Postconditioning: A Form of “Modified Reperfusion” Protects the Myocardium by Activating the Phosphatidylinositol 3-Kinase-Akt Pathway

MicroRNA-145 repairs infarcted myocardium by accelerating cardiomyocyte autophagy

We investigated whether microRNA-145 (miR-145) has a cardioprotective effect in a rabbit model of myocardial infarction (MI) and in H9c2 rat cardiomyoblasts. Rabbits underwent 30 min of coronary occlusion, followed by 2 days or 2 wk of reperfusion. Control microRNA (control group; 2.5 nmol/kg, n = 10) or miR-145 (miR-145 group, 2.5 nmol/kg, n = 10) encapsulated in liposomes was intravenously administered immediately after the start of reperfusion. H9c2 rat cardiomyoblasts were transfected with miR-145. The MI size was significantly smaller in the miR-145 group than in the control group at 2 days and 2 wk post-MI. miR-145 had improved the cardiac function and remodeling at 2 wk post-MI. These effects were reversed by chloroquine. Western blot analysis showed that miR-145 accelerated the transition of LC3B I to II and downregulated p62/SQSTM1 at 2 days or 2 wk after MI, but not at 4 wk, and activated Akt in the ischemic area at 2 days after MI. miR-145 inhibited the growth of H9c2 cells, accelerated the transition of LC3B I to II, and increased phosphorylated Akt in the H9c2 cells at 2 days after miR-145 transfection. Antagomir-145 significantly abolished the morphological change, the transition of LC3B I to II, and the increased phosphorylated Akt induced by miR-145 in H9c2 cells. We determined fibroblast growth factor receptor substrate 2 mRNA to be a target of miR-145, both in an in vivo model and in H9c2 cells. In conclusion, post-MI treatment with miR-145 protected the heart through the induction of cardiomyocyte autophagy by targeting fibroblast growth factor receptor substrate 2.

Protective effects of ellagic acid and ozone on rat ovaries with an ischemia/reperfusion injury

AIM

This study investigated the effects of the antioxidant agents, ozone (O) and ellagic acid (EA), on ischemia/reperfusion (I/R) injuries developed from an ovarian torsion-detorsion model.

MATERIALS AND METHODS

Arteries in the left ovaries of rats were clamped for two hours to achieve torsion, and then the clamps were removed for a two-hour detorsion period. Thirty-five female Sprague-Dawley rats were randomly divided into five groups: control: administered only with anesthesia, rats were not subjected to torsion-detorsion; I/R: subjected to torsion and subsequent detorsion, without administering any treatment agent; and I/R + EA, I/R + O and I/R + O + EA: subjected to torsion and detorsion processes and administered with EA, O or EA + O at the 75th minute of torsion. The rats were then sacrificed under general anesthesia and the ovarian tissues were excised. The tissues were homogenized and levels of glutathione reductase, catalase, superoxide dismutase and malondialdehyde (MDA) were analyzed. Tissue damage was evaluated in terms of histopathological parameters, such as hemorrhage, congestion, edema and inflammation.

RESULTS

Antioxidant enzyme activity and MDA levels in the ovary tissue increased in the I/R group and decreased in the O, EA and O + EA groups (P < 0.05). Histopathological examination revealed that tissue damage in the O, EA and O + EA groups decreased in comparison with the I/R group (P < 0.05).

CONCLUSIONS

These biochemical and histopathological findings suggest that EA and O are effective against ovarian I/R injury.

Sevoflurane postconditioning improves long-term learning and memory of neonatal hypoxia-ischemia brain damage rats via the PI3K/Akt-mPTP pathway

BACKGROUND

Volatile anesthetic postconditioning has been documented to provide neuroprotection in adult animals. Our aim was to investigate whether sevoflurane postconditioning improves long-term learning and memory of neonatal hypoxia-ischemia brain damage (HIBD) rats, and whether the PI3K/Akt pathway and mitochondrial permeability transition pore (mPTP) opening participate in the effect.

METHODS

Seven-day-old Sprague-Dawley rats were subjected to brain HI and randomly allocated to 10 groups (n=24 each group) and treated as follows: (1) Sham, without hypoxia-ischemia; (2) HI/Control, received cerebral hypoxia-ischemia; (3) HI+Atractyloside (Atr), (4) HI+Cyclosporin A (CsA), (5) HI+sevoflurane (Sev), (6) HI+Sev+ LY294002 (LY), (7) HI+Sev+ L-NAME (L-N), (8) HI+Sev+ SB216763 (SB), (9) HI+Sev+Atr, and (10) HI+Sev+CsA. Twelve rats in each group underwent behavioral testing and their brains were harvested for hippocampus neuron count and morphology study. Brains of the other 12 animals were harvested 24h after intervention to examine the expression of Akt, p-Akt, eNOS, p-eNOS, GSK-3β, p-GSK-3β by Western bolting and mPTP opening.

RESULTS

Sevoflurane postconditioning significantly improved the long-term cognitive performance of the rats, increased the number of surviving neurons in CA1 and CA3 hippocampal regions, and protected the histomorphology of the left hippocampus. These effects were abolished by inhibitors of PI3K/eNOS/GSK-3β. Although blocking mPTP opening simulated sevoflurane postconditioning-induced neuroprotection, it failed to enhance it.

CONCLUSIONS

Sevoflurane postconditioning exerts a neuroprotective effect against HIBD in neonatal rats via PI3K/Akt/eNOS and PI3K/Akt/GSK-3β pathways, and blockage of mPTP opening may be involved in attenuation of histomorphological injury.

Endogenous angiotensin-(1-7)/Mas receptor/NO pathway mediates the cardioprotective effects of pacing postconditioning

The aim of the present study was to investigate the role of the ANG-(1-7) receptor (Mas) and nitric oxide (NO) in pacing postconditiong (PPC)-mediated cardioprotection against ischemia-reperfusion injury. Cardiac contractility and hemodynamics were assessed using a modified Langendorff system, cardiac damage was assessed by measuring infarct size and creatinine kinase levels, and levels of phosphorylated and total endothelial NO synthase (eNOS) were determined by Western blot analysis. Isolated hearts were subjected to 30 min of regional ischemia, produced by fixed position ligation of the left anterior descending coronary artery, followed by 30 min of reperfusion (n = 6). Hearts were also subjected to PPC (three cycles of 30 s of left ventricular pacing alternated with 30 s of right atrial pacing) and/or treated during reperfusion with ANG-(1-7), N(G)-nitro-l-arginine methyl ester, or the Mas antagonist (d-Ala7)-ANG I/II (1-7). The PPC-mediated improvement in cardiac contractility and hemodyanamics, cardiac damage, and eNOS phosphorylation were significantly attenuated upon treatment with (d-Ala7)-ANG I/II (1-7) or N(G)-nitro-l-arginine methyl ester. Treatment with ANG-(1-7) improved cardiac function and reduced infarct size and creatinine kinase levels; however, the effects of ANG-(1-7) were not additive with PPC. In conclusion, these data provide novel insights into the cardioprotective mechanisms of PPC in that they involve the Mas receptor and eNOS and further suggest a potential therapeutic role for ANG-(1-7) in cardiac ischemic injury.

