The role of lipid peroxidation and myeloperoxidase in priming a respiratory burst in neutrophils under the action of combined constant and alternating magnetic fields

The enhancement of lipid peroxidation in neutrophils (the content of malonic dialdehyde increased by 10.2%) has been shown after a 1-h exposure to a combined constant (42 μT) magnetic field and a weak low-frequency magnetic field (1.0, 4.4, and 16.5 Hz; 860 nT) collinear to it. No correlation was found between this effect and the process of functional pre-activation (priming) of neutrophils as a result of the combined action of magnetic fields detected by chemiluminescence enhancement in response to the introduction of the bacterial peptide N-formyl–Met–Leu–Phe in the presence of luminol, since ionol (10 μM), an inhibitor of lipid peroxidation, did not reduce the neutrophil priming index in this case. Preliminary addition of histidine (0.1 and 1.0 mM), a singlet oxygen scavenger, also did not decrease the priming index. A myeloperoxidase inhibitor, sodium azide (0.1 mM), exerted a significant inhibitory effect on the chemiluminescence intensity of the neutrophil suspension; priming did not develop in the presence of this inhibitor after the action of combined magnetic fields.     

The role of hydroxyl radicals and calcium ions in the priming of a respiratory burst in neutrophils and the increase in luminol-dependent blood chemiluminescence on exposure to combined magnetic fields with a very weak low-frequency alternating component

The intracellular calcium chelator 1,2-bis(2-aminophenoxy)ethane N,N,N′,N′-tetraacetic acid acetoxymethyl ester (BAPTA AM) used at low concentrations (1.0 and 2.5 μM) was shown to block the priming effect of weak combined static (42 μT) and low-frequency collinear alternating (1.0, 4.4, and 16.5 Hz; 0.86 μT) magnetic fields. This blockage was inferred from a greater increase in chemiluminescence observed for a mouse neutrophil suspension exposed to combined magnetic fields in response to the bacterial peptide N-formyl–Met–Leu–Phe added in the presence of luminol. Similar results were obtained for the effect of BAPTA AM on luminol-dependent chemiluminescence of whole blood. The priming effect of weak combined magnetic fields on the respiratory burst in neutrophils did not depend on the presence of extracellular Ca²⁺ and was not affected by the hydroxyl radical scavenger dimethyl sulfoxide used at 0.025–1.0 mM.     

Modulation of cardiac rhythm in the humans exposed to extremely weak alternating magnetic fields

The effect of extremely weak alternating magnetic fields of various types with the amplitudes δ of 2 μT on the heart rate variability in humans was studied. Volunteers were placed in a large-volume coil system (2ω2ω2 m), which provided exposure of the whole body to extremely weak alternating magnetic fields uniform in their amplitude. It was shown for the first time that the exposure to such fields could both increase and decrease the magnitude of stress in humans. In particular, the field tuned to the nuclear spins of hydrogen atoms (amplitude, 1.6 μT and frequency, 76 Hz) decreased the Baevsky stress index, whereas the field tuned to the magnetic moments formed by the orbiting electrons in some atoms (amplitude, 0.192 μT and frequency, 3000 Hz) increased this index. These results provide a possible explanation for the mechanisms of adverse effects caused by extremely weak alternating magnetic fields of certain types of both technogenic and natural origins on the human cardiovascular system.     

Effect of weak combined static and low-frequency alternating magnetic fields on the Ehrlich ascites carcinoma in mice

The parameters of the low-frequency (1, 4.4, 16.5 Hz or the sum of these frequencies) extremely weak (300, 100, 150–300 nT, according to frequencies) alternating component of combined magnetic fields have been found, which in combination with a weak collinear static field of 42 μT (the induction corresponds to the range of the geomagnetic field) has a marked antitumor activity. The exposure to these magnetic fields inhibits the tumor growth in mice with an intraperitoneally transplanted Ehrlich ascites carcinoma. The effect manifests itself as an increase in the life of tumor-bearing animals and in the content of damaged tumor cells. It was found that the death of tumor cells by the action of weak fields occurs predominantly by the mechanism of necrosis.     

