The effect of bromodeoxyuridine and ultraviolet light on 9L rat brain tumor cells

Incorporation of the thymidine analog bromodeoxyuridine (BrdUrd) into DNA increases the sensitivity of a cell to uv light. We have examined the effect of uv light on cell killing and alkaline elution profiles in 9L rat brain tumor cells pretreated with BrdUrd. Combination treatment with BrdUrd and uv irradiation produced a dose enhancement ratio of 3.8 at the 10% survival level compared with uv-radiated control cells; cell killing depended on both the time of treatment and the concentration of BrdUrd used for incubation. Sequential treatment caused single-strand breaks and DNA-protein crosslinks in the portion of DNA containing BrdUrd; uv irradiation alone caused very few strand breaks and no DNA-protein crosslinks. Because of the presence of both lesions in cells treated with BrdUrd and uv light, it was possible to calculate crosslinking factors without using a charging X-ray dose to induce strand breaks, the method commonly used with crosslinking drugs. Results of repair studies suggested that single-strand breaks are repaired more rapidly than are DNA-protein crosslinks.     

Investigation of co-genotoxic effects of radiofrequency electromagnetic fields in vivo

We investigated the possible combined genotoxic effects of radiofrequency (RF) electromagnetic fields (900 MHz, amplitude modulated at 217 Hz, mobile phone signal) with the drinking water mutagen and carcinogen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX). Female rats were exposed to RF fields for a period of 2 years for 2 h per day, 5 days per week at average whole-body specific absorption rates of 0.3 or 0.9 W/kg. MX was given in the drinking water at a concentration of 19 microg/ml. Blood samples were taken at 3, 6 and 24 months of exposure and brain and liver samples were taken at the end of the study (24 months). DNA damage was assessed in all samples using the alkaline comet assay, and micronuclei were determined in erythrocytes. We did not find significant genotoxic activity of MX in blood and liver cells. However, MX induced DNA damage in rat brain. Co-exposures to MX and RF radiation did not significantly increase the response of blood, liver and brain cells compared to MX exposure only. In conclusion, this 2-year animal study involving long-term exposures to RF radiation and MX did not provide any evidence for enhanced genotoxicity in rats exposed to RF radiation.     

Synchronization of 9L rat brain tumor cells by centrifugal elutriation

Asynchronous 9L cells were separated into relatively homogeneously-sized populations using centrifugal elutriation with both a conventional collection method and a long collection method. A substantial increase in the homogeneity of the volume distributions and in the degree of synchrony of the separated fractions was obtained using the long collection method. Autoradiographic data indicated that fractions containing ≥97% G₁ cells, ≥80% S cells, and 70–75% G₂ cells could be routinely recovered with this procedure. Recovery in these fractions varied from 5 to 8% of the total number of cells elutriated. The colony forming efficiency (CFE) of cells from fractions representing each phase of the cell cycle was a constant 60–70%, which was comparable to the 60–80% usually found for asynchronous 9L cells. The percentage of cells in the G₁, S, and G₂ phases in the elutriated fractions was more accurately determined from the volume distribution than from computer fits of the DNA histogram obtained from flow cytometry. In general, the degree of synchrony was related to the coefficient of variation (CV) of the volume distributions of the elutriated fractions. The CV was about 14% for all elutriated fractions. When the ≥97% G₁ population was allowed to progress to S and G₂, the CVs were about 17 and 20.2%, respectively. Thus, the best nonperturbing method for obtaining synchronous 9L cells in the S or G₂ phases was direct elutriation with the long collection method.     