Exogenous hydrogen sulfide restores cardioprotection of ischemic post-conditioning via inhibition of mPTP opening in the aging cardiomyocytes

The physiological and pathological roles of hydrogen sulfide (H₂S) in the regulation of cardiovascular functions have been recognized. H₂S protects against the hypoxia/reoxygenation (H/R)-induced injury and apoptosis of cardiomyocytes, and ischemic post-conditioning (PC) plays an important role in cardioprotection from H/R injury in neonatal cardiomyocytes but not in aging cardiomyocytes. Whether H₂S is involved in the recovery of PC-induced cardioprotection in aging cardiomyocytes is unclear. In the present study, we found that both H/R and PC decreased cystathionine-γ-lyase (CSE) expression and the production rate of H₂S. Supplementation of NaHS protected against H/R-induced apoptosis, the expression of cleaved caspase-3 and cleaved caspase-9, the release of cytochrome c (Cyt c), and mPTP opening. The addition of NaHS also counteracted the reduction of cell viability caused by H/R and increased the phosphorylation of ERK1/2, PI3K, Akt, GSK-3β and mitochondrial membrane potential. Additionally, NaHS increased Bcl-2 expression, promoted PKC-ε translocation to the cell membrane, and activated mitochondrial ATP-sensitive K channels (mitoK_ATP). PC alone did not provide cardioprotection in H/R-treated aging cardiomyocytes, which was significantly restored by the supplementation of NaHS. In conclusion, our results suggest that exogenous H₂S restores PC-induced cardioprotection via the inhibition of mPTP opening by the activation of the ERK1/2-GSK-3β, PI3K-Akt-GSK-3β and PKC-ε-mitoK_ATP pathways in aging cardiomyocytes. These findings provide a novel target for the treatment of aging ischemic cardiomyopathy.

E2F1-dependent miR-421 regulates mitochondrial fragmentation and myocardial infarction by targeting Pink1

Mitochondrial fragmentation plays an important role in the progression of cardiac diseases, such as myocardial infarction and heart failure. Mitochondrial network is controlled by many factors in different cell types. Here we show that the interplay between E2F1, miR-421 and Pink1 regulates mitochondrial morphology and cardiomyocyte cell death. Pink1 reduces mitochondrial fragmentation and protects cardiomyocyte from apoptosis. On the other hand, miR-421 promotes cardiomyocyte mitochondrial fragmentation, apoptosis and myocardial infarction by suppressing Pink1 translation. Finally, we show that transcription factor E2F1 activates miR-421 expression. Knocking down E2F1 suppresses mitochondrial fragmentation, apoptosis and myocardial infarction by affecting miR-421 levels. Collectively, these data identify the E2F1/miR-421/Pink axis as a regulator of mitochondrial fragmentation and cardiomyocyte apoptosis, and suggest potential therapeutic targets in treatment of cardiac diseases.

Ischemic postconditioning altered microRNAs in human valve replacement

BACKGROUND

Although the involvement of microRNAs (miRNAs) has been intensively studied in myocardial infarction, there is no report on the regulation of miRNAs by ischemic postconditioning in patients undergoing cardiac surgery. We aim to explore the regulation of miRNAs by ischemic postconditioning in double valve replacement.

MATERIALS AND METHODS

In this prospective, controlled clinical study, consecutive 30 patients undergoing double valve replacement were enrolled. The patients were randomized into two groups, namely an ischemic postconditioning (IPO) group (n = 15) and a control (CON) group (n = 15). For ethical considerations, samples of right atrial muscle were harvested, respectively, 10 min before cardiopulmonary bypass (pre-CPB) and 5 min after aortic declamping (post-CPB) for analysis of miRNAs, genes and apoptosis.

RESULTS

Compared with the CON group, miR-1 was downregulated, whereas miR-21 was upregulated, and BCL2 messenger RNA (mRNA) was upregulated, whereas BAX mRNA and programmed cell death 4 mRNA remained unchanged in the IPO group. Likewise, a significant increase in BCL2 protein and a striking decrease in BAX protein were observed in the IPO group when compared with those in the CON group. The IPO group showed a significantly smaller increase of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive myocytes after CPB than CON group.

CONCLUSIONS

Ischemic postconditioning could regulate miR-1, miR-21, and downstream effectors and resulted in actual attenuation of apoptosis in patients undergoing valvular heart surgery.

Histone Deacetylases Exert Class-Specific Roles in Conditioning the Brain and Heart Against Acute Ischemic Injury

Ischemia-reperfusion (IR) injury comprises a significant portion of morbidity and mortality from heart and brain diseases worldwide. This enduring clinical problem has inspired myriad reports in the scientific literature of experimental interventions seeking to elucidate the pathology of IR injury. Elective cardiac surgery presents perhaps the most viable scenario for protecting the heart and brain from IR injury due to the opportunity to condition the organs prior to insult. The physiological parameters for the preconditioning of vital organs prior to insult through mechanical and pharmacological maneuvers have been heavily examined. These investigations have revealed new insights into how preconditioning alters cellular responses to IR injury. However, the promise of preconditioning remains unfulfilled at the clinical level, and research seeking to implicate cell signals essential to this protection continues. Recent discoveries in molecular biology have revealed that gene expression can be controlled through posttranslational modifications, without altering the chemical structure of the genetic code. In this scenario, gene expression is repressed by enzymes that cause chromatin compaction through catalytic removal of acetyl moieties from lysine residues on histones. These enzymes, called histone deacetylases (HDACs), can be inhibited pharmacologically, leading to the de-repression of protective genes. The discovery that HDACs can also alter the function of non-histone proteins through posttranslational deacetylation has expanded the potential impact of HDAC inhibitors for the treatment of human disease. HDAC inhibitors have been applied in a very small number of experimental models of IR. However, the scientific literature contains an increasing number of reports demonstrating that HDACs converge on preconditioning signals in the cell. This review will describe the influence of HDACs on major preconditioning signaling pathways in the heart and brain.

