Preconditioning limits myocardial infarct size in hypercholesterolemic rabbits

Hyperlipidaemia and cardioprotection: Animal models for translational studies

Hyperlipidaemia is a well-established risk factor for cardiovascular diseases and therefore, many animal model have been developed to mimic the human abnormal elevation of blood lipid levels. In parallel, extensive research for the alleviation of ischaemia/reperfusion injury has revealed that hyperlipidaemia is a major co-morbidity that attenuates the cardioprotective effect of conditioning strategies (preconditioning, postconditioning and remote conditioning) and that of pharmacological interventions by interfering with cardioprotective signalling pathways. In the present review article, we summarize the existing data on animal models of hypercholesterolaemia (total, low density and HDL abnormalities) and hypertriglyceridaemia used in ischaemia/reperfusion injury and protection from it. We also provide recommendations on preclinical animal models to be used for translations of the cardioprotective strategies into clinical practice. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc.

Dyslipidemia in Ischemia/Reperfusion Injury

Ischemic heart disease is the main cause of morbidity and mortality in the developed world. Although reperfusion therapies are currently the best treatment for this entity, the restoration of blood flow leads, under certain circumstances, to a form of myocardial damage called reperfusion injury. Several studies have shown that age, sex, smoking, diabetes and dyslipidemia are risk factors for cardiovascular diseases. Among these risk factors, dyslipidemias are present in 40% of patients with ischemic heart disease and represent the clinical factor with the greatest impact on the prognosis of patients with cardiovascular diseases. It is known that during reperfusion the increase of the oxidative stress is perhaps one of the most important mechanisms implicated in cell damage. That is why several researchers have studied protective mechanisms against reperfusion injury, such as the ischemic pre- and post- conditioning, making emphasis mainly on the reduction of oxidative stress. However, few of these efforts have been successfully translated into the clinical setting. The controversial results in regards to the relation between cardioprotective mechanisms and dyslipidemia/hypercholesterolemia are mainly due to the difference among quality, composition and the time of administration of hypercholesterolemic diets, as well as the difference in the species used in each of the studies. Therefore, in order to compare results, it is crucial that all variables that could modify the obtained results are taken into consideration.

Effect of hypercholesterolaemia on myocardial function, ischaemia-reperfusion injury and cardioprotection by preconditioning, postconditioning and remote conditioning

Hypercholesterolaemia is considered to be a principle risk factor for cardiovascular disease, having direct negative effects on the myocardium itself, in addition to the development of atherosclerosis. Since hypercholesterolaemia affects the global cardiac gene expression profile, among many other factors, it results in increased myocardial oxidative stress, mitochondrial dysfunction and inflammation triggered apoptosis, all of which may account for myocardial dysfunction and increased susceptibility of the myocardium to infarction. In addition, numerous experimental and clinical studies have revealed that hyperlcholesterolaemia may interfere with the cardioprotective potential of conditioning mechanisms. Although not fully elucidated, the underlying mechanisms for the lost cardioprotection in hypercholesterolaemic animals have been reported to involve dysregulation of the endothelial NOS-cGMP, reperfusion injury salvage kinase, peroxynitrite-MMP2 signalling pathways, modulation of ATP-sensitive potassium channels and apoptotic pathways. In this review article, we summarize the current knowledge on the effect of hypercholesterolaemia on the non-ischaemic and ischaemic heart as well as on the cardioprotection induced by drugs or ischaemic preconditioning, postconditioning and remote conditioning. Future perspectives concerning the mechanisms and the design of preclinical and clinical trials are highlighted.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Mechanisms involved in attenuated cardio-protective role of ischemic preconditioning in metabolic disorders

Myocardial infarction is a pathological state which occurs due to severe abrogation of the blood supply (ischemia) to a part of heart, which can cause myocardial damage. The short intermittent cycles of sub-lethal ischemia and reperfusion has shown to improve the tolerance of the myocardium against subsequent prolonged ischemia/reperfusion (I/R)-induced injury, which is known as ischemic preconditioning (IPC). Although, IPC-induced cardioprotection is well demonstrated in various species, including human beings, accumulated evidence clearly suggests critical abrogation of the beneficial effects of IPC in diabetes mellitus, hyperlipidemia and hyperhomocysteinemia. Various factors are involved in the attenuation of the cardioprotective effect of preconditioning, such as the reduced release of calcitonin gene-related peptide (CGRP), the over-expression of glycogen synthase kinase-3β (GSK-3β) and phosphatase and tensin homolog (PTEN), impairment of mito-KATP channels, the consequent opening of mitochondrial permeability transition pore (MPTP), etc. In this review, we have critically discussed the various signaling pathways involved in abrogated preconditioning in chronic diabetes mellitus, hyperlipidemia and hyperhomocysteinemia. We have also focused on the involvement of PTEN in abrogated preconditioning and the significance of PTEN inhibitors.

Genistein promotes endothelial colony-forming cell (ECFC) bioactivities and cardiac regeneration in myocardial infarction

Although stem cell-mediated treatment of ischemic diseases offers significant therapeutic promise, the limitation in the therapeutic efficacy of transplanted stem cells in vivo because of poor engraftment remains a challenge. Several strategies aimed at improving survival and engraftment of stem cells in the ischemic myocardium have been developed, such as cell transplantation in combination with growth factor delivery, genetic modification of stem cells, and/or cell therapy using scaffolds. To improve therapeutic efficacy, we investigated the effects of genistein on the engraftment of transplanted ECFCs in an acute myocardial ischemia model.

