Limitation Of Myocardial Infarct Size Research Articles

Adenosine 2 receptor regulates autophagy and apoptosis to alleviate ischemia reperfusion injury in type 2 diabetes via IRE-1 signaling

PurposeThis study aimed to determine the effect and mechanism of action of adenosine 2 receptor (A2R) activation on myocardial ischemia reperfusion injury (MIRI) under diabetic conditions.MethodsMIRI type 2 diabetic rats and H9C2 cardiomyocytes were treated with A2R agonist and then subjected to hypoxia for 6 h and reoxygenation for 18 h. Myocardial damage, and infarct size were determined by cardiac ultrasound. Indicators of cardiomyocyte injury, creatine kinase-MB and cardiac troponin I were detected by Enzyme Linked Immunosorbent Assay. Endoplasmic reticulum stress (ERS) was determined through measuring the expression levels of ERS related genes GRP78, p-IRE1/IRE1, and p-JNKJNK. The mechanism of A2R cardio protection in MIRI through regulating ERS induced autophagy was determined by investigating the ER resident protein IRE-1. The ER-stress inducer Tunicamycin, and the IRE-1 inhibitor STF in combination with the A2R agonist NECA were used, and the cellular responses were assessed through autophagy proteins expression Beclin-1, p62, LC3 and apoptosis.ResultsNECA improved left ventricular function post MIRI, limited myocardial infarct size, reduced myocardial damage, decreased cardiomyocytes apoptosis, and attenuated ERS induced autophagy through regulating the IRE-XBP1s-CHOP pathway. These actions resulted into overall protection of the myocardium against MIRI.ConclusionIn summary, A2R activation by NECA prior to ischemia attenuates apoptosis, reduces ERS induced autophagy and restores left ventricular function. This protective effect occurs through regulating the IRE1-XBPs-CHOP related mechanisms. NECA is thus a potential target for the treatment of MIRI in patient with type 2 diabetes.

Lycium barbarum polysaccharide antagonizes cardiomyocyte apoptosis by inhibiting the upregulation of GRK2 induced by I/R injury, and salvage mitochondrial fission/fusion imbalance and AKT/eNOS signaling

Ischemia–reperfusion (I/R) injury is the main reason why infarct size continues to progress during the process of restoring myocardial perfusion, and it significantly increases the risk of death. At present, the therapeutic effects of clinically used drugs are limited. Therefore, it is particularly necessary to explore myocardial-protective agents that effectively prevent I/R injury. Lycium barbarum polysaccharide (LBP) is a water-soluble polysaccharide extracted from wolfberry fruit. In this study, we found that LBP limited myocardial infarct size, improved adverse remodeling, and reduced cell death and oxidative stress. G protein-coupled receptor kinase-2 (GRK2) is a key molecule involved in myocardial I/R injury. In vivo and in vitro experiments showed that LBP inhibited the upregulation of GRK2 expression induced by I/R injury, which was related to the antiapoptotic effect of LBP. In addition, we found that LBP partially restored I/R-induced mitochondrial fission/fusion imbalance, as well as levels of phosphorylated protein kinase B (p-AKT) and phosphorylated endothelial cell nitric oxide synthase (p-eNOS), and this restorative effect could be attenuated by overexpression of GRK2. Overall, our findings suggest that LBP antagonizes cardiomyocyte apoptosis by inhibiting the upregulation of GRK2 induced by I/R injury and saves mitochondrial fission/fusion imbalance and AKT/eNOS signaling. This study may provide new ideas for the study of I/R injury and the rational application of the herbal medicine LBP.

Peoniflorin Preconditioning Protects Against Myocardial Ischemia/Reperfusion Injury Through Inhibiting Myocardial Apoptosis: RISK Pathway Involved.

