Protecting the ischaemic and reperfused myocardium in acute myocardial infarction: distant dream or near reality?

The cardioprotection granted by metoprolol is restricted to its administration prior to coronary reperfusion

BACKGROUND

Myocardial infarct size is a strong predictor of cardiovascular events. Intravenous metoprolol before coronary reperfusion has been shown to reduce infarct size; however, it is unknown whether oral metoprolol initiated early after reperfusion, as clinical guidelines recommend, is similarly cardioprotective. We compared the extent of myocardial salvage associated with intravenous pre-reperfusion-metoprolol administration in comparison with oral post-reperfusion-metoprolol or placebo. We also studied the effect on suspected markers of reperfusion injury.

METHODS

Thirty Yorkshire-pigs underwent a reperfused myocardial infarction, being randomized to pre-reperfusion-metoprolol, post-reperfusion-metoprolol or placebo. Cardiac magnetic resonance imaging was performed in eighteen pigs at day 3 for the quantification of salvaged myocardium. The amounts of at-risk and infarcted myocardium were quantified using T2-weighted and post-contrast delayed enhancement imaging, respectively. Twelve animals were sacrificed after 24h for reperfusion injury analysis.

RESULTS

The pre-reperfusion-metoprolol group had significantly larger salvaged myocardium than the post-reperfusion-metoprolol or the placebo groups (31 ± 4%, 13 ± 6%, and 7 ± 3% of myocardium at-risk respectively). Post-mortem analyses suggest lesser myocardial reperfusion injury in the pre-reperfusion-metoprolol in comparison with the other 2 groups (lower neutrophil infiltration, decreased myocardial apoptosis, and higher activation of the salvage-kinase phospho-Akt). Salvaged myocardium and reperfusion injury pair wise comparisons proved there were significant differences between the pre-reperfusion-metoprolol and the other 2 groups, but not among the latter two.

CONCLUSIONS

The intravenous administration of metoprolol before coronary reperfusion results in larger myocardial salvage than its oral administration initiated early after reperfusion. If confirmed in the clinical setting, the timing and route of β-blocker initiation could be revisited.

Thallium-201 and I-123 beta-methyl iodophenyl-pentadecanoic acid dual isotope single photon emission computed tomography for evaluating reperfusion injury after successful reperfusion therapy

We report a reperfusion injury after rotational coronary atherectomy (RA) in a 66-year-old man with coronary artery disease. Submaximal exercise with thallium-201 single photon emission computed tomography (SPECT) imaging before reperfusion showed partially reversible perfusion defects in the apex and reversible perfusion defects in the anteroseptal area. Thallium-201 and I-123 beta-methyl iodophenyl-pentadecanoic acid (BMIPP) dual isotope SPECT was performed 5 days before and 1 hour after RA, and 1 month after RA. SPECT images at 1 hour after recovery of no reflow phenomenon after RA revealed enlargement of the defect sizes on thallium-201 and BMIPP uptakes in the anteroseptal area including the apex compared with those before RA. The defect size of thallium-201 uptake was progressively improved on 5 hour delayed redistribution imaging and 1 month after reperfusion compared with that of BMIPP uptake. In conclusion, the changes for the worse of thallium-201 uptake and fatty acid metabolism immediately after the no reflow phenomenon may indicate an injured membrane integrity with altered myocardial metabolism rather than myocardial ischemia. Thallium-201 and I-123 BMIPP dual isotope SPECT is useful for evaluating reperfusion injury after successful reperfusion therapy in a patient with acute coronary syndrome.

Role of tumor necrosis factor receptor 1 in sex differences of stem cell mediated cardioprotection

BACKGROUND

Mesenchymal stem cells (MSCs) hold great therapeutic potential for the repair and regeneration of ischemic tissue, possibly through the release of beneficial paracrine factors. Sex differences have been observed in the paracrine function of MSCs. Female stem cells produce lower proinflammatory cytokines and higher levels of growth factors compared with their male counterparts. Ablation of tumor necrosis factor receptor 1 (TNFR1) increases protective growth factor production by male, but not by female, MSCs. We therefore hypothesized the following: (1) that female MSCs would improve myocardial recovery compared with male MSCs after ischemia-reperfusion injury (I/R); and (2) that MSCs isolated from TNFR1 knock out male, but not female, mice, would improve postischemic myocardial recovery compared with their wild type (WT) counterparts.

METHODS

Male adult Sprague-Dawley rat hearts were subjected to I/R by Langendorff isolated heart preparation. The MSCs were harvested from adult mice and cultured under normal conditions. Immediately prior to ischemia, one million MSCs were infused into the coronary circulation. Cardiac functional parameters were recorded continuously.

RESULTS

Pretreatment with MSCs from either sex significantly increased postischemic myocardial recovery as evidenced by improved left ventricular developed pressure, contractility, and rate of relaxation. Infusion with female MSCs was associated with a greater degree of myocardial recovery after I/R compared with male MSCs. The TNFR1 deficiency increased the degree of myocardial recovery associated with male MSCs, but not with female MSCs. No additional cardioprotection was observed when TNFR1 was ablated in female MSCs.

CONCLUSION

Sex differences influence the cardioprotective effects of both WT and TNFR1 ablated MSCs.

In vivo protein transduction: delivery of PEP-1-SOD1 fusion protein into myocardium efficiently protects against ischemic insult

Myocardial ischemia-reperfusion injury is a medical problem occurring as damage to the myocardium following blood flow restoration after a critical period of coronary occlusion. Oxygen free radicals (OFR) are implicated in reperfusion injury after myocardial ischemia. The antioxidant enzyme, Cu, Zn-superoxide dismutase (Cu, Zn-SOD, also called SOD1) is one of the major means by which cells counteract the deleterious effects of OFR after ischemia. Recently, we reported that a PEP-1-SOD1 fusion protein was efficiently delivered into cultured cells and isolated rat hearts with ischemia-reperfusion injury. In the present study, we investigated the protective effects of the PEP-1-SOD1 fusion protein after ischemic insult. Immunofluorescecnce analysis revealed that the expressed and purified PEP-1-SOD1 fusion protein injected into rat tail veins was efficiently transduced into the myocardium with its native protein structure intact. When injected into Sprague-Dawley rat tail veins, the PEP-1- SOD1 fusion protein significantly attenuated myocardial ischemia-reperfusion damage; characterized by improving cardiac function of the left ventricle, decreasing infarct size, reducing the level of malondialdehyde (MDA), decreasing the release of creatine kinase (CK) and lactate dehydrogenase (LDH), and relieving cardiomyocyte apoptosis. These results suggest that the biologically active intact forms of PEP-1-SOD1 fusion protein will provide an efficient strategy for therapeutic delivery in various diseases related to SOD1 or to OFR.

Myocardial protection with enalaprilat in patients unresponsive to ischemic preconditioning during percutaneous coronary intervention

Cardioprotection due to angiotensin enzyme inhibitors is attributed, at least in part, to the inhibition of bradykinin breakdown and the preconditioning effect of the elevated endogenous bradykinin level. We have previously shown that in patients undergoing percutaneous coronary intervention, one 120-second balloon inflation is insufficient to precondition the heart. The objective of the present study was to examine whether the administration of enalaprilat to these patients results in protection. Twenty patients underwent two 120-second coronary artery occlusions separated by a reperfusion interval of 10 min. Ten patients were given 50 µg·min–1 enalaprilat in an intracoronary infusion between the balloon inflations, whereas the others received an infusion of saline. In the latter control patients, there were no significant differences in ST-segment elevation between the consecutive occlusions (peak ST: 1.61 ± 0.17 vs. 1.61 ± 0.16 mV; time to reach 0.5 mV ST elevation: 16 ± 4 vs. 22 ± 7 s; mean ST: 1.03 ± 0.12 vs. 1.02 ± 0.11 mV). In the patients who received enalaprilat before the second balloon inflation, the ST-segment elevation was significantly less pronounced and slower during the second inflation than during the first (peak ST: 1.80 ± 0.18 vs. 1.41 ± 0.19 mV; time to reach 0.5 mV ST elevation: 18 ± 4 vs. 30 ± 4 s; mean ST: 1.04 ± 0.11 vs. 0.85 ± 0.14 mV). We conclude that enalaprilat administered during percutaneous coronary intervention provides protection to patients who do not have a protective response to the initial balloon inflation.

