Lack of a co-promotion effect of 60 Hz circularly polarized magnetic fields on spontaneous development of lymphoma in AKR mice

Carcinogenicity of extremely low-frequency magnetic fields: A systematic review of animal studies

Possible carcinogenicity of extremely low frequency (ELF) magnetic fields (MFs), associated with the use and transmission of electricity, has been under scientific and public debate for decades. This review aims to provide an update on studies testing carcinogenicity of ELF MFs in experimental animals. Emphasis was placed on identifying possible connections between study characteristics and the results obtained. This review followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement, and the methodological quality of the studies was evaluated using the Risk of Bias Rating Tool for Human and Animal Studies developed by the National Toxicology Program's Office of Health Assessment and Translation (OHAT). Publication bias was assessed using the caliper test. Fifty-four eligible studies were identified. Despite poor ratings in certain aspects of the risk of bias evaluation, the quality of the studies was generally relatively good, with only four studies receiving the weakest rating. Overall, there was very little evidence that ELF MFs alone are carcinogenic. Evidence of co-carcinogenicity, from studies that have used ELF MFs in combination with other agents, remains inconclusive. A clear indication of publication bias was observed, though it is unlikely that this bias alone explains all reported MF-modified effects. Based on the current literature, future studies on co-carcinogenicity of ELF MFs should employ approaches other than classical initiation-promotion models. Additionally, well-designed studies to better understand the reported effects of ELF MFs and the underlying mechanisms are warmly welcomed.

Effects of extremely low frequency magnetic fields on animal cancer and DNA damage: A systematic review and meta-analysis

The objective of this systematic review and meta-analysis was to assess the carcinogenic effects of extremely low frequency magnetic fields (ELF-MF) by analyzing animal and comet assay studies. We have performed a global meta-analysis on all the animal studies on the relation between ELF-MF and cancer incidence and separate meta-analyses on the incidence of cancer, leukemia, lymphoma, breast cancer, brain cancer and DNA damage assessed with the comet assay. Of the 5145 references identified, 71 studies have been included in our systematic review and 22 studies in our meta-analyses. Our global meta-analysis indicated that ELF-MF exposure had no significant impact on the incidence of cancers in rodents (19 studies, OR = 1.10; 95% CI 0.91-1.32). However, our separate meta-analyses showed that ELF-MF increased the odds of developing leukemia in mice (4 studies, OR = 4.45; 95% CI 1.90-10.38) but not in rats. Our systematic review also suggests that ELF-MF can damage DNA in certain cell types like brain cells. Nevertheless, a meta-analysis on three comet assay studies indicated that ELF-MF did not increase DNA damage in neuroblastoma cells (SMD = -0.08; 95% CI -0.18-0.01). Overall, our results suggest that exposure to ELF-MF does not represent a major hazard for mammals and the carcinogenic effects of these magnetic fields could be limited to leukemia.

LF-MF inhibits iron metabolism and suppresses lung cancer through activation of P53-miR-34a-E2F1/E2F3 pathway

Our previous studies showed that low frequency magnetic fields (LF-MF) suppressed tumor growth and influenced the function of immune system. Nevertheless the mechanisms behind the effect of LF-MF still remain to be elucidated. In this study, Tumor- bearing mice subcutaneously inoculated with Lewis lung cancer cells were exposed to a LF-MF (0.4T, 7.5 Hz) for 35 days and Survival rate, tumor growth and the tumor markers were measured. Results showed that tumor growth was obviously inhibited with a prolonged survival of tumor- bearing mice by LF-MF exposure. In vitro experiments, LF-MF was found to induce cell growth arrest, cell senescence and inhibit iron metabolism of lung cancer cells. Moreover, LF-MF stabilized p53 protein via inhibiting cell iron metabolism and the stabilized p53 protein enhanced miR-34a transcription. Furthermore, increased expression of miR-34a induced cell proliferation inhibition, cell cycle arrest and cell senescence of lung cancer cells by targeting E2F1/E2F3. We also detected the relevant indicator in tumor tissue such as the iron content, the level of miR-34a and related protein, corresponding results were obtained. Taken together, these observations imply that LF-MF suppressed lung cancer via inhibiting cell iron metabolism, stabilizing p53 protein and activation P53- miR-34a-E2F1/E2F3 pathway.

Low frequency magnetic fields enhance antitumor immune response against mouse H22 hepatocellular carcinoma

Objective

Many studies have shown that magnetic fields (MF) inhibit tumor growth and influence the function of immune system. However, the effect of MF on mechanism of immunological function in tumor-bearing mice is still unclear.

Methods

In this study, tumor-bearing mice were prepared by subcutaneously inoculating Balb/c mice with hepatocarcinoma cell line H22. The mice were then exposed to a low frequency MF (0.4 T, 7.5 Hz) for 30 days. Survival rate, tumor growth and the innate and adaptive immune parameters were measured.

Results

MF treatment could prolong survival time (n = 28, p<0.05) and inhibit tumor growth (n = 9, p<0.01) in tumor-bearing mice. Moreover, this MF suppressed tumor-induced production of cytokines including interleukin-6 (IL-6), granulocyte colony- stimulating factor (G-CSF) and keratinocyte-derived chemokine (KC) (n = 9–10, p<0.05 or 0.01). Furthermore, MF exposure was associated with activation of macrophages and dendritic cells, enhanced profiles of CD4⁺ T and CD8⁺ T lymphocytes, the balance of Th17/Treg and reduced inhibitory function of Treg cells (n = 9–10, p<0.05 or 0.01) in the mice model.

Conclusion

The inhibitory effect of MF on tumor growth was related to the improvement of immune function in the tumor-bearing mice.