Pravastatin restored the infarct size-limiting effect of ischemic preconditioning blunted by hypercholesterolemia in the rabbit model of myocardial infarction

The protective effect of remote ischemic conditioning is lost in patients with hypercholesterolemia

Remote ischemic conditioning (RIC), brief repetitive cycles of ischemia and reperfusion in remote tissues, is known to induce robust protection against myocardial ischemia-reperfusion (I/R) injury in preclinical studies. However, translation of the beneficial effects to the clinical setting has been challenging. A possibility is that comorbidities, including hypercholesterolemia, interfere with the protective mechanisms of RIC. The aim of this study was to test if hypercholesterolemia attenuates the efficacy of RIC in patients with hypercholesterolemia. Patients with familial hypercholesterolemia (FH) with high (≥5.5 mmol/L) low-density lipoprotein cholesterol (LDL-C), FH with low (≤2.5 mmol/L) and healthy control subjects (n = 12 in each group) were included. Flow-mediated vasodilatation (FMD) of the brachial artery was evaluated, before and after a 20-min period of forearm ischemia and 20 min reperfusion (I/R) as a measure of endothelial function. Study subjects were randomized to a RIC protocol consisting of four cycles of 5 min of leg ischemia or sham using a crossover design. Forearm I/R induced significant reduction in FMD in all three groups during the sham procedure. RIC protected from endothelial dysfunction induced by forearm ischemia-reperfusion in healthy controls [FMD baseline 2.8 ± 2.3 vs. FMD after I/R + RIC 4.5 ± 4.0%; means (SD)] and in patients with FH with low LDL-C (4.5 ± 3.5 vs. 4.4 ± 4.2%). By contrast, RIC fails to protect against I/R-induced endothelial dysfunction in patients with FH and high LDL-C (3.9 ± 3.0 vs. 1.1 ± 1.5%; P < 0.01). These findings provide the first evidence in humans that the protective effect of RIC is lost in patients with elevated cholesterol.NEW & NOTEWORTHY We investigated the impact of hypercholesterolemia on the protective effect of RIC on ischemia-reperfusion injury in a well-characterized patient population with isolated hypercholesterolemia. The results show that the protective effect of RIC is absent in patients with hypercholesterolemia but is apparent in patients with hypercholesterolemic following treatment with lipid-lowering drugs. The results are of importance for the understanding of how comorbidities affect the therapeutic potential of RIC.

Why Not Dipyridamole: a Review of Current Guidelines and Re-evaluation of Utility in the Modern Era

Dipyridamole is an old anti-platelet and coronary vasodilator agent that inhibits platelet phosphodiesterase and increases interstitial adenosine levels. Its use in coronary artery disease (CAD) has fallen out of practice in the modern era with the advent of new anti-platelet agents, and most modern guidelines on the management of CAD either neglect to comment on its utility or outright recommend against it. The majority of the studies used in these guidelines are outdated and took place in an era when high doses of aspirin were used and statins were not widely utilized. There is growing evidence in rat models of dipyridamole's synergy with statins through adenosine modulation resulting in significant myocardial protection against ischemia-reperfusion injury and limitation of infract size. The data in human studies are limited but show a similar potential synergy between dipyridamole and statins. It would thus be prudent to reconsider the recommendations against the use of dipyridamole in CAD and to re-evaluate its possible role and potential benefits through well-designed randomized trials combining it with statins, low-dose aspirin, and/or other anti-platelet agents.

Hypercholesterolemia attenuates cardioprotection of ischemic preconditioning and postconditioning with α7 nicotinic acetylcholine receptor agonist by enhancing inflammation and inhibiting the PI3K/Akt/eNOS pathway

The present study aimed to evaluate the effects of hypercholesterolemia on cardioprotection of ischemic preconditioning and α7 nicotinic acetylcholine receptor (α7nAChR) agonist postconditioning and explore the potential mechanisms that hypercholesterolemia affected their cardioprotection. Hypercholesterolemic and normal rats were divided into the four groups that received the following treatments: i) Hypercholesterolemic control and normal control groups; ii) hypercholesterolemic ischemia/reperfusion (HI) and normal ischemia/reperfusion (NI) groups; iii) hypercholesterolemic ischemic preconditioning (HIPC) and normal ischemic preconditioning (NIPC) groups; and iv) hypercholesterolemic PNU282987 postconditioning (HPNU) and normal PNU282987 postconditioning (NPNU) groups. Serum lactate dehydrogenase (LDH), creatine kinase isoenzyme MB (CK-MB), cardiac troponin I (cTnI), tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6) levels after ischemia/reperfusion were assayed. Furthermore, infarct size and expression levels of Akt, phosphorylated (p)-Akt and endothelial nitric oxide synthase (eNOS) in ischemic myocardium were assessed. Compared with the NI group, serum LDH, CK-MB, cTnI, TNF-α and IL-6 levels and infarct size were significantly decreased, and myocardial p-Akt/Akt and eNOS/GAPDH ratios were significantly increased in the NIPC and NPNU groups. Compared with the HI group, serum CK-MB, cTnI, TNF-α and IL-6 levels and infarct size were significantly decreased in the HIPC group; however, myocardial p-Akt/Akt and eNOS/GAPDH ratios did not significantly change in the HIPC group. Furthermore, there were no significant difference between the HI and HPNU groups in serum LDH, CK-MB, cTnI, TNF-α and IL-6 levels, infarct size, myocardial p-Akt/Akt and eNOS/GAPDH ratios. In conclusion, hypercholesterolemia could aggravate myocardial ischemia/reperfusion injury, attenuate cardioprotection of ischemic preconditioning and eliminate cardioprotection from α7nAChR agonist postconditioning by enhancing inflammation and inhibiting PI3K/Akt/eNOS pathway.

Effect of remote ischaemic preconditioning on mortality and morbidity after non-cardiac surgery: meta-analysis

BACKGROUND

Remote ischaemic preconditioning (RIPC) has been shown to have a protective role on vital organs exposed to reperfusion injury. The aim of this systematic review was to evaluate the effects of non-invasive RIPC on clinical and biochemical outcomes in patients undergoing non-cardiac surgery.

METHODS

A systematic literature search of PubMed, EMBASE, Scopus, and Cochrane databases was carried out in February 2020. RCTs investigating the effect of non-invasive RIPC in adults undergoing non-cardiac surgery were included. Meta-analyses and trial sequential analyses (TSAs) were performed on cardiovascular events, acute kidney injury, and short- and long-term mortality.

