Cardioprotective effects of 17 beta-estradiol produced by activation ofmitochondrial ATP-sensitive K(+)Channels in canine hearts

Myocardial protection in cardiac surgery: a comprehensive review of current therapies and future cardioprotective strategies

Cardiac surgery with cardiopulmonary bypass results in global myocardial ischemia-reperfusion injury, leading to significant postoperative morbidity and mortality. Although cardioplegia is the cornerstone of intraoperative cardioprotection, a number of additional strategies have been identified. The concept of preconditioning and postconditioning, despite its limited direct clinical application, provided an essential contribution to the understanding of myocardial injury and organ protection. Therefore, physicians can use different tools to limit perioperative myocardial injury. These include the choice of anesthetic agents, remote ischemic preconditioning, tight glycemic control, optimization of respiratory parameters during the aortic unclamping phase to limit reperfusion injury, appropriate choice of monitoring to optimize hemodynamic parameters and limit perioperative use of catecholamines, and early reintroduction of cardioprotective agents in the postoperative period. Appropriate management before, during, and after cardiopulmonary bypass will help to decrease myocardial damage. This review aimed to highlight the current advancements in cardioprotection and their potential applications during cardiac surgery.

Mitochondrial Dysfunction and Cardiovascular Disease: Pathophysiology and Emerging Therapies

Mitochondria ensure the supply of cellular energy through the production of ATP via oxidative phosphorylation. The alteration of this process, called mitochondrial dysfunction, leads to a reduction in ATP and an increase in the production of reactive oxygen species (ROS). Mitochondrial dysfunction can be caused by mitochondrial/nuclear DNA mutations, or it can be secondary to pathological conditions such as cardiovascular disease, aging, and environmental stress. The use of therapies aimed at the prevention/correction of mitochondrial dysfunction, in the context of the specific treatment of cardiovascular diseases, is a topic of growing interest. In this context, the data are conflicting since preclinical studies are numerous, but there are no large randomized studies.

17β-Oestradiol facilitates M2 macrophage skewing and ameliorates arrhythmias in ovariectomized female infarcted rats

Epidemiological studies have suggested a lower incidence of arrhythmia‐induced sudden cardiac death in women than in men. 17β‐oestradiol (E2) has been reported to have a post‐myocardial infarction antiarrhythmic effect, although the mechanisms have yet to be elucidated. We investigated whether E2‐mediated antioxidation regulates macrophage polarization and affects cardiac sympathetic reinnervation in rats after MI. Ovariectomized Wistar rats were randomly assigned to placebo pellets, E2 treatment, or E2 treatment +3‐morpholinosydnonimine (a peroxynitrite generator) and followed for 4 weeks. The infarct sizes were similar among the infarcted groups. At Day 3 after infarction, post‐infarction was associated with increased superoxide levels, which were inhibited by administering E2. E2 significantly increased myocardial IL‐10 levels and the percentage of regulatory M2 macrophages compared with the ovariectomized infarcted alone group as assessed by immunohistochemical staining, Western blot and RT‐PCR. Nerve growth factor colocalized with both M1 and M2 macrophages at the magnitude significantly higher in M1 compared with M2. At Day 28 after infarction, E2 was associated with attenuated myocardial norepinephrine levels and sympathetic hyperinnervation. These effects of E2 were functionally translated in inhibiting fatal arrhythmias. The beneficial effect of E2 on macrophage polarization and sympathetic hyperinnervation was abolished by 3‐morpholinosydnonimine. Our results indicated that E2 polarized macrophages into the M2 phenotype by inhibiting the superoxide pathway, leading to attenuated nerve growth factor‐induced sympathetic hyperinnervation after myocardial infarction.

Sex-Related Effects on Cardiac Development and Disease

Cardiovascular diseases (CVD) are the leading cause of morbidity and mortality. Interestingly, male and female patients with CVD exhibit distinct epidemiological and pathophysiological characteristics, implying a potentially important role for primary and secondary sex determination factors in heart development, aging, disease and therapeutic responses. Here, we provide a concise review of the field and discuss current gaps in knowledge as a step towards elucidating the “sex determination–heart axis”. We specifically focus on cardiovascular manifestations of abnormal sex determination in humans, such as in Turner and Klinefelter syndromes, as well as on the differences in cardiac regenerative potential between species with plastic and non-plastic sexual phenotypes. Sex-biased cardiac repair mechanisms are also discussed with a focus on the role of the steroid hormone 17β-estradiol. Understanding the “sex determination–heart axis” may offer new therapeutic possibilities for enhanced cardiac regeneration and/or repair post-injury.

Age- and gender-related differences in the del Nido cardioprotection protocol

BACKGROUND

The evidence regarding the impact of patient's age and gender on del Nido cardioplegia cadioprotection capability in adults is strongly limited.

METHODS

A group of 75 patients undergoing aortic valve replacement (AVR) with del Nido cardioplegia was divided into Group 1 (male) and Group 2 (female). Creatine kinase (CK-MB isoenzyme) and high sensitivity troponin T (hs-TnT) values at 24 hours and 48 hours, occurrence of cardiac activity during crossclamp and ventricular fibrillation (VF) during reperfusion were compared. The impact of age on hs-TnT,CK-MB, VF during reperfusion and cardiac activity during crossclamp was investigated using regression models.

RESULTS

No difference between the groups was reported in 24-hour CK-MB (median 15.57 ng/ml; IQR 12.13-22.82 ng/mL vs 13.97; 12.09-17.147 ng/mL; p= .168), 48-hour CK-MB (6.19; 4.22-7.71 ng/mL vs 6.07;4.56-7.06 ng/mL; p= .707), 24-hour hs-TnT (259.2; 172.0-376.9 pg/mL vs 193.0; 167.8-351 pg/mL.1; p= .339), 48-hour hs-TnT (169.1; 124.9-293.0 pg/mL vs 159.2; 123.12-211.77 pg/mL; p= .673), VF during reperfusion (25% vs 18,5%; p= .774) and cardiac activity during arrest (39.6% vs 37.1%; p= 1.0). Values of CK-MB at 24 hours, hs-TnT at 24 hours and hs-TnT at 48 hours were not dependent on age. The CK-MB at 48 hours was dependent on age (p=.039). Probit regression failed to reveal the impact of patients' age on post-clamp VF occurrence ( p=.11) or electrical activity during arrest (p=.57) .

CONCLUSIONS

Basing on study results, it can be hypothesised that the del Nido cardioplegia provides adequate myocardial protection in AVR patients regardless of age and gender.

[Protective effect of uridine on metabolic processes in rat myocardum during its ischemia/reperfusion damage]

The experimental study of the cardioprotective effect of uridine, the metabolic precursor of the endogenous activator of mitochondrial ATP-dependent K+-channels (mitoKATP-channels), was performed using the model of myocardial ischemia/reperfusion (I/RP) in rats. Ischemia for 30 min followed by reperfusion for 120 min resulted in a significant decrease in ATP and phosphocreatine (PC) content, intensification of lipid peroxidation (LPO), and inhibition of the antioxidant system (AOS) in cardiomyocytes. Uridine in a dose of 30 mg/kg, administered intravenously prior to reperfusion, had a protective effect on myocardial metabolism in the I/RP zone. It prevented the decrease of ATP and PC, limited the LPO processes, evaluated by the content of lipid hydroperoxides and conjugated dienes, and improved the AOS state by, preventing the decrease of superoxide dismutase (SOD) activity and increasing the content of reduced glutathione (GSH). The mitoKATP-channel blocker 5-hydroxydecanoate (5-HD, 5 mg/kg) eliminated the ability of uridine to maintain the ATP level and to exhibit its positive effect on the intensity of the LPO and activity of AOS. The obtained data allow us to conclude that activation of mitoKATP-channels play an important role in the mechanism of the cardioprotective effect of uridine in I/RP damage of myocardium.

Effects of Cardiac Hypertrophy, Diabetes, Aging, and Pregnancy on the Cardioprotective Effects of Postconditioning in Male and Female Rats

Background

Aging, left ventricular hypertrophy (LVH), diabetes mellitus, and pregnancy are well-recognized risk factors that increase the prevalence of cardio-ischemic events and are linked to poor clinical recovery following acute myocardial infarction. The coexistence of these risk factors with ischemic heart disease (IHD) deteriorates disease prognosis and could potentially lead to fatal arrhythmias and heart failure. The objective of this study was to investigate the vulnerability of hearts with aging, LVH, diabetes, and pregnancy to ischemic insult and their response to pacing postconditioning- (PPC-) induced heart protection.

Methods

Hearts isolated from aged, spontaneously hypertensive and diabetic male and female rats and hearts from pregnant female rats (n=8 per group) were subjected to coronary occlusion followed by reperfusion using a modified Langendorff system. Hemodynamics data were computed digitally, and cardiac damage was accessed by measurements of infarct size and cardiac enzyme release.

