EICESS 92 treatment is toxic, but manageable and compares favorably to international results. New strategies must be sought for certain risk groups of patients.
In previous studies we have demonstrated that 50 Hz, 100 μT magnetic field (MF) exposure of female Sprague‐Dawley rats for 13 weeks significantly enhances the development and growth of mammary tumors in a breast cancer model. The present study was designed to test the hypothesis that, at least in part, the tumor (co)promoting effect of MF exposure is due to MF effects on the immune surveillance system, which is of critical importance in protecting an organism against the development and growth of tumors. For this purpose, female Sprague‐Dawley rats of the same age as in the mammary tumor experiments were continuously exposed for different periods (2, 4, 8, and 13 weeks) to a 50 Hz, 100 μT MF. Control groups were sham‐exposed simultaneously. Following the different exposure periods, splenic lymphocytes were cultured and the proliferative responses to the T‐cell‐selective mitogen concanavalin A (Con A) and the B‐cell‐selective pokeweed mitogen (PWM) were determined. Furthermore, the production of interleukin‐1 (IL‐1) was determined in the splenocyte cultures. The mitogenic responsiveness of T cells was markedly enhanced after 2 weeks of MF exposure, suggesting a co‐mitogenic action of MF. A significant, but less marked increase in T‐cell mitogenesis was seen after 4 weeks of MF exposure, whereas no difference from sham controls was determined after 8 weeks, indicating adaptation or tolerance to this effect of MF exposure. Following 13 weeks of MF exposure, a significant decrease in the mitogenic responsiveness of lymphocytes to Con A was obtained. This triphasic alteration in T‐cell function (i.e., activation, tolerance, and suppression) during prolonged MF exposure resembles alterations observed during chronic administration of mild stressors, substantiating the hypothesis that cells respond to MF in the same way as they do to other environmental stresses. In contrast to T cells, the mitogenic responsiveness of B cells and IL‐1 production of PWM‐stimulated cells were not altered during MF exposure. The data demonstrate that MF in vivo exposure of female rats induces complex effects on the mitogenic responsiveness of T cells, which may lead to impaired immune surveillance after long‐term exposure. Bioelectromagnetics 19:259–270, 1998. © 1998 Wiley‐Liss, Inc.
In a series of experiments with the chemical carcinogen DMBA (7,12‐dimethyl[a]anthracene), we recently found that exposure of female Sprague‐Dawley rats in 50 Hz magnetic fields (MF) in the microtesla range significantly facilitates the development and growth of mammary tumors. One possible explanation for this finding would be enhanced proliferation of breast epithelial stem cells by MF exposure, thereby increasing the sensitivity of these cells to chemical carcinogens. In line with this possibility, we previously determined that 50 Hz, 50 μT MF exposure induces increases in ornithine decarboxylase (ODC), i.e., a key enzyme in cell proliferation, in the mammary gland of female Sprague‐Dawley rats. In the present study, we examined the time course of this effect, by using different periods of exposure to a 50 Hz, 100 μT MF. Furthermore, we determined ODC in different mammary complexes of the rat mammary gland to evaluate whether differences in response to MF exist over the anterior‐posterior extension of this organ. Exposure of young female Sprague‐Dawley rats induced marked increases in ODC in the mammary gland that were similar to ODC increases seen in “positive control” experiments with the tumor promoter 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA). However, this effect of MF critically depended on the duration of MF exposure, with no effect, or at least no consistent effect, for short (<1 week) or long (8 weeks and above) exposure periods, but a robust and reproducible enhancing effect on ODC activity after 2 weeks of exposure. Furthermore, we found that the effect of MF exposure depends on the part of the mammary complexes examined, the cranial thoracic (or cervical) complexes being particularly sensitive to ODC alterations in response to MF. This is in line with recent DMBA experiments of our group in which MF‐induced increases in tumor development and growth were predominantly seen in this large cranial/cervical part of the mammary gland. The most likely explanation for the observed ODC changes after MF exposure is the “melatonin hypothesis,” although other cellular and molecular effects of MF might be involved as well. Bioelectromagnetics 20:338–346, 1999. © 1999 Wiley‐Liss, Inc.
In previous studies we have demonstrated that 50 Hz, 100 microT magnetic field (MF) exposure of female Sprague-Dawley rats for 13 weeks significantly enhances the development and growth of mammary tumors in a breast cancer model. The present study was designed to test the hypothesis that, at least in part, the tumor (co)promoting effect of MF exposure is due to MF effects on the immune surveillance system, which is of critical importance in protecting an organism against the development and growth of tumors. For this purpose, female Sprague-Dawley rats of the same age as in the mammary tumor experiments were continuously exposed for different periods (2, 4, 8, and 13 weeks) to a 50 Hz, 100 microT MF. Control groups were sham-exposed simultaneously. Following the different exposure periods, splenic lymphocytes were cultured and the proliferative responses to the T-cell-selective mitogen concanavalin A (Con A) and the B-cell-selective pokeweed mitogen (PWM) were determined. Furthermore, the production of interleukin-1 (IL-1) was determined in the splenocyte cultures. The mitogenic responsiveness of T cells was markedly enhanced after 2 weeks of MF exposure, suggesting a co-mitogenic action of MF. A significant, but less marked increase in T-cell mitogenesis was seen after 4 weeks of MF exposure, whereas no difference from sham controls was determined after 8 weeks, indicating adaptation or tolerance to this effect of MF exposure. Following 13 weeks of MF exposure, a significant decrease in the mitogenic responsiveness of lymphocytes to Con A was obtained. This triphasic alteration in T-cell function (i.e., activation, tolerance, and suppression) during prolonged MF exposure resembles alterations observed during chronic administration of mild stressors, substantiating the hypothesis that cells respond to MF in the same way as they do to other environmental stresses. In contrast to T cells, the mitogenic responsiveness of B cells and IL-1 production of PWM-stimulated cells were not altered during MF exposure. The data demonstrate that MF in vivo exposure of female rats induces complex effects on the mitogenic responsiveness of T cells, which may lead to impaired immune surveillance after long-term exposure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.