Preconditioning of human myocardium with adenosine during coronary angioplasty

[Myocardial preconditioning with volatile anesthetics. General anesthesia as protective intervention?]

Reduction of the perioperative cardiovascular risk with pharmacological interventions plays a prominent role in routine anesthesia practice. For example, perioperative beta-blockade is well established in anesthesiological treatment of patients. There is a growing body of evidence supporting the cardioprotective effects of volatile anesthetics known as anesthetic-induced preconditioning. There are numerous and complex data from animal studies. The mechanisms of anesthetic-induced preconditioning have been extensively studied but have still not been clearly identified. Initial clinical data show the cardioprotective effects of volatile agents by looking at parameters of myocardial function and laboratory values and therefore, the question of the relevance of these data for routine clinical practice has been raised. This review gives a summary of the currently available data focusing on the mechanisms of anesthesiological preconditioning and clinical studies.

Brief repetitive balloon occlusions enhance reperfusion during percutaneous coronary intervention for acute myocardial infarction: a pilot study

The objective of this study was to determine whether acutely ischemic myocardium may be conditioned during percutaneous coronary intervention for acute myocardial infarction. Ischemic preconditioning is a powerful cardioprotective mechanism that limits infarct size in animal investigations and ischemic sequelae during percutaneous coronary intervention in man. However, the conditioning stimulus in all these studies has been applied prior to the defining episode of ischemia. Seventeen patients undergoing percutaneous coronary intervention for acute myocardial infarction were randomly assigned to a standard ischemic preconditioning protocol (n = 10) or a usual-care control group (n =7). ST segment shift response and Doppler-derived distal coronary velocity data were compared. Despite similar degrees of baseline ST segment elevation, the magnitude of final ST segment elevation in the conditioning group was less than that in controls at the protocol conclusion (conditioning, 1.60 +/- 0.8 mV; control, 4.0 +/- 0.5 mV; P < 0.001). The rate of ST segment resolution was greater in the conditioning group (conditioning, 0.28 +/- 0.1 mV/min; control, 0.12 +/- 0.1 mV/min; P = 0.02). Distal coronary velocimetry indicated significant improvement in coronary flow velocity reserve in the conditioning group at the protocol conclusion (conditioning, 1.8 +/- 0.2; control, 1.4 +/- 0.1; P < 0.008). Brief periods of occlusion and reperfusion during percutaneous intervention for acute myocardial infarction mitigate the extent of ischemic injury and improve distal myocardial perfusion. Such ischemic conditioning represents a potentially useful adjunct to strategies for enhancing reperfusion during acute myocardial infarction.

The Role of a Common Adenosine Monophosphate Deaminase (AMPD)-1 Polymorphism in Outcomes of Ischemic and Nonischemic Heart Failure

BACKGROUND

A common variant of the adenosine monophosphate deaminase (AMPD)-1 gene (C34T) results in enzymatic inactivity and may increase adenosine in cardiac muscle and confer cardioprotection through ischemic preconditioning.

METHODS AND RESULTS

We hypothesized that AMPD1 carriers with ischemic heart failure (HF) in the Beta-Blocker Evaluation of Survival Trial (BEST) might have a relative survival advantage. Patients (n = 1038, 20% black) with ischemic (58%) and nonischemic (42%) HF were followed for an average of 2.0 years for cardiovascular mortality. DNA was purified from blood using phenol/chloroform. Genotyping was performed by polymerase chain reaction with 5' exonuclease chemistry. Differences in survival were assessed by comparing Kaplan-Meier curves with the log-rank test. Genotype frequencies differed by ethnicity (P < .001) but not by disease etiology. AMPD1 genotype did not significantly modify survival in the entire study population (hazard ratio [HR] = 0.91, 95% CI = 0.61-1.37), among ischemics (HR = 0.73, CI = 0.44-1.22, P = .23), or ischemic non-blacks (HR = 0.74, CI = 0.44-1.24, P = .25). Genotype did not modify the effect of bucindolol on mortality.

CONCLUSIONS

Results of this study failed to confirm a reported survival benefit among HF patients carrying the AMPD1 T-allele. However, further studies in larger, more homogeneous populations should explore the possibility of a modest survival advantage for patients with ischemic HF.

Intravenous adenosine protects the myocardium primarily by activation of a neurogenic pathway

Endogenous adenosine is a trigger for ischemic myocardial preconditioning (IPC). Although intravascular administration of adenosine has been used to further unravel the mechanism of protection by IPC, it is questionable whether adenosine and IPC employ the same signaling pathways to exert cardioprotection. We therefore investigated whether the active metabolic barrier of the endothelium prevents an increase in myocardial interstitial adenosine concentrations by intravenous adenosine, using microdialysis, and also the role of NO and activation of a neurogenic pathway in the cardioprotection by adenosine. In pentobarbital-anesthetized rats, area at risk and infarct size (IS) were determined 120 min after a 60-min coronary artery occlusion (CAO), using trypan blue and nitro-blue-tetrazolium staining, respectively. IPC with a single 15-min CAO and a 15-min adenosine infusion (ADO, 200 microg min(-1) i.v.) limited IS to the same extent (IS = 41 +/- 6% and IS = 40 +/- 4%, respectively) compared to control rats (IS = 63 +/- 3%, both P < 0.05). However, IPC increased myocardial interstitial adenosine levels seven-fold from 4.3 +/- 0.7 to 27.1 +/- 10.0 microM (P < 0.05), while ADO had no effect on interstitial adenosine (4.1 +/- 1.2 microM), or any of the other purines. The NO synthase inhibitor N(omega)-nitro-L-arginine (LNNA), which did not affect IS (IS = 62 +/- 3%), attenuated the protection by ADO (IS = 56 +/- 3%; P < 0.05 vs ADO, P = NS vs LNNA). The ganglion blocker hexamethonium, which had also no effect on IS (IS = 66 +/- 3%), blunted the protection by ADO (IS = 55 +/- 4%; P < 0.05 vs ADO and vs hexamethonium). These observations demonstrate that cardioprotection by ADO is dependent on NO, and is primarily mediated by activation of a neurogenic pathway.

Myocardial function following cold ischemic storage is improved by cardiac-specific overexpression of A1-adenosine receptors

Cold ischemic storage of hearts for transplantation is limited to 4-6 h, and therefore the development of strategies to extend preservation time may increase the donor pool of hearts. Overexpression of A1-adenosine receptors (A1AR) can protect hearts from acute ischemic injury, and the purpose of this study was to test the hypothesis that overexpression of A1AR will improve tolerance to longer periods of cold ischemic preservation. Hearts from 18 wild type and 16 transgenic mice with overexpression of A1AR (A1AR Trans) were isolated and perfused, and then subjected to 18 h of preservation in 5 degrees C University of Wisconsin solution followed by 2 h of reperfusion. Left ventricular end diastolic pressure and left ventricular developed pressure were measured as indices of ventricular function. Cell viability was assessed by determination of infarct size and myocardial cell apoptosis. A1AR Trans hearts showed improved function following 18 h of ischemia, as shown by lower end diastolic pressure (p < 0.05) and higher recovery of left ventricular developed pressure (p < 0.05) during reperfusion. A1AR Trans hearts had markedly reduced infarct size (p < 0.05) and decreased apoptosis (p < 0.05). Overexpression of cardiac A1AR imparts cardioprotection during long-term cold ischemic preservation.

