emf- mechanism, cell signaling, bio processes, toxicity, radicals
DESCRIPTION
Despite the fact that the lack of a medical background in the authors is quite evident, they have managed to put together a remarkable document that explores cell signaling and ROS as related to electromagnetic syndromes. The bibliography is very valuable for us, the victims of cell phone telephony and wireless internet.TRANSCRIPT
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Electromagnetic Fields: Mechanism, Cell Signaling, Other Bioprocesses, Toxicity, Radicals,
Antioxidants and Beneficial Effects
Peter Kovacic1* and Ratnasamy Somanathan
2
1Department of Chemistry, San Diego State University, San Diego CA 92182 USA.
2 Centro de Graduados e Investigación del Instituto Tecnológico de Tijuana, Apdo postal 1166,
Tijuana, B.C. Mexico.
ABSTRACT
Electromagnetic fields (EMFs) played a role in the initiation of living systems, as well as
subsequent evolution. The more recent literature on electrochemistry is documented, as well as
magnetism. The large numbers of reports on interaction with living systems and the
consequences are presented. An important aspect is involvement with cell signaling and resultant
effects in which numerous signaling pathways participate. Much research has been devoted to
the influence of man-made EMFs, e.g., from cell phones and electrical lines, on human health.
The degree of seriousness is unresolved at present. The relationship of EMFs to reactive oxygen
species (ROS) and oxidative stress (OS) is discussed. There is evidence that indicates a
relationship involving EMFs, ROS and OS with toxic effects. Various articles deal with the
beneficial aspects of AOs in countering the harmful influence from ROS-OS associated with
EMFs. EMFs are useful in medicine, as indicated by healing bone fractures. Beneficial effects
are recorded from electrical treatment of patients with Parkinson’s disease, depression and
cancer.
Correspondence to: Peter Kovacic; Department of Chemistry; San Diego State University; San
Diego, CA 92182-1030 USA; E mail: [email protected]
2
KEY WORDS
Electromagnetic fields (EMFs), electron transfer (ET), oxidative stress (OS), reactive
oxygen species (ROS), antioxidants (AOs), cell phones
INTRODUCTION
Initiation and evolution of life involved chemical compounds and energy sources, such
as the sun and electromagnetism. Bioelectrical phenomena play a vital role in life processes (1).
Among the intrinsic features of living systems are the separation, transport and storage of
electrical charge (2). The participation of electron transfer (ET) is recognized as one of the
essential requirements for electrochemical communication between molecules. An
electromagnetic field is associated with the mobile, charged electron. In addition to
neurotransmission, electrochemistry is involved in electrostatics and electron transport.
Electromagnetic forces are primarily responsible for the structure of matter from atoms to more
complex substances (3) and have played a dominant role in cell division and other processes in
primitive cells as well as modern eukaryotic ones. As expected, electrical effects have been
reported in plant chemistry (4). The preponderance of bioactive substances or their metabolites
incorporate electron transfer (ET) functionalities, which, we believe, play an important role in
physiological responses. The main groups include quinones (or phenolic precursors), metal
complexes (or complexors), aromatic nitro compounds (or reduced nitroso or hydroxylamine
derivatives) and conjugated iminiums (or imines). There are two principal pathways that can
result from ET, one being redox cycling with generation of reactive oxygen species (ROS) and
oxidative stress (OS). The other involves interaction with the central nervous system (CNS).
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Electron transfer is probably the most prevalent and important process in chemical
transformation. The generality and unifying aspects are demonstrated by involvement in all areas
of the physical and biological sciences. Examples are receptor chemistry (5) and cell-signaling
mechanism (6). Extensive evidence is documented supporting mode of action for carcinogens
(7), mitochondrial toxins (8), and major organ toxins (9-14).
Since electrochemistry plays an important role in biofunctioning, including the
CNS, more attention should be devoted to this area, particularly fundamental aspects. A
neglected topic is determination of reduction potential which provides information concerning
the feasibility of ET by exogenous and endogenous agents. If the reduction potential is more
positive than -0.5 V, then ET is a possibility in vivo. Requisite electron donors reside mainly in
protein side chains in the form of disulfide, phenolic oxygen, or conjugated amine species.
In the electrochemical category, studies demonstrate a role for electrostatic forces in
a variety of areas. The term bioelectrostatics is a label used in the life science area in which
widespread participation is documented (4). Energetics appears to play a significant role.
Subjects addressed are enzymes, membranes, chromosomes, histamine, receptors, the Hofmeister
effect, plant chemistry and evolutionary development. A recent hypothesis proposes that
electrostatic force is a factor in receptor-ligand action, based on the molecular electrostatic
potential (MEP) associated with ions and dipoles (5). Energetics and bridging may be important
actors.
The mechanism of electrostatic action by phosphates and sulfates has been
discussed (15). A hypothesis was presented for the basic mode of action of phosphates and
sulfates in cell signaling, with phosphorylation being the center of attention. In both cases, the
anions provide strong electrostatic fields that are believed to be of major importance. It is
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probably not coincidental that the phosphates involved are mono- or di-esters containing at least
one free hydroxy group in anion form. A similar situation pertains to sulfation in which
monoesterification preserves an anion residue. The field may serve as a link that connects
existing electrochemical pathways or as an energy source.