RESULTS

We found that genistein treatment enhanced ECFCs' migration and proliferation, which was accompanied by increases in the expression of ILK, α-parvin, F-actin, and phospholylation of ERK 1/2 signaling. Transplantation of genistein-stimulates ECFCs (GS-ECFCs) into myocardial ischemic sites in vivo induced cellular proliferation and secretion of angiogenic cytokines at the ischemic sites and thereby enhanced neovascularization and decreased myocardial fibrosis as well as improved cardiac function, as shown by echocardiography. Taken together, these data suggest that pretreatment of ECFCs with genistein prior to transplantation can improve the regenerative potential in ischemic tissues, providing a novel strategy in adult stem cell therapy for ischemic diseases.

Dissecting active ingredients of Chinese medicine by content-weighted ingredient–target network

A novel approach integrating network pharmacology analysis with ingredient content and ingredient–target relationships to identify active ingredients of Chinese medicine.

High plasma concentrations of asymmetric dimethylarginine inhibit ischemic cardioprotection in hypercholesterolemic rats

A low concentration of nitric oxide associated with a high concentration of asymmetric dimethylarginine (ADMA) can explain the lack of ischemic cardioprotection observed in the presence of hypercholesterolemia. The objective of the present study was to evaluate the effect of hypercholesterolemia on ischemic pre- and postconditioning and its correlation with plasma concentrations of ADMA. Male Wistar rats (6-8 weeks old) fed a 2% cholesterol diet (n = 21) for 8 weeks were compared to controls (n = 25) and were subjected to experimental myocardial infarction and reperfusion, with ischemic pre- and postconditioning. Total cholesterol and ADMA were measured in plasma before the experimental infarct and the infarct area was quantified. Weight, total cholesterol and plasma ADMA (means ± SE; 1.20 ± 0.06, 1.27 ± 0.08 and 1.20 ± 0.08 vs 0.97 ± 0.04, 0.93 ± 0.05 and 0.97 ± 0.04 µM) were higher in animals on the hypercholesterolemic diet than in controls, respectively. Cardioprotection did not reduce infarct size in the hypercholesterolemic animals (pre: 13.55% and post: 8% compared to 7.95% observed in the group subjected only to ischemia and reperfusion), whereas infarct size was reduced in the animals on a normocholesterolemic diet (pre: 8.25% and post: 6.10% compared to 12.31%). Hypercholesterolemia elevated ADMA and eliminated the cardioprotective effects of ischemic pre- and postconditioning in rats.

High cholesterol diet effects on ischemia–reperfusion injury of the heart

Ischemic heart disease is the leading cause of morbi-mortality in developed countries. Both ischemia–reperfusion injury and mechanisms of cardioprotection have been studied for more than 50 years. It is known that the physiopathological mechanism of myocardial ischemia involves several factors that are closely related to its development, of which hypercholesterolemia is one of the main ones. Therefore, the objective of this review was to elucidate the effects of a high-cholesterol diet on normal ventricular function and ischemia–reperfusion injury associated phenomenon such as post-ischemic ventricular dysfunction (stunned myocardium). Although there exist many studies considering several aspects of this physiopathological entity, the majority were carried out on normal animals. Thus, experiments carried out on hypercholesterolemic models are controversial, in particular those evaluating different mechanisms of cardioprotection such as ischemic preconditioning and postconditioning, and cardioprotection granted by drugs such as statins, which apart from exerting a lipid-lowering effect, exert pleiotropic effects providing cardioprotection against ischemia–reperfusion injury. These controversial results concerning the mechanisms of cardioprotection vary according to quality, composition, and time of administration of the high-cholesterol diet, as well as the species used in each experiment. Thus, to compare the results it is necessary to take all of these variables into account, since they can change the obtained results.

Combination of opium smoking and hypercholesterolemia augments susceptibility for lethal cardiac arrhythmia and atherogenesis in rabbit

Opium consumption is increasing in some eastern societies, where it is grown. We investigated the effect of opium smoking on plasma atherogenic index and incidence of lethal cardiac arrhythmia, i.e. ventricular tachycardia (VT) and ventricular fibrillation (VF) in rabbits. Animals were divided into two-, normo- and hyper-cholesterolemic main groups fed with normal or high cholesterol diet prior and during short-term and long-term exposure to opium smoke. Then, isoproterenol (3mg/kg, i.p.) was injected to induce cardiac ischemia and animals were followed for 3h for counting of lethal arrhythmia incidence. Long-term opium smoking significantly increased the plasma atherogenic index. In ischemic hearts, opium smoking along with hypercholesterolemia significantly enhanced the incidence of fatal arrhythmia. This vulnerability was not mediated by changes in QT interval. These data suggest that opium smoking, especially in hypercholesterolemic conditions, can be a predisposing factor for atherogenesis and lethal arrhythmia.

Occult Cardiotoxicity—Toxic Effects on Cardiac Ischemic Tolerance

The outcome of cardiac ischemic events depends not only on the extent and duration of the ischemic stimulus but also on the myocardial intrinsic tolerance to ischemic injury. Cardiac ischemic tolerance reflects myocardial functional reserves that are not always used when the tissue is appropriately oxygenated. Ischemic tolerance is modulated by ubiquitous signal transduction pathways, transcription factors and cellular enzymes, converging on the mitochondria as the main end effector. Therefore, drugs and toxins affecting these pathways may impair cardiac ischemic tolerance without affecting myocardial integrity or function in oxygenated conditions. Such effect would not be detected by current toxicological studies but would considerably influence the outcome of ischemic events. The authors refer to such effect as “occult cardiotoxicity.” In this review, the authors summarize current knowledge about main mechanisms that determine cardiac ischemic tolerance, methods to assess it, and the effects of drugs and toxins on it. The authors offer a view that low cardiac ischemic tolerance is a premorbid status and, therefore, that occult cardiotoxicity is a significant potential source of cardiac morbidity. The authors propose that toxicologic assessment of compounds would include the assessment of their effect on cardiac ischemic tolerance.

