| Objective:1) To investigate the roles of reactive oxygen species (ROS), extracellular signal regulated kinase 1/2 (ERK 1/2) and mitochondrial permeability transition pore (mPTP), and their possible linkages in sevoflurane postconditioning (SpostC) in isolated healthy rat hearts exposed to myocardial ischemia-reperfusion injury (MIRI).2) To evaluate SpostC-induced cardioprotection against MIRI in chronically infarcted rat hearts in vitro, and investigate the roles of protein kinase B (PKB/Akt), ERK 1/2 and mPTP.3) To compare the cardioprotective effects of sevoflurane preconditioning (SpreC), sevoflurane postconditioning (SpostC) and sevoflurane preconditioning plus postconditioning (SpreC+SpostC), and to examine possible underlying mechanisms which might explain the relative efficacy of the three different modalities of sevoflurane conditioning.4) To determine whether sevoflurane has superior myocardial protection profiles than propofol in patients undertaking coronary artery bypass grafting surgery by systematically reviewing relevant randomized controlled trials (RCTs).Methods:1) Isolated rat hearts were subjected to 30 min of global ischemia, followed by 1 h of reperfusion with Krebs-Henseleit (K-H) buffer. SpostC was induced by perfusing the hearts with K-H buffer saturated with 3% sevoflurane during the first 15 min of reperfusion. To evaluate the role of ROS and ERK 1/2 in SpostC, ROS scavenger NAC (4 mM) or ERK 1/2 inhibitor PD98059 (20μM) was administered alone or together with sevoflurane during the first 15 min of reperfusion. Hemodynamics, infarct size, lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) were compared among groups. Additionally, myocardial malondialdehyde (MDA) content, an indicator of oxidative injury was also determined after 60 min of reperfusion. ERK 1/2 phosphorylation was measured by Western blotting analysis. The status of mPTP opening was determined by analyzing the nicotinamide adenine dinucleotide (NAD+) content in myocardium.2) Left anterior descending (LAD) coronary artery was ligated to induce myocardial infarction in rats. Six weeks later, chronically-infarcted hearts were isolated and subjected to 30 min of global ischemia, followed by 1 h of reperfusion with K-H buffer. SpostC was administered by perfusing the hearts with K-H buffer saturated with 3% sevoflurane during the first 15 min of reperfusion. To evaluate the role of PI3K-PKB/Akt and MEK 1/2-ERK 1/2 in SpostC, PI3K inhibitor LY294002 (15μM) and MEK 1/2 inhibitor PD98059 (20μM) were administered alone or together with sevoflurane during the first 15 min of reperfusion. Hemodynamics, infarct size, LDH and CK-MB were compared among groups. Phosphorylation of PKB/Akt and ERK 1/2 was measured by Western blotting analysis after 30 min of ischemia and 15 min of reperfusion. The status of mPTP opening was determined by analyzing the NAD+content in myocardium.3) After 10 min of equilibration, isolated rat hearts were randomly assigned into one of the four groups:CTRL group (30 min of ischemia followed by 120 min of reperfusion alone) served as non-treated control; SpreC group (3% sevoflurane preconditioning was administered for 15 min followed by 10 min of washout before ischemia); SpostC group (3% sevoflurane postconditioning was administered during the first 15 min of reperfusion after ischemia); SpreC+SpostC group (the protocols of SpreC and SpostC groups were combined). Hemodynamics was compared within and between groups. Infarct size was determined at the end of 120 min of reperfusion using TTC staining. LDH and CK-MB released from necrotic myocardium, were compared among groups. Time course of the two key pro-survival kinases, namely PKB/Akt and ERK 1/2 activation in four groups, were determined by Western blotting analysis. mPTP status was compared by assaying myocardium NAD+content. Additionally, myocardium samples were collected at the end of the experiment, to characterize the gene expression profiles of three modalities of sevoflurane treatment using Agilent high-intensity rat microarrays. 4) Electronic databases were searched to identify all RCTs comparing sevoflurane with propofol in adult patients undertaking CABG surgery. Two authors independently assessed the methodological quality of the included studies and extracted perioperative data, including patients'baseline characteristics, surgical variables and outcome data such as post-bypass cardiac index (CI), postoperative troponin I (cTnl), ventilation time, inotropic support, intensive care unit (ICU) and hospital stay length, mortality, myocardial infarction, myocardial ischemia and atrial fibrillation. Disagreement between two authors was solved by discussion. For continuous variables, treatment effects were calculated as weighted mean difference (WMD) and 95% confidential interval (CI). For dichotomous data, treatment effects were calculated as odds ratio (OR) and 95%CI. Each outcome was tested for heterogeneity, randomized-effects or fixed-effects model