Endogenous Cardioprotective Strategies:Optimization, Novel Mechanisms, And Clinical Influential Factor Analysis

Part I Delayed remote ischemic preconditioning produces an additive cardioprotection to sevoflurane postconditioning in an isolated rat heart modelObjective:Although both sevoflurane postconditioning (SPoC) and delayed remote ischemic preconditioning (DRIPC) have been proved effective in cardioprotection in various animal and human studies, the combined effect of these two strategies remain unclear. Therefore, this study was designed to investigate this effect and elucidate the related signal mechanisms in a Langendorff perfused rat heart model.Methods:Isolated rat hearts were perfused with95%oxygen oxygenated Krebs-Henseleit buffer solution (KHBs) in a Langendorff apparatus. After30-min balanced perfusion, hearts were subjected to30min ischemia followed by60min reperfusion except a total of90-min perfusion for control. DRIPC was conducted with4cycles5-min occlusion/5-min reflow at the unilateral hindlimb once per day for three days before heart isolation. A monitored concentration of3%(v/v) sevoflurane was bubbled in KHBs for SPoC at the onset of reperfusion for10min. Heart rate (HR), left ventricular developed pressure (LVDP), and maximum LVDP increase (+dp/dt) and decrease (-dp/dt) rate were continuously collected. Infarct size and cardiac troponin I levels was measured. Protein expression of PKB/Akt, ERK1/2, heme oxygenase (HO-1), and Nrf2(cytosol and nuclear) was detected with westernblotting analysis. Transcriptional level of HO-1was also detected in qRT-PCR.Results:A synergic cardioprotective effect of SPoC (3%v/v) and DRIPC was observed with faciliated cardiac functional recovery (HR, LVDP,±dp/dt) and decreased cardiac troponin I release (P<0.05). Coadministration with inhibitor LY294002or ZnPP for PKB/Akt or HO-1abolished the protective effect of SPoC or DRIPC(P<0.05).The infarct size-limiting effect was more pronounced in the combined group (6.76±2.18%) than the SPoC group (16.50±4.55%, P<0.001) or the DRIPC group (10.22±2.57%, P=0.047). Subsequent analysis revealed that an enhanced heme oxygenase (HO-1) expression, but neither PKB/AKt nor ERK1/2activation, was involved in the additive cardioprotective effect, which was further confirmed in the transcriptional level of HO-1. Such trend was also observed in the Nrf2nuclear translocation, a upstream regulation of HO-1. In addition, correlation analysis showed a significantly positive relationship between HO-1expression and Nrf2translocation (r=0.729, P<0.001).Conclusions:Both SPoC and DRIPC may provide cardioprotective effect. DRIPC may produce an additive cardioprotection to SPoC partly through an enhanced HO-1expression via Nrf2translocation. Part Ⅱ Effect of delayed remote ischemic preconditioning on the mitochondrial microRNA-181c level in isolated reperfused rat heartsObjective:Although delayed remote ischemic preconditioning (DRIPC) has been proved effective in cardioprotection in various animal and human studies, limited data concerning the underlying mechanisms has been reported. Mitochondrial microRNA-181c (miR-181c) has been found to confer cardioprotective potential. Hence, this study was designed to investigate this effect on the mitochondrial miR-181c level in isolated perfused rat hearts.Methods:Isolated rat hearts were perfused with95%oxygen oxygenated Krebs-Henseleit buffer solution (KHBs) in a Langendorff apparatus. After30-min balanced perfusion, hearts were subjected to30min ischemia followed by60min reperfusion except a total of90-min perfusion for control(ischema/reperfusion, I/R). DRIPC was conducted with4cycles5-min occlusion/5-min reflow at the unilateral hindlimb one day before heart isolation. Heart rate (HR), left ventricular developed pressure (LVDP), and maximum LVDP increase (+dp/dt) and decrease (-dp/dt) rate were continuously collected. Infarct size and cardiac troponin I levels was measured. The total RNAwas extracted in isolated mitochondrial pellet. The expression of miR-181c was detected by