Clinical cardioprotection and the value of conditioning responses

Adjunctive cardioprotective strategies for ameliorating the reversible and irreversible injuries with ischemia-reperfusion (I/R) are highly desirable. However, after decades of research, the promise of clinical cardioprotection from I/R injury remains poorly realized. This may arise from the challenges of trialing and effectively translating experimental findings from laboratory models to patients. One can additionally consider whether features of the more heavily focused upon candidates could limit or preclude therapeutic utility and thus whether we might shift attention to alternate strategies. The phenomena of preconditioning and postconditioning have proven fertile in identification of experimental means of cardioprotection and are the most intensely interrogated responses in the field. However, there is evidence these processes, which share common molecular signaling elements and end effectors, may be poor choices for clinical exploitation. This includes evidence of age dependence, limiting efficacy in target aged or senescent hearts; refractoriness to conditioning stimuli in diseased myocardium; interference from a variety of relevant pharmaceuticals; inadvertent induction of these responses by prior ischemia or commonly used drugs, precluding further benefit; and sex dependence of protective signaling. This review focuses on these features, raising questions about current research strategies, and the suitability of these widely studied phenomena as rational candidates for clinical translation.

Experimental hyperlipidaemia does not prevent preconditioning and it reduces ischemia-induced apoptosis

BACKGROUND

Although ischemic preconditioning (PC) is known to confer cardioprotection in healthy subjects, it is unclear whether this phenomenon exists in the presence of hyperlipidaemia. The goal of this study was to determine whether the cardioprotective effect of PC is affected by hyperlipidaemia in a guinea pig model.

METHODS

We investigated the influence of preconditioning in normo- and hyperlipidaemic animals on papillary muscle contractility and myocardial damage as expressed by the percentage of apoptotic cells. Guinea pigs were fed a normal diet or a hyperlipidaemic diet for 5 weeks. Experiments were performed on papillary muscles subjected to experimental ischemia-reperfusion with or without prior PC.

RESULTS

The dietary treatment resulted in significant changes in lipid parameters, which had not affected the functionality of the right ventricle papillary muscle, both at basal conditions and in response to ischemia-reperfusion injury. However, it was found that the hyperlipidaemic diet had an effect on ischemia-induced apoptosis. Papillary muscles of hyperlipidaemic animals with higher HDL plasma concentrations were less susceptible to ischemia-reperfusion injury.

CONCLUSIONS

This study demonstrates that hyperlipidaemia does not alter the benefits of ischemic preconditioning such as a reduction of apoptosis and preservation of myocardial contractility. Additionally, it has been shown that plasma HDL may protect cardiomyocytes against ischemia-induced apoptosis.

Design and synthesis of nitrate esters of aromatic heterocyclic compounds as pharmacological preconditioning agents

Ischemic preconditioning (IPC) constitutes an endogenous protective mechanism in which one or more brief periods of myocardial ischemia and reperfusion render the myocardium resistant to a subsequent more-sustained ischemic insult. Pharmacological preconditioning represents an ideal alternative of IPC. We now describe the design and synthesis of indole, quinoline, and purine systems with an attached pharmacophoric nitrate ester group. The indole and quinoline derivatives 4 and 5 possess structural features of the nitrate containing K(ATP) channel openers. Purine analogues 11 and 12, substituted at the position 6 by a piperidine moiety and at position 9 by an alkyl nitrate, could combine the effects of the nitrate containing K(ATP) channel openers and those of adenosine. Compound 13 bears the nicotinamide moiety of nicorandil instead of nitrate ester. Compounds 4, 5, and 11 reduced infarction and the levels of malondialdehyde (MDA) at reperfusion in anesthetized rabbits. Compounds 12 and 13 did not significantly reduce the infarct size. Analogues 4 and 5 increased cGMP and MDA during ischemia, while combined analogue 4 and mitoK(ATP) blocker 5-hydroxydecanoic acid (5-HD) abrogated this benefit suggesting an action through mitoK(ATP) channel opening. Treatment with derivative 11 combined with 5-HD as well as treatment with 11 and adenosine receptor blocker 8-(p-sulfophenyl)theophylline (SPT) did not abrogate cardioprotection. Compound 11 is a lead molecule for the synthesis of novel analogues possessing a dual mode of action through cGMP-mitoK(ATP) channel opening-free radicals and through adenosine receptors.

The late phase of preconditioning and its natural clinical application--gene therapy

There is little doubt that the discovery of ischemic preconditioning (PC) has been one of the fundamental milestones in the field of ischemic biology in the past 20 years. The purpose of this article is to review the pathophysiology and molecular basis of the late phase of myocardial PC. The exploitation of late PC for the development of novel gene therapy strategies aimed at inducing a permanently preconditioned cardiac phenotype (prophylactic cardioprotection) will also be discussed. Deciphering the mechanism of late PC has not only conceptual interest but also a considerable therapeutic implications, since transfer of the genes that underlie late PC would be expected to replicate the salubrious effects of this response of the heart to stress.

