Clinical progression of transplanted large granular lymphocytic leukemia in Fischer 344 rats exposed to 60 Hz magnetic fields

Abstract

The purpose of this study was to determine if 60 Hz magnetic fields can alter the clinical progression of leukemia in an animal model. Large granular lymphocytic (LGL) leukemia cells from spleens of leukemic rats were transplanted into young male Fischer 344 rats, producing signs of leukemia in approximately 2–3 months. The animals were randomly assigned to 4 treatment groups (108/group) as follows: 1) 10 G (1.0 mT) linearly polarized 60 Hz magnetic fields, 2) sham exposed [null energized unit with residual 20 mG (2 μT) fields], 3) ambient controls [<1 mG (0.1 μT)], and 4) positive controls (a single 5 Gy whole body exposure to 60Co 4 days prior to initiation of exposure). All rats were injected intraperitoneally (ip) with 2.2 × 107 LGL leukemic cells at the initiation of exposure or sham exposure. The magnetic fields were activated for 20 h/day, 7 days/week, allowing time for animal care. The experimental fields were in addition to natural ambient magnetic fields. Eighteen rats from each treatment group were bled, killed, and evaluated at 5, 6, 7, 8, 9, and 11 weeks of exposure. Peripheral blood hematological endpoints, changes in spleen growth, and LGL cell infiltration into the spleen and liver were measured to evaluate the leukemia progression. No significant or consistent differences were detected between the magnetic field exposed groups and the ambient control group, although the clinical progress of leukemia was enhanced in the positive control animals. These data indicate that exposure to sinusoidal, linearly polarized 60 Hz, 10 G magnetic fields did not significantly alter the clinical progression of LGL leukemia. Furthermore, the data are in general agreement with previous results of a companion repeated‐bleeding study in which animals were exposed for 18 weeks. Bioelectromagnetics 20:48–56, 1999. © 1999 Wiley‐Liss, Inc.

Assessing the Potential Carcinogenic Activity of Magnetic Fields Using Animal Models

“…As discussed above, since our review was published these experiments have been completed. Some of the results have been published in peer-reviewed format (81,82), and the complete study results are available in report form (79,80,101). These experiments were all conducted according to GLP, and their progress was periodically reviewed by an independent auditor.…”

“…In our previous review (1) we discussed experiments of Dieter and colleagues (100) and suggested that their report of enhancement effects may not be definitive. More (79)(80)(81)(82)101) appear to be well done, the significance of the results with respect to whether MFs have any leukemogenic potential is uncertain. Below, we review the experiments conducted by this group.…”

“…The first experiment (80)(81)(82) involving a total of 504 animals included chronic 18-week exposure to continuous, linearly polarized MFs (60 Hz, 1 mT). This experiment involved four treatment groups including the MF-exposed animals, a sham-exposed control group, ambient controls, and a positive control group that received 5-Gy whole-body irradiation.…”

“…This experiment involved four treatment groups including the MF-exposed animals, a sham-exposed control group, ambient controls, and a positive control group that received 5-Gy whole-body irradiation. At the initiation of MF (18 animals in each group were sacrificed at each time point) for additional morphologic, hematologic, and histopathologic evaluation (82). Investigators report that significant or consistent differences between exposed and control groups were not observed in any experimental parameter, whereas consistent statistically significant differences were observed for the positive control group in most experimental parameters.…”

“…The experiment employing conditions of a cell inoculum of 2.2 x 107 and exposure to continuous fields represents a replication of the first experiment discussed above (80)(81)(82). As in the first study, no significant differences were noted between ambient and MFexposed groups in any neoplastic parameter.…”