Results

There were no significant differences in the vulnerability of all hearts to ischemic insult compared to their respective controls. PPC improved cardiac hemodynamics and reduced infarct size and cardiac enzyme release in hearts isolated from aged and spontaneously hypertensive female rats and female rats with hypertrophied hearts subjected to PPC (P < 0.001). Aged or hypertrophied male hearts were not protected by PPC maneuver. Moreover, the protective effects of PPC were lost in diabetic male and female hearts although retained in hearts from pregnant rats.

Conclusions

We demonstrate that aging, LVH, diabetes mellitus, and pregnancy do not affect cardiac vulnerability to ischemic insult. Moreover, PPC mediates cardioprotection in a gender-specific manner in aged and spontaneously hypertensive rats. Diabetes mellitus provokes the protective effects of PPC on both genders equally. Finally, we demonstrate that PPC is a new cardioprotective maneuver in hearts from pregnant female rats.

Involvement of sex hormonal regulation of K+ channels in electrophysiological and contractile functions of muscle tissues

Sex hormones, such as testosterone, progesterone, and 17β-estradiol, control various physiological functions. This review focuses on the sex hormonal regulation of K⁺ channels and the effects of such regulation on electrophysiological and contractile functions of muscles. In the cardiac tissue, testosterone and progesterone shorten action potential, and estrogen lengthens QT interval, a marker of increased risk of ventricular tachyarrhythmias. We have shown that testosterone and progesterone in physiological concentration activate KCNQ1 channels via membrane-delimited sex hormone receptor/eNOS pathways to shorten the action potential duration. Mitochondrial K⁺ channels are also involved in the protection of cardiac muscle. Testosterone and 17β-estradiol directly activate mitochondrial inner membrane K⁺ channels (Ca²⁺ activated K⁺ channel (K_Ca channel) and ATP-sensitive K⁺ channel (K_ATP channel)) that are involved in ischemic preconditioning and cardiac protection. During pregnancy, uterine blood flow increases to support fetal growth and development. It has been reported that 17β-estradiol directly activates large-conductance Ca²⁺-activated K⁺ channel (BK_Ca channel) attenuating arterial contraction. Furthermore, 17β-estradiol increases expression of BK_Ca channel β1 subunit which enhances BK_Ca channel activity by DNA demethylation. These findings are useful for understanding the mechanisms of sex or generation-dependent differences in the physiological and pathological functions of muscles, and the mechanisms of drug actions.

Response of the human myocardium to ischemic injury and preconditioning: The role of cardiac and comorbid conditions, medical treatment, and basal redox status

BACKGROUND

The diseased human myocardium is highly susceptible to ischemia/reoxygenation (I/R)-induced injury but its response to protective interventions such as ischemic preconditioning (IPreC) is unclear. Cardiac and other pre-existing clinical conditions as well as previous or ongoing medical treatment may influence the myocardial response to I/R injury and protection. This study investigated the effect of both on myocardial susceptibility to I/R-induced injury and the protective effects of IPreC.

METHODS AND RESULTS

Atrial myocardium from cardiac surgery patients (n = 300) was assigned to one of three groups: aerobic control, I/R alone, and IPreC. Lactate dehydrogenase leakage, as a marker of cell injury, and cell viability were measured. The basal redox status was determined in samples from 90 patients. The response to I/R varied widely. Myocardium from patients with aortic valve disease was the most susceptible to injury whereas myocardium from dyslipidemia patients was the least susceptible. Tissue from females was better protected than tissue from males. Myocardium from patients with mitral valve disease was the least responsive to IPreC. The basal redox status was altered in the myocardium from patients with mitral and aortic valve disease.

CONCLUSIONS

The response of the myocardium to I/R and IPreC is highly variable and influenced by the underlying cardiac pathology, dyslipidemia, sex, and the basal redox status. These results should be taken into account in the design of future clinical studies on the prevention of I/R injury and protection.

Mechanistic Pathways of Sex Differences in Cardiovascular Disease

Major differences between men and women exist in epidemiology, manifestation, pathophysiology, treatment, and outcome of cardiovascular diseases (CVD), such as coronary artery disease, pressure overload, hypertension, cardiomyopathy, and heart failure. Corresponding sex differences have been studied in a number of animal models, and mechanistic investigations have been undertaken to analyze the observed sex differences. We summarize the biological mechanisms of sex differences in CVD focusing on three main areas, i.e., genetic mechanisms, epigenetic mechanisms, as well as sex hormones and their receptors. We discuss relevant subtypes of sex hormone receptors, as well as genomic and nongenomic, activational and organizational effects of sex hormones. We describe the interaction of sex hormones with intracellular signaling relevant for cardiovascular cells and the cardiovascular system. Sex, sex hormones, and their receptors may affect a number of cellular processes by their synergistic action on multiple targets. We discuss in detail sex differences in organelle function and in biological processes. We conclude that there is a need for a more detailed understanding of sex differences and their underlying mechanisms, which holds the potential to design new drugs that target sex-specific cardiovascular mechanisms and affect phenotypes. The comparison of both sexes may lead to the identification of protective or maladaptive mechanisms in one sex that could serve as a novel therapeutic target in one sex or in both.

Targeted basic research to highlight the role of estrogen and estrogen receptors in the cardiovascular system

Epidemiological, clinical and animal studies revealed that sex differences exist in the manifestation and outcome of cardiovascular disease (CVD). The underlying molecular mechanisms implicated in these sex differences are not fully understood. The reasons for sex differences in CVD are definitely multifactorial, but major evidence points to the contribution of sex steroid hormone, 17β-estradiol (E2), and its receptors, estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ). In this review, we summarize past and present studies that implicate E2 and ER as important determinants of sexual dimorphism in the physiology and pathophysiology of the heart. In particular, we give an overview of studies aimed to reveal the role of E2 and ER in the physiology of the observed sex differences in CVD using ER knock-out mice. Finally, we discuss recent findings from novel transgenic mouse models, which have provided new information on the sexual dimorphic roles of ER specifically in cardiomyocytes under pathological conditions.

The clinical relevance of altered fibrinogen packaging in the presence of 17β-estradiol and progesterone

BACKGROUND

The effect of endogenous hormone concentrations, specifically 17β-estradiol and progesterone, on fibrin network formation has not been established.

OBJECTIVES

It is essential to understand natural hormone mechanisms since these hormones are still present in circulation while hormonal contraceptives, which are associated with increased risk of venous thromboembolism, are used.

METHODS

Due to the fact that these hormones are known to increase hypercoagulability and the prothrombotic state scanning electron microscopy (SEM), atomic force microscopy (AFM), thromboelastography (TEG) and turbidimetry were employed to investigate the morphology, surface roughness, viscoelastic properties and formation and lysis of fibrin.

RESULTS

17β-estradiol and progesterone showed hypercoagulable viscoelastic properties and decreased the diameter and surface roughness of fibrin while increasing dense matted deposit occurrence. Our results suggest that the additional burden of hormonal load, together with the presence of endogenous estrogen and progesterone, may result in a prothrombotic and hypercoagulable state in females with an inflammatory predisposition.

CONCLUSION

Our results are of clinical importance when considering hormones as either pathological agent or therapeutic intervention as will be assessed in future investigation.

Rapid estrogen actions on ion channels: A survey in search for mechanisms

A survey of nearly two hundred reports shows that rapid estrogenic actions can be detected across a range of kinds of estrogens, a range of doses, on a wide range of tissue, cell and ion channel types. Striking is the fact that preparations of estrogenic agents that do not permeate the cell membrane almost always mimic the actions of the estrogenic agents that do permeate the membrane. All kinds of estrogens, ranging from natural ones, through receptor modulators, endocrine disruptors, phytoestrogens, agonists, and antagonists to novel G-1 and STX, have been reported to be effective. For actions on specific types of ion channels, the possibility of opposing actions, in different cases, is the rule, not the exception. With this variety there is no single, specific action mechanism for estrogens per se, although in some cases estrogens can act directly or via some signaling pathways to affect ion channels. We infer that estrogens can bind a large number of substrates/receptors at the membrane surface. As against the variety of subsequent routes of action, this initial step of the estrogen's binding action is the key.

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.