RESULTS

Some 43 RCTs including 3660 patients were included. The surgical areas comprised orthopaedic, vascular, abdominal, pulmonary, neurological, and urological surgery. Meta-analysis showed RIPC to be associated with fewer cardiovascular events in non-cardiac surgery (13 trials, 1968 patients, 421 events; odds ratio (OR) 0.68, 95 per cent c.i. 0.47 to 0.96; P = 0.03). Meta-analyses of the effect of RIPC on acute kidney injury (12 trials, 1208 patients, 211 events; OR 1.14, 0.78 to 1.69; P = 0.50; I2 = 9 per cent), short-term mortality (7 trials, 1239 patients, 65 events; OR 0.65, 0.37 to 1.12; P = 0.12; I2 = 0 per cent), and long-term mortality (4 trials, 1167 patients, 9 events; OR 0.67, 0.18 to 2.55; P = 0.56; I2 = 0 per cent) showed no significant differences for RIPC compared with standard perioperative care in non-cardiac surgery. However, TSAs showed that the required information sizes have not yet been reached.

CONCLUSION

Application of RIPC to non-cardiac surgery might reduce cardiovascular events, but not acute kidney injury or all-cause mortality, but currently available data are inadequate to confirm or reject an assumed intervention effect.

Hypercholesterolemia Interferes with Induction of miR-125b-1-3p in Preconditioned Hearts

Ischemic preconditioning (IPre) reduces ischemia/reperfusion (I/R) injury in the heart. The non-coding microRNA miR-125b-1-3p has been demonstrated to play a role in the mechanism of IPre. Hypercholesterolemia is known to attenuate the cardioprotective effect of preconditioning; nevertheless, the exact underlying mechanisms are not clear. Here we investigated, whether hypercholesterolemia influences the induction of miR-125b-1-3p by IPre. Male Wistar rats were fed with a rodent chow supplemented with 2% cholesterol and 0.25% sodium-cholate hydrate for 8 weeks to induce high blood cholesterol levels. The hearts of normo- and hypercholesterolemic animals were then isolated and perfused according to Langendorff, and were subjected to 35 min global ischemia and 120 min reperfusion with or without IPre (3 × 5 min I/R cycles applied before index ischemia). IPre significantly reduced infarct size in the hearts of normocholesterolemic rats; however, IPre was ineffective in the hearts of hypercholesterolemic animals. Similarly, miR-125b-1-3p was upregulated by IPre in hearts of normocholesterolemic rats, while in the hearts of hypercholesterolemic animals IPre failed to increase miR-125b-1-3p significantly. Phosphorylation of cardiac Akt, ERK, and STAT3 was not significantly different in any of the groups at the end of reperfusion. Based on these results we propose here that hypercholesterolemia attenuates the upregulation of miR-125b-1-3p by IPre, which seems to be associated with the loss of cardioprotection.

Ischaemic and hypoxic conditioning: potential for protection of vital organs

NEW FINDINGS

What is the topic of this review? Remote ischaemic preconditioning (RIPC) and hypoxic preconditioning as novel therapeutic approaches for cardiac and neuroprotection. What advances does it highlight? There is improved understanding of mechanisms and signalling pathways associated with ischaemic and hypoxic preconditioning, and potential pitfalls with application of these therapies to clinical trials have been identified. Novel adaptations of preconditioning paradigms have also been developed, including intermittent hypoxia training, RIPC training and RIPC-exercise, extending their utility to chronic settings.

ABSTRACT

Myocardial infarction and stroke remain leading causes of death worldwide, despite extensive resources directed towards developing effective treatments. In this Symposium Report we highlight the potential applications of intermittent ischaemic and hypoxic conditioning protocols to combat the deleterious consequences of heart and brain ischaemia. Insights into mechanisms underlying the protective effects of intermittent hypoxia training are discussed, including the activation of hypoxia-inducible factor-1 and Nrf2 transcription factors, synthesis of antioxidant and ATP-generating enzymes, and a shift in microglia from pro- to anti-inflammatory phenotypes. Although there is little argument regarding the efficacy of remote ischaemic preconditioning (RIPC) in pre-clinical models, this strategy has not consistently translated into the clinical arena. This lack of translation may be related to the patient populations targeted thus far, and the anaesthetic regimen used in two of the major RIPC clinical trials. Additionally, we do not fully understand the mechanism through which RIPC protects the vital organs, and co-morbidities (e.g. hypercholesterolemia, diabetes) may interfere with its efficacy. Finally, novel adaptations have been made to extend RIPC to more chronic settings. One adaptation is RIPC-exercise (RIPC-X), an innovative paradigm that applies cyclical RIPC to blood flow restriction exercise (BFRE). Recent findings suggest that this novel exercise modality attenuates the exaggerated haemodynamic responses that may limit the use of conventional BFRE in some clinical settings. Collectively, intermittent ischaemic and hypoxic conditioning paradigms remain an exciting frontier for the protection against ischaemic injuries.

Myocyte membrane and microdomain modifications in diabetes: determinants of ischemic tolerance and cardioprotection

Cardiovascular disease, predominantly ischemic heart disease (IHD), is the leading cause of death in diabetes mellitus (DM). In addition to eliciting cardiomyopathy, DM induces a ‘wicked triumvirate’: (i) increasing the risk and incidence of IHD and myocardial ischemia; (ii) decreasing myocardial tolerance to ischemia–reperfusion (I–R) injury; and (iii) inhibiting or eliminating responses to cardioprotective stimuli. Changes in ischemic tolerance and cardioprotective signaling may contribute to substantially higher mortality and morbidity following ischemic insult in DM patients. Among the diverse mechanisms implicated in diabetic impairment of ischemic tolerance and cardioprotection, changes in sarcolemmal makeup may play an overarching role and are considered in detail in the current review. Observations predominantly in animal models reveal DM-dependent changes in membrane lipid composition (cholesterol and triglyceride accumulation, fatty acid saturation vs. reduced desaturation, phospholipid remodeling) that contribute to modulation of caveolar domains, gap junctions and T-tubules. These modifications influence sarcolemmal biophysical properties, receptor and phospholipid signaling, ion channel and transporter functions, contributing to contractile and electrophysiological dysfunction, cardiomyopathy, ischemic intolerance and suppression of protective signaling. A better understanding of these sarcolemmal abnormalities in types I and II DM (T1DM, T2DM) can inform approaches to limiting cardiomyopathy, associated IHD and their consequences. Key knowledge gaps include details of sarcolemmal changes in models of T2DM, temporal patterns of lipid, microdomain and T-tubule changes during disease development, and the precise impacts of these diverse sarcolemmal modifications. Importantly, exercise, dietary, pharmacological and gene approaches have potential for improving sarcolemmal makeup, and thus myocyte function and stress-resistance in this ubiquitous metabolic disorder.