Neonatal rat hearts cannot be protected by ischemic postconditioning

Although there are abundant data on ischemic postconditioning (IPoC) in the adult myocardium, this phenomenon has not yet been investigated in neonatal hearts. To examine possible protective effects of IPoC, rat hearts isolated on days 1, 4, 7 and 10 of postnatal life were perfused according to Langendorff. Developed force (DF) of contraction was measured by an isometric force transducer. Hearts were exposed to 40 or 60 min of global ischemia followed by reperfusion up to the maximum recovery of DF. IPoC was induced by three cycles of 10, 30 or 60 s periods of global ischemia/reperfusion. To further determine the extent of ischemic injury, lactate dehydrogenase (LDH) release was measured in the coronary effluent. Tolerance to ischemia did not change from day 1 to day 4 but decreased to days 7 and 10. None of the postconditioning protocols tested led to significant protection on the day 10. Prolonging the period of sustained ischemia to 60 min on day 10 did not lead to better protection. The 3x30 s protocol was then evaluated on days 1, 4 and 7 without any significant effects. There were no significant differences in LDH release between postconditioned and control groups. It can be concluded that neonatal hearts cannot be protected by ischemic postconditioning during first 10 days of postnatal life.

Ischemic postconditioning of the isolated human myocardium: Role of the applied protocol

Background

Ischemic postconditioning (IPostC), has been proposed as a useful approach to reduce infarct size in all species, but its clinical utility remains unclear.

Objective

To investigate the role played by the protocol used on the efficacy of IPostC in protecting the diseased human myocardium.

Methods

Myocardial atrial samples from patients were subjected to a 90 min ischemia/120 min reoxygenation followed by different IPostC protocols to investigate the role of the time of ischemia (30, 60, 90 and 120 s) and the number of cycles (1, 2, 3 and 4) with 60 and 120 s of total ischemic time. Muscles were also subjected to ischemic preconditioning (IPreC). The release of lactate dehydrogenase (LDH) and the measurement of tetrazolium bromide (MTT) were determined.

Results

IPostC increased the LDH and decreased the MTT values from those of control, independently of the duration of the conditioning ischemia. LDH and MTT values also worsened by augmenting the number of IPostC cycles whereas they were significantly improved by IPreC. However, analysis of individual results indicated that in approximately 1/3 of the cases IPostC exhibited some degree of protection especially in the presence of increased ischemic injury.

Conclusions

The present findings show that IPostC of the human myocardium may be influenced by the protocol used and also by the degree of the preceding ischemic injury. IPostC was beneficial in approximately 1/3 of the cases; however in the remaining cases it increased ischemic damage and, therefore, these results raise a word of caution on its broad clinical use.

Novel perspectives on the PHD-HIF oxygen sensing pathway in cardioprotection mediated by IPC and RIPC

Reperfusion of ischemic cardiac tissue is the standard treatment for improving clinical outcome following myocardial infarction but is inevitably associated with ischemia-reperfusion injury (IRI). Ischemic myocardial injury can be alleviated by exposing the heart to brief episodes of sublethal ischemia-reperfusion prior to the ischemic insult, a phenomenon that has been termed ischemic preconditioning (IPC). Similarly, remote IPC (RIPC) is defined as transient episodes of ischemia at a distant site before a subsequent prolonged injury of the target organ. In this setting, adaptive responses to hypoxia/ischemia in peripheral tissues include the release of soluble factors that have the potential to protect cardiomyocytes remotely. Oxygen fluctuations is a hallmark of insufficient tissue perfusion and ischemic episodes. Emerging evidence indicates that prolyl hydroxylase oxygen sensors (PHDs) and hypoxia-inducible transcription factors (HIFs) are critical regulators of IPC and RIPC. In this review, we discuss recent findings concerning the role of the PHD-HIF axis in IPC and RIPC-mediated cardioprotection and examine molecular pathways and cell types that might be involved. We also appraise the therapeutic value of targeting the PHD-HIF axis to enhance cardiac tolerance against IRI.

Rapid ventricular pacing-induced postconditioning attenuates reperfusion injury: effects on peroxynitrite, RISK and SAFE pathways

BACKGROUND AND PURPOSE

Rapid ventricular pacing (RVP) applied before an index ischaemia has anti-ischaemic effects. Here, we investigated whether RVP applied after index ischaemia attenuates reperfusion injury and whether peroxynitrite, reperfusion injury salvage kinase (RISK) and survival activating factor enhancement (SAFE) pathways as well as haem oxygenase 1 (HO1) are involved in the mechanism of RVP-induced postconditioning.

EXPERIMENTAL APPROACH

Langendorff perfused rat hearts were subjected to 30 min regional ischaemia and 120 min reperfusion with or without ischaemic postconditioning (6 × 10/10 s reperfusion/ischaemia; IPost) or RVP (6 × 10/10 s non-pacing/rapid pacing at 600 bpm) applied at the onset of reperfusion.

KEY RESULTS

Meta-analysis of our previous studies revealed an association between longer reperfusion-induced ventricular tachycardia/fibrillation with decreased infarct size. In the present experiments, we tested whether RVP is cardioprotective and found that both IPost and RVP significantly decreased infarct size; however, only RVP attenuated the incidence of reperfusion-induced ventricular tachycardia. Both postconditioning methods increased the formation of cardiac 3-nitrotyrosine and superoxide, and non-significantly enhanced Akt phosphorylation at the beginning of reperfusion without affecting ERK1/2 and STAT3, while IPost alone induced HO1. Application of brief ischaemia/reperfusion cycles or RVP without preceding index ischaemia also facilitated peroxynitrite formation; nevertheless, only brief RVP increased STAT3 phosphorylation.

CONCLUSIONS AND IMPLICATIONS

Short periods of RVP at the onset of reperfusion are cardioprotective and increase peroxynitrite formation similarly to IPost and thus may serve as an alternative postconditioning method. However, downstream mechanisms of the protection elicited by IPost and RVP seem to be partially different.

LINKED ARTICLES

This article is part of a themed section on Conditioning the Heart - Pathways to Translation. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-8.

