Silver nanoparticles increase cytotoxicity induced by intermediate frequency low voltages

Abstract

Electrical properties of the cells play a key role in biological processes. Intermediate frequencies of electrical fields influence the cells proliferation without heat generation and electrical stimulation. Silver nanoparticle (SNP) as a metallic agent can change the electrical characteristics of the cells. We study the effect of low voltages at an intermediate frequency (300 kHz) on a human breast adenocarcinoma cell line (MCF7) in the presence of SNPs. At first, cell toxicity of SNPs was determined at different concentrations. Then three different voltages were applied to the cells for 15?min, both in the presence and absence of SNPs. The treatments efficiency was evaluated by MTT assay. The results showed that the intermediate frequency-low voltages with SNPs not only provide an additive efficacy on cytotoxicity, but also a synergism was observed between these factors. By increasing the voltage from 3 to 9?V, a rising synergistic rate was observed. It seems that the synergistic effect between SNPs and the 300?kHz low voltages can inhibit cell proliferation and/or increases cell death of MCF-7, and hence increases treatment efficiency of SNPs, effectively.     

Broadened population-level frequency tuning in human auditory cortex of portable music player users

Nowadays, many people use portable players to enrich their daily life with enjoyable music. However, in noisy environments, the player volume is often set to extremely high levels in order to drown out the intense ambient noise and satisfy the appetite for music. Extensive and inappropriate usage of portable music players might cause subtle damages in the auditory system, which are not behaviorally detectable in an early stage of the hearing impairment progress. Here, by means of magnetoencephalography, we objectively examined detrimental effects of portable music player misusage on the population-level frequency tuning in the human auditory cortex. We compared two groups of young people: one group had listened to music with portable music players intensively for a long period of time, while the other group had not. Both groups performed equally and normally in standard audiological examinations (pure tone audiogram, speech test, and hearing-in-noise test). However, the objective magnetoencephalographic data demonstrated that the population-level frequency tuning in the auditory cortex of the portable music player users was significantly broadened compared to the non-users, when attention was distracted from the auditory modality; this group difference vanished when attention was directed to the auditory modality. Our conclusion is that extensive and inadequate usage of portable music players could cause subtle damages, which standard behavioral audiometric measures fail to detect in an early stage. However, these damages could lead to future irreversible hearing disorders, which would have a huge negative impact on the quality of life of those affected, and the society as a whole.     

Functional significance of circulatory anemia, induced in the body by a weak superlow frequency magnetic field]

The effect of weak alternating magnetic field of ultralow frequency during many days naturally expresses in significant decrease of number of erythrocytes in blood, cytopenia of red blood elements of marrow, and in increase of volume of liver and splin. This leads to reduction of gas-transportation function of blood.     

Low frequency spectral density of ferrous heme: perturbations induced by axial ligation and protein insertion

Femtosecond coherence spectroscopy is used to probe low frequency (20-400 cm⁻¹) modes of the ferrous heme group in solution, with and without 2-methyl imidazole (2MeIm) as an axial ligand. The results are compared to heme proteins (CPO, P450_cam, HRP, Mb) where insertion of the heme into the protein results in redistribution of the low frequency spectral density and in (∼60%) longer damping times for the coherent signals. The major effect of imidazole ligation to the ferrous heme is the “softening” of the low frequency force constants by a factor of ∼0.6 ± 0.1. The functional consequences of imidazole ligation are assessed and it is found that the enthalpic CO rebinding barrier is increased significantly when imidazole is bound. The force constant softening analysis, combined with the kinetics results, indicates that the iron is displaced by only ∼0.2 Å from the heme plane in the absence of the imidazole ligand, whereas it is displaced by ∼0.4 Å when imidazole (histidine) is present. This suggests that binding of imidazole (histidine) as an axial ligand, and the concomitant softening of the force constants, leads to an anharmonic distortion of the heme group that has significant functional consequences.     

