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

Myocardial reperfusion injury management: erythropoietin compared with postconditioning

Ischemic postconditioning (IPost) and erythropoietin (EPO) have been shown to attenuate myocardial reperfusion injury using similar signaling pathways. The aim of this study was to examine whether EPO is as effective as IPost in decreasing postischemic myocardial injury in both Langendorff-isolated-heart and in vivo ischemia-reperfusion rat models. Rat hearts were subjected to 25 min ischemia, followed by 30 min or 2 h of reperfusion in the isolated-heart study. Rats underwent 45 min ischemia, followed by 24 h of reperfusion in the in vivo study. In both studies, the control group ( n = 12; ischemia-reperfusion only) was compared with IPost ( n = 16; 3 cycles of 10 s reperfusion/10 s ischemia) and EPO ( n = 12; 1,000 IU/kg) at the onset of reperfusion. The following resulted. First, in the isolated hearts, IPost or EPO significantly improved postischemic recovery of left ventricular developed pressure. EPO induced better left ventricular developed pressure than IPost at 30 min of reperfusion (73.18 ± 10.23 vs. 48.11 ± 7.92 mmHg, P < 0.05). After 2 h of reperfusion, the infarct size was significantly lower in EPO-treated hearts compared with IPost and control hearts (14.36 ± 0.60%, 19.11 ± 0.84%, and 36.21 ± 4.20% of the left ventricle, respectively; P < 0.05). GSK-3β phosphorylation, at 30 min of reperfusion, was significantly higher with EPO compared with IPost hearts. Phosphatidylinositol 3-kinase and ERK1/2 inhibitors abolished both EPO- and IPost-mediated cardioprotection. Second, in vivo, IPost and EPO induced an infarct size reduction compared with control (40.5 ± 3.6% and 28.9 ± 3.1%, respectively, vs. 53.7 ± 4.3% of the area at risk; P < 0.05). Again, EPO decreased significantly more infarct size and transmurality than IPost ( P < 0.05). In conclusion, with the use of our protocols, EPO showed better protective effects than IPost against reperfusion injury through higher phosphorylation of GSK-3β.

What is the optimal postconditioning algorithm?

Ischemic postconditioning has emerged as a clinically feasible intervention for limiting infarction in the setting of percutaneous intervention. In ischemic postconditioning, a number of cycles of a brief period of reperfusion followed by a brief period of occlusion are applied immediately upon reperfusion of the ischemic heart. Although ischemic postconditioning is protective in both animals and man, the animal studies reveal that the algorithm used in selecting the duration of the occlusion and reperfusion periods is critical to the degree of protection realized and it varies with species. The question then arises what is the best algorithm for man? The available animal and clinical data are examined in an attempt to shed light on this perplexing problem.

Molecular aspects of ischaemic postconditioning

Preconditioning, a well established phenomenon had been used since 1980s to attenuate ischaemia-reperfusion induced injury. However, inability to predict the onset of ischaemia in clinical settings led to the discovery of a new concept of postconditioning (PoCo), in 2000s whereby brief repetitive cycles of ischaemia with intermittent reperfusion followed by prolonged ischaemia-elicited tissue protection. There is an impressive array of molecular mechanisms contributing to PoCo-mediated tissue-protection, which include triggers like adenosine (ADO), opioid, erythropoietin (EPO), endogenous nitric-oxide, reactive oxygen species, acetylcholine, tissue factors, pro-inflammatory cytokines and bradykinin; mediators like reperfusion injury salvage kinase pathways including phosphoinositide-3-kinase, extra-cellular signal regulated kinase(1/2) pathway, protein kinase G and protein kinase C; end-effectors like mitochondrial permeability transition pore and mitochondrial potassium ATP channel. The clinical applicability of PoCo has been extended with the use of PoCo mimetic agents like insulin, glucagon like peptide, EPO, statins and ADO before reperfusion in patients with ischaemia reperfusion injury. Remote PoCo has also emerged as a new concept; however, considerable research is required for understanding its molecular mechanisms. In this review, an exhaustive attempt has been made to unearth some molecular aspects of PoCo.

