Metformin and tanshinone IIA as ethnodrugs protect heart against injury by inhibiting microRNA-1

OBJECTIVE To explore the protection mechanism of metformin and tanshinone IIA on myocardial injury.METHODS The cultured neonatal rat ventricular cells(NRVCs) were exposed to100 μmol·L^(-1) H2 O2 to simulate the in vitro model of ischemia-reperfusion injury.MTT,TUNEL and Viability/Cytotoxicity Assay were used to evaluate the effect of metformin on the viability of cardiomyocytes after treated with H2 O2.The target of miR-1 was verified by Dual luciferase reporter assay.ChIP analyses was adopted to reveal the relationship between C/EBP β and miR-1.Tanshinone IIA was administrated daily for 7 d before ligation of the left anterior descending artery(LAD) and lasted for 3 months after LAD.Whole-cell patch-clamp techniques were used to measure the inward rectifying K+ current(IK1) in rat isolated ventricular myocytes.GRP94,p-AMPKα,C/EBP β,CHOP,Caspase-3,Kir2.1,p38 MAPK,Cx43,MEF2 and SRF levels were analyzed by Western blot and miR-1 level was quantified by Realtime PCR.RESULTS The expression of miR-1 was significantly increased in NRVCs exposed to H2 O2 in vitro.miR-1 was shown to target the 3′-untranslated region(UTR) of GRP94,which results in the accumulation of un/misfolded proteins,leading to the endoplasmic reticulum(ER) stress.C/EBP β directly induces the upregulation of miR-1 by binding to its promoter.Furthermore,metformin,a direct allosteric AMPK activator,significantly reduces C/EBP β and miR-1 levels comparing with control group.Similarly,tanshinone IIA decreased the incidence of arrhythmias and relieved ischemia-induced injury.Moreover,tanshinone IIA depressed the elevated miR-1 level and inhibited the activation of p38 MAPK and heart special transcription factors SRF and MEF2 in ischemic cardiomyocytes.CONCLUSION Metformin protects cardiomyocytes against H2 O2 damage through AMPK/C/EBPβ/miR-1/GRP94 pathway.Tanshi.none IIA play a role in protection cardiomyocytes from ischemic injury based on inhibiting miR-1 expres.sion through p38 MAPK signal pathway.

The ionic mechanisms of long QT interval in diabetic rabbits

Objective Abnormal QT prolongation associated with arrhythmias is considered the major cardiac electrical disorder and a significant predictor of mortality in diabetic patients. The precise ionic mechanisms for diabetic QT prolongation remained unclear. The present study was designed to analyze the changes of ventricular repolarization and the underlying ionic mechanisms in diabetic rabbit hearts. Methods Diabetes was induced by a single injection ofalloxan （145mg/kg, Lv. ）. After the development of diabetes （10 weeks）, ECG was measured. Whole-cell patch-clamp technique was applied to record the action potential duration （APD50, APD90）, slowly activating outward rectifying potassium current （IKs）, L-type calcium current （ICa-L） and inward rectifying potassium current （IK1）. Results The action potential duration （APD50 and APD90） of ventricular myocytes was obviously prolonged from 271.5＋32.3 ms and 347.8＋36.3 ms to 556.6~72.5 ms and 647.9~72.2 ms respectively （P〈 0.05）. Meanwhile the normalized peak current densities of IKs in ventricular myocytes investigated by whole-cell patch clamp was smaller in diabetic rabbits than that in control group at test potential of＋50mV （1.27~0.20 pA/pF vs 3.08~0.67 pA/pF, P〈0.05）. And the density of the ICa-L was increased apparently at the test potential of 10 mV （-2.67~0.41 pA/pF vs -5.404-1.08 pA/pF, P〈0.05）. Conclusion Ventricular repolarization was prolonged in diabetic rabbits, it may be partly due to the increased L-type calcium current and reduced slow delayed rectifier K＋ current （IKs） （J Geriatr Cardio12010; 7：25-29）.