Low frequency electric and magnetic fields have different effects on the cell surface

There is a considerable controversy over the nature of weak electromagnetic-field effects in living organisms. Part of the controversy can be traced to a lack of understanding of whether electric or magnetic fields are involved in producing bioeffects. We find that both 60 Hz electric and magnetic fields alter the cell surface of Physarum polycephalum. Exposure to electric fields increases the negative charge on the cell surface while magnetic-field exposure decreases the hydrophobic character of the surface. These effects appear to be additive and independent of the waveform of the applied fields.     

Quantification of cellular properties from external fields and resulting induced velocity: magnetic susceptibility.

An experimental technique is discussed in which the magnetic susceptibility of immunomagnetically labeled cells can be determined on a cell-by-cell basis. This technique is based on determining the magnetically induced velocity that an immunomagnetically labeled cell has in a well-defined magnetic energy gradient. This velocity is determined through the use of video recordings of microscopic images of cells moving in the magnetic energy gradient. These video images are then computer digitized and processed using a computer algorithm, cell tracking velocimetry, which allows larger numbers (>10(3)) of cells to be analyzed.     

Electric fields induced by low frequency magnetic fields in inhomogeneous biological structures that are surrounded by an electric insulator

Electric fields induced by low-frequency magnetic fields into inhomogeneous structures, which have electric conductivities and dielectric permittivities of typical biological substances, are evaluated. Closed-form approximate and numerical solutions are obtained for nonconcentric cylinders with different electric properties (such as bone embedded in muscle), which are surrounded by a good electrical insulator (such as air). It is shown that even a single inhomogeneity in an otherwise homogenous cylinder, which is exposed to a uniform, axially directed magnetic field, can lead to substantial deviations from the direction and distribution of the induced electric field that would exist in the homogenous cylinder. Thus the induced field is not everywhere circumferential, nor does it magnitude at all angular positions increase linearly with the radial distance. Radially and circumferentially directed field components depend on size, electrical properties, and eccentricity of the inhomogeneities. Equations as well as graphical presentations are given that describe the induced fields when the enclosed inhomogeneities consist either of eccentrically located single cylinders or pairs of coaxial cylinders with different electrical conductivities or dielectric permittivities.     

Mutation frequency and spectrum resulting from a single abasic site in a single-stranded vector.

We have investigated the mutagenic properties of an abasic site in DNA by transfecting SOS-induced and uninduced cells of E. coli with a single-stranded M13mp7-based vector that carries a single example of this lesion at one or other of two unique and adjacent sites. Random samples of progeny phage were sequenced to determine the nature of the replication events that occurred at and around these locations. 5% to 7% of the vectors could be replicated in SOS-induced cells, but only 0.1% to 0.7% of them gave plaques in the absence of SOS induction. In SOS-induced cells, 93% and 96% of the phage replicated resulted from the insertion of a nucleotide opposite the abasic site, while the remainder resulted from a targeted omission of a single nucleotide. At one of the sites, nucleotide insertions were 54% dAMP, 25% dTMP, 20% dGMP and 1% dCMP. At the other site they were 80% dAMP, 4% dTMP, 15% dGMP and 1% dCMP. The sequence variation in all but two of the 204 sequences analyzed was restricted to the abasic site itself. In the remaining two, a change at the abasic site was accompanied by a mutation at an immediately flanking nucleotide.     

EGF receptor clustering is induced by a 0.4 mT power frequency magnetic field and blocked by the EGF receptor tyrosine kinase inhibitor PD153035

Atomic force microscopy (AFM), transmission electron microscopy (TEM), and confocal laser scanning microscopy were used to investigate the effects of a 50 Hz 0.4 mT magnetic field (MF) on the clustering of purified epidermal growth factor receptors (EGFRs) and EGFRs in Chinese hamster lung (CHL) cell membrane. The results demonstrate that exposing purified EGFRs to the MF for 30 min induces receptor clustering. The peak height of apparent clusters increased from 1.42 +/- 0.18 (sham-exposed) to 3.08 +/- 0.38 nm (exposed) while the mean half-width increased from 21.7 +/- 2.2 to 33.0 +/- 4.0 nm. A similar effect was also observed by TEM. Treatment of purified EGFR with PD153035 (PD), an EGFR-specific tyrosine kinase (TK) inhibitor, inhibited the MF-induced EGFR clustering of the purified proteins, an effect also observed for the receptors in cell membrane in the absence of EGF. These results strongly suggest that the 50 Hz 0.4 mT MF interferes with the EGFR signaling pathway, most likely by interacting with the cytoplasmic TK domain.     

