Enhancement of Cytotoxic Activity of Sodium Fluoride against Human Periodontal Ligament Fibroblasts by Water Pressure

Abstract

Whether or not water pressure enhances the cytotoxic activity of sodium fluoride (NaF) against human periodontal ligament fibroblast (HPLF) was investigated. Loading with water pressure (up to 5 g) alone did not affect the cell proliferation, but significantly enhanced the cytotoxic activity of millimolar concentrations of NaF. Cytotoxic activity of NaF was reduced by supplementation with Ca²⁺, whereas it was enhanced by removal of Ca²⁺ from the culture medium. However, the enhancement of cytotoxicity of NaF under water pressure was observed even in the Ca²⁺-free medium. NaF failed to induce apoptosis markers, such as the caspase-3, -8 and -9 activation, the internucleosomal DNA fragmentation, the loss of cell surface microvilli and the changes in intracellular concentration of polyamines. Transmission electron microscopy demonstrated that the combination of NaF and water pressure slightly increased the incidence of the formation of autophagosomes engulfing organella, suggesting the induction of non-apoptotic cell death in HPLF cells. The present study suggests that the external pressure is an additional factor that enhances the cytotoxicity of NaF against HPLF cells.