represent an acceleration of the ageing process. Chronic pulmonary diseases represents an important component of the increasingly prevalent multiple chronic debilitating diseases, which are a major cause of morbidity and mortality, particularly in the elderly. The lungs age and it has been suggested that chronic obstructive pulmonary disease (COPD) is a condition of accelerated lung ageing and that ageing may provide a mechanistic link between COPD and many of its extrapulmonary effects and comorbidities. In this article we will describe the physiological changes and mechanisms of ageing, with particular focus on the pulmonary effects of ageing and how these may be relevant to the development of COPD and its major extrapulmonary manifestations.

In vivo osteoprotegerin gene therapy preventing bone loss induced by periodontitis

OBJECTIVE

The objective of this study was to investigate the effects of osteoprotegerin (OPG) gene therapy on alveolar bone resorption caused by experimental periodontitis in rats, thus forming a foundation for potential clinical applications of OPG gene therapy in the treatment of periodontitis and peri-implantitis.

MATERIAL AND METHODS

To study the effects of OPG on alveolar bone protection, an experimental periodontitis model was used by placing a bacterial plaque retentive silk ligature in the gingival sulcus around the maxillary second molar tooth, injection of Porphyromonas gingivalis and high carbohydrate diet. A total of 30 Sprague-Dawley rats were randomly divided into three groups, with 10 rats in each group: group I (control) was treated with 10 μL normal saline injection; group II with 10 μL mock vector; and group III with 10 μL local OPG gene transfer by transfection with in vitro constructed pcDNA3.1-human OPG (pcDNA3.1-hOPG). A subperiosteal injection was done adjacent to the second molars on days 0, 7, 14 and 21. Four weeks later, all animals were killed and radiographic, histological and immunohistochemical examinations were performed. Statistical analysis included ANOVA and LSD-Bonferroni test.

RESULTS

Group III (OPG gene therapy) had significantly enhanced (p < 0.05) integrated optical density of OPG, had significantly decreased alveolar bone resorption volume and active osteoclast number (p < 0.05) through descriptive histological examination when compared with the other two groups at week 4.

CONCLUSION

Local recombinant OPG plasmid-mediated gene therapy suppresses osteoclastogenesis in vivo and inhibits alveolar bone height reduction caused by experimental periodontitis in rats. OPG gene therapy may be beneficial in preventing progressive periodontal bone loss.

Palliative Oncology

Bone metastases cause devastating clinical complications leading patients to have pain, poor quality of life, loss of mobility, and autonomy. Complications from osseous metastases cause a big economic burden reflected by repeated admissions for uncontrolled symptoms. Management of symptoms associated with bone metastasis includes systemic analgesics, glucocorticoids, radiation (external beam radiation and radiopharmaceuticals), ablative techniques (radiofrequency ablation and cryoablation), chemotherapeutic agents, hormonal therapies, interventional techniques (eg, kyphoplasty), and surgical approaches. Bisphosphonates have become a standard therapy for bony metastasis. They bind to bone eventually inhibiting osteoclast action. Bisphosphonates decrease fractures when given routinely. Adverse effects of bisphosphonates include osteonecrosis of the jaw and renal insufficiency. Late last year, the Food and Drug Administration approved denosumab to prevent skeletal-related events (SREs) associated with metastatic solid tumors. This drug is a monoclonal antibody that inhibits the receptor activator of nuclear factor κB (RANK)–RANK ligand interaction. Clinical trials have shown superiority over bisphosphonates for the prevention of SREs. This article reviews the mechanism of action, pharmacology, adverse effects, and clinical trial evidence for this new drug.

A new insight to bone turnover: role of ω-3 polyunsaturated fatty acids

Background. Evidence has shown that long-chain polyunsaturated fatty acids (LCPUFA), especially the ω-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are beneficial for bone health and turnover. Objectives. This review summarizes findings from both in vivo and in vitro studies and the effects of LC PUFA on bone metabolism, as well as the relationship with the oxidative stress, the inflammatory process, and obesity. Results. Some studies in humans indicate that LCPUFA can increase bone formation, affect peak bone mass in adolescents, and reduce bone loss. However, the cellular mechanisms of action of the LCPUFA are complex and involve modulation of fatty acid metabolites such as prostaglandins, resolvins and protectins, several signaling pathways, cytokines, and growth factors, although in certain aspects there is still some controversy. LCPUFA affect receptor activator of nuclear factor κβ (RANK), a receptor found on the osteoclast, causing bone resorption, which controls osteoclast formation. Conclusions. Since fatty acids are an endogenous source of reactive oxygen species, free radicals alter the process of bone turnover; however, although there are clinical evidences linking bone metabolism and dietary lipids, more clinical trials are necessary to prove whether ω-3 PUFA supplementation plays a major role in bone health.