Interaction between pre- and postconditioning in the in vivo rat heart

Patients with an impending myocardial infarction may be preconditioned by pre-infarct angina. Hence, it is important to establish whether ischemic postconditioning is still effective in preconditioned hearts. We therefore studied in anesthetized rats the effect of postconditioning after coronary artery occlusions (CAO) of 60 min in control hearts, hearts preconditioned by a single 15-min CAO (1IPC15) or a triple 3-min CAO (3IPC3). Furthermore, we studied the effect of postconditioning in hearts that had been pharmacologically preconditioned with intravenous adenosine and in hearts that had become tolerant to 1IPC15. Postconditioning limited infarct size in control hearts, but did not afford additional protection in preconditioned hearts, irrespective of the IPC stimulus. NO synthase inhibition abolished the cardioprotection by postconditioning, both IPC stimuli, and the combination of postconditioning and either IPC stimulus. Postconditioning also failed to afford cardioprotection in hearts protected by adenosine, and in hearts that had become tolerant to cardioprotection by 1IPC15. In accordance with previous observations, postconditioning paradoxically increased infarct size following a 30-min CAO. This detrimental effect was prevented by either IPC stimulus, in a NO synthase-dependent manner. In conclusion, postconditioning does not afford additional protection in preconditioned hearts, irrespective of the preconditioning stimulus and the presence of tolerance to preconditioning. Lack of additional protection may be related to the observation that postconditioning and preconditioning are both mediated via NO synthase. In contrast, the increase in infarct size by postconditioning following a 30-min CAO is abolished by either IPC stimulus. These findings indicate that the interaction between preconditioning and postconditioning is highly dependent on the duration of index ischemia, but independent of the preconditioning stimulus.

Sevoflurane- and desflurane-induced human myocardial post-conditioning through Phosphatidylinositol-3-kinase/Akt signalling

BACKGROUND

The role of phosphatidylinositol-3-kinase (PI3K) in sevoflurane- and desflurane-induced myocardial post-conditioning remains unknown.

METHODS

We recorded isometric contraction of isolated human right atrial trabeculae (oxygenated Tyrode's at 34 degrees C, stimulation frequency 1 Hz). In all groups, a 30-min hypoxic period was followed by a 60-min reoxygenation period. At the onset of reoxygenation, muscles were exposed to 5 min of sevoflurane 1%, 2%, and 3%, and desflurane 3%, 6%, and 9%. In separate groups, sevoflurane 2% and desflurane 6% were administered in the presence of 100 nM wortmannin, a PI3K inhibitor. Recovery of force after the 60-min reoxygenation period was compared between groups (mean +/- SD).

RESULT

As compared with the Control group (49 +/- 7% of baseline) PostC by sevoflurane 1%, 2%, and 3% (78 +/- 4%, 79 +/- 5%, and 85 +/- 4% of baseline, respectively) and desflurane 3%, 6%, and 9% (74 +/- 5%, 84 +/- 4%, and 86 +/- 11% of baseline, respectively) enhanced the recovery of force. This effect was abolished in the presence of wortmannin (56 +/- 5% of baseline for sevoflurane 2%+wortmannin; 56 +/- 3% of baseline for desflurane 6%+wortmannin). Wortmannin alone had no effect on the recovery of force (57 +/- 7% of baseline).

CONCLUSION

In vitro, sevoflurane and desflurane post-conditioned human myocardium against hypoxia through activation of phosphatidylinositol-3-kinase.

Transcriptional remodeling of rapidly stimulated HL-1 atrial myocytes exhibits concordance with human atrial fibrillation

During atrial fibrillation (AF), rapid stimulation causes atrial remodeling that increases arrhythmia susceptibility. Using an established atrial (HL-1) myocyte model, we investigated the transcriptional profile associated with early atrial myocyte remodeling. Spontaneously contracting HL-1 cells were cultured in the absence and presence of rapid stimulation for 24 h and RNA harvested for microarray analysis. We identified 758 genes that were significantly altered with rapid stimulation (626 up- and 132 down-regulated). Results were confirmed using real-time quantitative RT-PCR for selected genes based on physiological relevance in human AF and/or experimental atrial tachycardia (AT), and regulation in the microarray results. In some cases, transcriptional changes were rapid, occurring within 3 h. For a selected group of genes, results were validated for the expressed protein, with findings that correlated with observed transcriptional changes. Significantly regulated genes were classified using the Gene Ontology Database to permit direct comparison of our findings with previously published myocardial transcriptional profiles. For broad functional categories, there was strong concordance between rapidly stimulated HL-1 myocytes and human AF, but not for other remodeling paradigms (cardiomyopathy and exercise). Many individual gene changes were conserved with AF/AT, with marked up-regulation of genes encoding brain and atrial natriuretic peptide precursors, and heat shock proteins. For the conserved genes, both a cellular stress and survival response was evident. Our results demonstrate similarities with human AF/experimental AT with respect to large-scale patterns of transcriptional remodeling, as well as regulation of specific individual genes. Importantly, we identified novel pathways and molecules that were concordantly regulated in vivo.

