Lethal Ischemia-reperfusion Injury Research Articles

Does Disruption of Optic Atrophy-1 (OPA1) Contribute to Cell Death in HL-1 Cardiomyocytes Subjected to Lethal Ischemia-Reperfusion Injury?

Disruption of mitochondrial structure/function is well-recognized to be a determinant of cell death in cardiomyocytes subjected to lethal episodes of ischemia-reperfusion (IR). However, the precise mitochondrial event(s) that precipitate lethal IR injury remain incompletely resolved. Using the in vitro HL-1 cardiomyocyte model, our aims were to establish whether: (1) proteolytic processing of optic atrophy protein-1 (OPA1), the inner mitochondrial membrane protein responsible for maintaining cristae junction integrity, plays a causal, mechanistic role in determining cardiomyocyte fate in cells subjected to lethal IR injury; and (2) preservation of OPA1 may contribute to the well-documented cardioprotection achieved with ischemic preconditioning (IPC) and remote ischemic conditioning. We report that HL-1 cells subjected to 2.5 h of simulated ischemia displayed increased activity of OMA1 (the metalloprotease responsible for proteolytic processing of OPA1) during the initial 45 min following reoxygenation. This was accompanied by processing of mitochondrial OPA1 (i.e., cleavage to yield short-OPA1 peptides) and release of short-OPA1 into the cytosol. However, siRNA-mediated knockdown of OPA1 content did not exacerbate lethal IR injury, and did not attenuate the cardioprotection seen with IPC and a remote preconditioning stimulus, achieved by transfer of ‘reperfusate’ medium (TRM-IPC) in this cell culture model. Taken together, our results do not support the concept that maintenance of OPA1 integrity plays a mechanistic role in determining cell fate in the HL-1 cardiomyocyte model of lethal IR injury, or that preservation of OPA1 underlies the cardioprotection seen with ischemic conditioning.

Abstract 213: Disruption of Mitochondrial Cristae Integrity in Lethal Myocardial Ischemia-Reperfusion Injury: Association or Cause-and-Effect?

Background: Considerable attention has focused on the concept that disruption of mitochondrial structure/function is a determinant of cell death in cardiomyocytes subjected to ischemia-reperfusion (IR). However, the details of this relationship, and the precise mitochondrial event(s) that precipitate lethal IR injury, remain unresolved. Aim: Emerging evidence has revealed that cardiomyocytes subjected to IR display: i) degradation of optic atrophy protein-1 (OPA1), the inner mitochondrial membrane protein responsible for maintaining cristae junction integrity, followed by ii) inappropriate release of OPA1 into the cytosol. Accordingly, our goal was to establish whether degradation of OPA1 plays a causal, mechanistic role in determining cardiomyocyte fate. Methods and Results: In Protocol 1 , HL-1 cardiomyocytes underwent 2.5 hrs of simulated ischemia. This was preceded by either a classic intervention known to attenuate IR injury (ischemic preconditioning: IPC) or a matched control period. Cell viability was quantified at 24 hrs post-R, and release of OPA1 into the cytosol was measured at 30 min post-R. In Controls, IR resulted in ~50% cell death and a >15-fold increase in OPA1 in the cytosol - effects that were both attenuated by IPC (Figure: top). In Protocol 2 : to discern whether these data reflect an association between OPA1 degradation and cell death or cause-and-effect , HL-1 cells were transfected with either siRNA targeting OPA1 (resulting in near-total knockdown of OPA1 expression: data not shown) or scrambled siRNA. Cardiomyocytes then underwent IPC/no intervention and IR as in Protocol 1. If OPA1 disruption contributes to IR injury, we reasoned that OPA1 knockdown would exacerbate cell death in Controls and attenuate IPC-mediated protection. However, OPA1 knockdown had no effect on cell death in either cohort (Figure: bottom). Conclusion: Disruption of OPA1 and loss of cristae junction integrity does not play a causal role in lethal IR injury.

