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

Interactions between remote ischemic conditioning and post-stroke sleep regulation

Sleep disturbances are common in patients with stroke, and sleep quality has a critical role in the onset and outcome of stroke. Poor sleep exacerbates neurological injury, impedes nerve regeneration, and elicits serious complications. Thus, exploring a therapy suitable for patients with stroke and sleep disturbances is imperative. As a multi-targeted nonpharmacological intervention, remote ischemic conditioning can reduce the ischemic size of the brain, improve the functional outcome of stroke, and increase sleep duration. Preclinical/clinical evidence showed that this method can inhibit the inflammatory response, mediate the signal transductions of adenosine, activate the efferents of the vagal nerve, and reset the circadian clocks, all of which are involved in sleep regulation. In particular, cytokines tumor necrosis factor α (TNFα) and adenosine are sleep factors, and electrical vagal nerve stimulation can improve insomnia. On the basis of the common mechanisms of remote ischemic conditioning and sleep regulation, a causal relationship was proposed between remote ischemic conditioning and post-stroke sleep quality.

Preconditioning in neuroprotection: From hypoxia to ischemia

Sublethal hypoxic or ischemic events can improve the tolerance of tissues, organs, and even organisms from subsequent lethal injury caused by hypoxia or ischemia. This phenomenon has been termed hypoxic or ischemic preconditioning (HPC or IPC) and is well established in the heart and the brain. This review aims to discuss HPC and IPC with respect to their historical development and advancements in our understanding of the neurochemical basis for their neuroprotective role. Through decades of collaborative research and studies of HPC and IPC in other organ systems, our understanding of HPC and IPC-induced neuroprotection has expanded to include: early- (phosphorylation targets, transporter regulation, interfering RNA) and late- (regulation of genes like EPO, VEGF, and iNOS) phase changes, regulators of programmed cell death, members of metabolic pathways, receptor modulators, and many other novel targets. The rapid acceleration in our understanding of HPC and IPC will help facilitate transition into the clinical setting.

Ischemic preconditioning reduces hemodynamic response during metaboreflex activation

Ischemic preconditioning (IP) has been shown to improve exercise performance and to delay fatigue. However, the precise mechanisms through which IP operates remain elusive. It has been hypothesized that IP lowers the sensation of fatigue by reducing the discharge of group III and IV nerve endings, which also regulate hemodynamics during the metaboreflex. We hypothesized that IP reduces the blood pressure response during the metaboreflex. Fourteen healthy males (age between 25 and 48 yr) participated in this study. They underwent the following randomly assigned protocol: postexercise muscle ischemia (PEMI) test, during which the metaboreflex was elicited after dynamic handgrip; control exercise recovery session (CER) test; and PEMI after IP (IP-PEMI) test. IP was obtained by occluding forearm circulation for three cycles of 5 min spaced by 5 min of reperfusion. Hemodynamics were evaluated by echocardiography and impedance cardiography. The main results were that after IP the mean arterial pressure response was reduced compared with the PEMI test (means ± SD +3.37 ± 6.41 vs. +9.16 ± 7.09 mmHg, respectively). This was the consequence of an impaired venous return that impaired the stroke volume during the IP-PEMI more than during the PEMI test (-1.43 ± 15.35 vs. +10.28 ± 10.479 ml, respectively). It was concluded that during the metaboreflex, IP affects hemodynamics mainly because it impairs the capacity to augment venous return and to recruit the cardiac preload reserve. It was hypothesized that this is the consequence of an increased nitric oxide production, which reduces the possibility to constrict venous capacity vessels.