Synchronization of 9L rat brain tumor cells by centrifugal elutriation

Asynchronous 9L cells were separated into relatively homogeneously-sized populations using centrifugal elutriation with both a conventional collection method and a long collection method. A substantial increase in the homogeneity of the volume distributions and in the degree of synchrony of the separated fractions was obtained using the long collection method. Autoradiographic data indicated that fractions containing greater than or equal to 97% G1 cells, greater than or equal to 80% S cells, and 70-75% G2 cells could be routinely recovered with this procedure. Recovery in these fractions varied from 5 to 8% of the total number of cells elutriated. The colony forming efficiency (CFE) of cells from fractions representing each phase of the cell cycle was a constant 60-70%, which was comparable to the 60-80% usually found for asynchronous 9L cells. The percentage of cells in the G1, S, and G2 phases in the elutriated fractions was more accurately determined from the volume distribution than from computer fits of the DNA histogram obtained from flow cytometry. In genereal, the degree of synchrony was related to the coefficient of variation (CV) of the volume distributions of the elutriated fractions. The CV was about 14% for all elutriated fractions. When the greater than or equal to 97% G1 population was allowed to progress to S and G2, the CVs were about 17 and 20.2%, respectively. Thus, the best nonperturbing method for obtaining synchronous 9L cells in the S or G2 phases was direct elutriation with the long collection method.     

Prenatal exposure to 900 MHz, cell-phone electromagnetic fields had no effect on operant-behavior performances of adult rats

To clarify potential health risks of radio-frequency electromagnetic fields (EMFs) used in cellular telephone technology to the developing brain, Wistar rats were continuously exposed during pregnancy to a low-level (0.1 mW/cm(2)) 900 MHz, 217 Hz pulse modulated EMF that approximated the highest legal exposure of normal populations to the radiation of base antennas of the GSM digital cell-phone technology. Whole body average specific absorption rate (SAR) values for the freely roaming, pregnant animals were measured in models; they ranged between 17.5 and 75 mW/kg. The offspring of exposed and of sham-exposed dams were coded and tested later as adults in a battery of ten simultaneously operated test chambers (Skinner boxes) during night time. Eight groups of ten coded animals in each group were tested for learning deficits in a sequence of nine, computer-controlled, 15 h sessions of the food-reinforced contingency Differential Reinforcement of Rate with increasing performance requirements. Two different sets of events were recorded: The food-reinforced lever-pressing activity of the animals and the inter-response intervals (IRIs) between consecutive lever presses. IRI-occurence patterns discriminated consistently between "learners" and "non-learners". Analyses of performance scores and of IRI-patterns both showed that exposure in-utero to the GSM field did not induce any measurable cognitive deficits.     

Radiofrequency electromagnetic fields in swedish radio stations and tall FM/TV towers

Radiofrequency electric and magnetic fields have been measured around 11 large broadcast stations and tall FM/TV towers in Sweden. The results show that operating personnel may be exposed to fields exceeding by several times the present standard for occupational exposure to RF radiation. Maintenance personnel are especially vulnerable to exposure when climbing energized towers. The present study indicates that the transmitters should be switched off during the performance of certain tasks on the tower. Safe passage of maintenance personnel near energized antennas of certain types is impossible without a drastic reduction of the transmitted power. In the stations, the RF leakage radiation was generally low, but when work was done with the cabinet doors of the transmitter open, high field strengths were found in the vicinity of the transmitter even though it was switched off. It was found that the transmitter acted as a tuned receiver of energy from the other transmitters.     

Depletion of intracellular putrescine and spermidine by alpha-difluromethylornithine does not inhibit proliferation of 9L rat brain tumor cells.

Incubation of 9L rat brain tumor cells with 25 mM DL-α-difluoromethylornithine inhibits cell proliferation, while treatment with 10 mM and 1 mM do not. All three concentrations cause equal degrees of depletion of intracellular putrescine and spermidine content, but have no effect on spermine content. These observations show that 9L cells can continue to proliferate in spite of significant polyamine depletion and leads one to question the role of polyamines in 9L cell replication. These observations also suggest that inhibition of 9L cell proliferation by 25 mM DL-α-difluormethylornithine is probably not due to its effect on ornithine decarboxylase or on intracellular polyamine content.     

Delayed biological effect of electromagnetic fields action

The real possibility of the development of remote effects in people after longterm EMF-exposure was presented in the world scientific literature. Many authors decided that there is connection between long-term EMF-exposure and development of the breast cancer, brain tumours, leukaemia and neurodegenerative diseases (Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis). The analysis of up-to-date publications leads us to the conclusion that this problem is actual and further researches of conditions provoking development of last-term effects are required.     

