Effects Of Strong Geomagnetic Intervention On Myocardial Ischemia/Reperfusion Injury In Rats At Different Times And On TLR4/NF-κB Signaling Pathway

Objective:To explore the effects of strong geomagnetic intervention for 6h,24h and 48h on myocardial ischemia/reperfusion injury rats and the expression of TLR4/NF-κB signaling pathway.Methods:（1）A rat MI/RI model was established by ligating the left anterior descending branch of the coronary artery and reperfusing it for 30 min with ischemia for 2h.The SD male rats were randomly divided into normal environment sham-operated group（Sham group）,normal environment MI/RI group（I/R group）,normal environment MI/RI+high-intensity geomagnetic radiation intervention group（HIG+I/R group）and MI/RI+geomagnetic shielding group（GS+I/R group）.The rats in the above four groups were placed in the respective environments for 6h,24h and48h,where the normal environment group（Dst=0-20n T）,the high-intensity geomagnetic radiation group（Dst=500n T）and the geomagnetic shielding group（Dst=0n T）;（2）At the end of the intervention,blood was collected from the abdominal aorta and the heart was quickly removed.The Langendorff perfusion system was used to monitor the hemodynamic indexes and observe the cardiac function of each group of rats;The area of myocardial infarction was measured by triphenyl tetrazolium chloride（TTC）staining in each group of rats.Hematoxylin-eosin（HE）staining was performed to observe the histopathological changes in the myocardium of each group of rats.Myocardial injury markers:creatine kinase isoenzymes（CK-MB）,cardiac troponin I（CTn I）and inflammatory factors interleukin-1 beta（IL-1β）,interleukin-6（IL-6）,tumer necrosis factor-α（TNF-α）were measured in rat serum using ELISA kits.The m RNA and proteins expression of Toll-like receptor 4（TLR4）,myeloid differentiation factor 88（My D88）,tumor necrosis factor receptor associated factor 6（TRAF6）and nuclear factor-κB（NF-κB）in myocardial tissues of rats were detected by quantitative real-time PCR and Western Blot.Results:（1）（1）Geomagnetic intervention for 6h:Compared with the Sham group,the LVDP and+dp/dt_maxvalues of rats in the I/R group showed a tendency to increase and-dp/dt_maxvalues had a tendency to decrease,and the myocardial infarct area significantly increased（P<0.001）,myocardial histopathological morphology was significantly altered,and the levels of CK-MB,CTn I,IL-1β,IL-6,TNF-αlevels were significantly increased（P<0.05,P<0.001）.Compared with the I/R group,LVDP was significantly decreased in the HIG+I/R group（P<0.01）,±dp/dt_maxvalues were significantly increased（P<0.01,P<0.001）,the area of myocardial damage was expanded,and myocardial histopathological damage was aggravated in MI/RI rats.The levels of CTn I,IL-1β,IL-6 were significantly increased（P<0.001）,and the levels of CK-MB and TNF-αtended to increase.LVDP tended to decrease,+dp/dt_maxvalues tended to increase and-dp/dt_maxtended to decrease significantly（P<0.01）in the GS+I/R group,and the myocardial infarct area had an increased change in MI/RI rats,myocardial histopathological damage was aggravated,CK-MB,IL-1β,IL-6,TNF-αdid’nt change significantly,CTn I levels had a tendency to decrease.Compared with the HIG+I/R group,LVDP in the GS+I/R group had a tendency to increase,±dp/dt_maxsignificantly decreased（P<0.001）,myocardial infarction area had a trend of increasing,myocardial histopathological damage was reduced,there was no significant change in CK-MB,CTn I,IL-1β,IL-6 levels were significantly lower（P<0.01,P<0.001）,TNF-αlevels showed a trend of decreasing.（2）Geomagnetic intervention for 24h:Compared with the Sham group,the I/R group showed no change in LVDP,a significant decrease in±dp/dt_max（P<0.01）,a significant increase in the area of myocardial injury（P<0.001）,an enlarged area of myocardial injury,and significantly higher levels of CK-MB,CTn I,IL-1β,IL-6,and TNF-α（P<0.01,P<0.001,P<0.05）.Compared with the I/R group,the HIG+I/R group showed an increasing trend in LVDP,+dp/dt_maxand a decreasing trend in-dp/dt_max,an increase in the area of myocardial damage（P<0.05）,an enlarged area of myocardial damage,and significantly higher levels of CK-MB,CTn I,IL-1β,IL-6,and TNF-αLevels of CK-MB,CTn I,IL-1β,IL-6 and TNF-αwere significantly increased（P<0.001,P<0.01）,LVDP and+dp/dt_maxwere significantly increased in the GS+I/R group（P<0.05）,-dp/dt_maxtended to decrease,myocardial injury area tended to decrease,myocardial histopathological changes were reduced,CK-MB and CTn I did’nt change significantly,IL-1βtended to increase,IL-6 were significantly increased（P<0.01）and TNF-αwas decreased（P<0.01）.Compared with the HIG+I/R group,LVDP was significantly increased（P<0.01）and±dp/dt_maxwas increased in the GS+I/R group,myocardial infarct area was reduced,myocardial tissue damage was decreased,CK-MB,CTn I,IL-1β,IL-6,TNF-αlevels were significantly lower（P<0.001,P<0.05）.