The Sulfonylurea Glipizide Does Not Inhibit Ischemic Preconditioning in Anesthetized Rabbits

The K(ATP) channel blocker glibenclamide inhibits cardioprotection afforded by ischemic preconditioning (IPC), raising concern about sulfonylurea use by patients with cardiovascular disease. We examined the effects of the widely prescribed sulfonylurea glipizide (Glucotrol XL(R) ) on IPC in anesthetized rabbits. Initially, in parallel studies in pentobarbital-anesthetized rabbits, we identified doses of glipizide (GLIP, 0.17 mg/kg + 0.12 mg/kg/h, IV) and glibenclamide (GLIB, 0.05 mg/kg + 0.03 mg/kg/h, IV) that produced steady-state, clinically relevant plasma levels of both drugs; these doses also significantly increased plasma insulin by 51 +/- 17% (GLIP) and by 57 +/- 17% (GLIB, both p < 0.05 vs. their respective baseline levels). Subsequent parallel studies in ketamine-xylazine-anesthetized rabbits examined the effects of these doses of GLIP and GLIB on IPC. Myocardial injury (30 min coronary occlusion/120 min reperfusion), either with or without IPC (5 min occlusion/10 min reperfusion) was induced midway during a 2 h infusion of vehicle (VEH), GLIP or GLIB (n = 10-11 each). Infarct area (IA) normalized to area-at-risk (%IA/AAR) was 62 +/- 3% in the VEH group, and was significantly reduced to 39 +/- 5% by IPC (p < 0.05 vs. VEH). Neither GLIP nor GLIB treatment had any effect on %IA/AAR in the absence of IPC (p > 0.05). IPC-induced cardioprotection was preserved in the GLIP + IPC treatment group (45 +/- 4%) when compared to VEH alone (p < 0.05), but was attenuated in the presence of GLIB (GLIB+IPC: 53 +/- 4% IA/AAR, p > 0.05 vs. VEH). Thus, at a clinically relevant plasma concentration, glipizide did not limit the cardioprotective effects of IPC, and is unlikely to increase the severity of cardiac ischemic injury.

Ischemic Preconditioning of Skeletal Muscle

BACKGROUND

The time course of the late phase of ischemic preconditioning (IPC) was determined in latissimus dorsi muscle (LDM) flaps using viability and function as the endpoints.

MATERIALS AND METHODS

LDM flaps from Sprague-Dawley rats were allocated into 6 groups. LDMs were preconditioned with 2 30-minute periods of ischemia separated by 10 minutes of reperfusion and subjected to a 4-hour ischemic insult after 24, 48, 72, and 96 hours from IPC. LDMs were evaluated for percent necrosis and muscle contractile function and compared with controls.

RESULTS

The late phase of IPC provides significant protection against necrosis up to 72 hours. Conversely, when the end point used was muscle contractile function, the protection only lasted 48 hours.

CONCLUSION

The time course of late-phase protection in skeletal muscle is 2-3 days. Late phase IPC appears to protect muscle flaps during the most critical time period following elevation.

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.

A randomized, double-blinded, placebo-controlled multicenter trial of adenosine as an adjunct to reperfusion in the treatment of acute myocardial infarction (AMISTAD-II)

OBJECTIVES

The purpose of this research was to determine the effect of intravenous adenosine on clinical outcomes and infarct size in ST-segment elevation myocardial infarction (STEMI) patients undergoing reperfusion therapy.

BACKGROUND

Previous small studies suggest that adenosine may reduce the size of an evolving infarction.

METHODS

Patients (n = 2,118) with evolving anterior STEMI receiving thrombolysis or primary angioplasty were randomized to a 3-h infusion of either adenosine 50 or 70 microg/kg/min or of placebo. The primary end point was new congestive heart failure (CHF) beginning >24 h after randomization, or the first re-hospitalization for CHF, or death from any cause within six months. Infarct size was measured in a subset of 243 patients by technetium-99m sestamibi tomography.

RESULTS

There was no difference in the primary end point between placebo (17.9%) and either the pooled adenosine dose groups (16.3%) or, separately, the 50-microg/kg/min dose and 70-microg/kg/min groups (16.5% vs. 16.1%, respectively, p = 0.43). The pooled adenosine group trended toward a smaller median infarct size compared with the placebo group, 17% versus 27% (p = 0.074). A dose-response relationship with final median infarct size was seen: 11% at the high dose (p = 0.023 vs. placebo) and 23% at the low dose (p = NS vs. placebo). Infarct size and occurrence of a primary end point were significantly related (p < 0.001).

CONCLUSIONS

Clinical outcomes in patients with STEMI undergoing reperfusion therapy were not significantly improved with adenosine, although infarct size was reduced with the 70-microg/kg/min adenosine infusion, a finding that correlated with fewer adverse clinical events. A larger study limited to the 70-microg/kg/min dose is, therefore, warranted.

Repeated exercise stress testing identifies early and late preconditioning

BACKGROUND

The warm-up phenomenon has been considered to trigger preconditioning. We investigated whether repeated exercise treadmill tests in humans are capable of inducing adaptation to ischemia by triggering both the early and late phase of preconditioning.

METHODS

In 25 consecutive patients with stable coronary artery disease, four repeated treadmill tests were performed. Thirty minutes following the first test (T1) a second one was performed (T2), followed 6 h later by a third test (T3). Twenty-four hours later all patients were subjected to a fourth exercise test (T4). In every fifth patient, simultaneous echocardiographic examination was performed at the time of the exercise tests in an attempt to reveal ischemic abnormalities.

RESULTS

At baseline there was no difference between the variables. At ST segment depression >1.5 mm, the rate-pressure product (RPP) was higher in T2 and T4 (231.3+/-17.9 and 232.6+/-15.8 mm Hg s 10(2)) than in T1 and T3 (210+/-17 and 210.2+/-16.7 mm Hg s 10(2)), p<0.001. Additionally, time to the onset of chest pain was longer in T2 and T4 (430.8+/-60.5 and 438+/-47 s) than in T1 and T3 (345.6+/-69 and 345.6+/-58 s), p<0.001. At peak exercise, the RPP was higher in T2 and T4 (278.6+/-21.6 and 278.3+/-19.6 mm Hg s 10(2)) than in T1 and T3 (255.6+/-23.1 and 256.6+/-23 mm Hg s 10(2)), p<0.001. The wall motion score index was higher in T1 and T3 (1.65+/-0.17 and 1.53+/-0.16) than in T2 and T4 (1.3+/-0.07 and 1.37+/-0.1), p<0.001.

CONCLUSION

By using repeated exercise treadmill tests both the early and late phase of protection can be obtained.

Cardiac Preconditioning during Percutaneous Coronary Interventions

Ischemic preconditioning (PC) is a polygenic defensive cellular adaptive phenomenon of the heart to ischemic stress, whereby the heart changes its phenotype to become more resistant to subsequent ischemia. Early and late of PC represent two chronologically and pathophysiologically distinct phases of this phenomenon, which can be recruited pharmacologically. We represent a post hoc analysis examining the late PC-mimetic effects of nitroglycerin (NTG) on peri-procedural myocardial necrosis during percutaneous coronary intervention (PCI). A group of 66 patients presenting with angina were randomized, 24 h prior to a scheduled PCI for single obstructive CAD, to a 4 h pretreatment with intravenous NTG or saline. Measurements of electrocardiographic ST-segment shifts, echocardiographic regional wall motion and angina scores demonstrated that NTG pre-treatment preconditioned the heart by rendering it resistant to ischemia during balloon inflations. NTG-pretreated patients exhibited trends towards lower average peak CK (131.1 vs. 188.6 U/L, P = 0.38) and CK-MB levels (7.1 vs. 12.6 ng/ml, P = 0.40). NTG, however, had no significant impact on the incidence of post-procedural MI or any cardiac enzyme elevation. The exploitation of ischemic and pharmacological PC may prove a useful strategy to confer cardioprotection during high-risk PCI and is worth exploring.

Adenosine receptor agonists: from basic medicinal chemistry to clinical development

Adenosine is a physiological nucleoside which acts as an autocoid and activates G protein-coupled membrane receptors, designated A(1), A(2A), A(2B) and A(3). Adenosine plays an important role in many (patho)physiological conditions in the CNS as well as in peripheral organs and tissues. Adenosine receptors are present on virtually every cell. However, receptor subtype distribution and densities vary greatly. Adenosine itself is used as a therapeutic agent for the treatment of supraventricular paroxysmal tachycardia and arrhythmias and as a vasodilatatory agent in cardiac imaging. During the past 20 years, a number of selective agonists for A(1), A(2A) and A(3) adenosine receptors have been developed, all of them structurally derived from adenosine. Several such compounds are currently undergoing clinical trials for the treatment of cardiovascular diseases (A(1)and A(2A)), pain (A(1)), wound healing (A(2A)), diabetic foot ulcers (A(2A)), colorectal cancer (A(3)) and rheumatoid arthritis (A(3)). Clinical evaluation of some A(1) and A(2A) adenosine receptor agonists has been discontinued. Major problems include side effects due to the wide distribution of adenosine receptors; low brain penetration, which is important for the targeting of CNS diseases; short half-lifes of compounds; or a lack of effects, in some cases perhaps due to receptor desensitisation or to low receptor density in the targeted tissue. Partial agonists, inhibitors of adenosine metabolism (adenosine kinase and deaminase inhibitors) or allosteric activators of adenosine receptors may be advantageous for certain indications, as they may exhibit fewer side effects.