Postconditioning in rats and mice

OBJECTIVE

For subsequent studies on the molecular mechanisms of postconditioning, we aimed to identify a robust postconditioning protocol in rat and mouse heart.

DESIGN

Isolated rat hearts were subjected to different postconditioning protocols (study 1 and 2). The protection was compared to preconditioning. Rats (study 3) in vivo in two different laboratories were postconditioned. Isolated mouse hearts (study 4) and mice in vivo (study 5) were postconditioned.

RESULTS

Postconditioning did not protect isolated, perfused rat hearts, however, preconditioning improved function and reduced infarct size. Postconditioning tended to protect rat hearts in vivo in one laboratory (p = 0.10), whereas protection was seen in the other laboratory (infarct size 51+/-11% vs controls 62+/-3%, p = 0.01). Postconditioned mouse hearts were protected, both ex vivo (16+/-9% vs controls 33+/-18%, p = 0.02) and in vivo (21+/-5% vs 42+/-7%, p < 0.001).

CONCLUSIONS

Rat hearts are less suitable for studies of mechanisms of postconditioning. The results suggest that the signaling pathways differ between pre- and postconditioning. Mouse hearts were strongly protected by postconditioning, and genetically engineered mice may be useful for postconditioning research.

Remote ischemic conditioning: evolution of the concept, mechanisms, and clinical application

Remote ischemic conditioning is a novel concept of protection against ischemia-reperfusion injury. Brief controlled episodes of intermittent ischemia of the arm or leg may confer a powerful systemic protection against prolonged ischemia in a distant organ. This conditioning phenomenon is clinically applicable and can be performed before--preconditioning, during--perconditioning, or after--postconditioning prolonged distant organ ischemia. The remote ischemic conditioning may have an immense impact on clinical practice in the near future.

Ischemic postconditioning: experimental models and protocol algorithms

Ischemic postconditioning, a simple mechanical maneuver at the onset of reperfusion, reduces infarct size after ischemia/reperfusion. After its first description in 2003 by Zhao et al. numerous experimental studies have investigated this protective phenomenon. Whereas the underlying mechanisms and signal transduction are not yet understood in detail, infarct size reduction by ischemic postconditioning was confirmed in all species tested so far, including man. We have now reviewed the literature with focus on experimental models and protocols to better understand the determinants of protection by ischemic postconditioning or lack of it. Only studies with infarct size as unequivocal endpoint were considered. In all species and models, the duration of index ischemia and the protective protocol algorithm impact on the outcome of ischemic postconditioning, and gender, age, and myocardial temperature contribute.

The Mechanism by Which Ischemic Postconditioning Reduces Reperfusion Arrhythmias in Rats Remains Elusive

We have observed that ischemic postconditioning markedly reduces reperfusion-induced ventricular arrhythmias, but whether the mechanism is related to previously described pathways of preconditioning or postconditioning for infarct size reduction is unknown. The purpose of this study was to determine whether known pathways were involved in postconditioning's protective effect on arrhythmias.

Anesthetized female rats were subjected to 5 minutes of proximal coronary artery occlusion and 5 minutes of reperfusion. They were either not postconditioned or subjected to 4 cycles of 20 seconds reperfusion, 20 seconds reocclusion before final reperfusion (postconditioned). Electrocardiogram and blood pressure were monitored throughout. Alleged agonists and antagonists to postconditioning representing a number of mechanisms were evaluated.

Nonpostconditioned rats treated with the suppressor of the mitochondrial permeability transition pore, cyclosporine A, did not show a reduction in

reperfusion-induced ventricular arrhythmias compared to control nonpostconditioned rats. Neither Wortmannin (p13-kinase inhibitor), 5 hydroxydecanoate (selective inhibitor of mitochondrial KATP channel), nor 8-sulfophenyl theophylline (blocker of adenosine receptors) blocked the reduction in ventricular tachycardia of postconditioning.