Estrogen Regulates Angiotensin II Receptor Expression Patterns and Protects the Heart from Ischemic Injury in Female Rats

Previous studies have shown that female offspring are resistant to fetal stress-induced programming of ischemic-sensitive phenotype in the heart; however, the mechanisms responsible remain unclear. The present study tested the hypothesis that estrogen plays a role in protecting females in fetal programming of increased heart vulnerability. Pregnant rats were divided into normoxic and hypoxic (10.5% O2 from Day 15 to 21 of gestation) groups. Ovariectomy (OVX) and estrogen (E2) replacement were performed in 8-wk-old female offspring. Hearts of 4-mo-old females were subjected to ischemia and reperfusion injury in a Langendorff preparation. OVX significantly decreased postischemic recovery of left ventricular function and increased myocardial infarction, and no difference was observed between normoxic and hypoxic groups. The effect of OVX was rescued by E2 replacement. OVX decreased the binding of glucocorticoid receptor (GR) to glucocorticoid response elements at angiotensin II type 1 (Agtr1) and type 2 (Agtr2) receptor promoters, resulting in a decrease in Agtr1 and an increase in Agtr2 in the heart. Additionally, OVX decreased estrogen receptor (ER) expression in the heart and inhibited ER/GR interaction in binding to glucocorticoid response elements at the promoters. Consistent with the changes in Agtrs, OVX significantly decreased Prkce abundance in the heart. These OVX-induced changes were abrogated by E2 replacement. The results indicate that estrogen is not directly responsible for the sex dimorphism in fetal programming of heart ischemic vulnerability but suggest a novel mechanism of estrogen in regulating cardiac Agtr1/Agtr2 expression patterns and protecting female hearts against ischemia and reperfusion injury.

Sex-based differences in cardiac ischaemic injury and protection: therapeutic implications

Ischaemic heart disease (IHD) is the most frequent cause of mortality among men and women. Many epidemiological studies have demonstrated that premenopausal women have a reduced risk for IHD compared with their male counterparts. The incidence of IHD in women increases after menopause, suggesting that IHD is related to declining oestrogen levels. Experimental observations have confirmed the results of epidemiological studies investigating sex-specific differences in cardiac tolerance to ischaemia. Female sex appears also to favourably influence cardiac remodelling after ischaemia/reperfusion injury. Furthermore, sex-related differences in ischaemic tolerance of the adult myocardium can be influenced by interventions during the early phases of ontogenetic development. Detailed mechanisms of these sex-related differences remain unknown; however, they involve the genomic and non-genomic effects of sex steroid hormones, particularly the oestrogens, which have been the most extensively studied. Although the protective effects of oestrogen have many potential therapeutic implications, clinical trials have shown that oestrogen replacement in postmenopausal women may actually increase the incidence of IHD. The results of these trials have illustrated the complexity underlying the mechanisms involved in sex-related differences in cardiac tolerance to ischaemia. Sex-related differences in cardiac sensitivity to ischaemia/reperfusion injury may also influence therapeutic strategies in women with acute coronary syndrome. Women undergo coronary intervention less frequently and a lower proportion of women receive evidence-based therapy compared with men. Although our understanding of this important topic has increased in recent years, there is an urgent need for intensive experimental and clinical research to develop female-specific therapeutic strategies. Only then we will be able to offer patients better evidence-based treatment, a better quality of life and lower mortality.

Both GPER and membrane oestrogen receptor-α activation protect ventricular remodelling in 17β oestradiol-treated ovariectomized infarcted rats

Clinical and experimental studies have established that gender is a factor in the development of ventricular hypertrophy. We investigated whether the attenuated hypertrophic effect of oestradiol was via activation of phosphatidylinositol 3-kinase (PI3K)/Akt/endothelial nitric oxide synthase (eNOS) through non-genomic action. Twenty-four hours after coronary ligation, female Wistar rats were randomized into control, subcutaneous oestradiol treatment or a G-protein coupled oestrogen receptor (GPER) agonist, G-1 and treated for 4 weeks starting from 2 weeks after bilateral ovariectomy. Ventricular hypertrophy assessed by cardiomyocyte size after infarction was similarly attenuated by oestradiol or G-1 in infarcted rats. The phosphorylation of Akt and eNOS was significantly decreased in infarcted rats and restored by oestradiol and G-1, implying the GPER pathway in this process. Oestradiol-induced Akt phosphorylation was not abrogated by G-15 (a GPER blocker). Akt activation was not inhibited by actinomycin D. When a membrane-impermeable oestrogen-albumin construct was applied, similar responses in terms of eNOS activation to those of oestradiol were achieved. Furthermore, PPT, an ERα receptor agonist, activated the phosphorylation of Akt and eNOS. Thus, membrane ERα receptor played a role in mediating the phosphorylation of Akt and eNOS. The specific PI3K inhibitor, LY290042, completely abolished Akt activation and eNOS phosphorylation in infarcted hearts treated with either oestradiol or oestradiol + G-15. These data support the conclusions that oestradiol improves ventricular remodelling by both GPER- and membrane-bound ERα-dependent mechanisms that converge into the PI3K/Akt/eNOS pathway, unveiling a novel mechanism by which oestradiol regulates pathological cardiomyocyte growth after infarction.

Sex differences in animal models for cardiovascular diseases and the role of estrogen

Clinical findings show sex differences in the manifestation of a number of cardiovascular diseases (CVD). However, the underlying molecular mechanisms are incompletely understood. Multiple animal models suggest sex differences in the manifestation of CVD, and provide strong experimental evidence that different major pathways are regulated in a sex-specific manner. In most animal studies females display a lower mortality, less severe hypertrophy, and better preserved cardiac function compared with male counterparts. The data support the hypothesis that female sex and/or the sex hormone estrogen (17β-estradiol; E2) may contribute to the sexual dimorphism in the heart and to a better outcome of cardiac diseases in females. To improve our understanding of the sex-based molecular and cellular mechanisms of CVD and to develop new therapeutic strategies, the use of appropriate animal models is essential. This review highlights recent findings from animal models relevant for studying the mechanisms of sexual dimorphisms in the healthy and diseased heart, focusing on physiological hypertrophy (exercise), pathological hypertrophy (volume and pressure overload induced hypertrophy), and heart failure (myocardial infarction). Furthermore, the potential effects of E2 in these models will be discussed.

Neuroprotective effects of 17β-estradiol associate with KATP in rat brain

Previous studies have indicated that estrogen protects the brain from ischemic damage and regulates K(ATP) channel activity; the present study was designed to address the involvement of K(ATP) channels in the neuroprotective effects of estrogen in focal cerebral ischemia: in experiment 1, K(ATP) mRNA and protein in the cortices of rats were compared among groups of ovariectomized rats (Ovx-1), Sham-operated rats (Sham-1), and ovariectomized rats administered 17β-estradiol (Estr-1). In experiment 2, neurobehavioral scores and infarct volume of rats were evaluated after middle cerebral artery occlusion in ovariectomized rats (Ovx-2), Sham-operated rats (Sham-2), ovariectomized female rats administered 17β-estradiol (Estr-2), and ovariectomized rats administered both 17β-estradiol and stereotactic injections of glibenclamide (Estr+G). Our results showed that the Kir6.2 and SUR1 mRNA and protein levels in the brain cortices of female ovariectomized rats were lower than those in Sham rats. However, the expression levels of Kir6.2 and SUR1 in brain cortices of ovariectomized rats recovered after supplementation with 17β-estradiol. The protective effects of 17β-estradiol were abolished by glibenclamide, a K(ATP) channel blocker. This indicates that estradiol significantly upregulates the expression of K(ATP) channel subunits and channel activity in the brain cortices of ovariectomized rats. This regulation is associated with the neuroprotective effects of estradiol.

Concentration-dependent effects of the soy phytoestrogen genistein on the proteome of cultured cardiomyocytes

The soy-derived phytoestrogen genistein (GEN) has received attention for its potential benefits on the cardiovascular system by providing direct protection to cardiomyocytes against pathophysiological stresses. Here, we employed a proteomic approach to study the concentration-dependent effects of GEN treatments on cardiomyocytes. Cultured HL-1 cardiomyocytes were treated with low (1μM) and high (50μM) concentrations of GEN. Proteins were pre-fractionated by sequential hydrophilic/hydrophobic extraction and both protein fractions from each treatment group were separated by 2D gel electrophoresis (2DE). Overall, approximately 2,700 spots were visualized on the 2D gels. Thirty-nine and 99 spots changed in volume relative to controls (p<0.05) following the low- and high-concentration GEN treatments, respectively. From these spots, 25 and 62 protein species were identified by ESI-MS/MS and Mascot database searching, respectively. Identified proteins were further categorized according to their functions and possible links to cardioprotection were discussed. MetaCore gene ontology analysis suggested that 1μM GEN significantly impacted the anti-apoptosis process, and that both the low and high concentrations of GEN influenced the glucose catabolic process and regulation of ATPase activity. This proteomics study provides the first global insight into the molecular events triggered by GEN treatment in cardiomyocytes.

