Rehmanniae Radix Preparata suppresses bone loss and increases bone strength through interfering with canonical Wnt/β-catenin signaling pathway in OVX rats

A Summary Rehmanniae Radix Preparata (RRP) improves bone quality in OVX rats through the regulation of bone homeostasis via increasing osteoblastogenesis and decreasing osteoclastogenesis, suggesting it has a potential for the development of new anti-osteoporotic drugs. Introduction Determine the anti-osteoporotic effect of RRP in ovariectomized (OVX) rats and identify the signaling pathway involved in this process. Methods OVX rats were treated with RRP aqueous extract for 14 weeks. The serum levels of tartrate-resistant acid phosphatase (TRAP), receptor activator of nuclear factor kappa-B ligand(RANKL), alkaline phosphatase (ALP), and osteoprotegerin (OPG) were determined by ELISA. Bone histopathological alterations were evaluated by H&E, Alizarin red S, and Safranin O staining. Bone mineral density (BMD) and bone microstructure in rat femurs and lumbar bones were determined by dual-energy X-ray absorptiometry and micro-computed tomography. Femoral bone strength was detected by a three-point bending assay. The expression of Phospho-glycogen synthase kinase 3 beta (p-GSK-3), GSK-3, Dickkopf-related protein 1 (DKK1), cathepsin K, OPG, RANKL, IGF-1, Runx2, beta-catenin, and p-beta-catenin was determined by western blot and/or immunohistochemical staining. Results Treatment of OVX rats with RRP aqueous extract rebuilt bone homeostasis demonstrated by increasing the levels of OPG as well as decreasing the levels of TRAP, RANKL, and ALP in serum. Furthermore, RRP treatment preserved BMD and mechanical strength by increasing cortical bone thickness and epiphyseal thickness as well as improving trabecular distribution in the femurs of OVX rats. In addition, RRP downregulated the expression of DKK1, sclerostin, RANKL, cathepsin K, and the ratio of p-beta-catenin to beta-catenin, along with upregulating the expression of IGF-1, beta-catenin, and Runx2 and the ratio of p-GSK-3 beta to GSK-3 beta in the tibias and femurs of OVX rats. Echinacoside, jionoside A1/A2, acetoside, isoacetoside, jionoside B1, and jionoside B2 were identified in the RRP aqueous extract. Conclusion RRP attenuates bone loss and improves bone quality in OVX rats partly through its regulation of the canonical Wnt/beta-catenin signaling pathway, suggesting that RRP has the potential to provide a new source of anti-osteoporotic drugs.