Sclerostin Antibody Treatment Increases Bone Formation, Bone Mass, and Bone Strength of Intact Bones in Adult Male Rats

We investigated the systemic effect of sclerostin monoclonal antibody (Scl-Ab) treatment on intact non-operated bones in an open osteotomy male Sprague Dawley (SD) rat model. Six-month-old male SD rats were subjected to transverse osteotomy at the right femur mid-shaft. Rats were injected subcutaneously with vehicle or Scl-Ab (25 mg/kg, 2 times per week) treatment for 9 weeks. Compared with vehicle control, Scl-Ab treatment significantly improved trabecular and cortical bone mass and microarchitecture at L5 vertebrae and left femora by micro-CT at week 6 and 9. Mechanical testing showed that Scl-Ab treatment resulted in significantly higher stiffness, energy to failure and ultimate load at the femora at week 9. Mineral apposition rate, mineralizing surface and bone formation rate on the trabecular bone in the distal femora was significantly increased in Scl-Ab group at week 6 and 9. The administered Scl-Ab was localized in the osteocytes and beta-catenin was strongly expressed in osteoblasts. Scl-Ab treatment significantly increased serum P1NP level and there was no between-group difference in serum level of CTX-1. In conclusion, Scl-Ab treatment could induce rapid and sustained increase in bone formation, bone mass and bone strength in non-operated bones. Sclerostin inhibition might be advantageous to prevent secondary fracture(s).