Elsevier

Bone

Volume 42, Issue 1, January 2008, Pages 74-80
Bone

Deterioration of bone quality by long-term magnetic field with extremely low frequency in rats

https://doi.org/10.1016/j.bone.2007.08.040Get rights and content

Abstract

The aim of our study was to investigate the effects of long-term (45 days) magnetic field (50 Hz, 1 mT; MF) on femur biomechanical parameters of rats. Bone mineral density (BMD) and histological investigation were also evaluated. For this purpose, twenty-four 8-week-old, Wistar–Albino female and male rats were assigned randomly to female control (FC) and MF-exposed rats (F-MF); male control (MC) and MF-exposed rats (M-MF). BMD was measured by dual-energy X-ray absorptiometry. Cross-sectional area of the femoral shaft was evaluated by computerized tomography. Biomechanical measurements were performed at the mid-diaphysis of the left femur with tensile test. Maximum load, displacement, stiffness, energy absorption capacity (structural properties); ultimate stress, ultimate strain, elastic modulus and toughness (material properties) were calculated. Diaphysial cortical bone thickness was measured by using histological method from the right femur.

In respect to the cortical thickness of the rats' femurs, there was statistically significant interaction between the gender and group (P < 0.05), while the BMD and cortical area were not (P > 0.05). The BMD, cortical thickness and area values of the femurs of MF-exposed rats (F-MF, M-MF) were significantly decreased in comparison to that of the controls (FC, MC) (P < 0.05). There were no statistically significant differences between the control and the MF-exposed rats in respect to the femur length (P > 0.05). There were no statistically significant interaction between the gender and group with regard to the maximum load, displacement, stiffness, ultimate stress, ultimate strain, elastic modulus and toughness endpoints, while the energy absorption capacity was significant (P < 0.05). Maximum load, displacement and stiffness values of MF-exposed rats were significantly decreased compared to that of the controls (P < 0.05). Femurs of M-MF rats had less absorbed energy than that in controls (P < 0.05). Ultimate stress and elastic modulus parameters were significantly decreased in MF-exposed rats in comparison to that of the controls (P < 0.05). Ultimate strain was higher in MF-exposed rats than that in controls (P > 0.05). The mean of toughness was decreased in MF-exposed rats compared to that of the controls (P > 0.05).

In conclusion, the bone quality of rats is decreased by magnetic field exposure.

Introduction

Bone is a complex tissue and remodels continuously throughout life via resorption of old bone by osteoclasts and the subsequent formation of new bone by osteoblasts. These two events are tightly coupled to each other and are responsible for the renewal of the skeleton while maintaining its anatomical and structural integrity [1], [2]. Osteoblasts produce bone matrix during development, after bone injury, and during normal bone remodeling. In contrast, osteoclasts resorb bone matrix. An imbalance of osteoblast and osteoclast functions can result in skeletal abnormalities characterized by increased (osteopetrosis) or decreased (osteoporosis) bone mass [3].

The discovery of piezoelectricity [4] and bioelectric potentials [5] in bone raised the possibility that externally applied electric energy could modify the behavior of bone cells [6]. Although this seems to be true, the pathways of the effects are not clear. Despite that, electric stimulation has been used successfully to treat a wide range of bone disorders, including delayed and nonunion fractures [7], fresh fracture healing [8], prevention and reverse of osteoporosis [9], [10], [11], and congenital pseudarthrosis [12] among others. However, the clinical success contrasts with negative reports on the effects of electric stimulation on the cellular proliferation, differentiation, and bone formation in vitro [13], [14], [15], [16].

Electromagnetic energy has been very important in our lives, due to its extensive use in diagnosis and treatment in medicine. It is now well established that exogenously electromagnetic field (EMF) affect bone metabolism both in vivo and in vitro. EMFs can increase the maturation of the bone trabecula, bone volume, and bone formation. Basset et al. [17] have observed that an external magnetic field accelerated the healing of bone fracture. However, Yamada et al. [18] did not observe any effects on bone tissue. An extremely low frequency magnetic field (ELF-MF) can induce the differentiation of cartilage cells and alter alkaline phosphatase activity in rat osteoblastic cells [19]. ELF-MF could be effective in epiphysial growth, bone build-up, and fracture repair [20]. There are many studies about electrical stimulation of bone. However, it has not been investigated to date whether ELF-MF can change the biomechanical properties of bone.

Bone strength is measured by a biomechanical test of the bone specimen. Strength (maximum load), stiffness, energy absorption capacity, ultimate strain, ultimate stress, elastic modulus (young modulus), and toughness are evaluated by biomechanical tests, and all of these parameters affect bone fragility.

The aim of this study was to investigate the long-term (45 days) effects of ELF-MF (50 Hz, 1 mT) exposure on biomechanical properties of rats' bone. Bone mineral density (BMD) and histological investigation were also evaluated.

Section snippets

Animals

Twenty-four 8-week-old Wistar–Albino female (n = 12; 175 ± 13 g bw) and male (n = 12; 181 ± 10 g bw) rats (Mersin University Medical Faculty, Mersin, Turkey) were used in this study. The rats were divided randomly into four groups: female control (FC; n = 5) and MF-exposed rats (F-MF; n = 7); male control (MC; n = 5) and MF-exposed rats (M-MF; n = 7). The animals were acclimatized for 1 week to our laboratory conditions prior to experimental manipulation. The rats were randomly selected and housed in

Geometric properties and bone mineral density of diaphysial femur in control and MF-exposed groups of rats

Table 1 lists the BMD, cortical thickness, and geometric properties of diaphysial rat femur. There were no statistically significant interaction between gender and group with regard to the BMD, femur length, and cortical area values of the rats (P > 0.05), while the cortical thickness was significant (P < 0.05). The BMD values of the femurs of F-MF and M-MF rats were lower than that of the control rats by 14.6% and 13.5%, respectively (P < 0.01). There were no statistically significant differences

Discussion

In this study, we investigated the effects of long-term (45 days) 50 Hz, 1 mT ELF-MF exposure on biomechanical properties of healthy rat bone. Load–displacement data were recorded and maximum load (ultimate tensile strength), displacement, stiffness, and energy absorption capacity were determined from this curve. The load–displacement recordings were normalized by cross-sectional area and this curve was converted to a stress–strain curve. The ultimate stress, ultimate strain, elastic modulus,

Acknowledgments

This work has been supported by the grants from the Mersin University Scientific Projects Unit (BAP.SBE.BIF.(SG)/2003-2 YL).

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