| BackgroundMultiple sclerosis(MS)is a clinically common inflammatory demyelinating occurring in the central nervous system,which is the leading cause of non-traumatic neurologic disability among young population.Until today,there are no efficient therapeutic approaches available for promoting remyelination and improve patients'daily lives.Oxidative stress played a crucial role in the pathogenesis of MS and its animal model.Nuclear factor erythroid 2-related factor 2(Nrf2)is recognized as the main regulator of antioxidant and phase ? detoxification genes.Growing evidences have demonstrates that the upregulation of Nrf2 pathway to alleviate oxidative damage would be a potential therapeutic target for the treatment of MS disease.The use of electromagnetic fields(EMF)is a noninvasive therapeutic method for various diseases and gained increased attention.It is important to note,the neuroprotective effects of extremely low-frequency EMF(ELF-EMF,0-300 Hz)therapy have been documented in some studies to be associated with the modulation of endogenous antioxidant enzyme activity via activating Nrf2 pathway.Nevertheless,the studies investigating the effect and mechanism of ELF-EMF for MS have been scarce and deserve attention.We used cuprizone,a copper chelating agent,which mimics apoptosis in oligodendrocytes and induces demyelination in thecorpuscallosum through mechanisms of oxidative damage,provides an excellent background to evaluate ELF-EMF application of MS.ObjectiveIn this study,we investigated the effect of ELF-EMF administration on the behavioral dysfunction and demyelination induced by CPZ in MS model mice and its potential mechanism.MethodsAfter one week of acclimation,forty male mice were randomly divided into the normal group,Control(Con)group,ELF-EMF(EMF)group,cuprizone(CPZ)group,and cuprizone+ELF-EMF(CPZ+EMF).Con group and EMF group were fed ordinary feed,while EMF group and CPZ+EMF group were fed a 0.3%(w/w)CPZ for 5 weeks to establish MS animal model.For ELF-EMF treatment,mice were exposed to EMF(50 Hz,7 mT)starting from the second week(20 min/day,6 days/week,4 weeks in total).General condition of mice wereweekly evaluated by their weight.At the end of the fifth week of the experiment,their motor function and mental state were observed by the rotarod test and elevated plus maze(EPM).After the mice were sacrificed,LFB staining and myelin basic protein(MBP)immunohistochemistry staining were used to evaluate the changes of myelin in the corpus callosum(CC)region.The content of malondialdehyde(MDA)and the activity of superoxide dismutase(SOD)in CC were measured by biochemical analyses to evaluate the degree of oxidative damage.The Nrf2 and its downstream target heme oxygenase-1(HO-1)expression in brain tissue of mice was detected by immunohistochemistry,Western blot and quantitative real-time polymerasechain reaction.Results(1)At the end of the 5th week,body weight in CPZ and CPZ+EMF groups was both significantly less than it in Con group(P<0.001 and P<0.05,respectively).The body weight of CPZ+EMF group was significantly gained than that of CPZ group(P<0.05).Compared with Con group,the exercise time on the rotating bar of mice in CPZ group was shorter(P<0.001),the percentage of open arm entries(OE%)and percentage of residence time(OT%)at the EPM were both reduced(P<0.05,all),and LFB staining in the CC area of mice showed profound demyelination(P<0.001)and the average optical density(AOD)value of MBP was significantly reduced(P<0.001).Compared with the CPZ group,mice from the CPZ+EMF group had prolonged duration time(P<0.05),increased the OT%value at the EPM(P<0.05),less myelin loss in LFB staining of the CC(P<0.001)and significantly enhenced MBP AOD value(P<0.001).(2)Compared with Con group,the MDA content was increased and SOD activity was decreased in the CC of mice in CPZ group,and the difference was statistically significant(P<0.001,all).Compared with CPZ group,MDA was significantly reduced(P<0.001)and SOD was significantly enhanced in CPZ+EMF group(P<0.01).The number of Nrf2 nuclear translocation cells and the expression of Nrf2 protein in CPZ group were increased compared with Con group(P<0.01 and P<0.05,respectively),while there was no statistical difference in the expression of HO-1 protein and HO-1mRNA between the two groups(P>0.05,all).Compared with the CPZ group,the number of Nrf2 nuclear translocation cells and the Nrf2 protein in CPZ+EMF group increased significantly(P<0.05 and P<0.01,respectively),and the expressions of the downstream target HO-1 protein and HO-1mRNA were significantly up-regulated(P<0.05 and P<0.01,respectively).ConclusionsIn this study,it is reported for the first time that ELF-EMF provide a protective effect in CPZ-induced MS model,improving the general condition of the mice,promoting the recovery of neurofunction deficits and reducing the degree of demyelination in brain tissue.Its protective effect mechanism may be to attenuate CPZ-induced oxidative stress damage by upregulating the expression of Nrf2/HO-1 antioxidant pathway.Here,our current study provides a theoretical reference for clinical treatment of MS with ELF-EMF. |
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