Contribution of apoptosis in myocardial reperfusion injury and loss of cardioprotection in diabetes mellitus

Ischemic heart disease is one of the major causes of death worldwide. Ischemia is a condition in which blood flow of the myocardium declines, leading to cardiomyocyte death. However, reperfusion of ischemic regions decreases the rate of mortality, but it can also cause later complications. In a clinical setting, ischemic heart disease is always coincident with other co-morbidities such as diabetes. The risk of heart disease increases 2-3 times in diabetic patients. Apoptosis is considered to be one of the main pathophysiological mechanisms of myocardial ischemia-reperfusion injury. Diabetes can disrupt the anti-apoptotic intracellular signaling cascades involved in myocardial protection. Therefore, targeting these changes may be an effective cardioprotective approach in the diabetic myocardium against ischemia-reperfusion injury. In this article, we review the interaction of diabetes with the pathophysiology of myocardial ischemia-reperfusion injury, focusing on the contribution of apoptosis in this context, and then discuss the alterations of pro-apoptotic or anti-apoptotic pathways probably responsible for the loss of cardioprotection in diabetes.

Role of MEK, PI3, p38, Tyrosine, and mTOR Kinases in Regulation of Heart Resistance to the Arrhythmogenic Action of Short-Term Ischemia and Reperfusion

MEK, PI3, p38, tyrosine, and mTOR kinases are not involved in the regulation of heart resistance to the arrhythmogenic action of short-term ischemia/reperfusion in non-adapted rats.

The role of post-translational modifications in acute and chronic cardiovascular disease

Cardiovascular disease (CVD) in one of the leading causes of mortality and morbidity worldwide, accounting for both primary diseases of the heart and vasculature and arising as a co-morbidity with numerous pathologies, including type 2 diabetes mellitus (T2DM). There has been significant emphasis on the role of the genome in CVD, aiding in the definition of 'at-risk' patients. The extent of disease penetrance however, can be influenced by environmental factors that are not detectable by investigating the genome alone. By targeting the transcriptome in response to CVD, the interplay between genome and environment is more apparent, however this implies the level of protein expression without reference to proteolytic turnover, or potentially more importantly, without defining the role of PTMs in the development of disease. Here, we discuss the role of both brief and irreversible PTMs in the setting of myocardial ischemia/reperfusion injury. Key proteins involved in calcium regulation have been observed as differentially modified by phosphorylation/O-GlcNAcylation or phosphorylation/redox modifications, with the level of interplay dependent on the physiological or pathophysiological state. The ability to modify crucial sites to produce the desired functional output is modulated by the presence of other PTMs as exemplified in the T2DM heart, where hyperglycemia results in aberrant O-GlcNAcylation and advanced glycation end products. By using the signalling events predicted to be critical to post-conditioning, an intervention with great promise for the cardioprotection of the ischemia/reperfusion injured heart, as an example, we discuss the level of PTMs and their interplay. The inability of post-conditioning to protect the diabetic heart may be regulated by aberrant PTMs influencing those sites necessary for protection.

Molecular basis of cardioprotection: signal transduction in ischemic pre-, post-, and remote conditioning

Reperfusion is mandatory to salvage ischemic myocardium from infarction, but reperfusion per se contributes to injury and ultimate infarct size. Therefore, cardioprotection beyond that by timely reperfusion is needed to reduce infarct size and improve the prognosis of patients with acute myocardial infarction. The conditioning phenomena provide such cardioprotection, insofar as brief episodes of coronary occlusion/reperfusion preceding (ischemic preconditioning) or following (ischemic postconditioning) sustained myocardial ischemia with reperfusion reduce infarct size. Even ischemia/reperfusion in organs remote from the heart provides cardioprotection (remote ischemic conditioning). The present review characterizes the signal transduction underlying the conditioning phenomena, including their physical and chemical triggers, intracellular signal transduction, and effector mechanisms, notably in the mitochondria. Cardioprotective signal transduction appears as a highly concerted spatiotemporal program. Although the translation of ischemic postconditioning and remote ischemic conditioning protocols to patients with acute myocardial infarction has been fairly successful, the pharmacological recruitment of cardioprotective signaling has been largely disappointing to date.

Rapamycin protects cardiomyocytes against anoxia/reoxygenation injury by inducing autophagy through the PI3k/Akt pathway

The purpose of this study was to investigate the potential cardioprotection roles of Rapamycin in anoxia/reoxygenation (A/R) injury of cardiomyocytes through inducing autophagy, and the involvement of PI3k/Akt pathway. We employed simulated A/R of neonatal rat ventricular myocytes (NRVM) as an in vitro model of ischemial/reperfusion (I/R) injury to the heart. NRVM were pretreated with four different concentrations of Rapamycin (20, 50, 100, 150 μmol/L), and pretreated with 10 mmol/L 3-methyladenine (3MA) for inhibiting autophagy during A/R. Then, Western blot analysis was used to examine variation in the expression of LC3-II, LC3-I, Bim, caspase-3, p-PI3KI, PI3KI, p-Akt and Akt. In our model, Rapamycin had a preferential action on autophagy, increasing the expression of LC3-II/LC3-I, whereas decreasing the expression of Bim and caspase-3. Moreover, our results also demonstrated that Rapamycin inhibited the activation of p-PI3KI and enhanced the activation of p-Akt. It is concluded that Rapamycin has a cardioprotection effect by inducing autophagy in a concentration-dependent manner against apopotosis through PI3K/Akt signaling pathway during A/R in NRVM.

Transient carotid ischemia as a remote conditioning stimulus for myocardial protection in anesthetized rabbits: Insights into intracellular signaling

BACKGROUND

We investigated the effectiveness of perconditioning (Perc) applied at different time points along with the role of RISK, SAFE, STAT5 and eNOS pathways.

METHODS AND RESULTS

Anesthetized rabbits were subjected to 30-min ischemia/3-hour reperfusion. Perc, consisted of 4 cycles of 1-min ischemia/reperfusion, was applied in the carotid artery at different time points. Perc was started and ended during ischemia, started during ischemia and ended at the beginning of reperfusion, started at the end of ischemia and ended at reperfusion and started and ended during reperfusion. The PI3K inhibitor wortmannin, or the JAK-2 inhibitor AG490, was also applied and the infarct size was assessed. In another series assigned to the previous groups, the phosphorylation of Akt, PI3K, ERKs1/2, GSK3β, STAT3, and STAT5 was evaluated. All Perc groups had smaller infarction compared to those without Perc, independently of PI3K or JAK-2 inhibition. STAT5 was the only molecule that was phosphorylated in parallel with cardioprotection. Since Src and angiotensin II mediate the STAT5 pathway, we administered the Scr inhibitor PP1 and the angiotensin II receptor antagonist valsartan. PP1 and valsartan prevented STAT5 phosphorylation, but did not abrogate the effect of Perc. Furthermore, the NOS inhibitor L-NAME was administered and abrogated the infarct size limiting effect of Perc. In parallel, the expression of cleaved caspase-3 was elevated only in the control and Perc-A-L-NAME groups.