The therapeutic potential of agents acting via purine receptors

A host of physiological processes associated with the cardiovascular (CV) system, central nervous system (CNS), and a variety of other organ systems and tissues are regulated by agents, primarily adenosine (ado) and adenosine triphosphate (ATP), that act via cell-surface purine receptors. These receptors have therefore been the focus of a variety of programmes directed at the discovery and development of new therapeutic agents, most notably for the treatment of disorders of the CV system. Currently, only a handful of agents, including ado, theophylline, dipyridamole, and ticlopidine, are approved for clinical use. A variety of new agents intended for use in CV disease, disorders of the CNS, such as Parkinson's disease, treatment of pain, inflammatory disorders, and diverse other pathophysiological conditions are in clinical development. Historically, ado receptors have been the primary target. Recent research efforts have begun to examine alternative strategies including agents that modulate endogenous levels of extracellular ado and agents that act via P(2) receptors.

ATP-dependent potassium channels as a key target for the treatment of myocardial and vascular dysfunction

PURPOSE OF REVIEW

The aim of this review is to highlight the most recent and interesting articles on the physiologic properties and functions of ATP-dependent potassium channels in the cardiovascular system and on the role of the potassium channel openers for the treatment of cardiovascular dysfunction.

RECENT FINDINGS

The initial efforts in the development of potassium channel openers focused on the management of systemic hypertension. Lately, the range of possible indications for potassium channel openers has increased to include pulmonary hypertension and stable angina pectoris. The discovery of a connection between the mitochondrial ATP-dependent potassium channels and the phenomenon of cardiac preconditioning created potential new uses for potassium channel openers in myocardial ischemia, inn unstable angina, in preoperative and perioperative settings, and for the preservation of organs for transplant.

SUMMARY

The most recent data on the physiologic roles of sarcolemmal and mitochondrial ATP-dependent potassium channels and the pharmacology of potassium channel openers in the cardiovascular system are summarized and discussed. Finally, the effects of potassium channel opener drugs including minoxidil, nicorandil, pinacidil, bimakalin, and levosimendan, a dual-action potassium channel opener and calcium sensitizer with inodilator and cardioprotective activity, are discussed.

Collateral vessel physiology and functional impact– experimental evidence of collateral behaviour

The clinical variable predicting the development of collateral arteries in humans is the hemodynamic severity of coronary stenoses. Hyperemia induces an overall increase in coronary collateral flow in patients with coronary artery disease (CAD). There is a reduction in hyperemia-induced myocardial perfusion in the collateral-dependent vascular area in about 10% of patients with CAD and superior collateral vessels (collateral steal). Collateral recruitment has a major impact in the equation: ischemic tolerance=preconditioning+collateral recruitment.

Potassium-specific effects of levosimendan on heart mitochondria

In this study, we evaluated levosimendan, a new drug developed for the treatment of acute and decompensated heart failure, as a potential activator of ATP-sensitive potassium flux to the matrix of cardiac mitochondria. We estimated the KATP channel openers-induced increase in mitochondrial inner membrane permeability for potassium by registering changes in membrane potential of heart mitochondria, oxidizing endogenous substrates. We compared the effect of levosimendan with the effects of the known KATP channel openers diazoxide and pinacidil. Levosimendan (1 microM) accelerated potassium-specific DeltaPsi decrease by 0.15%/s, whereas 50 microM diazoxide by 0.10%/s, and 50 microM pinacidil by 0.08%/s, respectively. These results were confirmed by swelling experiments of non-respiring mitochondria in potassium nitrate medium. We found that levosimendan with an EC50 of 0.83 +/- 0.24 microM activates potassium flux to the mitochondrial matrix. This effect is discussed as a possible explanation of the anti-ischemic action of levosimendan.

A common variant of the AMPD1 gene predicts improved survival in patients with ischemic left ventricular dysfunction

BACKGROUND

A recent retrospective study suggested that the adenosine monophosphate deaminase (AMPD)-1 gene variant C34T predicts outcome in heart failure patients. This variant might lead to ischemic preconditioning by increasing tissue adenosine. We tested whether the survival benefit of C34T occurs preferentially in the setting of ischemic left ventricular dysfunction.

METHODS AND RESULTS

A consecutive cohort of patients (n=390) with left ventricular ejection fraction <40% was evaluated. In the ischemic patient subgroup (n=210) multivariate analysis identified AMPD1 T allele carriage (hazard ratio=0.43, confidence interval=0.20-0.94, P=.035) as an independent predictor of transplant-free cardiovascular survival. No benefit was found in the nonischemic group although the number of events was too small to reliably exclude a benefit by genotype.

CONCLUSION

The AMPD1 C34T polymorphism influences transplant-free cardiovascular survival in the setting of ischemic left ventricular dysfunction.

Cardiac protection during acute myocardial infarction: Where do we stand in 2004?

Despite better outcomes with early coronary artery reperfusion for the treatment of acute ST-elevation myocardial infarction (MI), morbidity and mortality from acute myocardial infarction (AMI) remain significant, the incidence of congestive heart failure continues to increase, and there is a need to provide better cardioprotection (therapy that reduces the amount of necrosis that may be coupled with better clinical outcome) in the setting of AMI. Since the introduction of the concept of cardiac protection over a quarter of a century ago, various interventions have been investigated to reduce myocardial infarct size. Intravenous beta-blockers administered in the early hours of infarction were clearly shown to be of benefit. Intravenous adenosine appeared promising for anterior wall AMIs, as did cariporide in some studies. Glucose-insulin-potassium infusion was beneficial in certain subgroups of patients, particularly diabetics. A variety of other medications were studied with negative or marginal results. The best strategy to limit infarct size is early reperfusion with percutaneous coronary stenting or thrombolytic therapy. Stenting is superior and should be adopted whenever there is a qualified laboratory available. Available resources should focus on decreasing time from onset of symptoms to start of reperfusion and maintaining vessel patency. Future studies powered to better assess clinical outcome are needed for adjunctive therapy with adenosine, K(ATP) channel openers, Na(+)/H(+) exchange inhibitors, and hypothermia.

[How to use the paradigm of ischemic preconditioning to protect the heart?]

Ischemic preconditioning affords the most powerful protection to a heart submitted to a prolonged ischemia-reperfusion. During the past decade, a huge amount of work allowed to better understand the features of this protective effect as well as the molecular mechanisms. Ischemic preconditioning reduces infarct size and improves functional recovery; its effects on arrhythmias remain debated. Triggering of the protection involves cell surface receptors that activate pro-survival pathways including protein kinase C, PI3-kinase, possibly Akt and ERK1/2, whose downstream targets remain to be determined. Much attention has been recently focused on the role of mitochondrial K(+)ATP channels and the permeability transition pore that seem to play a major role in the progression toward irreversible cellular injury. Based on these experimental studies attempts have been made to transfer preconditioning from bench to bedside. Human experimental models of ischemic preconditioning have been set up, including cardiac surgery, coronary angioplasty or treadmill exercise, to perform pathophysiological studies. Yet, protecting the heart of CAD (coronary artery disease) patients requires a pharmacological approach. The IONA trial has been an example of the clinical utility of preconditioning. It helped to demonstrate that chronic administration of nicorandil, a K(+)ATP opener that mimics ischemic preconditioning in experimental preparations, improves the cardiovascular prognosis in CAD patients. Recent experimental studies appear further encouraging. It appears that "postconditioning" the heart (i.e. performing brief episodes of ischemia-reperfusion at the time of reperfusion) is as protective as preconditioning. In other words, a therapeutic intervention performed as late as at the time of reflow can still significantly limit infarct size. Further work is needed to determine whether this may be transferred to the clinical practice.