was used in the presence or absence of significant heterogeneity (Q test P<0.05). Sensitivity analyses were done by examining the influence of statistical model on estimated treatment effects or eliminating some of the included RCTs. Publication bias were explored through visual inspection of funnel plots of the outcomes. Statistical significance was defined as P<0.05.Results:1)When compared with unprotected ISCH hearts, exposure of 3% sevoflurane during early reperfusion significantly improved functional recovery (improved LVDP,±dp/dt, CF, HR and reduced LVEDP), decreased myocardial infarct size and reduced LDH and CK-MB release (P<0.05). The protective effect of sevoflurane postconditioning was also manifested by reduced MDA content in myocardium after ischemia-reperfusion. However, these protective effects were all abolished in the presence of either NAC or PD98059, which was accompanied by prevention of ERK 1/2 phosphorylation and reduction of myocardial NAD+content.2)Exposure to 3% sevoflurane during early reperfusion significantly improved functional recovery (improved LVDP,±dp/dt, CF, HR and reduced LVEDP), decreased myocardial infarct size and reduced LDH and CK-MB release, when compared with unprotected hearts. However, these protective effects were abolished in the presence of either LY294002 or PD98059, which was accompanied by the prevention of PKB/Akt and ERK 1/2 phosphorylation, and reduction of myocardial NAD+content.3)When compared with unprotected CTRL ones, hearts in sevoflurane-treated groups (SpreC, SpostC and SpreC+SpostC) showed significantly better functional recovery (improved LVDP,+dp/dt,-dp/dt, CF, HR and reduced LVEDP), reduced myocardial infarct size, decreased LDH and CK-MB release (P<0.05). Comparison of the above-mentioned varibles among three sevoflurane-treated groups showed that, maximal cardioprotection was obtained in SpreC+SpostC group (P<0.05), and no difference was found between SpreC and SpostC groups (P>0.05). Western blotting analysis revealed that CTRL hearts showed increased PKB/Akt and ERK-1/2 phosphorylation after ischemia-reperfusion when compared to the baseline values. Both SpreC and SpreC+SpostC induced a biphasic response in PKB/Akt and ERK-1/2 phosphorylation during the preconditioning and reperfusion phases following ischemia. SpostC induced only one phase of enhanced PKB/Akt and ERK-1/2 phosphorylation, which occurred after sevoflurane postconditioning. And the effects on phosphorylation of both PKB/Akt and ERK-1/2 induced by SpreC and SpostC were found to be additive at 15 min and 120 min of reperfusion. The CTRL hearts have the lowest myocardial NAD+content among all groups (P<0.05). While SpreC+SpostC hearts retained higher contents of NAD+than either SpreC or SpostC ones (P＜0.05), suggesting that the combination of sevoflurane preconditioning and postconditioning had also additive effects on inhibiting mPTP opening induced by ischemia-reperfusion. Microarray analysis demonstrated that post-ischemic genome reprogramming was completely different among three sevoflurane-treatment groups. Of the more than 41,000 genes represented on the Agilent gene chips,21 transcripts in the SpreC group,289 in the SpostC group and 160 in the SpreC+SpostC group displayed significant (≥1.5 fold) up-regulation. And 19 transcripts in the SpreC group,310 in the SpostC group and 219 in the SpreC+SpostC group displayed significant (≥1.5 fold) down-regulation. Few genes were jointly regulated by SpreC, SpostC and SpreC+SpostC.4)Searching yielded 13 studies including 696 patients,402 patients were allocated into sevoflurane group, and 294 into propofol group. There was no significant difference in postoperative mechanical ventilation time, inotropic support, mortality, myocardial infarction and atrial fibrillation between the two groups (all P>0.05). Patients randomized into sevoflurane group had higher post-bypass cardiac index (P=0.003), lower troponin I (P<0.00001), lower incidence of myocardial ischemia (P=0.02), shorter ICU and hospital stay length (P=0.24 and P=0.21, respectively). Conclusion:1)Sevoflurane postconditioning protects isolated rat hearts against ischemia reperfusion injury via the recruitment of the ROS-ERK 1/2-mPTP signaling cascade.2)Sevoflurane postconditioning protects chronically infarcted rat hearts against ischemia reperfusion injury by inhibiting mPTP opening via recruitment of PKB/Akt and ERK 1/2.3)SpreC and SpostC were equally effective in protecting against MIRI, as manifested by functional recovery, infarct size and biomarkers reduction, kinase activation and mPTP inhibition. The combination of SpreC and SpostC offered additive protection in all these above aspects. However, microarray analysis provides evidence for distinctive cardioprotection phenotype in these three sevoflurane treatment strategies.4)Sevoflurane has better myocardial protection than propofol in coronary artery bypass grafting surgery.
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