real-time reverse transcription polymerase chain reaction using TaqMan method.Results:DRIPC improved the recovery of heart function (HR, LVDP,±dp/dt), and reduced the release of cTnI (P<0.05). DRIPC limited the infarct size caused by ischemic reperfusion injury (22.34±4.02%vs33.50±4.55%,P<0.001). Compared with control, I/R did not affect the miR-181c level (6.21±4.87vs4.61±0.63, P>0.05) However, DRIPC significantly increased this level (9.16±2.68vs4.61±0.63, P<0.05)Conclusions:DRIPC offers cardioprotective effect and increases the mitochondrial miR-181c level. Part Ⅲ β-blockers and Volatile Anesthetics May Attenuate Cardioprotection by Remote Preconditioning in Adult Cardiac Surgery: A Meta-analysis of15Randomized TrialsObjective:Clinical trials on cardioprotection by remote ischemic preconditioning (RIPC) for adult patients undergoing cardiac surgery revealed mixed results. Previous meta analyses have been conducted and found marked heterogeneity among studies. The aim of this meta analysis was to evaluate the factors affecting cardioprotection by RIPC in adult cardiac surgery.Methods:Randomized controlled trials (RCT) concerning the cardioprotection by RIPC were searched from PubMed, EMBase, and Cochrane Library (up to July2012) using related keywords. Studies published in English involving adult cardiac surgery with data on postoperative CK-MB or troponin levels were included. Standardized mean difference (SMD) with the corresponding95%confidence interval (CI) was used to pool the myocardial biomarkers. Random-effect model was used in case of significant heterogeneity (I2>50%). Test of publication bias was also performed. Meta-regression and subgroup analyses were conducted to explore the potential sources of significant heterogeneity(a p value of<0.1was accepted).Results:Fifteen trials with a total of1155study patients were identified. Compared with controls, RIPC significantly reduced postoperative biomarkers of myocardial injury (SMD=-0.31;95%CI,-0.60to-0.01; P=0.041; heterogeneity test:I2=83.5%). This effect seemed more significant in valve surgery (SMD=-0.74;95%CI,-1.21to-0.27; P=0.002) than that in coronary surgery (SMD=-0.23;95%CI,-0.23to0.10; P=0.17; P<0.00001for subgroup difference). No evidence of significant publication bias was observed in the present analysis as shown by the Begg’s (P<0.150) and Egger’s tests (P<0.128). Univariate meta-regression analyses suggested that the major sources of significant heterogeneity were β-blockers (%)(coefficient=0.0161;95%CI,0.0028to0.0295; P=0.022;adjusted R2=0.37) and volatile anesthetics (coefficient=0.6617;95%CI,-0.0481to1.3716; P=0.065; adjusted R2=0.22). These results were further confirmed in multivariate regression and subgroup analyses.Conclusion:Available data from this meta analysis further confirmed the cardioprotection conferred by RIPC in adult cardiac surgery. Moreover, the cardioprotective effect may be attenuated when combined with β-blockers or volatile anesthetics. Part IV Age and Gender are associated with Cardioprotection by Ischemic Postconditioning in STEMI patients:A Systematic Reveiw and Meta-analysisObjective:We sought to perform a systematic review and meta analysis to evaluate the potential factors affecting ischemic postconditioning(IPoC) for patients with ST segment elevation acute myocardial infarction (STEMI) in primary percutaneous coronary intervention(PCI).Methods:Randomized controlled trials (RCT) concerning the cardioprotection by IPoC were searched from PubMed, EMBase, and Cochrane Library (up to February2012) using related keywords. Studies published in English involving STEMI patients with data on myocardial enzyme levels or left ventricular ejection fraction (LVEF) were included. Standardized or weighted mean difference(SMD or WMD) with the corresponding95%confidence interval (CI) was used to pool the postoperative endpoints. Random-effect model was used in case of significant heterogeneity (I2≥50%). Test of publication bias was also performed. Meta-regression and subgroup analyses were conducted to explore