The role of Glucagon-Like Peptide 1 Loading on periprocedural myocardial infarction During elective PCI (GOLD-PCI study): A randomized, placebo-controlled trial

The incretin hormone glucagon-like peptide 1 (GLP-1) has been shown to protect against lethal ischemia-reperfusion injury in animal models and against nonlethal ischemia reperfusion injury in humans. Furthermore, GLP-1 receptor agonists have been shown to reduce major adverse cardiovascular and cerebrovascular events (MACCE) in large-scale studies. We sought to investigate whether GLP-1 reduced percutaneous coronary intervention (PCI)-associated myocardial infarction (PMI) during elective PCI. The study was a randomized, double-blind controlled trial in which patients undergoing elective PCI received an intravenous infusion of either GLP-1 at 1.2 pmol/kg/min or matched 0.9% saline placebo before and during the procedure. Randomization was performed in 1:1 fashion, with stratification for diabetes mellitus. Six-hour cardiac troponin I (cTnI) was measured with a primary end point of PMI defined as rise ≫×5 upper limit of normal (280 ng/L). Secondary end points included cTnI rise and MACCE at 12 months. A total of 192 patients were randomized with 152 (79%) male and a mean age of 68.1 ± 8.9 years. No significant differences in patient demographics were noted between the groups. There was no difference in the rate of PMI between GLP-1 and placebo (9 [9.8%] vs 8 [8.3%], P = 1.0) or in the secondary end points of difference in median cTnI between groups (9.5 [0-88.5] vs 20 [0-58.5] ng/L, P = .25) and MACCE at 12 months (7 [7.3%] vs 9 [9.4%], P = .61). In this randomized, placebo-controlled trial, GLP-1 did not reduce the low incidence of PMI or abrogate biomarker rise during elective PCI, nor did it influence the 12-month MACCE rate which also remained low. Clinicaltrials.gov Number: NCT02127996https://clinicaltrials.gov/ct2/show/NCT02127996.

Heat Shock Protein 70 Messenger RNA in Rat Leukocytes Elevates After Severe Intestinal Ischemia–Reperfusion

BackgroundHeat shock protein 70 (HSP70) confers protection against heat shock, oxidative stress, infection, and inflammation in many cell types. A recent study reported that the induction of HSP70 was associated with morphologic protection against ischemia–reperfusion injury (IRI) in the rat small intestine. This study investigated the dynamics of HSP70 in leukocytes during intestinal IRI in a rat model. Materials and methodsSerial blood samples were collected at 60-minute intervals up to 240 min from male Wistar rats (n = 15). The rats were divided into three groups of five each: the control group, the nonlethal IRI group, and the lethal IRI group. Rats belonging to the control group underwent a sham operation, and laparotomy was performed on rats in the lethal and nonlethal IRI groups. The nonlethal group experienced a 30-minute clamping of the superior mesenteric artery, and the lethal group experienced a 75-minute clamping of the superior mesenteric artery. The expression of HSP70 messenger RNA (mRNA) in leukocytes was measured by real-time quantitative polymerase chain reaction. Mixed-effects modeling of repeated measures was used to carry out the statistical analysis. The Bonferroni correction was applied to multiple comparisons. A P value < 0.0167 was considered to indicate statistical significance. ResultsThe expression of HSP70 mRNA in leukocytes increased 60 min after reperfusion in both IRI groups, and it was 12.8 times higher in the lethal group and 3.6 times higher in the nonlethal group compared with the control group. The expression of mRNA in the lethal group was significantly increased compared with the nonlethal group and the control group at 120 and 180 min after reperfusion. At 120 min after reperfusion, the expression of HSP70 mRNA was 6.1 times higher in the lethal group than in the nonlethal group (P = 0.0075) and 17.7 times higher than in the control group (P = 0.0011). At 180 min after reperfusion, the expression of HSP70 mRNA was 6.8 times higher in the lethal group than in the nonlethal group (P = 0.0007) and 4.3 times higher than in the control group (P = 0.0032). Although the expression of HSP70 mRNA in the nonlethal group was elevated in the early stages of reperfusion, there was no difference between the nonlethal group and the control group (P = 0.0212 at 60 min). ConclusionsThe expression of HSP70 mRNA in leukocytes may be a clinically useful indicator for evaluating pathologic conditions in intestinal IRI.

