Carcinogenesis, Vol 19, 1649-1653, Copyright © 1998 by Oxford University Press
DL McCormick, BM Ryan, JC Findlay, JR Gauger, TR Johnson, RL Morrissey and GA Boorman
The results of a number of epidemiology studies suggest that exposure to
power frequency (50 and 60 Hz) magnetic fields may be a risk factor for
hematopoietic neoplasia. To generate experimental data to test this
hypothesis, the influence of magnetic field exposure on lymphoma induction
was determined in two strains of mice that are genetically predisposed to
the disease. PIM mice, which carry the pim-1 oncogene, are highly sensitive
to lymphoma induction by N-ethyl-N-nitrosourea (ENU); ENU-treated PIM mice
were studied as a 'high incidence' lymphoma model. TSG-p53 (p53 knockout)
mice, in which the p53 tumor suppressor gene has been deleted from the germ
line, develop lymphoma as an age- related change; hemizygous TSG-p53 mice
were studied as a 'low incidence' lymphoma model. Beginning 1 day after a
single i.p. injection of 25 mg ENU/kg body wt, groups of 30 PIM mice/sex
were exposed for 18.5 h/day to pure, linearly polarized, transient-free 60
Hz magnetic fields at field strengths of 0 (sham control), 0.02, 2.0 or
10.0 Gauss (G). An additional group of 30 PIM mice/sex was exposed
intermittently (1 h on, 1 h off) to 10.0 G fields. Groups of 30 TSG-p53
mice/sex were exposed continuously to magnetic field strengths of 0 (sham
control) or 10.0 G; TSG-p53 mice received no ENU. Studies were terminated
after 23 weeks of magnetic field exposure. Lymphoma incidence in male PIM
mice exposed continuously to 10.0 G magnetic fields was significantly
reduced from that seen in sex-matched sham controls; survival, lymphoma
incidence and lymphoma latency in other groups of PIM mice did not differ
from sham controls. Survival and lymphoma incidence in all groups of
TSG-p53 mice was 7% or less, regardless of magnetic field exposure regimen.
These data do not support the hypothesis that exposure to magnetic fields
is a significant risk factor for lymphoid neoplasia in mice with a genetic
predisposition to the disease.
ARTICLES
Exposure to 60 Hz magnetic fields and risk of lymphoma in PIM transgenic and TSG-p53 (p53 knockout) mice
Life Sciences Department, IIT Research Institute, Chicago, IL 60616, USA. dmccormick@iitri.com
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