Effect of electric currents on DNA synthesis in rat osteosarcoma cells: dependence on conditions that influence cell growth

In vitro effects of low frequency electromagnetic fields on osteoblast proliferation and maturation in an inflammatory environment

An in vitro model was set up to investigate the effects of low frequency pulsed electromagnetic fields (PEMF) and its induced electric fields on osteoblast cells under inflammatory conditions. Osteoblasts (7F2) were seeded on top of chitosan scaffolds and co-cultured with macrophage cells (RAW 264.7) growing on the bottom of culture wells, stimulated by lipopolysaccharide to release reactive oxygen species including nitric oxide (NO). The co-culture was exposed to PEMF (magnitude of the magnetic field = 1.5 mT; induced electric voltage = 2.5 mV; frequency = 75 Hz; pulse duration = 1.3 ms) for 9 h. The osteoblasts were examined for their proliferation, viability, alkaline phosphatase (ALP) activity, and genetic expressions of type I collagen (COL I) and osteocalcin (OC), immediately and 7 days after PEMF exposure (days 0 and 7). Macrophage cell viability and NO concentration in the medium were monitored before and after PEMF exposure. The PEMF-exposed co-culture released a significantly higher amount of NO (65 µM) compared to control (17 µM) on day 7. Despite the high level of NO in the medium that was reported to be cytotoxic, PEMF-exposed osteoblasts had enhanced cell proliferation (23%), viability (36%), and COL I mRNA expression (3.4-fold) compared to the controls. The osteoblasts subjected to the PEMF had 41% less ALP activity than the control, which was associated with the active cell proliferation and COL I expression. The expression of OC mRNA was not seen in either the PEMF or control group, indicating cells had not entered the mineralization stage by day 7.

Real-time control of neutrophil metabolism by very weak ultra-low frequency pulsed magnetic fields

In adherent and motile neutrophils NAD(P)H concentration, flavoprotein redox potential, and production of reactive oxygen species and nitric oxide, are all periodic and exhibit defined phase relationships to an underlying metabolic oscillation of approximately 20 s. Utilizing fluorescence microscopy, we have shown in real-time, on the single cell level, that the system is sensitive to externally applied periodically pulsed weak magnetic fields matched in frequency to the metabolic oscillation. Depending upon the phase relationship of the magnetic pulses to the metabolic oscillation, the magnetic pulses serve to either increase the amplitude of the NAD(P)H and flavoprotein oscillations, and the rate of production of reactive oxygen species and nitric oxide or, alternatively, collapse the metabolic oscillations and curtail production of reactive oxygen species and nitric oxide. Significantly, we demonstrate that the cells do not directly respond to the magnetic fields, but instead are sensitive to the electric fields which the pulsed magnetic fields induce. These weak electric fields likely tap into an endogenous signaling pathway involving calcium channels in the plasma membrane. We estimate that the threshold which induced electric fields must attain to influence cell metabolism is of the order of 10(-4) V/m.

Timing of pulsed electromagnetic field stimulation does not affect the promotion of bone cell development

Pulsed electromagnetic field (PEMF) devices have been used clinically to promote the healing of surgically resistant fractures in vivo. However, there is a sparsity of data on how the timing of an applied PEMF effects the osteogenic cells that would be present within the fracture gap. The purpose of this study was to examine the response of osteoblast-like cells to a PEMF stimulus, mimicking that of a clinically available device, using four protocols for the timing of the stimulus. The PEMF signal consisted of a 5 ms pulse burst (containing 20 pulses) repeated at 15 Hz. Cultures of a human osteosarcoma cell line, SaOS-2, were exposed to the four timing protocols, each conducted over 3 days. Protocol one stimulated the cells for 8 h each day, protocol two stimulated the cells for 24 h on the first day, protocol three stimulated the cells for 24 h on the second day, and protocol four stimulated the cells for 24 h on the third day. Cells were seeded with either 25,000 or 50,000 cells/well (24-well cell culture plates). All assays showed reduced proliferation and increased differentiation (alkaline phosphatase activity) in the PEMF stimulated cultures compared with the control cultures, except for protocol four alkaline phosphatase measurements. No clear trend was observed between the four protocols; however this may be due to cell density. The results indicated that an osteoblast-like cell line is responsive to a 15 Hz PEMF stimulus, which will stimulate the cell line to into an increasing state of maturity.

