Low concentrations of zoledronic acid are better at regulating bone formation and repair.

The purpose of this study was to investigate optimal concentrations of zoledronic acid (ZA) in terms of their effect on the proliferation, differentiation, and mineralization of primary osteoblasts (OBs) and fibroblasts (FBs). Primary OBs and FBs isolated from patients with clinical osteogenesis imperfecta (OI) and developmental dysplasia of the hip (DDH) were treated in vitro with serial concentrations of ZA ranging from 10(-3) M to 10(-13) M. An MTT ((3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)) colorimetric assay, flow cytometry, alkaline phosphatase (ALP) determination activity, and alizarin red staining were used to measure the proliferation, differentiation, and mineralization of cells. The MTT assay indicated that high concentrations of ZA may be toxic to cultured cells. No obvious inhibition was observed with a ZA concentration of 10(-7) M to 10(-10) M. Proliferation was evident with a ZA concentration below 10(-11) M (p < 0.05). Flow cytometry analysis revealed that cell cycle was arrested at G1/G0 stage with a ZA concentration ranging from 10(-10) M to 10(-8) M. ZA did not enhance ALP activity at a concentration of 10(-8) M or 10(-10) M. Alizarin red staining indicated the mineralization of primary OBs with a low concentration of ZA (10(-12) M). In conclusion, this in vitro study indicated that ZA-mediated cell proliferation was dose-dependent and that ZA did not inhibit cell proliferation at concentrations below 10(-8) M. These findings suggest low concentrations of ZA have more of an effect on cell differentiation and mineralization, so low concentrations are better at regulating bone formation and repair.