Cellular Effects of Electromagnetic Fields

Jonne Naarala, Anne Höytö and Ari Markkanen

Studies at the cellular level are needed to reveal the cellular and molecular biological mechanisms underlying the biological effects and possible health implications of non-ionising radiation, such as extremely low frequency (ELF) magnetic fields (MFs) and radiofrequency (RF) fields. Our research group has studied the effects of 50Hz ELF MFs (caused by power lines and electric devices) and 872MHz or 900MHz RFs (emitted by mobile phones and their base stations) on cellular ornithine decarboxylase activity, cell cycle kinetics, cell proliferation, and necrotic or apoptotic cell death. For RFs, pulse-modulated (217Hz modulation frequency corresponding a global system for mobile communication-type signal) or continuous wave (unmodulated) signals were used. To expose
the cell cultures to MFs or RFs, specially developed exposure systems were used, where levels of electromagnetic field exposure and the conditions of cell culture could be precisely controlled. A coexposure approach was used in many studies, i.e. the cell cultures were exposed to other stressors in addition to MFs or RFs. Ultraviolet radiation, serum deprivation, or fresh medium addition, were used as co-exposures. The results presented in this short review show that the effects of mere MFs or RF on cell culture models are quite minor, but that various co-exposure approaches warrant additional study.
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Modelling of Normal and Premalignant Oral Tissue by using the Immortalised Cell Line, SVpgC2a: A Review of the Value of the Model

Claudia A. Staab, Martin Vondracek, Hipolito Custodio, Katarina Johansson, Jan Anders Nilsson, Peter Morgan, Jan-Olov Höög, Ian Cotgreave and Roland C. Grafström

Normal oral keratinocytes (NOKs), and a Simian virus 40 T-antigen-immortalised oral keratinocyte line termed SVpgC2a, were cultured in an effort to model the human oral epithelium in vitro, including normal and dysplastic tissue. Monolayer and organotypic cultures of NOKs and SVpgC2a were successfully established in a standardised serum-free medium with high levels of amino acids, by using regular tissue culture plastic for monolayers and collagen gels containing oral fibroblasts as the base for generating tissue equivalents. NOKs express many characteristics of normal tissue, including those associated with terminal squamous differentiation. After > 150 passages, SVpgC2a cells retained an immortal, nontumourigenic phenotype that, relative to NOKs, was associated with aberrant morphology, enhanced proliferation, deficiency in terminal differentiation, proneness to apoptosis, and variably altered expression of structural epithelial markers. Transcript and protein profiling, as well as activity assays, demonstrated the expression of multiple xenobiotic-metabolising enzymes in SVpgC2a cells, some of which were higher in comparison to NOKs. A generally preserved, or even activated, ability for xenobiotic metabolism in longterm cultures of SVpgC2a cells indicated that this cell line could be useful in safety testing protocols — for example, in the development of consumer products in the oral health care field. However, SVpgC2a cells displayed some features reminiscent of a severe oral dysplasia, implying that this cell line could also to some extent serve as a model of a premalignant oral epithelium
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Effects of Cadmium on Differentiation and Cell Cycle Progression in Cultured Xenopus Kidney Distal Epithelial (A6) Cells

Henning F. Bjerregaard

Cadmium (Cd) is an important industrial and environmental pollutant, and the kidney is the primary organ to be affected. To elucidate the effects of Cd on cell proliferation, an epithelial cell line (A6) originally derived from the distal part of the Xenopus laevis kidney was cultured in media containing 10% fetal bovine serum. The effects of Cd (added as CdCl2) on cellular growth and differentiation from single cells to confluent epithelia were investigated by visual inspection and by measurement of the degree to which living cells covered a unit area. Over a concentration range from 5 to 50μM, Cd did not affect the settling and adherence of single cells to the bottom of the culture well. The addition of 5μM Cd for 4 days did not affect the ability of the A6 cells to develop confluent epithelia, measured as the area covered by adherent living epithelial cells (99 ± 4% of the control value). However, 10μM Cd did effectively inhibit development of confluent epithelia to 13 ± 5% compared to control. Visual inspection of adherent cells exposed to 50μM Cd for 7 days revealed no increase in cell number or in cell death, which indicated the induction of cell cycle arrest. Flow cytometric analysis showed that treatment of cells with Cd (0.4mM) for 24 hours induced a significant increase in the proportion of G1 phase cells from 58.6 ± 3.9 to 80.6 ± 3.7%, and a corresponding reduction in the proportion of cells in both the S and G2 phases from 24.0 ± 3.6 to 13.4 ± 3.3% and 17.2 ± 1.7 to 5.8 ± 2.1%, respectively. This study showed that Cd stopped cell proliferation in a very narrow concentration range, between 5 and 10μM, and cell cycle analysis indicated that Cd arrested the cells in the G1 phase of the cell cycle.
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Responses of Human Gingival and Periodontal Fibroblasts to a Low-Zinc Environment

Emil Rudolf and Miroslav Červinka

Morphology, motility, proliferation rate and markers of oxidative stress in primary human gingival fibroblasts (GF) and periodontal ligamental fibroblasts (PDL-F) grown in zinc-deficient cultivation medium (ZDM), were studied over a 5-week culture period. A low-zinc environment effectively reduced the total, as well as the free, intracellular zinc content in both cell types, over the course of the experiment. Decreased intracellular zinc content resulted in altered cellular morphology, reduced motility, and rearrangement of actin and tubulin in the cytoskeleton. In addition, fibroblasts with low zinc content exhibited decreased proliferation, accompanied by changes in cell cycle distribution, expression of specific biochemical markers, increased oxidative stress and the activation of caspase-3. Supplementation of ZDM with exogenous zinc prevented the loss of intracellular zinc, while also restoring the morphology, cell proliferation and mitogenic signalling of the cultured cells. Moreover, such supplemented cells were protected against oxidative stress and cell death. Of the two primary cell cultures examined, GF were more sensitive to decreased intracellular zinc content, when compared to PDL-F. The results obtained suggest that the human primary cell cultures can be useful for the longer-term evaluation of the effects of nutritional factors originating from the environment.
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