Effect of Zoledronate on BMP induced osteoinduction in vitro

Background: Patients receiving bisphosphonates can develop bisphosphonate-associated osteonecrosis of the jaw (bONJ), the chronic exposure of necrotic bone in the oral cavity. It is hypothesized that BMP may be useful in the treatment of bONJ, however it is unclear whether bisphosphonates alter the osteoinductive activity of BMP.

Objective: To investigate the direct effect of the bisphosphonate zoledronate (ZOL) on BMP induced osteogenic cell differentiation.

Methods: C2C12 cells were cultured in the presence or absence of rhBMP-2 with increasing doses of ZOL (0–0.1mM). The toxic effect of ZOL was evaluated by measuring lactate dehydrogenase (LDH) activity in the medium. Alkaline phosphatase (ALP) activity and protein content of the cell layer was measured to assess cell response to BMP. Data was analyzed by 2-way ANOVA.

Results: LDH activity was not affected by ZOL, however in groups with and without rhBMP-2 ALP activity increased at the highest ZOL doses(P<0.001). BMP treatment significantly increased ALP activity (P<0.001) in all groups, however ZOL reduced cell response to BMP (P<0.001). Groups exposed to ZOL >0.01mM had reduced protein content in both BMP treated and control groups (P<0.001). We also noted an increased number of cells that were floating in the media of groups treated with the highest dose of ZOL.

Conclusions: The decrease in protein content in the absence of elevated LDH, and the associated observation of increased cell detachment, suggests ZOL may affect cell adhesion, without killing the cells. Zoledronate clearly suppressed the response of the C2C12 cells to BMP. However, even in the presence of very high levels of ZOL (above those estimated to be reached during IV infusions of ZOL), BMP is able to induce osteogenic differentiation suggesting that it may be useful in the treatment of bONJ.

Funding UofT Dentistry Summer Student program