Pharmacological postconditioning with atorvastatin calcium attenuates myocardial ischemia/reperfusion injury in diabetic rats by phosphorylating GSK3β

Diabetes is an independent risk factor for myocardial ischemia, and many epidemiological data and laboratory studies have revealed that diabetes significantly exacerbated myocardial ischemia/reperfusion injury and ameliorated protective effects. The present study aimed to determine whether pharmacological postconditioning with atorvastatin calcium lessened diabetic myocardial ischemia/reperfusion injury, and investigated the role of glycogen synthase kinase (GSK3β) in this. A total of 72 streptozotocin-induced diabetic rats were randomly divided into six groups, and 24 age-matched male non-diabetic Sprague-Dawley rats were randomly divided into two groups. Rats all received 40 min myocardial ischemia followed by 180 min reperfusion, except sham-operated groups. Compared with the non-diabetic ischemia/reperfusion model group, the diabetic ischemia/reperfusion group had a comparable myocardial infarct size, but a higher level of serum cardiac troponin I (cTnI) and morphological alterations to their myocardial cells. Compared with the diabetic ischemia/reperfusion group, the group that received pharmacological postconditioning with atorvastatin calcium had smaller myocardial infarct sizes, lower levels of cTnI, reduced morphological alterations to myocardial cells, higher levels of p-GSK3β, heat shock factor (HSF)-1 and heat shock protein (HSP)70. The cardioprotective effect conferred by atorvastatin calcium did not attenuate myocardial ischemia/reperfusion injury following application of TDZD-8, which phosphorylates and inactivates GSK3β. Pharmacological postconditioning with atorvastatin calcium may attenuate diabetic heart ischemia/reperfusion injury in the current context. The phosphorylation of GSK3β serves a critical role during the cardioprotection in diabetic rats, and p-GSK3β may accelerate HSP70 production partially by activating HSF-1 during myocardial ischemic/reperfusion injury.

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.

A review of strategies for infarct size reduction during acute myocardial infarction

Advances in medical and interventional therapy over the last few decades have revolutionized the treatment of acute myocardial infarction. Despite the ability to restore epicardial coronary artery patency promptly through percutaneous coronary intervention, tissue level damage may continue. The reported 30-day mortality after all acute coronary syndromes is 2 to 3%, and around 5% following myocardial infarction. Post-infarct complications such as heart failure continue to be a major contributor to cardiovascular morbidity and mortality. Inadequate microvascular reperfusion leads to worse clinical outcomes and potentially strategies to reduce infarct size during periods of ischemia-reperfusion can improve outcomes. Many strategies have been tested, but no single strategy alone has shown a consistent result or benefit in large scale randomised clinical trials. Herein, we review the historical efforts, current strategies, and potential novel concepts that may improve myocardial protection and reduce infarct size.

Sarcolemmal dependence of cardiac protection and stress-resistance: roles in aged or diseased hearts

Disruption of the sarcolemmal membrane is a defining feature of oncotic death in cardiac ischaemia-reperfusion (I-R), and its molecular makeup not only fundamentally governs this process but also affects multiple determinants of both myocardial I-R injury and responsiveness to cardioprotective stimuli. Beyond the influences of membrane lipids on the cytoprotective (and death) receptors intimately embedded within this bilayer, myocardial ionic homeostasis, substrate metabolism, intercellular communication and electrical conduction are all sensitive to sarcolemmal makeup, and critical to outcomes from I-R. As will be outlined in this review, these crucial sarcolemmal dependencies may underlie not only the negative effects of age and common co-morbidities on myocardial ischaemic tolerance but also the on-going challenge of implementing efficacious cardioprotection in patients suffering accidental or surgically induced I-R. We review evidence for the involvement of sarcolemmal makeup changes in the impairment of stress-resistance and cardioprotection observed with ageing and highly prevalent co-morbid conditions including diabetes and hypercholesterolaemia. A greater understanding of membrane changes with age/disease, and the inter-dependences of ischaemic tolerance and cardioprotection on sarcolemmal makeup, can facilitate the development of strategies to preserve membrane integrity and cell viability, and advance the challenging goal of implementing efficacious 'cardioprotection' in clinically relevant patient cohorts. Linked Articles This article is part of a themed section on Molecular Pharmacology of G Protein-Coupled Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.20/issuetoc.

Decreased effectiveness of ischemic heart preconditioning in the state of chronic inflammation

There is growing evidence, that beneficial effects of ischemic heart preconditioning (IPC) may be lost or limited due to diabetes, hyperlipidemia, hypertension, atherosclerosis, heart failure and senility. It is plausible, that these conditions interfere with the biochemical pathways underlying the IPC response, but the detailed explanation is not clear. Pro-inflammatory cytokines (IL-1β, IL-6, TNF-α), monocyte chemotactic protein-1 (MCP-1), histamine and many other agents used in a single dose before prolonged ischemia mimic IPC. However prolonged exposure to preconditioning mimetics leads to tolerance (tachyphylaxis). In the state of such tolerance ischemic preconditioning is no longer protective. Studies suggest that diabetes, hyperlipidemia, hypertension, atherosclerosis, heart failure and older age are accompanied by increased plasma levels of pro-inflammatory cytokines, MCP-1 and other inflammatory mediators. Therefore, we raised the hypothesis, that the reported lack of benefits of IPC in the listed states may be due to tolerance to IPC developed during prolonged exposure of the myocardium to preconditioning mimetics.

Hypercholesterolemia aggravates myocardial ischemia reperfusion injury via activating endoplasmic reticulum stress-mediated apoptosis

The effect of hypercholesterolemia on myocardial ischemia reperfusion injury (MIRI) is in controversy and the underlying mechanism is still not well understood. In the present study, we firstly detected the effects of hypercholesterolemia on MIRI and the role of endoplasmic reticulum (ER) stress-mediated apoptosis pathway in this process. The infarct size was determined by TTC staining, and apoptosis was measured by the TUNEL method. The marker proteins of ER stress response and ER stress-mediated apoptosis pathway were detected by Western blot. The results showed that high cholesterol diet-induced hypercholesterolemia significantly increased the myocardial infarct size, the release of myocardium enzyme and the ratio of apoptosis, but did not affect the recovery of cardiac function. Moreover, hypercholesterolemia also remarkably up-regulated the expressions of ER stress markers (glucose-regulated protein 78 and calreticulin) and critical molecules in ER stress-mediated apoptosis pathway (CHOP, caspase 12, phospho-JNK). In conclusion, our study demonstrated that hypercholesterolemia enhanced myocardial vulnerability/sensitivity to ischemia reperfusion injury involved in aggravation the ER stress and activation of ER stress-mediated apoptosis pathway and it gave us a new insight into the underlying mechanisms associated with hypercholesterolemia-induced exaggerated MIRI and also provided a novel target for preventing MIRI in the presence of hypercholesterolemia.

