Medical/biological study (experimental study)

Effect of extremely low frequency magnetic field exposure on DNA transposition in relation to frequency, wave shape and exposure time med./bio.

By: Giorgi G, Marcantonio P, Bersani F, Gavoci E, Del Re B

Published in: Int J Radiat Biol 2011; 87 (6): 601-608

Aim of study (acc. to author)

To examine the effect of extremely low frequency magnetic field exposure on transposon mobility in relation to the exposure time, the frequency and the wave shape of the field applied.

Exposure	Parameters
Exposure 1: 20–75 Hz Exposure duration: continuous for 15 min or 90 min	magnetic flux density: 1 mT effective value dB/dt = 0.66 T/s
Exposure 2: 20–75 Hz Modulation type: pulsed Exposure duration: continuous for 15 min or 90 min	magnetic flux density: 1 mT effective value dB/dt = 0.14 T/s

Exposure 1

Main characteristics

Frequency	20–75 Hz
Type	magnetic field
Waveform	sinusoidal
Exposure duration	continuous for 15 min or 90 min
Additional info	20, 50, 75 Hz

Exposure setup

Exposure source	Helmholtz coils
Setup	two pairs of double-wrapped Helmholtz coills with a diameter of 23 cm and 40 (20 + 20) turns, placed in an incubator with a constant temperature of 37° C; 10 cm high cylindrical exposure area with a diameter of 12 cm and a field homogeneity of 5% in the center of the coil system; samples placed in Petri dishes with 9 cm diameter in the center of the coil system where the field uniformity was within 1%
Sham exposure	A sham exposure was conducted.

Parameters

Measurand	Value	Type	Method	Mass	Remarks
magnetic flux density	1 mT	effective value	measured	-	-
cf. remarks	-	-	-	-	dB/dt = 0.66 T/s

Additional parameter details

geomagnetic field in the incubator: 50 µT AC field component in the incubator: 0.3 µT for sham exposure: horizontal field in coil 1: 10 +/- 0.8 µT horizontal field in coil 2: 20 +/- 1 µT vertical field in both coils: 45 +/- 2 µT

Exposure 2

Main characteristics

Frequency	20–75 Hz
Type	magnetic field
Exposure duration	continuous for 15 min or 90 min
Additional info	20, 50, 75 Hz

Modulation

Modulation type	pulsed
Rise time	1 ms
Duty cycle	50 %
Pulse type	rectangular

Exposure setup

Exposure source	same setup as exposure 1
Sham exposure	A sham exposure was conducted.

Parameters

Measurand	Value	Type	Method	Mass	Remarks
magnetic flux density	1 mT	effective value	measured	-	-
cf. remarks	-	-	-	-	dB/dt = 0.14 T/s

Additional parameter details

Reference articles

Del Re B et al. (2006): Synthesis of DnaK and GroEL in Escherichia coli cells exposed to different magnetic field signals

Exposed system:

bacterium
E. coli/Lac Z- (contains a plasmid with Tn10 derivative element expressing beta-galactosidase after transposition)); SURE (donor; carries plasmid F+ and transposon Tn5; kanamycin/chloramphenicol-resistent) & DK1 (recipient; streptomycin-resistent)

Methods Endpoint/measurement parameters/methodology

genotoxicity/mutation: transposition activity/transposition rate (measured via expression of beta-galactosidase; formation of a LacZ⁺ phenotype (forming dark clones within white LacZ^- colonies) or number of succesful conjugations (number of colonies with appropriate antibiotic resistence (kanamycin/chloramphenicol/streptomycin resistent))

Investigated system:

bacterium

Time of investigation:

after exposure

Main outcome of study (acc. to author)

Both Tn10 and Tn5 transpositions decreased under sinusoidal magnetic field and increased under pulsed square wave magnetic field, as compared to sham exposure. No significant difference was found between frequencies and between exposure times.
In conclusion, extremely low frequency magnetic field exposure affects transposition activity and the effects depended on the wave shape of the field, but not on the frequency and the exposure time, at least in the range observed.

Study character:

medical/biological study
experimental study
full/main study
blind study

Study funded by

Ministero dell' Università e della Ricerca (MIUR (formerly MURST (Ministero dell' Università e della Ricerca Scientifica e Tecnologica); Ministry of University and Research), Italy

Koyama S et al. (2005): Combined exposure of ELF magnetic fields and x-rays increased mutant yields compared with x-rays alone in pTN89 plasmids
Koyama S et al. (2004): ELF electromagnetic fields increase hydrogen peroxide (H2O2)-induced mutations in pTN89 plasmids
Del Re B et al. (2004): Various effects on transposition activity and survival of Escherichia coli cells due to different ELF-MF signals
Del Re B et al. (2003): Extremely low frequency magnetic fields affect transposition activity in Escherichia coli
Belyaev IY et al. (2001): Frequency-dependent effects of ELF magnetic field on chromatin conformation in Escherichia coli cells and human lymphocytes
Chow KC et al. (2000): Magnetic field exposure stimulates transposition through the induction of DnaK/J synthesis
Nakasono S et al. (2000): A 50 Hz, 14 mT magnetic field is not mutagenic or co-mutagenic in bacterial mutation assays

Effect of extremely low frequency magnetic field exposure on DNA transposition in relation to frequency, wave shape and exposure time med./bio.

Aim of study (acc. to author)

Background/further details

Endpoint

Exposure

Exposure 1

Main characteristics

Exposure setup

Parameters

Additional parameter details

Exposure 2

Main characteristics

Modulation

Exposure setup

Parameters

Additional parameter details

Reference articles

Methods Endpoint/measurement parameters/methodology

Main outcome of study (acc. to author)

Study funded by

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