Cardioprotection acquired through exercise: the role of ischemic preconditioning

A great bulk of evidence supports the concept that regular exercise training can reduce the incidence of coronary events and increase survival chances after myocardial infarction. These exercise-induced beneficial effects on the myocardium are reached by means of the reduction of several risk factors relating to cardiovascular disease, such as high cholesterol, hypertension, obesity etc. Furthermore, it has been demonstrated that exercise can reproduce the "ischemic preconditioning" (IP), which refers to the capacity of short periods of ischemia to render the myocardium more resistant to subsequent ischemic insult and to limit infarct size during prolonged ischemia. However, IP is a complex phenomenon which, along with infarct size reduction, can also provide protection against arrhythmia and myocardial stunning due to ischemia-reperfusion. Several clues demonstrate that preconditioning may be directly induced by exercise, thus inducing a protective phenotype at the heart level without the necessity of causing ischemia. Exercise appears to act as a physiological stress that induces beneficial myocardial adaptive responses at cellular level. The purpose of the present paper is to review the latest data on the role played by exercise in triggering myocardial preconditioning.

Cardioprotective effect of high-dose intragraft adenosine infusion on microvascular function and prevention of no-reflow during saphenous vein grafts intervention

BACKGROUND

Despite the use of embolic protection devices, no-reflow can still occur during saphenous vein grafts (SVGs) intervention. High-dose intracoronary adenosine infusion preconditions the myocardium, improves coronary flow, and prevents no-reflow. The role of high-dose intragraft adenosine infusion on protection of microvascular function and prevention of no-reflow has not been investigated

OBJECTIVES

We investigated the cardioprotective effect of high-dose intragraft adenosine infusion, compared with placebo, on microvascular function and prevention of no-reflow during SVGs intervention.

METHODS

We randomized 22 patients with SVGs stenoses to receive either a 10-min intragraft adenosine infusion (200 μg/min; total dose = 2,000 μg) or normal saline prior to stenting. Average peak velocity (APV), coronary flow velocity reserve (CVR), thrombolysis in myocardial infarction (TIMI) frame count (TFC), TIMI myocardial perfusion grade (TMPG), and the rate of no-reflow were compared between the two groups before adenosine or saline infusions and after stenting

RESULTS

After stenting, hyperemic APV, CVR, and TMPG were significantly higher in the adenosine-treated group than in the control group (60 ± 18 vs. 35 ± 10 cm/sec; 2.6 ± 0.54 vs. 1.8 ± 0.47; and 2.8 ± 0.90 vs. 2.1 ± 0.80, respectively; P < 0.05. TFC was significantly lower in the adenosine-treated group than in the control group (14 ± 3.0 vs. 26 ± 13; P < 0.05). In the control group, four patients (36%) developed no-reflow compared to none in the adenosine-treated patient; P < 0.05 CONCLUSIONS: This study provides the first evidence that high-dose intragraft adenosine infusion compared with placebo protects microvascular function and prevents no-reflow during SVGs intervention.

The myocardial protective effects of adenosine pretreatment in children undergoing cardiac surgery: a randomized controlled clinical trial

OBJECTIVE

Adenosine pretreatment reduces injury caused by ischemia-reperfusion. To investigate the hypothesis that adenosine pretreatment would modulate injury induced by cardiopulmonary bypass (CPB) and myocardial ischemia/reperfusion, we conducted a randomized controlled trial on the effects of adenosine pretreatment in children undergoing surgery to repair congenital heart defects.

METHODS

Children undergoing surgery to repair congenital heart defects were randomized to adenosine pretreatment or control treatment. Adenosine pretreatment was performed by infusing a total of 2.45 mg kg⁻¹ of adenosine over 10 min. Serum troponin I was measured pre- and postoperatively. Multiple clinical parameters, including postoperative use of inotropic medicine and duration in the intensive care unit (ICU), were recorded.

