Bisphosphonate modulates cementoblast behavior in vitro

Background: Cementum formation is deemed to be instrumental for the successful regeneration of periodontal tissues, and thus events and modifiers of cementum formation and mineralization need to be determined. This study aimed to determine whether the bisphosphonate 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) altered the behavior of immortalized cementoblasts (osteocalcin-cementoblasts [OCCM]). Methods: OCCM from transgenic mice were exposed to HEBP at concentrations ranging from 0.01 to 10.0 mu M. The assays performed included the count of cell number for proliferation, Northern blot analysis for gene expression (up to 10 days for core binding factor alpha-1 [Cbfa 11, bone sialoprotein [BSP], osteocalcin [OCN], and osteopontin [OPN], markers for cementoblast/osteoblast maturation/mineralization), von Kossa stain and alizarin red S stain for mineralization, and enzyme assay (p-nitrophenol phosphate cleavage) for alkaline phosphatase (ALP) activity. Results: Mineral nodule formation was inhibited at the higher doses of HEBP (1.0 and 10.0 mu M) only. At early stages (1, 3, and 6 days), gene expression assays revealed only subtle changes in treated cells versus untreated cells, but by day 10, groups treated with lower doses (0.01 and 0.1 mu M) were markedly different at the gene expression level. OCN was significantly downregulated (70%) at the lowest dose, with less pronounced effects at higher doses. In concurrence, the master switch gene for osteoblasts, Cbfa1, was also downregulated at the lower doses. Inversely, OPN mRNA was enhanced at the lower doses. ALP activity was not altered by HEBP. Conclusion: Bisphosphonate alters cementoblast function in vitro through the regulation of gene expression and mineral formation.