Deficits in water maze performance and oxidative stress in the hippocampus and striatum induced by extremely low frequency magnetic field exposure

The exposures to extremely low frequency magnetic field (ELF-MF) in our environment have dramatically increased. Epidemiological studies suggest that there is a possible association between ELF-MF exposure and increased risks of cardiovascular disease, cancers and neurodegenerative disorders. Animal studies show that ELF-MF exposure may interfere with the activity of brain cells, generate behavioral and cognitive disturbances, and produce deficits in attention, perception and spatial learning. Although, many research efforts have been focused on the interaction between ELF-MF exposure and the central nervous system, the mechanism of interaction is still unknown. In this study, we examined the effects of ELF-MF exposure on learning in mice using two water maze tasks and on some parameters indicative of oxidative stress in the hippocampus and striatum. We found that ELF-MF exposure (1 mT, 50 Hz) induced serious oxidative stress in the hippocampus and striatum and impaired hippocampal-dependent spatial learning and striatum-dependent habit learning. This study provides evidence for the association between the impairment of learning and the oxidative stress in hippocampus and striatum induced by ELF-MF exposure.     

Asthma induced by house dust mites: benefits resulting from a correct environmental hygienization

Summary The aim of the present work has been the determination of the effectiveness of a primary prevention in the allergopathy induced by house dust mites weighing its benefits as regards asthmatic symptomatology.A sample of 56 subjects, aged 6 to 30 years, monosensitive to house dust mites (DTP and DTF) and with a diagnosis of bronchial asthma has been examined. The patients have entered a study plan whose purpose has been the evaluation of the effects of an environmental improvement on symptomatology. The diagnosis of asthma induced by house dust mites has been confirmed both by in vivo (Prick-test) and in vitro (PRIST and RAST) investigations.A follow-up after 3 months has shown that the hygienic measures have produced beneficial effects on symptomatology in as many as 22 patients (52.4%) out of a total of 42 who have put into practice the environmental improvement. These results encourage to proceed on this path in the choice of the therapy for those subjects affected by respiratory allergopathy to house dust mites.     

Spike suppression in a local cortical circuit induced by transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) noninvasively interferes with human cortical function, and is widely used as an effective technique for probing causal links between neural activity and cognitive function. However, the physiological mechanisms underlying TMS-induced effects on neural activity remain unclear. We examined the mechanism by which TMS disrupts neural activity in a local circuit in early visual cortex using a computational model consisting of conductance-based spiking neurons with excitatory and inhibitory synaptic connections. We found that single-pulse TMS suppressed spiking activity in a local circuit model, disrupting the population response. Spike suppression was observed when TMS was applied to the local circuit within a limited time window after the local circuit received sensory afferent input, as observed in experiments investigating suppression of visual perception with TMS targeting early visual cortex. Quantitative analyses revealed that the magnitude of suppression was significantly larger for synaptically-connected neurons than for isolated individual neurons, suggesting that intracortical inhibitory synaptic coupling also plays an important role in TMS-induced suppression. A conventional local circuit model of early visual cortex explained only the early period of visual suppression observed in experiments. However, models either involving strong recurrent excitatory synaptic connections or sustained excitatory input were able to reproduce the late period of visual suppression. These results suggest that TMS targeting early visual cortex disrupts functionally distinct neural signals, possibly corresponding to feedforward and recurrent information processing, by imposing inhibitory effects through intracortical inhibitory synaptic connections.     