CONCLUSION

Perc reduces infarction independently of RISK, SAFE and STAT5 pathways. Src kinase and angiotensin II play a predominant role in STAT5 activation. eNOS may protect the myocardium through inhibition of apoptosis.

Ischemic postconditioning enhances glycogen synthase kinase-3β expression and alleviates cerebral ischemia/reperfusion injury

The present study established global brain ischemia using the four-vessel occlusion method. Following three rounds of reperfusion for 30 seconds, and occlusion for 10 seconds, followed by reperfusion for 48 hours, infarct area, the number of TUNEL-positive cells and Bcl-2 expression were significantly reduced. However, glycogen synthase kinase-3β activity, cortical Bax and caspase-3 expression significantly increased, similar to results following ischemic postconditioning. Our results indicated that ischemic postconditioning may enhance glycogen synthase kinase-3β activity, a downstream molecule of the phosphatase and tensin homolog deleted on chromosome 10/phosphatidylinositol 3-kinase/protein kinase B signaling pathway, which reduces caspase-3 expression to protect the brain against ischemic injury.

Two-dimensional longitudinal strains and torsion analysis to assess the protective effects of ischemic postconditioning on myocardial function: a speckle tracking echocardiography study in rabbits

The reperfusion injury that occurs in the early reperfusion often results in myocardial dysfunction. This study evaluated global and regional left ventricular (LV) function using speckle tracking echocardiography (STE) in a rabbit ischemia-reperfusion (I/R) model with and without ischemic postconditioning (I-PostC). The aim is to investigate the potential benefit of I-PostC for myocardial function and validate whether regional longitudinal strain is an appropriate index to indicate myocardial dysfunction. Forty rabbits were divided into an ischemia-reperfusion group (group I) and an I-PostC group (group II). After the coronary arteries were ligated, LV systolic strain and twist parameters decreased, and absolute value of strain rate of isovolumetric relaxation period (SRivr) and post-systolic strain index (PSI) increased significantly in both groups (all p<0.05). After reperfusion, regional longitudinal systolic strain rate (SRsys), systolic strain (Ssys), LV twist and untwisting rate increased, and SRivr and PSI decreased in group II. These changes were not seen in group I. All STE parameters were correlated with area of necrosis (AN)/area at risk (AR) (all p<0.05). The correlations were morerelevant between SRsys and AN/AR (r=-0.673) and between Ssys and AN/AR (r=-0.777) (both p<0.001). The intra- and inter-observer repeatability of STE parameters were good with correlation coefficients (CCs) >0.8 or 0.6. The sensitivities of GSRsys, GSsys, SRsys, Ssys, and LV twist to detect the myocardial infarction were 81.3%, 62.5%, 87.5%, 93.8% and 81.3%, respectively. And the specificities of those parameters were 75.0%, 81.2%, 75.0%, 87.5% and 68.7%. These results indicate that STE is useful for quantitative detection on myocardial function improvement induced by I-PostC in a rabbit I/R model. The regional index-Ssys is an appropriate parameter to indicate myocardial dysfunction because of its sensitivity, specificity, and repeatability.

Mechanisms of myocardial ischemia–reperfusion injury and the cytoprotective role of minocycline: scope and limitations

ABSTRACT 

Deep insight into the complex mechanisms of myocardial ischemia–reperfusion injury has been attained in the past years. Minocycline is a second-generation tetracycline with US FDA approval for clinical use in various infections. Lately, several noninfectious cytoprotective activities of minocycline have been discovered as well. There now exists encouraging evidence of its protective role in cardiovascular pathology and its activity against myocardial ischemia–reperfusion injury. In this article, an overview of the major mechanisms involved in myocardial ischemia–reperfusion injury is presented. This is followed by an analysis of the mechanisms by which minocycline exerts its cytoprotective role and of studies that have been conducted in order to analyze minocycline, along with a review of the scope and limitations of its role as a cytoprotective agent.

Postconditioning signalling in the heart: mechanisms and translatability

The protective effect of ischaemic postconditioning (short cycles of reperfusion and reocclusion of a previously occluded vessel) was identified over a decade ago commanding intense interest as an approach for modifying reperfusion injury which contributes to infarct size in acute myocardial infarction. Elucidation of the major mechanisms of postconditioning has identified potential pharmacological targets for limitation of reperfusion injury. These include ligands for membrane-associated receptors, activators of phosphokinase survival signalling pathways and inhibitors of the mitochondrial permeability transition pore. In experimental models, numerous agents that target these mechanisms have shown promise as postconditioning mimetics. Nevertheless, clinical studies of ischaemic postconditioning and pharmacological postconditioning mimetics are equivocal. The majority of experimental research is conducted in animal models which do not fully portray the complexity of risk factors and comorbidities with which patients present and which we now know modify the signalling pathways recruited in postconditioning. Cohort size and power, patient selection, and deficiencies in clinical infarct size estimation may all represent major obstacles to assessing the therapeutic efficacy of postconditioning. Furthermore, chronic treatment of these patients with drugs like ACE inhibitors, statins and nitrates may modify signalling, inhibiting the protective effect of postconditioning mimetics, or conversely induce a maximally protected state wherein no further benefit can be demonstrated. Arguably, successful translation of postconditioning cannot occur until all of these issues are addressed, that is, experimental investigation requires more complex models that better reflect the clinical setting, while clinical investigation requires bigger trials with appropriate patient selection and standardization of clinical infarct size measurements.

Hydrogen sulfide augments survival signals in warm ischemia and reperfusion of the mouse liver

BACKGROUND AND PURPOSE

Hydrogen sulfide (H2S) ameliorates hepatic ischemia and reperfusion injury (IRI), but the precise mechanism remains elusive. We investigated whether sodium hydrogen sulfide (NaHS), a soluble derivative of H2S, would ameliorate hepatic IRI, and if so, via what mechanism.

METHODS

Mice were subjected to partial warm ischemia for 75 min followed by reperfusion. Either NaHS or saline was administered intravenously 10 min before reperfusion. The liver and serum were collected 3, 6, and 24 h after reperfusion.

RESULTS

In the NaHS(-) group, severe IRI was apparent by the ALT leakage, tissue injury score, apoptosis, lipid peroxidation, and inflammation (higher plasma TNF-α, IL-6, IL-1β, IFN-γ, IL-23, IL-17, and CD40L), whereas IRI was significantly ameliorated in the NaHS(+) group. These effects could be explained by the augmented nuclear translocation of Nrf2, and the resulting up-regulation of HO-1 and thioredoxin-1. Phosphorylation of the PDK-1/Akt/mTOR/p70S6k axis, which is known to mediate pro-survival and anti-apoptotic signals, was significantly augmented in the NaHS(+) group, with a higher rate of PCNA-positive cells thereafter.