Angina pectoris prior to myocardial infarction protects against subsequent left ventricular remodeling

OBJECTIVES

To investigate the hypothesis that prior angina pectoris confers protection from remodeling occurring after myocardial infarction (MI), we analyzed echocardiograms from the Healing and Early Afterload Reducing Therapy (HEART) trial.

BACKGROUND

Ischemia occurring before MI has been shown to reduce infarct size in experimental models and to improve outcomes in patients. The extent to which ischemia occurring before MI influences subsequent changes in ventricular size and function is unclear.

METHODS

We studied 283 patients enrolled in the HEART trial who had echocardiograms at days 1 and 90 after MI. Left ventricular (LV) dilation from days 1 to 90 was used as a measure of LV remodeling. We explored the relationship between symptomatic angina occurring before infarction and subsequent LV remodeling.

RESULTS

In patients who reported angina (n = 111) during the three months preceding MI, LV volume change was -0.73 +/- 2.6 ml over the 90-day post-MI period, compared with 6.8 +/- 2.6 ml for patients (n = 172) without angina (p = 0.017). In contrast, there were no differences in changes in ejection fraction based on prior angina. Maximal creatine kinase was significantly lower in patients with prior angina (2,119 +/- 1,729 vs. 2,701 +/- 2,088, p = 0.016). In a multivariate model, prior angina remained protective for ventricular remodeling after adjusting for age, gender, baseline ejection fraction, Killip class, baseline end-diastolic volume, and drug treatment group (p = 0.042). However, the protective effect of pre-infarction angina appeared to be attenuated in diabetic patients.

CONCLUSIONS

Ischemic symptoms occurring before MI may protect against LV remodeling. These protective effects may be secondary to recruitment of collaterals or ischemic preconditioning of the myocardium, and they appear to be attenuated in diabetic patients.

Pharmacological modulation of the ATP sensitive potassium channels during repeated coronary occlusions: no effect on myocardial ischaemia or function

BACKGROUND

Repeated episodes of myocardial ischaemia may lead to ischaemic preconditioning. This is believed to be mediated by the ATP sensitive potassium channels.

OBJECTIVE

To examine the effect of pharmacological modulation of the ATP sensitive potassium channels during repeated coronary occlusions.

DESIGN

Double blind, double dummy study.

METHODS

38 patients with a proximal stenosis of the left anterior descending coronary artery and no visible coronary collateral vessels underwent three identical 90 second balloon occlusions, each followed by five minutes of reperfusion. The patients were randomised to pinacidil 25 mg, glibenclamide 10.5 mg, or matching placebo 90 minutes before the start of the procedure. Myocardial ischaemia was measured by continuous monitoring of ECG ST segment changes. Changes in left ventricular function were recorded with a miniature radionuclide detector, and angina was scored on the Borg scale.

RESULTS

In all patients the first balloon occlusion led to significant ST segment elevation, a clear decrease in left ventricular ejection fraction, and angina pectoris. This response was not attenuated at the second or third balloon occlusion, either in the placebo group or in the patients pretreated with pinacidil or glibenclamide.

CONCLUSIONS

Under the given experimental conditions, this randomised and double blind study did not support the view that the human myocardium has an intrinsic protective mechanism that is activated by short lasting episodes of ischaemia.

Ischaemic preconditioning and myocardial adaptation to serial intracoronary balloon inflation: cut from the same cloth?

Elective percutaneous coronary intervention fulfils many of the criteria needed of a clinical model of ischaemic preconditioning. But is this really a reflection of the laboratory phenomenon of ischaemic preconditioning?

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.

Novel N6-substituted adenosine 5'-N-methyluronamides with high selectivity for human adenosine A3 receptors reduce ischemic myocardial injury

We recently reported the identification of a novel human adenosine A3 receptor-selective agonist, (2S,3S,4R,5R)-3-amino-5-[6-[5-chloro-2-(3-methylisoxazol-5-ylmethoxy)benzylamino]purin-9-yl]-4-hydroxytetrahydrofuran-2-carboxylic acid methylamide (CP-608,039), with 1,260-fold selectivity for the human A3 versus human A1 receptor (DeNinno et al., J Med Chem 46: 353-355, 2003). However, because the modest (20-fold) rabbit A3 receptor selectivity of CP-608,039 precludes demonstration of A3-mediated cardioprotection in rabbit models, we identified another member of this class, (2S,3S,4R,5R)-3-amino-5-[6-(2,5-dichlorobenzylamino)purin-9-yl]-4-hydroxytetrahydrofuran-2-carboxylic acid methylamide (CP-532,903), which both retained human A3 receptor selectivity (210-fold; human A3/human A1 Ki: 23/4,800 nM) and had improved rabbit A3 receptor selectivity (90-fold; rabbit A3/rabbit A1 Ki: 23/2,000 nM). Infarct size was measured in Langendorff hearts or in vivo after 30 min of regional ischemia and 120 min of reperfusion. Five-minute perfusion with CP-532,903 before ischemia-reperfusion elicited a concentration-dependent reduction in infarct size in isolated hearts (EC50: 0.97 nM; maximum reduction in infarct size: 77%, P < 0.05 vs. control). Furthermore, administration of CP-532,903 (150 nM) at reperfusion also significantly reduced infarct size by 64% (P < 0.05 vs. control), which was not different (P > or = 0.05) from the cardioprotection provided by the same concentration of drug given before ischemia. The selective rabbit A1 receptor antagonist BWA1433 did not affect CP-532,903-dependent cardioprotection. In vivo, CP-532,903 (1 mg/kg) reduced infarct size by 50% in the absence of significant hemodynamic effects (mean arterial pressure, heart rate, rate-pressure product). CP-532,903 and CP-608,039 represent a novel class of human A3 receptor-selective agonists that may prove suitable for investigation of the clinical cardioprotective efficacy of A3 receptor activation.

Frequency and clinical significance of ischemic preconditioning during percutaneous coronary intervention

OBJECTIVES

We sought to examine the short- and long-term clinical consequences of ischemic preconditioning (IP) during percutaneous coronary intervention (PCI).

BACKGROUND

Ischemic preconditioning has been demonstrated in animal models to significantly diminish the extent of myocardial necrosis consequent to coronary occlusion. Surrogate markers of ischemic injury (ST segment shift, lactate release, creatine kinase release) in humans have been shown to be similarly diminished with IP elicited during PCI. There are no studies of the frequency of inducibility of IP during PCI, nor are there longer-term data on the clinical relevance of IP.

METHODS

A total of 382 patients underwent elective PCI employing a previously validated protocol to elicit IP. Procedural, in-hospital, and one-year outcomes were recorded.

RESULTS

Ischemic preconditioning was elicited in 80% of patients and was associated with a significant reduction in the likelihood of in-hospital adverse cardiac events (IP group, 12.1%; non-IP group, 44.1%; p < 0.0001). Women and diabetic patients were less likely to exhibit IP. By one year, patients failing to manifest IP were at significantly greater risk of post-discharge death or non-fatal myocardial infarction (MI) (non-IP group, 25.9%; IP group, 11.1%; p < 0.002). Failure to manifest IP was significantly and independently associated with an increased risk of death or non-fatal MI by one year.

CONCLUSIONS

Clinically relevant short- and long-term cardioprotection can be found in association with IP during PCI. In-hospital adverse ischemic events are significantly diminished in patients with IP, as are the risks of death or non-fatal MI at one year. Failure to elicit IP during PCI serves as an independent marker of increased risk of future ischemic events.