Effects of low-level combined static and weak low-frequency alternating magnetic fields on cytokine production and tumor development in mice

We investigated the effects of weak combined magnetic fields (MFs) produced by superimposing a constant MF (in the range 30 - 150 µT) and an alternating MF (100 or 200 nT) on cytokine production in healthy Balb/C male mice exposed 2 h daily for 14 days. The alternating magnetic field was a sum of several frequencies (ranging from 2.5 - 17.5 Hz). The frequencies of the alternating magnetic field were calculated formally based on the cyclotron resonance of ions of free amino acids (glutamic and aspartic acids, arginine, lysine, histidine, and tyrosine). The selection of different intensity and frequency combinations of constant and alternating magnetic fields was performed to find the optimal characteristics for cytokine production stimulation in immune cells. MF with a constant component of 60 μT and an alternating component of 100 nT, which was a sum of six frequencies (from 5 to 7 Hz), was found to stimulate the production of tumor necrosis factor-α, interferon-gamma, interleukin-2, and interleukin-3 in healthy mouse cells and induce cytokine accumulation in blood plasma. Then, we studied the effect of this MF on tumor-bearing mice with solid tumors induced by Ehrlich ascite carcinoma cells by observing tumor development processes, including tumor size, mouse survival rate, and average lifespan. Tumor-bearing mice exposed to a combined constant magnetic field of 60 μT and an alternating magnetic field of 100 nT containing six frequencies showed a strong suppression of tumor growth with an increase in survival rate and enhancement of average lifespan.     

Effects of extremely weak alternating magnetic fields on the plant gravitropism

It was shown that the rate of gravitropic response in apical segments excised from the 4-day-old seedlings of flax (Linum bienne) may be substantially influenced by combined magnetic fields (CMF) of two different types: 1) CMF tuned to the parametric resonance for Ca2+; 2) CMF containing extremely weak alternating component with the values of magnetic density ranging from 10(-6) to 10(-10) T. Our experimental data indicate that CMF affect the gravitropic response via at least two different mechanisms. The first one corresponds to the ion parametric resonance well established earlier in studies with test-systems prepared from animals. The origin of the bioeffects induced by CMF containing extremely weak alternating component remains to be established.     

Effect of weak static and low-frequency alternating magnetic fields on the fission and regeneration of the planarian dugesia (Girardia) tigrina

The effect of weak static (DC) and alternating (AC) magnetic fields (MFs), as well as combined (AC/DC) collinear MFs on the intensity of morphogenesis processes in the planarian Dugesia (Girardia) tigrina has been studied. It was found that combined MFs produce a stimulating effect on the fission and regeneration of planarians. Both components of the combined MFs, the direct (DC) and the alternating (AC), are important in the realization of the effects of weak MFs. The practically complete absence of one of the components (DC) reverses the sign of the effect. It was shown that the presence of concomitant background MFs does not substantially influence the effects of combined MFs with a very small AC component (100 nT). The effect of the "zero" field is significant and comparable in magnitude with the effects of combined MFs at effective frequencies. Narrow zones of effective amplitudes (in the region of tens and hundreds of nT) of the AC component of the combined MFs, with the DC component close to the value of the geomagnetic field were found, which alternate with regions where the response of the biological object to the influence is absent.     

Priming effect of calcium ionophores on phorbol ester-induced respiratory burst in mouse peritoneal neutrophils.

The abilities of three calcium ionophores (A23187, 4-bromo-A23187, and ionomycin) to modulate the respiratory burst of neutrophils induced by phorbol ester and to increase the concentration of free intracellular Ca2+ ([Ca2+]i) were compared. The production of reactive oxygen species (ROS) was determined by luminol-dependent chemiluminescence and [Ca2+]i was determined with the Fura-2 fluorescent probe. A23187 (0.05-2 microM) and ionomycin (0.001-0.5 microM) but not 4-bromo-A23187 amplified 3-4-fold the respiratory burst induced by phorbol ester. The integral response (total production of ROS over 6 min) had a bell-shaped dependence on the concentration of ionomycin and A23187 with increase and decrease at low and high concentrations of the ionophores, respectively. The maximal effect was found at 0.5 microM ionomycin and 2 microM A23187, these concentrations resulting in transient increases in [Ca2+]i to 1776 +/- 197 and 955 +/- 27 nM, respectively. The ionophores had no effect in calcium-free media, though they increased [Ca2+]i to approximately 400 nM through the mobilization of intracellular Ca2+. In cells with exhausted stores of Ca2+, the addition of 1.5 mM Ca2+ combined with phorbol ester amplified twofold the production of ROS. The inhibition of phospholipase A2 with 4-bromophenacyl bromide significantly decreased the production of ROS. Thus, the entrance of Ca2+ and generation of arachidonic acid under the influence of phospholipase A2 are necessary for the ionophore-induced priming of production of ROS during cell activation with phorbol esters.     

