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.

中文翻译：

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0.2~0.4T静磁场促进小鼠后肢卸荷骨丢失恢复

摘要

目的

骨质流失是长期太空飞行任务中与长时间失重相关的最严重的医学问题之一。长时间太空飞行后骨骼重新加载表明丢失的骨骼恢复不完全，这可能导致宇航员返回地球时骨折的风险增加。大量研究揭示了静磁场 (SMF) 在治疗各种骨病方面的能力，但尚不清楚 SMF 在卸载过程中是否对卸载小鼠的骨骼质量具有潜在的调节作用。本研究旨在研究 0.2-0.4 T 全身 SMF 暴露对卸载引起的骨质流失恢复的潜在影响。

材料和方法

8 周龄雄性 C57BL/6J 小鼠进行后肢卸载 (HLU) 4 周，然后在地磁场 (GMF) 和 SMF 0.2-0.4 T 下重新加载小鼠 4 周。骨质量指标，包括骨通过双能 X 射线吸收仪 (DEXA)、微型计算机断层扫描 (Micro-CT) 和 3-point弯曲。通过骨组织形态计量学和血清生化测定评估骨转换。

结果

我们发现，SMF 暴露 4 周显着促进了 HLU 诱导的 BMD 和 BMC 降低、骨微结构恶化和骨强度降低的恢复。骨转换测定的结果显示，SMF 暴露 4 周后，重新加载小鼠的骨小梁破骨细胞数量和血清 TRAP-5b 水平降低，而 SMF 显示骨骼成骨细胞数量和血清骨钙素水平没有显着改变。

结论

总之，我们的研究结果表明，0.2-0.4 T 的 SMF 通过抑制重载小鼠骨吸收的增加促进了卸载引起的骨质流失的恢复，并表明 SMF 可能成为维持宇航员着陆后骨骼健康的有希望的生物物理对策.