Hirohisa Arakawa

Involvement of HMGB1 and RAGE in IL-1β-induced gingival inflammation.

OBJECTIVE Extracellularly released high mobility group box 1 (HMGB1) protein behaves as a cytokine, promotes inflammation and participates in the pathogenesis of several disorders in peripheral organs. The role of HMGB1 and receptor for advanced glycation end products (RAGE) expressed in gingival inflammatory tissues was explored. METHODS Real time PCR was applied to assay HMGB1 and RAGE mRNA expression in gingival epithelial and fibroblast cells induced by interleukin-1β (IL-1β). A highly selective inhibitor of inducible nitric oxide (iNOS) was employed. ELISA was done for measurement of HMGB1 concentrations in cell culture media of gingival epithelial and fibroblast cells. Immunohistochemistry was performed to analyse the expression and sub-cellular localization of HMGB1, together with RAGE, in specimens obtained from patients with chronic inflammation. RESULTS A time-dependent response of HMGB1 and RAGE expression in gingival cells to IL-1β induction was observed. IL-1β promotes HMGB1 production in human gingival epithelial cells in a nitric oxide-dependent manner. HMGB1 and RAGE appeared highly expressed in gingival inflammatory tissues. CONCLUSION These results demonstrate that HMGB1 and RAGE are abundantly expressed in gingiva and promptly released during gingival inflammation. We suggest a role for HMGB1/RAGE/iNOS signalling on inflamed gingival epithelial cells.

Fluoride-Treated Bio-Resorbable Synthetic Hydroxyapatite Promotes Proliferation and Differentiation of Human Osteoblastic MG-63 Cells

When resorbable hydroxyapatite (HA) granules, which are used as a bone supplement material, were treated in neutral 4% sodium fluoride (NaF) solution, formation of a reactant resembling calcium fluoride was observed on the surface of the granules. Immediate and slow release of fluoride from fluoridated HA (HA+F) granules was observed after immersion in culture fluid, and the concentration increased over time to 1.25 ± 0.05 ppm F at 0.5 hours, 1.57 ± 0.12 ppm F at 24 hours, and 1.73 ± 0.15 ppm F at 48 hours. On invasion assay, migration of human osteoblast-like MG-63 cells exposed to the released fluoride was confirmed in comparison to the cells incubated with a nonfluoridated control sample (P < .01). In addition, fluoride added to the medium increased MG-63 cell proliferation in a manner dependent on fluoride concentrations up to 2.0 ppm (P < .05). At 5.0 ppm, however, fluoride significantly inhibited cell proliferation (P < .005). Activity of the osteogenic differentiation marker, alkaline phosphatase (ALP), also increased with fluoride after exposure for 1 week, increasing significantly at 1.0 ppm (P < .05). The promotion of MG-63 cell migration and proliferation, as well as increased ALP activity, suggested that fluoride released from the surface of resorbable HA granules, which were fluoridated by prior treatment with neutral 4% NaF solution, can provide a superb method to supply fluoride and promote osteogenic cell differentiation.

Micromolar sodium fluoride mediates anti-osteoclastogenesis in Porphyromonas gingivalis-induced alveolar bone loss.

Osteoclasts are bone-specific multinucleated cells generated by the differentiation of monocyte/macrophage lineage precursors. Regulation of osteoclast differentiation is considered an effective therapeutic approach to the treatment of bone-lytic diseases. Periodontitis is an inflammatory disease characterized by extensive bone resorption. In this study, we investigated the effects of sodium fluoride (NaF) on osteoclastogenesis induced by Porphyromonas gingivalis, an important colonizer of the oral cavity that has been implicated in periodontitis. NaF strongly inhibited the P. gingivalis-induced alveolar bone loss. That effect was accompanied by decreased levels of cathepsin K, interleukin (IL)-1β, matrix metalloproteinase 9 (MMP9), and tartrate-resistant acid phosphatase, which were up-regulated during P. gingivalis-induced osteoclastogenesis. Consistent with the in vivo anti-osteoclastogenic effect, NaF inhibited osteoclast formation caused by the differentiation factor RANKL (receptor activator of nuclear factor κB ligand) and macrophage colony-stimulating factor (M-CSF). The RANKL-stimulated induction of the transcription factor nuclear factor of activated T cells (NFAT) c1 was also abrogated by NaF. Taken together, our data demonstrate that NaF inhibits RANKL-induced osteoclastogenesis by reducing the induction of NFATc1, ultimately leading to the suppressed expression of cathepsin K and MMP9. The in vivo effect of NaF on the inhibition of P. gingivalis-induced osteoclastogenesis strengthens the potential usefulness of NaF for treating periodontal diseases.