The challenge of translating ischemic conditioning from animal models to humans: the role of comorbidities

Following a period of ischemia (local restriction of blood supply to a tissue), the restoration of blood supply to the affected area causes significant tissue damage. This is known as ischemia-reperfusion injury (IRI) and is a central pathological mechanism contributing to many common disease states. The medical complications caused by IRI in individuals with cerebrovascular or heart disease are a leading cause of death in developed countries. IRI is also of crucial importance in fields as diverse as solid organ transplantation, acute kidney injury and following major surgery, where post-operative organ dysfunction is a major cause of morbidity and mortality. Given its clinical impact, novel interventions are urgently needed to minimize the effects of IRI, not least to save lives but also to reduce healthcare costs. In this Review, we examine the experimental technique of ischemic conditioning, which entails exposing organs or tissues to brief sub-lethal episodes of ischemia and reperfusion, before, during or after a lethal ischemic insult. This approach has been found to confer profound tissue protection against IRI. We discuss the translation of ischemic conditioning strategies from bench to bedside, and highlight where transition into human clinical studies has been less successful than in animal models, reviewing potential reasons for this. We explore the challenges that preclude more extensive clinical translation of these strategies and emphasize the role that underlying comorbidities have in altering the efficacy of these strategies in improving patient outcomes.

WITHDRAWN: Hypercholesterolemia aggravates myocardial ischemia reperfusion injury via activating endoplasmic reticulum stress-mediated apoptosis

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Exercise training prevents the attenuation of anesthetic pre-conditioning-mediated cardioprotection in diet-induced obese rats

BACKGROUND

Obesity abolishes anesthetic pre-conditioning-induced cardioprotection due to impaired reactive oxygen species (ROS)-mediated adenosine monophosphate-activated protein kinase (AMPK) pathway, a consequence of increased basal myocardial oxidative stress. Exercise training has been shown to attenuate obesity-related oxidative stress.

OBJECTIVE

This study tests whether exercise training could normalize ROS-mediated AMPK pathway and prevent the attenuation of anesthetic pre-conditioning-induced cardioprotection in obesity.

METHODS

Male Sprague-Dawley rats were divided into lean rats fed with control diet and obese rats fed with high-fat diet. After 4 weeks of feeding, lean and obese rats were assigned to sedentary conditions or treadmill exercise for 8 weeks.

RESULTS

There was no difference in infarct size between lean sedentary and obese sedentary rats after 25 min of myocardial ischemia followed by 120 min reperfusion. In lean rats, sevoflurane equally reduced infarct size in lean sedentary and lean exercise-trained rats. Molecular studies revealed that AMPK activity, endothelial nitric oxide synthase, and superoxide production measured at the end of ischemia in lean rats were increased in response to sevoflurane. In obese rats, sevoflurane increased the above molecular parameters and reduced infarct size in obese exercise-trained rats but not in obese sedentary rats. Additional study showed that obese exercise-trained rats had decreased basal oxidative stress than obese sedentary rats.

CONCLUSION

The results indicate that exercise training can prevent the attenuation of anesthetic cardioprotection in obesity. Preventing the attenuation of this strategy may be associated with reduced basal oxidative stress and normalized ROS-mediated AMPK pathway, but the causal relationship remains to be determined.

Most appropriate animal models to study the efficacy of statins: a systematic review

BACKGROUND

In animal models and clinical trials, statins are reported as effective in reducing cholesterol levels and lowering the risk of cardiovascular diseases. We have aggregated the findings in animal models - mice, rats and rabbits - using the technique of systematic review and meta-analysis to highlight differences in the efficacy of statins.

MATERIALS AND METHODS

We searched Medline and Embase. After examining all eligible articles, we extracted results about total cholesterol and other blood parameters, blood pressure, myocardial infarction and survival. Weighted and standard mean difference random effects meta-analysis was used to measure overall efficacy in prespecified species, strains and subgroups.

RESULTS

We included in systematic review 161 animal studies and we analysed 120 studies, accounting for 2432 animals. Statins lowered the total cholesterol across all species, although with large differences in the effect size: -30% in rabbits, -20% in mice and -10% in rats. The reduction was larger in animals fed on a high-cholesterol diet. Statins reduced infarct volume but did not consistently reduce the blood pressure or effect the overall survival. Few studies considered strains at high risk of cardiovascular diseases or hard outcomes.

CONCLUSIONS

Although statins showed substantial efficacy in animal models, few preclinical data considered conditions mimicking human pathologies for which the drugs are clinically indicated and utilized. The empirical finding that statins are more effective in lowering cholesterol derived from an external source (i.e. diet) conflicts with statin's supposed primary mechanism of action.

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.

Diabetic cardiomyopathy: pathophysiology and clinical features

Since diabetic cardiomyopathy was first reported four decades ago, substantial information on its pathogenesis and clinical features has accumulated. In the heart, diabetes enhances fatty acid metabolism, suppresses glucose oxidation, and modifies intracellular signaling, leading to impairments in multiple steps of excitation–contraction coupling, inefficient energy production, and increased susceptibility to ischemia/reperfusion injury. Loss of normal microvessels and remodeling of the extracellular matrix are also involved in contractile dysfunction of diabetic hearts. Use of sensitive echocardiographic techniques (tissue Doppler imaging and strain rate imaging) and magnetic resonance spectroscopy enables detection of diabetic cardiomyopathy at an early stage, and a combination of the modalities allows differentiation of this type of cardiomyopathy from other organic heart diseases. Circumstantial evidence to date indicates that diabetic cardiomyopathy is a common but frequently unrecognized pathological process in asymptomatic diabetic patients. However, a strategy for prevention or treatment of diabetic cardiomyopathy to improve its prognosis has not yet been established. Here, we review both basic and clinical studies on diabetic cardiomyopathy and summarize problems remaining to be solved for improving management of this type of cardiomyopathy.

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.

Effects of diabetes on myocardial infarct size and cardioprotection by preconditioning and postconditioning

In spite of the current optimal therapy, the mortality of patients with ischemic heart disease (IHD) remains high, particularly in cases with diabetes mellitus (DM) as a co-morbidity. Myocardial infarct size is a major determinant of prognosis in IHD patients, and development of a novel strategy to limit infarction is of great clinical importance. Ischemic preconditioning (PC), postconditioning (PostC) and their mimetic agents have been shown to reduce infarct size in experiments using healthy animals. However, a variety of pharmacological agents have failed to demonstrate infarct size limitation in clinical trials. One of the possible reasons for the discrepancy between the results of animal experiments and clinical trials is that co-morbidities, including DM, modified myocardial responses to ischemia/reperfusion and to cardioprotective agents. Here we summarize observations of the effects of DM on myocardial infarct size and ischemic PC and PostC and discuss perspectives for protection of DM hearts.

