Exposure to 60 Hz magnetic fields and risk of lymphoma in PIM transgenic and TSG-p53 (p53 knockout) mice

Abstract

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.

Chronic Toxicity/Oncogenicity Evaluation of 60 Hz (Power Frequency) Magnetic Fields in F344/N Rats

“…We have previously reported the results of subchronic toxicity studies in rats and mice (7), a developmental toxicology study in rats (44), and a battery of immunotoxicology studies in mice and rats (26); all studies were considered negative for evidence of toxicity. Studies of the influence of magnetic fields on lymphoma induction in 2 strains of transgenic mice were also negative for an effect on lymphoma induction (31), as were the results of a multigeneration reproductive toxicity evaluation in rats (37,45 Tissues were excised, fixed in 10% neutral-buffered formalin, embedded in paraffin, cut, stained with hematoxylin and eosin, and evaluated using methods defined in NTP pathology specifications. All gross lesions and approximately 45 additional tissues from all animals in all study groups were examined histopathologically.…”

Assessing the Potential Carcinogenic Activity of Magnetic Fields Using Animal Models

“…In the transgenic models involving the pim oncogene that have been used to test for possible effects of EMF (77,83), pim-1 is linked to the immunoglobulin heavy chain enhancer (Eg). This linkage mimics the chromosomal translocation associated with lymphoid tumors and promotes transgene expression in both T and B cells (105,111).…”

Champs magnétiques 50–60 Hz et santé : quoi de neuf ?

“…En expérimentation animale, les études d'initiation (Mandeville et al, 1997 ;Yasui et al, 1997 ;McCormick et al, 1998McCormick et al, , 1999 et de promotion tumorale (Bernard et al, 2008 ;SCENIHR, 2009SCENIHR, , 2013, qui n'ont pas montré d'effet du champ magnétique, s'intègrent dans cette analyse.…”