The mechanism by which postconditioning reduces reperfusion-induced ventricular arrhythmias may be independent of known pathways that have been implicated in the infarct sparing effects of preconditioning and postconditioning—including adenosine, mitochondrial KATP channel, mitochondrial permeability transition pore, and p13-kinase-pAKt pathways. Alternative protective pathways may exist to explain the antiarrhythmic effect of postconditioning.

Hyperthermia-Induced Cardioprotection Is Potentiated by Ischemic Postconditioning in Rats

We tested the hypothesis that the protective effects of hyperthermia (HT) could be augmented by ischemic postconditioning (PostC) via enhancement of reperfusion-induced Akt phosphorylation. The role of the mitoKATP channel as an effecter to protect hearts against ischemia/reperfusion injury was also investigated. In isolated perfused heart experiments using a Langendorff apparatus, 30 min of no-flow global ischemia was followed by 120 min of reperfusion. Ischemic PostC, 5 cycles of 10-sec reperfusion/10-sec ischemia, was achieved at the initial moment of reperfusion. Hyperthermia (HT, 43°C for 20 min) was applied 24 hr before ischemia onset. Ischemic PostC alone did not show significant protection, but HT did. The HT-induced protection in terms of infarct size, recovery of left ventricular performance, amount of released creatine kinase and apoptosis were enhanced by ischemic PostC. These protective effects were consistent with the levels of Akt phosphorylation 7 min after reperfusion and were completely blocked by the pretreatment with the phosphatidylinositol 3-kinase inhibitor wortmannin. HT-induced protection was also completely abolished by concomitant perfusion with 5-hydroxydecanoate (5HD, 100 μM), an inhibitor of the mitochondrial ATP-sensitive potassium (mitoKATP) channel. However, the potentiated protection by ischemic PostC remained, even in the presence of 5HD. In conclusion, ischemic PostC could potentiate the protective effects of HT possibly via enhancement of reperfusion-induced Akt phosphorylation. Although the opening of the mitoKATP channel is predominantly involved as an effecter in HT-induced protection, potentiated protection by ischemic PostC may involve mechanisms other than the mitoKATP channel.

AMP-activated protein kinase: a core signalling pathway in the heart

Over the past decade, AMP-activated protein kinase (AMPK) has emerged as an important intracellular signalling pathway in the heart. Activated AMPK stimulates the production of ATP by regulating key steps in both glucose and fatty acid metabolism. It has an inhibitory effect on cardiac protein synthesis. AMPK also interacts with additional intracellular signalling pathways in a coordinated network that modulates essential cellular processes in the heart. Evidence is accumulating that AMPK may protect the heart from ischaemic injury and limit the development of cardiac myocyte hypertrophy to various stimuli. Heart AMPK is activated by hormones, cytokines and oral hypoglycaemic drugs that are used in the treatment of type 2 diabetes. The tumour suppressor LKB1 is the major regulator of AMPK activity, but additional upstream kinases and protein phosphatases also contribute. Mutations in the regulatory gamma2 subunit of AMPK lead to an inherited syndrome of hypertrophic cardiomyopathy and ventricular pre-excitation, which appears to be due to intracellular glycogen accumulation. Future research promises to elucidate the molecular mechanisms responsible for AMPK activation, novel downstream AMPK targets, and the therapeutic potential of targeting AMPK for the prevention and treatment of myocardial ischaemia or cardiac hypertrophy.

Protective ischaemia in patients: preconditioning and postconditioning

Infarct size can be limited by reducing the determinants of infarct size or increasing collateral blood flow by treatment initiated before the ischaemic event. Reperfusion is the definitive treatment for permanently reducing infarct size and restoring some degree of contractile function to the affected myocardium. Innate survival mechanisms in the heart can be stimulated by short, non-lethal periods of ischaemia and reperfusion, applied either before or after the ischaemic event. Preconditioning, a series of transient intervals of ischaemia and reperfusion applied before the lethal 'index' ischaemic event, sets in motion molecular and cellular mechanisms that increase cardiomyocyte survival to a degree that had not hitherto been seen before. The cardioprotective ischaemic-reperfusion protocol applied at onset of reperfusion, termed 'postconditioning' (Postcon), is also associated with significant cardioprotection that can be applied at the point of reperfusion treatment in the catheterization laboratory or operating room. Both preconditioning and Postcon have been successfully applied to the clinical setting and have been found to reduce infarct size and other attributes of post-ischaemic injury. This review will summarize the physiological preclinical data on preconditioning and Postcon that are relevant to their translation to clinical therapeutics and treatment.

