Protective effect of steroidal saponins from rhizome of Anemarrhena asphodeloides on ovariectomy-induced bone loss in rats

Aim: To investigate the protective effect of steroidal saponins from Anemarrhena asphodeloides (ATS) on ovariectomy (OVX)-induced bone loss. Methods: Sprague-Dawley rats were divided into sham and OVX groups. The OVX rats were treated with vehicle, nylestriol or steroidal saponins extract for 12 weeks. Serum calcium, phosphorus, estradiol (E2), osteocalcin concentration and serum alkaline phosphatase activity were measured. Bone density was assayed by dual-energy X-ray absorptiometry. The undecalcified longitudinal proximal tibial metaphysical (PTM) sections were cut and stained for histomorphometric analysis of the bone. Results: In OVX rats, alkaline phosphatase activities in serum were markedly increased and concentrations of osteocalcin were decreased by ATS treatment, which had no influence on the body weight. Meanwhile, atrophy of the uterus and descent of bone mineral density (BMD) was suppressed by treatment with ATS. In addition, ATS completely corrected the decreased the concentration of calcium and E2 in serum observed in OVX rats. Histological results showed ATS prevented decreases in trabecular thickness and increases in trabecular separation of proximal tibia metaphysis (PTM) in OVX rats. However, it did not alter osteoclast number in OVX rats. Moreover, ATS (300 mg/kg) had a remarkable effect on promoting bone formation action in OVX rats. Nylestriol treatment decreased the bone formation rate and mineral apposition rate. Conclusion: An adequate supply of steroidal saponins of Anemarrhena asphodeloides prevented OVX-induced bone loss in rats through the promotion of bone formation but not the inhibition of bone resorption.