Effect of weak and superweak combined permanent and low-frequency alternating magnetic fields and low-intensity millimeter waves on regeneration of planaria Dugesia tigrina

It has been shown that exposure to weak combined collinear magnetic fields (permanent component 42 mT; amplitude of alternating component 40 nT, frequency 3.7 Hz) or millimeter waves with a frequency of 36 GHz and power density of 100 mT/cm2 substantially stimulates the growth of the regeneration blastema in the tail fragment of planaria when the exposure to fields precedes the cutting of the planaria body. This effect is more clearly pronounced during the treatment of planaria with magnetic field. If the treatment with weak physical factors is carried out after the cutting of planaria, the effect of the field is two times less pronounced (exposure to magnetic waves) or is not evident at all (exposure to electromagnetic radiation).     

Effect of magnetic resonance imaging on human respiratory burst of neutrophils

It is known that low intensity magnetic fields increase superoxide anion production during the respiratory burst of rat peritoneal neutrophils in vitro. We investigated whether the high intensity magnetic fields (1.5 T) during magnetic resonance imaging can influence the human neutrophil function under in vivo conditions. Blood samples were obtained from 12 patients immediately before and after magnetic resonance imaging (mean time 27.6(+/-11.4 min)). The induced respiratory burst was investigated by the intracellular oxidative transformation of dihydrorhodamine 123 to the fluorescent dye rhodamine 123 via flow cytometry. The respiratory burst was induced either with phorbol 12-myristate 13-acetate, Escherichia coli, N-formyl-methionyl-leucylphenylalanine or priming with tumor necrosis factor followed by FMLP stimulation. There was no significant difference between the respiratory burst before and after magnetic resonance imaging, irrespective of the stimulating agent. Short time exposure to a high intensity magnetic field during magnetic resonance imaging seems not to influence the production of radical species in living neutrophils.     

The effect of weak low-frequency magnetic fields on the intracellular calcium-dependent proteinases of fish

The in vivo and in vitro effects of weak, low-frequency magnetic fields with resonance parameters for calcium ions upon intracellular calcium-dependent proteinases (calpains) in the crucian carp (Carassius carassius (L.)) and roach (Rutilus rutilus (L.)) were studied. It has been revealed that the impact of a weak lowfrequency magnetic field leads to considerable decrease in the activity of calpains in the fish skeletal muscles and brain.     

Priming action of inositol hexakisphosphate (InsP6) on the stimulated respiratory burst in human neutrophils.

After priming by a number of different host, bacterial and chemical agents, human neutrophils may be stimulated to produce a greater respiratory burst than would be elicited by the stimulus alone. Other neutrophil functions may be similarly enhanced by pre-exposure to a priming agent. We describe here a new extracellular role for inositol hexakisphosphate (InsP6) as a priming agent for a variety of human neutrophil functional responses. Preincubation of the cells with InsP6 alone (up to 250 microM) has no stimulatory effect upon the basal production of reactive oxygen intermediates but the response to a subsequent stimulus (FMLP, PMA or phagocytic particles) is substantially enhanced. Levels 100-200% higher than 'stimulus only' controls have been recorded. Peak enhancement of the FMLP-induced oxidative response occurs after 1-2 min preincubation with InsP6 and the effect is dose-dependent (maximum at approx. 100 microM InsP6). As others have shown FMLP stimulation of superoxide anion production has no external Ca2+ dependence but the presence of low levels of Ca2+ and Mg2+ (0.1 mM) during priming appears to be an essential requirement for full expression. Reports of intracellular concentrations of InsP6 in mammalian cells in the 30-100 microM range suggest that the local release of this inositol polyphosphate from damaged or effect cells could have a physiologically important modulatory role on neutrophil functions.     