Preconditioning with Peoniflorin, a component of traditional Chinese prescriptions, was proposed to be a potential strategy for cardioprotection against ischemia/reperfusion (I/R) injury. However, the cardioprotective effect of Peoniflorin preconditioning has not been thoroughly confirmed, and the underlying mechanism remains unclear. Here, we examined the cardioprotective effect and its mechanism of Peoniflorin preconditioning against myocardial I/R injury. Rats were subjected to 30min of transient ischemia followed by 2h of reperfusion with or without Peoniflorin (100mg/kg) prior to reperfusion. Peoniflorin preconditioning significantly limited myocardial infarct size and reperfusion arrhythmias, as well as obviously attenuated the histomorphological and micromorphological damages induced by I/R injury. The reduced myocardial injury was also associated with the anti-apoptotic effect of Peoniflorin, as evidence by decreased TUNEL-positive cells, upregulation of BCL-2 expression, and downregulation of Bax and caspase-3 expression. In an effort to evaluate the mechanism responsible for the observed cardioprotective and anti-apoptotic effect, Western blot of phosphorylated protein was performed after 20min of reperfusion. Results showed that Peoniflorin preconditioning activated both the Akt and ERK1/2 arm of the reperfusion injury salvage kinase (RISK) pathway. To further confirm this mechanism, the PI3K signaling inhibitor LY294002 and ERK1/2 signaling inhibitor PD98059 were administered in vivo. The cardioprotective and anti-apoptotic effects of Peoniflorin preconditioning were diminished but not abolished by pretreatment with LY294002 or PD98059. Taken together, these results indicate that Peoniflorin preconditioning protects the myocardial against I/R injury and inhibits myocardial apoptosis via the activation of the RISK pathway, highlighting the potential therapeutic effects of Peoniflorin on reducing myocardial I/R injury.

Chronic treatment with rofecoxib but not ischemic preconditioning of the myocardium ameliorates early intestinal damage following cardiac ischemia/reperfusion injury in rats

There is some recent evidence that cardiac ischemia/reperfusion (I/R) injury induces intestinal damage within days, which contributes to adverse cardiovascular outcomes after myocardial infarction. However, it is not clear whether remote gut injury has any detectable early signs, and whether different interventions aiming to reduce cardiac damage are also effective at protecting the intestine. Previously, we found that chronic treatment with rofecoxib, a selective inhibitor of cyclooxygenase-2 (COX-2), limited myocardial infarct size to a comparable extent as cardiac ischemic preconditioning (IPC) in rats subjected to 30-min coronary artery occlusion and 120-min reperfusion. In the present study, we aimed to analyse the early intestinal alterations caused by cardiac I/R injury, with or without the above-mentioned infart size-limiting interventions. We found that cardiac I/R injury induced histological changes in the small intestine within 2 h, which were accompanied by elevated tissue level of COX-2 and showed positive correlation with the activity of matrix metalloproteinase-2 (MMP-2), but not of MMP-9 in the plasma. All these changes were prevented by rofecoxib treatment. By contrast, cardiac IPC failed to reduce intestinal injury and plasma MMP-2 activity, although it prevented the transient reduction in jejunal blood flow in response to cardiac I/R. Our results demonstrate for the first time that rapid development of intestinal damage follows cardiac I/R, and that two similarly effective infarct size-limiting interventions, rofecoxib treatment and cardiac IPC, have different impacts on cardiac I/R-induced gut injury. Furthermore, intestinal damage correlates with plasma MMP-2 activity, which may be a biomarker for its early diagnosis.

Postconditioning with Calreticulin Attenuates Myocardial Ischemia/Reperfusion Injury and Improves Autophagic Flux.

Impaired autophagic flux contributes to cardiomyocyte death in ischemia/reperfusion (I/R) injury. Restoring the impaired autophagic flux by using agents may be a promising strategy that alleviates myocardial I/R injury. The present study aimed to evaluate the effect of exogenous calreticulin (CRT) postconditioning on impaired autophagic flux induced by hypoxia/reoxygenation (H/R) injury in H9c2 cells. Rat myocardial I/R injury model was prepared. CRT postconditionging was fulfilled by an intraperitoneal injection of CRT (0.5 mg/kg body weight) 5 min before reperfusion. Hemodynamics, serum lactate dehydrogenase (LDH) activity and Cardiac troponin T (TnT) content, and infarct size were measured. The H/R injury model of H9c2 cells was prepared. CRT postconditioning was performed by adding 25 pg/mL CRT to the medium at the onset of reoxygenation. Cell death rate, lactate dehydrogenase (LDH) leakage, intracellular reactive oxygen species (ROS), and malondialdehyde (MDA) were assessed. Autophagic flux was monitored by mRFP-GFP-LC3 adenovirus infection. The number of autophagosomes and autolysosomes in cells were determined by counting the fluorescence dots. Western blot assay was used to determine the expression of autophagy-related proteins. CRT postconditionging improved cardiac function, reduced serum LDH activity and TnT content, and limited myocardial infarct size after myocardial I/R injury in rat. H/R induced H9c2 cells injury and autophagosomes accumulation in cells. CRT postconditioning attenuated H/R-induced cell death, LDH leakage, and the increase of intracellular ROS and MDA. Meanwhile, CRT postconditioning suppressed H/R-induced excessive formation of autophagosomes, as shown by a decrease of autophagosomes and the ratio of LC3-II/LC3-I, LC3-II, and Beclin1. It also improved H/R-induced impaired autophagosomes clearance, as shown by an increase of autolysosomes and the level of LAMP-2, and a decrease of the level of p62. These findings suggested that CRT postconditioning reduced myocardial I/R injury. CRT postconditioning also inhibited the excessive formation of autophagosomes, promoted the clearance of autophagosomes, and resorted the autophagic flux, consequently reduced the H/R injury in H9c2 cells.

