Structure-Dependent Effects of Bisphosphonates on Inflammatory Responses in Cultured Neonatal Mouse Calvaria.

Bisphosphonates (BPs) are classified into two groups, according to their side chain structures, as nitrogen-containing BPs (NBPs) and non-nitrogen-containing BPs (non-NBPs). In this study, we examined the effects of NBPs and non-NBPs on inflammatory responses, by quantifying the inflammatory mediators, prostaglandin E2 (PGE2) and nitric oxide (NO), in cultured neonatal mouse calvaria. All examined NBPs (pamidronate, alendronate, incadronate, risedronate, zoledronate) stimulated lipopolysaccharide (LPS)-induced PGE2 and NO production by upregulating COX-2 and iNOS mRNA expression, whereas non-NBPs (etidronate, clodronate, tiludronate) suppressed PGE2 and NO production, by downregulating gene expression. Additionally, [4-(methylthio) phenylthio] methane bisphosphonate (MPMBP), a novel non-NBP with an antioxidant methylthio phenylthio group in its side chain, exhibited the most potent anti-inflammatory activity among non-NBPs. Furthermore, results of immunohistochemistry showed that the nuclear translocation of NF-κB/p65 and tyrosine nitration of cytoplasmic protein were stimulated by zoledronate, while MPMBP inhibited these phenomena, by acting as a superoxide anion (O2-) scavenger. These findings indicate that MPMBP can act as an efficacious agent that causes fewer adverse effects in patients with inflammatory bone diseases, including periodontitis and rheumatoid arthritis.

Effects of mevastatin on grafted bone in MRL/MpJ mice.

Statins, lipid-lowering drugs, have been reported to influence bone metabolism. However, the available information about their effects on bone formation and resorption in vivo is still limited. The present study was undertaken to determine whether the topical administration of mevastatin could increase the bone mass of isografted bone. The tibiae were bilaterally dissected from a donor MRL/MpJ mouse and transplanted subcutaneously in the dorsal region of a recipient mouse. One grafted tibia was topically infused for either 1, 2, 3, or 4 weeks with mevastatin, using an osmotic minipump at a dose of 2.5 pmol/hr. The other tibia was infused with 0.9% NaCl (control). Our three results were: (1) Topical mevastatin stimulated bone formation and numerous cuboidal osteoblasts appeared on the surface of newly formed bone. Bone mineral density and bone area in mevastatin-treated bone were significantly increased. (2) Topical mevastatin increased the number of osteoclasts. (3) The expression of bone morphogenetic protein-2 (BMP-2) mRNA and receptor activator of NF-kB ligand (RANKL) mRNA were upregulated in mevastatin-treated bone. These results suggest that the topical infusion of mevastatin increases bone mass of isografted bone by increasing bone turnover and, at least in part, by promoting the expression of BMP-2 and RANKL mRNA.

Oral squamous cell carcinomas stimulate osteoclast differentiation.

Matrix metalloproteinases (MMPs) play important roles in the invasion and metastasis to soft tissues of carcinomas including, oral squamous cell carcinomas (SCCs). Although, osteoclastic bone resorption is an important step in bone involvement in a variety of malignancies, the mechanism of bone involvement of oral SCC remains unclear. Once cancer cells arrest in bone, the bone is a storehouse of a variety of cytokines and growth factors and thus provides an extremely fertile environment for cell growth. The bone-invasive oral cancer cell line, BHY, transcriptionally expressed detectable levels of TGF-beta, IL-1beta, IL-8, parathyroid hormone-related protein (PTHrP) and vascular endothelial growth factor (VEGF) mRNAs and failed to express GM-CSF, IL-6, and TNF-alpha. Furthermore, the BHY-conditioned medium greatly upregulated IL-6 and RANKL/ODF mRNA expression in osteoblasts, suggesting a potential indirect stimulation of osteoclastogenesis via the osteogenic lineage. Seven out of eleven patients with carcinomas of the lower alveolus and gingiva showing infiltrative bone involvement expressed PTHrP mRNA. These data suggest that the occurrence of PTHrP may be an indication of developing oral malignant carcinomas.

