Icariin Ameliorates Postmenopausal Osteoporosis by Modulating Phosphodiesterase 5A-Mediated RANKL/OPG Signaling

To investigate the effects of icariin on postmenopausal osteoporosis (PMOP) and its underlying molecular mechanisms. A PMOP rat model was established by ovariectomy and treated with icariin alone or combined with estrogen. Bone mineral density (BMD), serum estradiol (E2), osteocalcin (OCN), and CTX-I were measured. Bone histomorphology was assessed using HE staining and immunohistochemistry. In vivo safety was evaluated by body weight, organ indices, serum ALT, AST, BUN, CREA, and liver/kidney HE staining. In vitro, a co-culture system of MC3T3-E1 osteoblasts and RAW264.7 osteoclasts was constructed to evaluate icariin's effects on osteogenesis and osteoclastogenesis, with CCK-8 and lactate dehydrogenase assays for safety. Mechanisms were further explored via ALP/ARS staining, molecular docking, RT-qPCR, Western blot, dual-luciferase assays, and PDE5A knockdown/overexpression. Icariin significantly increased BMD, elevated serum E2 and OCN, reduced CTX-I, and improved trabecular microarchitecture in PMOP rats. Icariin promoted osteoblastic differentiation/mineralization while suppressing osteoclast activity in vitro. PDE5A was highly expressed in PMOP; icariin downregulated PDE5A, inhibited RANKL, and upregulated OPG, thereby blocking NF-κB activation, enhancing Runx2 and OCN expression, and reducing cathepsin K and NFATc1. PDE5A overexpression partially reversed icariin's effects. Icariin at high doses showed no hepatorenal or osteoblast toxicity in vivo or in vitro, as per serum, histopathology, and LDH. Icariin promotes osteogenesis and inhibits osteoclastogenesis by downregulating PDE5A and modulating RANKL/OPG signaling, thereby restoring bone metabolic balance and exerting osteoprotective effects against PMOP, with a synergistic action when combined with estrogen and a favorable safety profile both in vivo and in vitro.