The cell is able to couple the energy of ATP hydrolysis directly to endergonic processes
by transferring a phosphate from ATP to some other molecule, which then becomes more
reactive [15,16]. Nearly all cellular work depends on energizing by ATP of other molecules via
transfer of phosphate. This situation may apply to phosphate insertion by ATP into signaling
molecules with resulting enhanced energy.
Reports on electrochemical effects of metal cations mainly involve Mg, Zn, Fe, Ca, and
Cu (17). Of these, calcium has received the most attention in relation to cell communication and
receptor binding. Calcium and other alkaline earth cations change the electrostatic potential
adjacent to negatively charged bilayer membranes. Organic cations, such as dimethonium, were
also employed in investigations of electrostatic effects.
Electromagnetic phenomena are associated with charged radicals and electrons in motion.
Although this idea has been advanced previously, it has attracted little attention. A crude
hypothesis for ET involvement in neurotransmission was advanced in 1983. Two years later,
electron translocation brought about by redox reactions was visualized as being the primary
mechanism whereby electric fields are generated in the living cell (18). Fast movement of
electrons results in polarization, which establishes an electrical gradient. Electron migration
conceivably progresses by means of radical intermediates. In 1996, the ET concept was applied
to regulatory action of NO in neurotransmission, toxicity, and immunological reactions (19, 20).
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A 2004 review summarizes the present status of electrophysiological effects, and
deserves special attention (21). After a burst of research dealing with electrical coupling, gap
junctions became less popular among neurobiologists vs. the ionic approach. Recent reports have
brought gap junction back into the spotlight, suggesting that this type of cell-cell signaling may
be interrelated with, rather than alternative to, chemical transmission.
Besides the trivial primary effects of electromagnetic fields (EMF) on ionic charges and
dipolar matter, cellular biochemical reaction and channel transport processes are field dependent
(22). Interaction of signaling systems with low energy EMFs may produce metabolic responses
in the body (23). The applied field might modify existing signal transduction processes in cell
membranes, thus producing both transduction and biochemical amplification of the existing field
effects. A practical example comprises the physiological effects of the external field in the
healing of bone fractures (24).
Investigations of volatile anesthetics provide valuable insight concerning the role of
electrostatics (5). At clinically relevant concentrations, ethers, alkyl halides and alcohols
enhance agonist action on the GABA (A) receptor, whereas alkanes do not. A good correlation
exists between dipole moments and receptor activity. Dipole moments are related to
electrostatics. Other relevant studies involve local anesthetics.
Electrostatic forces are relatively weak. Can such low levels have an influence in living
systems? A recent study provides evidence for involvement. Investigators have gained insight
into physiological events in which weak forces, as low as 0.5 picoNewtons, play a regulatory
role e.g., in ion channel functioning (25). It is fascinating that at the cellular level, weak forces
may be more important than strong ones. Weak magnetic forces that operate over short distances
are associated with prevalent radicals. Mounting evidence indicates that energy is a significant
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factor in electrostatic operation (4). Support is available from studies in a variety of fields both
animal and plant, including enzymes, membranes and other systems.
Living creatures can be regarded as complex electrochemical systems that evolved over
billions of years (6). Organisms interact with and adapted to an environment of electrical and
magnetic fields. Humans are now immersed in a man-made environment of such fields whose
long-term effects are unknown.
Useful comparisons can be made with electrical conductance in non-biological systems. In
copper, the metal serves as conduit for electrons. The electrical energy is converted into a useful
end result. Electrons and holes are also involved in semi-conductor operation. Other examples
exist among conducting polymers, e.g., polyaniline.
The present review deals with electromagnetism in biological systems and in medicine.
The electrochemical aspects are updated. The magnetic portion is also the center of attention.
The approach is in an integrated manner involving general aspects, cell signaling, electron
transfer, electromagnetic effects, radicals, oxidative stress and antioxidants. Various toxic
manifestations are addressed, as with brain illnesses, electrical power lines and cell phones. A
beneficial medical feature is use in bone fracture repair.
It should be emphasized that physiological activity of endogenous and exogenous
agents is often complex and multifaceted. There is greater need of interdisciplinary approaches
of the type in this review. Knowledge of events at the basic molecular level can result in practical
application to medicine. This review is representative, rather that exhaustive. Neurotransmission
is not included in depth in the major topics. In some cases, original references are present in the
reviews or articles.
INTERACTIONS WITH BIOLOGICAL SYSTEMS (GENERAL)
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A number of articles present a broad view of the effects of electromagnetic fields
(EMFs) on living systems. Magnetic fields (MF) are widely distributed in the environment and
their effects are increasing with burgeoning development of electrical machines. It has been
suggested that EMF, especially weak ones, may affect various functions of living things and
several experiments to evaluate the idea have been carried out (26). Studies in cell biology have
demonstrated that weak EMF can affect various cellular functions and important EMF targets in
cells are signal transduction cascades. Furthermore, EMF affects not only specific gene
transcription and cell growth, but also membrane mediated signal transduction processes,
especially the Ca2+
transport system. Effects of MF on mitochondrial functions, cell growth and
transformation, signal transduction of neutrophils, cell apoptosis, gene expression and lipid
peroxidation of biological membrane were examined. Static strong MF induced lipid
peroxidation of biological membrane.
