| Summary: | 博士 === 中原大學 === 醫學工程研究所 === 91 === Bioelectromagnetics (BEM) is the emerging science that studies how living organisms interact with electromagnetic (EM) fields. Electrical phenomena are found in all living organisms such as bone, nerve, cartilage, muscle…etc. Consequently, they can be influenced by external magnetic and EM fields as well. In fact, there is growing evidence that environmental electric and magnetic fields in the extremely low frequency (ELF) band below 300 Hz can influence biological functions by mechanisms that are only poorly understood at the present time. In spite of the ambiguous and controversial mechanistic issues, which have been confused and hamper the advance and application of BEM in medical community, selected, time-varying electric and magnetic fields have played an increasingly successful role in the care of several challenging medical problems, mainly fractures that have failed to heal in children and adults and chronic skin wounds during the past three decades. Recently, due to the prolonged lifespan of average population, the prevalence of another kind of bone disease-osteoporosis has caught the attention of BEM scientists. Again, EMF, especially pulsed electromagnetic fields (PEMF) was proved to be effective on the management of osteoporosis.
With an attempt to clarify and substantiate the efficacy of PEMF on osteoporosis management, a series of in vitro experiments were designed and performed this dissertation. The primary objectives of this dissertation are to investigate the interactions between PEMF and bone tissues at the cellular level, and the underlying mechanisms that lead to the explanation for the PEMF efficacy. In succeeding paragraphs we present the synopsis of different but connected experiments carried out in this thesis in terms of chapters. In Chapter 2 we developed the PEMF stimulators and employed Helmholtz coils to stimulate female rats that have been ovariectomized bilaterally. The total stimulation time was one month. Histomorphometric analyses and radioimmunoassay (RIA) were used to evaluate the effects of PEMF on ovariectomy-induced trabecular bone loss and serum PGE2 concentration. These experiments demonstrated that PEMF may be useful in the prevention of osteoporosis resulted from estrogen deficiency, and PGE2 might relate to this preventive effects.
The effects of extremely low frequency pulsed electromagnetic fields (ELF-PEMF) on osteoclastogenesis, cultured from murine bone marrow cells and stimulated by 1,25(OH)2D3, were examined in Chapter 4. Primary bone marrow cells were cultured from mature Wistar rats and exposed to ELF-PEMF stimulation daily for 7 days with different intensities of induced electric field (4.8 μv/cm, 8.7 μv/cm, and 12.2 μv/cm; peak value) and stimulation times (0.5 h/day, 2 h/day, and 8 h/day). During the experiments, cytokines such as tumor necrosis factor-α (TNF-α), interleukin -1β (IL-1β), and prostaglandin-E2 (PGE2) were assayed by using enzyme-linked immunosorbent assay (ELISA). Results showed that PEMF can affect osteoclastogenesis and TNF-α and IL-1β might involve in this process.
The purpose of Chapter 5 was to examine the effects of a specific PEMF stimulation on osteoclast formation in bone marrow cells from ovariectomized rats and to determine if the signal modulates the production of cytokines associated with osteoclast formation. Under the stimulation of 4.8 μv/cm electric field intensity, the PEMF signal caused significant reductions in osteoclast formation in both Subgroups I (4 days after surgery) (-55%) and II (7 days after surgery) (-43%). Tumor necrosis factor-α (TNF-α), interleukin 1β (IL-1β), and interleukin 6 (IL-6) in PEMF group of Subgroup I were significantly reduced at 5, 7, and 9 days as compared to OVX group. The results found in this study suggest that osteoclastogenesis can be inhibited by PEMF stimulation, putatively due to a concomitant decrease in local factor production.
In order to further clarify the underlying mechanism of PEMF bioeffects on osteoporosis, the effect of pulsed electromagnetic fields (PEMF) on induction of osteoclasts apoptosis was investigate in Chapter 6. A statistically significant increase of apoptotic rate in osteoclasts (48 hours after isolation) was found when exposed to 7.5 Hz PEMF with induced electric fields intensity of 3.0 μv/cm for 8 (105%, p<0.001) (PEMF-8) and 16 (30%, p<0.05) (PEMF-16) hours. However, exposure of osteoclasts to PEMF for only 1 hour (PEMF-1) showed no statistically significant differences when compared with controls. These findings suggest that PEMF have the ability to induce apoptosis of osteoclasts derived from primary osteoblasts and bone marrow cells cocultures. This in vitro study, therefore, could be considered as groundwork for in vivo PEMF applications on some osteoclasts-associated bone diseases.
Chapter 7 described an experiment that is similar to Chapter 4. However, cytokines closely related to osteoclastogenesis such as osteoprotegerin (OPG), receptor activator of NFκB-ligand (RANKL), macrophage colony-stimulating factor (M-CSF) were determined in order to further clarify the underlying mechanism. The results found in this study suggest that osteoclastogenesis can be modulated by PEMF stimulation, putatively due to concomitant variations in local factors production. Moreover, due to the induced electric field intensity in in vivo and in vitro situations was different, some related literatures were reviewed and presented in Chapter 3. In this chapter, exposure systems for in vitro studies, measurement of magnetic fields, measurement of electric fields, effects of experimental geometry of culture dishes, and some practically calculated examples of induced electric field intensity in our experiment were discussed.
The conclusion that electromagnetic energy can produce varied and nontrivial biological effects on osteoclasts differentiation and apoptosis modulation is inescapable based on our findings. Furthermore, the evidence that such interactions can occur well below the thermal level is similarly inescapable. With these findings of experiments, we can infer that the effects of PEMF stimulation on osteoporosis management might partially due to its modulating ability on osteoclasts. This inference might in the future become the cornerstone for PEMF stimulation to be adopted as an adjunct alternative not only for osteoporosis management in clinical orthopedics but also in other medical frontiers.
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