To study the effects of magnetic fields on the levels of proteins involved in redox homeostasis and endocytosis processes in macrophages. Furthermore certain interacting signal transduction pathway components which modulate important cell functions in macrophages (phosphoinositide-3-kinase, protein kinase B, and the protein phosphatase), and the stress proteins Hsp70 and Hsp110 in mouse macrophages were investigated.
Enzymes such as NAD(P)H-oxidases mediate the main production of free radicals (ROS) in macrophages. The authors assume that the activation of NADH-oxidase plays a major role in phagocytic cells (such as macrophages) and is responsible for the magnetic field-induced free radical production.
LPS (lipopolysaccharides) and TPA (tetradecanoylphorbol acetate) were used as positive controls. LPS are used to study the influence of the magnetic field on differentiated macrophages and their nitric oxide production because LPS activates the nitric oxide synthase. TPA is known to induce a direct activation of NADPH-oxidase and stimulates ROS production. Heat treated cells (42°C) were also investigated.
The data showed the evidence that exposure of mouse macrophages to 50 Hz magnetic field (1 mT) led to immune cell activation: There was an increased production of reactive oxygen species, which possibly can be explained by noted oscillations (between increased and normal levels) in gp91phox levels (i.e. modulation of NAD(P)H oxidase). This is different from how LPS/TPA induces ROS formation. The release of radical oxygen species led to the activation of phagocytic related actions as demonstrated by the changed clathrin and adaptin levels. Modulations of the expression levels of phosphoinositide-3-kinase, protein kinase B, protein phosphatase indicate the participation, but not the primary activation, of these signal pathways. The magnetic field exposure caused slight and transient decreases after short-term exposures (two hours or less) of clathrin, adaptin, phosphoinositide-3-kinase, protein kinase B, and the protein phosphatase 2A, whereas longer exposures had no effect.
The protein expression of Hsp70 and Hsp110 exhibited increased levels at certain time points, but not generally.
The effects of the magnetic field exposure on protein levels are different from the effects exerted by TPA or LPS, although all three factors caused increases in reactive oxygen species release. This suggests that extremely low frequency magnetic field interacts with other cellular constituents than these chemicals, although induced signal pathways at least partially converge.