Moderate-intensity rotating magnetic fields do not affect bone quality and bone remodeling in hindlimb suspended rats.

Da Jing,Shichao Tong,Jing Cai,Xinmin Xu,Xiaoming Wu,Yan Wu,Kangning Xie,Qiaoling Xu,Chi Tang,Erping Luo,Guanghao Shen,Juan Liu,Wei Guo,Mingming Zhai,Maogang Jiang,Robert Lafrenie

doi:10.1371/journal.pone.0102956

Abstract

Abundant evidence has substantiated the positive effects of pulsed electromagnetic fields (PEMF) and static magnetic fields (SMF) on inhibiting osteopenia and promoting fracture healing. However, the osteogenic potential of rotating magnetic fields (RMF), another common electromagnetic application modality, remains poorly characterized thus far, although numerous commercial RMF treatment devices have been available on the market. Herein the impacts of RMF on osteoporotic bone microarchitecture, bone strength and bone metabolism were systematically investigated in hindlimb-unloaded (HU) rats. Thirty two 3-month-old male Sprague-Dawley rats were randomly assigned to the Control (n = 10), HU (n = 10) and HU with RMF exposure (HU+RMF, n = 12) groups. Rats in the HU+RMF group were subjected to daily 2-hour exposure to moderate-intensity RMF (ranging from 0.60 T to 0.38 T) at 7 Hz for 4 weeks. HU caused significant decreases in body mass and soleus muscle mass of rats, which were not obviously altered by RMF. Three-point bending test showed that the mechanical properties of femurs in HU rats, including maximum load, stiffness, energy absorption and elastic modulus were not markedly affected by RMF. µCT analysis demonstrated that 4-week RMF did not significantly prevent HU-induced deterioration of femoral trabecular and cortical bone microarchitecture. Serum biochemical analysis showed that RMF did not significantly change HU-induced decrease in serum bone formation markers and increase in bone resorption markers. Bone histomorphometric analysis further confirmed that RMF showed no impacts on bone remodeling in HU rats, as evidenced by unchanged mineral apposition rate, bone formation rate, osteoblast numbers and osteoclast numbers in cancellous bone. Together, our findings reveal that RMF do not significantly affect bone microstructure, bone mechanical strength and bone remodeling in HU-induced disuse osteoporotic rats. Our study indicates potentially obvious waveform-dependent effects of electromagnetic fields-stimulated osteogenesis, suggesting that RMF, at least in the present form, might not be an optimal modality for inhibiting disuse osteopenia/osteoporosis.

Highlights

Osteoporosis, a progressive ‘silent bone disease’ caused by age, disuse or disease, is characterized by loss of bone mass and deterioration of bone microarchitecture, resulting in pain and deformity and increased risk of bone fracture [1,2]
In the present investigation, the efficiency of rotating magnetic fields (RMF) exposure on disuse-induced bone loss was systematically evaluated via analyses for serum biochemical, bone biomechanical, mCT and histomorphometric parameters in rats subjected to tail suspension
Accumulating evidence has demonstrated the promotional effects of pulsed electromagnetic fields (PEMF) and static magnetic fields (SMF) on osteogenesis both in vivo and in vitro, whereas few studies have reported the efficiency of RMF in the musculoskeletal system

Summary

Introduction

Osteoporosis, a progressive ‘silent bone disease’ caused by age, disuse or disease, is characterized by loss of bone mass and deterioration of bone microarchitecture, resulting in pain and deformity and increased risk of bone fracture [1,2]. Bone loss due to the removal of weight-bearing physical activities, which occurs during therapeutic bed rest, limb immobilization and spaceflight, has become a non-negligible health concern in clinics and space medicine. Mechanical unloading induces negative skeletal calcium homeostasis, uncoupling of osteoclast and osteoblast activities, and resultant bone mineral loss [3]. It has been proved that individuals subjected to long-term bed rest or immobilization exhibited dramatic bone mass loss, deterioration of cancellous and cortical bone microarchitecture, and increased risk of falls and bone fracture [7,8]. In view of the side effects or high cost of antiosteoporosis drugs (e.g., bisphosphonates, calcitonin and hormones) [9,10,11], safe and noninvasive biophysical stimuli for the prevention and treatment of disuse osteoporosis might be more promising in clinical application, and especially favorable for the use of spaceflight

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Results

Conclusion