Tamim Diab, Jason Wang, Susan Reinwald, Robert E. Guldberg, David B. Burr
Raloxifene (RAL) and alendronate (ALN) improve the biomechanical properties of bone by different mechanisms. The goal here was to investigate the effects of combination treatment of RAL and ALN on the biomechanical properties of vertebral bone. Six-month-old Sprague-Dawley rats (n=80) were randomized into 5 experimental groups (Sham, OVX, OVX+RAL, OVX+ALN, OVX+RAL+ALN; n=16/group). Following sacrifice, structural and derived material biomechanical properties of vertebral bodies were assessed. Density and dynamic histomorphometric measurements were made on cancellous bone. The results demonstrate that the structural biomechanical properties of vertebral bone are improved with the combination treatment. Stiffness and ultimate load of the OVX+RAL and OVX+ALN groups were significantly lower than sham, but the combination treatment with RAL+ALN was not significantly different than sham. Furthermore, the OVX+RAL+ALN group was the only agent-treated group in which the ultimate load was significantly higher than OVX (p<0.05). Cancellous bone fractional volume (BV/TVcanc) and mineral density (aBMD) were also improved with the combination treatment. BV/TVcanc of the OVX+RAL+ALN group was 6.7% and 8.7% greater than the OVX+RAL (p<0.05) and OVX+ALN (p<0.05) groups, respectively. aBMD of the OVX+RAL or OVX+ALN groups were not significantly different than OVX, but the combination treatment was significantly higher than OVX or OVX+RAL alone, and not significantly different from sham. Turnover rates of both the RAL+ALN and ALN alone groups were lower than the RAL alone group (p<0.05). We conclude that the combination treatment of raloxifene and alendronate has beneficial effects on bone volume, resulting in an improvement of the structural properties of vertebral bone.