Madecassoside reduces ischemia-reperfusion injury on regional ischemia induced heart infarction in rat

Madecassoside (MA), one of the principle terpenoids in Centella asiatica, has shown protect effect on isolated rat hearts and isolated cardiomyocytes against reperfusion injury in our previous studies. The aim of this study is to investigate if MA also protected against myocardial ischemia-reperfusion injury in vivo. The ischemia infarction model was established in rats. Left ventricular function was monitored during the ischemia-reperfusion period by a multi-channel recorder. After the ischemia-reperfusion process the infarcted areas were assessed. The levels of lactate dehydrogenase (LDH), creatinephosphokinase (CK), malondialdehyde (MDA), super-oxide dismutase (SOD) and C-reactive protein (CRP) in serum were determined. Cardiomyocytic apoptosis was measured by terminal-deoxynucleotidyl transferase mediated nick end labeling (TUNEL) staining. Pre-treatment with MA (50, 10 mg/kg) attenuated myocardial damage characteristic of decreasing infarct size, decreasing LDH and CK release. Activities of SOD were increased and MDA level increased obviously in control group whereas pretreatment with MA blunted the decrease of SOD activity, markedly reduced the level of MDA and the activity of CRP, and relieved myocardial cell apoptosis. These results suggest that MA has the protective effect on myocardial ischemia-reperfusion injury. This protection ability possibly due to its anti-lipid peroxidation, anti-inflammation and anti-apoptosis function and the enhancement of SOD activity.

Prevention of atrial fibrillation following cardiac surgery: basis for a novel therapeutic strategy based on non-hypoxic myocardial preconditioning

Atrial fibrillation is the most common complication of cardiac surgical procedures performed with cardiopulmonary bypass. It contributes to increased hospital length of stay and treatment costs. At present, preventive strategies offer only suboptimal benefits, despite improvements in anesthesia, surgical technique, and medical therapy. The pathogenesis of postoperative atrial fibrillation is considered to be multifactorial. However oxidative stress is a major contributory factor representing the unavoidable consequences of ischemia/reperfusion cycle occurring in this setting. Considerable evidence suggests the involvement of reactive oxygen species (ROS) in the pathogenic mechanism of this arrhythmia. Interestingly, the deleterious consequences of high ROS exposure, such as inflammation, cell death (apoptosis/necrosis) or fibrosis, may be abrogated by a myocardial preconditioning process caused by previous exposure to moderate ROS concentration known to trigger survival response mechanisms. The latter condition may be created by n-3 PUFA supplementation that could give rise to an adaptive response characterized by increased expression of myocardial antioxidant enzymes and/or anti-apoptotic pathways. In addition, a further reinforcement of myocardial antioxidant defenses could be obtained through vitamins C and E supplementation, an intervention also known to diminish enzymatic ROS production. Based on this paradigm, this review presents clinical and experimental evidence supporting the pathophysiological and molecular basis for a novel therapeutic approach aimed to diminish the incidence of postoperative atrial fibrillation through a non-hypoxic preconditioning plus a reinforcement of the antioxidant defense system in the myocardial tissue.

MsrA protects cardiac myocytes against hypoxia/reoxygenation induced cell death

Reactive oxygen species (ROS) are critical in tissue responses to ischemia-reperfusion. The enzyme methionine sulfoxide reductase-A (MsrA) is capable of protecting cells against oxidative damage by reversing damage to proteins caused by methionine oxidation or by decreasing ROS through a scavenger mechanism. The current study employed adenovirus mediated over-expression of MsrA in primary neonatal rat cardiac myocytes to determine the effect of this enzyme in protecting against hypoxia/reoxygenation in this tissue. Cells were transduced with MsrA encoding adenovirus and subjected to hypoxia/reoxygenation. Apoptotic cell death was decreased by greater than 45% in cells over-expressing MsrA relative to cells transduced with a control virus. Likewise total cell death as determined by levels of LDH release was dramatically decreased by MsrA over-expression. These observations indicate that MsrA is protective against hypoxia/reoxygenation stress in cardiac myocytes and point to MsrA as an important therapeutic target for ischemic heart disease.

The antiarrhythmic effect and clinical consequences of ischemic preconditioning

Potentially hazardous short ischemic episodes increase the tolerance of myocardium to ischemia paradoxically. This condition decreases the infarct area markedly caused by a longer duration of coronary occlusion. This phenomenon is known as 'ischemic preconditioning' and its powerful cardioprotective effect has been shown in experimental and clinical studies. Ischemic preconditioning decreases cardiac mortality markedly by preventing the development of left ventricular dysfunction and ventricular and supraventricular arrhythmias after acute myocardial infarction. Ischemia-induced opening of ATP-sensitive potassium channels and synthesis of stress proteins via activation of adenosine, bradykinin and prostaglandin receptors seem to be the possible mechanisms. By understanding the underlying mechanisms of ischemic preconditioning, it may be possible to develop new pharmacologic agents that cause ischemic preconditioning with antiischemic and antiarrhythmic properties without causing myocardial ischemia.

Cyclic GMP and protein kinase-G in myocardial ischaemia-reperfusion: opportunities and obstacles for survival signaling

It is clear that multiple signalling pathways regulate the critical balance between cell death and survival in myocardial ischaemia-reperfusion. Recent attention has focused on the activation of survival or salvage kinases, particularly during reperfusion, as a common mechanism of many cardioprotective interventions. The phosphatidyl inositol 3'-hydroxy kinase/Akt complex (PI3K/Akt) and p42/p44 mitogen-activated protein kinase cascades have been widely promoted in this respect but the cyclic guanosine 3',5'-monophosphate/cGMP-dependent protein kinase (cGMP/PKG) signal transduction cassette has been less systematically investigated as a survival cascade. We propose that activation of the cGMP/PKG signalling pathway, following activation of soluble or particulate guanylate cyclases, may play a pivotal role in survival signalling in ischaemia-reperfusion, especially in the classical preconditioning, delayed preconditioning and postconditioning paradigms. The resurgence of interest in reperfusion injury, largely as a result of postconditioning-related research, has confirmed that the cGMP/PKG pathway is a pivotal salvage mechanism in reperfusion. Numerous studies suggest that the infarct-limiting effects of preconditioning and postconditioning, exogenously donated nitric oxide (NO), natriuretic peptides, phosphodiesterase inhibitors, and other diverse drugs and mediators such as HMG co-A reductase inhibitors (statins), Rho-kinase inhibitors and adrenomedullin, whether given before and during ischaemia, or specifically at the onset of reperfusion, may be mediated by activation or enhancement of the cGMP pathway, either directly or indirectly via endogenous NO generation downstream of PI3K/Akt. Putative mechanisms of protection include PKG regulation of Ca(2+) homeostasis through the modification of sarcoplasmic reticulum Ca(2+) uptake mechanisms, and PKG-induced opening of ATP-sensitive K(+) channels during ischaemia and/or reperfusion. At present, significant technical obstacles in defining the precise roles played by cGMP/PKG signalling include the heavy reliance on pharmacological PKG inhibitors of uncertain selectivity, difficulties in determining PKG activity in intact tissue, and the growing recognition that intracellular compartmentalisation of the cGMP pool may contribute markedly to the nucleotide's biological actions and biochemical determination. Overall, the body of experimental evidence suggests that cGMP/PKG survival signalling ameliorates irreversible injury associated with ischaemia-reperfusion and may be a tractable therapeutic target.

Potent mitochondria-targeted peptides reduce myocardial infarction in rats

OBJECTIVE

Previously, we demonstrated that a novel opiate peptide, 2',6'-dimethyl-tyrosine-D-Arg-Phe-Lys-NH2, provided cardioprotection against myocardial stunning in vivo. We subsequently showed that this peptide targeted mitochondria and can scavenge reactive oxygen species. The objective of this study was to determine the role of opioid versus antioxidant activity in cardioprotection.

METHODS

We compared two mitochondria-targeted peptide analogs that lacked opioid activity: SS-31 (D-Arg-2',6'-dimethyl-tyrosine-Lys-Phe-NH2) and SS-20 (Phe-D-Arg-Phe-Lys-NH2). They differ in that only SS-31 has scavenging ability. Rats (n=8/group) were randomized to SS-31, SS-20 or placebo. The drugs (3 mg/kg) or saline was administered intraperitoneally 30 min before ligation of the left anterior descending artery for 60 min, and another dose given intraperitoneally 5 min before reperfusion for 60 min. Study endpoints included myocardial infarct size, cardiac arrhythmia and myocardial lipid peroxidation.

