Xylitol is a sugar alcohol with a variety of functions including bactericidal and anticariogenic effects. However, the cellular mechanisms underlying the role of xylitol in bone metabolism are not yet clarified. In our present study, we exploited the physiological role of xylitol on osteoclast dif-ferentiation in a co-culture system of osteoblastic and RAW 264.7 cells. Xylitol treatment of these co-cultures reduced the number of tartrate-resistant acid phosphatase (TRAP)- positive multinucleated cells induced by 10 nM 1α,25(OH)2 D3 in a dose‐dependent manner. A cell viability test revea-led no marked cellular damage by up to 100 mM of xylitol. Exposure of osteoblastic cells to xylitol decreased RANKL, but not OPG, mRNA expression in the presence of 10-8 M 1α,25(OH)2D3 in a dose‐dependent manner. Furthermore, bone resorption activity, assessed on bone slices in the co- culture system, was found to be dramatically decreased with increasing xylitol concentrations. RANKL and OPG proteins were assayed by ELISA and the soluble RANKL (sRANKL) concentration was decreased with an increased xylitol con-centration. In contrast, OPG was unaltered by any xylitol con-centration in this assay. These results indicate that xylitol inhibits 1α,25(OH)2D3-induced osteoclastogenesis by reducing the sRANKL/OPG expression ratio in osteoblastic cells.

Tumor necrosis factor alpha (TNFα) is a multifunctional inflammatory cytokine that regulates various cellular and bio-logical processes. Increased levels of TNFα have been im-plicated in a number of human diseases including diabetes and arthritis. Sympathetic nervous system stimulation via the beta2-adrenergic receptor (β2AR) in osteoblasts suppresses osteogenic activity. We previously reported that TNFα up- regulates β2AR expression in murine osteoblastic cells and that this modulation is associated with TNFα inhibition of osteoblast differentiation. In our present study, we explored whether TNFα induces β2AR expression in human osteo-blasts and then identified the downstream signaling path-way. Our results indicated that β2AR expression was increa-sed in Saos-2 and C2C12 cells by TNFα treatment, and that this increase was blocked by the inhibition of NF-κB acti-vation. Chromatin immunoprecipitation and luciferase reporter assay results indicated that NF-κB directly binds to its cog-nate elements on the β2AR promoter and thereby stimulates β2AR expression. These findings suggest that the activation of TNFα signaling in osteoblastic cells leads to an upregu-lation of β2AR and also that TNFα induces β2AR exp-ression in an NF-κB-dependent manner.

Tumor necrosis factor alpha (TNFα) is a multifunctional cytokine that is elevated in inflammatory diseases such as atherosclerosis, diabetes and rheumatoid arthritis. Recent evidence has suggested that β2 adrenergic receptor(β2AR) activation in osteoblasts suppresses osteogenic activity. In the present study, we explored whether TNFα modulates βAR expression in osteoblastic cells and whether this regulation is associated with the inhibition of osteoblast differentiation by TNFα. In the experiments, we used C2C12 cells, MC3T3- E1 cells and primary cultured mouse bone marrow stromal cells. Among the three subtypes of βAR, β2 and β3AR were found in our analysis to be upregulated by TNFα. Moreover, isoproterenol-induced cAMP production was observed to be significantly enhanced in TNFα-primed C2C12 cells, indicating that TNFα enhances β2AR signaling in osteoblasts. TNFα was further found in C2C12 cells to suppress bone morphogenetic protein 2-induced alkaline phosphatase (ALP) activity and the expression of osteogenic marker genes including Runx2, ALP and osteocalcin. Propranolol, a β2AR antagonist, attenuated this TNFα suppression of osteogenic differentiation. TNFα increased the expression of receptor activator of NF-κB ligand (RANKL), an essential osteoclastogenic factor, in C2C12 cells which was again blocked by propranolol. In summary, our data show that TNFα increases β2AR expression in osteoblasts and that a blockade of β2AR attenuates the suppression of osteogenic differentiation and stimulation of RANKL expression by TNFα. These findings imply that a crosstalk between TNFα and β2AR signaling pathways might occur in osteoblasts to modulate their function.

