Raloxifene inhibits bone loss and improves bone strength through an Opg-independent mechanism

The osteoblast-derived paracrine factor osteoprotegerin (OPG) is considered to play a key role in inhibition of osteoclast formation and activity. Recently, raloxifene, a nonsteroidal benzothiophene, was found to exert anti-resorptive effects via modulating OPG expression in osteoblasts. To explore whether raloxifene regulates bone metabolism via an OPG-dependant pathway in vivo, we investigated the effects of raloxifene on bone loss in Opg-deficient mice. The results show that bone mineral density and bone strength are increased in mice deficient for Opg after treatment with raloxifene for 30 days. Histomorphometric analysis shows that raloxifene can increase bone trabecular area and decrease the number of osteoclasts in Opg (-/-) mice. Moreover, raloxifene reduces Rankl transcription and serum level of Rankl, which is dramatically increased in Opg knockout mice. These results suggest that raloxifene-induced inhibition of bone resorption may be independent of Opg pathway in mice.