Dose and timing of injections for effective cyclosporine A pretreatment before renal ischemia reperfusion in mice

BackgroundThere is experimental evidence that lethal ischemia-reperfusion injury (IRI) is largely due to mitochondrial permeability transition pore (mPTP) opening, which can be prevented by cyclosporine A (CsA). The aim of our study is to show that a higher dose of CsA (10 mg/kg) injected just before ischemia or a lower dose of CsA (3 mg/kg) injected further in advance of ischemia (1 h) protects the kidneys and improves mitochondrial function.MethodsAll mice underwent a right unilateral nephrectomy followed by 30 min clamping of the left renal artery. Mice in the control group did not receive any pharmacological treatment. Mice in the three groups treated by CsA were injected at different times and with different doses, namely 3 mg/kg 1 h or 10 min before ischemia or 10 mg/kg 10 min before ischemia. After 24 h of reperfusion, the plasma creatinine level were measured, the histological score was assessed and mitochondria were isolated to calculate the calcium retention capacity (CRC) and level of oxidative phosphorylation.ResultsMortality and renal function was significantly higher in the CsA 10 mg/kg-10 min and CsA 3mg/kg-1 h groups than in the CsA 3mg/kg-10 min group. Likewise, the CRC was significantly higher in the former two groups than in the latter, suggesting that the improved renal function was due to a longer delay in the opening of the mPTP. Oxidative phosphorylation levels were also higher 24 h after reperfusion in the protected groups.ConclusionsOur results suggest that the protection afforded by CsA is likely limited by its availability. The dose and timing of the injections are therefore crucial to ensure that the treatment is effective, but these findings may prove challenging to apply in practice.

A novel recombinant antibody specific to full-length stromal derived factor-1 for potential application in biomarker studies.

BackgroundStromal derived factor-1α (SDF-1α/CXCL12) is a chemokine that is up-regulated in diseases characterised by tissue hypoxia, including myocardial infarction, ischaemic cardiomyopathy and remote ischaemic conditioning (RIC), a technique of cyclical, non-injurious ischaemia applied remote from the heart that protects the heat from lethal ischaemia-reperfusion injury. Accordingly, there is considerable interest in SDF-1α as a potential biomarker of such conditions. However, SDF-1α is rapidly degraded and inactivated by dipeptidyl peptidase 4 and other peptidases, and the kinetics of intact SDF-1α remain unknown.Methods & resultsTo facilitate investigation of full-length SDF-1α we established an ELISA using a novel recombinant human antibody we developed called HCI.SDF1. HCI.SDF1 is specific to the N-terminal sequence of all isoforms of SDF-1 and has a comparable KD to commercially available antibodies. Together with a detection antibody specific to the α-isoform, HCI.SDF1 was used to specifically quantify full-length SDF-1α in blood for the first time. Using RIC applied to the hind limb of Sprague-Dawley rats or the arms of healthy human volunteers, we demonstrate an increase in SDF-1α using a commercially available antibody, as previously reported, but an unexpected decrease in full-length SDF-1α after RIC in both species.ConclusionsWe report for the first time the development of a novel recombinant antibody specific to full-length SDF-1. Applied to RIC, we demonstrate a significant decrease in SDF-1α that is at odds with the literature and suggests a need to investigate the kinetics of full-length SDF-1α in conditions characterised by tissue hypoxia.

Small interfering RNA targeting TNF-α gene significantly attenuates renal ischemia-reperfusion injury in mice.

Tumor necrosis factor-alpha (TNF-α) has been found to be centrally involved in the development of ischemia-reperfusion injury (IRI)-induced inflammation and apoptosis. Knockdown of TNF-α gene using small interfering RNA (siRNA) may protect renal IRI. Renal IRI was induced in mice by clamping the left renal pedicle for 25 or 35 min. TNF-α siRNA was administered intravenously to silence the expression of TNF-α. The therapeutic effects of siRNA were evaluated in terms of renal function, histological examination, and overall survival following lethal IRI. A single systemic injection of TNF-α siRNA resulted in significant knockdown of TNF-α expression in ischemia-reperfusion injured kidney. In comparison with control mice, levels of BUN and serum creatinine were significantly reduced in mice treated with siRNA. Pathological examination demonstrated that tissue damage caused by IRI was markedly reduced as a result of TNF-α siRNA treatment. Furthermore, survival experiments showed that nearly 90% of control mice died from lethal IRI, whereas more than 50% of siRNApretreated mice survived until the end of the eight-day observation period. We have demonstrated for the first time that silencing TNF-α by specific siRNA can significantly reduce renal IRI and protect mice against lethal kidney ischemia, highlighting the potential for siRNA-based clinical therapy.