Inhibition of osteoclastogenic differentiation by Ikarisoside A in RAW 264.7 cells via JNK and NF-kappaB signaling pathways

Osteoclasts are specialized bone-resorbing cells derived from multipotent myeloid progenitor cells. They play a crucial homeostatic role in skeletal modeling and remodeling and destroy bone in many pathologic conditions. Receptor activator of NF-kappaB ligand (RANKL) is essential to osteoclastogenesis. In this study, we investigated the effects of Ikarisoside A, isolated from Epimedium koreanum (Berberidaceae), on osteoclastogenesis in RANKL-treated murine monocyte/macrophage RAW 264.7 cells. The results indicate that Ikarisoside A is a potent inhibitor of osteoclastogenesis in RANKL-stimulated RAW 264.7 cells as well as in bone marrow-derived macrophages. The inhibitory effect of Ikarisoside A resulted in decrease of osteoclast-specific genes like matrix metalloproteinase 9 (MMP9), tartrate-resistant acid phosphatase (TRAP), receptor activator of NF-kappaB (RANK), and cathepsin K. Moreover, Ikarisoside A blocked the resorbing capacity of RAW 264.7 cells on calcium phosphate-coated plates. Ikarisoside A also has inhibitory effects on the RANKL-mediated activation of NF-kappaB, JNK, and Akt. Finally, Ikarisoside A clearly decreased the expression of c-Fos and nuclear factor of activated T cells c1 (NFATc1) as well as the transcriptional activity of NFATc1, the master regulator of osteoclast differentiation. The data indicate that Ikarisoside A has potential for use in treatment of diseases involving abnormal bone lysis such as osteoporosis, rheumatoid arthritis, and periodontal bone erosion.

MRI for assessing erosion and joint space narrowing in inflammatory arthropathies

The superior soft tissue contrast and multiplanar capability of magnetic resonance imaging has contributed to earlier diagnosis and implementation of effective treatment for a variety of arthropathies. Owing to overlapping clinical signs and symptoms, MRI plays a role in delineating the features and stages of these conditions. With the advent of disease-modifying therapies, it is important to diagnose inflammatory arthropathy as early as possible. In this chapter, we discuss the pathophysiology of bone erosion and joint space narrowing, as well as the role of MRI in the imaging of the seropositive and seronegative inflammatory arthropathies.

Role of RANKL in bone diseases

Bone remodeling is a tightly regulated process of osteoclast-mediated bone resorption, balanced by osteoblast-mediated bone formation. Disruption of this balance can lead to increased bone turnover, resulting in excessive bone loss or extra bone formation and consequent skeletal disease. The receptor activator of nuclear factor kappaB ligand (RANKL) (along with its receptor), the receptor activator of nuclear factor kappaB and its natural decoy receptor, osteoprotegerin, are the final effector proteins of osteoclastic bone resorption. Here, I provide an overview of recent studies that highlight the key role of RANKL in the pathophysiology of several bone diseases and discuss the novel therapeutic approaches afforded by the modulation of RANKL.

Osteoporosis in chronic obstructive pulmonary disease patients

PURPOSE OF REVIEW

The purpose of this review is to examine the state of knowledge and clinical practice in the association of chronic obstructive pulmonary disease to osteoporosis and fracture incidence.

RECENT FINDINGS

There is a clear association between chronic obstructive pulmonary disease and excessive bone loss/risk of fractures. Little is known about the pathophysiological processes involved in the bone loss, but recent reports point to a continuous systemic inflammatory state in patients with chronic obstructive pulmonary disease. This inflammation involves the release of inflammatory cytokines such as tumour necrosis factor-alpha and interleukin-1. During the course of chronic obstructive pulmonary disease, a protein catabolic process takes place, including increased production of catalytic enzymes (matrix metalloproteinases etc.), which together with the inflammatory cytokines induces bone resorption.

SUMMARY

Patients with chronic obstructive pulmonary disease are at increased risk of osteoporosis and fractures. Risk factors such as smoking, advanced age, physical inactivity, malnutrition, and low weight may be responsible, but a number of pathophysiological explanations including the presence of a chronic inflammatory state with increased levels of proinflammatory cytokines and protein catalytic enzymes may also be involved. The use of oral glucocorticoids is also a significant risk factor. Increased awareness is highly warranted to diagnose osteoporosis at an early stage, and professionals should be aware of the risk of osteoporosis in this patient population.

Proteinases in the joint: clinical relevance of proteinases in joint destruction

Proteinases are involved in essential steps in cartilage and bone homeostasis. Consequently, efforts have been made to establish their potential role in the pathology of rheumatic conditions such as rheumatoid arthritis, osteoarthritis and spondyloarthritis. Matrix metalloproteinases (MMPs) are sensitive markers of disease severity and response to treatment, and therefore they have potential in the assessment of rheumatic diseases. Despite disappointing early results with synthetic inhibitors of MMPs, there is still much scope for developing effective and safe MMPs inhibitors, and consequently to deliver new options to inhibit joint destruction.

Vitamin D status in gastrointestinal and liver disease

PURPOSE OF REVIEW

The purpose of this review is to report on the vitamin D status and its relationship with bone health in individuals with gastrointestinal and liver disorders. In addition, recommendations regarding replacement and maintenance of optimal vitamin D stores, as well as the state of knowledge regarding its effect on the disease through its actions on the immune system, will be reviewed.

