## 4 Discussion
PANTHER analysis of target genes was performed to better understand the function of differentially expressed genes associated with melatonin pathways and explain the mechanism of protective role of static magnetic field on fluoride-treated cells. This analysis confirmed the participation of the differentially expressed genes primarily in the biological processes that are associated with the cellular response to various factors and the regulation of cellular processes, mainly in the cells of the immune system, which ensures a body's defense against a variety of factors, such as toxic substances, viruses, and bacteria. These categories of target genes were overrepresented in fluoride and static magnetic field-treated cells. This indicates a protective function for the cells of the proteins that are encoded by the differentially expressed genes, which is essential from the point of view of the mechanism of action of a static magnetic field. Moreover, conducting this analysis eliminated the problem of the genes whose differences in their expression and statistical significance did not translate into the influence of a specific gene on the cells. As a screening technique, oligonucleotide microarrays enable genome-scale expression analysis. Therefore, the genes with the greatest change in expression, which is expressed as a fold change were selected for the next steps in order to validate the obtained microarray results. The RT-qPCR technique showed that the direction of changes in the expression of the studied genes was in accordance with the microarray results. We did not statistically confirm the up-regulation of the \(NR1D1\) gene in the cells that had only been exposed to a static magnetic field compared to the control, but the tendency to increase its expression under the influence of an exposure to a static magnetic field was also visible in RT-qPCR results. The lack of a confirmation of the changes in its expression may be due to the separation between the location of the PCR primers and the microarray probes [33]. However, it should be noted that the research showed a high correlation between these two techniques [34]. In order to confirm the protective role of a static magnetic field for fibroblasts, we determined the concentration of the DNA/RNA oxidative damage markers. It is considered that 8-OH-dG is a biomarker for oxidative damage to the nucleic acids. Higher levels of 8-OH-dG are observed in various diseases whose pathogenesis is played by oxidative stress, for example, in cancers, diabetes or neurodegenerative diseases. At the same time, it was shown earlier that many antioxidant compounds can reduce the 8-OH-dG level [35]. In our study, it was revealed that a moderate-strength static magnetic field has a beneficial effect on cells by lowering the concentration of the DNA/RNA oxidative damage markers in fluoride-treated cells. In the cells that had simultaneously been exposed to fluoride and a static magnetic field, there was a tendency to compensate for expression of the differentially expressed genes that was altered by the presence of fluoride, which suggests a protective role of a static magnetic field against the factors that cause changes in the cell signaling cascades. However, it should be taken into account that the limitation of this study is the selection of the fluoride concentration, which is not observed in vivo in non-fluoridated areas.