Biomedical subjects

Junji Miyakoshi

Publications and source records attributed to Junji Miyakoshi.

25 records · Page 2Linked to original sources

PubMed2002

Exposure to power frequency magnetic fields suppresses X-ray-induced apoptosis transiently in Ku80-deficient xrs5 cells.

In an attempt to determine whether exposure to extremely low frequency (ELF) electromagnetic fields can affect cells, Ku80-deficient cells (xrs5) and Ku80-proficient cells (CHO-K1) were exposed to ELF electromagnetic fields. Cell survival, and the levels of the apoptosis-related genes p21, p53, phospho-p53 (Ser(15)), caspase-3 and the anti-apoptosis gene bcl-2 were determined in xrs5 and CHO-K1 cells following exposure to ELF electromagnetic fields and X-rays. It was found that exposure of xrs5 and CHO-K1 cells to 60 Hz ELF electromagnetic fields had no effect on cell survival, cell cycle distribution and protein expression. Exposure of xrs5 cells to 60 Hz ELF electromagnetic fields for 5 h after irradiation significantly inhibited G(1) cell cycle arrest induced by X-rays (1 Gy) and resulted in elevated bcl-2 expression. A significant decrease in the induction of p53, phospho-p53, caspase-3 and p21 proteins was observed in xrs5 cells when irradiation by X-rays (8 Gy) was followed by exposure to 5 mT ELF magnetic fields. Exposure of xrs5 cells to the ELF electromagnetic fields for 10 h following irradiation significantly decreased X-ray-induced apoptosis from about 1.7% to 0.7%. However, this effect was not found in CHO-K1 cells within 24 h of irradiation by X-rays alone and by X-rays combined with ELF electromagnetic fields. Exposure of xrs5 cells to 60 Hz ELF electromagnetic fields following irradiation can affect cell cycle distribution and transiently suppress apoptosis by decreasing the levels of caspase-3, p21, p53 and phospho-p53 and by increasing bcl-2 expression.

Animals↗

PubMed2002

Exposure to power frequency magnetic fields and X-rays induces GAP-43 gene expression in human glioma MO54 cells.

We investigated the distribution and expression of growth associated protein-43 (GAP-43) in human glioma cells (MO54) after exposure to a magnetic field (60 Hz, 5 mT), with or without initial X-ionizing radiation (2 Gy), by using immunocytochemistry and the reverse transcription polymerase chain reaction (RT-PCR). GAP-43 was present in the cytoplasm, accumulating in the perinuclear area. An increase in GAP-43 expression was observed with a peak at 10 h at the mRNA level and at 12 h at the protein level, after exposure to the magnetic field. The increased level of GAP-43 protein returned to a normal level within 24 h of exposure to a 5 mT magnetic field. The kinetic pattern of GAP-43 expression induced by X-ionizing radiation was very similar to that induced by the magnetic field. These results suggest that the stimulation of GAP-43 expression could occur by a similar mechanism following exposure to X-rays or magnetic fields. We have provided the first evidence that exposure to a 5 mT magnetic field can induce GAP-43 gene expression in human glioma MO54 cells.

Dose-Response Relationship, Radiation↗

PubMed2002

Effects of exposure of CHO-K1 cells to a 10-T static magnetic field.

PURPOSE: To evaluate whether exposure to strong static magnetic fields (SMFs), of up to 10 T, affects the growth and cycle distribution of and the micronucleus formation in monolayered Chinese hamster ovary CHO-K1 cells. MATERIALS AND METHODS: The authors developed a system to expose cultured cells to strong SMFs immediately after the cells are seeded. Cell growth rate was evaluated according to cell number count. Cell cycle distribution experiments were performed by using flow cytometric analysis. In these experiments, the cells were exposed to SMFs for up to 4 days. The frequency of micronucleus formation with only SMF exposure at x-ray irradiation was analyzed at microscopic observation. RESULTS: Long-term exposure to a 10-T SMF for up to 4 days did not affect cell growth rate or cell cycle distribution. Exposure to SMFs alone did not affect micronucleus frequency. In x-ray-irradiated cells, exposure to a 1-T SMF did not affect micronucleus frequency, but exposure to a 10-T SMF resulted in a significant (P <.05) increase in micronucleus frequency. CONCLUSION: Strong (10-T) SMFs have no effect on cell growth, cell cycle distribution, or micronucleus frequency, but they may cause an increase in the micronucleus formation induced by 4-Gy x rays.

Animals↗

PubMed2002

Radiosensitization by overexpression of the nonphosphorylation form of IkappaB-alpha in human glioma cells.