RECENT FINDINGS

The scientific community has revised upward the serum levels of vitamin D considered optimal, and doses of vitamin D much larger than those currently recommended may be needed to maintain these levels, especially in individuals with gastrointestinal and liver disorders. The relationship between vitamin D and bone health in this population is controversial. The role of vitamin D in the regulation of the immune system continues to be elucidated.

SUMMARY

Hypovitaminosis D is prevalent among individuals with gastrointestinal and liver disease. Although replacement and supplementation guidelines have not been well defined, practitioners should aim for a serum 25-hydroxyvitamin D level of at least 32 ng/ml. The contribution of vitamin D to the bone health of these individuals and its role in altering disease course through its actions on the immune system remain to be elucidated.

Suppression of inflammation and structural damage in experimental arthritis through molecular targeted therapy with PPI-2458

OBJECTIVE

To determine the disease-modifying activity and mechanism of action of the orally available methionine aminopeptidase type 2 inhibitor, [(1R)-1-carbamoyl-2-methyl-propyl]-carbamic acid-(3R,4S,5S,6R)-5-methoxy-4-[(2R,3R)-2-methyl-3-(3-methyl-but-2-enyl)-oxiranyl]-1-oxa-spiro [2.5] oct-6-yl ester (PPI-2458), in a rat model of peptidoglycan-polysaccharide (PG-PS)-induced arthritis.

METHODS

Arthritis was induced in rats by administration of PG-PS, causing tarsal joint swelling and histopathologic changes characteristic of rheumatoid arthritis (RA). PPI-2458, a potent irreversible methionine aminopeptidase type 2 inhibitor, was administered orally every other day at 1, 5, or 10 mg/kg.

RESULTS

In an in vitro osteoclastogenesis model, PPI-2458 potently inhibited osteoclast differentiation and bone resorption. In the rat PG-PS arthritis model, PPI-2458 afforded significant protection against established disease after therapeutic dosing. This in vivo activity of PPI-2458 was linked to the inhibition of methionine aminopeptidase type 2. Histopathologic assessment of affected joints showed improvement in processes of inflammation, bone resorption, and cartilage erosion, associated with significant improvement in all clinical indices. The protective effects of PPI-2458 against bone destruction in vivo, including the structural preservation of affected hind joints, correlated with improvements in bone histomorphometric markers, as determined by microfocal computed tomography and a significant decrease in systemic C-telopeptide of type I collagen, suggesting decreased osteoclast activity in vivo. Moreover, PPI-2458 prevented cartilage erosion as shown by a significant decrease in systemic cartilage oligomeric matrix protein.

CONCLUSION

The findings of this study suggest that PPI-2458 exerts disease-modifying activity in experimental arthritis through its direct inhibition of several pathophysiologic processes of this disease. These results provide a rationale for assessing the potential of PPI-2458 as a novel RA therapy.

Mechanisms of Disease: molecular insights into aseptic loosening of orthopedic implants

Despite the success of treating rheumatic disorders with biologic therapies, joint replacement surgery still remains the final treatment option in many cases. Approximately 1.5 million joint arthroplastic operations are performed annually worldwide. Implant failure due to massive bone loss and aseptic loosening of prostheses, however, is a major complication of joint replacement, which can lead to high socioeconomic burdens both for the individual patient and for health-care systems. To date, there is no approved drug therapy to prevent or inhibit periprosthetic osteolysis, and aseptic loosening of prostheses can only be overcome by surgical revision. Research during the past decade, however, has unravelled much of the pathogenesis of aseptic prosthesis loosening and preclinical studies have identified potential targets for pharmaceutical treatments. This article highlights the importance of a cooperative interaction between rheumatologists and orthopedic surgeons, and presents novel insights into the molecular mechanisms behind aseptic loosening of prostheses. In addition, we outline potential perspectives for the development of future therapeutic strategies for this devastating complication.

Trigger osteoclast formation and activation: Molecular treatment strategy of delayed tooth eruption

Delayed tooth eruption (DTE) is the emergence of a tooth into the oral cavity at a time that delays significantly from norms. It causes a significant impact on a patient's oral health. Some methods have been suggested to rescue the delayed tooth eruption. However, no approach aims to accelerate the biological process of tooth eruption and rescue these eruption disorders. Recent researches have shown that tooth eruption depends on the presence of osteoclasts to create an eruption pathway through the alveolar bone. We postulate a new approach that targets osteoclast formation and activation to accelerate the eruption of the affected tooth. These strategies include stimulating osteoclastogenesis by applying the cytokines or small molecules, such as TNF-alpha, IL-1 alpha and MCP-1; triggering osteoclast differentiation by applying molecules associated RANKL signaling, such as RANKL-Fc and OPG antibody; enhancing the function of osteoclasts by applying proteinases, such as CTSK. For the clinical point of view, we can inject these molecules in the oral mucosa of the affected tooth to induce bone resorption, then to rebuild the pathway of tooth eruption.