Down-regulation of GAS5 ameliorates myocardial ischaemia/reperfusion injury via the miR-335/ROCK1/AKT/GSK-3β axis.

Growth arrest‐specific transcript 5 (GAS5), along non‐coding RNA (LncRNA), is highly expressed in hypoxia/reoxygenation (H/R)‐cardiomyocytes and promotes H/R‐induced apoptosis. In this study, we determined whether down‐regulation of GAS5 ameliorates myocardial ischaemia/reperfusion (I/R) injury and further explored its mechanism. GAS5 expression in cardiomyocytes and rats was knockdown by transfected or injected with GAS5‐specific small interfering RNA or adeno‐associated virus delivering small hairpin RNAs, respectively. The effects of GAS5 knockdown on myocardial I/R injury were detected by CCK‐8, myocardial enzyme test, flow cytometry, TTC and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining. qRT‐PCR and luciferase reporter assay were carried out to analyse the relationship between GAS5 and miR‐335. The regulation of GAS5 on Rho‐associated protein kinase 1 (ROCK1) expression, the activation of PI3K/AKT/GSK‐3β pathway and mitochondrial permeability transition pore (mPTP) opening was further evaluated. The results indicated that GAS5 knockdown enhanced the viability, decreased apoptosis and reduced the levels of lactate dehydrogenase and creatine kinase‐MB in H/R‐treatment cardiomyocytes. Meanwhile, down‐regulation of GAS5 limited myocardial infarct size and reduced apoptosis in I/R‐heart. GAS5 was found to bind to miR‐335 and displayed a reciprocal inhibition between them. Furthermore, GAS5 knockdown repressed ROCK1 expression, activated PI3K/AKT, thereby leading to inhibition of GSK‐3β and mPTP opening. These suppressions were abrogated by miR‐335 inhibitor treatment. Taken together, our results demonstrated that down‐regulation of GAS5 ameliorates myocardial I/R injury via the miR‐335/ROCK1/AKT/GSK‐3β axis. Our findings suggested that GAS5 may be a new therapeutic target for the prevention of myocardial I/R injury.

Upregulation of vascular endothelial growth factor receptor-1 contributes to sevoflurane preconditioning-mediated cardioprotection.

PurposeSevoflurane preconditioning (SPC) can provide myocardial protective effects similar to ischemic preconditioning. However, the exact mechanism of SPC remains unclear. Previous studies indicate that vascular endothelial growth factor receptor 1 (VEGFR-1) is involved in ischemic preconditioning-mediated cardioprotection. This study was designed to determine the significance of VEGFR-1 signaling in SPC-mediated cardioprotection.Materials and methodsMyocardial ischemia–reperfusion (I/R) rat model was established using the Langendorff isolated heart perfusion apparatus. Additionally, after 15 min of baseline equilibration, the isolated hearts were pretreated with 2.5% sevoflurane, 2.5% sevoflurane+MF1 10 μmol/L, or 2.5% sevoflurane+placental growth factor 10 μmol/L, and then subjected to 30 min of global ischemia and 120 min of reperfusion. The changes in hemodynamic parameters, myocardial infarct size, and the levels of creatine kinase-MB, lactate dehydrogenase, cardiac troponin-I, tumor necrosis factor-α, and interleukin 6 in the myocardium were evaluated.ResultsCompared to the I/R group, pretreatment with 2.5% sevoflurane significantly improved the cardiac function, limited myocardial infarct size, reduced cardiac enzyme release, upregulated VEGFR-1 expression, and decreased inflammation. In addition, the selective VEGFR-1 agonist, placental growth factor, did not enhance the cardioprotection and anti-inflammation effects of sevoflurane, while the specific VEGFR-1 inhibitor, MF1, completely reversed these effects.ConclusionOur data have demonstrated that 2.5% sevoflurane preconditioning alleviates heart I/R injury, which is probably mediated by the anti-inflammatory property and upregulation of VEGFR-1.