Interaction of cardiovascular risk factors with myocardial ischemia/reperfusion injury, preconditioning, and postconditioning

Therapeutic strategies to protect the ischemic myocardium have been studied extensively. Reperfusion is the definitive treatment for acute coronary syndromes, especially acute myocardial infarction; however, reperfusion has the potential to exacerbate lethal tissue injury, a process termed "reperfusion injury." Ischemia/reperfusion injury may lead to myocardial infarction, cardiac arrhythmias, and contractile dysfunction. Ischemic preconditioning of myocardium is a well described adaptive response in which brief exposure to ischemia/reperfusion before sustained ischemia markedly enhances the ability of the heart to withstand a subsequent ischemic insult. Additionally, the application of brief repetitive episodes of ischemia/reperfusion at the immediate onset of reperfusion, which has been termed "postconditioning," reduces the extent of reperfusion injury. Ischemic pre- and postconditioning share some but not all parts of the proposed signal transduction cascade, including the activation of survival protein kinase pathways. Most experimental studies on cardioprotection have been undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of other disease processes. However, ischemic heart disease in humans is a complex disorder caused by or associated with known cardiovascular risk factors including hypertension, hyperlipidemia, diabetes, insulin resistance, atherosclerosis, and heart failure; additionally, aging is an important modifying condition. In these diseases and aging, the pathological processes are associated with fundamental molecular alterations that can potentially affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Among many other possible mechanisms, for example, in hyperlipidemia and diabetes, the pathological increase in reactive oxygen and nitrogen species and the use of the ATP-sensitive potassium channel inhibitor insulin secretagogue antidiabetic drugs and, in aging, the reduced expression of connexin-43 and signal transducer and activator of transcription 3 may disrupt major cytoprotective signaling pathways thereby significantly interfering with the cardioprotective effect of pre- and postconditioning. The aim of this review is to show the potential for developing cardioprotective drugs on the basis of endogenous cardioprotection by pre- and postconditioning (i.e., drug applied as trigger or to activate signaling pathways associated with endogenous cardioprotection) and to review the evidence that comorbidities and aging accompanying coronary disease modify responses to ischemia/reperfusion and the cardioprotection conferred by preconditioning and postconditioning. We emphasize the critical need for more detailed and mechanistic preclinical studies that examine car-dioprotection specifically in relation to complicating disease states. These are now essential to maximize the likelihood of successful development of rational approaches to therapeutic protection for the majority of patients with ischemic heart disease who are aged and/or have modifying comorbid conditions.

Myocardial protection in man--from research concept to clinical practice

Myocardial protection aims at preventing myocardial tissue loss: (a) In the acute stage, i.e., during primary angioplasty in acute myocardial infarction. In this setup, the attenuation of reperfusion injury is the main target. As a "mechanical" means, post-conditioning has already been tried in man with encouraging results. Pharmacologic interventions that could be of promise are statins, insulin, peptide hormones, including erythropoietin, fibroblast growth factor, and many others. (b) The patient with chronic coronary artery disease offers another paradigm, with the target of avoidance of further myocyte loss through apoptosis and inflammation. Various pharmacologic agents may prove useful in this context, together with exercise and "mechanical" improvement of cardiac function with attenuation of myocardial stretch, which by itself is a noxious influence. A continuous effort toward acute and chronically preserving myocardial integrity is a concept concerning both the researcher and the clinician.

Ischemic Postconditioning Reduces Infarct Size by Activation of A1 Receptors and K+ ATP Channels in Both Normal and Hypercholesterolemic Rabbits

The effect of ischemic postconditioning (Postcon) in hypercholesterolemic animals is unknown. The objectives were to determine if ischemic preconditioning (IPC) and Postcon reduce infarct size in hypercholesterolemic animals and to assess if A1 receptors and K+(ATP) channels are involved in Postcon mechanisms. Isolated rabbit hearts were perfused according to the Langendorff technique and subjected to 30 minutes of ischemia and 30 minutes of reperfusion (G1). In Group 2, IPC was performed (1 cycle of 5 minutes ischemia/reperfusion) before 30 minutes of ischemia. In Group 3 (G3), Postcon was performed (2 cycles of 30-second reperfusion/ischemia) after 30 minutes of ischemia. The G3 protocol was repeated in G4 and G5, but during Postcon, an A1 receptor blocker (DPCPX, 200 nM) and glybenclamide (K+(ATP), blocker, 0.3 microM) were administered, respectively. The G1 to G5 protocols were repeated in animals fed with an enriched cholesterol diet (1%) for 4 weeks (G6 to G10). The infarct size was measured by triphenyltetrazolium. The infarct size was 16.6 +/- 4.6% in G1 and 25.8 +/- 7.3% in G6, and IPC and Postcon reduced the infarct area in both normal and hypercholesterolemic animals (G2: 5.1 +/- 1.7% [P < 0.05] and G3: 5.4 +/- 0.9% [P < 0.05] in normal animals; G7: 4.1 +/- 1.6% [P < 0.05] and G8 4.8 +/- 0.9% [P < 0.05], in hypercholesterolemic animals). Both DPCPX and glybenclamide abolished the effect reached by Postcon. Thus, Postcon reduces infarct size in normal and hypercholesterolemic animals through the activation of A1 and K+(ATP) channels.