It is now well established that low frequency (<300 Hz) EMF fields induce
biological changes that include effects ranging from increased enzyme reaction rates to increased
transcript levels for specific genes (27). The induction of stress gene HSP70 expression by
exposure to EMF provides insight into how these fields interact with cells and tissues. The large
amount of published data available on the heat-induced stress response (i.e., ‘heat shock’) offers
a model for studying and comparing the EMF-induced stress response. Results from these and
other studies have yielded important clues to EMF interaction with cellular systems, particularly
at the molecular level.
Insight into the mechanism(s) are also provided by examination of the interaction of
EMF with moving charges and their influence on enzyme reaction rates in cell-free systems. In
general, biological studies with in vitro model systems have focused on the nature of the signal
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transduction pathways involved in response to EMF. Based on evidence of the electron
transport/charge flow in DNA, it is likely that EMF interact directly with electrons in DNA to
stimulate biosynthesis.
Studies of EMF induction of the stress response proteins, point to the application of
EM fields in two biomedical applications: cytoprotection and gene therapy. Therapeutic use of
EMFs has met with great success since the early 1970’s in accelerating the healing of bone
fractures and soft tissue wounds.
Paradoxically, it is the health risk issue that has in recent years dominated EMF
research. Epidemiological studies have indicated that EMFs can also induce health adverse
effects and EMF are perceived by biological systems as a possible hazard. However, exposure to
EMFs also has beneficial effects (28), as understanding of mechanisms expands. Specific
requirements for field energies are being defined and the range of treatable ills broadened. These
include nerve regeneration, wound healing, graft behavior, diabetes, and myocardial and cerebral
ischemia, among other conditions.
Life on earth has evolved in a sea of natural EMFs. Over the past century, this natural
environment has sharply changed with introduction of a vast and growing spectrum of man-made
EMFs (29). From models based on equilibrium thermodynamics and thermal effects, these fields
were initially considered too weak to interact with biomolecular systems, and thus incapable of
influencing physiological functions. Laboratory studies have tested a spectrum of EMF fields for
bioeffects at cell and molecular levels. Modulation of cell surface chemical events by EMFs
indicates a major amplification of initial weak effects is associated with binding of hormones,
antibodies, and neurotransmitters to their specific sites. Calcium ions play a key role in this
amplification. These studies support new concepts of communication between cells.
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In cellular aggregates that form tissues of higher animals, cells are separated by
narrow fluid channels that take on special importance in signaling from cell to cell. These
channels act as windows on the electrochemical world surrounding each cell. Hormones,
antibodies, neurotransmitters and chemical cancer promoters, for example, move along them to
reach binding sites on cell membrane receptors. These narrow fluid “gutters,” typically not more
than 150 A wide, are also preferred pathways for intrinsic and environmental EMFs, since they
offer much lower electrical impedance than cell membranes. Although this intercellular space
(ICS) forms only about 10% of the conducting cross section of typical tissue, it carries at least
90% of any imposed or intrinsic current, directing it along cell membrane surfaces. Numerous
stranded protein molecules protrude from within the cell into this narrow ICS. Their glycoprotein
tips form the glycocalyx, which senses chemical and electrical signals in surrounding fluid. Their
negatively charged tips form receptor sites for hormones, antibodies, neurotransmitters, and for
many metabolic agents, including cancer promoters. These charged terminals form an anatomical
substrate for the first detection of weak electrochemical oscillations in pericellular fluid,
including field potentials arising in activity of adjacent cells or as tissue components of
environmental fields.
If one used electromagnetic energy sensors to view the world from space 100 years ago,
the world would have looked quite dim (30). Now the world glows with electromagnetic energy
emissions at the nonionizing portion of the spectrum, such as power line fields, radio waves,
microwaves, etc.
Living organisms are complex electrochemical systems that evolved over billions of
years in a world with relatively simple weak magnetic field and with few EM energy emitters.
As is characteristic of living organisms, they interact with and adapted to this environment of
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electric and magnetic fields. One example of this adaptation is the visual system, which is
exquisitely sensitive to emissions in the very narrow portion of the EM spectrum that we call
light. Organisms also adapt to another portion of the spectrum, the UV, by developing filtering
systems in the eye and the skin to protect them from it.
A wide range of living organisms, including humans, adapted by using EM energy to
regulate various critical cellular systems; we see this in the complex of circadian rhythms. Fish,
birds, and the duckbill platypus developed systems to use electromagnetic fields to sense prey
and to navigate. EM fields are involved in neural membrane function. Even protein conformation
effects involve the interactions of electrical fields.
Thus, it is not surprising that massive introduction of EMF in an enormous range of new
frequencies, modulations, and intensities in recent years have affected living organisms. In fact,
it would be incredible and beyond belief if these EMF did not affect the electrochemical systems
we call living organisms.
Electrification in developed countries has progressively increased the mean level of
extremely low-frequency EMF to which populations are exposed; these human- made fields are
substantially above the naturally occurring ambient electric and magnetic fields of ~10-4
Vm-1
and ~10-13
T, respectively (31). Several epidemiology studies have concluded that low frequency
EMF may be linked to an increased risk of cancer, particularly childhood leukemia. These
observations have been reinforced by cellular studies reporting EMF-induced effects on
biological systems, most notably on the activity of components of the pathways that regulate cell
proliferation. However, the limited number of attempts to directly replicate these experimental
findings have been almost uniformly unsuccessful, and no EMF-induced biological response has
yet been replicated in independent laboratories. Many of the most well-defined effects have
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come from gene expression studies; several attempts have been made recently to repeat these
findings. This review analyzes these studies and summarizes other reports of major cellular
responses to EMF and the published attempts at replication.