RESULTS

The area at risk was similar among the groups. The infarct area/area at risk, however, was significantly smaller in the treatment groups (53.9+/-1.1% in SS-31 group, 47.1+/-1.4% in SS-20 group, versus 59.9+/-1% in the controls, P<0.01). Lipid peroxidation was significantly reduced by both SS-31 and SS-20 treatment. Arrhythmia occurred only during the early period of coronary occlusion and was less frequent and less severe in the peptide treatment groups than in the controls (Lambeth score 5 points, 3 points, versus 13 points in the controls, P<0.05).

CONCLUSIONS

This study shows that pretreatment with both SS-31 and SS-20 significantly reduced myocardial lipid peroxidation and infarct size in ischemia-reperfusion injury, and suggests that the cardioprotective properties of 2',6'-dimethyl-tyrosine-D-Arg-Phe-Lys-NH2 was primarily mediated by its antioxidant properties. As SS-20 does not scavenge reactive oxygen species, it most likely reduces reactive oxygen species production during ischemia-reperfusion.

Fibroblast growth factor-2 and cardioprotection

Boosting myocardial resistance to acute as well as chronic ischemic damage would ameliorate the detrimental effects of numerous cardiac pathologies and reduce the probability of transition to heart failure. Experimental cardiology has pointed to ischemic and pharmacological pre- as well as post-conditioning as potent acute cardioprotective manipulations. Additional exciting experimental strategies include the induction of true regenerative and/or angiogenic responses to the damaged heart, resulting in sustained structural and functional beneficial effects. Fibroblast growth factor-2 (FGF-2), an endogenous multifunctional protein with strong affinity for the extracellular matrix and basal lamina and well-documented paracrine, autocrine and intracellular modes of action, has been shown over the years to exert acute and direct pro-survival effects, irrespectively of whether it is administered before, during or after an ischemic insult to the heart. FGF-2 is also a potent angiogenic protein and a crucial agent for the proliferation, expansion, and survival of several cell types including those with stem cell properties. Human clinical trials have pointed to a good safety record for this protein. In this review, we will present a case for the low molecular weight isoform of fibroblast growth factor-2 (lo-FGF-2) as a very promising therapeutic agent to achieve powerful acute as well as sustained benefits for the heart, due to its cytoprotective and regenerative properties.

12‐Lipoxygenase‐derived eicosanoids protect against myocardial ischemia/reperfusion injury via activation of neuronal TRPV1

Recent evidence implicates the neuronal transient receptor potential vanilloid receptor 1 (TRPV1), expressed on sensory C-fibers, as playing an important endogenous protective role in limiting the damaging effects of myocardial I/R injury. In neurons the 12-lipoxygenase (12-LOX) arachidonic acid (AA) metabolite, 12(S)-HpETE, has been proposed as the endogenous ligand for TRPV1. However, whether 12(S)-HpETE underlies TRPV1 channel activation during I/R is unknown. Treatment of isolated Langendorff rat hearts with a 12-LOX/AA cocktail significantly attenuated I/R injury (approximately 40% inhibition of infarct size), an effect reversed by the 12-LOX inhibitor baicalein or after chemical desensitization of local sensory C-fiber afferents using capsaicin. Both 12(S)-HpETE and AA caused dose-dependent coronary vasodilatation (approximately EC50s of 6x10(-19) and 1x10(-7), respectively) that was profoundly suppressed by the TRPV1 antagonist capsazepine, in hearts of TRPV1 knockout mice compared with wild-type mice, or by treatment with a CGRP antagonist. In addition, I/R itself stimulates up-regulation of TRPV1 expression in both the cell bodies located within the dorsal root ganglia and locally within the myocardium. Together, our data identify a novel 12-LOX/AA/TRPV1 pathway activated and up-regulated during I/R injury, providing an endogenous damage-limiting mechanism whose targeting may prove useful in treating myocardial infarction.

Inflammation, proinflammatory mediators and myocardial ischemia-reperfusion Injury

Ischemic myocardium must be reperfused to terminate the ischemic event; otherwise the entire myocardium involved in the area at risk will not survive. However, there is a cost to reperfusion that may offset the intended clinical benefits of minimizing infarct size, postischemic endothelial and microvascular damage, blood flow defects, and contractile dysfunction. There are many contributors to this reperfusion injury. Targeting only one factor in the complex web of reperfusion injury is not effective because the untargeted mechanisms induce injury. An integrated strategy of reducing reperfusion injury in the catheterization laboratory involves controlling both the conditions and the composition of the reperfusate. Mechanical interventions such as gradually restoring blood flow or applying postconditioning may be used independently in or conjunction with various cardioprotective pharmaceuticals in an integrated strategy of reperfusion therapeutics to reduce postischemic injury.

Impaired perfusion after myocardial infarction is due to reperfusion-induced deltaPKC-mediated myocardial damage

OBJECTIVE

To improve myocardial flow during reperfusion after acute myocardial infarction and to elucidate the molecular and cellular basis that impedes it. According to the AHA/ACC recommendation, an ideal reperfusion treatment in patients with acute myocardial infarction (AMI) should not only focus on restoring flow in the occluded artery, but should aim to reduce microvascular damage to improve blood flow in the infarcted myocardium.

METHODS

Transgenic mouse hearts expressing the deltaPKC (protein kinase C) inhibitor, deltaV1-1, in their myocytes only were treated with or without the deltaPKC inhibitor after ischemia in an ex vivo AMI model. deltaV1-1 or vehicle was also delivered at reperfusion in an in vivo porcine model of AMI. Microvascular dysfunction was assessed by physiological and histological measurements.

RESULTS

deltaPKC inhibition in the endothelial cells improved myocardial perfusion in the transgenic mice. In the porcine in vivo AMI model, coronary flow reserve (CFR), which is impaired for 6 days following infarction, was improved immediately following a one-minute treatment at the end of the ischemic period with the deltaPKC-selective inhibitor, deltaV1-1 ( approximately 250 ng/kg), and was completely corrected by 24 h. Myocardial contrast echocardiography, electron microscopy studies, and TUNEL staining demonstrated deltaPKC-mediated microvascular damage. epsilonPKC-induced preconditioning, which also reduces infarct size by >60%, did not improve microvascular function.

CONCLUSIONS

These data suggest that deltaPKC activation in the microvasculature impairs blood flow in the infarcted tissue after restoring flow in the occluded artery and that AMI patients with no-reflow may therefore benefit from treatment with a deltaPKC inhibitor given in conjunction with removal of the coronary occlusion.

Corydalis yanhusuo rhizoma extract reduces infarct size and improves heart function during myocardial ischemia/reperfusion by inhibiting apoptosis in rats

The aim of the present investigation was to evaluate the effect of an extract from Corydalis yanhusuo W.T., a Chinese herbal medicine, on ischemia/reperfusion (I/R) injury and to determine the mechanism(s) involved. In rats, the left anterior descending (LAD) coronary artery was occluded for 30 min and then reperfused for 6 h. 0.5% carboxymethyl cellulose sodium was used as a vehicle (I/R control group) and Corydalis yanhusuo rhizoma extract (I/R + CY 200, 100 mg/kg groups) were given. Infarct size and hemodynamic parameters were measured. Apoptosis was detected quantitatively by the terminal transferase dUTP nick end-labeling (TUNEL) method and confirmed by DNA laddering on agarose gel. The expression of anti-apoptotic Bcl-2 and pro-apoptotic Bax proteins was visualized by western blot analysis. In contrast to the I/R control group, administration with CY 200 mg/kg resulted in a significant reduction in the infarct size and an improvement in heart function as evidenced by higher LVSP and +/-dp/dtmax. TUNEL-positive cells in the ischemic myocardium were also significantly reduced in the I/R + CY 200, 100 mg/kg groups, consistent with little DNA laddering in these two groups. Furthermore, greater Bcl-2 and attenuated Bax expression was found in the CY treated rats. These results suggest that the protective effect of Corydalis yanhusuo on myocardial I/R injury is closely associated with the inhibition of myocardial apoptosis through modulation of the Bcl-2 family.

