Masumi Horibe

Topical administration of simvastatin recovers alveolar bone loss in rats

BACKGROUND AND OBJECTIVE Simvastatin, a cholesterol-lowering drug, has been reported to show anabolic effects on bone metabolism. We examined the effects of simvastatin in vitro using cultured rat calvaria cells and in vivo using periodontitis-induced rats. MATERIAL AND METHODS Alkaline phosphatase activity and bone nodule formation were measured in cultured rat calvaria cells. Nylon ligature was placed around the maxillary molars of Fischer male rats for 20 d to induce alveolar bone resorption. After ligature removal, simvastatin was topically injected into the buccal gingivae for 70 d and then microcomputed tomography and histological examinations were performed. RESULTS Simvastatin maintained high alkaline phosphatase activity and increased bone nodule formation in rat calvaria cells in a dose-dependent manner, showing that simvastatin increased and maintained a high level of osteoblastic function. Microcomputed tomography images revealed that treatment with simvastatin recovered the ligature-induced alveolar bone resorption, showing a 46% reversal of bone height. Histological examination clarified that low-mineralized alveolar bone was formed in simvastatin-treated rats. CONCLUSION These findings demonstrate that simvastatin has the potential to stimulate osteoblastic function and that topical administration of simvastatin may be effective for the recovery of alveolar bone loss in rats.

Topical and intermittent application of parathyroid hormone recovers alveolar bone loss in rat experimental periodontitis

BACKGROUND AND OBJECTIVE Periodontitis is characterized by periodontal tissue inflammation and alveolar bone loss. The intermittent administration of parathyroid hormone (PTH), a major regulator of bone remodeling, has been demonstrated to stimulate osteoblastic activity. Although the systemic administration of PTH has been reported to protect against periodontitis-associated bone loss, the effect of the topical administration of PTH is unclear. In this study, the effect of intermittent administration of PTH on osteoblastic differentiation was examined in cultured calvaria cells and then the effect of topical and intermittent administration of PTH was determined by measuring the recovery of alveolar bone loss after inducing experimental periodontitis in rats. MATERIAL AND METHODS Alkaline phosphatase activity and bone nodule formation were measured in fetal rat calvaria cells. Experimental periodontitis was induced by placing nylon ligature around rat maxillary molars for 20 d. After ligature removal (day 0), PTH was topically injected into buccal gingiva three times a week for 10 wk. Micro-computed tomography analysis and histological examination were performed on days 35 and 70. RESULTS Intermittent exposure of PTH in calvaria cells increased alkaline phosphatase activity and bone nodule formation by 1.4- and 2.4-fold, respectively. Ligature procedures induced marked alveolar bone loss around the molars on day 0 and greater bone recovery was observed in the PTH-treated rats on day 70. An increase in osteoid formation on the surface of alveolar bone was detected in the PTH-treated rats. CONCLUSION Intermittent treatment with PTH stimulated osteoblastic differentiation in fetal rat calvaria cell cultures, and topical and intermittent administration of PTH recovered alveolar bone loss in rat experimental periodontitis.

Effect of retinoic acid on osteopontin expression in rat clonal dental pulp cells

We studied the effect of retinoic acid on osteopontin synthesis and the mRNA expression in rat clonal dental pulp cells, RPC-C2A. An immunoprecipitation assay clarified that retinoic acid caused an increase in phosphorylated osteopontin synthesis that was dose-dependent, and marked increases were observed at retinoic acid concentrations of 10(-6) to 10(-5) M (1.7-fold). A Northern blotting analysis revealed a similar pattern of increase in osteopontin mRNA expression of up to 6.2-fold of control levels. Because osteopontin has an important role in the mineralization process, these results suggest that retinoic acid regulates mineralization, which takes place in the pulp cavity, including reparative dentin formation.

Regulation of tenascin expression in cultured rat dental pulp cells

Tenascin (TN) is a glycoprotein of extracellular matrix abundantly present in embryonic mesenchymal tissues. Transforming growth factor-β1 (TGF-β1), basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), hepatocyte growth factor (HGF), and retinoic acid (RA) are important regulators of dentinogenesis. Dental pulp cells have the capacity to differentiate into odontoblast-like cells. In this study, we investigated the effects of growth factors on TN expression and adhesive function using rat clonal dental pulp cells, RPC-C2A. Analyses of reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting revealed that RPC-C2A cells expressed TN molecules and that TGF-β1, HGF, and RA increased expression of TN at the mRNA and protein level, while bFGF and EGF showed a weak effect. An adhesion assay revealed that treatment with TGF-β1, HGF, and RA induced a marked reduction of cell attachment to fibronectin (FN)-coated surfaces, whereas there was no change with bFGF and EGF. Functional blocking of growth factor-stimulated TN protein by pretreating cells with anti-TN antibodies restored cell attachment to control levels. These findings suggest that TGF-β1, HGF, and RA may regulate pulpal cell adhesion to FN-coated surfaces and that this effect is mediated by TN.

Association between periodontal condition and kidney dysfunction in Japanese adults: A cross-sectional study

Recent studies have demonstrated that chronic kidney disease (CKD) may be associated with the progression of periodontal disease. Diabetes mellitus (DM) is a major risk factor for CKD. The objective of this study was to clarify the relationship between periodontal condition and kidney dysfunction in patients who had kidney failure with or without DM. One hundred sixty‐four patients with kidney dysfunction were enrolled (male: N = 105; female: N = 59), and the relationship between periodontal condition and kidney dysfunction was analyzed in a cross‐sectional study. The subjects were divided into three groups: (a) patients with DM, (b) dialysis patients with nephropathy due to various kidney diseases, and (c) dialysis patient with nephropathy due to DM (diabetic nephropathy). Then, the effect of DM on the periodontal condition was analyzed. The patients were also stratified by CKD stage (into G1–G5) using the estimated glomerular filtration rate (eGFR), and the G5 group was divided in patients with or without DM. Correlations between eGFR and parameters of periodontal condition were calculated in patients from G1 to G4. The number of missing teeth was significantly higher in dialysis patients with diabetic nephropathy than in patients with DM, whereas alveolar bone loss did not show a significant difference among the three groups. In addition, the G5 patients with DM had a significantly higher number of missing teeth than the other CKD groups, whereas alveolar bone loss did not show a significant difference. In G5 patients with DM, Community Periodontal Index and Oral Hygiene Index scores were significantly higher than in G1‐4 patients with DM. There was a significant negative correlation between eGFR and the number of missing teeth. Patients with diabetic nephropathy have a higher rate of periodontal problems such as missing teeth in Japanese adults.