Study type: Medical/biological study (experimental study)

Sinusoidal Electromagnetic Fields Increase Peak Bone Mass in Rats by Activating Wnt10b/β-Catenin in Primary Cilia of Osteoblasts med./bio.

By: Zhou J, Gao YH, Zhu BY, Shao JL, Ma HP, Xian CJ, Chen KM
Published in: J Bone Miner Res 2019; 34 (7): 1336-1351
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Aim of study (acc. to author)

The effects of exposure of young rats to sinusoidal 50 Hz magnetic fields of different intensities on peak bone mass and the underlying mechanisms of action should be investigated.

Background/further details

Optimizing peak bone mass is considered one of the fundamental ways to prevent osteoporosis. In a previous study, the authors could show that exposure to a 50 Hz magnetic field could increase the peak bone mass in rats (Zhu et al. 2018), disclosing a potential therapeutic tool. In the current study, the optimal magnetic flux density and underlying mechanisms of action should be investigated.
The study comprised an in vivo and an in vitro part. For the in vivo tests, young rats were randomly divided into the following groups (n=10, respectively): exposure to a magnetic field of 1) 0,1 mT, 2) 0,6 mT, 3) 1,2 mT, 4) 1,8 mT, 5) 2,4 mT and a control group.
For in vitro experiments, calvarial osteoblasts were isolated from young rats and exposed like group 1-5. Moreover, they were exposed to a 1,8 mT magnetic field for 5 min, 10 min, 15 min, 30 min, 45 min, 60 min and 90 min and in a control group. To test whether osteogenic differentiation was mediated via the Wnt10b/b-catenin signaling pathway, cells were partially tested with the addition of Dickkopf-1 (DKK-1), an inhibitor of the Wnt signaling pathway. To investigate whether the primary cilium is involved in osteogenic differentiation of osteoblasts, the ciliogenesis was blocked using a siRNA sequence.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 50 Hz
Exposure duration: in vivo: 90 min/day for 2 months, in vitro: 90 min
Exposure 2: 50 Hz
Exposure duration: in vivo: 90 min/day for 2 months, in vitro: 90 min
Exposure 3: 50 Hz
Exposure duration: in vivo: 90 min/day for 2 months, in vitro: 90 min
Exposure 4: 50 Hz
Exposure duration: in vivo: 90 min/day for 2 months, in vitro: 90 min
Exposure 5: 50 Hz
Exposure duration: in vivo: 90 min/day for 2 months, in vitro: 90 min
Exposure 6: 50 Hz
Exposure duration: 5 min
only for in vitro tests
Exposure 7: 50 Hz
Exposure duration: 10 min
only for in vitro tests
Exposure 8: 50 Hz
Exposure duration: 15 min
only for in vitro tests
Exposure 9: 50 Hz
Exposure duration: 30 min
only for in vitro tests
Exposure 10: 50 Hz
Exposure duration: 45 min
only for in vitro tests
Exposure 11: 50 Hz
Exposure duration: 60 min
only for in vitro tests
Exposure 12: 50 Hz
Exposure duration: 90 min
only for in vitro tests

Exposure 1

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration in vivo: 90 min/day for 2 months, in vitro: 90 min
Exposure setup
Exposure source
Setup the solenoid for in vitro tests was 27 cm long and 14 cm in diameter and could create magnetic fields of high uniformity; the exposure system for in vivo tests based on the same patent and also produced homogeneous magnetic fields (no further details provided)
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 0.1 mT - calibration - -

Exposure 2

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration in vivo: 90 min/day for 2 months, in vitro: 90 min
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 0.6 mT - calibration - -

Exposure 3

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration in vivo: 90 min/day for 2 months, in vitro: 90 min
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1.2 mT - calibration - -

Exposure 4

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration in vivo: 90 min/day for 2 months, in vitro: 90 min
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1.8 mT - calibration - -

Exposure 5

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration in vivo: 90 min/day for 2 months, in vitro: 90 min
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 2.4 mT - calibration - -

Exposure 6

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 5 min
Additional info only for in vitro tests
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1.8 mT - calibration - -

Exposure 7

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 10 min
Additional info only for in vitro tests
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1.8 mT - calibration - -

Exposure 8

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 15 min
Additional info only for in vitro tests
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1.8 mT - calibration - -

Exposure 9

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 30 min
Additional info only for in vitro tests
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1.8 mT - calibration - -

Exposure 10

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 45 min
Additional info only for in vitro tests
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1.8 mT - calibration - -

Exposure 11

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 60 min
Additional info only for in vitro tests
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1.8 mT - calibration - -

Exposure 12

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 90 min
Additional info only for in vitro tests
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1.8 mT - calibration - -

Reference articles

  • Wang YY et al. (2019): Pulsed electromagnetic fields promote bone formation by activating the sAC-cAMP-PKA-CREB signaling pathway
  • Zhu BY et al. (2018): Exposure Duration Is a Determinant of the Effect of Sinusoidal Electromagnetic Fields on Peak Bone Mass of Young Rats
  • Yan JL et al. (2015): Pulsed electromagnetic fields promote osteoblast mineralization and maturation needing the existence of primary cilia

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • before exposure
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

Exposure to a 0.1 mT (group 1) and 1.8 mT (group 4) magnetic field increased the peak bone mass of young rats significantly compared to the control group by increasing bone formation. Group 4 showed the most distinct increase, in groups 2 and 3, no effects were found. The gene expression levels of COL1α1 and Wnt10b, a ligand of the osteogenic Wnt/b-catenin signal pathway, were significantly increased compared to the control group.
In in vitro-tests, exposure to the magnetic field promoted osteogenic differentiation and maturation of rat calvarial osteoblasts through activating the Wnt10b/b-catenin signal pathway. This effect was most distinct and statistically significant compared to the control group after an exposure duration of 90 min. This osteogenesis-promoting effect was found to depend on the primary cilium in osteoblasts. Wnt10b was normally localized at the bases of primary cilia, and disappeared (or was released) upon magnetic field exposure. The primary cilium showed the greatest length upon exposure to a 1.8 mT magnetic field with the largest amount of Wnt10b at the same time.
The authors conclude that exposure to a 1.8 mT sinusoidal magnetic field might increase the peak bone mass of young rats by promoting osteogenic differentiation of osteoblasts. This might be mediated by Wnt10b at the primary cilium and the subsequent activation of the Wnt/b-catenin signal pathway.

Study character:

Study funded by

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