Regulation of K(ATP) channel by 17β-estradiol in pancreatic β-cells

ATP-sensitive potassium channels (K(ATP)) regulate electrical activity and insulin secretion in pancreatic β-cells. When glucose concentration increases, the [ATP]/[ADP] ratio rises closing K(ATP) channels, and the membrane potential depolarizes, triggering insulin secretion. This pivotal role of K(ATP) channels is used not only by glucose but also by neurotransmitters, hormones and other physiological agents to modulate electrical and secretory β-cell response. In recent years, it has been demonstrated that estrogens and estrogen receptors are involved in glucose homeostasis, and that they can modulate the electrical activity and insulin secretion of pancreatic β-cells. The hormone 17β-estradiol (E2), at physiological levels, is implicated in maintaining normal insulin sensitivity for β-cell function. Long term exposure to E2 increases insulin content, insulin gene expression and insulin release via the estrogen receptor α (ERα), while rapid responses to E2 can regulate K(ATP) channels increasing cGMP levels through the estrogen receptor β (ERβ) and type A guanylate cyclase receptor (GC-A). This review summarizes the main actions of 17β-estradiol on K(ATP) channels and the subsequent insulin release in pancreatic β-cells.

The impact of gender difference on the effects of preinfarction angina on microvascular damage with reperfused myocardial infarction

BACKGROUND

Few studies have addressed gender differences in evoking preconditioning. In an experimental study, it was reported that the preconditioning effect disappeared after gonadectomy.

OBJECTIVES

We sought to determine the effects of preinfarction angina (PA) on myocardial damage using intravenous contrast echocardiography.

METHODS

We studied 334 consecutive patients with anterior myocardial infarction (AMI) who underwent successful angioplasty. All patients underwent myocardial contrast echocardiography (MCE) 14 days after percutaneous coronary intervention (PCI). Contrast defect was calculated as contrast defect area/myocardial area. Typical angina occurring in the 24-hour period preceding myocardial infarction was present in 133 patients (29 women) (group PA) and absent in 201 patients (43 women) (group non-PA). All women were postmenopausal.

RESULTS

The contrast defect size and peak creatinine phosphokinase (max CPK) level in women were both significantly higher than that of men in group PA (18.3% +/- 6.3% vs 11.9% +/- 9.0%; P < 0.01 and 5000 +/- 599 IU/L vs 2672 +/- 221 IU/L; P < 0.005). The functional status of the myocardium among group PA, as expressed by risk area wall motion score index, was better in men than in women at 14 days (1.1 +/- 0.8 vs 1.7 +/- 0.8; P < 0.01) and at 6 months (0.7 +/- 0.4 vs 1.6 +/- 0.6; P < 0.01). However there were no significant gender differences in group non-PA. Multivariate regression analysis showed that the female gender (P < 0.05) was a significant independent predictor for microvascular damage.

CONCLUSIONS

These findings suggest that preconditioning effects were attenuated in women with reperfused AMI.

Sex differences in the phosphorylation of mitochondrial proteins result in reduced production of reactive oxygen species and cardioprotection in females

RATIONALE

Although premenopausal females have a lower risk for cardiovascular disease, the mechanism(s) are poorly understood.

OBJECTIVE

We tested the hypothesis that cardioprotection in females is mediated by altered mitochondrial protein levels and/or posttranslational modifications.

METHODS AND RESULTS

Using both an in vivo and an isolated heart model of ischemia and reperfusion (I/R), we found that females had less injury than males. Using proteomic methods we found that female hearts had increased phosphorylation and activity of aldehyde dehydrogenase (ALDH)2, an enzyme that detoxifies reactive oxygen species (ROS)-generated aldehyde adducts, and that an activator of ALDH2 reduced I/R injury in males but had no significant effect in females. Wortmannin, an inhibitor of phosphatidylinositol 3-kinase, blocked the protection and the increased phosphorylation of ALDH2 in females, but had no effect in males. Furthermore, we found an increase in phosphorylation of alpha-ketoglutarate dehydrogenase (alphaKGDH) in female hearts. alphaKGDH is a major source of ROS generation particularly with a high NADH/NAD ratio which occurs during I/R. We found decreased ROS generation in permeabilized female mitochondria given alphaKGDH substrates and NADH, suggesting that increased phosphorylation of alphaKGDH might reduce ROS generation by alphaKGDH. In support of this hypothesis, we found that protein kinase C-dependent phosphorylation of purified alphaKGDH reduced ROS generation. Additionally, myocytes from female hearts had less ROS generation following I/R than males and addition of wortmannin increased ROS generation in females to the same levels as in males.

CONCLUSIONS

These data suggest that posttranslational modifications can modify ROS handling and play an important role in female cardioprotection.

17beta-Estradiol decreases vulnerability to ventricular arrhythmias by preserving connexin43 protein in infarcted rats

Epidemiological studies showed that a lower mortality rate of sudden cardiac death among women than among men may depend on the action of female sex hormones. This study assessed whether 17beta-estradiol exerts anti-arrhythmic effects through enhanced Connexin43 (Cx43) expression after infarction. Two weeks after ovariectomy, female Wistar rats were randomly assigned to coronary artery ligation or sham-operation. Twenty-four hours after coronary ligation, ovariectomized rats were randomized into vehicle, subcutaneous estradiol treatment, tamoxifen, or subcutaneous estradiol treatment+tamoxifen and followed for 4weeks. To verify the role of estradiol-related nitric oxide in modulating the expression of Cx43, N-nitro-L-arginine methyl ester was also assessed in an in vitro study. Myocardial Cx43 expression revealed a significant decrease in vehicle-treated infarcted rats compared with sham-operated rats at 24h and 4weeks after infarction. Attenuated Cx43 expression was blunted after administering estradiol, assessed by immunofluorescent analysis, Western blotting, and real-time quantitative RT-PCR of Cx43. The vulnerability for ventricular arrhythmia during programmed stimulation in estradiol-treated infarcted rats was significantly lower than in vehicle-treated infarcted rats. The beneficial effect of estradiol on Cx43 was abolished by tamoxifen. In addition, the invitro study demonstrated that the amount of Cx43 showed significant reduction after adding N-nitro-L-arginine methyl ester. Chronic administration of estradiol after infarction is associated with attenuated reduction of gap junction proteins probably through a nitric oxide-dependent pathway via the estrogen receptor and thus plays a critical role in the beneficial effect on arrhythmic vulnerability response to programmed electrical stimulation.

PKC-permitted elevation of sarcolemmal KATP concentration may explain female-specific resistance to myocardial infarction

The female myocardium, relative to that of the male, exhibits sustained resistance to ischaemic tissue injury, a phenomenon termed sex-specific cardioprotection (SSC). SSC is dependent upon the sarcolemmal K(ATP) channel (sarcK(ATP)), and protein kinase C (PKC). Here we investigate whether PKC-mediated regulation of sarcK(ATP) concentration can explain this endogenous form of protection. Hearts from male (M) and female (F) rats were Langendorff-perfused for 30 min prior to either regional ischaemia-reperfusion (I/R), or global ischaemia (GISC). For both protocols, pre-ischaemic blockade of PKC was achieved by chelerythrine (Chel) in male (M + C) and female (F + C) hearts. Additional female hearts underwent sarcK(ATP) antagonism during I/R by HMR-1098 (HMR), either alone or in combination with Chel (HMR + Chel). GISC hearts were fractionated to assess cellular distribution of PKC and sarcK(ATP). Sex-specific infarct resistance was apparent under control I/R (F, 23 +/- 3% vs. M, 36 +/- 4%, P < 0.05) and abolished by Chel (F + C, 36 +/- 3%). Female infarct resistance was susceptible to sarcK(ATP) blockade (Control, 16 +/- 2% vs. HMR, 27 +/- 3%), and PKC blockade had no additional effect (HMR + Chel, 26 +/- 2%). The prevalence of Kir6.2 and SUR2 was higher in the sarcolemmal fractions of females (Kir6.2: F, 1.24 +/- 0.07 vs. M, 1.02 +/- 0.06; SUR2: F, 3.16 +/- 0.22 vs. M, 2.45 +/- 0.09; ratio units), but normalized by Chel (Kir6.2: F, 1.06 +/- 0.07 vs. M, 0.99 +/- 0.06; SUR2: F, 2.99 +/- 0.09 vs. M, 2.82 +/- 0.22, M; ratio units). Phosphorylation of sarcolemmal PKC was reduced by Chel (p-PKC/PKC: control, 0.43 +/- 0.02; Chel, 0.29 +/- 0.01; P < 0.01). We conclude that PKC-mediated regulation of sarcK(ATP) may account for the physiologically sustainable dependence of SSC upon both PKC and sarcK(ATP), and that this regulation involves PKC-permitted enrichment of the female sarcolemma with sarcK(ATP). As such, the PKC-sarcK(ATP) axis may represent a target for sustainable prophylactic induction of cardioprotection.