Cardioprotection from ischemia/reperfusion injury: basic and translational research

Because ischemic heart diseases (IHDs) are a major cause of mortality and heart failure, novel therapeutic approaches are expected to improve the clinical outcomes of patients with IHDs such as acute myocardial infarction and ischemic heart failure. Brief episodes of nonlethal ischemia and reperfusion before sustained ischemia or at the onset of reperfusion can reduce ischemia-reperfusion injury. These ischemic conditioning phenomena are termed "ischemic preconditioning" and "ischemic postconditioning", respectively. Furthermore, brief episodes of nonlethal ischemia and reperfusion applied to the organ or tissue distal to the heart reduce myocardial infarct size, known as "remote ischemic conditioning". The cardioprotection afforded by these ischemic conditionings can be used to treat patients with acute myocardial infarction or cardiac operations. Extensive research has determined that autacoids (eg, adenosine, bradykinin opioid) and cytokines, their respective receptors, kinase signaling pathways and mitochondrial modulation are involved in ischemic conditioning. Modification of these factors by pharmacological agents mimics the cardioprotection by ischemic conditioning and provides a novel therapeutic intervention for IHDs. Here, the potential mechanisms of ischemic conditioning and its "proof-of-concept" translational studies are reviewed. In the near future, large, multicenter, randomized, placebo-controlled, clinical trials will be required to determine whether pharmacological and ischemic conditioning can improve the clinical outcomes of patients with IHDs.

Short-term statin administration in hypercholesterolaemic rabbits resistant to postconditioning: effects on infarct size, endothelial nitric oxide synthase, and nitro-oxidative stress

AIMS

The effectiveness of postconditioning (POC) in hypercholesterolaemia is in dispute. We investigated the effects of 3-day lipophilc (simvastatin) or hydrophilic (pravastatin) statin treatment, without or with POC in normocholesterolaemic (Norm) and hypercholesterolaemic (Chol) rabbits.

METHODS AND RESULTS

Norm or Chol rabbits were subjected to 30 min ischaemia and randomized in two series of 12 groups each: control, simvastatin (Sim), pravastatin (Prav), POC, Sim-POC, Prav-POC, Chol, Sim-Chol, Prav-Chol, POC-Chol, Sim-POC-Chol, Prav-POC-Chol. After ischaemia, rabbits of the first series underwent 3 h reperfusion, followed by infarct size, total cholesterol, and low density lipoprotein plasma level evaluation; animals of the second series underwent 10 min reperfusion followed by tissue sampling for nitrotyrosine (NT), malondialdehyde, endothelial nitric oxide synthase (eNOS), and Akt analyses. N-nitro-l-arginine methylester (L-NAME) was given in two additional groups (POC-L-NAME and Prav-Chol-L-NAME) for infarct size assessment. All interventions reduced infarction in Norm (24.3 ± 1.3, 25.9 ± 2.8, 27.9 ± 3.1, 23.3 ± 2.3, and 33.4 ± 2.5%, in POC, Sim, Prav, Sim-POC, and Prav-POC groups, respectively, vs. 49.3 ± 1.9% in control, P < 0.05), but only Prav did so in Chol animals (25.7 ± 3.3 and 25.3 ± 3.9% in Prav-Chol and Prav-POC-Chol vs. 50.9 ± 1.7, 44.8 ± 4.3, 41.5 ± 3.5, and 49.3 ± 5.5% in Chol, Sim-Chol, POC-Chol, and Sim-POC-Chol, respectively, P < 0.05). L-NAME abolished the infarct size-limiting effect of POC and Prav-Chol. Prav induced the greatest reduction in NT, while it was the only intervention that increased myocardial eNOS and Akt in Chol rabbits (P < 0.05 vs. all others).

CONCLUSION

Prav, in contrast to same-dose Sim or POC, reduces infarction in Chol rabbits independently of lipid lowering, potentially through eNOS activation and nitro-oxidative stress attenuation.

Hypercholesterolemia increases mitochondrial oxidative stress and enhances the MPT response in the porcine myocardium: beneficial effects of chronic exercise

Hypercholesterolemia has been suggested to have direct negative effects on myocardial function due to increased reactive oxygen species (ROS) generation and increased myocyte death. Mitochondrial permeability transition (MPT) is a significant mediator of cell death, which is enhanced by ROS generation and attenuated by exercise training. The purpose of this study was to investigate the effect of hypercholesterolemia on the MPT response of cardiac mitochondria. We tested the hypothesis that familial hypercholesterolemic (FH) pigs would have an enhanced MPT response and that exercise training could reverse this phenotype. MPT was assessed by mitochondrial swelling in response to 10-100 μM Ca(2+). FH pigs did show an increased MPT response to Ca(2+) that was associated with decreases in the expression of the putative MPT pore components mitochondrial phosphate carrier (PiC) and cyclophilin-D (CypD). FH also caused increased oxidative stress, depicted by increased protein nitrotyrosylation, as well as decreased levels of reduced GSH in cardiac mitochondria. Expression of the mitochondrial antioxidant enzymes manganese superoxide dismutase (MnSOD), thioredoxin-2 (Trx2), and peroxiredoxin-3 (Prx3) was greatly reduced in the FH pigs. In contrast, cytosolic catalase expression and activity were increased. However, chronic exercise training was able to normalize the MPT response in FH pigs, reduce mitochondrial oxidative stress, and return MnSOD, Trx2, Prx3, and catalase expression/activities to normal. We conclude that FH reduces mitochondrial antioxidants, increases mitochondrial oxidative stress, and enhances the MPT response in the porcine myocardium, and that exercise training can reverse these detrimental alterations.

Pathophysiology of myocardial reperfusion injury: preconditioning, postconditioning, and translational aspects of protective measures

Heart diseases due to myocardial ischemia, such as myocardial infarction or ischemic heart failure, are major causes of death in developed countries, and their number is unfortunately still growing. Preliminary exploration into the pathophysiology of ischemia-reperfusion injury, together with the accumulation of clinical evidence, led to the discovery of ischemic preconditioning, which has been the main hypothesis for over three decades for how ischemia-reperfusion injury can be attenuated. The subcellular pathophysiological mechanism of ischemia-reperfusion injury and preconditioning-induced cardioprotection is not well understood, but extensive research into components, including autacoids, ion channels, receptors, subcellular signaling cascades, and mitochondrial modulators, as well as strategies for modulating these components, has made evolutional progress. Owing to the accumulation of both basic and clinical evidence, the idea of ischemic postconditioning with a cardioprotective potential has been discovered and established, making it possible to apply this knowledge in the clinical setting after ischemia-reperfusion insult. Another a great outcome has been the launch of translational studies that apply basic findings for manipulating ischemia-reperfusion injury into practical clinical treatments against ischemic heart diseases. In this review, we discuss the current findings regarding the fundamental pathophysiological mechanisms of ischemia-reperfusion injury, the associated protective mechanisms of ischemic pre- and postconditioning, and the potential seeds for molecular, pharmacological, or mechanical treatments against ischemia-reperfusion injury, as well as subsequent adverse outcomes by modulation of subcellular signaling mechanisms (especially mitochondrial function). We also review emerging translational clinical trials and the subsistent clinical comorbidities that need to be overcome to make these trials applicable in clinical medicine.