Increased resorptions in CBA mice exposed to low-frequency magnetic fields: An attempt to replicate earlier observations

This paper has two aims. First, it reports the findings of a study on the effects of low-frequency magnetic fields on reproduction. Second, it serves as an example of an attempt to replicate the results of an experimental study in an independent laboratory and discusses some of the problems of replication studies. To try to replicate the findings of a study reporting increased resorptions (fetal loss) in mice exposed to 20 kHz magnetic fields with sawtooth waveform and to study the possible effects of 50 Hz sinusoidal fields, pregnant mice were exposed to magnetic fields from day 0 to 18 of pregnancy, 24 h per day. The flux densities of the vertical magnetic fields were 15 μT (peak-to-peak) at 20 kHz and 13 or 130 μT (root mean square) at 50 Hz. Two strains of animals were used: CBA/S mice imported from the laboratory reporting the original observations, and a closely related strain CBA/Ca. The CBA/S mice were cleaned of pathogenic microbes and parasites before they were imported into our laboratory. The magnetic field exposures did not affect resorption rate in CBA/Ca mice. In CBA/S, the frequency of resorptions was higher in the exposed mice than in the control group. However, the increase was not significantly different from either the no-effect hypothesis or the results of the original study we were attempting to replicate. Differences between the two studies and difficulties in interpreting the results are discussed. It is concluded that the results tend more to support than argue against increased resorptions in CBA/S mice exposed to the 20 kHz magnetic field. The results demonstrate that animal strain is an important variable in bioelectromagnetics research: even closely related strains may show different responses to magnetic field exposure. Bioelectromagnetics 18:410–417, 1997. © 1997 Wiley-Liss, Inc.     

The effect of weak magnetic fields on the production of reactive oxygen species in neutrophils

It was shown that a 1-h-long exposure of mouse peritoneal neutrophils to a combination of a weak constant magnetic field (42 μT) and low-frequency alternating magnetic fields collinear to the weak constant magnetic field (the sum of the frequencies 1.0, 4.4, and 16.5 Hz; amplitude, 0.86 μT) at physiological temperatures caused an increase in the intracellular production of reactive oxygen species, as measured by the changes in fluorescence of the products of 2,7-dichlorodihydrofluorescein and dihydrorhodamine 123 oxidation. The effect of weak magnetic fields was significantly more pronounced in the presence of low concentrations of respiratory burst activators (N-formyl-Met–Leu–Phe or phorbol 12-meristate-13-acetate).

     

Fluoride-mediated activation of the respiratory burst in electropermeabilized neutrophils

Electropermeabilization creates small pores in the plasma membrane allowing the introduction of low-molecular-weight modulatory components, such as ions and nucleotides, into the cytosol. The present study investigates fluoride-mediated stimulation of the signal transduction pathway that activates the respiratory burst in electropermeabilized neutrophils. In marked contrast to intact (i.e., non-electropermeabilized) neutrophils, cells permeabilized by this technique demonstrated an immediate and potent stimulation of the superoxide (O2-)-generating NADPH oxidase in response to the addition of fluoride. Furthermore, permeabilization of neutrophils in the presence of exogenously added ATP enhanced the rate of F(-)-mediated O2- production. Fluoride-stimulated O2- production in electropermeabilized neutrophils was antagonized by GDP beta S and dependent upon the presence of Mg2+ in the medium, but was insensitive to pertussis toxin treatment, consistent with the hypothesis that fluoride activates a G protein, probably Gp, by interacting with the nucleotide-binding site on the G alpha subunit. In addition, electropermeabilized neutrophil O2- release triggered by F- was blocked by staurosporine and H-7, indicating that this pathway proceeds largely through protein kinase C activation. However, nucleotide-enhanced O2- production was only partially blocked by these inhibitors, suggesting that under such conditions ATP either competes with the inhibitor-protein kinase interaction or affects the signaling pathway(s) in such a way that protein kinase C may no longer be necessary for the activation of NADPH oxidase.     

Inhibition of growth rate of escherichia coli induced by extremely low-frequency weak magnetic fields

Cultures of Escherichia coli kept at 0 °C in a phosphate buffer solution were exposed to a sinusoidal weak 60- or 600-Hz magnetic field of strength 2 × 10^?3 Tesla. A decrease of more than 40% in bacterial count was observed after a 60-h exposure to the magnetic field. Electron micrographs of exposed bacteria show ruptured cell walls, possibly due to the breaking away of flagella under the influence of the sinusoidally varying electromotive force.