Pharmacological topics of bone metabolism: a novel bisphosphonate for the treatment of periodontitis.

It has been reported that the pharmacological characteristics of bisphosphonates vary depending on the side chain attached to the carbon atom of the P-C-P bond. TRK-530 is a novel synthetic bisphosphonate with an anti-oxidant methylthio-phenylthio side chain. This compound has been suggested to have both anti-inflammatory and anti-bone-resorbing effects. Such a compound could be effective for the treatment of diseases with excessive bone resorption accompanied by inflammation. We have been studying this compound as a potential therapeutic agent for periodontitis. To date, we have found that 1) TRK-530 inhibited osteoclastic bone resorption in animals and in bone organ culture, 2) both systemic and topical administration of TRK-530 prevented alveolar bone loss in animals with experimental periodontitis, 3) TRK-530 prevented prostaglandin E(2) synthesis by inhibiting the expression of cyclooxygenase (COX)-2 mRNA, and 4) TRK-530 inhibited the formation of dental calculus. The above results suggest that TRK-530 might be useful for the treatment of alveolar bone loss in periodontitis.

Current topics in pharmacological research on bone metabolism: inhibitory effects of bisphosphonates on the differentiation and activity of osteoclasts.

Despite the extensive use of bisphosphonates (BPs) in the treatment of metabolic bone diseases associated with increased osteoclastic bone resorption, the precise mechanism of their action on bone metabolism is still unclear. To clarify at which stages of osteoclast differentiation and activation that BPs influence, we examined the osteoclasts generated from mononuclear precursors and osteoclasts in the calvaria by laser scanning confocal microscopy. The studies showed that BPs inhibit lipopolysaccharide- or parathyroid hormone-induced osteoclast differentiation, fusion, attachment, actin ring formation, and activation and that both beta3 integrin and osteopontin have an important role in cytoskeletal rearrangements associated with cell attachment and resorption in osteoclasts.

[Application of bisphosphonates for periodontitis].

Bisphosphonates are known as highly effective inhibitors of osteoclastic bone resorption that selectively affect osteoclasts. They are world-wildly used for the treatment of metabolic bone diseases with excessive bone resorption such as osteoporosis and Paget's disease. Alveolar bone loss in periodontitis results from local inflammatory reactions by periodontopathic bacteria. It has been reported that bisphosphonates efficiently prevent experimentally induced alveolar bone resorption in animals with periodontitis, and that bisphosphonate therapy improves the outcome of periodontal treatment in human being. Administration of bisphosphonates may be an appropriate adjunctive treatment to preserve periodontal bone mass. Further studies are needed regarding topical drug delivery system, effective dose and frequency of administration, possible side effects, and which bisphosphonate is suitable for periodontitis.

Osteoclast responses to lipopolysaccharide, parathyroid hormone and bisphosphonates in neonatal murine calvaria analyzed by laser scanning confocal microscopy.

Because the development and activity of osteoclasts in bone remodeling is critically dependent on cell-cell and cell-matrix interactions, we used laser confocal microscopy to study the response of osteoclasts to lipopolysaccharide (LPS; 10 microg/ml), parathyroid hormone (PTH; 10(-8) M), and bisphosphonates (BPs; 1-25 microM clodronate or 0.1-2.5 microM risedronate) in cultured neonatal calvaria. Following treatment with LPS or PTH (<48 hr), osteopontin (OPN) and the alphavbeta3 integrin were found colocalized with the actin ring in the sealing zone of actively resorbing osteoclasts. In contrast, non-resorbing osteoclasts in BP-treated cultures showed morphological abnormalities, including retraction of pseudopods and vacuolization of cytoplasm. In the combined presence of LPS and BP, bone-resorbing osteoclasts were smaller and the sealing zone diffuse, reflecting reduced actin, OPN, and beta3 integrin staining. Depth analyses of calvaria showed that the area of resorbed bone was filled with proliferating osteoblastic cells that stained for alkaline phosphatase, collagen type I, and bone sialoprotein, regardless of the presence of BPs. These studies show that confocal microscopy of neonatal calvaria in culture can be used to assess the cytological relationships between osteoclasts and osteoblastic cells in response to agents that regulate bone remodeling in situ, avoiding systemic effects that can compromise in vivo studies and artifacts associated with studies of isolated osteoclasts.

