Calcium Phosphate Particles Induce Interleukin-8 Expression in a Human Gingival Epithelial Cell Line via the Nuclear Factor-κB Signaling Pathway

Background: Dental calculus is calcified plaque composed primarily of calcium phosphate mineral salts, and there is a clear association between the presence of calculus and the initiation/progression of periodontitis. However, it is still inconclusive whether dental calculus can be a direct causative factor. The authors examined the effect of nano/microsized calcium phosphate particles, which may be generated in the process of early precipitation and/or dissolution of calcium phosphate mineral, on the expression of interleukin (IL)-8 in human gingival epithelial cells. Methods: Primary human gingival epithelial cells and/or a human gingival carcinoma cell line (Ca9-22) were stimulated with calcium phosphate particles. Gene and protein levels were assessed by real-time polymerase chain reaction analysis and enzyme-linked immunosorbent assay, respectively. The activity of nuclear factor (NF)-kappa B signaling was measured by an immunofluorescence assay to evaluate NF-kappa B p65 nuclear translocation. Results: The results show that nano/microsized particles stimulate IL-8 expression in human gingival epithelial cells at gene and protein levels. The activity to induce IL-8 expression depends on the particle size: particles with a diameter of 200 nm are more effective than those of 40-nm and 5-mm diameters. Calcium phosphate particles (diameter 200 nm) stimulated NF-kappa B activity. Pretreatment with BMS-345541, an NF-kappa B signaling inhibitor, inhibited the particle-mediated IL-8 gene induction, suggesting a requirement for the NF-kappa B signaling pathway. Conclusion: These findings suggest that calcium phosphate particles, which may be related to calculus development, may act as a direct causative factor in the pathogenesis of gingival epithelium.