Therapeutic Potential of Heme Oxygenase 1 in Ischemia Reperfusion Injury

Ischemia/reperfusion injury is a reaction occurring after successful treatment of an acute myocardial infarction or in the setting of solid organ transplantation. After successful reperfusion of a previously occluded vessel or a transplanted organ, an additional loss of otherwise vital cells may occur, the so-called lethal ischemia-reperfusion injury. This lethal reperfusion injury is based on rapid tissue oxygenation, leading to a release of reactive oxygen species (ROS) and inducing oxidative stress, endothelial cell activation and inflammation. Experimentally the reperfusion injury can be attenuated via ROS-scavenging, vessel stabilizing and anti-inflammatory interventions. Cytoprotective genes, such as heme oxygenase-1 (HO-1), offer a therapeutic approach to address this problem. Therefore, this review will focus on the beneficial effects of HO-1 in ischemia/reperfusion injury.

Stromal derived factor 1α: A chemokine that delivers a two-pronged defence of the myocardium

Alleviating myocardial injury associated with ST elevation myocardial infarction is central to improving the global burden of coronary heart disease. The chemokine stromal cell-derived factor 1α (SDF-1α) has dual potential benefit in this regard. Firstly, SDF-1α is up-regulated in experimental and clinical studies of acute myocardial infarction (AMI) and regulates stem cell migration to sites of injury. SDF-1α delivery to the myocardium after AMI is associated with improved stem cell homing, angiogenesis, and left ventricular function in animal models, and improvements in heart failure and quality of life in humans. Secondly, SDF-1α may have a role in remote ischaemic conditioning (RIC), the phenomenon whereby non-lethal ischaemia–reperfusion applied to an organ or tissue remote from the heart protects the myocardium from lethal ischaemia–reperfusion injury (IRI). SDF-1α is increased in the serum of rats subjected to RIC and protects against myocardial IRI in ex vivo studies. Despite these potential pleiotropic effects, a limitation of SDF-1α is its short plasma half-life due to cleavage by dipeptidyl peptidase-4 (DPP-4). However, DPP-4 inhibitors increase the half-life of SDF-1α by preventing its degradation and are also protective against lethal IRI. In summary, SDF-1 potentially delivers a ‘two-pronged’ defence of the myocardium: acutely protecting it from IRI while simultaneously stimulating repair by recruiting stem cells to the site of injury. In this article we examine the evidence for acute and chronic cardioprotective roles of SDF-1α and discuss potential therapeutic manipulations of this mechanism with DPP-4 inhibitors to protect against lethal tissue injury in the clinical setting.

Powerful Protection Against Renal Ischemia Reperfusion Injury by T Cell–Specific NF-κB Inhibition

NF-κB plays a key role in ischemia reperfusion injury (IRI). Systemic inhibition of NF-κB by various methods has been proven to ameliorate IRI. However, NF-κB is also responsible for tissue protection against IRI. Systemic NF-κB inhibition may not be the optimal way for preventing IRI because of its complex roles. T cells are essential in mediating IRI. NF-κB is an important molecule during T cell activation. It is not clear the effect of T cell-specific NF-κB inhibition on IRI. We aimed to study the effect of T cell-specific NF-κB inhibition on renal IRI in IκBαΔN-Tg mice. We also compared the different effects between T cell-specific and systemic NF-κB inhibition on IRI. Renal IRI was induced by left renal pedicle clamping for 60 or 80 min in wild-type, ursolic acid-treated or IκBαΔN-Tg mice. Renal function, histologic examination and overall survival after lethal IRI was evaluated in each group. Serum creatinine, BUN, and pathologic damage were all reduced in IκBαDN-Tg mice and ursolic acid-treated mice than those in the control group. All the above indexes were improved better in IκBαDN-Tg mice than those in ursolic acid-treated mice. The survival rate of IκBαDN-Tg mice was higher than that of ursolic acid-treated mice after lethal kidney ischemia reperfusion injury. Immunohistochemistry showed a significant reduced CD4+ T cells and neutrophil infiltration in IκBαDN-Tg mice. T cell-specific NF-κB inhibition provides powerful protective effect against renal IRI.