Geomagnetic fields can serve as the combined magnetic field, affecting different
biochemical ions in cells (32). Also influenced are electrostatic processes including phosphate
group transfer. Ligand-receptor effects can be due to field influence on substances abundant in
the cell, as well as on molecules participating in intracellular signaling and membrane transport
whose perturbation can be amplified by enzyme cascades or ion fluxes. Weak extremely low-
frequency magnetic field effects can be amplified by nonlinear mechanisms.
A recent review concentrates on findings described in the recent literature on the response
of cells and tissues to EMFs (33). Models of the interaction between different forms of EMF and
ions, biomolecules in the cell and cell surface recognition are discussed. Naturally occurring
electric fields are not only important for cell-surface interactions, but are also pivotal for the
normal development of the organism and its physiological functions. The review also bridges the
gap between recent cell biological studies (EMF actions) and aspects of EMF-based therapy,
e.g., in wounds and bone fractures.
OS
A study demonstrated the effects of 900 MHz EMF emitted from cellular phone on
brain tissues and also blood malondialdehyde, glutathione, retinol, vitamin D3, tocopherol and
catalase enzyme activity of guinea pigs (34). Results indicated production of OS in brain tissue.
A similar study showed 900 MHz mobile phone-induced oxidative endometrial impairment (35).
The modulation of OS with vitamin E and C reduces the endometrial damage, both at
biochemical and histological levels. Similar exposure also enhanced lipid peroxidation and H2O2
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content accompanied by diminished antioxidative enzyme activity, indicating OS could be partly
due to reduced activities of AO enzymes in duckweed (36). Rats exposed to EMF showed
increase in malondialdehyde levels and decrease in GSH levels (37). A study demonstrated
protective effects of melatonin and caffeic acid phenethyl ester (CAPE) against retinal oxidative
stress in long-term use of mobile phone (38). Mobile phone-induced myocardial OS protection
by the AO CAPE was shown (39). CAPE may prevent the 900 MHz EMF-induced oxidative
changes in liver by ROS reducing and increasing AO enzyme activities (40). Radiofrequency
electromagnetic radiation from mobile phones induces OS and reduces sperm motility in rats
(41). Thus, semen quality and male fertility may be negatively affected. The protective effects
of the AOs N-acetyl-L-cysteine and epigallocatecin-3-gallate on electric field-induced hepatic
OS was reported (42). Results indicate significant increase in the levels of oxidative products
e.g., malondialdehyde, and significant decrease in the AO enzyme SOD; GSH-Px activity was
affected on exposure to EMF. Addition of AOs resulted in the reduction of OS prior to EMF
application.
REACTIVE OXYGEN SPECIES (ROS)
Results demonstrate 60-Hz sinusoidal MF-activated cell growth inhibition of prostate
cancer in vitro (43). Apoptosis together with cell cycle arrest were the dominant causes of the
MF-elicited cell growth inhibition, mediated by MF-induced ROS. These results suggest
possibility of using 60-Hz MF in radiation therapy of prostate cancer. There is formation of ROS
in cells after exposure to 900 MHz radio frequency radiation (44). Results showed that hydrogen
peroxide is produced in aqueous solutions under exposure to electromagnetic radiation as a result
of the influence of heat and thermoacoustic waves (45). The induction of intracellular ROS by
blue light implies that redox effects may mediate the cellular responses. This result suggests the
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opportunity to mitigate any effects of direct or coincident exposure during dental treatment via
AO (46). A recent study suggests that 872 MHz RF radiation might enhance chemically induced
ROS production and thus cause secondary DNA damage (47).
ANTIOXIDANTS (AOs)
A study suggests that mobile telephone radiation leads to oxidative stress in corneal
and lens tissues and the AOs, such as vitamin C, can help to prevent these effects (48). Mobile
phones caused oxidative damage biochemically by increasing the levels of malondialdehyde,
carbonyl groups, xanthine oxidase activity and decreasing catalase activity, and that treatment
with melatonin significantly prevented oxidative damage in the brain (49). Increase in
malondialdehyde levels of renal tissue and also the decrease in renal SOD, catalase, GSH
peroxidase activities demonstrate the role of OS induced by mobile phone exposure. Melatonin,
via its free radical scavenging and AO properties, ameliorated oxidative tissue injury in rat
kidney (50). A similar study suggested that EMF at the frequency generated by a cell phone
causes OS and peroxidation in the ertythrocytes and kidney tissues from rats. In the erythrocytes,
vitamin C seems to protect against the OS (51). A citrus flavoglycoside, naringin protects mouse
liver and intestine against the radiation-induced damage by elevating the AO status and reducing
the lipid peroxidation (52).