RESULTS

A total of 82 patients were enrolled in the study. There were 42 control patients and 40 patients in the adenosine pretreatment group. The mean age and weight of the two groups were not significantly different, nor were cardiopulmonary bypass and cross-clamp times. There were no deaths and severe complications in both groups. The adenosine pretreatment protocol caused significant hypotension but had no significant effect on heart rate. One patient had severe tachycardia shortly after the adenosine pretreatment protocol was completed, and adenosine infusion was continued until CPB was started. Postoperative levels of serum troponin I were greater in the control patients than in the adenosine pretreatment group, indicating that the control group suffered greater myocardial injury. Control group patients required more postoperative inotropic agents than those in the adenosine pretreatment group at 0, 1, and 3 h, indicating that the adenosine pretreatment group had a better cardiac function. The adenosine pretreatment group also required significantly less time in the ICU than the control group (3.2 ± 1.2 days vs 3.9 ± 1.2 days, p = 0.013).

CONCLUSIONS

This study demonstrates that adenosine pretreatment is protective of the myocardium during open-heart surgery in pediatric patients.

Microcirculatory effects of local and remote ischemic preconditioning in supraceliac aortic clamping

INTRODUCTION

Supraceliac aortic clamping in major vascular procedures promotes splanchnic ischemia and reperfusion (I/R) injury that may induce endothelial dysfunction, widespread inflammation, multiorgan dysfunction, and death. We tested the hypothesis that local or remote ischemic preconditioning (IPC) may be protective against injury after supraceliac aortic clamping through the modulation of mesenteric leukocyte-endothelial interactions, as evaluated with intravital microscopy and expression of adhesion molecules.

METHODS

Fifty-six male Wistar rats (weight, 190 to 250 g), were divided into four groups of 14 rats each: control-sham surgery without aortic occlusion; I/R through supraceliac aortic occlusion for 20 minutes, followed by 120 minutes of reperfusion; local IPC through supraceliac aortic occlusion for two cycles of 5 minutes of ischemia and 5 minutes of reperfusion, followed by the same protocol of the IR group; remote IPC through infrarenal aortic occlusion for two cycles of 10 minutes of ischemia and 10 minutes of reperfusion, followed by the same protocol of the IR group. Seven animals per group were used to evaluate in vivo leukocyte-endothelial interactions in postcapillary venules with intravital microscopy and another seven animals per group were used to collect mesentery samples for immunohistochemistry demonstration of adhesion molecules expression.

RESULTS

Supraceliac aortic occlusion increased the number of rolling leukocytes with slower velocities and increased the number of adherent leukocytes to the venular surface and leukocyte migration to the interstitium. The expression of P-selectin, E-selectin, and intercellular adhesion molecule-1 was also increased significantly after I/R. Local or remote IPC reduced the leukocyte recruitment in vivo and normalized the expression of adhesion molecules.

CONCLUSIONS

Local or remote IPC reduces endothelial dysfunction on mesenteric microcirculation caused by I/R injury after supraceliac aortic clamping.

Searching for NF-kappaB-based treatments of ischemia reperfusion injury

When a tissue becomes ischemic, a host of changes occur at the cellular level that lead to a shift in transcriptional activity of many inflammatory and cytoprotective compounds, a process which is extensively controlled through a family of transcription factors known as nuclear factor kappa-B (NF-kappaB). This shift in activity paradoxically results in both a cytoprotective effect at the cellular level and upon reperfusion, a generally destructive inflammatory response, a phenomenon referred to as ischemia reperfusion (IR) injury. To date, a number of methods of modifying the activity of NF-kappaB through either physiologic or pharmacologic manipulation have been developed and studied in animal models of IR injury and in some cases in human clinical trials. Nearly every method of NF-kappaB antagonism has demonstrated a discrete protective effect allowing investigators to reduce myocardial infarct sizes by 60% and cerebral infarct sizes by 57% relative to untreated control animals. The problem of IR injury is all too common and represents a discrete threat not only to the tissues directly involved in the ischemic event, but also to distal sites as well as is seen in the evolution of acute respiratory distress and severe inflammatory response syndromes. In the course of this review, the nature of NF-kappaB and its involvement in IR injury is examined along with the efficacy of the various NF-kappaB-based investigational treatment developed to date.