（3）Geomagnetic intervention for 48h:Compared with the Sham group,LVDP in the I/R group tended to increase,+dp/dt_maxwas significantly lower（P<0.05）,-dp/dt_maxwas unchanged,the area of myocardial injury was significantly increased（P<0.001）,the area of myocardial injury was expanded,and the levels of CK-MB,CTn I,IL-1β,IL-6 and TNF-αwere elevated.Compared with the I/R group,LVDP in the HIG+I/R group tended to decrease,+dp/dt_maxincreased significantly（P<0.01）,-dp/dt_maxdid not change significantly,myocardial damage area increased significantly（P<0.001）,myocardial damage area expanded,and CK-MB,CTn I,IL-1β,IL-6,and TNF-αlevels were significantly increased（P<0.001,P<0.01）;LVDP and+dp/dt_maxshowed an increasing trend and-dp/dt_maxshowed a decreasing trend in the GS+I/R group,and the area of myocardial infarction was reduced（P<0.001）,and CK-MB,CTn I,IL-1β,IL-6,and TNF-α（P<0.01,P<0.05,P<0.001）levels were significantly reduced.Compared with the HIG+I/R group,LVDP,+dp/dt_maxwere significantly increased（P<0.001）and-dp/dt_maxwere reduced in the GS+I/R group,and myocardial infarct area was significantly reduced（P<0.001）.Myocardial histomorphological changes were reduced,and CK-MB,CTn I,IL-1β,IL-6 and TNF-αlevels were significantly lower（P<0.01,P<0.05,P<0.001）.（4）Three time points were compared:Compared with the 24h HIG+I/R group,the 6h HIG+I/R group showed significantly lower LVDP,+dp/dt_max（P<0.001）,-dp/dtmax showed a decreasing trend,myocardial infarct area was significantly reduced（P<0.05）,myocardial histopathological changes were reduced,CK-MB,IL-1β,IL-6,and TNF-αlevels were significantly reduced（P<0.001,P<0.01,P<0.05）,and CTn I levels showed a decreasing trend;48h HIG+I/R group showed a decreasing trend of LVDP,a significant decrease of+dp/dt_maxvalues（P<0.001）,an increasing trend of-dp/dt_max,and a significant increase of myocardial infarct area（P<0.01）,increased area of myocardial tissue damage,and significantly higher levels of CK-MB,CTn I,IL-1β,IL-6,and TNF-α（P<0.01,P<0.05）.（2）（1）Geomagnetic intervention for 6h:Compared with the Sham group,TLR4,My D88,TRAF6,NF-κB m RNA and protein expression in myocardial tissue were significantly increased in the I/R group（P<0.001,P<0.01,P<0.05）.Compared with the I/R group,TLR4,TRAF6 m RNA expression in the HIG+I/R group showed an elevated trend,My D88 m RNA level showed a decreasing trend,NF-κB m RNA and protein expression was elevated（P<0.001,P<0.05）,TLR4 and TRAF6 protein expression was elevated（P<0.05）,and My D88 expression was elevated in the GS+I/R group;TLR4,TRAF6,My D88,and NF-κB m RNA did not change significantly,TLR4,My D88,TRAF6 protein expression showed an elevated trend,and NF-κB protein expression did not change significantly.Compared with the HIG+I/R group,TLR4,TRAF6 m RNA and protein expression in the GS+I/R group showed a decreasing trend,My D88 m RNA and protein expression showed an increasing trend,NF-κB m RNA expression was significantly lower（P<0.001）,and NF-κB protein expression showed a decreasing trend.（2）Geomagnetic intervention for 24h:Compared with Sham group,TLR4,TRAF6,NF-κB m RNA and protein expression were significantly increased in I/R group（P<0.001,P<0.01,P<0.05）,My D88 m RNA and protein expression had a tendency to increase.Compared with I/R group,HIG+I/R group TLR4,TRAF6,NF-κB m RNA and protein expression were significantly higher in the HIG+I/R group compared with the I/R group（P<0.001,P<0.01,P<0.05）,My D88 m RNA expression had a decreasing trend,My D88 protein expression had an increasing trend,and TLR4,TRAF6,My D88,NF-κB m RNA did not change significantly,and their protein expression had an elevated trend in the GS+I/R group;compared with the HIG+I/R group,TLR4,TRAF6 m RNA and protein expression were significantly lower in the GS+I/R group（P<0.001,P<0.01）,NF-κB m RNA expression was significantly lower（P<0.01）,NF-κB protein expression had a decreasing trend,and My D88 m RNA and protein expression showed an increasing trend.（3）Geomagnetic intervention for 48h:Compared with Sham group,TLR4,My D88,NF-κB m RNA and protein expression were significantly increased in I/R group（P<0.001,P<0.01）,TRAF6 m RNA expression was significantly increased（P<0.01）,and protein expression had a tendency to increase;compared with HIG+I/R group,GS+I/R group,TLR4,NF-κB m RNA and protein expression were significantly decreased（P<0.001,P<0.01）,TRAF6 m RNA expression was decreased（P<0.01）,My D88 and TRAF6 protein expression had a decreasing trend,and My D88 m RNA expression did not change significantly.（4）Three time points were compared:Compared with 24h HIG+I/R group,TLR4,NF-κB m RNA expression was significantly lower in 6h HIG+I/R group（P<0.01）,TRAF6 m RNA expression had a decreasing trend,TLR4,TRAF6,NF-κB protein expression had a decreasing trend,My D88 m RNA expression had no significant trend protein expression had an increasing trend,48h HIG+I/R group TLR4,TRAF6 m RNA expression was significantly increased（P<0.001,P<0.01）,NF-κB,My D88 m RNA and protein showed an increasing trend,TRAF6 protein expression showed an increasing trend.Conclusion:（1）Strong Geomagnetic intervention led to increased injury in MI/RI rats,and the degree of injury increased with the increase of intervention time（6h,24h,48h）,geomagnetic shielding could reduce the injury in MI/RI rats;（2）Strong magnetic field aggravated myocardial injury in MI/RI rats by activating TLR4/NF-κB signaling pathway and promoting the inflammatory response.