Electromagnetic radiation triggered extracellular–signal-regulated kinase-survival
signaling and activated JNK-apoptotic signaling in Dorsophila (53). Near infrared increased
ROS production independent of ischemia and reperfusion, and this effect was blocked by N-
acetylcysteine. Near-infrared electromagnetic radiation also enhanced NO generation during
early reperfusion (54). Radiofrequency-electromagnetic radiation in both power density and
frequency of mobile phones enhances mitochondrial ROS generation by human spermatozoa,
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decreasing the motility and vitality of these cells while stimulating DNA base adduct formation
and, ultimately DNA fragmentation. These findings have clear implications for the safety of
extensive mobile phone use by males of reproductive age, potentially affecting both their fertility
and health, as well as wellbeing of their offspring (55). There is ample evidence that
radiofrequency-electromagnetic radiation can alter the genetic material of exposed cells in vivo
and in vitro and in more than one way (56). This genotoxic action may be mediated by
microthermal effects in cellular structures, formation of free radicals, or an interaction with
DNA-repair mechanisms. A study showed the gene expression of rat neuron could be altered by
exposure to radio frequency EMF under experimental conditions (57). EMF is a stressor agent
that induces an imbalance between ROS generation and AO defense response (58). Calcium ions
may play a pivotal role in enhancing OS, pro-inflammatory reactions and apoptosis associated
with EMF exposure.
CELL SIGNALING
There is extensive literature on the relationship of electromagnetic effects on cells.
Interaction with signaling systems is a potential mechanism by which very low-energy EMfs
might produce metabolic responses in the body (59). Hormone and neurotransmitter receptors
are specialized protein molecules that use a variety of biochemical processes to pass chemical
signals from the outside of a cell across the plasma membrane to the interior. Since many low-
energy EMFs have too little energy to directly traverse the membrane, it is possible that they
may modify the existing signal transduction process in cell membranes, thus providing both
transduction and biochemical amplification of the effects of the field itself. As an example, one
metabolic process in which the physiological effects of low-energy EMFs is well established in
the healing of bone fractures. The process of regulation of bone turnover and healing is reviewed
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in the context of clinical applications of electromagnetic energy to the healing process. A
hypothetical molecular mechanism is presented that might account for the observed effects of
EMF on bone cell metabolism in terms of the field interference with signal transduction events
involved in the hormonal regulation of osteoblast function and differentiation.
There are miscellaneous, additional articles dealing with cell signaling. Exposure of
murine cells to pulsed EMFs rapidly activates the mTOR signaling pathway (60). These findings
suggest that pulsed EMF exposure might function in a manner analogous to soluble growth
factors by activating a unique set of signaling pathways. A recent study reported that pulsed
EMF treatment of osteoblastic cells stimulated the rapid phosphorylation of the mammalian
target rapamycin and its downstream mediators (61). Exposure to 900 MHz EMF induces an
unbalance between pro-apoptotic and pro-survival signals in leukemia cells (62). Pulsed electric
fields with long durations can induce cell fusion or introduce xenomolecules into cells (63). As
the pulse duration decreased, plasma membrane electroporation decreased and appearance of
apoptosis markers were delayed. The results suggest that with decreasing pulse durations,
nanosecond pulsed electric fields modulate cell signaling from plasma membrane to intracellular
structures and functions. Injection of electric field pulses of high intensity and short duration
increases the membrane permeability due to reversible electrical breakdown of the cell
membrane. Such pulses lead to apoptosis in Jurkat T-lymphoblasts and in HL-60 cells including
DNA fragmentation and cleavage of poly(ADP ribose) polymerase (64).
Studies with human hematopoietic cell line TF-1 suggest multifarious effects of EMF
on lipid signal transduction, with doses of 30 or 40 pulses having an anti-proliferative effect (65).
Changes in the lipid second messengers and shift in some molecular species, such as phosphates,
were observed. Static magnetic field on normal human neuronal cell culture induced dramatic
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changes of morphology, formed vortex of cells and exposed branched neuritis featuring synaptic
buttons (66). Inositol lipid signaling was significantly reduced. Endothelin-1 release from FNC-
B4 cells was also dramatically reduced. Results suggest fields below 0.5T have significant
biological effects on human neurons.
Various reports show interaction of EMF and tyrosine kinase. Exposure of lymphoma
cells to low energy EMF results in tyrosine kinase-dependent activation of phospholipase leading
to increased inositol phospholipids turnover (67). Exposure of human skin fibroblasts and rat
osteoblasts to extremely low-frequency EMF induced increase in protein kinase activity (68). A
similar study showed extremely low frequency magnetic fields initiate protein tyrosine
phosphorylation of the T cell receptor complex (69). Findings are in line with earlier reports on
how magnetic field exposure affects signal transduction in Jurkat. In a related study it was shown
that extremely low frequency magnetic fields alter the intracellular calcium concentrations in the
human leukemia T cell line Jurkat (70).
There is extensive literature on calcium in cell signaling. Numerous reports
demonstrate that weak EMFs can elicit in vivo and in vitro bioeffects from several different
biological systems (71). Of particular interest are those studies that report the existence of
“window” effects or resonance-type response of biological systems to the amplitude and
frequency of EMF. The significance of DC magnetic fields for “window” or “resonance” effects
was pointed out two decades ago. The importance of weak EMF bioeffects is now well
established. The phenomenon of signal transduction is central to a wide range of cellular
activities triggered by ligand-gated binding of hormones, antigen molecules, growth factor and
other cell surface agonists which are key pathways for the activation, differentiation and
proliferation of many cell types. Calcium ions appear to be essential in the first steps of
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transduction coupling of exogenous physical signals at the cell membrane and in the ensuing
steps of calcium-dependent signaling in intracellular enzyme systems. The early modulation of
calcium signaling by EMF has, thus, been suggested to be a plausible candidate for activation of
a number of biochemical reactions. EMF coupling with cellular targets may occur via highly
cooperative steps. For example, calcium-dependent steps in the target pathway may include: (i)
initial detection of EMF with resultant electrochemical changes at specific binding sites; (ii)
membrane bound proteins signaling to the cell interior; (iii) EMF coupling with the cytoskeleton
and other subcellular constituents.