Effects of single-dose morning and evening administration of pravastatin on antioxidant markers in cholesterol-fed rabbits

BACKGROUND

Accurate timing of statin administration is considered important to obtain the best hypolipidemic effect. Pravastatin is one of the currently prescribed hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, and was chosen in this study to evaluate its antioxidant effect when administered as a single daily dose in the morning versus evening in cholesterol-fed rabbits.

METHODS

This 12-week study was performed in New Zealand rabbits, divided into four groups (n = 6 each), ie, normocholesterolemic controls; cholesterol 1% diet, nontreated ; cholesterol 1% diet treated with pravastatin in the morning; and cholesterol 1% diet treated with pravastatin in the evening. Plasma total cholesterol levels, superoxide dismutase enzyme levels in erythrocyte lysates, thiobarbituric acid-reactive substance content, catalase, and glutathione enzyme activity in liver homogenates from the tested rabbits were measured.

RESULTS

Both morning and evening treatment with pravastatin significantly improved all the measured antioxidant markers in comparison with nontreated cholesterol-fed rabbits. However, results obtained with evening dosing were better than with morning dosing.

CONCLUSION

The antioxidant profile of pravastatin is better when the drug is administered in the evening rather than in the morning.

Cyclosporine A administered during reperfusion fails to restore cardioprotection in prediabetic Zucker obese rats in vivo

BACKGROUND AND AIMS

Hyperglycaemia blocks sevoflurane-induced postconditioning, and cardioprotection in hyperglycaemic myocardium can be restored by inhibition of the mitochondrial permeability transition pore (mPTP). We investigated whether sevoflurane-induced postconditioning is also blocked in the prediabetic heart and if so, whether cardioprotection could be restored by inhibiting mPTP.

METHODS AND RESULTS

Zucker lean (ZL) and Zucker obese (ZO) rats were assigned to one of seven groups. Animals underwent 25 min of ischaemia and 120 min of reperfusion. Control (ZL-/ZO Con) animals were not further treated. postconditioning groups (ZL-/ZO Sevo-post) received sevoflurane for 5 min starting 1min prior to the onset of reperfusion. The mPTP inhibitor cyclosporine A (CsA) was administered intravenously in a concentration of 5 (ZO CsA and ZO CsA+Sevo-post) or 10 mg/kg (ZO CsA10+Sevo-post) 5 min before the onset of reperfusion. At the end of reperfusion, infarct sizes were measured by TTC staining. Blood samples were collected to measure plasma levels of insulin, cholesterol and triglycerides. Sevoflurane postconditioning reduced infarct size in ZL rats to 35±12% (p<0.05 vs. ZL Con: 60±6%). In ZO rats sevoflurane postconditioning was abolished (ZO Sevo-post: 59±12%, n.s. vs. ZO Con: 58±6%). 5 mg and 10 mg CsA could not restore cardioprotection (ZO CsA+Sevo-post: 59±7%, ZO CsA10+Sevo-post: 57±14%; n.s. vs. ZO Con). In ZO rats insulin, cholesterol and triglyceride levels were significant higher than in ZL rats (all p<0.05).

CONCLUSION

Inhibition of mPTP with CsA failed to restore cardioprotection in the prediabetic but normoglycaemic heart of Zucker obese rats in vivo.

Effect of pravastatin on ventricular arrhythmias in infarcted rats: role of connexin43

Epidemiologic studies showed that men treated with statins appear to have a lower incidence of sudden death than men without statins. However, the specific factor for this remained disappointingly elusive. We assessed whether pravastatin enhanced connexin43 expression after myocardial infarction through attenuation of endothelin-1. Twenty-four hours after ligation of the anterior descending artery, male Wistar rats were randomized to vehicle, pravastatin, mevalonate, bosentan, or a combination of pravastatin and mevalonate or pravastatin and bosentan for 4 wk. Myocardial endothelin-1 levels were significantly elevated in vehicle-treated rats at the border zone compared with sham-operated rats. Myocardial connexin43 expression at the border zone was significantly decreased in vehicle-treated infarcted rats compared with sham-operated rats. Attenuated connexin43 expression was blunted after administration of pravastatin, as assessed by immunofluorescence analysis, Western blotting, and real-time quantitative RT-PCR of connexin43. Bosentan enhanced connexin43 amount in infarcted rats and did not have additional beneficial effects on pravastatin-treated rats. Arrhythmic scores during programmed stimulation in vehicle-treated rats were significantly higher than scores in those treated with pravastatin. In contrast, the beneficial effects of pravastatin-induced connexin43 were abolished by the addition of mevalonate and a protein kinase C inducer. In addition, the amount of connexin43 showed significant increase after addition of bisindolylmaleimide, implicating that protein kinase C is a relevant target in endothelin-1-mediated connexin43 expression. Thus chronic use of pravastatin after infarction, resulting in enhanced connexin43 amount by attenuation of mevalonate-dependent endothelin-1 through a protein kinase C-dependent pathway, may attenuate the arrhythmogenic response to programmed electrical stimulation.

Modulation of the cardioprotective effect of ischemic preconditioning in hyperlipidaemic rat heart

Ischemic preconditioning (IPC) produces cardioprotection by phosphorylation of glycogen synthaes kinase-3beta (GSK-3beta) that inhibits the opening of mitochondrial permeability transition pore (MPTP), and this cardioprotective action of IPC is attenuated by hyperlipidaemia. The present study investigated the role of GSK-3beta in attenuation of cardioprotective effect of IPC, by hyperlipidaemia in the rat heart. Hyperlipidaemia was produced in rat by feeding high fat diet for six weeks. Isolated perfused rat heart was subjected to 30 min of ischemia followed by 120 min of reperfusion. Myocardial infarct size was estimated by triphenyltetrazolium chloride (TTC) staining and lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) was analyzed from coronary effluent. IPC significantly decreased the myocardial infarct size and the release of LDH and CK-MB from normal rat heart. IPC induced myocardial protection was attenuated in hyperlipidaemic rat heart. However, cardioprotective effect of pharmacological preconditioning with GSK-3beta inhibitors i.e. Lithium Chloride (LiCl) (20mM), Indirubin - 3 Monooxime (1 microM) and 3-(2, 4-dichlorophenyl)-4-(1-methyl-1H-indol-3-yl)-1H-pyrrole-2, 5-dione (SB216763) (3 microM), was not attenuated. This differential attenuation by hyperlipidaemia, of IPC and pharmacological preconditioning induced cardioprotection is a new finding in our study. GSK-3beta inhibition is reported to increase the threshold of opening for MPTP during reperfusion. Administration of atractyloside (20 microM), an opener of MPTP, significantly attenuated the cardioprotective effect of IPC in normal heart, and pharmacological preconditioning in the hyperlipidaemic rat heart. Thus, the attenuation of cardioprotective effect of IPC in hyperlipidaemic heart may be due to inhibition of protective signaling pathways upstream of GSK-3beta and inhibition of opening of MPTP.