Delivery of Hydrogen Sulfide by Ultrasound Targeted Microbubble Destruction Attenuates Myocardial Ischemia-reperfusion Injury.

Hydrogen sulfide (H2S) is an attractive agent for myocardial ischemia-reperfusion injury, however, systemic delivery of H2S may cause unwanted side effects. Ultrasound targeted microbubble destruction has become a promising tool for organ specific delivery of bioactive substance. We hypothesized that delivery of H2S by ultrasound targeted microbubble destruction attenuates myocardial ischemia-reperfusion injury and could avoid unwanted side effects. We prepared microbubbles carrying hydrogen sulfide (hs-MB) with different H2S/C3F8 ratios (4/0, 3/1, 2/2, 1/3, 0/4) and determined the optimal ratio. Release of H2S triggered by ultrasound was investigated. The cardioprotective effect of ultrasound targeted hs-MB destruction was investigated in a rodent model of myocardial ischemia-reperfusion injury. The H2S/C3F8 ratio of 2/2 was found to be an optimal ratio to prepare stable hs-MB with higher H2S loading capability. Ultrasound targeted hs-MB destruction triggered H2S release and increased the concentration of H2S in the myocardium and lung. Ultrasound targeted hs-MB destruction limited myocardial infarct size, preserved left ventricular function and had no influence on haemodynamics and respiratory. This cardioprotective effect was associated with alleviation of apoptosis and oxidative stress. Delivery of H2S to the myocardium by ultrasound targeted hs-MB destruction attenuates myocardial ischemia-reperfusion injury and may avoid unwanted side effects.

Effects of pretreatment with recombinant human B-type natriuretic peptide on infarct size in patients with acute ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention

To investigate whether the administration of recombinant human B-type natriuretic peptide (rhBNP) before primary percutaneous coronary intervention (PCI) could further limit the infract size, improve left ventricular function, and alleviate cardiac dilation in patients with acute ST-segment elevation myocardial infarction(STEMI). A total of 93 consecutive patients presenting chest pain within 12 hours from the onset, suspicious of first STEMI located at anterior wall undergoing primary PCI, were eligible for enrollment and randomly assigned to either rhBNP group (rhBNP administration starting at 5 min before PCI, 1.5 µg/kg bolus intravenous injection followed by 0.007 5-0.03 µg·kg(-1)·min(-1) for up to 120 hours, n=48) or nitroglycerin (NIT) group (NIT treatment starting at 5 min before PCI, 10-100 µg/min intravenous infusion for 120 hours, n=45). Primary PCI was performed in both groups using post-conditioning (PC) technique. TIMI flow grade, corrected TIMI frame count, and TIMI myocardial perfusion grade were compared between the two groups at the time of infarct related artery (IRA) re-patency. The levels of serum creatine kinase MB isoenzyme (CK-MB) and troponin I (TnI) were measured. Echocardiography was performed at baseline 7 days and 6 months later. Baseline characteristics were similar between the two groups. The percentage of TIMI grade 3 and TIMI myocardial perfusion grade 3 after PCI both tended to be higher in rhBNP group than those in NIT group (95.8%(46/48) vs. 86.7%(39/45), P=0.162) and (72.9%(35/48) vs. 62.2%(28/45), P=0.500). The corrected TIMI frame count was significantly decreased in rhBNP group (21.0±8.7 vs. 28.2±14.8, P=0.005). The myocardial infarct size expressed as the AUC of CK-MB ((3 249±1 101) U/L vs. (4 474±1 661)U/L, P=0.010) or AUC of TnI ((3 670±942) µg/L vs. (4 541±1 098) µg/L, P=0.021) was significantly decreased in rhBNP group compared with those in NIT group. At 7 days after primary PCI, the left ventricular ejection fraction (LVEF) tended to be higher (P>0.05), while the E/e' index and wall motion score index (WMSI) ((11.95±3.31 vs. 14.60±4.09, P=0.030) and (1.74±0.17 vs. 2.40±0.55, P<0.001)) were significantly improved in rhBNP group compared with those in NIT group. BNP level was also significantly lower in rhBNP group compared that in NIT group ((68.3±37.8) ng/L vs. (129.4±64.4) ng/L, P<0.001). During 6-month follow-up, LVEF and WMSI were significantly improved in rhBNP group compared those in NIT group(51.7%±12.7% vs. 46.9%±9.6%, P=0.024 and 1.69±0.35 vs. 1.92±0.47, P=0.020). Administration of rhBNP before PCI with post-conditioning procedure can further improve myocardial perfusion, limit myocardial infarct size, ameliorate cardiac dysfunction and postpone left ventricular early-stage and long-term remodeling in STEMI patients undergoing primary PCI.