Limb ischemic preconditioning reduces heart and lung injury after an open heart operation in infants

Open heart surgery supported by cardiopulmonary bypass is associated with heart and lung ischemia-reperfusion injury (IRI). Limb remote ischemic preconditioning (RIPC) reduces injury caused by ischemia-reperfusion in multiple distant organs. We conducted a prospective clinical trial (randomized and controlled) to test the feasibility and safety of limb RIPC, as well as its protective effects against myocardial and pulmonary IRI for infants undergoing repair of simple congenital heart defects. Infants undergoing repair of ventricular septal defects were enrolled in our study and randomly assigned to one of two treatment groups: limb RIPC or control. RIPC was induced twice (24 h and 1 h preoperatively) via three 5-min cycles of ischemia and reperfusion on the left upper arm using a blood pressure cuff. Lung compliance, respiratory index (RI), and cardiac inotropic score (IS) were calculated for each patient. Serum concentrations of the following factors were measured perioperatively: interleukin (IL)-6, IL-8, IL-10, and tumor necrosis factor (TNF)-alpha; lactate dehydrogenase (LDH), creatine kinase (CK), and its isoenzyme (CK-MB), and troponin I (TnI); malondialdehyde (MDA) and superoxide dismutase (SOD). The expression of heat shock protein 70 (HSP 70) in cardiomyocytes was analyzed by Western blot. Surgical outcomes, including limb movement and sensory function, were recorded in detail. Sixty infants weighting less than 7 kg were studied, with 30 patients in the RIPC group and 30 in the control group. Within 6 months of discharge from the hospital, no limb disability, sensory disturbance, or other surgical complications were found in any patient. Compared with the control group, patients in the RIPC group had higher Cs and Cd, along with lower RI and IS at various postoperative phases. At the beginning of the operation, serum concentrations of IL-6, IL-8, IL-10, TNF-alpha, LDH, CK, and TnI were higher in the RIPC group than the control group. Postoperatively, release of cytokines and leakage of heart enzymes were attenuated in the RIPC group; serum concentrations of cytokines and heart enzymes were lower in the RIPC group at some, but not all, postoperative time points. Furthermore, the RIPC group had lower coronary sinus venous concentrations of MDA and higher concentrations of SOD. Similarly, the expression of HSP 70 was upregulated in cardiomyocytes from the RIPC group. Limb RIPC can be applied safely and easily in infants, can attenuate systemic inflammatory response syndrome, and can increase systemic tolerance to IRI, imparting a protective effect against myocardial and pulmonary IRI. The expression of HSP 70 has an important role in the mechanism of action for RIPC.

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

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

Cardioprotective action of urocortin in early pre- and postconditioning

Pre- and postconditioning are powerful endogenous adaptive phenomenon of the organism whereby different stimuli enhance the tolerance against various types of stress. Urocortin (Ucn), member of the corticotropin-releasing factor (CRF) family has potent effects on the cardiovascular system. The aim of this article was to investigate the action of Ucn on cultured cardiomyocytes in the process of pre- and postconditioning. Isolated neonatal rat ventricular myocytes were preconditioned with adenosine, simulated ischemia, and Ucn (10-min treatment followed by 10-min reperfusion/recovery). For detecting the effect of alternative types of preconditioning, necrosis enzyme (lactate dehydrogenase [LDH]) release, vital staining (trypan blue), and ratio of apoptosis/necrosis were examined after cardiac cells were exposed to 3-h sustained ischemia and 2-h reperfusion. Same parameters were measured in the postconditioned groups (30- or 60-min ischemia followed by postconditioning with 10-min ischemic stimulus or Ucn and 2-h reperfusion). Cells exposed to 3-h ischemia followed by 2-h reperfusion were shown as control. Our results show that LDH release a number of trypan blue-stained dead cells and the ratio of apoptotized and necrotized cells was decreased in all preconditioned groups compared with control group. In postconditioned groups LDH content of culture medium, trypan blue-positive cardiomyocytes, and the rate of apoptotic/necrotic cells was reduced contrasted with non-postconditioned group. We can conclude that preconditioning with Ucn induced such a powerful cell protective effect as adenosine and ischemia. Furthermore, postconditioning with Ucn after 60-min ischemia was more cardioprotective than ischemic postconditioning.