the potential sources of significant heterogeneity(a p value of<0.1was accepted).Results:Ten RCTs with a total of560STEMI patients were identified. Compared with controls, IPoC significantly reduced elevated cardiac enzyme levels (SMD=-0.84;95%CI,-1.26to-0.43;P<0.00001; heterogeneity test,I2=81.0%) and improved LVEF (WMD=3.98%;95%CI,1.27%to6.70%;P=0.004;heterogeneitytest,I2=87.1%). The effect on LVEF remained significant after one year (WMD=5.04%;95%CI,4.20%to5.88%; P<0.00001; heterogeneity test,I2=0.0%). No evidence of significant publication bias was observed for cardiac enzyme (P=0.089, Begg’s test; P=0.088, Egger’s test) and LVEF (P=0.98, Begg’s test; P=0.064, Egger’s test). Univariate meta-regression analysis suggested that the major sources of significant heterogeneity(P<0.1) were male proportion(%)(coefficient=-0.022;95%CI,-0.049to0.005P=0.098;adjusted R2=0.28) for myocardial enzyme levels, and age (coefficient=-1.34;95%CI,-2.461to-0.216; P=0.025;adjusted R2=0.55) for LVEF(%). Subsequent multivariate regression and subgroup analysis confirmed these results.Conclusions:Available evidence from this systematic review and meta analysis of10RCTs suggests that IPoC may confer cardioprotection in terms of myocardial enzyme levels and LVEF for STEMI during primary PCI. These effects are more pronounced among young and male patients. Future studies should focus on the mortality in high-quality, large-scale clinical trials with long-term follow-up. Part V Remote Ischemic Conditioning offers Cardiorenal Protection in Patients undergoing Percutaneous Coronary Intervention:A Systematic Review and Meta-AnalysisObjective Results from randomized controlled trials (RCT) concerning clinical effect of remote ischemic conditioning (RIC) in percutaneous coronary intervention (PCI) are inconsistent. The aim of this study was to evaluate the cardiac or renal effect of RIC in patients undergoing percutaneous revascularization.Methods:Randomized controlled trials (RCT) concerning the cardiorenal protection by RIC were searched from PubMed, EMBase, and Cochrane Library (up to February2013) using related keywords. Studies published in English involving patients undergoing PCI with data on cardiac or renal points were included. Standardized or weighted mean difference(SMD or WMD), and odds ratio (OR) with the corresponding95%confidence intervals (CI) were used to pool the postoperative endpoints. Random-effect model was used in case of significant heterogeneity (I2≥48%). Meta-regression and subgroup analyses were conducted to explore the potential sources of significant heterogeneity(a p value of<0.1was accepted).Results Nine RCTs enrolling a total of1197patients were selected. Compared with controls, RIC significantly reduced postoperative elevated myocardial troponin levels (standardized mean difference=-0.51;P=0.002;I2=85.0%), decreased the incidence of myocardial infarction (MI)[odds ratio(OR)=0.55; P=0.01; I2=48.0%], major adverse cardiac event (MACE)(OR=0.57; P=0.03; I2=47.0%), and acute kidney injury (OR=0.35; P=0.001; I2=26.0%). Univariate meta-regression analyses suggested that the major sources of significant heterogeneity (P<0.1) were emergency PCI (coefficient=0.691; P=0.084; adjusted R2=46.0%), β-blockers(%)(coefficient=-0.064; P=0.052; adjusted R2=86.0%) and non-hypertension (%)(coefficient=-0.024; P=0.028; adjusted R2=68.2%) for myocardial enzyme levels, and Jadad score (coefficient=-0.277; P=0.061; adjusted R2=100.0%) and non-smoke (%)(coefficient=-0.020; P=0.062; adjusted R2=100.0%) for incidence of MI (natural logarithm form of OR). These results were further confirmed in the subgroup analyses.Conclusions The present meta-analysis of RCTs suggests that RIC may offer cardiorenal protection and improve clinical outcomes about MI and MACE in patients undergoing PCI. Such cardioprotective effect may be more pronounced among emergency, non-hypertensive, or non-smoking patients, and those who medicated with β-blockers. However, clinical trials with lower quality may tend to obtain a negative cardiac effect.