Postconditioning fails to prevent radial artery endothelial dysfunction induced by ischemia and reperfusion: evidence from a human in vivo study

Animal studies have shown that, as compared with unrestricted reperfusion, exposure to brief periods of controlled ischemia (postconditioning) at the end of a prolonged ischemia reduces the extent of tissue damage. We set out to test whether postconditioning can prevent endothelial dysfunction induced by ischemia and reperfusion in a human in vivo model. Ten healthy young non-smoking volunteers were enrolled in this cross-over, controlled, investigator-blinded study. Subjects were exposed to 15 min of forearm ischemia followed by either unrestricted reperfusion or postconditioning (3 periods of 20 s of ischemia separated by 10 s of reperfusion). Endothelium-dependent flow-mediated dilation (FMD) was measured at the level of the radial artery before and after ischemia (with or without postconditioning). Forearm ischemia blunted FMD in both study visits (unrestricted reperfusion visit: before ischemia, 7.7% ± 1.3%; after ischemia, 2.5% ± 1.4%; and postconditioning visit: before, 7.3% ± 1.2%; after, 2.6 ± 1.6%; P < 0.05 for both, P = not significant (NS) between visits). In contrast with data from animal studies, postconditioning (20 s ischemia – 10 s reperfusion repeated 3 times) does not limit post-ischemic endothelial dysfunction in this human in vivo model. Further human studies are necessary to evaluate other reperfusion protocols in an attempt to limit post-ischemic tissue damage.

Rationale of the REPARATOR study: A randomised trial with serial cardiac MRI follow-up testing the ability of atorvastatin to reduce reperfusion damage after primary PCI for acute MI

The REPARATOR study is a multicentre clinical trial in which the effect of 80 mg atorvastatin on microvascular (re)perfusion and late ventricular remodelling, and infarct size in patients presenting with an acute ST-elevation myocardial infarction is studied. Primary endpoint is end-systolic volume index at three months measured by quantitative cine magnetic resonance imaging (MRI). Secondary endpoints are cardiac MI (CMR) measurements of global and regional left ventricular function, MRI measurements of infarct size on admission, one week and three months as well as changes between MRI investigations, biochemical markers of infarct size, blush grade, and TIMI frame count. A total of 50 patients will be enrolled. Including three months follow-up, the study will last for six months.

Attenuation of post-ischemia reperfusion injury by thaliporphine and morphine in rat hearts

Pretreatment with thaliporphine before ischemia affords cardioprotective effects against reperfusion injury via antioxidant activity. This study evaluated whether thaliporphine administered at a certain period after myocardial ischemia conferred the same cardioprotection and assessed its possible new mechanism. The left main coronary artery of anaesthetized rats was occluded for 1 h and then reperfused for 2 h. Thaliporphine was administered at 10 min before reperfusion. Controls received saline only. Morphine, a nonselective opioid receptor agonist, was used as reference compound at 0.3 mg/kg. Thaliporphine at 0.05 and 0.5 mg/kg were found to reduce the infarct size. Recovery of cardiac function was higher in thaliporphine (0.5 mg/kg) group, as assessed by a significant improvement in the rates of pressure development (+dp/dt (max)). This compound also reduced plasma creatine kinase and cardiac MPO activity. These protective effects afforded by thaliporphine were diminished by the opioid receptor antagonists (naloxone or naltrexone) and by the mitochondrial K(ATP) blocker 5HD. In comparison, morphine reduced infarct size and MPO activity in the myocardium but produced slightly improvement in cardiac function after ischemia-reperfusion. These results demonstrate that reperfusion therapy with thaliporphine protect cardiac injury through further mechanism via activation of opioid receptor and opening of mitochondrial K(ATP) channels as morphine but with stronger activity.

Activation of an efferent cholinergic pathway produces strong protection against myocardial ischemia/reperfusion injury in rats

OBJECTIVE

A vagus nerve-mediated, brain cholinergic protective mechanism activated by melanocortin peptides is operative in conditions of circulatory shock; moreover, there is anatomical evidence of dual vagal-cardiac efferent pathways in rats, which could play different roles in controlling heart function. Therefore, we investigated the role and functional mechanism of such vagal efferent pathway(s) in an experimental model of ischemic heart disease.

DESIGN

Randomized experimental study.

SETTING

Research laboratory.

SUBJECTS

Adult Wistar rats of either sex.

INTERVENTIONS

After bilateral cervical vagotomy (with or without pretreatment with atropine), efferent vagal fibers were electrically stimulated in rats subjected to coronary artery occlusion (5 mins) followed by reperfusion (5 mins). Other rats (intact, vagotomized, or pretreated with atropine) were treated with nanomolar doses of melanocortin peptides.

MEASUREMENTS AND MAIN RESULTS

Electrical stimulation of efferent vagal fibers (5 V, 2 m secs, 1-9 Hz, for the whole period of ischemia/reperfusion) strongly reduced the high incidence of severe arrhythmias and lethality, reduced the increase in free radical blood levels and left-ventricle histologic alterations, and augmented the extracellular signal-regulated kinase activation. Treatment with the melanocortin peptides adrenocorticotropin and gamma2-melanocyte-stimulating hormone (162 nmol/kg intravenously or 16.2 nmol/kg intracerebroventricularly, during coronary occlusion) produced the same protective effects of electrical stimulation and with the same muscarinic acetylcholine receptor-dependent mechanism, seemingly through brain activation (mediated by melanocortin MC3 receptors, as previously described) of such efferent vagal pathway.

CONCLUSIONS

The present results give evidence for the identification of a protective, melanocortin-activated, efferent vagal cholinergic pathway, operative in conditions of myocardial ischemia/reperfusion. These data suggest that melanocortins and pertinent compounds able to activate such a pathway could provide the potential for development of a new class of drugs for a novel approach to management of ischemic heart disease.

Postconditioning via stuttering reperfusion limits myocardial infarct size in rabbit hearts: role of ERK1/2

Emerging evidence suggests that restoration of blood flow in a stuttering manner may limit lethal myocardial ischemia-reperfusion injury. However, the mechanisms contributing to this phenomenon, termed postconditioning (post-C), remain poorly defined. Our aim was to test the hypothesis that activation of classic “survival kinases,” phosphatidylinositol 3-kinase (PI3-kinase) and/or extracellular signal-regulated kinase (ERK)1/2, may play a role in post-C-induced cardioprotection. In protocol 1, isolated buffer-perfused rabbit hearts underwent 30 min of sustained coronary artery occlusion and were randomized to receive abrupt reperfusion (controls) or four cycles of 30 s of reperfusion and 30 s of reocclusion before full restoration of flow (post-C). Protocol 2 was identical except control and postconditioned hearts received the PI3-kinase inhibitor LY-294002 ( protocol 2A) or the ERK1/2 antagonist PD-98059 ( protocol 2B) throughout the first 25 min of reperfusion, whereas in protocol 3, myocardial samples were obtained during the early minutes of reflow from additional control, postconditioned, and nonischemic sham hearts for the assessment, by standard immunoblotting, of phospho-Akt (downstream target of PI3-kinase) and phospho-ERK. Protocols 1 and 2 corroborated that infarct size (delineated by tetrazolium staining and expressed as a percent of risk region) was reduced in postconditioned hearts vs. control hearts and also revealed that post-C-induced cardioprotection was maintained despite LY-294002 treatment but was abrogated by PD-98059. These pharmacological data were supported by protocol 3, which showed increased immunoreactivity of phospho-ERK but not phospho-Akt with post-C. Thus our results implicate the involvement of ERK1/2 rather than PI3-kinase/Akt in the reduction of infarct size achieved with post-C.

Harnessing the preconditioning phenomenon: does remote organ ischaemia provide the answer?

Despite progress in defining the cellular mechanisms of the ischaemic preconditioning phenomenon, its conversion into convenient clinical practice has been slow. The possibility that an innate mechanism of tissue resistance to ischaemia could be harnessed as a clinical tool is an attractive and enticing prospect.

Beyond angiogenesis: the cardioprotective potential of fibroblast growth factor-2

In the field of cardiovascular research, a number of independent approaches have been explored to protect the heart from acute and chronic ischemic damage. Fibroblast growth factor-2 (FGF-2) recently has received considerable attention with respect to its angiogenic potential. While therapeutic angiogenesis may serve to salvage chronically ischemic myocardium, more acute treatments are in demand to increase cardiac resistance to injury (preconditioning) and to guard against secondary injury after an acute ischemic insult. Here, we look beyond the angiogenic potential of FGF-2 and examine its acute cardioprotective activity as demonstrated under experimental conditions, both as an agent of a preconditioning-like response and for secondary injury prevention at the time of reperfusion. Factors to consider in moving to the clinical setting will be discussed, including issues of dosage, treatment duration, and routes of administration. Finally, issues of safety and clinical trial design will be considered. The prospect of such a multipotent growth factor having clinical usefulness opens the door to effective treatment of both acute and chronic ischemic heart disease, something well worth the attention of the cardiovascular community.