Pretreatment With Intracoronary Enalaprilat Protects Human Myocardium During Percutaneous Coronary Angioplasty

OBJECTIVES

We tested the hypothesis that enalaprilat induces preconditioning (PC)-mimetic actions in patients with stable coronary artery disease.

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors increase the bioavailability of bradykinin, which induces cardiac PC.

METHODS

Twenty-two patients undergoing coronary angioplasty were randomized to an intracoronary infusion of enalaprilat or placebo, followed 10 min later by a PC protocol.

RESULTS

In control patients, the ST-segment shift was greater during the first inflation than during the second and third inflations, both on the intracoronary electrocardiogram (ECG) (21.0 +/- 2.8 mm vs. 13.0 +/- 2.0 mm and 13.0 +/- 2.0 mm, p < 0.05) and the surface ECG (16.0 +/- 4.0 mm vs. 10.0 +/- 2.0 mm and 9.0 +/- 2.0 mm, p < 0.05). In contrast, enalaprilat-pretreated patients showed no change in ST-segment shift during inflations on either the intracoronary or the surface ECG. During the first inflation, the ST-segment shift was significantly smaller in treated versus control patients. The chest pain score during the first inflation was also significantly smaller in treated patients versus control patients (33.0 +/- 6.0 mm vs. 64.0 +/- 6.0 mm) and did not change in treated patients during the second and third inflations, whereas it decreased significantly in control patients. In a subset of 6 patients, enalaprilat increased coronary blood flow during infusion, but this effect dissipated before the beginning of angioplasty.

CONCLUSIONS

Pretreatment with enalaprilat attenuates the manifestations of myocardial ischemia during angioplasty. This is the first in vivo evidence showing that an ACE inhibitor protects human myocardium, possibly via PC-mimetics actions, a novel property that might explain the cardioprotective actions of these drugs.

Randomized Controlled Trial of the Effects of Remote Ischemic Preconditioning on Children Undergoing Cardiac Surgery

OBJECTIVES

We conducted a randomized controlled trial of the effects of remote ischemic preconditioning (RIPC) in children undergoing repair of congenital heart defects.

BACKGROUND

Remote ischemic preconditioning reduces injury caused by ischemia-reperfusion in distant organs. Cardiopulmonary bypass (CPB) is associated with multi-system injury. We hypothesized that RIPC would modulate injury induced by CPB.

METHODS

Children undergoing repair of congenital heart defects were randomized to RIPC or control treatment. Remote ischemic preconditioning was induced by four 5-min cycles of lower limb ischemia and reperfusion using a blood pressure cuff. Measurements of lung mechanics, cytokines, and troponin I were made pre- and postoperatively.

RESULTS

Thirty-seven patients were studied. There were 20 control patients and 17 patients in the RIPC group. The mean age and weight of the RIPC and control patients were not different (0.9 +/- 0.9 years vs. 2.2 +/- 3.4 years, p = 0.4; and 6.9 +/- 2.9 kg vs. 11.5 +/- 10 kg, p = 0.06). Bypass and cross-clamp times were not different (80 +/- 24 min vs. 88 +/- 25 min, p = 0.3; and 55 +/- 13 min vs. 59 +/- 13 min, p = 0.4). Levels of troponin I postoperatively were greater in the control patients compared with the RIPC group (p = 0.04), indicating greater myocardial injury in control patients. Postoperative inotropic requirement was greater in the control patients compared with RIPC patients at both 3 and 6 h (7.9 +/- 4.7 vs. 10.9 +/- 3.2, p = 0.04; and 7.3 +/- 4.9 vs. 10.8 +/- 3.9, p = 0.03, respectively). The RIPC group had significantly lower airway resistance at 6 h postoperatively (p = 0.009).