Cardiac fibroblasts protect cardiomyocytes against lethal ischemia–reperfusion injury

Roles of cardiac fibroblasts (CFs) in the regulation of myocardial structure and function have been emphasized in the last decade. Their implications in pathophysiological aspects of chronic heart diseases such as myocardial remodeling and fibrosis are now well established; however their contribution to the acute phase of ischemia–reperfusion injury still remains elusive. We hypothesized that CF may contribute to cardiomyocyte (CM) protection against ischemia–reperfusion injuries. Experiments performed on isolated neonatal rat CF and CM demonstrated that the presence of CF in co-cultures increases CM viability (58±2% versus 30±2% in control) against hypoxia–reoxygenation injury, in a paracrine manner. It was confirmed by a similar effect of hypoxic CF secretome alone on CM viability (51±9% versus 31±4% in untreated cells). These findings were corroborated by in vivo experiments in a mice model of myocardial infarction in which a 25% infarct size reduction was observed in CF secretome treated mice compared to control. Tissue inhibitor of metalloproteinases-1 (TIMPs-1) alone, abundantly detected in CF secretome, was able to decrease CM cell death (35%) and experiments with pharmacological inhibitors of PI3K/Akt and ERK1/2 pathways provided more evidence that this paracrine protection is partly mediated by these signaling pathways. In vivo experiments strengthened that TIMP-1 alone was able to decrease infarct size (37%) and were validated by depletion experiments demonstrating that CF secretome cardioprotection was abolished by TIMP-1 depletion. Our data demonstrated for the first time that CFs participate in cardioprotection during the acute phase of ischemia–reperfusion via a paracrine pathway involving TIMP-1.

Endoplasmic reticulum stress contributes to heart protection induced by cyclophilin D inhibition

Preventing cyclophilin D (cypD) translocation to the inner mitochondrial membrane can limit lethal reperfusion injury through the inhibition of the opening of the mitochondrial permeability transition pore. Inhibition or loss of function of cypD may also result into an endoplasmic reticulum (ER) stress that has been shown to alter cell survival. We therefore questioned whether ER stress might play a role in the protection induced by CypD deficiency or inhibition. CypD-KO and NIM811 (a CypD inhibitor)-treated mice were subjected to a prolonged ischemia-reperfusion (I/R). Area at risk and infarct size was measured using blue dye and triphenyltetrazolium chloride staining. ER stress markers were measured in the hearts during the reperfusion phase. As expected, cypD-KO mice exhibited a decreased infarct size when compared to wild-type mice (8 ± 1 vs. 20 ± 4% of left ventricular weight; p < 0.01). CypD-deficient mice displayed an increased expression of ER stress proteins such as eukaryotic initiation factor 2α (eIF2α) or glucose regulated protein 78 (Grp78 or Bip). The ER stress inhibitor TUDCA prevented the infarct size reduction afforded by the loss of cypD function (mean infarct size averaged 21 ± 4% of LV weight, p < 0.01 vs. cypD-KO). Similar results were obtained when NIM811, an analog of cyclosporine A, was used to pharmacologically (instead of genetically) inhibit cypD function. This study suggests that the ER stress induced by the inhibition of cypD function plays a key role in protecting the heart against lethal ischemia-reperfusion injury.

The Emerging Application of Remote Ischemic Conditioning in the Clinical Arena

Remote ischemic conditioning (RIC) is an intervention, in which intermittent episodes of ischemia and reperfusion in an organ or tissue distant from the target organ requiring protection, provide armour against lethal ischemia-reperfusion injury. Although the exact mechanisms underlying the protection mediated through RIC have not been clearly established, the release of humoral factors and the activation of neural pathways have been implicated. There is now clinical evidence suggesting that this form of protection can be induced by a simple, noninvasive, and cost-effective procedure such as inflation and deflation of a blood pressure cuff and that this intervention provides increased organ protection in a variety of clinical scenarios, for example, in myocardial infarction. Here we provide an overview of the history and evolution of RIC, the potential mechanisms underlying its protective effects, and published randomized clinical trials in cardiovascular procedures.

