Icariin alleviates ovariectomy-induced osteoporosis by promoting M2 macrophage polarization and suppressing osteoclast activation.

BACKGROUND

Osteoporosis is a prevalent skeletal disorder marked by reduced bone strength and increased fragility, especially in postmenopausal women and older adults. Icariin (ICA), a natural flavonoid, has been reported to stimulate osteoblastogenesis and suppress osteoclast activity.

METHODS

Female BALB/c mice underwent bilateral ovariectomy (OVX) or sham surgery and were maintained for 12 weeks. ICA (80 mg/kg in distilled water, oral gavage) was administered once daily from postoperative week 1 through week 12. Femoral bone mineral density (BMD) and trabecular architecture were evaluated by dual-energy X-ray absorptiometry, hematoxylin-eosin (H&E) staining, and micro-computed tomography (micro-CT). Cathepsin K (CTSK) immunohistochemistry was used to assess osteoclast activity in situ. Macrophage polarization and inflammatory mediators were assessed by RT-qPCR and Western blotting. Osteoclast activation markers were evaluated by Nfatc1 and Mmp9 expression.

RESULTS

ICA significantly increased BMD, improved trabecular microarchitecture on H&E and micro-CT, and reduced CTSK-positive osteoclast area in OVX mice. ICA promoted M2 macrophage polarization while suppressing M1 markers, as evidenced by increased Arg1 and CD206 expression and decreased iNOS (inducible nitric oxide synthase) and CD86 levels, and reduced inflammation by decreasing Tnf/Il1b while increasing Il10 (qPCR also showed upregulation of Tgfb1 and IL-4). ICA further suppressed osteoclast activation, as indicated by lower Nfatc1 and Mmp9 levels.

CONCLUSIONS

In a murine model of ovariectomy-induced postmenopausal osteoporosis, ICA promotes M2 macrophage polarization, mitigates inflammation, and attenuates osteoclast activation, as evidenced by decreased expression of NFATc1, MMP-9, and CTSK, thereby improving bone density and structure.