The cardioprotective effect of postconditioning is mediated by ARC through inhibiting mitochondrial apoptotic pathway

OBJECTIVE

Postconditioning protects the heart against ischemia/reperfusion injury by inhibiting cardiomyocyte apoptosis. However, the molecular mechanism by which postconditioning suppresses apoptosis remains to be fully understood. Apoptosis repressor with caspase recruitment domain (ARC) has been demonstrated to possess the ability to protect cardiomyocytes from apoptosis induced by ischemia/reperfusion. It is not yet clear as to whether ARC contributes to the inhibitory effect of postconditioning against cardiomyocyte apoptosis.

METHODS

The cultured cardiomyocytes from 1-day old male Sprague-Dawley rats were exposed to 3 h hypoxia followed by 3 h of reoxygenation. Cells were postconditioned by three cycles each of 5 min reoxygenation and 5 min hypoxia before 3 h of reoxygenation.

RESULTS

Hypoxia/reoxygenation led to a decrease of endogenous ARC protein levels. In contrast, postconditioning could block the reduction of endogenous ARC protein levels. Interestingly, inhibition of endogenous ARC expression by ARC antisense oligodeoxynucleotides reduced the inhibitory effect of postconditioning against apoptosis. Furthermore, our data showed that postconditioning suppressed the loss of mitochondrial membrane potential, Bax activation and the release of mitochondrial cytochrome c to cytosol. However, these inhibitory effects of postconditioning disappeared upon knockdown of endogenous ARC.

CONCLUSION

Our data for the first time demonstrate that ARC plays an essential role in mediating the cardioprotective effect of postconditioning against apoptosis initiated by the mitochondrial pathway.

Physiology and pharmacology of myocardial preconditioning and postconditioning

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 2 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. This article reviews 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 are reviewed and recommendations given for the use of perioperative anesthetics and medications.

Postconditioning induces an anti-apoptotic effect and preserves mitochondrial integrity in isolated rat hearts

Postconditioning (PostC) may limit mitochondrial damage and apoptotic signaling. We studied markers of apoptosis and mitochondrial protection in isolated rat hearts, which underwent a) perfusion without ischemia (Sham), b) 30-min ischemia (I) plus 2-hour reperfusion (R), or c) PostC protocol (5 intermittent cycles of 10-s reperfusion and 10-s ischemia immediately after the 30-min ischemia). Markers were studied in cytosolic (CF) and/or mitochondrial (MF) fractions. In CF, while pro-apoptotic factors (cytochrome c and caspase-3) were reduced, the anti-apoptotic markers (Bcl-2 and Pim-1) were increased by PostC, compared to the I/R group. Accordingly, phospho-GSK-3beta and Bcl-2 levels increased in mitochondria of PostC group. Moreover, I/R reduced the level of mitochondrial structural protein (HSP-60) in MF and increased in CF, thus suggesting mitochondrial damage and HSP-60 release in cytosol, which were prevented by PostC. Electron microscopy confirmed that I/R markedly damaged cristae and mitochondrial membranes; damage was markedly reduced by PostC. Finally, total connexin-43 (Cx43) levels were reduced in the CF of the I/R group, whereas phospho-Cx43 level resulted in higher levels in the MF of the I/R group than the Sham group. PostC limited the I/R-induced increase of mitochondrial phospho-Cx43. Data suggest that PostC i) increases the levels of anti-apoptotic markers, including the cardioprotective kinase Pim-1, ii) decreases the pro-apoptotic markers, e.g. cytochrome c, iii) preserves the mitochondrial structure, and iv) limits the migration of phospho-Cx43 to mitochondria.

Sequential limb ischemia demonstrates remote postconditioning protection of murine skeletal muscle

BACKGROUND

Ischemic postconditioning, the process of exposing tissues to brief cycles of ischemia-reperfusion after critical ischemia, can mitigate local ischemia-reperfusion injury. Remote protection of skeletal muscle has never been demonstrated in postconditioning models of ischemia-reperfusion injury.