Clinical benefit of adenosine as an adjunct to reperfusion in ST-elevation myocardial infarction patients: An updated meta-analysis of randomized controlled trials

BackgroundAdenosine administered as an adjunct to reperfusion can reduce coronary no-reflow and limit myocardial infarct (MI) size in ST-segment elevation myocardial infarction (STEMI) patients. Whether adjunctive adenosine therapy can improve clinical outcomes in reperfused STEMI patients is not clear and is investigated in this meta-analysis of 13 randomized controlled trials (RCTs). MethodsWe performed an up-to-date search for all RCTs investigating adenosine as an adjunct to reperfusion in STEMI patients. We calculated pooled relative risks using a fixed-effect meta-analysis assessing the impact of adjunctive adenosine therapy on major clinical endpoint including all-cause mortality, non-fatal myocardial infarction, and heart failure. Surrogate markers of reperfusion were also analyzed. Results13 RCTs (4273 STEMI patients) were identified and divided into 2 subgroups: intracoronary adenosine versus control (8 RCTs) and intravenous adenosine versus control (5 RCTs). In patients administered intracoronary adenosine, the incidence of heart failure was significantly lower (risk ratio [RR] 0.44 [95% CI 0.25–0.78], P=0.005) and the incidence of coronary no-reflow was reduced (RR for TIMI flow<3 postreperfusion 0.68 [95% CI 0.47–0.99], P=0.04). There was no difference in heart failure incidence in the intravenous adenosine group but most RCTs in this subgroup were from the thrombolysis era. There was no difference in non-fatal MI or all-cause mortality in both subgroups. ConclusionWe find evidence of improved clinical outcome in terms of less heart failure in STEMI patients administered intracoronary adenosine as an adjunct to reperfusion. This finding will need to be confirmed in a large adequately powered prospective RCT.

Ischemic Preconditioning Inhibits Mitochondrial Permeability Transition Pore Opening through the PTEN/PDE4 Signaling Pathway

Objectives: Ischemic preconditioning (IPC) induces cardioprotection against ischemia-reperfusion (IR) injury by inhibiting the mitochondrial permeability transition pore (mPTP). Here, we tested the hypothesis that IPC-induced cardioprotection is mediated by the phosphatase PTEN and PDE4 (phosphodiesterase 4). Methods: Isolated hearts from wild-type mice (WT, n = 110) and myocyte-specific PTEN-knockout mice (PKO, n = 94) were exposed to IPC or control conditions followed by IR. Subcellular fractionation was performed by sucrose gradient ultracentrifugation. Results: IPC limited myocardial infarct size (IS) in WT mice. The PDE4 inhibitor rolipram abolished the protective effect of IPC. However, small IS was found in PKO hearts after IR, and IPC did not decrease IS but enlarged it in PKO hearts. IPC promoted PDE4D localization to caveolin-3-enriched fractions in WT mice by increasing Akt levels at the caveolae. In PKO hearts, basal PDE4D levels were elevated at the caveolae, and IPC decreased PDE4D levels. Consistent with the subcellular PDE4D protein levels and its activity, elevation in intracellular Ca²⁺ levels in the ischemic heart and opening of mPTP after IR were inhibited by IPC in WT mice, but not by IPC in PKO mice. Conclusions: IPC inhibits mPTP opening by regulating the PTEN/PDE4 signaling pathway.

Paradigm shifts in cardioprotection research: the importance of the MPTP as a therapeutic target: AUTHORS' RETROSPECTIVE