Prevention of lethal murine pancreas ischemia reperfusion injury is specific for tetrahydrobiopterin

SummaryTetrahydrobiopterin has been shown to efficiently abrogate ischemia reperfusion injury (IRI). However, it is unclear, whether its beneficial action relies on cofactor activity of one of the five known tetrahydrobiopterin-dependent reactions or on its antioxidative capacity. We therefore compared tetrahydrobiopterin with the pterin derivate tetrahydroneopterin (similar biochemical properties, but no nitric oxide synthase cofactor activity) and the antioxidants vitamin C and 5-methyltetrahydrofolate. Donor mice were pretreated with tetrahydrobiopterin, tetrahydroneopterin, vitamin C, or 5-methyltetrahydrofolate. Pancreatic grafts were subjected to 16-h cold ischemia time and implanted in syngeneic recipients. Untreated and nontransplanted animals served as controls. Following 2-h reperfusion, microcirculation was analyzed by intravital fluorescence microscopy. Graft damage was assessed by histology and nitrotyrosine immunostaining, and tetrahydrobiopterin levels were determined by HPLC. Recipient survival served as ultimate readout. Prolonged cold ischemia time resulted in microcirculatory breakdown. Only tetrahydrobiopterin pretreatment succeeded to preserve the capillary net, whereas all other compounds showed no beneficial effects. Along with increased intragraft tetrahydrobiopterin levels during recovery and implantation, only tetrahydrobiopterin pretreatment led to significant reduction of IRI-related parenchymal damage enabling recipient survival. These results show a striking superiority of tetrahydrobiopterin in preventing lethal IRI compared with related compounds and suggest nitric oxide synthases as treatment target.

Intracellular Signaling MAPK Pathway After Cerebral Ischemia–Reperfusion Injury

The MAPK/ERK/p38 are signal transduction pathways that couple intracellular responses to the external stimuli. Contrary to ERK protein which is part of the survival route, presence of p38 could have an impact on cell injury. Tolerance induced by ischemic preconditioning (IPC) is a phenomenon of tissue adaptation, which results in increased tolerance to lethal ischemia-reperfusion injury (IRI). Paper describes changes in MAPK protein pathways after brain IPC. Ischemia was induced by 4-vessels occlusion and rats were preconditioned by sub-lethal ischemia. Western blot and immunohistochemistry identified ERK/p38 proteins in injured areas. The highest level of the pERK was detected at 24 h in IPC groups. A contrary pattern of MAPK/p38 activation was observed in this group, where the lowest level of p38 was displayed at 24 h after ischemia. This suggests that the MAPK signal transduction might have a potential role in tissues response subjected to IRI and in the phenomenon of tolerance.

Activation of the ERK1/2 pathway by the CaMEK gene via adeno-associated virus serotype 9 in cardiomyocytes

Extracellular signal-regulated kinase (ERK1/2) is one of the mitogen-activated protein kinases, key components of the reperfusion injury salvage kinase pathway, which plays an important role in protecting the myocardium from lethal ischemia-reperfusion injury. Constitutive activation of the mitogen-activated protein kinase kinase 1 (CaMEK) can promote ERK1/2 expression, which is thereby expected to exert protective action on the heart against ischemia-reperfusion injury. The adeno-associated virus serotype 9 vector (AVV9) is a novel tool for gene therapies targeting human diseases owing to its nonpathogenic capability for transducing nondividing cells and its long-term transgene expression. We used a recombinant AAV9 vector to deliver the CaMEK gene into cardiomyocytes and assessed whether AAV9 vector-mediated CaMEK gene transfection could enhance the long-term expression and activity of ERK1/2. Our observations suggest that AAV9-mediated gene expression is preferentially restricted to cardiomyocytes and that mediated CaMEK gene transfection enhanced the expression of ERK1/2 phosphorylation and consequently upregulated the expression of downstream components of ERK1/2 and its transcription factors.

Remote Ischemic Conditioning: From Bench to Bedside

Remote ischemic conditioning (RIC) is a therapeutic strategy for protecting organs or tissue against the detrimental effects of acute ischemia-reperfusion injury (IRI). It describes an endogenous phenomenon in which the application of one or more brief cycles of non-lethal ischemia and reperfusion to an organ or tissue protects a remote organ or tissue from a sustained episode of lethal IRI. Although RIC protection was first demonstrated to protect the heart against acute myocardial infarction, its beneficial effects are also seen in other organs (lung, liver, kidney, intestine, brain) and tissues (skeletal muscle) subjected to acute IRI. The recent discovery that RIC can be induced non-invasively by simply inflating and deflating a standard blood pressure cuff placed on the upper arm or leg, has facilitated its translation into the clinical setting, where it has been reported to be beneficial in a variety of cardiac scenarios. In this review article we provide an overview of RIC, the potential underlying mechanisms, and its potential as a novel therapeutic strategy for protecting the heart and other organs from acute IRI.