Calcium influx increased during mitogen-activated signal transduction in thymic
lymphocytes exposed to a magnetic field (72), providing evidence for an electric field metric and
site of interaction involving the calcium ion channel. A similar study showed a membrane
mediated Ca2+
signaling process is involved in the mediation of EMF in the immune system (73).
High frequency (900 MHz) low amplitude (5 Vm-1
) electromagnetic field stimulus affects
transcription, translation, calcium and energy charge in tomato (74). Within minutes of exposure
to electromagnetic stimulation, stress-related mRNA (clamodulin, calcium-dependent protein
kinase inhibitor) accumulated in a rapid, large and 3-phase manner typical of an environmental
stress response. Extremely low frequency, time-varying fields act in combination with static
magnetic fields to alter calcium signaling in the lymphocytes (75) and inhibits calcium influx
triggered by the mitogen Concanavalin A. Only mitogen-activated cells undergo calcium
signaling and exhibit field response. The interaction of low intensity magnetic field predicts the
occurrence of biological effects at specific values for the frequency and field intensity of the
EMF and static magnetic fields. In a similar study calcium influx was elevated 1.5-fold when
lymphocytes were exposed to Con-A plus magnetic field (76). The signal transduction
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hypothesis is supported by experimental evidence for a general biological framework for
understanding magnetic field interactions with the cell through signal transduction. Magnetic
fields can act as a co-stimulus at suboptimal levels of mitogen; pronounced physiological
changes in lymphocytes, such as calcium influx and c-MYC mRNA induction, were not
triggered by weak mitogenic signal unless accompanied by a magnetic field. Thus, magnetic
fields have the ability to potentiate or amplify cell signaling. In a study using radioactive 45
Ca2+
and murine leukemia cell line, significant increase of calcium influx was shown when exposed to
EMF (77).
In a study, the influence 50 Hz electromagnetic fields in combination with a tumor
promoting phorbol ester on protein kinase C and cell cycle in human cells was carried out;
results indicated lower concentration of phorbol ester induces a less maximum effect on PKC
pathway, which can be enhanced by the applied EMF (78).
Effects of 50-Hz magnetic fields on the signaling pathways of N-formyl-meth-leu-phe-
induced shape changes in invertebrate immunocytes and the activation of an alternative “stress
pathway” were discussed (79). Exposure of Mytilus galloprovincialis to magnetic fields in the
range of 200-1000 μT provokes intensity-correlated effects on potassium and calcium channels
of immunocytes. An intensity of 200 μT was ineffective, while 300 and 400 μT provoked a
temporary damage, and above this level damage progressively became permanent.
The fundamental mechanistic aspects of cell signaling have been addressed (80).
EMF AND CELL PHONES
In a study, detailed molecular mechanism by which electromagnetic irradiation from
mobile phones induces the activation of the extracellular-signal regulated kinase cascade and
how it induces transcription and other cellular processes were described (81). Upon irradiation
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(mobile phone frequencies) on MAPK cascades and ERKs are rapidly activated in response to
various frequencies and intensities of EMF. The first step is mediated in the plasma membrane
by NADH oxidase, which rapidly generates ROS. These ROS then directly stimulate matrix
metalloproteinases and allow them to cleave and release heparin-binding epidermal growth
factor, which, in turn, further activates the extracellular-signal regulated kinase cascade. Mobile
phone radiation-induced activation of hsp27 may (i) facilitate the development of brain cancer by
inhibiting the cytochrome c/caspase-3 apoptotic pathway and (ii) cause an increase in blood
brain barrier permeability through stabilization of endothelial cell stress fibers (82). Authors
postulate that these events, when occurring repeatedly over a long period of time, might become
a health hazard because of the possible accumulation of brain tissue damage. Furthermore, other
brain damaging factors may co-participate in mobile phone radiation-induced effects.
BONE REPAIR
Appreciable attention has been paid to the practical, medical effects of electrical field
exposure on bone injury. There has been renewed interest in the use of magnets for enhancing
tooth movements (83). The major premise upon which magnetic effects alter cell reactions is
based upon electrically based theories of cellular signaling or perturbation of polar proteins
within the cell membrane. The two major theories are based upon electrically based phenomena,
i.e. piezoelectricity and streaming potentials.
Both mechanical and electrical signals have been shown to regulate the synthesis of
extracellular matrix and may do so through the stimulation of signaling pathways at the cell
membrane resulting in the appearance of intracellular second messengers, particularly cyclic
nucleotides (84). The therapeutic use of electric fields is derived from the observation that when
bones are placed under mechanical load (stress) the deformation (strain) is accompanied by an
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electrical signal and the signal is related to strain characteristics. This strain-related or
straingenerated electric potential has been hypothesized to consist of information transfer to the
osteocyte regarding the nature of its mechanical environment and the state of the extracellular
matrix. The origin of the electric signal was thought initially to be related to defamation of the
crystalline structure of extracellular matrix collagen, involving the piezoelectric effect. Other
data, however, have suggested that alterations in fluid flow might produce electrokinetic events,
specifically streaming potentials, which might be partly or wholly responsible for the observed
electric potential.
