Aminobisphosphonates Cause Osteoblast Apoptosis an

Authors: Aymen I Idris Javier Rojas Iain R Greig Rob J van’t Hof Stuart H Ralston

Publish Date: 2008/02/08

Volume: 82, Issue: 3, Pages: 191-201

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Abstract

Bisphosphonates are widely used for the treatment of bone diseases associated with increased osteoclastic bone resorption Bisphosphonates are known to inhibit biochemical markers of bone formation in vivo but it is unclear to what extent this is a consequence of osteoclast inhibition or a direct inhibitory effect on cells of the osteoblast lineage In order to investigate this issue we studied the effects of various bisphosphonates on osteoblast growth and differentiation in vitro The aminobisphosphonates pamidronate and alendronate inhibited osteoblast growth caused osteoblast apoptosis and inhibited protein prenylation in osteoblasts in a dosedependent manner over the concentration range 20−100 μM Further studies showed that alendronate in a dose of 01 mg/kg inhibited protein prenylation in calvarial osteoblasts in vivo indicating that alendronate can be taken up by osteoblasts in sufficient amounts to inhibit protein prenylation at clinically relevant doses Pamidronate and alendronate inhibited bone nodule formation at concentrations 10fold lower than those required to inhibit osteoblast growth These effects were not observed with nonnitrogencontaining bisphosphonates or with other inhibitors of protein prenylation and were only partially reversed by cotreatment with a fourfold molar excess of ßglycerol phosphate We conclude that aminobisphosphonates cause osteoblast apoptosis in vitro at micromolar concentrations and inhibit osteoblast differentiation at nanomolar concentrations by mechanisms that are independent of effects on protein prenylation and may be due in part to inhibition of mineralization While these results need to be interpreted with caution because of uncertainty about the concentrations of bisphosphonates that osteoblasts are exposed to in vivo our studies clearly demonstrate that bisphosphonates exert strong inhibitory effects on cells of the osteoblast lineage at similar concentrations to those that cause osteoclast inhibition This raises the possibility that inhibition of bone formation by bisphosphonates may be due in part to a direct inhibitory effect on cells of the osteoblast lineage

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