Bioelectromagnetics in morphogenesis

Understanding the factors that allow biological systems to reliably self-assemble consistent, highly complex, four dimensional patterns on many scales is crucial for the biomedicine of cancer, regeneration, and birth defects. The role of chemical signaling factors in controlling embryonic morphogenesis has been a central focus in modern developmental biology. While the role of tensile forces is also beginning to be appreciated, another major aspect of physics remains largely neglected by molecular embryology: electromagnetic fields and radiations. The continued progress of molecular approaches to understanding biological form and function in the post genome era now requires the merging of genetics with functional understanding of biophysics and physiology in vivo. The literature contains much data hinting at an important role for bioelectromagnetic phenomena as a mediator of morphogenetic information in many contexts relevant to embryonic development. This review attempts to highlight briefly some of the most promising (and often underappreciated) findings that are of high relevance for understanding the biophysical factors mediating morphogenetic signals in biological systems. These data originate from contexts including embryonic development, neoplasm, and regeneration.

Ets1 oncogene induction by ELF-modulated 50 MHz radiofrequency electromagnetic field

We have analyzed gene expression in hemopoietic and testicular cell types after their exposure to 50 MHz radiofrequency (RF) non-ionizing radiation modulated (80%) with a 16 Hz frequency. The exposure system generates a 0.2 microT magnetic field parallel to the ground and a 60 V/m electric field orthogonal to the earth's magnetic field. Exposure conditions were selected so as to interfere with the calcium ion flow. Under these electromagnetic field (EMF) conditions, we observed an overexpression of the ets1 mRNA in Jurkat T-lymphoblastoid and Leydig TM3 cell lines. This effect was observed only in the presence of the 16 Hz modulation, corresponding to the resonance frequency for calcium ion with a DC magnetic field of 45.7 microT. We have also identified a putative candidate gene repressed after EMF exposure. The experimental model described in this paper may contribute to the understanding of the biological mechanisms involved in EMF effects.

Effects of electromagnetic fields in experimental fracture repair

The clinical benefits of electromagnetic fields have been claimed for 20 centuries, yet it still is not clear how they work or in what circumstances they should be used. There is a large body of evidence that steady direct current and time varying electric fields are generated in living bone by metabolic activity and mechanical deformation, respectively. Externally supplied direct currents have been used to treat nonunions, appearing to trigger mitosis and recruitment of osteogenic cells, possibly via electrochemical reactions at the electrode-tissue interface. Time varying electromagnetic fields also have been used to heal nonunions and to stabilize hip implants, fuse spines, and treat osteonecrosis and osteoarthritis. Recent research into the mechanism(s) of action of these time varying fields has concentrated on small, extremely low frequency sinusoidal electric fields. The osteogenic capacity of these fields does not appear to involve changes in the transmembrane electric potential, but instead requires coupling to the cell interior via transmembrane receptors or by mechanical coupling to the membrane itself.

Effect of electromagnetic stimulation with different waveforms on cultured chick tendon fibroblasts

An energy efficient electromagnetic stimulator device for fracture healing was compared to a commercially available device in stimulating cell growth in tissue cultures. The energy efficient device, which conserves energy by using a bidirectional time-dependent magnetic wave form, and the commercially available stimulator, which uses a unidirectional time-dependent magnetic wave form, were tested on chick tendon fibroblasts in primary culture. Comparing non-stimulated control and cells electromagnetically stimulated with unidirectional and bidirectional waveforms showed that at the growth phase between days 2 and 3, both electrical stimulation techniques increased cell division as measured by DNA synthesis. When cells were dividing rapidly, collagen synthesis was reduced. When the cells reached the confluence there was no difference among the groups (control, unidirectionally stimulated, and bidirectionally stimulated) in terms of number of cells or collagen produced.