Myocardial ischemia/reperfusion-injury, a clinical view on a complex pathophysiological process

Myocardial infarction is the major cause of death in the world. Over the last two decades, coronary reperfusion therapy has become established for the management of acute myocardial infarction (AMI). However, restoration of blood flow to previously ischemic myocardium results in the so-called ischemia/reperfusion (IR)-injury. The different clinical manifestations of this injury include myocardial necrosis, arrhythmia, myocardial stunning and endothelial- and microvascular dysfunction including the no-reflow phenomenon. The pathogenesis of ischemia/reperfusion injury consists of many mechanisms. Recently, there's increasing evidence for an important role in IR-injury on hypercontracture induced by high levels of cytosolic calcium or by low concentrations of ATP. In the last years, many studies on experimental models were investigated, but the clinical trials confirming these effects remain spare. Recently, the beneficial effect of Na(+)/H(+)-exchange inhibitor cariporide and of the oxygen-derived free radical (ODFR) scavenger vitamin E on coronary bypass surgery-induced IR-injury were demonstrated. Also recently, the beneficial effect of allopurinol on the recovery of left ventricular function after rescue balloon-dilatation was demonstrated. The beneficial effect of magnesium and trimetazidine on IR-injury remains controversial. The beneficial effect of adenosine remains to be further confirmed. There's also increasing interest in agentia combining the property of upregulating NO-synthase (e.g. L-arginine) and restoring the balance between NO and free radicals (e.g. tetrahydrobiopterin). One of such agents could be folic acid. In this review article the authors give an overview of the recent insights concerning pathogenesis and therapeutic possibilities to prevent IR-induced injury.

The role of intensive glycemic control in the management of patients who have acute myocardial infarction

Hyperglycemia is associated with excess mortality in AMI and should be treated aggressively in the intensive care setting. The exact goal of therapy is unclear because different blood glucose targets were used in earlier studies (eg, 215 mg/dL in DIGAMI versus 110 mg/dL in the Belgian study of critically-ill patients). In the setting of AMI, it is prudent to avoid excessive hypoglycemia and, thus, more modest goals for blood glucose may be considered until more definitive data are present. Aggressive therapy with continuous infusion of insulin seems to improve a host of metabolic and physiologic effects that are associated with acute hyperglycemia and improves mortality in the acute setting. Aggressive glycemic control should be coupled with appropriate use of reperfusion therapies, glycoprotein IIb/IIa inhibitors, aspirin, 1-blockers, ACE inhibitors, and antithrombotic agents. The role of intensive chronic glucose control in reducing CV events is less clear but earlier studies were not well-powered; did not achieve aggressive, durable glycemic control; and did not use insulin-sensitizing agents routinely. Given the results of the DIGAMI trial, the goal of therapy postdischarge should include strict glycemic control while future studies help to delineate the role of insulin-sensitizing agents versus insulin-providing agents in reducing recurrent macrovascular events. Careful attention also should be paid to aggressive lifestyle modifications and treatment of hypertension, hyperlipidemia, and left ventricular dysfunction, as well as appropriate use of anti-platelet and antithrombotic agents.

Glucose-insulin-potassium and reperfusion in acute myocardial infarction: rationale and design of the Glucose-Insulin-Potassium Study-2 (GIPS-2)

BACKGROUND

The combination of reperfusion therapy and high-dose glucose-insulin-potassium (GIK) infusion seems beneficial in acute myocardial infarction (MI). Current evidence, however, is not considered conclusive.

STUDY DESIGN

The Glucose-Insulin-Potassium Study-2 (GIPS-2) will investigate whether GIK, in adjunction to reperfusion therapy, is beneficial in MI patients without signs of heart failure at admission. A total of at least 1044 patients with an acute MI treated with either thrombolysis or primary percutaneous coronary intervention will be randomized to an infusion of high-dose GIK or no infusion. The primary end point of the study is 30-day mortality. Secondary end points are mortality at 1 year, recurrence of MI, repeat intervention, and infarct size.

IMPLICATIONS

If high-dose GIK significantly reduces mortality at 30 days in all patients, the adjunction of this treatment to reperfusion therapy may become part of standard regimen for patients with acute MI without heart failure.

Cardioprotective effect of SEA0400, a selective inhibitor of the Na(+)/Ca(2+) exchanger, on myocardial ischemia-reperfusion injury in rats

In this study, we investigated whether the Na(+)/Ca(2+) exchanger (NCX) inhibitor SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy]phenoxy-5-ethoxyaniline) might have a protective effect against myocardial ischemia-reperfusion injury in rats. In particular, we focused on cardiac function using Doppler echocardiography and cardiac gene expression. We intravenously administered either SEA0400 and delivery vehicle or only the vehicle (as a control) to Wistar rats 5 min before ischemia was induced. Reperfusion was performed after 30 min of ischemia. At 1 week after ischemia-reperfusion injury, we assessed hemodynamics by inserting a polyethylene-tubing catheter, cardiac function by Doppler echocardiography, and myocardial mRNA expression was determined by Northern blot analysis. Left ventricular (LV) end-diastolic dimensions (LVDd) and LV end-diastolic volume (LVEDV) were significantly increased in the ischemia-reperfusion rat model group compared to the control group. The SEA0400-treated group had a significantly attenuated LVDd (P<0.05) and LVEDV (P<0.01) increase, compared to the vehicle-treated group. A decrease in the LV ejection fraction (P<0.05) was significantly prevented in the SEA0400-treated group compared to the vehicle-treated group. Moreover, mRNA expression of plasminogen activator inhibitor-1 in the non-infarcted LV of the SEA0400-treated group was significantly lower than in the vehicle-treated group (P<0.05). This study demonstrates that the NCX is an important mechanism for cell death in myocardial ischemia and reperfusion in rats. SEA0400 may prove to be a promising new drug in the clinical treatment of myocardial ischemia and reperfusion.

Protein Kinase Cδ Activation Induces Apoptosis in Response to Cardiac Ischemia and Reperfusion Damage

Heart attacks caused by occlusion of coronary arteries are often treated by mechanical or enzymatic removal of the occlusion and reperfusion of the ischemic heart. It is now recognized that reperfusion per se contributes to myocardial damage, and there is a great interest in identifying the molecular basis of this damage. We recently showed that inhibiting protein kinase Cdelta (PKCdelta) protects the heart from ischemia and reperfusion-induced damage. Here, we demonstrate that PKCdelta activity and mitochondrial translocation at the onset of reperfusion mediates apoptosis by facilitating the accumulation and dephosphorylation of the pro-apoptotic BAD (Bcl-2-associated death promoter), dephosphorylation of Akt, cytochrome c release, PARP (poly(ADP-ribose) polymerase) cleavage, and DNA laddering. Our data suggest that PKCdelta activation has a critical proapoptotic role in cardiac responses following ischemia and reperfusion.

Effects of acetaminophen on myocardial infarct size in rats

OBJECTIVE

Acetaminophen is widely prescribed as an analgesic agent in hospitals and clinics. However, acetaminophen theoretically could influence myocardial infarct size by reducing prostaglandin synthesis in vivo. To date, the effect of acetaminophen on myocardial infarct size is unknown. The present study investigated (1) whether acetaminophen has any effect on myocardial infarct size when given in an analgesic dose and (2) whether acetaminophen can affect the cardioprotective effect of the early phase of ischemic preconditioning in rats.

METHODS

Female Sprague-Dawley rats were randomly assigned to four groups (n=12 each). Group 1 (no preconditioning): Vehicle (intravenous ethanol, 0.9 mL/kg) was given 39 minutes prior to ischemia. Group 2 (acetaminophen plus no preconditioning): intravenous acetaminophen (125 mg/kg) was given 39 minutes prior to ischemia. Group 3 (preconditioning): The heart was preconditioned before ischemia, and the vehicle (intravenous ethanol, 0.9 mL/kg) was given 39 minutes prior to the ischemia. Group 4 (acetaminophen plus preconditioning): The heart was preconditioned before ischemia, and intravenous acetaminophen (125 mg/kg) was given 39 minutes prior to the ischemia. The preconditioning protocol consisted of three cycles of 3 minutes of coronary occlusion and 5 minutes of reperfusion. The left coronary artery was then occluded for 60 minutes, followed by 3 hours of reperfusion. The end points were hemodynamics, body temperature, and risk area and area of necrosis of the left ventricle.

