Different Orientations Moderate Static Magnetic Fields Prevent Bone Loss and Improve the Mechanical Properties in Ovariectomized Mice.

Various studies have indicated that moderate static magnetic fields (MMFs) could inhibit bone loss and facilitate bone fracture healing. The biological effects of static magnetic fields vary depending on their orientation. Herein, we investigated the effects of MMF in different orientations on bone loss in ovariectomized (OVX) mice. The OVX mice were exposed to 20-100 mT MMFs with magnetic field lines oriented in the N-upward and S-upward directions for 8 weeks, respectively. Then, the bone mass, microarchitecture, mechanical properties, and turnover markers were evaluated. The results showed that both N-upward and S-upward MMFs exposure prevented the decrease of bone mineral density (BMD) and bone mineral content (BMC) induced by OVX, improved the bone microstructure, and enhanced the bone mechanical properties. The serum bone formation markers propeptide of type I procollagen (P1NP) and osteocalcin (OCN) have been increased by MMFs exposure, while bone resorption marker beta-isomer of the C-terminal telopeptide of type I collagen (β-CTX) has been decreased by MMFs exposure in OVX mice. Meanwhile, MMFs exposure decreased osteoclast distribution on the surface of trabecular bone and cortical bone. N-upward MMF exposure increased osteoblast number per bone surface (N.Ob/BS) in trabecular bone. Moreover, mice under N-upward orientation MMFs exposure exhibited higher stiffness, elastic modulus, and total energy absorption in terms of tibial mechanical properties compared to S-upward orientation MMFs exposure. In conclusion, these results demonstrate that 20-100 mT MMFs exposure with different orientations suppressed the ovariectomized-induced bone loss and mechanical properties degradation in mice, and the N-upward MMFs hold superior effects.