Zoledronic acid suppresses mineralization through direct cytotoxicity and osteoblast differentiation inhibition

Abstract

Zoledronic acid (ZA) is prescribed to treat various metabolic bone diseases. Despite its efficacy in preventing bone loss, ZA has been linked to osteonecrosis of the jaw in several reports. However, a mechanism underlying this occurrence is still unclear. This study was to investigate causative roles of ZA on osseous cellular activities of pre-osteoblastic cell line MC3T3-E1 (MC3T3) and mesenchymal stem cell (MSC). Morphological analysis, RT-PCR, annexin V/PI staining, together with mineralization, cell viability, and alkaline phosphatase (ALP) activity assays were performed. Zoledronic acid treatment decreased bone nodule formation at all concentrations tested (0.01-100 μM). Cell morphologies of both cell types were altered from their normal appearances after the addition of ZA (≥ 5 μM), and cell viability was significantly inhibited at concentrations ≥ 0.1 μM for MC3T3 and at concentrations ≥ 10 μM for MSC. ZA (100 μM) induced apoptosis in MC3T3 and MSC. Furthermore, ALP activity from both cells was strongly reduced when exposed to ZA (≥ 1 μM for MC3T3 and ≥ 5 μM for MSC). ZA also down-regulated Runx 2 and Col I mRNA expressions. With this in vitro study, ZA mediated defective bone mineralization by directly disrupting osteoblast/osteoprogenitor cellular activities at several levels, that is, cell proliferation, osteoblast differentiation, and osteoblast function of both pre-osteoblastic cells and MSC.