Optimization of electric field parameters for the control of bone remodeling: exploitation of an indigenous mechanism for the prevention of osteopenia

The discovery of piezoelectric potentials in loaded bone was instrumental in developing a plausible mechanism by which functional activity could intrinsically influence the tissue's cellular environment and thus affect skeletal mass and morphology. Using an in vivo model of osteopenia, we have demonstrated that the bone resorption that normally parallels disuse can be prevented or even reversed by the exogenous induction of electric fields. Importantly, the manner of the response (i.e., formation, turnover, resorption) is exceedingly sensitive to subtle changes in electric field parameters. Fields below 10 microV/cm, when induced at frequencies between 50 and 150 Hz for 1 h/day, were sufficient to maintain bone mass even in the absence of function. Reducing the frequency to 15 Hz made the field extremely osteogenic. Indeed, this frequency-specific sinusoidal field initiated more new bone formation than a more complex pulsed electromagnetic field (PEMF), though inducing only 0.1% of the electrical energy of the PEMF. The frequencies and field intensities most effective in the exogenous stimulation of bone formation are similar to those produced by normal functional activity. This lends strong support to the hypothesis that endogenous electric fields serve as a critical regulatory factor in both bone modeling and remodeling processes. Delineation of the field parameters most effective in retaining or promoting bone mass will accelerate the development of electricity as a unique and site-specific prophylaxis for osteopenia. Because fields of these frequencies and intensities are indigenous to bone tissue, it further suggests that such exogenous treatment can promote bone quantity and quality with minimal risk or consequence.

Electric fields modulate bone cell function in a density-dependent manner

The influence of an extremely low frequency (ELF) electric field stimulus (30 Hz at 6 microV/cm rms), known to promote bone formation in vivo, was evaluated for its ability to affect bone cell function in vitro. To accomplish this, we developed an apparatus for the exposure of monolayer cell systems to electric fields in a manner that provides relatively uniform electric field exposure of multiple cell samples as well as a rigorous sham exposure. We show that field exposure significantly limits the normal increase in osteoblastic cell number and enhances alkaline phosphatase activity compared to sham-exposed samples. Moreover, these alterations are shown to occur in a cell density-dependent manner. Samples plated at 6 x 10(3) cells/cm2 show no effect of field exposure. In samples plated at 30 x 10(3) cells/cm2, 72 h of field exposure resulted in 25% fewer cells in the exposed samples, and a doubling of alkaline phosphatase activity in those cells compared to sham exposure. Experiments using a 12 h exposure to preclude significant changes in cell number during the exposure show this density-dependent response to be biphasic. Sparse cultures (< 50 x 10(3) cells/cm2) were not found to be affected by the field exposure, but increases in alkaline phosphatase activity occurred in cultures at densities of 50-200 x 10(3) and 200-350 x 10(3) cells/cm2 and no effect on alkaline phosphatase activity was seen in confluent cell cultures of greater than 350 x 10(3) cells/cm2.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of magnetic resonance imaging (MRI) on the formation of mouse dentin and bone

The effects of magnetic resonance imaging (MRI) on dentin and bone formation in mice were examined using standard autoradiographic and liquid scintillation procedures. It was observed that exposure to a standard 23.2 min clinical multislice MRI (0.15T) procedure caused a significant increase in the synthesis of the collagenous matrix of dentin in the incisors of mice. There were no significant effects on alveolar and tibial bone matrix synthesis. These results suggest that the magnetic fields associated with MRI can affect the activity of cells and/or tissues that are involved in rapid synthetic activity.

Electric fields stimulate DNA synthesis of mouse osteoblast-like cells (MC3T3-E1) by a mechanism involving calcium ions

A cell culture system was designed to study the effect of an electric field on bone cells. This system subjected cultured bone cells to a series of high-voltage pulses at varying amplitudes of electric field without changing the ion concentrations of the culture medium. When mouse osteoblast-like cells (MC3T3-E1) were stimulated for 5 min to 20 hr by an electric field (3.19 kV/m, 3 msec, 10 Hz pulses), DNA synthesis was greatly increased. The stimulation occurred only during the growth phase. The electric field also increased incorporation of 45Ca into the cells, but it did not stimulate cAMP production. Adding calcium ionophore A23187 stimulated both 45Ca uptake and DNA synthesis, but dibutyryl cAMP did not stimulate either of them. These results suggest that the electric field stimulates the DNA synthesis of growing osteoblasts by a mechanism involving calcium ions.