Publikationsserver der RWTH Aachen University
Autoradiographische Modelluntersuchungen an der Maus zum Einfluss einer achtwöchigen 50-Hz-Magnetfeld-Exposition auf DNA-Reparatur und mitochondriale DNA-Synthese von Tubulusepithelzellen der Niere
Abstract
dc:description1.) The aim of this study was to use autoradiographic analyses after the injection of 3H-thymidine (TdR) to investigate the nuclear DNA repair synthesis rate ("unscheduled DNA synthesis" = UDS) and the mitochondrial DNA synthesis rate of proximal and distal tubular epithelium cells in the kidney of the 9-month-old mouse after an eight-week exposure to a magnetic field (MF) of varying intensity.2.) Out of a total of 80 test animals, 29 animals were exposed to a magnetic field at 50 Hz with a mean magnetic flux density of 1 mT or 0.1 mT respectively, while 15 animals were subjected to a control exposure (0 mT). The remaining seven inactive animals, which had neither been exposed to a magnetic field nor injected with 3H-thymidine, were used for control of background labelling. The animals exposed to a magnetic field were injected 5 minutes (in Group A) or 24 hours (Group B) or 7 days (Group C) with 555 kBq 3H-thymidine per gram of body weight after the end of the MF-exposure. Two hours later, they were sacrificed, some organs (e. g. kidney) removed and preserved with a fixative for several weeks. Subsequently, 3 µm thick paraffin sections were prepared, Feulgen stained, and finally, after an exposure of 250 days, autoradiograms were produced, which were examined under the microscope at a 1250x primary magnification. 100 consecutive cells per cell type were analyzed with regard to the number of nuclear grain number or cytoplasmic grain number inclusive the corresponding profile areas of the cells. By correcting for the background labelling, normalization the mean nuclear grain numbers concerning the diploid DNA content of the section volume, standardizing the nucleus marker to a uniform DNA quantity per segment volume or calculating cytoplasmic silver grain densities, respectively, a direct comparison of the labelling of different cell types was possible.3.) The possible autoradiographic artifacts as well as animal specific effects were detected by studying cumulative frequency distributions of the grain counts. The data of the different groups were compared by univariance analysis and post-hoc t-tests with consideration of a Bonferroni correction. All probabilities with p<0.05 were considered statistically significant. Finally, linear regression analyses were used to determine whether dose-dependent effects exist.4.) In relation to the UDS, the univariance analyses did not show any significant results either in the proximal nor distal tubulus. However, when the data from the earlier investigations performed by Keller (2003) and Freuding (2004) with the same methodology for a magnetic field exposure of 1.5 mT were included, the linear regression analysis resulted in a UDS which increased significantly with the dose, but only for the tubular epithelial cells of the proximal tubulus. This is fully consistent with earlier findings of Keller (2003), but not with those of Freuding (2004). However, the univariance analyses for nuclear profile areas and also for cytoplasmic silver grain densities showed no statistical significances. 5.) Regarding the influence of the time of the 3H-thymidine injection on the UDS, no statistical significances were found in the univariance analyses. However, with regard to the cytoplasmic silver grain density, a significant result was found for both the proximal and distal tubular epithelial cells, although this result could not be confirmed in the subsequent post-hoc t-tests.6.) With regard to the relative range of the measured values achieved here, a clear increase occurred in comparison to Keller (2003) and Freuding (2004); however, no correlations with the magnetic field intensity could be detected. These large ranges were possibly responsible for the fact that no significant results were achieved.7.)Summarizing the findings of previous studies concerning MF-induced DNA damage in the kidney, it is apparent that damage to the nuclear DNA is to be expected after magnetic field exposure at 50 Hz. However, such damage should be repaired, directly after it occurs.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2009
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Salimi, Sepideh
- Contributors dc:contributor
-
- Korr, Hubert
Subjects
dc:subject × 12Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- ger