Gender Differences in Cardiac Ischemic Injury and Protection—Experimental Aspects

This review summarizes some available information on gender differences of myocardial injury with particular attention to experimental approach. It has been observed that significant gender differences exist already in normal heart. They involve among others cardiac growth, contractile function, calcium metabolism and function of mitochondria. Differences, characteristic of the normal myocardium, generate the logical presumption of the different reaction of the male and female heart to various pathogenic factors. Most of the experimental studies confirm the clinical observations: increased resistance of the female heart to ischemia/reperfusion injury was shown in dogs, rats, mice and rabbits. Furthermore, gender differences in the ischemic tolerance of the adult myocardium can be influenced by interventions (e.g. hypoxia) imposed during the early phases of ontogenetic development. The already high tolerance of the adult female heart can be increased by adaptation to chronic hypoxia and ischemic preconditioning. It seems that the protective effect depends on age: it was absent in young, highly tolerant heart but it appeared with the decrease of natural resistance during aging. Both experimental and clinical studies have indicated that female gender influences favorably also the remodeling and the adaptive response to myocardial infarction. It follows from the data available that male and female heart differs significantly in many parameters under both physiological and pathological conditions. Detailed molecular and cellular mechanisms of these differences are still unknown; they involve genomic and non-genomic effects of sex steroid hormones, particularly the most frequently studied estrogens. The cardiovascular system is, however, influenced not only by estrogens but also by other sex hormones, e.g. androgens. Moreover, steroid hormone receptors do not act alone but interact with a broad array of co-regulatory proteins to alter transcription. The differences are so important that they deserve serious consideration in clinical practice in search for proper diagnostic and therapeutic procedures.

Molecular aspects of ischaemic postconditioning

Preconditioning, a well established phenomenon had been used since 1980s to attenuate ischaemia-reperfusion induced injury. However, inability to predict the onset of ischaemia in clinical settings led to the discovery of a new concept of postconditioning (PoCo), in 2000s whereby brief repetitive cycles of ischaemia with intermittent reperfusion followed by prolonged ischaemia-elicited tissue protection. There is an impressive array of molecular mechanisms contributing to PoCo-mediated tissue-protection, which include triggers like adenosine (ADO), opioid, erythropoietin (EPO), endogenous nitric-oxide, reactive oxygen species, acetylcholine, tissue factors, pro-inflammatory cytokines and bradykinin; mediators like reperfusion injury salvage kinase pathways including phosphoinositide-3-kinase, extra-cellular signal regulated kinase(1/2) pathway, protein kinase G and protein kinase C; end-effectors like mitochondrial permeability transition pore and mitochondrial potassium ATP channel. The clinical applicability of PoCo has been extended with the use of PoCo mimetic agents like insulin, glucagon like peptide, EPO, statins and ADO before reperfusion in patients with ischaemia reperfusion injury. Remote PoCo has also emerged as a new concept; however, considerable research is required for understanding its molecular mechanisms. In this review, an exhaustive attempt has been made to unearth some molecular aspects of PoCo.

Isolated Heart Function after Ischemia and Reperfusion in Sucrose-Fed Rats: Influence of Gender and Treatment

Sucrose-fed rats (HTG) develop hypertension, hypertriglyceridemia, and other features of the metabolic syndrome. This condition, nowadays a world epidemic, is more prevalent in males and increases the risk of cardiovascular diseases. Weanling male and female rats were given either tap water in control (C) or 30% sucrose solution in HTG groups and commercial rat chow for 3, 5, or 8 months. We studied possible variations in cardiac function, due to gender and length of treatment, in isolated heart after ischemia-reperfusion, since an impaired performance may be more easily detected under stress. Together, sucrose treatment and age affected all cardiac variables. Gender had significant effect on coronary vascular resistance and postischemic levels of the enzyme CK-MB; the percentages of retained cardiac enzymes after ischemia were higher in C and HTG females. C and HTG males had a higher incidence of arrhythmias than females, but only HTG males suffered lethal ventricular fibrillation.

Prenatal cocaine exposure abolished ischemic preconditioning-induced protection in adult male rat hearts: role of PKCepsilon

Prenatal cocaine exposure in rats resulted in decreased PKCepsilon protein expression in the heart of adult male but not female offspring. The present study determined its functional consequence of inhibiting cardioprotection mediated by ischemic preconditioning. Pregnant Sprague-Dawley rats were administered intraperitoneally saline or cocaine (30 mg.kg(-1).day(-1)) from day 15 to day 21 of gestational age. Hearts were isolated from 3-mo-old offspring and were subjected to ischemia and reperfusion injury in a Langendorff preparation, with or without prior ischemic preconditioning. Preischemic values of left ventricular function were the same between the saline control and cocaine-treated animals. Ischemic preconditioning of two episodes of 5-min ischemia significantly decreased infarct size and enhanced postischemic functional recovery of the left ventricle in the saline control animals. This ischemic preconditioning was associated with increased phospho-PKCepsilon, but not phospho-PKCdelta, levels and was blocked by a PKCepsilon translocation inhibitor peptide. Prenatal cocaine treatment abolished the ischemic preconditioning-mediated increase in phospho-PKCepsilon and cardioprotection in the heart of male offspring. In contrast, the cardioprotective effect was fully maintained in female offspring that were exposed to cocaine before birth. The results suggest that prenatal cocaine exposure causes a sex-specific loss of cardioprotection by ischemic preconditioning in adult offspring, which is most likely due to fetal programming of PKCepsilon gene repression, resulting in a downregulation of PKCepsilon function in the heart of adult male offspring.

Prognostic value of troponin I levels for predicting adverse cardiovascular outcomes in postmenopausal women undergoing cardiac surgery

BACKGROUND

Adverse cardiac events that follow cardiac surgery are an important source of perioperative morbidity and mortality for women. Troponin I provides a sensitive measure of cardiac injury, but the levels after cardiac surgery may vary between sexes. Our purpose in this study was to evaluate the prognostic value of troponin I levels for predicting cardiovascular complications in postmenopausal women undergoing cardiac surgery.

METHODS

The cohort of this study were women enrolled in a previously reported clinical trial evaluating the neuroprotective potential of 17beta-estradiol in elderly women. In that study, 175 postmenopausal women not receiving estrogen replacement therapy and scheduled to undergo coronary artery bypass graft (with or without valve surgery) were prospectively randomized to receive 17beta-estradiol or placebo in a double-blind manner beginning the day before surgery and continuing for 5 days postoperatively. Serial 12-lead electrocardiograms were performed and serum troponin I concentrations were measured before surgery, after surgery on arrival in the intensive care unit, and for the first four postoperative days. The primary end-point of the present study was major adverse cardiovascular events (MACE) defined as a Q-wave myocardial infarction, low cardiac output state or death within 30 days of surgery. The diagnosis of Q-wave myocardial infarction was made independently by two physicians blinded to treatment and patient outcomes with the final diagnosis requiring consensus. Low cardiac output state was defined as cardiac index <2.0 L x min(-1) x m(-2) for >8 h regardless of treatment.

RESULTS

Troponin I levels on postoperative day 1 were predictive of MACE (area under the receiver operator curve = 0.862). A cutoff point for troponin I of >7.6 ng/mL (95% confidence interval, 6.4-10.8) provided the optimal sensitivity and specificity for identifying patients at risk for MACE. The negative predictive value of a troponin I level for identifying a patient with a composite cardiovascular outcome was high (96%) and the positive predictive value moderate (40%). Postoperative troponin I levels were not different between women receiving perioperative 17beta-estradiol treatment compared with placebo and the frequency of MACE was not influenced by 17beta-estradiol treatment.

CONCLUSIONS

In postmenopausal women, elevated troponin I levels on postoperative day 1 are predictive of MACE. Monitoring of perioperative troponin I levels might provide a means for stratifying patients at risk for adverse cardiovascular events.

Persistent beneficial effect of postconditioning against infarct size: role of mitochondrial K(ATP) channels during reperfusion

This study tested the hypothesis that inhibition of myocardial injury and modulation of mitochondrial dysfunction by postconditioning (Postcon) after 24 h of reperfusion is associated with activation of K(ATP) channels. Thirty dogs undergoing 60 min of ischemia and 24 h of reperfusion (R) were randomly divided into four groups:

CONTROL

no intervention at R; Postcon: three cycles of 30 s R alternating with 30 s re-occlusion were applied at R; 5-hydroxydecanoate (5-HD): the mitochondrial K(ATP) channel blocker was infused 5 min before Postcon; HMR1098: the sarcolemmal K(ATP) channel blocker was administered 5 min before Postcon. After 24 h of R, infarct size was smaller in Postcon relative to CONTROL (27 +/- 4%* Vs. 39 +/- 2% of area at risk), consistent with a reduction in CK activity (66 +/- 7* Vs. 105 +/- 7 IU/g). The infarct-sparing effect of Postcon was blocked by 5-HD (48 +/- 5%(dagger)), but was not altered by HMR1098 (29 +/- 3%*), consistent with the change in CK activity (102 +/- 8(dagger) in 5-HD and 71 +/- 6* IU/g in HMR1098). In H9c2 cells exposed to 8 h hypoxia and 3 h of reoxygenation, Postcon up-regulated expression of mito-K(ATP) channel Kir6.1 protein, maintained mitochondrial membrane potential and inhibited mitochondrial permeability transition pore (mPTP) opening evidenced by preserved fluorescent TMRE and calcein staining. The protective effects were blocked by 5-HD, but not by HMR1098. These data suggest that in a clinically relevant model of ischemia-reperfusion (1) Postcon reduces infarct size and decreases CK activity after prolonged reperfusion; (2) protection by Postcon is achieved by opening mitochondrial K(ATP) channels and inhibiting mPTP opening. *P < 0.05 Vs. CONTROL; P < 0.05 Vs. Postcon.