Preprocedural statin therapy to prevent myocardial damage in percutaneous coronary intervention: a review of randomized trials

Multiple landmark clinical trials have demonstrated the beneficial effects of statin therapy for primary and secondary prevention of cardiovascular disease, but the exact timing of how early to treat relative to acute presentation has been less clear. The benefits of statin in cardiovascular disease can be explained not only by their lipid-lowering potential but also by non-lipid-related mechanisms, called pleiotropic effects. Percutaneous coronary intervention (PCI) can result in myocardial injury that is reflected by an increase in creatine kinase-MB and troponin I isoenzymes with worsened long-term prognosis following PCI. Observational studies suggested that pretreatment with statins might reduce the incidence of myocardial infarction after coronary intervention and prevent myocardial injury. Thus, several randomized controlled trials were conducted. They showed that pretreatment with statin before elective PCI reduces periprocedural myocardial injury in patients with stable angina. Moreover, short-term high-dose statin administration before coronary procedures also improves clinical outcome in patients with acute coronary syndromes and/or high preprocedural C-reactive protein levels. Thus, this evidence strongly supports routine utilization of high-dose statins as adjuvant pharmacological therapy before percutaneous coronary revascularization.

Cholesterol diet-induced hyperlipidemia impairs the cardioprotective effect of postconditioning: role of peroxynitrite

The aim of the present study was to investigate if hyperlipidemia interferes with the infarct size-limiting effect of postconditioning and to study the involvement of peroxynitrite in this phenomenon. Rats were fed a 2% cholesterol-enriched or normal diet for 12 wk. Infarct size by triphenyltetrazolium chloride staining was measured in hearts isolated from both groups and subjected to 30 min coronary occlusion followed by 120 min reperfusion with or without the postconditioning protocol induced by six cycles of 10 s coronary occlusion and 10 s reperfusion at the onset of the reperfusion. Postconditioning significantly decreased infarct size in the normolipidemic but not in the hyperlipidemic group. Postconditioning increased cardiac 3-nitrotyrosine concentration (a marker for peroxynitrite formation) in the normal but not in the cholesterol-fed group when measured at the 5th min of reperfusion. Next, we tested if the postconditioning-induced acute increase in peroxynitrite is involved in the cardioprotection in normolipidemic animals in separate experiments. Postconditioning failed to decrease infarct size in the presence of the peroxynitrite decomposition catalyst 5,10,15,20-tetrakis-[4-sulfonatophenyl]-porphyrinato-iron [III] (20 mg/l) in normolipidemic animals. We conclude that an early increase in peroxynitrite after postconditioning plays a role in cardioprotection. Furthermore, hyperlipidemia blocks the cardioprotective effect of postconditioning at least in part via deterioration of the postconditioning-induced early increase in peroxynitrite formation.

Hyperlipidaemia induced by a high-cholesterol diet leads to the deterioration of guanosine-3',5'-cyclic monophosphate/protein kinase G-dependent cardioprotection in rats

BACKGROUND AND PURPOSE

Hyperlipidaemia interferes with cardioprotective mechanisms, but the cause of this phenomenon is largely unknown, although hyperlipidaemia impairs the cardioprotective NO-cGMP system. However, it is not known if natriuretic peptide-cGMP-protein kinase G (PKG) signalling is affected by hyperlipidaemia. Therefore, we investigated the cardioprotective efficacy of cGMP-elevating agents in hearts from normal and hyperlipidaemic rats.

EXPERIMENTAL APPROACH

Male Wistar rats were rendered hyperlipidaemic by feeding with 2% cholesterol-enriched chow for 12 weeks. Hearts isolated from normal and hyperlipidaemic rats were perfused (Langendorff mode) and subjected to 30 min occlusion of the left main coronary artery, followed by 120 min reperfusion. 8-Br-cGMP (CG, 10 nM), B-type natriuretic peptide-32 (BNP, 10 nM), S-nitroso-N-acetyl-penicillamine (SNAP, 1 microM) were perfused from 10 min prior to coronary occlusion until the 15th min of reperfusion. Infarct size (% of ischaemic risk zone) was determined by triphenyltetrazolium staining.

KEY RESULTS

Treatment with CG, SNAP or BNP decreased infarct size significantly in normal hearts from its control value of 41.6 +/- 2.9% to 15.5 +/- 2.4%, 23.3 +/- 3.0% and 25.3 +/- 4.6%, respectively (P < 0.05). Protection by BNP was abolished by co-perfusion of PKG inhibitors KT5823 (600 nM) or Rp-8pCPT-PET-cGMPs (1 microM), confirming its PKG dependence. In hearts from hyperlipidaemic rats, CG, SNAP or BNP failed to decrease infarct size. Hyperlipidaemia did not alter basal myocardial PKG content, but decreased its activity as assessed by phosphorylation of cardiac troponin I.

CONCLUSIONS AND IMPLICATIONS

This is the first demonstration that defects in the cardioprotective cGMP-PKG system could be a critical biochemical anomaly in hyperlipidaemia.

Effect of two-day atorvastatin pretreatment on the incidence of periprocedural myocardial infarction following elective percutaneous coronary intervention: a single-center, prospective, and randomized study

Both randomized and observational studies have suggested that pretreatment with statins may reduce the incidence of periprocedural myocardial infarction (PMI) in patients with stable angina during elective percutaneous coronary intervention (PCI). The purpose of this randomized study (Clinical Trial Registration No. NCT00469326) was to investigate the effect of 2-day atorvastatin therapy on the incidence of PMI in patients with stable angina pectoris undergoing elective PCI. A total of 200 patients with stable angina pectoris who were not taking statins and who had been referred for PCI were enrolled and randomized (ratio 1:1) to a 2-day pretreatment regimen with atorvastatin 80 mg/day and subsequent PCI or immediate PCI. The serum concentration of creatine kinase-MB mass and troponin I were measured before and 16 to 24 hours after PCI. The incidence of PMI was assessed using established criteria. Of the patients, 10% in the atorvastatin group and 12% in the control group had a postprocedural creatine kinase-MB mass elevation > or =3 times the upper limit of normal (p = 0.65). The incidence of PMI as determined by the postinterventional release of troponin I > or =3 times the upper limit of normal was 17% in the atorvastatin group and 16% in the control group (p = 0.85). The median creatine kinase-MB mass peak after PCI was 1.46 ng/ml (interquartile range 0.83 to 2.52) in the atorvastatin group and 1.40 ng/ml (interquartile range 0.90 to 2.54) in the control group (p = 0.70). The median peak troponin I level after PCI was 0.100 ng/ml (0.096 to 0.385) in the atorvastatin group and 0.100 ng/ml (0.60 to 0.262) in the control group (p = 0.54). On multivariate analysis, the only independent predictor of PMI was patient age (odds ratio 1.09, 95% confidence interval 1.025 to 1.159, p = 0.006). In conclusion, in the present study 2-day pre-PCI therapy with atorvastatin did not reduce the occurrence of PMI in patients with stable angina pectoris undergoing elective PCI.