Myocardial postconditioning: Next step to cardioprotection

Myocardial ischemia is a condition in which lack of blood flow to the cardiac muscle occurs resulting in deficient oxygen and nutrient supply to the heart. The restoration of blood flow to an organ or tissue is termed reperfusion. Brief episodes of ischemia and reperfusion given after prolonged ischemia and at the onset of reperfusion denotes postconditioning. Myocardial postconditioning is a phenomenon in which myocardium from lethal ischemia-reperfusion injury is protected. However, numerous experimental studies reveal that the cardioprotective effects of postconditioning are suppressed in various pathological states. This review critically discusses the mechanisms involved in the cardioprotective effects of postconditioning and factors affecting the cardioprotective potential of myocardial postconditioning.

014 Atorvastatin protects human myocardium from lethal ischaemia-reperfusion injury by activating the risk pathway

Background Previous animal studies have demonstrated that acute treatment with atorvastatin at reperfusion reduces myocardial infarct size by up-regulating the Akt and Erk1/2 components of the Reperfusion Injury Salvage Kinase (RISK) pathway. Whether this cardioprotective strategy applies to human cardiac tissue is unknown. Objective To determine whether atorvastatin, administered at reperfusion, protects human atrial tissue from ischaemia-reperfusion injury (IRI) via activation of the RISK pathway. Methods Local UCLH/UCL Ethical Committee approval was granted. Human atrial trabeculae were isolated from right atrial appendage tissue harvested from consenting adult patients undergoing elective cardiac surgery. The atrial trabeculae were subjected to 90 min of hypoxia followed by 120 min reoxygenation as simulated ischaemia-reperfusion injury. Following this, recovery of contractile function was determined and compared to baseline. Atrial trabeculae were randomised to the following groups: 1. Control (N=14); 2. Hypoxic preconditioning positive control (N=4); 3. Atorvastatin (25 μM) at reperfusion (N=9); 4. Atorvastatin plus UO126 (10 μM), a MEK1/2-Erk1/2 inhibitor (N=4); 5. Atorvastatin plus LY294002 (15 μM), a PI3K-Akt inhibitor (N=4); 6. Atorvastatin plus L-NAME (100 μM), a non-specific nitric oxide synthase inhibitor (N=7); 7. Atorvastatin plus 1400W (5μM), a specific inducible nitric oxide synthase inhibitor (N=5); 8. Inhibitor-only controls (N=18). Results Control atrial trabeculae recovered 37.5±1.6% of baseline contractile function following simulated IRI. Treatment with atorvastatin 25 μM at reperfusion significantly improved the recovery of contractile function (61.1±3.8%, p Conclusions Atorvastatin, administered at reperfusion, protects human atrial muscle from simulated IRI via activation of the Akt and Erk1/2 components of the RISK pathway and nitric oxide synthase.

Small Interfering RNA Targeting RelB Protects Against Renal Ischemia-reperfusion Injury

Nuclear factor kappaB (NF-kappaB) has been found to be critical to the pathogenesis of renal ischemia-reperfusion injury (IRI). Using small interfering RNA (siRNA) to silence the expression of RelB, a component of the transcription factors Rel/nuclear factor kappaB, may protect renal IRI. Here, we report an siRNA-based treatment of preventing IRI. Renal IRI was induced in mice by clamping the left renal pedicle for 25 or 35 min. The therapeutic effects of siRNA were evaluated in renal function, histologic examination, and overall survival after lethal IRI. A single injection of RelB siRNA resulted in knockdown of renal RelB expression. In comparison with control mice, levels of blood urea nitrogen and serum creatinine were significantly decreased in mice treated with siRNA. Pathologic examination demonstrated that tissue injury caused by IRI was markedly reduced as a result of RelB siRNA treatment. Additionally, with RelB siRNA treatment, immunohistochemistry showed a significant attenuation of tumor necrosis factor-alpha expression. Furthermore, survival experiments revealed that more than 90% of control mice died from lethal IRI, whereas 80% of siRNA-pretreated mice survived until the end of the 8-day observation period. Silencing RelB, using siRNA, can significantly attenuate IRI-induced renal dysfunction and protect mice against lethal kidney ischemia, highlighting the potential for siRNA-based clinical therapy.