RESULTS

The area of risk was similar among the four groups. The area of necrosis, expressed as a percentage of the area at risk, was 55.7% +/- 6.1% in the no-preconditioning group, 62.8% +/- 2.4% in the acetaminophen plus no-preconditioning group, 24.7% +/- 7.3% in the preconditioning group, and 17.2% +/- 6.4% in the acetaminophen plus preconditioning group. The area of necrosis/area at risk was decreased significantly in the preconditioning group and in the acetaminophen plus preconditioning group compared with the no-preconditioning group (P<.05); but there were no significant differences between the no-preconditioning group and the acetaminophen plus no-preconditioning group (P=.29), or between the preconditioning group and acetaminophen plus preconditioning group (P=.45). Among the four groups, heart rate and body temperature were similar. The infusion of the vehicle or acetaminophen increased blood pressure in the four groups, but to a lesser extent in the acetaminophen group. However, during coronary artery occlusion and reperfusion, the four groups had comparable blood pressures.

CONCLUSION

Acetaminophen had no beneficial or adverse effects on infarct size in nonpreconditioned rats, and the beneficial effects of preconditioning were not blocked or prevented by acetaminophen at this analgesic dose.

Ischemia, reperfusion, and the role of surgery in the treatment of cardiogenic shock secondary to acute myocardial infarction: an interpretative review

Cardiogenic shock (CS) is the leading cause of death for patients hospitalized with acute myocardial infarction (AMI). Despite contemporary management of AMI, the incidence of shock due to left ventricular failure has not declined and its mortality continues to be in excess of 50%. Furthermore, the role and indications of the different means of acute revascularization remain unclear. Recent observational and randomized studies have shown improved survival in patients acutely revascularized by either percutaneous interventions or conventional surgery, particularly in patients younger than 75 years of age. Current guidelines recommend surgical revascularization in selected patients with multiple vessel disease who develop shock due to progressive ischemia of the remote myocardium up to 18 h from the onset of shock. However, patients with single-vessel disease who develop shock as a consequence of the initial infarction can only be helped if revascularization is achieved during the first 4 to 6 h after the occlusion of the infarct related artery, preferable by percutaneous techniques. Not all ischemic myocytes become irreversibly injured at the same time. Due to variability in the distribution of collateral flow, there is great variability in the severity of ischemia. Myocytes can exhibit different metabolic responses including hibernation, ischemic preconditioning, stunning, reperfusion injury, and necrosis. Precise knowledge of these biochemical and metabolic changes that take place in the myocardium after arterial occlusion and following reperfusion is paramount to the understanding of the indications for acute revascularization, the implementation of the different management strategies to enhance myocardial preservation and recovery, and the role of circulatory support in these exceedingly sick patients.

Pharmacological prevention of reperfusion injury in acute myocardial infarction. A potential role for adenosine as a therapeutic agent

The concept of reperfusion injury, although first recognized from animal studies, is now recognized as a clinical phenomenon that may result in microvascular damage, no-reflow phenomenon, myocardial stunning, myocardial hibernation and ischemic preconditioning. The final consequence of this event is left ventricular (LV) systolic dysfunction leading to increased morbidity and mortality. The typical clinical case of reperfusion injury occurs in acute myocardial infarction (MI) with ST segment elevation in which an occlusion of a major epicardial coronary artery is followed by recanalization of the artery. This may occur either spontaneously or by means of thrombolysis and/or by primary percutaneous coronary intervention (PCI) with efficient platelet inhibition by aspirin (acetylsalicylic acid), clopidogrel and glycoprotein IIb/IIIa inhibitors. Although the pathophysiology of reperfusion injury is complex, the major role that neutrophils play in this process is well known. Neutrophils generate free radicals, degranulation products, arachidonic acid metabolites and platelet-activating factors that interact with endothelial cells, inducing endothelial injury and neutralization of nitrous oxide vasodilator capacity. Adenosine, through its multi-targeted pharmacological actions, is able to inhibit some of the above-mentioned detrimental effects. The net protective of adenosine in in vivo models of reperfusion injury is the reduction of the infarct size, the improvement of the regional myocardial blood flow and of the regional function of the ischemic area. Additionally, adenosine preserves the post-ischemic coronary flow reserve, coronary blood flow and the post-ischemic regional contractility. In small-scale studies in patients with acute MI, treatment with adenosine has been associated with smaller infarcts, less no-reflow phenomenon and improved LV function. During elective PCI adenosine reduced ST segment shifts, lactate production and ischemic symptoms. During the last years, three relatively large placebo-controlled clinical trials have been conducted: Acute Myocardial Infarction Study of Adenosine Trial (AMISTAD) I and II and Attenuation by Adenosine of Cardiac Complications (ATTACC). In the AMISTAD trials, the final infarct size was reduced and the LV systolic function was improved by adenosine treatment, mainly in patients with anterior MI localization. However, morbidity and mortality were not affected. In the ATTACC study, the LV systolic function was not affected by adenosine, however, trends towards improved survival were observed in patients with anterior MI localization. The possibility of obtaining a Thrombolysis in Myocardial Infarction (TIMI) grade 3 flow in the infarct-related artery in up to 95% of patients with acute MI (increasing the occurrence of reperfusion injury) has turned back the interest towards the protection of myocardial cells from the impending ischemic and reperfusion injury in which adenosine alone or together with other cardio-protective agents may exert important clinical effects.

Opposing roles of δ and εPKC in cardiac ischemia and reperfusion: targeting the apoptotic machinery

Heart attacks, or acute myocardial infarctions (AMI), affect more than one million people in the US every year. The damage that occurs to the heart by AMI is often permanent and as a result, the morbidity and mortality rates of patients that experience AMIs continue to be high. Consequently, AMI patients are at significantly increased risks for future myocardial infarctions, decreased heart function, heart failure, and death [Heart and Stroke statistical update. In American Heart Association (2002) 4]. In this review, we discuss the events that lead to cardiac damage by AMI. Specifically, we discuss the current understanding of the role of ischemic damage vs. reperfusion damage, which is induced by the return of blood, oxygen, and nutrients to the organ. We also discuss the role of apoptosis and necrosis in cardiac damage, the means to protect the heart from damage by ischemia and reperfusion, and the role of protein kinase C in these processes.

Inhibition of δ-Protein Kinase C Protects Against Reperfusion Injury of the Ischemic Heart In Vivo

Background— Current treatment for acute myocardial infarction (AMI) focuses on reestablishing blood flow (reperfusion). Paradoxically, reperfusion itself may cause additional injury to the heart. We previously found that δ-protein kinase C (δPKC) inhibition during simulated ischemia/reperfusion in isolated rat hearts is cardioprotective. We focus here on the role for δPKC during reperfusion only, using an in vivo porcine model of AMI.

Methods and Results— An intracoronary application of a selective δPKC inhibitor to the heart at the time of reperfusion reduced infarct size, improved cardiac function, inhibited troponin T release, and reduced apoptosis. Using 31 P NMR in isolated perfused mouse hearts, we found a faster recovery of ATP levels in hearts treated with the δPKC inhibitor during reperfusion only.

Conclusions— Reperfusion injury after cardiac ischemia is mediated, at least in part, by δPKC activation. This study suggests that including a δPKC inhibitor at reperfusion may improve the outcome for patients with AMI.