Currents induced in anatomic models of the human for uniform and nonuniform power frequency magnetic fields

We have used the quasi-static impedance method to calculate the currents induced in the nominal 2 x 2 x 3 and 6 mm resolution anatomically based models of the human body for exposure to magnetic fields at 60 Hz. Uniform magnetic fields of various orientations and magnitudes 1 or 0.417 mT suggested in the ACGIH and ICNIRP safety guidelines are used to calculate induced electric fields or current densities for the various glands and organs of the body including the pineal gland. The maximum 1 cm(2) area-averaged induced current densities for the central nervous system tissues, such as the brain and the spinal cord, were within the reference level of 10 mA/m(2) as suggested in the ICNIRP guidelines for magnetic fields (0.417 mT at 60 Hz). Tissue conductivities were found to play an important role and higher assumed tissue conductivities gave higher induced current densities. We have also determined the induced current density distributions for nonuniform magnetic fields associated with two commonly used electrical appliances, namely a hair dryer and a hair clipper. Because of considerably higher magnetic fields for the latter device, higher induced electric fields and current densities were calculated.     

A possible involvement of beta-endorphin, substance P, and serotonin in rat analgesia induced by extremely low frequency magnetic field

Most of the research concerning magnetic antinociception was focused on brief exposure less than 1 h. The main purpose of the present study was to determine the effect of extremely low frequency (ELF) magnetic field (MF) repeated exposures on rats in inducing antinociception and to find the effective analgesic "time window." Meanwhile this investigation was to examine the role of central beta-endorphin, substance P, and 5-HT in magnetic analgesia. We found tail flick latencies (TFLs) increased significantly after the rats were exposed to 55.6 Hz, 8.1 mT magnetic field for 4 days, 6 h each day. The analgesic effects seemed to decrease gradually when the rats were exposed daily for another 10 days. Their levels of TFLs decreased within 1 day when the rats were removed after a 4-day exposure. The concentrations of hypothalamus beta-endorphin, substance P, and brainstem serotonin (5-HT) were increased significantly on Day 4. However, no differences were found when rats were exposed for another 10 days, and there were no significant increases when rats were removed after the fourth day of exposure and tested for nociception on Days 5 and 7 with no changes in the biochemical markers at 7 days. These results suggest that the ELF magnetic field has analgesic effect, but only on Days 3 and 4. The effect may be associated with increases in endogenous beta-endorphin, substance P, and 5-HT stimulated by the 55.6 Hz, 8.1 mT magnetic field.     

High frequency dynamics in hemoglobin measured by magnetic relaxation dispersion

The magnetic relaxation dispersion profiles for formate, acetate, and water protons are reported for aqueous solutions of hemoglobin singly and doubly labeled with a nitroxide and mercury(II) ion at cysteines at beta-93. Using two spin labels, one nuclear and one electron spin, a long intramolecular vector is defined between the two beta-93 positions in the protein. The paramagnetic contributions to the observed 1H spin-lattice relaxation rate constant are isolated from the magnetic relaxation dispersion profiles obtained on a dual-magnet apparatus that provides spectral density functions characterizing fluctuations sensed by intermoment dipolar interactions in the time range from the tens of microseconds to approximately 1 ps. Both formate and acetate ions are found to bind specifically within 5 angstroms of the beta-93 spin-label position and the relaxation dispersion has inflection points corresponding to correlation times of 30 ps and 4 ns for both ions. The 4-ns motion is identified with exchange of the anions from the site, whereas the 30-ps correlation time is identified with relative motions of the spin label and the bound anion in the protein environment close to beta-93. The magnetic field dependence of the paramagnetic contributions in both cases is well described by a simple Lorentzian spectral density function; no peaks in the spectral density function are observed. Therefore, the high frequency motions of the protein monitored by the intramolecular vector defined by the electron and nuclear spin are well characterized by a stationary random function of time. Attempts to examine long vector fluctuations by employing electron spin and nuclear spin double-labeling techniques did not yield unambiguous characterization of the high frequency motions of the vector between beta-93 positions on different chains.