There are different transduction pathways for ultrasound and pulsed electromagnetic
field stimulation that lead to an upgrade of osteoblast proliferation, with their pathways all
leading to an increase in cytocolic Ca2+
and activation of calmodulin (85). These findings offer a
biochemical mechanism to support the process of ultrasound and pulsed electromagnetic field-
induced enhanced healing of bone fractures.
Pulsed EMFs affect phenotype and connexin 43 protein expression (86). The mechanism
by which EMFs affect bone turnover are unclear. They can directly affect osteoclastic cells, and
there is evidence that cells in the osteoblast lineage are sensitive to EMFs. Pulsed EMF can
influence MG63 osteoblst-like cells by increasing transforming growth factor beta-1 (TGF- 1),
levels but decreasing levels of prostaglandin E2 (PGE2) in the conditioned media. Pulsed EMFs
also increase TGF- 1 production by atrophic and hypertrophic nonunion cells. Others have
shown that EMFs increase ostoblastic proliferation, extracellular matrix production.
MISCELLANEOUS
A study showed EMF induced stimulation of mouse bone marrow-derived macrophages
(87). Furthermore, a significant increase in superoxide production after exposure to EMF was
21
detected. Extremely low frequency EMF can partially block the differentiation of Friend
erythroleukemia cells, and this results in a larger population of cells remaining in the
undifferentiated, proliferative state (88).
Non-additivity of electrostatic and hydrophobic interactions on protein in membrane
interfaces was studied (89). The specific ligand-binding sites are generally flanked by basic
and/or hydrophobic side-chains which mediate electrostatic and hydrophobic interactions
responsible for the non-specific component of binding.
Biophysical input, including electric and EMFs, regulate the expression of genes in
connective tissues for structural extracellular matrix proteins resulting in an increase in cartilage
and bone production (90). Electric and EMF increase gene expression for, and synthesis of,
growth factors and this may function to amplify field effects through autocrine and paracrine
signaling. Electric and EMFs can produce a sustained upregulation of growth factors, which
enhance bone formation.
Microwaves generated by an EMF can affect three dimensional structure of
eukaryotic proteins, also suggesting possible biological effects in living cells (91). Moreover, it
has been demonstrated that prolonged exposure to low-intensity microwave fields can induce
heat-shock responses.
EMFs affect transcript levels of apoptosis related genes in embryonic neural cells
(92). EMF exposure of neural progenitor cells transiently affects the transcript level of genes
related to apoptosis and cell cycle control.
Individuals occupationally exposed to EMFs undergo an increased risk of brain
tumors, particularly astrocytomas (93). For example a study revealed more risk of brain tumors
in electric utility workers linked in a dose-dependent manner to exposure to EMF. A related
22
study, particularly compelling, showed employment in occupations that entail exposure to EMF
presents an elevated risk of 1.7 for all gliomas, and a risk of 10.3 for astrocytomas. Though a
recent study did not support the hypothesis of an increased risk of brain cancer associated with
occupational exposure to magnetic fields, a metaanalysi of 52 studies recently concluded that
there is a small, pervasive association between brain cancer and exposure to EMF. The biological
basis for such association, i.e., the cellular and molecular mechanisms underlying these effects of
EMF, are, however, poorly understood.
A prevailing hypothesis is that EMF may not cause cancer initiation, but may instead
act as a promoter (93). Several studies suggest possible mechanisms to explain the association
between EMF exposure and cancer. One of the most interesting and unifying hypotheses
involving interaction of EMF with signal transduction systems. Specifically, EMF may influence
the signal transduction cascade at the level of the cell membrane, trigger changes in calcium
influx and/or receptor binding, and induce gene expression and protein synthesis, which may
ultimately lead to cell proliferation. Preliminary evidence also suggests that exposure to EMF
causes an increase in protein kinase C activity. PKC is recognized as a key component of the
cellular signal transduction cascade and has been implicated in modulating the expression of
certain genes and regulating cell proliferation.
Magnetic fields increase cell survival by inhibiting apoptosis via modulation of
Ca2+
influx (94). The rescue of damaged cells may be the mechanism explaining why magnetic
fields that are not mutagenic per se are often able to increase mutation and tumor frequencies.
Recent studies investigating changes in susceptibility to apoptosis with regard to
EMF exposure have reported both decreased and increased susceptibility (95). Interestingly,
previous studies involving DNA repair and EMF exposure have reported no effect.
23
The interaction of static magnetic fields (SMFs) with living organisms is a rapidly
growing field of investigation (96). However, despite an increasing number of studies on the
effects of the interaction of SMFs with living organisms, many gaps in our knowledge still
remain. One reason why it is extremely important to understand the mode of action of magnetic
fields on living organisms, is the need to protect human health in consideration of the increasing
introduction of new technologies, such as magnetically levitated trains and the therapeutical use
of magnetic fields( e.g., magnetic resonance imaging ( MRI), coupling of magnetic field
exposure with chemotherapy).
