Medical/biological study (experimental study)

Effects of 50-Hz magnetic field exposure on superoxide radical anion formation and HSP70 induction in human K562 cells med./bio.

By: Mannerling AC, Simko M, Hansson Mild K, Mattsson MO

Published in: Radiat Environ Biophys 2010; 49 (4): 731-741

Aim of study (acc. to author)

To study whether a 50 Hz sine wave magnetic field (vertical or horizontal) of various magnetic flux densities can affect cell proliferation and cell cycle kinetics in the human cell line K562 and whether stress responses in the form of changed levels of Hsp70 protein and the superoxide anion radical are consequences of the magnetic field exposure.

Background/further details

Positive controls were peformed with heat treatment (42°C, 1h). Additionally, as positive control for radical production, the phorbol ester PMA was used. Cells were investigated before and at different time points after exposure.

Endpoint

molecular biosynthesis: stress response (Hsp70 expression and superoxide anion radical level)
cell viability/cell division/proliferation: cell proliferation, cell cycle distribution

Exposure

Exposure	Parameters
Exposure 1: 50 Hz Exposure duration: continuous for 1 h	magnetic flux density: 0.025 mT effective value magnetic flux density: 0.05 mT effective value magnetic flux density: 0.1 mT effective value

General information

cells were treated with i) exposure to magnetic fields ii) sham exposure iii) heat of 42°C

Exposure 1

Main characteristics

Frequency	50 Hz
Type	magnetic field
Waveform	sinusoidal
Exposure duration	continuous for 1 h
Additional info	vertical or horizontal field

Exposure setup

Exposure source	Helmholtz coils
Setup	two pairs of Helmholtz coils, one horizontal, one vertical, with a diameter of 40 cm and 42 cm respectively and in each coil 3 separate windings with 30 turns each; coil system placed in an incubator
Sham exposure	A sham exposure was conducted.

Parameters

Measurand	Value	Type	Method	Mass	Remarks
magnetic flux density	0.025 mT	effective value	measured	-	-
magnetic flux density	0.05 mT	effective value	measured	-	-
magnetic flux density	0.1 mT	effective value	measured	-	-

Additional parameter details

ambient DC field in the incubator 30.5 µT and 41.8 µT

Exposed system:

intact cell/cell culture
K562 cells (human erythroleukemic cell line)

Methods Endpoint/measurement parameters/methodology

molecular biosynthesis: stress response: Hsp70 expression (Western blot and flow cytometry) and superoxide anion radical level (nitro blue tetrazolium assay)
cell viability/cell division/proliferation: cell proliferation (haemocytometer), cell cycle distribution (DNA content, propidium iodide stain, flow cytometry), cell viability (Trypan blue exclusion assay)

Investigated system:

isolated bio./chem. substance
DNA/RNA
intact cell/cell culture
cell suspensions

Time of investigation:

before exposure
after exposure

Main outcome of study (acc. to author)

The data showed that magnetic field exposure (0.1 mT (data of other magnetic flux densities not shown)) did not affect either cell cycle kinetics or cell proliferation.
Both vertical and horizontal magnetic field exposures caused significantly and transiently increased Hsp70 levels (>twofold) at several magnetic flux densities, compared to sham exposure and to heat treatment. The strongest effect was found after vertical exposure to 0.025 mT. The twofold increase was observed directly after exposure and persisted until 24 h after exposure, although levels were returning towards base line at 24 h. The highest exposure (0.1 mT) was the weakest inducer of Hsp70 expression.
Exposure to the magnetic field also increased (30-40%) the levels of the superoxide radical anion at all investigated magnetic flux densities, comparable to the positive control PMA.
In conclusion, an early response to extremely low frequency magnetic field in K562 cells seems to be an increased amount of oxygen radicals, leading to Hsp70 induction. Furthermore, the findings suggest that there is a flux density threshold where 50 Hz magnetic field exerts its effects on K562 cells, at or below 0.025 mT. Additionally, it is the magnetic field, and not the induced electric field, which is the active parameter (because Hsp induction occurs both during vertical and horizontal magnetic field exposures).

Study character:

medical/biological study
experimental study
full/main study

Study funded by

Bundesamt für Strahlenschutz (BfS; Federal Office for Radiation Protection), Salzgitter, Germany
Deutsche Forschungsgemeinschaft (DFG; German Research Foundation)

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