This editorial refers to an article by D.J. Hausenloy et al . [12][1] published in Cardiovascular Research in 2002 (see [Box 1][2]). It is accompanied by an editorial by M. Ruiz-Meana, pp. 157–159, this issue, as part of this Spotlight on Landmark Papers in Cardiovascular Research . Our interest in the mitochondrial permeability transition pore (MPTP) as a target for cardioprotection was first aroused by a seminar given at University College London by John Lemasters and during one of our weekly journal clubs, back in early 2001. The research article which attracted our attention was by two pioneers in MPTP research, Fabio Di Lisa and Paulo Bernardi at the University of Padova.1 In their experimental study, they had demonstrated that pre-treating isolated perfused rat hearts with the immunosuppressant agent cyclosporin-A (CsA) could decrease myocardial injury (measured by lactate dehydrogenase release) following an episode of acute lethal ischaemia and reperfusion injury (IRI) and that the cardioprotective effect was associated with inhibition of MPTP opening at the time of myocardial reperfusion. At that time, our research group had been keen to discover novel therapeutic agents which were able to prevent lethal myocardial reperfusion injury and limit myocardial infarct (MI) size when administered at the onset of myocardial reperfusion. In addition, we were keen to unravel the mechanistic pathways underlying the phenomenon of ischaemic preconditioning (IPC),2 in which the heart could be rendered resistant to an episode of acute lethal ischaemia and reperfusion by preconditioning it with one or more brief cycles of non-lethal ischaemia and reperfusion. Therefore, the suggestion that the opening of the MPTP at the onset of reperfusion was a critical mediator of lethal myocardial reperfusion injury made it an obvious target for investigation. This was the first time our research group had come across the MPTP, and so we … [1]: #ref-12 [2]: #F1

Regulation of phosphatase and tensin homolog on chromosome 10 in response to hypoxia

Phosphatase and tensin homolog on chromosome 10 (PTEN) is downregulated during hypertrophic and cancerous cell growth, leading to activation of the prosurvival Akt pathway. However, PTEN regulation in cardiac myocytes upon exposure to hypoxia remains unclear. We explored the role of PTEN in response to hypoxia/ischemia in the myocardium. We validated that PTEN is a transcriptional target of activating transcription factor 2 (ATF-2) and is positively regulated via a p38/ATF-2 signaling pathway. Accordingly, hypoxia-induced upregulation of phosphorylation of ATF-2 and PTEN were reversed by a dominant negative mutant p38. Inhibition of PTEN in cardiomyocytes attenuated hypoxia-induced cell death and apoptosis. Cardiac-specific knockout of PTEN resulted in increased phosphorylation of Akt and forkhead box O 1 (forkhead transcription factors), limited infarct size in animals exposed to ischemia-reperfusion injury, and ameliorated deterioration of left ventricular function and remodeling following permanent coronary artery occlusion. In addition, the activation of Bim, FASL, and caspase was coupled with PTEN activation, all of which were attenuated by PTEN inhibition. In conclusion, cardiomyocyte-specific conditional PTEN deletion limited myocardial infarct size in an in vivo model of ischemia-reperfusion injury and attenuated adverse remodeling in a model of chronic permanent coronary artery ligation.

Aliskiren and Valsartan Reduce Myocardial AT1 Receptor Expression and Limit Myocardial Infarct Size in Diabetic Mice

We assessed the ability of Aliskiren (AL), a direct renin inhibitor, and Valsartan (VA), an angiotensin receptor blocker, to limit myocardial infarct size (IS) in mice with type-2 diabetes mellitus. Db/Db mice, fed Western Diet, received 15-day pretreatment with: 1) vehicle; 2) AL 25mg/kg/d; 3) AL 50mg/kg/d; 4) VA 8mg/kg/d; 5) VA 16mg/kg/d; 6) AL 25+VA 16mg/kg/d; or 7) AL 50+VA 16mg/kg/d. Mice underwent 30min coronary artery occlusion and 24h reperfusion. Area at risk (AR) was assessed by blue dye and IS by TTC staining. Protein expression was assessed by immunobloting. IS in the control group was 42.9 ± 2.1% of the AR. AL at 25 (21.9 ± 2.9%) and 50mg/kg/d (15.5 ± 1.3%) reduced IS. VA at 16mg/kg/d (18.8 ± 1.2%), but not at 8mg/kg/d (35.2 ± 4.0%), limited IS. IS was the smallest in the AL50+VA16 group (6.3 ± 0.9%). Both AL and VA reduced myocardial AT1R levels, without affecting AT2R levels, and increased the expression of Sirt1 and PGC-1α with increased phosphorylation of Akt and eNOS. AL, dose dependently limited myocardial IS in mice with type-2 diabetes mellitus. At doses shown to limit IS in non-diabetic animals, VA failed to reduce IS in Db/Db mice. However, at higher dose (16mg/kg/d), VA reduced IS. Both drugs reduced the expression of AT1R and increased myocardial levels of the longevity genes Sirt1 and PGC-1α along with increased Akt and eNOS phosphorylation.