Estradiol abolishes reduction in cell death by the opioid agonist Met5-enkephalin after oxygen glucose deprivation in isolated cardiomyocytes from both sexes

There is evidence for differences in the response to the treatment of cardiovascular disease in men and women. In addition, there are conflicting results regarding the effectiveness of pharmacologically induced protection or ischemic preconditioning in females. We investigated whether the ability of Met5-enkephalin (ME) to reduce cell death after oxygen-glucose deprivation (OGD) is influenced by the presence of 17β-estradiol (E2) in a nitric oxide (NO)- and estrogen receptor-dependent manner. On postnatal day 7 to 8, murine cardiomyocytes from wild-type or inducible NO synthase (iNOS) knockout mice were separated by sex, isolated by collagenase digestion, cultured for 24 h, and subjected to 90 min OGD and 180 min reoxygenation at 37°C ( n = 4 to 5 replicates). Cell cultures were incubated in E2 for 15 min or 24 h before OGD. ME was used to increase cell survival. Cell death was assessed by propidium iodide. More than 300 cells were examined for each treatment. Data are presented as means ± SE. As a result, in both sexes, ME-induced cell survival was lost in the presence of E2, and the ability of ME to improve cell survival was restored after treatment with the estrogen receptor antagonist ICI-182780. Furthermore, iNOS was necessary for ME to increase cell survival following OGD in vitro. We conclude that ME-induced reduction in cell death is abolished by E2 in a sex-independent manner via activation of estrogen receptors, and this interaction is dependent on iNOS.

Ovarian steroids stimulate adenosine triphosphate-sensitive potassium (KATP) channel subunit gene expression and confer responsiveness of the gonadotropin-releasing hormone pulse generator to KATP channel modulation

The ATP-sensitive potassium (K(ATP)) channels couple intracellular metabolism to membrane potential. They are composed of Kir6.x and sulfonylurea receptor (SUR) subunits and are expressed in hypothalamic neurons that project to GnRH neurons. However, their roles in regulating GnRH secretion have not been determined. The present study first tested whether K(ATP) channels regulate pulsatile GnRH secretion, as indirectly reflected by pulsatile LH secretion. Ovariectomized rats received sc capsules containing oil, 17beta-estradiol (E(2)), progesterone (P), or E(2)+P at 24 h before blood sampling. Infusion of the K(ATP) channel blocker tolbutamide into the third ventricle resulted in increased LH pulse frequency in animals treated with E(2)+P but was without effect in all other groups. Coinfusion of tulbutamide and the K(ATP) channel opener diazoxide blocked this effect, whereas diazoxide alone suppressed LH. Effects of steroids on Kir6.2 and SUR1 mRNA expression were then evaluated. After 24hr treatment, E(2)+P produced a modest but significant increase in Kir6.2 expression in the preoptic area (POA), which was reversed by P receptor antagonism with RU486. Neither SUR1 in the POA nor both subunits in the mediobasal hypothalamus were altered by any steroid treatment. After 8 d treatment, Kir6.2 mRNA levels were again enhanced by E(2)+P but to a greater extent in the POA. Our findings demonstrate that 1) blockade of preoptic/hypothalamic K(ATP) channels produces an acceleration of the GnRH pulse generator in a steroid-dependent manner and 2) E(2)+P stimulate Kir6.2 gene expression in the POA. These observations are consistent with the hypothesis that the negative feedback actions of ovarian steroids on the GnRH pulse generator are mediated, in part, by their ability to up-regulate K(ATP) channel subunit expression in the POA.

Effect of ATP-sensitive potassium channel agonists on ventricular remodeling in healed rat infarcts

OBJECTIVES

The purpose of this study was to determine whether ATP-sensitive potassium (K(ATP)) channel agonists exert a beneficial effect on the structural, functional, and molecular features of the remodeling heart in infarcted rats.

BACKGROUND

Myocardial K(ATP) channels have been implicated in the ventricular remodeling after myocardial infarction by inhibition of 70-kDa S6 (p70S6) kinase.

METHODS

Male Wistar rats after induction of myocardial infarction were randomized to either vehicle, agonists of K(ATP) channels nicorandil and pinacidil, an antagonist of K(ATP) channels glibenclamide, or a combination of nicorandil and glibenclamide or pinacidil and glibenclamide for 4 weeks. To verify the role of p70S6 kinase in ventricular remodeling, rapamycin was also assessed.

RESULTS

Significant ventricular hypertrophy was detected by increased myocyte size at the border zone isolated by enzymatic dissociation after infarction. Increased synthesis of p70S6 kinase messenger ribonucleic acid after infarction in vehicle-treated rats was confirmed by reverse transcription-polymerase chain reaction, consistent with the results of immunohistochemistry and Western blot for phosphorylated p70S6 kinase. Rats in the nicorandil- and pinacidil-treated groups significantly attenuated cardiomyocyte hypertrophy and phosphorylated p70S6 kinase expression with similar potency, as compared with vehicle. The beneficial effects of nicorandil and pinacidil were abolished by administering either glibenclamide or 5-hydroxydecanoate. Addition of rapamycin attenuated ventricular remodeling and did not have additional beneficial effects compared with those seen in rats treated with either nicorandil or pinacidil alone.

CONCLUSIONS

Activation of K(ATP) channels by either nicorandil or pinacidil can attenuate ventricular remodeling, probably through a p70S6 kinase-dependent pathway after infarction.

Physiological concentration of 17beta-estradiol on sympathetic reinnervation in ovariectomized infarcted rats

17beta-Estradiol (E2) has been shown to exert antiarrhythmic effect after myocardial infarction; however, the mechanisms remain unclear. This study was performed to determine whether E2 exerts beneficial effects through attenuated sympathetic hyperreinnervation after infarction. Two weeks after ovariectomy, female Wistar rats were assigned to coronary artery ligation or sham operation. Twenty-four hours after coronary ligation, rats underwent one of five treatments: 1) sc vehicle treatment (control), 2) sc E2 treatment, 3) sc E2 treatment + tamoxifen (a potent estrogen receptor antagonist), 4) bosentan (an endothelin receptor blocker), or 5) sc E2 treatment + bosentan and followed for 4 wk. Myocardial endothelin-1 and norepinephrine levels at the remote zone revealed a significant elevation in control infarcted rats, compared with sham-operated rats, which is consistent with sympathetic hyperinnervation after infarction. Sympathetic hyperinnervation was blunted after giving the rats either E2 or bosentan, assessed by immunohistochemical analysis of tyrosine hydroxylase, growth-associated protein 43 and neurofilament, and Western blotting and real-time quantitative RT-PCR of nerve growth factor. Arrhythmic scores during programmed stimulation in E2-treated infarcted rats were significantly lower than in control-infarcted rats. Addition of bosentan did not have additional beneficial effects, compared with rats treated with E2 alone. The beneficial effect of E2 on sympathetic hyperinnervation was abolished by tamoxifen. Our data indicated that E2 has a role for sympathetic hyperinnervation after infarction, probably through an endothelin-1-depedent pathway. Chronic administration of E2 after infarction may attenuate the arrhythmogenic response to programmed electrical stimulation.

A gender-independent proarrhythmic action of 17β-estradiol in anaesthetized rabbits

Women are at increased risk of having drug-induced arrhythmias such as torsade de pointes but less susceptible to arrhythmias associated with myocardial ischaemia. We have shown previously that 17beta-estradiol had greater antiarrhythmic activity in female rats than in male rats subject to myocardial ischaemia. The aim of this work was to investigate the effects of acute administration of 17beta-estradiol in both sexes in an established in vivo model of drug-induced arrhythmias. In alpha(1)-adrenoceptor-stimulated, pentobarbital-anaesthetized rabbits, 17beta-estradiol (100, 300 or 1000 ng/kg bolus followed by 10, 30 or 100 ng/kg/min infusion) tended to increase the incidence of torsade de pointes, induced by clofilium, in both sexes: from 50% in controls to 80%, 70% and 80% in females; from 40% in controls to 60%, 70% and 80% in males with increasing doses of 17beta-estradiol (n=10 per group). The total duration of all episodes of torsade de pointes was increased significantly by the highest dose of 17beta-estradiol compared to vehicle in both female and male rabbits: from 9+/-4 s to 93+/-26 s in females; from 26+/-14 s to 96+/-20 s in males. There were no baseline differences between the sexes in heart rate, QTc interval or epicardial monophasic action potential duration. The proarrhythmic effect of acute administration of 17beta-estradiol in the alpha(1)-adrenoceptor-stimulated anaesthetized rabbit model was independent of gender. This indicates that the underlying mechanism differs from that involved in the gender-selective reduction of ischaemia-induced arrhythmias by 17beta-estradiol.