The regeneration of periodontium is the goal of periodontal therapy. Many periodontologists try to achieve this goal by using guided tissue regeneration(GTR) method. However, these procedures always include several disadvantages. Recombinant human bone morphogenetic protein-2 (rhBMP-2) stimulated ectopic bone formation when it was implanted in rat muscles with insoluble bone matrix by differentiating muscle cells into chondrocytes and osteoblasts. The purpose of this study was to evaluate the osteoinductive potential of the mixture of rhBMP-2 (5 μg/ml) and heparin (0.25 or 25 μg/ml ) at the critically sized rabbit calvarial defects. And this study aimed to reveal that heparin also acts to enhance the bone forming activity of rhBMP-2. The 12 rabbits (4-month-old; NewZealand White) were used in the present study. 5 μg/ml of rhBMP-2 and 0, 0.25 or 25 μg/ml of heparin were mixed and blotted into anorganic bovine bone and filled cranial defects. The animals were sacrificed following a time schedule (1, 3, and 6 weeks). Sections were made in 7 μm thicknesses, stained with H&E and Masson's trichrome method, and examined under a light microscope. The differences among each obtained percent value were evaluated by one-way analysis of variance. A p value of p<0.05 was considered statistically significant and an ANOVA test was performed to verify significant differences. To adjust for multiple comparisons when one-way analysis of variance showed a significant difference between groups (p<0.05), Scheffe`s post hoc test was used to identify which group differences accounted for the significant p-value. In control group, osteoinduction was not outstanding, however, in experimental groups, osteoinduction was significantly outstanding, and as the concentration of heparin mixed with rhBMP-2 increased, osteoinduction was increased. Mixtures of rhBMP-2 and heparin affect bone formation at initial bone formation, but that effect disappeared following a time lapse.

Luteolin is a flavonoid that exists in a glycosylated form in celery and green pepper. Flavonoids possess antioxidant and anti-inflammatory properties and can reduce the expression of key inflammatory molecules in macrophages and monocytes. It has been reported also that some flavonoids have effects on bone metabolism. The effects of luteolin on the function of osteoblasts were investigated by measuring cell viability, alkaline phosphatase activity, type I collagen production, osteoprotegerin secretion, Wnt promoter activity, BMP-2 and Runx2 expression and calcified nodule formation. Luteolin has no effects upon osteoblast viability but induced an increase in alkaline phosphatase activity, type I collagen production and a decrease in osteoprotegerin secretion in these cells. Luteolin treatment also upregulated BMP-2 mRNA expression. These results suggest that luteolin may be a regulatory molecule that facilitates the differentiation of osteoblasts.

Calcium concentration in the bone resorption lacunae is high and is in the mM concentration range. Both osteoblast and osteoclast have calcium sensing receptor in the cell surface, suggesting the regulatory role of high extracellular calcium in bone metabolism. In vitro, high extracellular calcium stimulated osteoclastogenesis in coculture of mouse osteoblasts and bone marrow cells. Therefore we examined the genes that were commonly regulated by both high extracellular calcium and 1.25(OH)₂vitaminD₃(VD3) by using mouse oligo 11 K gene chip. In the presence of 10 mM [Ca²+]e or 10 nM VD3, mouse calvarial osteoblasts and bone marrow cells were co-cultured for 4 days when tartrate resistant acid phosphatase-positive multinucleated cells start to appear. Of 11,000 genes examined, the genes commonly regulated both by high extracellular calcium and by VD3 were as follows; 1) the expression of genes which were osteoclast differentiation markers or were associated with osteoclastogenesis were up-regulated both by high extracellular calcium and by VD3; trap, mmp9, car2, ctsk, ckb, atp6b2, tm7sf4, rab7, 2) several chemokine and chemokine receptor genes such as sdf1, scya2, scyb5, scya6, scya8, scya9, and ccr1 were up-regulated both by high extracellular calcium and by VD3, 3) the genes such as mmp1b, mmp3 and c3 which possibly stimulate bone resorption by osteoclast, were commonly up-regulated, 4) the gene such as c1q and msr2 which were related with macrophage function, were commonly down-regulated, 5) the genes which possibly stimulate osteoblast differentiation and/or mineralization of extracellular matrix, were commonly down-regulated; slc8a1, admr, plod2, lox, fosb, 6) the genes which possibly suppress osteoblast differentiation and/or mineralization of extracellular matrix, were commonly up-regulated; s100a4, npr3, mme, 7) the genes such as calponin 1 and tgfbi which possibly suppress osteoblast differentiation and/or mineralization of extracellular matrix, were up-regulated by high extracellular calcium but were down-regulated by VD3. These results suggest that in coculture condition, both high extracellular calcium and VD3 commonly induce osteoclastogenesis but suppress osteoblast differentiation/mineralization by regulating the expression of related genes.