The potential effects of anti-diabetic medications on myocardial ischemia–reperfusion injury

Heart disease and stroke account for 65% of the deaths in people with diabetes mellitus (DM). DM and hyperglycemia cause systemic inflammation, endothelial dysfunction, a hypercoagulable state with impaired fibrinolysis and increased platelet degranulation, and reduced coronary collateral blood flow. DM also interferes with myocardial protection afforded by preconditioning and postconditioning. Newer anti-diabetic agents should not only reduce serum glucose and HbA1c levels, but also improve cardiovascular outcomes. The older sulfonylurea agent, glyburide, abolishes the benefits of ischemic and pharmacologic preconditioning, but newer sulfonylurea agents, such as glimepiride, may not interfere with preconditioning. GLP-1 analogs and sitagliptin, an oral dipeptidyl peptidase IV inhibitor, limit myocardial infarct size in animal models by increasing intracellular cAMP levels and activating protein kinase A, whereas metformin protects the heart by activating AMP-activated protein kinase. Both thiazolidinediones (rosiglitazone and pioglitazone) limit infarct size in animal models. The protective effect of pioglitazone is dependent on downstream activation of cytosolic phospholipase A(2) and cyclooxygenase-2 with subsequent increased production of 15-epi-lipoxin A(4), prostacyclin and 15-d-PGJ(2). We conclude that agents used to treat DM have additional actions that have been shown to affect the ability of the heart to protect itself against ischemia-reperfusion injury in preclinical models. However, the effects of these agents in doses used in the clinical setting to minimize ischemia-reperfusion injury and to affect clinical outcomes in patients with DM have yet to be shown. The clinical implications as well as the mechanisms of protection should be further studied.

MicroRNA-24 Regulates Vascularity After Myocardial Infarction

Myocardial infarction leads to cardiac remodeling and development of heart failure. Insufficient myocardial capillary density after myocardial infarction has been identified as a critical event in this process, although the underlying mechanisms of cardiac angiogenesis are mechanistically not well understood. Here, we show that the small noncoding RNA microRNA-24 (miR-24) is enriched in cardiac endothelial cells and considerably upregulated after cardiac ischemia. MiR-24 induces endothelial cell apoptosis, abolishes endothelial capillary network formation on Matrigel, and inhibits cell sprouting from endothelial spheroids. These effects are mediated through targeting of the endothelium-enriched transcription factor GATA2 and the p21-activated kinase PAK4, which were identified by bioinformatic predictions and validated by luciferase gene reporter assays. Respective downstream signaling cascades involving phosphorylated BAD (Bcl-XL/Bcl-2-associated death promoter) and Sirtuin1 were identified by transcriptome, protein arrays, and chromatin immunoprecipitation analyses. Overexpression of miR-24 or silencing of its targets significantly impaired angiogenesis in zebrafish embryos. Blocking of endothelial miR-24 limited myocardial infarct size of mice via prevention of endothelial apoptosis and enhancement of vascularity, which led to preserved cardiac function and survival. Our findings indicate that miR-24 acts as a critical regulator of endothelial cell apoptosis and angiogenesis and is suitable for therapeutic intervention in the setting of ischemic heart disease.

Dipyridamole with Low-Dose Aspirin Augments the Infarct Size-Limiting Effects of Simvastatin

PurposeStatins protect against ischemia-reperfusion injury and limit myocardial infarct size (IS). This effect is dependent on increased generation of adenosine by ecto-5′ nucleotidase and downstream activation of cyclooxygenase-2 (COX2). Dipyridamole (DIP) augments the IS-limiting effects of statins by blocking the cellular reuptake of adenosine; whereas aspirin (ASA) attenuates the effect by inhibiting COX2. We studied the effect of acute administration of DIP, ASA and their combination on the IS-limiting effect of simvastatin (SIM).MethodsRats received oral SIM (10 mg/kg/d) or vehicle for 3 days. Rats underwent 30 min of coronary artery occlusion and 4 h reperfusion. After 5 min of ischemia rats received i.v. DIP (5 mg/kg), ASA (20 mg/kg or 2 mg/kg) or DIP+ASA (2 mg/kg) or vehicle alone. Ischemia area at risk (AR) was assessed by blue dye and IS by TTC. Myocardial samples were analyzed for the activation of Akt, ERK 1/2, endothelial nitric oxide synthase (eNOS), and cyclic-AMP-response-element-binding-protein (CREB).ResultsSIM limited IS. High- or low-dose ASA alone had no effect on IS. DIP alone or with low-dose ASA significantly reduced IS. Low-dose ASA did not attenuate the SIM effect, whereas high-dose ASA completely blocked the effect. The combination of DIP+low-dose ASA+SIM resulted in the smallest IS. Both SIM and DIP+low-dose ASA augmented Akt phosphorylation and their effect was additive. Both SIM and DIP+low-dose ASA augmented eNOS, ERK 1/2 and CREB phosphorylation.ConclusionsDuring acute myocardial ischemia, DIP alone or with low-dose ASA limits IS and does not attenuate the IS-limiting effect of SIM as high-dose ASA.

