Alendronate-induced atypical bone fracture: evidence that the drug inhibits osteogenesis.

Alendronate (ALN) is used for the treatment of post-menopausal osteoporosis. By reducing bone turnover, it increases bone mineral density. However, recent reports suggest an increased risk of atypical bone fractures after long-term ALN administration. Despite its well-known anti-osteoclastic activity, it is unclear whether ALN also suppresses human mesenchymal stem cell (hMSC)-mediated osteogenesis, thus possibly resulting in atypical bone fragility. We hypothesized that ALN does this and we look at its in vitro effects on osteogenesis. Morphological analysis, reverse transcriptase polymerase chain reaction, cell viability, alkaline phosphatase (ALP) activity and mineralization assays were investigated in hMSCs treated with a wide range of ALN. After treatment with high concentrations of ALN for 3 and 7 days, cell viability was significantly reduced and cell morphology was altered. Osteogenic differentiation of hMSCs was also substantially suppressed as demonstrated by decreased ALP activity although ALN did not affect osteogenic-related genes tested. Furthermore, ALN at all concentrations tested drastically inhibited alizarin red S-positive mineralized matrix. ALN has a strong inhibitory effect on hMSC-mediated osteogenesis by suppressing cell proliferation, osteoblast differentiation and function. The insight gained may help in the development of safer alternatives.