Ectopic pacing at physiological rate improves postanoxic recovery of the developing heart

Recently, rapid and transient cardiac pacing was shown to induce preconditioning in animal models. Whether the electrical stimulation per se or the concomitant myocardial ischemia affords such a protection remains unknown. We tested the hypothesis that chronic pacing of a cardiac preparation maintained in a normoxic condition can induce protection. Hearts of 4-day-old chick embryos were electrically paced in ovo over a 12-h period using asynchronous and intermittent ventricular stimulation (5 min on-10 min off) at 110% of the intrinsic rate. Sham (n = 6) and paced hearts (n = 6) were then excised, mounted in vitro, and subjected successively to 30 min of normoxia (20% O(2)), 30 min of anoxia (0% O(2)), and 60 min of reoxygenation (20% O(2)). Electrocardiogram and atrial and ventricular contractions were simultaneously recorded throughout the experiment. Reoxygenation-induced chrono-, dromo-, and inotropic disturbances, incidence of arrhythmias, and changes in electromechanical delay (EMD) in atria and ventricle were systematically investigated in sham and paced hearts. Under normoxia, the isolated heart beat spontaneously and regularly, and all baseline functional parameters were similar in sham and paced groups (means +/- SD): heart rate (190 +/- 36 beats/min), P-R interval (104 +/- 25 ms), mechanical atrioventricular propagation (20 +/- 4 mm/s), ventricular shortening velocity (1.7 +/- 1 mm/s), atrial EMD (17 +/- 4 ms), and ventricular EMD (16 +/- 2 ms). Under anoxia, cardiac function progressively collapsed, and sinoatrial activity finally stopped after approximately 9 min in both groups. During reoxygenation, paced hearts showed 1) a lower incidence of arrhythmias than sham hearts, 2) an increased rate of recovery of ventricular contractility compared with sham hearts, and 3) a faster return of ventricular EMD to basal value than sham hearts. However, recovery of heart rate, atrioventricular conduction, and atrial EMD was not improved by pacing. Activity of all hearts was fully restored at the end of reoxygenation. These findings suggest that chronic electrical stimulation of the ventricle at a near-physiological rate selectively alters some cellular functions within the heart and constitutes a nonischemic means to increase myocardial tolerance to a subsequent hypoxia-reoxygenation.

Insulin therapy as an adjunct to reperfusion after acute coronary ischemia: a proposed direct myocardial cell survival effect independent of metabolic modulation

Reperfusion therapy has become a practical and effective strategy in the salvage of ischemic myocardium. The direct enhancement of cardiac cellular tolerance against ischemic and reperfusion injury should further improve patient outcome in acute coronary syndromes (ACS). This approach has been explored for many decades, and although we await mortality-weighted randomized clinical trials, the infusion of glucose-insulin-potassium (GIK) has shown promise in protecting post-infarct myocardium. The current dogma is that this cardioprotective effect of GIK acts via the modulation of cardiac and circulating metabolites to provide the heart with an optimal metabolic milieu to resist ischemia and reperfusion injury. This concept of metabolic modulation has gained favor in coronary heart disease, and its efficacy currently is being investigated in stable angina using the new class of partial fatty acid oxidation inhibitors, including trimetazidine and ranolazine. We contend that the mitogen insulin, itself, promotes tolerance against ischemic cell death via the activation of innate cell-survival pathways in the heart. To advance this viewpoint, we will present clinical data that support a dose-dependent effect of insulin's beneficial action in the management of acute myocardial infarction. Furthermore, we present experimental data that identify cell-survival programs that are directly activated by the administration of insulin. Finally, as intravenous insulin therapy is both labor intensive and associated with metabolic perturbations, we propose that the development of pharmaco-therapeutic agents that target downstream cell-survival insulin-activated signaling molecules may be an alternate approach to promote cardioprotection during ACS.

Lazaroid (U74389G)-supplemented cardioplegia: results of a double-blind, randomized, controlled trial in a porcine model of orthotopic heart transplantation

BACKGROUND

U74389G (16-desmethyl tirilazad), a 21-aminosteroid or "lazaroid," inhibits lipid peroxidation, which is an important element of ischemia-reperfusion injury. The aim of this study was to determine whether the addition of U74389G to the cardioplegic preservation solution could improve early cardiac allograft function.

METHODS

A porcine model of donor brain death and orthotopic cardiac transplantation was used. Hearts were arrested and preserved for 6 hours in an aspartate-enriched extracellular cardioplegia that had been supplemented with either U74389G and its carrier (n = 7) or the carrier alone (n = 9). Epicardial sonomicrometry and transmyocardial micromanometry were used to obtain pressure-volume loops before and after transplantation. Left ventricular wall volume was measured by volume displacement.

RESULTS

A higher proportion of U74389G-treated hearts were weaned successfully from cardiopulmonary bypass, but this difference did not achieve statistical significance (86% [6 of 7] vs 56% [5 of 9]; p = 0.308). In the hearts that were weaned successfully, preservation of left ventricular contractility, as judged by the pre-load recruitable stroke work relationship, was significantly better in the U74389G-treated hearts (p = 0.0271). In contrast, left ventricular compliance, as judged by the end-diastolic pressure-volume relationship, was significantly better preserved in the control group (p < 0.0001). U74389G-treated hearts developed less myocardial edema, as judged by the post-transplant left ventricular wall volume/baseline steady-state epicardial end-diastolic volume ratio (64 +/- 9% vs 76 +/- 11%; p = 0.045).

CONCLUSIONS

The benefit obtained from U74389G-supplemented cardioplegic preservation solution was marginal for hearts stored for 6 hours. After longer ischemic times, the benefit may be clearer.

Role of nuclear factor-kappa B activation in acute ischaemia-reperfusion injury in myocardium

(1) Our aims were to characterize activation of the transcription factor, nuclear factor kappa-B(NF-kappaB), during myocardial ischaemia-reperfusion and to assess its functional role in the evolution of acute ischaemia-reperfusion injury in intact myocardium in vivo. (2) Under pentobarbitone anaesthesia, rabbits underwent sham operation, 30 min left coronary artery occlusion followed by 0, 10 or 180 min reperfusion. Saline or NF-kappaB inhibitor diethyldithiocarbamic acid (DDTC, 50, 100 or 200 mg kg(-1)) was given intravenously 5 min prior to reperfusion. (3) Electromobility shift assay revealed that 30 min ischaemia alone did not activate NF-kappaB compared to time-matched sham-operated controls (85+/-13% vs 100+/-28%, respectively). However, ischaemia plus 10 min reperfusion markedly increased activation of NF-kappaB (295+/-77%). DDTC 50 mg kg(-1) did not inhibit NF-kappaB activation (278+/-67%) but at the higher doses complete inhibition was observed (54+/-20%, 31+/-16%, respectively). (4) Infarct to risk ratio was determined by triphenyltetrazolium chloride staining after 30 min ischaemia and 180 min reperfusion. DDTC 50 or 100 mg kg(-1) significantly reduced infarct size compared to the saline-treated control group (34.9+/-5.2%, 37.1+/-5.9%, vs 51.3+/-3.6%, P<0.05, respectively), whereas there was no protection with 200 mg kg(-1) (45.6+/-5.3%). (5) We conclude that ischaemia alone does not activate NF-kappaB, but post-ischaemic reperfusion robustly activates NF-kappaB in the myocardium. DDTC limited irreversible injury at low doses, but this effect appears to be dissociated from inhibition of NF-kappaB. Thus, activation of NF-kappaB during reperfusion does not appear to play a role in the evolution of myocardial infarction during the early phase of reperfusion.

Atorvastatin, administered at the onset of reperfusion, and independent of lipid lowering, protects the myocardium by up-regulating a pro-survival pathway

OBJECTIVES

The purpose of this study was to determine whether atorvastatin, a 3-hydroxy-3-methylglutaryl (HMG)-co-enzyme A (CoA) reductase inhibitor, limits myocardial necrosis when administered as an adjunct to reperfusion.

BACKGROUND

Statins inhibit HMG-CoA reductase to reduce the synthesis of cholesterol. However, it is proposed that statins have cardiovascular effects beyond their ability to lower cholesterol, possibly via recruitment of phosphatidyl inositol 3-kinase (PI3K) and the serine/threonine kinase, Akt. This signaling pathway has recently been linked to growth factor-mediated reperfusion salvage.

METHODS

Isolated perfused mouse hearts were subjected to 35 min of global ischemia and reperfused for 30 min in the presence of incremental concentrations of atorvastatin. Infarct size was determined by triphenyltetrazolium chloride staining, and the activity of the PI3K signaling cascade was determined by Western blot analysis.

RESULTS

We found that there was a profound dose-dependent reduction of infarct size with atorvastatin in the range of 25 to 100 micromol/l (optimal protection was seen at 50 micromol/l with infarct size of 16 +/- 2% vs. control, 33 +/- 2%, p < 0.01). Moreover, this protection was sensitive to inhibition with the PI3 kinase inhibitor, wortmannin, and was absent in endothelial nitric oxide synthase (eNOS) knockout mice. Western blot analysis revealed that atorvastatin resulted in rapid activation of the PI3K/Akt signaling cascade (within 5 min) and that both Akt and eNOS phosphorylation were significantly increased by 4.1-fold and 2.9-fold, respectively (p < 0.01). Moreover, phosphorylation of the PI3K substrates was abrogated by the administration of wortmannin.