Recent insights on the mechanisms of liver preconditioning

Ischemia/reperfusion is the main cause of hepatic damage consequent to temporary clamping of the hepatoduodenal ligament during liver surgery as well as graft failure after liver transplantation. In recent years, a number of animal studies have shown that pre-exposure of the liver to transient ischemia, hyperthermia, or mild oxidative stress increases the tolerance to reperfusion injury, a phenomenon known as hepatic preconditioning. The development of hepatic preconditioning can be differentiated into 2 phases. An immediate phase (early preconditioning) occurs within minutes and involves the direct modulation of energy supplies, pH regulation, Na(+) and Ca(2+) homeostasis, and caspase activation. The subsequent phase (late preconditioning) begins 12-24 hours after the stimulus and requires the synthesis of multiple stress-response proteins, including heat shock proteins HSP70, HSP27, and HSP32/heme oxygenase 1. Hepatic preconditioning is not limited to parenchymal cells but ameliorates sinusoidal perfusion, prevents postischemic neutrophil infiltration, and decreases the production of proinflammatory cytokines by Kupffer cells. This latter effect is important in improving systemic disorders associated with hepatic ischemia/reperfusion. The signals triggering hepatic preconditioning have been partially characterized, showing that adenosine, nitric oxide, and reactive oxygen species can activate multiple protein kinase cascades involving, among others, protein kinase C and p38 mitogen-activated protein kinase. These observations, along with preliminary studies in humans, give a rationale to perform clinical trials aimed at verifying the possible application of hepatic preconditioning in preventing ischemia/reperfusion injury during liver surgery.

Preconditioning the Myocardium: From Cellular Physiology to Clinical Cardiology

Yellon, Derek M., and James M. Downey. Preconditioning the Myocardium: From Cellular Physiology to Clinical Cardiology. Physiol Rev 83: 1113-1151, 2003; 10.1152/physrev.00009.2003.—The phenomenon of ischemic preconditioning, in which a period of sublethal ischemia can profoundly protect the cell from infarction during a subsequent ischemic insult, has been responsible for an enormous amount of research over the last 15 years. Ischemic preconditioning is associated with two forms of protection: a classical form lasting ∼2 h after the preconditioning ischemia followed a day later by a second window of protection lasting ∼3 days. Both types of preconditioning share similarities in that the preconditioning ischemia provokes the release of several autacoids that trigger protection by occupying cell surface receptors. Receptor occupancy activates complex signaling cascades which during the lethal ischemia converge on one or more end-effectors to mediate the protection. The end-effectors so far have eluded identification, although a number have been proposed. A range of different pharmacological agents that activate the signaling cascades at the various levels can mimic ischemic preconditioning leading to the hope that specific therapeutic agents can be designed to exploit the profound protection seen with ischemic preconditioning. This review examines, in detail, the complex mechanisms associated with both forms of preconditioning as well as discusses the possibility to exploit this phenomenon in the clinical setting. As our understanding of the mechanisms associated with preconditioning are unravelled, we believe we can look forward to the development of new therapeutic agents with novel mechanisms of action that can supplement current treatment options for patients threatened with acute myocardial infarction.

Anaesthetics and cardiac preconditioning. Part II. Clinical implications

There is compelling evidence that preconditioning occurs in humans. Experimental studies with potential clinical implications as well as clinical studies evaluating ischaemic, pharmacological and anaesthetic cardiac preconditioning in the perioperative setting are reviewed. These studies reveal promising results. However, there are conflicting reports on the efficacy of preconditioning in the diseased and aged myocardium. In addition, many anaesthetics and a significant number of perioperatively administered drugs affect the activity of cardiac sarcolemmal and mitochondrial K(ATP) channels, the end-effectors of cardiac preconditioning, and thereby markedly modulate preconditioning effects in myocardial tissue. Although these modulatory effects on K(ATP) channels have been investigated almost exclusively in laboratory investigations, they may have potential implications in clinical medicine. Important questions regarding the clinical utility and applicability of perioperative cardiac preconditioning remain unresolved and need more experimental work and randomized controlled clinical trials.

Nonelectrocardiographic evidence that both ischemic preconditioning and adenosine preconditioning exist in humans

OBJECTIVES

The objective of this study was to use electrocardiogram (ECG)-independent parameters to determine whether preconditioning (PC) exists in humans during percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Several studies suggest that both ischemia and adenosine induce PC in the human heart during PTCA. However, because almost all of these studies relied on ST-segment shifts as indicators of the severity of ischemia, their conclusions continue to be questioned, and the very existence of ischemic or adenosine PC in humans remains controversial.

METHODS

Eighteen patients received either intracoronary adenosine (n = 9) or normal saline (n = 9); 10 min later, they underwent PTCA (three 2-min balloon inflations 5 min apart).

RESULTS

Compared with the first inflation, in untreated patients the second and third inflations were associated with less systolic dysfunction (two-dimensional echocardiography), less diastolic dysfunction (color M-mode echocardiography), less lactate production, and less H(+) release into the great cardiac venous blood. In adenosine-treated patients, the extent of all of these abnormalities during the first inflation was less than in untreated patients and did not change with subsequent inflations.

CONCLUSIONS

Previous exposure to a brief episode of ischemia (first balloon inflation) or to adenosine produces concordant decreases in ECG, subjective, mechanical, and metabolic manifestations of ischemia during PTCA. These data support the concept that both ischemic PC and pharmacologic PC exist in humans and that PTCA is a useful clinical setting in which to discern their mechanism.

A3 adenosine receptor agonist IB-MECA reduces myocardial ischemia-reperfusion injury in dogs

We examined the effect of the A3 adenosine receptor (AR) agonist IB-MECA on infarct size in an open-chest anesthetized dog model of myocardial ischemia-reperfusion injury. Dogs were subjected to 60 min of left anterior descending (LAD) coronary artery occlusion and 3 h of reperfusion. Infarct size and regional myocardial blood flow were assessed by macrohistochemical staining with triphenyltetrazolium chloride and radioactive microspheres, respectively. Four experimental groups were studied: vehicle control (50% DMSO in normal saline), IB-MECA (100 microg/kg iv bolus) given 10 min before the coronary occlusion, IB-MECA (100 microg/kg iv bolus) given 5 min before initiation of reperfusion, and IB-MECA (100 microg/kg iv bolus) given 10 min before coronary occlusion in dogs pretreated 15 min earlier with the ATP-dependent potassium channel antagonist glibenclamide (0.3 mg/kg iv bolus). Administration of IB-MECA had no effect on any hemodynamic parameter measured including heart rate, first derivative of left ventricular pressure, aortic pressure, LAD coronary blood flow, or coronary collateral blood flow. Nevertheless, pretreatment with IB-MECA before coronary occlusion produced a marked reduction in infarct size ( approximately 40% reduction) compared with the control group (13.0 +/- 3.2% vs. 25.2 +/- 3.7% of the area at risk, respectively). This effect of IB-MECA was blocked completely in dogs pretreated with glibenclamide. An equivalent reduction in infarct size was observed when IB-MECA was administered immediately before reperfusion (13.1 +/- 3.9%). These results are the first to demonstrate efficacy of an A3AR agonist in a large animal model of myocardial infarction by mechanisms that are unrelated to changes in hemodynamic parameters and coronary blood flow. These data also demonstrate in an in vivo model that IB-MECA is effective as a cardioprotective agent when administered at the time of reperfusion.

A randomized, double-blinded, placebo-controlled, dose-ranging study measuring the effect of an adenosine agonist on infarct size reduction in patients undergoing primary percutaneous transluminal coronary angioplasty: the ADMIRE (AmP579 Delivery for Myocardial Infarction REduction) study

BACKGROUND

Evidence suggests that myocardial ischemic preconditioning and reperfusion injury may be mediated by adenosine A1 and A2 receptors. AMP579 is a mixed adenosine agonist with both A1 and A2 effects. In animal models of acute myocardial infarction (MI), AMP579 reduced infarct size at serum levels of 15 to 24 ng/mL.

METHODS

The AMP579 Delivery for Myocardial Infarction REduction study evaluated AMP579 in a double-blind, multicenter, placebo-controlled trial of 311 patients undergoing primary percutaneous transluminal coronary angioplasty (PTCA) after acute ST-segment elevation MI. Patients were randomly assigned to placebo or to 3 different doses of AMP579 continuously infused over 6 hours. The primary end point was final MI size measured by technetium Tc-99m sestamibi scanning at 120 to 216 hours after PTCA. Secondary end points included myocardial salvage and salvage index at the same time interval (in a subset of patients who underwent baseline technetium Tc-99m sestamibi scan), left ventricular ejection fraction and heart failure at 4 to 6 weeks, duration of hospitalization, and cardiac events at 4 weeks and 6 months.

