Modifications of bone material properties in postmenopausal osteoporotic women long-term treated with alendronate

Objective: Given recent concern about long-term safety of bisphosphonate (BP) therapy, the effects of long-term alendronate (ALN) therapy on intrinsic bone properties were studied among postmenopausal osteoporotic (PMOP) women. Design and methods: Transiliac bone biopsies were obtained from 32 outpatient clinic PMOP women treated with oral ALN for 6.4 +/- 2.0 years. Variables reflecting bone mineralization were measured both at tissue level using quantitative microradiography and at crystal level by Fourier transform infrared microspectroscopy. Bone microhardness was investigated by Vickers indentation tests. Results were compared with those from 22 age-matched untreated PMOP women. Results: Long-term treatment with ALN was associated with a 84% (P<0.001) lower remodeling activity compared with untreated PMOP women, leading to an increased degree of mineralization in both cortical and trabecular bone (+9 and +6%, respectively, P<0.05). Despite a more mature and more mineralized bone matrix, after treatment, cortical and trabecular microhardness and crystallinity were lower than that measured in untreated patients. None of the variables reflecting material properties were significantly correlated to the duration of the treatment. Conclusion: Increased degree of mineralization associated with lower crystallinity and microhardness in ALN long-term-treated PMOP women suggests that ALN could alter the quality of bone matrix. The study also suggested that after 3 years of treatment, the changes in material properties are not dependent on the duration of the treatment. Further studies are requested to assess the short-term (<3 years) effects of BPs on bone intrinsic properties.