METHODS

Mice were subjected to 2 hours of ipsilateral hind limb ischemia followed by reperfusion. Contralateral limb ischemia was subsequently induced for 2 hours after either 0 (n = 6), 20 (n = 6), or 120 (n = 5) minutes of ipsilateral limb reperfusion. These groups were compared with animals subjected to bilateral simultaneous injury (n = 8) and sham animals that did not undergo ischemia (n = 6). The gastrocnemius muscles were harvested for histologic evaluation, and injury was recorded as the percentage of injured fibers.

RESULTS

The first limbs undergoing injury in the 20-minute interval group had a 59 percent injury reduction compared with contralateral limbs (16.0 +/- 2.4 percent versus 39.5 +/- 6.5 percent) after 24 hours of reperfusion and 62 percent reduction after 48 hours (24.4 +/- 3.0 percent versus 63.6 +/- 5.5 percent). In animals with no interval or a 120-minute interval between the onset of limb ischemia, there was no significant difference in injury between hind limbs. The injury in these groups was similar to that in hind limbs subjected to simultaneous bilateral ischemia.

CONCLUSIONS

A 20-minute reperfusion interval between hind limb ischemia significantly protects against injury in the initially ischemic limb, while similar injury is observed with simultaneous ischemia or an interval of 120 minutes. This study demonstrates remote postconditioning of skeletal muscle and may lead to the development of post hoc therapies.

The mitochondrial permeability transition pore as a target for preconditioning and postconditioning

The experimental evidence supporting the mitochondrial permeability transition pore (mPTP) as a major mediator of lethal myocardial reperfusion injury and therefore a critical target for cardioprotection is persuasive. Although, its molecular identity eludes investigators, it is generally accepted that mitochondrial cyclophilin-D, the target for the inhibitory effects of cyclosporine-A on the mPTP, is a regulatory component of the mPTP. Animal myocardial infarction studies and a recent clinical proof-of-concept study have demonstrated that pharmacologically inhibiting its opening at the onset of myocardial reperfusion reduces myocardial infarct size in the region of 30-50%. Interestingly, the inhibition of mPTP opening at this time appears to underpin the infarct-limiting effects of the endogenous cardioprotective strategies of ischemic preconditioning (IPC) and postconditioning (IPost). However, the mechanism underlying this inhibitory action of IPC and IPost on mPTP opening is unclear. The objectve of this review article will be to explore the potential mechanisms which link IPC and IPost to mPTP inhibition in the reperfused heart.

Loss of cardioprotection with ageing

Not only the prevalence, but also the mortality due to ischaemic cardiovascular disease is higher in older than in young humans, and the demographic shift towards an ageing population will further increase the prevalence of age-related cardiovascular disease. In order to develop strategies aimed to limit reversible and irreversible myocardial damage in older patients, there is a need to better understand age-induced alterations in protein expression and cell signalling. Cardioprotective phenomena such as ischaemic and pharmacological pre and postconditioning attenuate ischaemia/reperfusion injury in young hearts. Whether or not pre and postconditioning are still effective in aged organs, animals, or patients, i.e. under conditions where such cardioprotection is most relevant, is still a matter of debate; most studies suggest a loss of protection in aged hearts. The present review discusses changes in protein expression and cell signalling important to ischaemia/reperfusion injury with myocardial ageing. The efficacy of cardioprotective manoeuvres, e.g. ischaemic pre and postconditioning in aged organs and animals will be discussed, and the development of strategies aimed to antagonize the age-induced loss of protection will be addressed.

Phosphoinositide 3-kinase signalling in the vascular system

Phosphoinositide 3-kinases (PI3Ks) are protein and lipid kinases activated by different classes of membrane receptors, including G-protein coupled and tyrosine kinase receptors. Several lines of evidence have uncovered specific roles for distinct PI3K isoforms in the vascular system in both physiology and disease. The present review will summarize and discuss the most recent advances regarding PI3K-Akt signalling in endothelial cells, vascular smooth muscle cells, platelets, and inflammatory cells involved in the atherosclerotic process. Of interest, the development of novel isoform-selective PI3K inhibitor drugs offers a unique opportunity to selectively and differentially target PI3K-driven pathways in the vascular system and may give rise to new strategies for the treatment of cardiovascular diseases.

