Sequential treatment of ovariectomized mice with bFGF and risedronate restored trabecular bone microarchitecture and mineralization

Abstract

Basic fibroblast growth factor (bFGF), a potent mitogen, has been found to restore trabecular bone mass and connectivity in osteopenic rats. The purpose of this study was to determine how sequential treatment of ovariectomized (OVXed) mice with bFGF followed by risedronate would restore trabecular microarchitecture and improve bone strength through alterations in bone mineralization. Six-month old female Swiss-Webster mice were OVXed or sham-operated and left untreated for 4 weeks to develop osteopenia. At week 5, a group of Sham and OVXed mice were treated with vehicle, and 3 other groups of OVXed mice were treated with bFGF (1 mg/kg daily, s.c., 5x/week) for 3 weeks. At week 8, one group of bFGF-treated mice was sacrificed and the other two bFGF-treated groups were treated with vehicle or risedronate (Ris, 5 microg/kg, s.c., 3x/week) for an additional 6 weeks. Study endpoints included trabecular microarchitecture by microCT, histomorphometry, bone turnover, degree of bone mineralization (DBM), and whole bone strength for the lumbar vertebral body. Compared to sham-operated animals, OVXed mice had significant reductions in trabecular bone volume, connectivity density, DBM, and bone biomechanical properties (P < 0.05). Treatment with bFGF resulted in higher trabecular bone structure and bone strength compared to pre-treatment sham control (P < 0.05). Treatment of OVXed mice with bFGF for 3 weeks followed by 6 weeks Ris maintained the trabecular microarchitecture gained by bFGF treatment, and DBM and bone strength were restored to baseline control levels. Also compared to Sham-operated animals, serum TGF-beta1 was transiently increased after OVX, increased an additional 100% after bFGF withdrawal, and decreased by 30% with risedronate. In addition, DBM was the strongest predictor for bone biomechanical properties (R2 > 0.7, P < 0.001). Serum TGF-beta1 correlated with bone turnover (DPD/Cr, osteocalcin) and was negatively correlated to DBM. Thus, in osteopenic mice, sequential treatment with bFGF followed by risedronate increased trabecular bone microarchitecture, DBM, and bone strength. In addition, suppression of the serum TGF-beta1 with risedronate was associated with increased DBM. Therefore, sequential treatment with bFGF and Ris restores trabecular architecture and allows mineralization of bone to increase, which appears to be beneficial to bone strength.