Perspectives in innate and acquired cardioprotection: cardioprotection acquired through exercise

Emerging evidence indicates that exercise training can provide significant protection against myocardial ischemia-reperfusion injury. In this brief review, we provide a synthesis of current literature in the field and summarize the findings to date. Our intent is to identify the unique elements of cardioprotection acquired by exercise, and to illustrate what distinguishes this physiological acquisition of cardioprotection from all other known types of acquired cardioprotection. Finally, we point to future directions for research in this exciting area.

Cardioprotection in females: a role for nitric oxide and altered gene expression

A number of epidemiological and animal studies have suggested a cardioprotective role for estrogen. This review will focus on the cardioprotective role of estrogen in ischemia-reperfusion injury. Estrogen binding to receptors can lead to altered gene expression and estrogen has been shown to induce expression of a number of genes that have been suggested to be important in cardioprotection. Estrogen is reported to increase expression of the plasma membrane glucose transporter GLUT4 and to increase carbohydrate metabolism. Estrogen has also been reported to increase mitochondrial biogenesis and to alter mitochondrial generation of reactive oxygen species. Estrogen results in upregulation of cardiac eNOS and nNOS, which have been shown previously to be important mediators of cardioprotection. Nitric oxide has been shown to result in S-nitrosylation and inhibition of the L-type calcium channel, thereby reducing calcium loading during ischemia. Nitric oxide has also been reported to inhibit complex I and inhibition of complex I has been reported to reduce activation of the mitochondrial permeability transition pore. Nitric oxide has been shown to result in activation of the mitochondrial K(ATP) channel, which has been shown to be involved in cardioprotection. Estrogen can also activate rapid non-genomic pathways that activate cardioprotective-signaling pathways such as the phosphatidylinositol-3-kinase (PI-3 kinase) pathway which has also been shown to initiate protection. Taken together, estrogen by genomic and non-genomic pathways can result in the initiation of a number of signaling pathways that enhance cardioprotection.

Pharmacological postconditioning with the phytoestrogen genistein

Estrogens are known to activate the phosphatidyl-inosityl 3-kinase (PI3K)/Akt pathway, which is central in the cardioprotection afforded by ischemic postconditioning. Therefore, our goal was to investigate whether a phytoestrogen, genistein, could induce a pharmacological postconditioning and to investigate potential mechanisms. We used low doses of genistein in order to avoid tyrosine kinases inhibition. Thus, pentobarbital-anesthetized rabbits underwent a coronary artery occlusion followed by 4 h of reperfusion. Prior to reperfusion, they randomly received an i.v. injection of either saline (Control), 100 or 1000 microg/kg of genistein (Geni(100) and Geni(1000), respectively), and 10 or 100 microg/kg of 17beta-estradiol (17beta(10) and 17beta(100), respectively). Infarct size (IS, % area at risk) was significantly reduced in Gen(100), Gen(1000) and 17beta(100) but not in 17beta(10) (6+/-2, 16+/-5, 12+/-3 and 29+/-7%, respectively) vs. Control (35+/-4%). A significant decrease in the percentage of TUNEL-positive nuclei within infarcted area was observed in Gen(100) and 17beta(100) vs. Controls. The estrogen receptor antagonist fulvestrant (1 mg/kg i.v.) and the PI3K inhibitor wortmaninn (0.6 mg/kg) abolished the cardioprotective effect of genistein. Western blots also demonstrated an increase in Akt posphorylation in Gen(100). In the same group, in vitro mitochondrial swelling studies demonstrated a significant inhibition of calcium-induced opening of mitochondrial transition pore vs. Controls. In conclusion, genistein exerts pharmacological postconditioning with a similar potency as 17beta-estradiol through a pathway involving activation of the estrogen receptor, of PI3K/Akt and mitochondrial preservation. Therefore, genistein should not be only considered as an inhibitor of tyrosine kinase but also as a cardioprotective estrogen.

The pathway-selective estrogen receptor ligand WAY-169916 displays differential activity in ischemia-reperfusion injury models

We previously reported on the development of a pathway-selective estrogen receptor (ER) ligand, WAY-169916, that has ER-dependent antiinflammatory activity and is devoid of classic ER transcriptional activity. In the current study, WAY-169916 and 17beta-estradiol (17beta-E2) were evaluated for protective activity in models of cardiac ischemia-reperfusion injury. In rats subjected to cardiac ischemia-reperfusion injury by occlusion of the left coronary artery, infarct size relative to the area at risk in the left ventricle was significantly attenuated by a single dose of 17beta-E2 (20 microg/kg, SC), and WAY-169916 administered SC (10 mg/kg) or IV (1 mg/kg) during the ischemia phase. In isolated hearts perfused on a Langendorff apparatus and subjected to global ischemia and reperfusion, 17beta-E2 and WAY-169916 both had direct cardioprotective activity when perfused at 1 microM but their effects varied between different end points. Perfusion with 17beta-E2 only improved recovery of left ventricle-developed pressure. Perfusion with WAY-169916 attenuated the elevation in perfusion pressure, diastolic pressure, and release of creatine kinase after ischemia. In contrast to 17alpha-ethinylestradiol, WAY-169916 had no classic estrogen effects on uterine weight or total serum cholesterol in rats treated for 4 days. The data demonstrate that the pathway-selective ER ligand WAY-169916 displays differential activity in vivo on different cardiovascular end points.

Cytochrome P450 enzymes: Central players in cardiovascular health and disease

Cardiovascular disease (CVD) is a human health crisis that remains the leading cause of death worldwide. The cytochrome P450 (CYP) class of enzymes are key metabolizers of both xenobiotics and endobiotics. Many CYP enzyme families have been identified in the heart, endothelium and smooth muscle of blood vessels. Furthermore, mounting evidence points to the role of endogenous CYP metabolites, such as epoxyeicosatrienoic acids (EETs), hydroxyeicosatetraenoic acids (HETEs), prostacyclin (PGI(2)), aldosterone, and sex hormones, in the maintenance of cardiovascular health. Emerging science and the development of genetic screening have provided us with information on the differences in CYP expression among populations and groups of individuals. With this information, a link between CYP expression and activity and CVD, such as hypertension, coronary artery disease (CAD), myocardial infarction, heart failure, stroke, and cardiomyopathy and arrhythmias, has been established. In fact many currently used therapeutic modalities in CVD owe their therapeutic efficacy to their effect on CYP metabolites. Thus, the evidence for the involvement of CYP in CVD is numerous. Concentrating on treatment modalities that target the CYP pathway makes ethical sense for the affected individuals and decreases the socioeconomic burden of this disease. However, more research is needed to allow the integration of this information into a clinical setting.

Effects of pravastatin on ventricular remodeling by activation of myocardial KATP channels in infarcted rats: role of 70-kDa S6 kinase

Reactive cardiomyocyte hypertrophy after myocardial infarction is an important risk factor for arrhythmias. Myocardial ATP-sensitive potassium (K(ATP)) channels have been implicated in attenuating cardiac hypertrophy by inhibition of 70-kDa S6 kinase. We investigated the effect of pravastatin on ventricular hypertrophy during remodeling after myocardial infarction and whether the attenuated hypertrophic effect was via activation of myocardial K(ATP) channels. Twenty-four hours after ligation of the anterior descending artery, male Wistar rats were randomized to either vehicle, nicorandil (an agonist of K(ATP) channels), pravastatin, glibenclamide (an antagonist of K(ATP) channels), or a combination of nicorandil and glibenclamide or pravastatin and glibenclamide for 4 weeks. Infarct size and mortality were similar among the infarcted groups. Cardiomyocyte sizes isolated by enzymatic dissociation after infarction significantly increased at the border zone in vehicle-treated infarcted rats compared with sham-operated rats. Rats in the nicorandil- and pravastatin-treated groups significantly attenuated cardiomyocyte hypertrophy, as compared with the vehicle-treated group. Arrhythmic scores during programmed stimulation mirrored those of cardiomyocyte hypertrophy. Increased 70-kDa S6 kinase mRNA expression in cardiac remodeling was confirmed by reverse transcription-polymerase chain reaction, consistent with the results of immunohistochemistry and Western blot for the phosphorylation of 70-kDa S6 kinase. Nicorandil-induced effects were abolished by administering glibenclamide. Similarly, the beneficial effects of pravastatin were abolished by administering glibenclamide, implicating K(ATP) channels as the relevant target. Activation of K(ATP) channels by pravastatin administration can attenuate ventricular remodeling through a S6 kinase-dependent pathway after infarction.

