Mechanical force plays an important role in the regulation of bone remodelling in intact bone and bone repair. In vitro, bone cells demonstrate a high responsiveness to mechanical stimuli. Much debate exists regarding the critical components in the load profile and whether different components, such as fluid shear, tension or compression, can influence cells in differing ways. During dynamic loading of intact bone, fluid is pressed through the osteocyte canaliculi, and it has been demonstrated that fluid shear stress stimulates osteocytes to produce signalling molecules. It is less clear how mechanical loads act on mature osteoblasts present on the surface of cancellous or trabecular bone. Although tissue strain and fluid shear stress both cause cell deformation, these stimuli could excite different signalling pathways. This is confirmed by our experimental findings, in human bone cells, that strain applied through the substrate and fluid flow stimulate the release of signalling molecules to varying extents. Nitric oxide and prostaglandin E2 values increased by between two- and nine-fold after treatment with pulsating fluid flow (0.6 +/- 0.3 Pa). Cyclic strain (1000 microstrain) stimulated the release of nitric oxide two-fold, but had no effect on prostaglandin E2. Furthermore, substrate strains enhanced the bone matrix protein collagen I two-fold, whereas fluid shear caused a 50% reduction in collagen I. The relevance of these variations is discussed in relation to bone growth and remodelling. In applications such as tissue engineering, both stimuli offer possibilities for enhancing bone cell growth in vitro.

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The BCP and DBA materials showed similar osteoconductive patterns and mineralized bone, although signs of more active bone formation and remodeling were observed in BCP- than in DBA-grafted biopsies.

Tumor cells in the bone microenvironment are able to initiate a vicious cycle of bone degradation by mobilizing osteoclasts, multinucleated cells specialized in bone degradation. c-Src is highly expressed both in tumors and in osteoclasts. Therefore, drugs like AZD0530, designed to inhibit Src activity, could selectively interfere with both tumor and osteoclast activity. Here we explored the effects of AZD0530 on human osteoclast differentiation and activity. The effect on osteoclasts formed in vivo was assessed in mouse fetal calvarial explants and in isolated rabbit osteoclasts, where it dose-dependently inhibited osteoclast activity. Its effect on formation and activity of human osteoclasts in vitro was determined in cocultures of human osteoblasts and peripheral blood mononuclear cells. AZD0530 was most effective in inhibiting osteoclast-like cell formation when present at the onset of osteoclastogenesis, suggesting that Src activity is important during the initial phase of osteoclast formation. Formation of active phosphorylated c-Src, which was highly present in osteoclast-like cells in cocultures and in peripheral blood mononuclear cell monocultures, was significantly reduced by AZD0530. Furthermore, it reversibly prevented osteoclast precursor migration from the osteoblast layer to the bone surface and subsequent formation of actin rings and resorption pits. These data suggest that Src is pivotal for the formation and activity of human osteoclasts, probably through its effect on the distribution of the actin microfilament system. The reversible effect of AZD0530 on osteoclast formation and activity makes it a promising candidate to temper osteoclastic bone degradation in bone diseases with enhanced osteoclast activity such as osteolytic metastatic bone disease. (Mol Cancer Res 2009;7(4):476-88)

Our findings provide more insight into bone-site-specific effects of bisphosphonates and into the aetiology of osteonecrosis of the jaw. We demonstrated that bisphosphonates can stimulate osteoclast activity at the molar roots.

The aim of this study was to evaluate the toxic effects of actinomycin D on the developing hamster tooth germ in organ culture. Hamster tooth germs during early secretory amelogenesis were exposed in vitro for 24 h to 10(-9) M-5 x 10(-5) M actinomycin D. Actinomycin D dose-dependently (> or = 10(-7) M) decreased the tooth germ dry weight but mineralization was affected only by doses > or = 10(-5) M. However, the uptakes of TCA-insoluble 32P and [3H]thymidine were significantly reduced dose-dependently from > or = 10(-8) M actinomycin D, indicating that the drug inhibits the synthesis of phosphate-containing macromolecules as well as DNA synthesis. Histologically, 10(-8) M actinomycin D was the lowest dose which was not toxic to any cell type in the developing tooth germ. At 10(-7) M actinomycin D, the most sensitive cells were the proliferating pre-odontoblasts followed by pre-ameloblasts; the mature secretory ameloblasts and odontoblasts appeared unaffected. Higher doses resulted in increased cytotoxicity to the secretory cells and, eventually, total degeneration of most cells. The data suggest that children treated for cancer during tooth development using anti-chemotherapy cocktails containing actinomycin D (serum levels > 10(-7) M) may develop defects later on in the mature dentition as a direct consequence of the toxicity of the drug to the tooth organ.

Vincristine is one of the cytostatic drugs present in cocktails commonly used for the treatment of cancer in children. The aim of this study was to evaluate biochemically and histologically the toxic effects of this drug on the developing tooth in vitro using the organ culture model in order to be able to predict what damage the drug can induce in the developing teeth from children undergoing anti-neoplastic chemotherapy. The most profound effect of the drug (10(-8)M-10(-4)M vincristine) on the developing tooth germ was the induction of mitotic arrests at the cervical loop and in the inter-cuspal regions. The 10(-4)M-10(-6)M vincristine doses were cytotoxic to most cells in the developing tooth germ. The 10(-7)M vincristine dose apart from induction of mitotic arrests, did not appear to be cytotoxic to the mature differentiated secretory cells. However, this dose induced incomplete nuclear polarization of the differentiating ameloblasts and odontoblasts. At 10(-8)M vincristine, the only effect observed were mitotic arrests; the secretory cells did not appear to have been affected at all. On the other hand, mineralization (TCA-soluble 45Ca and 32P uptake) was dose-dependently decreased from 10(-7)M vincristine upwards. 10(-9)M vincristine, the lowest dose tested, did not induce any changes in the developing tooth germ. The organ culture data indicate that 10(-9)M vincristine is the highest (safe) dose which does not induce any toxic effects in the developing hamster tooth germ.(ABSTRACT TRUNCATED AT 250 WORDS)

The aim of this study was to evaluate, under organ culture conditions, the cytotoxic effects of daunorubicin on tooth development. Three-day-old maxillary hamster second molars were exposed for 24 h in vitro to 108-10-4 M daunorubicin and then evaluated biochemically and histologically. At 10-6 M daunorubicin dose-dependently decreased tooth germ dry weight, cell proliferation ([3H]thymidine uptake), and insoluble [32P] phosphate uptake (phosphorylation of macromolecules). [45Ca]calcium uptake, a marker for mineralization, was significantly affected only at the highest concentration (10-4 M) tested. Histologically, 10-6 M daunorubicin induced necrosis of the proliferating but not the differentiated protein-secreting cells. At 10-4 M, however, all cells were dead. These results indicate that daunorubicin is particularly toxic to the proliferating cells of the tooth germ. Thus, it can be postulated that children treated with daunorubicin may develop defects in the erupted teeth mainly associated with those regions that were in the proliferating stage at the onset of anticancer chemotherapy.