CONCLUSIONS

This study demonstrates the myocardial protective effects of RIPC using a simple noninvasive technique of four 5-min cycles of lower limb ischemia and reperfusion. These novel data support the need for a larger study of RIPC in patients undergoing cardiac surgery.

Hypercholesterolemia attenuates the anti-ischemic effect of preconditioning during coronary angioplasty

BACKGROUND

Cardioprotection by preconditioning is limited in some animal models of hypercholesterolemia. We studied ischemic preconditioning induced by coronary angioplasty in hypercholesterolemic and normocholesterolemic patients by means of a beat-to-beat analysis of ST segments.

METHODS

Thirty coronary disease patients were classified into normocholesterolemic and hypercholesterolemic groups. Intracoronary ECG was recorded during three consecutive balloon inflations of 2-min duration with 5-min intervals.

RESULTS

In normocholesterolemic patients, the ST segment was continuously elevated during the occlusions and rapidly normalized after balloon deflations. Repeated occlusions significantly attenuated ST-segment elevation from 1.28 +/- 0.67 to 0.88 +/- 0.51 mV (p < 0.001) and decreased the time to normalization of ST segment. In hypercholesterolemic patients, the ST segment was rapidly elevated in the first 30 s of the first occlusion, and normalization of the ST segment was longer on the first reperfusion. However, in these patients, repeated occlusions abolished the initial elevation of the ST segment but did not attenuate maximal ST-segment elevation (1.24 +/- 1.11 mV vs 1.21 +/- 1.09 mV) and failed to decrease the time to normalization of the ST segment.

CONCLUSIONS

Hypercholesterolemia accelerates the evolution of myocardial ischemia, delays recovery on reperfusion, and deteriorates the anti-ischemic effect of preconditioning in humans.

Platelet-activating factor induces cardioprotection in isolated rat heart akin to ischemic preconditioning: role of phosphoinositide 3-kinase and protein kinase C activation

Ischemic preconditioning (IP) is a cardioprotective mechanism against myocellular death and cardiac dysfunction resulting from reperfusion of the ischemic heart. At present, the precise list of mediators involved in IP and the pathways of their mechanisms of action are not completely known. The aim of the present study was to investigate the role of platelet-activating factor (PAF), a phospholipid mediator that is known to be released by the ischemic-reperfused heart, as a possible endogenous agent involved in IP. Experiments were performed on Langendorff-perfused rat hearts undergoing 30 min of ischemia followed by 2 h of reperfusion. Treatment with a low concentration of PAF (2 × 10−11 M) before ischemia reduced the extension of infarct size and improved the recovery of left ventricular developed pressure during reperfusion. The cardioprotective effect of PAF was comparable to that observed in hearts in which IP was induced by three brief (3 min) periods of ischemia separated by 5-min reperfusion intervals. The PAF receptor antagonist WEB-2170 (1 × 10−9 M) abrogated the cardioprotective effect induced by both PAF and IP. The protein kinase C (PKC) inhibitor chelerythrine (5 × 10−6 M) or the phosphoinositide 3-kinase (PI3K) inhibitor LY-294002 (5 × 10−5 M) also reduced the cardioprotective effect of PAF. Western blot analysis revealed that following IP treatment or PAF infusion, the phosphorylation of PKC-ε and Akt (the downstream target of PI3K) was higher than that in control hearts. The present data indicate that exogenous applications of low quantities of PAF induce a cardioprotective effect through PI3K and PKC activation, similar to that afforded by IP. Moreover, the study suggests that endogenous release of PAF, induced by brief periods of ischemia and reperfusion, may participate to the triggering of the IP of the heart.

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.