RESULTS

Final infarct size did not differ among the placebo group and the active treatment groups for either anterior MI or nonanterior MI. In patients with anterior MI, median myocardial salvage was increasingly higher in the groups receiving ascending dosages of AMP579 plus PTCA. Serum levels approaching levels shown to reduce infarct size in animal models were achieved only in the 60-mcg/kg treatment group.

CONCLUSION

AMP579 was safe at the doses tested, but it did not reduce infarct size. There was a trend toward greater myocardial salvage in treated patients with anterior MI.

Left ventricular function and cardiovascular events following adjuvant therapy with adenosine in acute myocardial infarction treated with thrombolysis, results of the ATTenuation by Adenosine of Cardiac Complications (ATTACC) study

BACKGROUND

Reperfusion therapy for acute myocardial infarction (AMI) reduces mortality but is also associated with reperfusion injury. The present study tested the hypothesis that adjuvant therapy with a low anti-inflammatory dose of adenosine might prevent reperfusion injury and preserve left ventricular function.

METHODS

Six hundred and eight patients with ST-elevation AMI were randomised to receive infusions of adenosine (10 microg x kg(-1) x min(-1)) or placebo (saline) to be started with thrombolysis and maintained for 6 h. The primary endpoint was global and regional left ventricular systolic and diastolic function, as assessed by two-dimensional and Doppler echocardiography before hospital discharge. The secondary end-point was all cause and cardiovascular mortality, and non-fatal myocardial infarction during 12 months of follow-up.

RESULTS

No beneficial effect of adenosine was found regarding echocardiographic indices of left ventricular systolic or diastolic function. Recruitment was stopped due to this apparent lack of effect after an interim analysis. However, after 12 months of follow-up, cardiovascular mortality was 8.9% with adenosine and 12.1% with placebo treatment [odds ratio (OR) 0.71, 95% confidence interval (C.I.) 0.4-1.2, P=0.2] among all patients and 8.4% vs 14.6% (OR 0.53, 95% C.I. 0.23-1.24, P=0.09) among patients with anterior AMI. All cause mortality differed similarly. Non-fatal AMI was not reduced similarly by adenosine treatment. Survival curves indicate that possible survival benefits are maintained after the first year of follow-up.

CONCLUSIONS

Adenosine, given as adjunctive treatment with thrombolysis, did not provide detectable improvement of echocardiographic indices of left ventricular function when assessed before hospital discharge. Cardiovascular and all cause mortality appear to have been reduced by low-dose adenosine treatment, and the size of the effect appears to be clinically relevant (absolute risk reductions of approximately 4%). The power of the study regarding morbidity and mortality was, however, limited. The results are compatible with a beneficial anti-inflammatory effect of adenosine treatment on reperfusion injury after thrombolysis, which may be mediated by inhibition of leukocytes in peripheral blood. A larger trial is warranted to possibly establish beneficial effects of low-dose adenosine on survival after thrombolysis.

Ischaemic preconditioning and outcomes after angioplasty: effects of drug therapy

Ischaemic preconditioning is one of the mechanisms by which human myocardium and human life are protected from ischaemic insults. One of the clinical situations in which we can discuss preconditioning is repetitive coronary occlusions by balloon inflation during elective percutaneous transluminal coronary angioplasty (PTCA) for stable angina pectoris. The severity of myocardial ischaemia assessed by ST-segment elevation or chest pain is less during the second balloon inflation compared with the first, if the duration of the first coronary occlusion is sufficient to precondition the myocardium. Many drugs have been identified that produce a reduction or induction in indices of preconditioning during PTCA. Preconditioning-mimetic drugs include adenosine, bradykinin, nitroglycerin and nicorandil. It is of paramount importance that we investigate and develop preconditioning-mimetic drugs which may enable an increased tolerance to effort angina, limit infarction size in susceptible patients, and decrease the incidence of sudden cardiac death as a result of ventricular tachyarrhythmias.

Effect of aspirin on late preconditioning against myocardial stunning in conscious rabbits

OBJECTIVES

The goal of this study was to investigate the effect of three different doses of acetylsalicylic acid (aspirin) (ASA) on the late phase of ischemic preconditioning (PC) against myocardial stunning.

BACKGROUND

Although recent evidence indicates that the late phase of ischemic PC is mediated by cyclooxygenase-2 (COX-2), the effect of nonsteroidal anti-inflammatory drugs (NSAIDs) that inhibit COX-2 activity on late PC has not been evaluated; ASA is the most widely used NSAID. Therefore, we determined whether ASA impedes the development of late PC.

METHODS

Conscious rabbits underwent a protocol consisting of three days of six 4-min coronary occlusion/4-min reperfusion cycles.

RESULTS

Neither 5 mg/kg nor 10 mg/kg x 3 of ASA interfered with the protective effects of late PC against stunning. In contrast, the late PC effect was completely abrogated by 25 mg/kg of ASA. Low-dose (5 mg/kg) ASA effectively inhibited platelet aggregation but did not prevent the increase in COX-2 activity, whereas the highest dose (25 mg/kg) completely blocked COX-2 activity.

CONCLUSIONS

The administration of ASA either at antithrombotic doses (5 mg/kg), which are widely used to prevent cardiovascular events in patients, or at analgesic/antipyretic doses (10 mg/kg) does not interfere with the cardioprotective effects of late PC against myocardial stunning. In contrast, high doses of ASA (25 mg/kg), which are used as antirheumatic therapy, abrogate both COX-2 activity and late PC, suggesting that nonselective doses of NSAIDs should be used with caution in patients with atherosclerotic cardiovascular disease because they may deprive the heart of its innate defensive response.

Cardioprotective effects of adenosine transport inhibition during reversible ischaemia in patients with coronary artery disease

BACKGROUND: Adenosine plays a major role in protecting ischaemic myocardium and may potentiate ischaemic preconditioning. Nucleosine transport inhibition may enhance these favourable effects. DESIGN: Randomized, double blind, placebo controlled study, to investigate the haemodynamic and cardioprotective effects of nucleoside transport inhibition during ischaemia in patients with coronary artery disease. PATIENTS AND METHODS: Elective left anterior descending (LAD) coronary angioplasty was used to produce reversible ischaemia in 24 patients with stable angina and a single LAD lesion. They were randomized to receive either the nucleoside transport inhibitor draflazine or placebo. The study medication was infused between the 2nd and 3rd balloon inflation. The primary endpoint was ischaemia-induced wall motion abnormalities as measured by left septal echo amplitude, which was plotted against time to produce an area under the curve. RESULTS: No differences were observed in the systemic haemodynamics or the myocardial collateral circulation of the two groups. The ischaemia-induced regional wall motion abnormalities improved significantly after draflazine, while no difference was observed in the placebo group. This improvement was even more pronounced in patients with low caffeine levels compared with those with high caffeine levels. CONCLUSIONS: Draflazine, in the dose and route used, is associated with a significant improvement in regional myocardial function of the ischaemic area, without affecting systemic or collateral circulation, when compared with placebo. This implies that draflazine has a cardio-protective effect in ischaemic myocardium. High caffeine blood levels reduce these effects.