Acute administration of vitamin E triggers preconditioning via K(ATP) channels and cyclic-GMP without inhibiting lipid peroxidation

Vitamin E (VitE) is considered an antioxidant agent. One or more brief periods of ischemia (isc), followed by short reperfusion (rep), increase the tolerance of the heart to a subsequent prolonged ischemia, a phenomenon known as ischemic preconditioning (PC). Mitochondrial KATP channels (mitoKATP), cyclic-GMP (cGMP), and free radicals are involved in the mechanism of PC, whereas some antioxidants abolish this benefit. The purpose of this study was to evaluate the effect of VitE on infarct size, PC, and the oxidative status in vivo. Male rabbits were divided into seven groups and were subjected to myocardial ischemia (isc) and reperfusion (rep) with the following interventions: (1) control (no intervention); (2) E150 (iv VitE at a dose of 150 mg/kg for 75 min, starting 40 min before index isc and lasting through 5 min of rep); (3) E300 (iv VitE 300 mg/kg as previously described); (4) PC (two cycles of 5 min isc and 10 min rep), (5) combined E150-PC; and (6) combined E300-PC. In the last two groups VitE was given 40 min before index ischemia. Blood samples were taken for malondialdehyde (MDA) and conjugated dienes (CDs) measurement. In a second series of experiments heart tissue samples were taken at the time of long ischemia for MDA and CD determination and for cGMP assay. In order to test whether combined treatment with VitE (as the E150 group) and the mitoKATP blocker 5-hydroxydecanoic acid (5-HD) changes the infarct size, an additional group was assessed in the first series of experiments. Tissue VitE concentration was evaluated in myocardium. VitE at both doses reduced the infarct size (19.7 +/- 2.8% for E150 and 18.8 +/- 4.9% for E300 vs 47.4 +/- 2.6% in control, P < 0.05) without attenuating the effect of PC (10.2 +/- 3.1% for E150-PC, 12.4 +/- 2.2% for E300-PC, vs 13.5 +/- 3.3% for PC). Combined VitE and 5-HD treatment abrogates this benefit (37.4 +/- 6.5%, P < 0.05 vs E150 and NS vs control). VitE increases intracellular cGMP and CDs levels (P < 0.05 vs control) to the same extent as PC (P < 0.05 vs control), with no effect on MDA (P = NS between all the groups). Peripheral markers of oxidative stress are increased during reperfusion in all groups (P < 0.05 vs baseline). Overall, VitE limits infarct size via mitoKATP and cGMP, while preserving the benefit of ischemic PC.

The effectiveness of postconditioning and preconditioning on infarct size in hypercholesterolemic and normal anesthetized rabbits

BACKGROUND

Postconditioning with multiple very short coronary occlusions immediately after prolonged ischemia is a new endogenous mechanism for protection of the ischemic heart. We tested whether postconditioning is effective in limiting infarct size in hypercholesterolemic rabbits.

METHODS

Male rabbits were fed a cholesterol-enriched diet for 6 weeks. Animals were subjected to 30 min of regional ischemia of the heart and 3h of reperfusion with the following additional interventions: Control group no additional intervention, ischemic preconditioning (IPC) group to two cycles of 5 min ischemia separated by 10 min reperfusion before the index ischemia, 6/10 IPostC group to six cycles of 10s ischemia separated by 10s reperfusion and 4/30 IPostC group to four cycles of 30s ischemia separated by 30s reperfusion immediately after the end of the index ischemia. In a second series of experiments the same interventions were applied to animals fed with a normal diet. Infarct size (I) was determined by triphenyltetrazolium chloride staining.

RESULTS

The I/R in hypercholesterolemic rabbits was 55.2+/-5.9% in Control, 17.9+/-4.2% in IPC (P<0.01 versus Control), 63.4+/-4.8% in 6/10 IPostC and 55.6+/-8.2% in 4/30 IPostC (P=NS between them and the Control group). In the normal diet rabbits, the I/R was 48.2+/-4.3% in Control, 15.1+/-2.1% in IPC, 20.4+/-2.9% in 6/10 IPostC (P<0.01 versus Control) and 45.1+/-8.9% in 4/30 IPostC (P=NS versus Control). Blood cholesterol levels were increased and atheromatic lesions were present in the first series.

CONCLUSION

Postconditioning is ineffective in limiting the infarct size in rabbits with hypercholesterolemia and atherosclerosis while preconditioning continued to be effective under the same conditions.

Preconditioning: a paradigm shift in the biology of myocardial ischemia

The discovery of preconditioning (PC) has arguably been the single most important development in the field of ischemic biology in the past 20 years. The significance of this phenomenon transcends cardiovascular medicine, since it is ubiquitously observed in virtually every tissue of the body. This article reviews the pathophysiology and molecular basis of myocardial PC, with particular emphasis on the late phase of this cardioprotective adaptation. The article also discusses the exploitation of late PC for the development of novel gene therapy strategies aimed at inducing a permanently preconditioned cardiac phenotype (prophylactic cardioprotection). Besides its conceptual interest, deciphering the mechanism of late PC has considerable therapeutic reverberations, since transfer of the genes that underlie late PC would be expected to emulate the salubrious effects of this response of the heart to stress.

The Effect of the Phytoestrogen Genistein on Myocardial Protection, Preconditioning and Oxidative Stress

INTRODUCTION

We have previously shown that estrogen administered in ovariectomized female rabbits significantly reduce myocardial infarct size. We now investigated whether the phytoestrogen genistein similarly protects ischemic myocardium and whether this is associated with its antioxidant properties. In addition, we examined whether genistein abolishes preconditioning, since at high doses, it inhibits tyrosine kinase.