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.

Rosuvastatin increases extracellular adenosine formation in humans in vivo: a new perspective on cardiovascular protection

OBJECTIVE

Statins may increase extracellular adenosine formation from adenosine monophosphate by enhancing ecto-5'-nucleotidase activity. This theory was tested in humans using dipyridamole-induced vasodilation as a read-out for local adenosine formation. Dipyridamole inhibits the transport of extracellular adenosine into the cytosol resulting in increased extracellular adenosine and subsequent vasodilation. In addition, we studied the effect of statin therapy in a forearm model of ischemia-reperfusion injury.

METHODS AND RESULTS

Volunteers randomly received rosuvastatin or placebo in a double-blind parallel design (n=21). The forearm vasodilator response to intraarterial dipyridamole was determined in the absence and presence of the adenosine antagonist caffeine. During a separate visit the vasodilator response to nitroprusside and adenosine was established. In addition, healthy men were randomly divided in 3 groups to receive either placebo (n=10), rosuvastatin (n=22), or rosuvastatin combined with intravenous caffeine (n=12). Subsequently, volunteers performed forearm ischemic exercise. At reperfusion, Tc-99m-labeled annexin A5 was infused intravenously and scintigraphic images were acquired, providing an early marker of cell injury. Rosuvastatin treatment significantly increased the vasodilator response to dipyridamole, which was prevented by caffeine. Rosuvastatin did not influence the response to either sodium nitroprusside or adenosine indicating a specific interaction between rosuvastatin and dipyridamole, which does not result from an effect of rosuvastatin on adenosine clearance nor adenosine-receptor affinity or efficacy. Rosuvastatin increased tolerance to ischemia-reperfusion injury, which was attenuated by caffeine.

CONCLUSIONS

Rosuvastatin increases extracellular adenosine formation, which provides protection against ischemia-reperfusion injury in humans in vivo. Therefore, statins and dipyridamole may interact synergistically.

Physiology and pharmacology of myocardial preconditioning and postconditioning

Perioperative myocardial ischemia and infarction are not only major sources of morbidity and mortality in patients undergoing surgery but also important causes of prolonged hospital stay and resource utilization. Ischemic and pharmacological preconditioning and postconditioning have been known for more than 2 decades to provide protection against myocardial ischemia and reperfusion and limit myocardial infarct size in many experimental animal models, as well as in clinical studies. This article reviews the physiology and pharmacology of ischemic and drug-induced preconditioning and postconditioning of the myocardium with special emphasis on the mechanisms by which volatile anesthetics provide myocardial protection. Insights gained from animal and clinical studies are reviewed and recommendations given for the use of perioperative anesthetics and medications.

Limitation of myocardial infarct size in the clinical setting: current status and challenges in translating animal experiments into clinical therapy

This review takes a critical look at the current effectiveness of reperfusion therapy for acute myocardial infarction and at the potential for cardioprotective agents to improve it. Reperfusion alone limits the median value of infarct size to approximately 50% of the ischemic region. However, the range of infarct sizes is very wide, and one-fourth of these patients have more than 75% of the ischemic zone infarcted despite successful coronary reperfusion. Available studies suggest that mortality and morbidity is increased when more than 20% of the left ventricle is infarcted. Therefore, to be effective infarct size-limiting therapy would have to reduce infarction to or below this 20% target. To achieve this goal in the quartile of patients with the biggest infarcts the cardioprotective agent would have to be potent enough to reduce infarct size from its current value of 75% of the ischemic zone to 40% or less. While ischemic preconditioning and some pretreatment drugs might be potent enough to achieve this goal, few of the agents given at the clinically relevant time of at or just before reperfusion have exhibited such potency. Several cardioprotective agents have recently been evaluated in clinical trials but their results have been disappointing. Some of the poor clinical trial performance may stem from study designs which fail to identify those patients falling within the upper quartile of infarct sizes, presumably the only group that would be expected to actually benefit from a reduction in infarct size. Other possible causes could be that co-morbidities or drugs patients are taking may block the pathways involved in the anti-infarct effect or that the drugs simply do not protect even in animal models. Few agents have been thoroughly tested in clinically relevant animal models prior to their testing in man.

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.

The cardioprotective effect of a statin and cilostazol combination: relationship to Akt and endothelial nitric oxide synthase activation

BACKGROUND

Atorvastatin (ATV) protects against ischemia-reperfusion by upregulating Akt and subsequently, endothelial nitric oxide synthase (eNOS) phosphorylation at Ser-1177. However, when given orally, high doses of ATV (10 mg/kg/d) are needed to achieve maximal protective effect in the rat. Protein kinase A (PKA) also phosphorylates eNOS at Ser-1177. As PKA activity depends on cAMP, cilostazol (CIL), a phosphodiesterase type III inhibitor, may stimulate NO production by activating PKA.

HYPOTHESIS

CIL and ATV may have synergistic effects on eNOS phosphorylation and myocardial infarct size (IS) reduction.

METHODS

Sprague-Dawley rats received 3-day oral pretreatment with: (1) water; (2) low dose ATV (2 mg/kg/d); (3) CIL (20 mg/kg/d): (4) ATV+CIL. Rats underwent 30 min coronary artery occlusion and 4 h reperfusion, or hearts explanted for immunoblotting without being subjected to ischemia. Area at risk (AR) was assessed by blue dye and IS by triphenyl-tetrazolium-chloride.

RESULTS

Body weight and the size of AR were comparable among groups. There were no significant differences among groups in mean blood pressure and heart rate. CIL, but not ATV, reduced IS. IS in the ATV+CIL group was significantly smaller than the other three groups (P < 0.001 for each comparison). ATV, CIL and their combination did not affect total eNOS expression. ATV at 2 mg/kg/d did not affect Ser-1177 P-eNOS levels, whereas CIL increased it (258 +/- 15%). The level of myocardial P-eNOS levels was highest in the ATV+CIL group (406 +/- 7%).

CONCLUSIONS

ATV and CIL have synergistic effect on eNOS phosphorylation and IS reduction. By increased activation of eNOS, CIL may augment the pleiotropic effects of statins.