Since ancient Eygypt, various dental materials were used for lost teeth including gold. The key point of this materials were nontoxic to human body. Since early of 1990's, dental implant was done for recovery of maxillofacial defects. From middle of 1970's, osseointergation concept of implant was introduced and performed in dental field. Biocompatibility of titanium showed good effect for osseointergration but had some problems (Galvance current and toxic corrosion) with suprastructures such as gold crowns. This study was performed to make safe dental implants which have reduced Galvanic currents and corrosion. 3 kind of dental casting gold alloys (different Gold contents, 1㎝×1㎝×0.1㎝ plates.) were used as experimental group, while Titanium were used as control group. Normal human osteoblasts(NHOsts)were cultured during 1-4weeks for histologic study. For analysing the calcium(Ca), Phosphorus(P) and alkaline phosphatase(ALP), NHosts were cultred during 2-23days. After experiments, histologic finding were observed by LSM and SEM. Ca, P, ALP concentration by automatic biochemical analyzer were analyzed by ANOVA test and linear regression method. The results were as follows. Biocompatibility of dental casting gold alloys were similar to titianium alloys histolgically. Biochemical analysis of dental casting gold alloys had no significant difference to titianium alloy except AIGIS-Fine. We could conclude that biocompatibility of dental casting gold alloys with high contents of gold were superior to that of low contents and alloys with high contents of gold had no significant difference from titanium on NHost culture. Gold dental implant might be better than titanium implant due to similar biocompatibility and no galvanic currency.

The present study was performed to investigate whether Achyranthes Radix extracts play roles in the bone metabolism. Three kinds of Achyranthes Radix extracts (methylene chloride (MC), ethylacetate (Ea), and water (W)) were used for bioassay. We examined cellular activities of osteoblasts by measurement of cell proliferation rate, alkaline phosphatase (ALP) activity, and calcified nodule formation. Osteoclast generation was assayed by measuring the number of tartrate-resistant acid phosphatase (TRAP) (+) multinucleated cells after culture of osteoclast precursor cells. There was a maximum 20% increase in proliferation rate of osteoblastic cells after treatment with MC. First and second subfraction of MC layer increased proliferation of osteoblast. Ea layer and second subfraction of MC layer increased ALP activity. Also MC layer and second subfraction of MC layer from Achyranthes Radix extracts increased the calcified nodule. MC layer and second subfraction of MC layer from Achyranthes Radix extracts significantly decreased in the number of TRAP (+) multinucleated cells. Taken together, Achyranthes Radix stimulates the proliferation and bioactivities of bone-forming osteoblasts, and inhibits activities of bone-resorbing osteoclasts.

골다공증의 유발제인 카드뮴(cadmium, Cd)에 대한 세포 독성과 이에 대한 우슬(Achyranthis radix, AR) 추출물의 영향을 배양 골모세포(HFOB-1)를 재료로 항산화 측면에서 조사하여 다음과 같은 결과를 얻었다. 본 연구에서 Cd의 일종인 CdCl2는 처리 농도에 비례하여 배양 HFOB-1세포의 생존율(cell viability)을 유의하게 감소시킴으로서 세포 독성을 나타냈다. 한편, 항산화제인 superoxide dismutase(SOD)와 butylated hydroxytoluene(BHT)는 CdCl2에 의해 감소된 세포 생존율을 유의하게 증가시킴으로서 CdCl2에 의한 세포독성을 방어하였다. 한편, CdCl2의 세포 독성에 대한 AR 추출물의 영향에 있어서, AR 추출물은 CdCl2에 의하여 감소된 세포 생존율을 유의하게 증가시킴으로서 CdCl2에 의한 세포 독성을 방어하였으며, 또한 전자공여능(electron donating activity, EDA)과 지질과산화(lipid peroxidation, LP) 억제능을 보였다. 이상의 결과에서 CdCl2의 세포 독성에 산화적 손상이 관여하고 있으며 CR 추출물은 CdCl2에 의하여 감소된 세포생존율의 증가는 물론, EDA 및 LP 억제능과 같은 항산화 효과(antioxidative effect)에 의하여 세포 독성을 방어한 것으로 나타났다. 따라서 AR 추출물과 같은 천연성분은 뇌졸중(stroke)이나 허혈(ischemia)과 같이 산화적 손상으로 매개되는 난치성 질환의 치료적 접근을 위한 소재로서의 적용가치가 클 것으로 생각된다.