Additive Effect of TAK-491, a New Angiotensin Receptor Blocker, and Pioglitazone, in Reducing Myocardial Infarct Size

We assessed the effects of TAK-491 (a newly designed potent and selective ARB) alone and in combination with pioglitazone (PIO) on myocardial infarct size (IS). Rats received TAK-491 (0.3, 1, 3, or 10 mgkg(-1)d(-1)), PIO (1.0 or 2.5 mgkg(-1)d(-1)), or PIO 2.5 mgkg(-1)d(-1) with TAK-491 (1 or 3 mgkg(-1)d(-1)) for 4 days. On day 5 rats underwent 30-minute coronary artery occlusion and 4-hour reperfusion. Area at risk (AR) was assessed by blue dye and IS by TTC. Left ventricular (LV) dimensions and function was assessed by echocardiography 35 days after infarction. TAK (1.0-10 mgkg(-1)d(-1)), PIO (1.0 to 2.5 mgkg(-1)d(-1)), PIO2.5+TAK1.0, and PIO2.5+TAK3.0 significantly reduced IS. IS was the smallest in the TAK 10.0, followed by PIO+TAK 3.0. The protective effects of TAK and PIO were additive, as IS was smaller in the PIO2.5+TAK1.0 than in PIO 2.5 alone (p = 0.008) or TAK1.0 alone (p = 0.002); and in PIO2.5+TAK3.0 than in PIO alone (p < 0.001) or TAK3.0 alone (p < 0.001). TAK, PIO and their combination tended to attenuate LV remodeling and improved LV function 35 days after infarction; however, the differences among individual groups were not statistically significant. Both TAK-491 and PIO increased calcium-dependent nitric oxide synthase activity, whereas only PIO increased COX2 expression and activity. Both PIO and TAK-491 increased Akt, ERK 1/2 and eNOS phosphorylation and inhibited BAX activation. TAK-491 and PIO independently limited myocardial IS in a dose-dependent fashion; and the effects were additive. The mechanism of protection and the role of TAK-491 in this clinical setting should be further investigated.

Physiology and Pharmacology of Myocardial Preconditioning

Perioperative myocardial ischemia and infarction are not only major sources of morbidity and mortality in patients undergoing surgery but also important causes of prolonged hospital stay and resource utilization. Ischemic and pharmacological preconditioning and postconditioning have been known for more than two decades to provide protection against myocardial ischemia and reperfusion and limit myocardial infarct size in many experimental animal models, as well as in clinical studies (1-3). This paper will review the physiology and pharmacology of ischemic and drug-induced preconditioning and postconditioning of the myocardium with special emphasis on the mechanisms by which volatile anesthetics provide myocardial protection. Insights gained from animal and clinical studies will be presented and reviewed and recommendations for the use of perioperative anesthetics and medications will be given.

Dose-Dependent Effects of Intravenous Allogeneic Mesenchymal Stem Cells in the Infarcted Porcine Heart

Intravenous delivery of mesenchymal stem cells (MSCs) preserves myocardial function after infarction. This dose-escalating study was performed to examine pathologic remodeling and scar formation in a pig model of permanent coronary occlusion without restoration of reperfusion. MSCs labeled with fluorescent dye 48 h or saline (negative control, n = 8) were given intravenously 48 h post proximal left anterior descending artery occlusion. Animals received either autologous or allogeneic MSCs in doses from 1 x 10(3) up to 1 x 10(6) per kg bodyweight from an unrelated donor pig. Infarct size and myocardial function were assessed after 1 month. Morphologic analysis revealed that labeled autologous MSCs migrated in the peri-infarct region resulting in smaller infarct size (19 +/- 7% vs. 32 +/- 7%, p < 0.008) and higher fractional area shortening (33 +/- 7% vs. 21 +/- 3%, p < 0.001). Similarly, allogeneic MSCs had dose-dependent beneficial effects on cardiac function, statistically significant at 1 x 10(5) and 1 x 10(6) cells per kg bodyweight. Autologous as well as allogeneic MSCs specifically "home" to the heart after systemic delivery, leading to limited myocardial infarct size and improved functional outcome, even without coronary reperfusion. Therefore, intravenously administration of MSCs is an attractive minimal-invasive approach for cardiac tissue repair.