© Borgis - New Medicine 3/2009, s. 58-60
*Ewa Ogłodek1, Danuta Mo?1, 2
The Effect of Extremely Low Frequency Magnetic Fields on Osteogenesis
1Department of Clinical Psychiatry of the Nicolaus Copernicus University in Toruń, Collegium Medicum in Bydgoszcz, Poland
Head of Clinic: prof. dr hab med. Aleksander Araszkiewicz
2Individual medical practice
Extremely low frequency magnetic fields (ELF-MF) which are applied in the treatment of humans are distinguished from various sorts of magnetic fields. They are magnetic fields of frequency not higher than 60 Hz, induction value ranging from 1 pT to 15 mT, with volume of 130 V/m, and both rectangular and triangular waveform of the magnetic field. The essential problem raised is the effect of the magnetic field on particular metabolic processes of living organisms. The long-term exposure of an organism to extremely low frequency magnetic fields intensifies the process of membrane transmission, resulting in morphological changes in the bone. The use of magnetic fields is gaining acceptance for the treatment of ununited fractures. As a reaction to the stress stimulus in the form of extremely low frequency magnetic fields activity, an increase of biosynthesis of cellular proteins and of transcription in a cell are observed and also changes in expression and differentiation of genes occur.
Extremely low frequency magnetic fields stimulate bone formation by promoting osteoblastic differentiation and activation. In the matrix development and mineralization stages, the calcium content in the matrix and two markers of osteoblastic phenotype (alkaline phosphatase and osteocalcin) also showed a significant increase. The objective of this research was to evaluate the influence of extremely low frequency magnetic fields on osteogenesis.
Extremely low frequency magnetic fields have now been in use in orthopaedics and traumatology for over twenty years [1, 2]. Clinical trials have shown that magnetic stimulation enhances calcification of bones . The technique is employed to promote osteogenesis and hence to favour bone repair processes. It has recently been shown that extremely low frequency magnetic field (ELF-MF) may be the treatment of choice in avascular necrosis of the femoral head. The effect of ELF-MF on the proliferative activity of osteoblasts in vitro and on the speed of the osteogenic repair process in vivo is more evident and ample when cultures of cells are taken from elderly donors or when the examined subject is in advanced age [4, 5].
The objective of this study was to evaluate the influence of extremely low frequency magnetic fields on the growth of osteoblast cells.
Mechanism of the effect of extremely low frequency magnetic field on bone cells
The proliferation and differentiation, which are responsible for growth, remodelling, and repair of bones are modulated by several extracellular factors, such as cytokines and hormones . Bone formation is also affected by pulsed magnetic fields. Extremely low frequency magnetic fields are extensively applied in the clinical treatment of non-union bone fractures, bone grafts, fresh fractures and osteoporosis. As for the effects of pulsed electromagnetic fields on bone, much evidence suggests that they enhance the activities of osteoblasts, proliferation and differentiation, extracellular matrices, alkaline phosphatase and net flux and the uptake of calcium [7, 8].
While several different mechanisms may contribute to the overall healing effectiveness of ELF-MF (increased proliferation and differentiation of pre-osteogenic cells, increased blood flow, increased ion concentration in bone), altered hormone receptor activity seems to play a pivotal role [9, 10]. Osteoblasts exposed for as little as 10 min to pulsed ELF-MF with peak fields in the range of 1 mT show persistent desensitization of the PTH receptor resulting in a rate of collagen synthesis elevated by the osteoblasts, and a rate of bone resorption decreased by osteoclasts [11, 12]. Exposure to the extremely low frequency magnetic field caused increased calcium, leading to phosphorylation of membrane proteins, PKC-induced desensitization of the PTH receptor, and other signal transduction to the cellular membrane. The ELF-MF caused changes in the charge and/or affinity properties of membrane proteins [13, 14].
The effects of exposure to magnetic field on PTH responses were found to be consistent with decreased density of receptors of adenylate cyclase via the stimulatory G protein. A release of interleukin growth factor II, or other growth factor, as suggested by Varani K et al. , could be important in the proliferative responses of less differentiated cells and the release of the transforming growth factors might induce differentiation. One key observation is that osteoblasts exposed to low frequency magnetic fields for as little time as 10 min exhibit a persistent desensitization to the effects of PTH on adenylate cyclase [16, 17]. Studies using biochemical probes of coupling G-protein indicate that the ability of activating bound hormone-receptor complex of G-protein alpha subunits is impaired by treatment of osteoblasts with pulsed fields. The desensitization of the PTH receptors results in an increased rate of synthesis of collagen by osteoblasts and a decreased rate of bone resorption by osteoclasts [18, 19]. Desensitization of other G-protein linked receptors is known to be associated with changes in the configuration of the transmembrane domains adjacent to the intracellular phosphorylation sites, leading to phosphorylation of the receptor by intracellular enzymes [20, 21]. PKC is known to be involved in regulation of PTH-receptor desensitization and the PTH receptor is known to contain phosphorylation sites for PKC but not any other protein kinases [22, 23].
The osteogenic potential of low frequency magnetic fields
The development of effective procedures for the prevention of bone loss due to aging, menopause, immobilization, or spaceflight requires an understanding of the factors which normally regulate remodelling activity. Some of the most important determinants of bone mass and architecture are magnetic stimuli. The basis of the osteogenic stimulus depends on a time-dependent transduction mechanism [24, 25]. One of the most intriguing hypotheses about time-dependent mechanisms for signal transduction focuses on the fact that low frequency magnetic fields are generated when stresses are applied to bone [26, 27]. Magnetic current generated in bone under load has at least two sources: the piezoelectrical currents arising from the deformation of collagen and the relatively large electrokinetic currents that are produced by the ionic constituents of fluid flowing past the mineral phase of the matrix [28, 29]. These electrical currents amplify the small mechanical strains that are produced by functional activity, promoting their potential role in signal transduction .
Pre-clinical studies have shown that pulsed electromagnetic fields (PEMFs) in vitro favour the proliferation of chondrocytes, stimulate proteoglycan synthesis and demonstrate A2 adenosine receptor agonist activity . Electromagnetic fields in vivo prevent degeneration of articular cartilage and down-regulate the synthesis and release of pro-inflammatory cytokines in the synovial fluid . These findings suggest that electromagnetic fields may be used to control joint inflammation and to stimulate cartilage anabolic activities, finally resulting in chondroprotection .
Joint inflammation has a catabolic effect on extracellular matrix and inhibits chondrocyte activity, which allows for local control of the inflammation. The control process prevents the onset and limits the progression of cartilage damage. Furthermore, unlike bone tissue after damage, cartilage will not completely recover its functions: once lost, the articular cartilage does not reform [34, 35].
Extremely low frequency magnetic fields are used clinically in the treatment of fracture of non-unions. In order to achieve a beneficial response in this type of fracture, it is necessary to apply higher values of ELF-MF than in uncomplicated fractures.
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