Primary mechanisms of the biological effect of electromagnetic fields

Based on the model of a bulk knitted structure, a possible mechanism of action of an external electromagnetic field on biological systems was proposed. The electromagnetic field affects biological processes through changes in the rates of biochemical reactions in response to changes in the conformational properties of water in the electromagnetic field.     

Low-energy electromagnetic fields promote proliferation of vascular smooth muscle cells

The rationale was to investigate the effects of low-energy electromagnetic fields (EMF) on the proliferation of bovine coronary and murine aortic smooth muscle cells (SMC). EMF were applied to SMC at field frequencies of 25, 50, or 100 Hz, and exposure time was set to 5, 15, or 30 minutes. Significant increases in SMC-counts compared with sham exposed controls were found for all EMF-frequencies tested. The effect was most pronounced for 50 Hz fields with maximum increases of 1.2-fold over controls. Sequential double exposure of mouse aortic SMC to 50 Hz fields revealed significantly enhanced cell proliferation by 1.2 fold compared with single exposure (p < 0.05). Experiments performed on bovine SMC also revealed significant increases in cell proliferation. The results demonstrate that EMF are capable of significantly enhancing the proliferation of vascular SMC. These results rise the question whether EMF would qualify as supportive means to angio-/arteriogenic approaches.     

Influence of ELF sinusoidal electromagnetic fields on proliferation and metabolite yield of fungi

The response of mycelium proliferation in 12 strains of fungi were tested by sinusoidal ELF 50 Hz electromagnetic field treatment in the range B = 0.6-10 mT over 10 days. The ratio of experiment/control indicated three types of proliferation changes: a) no significant change, b) a strong decrease down to E/C = 0.2, c) a maximization of mycelium diameter by treatment at 5-7 mT. According to these results, effects can be produced noninvasively by varying either magnetic intensities or time of treatment. As yet, systematic bioelectromagnetic research using sinusoidal electromagnetic fields (SEMF)-on fermentation of fungi is still in its initial stages.     

Mechanism of the effect of weak electromagnetic fields on the living body]

By using the model conceptions of the dielectric polarization theory, a new mechanism for the effect of electromagnetic field was proposed. The model enables one to explain the experimentally observed influence of low-frequency weak electromagnetic field on biological objects. It was shown that, at the cellular and subcellular levels, an increase in the intensity of the electric component of external electromagnetic field can occur. The magnitude of this increase is determined by the ratio of the contributions of the medium polarization and the depolarizing factor (which depends on body shape) to the total effect. As a result of this increase, a potential comparable with intrinsic biological values can be generated on neuron membranes, which must elicit nervous and physiological responses of the organism.     

Pulsed electromagnetic fields affect osteoblast proliferation and differentiation in bone tissue engineering

Bone tissue engineering is an interdisciplinary field involving both engineers and cell biologists, whose main purpose is to repair bone anatomical defects and maintain its functions. A novel system that integrates pulsed electromagnetic fields (PEMFs) and bioreactors was applied to bone tissue engineering for regulating osteoblast proliferation and differentiation in'vitro. Osteoblasts were acquired from the calvaria of newborn Wistar rats and isolated after sequential digestion. Poly(DL-lactic-co-glycolic acid) (PLGA) scaffolds were made by the solvent merging/particulate leaching method. Osteoblasts were seeded into porous PLGA scaffolds with 85% porosity and cultured in bioreactors for the 18-day culture period. Cells were exposed to PEMF pulsed stimulation with average (rms) amplitudes of either 0.13, 0.24, or 0.32 mT amplitude. The resulting induced electric field waveform consisted of single, narrow 300 micros quasi-rectangular pulses with a repetition rate of 7.5'Hz. The results showed that PEMF stimulation for 2 and 8 h at .13 mT increased the cell number on days 6 and 12, followed by a decrease on day 18 using 8 h stimulation. However, ALP activity was decreased and then increased on days 12 and 18, respectively. On the other hand, PEMF-treated groups (irrespective of the stimulation time) at 0.32 mT inhibited cell proliferation but enhanced ALP activity during the culture period. These findings suggested that PEMF stimulation with specific parameters had an effect on regulating the osteoblast proliferation and differentiation. This novel integrated system may have potential in bone tissue engineering.