Dose-dependent metabolic effect of zoledronate on primary human osteoblastic cell cultures.

OBJECTIVES: To evaluate the in vitro effect of the bisphosponate zoledronate on metabolic activity, proliferation and viability of human osteoblasts.
METHODS: Primary human osteoblasts cultures were obtained from cancellous bone of healthy subjects undergoing bone marrow biopsy. Cell cultures were treated with crescent concentrations of zoledronate (10⁻¹⁰to 10⁻³), with and without 1,25(OH)2 vitamin D3. In these experimental conditions we evaluated cells viability and proliferation using the MMT colorimetric test, cell apoptosis by measurement of Caspase 3 activity and metabolic cell activity through alkaline phosphatase activity and osteocalcin production.
RESULTS: Osteocalcin and alkaline phosphatase synthesis was significantly enhanced by 10⁻¹⁰ M to 10⁻⁵ M zoledronate concentrations, whereas was dramatically decreased by higher drug concentrations. Vitamin D3 enhanced the positive metabolic effect of zoledronate. The effect of zoledronate on cell proliferation was variable and dose-dependent. While no effect was observed with lower drug concentrations (10⁻¹⁰ M to 10⁻⁸ M), zoledronate 10⁻⁷ M increased cell proliferation. Conversely, concentrations higher than 10⁻⁷ M significantly reduced cell proliferation, in a dose-dependent manner. Osteoblast apoptosis was enhanced after treatment with the highest zoledronate concentrations. The maximum positive effect on osteoblasts metabolic activity and proliferation was observed with the zoledronate concentrations corresponding to those theoretically reached in bone microenvironment when zoledronate is used in clinical practice for post-menopausal osteoporosis treatment.
CONCLUSIONS: The results of this study confirm that bisphosphonates exert different cellular biochemical effects depending on dosage and support the hypothesis that their positive effect on bone mineral density could be partially due to an anabolic action on bone forming cells.