Study type: Medical/biological study (experimental study)

Ornithine decarboxylase activity of L929 cells after exposure to continuous wave or 50 Hz modulated radiofrequency radiation--a replication study. med./bio.

Published in: Bioelectromagnetics 2007; 28 (7): 501-508

Aim of study (acc. to author)

A replication study with some extensions was made to confirm enhancement of ornithine decarboxylase enzyme activity in murine L929 fibroblasts after radiofrequency electromagnetic field exposure reported in earlier studies (publication 1718 and publication 3382).

Background/further details

L929 cells purchased from two cell banks were exposed for 2, 8, or 24 h to continuous wave or D-AMPS signal. In positive control experiments, medium change was used to induce and serum deprivation to suppress ornithine decarboxylase activity.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 835 MHz
Modulation type: CW
Exposure duration: continuous for 2, 8, or 24 h
Exposure 2: 835 MHz
Modulation type: pulsed
Exposure duration: continuous for 2, 8, or 24 h
Exposure 3: 872 MHz
Modulation type: pulsed
Exposure duration: continuous for 8 h

General information

RF and sham exposures were carried out in Crawford chambers and in waveguide exposure chambers. In sham-sham experiments, cell flasks or dishes were placed in both exposure chambers, and no RF field was applied.

Exposure 1

Main characteristics
Frequency 835 MHz
Type
Charakteristic
  • guided field
Exposure duration continuous for 2, 8, or 24 h
Modulation
Modulation type CW
Exposure setup
Exposure source
Chamber The Crawford chambers were housed in a water jacketed CO2 incubator. Compared to the design used by Penafiel et al. [1997], a few modifications were made to improve the setup: The doors were enlarged, shelves were added inside, power sensors were fitted, and ventilators were introduced. These improvements increased the accuracy and reproducibility of exposures.
Setup Cells seeded into two sealed 25 cm² plastic flasks were placed in each of the two chambers, one for RF and one for sham exposure.
Sham exposure A sham exposure was conducted.
Additional info The air flow was on to cool the exposed cells, except for a series of experiments performed without air cooling at 6.0 W/kg. The computerised setup enabled performing experiments in a blinded manner.
Parameters
Measurand Value Type Method Mass Remarks
SAR 2.5 W/kg - - - -
SAR 6 W/kg - - - -

Exposure 2

Main characteristics
Frequency 835 MHz
Type
Charakteristic
  • guided field
Exposure duration continuous for 2, 8, or 24 h
Modulation
Modulation type pulsed
Duty cycle 33.3 %
Repetition frequency 50 Hz
Additional info

D-AMPS modulated signal

Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
SAR 2.5 W/kg - - - -
SAR 6 W/kg - - - -

Exposure 3

Main characteristics
Frequency 872 MHz
Type
Charakteristic
  • guided field
Exposure duration continuous for 8 h
Modulation
Modulation type pulsed
Duty cycle 33.3 %
Repetition frequency 50 Hz
Additional info

modulation similar to that used in the D-AMPS system

Exposure setup
Exposure source
Chamber The waveguide exposure system described previously [Hoyto et al., 2006] provided a uniform SAR distribution (±35%) in cell cultures, and a water cooling system enabled exposure in controlled temperature (±0.3°C).
Setup Cells plated in two 55-mm glass Petri dishes were placed in each of the two chambers, one for RF and one for sham exposure.
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
SAR 6 W/kg - - - -

Reference articles

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

The study did not confirm previous data reporting increased ornithine decarboxylase enzyme activity. When an exposure system was used similar to that of previous studies (Crawford cell), ornithine decarboxylase activity was either not affected (8 or 24 h exposures) or decreased (after a 2 h exposure at 6 W/kg). The decrease was statistically significant only for L929 cells purchased from ATCC cell bank and most pronounced when cooling with air flow was not used.
Different results were found in experiments with another exposure system with more efficient temperature control: ornithine decarboxylase activity was increased after 8 h of exposure at 6 W/kg when the temperatures of exposed cultures and control groups were kept identical (statistically significant for D-AMPS signal). Further studies are warranted to explore whether this finding reflect a true non-thermal effect.
The present study did not provide evidence for modulation-specific effects (no difference between CW- and D-AMPS signals in any of the experiments).

Study character:

Study funded by

Replicated studies

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