| Acute Myocardial Infarction(AMI)is one of the leading causes of mortality in the world.Acute Myocardial Infarction(AMI)is one of the leading causes of mortality in the world.Common clinical therapies can rapidly restore blood flow to ischemic zone,such as Percutaneous Coronary Intervention(PCI)and Coronary Artery Bypass Graft(CABG).However,it will cause myocardial tissue damage,even heart failure and death.This myocardial injury due to the rapid restoration of blood flow is named as Ischemic Reperfusion Injury(I/R)injury.Studies have reported that transient ischemic/reperfusion cycles before ischemia can prevent I/R injury,known as ischemic preconditioning(IPC).IPC is considered as one of the most effective treantments to prevent I/R injury.In recent years,studies on tea with I/R injury have focused on green tea extracts,catechins,and Epigallocatechin gallate(EGCG),and it has been confirmed in vitro that tea polyphenols prevent I/R injury via IPC.Our previous studies suggest that Epicatechin gallate(ECG)is the most effective compound in catechins to enhance myocardial contractility in isolated rat heart which perfused with normal conditions.Its effect is better than that of EGCG;Theaflavin-3,3’-digallate(TFDG),the oxidation product of catechins,has most effect on improving the myocardial contractility of rats than other compound in theaflavins.Meanwhile,we found that low concentrations of ECG(1.0μg/m L)can activate protein kinase C epsilon(PKCε)which is the key protein in the mechanism of IPC.Therefore,to further establish the rat heart I/R model to test whether ECG,or TFDG preconditioning with 100 ng/m L,500 ng/m L at a physiological concentration protect the isolated rat heart from I/R injury.Firstly,we established I/R injury model in isolated rat heart of Langendorff.It found that the 100ng/m L and 500 ng/m L ECG significantly increase the recovery of left ventricular developed pressure(LVDP)with 75.4%and 96.0%,respectively,compared to the I/R group(42.7±5.7%).And ECG preconditioning with two concentrations significantly decreased Left Ventricular End-diastolic Pressure(LVEDP)from 59.1±2.9 mm Hg in I/R group to 38.9±9.2 mm Hg and 20.28±9.1 mm Hg,respectively.These key cardiac functional indexes show that ECG preconditioning with low concentration has significant effect on preventing I/R injury.Further studies on activity of Na~+,K~+-ATPase(NKA),a key membrane protease,results shown of ECG preconditioning with 100 ng/m L and 500ng/m L significantly increased NKA activity in isolated rat hearts,from 4.48±0.42μmol Pi/mg/h in I/R increased to 6.25±0.458μmol Pi/mg/h and 7.26±0.81μmol Pi/mg/h,respectively.In addition,two concentrations of ECG significantly increased the PKCεtranslocation(cytosolic to particulate)which is a protein closely related to the calcium sensitivity of cardiac contractile,and the translocation expression rates were 1.74 and 1.93times that of the control group,respectively.Through the activation of PKCεto enhance the contractile of I/R hearts.Meantime,we study on the key signal proteins ERK and AKT,which are closely related to the survival of cardiomyocytes.The results shown that after treatment with two concentrations of ECG,the phosphorylation of ERK in MAPK signaling pathway can be activated.The activation rate of ERK phosphorylation was 1.93and 2.44 times that of the control group;it also activated AKT phosphorylation in the PI3K signaling pathway,and the activation rates were 1.86 and 2.09 times that of the control;The study of NFκB signaling pathway that may be related to inflammation showed that500 ng/m L ECG preconditioning significantly inhibited its phosphorylation relative to the I/R group,but there was no significant inhibitory effect of 100 ng/m L ECG.These results indicate that ECG preconditioning at closely physiological concentrations can significantly increase NKA activity,activate translocation of PKCε,and thus restore cardiac contractile function of I/R hearts,in addition to through activation of the signaling proteins ERK and AKT,and inhibited NFκB to protect the I/R injured cardiomyocytes,and improve the survival rate of myocardial cells,thereby maintain the normal function of cardiomyocytes and alleviate I/R injury.Based on epidemiological investigations,black tea and green tea have similar cardiovascular protective efficacy.Therefore,the TFDG,the most bioactivity Polyphenols in black tea,was further detected for I/R injury protection.The results showed that the effects of TFDG and ECG preconditioning with 100ng/m L and 500ng/m L were similar in the isolated rat heart I/R model,which could significantly increase the recovery of LVDP,and the rate of recovery increased to 108.2%and 78.6%from 42.7%that of the I/R group,respectively.At the same time,it significantly reduced LVEDP from 59.1 mm Hg in I/R group to 16.8 mm Hg and 32.3 mm Hg,respectively.The study of mechanism on TFDG preconditioning showed that TFDG did not increase the NKA activity in I/R injured rat hearts,nor did it significantly increase the PKCεtranslocation and phosphorylation of ERK from MAPK pathway,it is unlike ECG preconditioning.But the treatment of TFDG at both two concentrations significantly increase the phosphorylation of AKT,with 2.45 and 2.01times of control,respectively.It significantly inhibits the phosphorylation of NFκB signaling pathway compared to I/R group,respectively.These results suggest that TFDG as a dimer formed from the oxidative condensation of ECG and EGCG in black tea,although there are similar effects between TFDG and EGCG,their mechanism is different.TFDG preconditioning did not increase NKA activity and PKCεtranslocation,nor did it activate ERK phosphorylation.However,the effects of inhibiting NFκB phosphorylation and increase AKT phosphorylation are better than that of ECG.In conclusion,the present study suggests that the ECG and TFDG preconditioning closely physiological concentrations significantly protect I/R injury in isolated rat hearts.Although there is difference of mechanism between ECG and TFDG,they both show the protective effects of drinking tea on myocardial I/R injury. |
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