| dc.description.abstract | The overall aim of the thesis work has been to explore the effects of electromagnetic fields on biological systems. This exploration has taken three main directions. The first direction has been to develop methodology and protocols to study different biological model systems and their response to electromagnetic fields, with particular attention towards intracellular free calcium ([Ca2+]i) regulation. Biological systems studied were the bacterium Propionibacterium acnes (P. acnes), the human T-cell line Jurkat (clone E6.1), and single plant cells (protoplasts) of the Brassica napus species (rapeseed). The second direction has been to measure magnetic field exposure experienced by a potentially vulnerable group of children, viz. premature infants treated in a neonatal intensive care unit (NICU). The third direction has been to perform a literature study to assess whether non-thermal radio frequency (RF) field exposure of men can later give rise to congenital malformations in their offspring. In addition to the above, four relevant appendices are included for reference purposes.
Paper I is a paper published in Journal of Photochemistry and Photobiology B:Biology on the Gram-positive skin bacterium P. acnes. In this work methodology and protocols were developed that were further used to study various biological responses to electromagnetic fields in Paper II. The main results of the paper were that photosensitising of P. acnes with protoporphyrin IX (PpIX) and broadband red light, induces an elevation of the [Ca2+]i of the bacteria. In both cases, reducing the calcium level of the medium (i.e. extracellular calcium) resulted in an enhancement in the cell survival after photosensitisation, indicating that induced [Ca2+]i changes at least partly participate in photoinactivation. PpIX is hydrophobic and aggregate in the cell membrane so damage is likely to involve damage of the membrane (e.g. lipid peroxidation) and/or membrane-associated components. This is supported by the experiments on photosensitisation with more hydrophilic porphyrins (copro- /uroporphyrins) that resulted in no [Ca2+]i elevation, although a high level of cell inactivation was still obtained. The experiments in Paper I represent a relevant starting point for assessing the effects of ELF electromagnetic fields; with special focus on the cell membrane as a primary site of interaction, as well as potential alterations in ion transport across the membrane.
Paper II is a paper published in Bioelectromagnetics where the effects of 50 Hz sinusoidal electric currents and magnetic fields on P. acnes were investigated. Possible effects on [Ca2+]i, intracellular pH (pHi) and cell viability were assessed. It was found that exposure to 50 Hz sinusoidal magnetic fields (0.2 mT) for up to 30min. had no effect on [Ca2+]i or cell viability. Further, 50 Hz sinusoidal current densities (0.015 - 1500 A/m2) did not induce changes in [Ca2+]i. Also, current densities greater than 800 A/m2 were required before a reduction in pHi was detected. However, a pH-gradient across the cell membrane was maintained even when exposure resulted in less than 0.2% survival (1400 A/m2). In an attempt to explain the observed results, the thermal noise limit was discussed (cf. Introduction to the thesis, Ch. 2.6).
Paper III describes a study where the model system Jurkat (clone E6.1) human Tleukemia cells was used to explore possible mechanisms whereby electromagnetic fields might affect the immune system or developing cancer cells. The Tlymphocytes were exposed to 50 Hz electric currents (0.3 A/m2) in combination with the mitogenic lectin concanavalin A (Con A). The [Ca2+]i of exposed and sham-exposed cell suspensions was determined during exposure using the fluorescent calcium probe fura-2. It was found that weak (non-thermal) currents could induce an effect on calcium regulation in Jurkat cells when they were stimulated by Con A. In unstimulated cells no effect on calcium was found. Further, it was found that the results depended on the cell medium used during exposure. The above effects were found when exposing cells in a simple Na-HEPES based buffer, whereas using a complex CO2/HCO3- based growth medium, RPMI 1640, resulted in no effect.
Paper IV describes a study where plant protoplasts of rapeseed(Brassica napus) hypocotyls were assessed in order to determine their suitability as a model system in the study of potential effects from electromagnetic fields. Some simple biological parameters were tested; cell viability and the cell division rate. In addition, an attempt was made to determine the [Ca2+]i using calcium-sensitive fluorescent probes. The protoplasts were exposed to 50 Hz magnetic fields and 27 MHz electromagnetic fields. It was found that ester loading using indo-1 acetoxymethyl (AM) ester could not be used for rapeseed hypocotyl protoplasts due to limited hydrolysis of the AM esters. This may be due to limited esterase activity. Acid loading with indo-1 gave better results and it was possible to determine the intracellular free calcium. However, the signal-to-noise ratio was small and there was a large amount of dye leakage which greatly reduced the utility of the method. Also, the cell viability after the loading procedure was low. It was found that 50 Hz magnetic field exposure (100 µT) had no effect on protoplast viability (measured after 1, 2, 3, 5, and 8 days of exposure), nor on the percentage of dividing cells (measured after 2, 3, 6 and 7 days)Likewise, the cell viability was not affected after 2 hrs. of 27.12 MHz electromagnetic field exposure (150 W/m2) when the viability was measured 24 hrs. after the exposure. As 27 MHz electromagnetic field expo sure can potentially induce temperature elevations, it was also tested whether elevating the normal incubation temperature of 21 °C up to 37 °C had any effect on the viability. No effect was found. Electromagnetic field effects on plants/plant cells in general are also treated in Appendix 1.
Paper V is a paper published in Hong Kong Journal of Paediatrics where the magnetic flux densities in a neonatal incubator, as well as other commonly used equipment at a NICU, were registered and mapped. The mean magnetic flux densities (measured between 40 and 800 Hz), were typically within the range 0.2 - 1.0 µT inside the incubator, with maximum values around 1.5 µT. The magnetic field strength varied considerably as a function of time and position on the mattress in the incubator. The magnetic field originated mainly from the temperatureregulating unit. Moving this unit 25 or 50 cm below the original position, reduced the magnetic field by approximately 7 and 18 times, respectively. This provides a simple method to reduce the magnetic fields to which the infants are exposed, often for considerable periods of time. In relation to this, some further considerations have been discussed in Appendix 2, such as using high permeability mu-metal for shielding the magnetic fields.
Paper VI is a literature study where the following question was assessed: “Can radio frequency electromagnetic field exposure of men later lead to congenital malformations in offspring?” It was found that the interpretation of the literature on male reproduction and possible effects of non-thermal RF electromagnetic fields on offspring was complicated by the many variables involved with RF exposure. Further, the available literature on non-thermal exposure was limited. For instance, there were few epidemiological studies available, and the ones available can be criticised for being incomplete from a methodological point of view, particularly in terms of exposure histories. Thus, drawing a conclusion on whether RF fields may induce gene damage in the germ cells of fathers, and whether this may give rise to congenital anomalies in their children, will for the time being be based on limited data. However, one purpose of the review was to describe potential mechanisms, look at the data from both laboratory and epidemiological studies, and point out limitations of previous studies using a variety of biological endpoints; including gene mutations, chromosome abnormalities, congenital malformations, etc. The main conclusion of the work was that sufficient support could so far not be revealed for the above-suggested hypothesis. In relation to the above, both Appendix 3 and Appendix 4 may be consulted. Appendix 3 shortly describes a cluster case involving congenital malformations in children of RF exposed fathers and Appendix 4 outlines some potential health effects involved with the use of mobile phones. | nb_NO |
