Recently, a research team led by Prof. ZHANG Xin from the High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, made a series of new advances in the effects of moderate and high static magnetic fields (SMFs) on mice models of various diseases, including the delay of natural ageing in healthy mice by continuous exposure to moderate intensity quasi-uniform SMFs, the mitigation of kidney damage in mice induced by the chemotherapeutic drug cisplatin, and the harmful effects of high gradient SMF exposure on mice with severe type 1 diabetes.
The three studies were recently published in Antioxidants and Zoological Research respectively.
Previously the team explored the safety of healthy mice in high SMFs. No detectable harmful effects were found in healthy mice exposed to 3.5–23.0 T high SMFs for 2 hours or 7.0–33.0 T high SMFs for 1 hour, while potential positive effects on memory, cognition and antidepressant in mice were revealed. However, it remains unclear whether prolonged SMF exposure, and/or mice in different pathological states would have safety issues.
The Zhang group first exposed normal mice to a 0.1 T moderate quasi-uniform SMF provided by a permanent magnet plate continuously for 1.7 years. Not only was it found to have no adverse effects, but it also improved their survival status, including the activity of behavior, and even delayed their natural ageing process and extended lifespan. In addition, the same SMF also alleviated chronic kidney injury induced by the chemotherapeutic drug cisplatin in breast cancer MDA-MB231 tumor-bearing mice and ameliorated acute kidney injury induced by high dose cisplatin. Both works were related to reduced oxidative stress levels in cells and tissues induced by SMFs.
On the other hand, magnetic resonance imaging (MRI) techniques have been widely used for disease diagnosis and higher SMF strength has been crucial for improving MRI image quality. In fact, 9.4 T MRI has been tested in healthy volunteers, but their effects on diabetic patients were unknown. Thus, the Zhang group evaluated the effects of 1.0–9.4 T SMFs on two types of type 1 diabetes (T1D) and one type 2 diabetes (T2D) mice, including >10 T/m and 0-10 T/m. A prolonged duration of 14 hours of magnetic field exposure was used to explore the upper limit of magnetic field safety.
The results showed that the treatment with gradient high SMFs (1.0–8.6 T) lasting 14 hours produced some deleterious effects in both T1D and T2D mice, including spleen, liver and kidney tissue damage, as well as elevated levels of blood glucose, glycosylated serum proteins, inflammation and anxiety; whereas low gradient or quasi-uniform 0-10 T/m ~9.4 T high SMFs were safer and did not show the above phenomena.
In addition, they found that in the kidneys of T1D mice with blood glucose ≥16.7 mM, high SMFs with gradients >10 T/m increased tissue malondialdehyde levels and decreased superoxide dismutase levels. However, in severe T1D mice of glucose ≥30.0 mM, >10 T/m gradient high SMFs not only significantly increased multi-organ damage but also decreased mice survival. In vitro cellular studies showed that gradient magnetic fields increased reactive oxygen levels in mouse islet endothelial cells (MS-1), promoted apoptosis, and reduced cell proliferation.
These results indicated that exposure to >10 T/m gradient high magnetic fields (35–1380 times higher than current clinical MRI) for 14 hours (significantly longer than clinical MRI) produced deleterious effects in diabetic mice, especially in severe T1D mice. In contrast, the ~9.4 T near-uniform high SMFs that were directly associated with MRI had no significant adverse effects, which provided essential information for the future development and clinical application of SMFs, especially for high-field MRI.
These studies were supported by the National Natural Science Foundation of China and International Partnership Program of Chinese Academy of Sciences.
Figure 1. Long-term exposure to moderate quasi-uniform static magnetic field delays aging in normal mice. (Image by YU Biao)
Figure 2. Moderate quasi-uniform static magnetic field ameliorates renal injury induced by the chemotherapy drug cisplatin. (Image by YU Biao)
Figure 3. Exposure to >10 T/m gradient high static magnetic field for 14 hours causes damage to severe type 1 diabetic mice and MS-1 cells. (Image by YU Biao)