Effect of bisphosphonates on human gingival fibroblast production of mediators of osteoclastogenesis: RANKL, osteoprotegerin and interleukin-6

Background and Objective: Osteonecrosis of the jaw (ONJ) is associated with bisphosphonate (BP) therapy. BPs alter osteoblast production of mediators of osteoclastogenesis, including interleukin (IL)-6, RANKL and osteoprotegerin (OPG), a RANKL antagonist. This can inhibit bone turnover and lead to necrosis. There is little information on the contribution of gingival fibroblasts, near bone-resorption sites, to the IL-6/RANKL/OPG network, the effects of BPs, or fibroblast involvement in ONJ pathogenesis. Therefore, the objective of this study was to determine the effects of alendronate and pamidronate on the constitutive production, or the lipopolysaccharide (LPS)- or IL-1 beta-stimulated production, of IL-6, RANKL and OPG by human gingival fibroblasts. Material and Methods: Human gingival fibroblasts were derived from explants obtained from healthy individuals with noninflamed gingiva. Cytotoxicity was determined by measuring the activity of a mitochondrial enzyme. Fibroblasts were pre-incubated or not with BPs (0.01 nm-1 mu m), then incubated or not with LPS or IL-1 beta. The concentrations of IL-6, OPG and RANKL were measured using ELISA. Data were analyzed using analysis of variance (ANOVA) and Scheffe's F procedure. Results: LPS and BPs were not cytotoxic. The cells produced IL-6, OPG and RANKL, all of which were stimulated by IL-1 beta or LPS (p < 0.04). BPs generally increased the production of IL-6 and OPG (p < 0.04) and decreased the production of RANKL (p < 0.02). BPs generally further increased the production of LPS- or IL-1 beta-stimulated IL-6 (p < 0.04) and had no effect on, or further increased, the production of LPS- or IL-1 beta-stimulated OPG (p < 0.04). BPs decreased the production of LPS- or IL-1 beta-stimulated RANKL (p < 0.04) and decreased constitutive, LPS-stimulated and IL-1 beta-stimulated RANKL/OPG ratios (p < 0.02). Conclusion: The action of alendronate and pamidronate on human gingival fibroblasts, through altering the production of RANKL and OPG, appears to contribute to a microenvironment favoring the inhibition of bone resorption and ONJ.