The lack of knowledge of the morphological modifications brought about by
exposure to moderate-intensity SMFs prompted the authors to investigate the bioeffects of 6 mT
SMFs on different cell types, by means of light and electron microscopy, confocal laser scanning
microscopy and immuno- or cytochemistry (96). The morphological modifications related to cell
shape, cell surface, cytoskeleton, and plasma membrane expression of molecules and
carbohydrate residues were studied. The effects of exposure to moderate-intensity SMF on
apoptosis, apoptotic related gene products, macrophagic differentiation and on phagocytosis of
apoptotic cells in primary cell cultures were studied. Results showed moderate-intensity (6 mT)
SMFs induced modifications of cell shape, cell surface and cytoskeleton. Apoptosis was
influenced in all cell type-dependent manner.
Several physical mechanisms have been proposed to account for the initial
interactions with cells (97). Magnetic fields interact with moving charges in cells and change
their velocities, as in the classic interaction of magnetic field with any moving charge. Charge
flow associated with a biological function, as for enzyme activity, has been demonstrated in Na,
K-ATPase and cytochrome oxidase reactions.
24
Interaction of weak EMF with living cells is a most important, but unresolved
biophysical problem (98). Regulation of ion and substrate pathways through microvilli provides
a possible theoretical basis for the comprehension of physiological effects of even extremely low
magnetic fields.
Erythroleukemia K562 cells and lentil root protoplasts have been subjected to pore-
forming electric fields suitable for transfection experiments (99). Evidence showed the amount
of hydroperoxides formed in cell membranes of both cell-types is a function of field strength
applied. On the other hand, electroporation-induced lipid peroxidation paralleled the
enhancement of membrane permeability and was associated with greater membrane fluidity.
The membrane hydroperoxides formed upon electric shock enhanced cell luminescence, and
lipoxygenase activity appeared to be involved in the process.
A recent book on cell signaling contains only limited material on electrochemistry
[100]. Electrical signaling is involved with changes in membrane potential and electrical
impulses in nerve cells for use in communication with other cells. The process entails conversion
of electrical signals into chemical ones. There is knowledge of phosphorylations that affects
enzyme activity solely by electrostatic effects.
There is speculation that biomolecular radicals are the basis for a magnetosensitive
compass that guides migrating birds. The magnetosensitivity of photo-induced radical pairs serve
as a probe of protein substrate interactions [101]. The technique, involving a weak magnet, may
be used to gain information on molecular dynamics, diffusion on surface, charge interactions and
surface potentials.
A novel hypothesis about visual perception and imagery has been proposed recently,
which states that external electromagnetic visible photons are converted into electrical signals in
25
the retina and are then conveyed to the V1 area (102). These electrical signals can be converted
subsequently to bioluminescent photon signals. There is a role for ROS and reactive nitrogen
species.
Very complex magnetic fields rotating around and within the brain can interact with
cerebral processes generating consciousness (103). Evidence is presented showing that
transcranial magnetic stimulation represents a promising tool for elucidating the
pathophysiological sequelae of impaired consciousness with the potential for therapeutic
interaction (104). The literature provides related studies involving magnetic stimulation (105-
110).
Various studies are reported on electrical therapy for Parkinson’s disease. Rapid electrical
stimulation is safe and efficient in treatment of patients (111, 112). The literature contains similar
findings (113, 114).
Favorable results occur in electrotherapy of patients with depression. Electrical treatment
obtained good outcomes with high safety and tolerability (115). There is evidence for electrical
nerve stimulation as the treatment of choice for pain and depression (116). Another investigation
deals with the influence of transcranial current stimulation coupled with repetitive electrical
stimulation on depression (117).
There is application of magnetic nanoparticles as thermal agents in hyperthermic
treatment of cancer (118, 119). Gold nanoparticles efficiently convert the absorbed light into
localized heat which can be exploited for the selective laser photothermal therapy of cancer
(120).
There are recent articles dealing with electric and EMFs that regulate extracellular
matrix synthesis and stimulate repair of fractures and nonunions (121). The study suggests that
26
exposure to EMFs can accomplish the following: 1) regulate proteoglycan and collagen synthesis
and increase bone formation in models of endochondral ossification, 2) accelerate bone
formation and repair, 3) increase union rates in fractures and 4) produce results equivalent to
bone grafts. Chang et al. demonstrated that pulsed EMF with different intensities could regulate
osteoclastogenesis, bone resorption, osteoprotegrin, NFkappaB-ligand, and macrophage-colony-
stimulating factor in marrow culture system (122). A clinical study with 64 patients undergoing
hindfoot arthrodesis (144 joints) showed, if all parameters are equal, the adjunctive use of pulsed
EMF increases the rate and speed of radiographic union of joints (123). A similar study with 100
patients with symptomatic pseudarthrosis lumber spine fusion, pulsed EMF was shown to be an
effective nonoperative salvage approach to achieving fusion (124).
CONCLUSION
There is considerable literature devoted to electromagnetism in the life sciences and
medicine. However, many workers in these areas have little knowledge of the subject and its
importance. This review documents the many interactions of electromagnetic fields (EMFs) with
biological systems and the consequences. Cell signaling has been the subject of much attention
in this connection. Using an integrated approach, interaction is demonstrated involving reactive
oxygen species and oxidative stress, which may lead to toxicity and high levels of the harmful
radicals. The unresolved question of danger associated with man-made EMFs is included.
Beneficial effects of EMFs are discussed, such as in the healing of bone fracture, Parkinson’s
disease, depression and cancer.
ACKNOWLEDGMENT
Editorial assistance by Thelma Chavez is acknowledged.
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