Oral nicorandil recaptures the waned protection from preconditioning in vivo

1. Protection from preconditioning (PC) wanes and is eventually lost when multiple bouts of short ischemia or a prolonged reperfusion interval precedes the following sustained ischemia. The activation of mitochondrial K(ATP) channels plays a pivotal role in the intracellular signaling of PC. We tested whether the K(ATP) channel opener nicorandil (nic) preserves the given protection from PC in conditions where this benefit decays and is lost. 2. Eight groups of rabbits were divided into two equal series of experiments, one without nic (placebo) and one with nic treatment. Nic was given orally for 5 consecutive days in a dose of 5 mg kg(-1) d(-1). In a second step, four additional groups were treated with nic plus the K(ATP) channel blocker 5HD and 1 additional control group with nitroglycerin only. All the animals were anesthetized and then subjected to 30 min of myocardial ischemia and 2 h of reperfusion with one of the following interventions before the sustained ischemia: Control groups to no intervention; 3PC groups to three cycles of 5-min ischemia-10-min reperfusion; 8PC groups to eight cycles of 5-min ischemia - 10-min reperfusion; and 3PC90 groups to the same interventions as the 3PC groups but with a prolonged (90 min) intervening reperfusion interval before the sustained ischemia. The infarcted and the risk areas were expressed in percent. 3. There was no significant change in infarct size between the placebo, the nic and the 5HD-nic in the control groups (41.5+/-4.7, 43.9+/-7.1 and 48.7+/-6.4%) and 3PC groups (10.3+/-3.4, 12.2+/-3.9 and 12.6+/-4.5%). However, there was a significant decrease after nic treatment in groups 8PC (47.7+/-8.8% vs 13.0+/-2.6%, P<0.01) and 3PC90 (37.3+/-6.0% vs 14.2+/-2.4%, P<0.01), which was abrogated (38.2+/-4.7 and 42.7+/-4.4%, respectively, for 8PC and 3PC90 groups). Nitroglycerin had no effect on infarct size (39.1+/-3.1%, P=NS vs other controls). 4. Oral treatment with nic recaptures the waned protection of PC, both after repetitive bouts of short ischemia or after a prolonged reperfusion interval, preserving the initially obtained benefit. Nic by itself is insufficient to initiate PC in vivo.

Adenosine in myocardial protection in on-pump and off-pump cardiac surgery

Adenosine is most well known for its potent vasodilation of the vasculature. However, it also promotes glycolysis, and activates potassium-sensitive adenosine triphosphate (K(ATP)) channels. Adenosine also strongly inhibits neutrophil function such as superoxide anion production, protease release, and adherence to coronary endothelial cells. Hence adenosine attenuates ischemic injury as well as neutrophil-mediated reperfusion injury. Adenosine has also been implicated in the cardioprotective phenomenon of ischemic preconditioning. Accordingly experimental evidence shows that adenosine reduces postischemic injury when administered before ischemia and at the onset of reperfusion. Clinical studies in cardiology and cardiac surgery show cardioprotective trends with adenosine treatment but the effects are not as dramatic as those reported by experimental studies.

Role of the JAK-STAT pathway in protection against myocardial ischemia/reperfusion injury

The Janus kinase (JAK)-signal transducers and activators of transcription (STAT) pathway is a stress-responsive mechanism that transduces signals from the cell surface to the nucleus, thereby modulating gene expression. Recent studies have demonstrated that myocardial ischemia and reperfusion induce rapid activation of this pathway. Although the functional consequences of this event remain to be elucidated, there is emerging evidence that JAK-STAT signaling plays an important role in the development of the cardioprotected phenotype associated with ischemic preconditioning. Specifically, brief episodes of myocardial ischemia/reperfusion activate JAK1 and JAK2, followed by recruitment of STAT1 and STAT3, resulting in transcriptional upregulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), which then mediate the infarct-sparing effects of the late phase of preconditioning. The present review focuses on this novel cardioprotective role of JAK-STAT signaling and on its potential exploitation for developing therapeutic strategies aimed at limiting ischemia/reperfusion injury.

Assessment of the cytoprotective role of adenosine in an in vitro cellular model of myocardial ischemia

This work aimed to detect functional adenosine receptors in isolated rat cardiomyocytes and to study the influence of stimulation of these receptors in an in vitro model of ischemia. Cultures of cardiomyocytes were prepared from newborn rat ventricles. The contractions were photometrically monitored. In this preparation, adenosine induced a positive chronotropic response. This effect was reproduced by CGS 21680 (2-(4-[2-carboxyethyl]-phen-ethyl-amino) adenosine-5'N-ethylunosamide), a specific adenosine A(2) receptor agonist, and antagonized by DMPX (3,7-dimethyl-1-propargylxanthine), an adenosine A(2) receptor antagonist. However, R-PIA (R-N(6)-(2-phenylisopropyl)-adenosine; a specific adenosine A(1) receptor agonist) induced a negative chronotropic effect that was abolished by its corresponding adenosine A(1) antagonist DPCPX (1,3-dipropyl-8-cyclo-pentyl-adenosine). Substrate-free hypoxia, as simulation of ischemia, induced a progressive decrease and then arrest of spontaneous cell contractions. The spontaneous rhythmic contractile activity was restored during reoxygenation following simulated ischemia. Adenosine A(1) receptor stimulation with R-PIA induced a decrease of hypoxia-induced damage. This effect was antagonized by DPCPX, an adenosine A(1) receptor antagonist. Conversely, the cells treated with CGS 21680 did not display complete recovery after reoxygenation. In addition, this effect was abolished by DMPX, since the cells recovered normal function after reoxygenation. To conclude, it appeared that cardiomyocytes possess both functional adenosine A(1) and A(2) receptors and that only the activation of adenosine A(1) receptor had a cytoprotective effect against simulated ischemia-induced cardiac cell injury.

Overexpression of A(3) adenosine receptors decreases heart rate, preserves energetics, and protects ischemic hearts

To determine whether A(3) adenosine receptor (A(3)AR) signaling modulates myocardial function, energetics, and cardioprotection, hearts from wild-type and A(3)AR-overexpressor mice were subjected to 20-min ischemia and 40-min reperfusion while (31)P NMR spectra were acquired. Basal heart rate and left ventricular developed pressure (LVDP) were lower in A(3)AR-overexpressor hearts than wild-type hearts. Ischemic ATP depletion was delayed and postischemic recoveries of contractile function, ATP, and phosphocreatine were greater in A(3)AR-hearts. To determine the role of depressed heart rate and to confirm A(3)AR-specific signaling, hearts were paced at 480 beats/min with or without 60 nmol/l MRS-1220 (A(3)AR-specific inhibitor) and then subjected to ischemia-reperfusion. LVDP was similar in paced A(3)AR-overexpressor and paced wild-type hearts. Differences in ischemic ATP depletion and postischemic contractile and energetic dysfunction remained in paced A(3)AR-overexpressor hearts versus paced wild-type hearts but were abolished by MRS-1220. In summary, A(3)AR overexpression decreased basal heart rate and contractility, preserved ischemic ATP, and decreased postischemic dysfunction. Pacing abolished the decreased contractility but not the ATP preservation or cardioprotection. Therefore, A(3)AR overexpression results in cardioprotection via a specific A(3)AR effect, possibly involving preservation of ATP during ischemia.

Nicorandil-induced preconditioning as evidenced by troponin T measurements after coronary angioplasty in patients with stable angina pectoris

Nicorandil has been reported to have a preconditioning effect which suppresses the ST-segment shift or lactate production during coronary angioplasty in patients with stable angina pectoris. The present study investigated whether the preconditioning effect of nicorandil affects troponin T (TnT) levels after coronary angioplasty. Twenty-four patients with stable angina pectoris were randomized to receive a 1-minute intravenous infusion of nicorandil (100 microg/kg) or normal saline. Five minutes later they underwent three 2-minute balloon inflations 5 minutes apart. The sum of ST-segment elevation in all leads (Sum-ST) was determined at the end of each balloon inflation. Serum levels of TnT were measured 6 and 18 hours after the procedure, and the higher value of the two measurements was compared between the groups. SumST decreased progressively during the three sequential balloon inflations in both groups and was less in the nicorandil group than in the control group. The TnT level after the procedure was significantly lower in the nicorandil group than in the control group (0.05+/-0.05 vs 0.11+/-0.10 ng/mL). In conclusion, pretreatment with intravenous nicorandil suppresses TnT release after coronary angioplasty as well as ST-segment elevation during coronary angioplasty, suggesting pharmacological preconditioning by nicorandil.