CONCLUSION

NaHS ameliorated hepatic IRI by direct and indirect anti-oxidant activities by augmenting pro-survival, anti-apoptotic, and anti-inflammatory signals via mechanisms involving Nrf-2, and by accelerating hepatic regeneration via mechanisms involving Akt-p70S6k.

Cordycepin, 3'-deoxyadenosine, prevents rat hearts from ischemia/reperfusion injury via activation of Akt/GSK-3β/p70S6K signaling pathway and HO-1 expression

Cordycepin (3'-deoxyadenosine) isolated from Cordyceps militaris, a species of the fungal genus Cordyceps, has been shown to exhibit many pharmacological functions, such as anticancer, anti-inflammatory, and antioxidant activities. In this study, we investigated the preventive role of cordycepin in ischemic/reperfusion (I/R) injury of isolated rat hearts and anesthetized rats. After Sprague-Dawley rats received cordycepin (3, 10, and 30 mg/kg) or control (0.5 % carboxyl methylcellulose) orally once a day for a week, hearts were isolated and mounted on Langendorff heart perfusion system. Isolated hearts were perfused with Krebs-Henseleit buffer for 15-min pre-ischemic stabilization period and subjected to 30-min global ischemia and 30-min reperfusion. Cordycepin administration (10 mg/kg, p.o.) significantly increased left ventricular developed pressure during the reperfusion period compared to that in the control group, but without any effect on coronary flow. Cordycepin (10 mg/kg, p.o.) significantly increased the phosphorylation of Akt/GSK-3β/p70S6K pathways, which are known to modulate multiple survival pathways. In addition, cordycepin decreased Bax and cleaved caspase-3 expression while increasing Bcl-2 expression, Bcl-2/Bax ratio, and heme oxygenase (HO-1) expression in isolated rat hearts. In anesthetized rats subjected to 30 min occlusion of left anterior descending coronary artery/2.5-h reperfusion, cordycepin (1, 3, and 10 mg/kg, i.v.) administered 15 min before the onset of ischemia dose-dependently decreased the infarct size in left ventricle. In conclusion, cordycepin could be an attractive therapeutic candidate with oral activity against I/R-associated heart diseases such as myocardial infarction.

Akt protects the heart against ischaemia-reperfusion injury by modulating mitochondrial morphology

The mechanism through which the protein kinase Akt (also called PKB), protects the heart against acute ischaemia-reperfusion injury (IRI) is not clear. Here, we investigate whether Akt mediates its cardioprotective effect by modulating mitochondrial morphology. Transfection of HL-1 cardiac cells with constitutively active Akt (caAkt) changed mitochondrial morphology as evidenced by an increase in the proportion of cells displaying predominantly elongated mitochondria (73 ± 5.0 % caAkt vs 49 ± 5.8 % control: N=80 cells/group; p< 0.05). This effect was associated with delayed time taken to induce mitochondrial permeability transition pore (MPTP) opening (by 2.4 ± 0.5 fold; N=80 cells/group: p< 0.05); and reduced cell death following simulated IRI (32.8 ± 1.2 % caAkt vs 63.8 ± 5.6 % control: N=320 cells/group: p< 0.05). Similar effects on mitochondrial morphology, MPTP opening, and cell survival post-IRI, were demonstrated with pharmacological activation of Akt using the known cardioprotective cytokine, erythropoietin (EPO). The effect of Akt on inducing mitochondrial elongation was found to be dependent on the mitochondrial fusion protein, Mitofusin-1 (Mfn1), as ablation of Mfn1 in mouse embryonic fibroblasts (MEFs) abrogated Akt-mediated mitochondrial elongation. Finally, in vivo pre-treatment with EPO reduced myocardial infarct size (as a % of the area at risk) in adult mice subjected to IRI (26.2 ± 2.6 % with EPO vs 46.1 ± 6.5 % in control; N=7/group: p< 0.05), and reduced the proportion of cells displaying myofibrillar disarray and mitochondrial fragmentation observed by electron microscopy in adult murine hearts subjected to ischaemia from 5.8 ± 1.0 % to 2.2 ± 1.0 % (N=5 hearts/group; p< 0.05). In conclusion, we found that either genetic or pharmacological activation of Akt protected the heart against acute ischaemia-reperfusion injury by modulating mitochondrial morphology.

Classical and remote post-conditioning effects on ischemia/reperfusion-induced acute oxidant kidney injury

The present study aimed to analyze and compare the effects of classical and remote ischemic postconditioning (POC) on rat renal ischemia/reperfusion (IR)-induced acute kidney injury. After right nephrectomy, male rats were randomly assigned into four groups (n = 8). In the IR group, 45 min of left renal artery occlusion was induced followed by 24 h of reperfusion. In the classical POC group, after induction of 45 min ischemia, 4 cycles of 10 s of intermittent ischemia and reperfusion were applied to the kidney before complete restoring of renal blood. In the remote POC group, 4 cycles of 5 min ischemia and reperfusion of left femoral artery were applied after 45 min renal ischemia and right at the time of renal reperfusion. There was a reduction in renal function (increase in blood urea and creatinine) in the IR group. Application of both forms of POC prevented the IR-induced reduction in renal function and histology. There were also significant improvements in kidney oxidative stress status in both POC groups demonstrated by a reduction in malondialdehyde (MDA) formation and preservation of antioxidant levels comparing to the IR group. We concluded that both methods of POC have protective effects on renal function and histology possibly by a reduction in IR-induced oxidative stress.

RISK and SAFE signaling pathway involvement in apolipoprotein A-I-induced cardioprotection

Recent findings indicate that apolipoprotein A-I (ApoA-I) may be a protective humoral mediator involved in remote ischemic preconditioning (RIPC). This study sought to determine if ApoA-I mediates its protective effects via the RISK and SAFE signaling pathways implicated in RIPC. Wistar rats were allocated to one of the following groups. Control: rats were subjected to myocardial ischemia/reperfusion (I/R) without any further intervention; RIPC: four cycles of limb I/R were applied prior to myocardial ischemia; ApoA-I: 10 mg/Kg of ApoA-I were intravenously injected prior to myocardial ischemia; ApoA-I + inhibitor: pharmacological inhibitors of RISK/SAFE pro-survival kinase (Akt, ERK1/2 and STAT-3) were administered prior to ApoA-I injection. Infarct size was significantly reduced in the RIPC group compared to Control. Similarly, ApoA-I injection efficiently protected the heart, recapitulating RIPC-induced cardioprotection. The ApoA-I protective effect was associated with Akt and GSK-3β phosphorylation and substantially inhibited by pretreatment with Akt and ERK1/2 inhibitors. Pretreatment with ApoA-I in a rat model of I/R recapitulates RIPC-induced cardioprotection and shares some similar molecular mechanisms with those of RIPC-involved protection of the heart.