Ischemic postconditioning in pigs: no causal role for RISK activation

Ischemic postconditioning (IPoC) reduces infarct size following ischemia/reperfusion. Whether or not phosphorylation of RISK (reperfusion injury salvage kinases) (AKT, ERK1/2, P70S6K, GSK3beta) is causal for protection by IPoC is controversial. We therefore studied the impact of RISK on IPoC in anesthetized pigs subjected to 90 minutes of left anterior descending coronary artery hypoperfusion and 120 minutes of reperfusion. In protocol 1, IPoC, by 6 cycles of 20/20 seconds of reperfusion/reocclusion (n=13), was compared with immediate full reperfusion (IFR) (n=15). In protocol 2, IPoC (n=4) or IFR (n=4) was performed with pharmacological RISK blockade by IC coinfusion of Wortmannin and U0126. Infarct size was determined by TTC staining, and the expression of phosphorylated RISK proteins by Western blot analysis in biopsies. In protocol 1, infarct size was 20+/-3% (percentage of area at risk; mean+/-SEM) with IPoC and 33+/-4% (P<0.05) with IFR. RISK phosphorylation increased with reperfusion but was not different between IPoC and IFR. In protocol 2, Wortmannin and U0126 blocked the increases in RISK phosphorylation during reperfusion, but infarct size was still smaller with IPoC (15+/-7%) than with IFR (35+/-6%; P<0.05).

Acute effects of "delayed postconditioning" with periodic acceleration after asphyxia induced shock in pigs

Asphyxia cardiac arrest and shock are models for whole body ischemia reperfusion injury. Periodic acceleration (pGz) achieved by moving the body on a platform is a novel method for inducing pulsatile vascular shear stress and endogenous production of endothelial nitric oxide, prostaglandin E2, tissue plasminogen activator, and adrenomedullin. The aforementioned are cardioprotective during and after ischemia reperfusion injury. We investigated whether pGz, applied 15 min after return of spontaneous circulation (ROSC) would serve as an effective "delayed" post conditioning tactic to lessen acute reperfusion injury markers in a pediatric swine model of asphyxia induced shock. Asphyxia shock was induced in 20 swine weight 3.9 +/- 0.6 kg. Fifteen minutes after ROSC, the animals were randomized to receive conventional mechanical ventilation (CMV, [Control]) or CMV with pGz. All animals had ROSC and no significant differences in blood gases or hemodynamics after ROSC. pGz treated had significantly less myocardial dysfunction post resuscitation, (i.e. better % ejection fraction (EF), % fractional shortening (FS), and wall motion score index) and lower biochemical indices of reperfusion injury (lower TNF-alpha, IL-6, and Troponin I, and myeloperoxidase activity). Delayed postconditioning with pGz ameliorates acute post resuscitation reperfusion injury and improves myocardial dysfunction after asphyxia-induced shock.

Loss of myocardial ischemic postconditioning in adenosine A1 and bradykinin B2 receptors gene knockout mice

BACKGROUND

Ischemic postconditioning (PostC) is a recently described cardioprotective modality against reperfusion injury, through series of brief reflow interruptions applied at the very onset of reperfusion. It is proposed that PostC can activate a complex cellular signaling cascade, in which cell membrane receptors could serve as the upstream triggers of PostC. However, the exact subtypes of such receptors remain controversial or uninvestigated. To this context, the purpose of present study was to determine the definitive role of adenosine A(1) and bradykinin B(1) and B(2) receptors in PostC.

METHODS AND RESULTS

The hearts isolated from adult male C57BL/6J wild-type mice or the mice lacking adenosine A(1), or bradykinin B(1) or B(2) receptors subjected to zero-flow global ischemia and reperfusion in a Langendorff model. PostC, consisting of 6 cycles of 10 seconds of reperfusion and 10 seconds of ischemia, demonstrated significantly reduced myocardial infarct size (22.8+/-3.1%, mean+/-SEM) as compared with the non-PostC wild-type controls (35.1+/-2.8%, P<0.05). The infarct-limiting protection of PostC was absent in adenosine A(1) receptor knockout mice (34.9+/-2.7%) or bradykinin B(2) receptor knockout mice (33.3+/-1.7%) and was partially attenuated in bradykinin B(1) receptor-deficient mice (25.6+/-2.9%; P>0.05). On the other hand, PostC did not significantly alter postischemic cardiac contractile function and coronary flow.

CONCLUSIONS

With the use of three distinctive strains of gene knockout mice, the current study has provided the first conclusive evidence showing PostC-induced infarct-limiting cardioprotection could be triggered by activation of multiple types of cell membrane receptors, which include adenosine A(1) and bradykinin B(2) receptors.