To assess the role of NF-kappaB in cellular radiosensitivity, we constructed mutated IkappaB expression plasmids for SY-IkappaB (with mutations at residues of 32, 36 and 42) expression in human malignant glioma cells (radiosensitive MO54 and radioresistant T98 cells), giving respective cell types referred to as MO54-SY4 and T98-SY14. Both of the clones expressing SY-IkappaB became radiosensitive, compared with the parental MO54 and T98 cells. A treatment with herbimycin A or genistein did not change the radiosensitivity of cells expressing SY-IkappaB, but made both the MO54 and T98 parental cells more sensitive to ionizing radiation. A treatment with TNF-alpha induced DNA fragmentation and apoptosis in cells expressing SY-IkappaB, but not in MO54 and T98 cells. The survival after X-ray exposure of the parental MO54 cells was slightly increased by a TNF-alpha treatment, but that of the parental T98 cells did not change. The change in sensitivity to ultra-violet (UV) radiation and adriamycin in MO54-SY4 cells was very similar to that for X-ray sensitivity, but no change was observed in T98-SY14 cells. Significant sublethal damage repair was observed in T98 cells, whereas MO54 cells showed little repair activity. The expression of p53 was enhanced in the parental MO54 cells, while the p53 levels in the MO54-SY4, and in the parent and clonal T98 cells, did not change. Our data suggest that the serine and tyrosine phosphorylation of IkappaB-alpha may play a role in determining the radiosensitivity of malignant glioma cells.

Glioma↗

PubMedDate not supplied

Magnetic field effects on assembly pattern of smooth muscle cells.

Under a strong magnetic field, the diamagnetic properties of biological cells modulate the behavior of the cells themselves, under conditions of both floating and adherence. The morphological effects of strong static magnetic fields on adherent cells are less well understood than the effects of magnetic fields on red blood cells. In the present study, a high-intensity magnetic field of 14 T affected the morphology of smooth muscle cell assemblies, and the shapes of the cell colonies extended along the direction of the magnetic flux. The phenomenon was most notable under magnetic fields of more than 10 T, where an ellipsoidal pattern of smooth muscle cell colonies was clearly observed. The ellipticity of the cell colony pattern with a 14-T magnetic field was 1.3, whereas that with a field of 0-8 T was close to a circle at about 1.0. The evidence that smooth muscle cells detect high-density magnetic flux and thus change their cell orientation was shown as a visible pattern of cellular colonies. The speculated mechanism is a diamagnetic torque force acting on cytoskeleton fibers, which are dynamically polymerizing-depolymerizing during cell division and cell migration.

Animals↗

PubMedDate not supplied

Effects of static magnetic fields at the cellular level.

There have been few studies on the effects of static magnetic fields at the cellular level, compared to those of extremely low frequency magnetic fields. Past studies have shown that a static magnetic field alone does not have a lethal effect on the basic properties of cell growth and survival under normal culture conditions, regardless of the magnetic density. Most but not all studies have also suggested that a static magnetic field has no effect on changes in cell growth rate. It has also been shown that cell cycle distribution is not influenced by extremely strong static magnetic fields (up to a maximum of 10 T). A further area of interest is whether static magnetic fields cause DNA damage, which can be evaluated by determination of the frequency of micronucleus formation. The presence or absence of such micronuclei can confirm whether a particular treatment damages cellular DNA. This method has been used to confirm that a static magnetic field alone has no such effect. However, the frequency of micronucleus formation increases significantly when certain treatments (e.g., X-irradiation) are given prior to exposure to a 10 T static magnetic field. It has also been reported that treatment with trace amounts of ferrous ions in the cell culture medium and exposure to a static magnetic field increases DNA damage, which is detected using the comet assay. In addition, many studies have found a strong magnetic field that can induce orientation phenomena in cell culture.

Animals↗

PubMedDate not supplied

Static magnetic field with a strong magnetic field gradient (41.7 T/m) induces c-Jun expression in HL-60 cells.

We investigated the effects of 6- and 10-T static magnetic fields (SMFs) on the expression of protooncogenes using Western blot immunohybridization methods. We used a SMF exposure system, which can expose cells to a spatially inhomogeneous 6 T with a strong magnetic field (MF) gradient (41.7 T/m) and a spatially homogeneous 10 T of the highest magnetic flux density in this experiment. HL-60 cells exposed to either 6- or 10-T SMF for periods of 1 to 48 h did not exhibit remarkable differences in levels of c-Myc and c-Fos protein expression, as compared with sham-exposed cells. In contrast, c-Jun protein expression increased in HL-60 cells after exposure to 6-T SMF for 24, 36, 48, and 72 h. These results suggest that a homogeneous 10-T SMF does not alter the expression of the c-jun, c-fos, and c-myc protooncogenes. However, our observation that exposure to a strong MF gradient induced c-Jun expression suggests that a strong MF gradient may have significant biological effects, particularly regarding processes related to an elevation of c-jun gene expression.

Electromagnetic Fields↗