Far red/near infrared light-induced protection against cardiac ischemia and reperfusion injury remains intact under diabetic conditions and is independent of nitric oxide synthase

Far red/near-infrared light (NIR) promotes a wide range of biological effects including tissue protection but whether and how NIR is capable of acutely protecting myocardium against ischemia and reperfusion injury in vivo is not fully elucidated. Our previous work indicates that NIR exposure immediately before and during early reperfusion protects the myocardium against infarction through mechanisms that are nitric oxide (NO)-dependent. Here we tested the hypothesis that NIR elicits protection in a diabetic mouse model where other cardioprotective interventions such as pre- and postconditioning fail, and that the protection is independent of nitric oxide synthase (NOS). NIR reduced infarct size dose dependently. Importantly, NIR-induced protection was preserved in a diabetic mouse model (db/db) and during acute hyperglycemia, as well as in endothelial NOS(-/-) mice and in wild type mice treated with NOS inhibitor L-NAME. In in vitro experiments NIR light liberates NO from nitrosyl hemoglobin (HbNO) and nitrosyl myoglobin (MbNO) in a wavelength-(660-830 nm) and dose-dependent manner. Irradiation at 660 nm yields the highest release of NO, while at longer wavelengths a dramatic decrease of NO release can be observed. Similar wavelength dependence was observed for the protection of mice against cardiac ischemia and reperfusion injury in vivo. NIR-induced NO release from deoxymyoglobin in the presence of nitrite mildly inhibits respiration of isolated mitochondria after hypoxia. In summary, NIR applied during reperfusion protects the myocardium against infarction in an NO-dependent, but NOS-independent mechanisms, whereby mitochondria may be a target of NO released by NIR, leading to reduced reactive oxygen species generation during reperfusion. This unique mechanism preserves protection even during diabetes where other protective strategies fail.

Comparing different postconditioning cycles after ischemia reperfusion injury in the rat skin flap

Ischemic postconditioning is a useful manipulation to reduce the undesirable effects of ischemia-reperfusion (I/R) injury. The beneficial results of this phenomenon against I/R injury have been seen in several flap models. However, there are no published works comparing different postconditioning (post-con) cycles in skin flaps. In this study, we investigated the effectiveness of different post-con cycles in a skin flap model. Epigastric island flap (6 × 3 cm) model which was based on the left superficial epigastric artery and vein was used, and complete 6 hours of ischemia was generated by occlusion of the pedicle. Forty male Wistar rats were allocated into 5 groups (n = 8 in each group). Group 1 (sham group): the elevated skin flap was repositioned without an episode of ischemia. Group 2 (control group): skin flap was elevated and 6 hours of complete ischemia was induced by clamping the pedicle. Group 3 (post-con 1): After ischemia, post-con was performed by 6 cycles of 15 seconds of repeated I/R periods. Group 4 (post-con 2): After ischemia, post-con was performed by 6 cycles of 30 second of repeated I/R periods. Group 5 (post-con 3): After ischemia, post-con was performed by 6 cycles of 60 second of repeated I/R periods. Flap viability was assessed 1 week after the surgical procedure, the necrotic area of the skin flap was measured using image analysis on the computer. The area of flap necrosis was statistically significant between the control and post-con group 4 and group 5, and no statistically significant difference was obtained between the control and post-con group 3. Groups 4 and 5 demonstrated lesser area of flap necrosis than the control group and group 4 was superior to group 5. The results revealed that the post-con applied by means of 6 cycles of 30 seconds yields the best protection against I/R injury in the rat skin flap model.

Catestatin increases the expression of anti-apoptotic and pro-angiogenetic factors in the post-ischemic hypertrophied heart of SHR

Background

In the presence of comorbidities the effectiveness of many cardioprotective strategies is blunted. The goal of this study was to assess in a hypertensive rat model if the early reperfusion with anti-hypertensive and pro-angiogenic Chromogranin A-derived peptide, Catestatin (CST:hCgA_352–372; CST-Post), protects the heart via Reperfusion-Injury-Salvage-Kinases (RISK)-pathway activation, limiting infarct-size and apoptosis, and promoting angiogenetic factors (e.g., hypoxia inducible factor, HIF-1α, and endothelial nitric oxide synthase, eNOS, expression).

Methods and Results

The effects of CST-Post on infarct-size, apoptosis and pro-angiogenetic factors were studied in isolated hearts of spontaneously hypertensive rats (SHR), which underwent the following protocols: (a) 30-min ischemia and 120-min reperfusion (I/R); (b) 30-min ischemia and 20-min reperfusion (I/R-short), both with and without CST-Post (75 nM for 20-min at the beginning of reperfusion). In unprotected Wistar-Kyoto hearts, used as normal counterpart, infarct-size resulted smaller than in SHR. CST-Post reduced significantly infarct-size and improved post-ischemic cardiac function in both strains. After 20-min reperfusion, CST-Post induced S-nitrosylation of calcium channels and phosphorylation of RISK-pathway in WKY and SHR hearts. Yet specific inhibitors of the RISK pathway blocked the CST-Post protective effects against infarct in the 120-min reperfusion groups. Moreover, apoptosis (evaluated by TUNEL, ARC and cleaved caspase) was reduced by CST-Post. Importantly, CST-Post increased expression of pro-angiogenetic factors (i.e., HIF-1α and eNOS expression) after two-hour reperfusion.

Conclusions

CST-Post limits reperfusion damages and reverses the hypertension-induced increase of I/R susceptibility. Moreover, CST-Post triggers antiapoptotic and pro-angiogenetic factors suggesting that CST-Post can be used as an anti-maladaptive remodeling treatment.

