Lipopolysaccharide- TLR-4 Axis regulates Osteoclastogenesis independent of RANKL/RANK signaling.

BACKGROUND: Lipopolysaccharide (LPS) is an endotoxin and a vital component of gram-negative bacteria's outer membrane. During gram-negative bacterial sepsis, LPS regulates osteoclast differentiation and activity, in addition to increasing inflammation. This study aimed to investigate how LPS regulates osteoclast differentiation of RAW 264.7 cells in vitro. RESULTS: Herein, we revealed that RAW cells failed to differentiate into mature osteoclasts in vitro in the presence of LPS. However, differentiation occurred in cells primed with receptor activator of nuclear factor-kappa-Β ligand (RANKL) for 24 h and then treated with LPS for 48 h (henceforth, denoted as LPS-treated cells). In cells treated with either RANKL or LPS, an increase in membrane levels of toll-like receptor 4 (TLR4) receptor was observed. Mechanistically, an inhibitor of TLR4 (TAK-242) reduced the number of osteoclasts as well as the secretion of tumor necrosis factor (TNF)-α in LPS-treated cells. RANKL-induced RAW cells secreted a very basal level TNF-α. TAK-242 did not affect RANKL-induced osteoclastogenesis. Increased osteoclast differentiation in LPS-treated osteoclasts was not associated with the RANKL/RANK/OPG axis but connected with the LPS/TLR4/TNF-α tumor necrosis factor receptor (TNFR)-2 axis. We postulate that this is because TAK-242 and a TNF-α antibody suppress osteoclast differentiation. Furthermore, an antibody against TNF-α reduced membrane levels of TNFR-2. Secreted TNF-α appears to function as an autocrine/ paracrine factor in the induction of osteoclastogenesis independent of RANKL. CONCLUSION: TNF-α secreted via LPS/TLR4 signaling regulates osteoclastogenesis in macrophages primed with RANKL and then treated with LPS. Our findings suggest that TLR4/TNF-α might be a potential target to suppress bone loss associated with inflammatory bone diseases, including periodontitis, rheumatoid arthritis, and osteoporosis.

The burden of root caries: Updated perspectives and advances on management strategies.

BACKGROUND: Root caries has gained much attention in the last few years. As the world's population is ageing and people currently tend to retain more teeth compared with older generations, there is an increased prevalence of periodontal disease and gingival recession, which may accelerate the onset of root caries. OBJECTIVE: This review aims to summarise recent findings related to the diagnosis, prevention and treatment of root caries. MATERIALS AND METHODS: MEDLINE (OVID) and Scopus (Elsevier) searches were performed to identify and discuss articles that address the pathogenicity and clinical management of root caries. RESULTS: Root caries is a multifactorial disease. Cariogenic species involved in root caries are less dependent on carbohydrates since collagen degradation inside the dentinal tubules can provide nutrients and microcavities for the invading microorganisms. Furthermore, the root surface has fewer minerals in comparison with enamel, which may accelerate the onset of demineralisation. Root caries could be prevented by patient education, modification of risk factors, and the use of in-office and home remineralisation tools. The use of non-invasive approaches to control root caries is recommended, as the survival rate of root caries restorations is poor. When plaque control is impossible and a deep/large cavity is present, glass ionomer or resin-based restorations can be placed. CONCLUSION: The assessment of root carious lesions is critical to determine the lesion activity and the required intervention. Dental practitioners should also be aware of different prevention and treatment approaches to design optimum oral health care for root caries-affected patients.

Light Energy Dose and Photosensitizer Concentration Are Determinants of Effective Photo-Killing against Caries-Related Biofilms.

