Department of Spine Surgery, People's Hospital of Longhua, Affiliated Hospital of Southern Medical University, Shenzhen, China.
Research & Development Institute of Northwestern Polytechnical University in Shenzhen, Shenzhen, China.
Int J Radiat Biol. 2021;97(5):746-754. doi: 10.1080/09553002.2021.1900944. Epub 2021 Apr 19.
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.
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.
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.
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.
在长期的太空飞行任务中，骨丢失是与长时间失重相关的最严重的医学问题之一。长期太空飞行后的骨骼再加载表明丢失的骨没有完全恢复，这可能会增加宇航员返回地球时骨折的风险。大量研究表明，静磁场（SMFs）在治疗各种骨骼疾病方面具有潜力，然而，目前尚不清楚 SMFs 是否对未加载小鼠在卸载过程中骨骼质量具有潜在的调节作用。本研究旨在研究全身 SMF 暴露在 0.2-0.4 T 对缓解骨骼丢失的恢复的潜在影响。
8 周龄雄性 C57BL/6J 小鼠接受后肢去负荷（HLU）4 周，随后在 GMF 和 0.2-0.4 T 的 SMF 下重新加载 4 周。通过双能 X 射线吸收法（DEXA）、微计算机断层扫描（Micro-CT）和三点弯曲测量，检测骨质量指标，包括骨矿物质密度（BMD）和骨矿物质含量（BMC）、骨微结构和骨机械性能。通过骨组织形态计量学和血清生化分析评估骨转换。
我们发现，SMF 暴露 4 周可显著促进 HLU 引起的 BMD 和 BMC 下降、骨微结构恶化和骨强度降低的恢复。骨转换测定结果表明，SMF 暴露 4 周可降低再加载小鼠骨小梁的破骨细胞数量和血清 TRAP-5b 水平，而 SMF 对骨骼成骨细胞数量和血清骨钙素水平无明显影响。
综上所述，我们的研究结果表明，0.2-0.4 T 的 SMF 通过抑制再加载小鼠骨吸收的增加促进了骨骼丢失的恢复，表明 SMF 可能成为宇航员着陆后维持骨骼健康的一种有前途的物理对策。