Pharmacological postconditioning with tanshinone IIA attenuates myocardial ischemia-reperfusion injury in rats by activating the phosphatidylinositol 3-kinase pathway

Tanshinone IIA, one of the active ingredients in the Chinese medicine Danshen, is cardioprotective when applied prior to sustained myocardial ischemia. The present study aimed to investigate whether pharmacological postconditioning with tanshinone IIA attenuates myocardial ischemia-reperfusion injury when applied prior to prolonged reperfusion following a sustained ischemia. A total of 88 Sprague-Dawley rats received 30 min myocardial ischemia followed by 5 or 120 min reperfusion. Compared with the ischemia-reperfusion model group, the group that received an intravenous injection of 10 mg/kg tanshinone IIA prior to reperfusion had a reduced myocardial infarct size, higher levels of phospho-Akt and phospho-endothelial nitric oxide synthase and less reduction in the optical density of the mitochondria at 540 nm, indicating that the mitochondrial permeability transition (MPT) was attenuated. The cardioprotective effect conferred by tanshinone IIA was abolished by LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K). These results demonstrate that tanshinone IIA postconditioning protects the myocardium from ischemia-reperfusion injury through the PI3K/Akt pathway, and the MPT may be also involved in this process.

Telmisartan activates endothelial nitric oxide synthase via Ser1177 phosphorylation in vascular endothelial cells

Because endothelial nitric oxide synthase (eNOS) has anti-inflammatory and anti-arteriosclerotic functions, it has been recognized as one of the key molecules essential for the homeostatic control of blood vessels other than relaxation of vascular tone. Here, we examined whether telmisartan modulates eNOS function through its pleiotropic effect. Administration of telmisartan to mice significantly increased the phosphorylation level of eNOS (Ser1177) in the aortic endothelium, but administration of valsartan had no effect. Similarly, telmisartan treatment of human umbilical vein endothelial cells significantly increased the phosphorylation levels of AMP-activated protein kinase (Thr172) and eNOS and the concentration of intracellular guanosine 3′,5′-cyclic monophosphate (cGMP). Furthermore, pretreatment with a p38 mitogen-activated protein kinase (p38 MAPK) inhibitor suppressed the increased phosphorylation level of eNOS and intracellular cGMP concentration. These data show that telmisartan increases eNOS activity through Ser1177 phosphorylation in vascular endothelial cells mainly via p38 MAPK signaling.

Novel therapeutic strategies for cardioprotection

The morbidity and mortality from ischemic heart disease (IHD) remain significant worldwide. The treatment for acute myocardial infarction has improved over the past decades, including early reperfusion of occluded coronary arteries. Although it is essential to re-open the artery as soon as possible, paradoxically this leads to additional myocardial injury, called acute ischemia-reperfusion injury (IRI), for which currently no effective therapy is available. Therefore, novel therapeutic strategies are required to protect the heart from acute IRI in order to reduce myocardial infarction size, preserve cardiac function and improve clinical outcomes in patients with IHD. In this review article, we will first outline the pathophysiology of acute IRI and review promising therapeutic strategies for cardioprotection. These include novel aspects of mitochondrial function, epigenetics, circadian clocks, the immune system, microvesicles, growth factors, stem cell therapy and gene therapy. We discuss the therapeutic potential of these novel cardioprotective strategies in terms of pharmacological targeting and clinical application.

Deletion of the aquaporin-4 gene alters expression and phosphorylation of protective kinases in the mouse heart

AIM

Aquaporins are channel-forming proteins highly permeable to water and some small molecular solutes. We have previously shown that aquaporin-4 knockout mice have increased tolerance to ischemia. However, the mechanism of cardioprotection was unclear. The aim of the current study was to investigate the effects of aquaporin-4 deletion on baseline expression and phosphorylation of some cardioprotective protein kinases.

METHODS

Proteins were extracted from hearts of aquaporin-4 knockout mice and littermate wild-type controls and analyzed with Western blot. Samples were taken from young (≤ 6 months of age), and old (≥ 1 year) mice.

RESULTS

Western blots showed three different isoforms of aquaporin-4 in wild types, likely representing M1, M23, and Mz. Total AMP-dependent kinase expression was decreased in aquaporin-4 knockout hearts by 18 ± 13% (p = 0.02), while the expression of Akt kinase, extracellular signal regulated kinase 1/2, protein kinase C-epsilon, mitogen-associated kinase P38 and C-Jun N-terminal kinase was unchanged. The phosphorylation of Akt kinase was reduced in hearts from knockout mice by 41 ± 16% (p = 0.01). No other alterations in phosphorylation were found. These effects were only detected in young mice.

CONCLUSION

Deletion of the aquaporin-4 gene decreased AMP-dependent kinase expression and Akt kinase phosphorylation in the heart. These changes may influence energy metabolism and endogenous cardioprotection.

TAT-protein blockade during ischemia/reperfusion reveals critical role for p85 PI3K-PTEN interaction in cardiomyocyte injury

Recent work shows that cooling protection after mouse cardiac arrest and cardiomyocyte ischemia is mediated by Akt activation. The PI3K p85 subunit can either augment or inhibit Akt activation depending on its binding to p110 or PTEN respectively. To further clarify the role of PI3K p85 in cardioprotection, we studied novel TAT-p85 fusion proteins that selectively inhibit PI3K p85 binding. We hypothesized that TAT fused p85 lacking the PTEN binding site (TAT-ΔPTEN p85) would enhance Akt phosphorylation to afford cardioprotection. Conversely, TAT fused p85 lacking the p110 binding site (TAT-Δp110p85) would decrease Akt phosphorylation and abrogate cardioprotection. Microscopy and Western blot analysis demonstrated that TAT fusion protein was transduced into cardiomyocytes within 5 min and remained more than 2 h. Inhibition of PI3K/Akt by TAT-Δp110 p85 significantly increased cell death from 44.6±2.7% to 92.5±3.4% after simulated ischemia and reperfusion. By contrast, PTEN inhibition using TAT-ΔPTEN p85 decreased cell death to 11.9±5.3%, a similar level of cardioprotection seen with past cooling studies. Additional studies with the small molecule PTEN inhibitor VO-OHpic confirmed that PTEN inhibition was highly protective against cell death induced by ischemia and reperfusion. We conclude that blockade of p85-PTEN interaction and PTEN inhibition may be promising strategies for rescuing the heart from ischemia and reperfusion injury.

Molecular mechanisms of ischemic conditioning: translation into patient outcomes

Following the initiation of an ischemic insult, reperfusion injury (RI) can result in numerous deleterious cardiac effects, including cardiomyocyte death. Experimental data have suggested that ischemic conditioning, when delivered either before or after the ischemic event, can provide considerable cardioprotection against RI. Ischemic conditioning involves delivering brief repetitive cycles of ischemia to the myocardium (local) or to another distal organ or structure (remote). This review will discuss recent advances in the molecular mechanisms involved in RI, the signaling pathways recruited by ischemic conditioning and conclude with an appraisal of the evidence for the use of ischemic conditioning in current clinical practice.