Testosterone is required for delayed cardioprotection and enhanced heat shock protein 70 expression induced by preconditioning

Ischemic preconditioning fails to confer immediate cardioprotection in the absence of testosterone, indicating that the hormone is required for the process. Here we set out to determine whether testosterone is also necessary for delayed cardioprotection and, if so, how it acts. Male Sprague Dawley rats (7-8 wk) underwent sham operation or gonadectomy without (G) or with testosterone replacement (GT) for 8 wk. Isolated ventricular myocytes were preconditioned either by metabolic inhibition or with U50,488H, a kappa-opioid receptor agonist. In intact rats, U50,488H was administered systemically and 24 h later the hearts were removed. Ventricular myocytes were then subjected to metabolic inhibition and anoxia and isolated hearts to regional ischemia, followed by reperfusion to induce injury. Both types of preconditioning significantly increased the viability and decreased the lactate dehydrogenase release in ventricular myocytes from sham rats. They also activated heat shock transcription factor-1 and increased heat shock protein 70 expression. In contrast, all these effects were absent in myocytes from G rats and were restored by testosterone replacement. Parallel results were found in isolated hearts. In addition, preconditioning improved contractile functions impaired by ischemic insults in sham and rats gonadectomized with testosterone replacement but not G rats. The effects of testosterone replacement in ventricular myocytes were abolished by androgen receptor blockade. In conclusion, preconditioning requires testosterone to increase heat shock protein 70 synthesis, which mediates delayed cardioprotection in the male. These effects of testosterone are mediated by the androgen receptor.

Preconditioning by 17β-estradiol in isolated rat heart depends on PI3-K/PKB pathway, PKC, and ROS

To study the cell signaling events leading to 17β-estradiol (E2)-induced acute cardioprotection, we subjected isolated rat hearts to three 5-min cycles of 10 μM E2 before 30 min of regional ischemia, followed by 2 h of reperfusion. Protection was judged by changes in infarct size in percentage of risk zone volume. To test the importance of phosphoinositide 3-kinase (PI3-K), protein kinase C (PKC), or reactive oxygen species (ROS) in E2-induced protection, we combined wortmannin (1 μM), chelerythrine (2 μM), and 2-mercaptopropionylglycine (300 μM), respectively, with E2 exposure. Changes in phosphorylation of protein kinase B (PKB) and selected PKC isoforms were tested by immunoblotting of total lysates and subcellular fractions, along with assessment of PKC translocation from soluble to membrane fraction of heart tissue homogenates. Intracellular ROS levels induced by E2 preconditioning were investigated. E2 preconditioning led to significant reduction in infarct size from 31.8 ± 5.3 to 20.2 ± 2.6% in male hearts and from 42.7 ± 4.7 to 17.1 ± 3.4% in female hearts ( P < 0.05). Protection was abolished by wortmannin (30.0 ± 3.2%), chelerythrine (45.1 ± 4.4%), and 2-mercaptopropionylglycine (36.8 ± 4.7%). E2 preconditioning induced phosphorylation of PKB, PKCα, and PKCε and membrane translocation of PKCε and PKCδ. Intracellular ROS levels were found elevated after transient treatment with hormone. Therefore, our data demonstrate the ability of E2 to induce preconditioning-like cardioprotection via cell signaling events shared by classic ischemic preconditioning.

Greater antiarrhythmic activity of acute 17beta-estradiol in female than male anaesthetized rats: correlation with Ca2+ channel blockade

BACKGROUND AND PURPOSE

Female sex hormones may protect pre-menopausal women from sudden cardiac death. We therefore investigated the effects of the main female sex hormone, 17beta-estradiol, on ischaemia-induced cardiac arrhythmias and on the L-type Ca2+ current (ICaL).

EXPERIMENTAL APPROACH

In vivo experiments were performed in pentobarbital-anaesthetized rats subjected to acute coronary artery occlusion. ICaL was measured by the whole-cell patch-clamp technique, in rat isolated ventricular myocytes.

KEY RESULTS

Acute intravenous administration of 17beta-estradiol as a bolus dose followed by a continuous infusion, commencing 10 min before coronary artery occlusion, had dose-dependent antiarrhythmic activity. In female rats 300 ng kg(-1) + 30 ng kg(-1) min(-1) 17beta-estradiol significantly reduced the number of ventricular premature beats (VPBs) and the incidence of ventricular fibrillation (VF). A ten fold higher dose of 17beta-estradiol was required to cause similar effects in male rats. In vitro 17beta-estradiol reduced peak ICaL in a concentration-dependent manner. The EC50 was ten-fold higher in male myocytes (0.66 microM) than in females (0.06 microM).

CONCLUSIONS AND IMPLICATIONS

These results indicate that 17beta-estradiol has marked dose-dependent antiarrhythmic activity that is greater in female rats than in males. A similar differential potency in blocking ICaL in myocytes from female and male rats can account for this effect. This provides an explanation for the antiarrhythmic activity of 17beta-estradiol and gender-selective protection against sudden cardiac death.

EFFECT OF PERINATAL HYPOXIA ON CARDIAC TOLERANCE TO ACUTE ISCHAEMIA IN ADULT MALE AND FEMALE RATS

1. The number of adult patients undergoing surgery for congenital cyanotic defects in childhood has increased significantly. Therefore, the aim of the present study was to examine the effect of perinatal hypoxia on the tolerance of the adult myocardium to acute ischaemia-reperfusion injury. 2. Pregnant Wistar rats were exposed to intermittent hypobaric hypoxia 7 days before delivery; pups were born under normoxic conditions and exposed to hypoxia again for 10 postnatal days. After the last hypoxic exposure, all animals were kept for an additional 3 months under normoxic conditions. All experiments were performed on 90-day-old rats. 3. Ventricular arrhythmias were assessed on isolated perfused hearts during 30 min occlusion of the left anterior descending coronary artery. Infarct size was measured on isolated hearts (40 min regional ischaemia and 120 min reperfusion) and on open-chest animals (20 min regional ischaemia and 3 h reperfusion). 4. Perinatal exposure to hypoxia significantly increased cardiac tolerance to ischaemic injury in adult females, as evidenced by the lower incidence and severity of ischaemic ventricular arrhythmias, compared with the normoxic group. The effect of perinatal hypoxia on ischaemic arrhythmias in males was quite the opposite. Myocardial infarct size measured in open-chest animals only was significantly smaller in normoxic females compared with normoxic males. Perinatal exposure to hypoxia had no effect on infarct size in either setting or sex. 5. The results of the present study support the hypothesis that perinatal hypoxia is a primary programming stimulus in the heart that may lead to sex-dependent changes in cardiac tolerance to acute ischaemia in later adult life. This would have important implications for patients who have experienced prolonged hypoxaemia in early life.

Age- and gender-related differences in ischemia/reperfusion injury and cardioprotection: effects of diazoxide

BACKGROUND

Recent studies have demonstrated that aging is associated with reduced tolerance to ischemia and that the aged (not senescent) female heart has greater susceptibility to ischemia as compared with the aged male heart. Previously, we have shown that ischemia can be modulated with cardioplegia in the male heart; however, efficacy in the female heart was unknown.

METHODS

In this study, male and female mature (15 to 20 weeks) aged (>32 months) rabbit hearts (n = 134) were subjected to Langendorff perfusion. Control hearts were perfused for 180 minutes. Global ischemia hearts received 30 minutes of equilibrium, 30 minutes of global ischemia, and 120 minutes of reperfusion. Cardioplegia +/- diazoxide was infused separately, 5 minutes before global ischemia.

RESULTS

Global ischemia significantly decreased postischemic functional recovery and significantly increased infarct size in the mature and aged male and female heart (p < 0.05 versus control). The effects of global ischemia were significantly exacerbated (p < 0.05) in the aged heart as compared with the mature heart. Cardioplegia +/- diazoxide significantly increased postischemic functional recovery and significantly decreased infarct size in mature male and female hearts, but these effects were significantly decreased in the aged heart (p < 0.05) and in the aged female as compared with the aged male heart.

CONCLUSIONS

Postischemic functional recovery and infarct size are affected by age but not by gender. The cardioprotection afforded by cardioplegia is affected by age and gender with a strong age-by-gender interaction for end-diastolic pressure and infarct size. Our results indicate that currently optimized cardioplegia protocols effective in the male heart are not as efficacious in the aged female heart.