MATERIALS AND METHODS

We studied five groups of New Zealand white female rabbits. Group A (n = 12) were normal controls, group B (n = 14) were ovariectomized 4 weeks prior to the experiment, group C (n = 10) were ovariectomized and treated with genistein (0.2 mg kg(-1) day(-1) subcutaneously) for 4 weeks before the experiment, group D (n = 12) had intact gonads and were treated with genistein (0.2 mg kg(-1) day(-1) subcutaneously) for 4 weeks before the experiment and group E (n = 8) were ovariectomized 4 weeks prior to the experiment and treated with a single dose of genistein (0.2 mg kg(-1) day(-1) subcutaneously) just prior to the experiment. All animals underwent 30 min of heart ischemia and 120 min of reperfusion, with (subgroup I) or without (subgroup II) preconditioning. Malondialdehyde (MDA) concentration just before the experiment was determined.

RESULTS

We found significant differences between the groups-p < 0.0001 in factorial ANOVA. The groups with preconditioning had significant smaller infarcts compared to those without-AI vs AII (10.66 +/- 1.42% vs 43.22 +/- 2.67%), BI vs BII (18.53 +/- 2.36% vs 43.05 +/- 8.37%), CI vs CII (10.17 +/- 2.07% vs 44.5 +/- 5.47%), DI vs DII (14.98 +/- 2.36% vs 37.79 +/- 3.92%) and EI vs EII (17.11 +/- 3.24% vs 42.08 +/- 3.42%), p < 0.0005. Ovariectomy was not associated with larger myocardial infarctions-AII vs BII, p = NS. Genistein, for 4 weeks, did not protect ischemic myocardium in either ovariectomized or non-ovariectomized animals-BII vs CII and AII vs DII, p = NS. There was no significant difference between the preconditioned animals, with intact gonads or ovariectomized (AI vs BI, p = NS), ovariectomized with or without genistein (BI vs CI, p = NS) and non-ovariectomized whether treated with genistein or not (AI vs DI, p = NS). A single dose of genistein did not offer any protection (EII vs BII, p = NS), nor did it modify the preconditioning effect (EI vs BI, p = NS). We found no significant difference in MDA plasma levels between the groups.

CONCLUSION

Genistein, at this dose, does not reduce infarct size per se nor abolishes the protection induced by preconditioning, in both ovariectomized and non-ovariectomized animals. Preconditioning offers myocardial protection in animals with intact gonads as well as estrogen deprived; bilateral ovariectomy, at least during short-term, is not associated with larger myocardial infarcts compared to control animals. In addition estrogen deprivation, during short term, as well as genistein do not modify oxidative stress.

The olive constituent oleuropein exhibits anti-ischemic, antioxidative, and hypolipidemic effects in anesthetized rabbits

Thgoal of this study was to evaluate the efficacy of the antioxidant olive constituent, oleuropein, on infarct size, oxidative damage, and the metabolic profile in rabbits subjected to ischemia. Oleuropein, 10 or 20 mg/(kg x d), was administered to 8 groups that consumed a normal or hypercholesterolemic diet for 6 wk or only the higher dose for 3 wk. Circulating levels of malondialdehyde, protein carbonyl, nitrite+nitrate, cholesterol, triglycerides, SOD activity, and the metabolic profile were measured using 1H NMR spectra. In rabbits that consumed the normal diet, the infarct size (percentage of infarct to risk areas) was reduced by the administration of 10 mg oleuropein/(kg x d) (16.1 +/- 2.9%) or 20 mg oleuropein/(kg x d) for 3 wk (21.7 +/- 2.2%) or for 6 wk (24.3 +/- 1.3%) compared with the control group (48.05 +/- 2.0%, P < 0.05). Only the higher dose of 20 mg/(kg x d) reduced the infarct size in hypercholesterolemic rabbits (34.7 +/- 4.4% for 6 wk and 34.8 +/- 6.1% for 3 wk) compared with the cholesterol-fed control group (52.8 +/- 2.4%, P < 0.05). Oleuropein decreased the plasma lipid peroxidation product and protein carbonyl concentrations compared with the control groups, in which these factors increased relative to baseline due to ischemia and reperfusion. Furthermore, in rabbits administered oleuropein, RBC superoxide dismutase activity did not change during ischemia and reperfusion. This activity was significantly higher than in both control groups in which it was reduced by ischemia and reperfusion compared with baseline. Treatment for 6 wk with both doses of oleuropein reduced total cholesterol and triglyceride concentrations. 1H NMR spectra revealed a different profile of glycolysis metabolites in the oleuropein-treated groups compared with the controls. Oleuropein, for 3 or 6 wk, reduced the infarct size, conferred strong antioxidant protection and reduced the circulating lipids. This is the first experimental study in vivo that suggests the possibility of using an olive constituent in the treatment of ischemia.

