Static magnetic field of 0.2–0.4 T promotes the recovery of hindlimb unloading-induced bone loss in mice

Abstract

Purpose

Bone loss is one of the most serious medical problem associated with prolonged weightlessness in long-term spaceflight mission. Skeletal reloading after prolonged spaceflight have indicated incomplete recovery of lost bone, which may lead to an increased risk of fractures in astronauts when returning to Earth. Substantial studies have revealed the capacity of static magnetic fields (SMFs) on treating various bone disorders, whereas it is unknown whether SMFs have the potential regulatory effects on bone quality in unloaded mice during unloading. This study was conducted to investigate the potential effects of whole-body SMF exposure with 0.2–0.4 T on the recovery of unloading-induced bone loss.

Materials and methods

Eight‐week‐old male C57BL/6J mice were subjected to hindlimb unloading (HLU) for 4 weeks, following the mice were reloaded for 4 weeks under geomagnetic field (GMF) and SMF of 0.2–0.4 T. Bone quality indexes, including bone mineral density (BMD) and bone mineral content (BMC), bone microarchitecture, and bone mechanical properties were examined by the measurement of dual energy X-ray absorptiometry (DEXA), micro-computed tomography (Micro-CT), and 3-point bending. Bone turnover was evaluated by bone histomorphometric and serum biochemical assay.

Results

We found that SMF exposure for 4 weeks significantly promoted the recovery in HLU-induced decrease of BMD and BMC, deterioration of bone microarchitecture, and reduction of bone strength. The results from bone turnover determination revealed that SMF exposure for 4 weeks induced lower osteoclast number of trabecular bone and serum TRAP-5b levels in reloaded mice, whereas SMF showed no significant alteration in skeletal osteoblast number and serum osteocalcin levels.

Conclusions

Together, our findings suggest that SMF of 0.2–0.4 T facilitated the recovery of unloading-induced bone loss by inhibiting the increase of bone resorption in reloaded mice, and indicate that SMF might become a promising biophysical countermeasure for maintaining bone health in astronauts after landing.

Keywords:

• Static magnetic fields
• mechanical unloading
• bone loss
• bone recovery
• bone turnover

Acknowledgments

We would like to thank Yi Lyu in the Key Laboratory for Space Bioscience and Biotechnology for the technical assistance.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [52037007 and 51777171].

Notes on contributors

Jiancheng Yang

Jiancheng Yang, PhD, is a Research Assistant in Department of Spine Surgery, People's Hospital of Longhua, Affiliated Hospital of Southern Medical University. His research focuses on biological effects under magnetic field. In particular, he works in the effect of static magnetic field on bone remodeling and osteoporosis.

Shaojie Zhou

Shaojie Zhou is a Graduate Student in Northwestern Polytechnical University. His research focuses on the effect of static magnetic field on osteoporosis.

Huanhuan Lv

Huanhuan Lv, PhD, is an Assistant Professor in School of Life Sciences, Northwestern Polytechnical University. Her research areas include natural pharmacological chemistry, bioactivity screening, metabolomics, iron metabolism, and redox stress. Recently, she has also gradually paid attention to the changes of bone metabolism under magnetic fields.

Min Wei

Min Wei, PhD, is a Dean of the Zhejiang Heye Health Technology Co., Ltd. Main research interests including mechanisms of oxidative stress, inflammation and regulation of body aging, effects of heredity and environment (especially nutrition and diet) on aging, signal pathway screening of senile diseases.

Yanwen Fang

Yanwen Fang is a CEO Assistant of the Zhejiang Heye Health Technology Co., Ltd. She obtained her master degree at Davis School of Gerontology, University of Southern California. Her research focuses on biological effects under magnetic field.

Peng Shang

Peng Shang, PhD, is a Professor in Research & Development Institute of Northwestern Polytechnical University in Shenzhen. He is engaged in biological and medical research on skeletal system and metabolic regulation under special environments, including microgravity and magnetic fields, and the effects of magnetic targeting drugs on osteosarcoma and other cancers.