CONCLUSIONS

Atorvastatin attenuates lethal reperfusion-induced injury in a manner that is reliant on PI3K and Akt activity and the presence and activity of eNOS.

Adenosine A(3) receptor activation protects the myocardium from reperfusion/reoxygenation injury

Ischemia-reperfusion induces both necrotic and apoptotic cell death. The ability of adenosine to attenuate reperfusion-induced injury (RI) and the role played by adenosine receptors are unclear. We therefore studied the role of the A(3) receptor (A(3)R) in ameliorating RI using the specific A(3)R agonist 1-[2-chloro-6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxi-N-methyl-b-D-ribofuranuronamide (2-Cl-IB-MECA). Isolated rat hearts and cardiomyocytes were subjected to ischemia or simulated ischemia, followed by reperfusion/reoxygenation. The end points were percent infarction/risk zone and annexin-V (apoptosis) and/or propidium iodide positivity (necrosis), respectively. In isolated hearts, 2-Cl-IB-MECA significantly limited infarct size (44.2 +/- 2.7% in control vs. 21.9 +/- 2.4% at 1 nM and 35.8 +/- 3.3% at 0.1 nM, P < 0.05). In isolated myocytes, apoptosis and necrosis were significantly reduced compared with controls (5.7 +/- 2.6% vs. 17.1 +/- 1.3% and 13.7 +/- 2.0% vs. 23.1 +/- 1.5%, respectively, P < 0.0001). In both models, the beneficial effects were abrogated using the A(3)R antagonist MRS-1191. The involvement of A(2a) receptor activation was also examined. This is the first study to demonstrate that A(3)R activation at reperfusion limits myocardial injury in the isolated rat heart and improves survival in isolated myocytes, possibly by antiapoptotic and antinecrotic mechanisms.

Acute protection of ischemic heart by FGF-2: involvement of FGF-2 receptors and protein kinase C

We examined the effect of fibroblast growth factor (FGF)-2 on myocardial resistance to injury when administered after the onset of ischemia, in vivo and ex vivo, and the role of FGF-2 receptors and protein kinase C (PKC). FGF-2 was injected into the left ventricle of rats undergoing permanent surgical coronary occlusion leading to myocardial infarction (MI). After 24 h, FGF-2-treated hearts displayed significantly reduced injury, determined by histological staining and troponin T release, and improved developed pressure compared with untreated controls. An FGF-2 mutant with diminished affinity for the tyrosine kinase FGF-2 receptor 1 (FGFR1) was not cardioprotective. FGF-2-treated hearts retained improved function and decreased damage at 6 wk after MI. In the ex vivo heart, FGF-2 administration during reperfusion after 30-min ischemia improved functional recovery and increased relative levels of PKC subtypes alpha, epsilon, and zeta in the particulate fraction, in a chelerythrine-preventable mode; it also decreased loss of energy metabolites. We conclude that intramyocardial FGF-2 administration shortly after the onset of ischemia confers protection from acute and chronic cardiac dysfunction and damage; FGF-2 delivered during reperfusion protects from ischemia-reperfusion injury; and protection by FGF-2 requires intact binding to FGFR1 and is likely mediated by PKC.

Revascularization improves survival in ischemic cardiomyopathy regardless of electrocardiographic criteria for prior small-to-medium myocardial infarcts

BACKGROUND

The purpose of the current study was to determine whether survival after revascularization (coronary artery bypass grafting or percutaneous transluminal coronary angioplasty) is influenced by the extent of electrocardiographic (ECG) evidence of previous myocardial infarction (MI) in patients with ischemic cardiomyopathy by use of the 50-criteria, 31-point Selvester QRS scoring system.

METHODS

Patients with ischemic cardiomyopathy documented by a left ventricular ejection fraction (LVEF) < or =30% undergoing coronary angiography between January 1984 and July 1996, with no acute MI within the last 30 days, follow-up through 1996, and > or =75% occlusion in at least 1 major coronary artery at catheterization were included. These patients were subdivided on the basis of subsequent treatment: revascularization or no revascularization. The complete Selvester QRS system was applied to each patient's ECG and the subgroups were further subdivided by QRS score.

RESULTS

The 141 patients receiving revascularization had better survival at 5 years compared with the 298 patients receiving no revascularization (adjusted 5-year survival rate 73% vs 47%, P =.0001). No significant treatment differences were observed for low (< or =3 points) versus high (>3 points) QRS levels in either of the 2 treatment groups (revascularized patients: P =.215, patients without revascularization: P =.126) between the 2 treatment groups. Although all patients had LVEF < or =30%, only 8% of patients had QRS scores >10 points, the level that would be expected if the decrease in LVEF could be attributed entirely to infarcted myocardium.

CONCLUSIONS

Hibernating myocardium may contribute significantly to the decreased function in patients with ischemic cardiomyopathy, and the QRS score cannot be used as an independent predictor of survival in those patients with a marked decrease in LVEF but small to moderate infarct sizes.

Cardioprotection: emerging pharmacotherapy

By the year 2020, it is predicted that acute coronary occlusion will be the major cause of death in the world. Recent advances in reperfusion therapy have substantially improved survival of patients with acute coronary syndromes. While early reperfusion reduces mortality, a time limitation exists with regard to myocardial salvage. In fact, the major limiting factor in further improving survival of patients with myocardial ischaemia is the susceptibility of the cardiomyocyte to ischaemic insult and lethal cell injury. Over the last decade substantial progress has been made in our understanding of the fundamental mechanisms of ischaemia/reperfusion injury. From this work novel means which limit or delay myocyte death have emerged and are currently under development as therapeutic candidates for the management of acute coronary syndromes. This report examines cardioprotective mechanisms and reviews clinical evidence for myocardial protective therapies.

Pharmacological modulation, preclinical studies, and new clinical features of myocardial ischemic preconditioning

The term "ischemic preconditioning (PC)" was first applied to canine myocardium subjected to brief episodes of ischemia and reperfusion that tolerated a more prolonged episode of ischemia better than myocardium not previously exposed to ischemia. Protective effect of myocardial ischemic PC was demonstrated in several animal species, resulting in the strongest endogenous form of protection against myocardial injury, jeopardized myocardium, infarct size, and arrhythmias other than early reperfusion. New onset angina before acute myocardial infarction, episodes of myocardial ischemia during coronary angioplasty or bypass surgery, and the "warm-up" phenomenon may represent clinical counterparts of the PC phenomenon in humans. Here, we have attempted to summarize pharmacological modulation, preclinical studies, and new clinical features of ischemic PC. To date, the pathophysiological basis of the "chemical PC" is still not well established, and "putting PC in a bottle" for clinical applications still remains a new pharmacological venture.

Insulin administered at reoxygenation exerts a cardioprotective effect in myocytes by a possible anti-apoptotic mechanism

The metabolic cocktail of glucose-insulin-potassium (GIK) has been shown to reduce mortality in humans and reduce infarct size in the rat when administered from the onset of reperfusion following an ischemic insult. The mechanisms underlying GIK mediated cardioprotection are, however, still unclear. Recent data implicates insulin "alone" as the major protagonist of cardioprotection when administered at the time of reperfusion. We have therefore begun to investigate an insulin activated signalling pathway and the putative role of apoptosis in this insulin-induced cardioprotection. Simulated ischemia and reoxygenation were induced in rat neonatal cardiocyte experiments. The administration of insulin [0.3 mU/ml] at the moment of reoxygenation (Ins(R)) enhanced myocardial cell viablility as assessed by trypan blue exclusion compared to vehicle alone treated control myocytes (Ins(R)50+/-2%v controls 70+/-1%, P<0.001). This insulin-mediated cardioprotection was due, in part to a reduction in myocyte apoptosis as measured by TUNEL (Ins(R)29+/-2%v controls 49+/-3%, P<0.001) and Annexin V staining (Ins(R)34+/-2%v controls 65+/-3%, P<0.001). These cardioprotective and anti-apoptotic effects of insulin were completely abolished by the tyrosine kinase inhibitor lavendustin A and by the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor wortmannin. Thus, we conclude that the early administration of insulin appears to be an effective modality to reduce reoxgygenation injury in cardiocytes, in part, via the attenuation of ischemia/reoxygenation-induced apoptosis. Moreover, the cardioprotective and anti-apoptotic effects of insulin are mediated via tyrosine kinase and PI3-kinase signalling pathways.