Hyperlipidemia attenuates the infarct size-limiting effect of ischemic preconditioning: role of matrix metalloproteinase-2 inhibition

Hyperlipidemia attenuates the cardioprotective effect of preconditioning via unknown mechanisms. We have reported previously that in normolipidemic rats, preconditioning decreased ischemia-induced activation and release of myocardial matrix metalloproteinase (MMP)-2 into the coronary perfusate. Here, we investigated whether hyperlipidemia interferes with the cardioprotective effect of preconditioning through modulation of MMP-2. Hearts isolated from male Wistar rats fed 2% cholesterol-enriched or control chow for 9 weeks were subjected to a preconditioning protocol (three intermittent periods of ischemia/reperfusion of 5-min duration each) or a time-matched nonpreconditioning protocol. This was followed by a test ischemia/reperfusion (30-min ischemia and 120-min reperfusion) in both groups. Preconditioning decreased infarct size in the control but not the cholesterol-fed group. Cardioprotection in the preconditioned control group but not in the cholesterol-fed group was associated with an 18 +/- 3% (p < 0.05) inhibition of test ischemia/reperfusion-induced activation and release of myocardial MMP-2 into the perfusate. Myocardial protein levels of tissue inhibitors of MMPs [tissue inhibitor of metalloproteinases (TIMP)-2 and TIMP-4] were not changed in either group. A reduction of infarct size in nonpreconditioned hearts from both control and cholesterol-fed group was produced by the MMP inhibitor ilomastat at 0.25 microM, a concentration producing MMP-2 inhibition comparable with that of preconditioning in the control group. We conclude that hyperlipidemia blocks preconditioning-induced cardioprotection, hyperlipidemia abolishes preconditioning-induced inhibition of myocardial MMP-2 activation and release, preconditioning-induced inhibition of MMP-2 activation and release is not mediated by TIMPs, and pharmacological inhibition of MMPs produces cardioprotection in both normal and hyperlipidemic rats.

Hypercholesterolemia blunts NO donor-induced late preconditioning against myocardial infarction in conscious rabbits

Although NO donors have been shown to confer late preconditioning (PC) against myocardial ischemia/reperfusion injury in healthy rabbits, it is unknown whether concurrent systemic disorders affect NO donor-induced cardioprotection. Since many patients with coronary artery disease have hypercholesterolemia (HC), we examined the effect of this condition on late PC induced by the NO donor diethylenetriamine/nitric oxide (DETA/ NO). Chronically instrumented rabbits were fed a normal diet (normocholesterolemia, NC) or a diet enriched with 1% cholesterol (HC) for 4 weeks. Plasma cholesterol levels were significantly elevated and the arterial pressure response to the endothelium-dependent vasodilator bradykinin was blunted in cholesterol diet-fed rabbits. Conscious rabbits underwent a 30-minute coronary occlusion followed by 3 days of reperfusion. When NC rabbits were pretreated with DETA/NO (0.1 mg/kg, i. v. x 4, group II, n = 7) 24 hours before the 30-minute occlusion, infarct size was reduced by 52% (29.7 +/- 3.4% versus 62.4 +/- 4.0% of the region at risk in NC controls [group I, n = 5], P < 0.05), indicating that DETA/NO induced a late PC effect against myocardial infarction. In contrast, when HC rabbits were pretreated with the same dose of DETA/NO (group IV, n = 6), infarct size was not significantly reduced (61.0 +/- 5.7% versus 68.1 +/- 4.5% of the region at risk in HC [group III, n = 5], P = NS), suggesting that DETA/NO failed to induce a delayed cardioprotective effect. These data demonstrate, for the first time, that HC blunts NO donor-induced late PC against myocardial infarction, implying that the inhibitory effects of HC on ischemia-induced and NO donor-induced late PC are caused by disruption of biochemical pathways distal to the generation of NO that triggers these adaptations.

Melatonin does not prevent the protection of ischemic preconditioning in vivo despite its antioxidant effect against oxidative stress

Free radicals are involved in the protective mechanism of preconditioning (PC), whereas antioxidant compounds abolish this benefit. Melatonin is a hormone with antioxidant properties. The aim of our study was to evaluate the effect of melatonin on infarct size in ischemic preconditioning in vivo. We randomly divided 33 male rabbits into four groups and subjected them to 30 min of myocardial ischemia and 3 h of reperfusion with the following prior interventions: (i) no intervention, (ii) iv melatonin at a total dose of 50 mg/kg, (iii) PC with two cycles of 5 min ischemia and 10 min reperfusion, and (iv) combined melatonin and PC. In a second series of experiments, another antioxidant agent N-acetylcysteine (NAC) was used in a control and in a PC group. Myocardial infarct size was determined and blood samples were drawn at different time points for the determination of lipid peroxidation products, total superoxide dismutase (SOD) activity, and (1)H-NMR spectra to evaluate the changes in the metabolic profile. Melatonin showed no effect on myocardial infarct size in the group of sustained ischemia (42.9 +/- 3.6% vs 47.4 +/- 4.9%) and it did not attenuate the reduction of myocardial infarct size in the PC group (13.6 +/- 2.4% vs 14.0 +/- 1.7%). A similar effect was found in NAC-treated groups (44.8 +/- 3.4% vs 14.3 +/- 1.3%). Lipid peroxidation product levels were significantly elevated in the control and PC groups, whereas melatonin decreased them in both groups. The SOD activity was enhanced in the PC group compared to controls; melatonin kept SOD activity unchanged during ischemia/reperfusion and enhanced its activity when it was combined with PC. Melatonin did not change the metabolic profile of the control and PC groups. Melatonin does not prevent the beneficial effect of ischemic PC on infarct size despite its antioxidant properties.