Caries-related biofilms and associated complications are significant threats in dentistry, especially when biofilms grow over dental restorations. The inhibition of cariogenic biofilm associated with the onset of carious lesions is crucial for preventing disease recurrence after treatment. This in vitro study defined optimized parameters for using a photosensitizer, toluidine blue O (TBO), activated via a red light-emitting diode (LED)-based wireless device to control the growth of cariogenic biofilms. The effect of TBO concentrations (50, 100, 150, and 200 µg/mL) exposed to light or incubated in the dark was investigated in successive cytotoxicity assays. Then, a mature Streptococcus mutans biofilm model under sucrose challenge was treated with different TBO concentrations (50, 100, and 150 µg/mL), different light energy doses (36, 108, and 180 J/cm2), and different incubation times before irradiation (1, 3, and 5 min). The untreated biofilm, irradiation with no TBO, and TBO incubation with no activation represented the controls. After treatments, biofilms were analyzed via S. mutans colony-forming units (CFUs) and live/dead assay. The percentage of cell viability was within the normal range compared to the control when 50 and 100 µg/mL of TBO were used. Increasing the TBO concentration and energy dose was associated with biofilm inhibition (p < 0.001), while increasing incubation time did not contribute to bacterial elimination (p > 0.05). Irradiating the S. mutans biofilm via 100 µg/mL of TBO and ≈180 J/cm2 energy dose resulted in ≈3-log reduction and a higher amount of dead/compromised S. mutans colonies in live/dead assay compared to the control (p < 0.001). The light energy dose and TBO concentration optimized the bacterial elimination of S. mutans biofilms. These results provide a perspective on the determining parameters for highly effective photo-killing of caries-related biofilms and display the limitations imposed by the toxicity of the antibacterial photodynamic therapy's chemical components. Future studies should support investigations on new approaches to improve or overcome the constraints of opportunities offered by photodynamic inactivation of caries-related biofilms.

C-phycocyanin attenuates RANKL-induced osteoclastogenesis and bone resorption in vitro through inhibiting ROS levels, NFATc1 and NF-κB activation.

Excessive bone loss occurs in inflammatory disorders such as periodontitis and osteoporosis. The underlying mechanism is related to the differentiation of macrophages into multinucleated giant osteoclasts and their bone resorptive activity. C-Phycocyanin (C-PC) is a phycobiliprotein extracted from the blue-green algae, which has been shown to have various pharmacological effects. The role of C-PC on bone metabolism needs revelation. In this study, we determined the effectiveness of C-PC as an inhibitor of osteoclast differentiation, activity, and survival in vitro. We found that C-PC strongly inhibited the differentiation of macrophages to TRAP-positive osteoclasts, distinctive osteoclast specific podosomal organization, and dentine matrix resorption without any cytotoxicity. Also, it suppressed the expression of osteoclast specific markers, such as cathepsin K and integrin ß3 at mRNA and protein levels. RANKL mediated signaling utilizes reactive oxygen species (ROS) for the differentiation of osteoclasts. C-PC attenuated RANKL stimulated ROS. Mechanistic studies indicate that C-PC has the potential to reduce osteoclast formation via blocking the degradation of cytosolic IκB-α and hence, the activation of downstream markers such as c-Fos and NFATc1. However, it does not have any effect on osteoblast-mediated bone formation in vitro. Collectively, our data suggest that C-PC may be utilized as a therapeutic agent that can target bone loss mediated by excessive osteoclastic bone resorption without affecting osteoblastic activity in bone.

Osteoclastogenesis in periodontal diseases: Possible mediators and mechanisms.

BACKGROUND: Periodontitis is the inflammation of the tooth-supporting structures and is one of the most common diseases of the oral cavity. The outcome of periodontal infections is tooth loss due to a lack of alveolar bone support. Osteoclasts are giant, multi-nucleated, and bone-resorbing cells that are central for many osteolytic diseases, including periodontitis. Receptor activator of nuclear factor-kB ligand (RANKL) is the principal factor involved in osteoclast differentiation, activation, and survival. However, under pathological conditions, a variety of pro-inflammatory cytokines secreted by activated immune cells also contribute to osteoclast differentiation and activity. Lipopolysaccharide (LPS) is a vital component of the outer membrane of the Gram-negative bacteria. It binds to the Toll-like receptors (TLRs) expressed in many cells and elicits an immune response. HIGHLIGHTS: The presence of bacterial LPS in the periodontal area stimulates the secretion of RANKL as well as other inflammatory mediators, activating the process of osteoclastogenesis. RANKL, either independently or synergistically with LPS, can regulate osteoclastogenesis, while LPS alone cannot. MicroRNA, IL-22, M1/M2 macrophages, and memory B cells have recently been shown to modulate osteoclastogenesis in periodontal diseases. CONCLUSION: In this review, we summarize the mechanism of osteoclastogenesis accompanying periodontal diseases at the cellular level. We discuss a) the effects of LPS/TLR signaling and other cytokines on RANKL-dependent and -independent mechanisms involved in osteoclastogenesis; b) the recently identified role of several endogenous factors such as miRNA, IL-22, M1/M2 macrophages, and memory B cells in regulating osteoclastogenesis during periodontal pathogenesis.