The mechanism of helium-induced preconditioning: a direct role for nitric oxide in rabbits

BACKGROUND

Helium produces preconditioning against myocardial infarction by activating prosurvival signaling, but whether nitric oxide (NO) generated by endothelial NO synthase plays a role in this phenomenon is unknown. We tested the hypothesis that NO mediates helium-induced cardioprotection in vivo.

METHODS

Rabbits (n = 62) instrumented for hemodynamic measurement were subjected to a 30-min left anterior descending coronary artery occlusion and 3 h reperfusion, and received 0.9% saline (control) or three cycles of 70% helium-30% oxygen administered for 5 min interspersed with 5 min of an air-oxygen mixture before left anterior descending coronary artery occlusion in the absence or presence of pretreatment with the nonselective NOS inhibitor N-nitro-l-arginine methyl ester (L-NAME; 10 mg/kg), the selective inducible NOS inhibitor aminoguanidine hydrochloride (AG; 300 mg/kg), or selective neuronal NOS inhibitor 7-nitroindazole (7-NI; 50 mg/kg). In additional rabbits, the fluorescent probe 4,5-diaminofluroscein diacetate (DAF-2DA) and confocal laser microscopy were used to detect NO production in the absence or presence of helium with or without L-NAME pretreatment.

RESULTS

Helium reduced (P < 0.05) infarct size (24% +/- 4% of the left ventricular area at risk; mean +/- sd) compared with control (46% +/- 3%). L-NAME, AG, and 7-NI did not alter myocardial infarct size when administered alone. L-NAME, but not 7-NI or AG, abolished helium-induced cardioprotection. Helium enhanced DAF-2DA fluorescence compared with control (26 +/- 8 vs 15 +/- 5 U, respectively). Pretreatment with L-NAME abolished these helium-induced increases in DAF-2DA fluorescence.

CONCLUSIONS

The results indicate that cardioprotection by helium is mediated by NO that is probably generated by endothelial NOS in vivo.

Inhibition of myocardial apoptosis by postconditioning is associated with attenuation of oxidative stress-mediated nuclear factor-kappa B translocation and TNF alpha release

Oxidative stress-stimulated nuclear factor-kappa B (NF-kappa B) activation has been associated with rapid transcription of TNF-alpha and induction of apoptosis. This study tested the hypothesis that postconditioning (Postcon) reduces myocardial apoptosis and inhibits translocation of NF-kappa B and release of TNF-alpha secondary to an attenuation of oxidant generation during reperfusion. Anesthetized rats were subjected to 30 min of ischemia and 3 h of reperfusion and divided randomly to Control or Postcon (three cycles of 10-s reperfusion and 10-s reocclusion applied at the onset of reperfusion) group, respectively. Relative to Control, Postcon reduced the plasma malondialdehyde (1.21 +/- 0.08 vs. 0.8 +/- 0.06* microM/mL) and decreased the generation of superoxide radical in area at risk myocardium (dihydroethidium staining). Compared with Control, Postcon also inhibited translocation of NF-kappa B to nuclei (167% +/- 21% vs. 142% +/- 18%*), decreased the level of plasma TNF-alpha (1,994 +/- 447 vs. 667 +/- 130* pg/mL), and inhibited caspase-3 activity (0.57% +/- 0.1% vs. 0.21% +/- 0.1%*). The number of apoptotic cells (percent total nuclei) in ischemic myocardium was reduced (20% +/- 1% vs. 11% +/- 2%*), consistent with reduced appearance of DNA fragmentation. To support whether oxidant generation is important in the triggering of cytokine release and apoptosis, N-acetylcysteine (NAC), a potent antioxidant agent, was administered before ischemia and at reperfusion. Treatment with NAC inhibited superoxide radical generation and decreased plasma malondialdehyde to a comparable level to that in Postcon, concomitant with an inhibition of NF-kappa B expression (42% +/- 8%*) and reduction of release of TNF-alpha (231 +/- 72* pg/mL). Caspase-3 activity (0.33% +/- 0.1%*) and apoptotic cells (12% +/- 1%*) were also comparably reduced by NAC. These data suggest that Postcon attenuates myocardial apoptosis, reduces caspase-3 activity, and is potentially mediated by inhibiting oxidant-activated NF-kappa B-TNF-alpha signaling pathway. *P < 0.05 Postcon and NAC vs. Control.