[Pharmacological actions and pharmacokinetics of bisphosphonates].

Bisphosphonates are potent inhibitors of osteoclastic bone resorption and have been used for the treatment of various metabolic bone diseases such as osteoporosis and hypercalcemia of malignancy. However, the pharmacological action, the mechanism of action, and even side effects vary depending on the chemical structure of the side chain attached to the carbon atom of P-C-P bond. This review discussed about the pharmacological characteristics and possible application of different classes of bisphosphonates with different side chains.

Expression of receptor activator of NF-kappa B ligand and osteoprotegerin in culture of human periodontal ligament cells.

The receptor activator of NF-kappa B ligand (RANKL) and its decoy receptor, osteoprotegerin (OPG), are the important proteins implicated in osteoclastogenesis. In this study, we investigated the expressions of RANKL and OPG in cultured human periodontal ligament (PDL) cells and their roles in osteoclastogenesis. Northern blotting revealed that the OPG mRNA was down-regulated remarkably by application of 10-8 m one-alpha, 25-dihydroxyvitamin D3[1,25-(OH)2D3] and 10-7 m dexamethasone (Dex). In contrast, RANKL mRNA was up-regulated by the same treatment. Western blotting demonstrated decrease of OPG by the application of 1,25-(OH)2D3 and Dex. Tartrate-resistant acid phosphatase-positive multinuclear cells were markedly induced when the PDL cells were cocultured with mouse bone marrow cells in the presence of an anti-OPG antibody together with 1,25-(OH)2D3 and Dex. These results indicate that PDL cells synthesize both RANKL and OPG and that inactivation of OPG may play a key role in the differentiation of osteoclasts.

Histamine stimulates production of osteoclast differentiation factor/receptor activator of nuclear factor-kappaB ligand by osteoblasts.

Histamine H(1),H(2), and H(3) receptors are expressed by osteoblastic MC3T3-E1 (E1) cells derived from mouse calvaria. Expression of the osteoclast differentiation factor (ODF)/receptor activator of nuclear factor-kappaB ligand (RANKL) transcript was induced in E1 cells and bone marrow stromal cells (ST2). Histamine markedly increased the steady-state level of ODF/RANKL mRNA in a dose-dependent manner. The effect of histamine on expression of ODF/RANKL mRNA by E1 cells was transient, with a peak at 6h. Western blot analysis revealed that histamine increased production of ODF/RANKL protein by E1 cells at 12h. In cocultures of E1 cells and mouse bone marrow cells, histamine stimulated osteoclastogenesis in the presence of 1,25-dihydroxyvitamin D(3) and this effect was blocked by preincubation with neutralizing antibody against ODF/RANKL. These results suggest that histamine regulates osteoclastogenesis, at least in part, through induction of ODF/RANKL expression by osteoblasts and bone marrow stromal cells.

[Bisphosphonates and adhesion molecules].

Bisphosphonates are highly effective inhibitors of osteoclastic bone resorption. They can be divided into two groups with distinct mechanisms of action. The nitrogen-containing bisphosphonates (pamidronate, alendronate, risedronate, incadronate etc) can inhibit the mevalonate pathway in osteoclasts and inhibit protein prenylation of small G proteins including Rho, which might lead to alter cytoskeletal organization and cell motility. Others, like etidronate and clodronate, do not inhibit protein prenylation and can be incorporated into ATP-containing compounds that may be cytotoxic to osteoclasts. Further studies would be required to elucidate the molecular mechanism of bisphosphonate actions.