Static magnetic field selects undifferentiated myelomonocytes from low-glutamine concentration stimulated U937 cells.

Reduced glutamine (GLN) concentration in the culture medium of a U937 cell line caused them to be differentiated along the monocytic pathway; cells attached to the matrix and to each other by extending pseudopodia and acquired specific functional characteristics, such as the expression of alpha-naphthyl-acetate esterase and the capacity to reduce nitroblue tetrazolium, as well as becoming active phagocytes. When U937 cells were differentiated under continuous exposure to a 6mT static magnetic field (MF) the overall differentiation process was perturbed. Surprisingly, after 5 days' exposure to the static MF, higher cell viability and differentiation were observed in cells cultured in a GLN-deprived medium than in cells grown in the same medium but in the absence of a static MF. The latter cells, particularly those that were still floating in the medium, were stimulated with TPA for a further 3 days. These cells differentiated and attached to the substrate. Conversely, the same treatment applied to cells cultured in GLN-deprived medium in the presence of the static MF resulted in resistance to TPA-induced differentiation. Indeed, these cells exhibited a round shape and in-suspension growth.

Differentiation of monocytic U937 cells under static magnetic field exposure.

We present here a morphological, cytochemical and biochemical study of the macrophagic differentiation of human pro-monocytic U937 cells exposed to moderate intensity (6 mT) static magnetic fields (MF). It was found that the following substances induced differentiation in U937 cells to a progressively lower degree: 50 ng/mL 12-0-tetradecanoyl-13-phorbol acetate (TPA), low concentration of glutamine (0,05 mM/L), 10% dimethyl sulfoxide (DMSO) and 100 mM/L Zn++. Differentiated U937 cells shift from a round shape to a macrophage-like morphology, from suspension to adhesion growth and acquire phagocytotic activity, the cytoskeleton adapting accordingly. Exposure to static MF at 6 mT of intensity decreases the degree of differentiation for all differentiating molecules with a consequent fall in cell adhesion and increased polarization of pseudopodia and cytoplasmic protrusions. Differentiation alone, or in combination with exposure to static MFs, affects the distribution and quantity of cell surface sugar residues, the surface expression of markers of macrophage differentiation, and phagocytotic capability. Our results indicate that moderate-intensity static MFs exert a considerable effect on the process of macrophage differentiation of pro-monocytic U937 cells and suggest the need for further studies to investigate the in vivo possible harmful consequences of this.

Cell shape and plasma membrane alterations after static magnetic fields exposure.

The biological effects of static magnetic fields (MFs) with intensity of 6 mT were investigated in lymphocytes and U937 cells in the presence or absence of apoptosis-inducing drugs by transmission (TEM) and scanning (SEM) electron microscopy. Lectin cytochemistry of ConA-FITC conjugates was used to analyze plasma membrane structural modifications. Static MFs modified cell shape, plasma membrane and increased the level of intracellular [Ca++] which plays an antiapoptotic role in both cell types. Modifications induced by the exposure to static MFs were irrespective of the presence or absence of apoptotic drugs or the cell type. Abundant lamellar-shaped microvilli were observed upon 24 hrs of continuous exposure to static MFs in contrast to the normally rough surface of U937 cells having numerous short microvilli. Conversely, lymphocytes lost their round shape and became irregularly elongated; lamellar shaped microvilli were found when cells were simultaneously exposed to static MFs and apoptosis-inducing drugs. In our experiments, static MFs reduced the smoothness of the cell surface and partially impeded changes in distribution of cell surface glycans, both features being typical of apoptotic cells. Cell shape and plasma membrane structure modifications upon static MFs exposure were time-dependent. Lamellar microvilli were clearly observed before the distortion of cell shape, which was found at long times of exposure. MFs exposure promoted the rearrangement of F-actin filaments which, in turn, could be responsible for the cell surface modifications. Here we report data that support biological effects of static MFs on U937 cells and human lymphocytes. However, the involvement of these modifications in the onset of diseases needs to be further elucidated.