Type of cell death induced by seven metals in cultured mouse osteoblastic cells.

The use of dental metal alloys in the daily clinic makes it necessary to evaluate the cytotoxicity of eluted metal components against oral cells. However, the cytotoxic mechanism and the type of cell death induced by dental metals in osteoblasts have not been well characterized. This study investigated the cytotoxicity of seven metals against the mouse osteoblastic cell line MC3T3-E1. alpha-MEM was used as a culture medium, since this medium provided much superior proliferation of MC3T3-E1 cells over DMEM. Ag (NH(3))(2)F was the most cytotoxic, followed by CuCl>CuCl(2) >CoCl(2), NiCl(2)>FeCl(3) and FeCl(2) (least toxic). None of the metals showed any apparent growth stimulating effect (so-called 'hormesis') at lower concentrations. A time course study demonstrated that two hours of contact between oral cells and Ag (NH(3))(2)F, CuCl, CoCl(2) or NiCl(2) induced irreversible cell death. Contact with these metals induced a smear pattern of DNA fragmentation without activation of caspase-3. Preincubation of MC3T3-E1 cells with either a caspase inhibitor (Z-VAD-FMK) or autophagy inhibitors (3-methyladenine, bafilomycin) failed to rescue them from metal cytotoxicity. These data suggest the induction of necrotic cell death rather than apoptosis and autophagy by metals in this osteoblastic cell line.

Type of cell death induced by various metal cations in cultured human gingival fibroblasts.

Metal ions are released from casting alloys and cause damage to cell structures and local inflammation. However, the cytotoxic mechanism and the type of cell death induced in human gingival fibroblast (HGF) by contact with dental metals have not been well characterized. Here the cytotoxicity of eight metals against HGF was investigated. Cytoxicity of metals against HGF was in the following order: Ag(NH(3))(2)F (most cytotoxic)>AgCl>CuCl(2)>CuCl, CoCl(2)> NiCl(2)>FeCl(2), FeCl(3) (least cytotoxic). None of the metals showed any apparent hormetic growth stimulation at lower concentrations, except for Ag(NH(3))(2)F at 20 or higher population-doubling level of HGF. The sensitivity of HGF against Ag(NH(3))(2)F was reduced during in vitro aging, similar to previous report with sodium fluoride. Contact with Ag(NH(3))(2)F for only one hour induced irreversible cell death, whereas longer duration of contact with AgCl or CuCl(2) was necessary to induce irreversible cell death. These metals induced neither DNA fragmentation nor caspase-3 activation. Pan-caspase inhibitor (Z-VAD-FMK) and autophagy inhibitors (3-methyladenine, bafilomycin) did not apparently affect the cytotoxicity of metals, when corrected for the effect of inhibitor alone on growth. We also found that Ag(NH(3))(2)F induced much higher cytotoxicity than AgCl in mouse osteoblastic cell line MC3T3-E1, possibly inducing necrosis. These data suggest the importance of cautious application of Ag(NH(3))(2)F to the oral cavity.

Quantification of enhanced osteoblastic adhesion to ultraviolet-treated titanium plate.

Although the advantage of ultraviolet (UV) irradiation of titanium plates for the attachment of osteoblast is known, the details of the experimental conditions have not been described in previous literature. We established optimal conditions of UV irradiation of titanium plate for the adhesion of mouse osteoblast MC3T3-E1 cells. The viable cell number was determined by MTT method. UV irradiation at two different wavelengths (253.7 and 365 nm) enhanced the cell attachment on titanium plate to comparable extents. The optimal UV exposure duration was 20 minutes and prolonged irradiation slightly reduced cell attachment. The attached cells proliferated during 24 hours, accompanied by the enhanced consumption of extracellular glutamine and arginine. The present study supports the previous reports of the efficacy of UV irradiation, and this simple and rapid assay system may be applicable for the study of the interaction of osteoblast and UV-activated titanium plates.