Therapeutic receptor targets of ischemic preconditioning

This review focuses on target receptors that have been shown to have the potential to mimic the cardioprotective effect of ischemic preconditioning (IPC). There is an abundance of information concerning the intracellular mechanisms and membrane-bound receptors responsible for IPC. Important intracellular mediators of this cardioprotection likely reside in the activation of multiple kinase cascades. The major players in IPC are thought to include protein kinase C, tyrosine kinases, and members of the mitogen-activated protein kinase signaling family and these topics will be covered in more detail in other papers of this focused issue. However, many of these kinase-mediated mechanisms are triggered by the activation of transmembrane spanning receptors, some of which may be manipulated therapeutically to induce cardioprotection in humans with unstable angina or who are at risk for myocardial infarction. In this review, we will discuss the evidence supporting the possibility of manipulating several of these G protein-coupled receptors as potential therapeutic targets. Stimulation of numerous receptors has been targeted as possible triggers for IPC. Some of those that have been identified include A(1) adenosine, alpha(1) adrenergic, M(2) muscarinic, B(2) bradykinin, delta(1) opioid, AT(1) angiotensin, and endothelin-1 receptors. In general, these receptors are thought to couple to inhibitory G proteins. In this review, we will focus on the most likely therapeutic candidates for cardioprotection, namely adenosine, opioid, and bradykinin receptors since selective agonists and antagonists, either alone or in combination, have most often been shown to mimic or block IPC in numerous animal models and man, respectively. This is not meant to completely rule out other receptors since it is clear that IPC is a phenomenon with multiple pathways that appear to be responsible for the cardioprotection observed.

Pharmacological and ischemic preconditioning of the human myocardium: mitoK(ATP) channels are upstream and p38MAPK is downstream of PKC

BACKGROUND

These studies investigate the role of mitoK(ATP) channels, protein kinase C (PKC) and Mitogen activated protein kinase (p38MAPK) on the cardioprotection of ischemic (IP) and pharmacological preconditioning (PP) of the human myocardium and their sequence of activation.

RESULTS

Right atrial appendages from patients undergoing elective cardiac surgery were equilibrated for 30 min and then subjected to 90 min of simulated ischemia followed by 120 min reoxygenation. At the end of each protocol creatinine kinase leakage (CK U/g wet wt) and the reduction of MTT to formazan dye (mM/g wet wt) were measured. Similar protection was obtained with alpha1 agonist phenylephrine, adenosine and IP and their combination did not afford additional cardioprotection. Blockade of mitoK(ATP) channels with 5-hydroxydecanoate, PKC with chelerythrine, or p38MAPK with SB203580 abolished the protection of IP and of PP. In additional studies, the stimulation of mitoK(ATP) channels with diazoxide or activation of PKC with PMA or p38MAPK with anisomycin induced identical protection to that of IP and PP. The protection induced by diazoxide was abolished by blockade of PKC and by blockade of p38MAPK. Furthermore, the protection induced by PMA was abolished by SB203580 but not by 5-hydroxydecanoate, whereas the protection induced by anisomycin was unaffected by either 5-hydroxydecanoate or chelerythrine.

CONCLUSIONS

Opening of mitoK(ATP) channels and activation of PKC and p38MAPK are obligatory steps in the signal transduction cascade of IP and PP of the human myocardium with PKC activation being downstream of the opening of mitoK(ATP) channels and upstream of p38MAPK activation.

Preconditioning of rat hearts by adenosine A1 or A3 receptor activation

Our study in rat hearts examined whether activation of adenosine A(1) or A(3) receptors improved functional recovery and reduced apoptosis resulting from low-flow ischemia. Prior to 30 min low-flow ischemia (0.6 ml/min; 6% of baseline flow), Langendorff rat hearts were preconditioned with two 5-min cycles of (a) ischemia (PC; n=7), (b) infusion of 250 nM adenosine A(1) receptor agonist 2-chloro-N(6)-cyclopentyladenosine (CCPA; n=6), or (c) infusion of 50 nM adenosine A(3) receptor agonist N(6)-(3-iodobenzyl)-adenosine-5'-N-methyl-uronamide (IB-MECA; n=8). Recovery of function was improved in PC (71+/-3%), CCPA (68+/-6%) and IB-MECA (68+/-4%) groups compared to control hearts (46+/-5%; P<0.05). Cumulative release of total purines during ischemia-reperfusion was approx. 50% lower in PC, CCPA and IB-MECA groups compared to controls (P<0.05) and was significantly correlated to the percentage functional recovery (R(2)=0.55; P<0.05). The number of cytosolic histone-associated-DNA fragments, a hallmark of apoptosis and measured by Enzyme Linked ImmunoSorbent Assay (ELISA), was small and not different between groups after 30 min reperfusion. However, CCPA (0.6+/-0.1 absorbance units) and MECA (0.7+/-0.1 units; P<0.05 vs. PC) decreased apoptosis after 150 min reperfusion compared to PC (1.4+/-0.3 units) and control (1.2+/-0.1 units) hearts. This study shows that adenosine triggers protection of function in preconditioned rat hearts via both the adenosine A(1) and A(3) receptor. In clinical practice, pharmacological stimulation of adenosine A(3) receptors may be advantageous over adenosine A(1) receptor activation due to a lack of contractile side-effects. In contrast to ischemic preconditioning, pharmacological stimulation of adenosine A(1) or A(3) receptors reduced apoptosis. Furthermore, total purine release may serve as a marker of the degree of functional protection.

Hyperlipidemia prevents the expected reduction of myocardial ischemia on repeated balloon inflations during angioplasty

BACKGROUND

Controversy exists regarding inhibition of ischemic preconditioning in hyperlipidemic animals. In this study, we tested the hypothesis that hyperlipidemia inhibits the normal reduction of myocardial ischemia on repeated balloon inflations (BIs) during angioplasty.

METHODS

We studied 33 patients undergoing coronary angioplasty. All underwent a minimum of three BIs. Patients were grouped according to the following plasma cholesterol levels: 13 patients had total cholesterol levels < 200 mg/dL (the normal cholesterol group); and 20 patients had total cholesterol levels > or = 200 mg/dL (the elevated cholesterol group). Surface ST-segment elevations were recorded at the end of each BI.

RESULTS

In the normal cholesterol group, the mean (+/- SD) ST-segment elevation decreased from 0.21 +/- 0.15 mV during the first BI to 0.11 +/- 0.11 mV during the third BI (p < 0.05). In the elevated cholesterol group, the respective decrease was from 0.18 +/- 0.16 to 0.14 +/- 0.15 mV (p = not significant) [between-group comparisons: F = 3.97; p = 0.02]. The decrease in ST-segment elevation was correlated with the total cholesterol levels (r = -0.48; p = 0.005), the low-density lipoprotein (LDL) cholesterol levels (r = -0.50; p = 0.003), and the high-density lipoprotein/LDL levels (r = 0.44; p = 0.01).

CONCLUSION

Hyperlipidemia prevents the normal reduction of myocardial ischemia on repeated BIs during angioplasty. This leads to the clinical implication that reduction of cholesterol plasma levels, apart from its other known benefits, could also have a beneficial effect on cardioprotection.

Nicorandil enhances myocardial tolerance to ischemia without progressive collateral recruitment during coronary angioplasty

Nicorandil, a hybrid nitrate and ATP-sensitive potassium channel opener, has had a preconditioning effect in some coronary angioplasty studies. The present study investigated whether the cardioprotective effects of nicorandil involve coronary collateral function. Thirty-two patients with stable angina pectoris were randomized to receive a 1-min intravenous infusion of nicorandil (100 microg/kg) or normal saline. Five minutes later they underwent three 2-min balloon inflations 5-min apart. The maximum ST-segment elevation (deltaSTmax), the sum of ST-segment elevations in all leads (sigmaST), and the chest pain score were determined at the end of each balloon inflation. The collateral flow index (CFI) was derived from simultaneous measurement of the mean aortic pressure and the coronary wedge pressure obtained from a pressure guidewire during balloon inflation. The deltaSTmax, sigmaST, and chest pain score decreased progressively during the 3 sequential balloon inflations in both groups, and the deltaSTmax and sigmaST were less in the nicorandil group than in the control group during each inflation. The CFI did not change during the 3 inflations in either group and was similar in the 2 groups during each inflation. In conclusion, pretreatment with intravenous nicorandil enhances myocardial tolerance to ischemia without progressive collateral recruitment during coronary angioplasty.