IL-1β-mediated up-regulation of DEC1 in human gingiva cells via the Akt pathway†

Growing evidence indicates that inflammation is a contributing factor leading to cancer development. However, pathways involved in this progression are not well understood. The involvement of DEC1 in cancer prompted us to examine whether pro‐inflammatory cytokine interleukin‐1β (IL‐1β) induces the expression of DEC1 in oral inflammation. We found that IL‐1β up‐regulated DEC1 and hypoxia‐inducible factor‐1α (HIF‐1α) protein and elevated the HIF‐1α‐responsive gene vascular endothelial growth factor (VEGF) expression in human primary gingival cells. HIF‐1α and DEC1 immunoreactivity were significantly higher in the cases of gingival inflammation. We demonstrate that IL‐1β up‐regulates DEC1 and HIF‐1α protein through a classical inflammatory signaling pathway involving Akt. Our data strongly suggest that PI‐3K–Akt is an upstream participant in IL‐1β‐mediated DEC1 and HIF‐1α induction. This is supported by the following data: (1) IL‐1β induces 473 serine phosphorylation of Akt; (2) IL‐1β‐mediated Akt activation occurs in a PI‐3K‐dependent manner, and specific inhibition of PI‐3K prevents Akt phosphorylation; and (3) inhibition of Akt prevents IL‐1β‐mediated DEC1 and HIF‐1α induction. Taken together, these results suggest that DEC1 is one of the important transcription factors in inflammation. J. Cell. Biochem. 113: 3246–3253, 2012.

Evaluation of layer thickness in human teeth using higher-order-mode leaky Lamb wave interdigital transducers

An ultrasonic nondestructive evaluation technique of the layer thickness in human teeth is proposed using a leaky Lamb wave device with two arch-shaped interdigital transducers, operating at a plate∕water interface. The use of a higher-order-mode leaky Lamb wave with a phase velocity higher than the longitudinal wave velocity in the human tooth is essential to detect reflected ultrasound beams from the tooth section The layer thickness of dentin, estimated from the measured time interval between two reflected echoes, is in good agreement with the optically measured data.

Relationship between Duration of Fluoride Exposure in School-Based Fluoride Mouthrinsing and Effects on Prevention and Control of Dental Caries

The objective of this paper was to assess the effects of school-based fluoride mouthrinsing (S-FMR: weekly using 0.2% NaF solution) in two groups of school children with different periods of exposure to S-FMR in elementary school. Subjects were the S-FMR group consisted of 599 children, participated for six years. The control group consisted of 282 children, participated for less than one year in the sixth year of elementary school. From the results of the present survey, the caries reduction rate of S-FMR in the permanent teeth was 36.6% for DMFT and 42.8% for DMFS, and person rates with DMF, DMFT, DMFS, and CO (questionable caries under observation) were inhibited in both boys and girls. Girls in the control group showed clearly higher values for all parameters of dental caries because of earlier teeth eruption; however, no gender differences were observed in the S-FMR group. As caries prevalence in the first molars accounted for about 85% regardless of participation to S-FMR, and first molar caries were more common in the mandible than in the maxilla, consideration should be given to preventive measures against pit-and-fissure-caries in addition to S-FMR.

Fluoride Retention following the Professional Topical Application of 2% Neutral Sodium Fluoride Foam.

The objective of the present research was to determine the appropriate amount of fluoride to use professional topical application and the residual amounts of fluoride in the oral cavity using a 2% neutral sodium fluoride (NaF) foam with a dedicated tray. Using dentition study models, a method for determining the appropriate amount of NaF foam was investigated. In eight adult subjects, the appropriate amount of NaF foam, the concentration of fluoride in the saliva following professional topical application, and the amount of residual fluoride in the oral cavity following professional topical application was examined. The results indicated that the appropriate amount of NaF foam was approximately 0.8 g, the amount of residual fluoride in the oral cavity was approximately 25% of the amount of foam used.

Correlation of Dental Health Behavior With Health Awareness and Subjective Symptoms in a Rural Population in Japan

The aim of this study was to determine the association of dental health behavior with health awareness, oral condition, and subjective symptoms in Japan. The present study included 1699 individuals who underwent dental checkups at the public health center of Miura City. All those who underwent dental checkups were asked to fill out a questionnaire. The correlation between having a regular dentist and each of the other items was analyzed. Undergoing regular checkups was significantly related to having a regular dentist. To analyze the correlation of dental health behavior with Subjective symptoms and Health awareness, structured equation modeling was performed following factor analysis. As a result, only the regression weight between dental health behavior and health awareness was found to be statistically significant. The present survey indicates that dental health behavior was significantly related to Health awareness but not to Subjective symptoms.