Estrogen alone or combined with medroxyprogesterone but not raloxifene reduce myocardial infarct size

We investigated whether estrogen protects the ischemic myocardium in oophorectomized female rabbits fed with a cholesterol-enriched diet, whether the addition of a progestin compound attenuates the beneficial effect of estrogen and whether raloxifene also limits myocardial necrosis. We treated 32 female oophorectomized hypercholesterolemic rabbits with (a) placebo (N=8, group I), (b) conjugated estrogens alone (N=8, group II), (c) conjugated estrogens combined continuously with medroxyprogesterone acetate (N=8, group III) and (d) raloxifene (N=8, group IV) all for 4 weeks. All rabbits underwent 30 min of ischemia and 120 min of reperfusion. Both infarct size (0.38+/-0.08 and 0.45+/-0.05 in groups II and III, respectively, vs. 0.78+/-0.07 in group I, P<0.005) and infarct size/risk zone% (26.34+/-4.18 and 35.01+/-4.39 in groups II and III, respectively, vs. 52.18+/-7.84 in group I, P<0.05) were significantly smaller in the estrogen treatment groups compared to placebo. No significant difference was observed between groups II and III. There was no significant difference between groups I and IV for infarct size (0.78+/-0.07 vs. 0.69+/-0.08, respectively) or for infarct size/risk zone% (52.18+/-7.84 vs. 47.17+/-4.3). Short-term estrogen protects ischemic myocardium in hypercholesterolemic oophorectomized female rabbits; this effect is not attenuated by the addition of a progestin compound. Raloxifene, however, does not decrease infarct size compared to placebo.

Attenuation of increased myocardial ischaemia-reperfusion injury conferred by hypercholesterolaemia through pharmacological inhibition of the caspase-1 cascade

1. Hypercholesterolaemia has been shown to be associated with greater myocardial ischaemia-reperfusion injury, in which apoptosis and inflammation-mediated necrosis both play a key role. 2. Caspase-1 is involved in the activation of both apoptosis and inflammation, through the intermediate of interleukin-1beta (IL-1beta). We herein examined whether pharmacological inhibition of the caspase-1 cascade, using Ac-Tyr-Val-Ala-Asp-CH(2)Cl (Ac-YVAD.cmk), after myocardial ischaemia have greater protective effects on myocardial ischaemia-reperfusion injury in diet-induced hypercholesterolaemic rabbits. 3. Male rabbits fed with standard chow or chow supplemented with 0.5% cholesterol and 10% coconut oil for 8 weeks were subjected to 30 min of left circumflex artery occlusion followed by 4 h of reperfusion. An intravenous bolus of Ac-YVAD.cmk (1.6 mg kg(-1)) or vehicle was given 20 min after coronary occlusion. 4. Postischaemic administration of Ac-YVAD.cmk markedly decreased infarct size from 26+/-3% to 12+/-2% in normally fed rabbits (P=0.005) and from 41+/-6% to 14+/-2% in cholesterol-fed rabbits (P<0.001). 5. In the ischaemic non-necrotic area, treatment with Ac-YVAD.cmk markedly reduced the percentage of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL)-positive cardiomyocytes from 15.5+/-0.8% to 2.2+/-0.1% in normally fed rabbits (P<0.001) and from 39.0+/-2.3% to 2.2+/-0.1% in cholesterol-fed rabbits (P<0.001). 6. Ac-YVAD.cmk treatment resulted in a reduction not only of IL-1beta and caspase-1, but also of caspase-3 in the ischaemic myocardium in both normally fed and cholesterol-fed rabbits. 7. No differences in infarct size, the percentage of TUNEL-positive cardiomyocytes, IL-1beta levels or activity of caspase-1 and caspase-3 were observed between Ac-YVAD.cmk-treated normally fed and cholesterol-fed rabbits. 8. This study demonstrates that injection of a selective caspase-1 inhibitor after myocardial ischaemia markedly reduced the detrimental effect conferred by hypercholesterolaemia on myocardial ischaemia-reperfusion injury by attenuating both necrotic as well as apoptotic cell death pathways through inhibition of IL-1beta production and activation of caspase-1 and caspase-3.

Reduction of myocardial infarct size in rabbits by a novel indole derivative with antioxidant and free radical scavenging properties

We investigated the cardioprotective efficacy of a new compound, 3-[(1H-1-indolyl)methyl] -4-amino 4,5-dihydro-1H,1,2,4 triazole-5-thione (C6458). The effect of C6458 on the reduction of the infarct size and its protective ability against oxidative damage of the myocardium after ischemia-reperfusion was examined in rabbits that were subjected to 30 min regional ischemia and 2 h reperfusion. C6458 was administered by continuous infusion for 30 min starting at the 10th minute of sustained ischemia and ending at the 10th minute of reperfusion (two doses, 100 and 200 micromol/kg BW). Infarct and risk areas were delineated with Zn2+-Cd2+ particles and triphenyl tetrazolium chloride staining. Antioxidant activity was detected spectrophotometrically by the measurement of malondialdehyde formation. C6458 reduced significantly the level of malondialdehyde in rabbits under ischemia-reperfusion at both doses. Interestingly, at the dose of 200 micromol/kg, the compound decreased the malondialdehyde levels from the 1st minute of reperfusion and significantly reduced infarct size. The free radical scavenging properties of the compound were examined in vitro by determination of the interaction with the 1,1-diphenyl-2-picrylhydrazyl (DPPH) stable free radical. The ability of the C6458 to scavenge HO* was established by its competition with dimethyl sulfoxide (DMSO) for HO radicals. The compound tested showed a significant effect in the above assays. We conclude that C6458 possesses a protective effect against both damaged myocardium and infarct size in anesthetized rabbits. This beneficial effect may be attributed, at least in part, to its antioxidant and free radical scavenging activity.

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.

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

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