Myocardium tolerant to an adenosine-dependent ischemic preconditioning stimulus can still be protected by stimuli that employ alternative signaling pathways

Clinical studies on cardioprotection by preinfarct angina are ambiguous, which may involve development of tolerance to repeated episodes of ischemia. Not all preconditioning stimuli use identical signaling pathways, and because patients likely experience varying numbers of episodes of preinfarct angina of different degrees and durations, it is important to know whether myocardium tolerant to a particular preconditioning stimulus can still be protected by stimuli employing alternative signaling pathways. We tested the hypothesis that development of tolerance to a particular stimulus does not affect cardioprotection by stimuli that employ different signaling pathways. Anesthetized rats underwent classical, remote or pharmacological preconditioning. Infarct size (IS), produced by a 60-min coronary artery occlusion (CAO), was determined after 120 min of reperfusion. Preconditioning by two 15-min periods of CAO (2CAO15, an adenosine-dependent stimulus) limited IS from 69 ± 2% to 37 ± 6%, but when 2CAO15 was preceded by 4CAO15, protection by 2CAO15 was absent (IS = 68 ± 1%). This development of tolerance coincided with a loss of cardiac interstitial adenosine release, whereas two 15-min infusions of adenosine (200 μg/min iv) still elicited cardioprotection (IS = 40 ± 4%). Furthermore, cardioprotection was produced when 4CAO15 was followed by the adenosine-independent stimulus 3CAO3 (IS = 50 ± 8%) or the remote preconditioning stimulus of two 15-min periods of mesenteric artery occlusion (IS = 49 ± 6%). In conclusion, development of tolerance to cardioprotection by an adenosine-dependent preconditioning stimulus still allows protection by pharmacological or ischemic stimuli intervention employing different signaling pathways.

Cellular and molecular events in ischemic preconditioning: potential therapeutic applications in cardioprotection

Cardioprotection is a mechanism of guarding the heart from damage secondary to different insults including ischaemia, ischaemia/reperfusion, chemical, metabolic and physical stressors. Ischemic preconditioning, by single or multiple brief periods of ischaemia, protects the heart against a more prolonged ischemic insult (index ischaemia). Understanding the cellular, molecular and biochemical events occurring in cardioprotection will allow the development of new interventions to improve the outcome of patients with myocardial diseases. Most of the present experience with cardioprotection has been obtained from studies in young and middle-aged animals, and cells. In the future, cardioprotection research should be carried out mainly in the aging or senescent heart since this will be most relevant to humans. With aging, the heart has a decreased capacity to tolerate and respond to various forms of stress, and the likelihood of myocardial ischaemia and cardiac dysfunction increases.

Exercise-induced and nitroglycerin-induced myocardial preconditioning improves hemodynamics in patients with angina

In humans, regional myocardial dysfunction during ischemia may be improved by ischemic and pharmacological preconditioning. We assessed the possibility that exercise- and nitroglycerin-induced myocardial preconditioning may improve global cardiac performance during subsequent efforts in patients with angina. Ten patients suffering from chronic stable angina and ten healthy volunteers were studied. Through impedance cardiography we assessed hemodynamics during a maximal exercise test, which was used as a baseline (Bas test) and considered as a preconditioning exercise. The Bas test was followed by a sequence of maximal efforts performed during the first (FWOP; 30 min after the Bas test) and second (SWOP; 48 h after the Bas test) windows of protection conferred by ischemic preconditioning. Hemodynamics was further evaluated during maximal exercise performed 48 h later with pharmacologically induced SWOP (PI-SWOP) obtained by transdermal administration of 10 mg of nitroglycerin. In the angina patients, FWOP, SWOP, and PI-SWOP delayed the time to ischemia and allowed them to achieve higher workloads compared with the Bas test. Furthermore, heart rate and cardiac output at peak exercise were enhanced during all the preconditioning phases with respect to the Bas test. However, only SWOP and PI-SWOP increased myocardial contractility and stroke volume. No changes in hemodynamics were detectable in the control subjects. This study demonstrates that in patients with stable angina, although hemodynamics during exercise can be positively improved during both FWOP and SWOP, differences exist between these two phases. Furthermore, the mimicking of exercise-induced SWOP by PI-SWOP with transdermal nitroglycerin may represent an important clinical aspect.