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

Determinants of Inadequate Cardioprotection in Adult Patients with Left Ventricular Dysfunction

BACKGROUND

 Perioperative cardioprotection is essential for achieving satisfactory clinical outcomes in heart failure patients. It is important to understand the factors affecting perioperative cardioprotection.

METHODS

 The institutional database was searched for patients with reduced ejection fraction (EF, < 40%) who underwent surgery with cardioplegia-induced arrest. Patients were divided into del Nido cardioplegia (DN) and cold blood cardioplegia (CB) groups. The relationships between age, preoperative blood parameters, creatinine, cross-clamp time (CCT), extracorporeal circulation time (ECT), and postoperative troponin values at 12 hours or deterioration of EF (≥5%) were evaluated. Baseline characteristics, operative parameters, and outcomes were analyzed.

RESULTS

 There were 508 patients with reduced EF (331 DN and 177 CB). In the entire cohort, anemic patients had greater troponin values (p = 0.004) as well as in the DN group (p = 0.002). However, this was not detected in the CB group (flat regression line; p = 0.674). Patients with high leukocyte values had greater troponin release (entire cohort: p < 0.001; DN group: p < 0.001; CB group: steep regression line with p = 0.042). Longer CCT and ECT were associated with greater troponin release (entire cohort; both groups) and greater risk of fall in EF. In a direct comparison, fewer patients had significant deterioration of EF in the DN group than CB group (3.9 vs. 11.9%; p < 0.001).

CONCLUSION

 The use of CB cardioplegia may be beneficial in anemic patients, whereas the use of DN cardioplegia may be beneficial for expected long CCT and high leukocytosis.

Mitochondrial transplantation preserves myocardial function and viability in pediatric and neonatal pig hearts donated after circulatory death

OBJECTIVE

Mitochondrial transplantation has been shown to preserve myocardial function and viability in adult porcine hearts donated after circulatory death (DCD) . Herein, we investigate the efficacy of mitochondrial transplantation for the preservation of myocardial function and viability in neonatal and pediatric porcine DCD heart donation.

METHODS

Circulatory death was induced in neonatal and pediatric Yorkshire pigs by cessation of mechanical ventilation. Hearts underwent 20 or 36 minutes of warm ischemia time (WIT), 10 minutes of cold cardioplegic arrest, and then were harvested for ex situ heart perfusion (ESHP). Following 15 minutes of ESHP, hearts received either vehicle (VEH) or vehicle containing isolated autologous mitochondria (MITO). A sham nonischemic group (SHAM) did not undergo WIT, mimicking donation after brain death heart procurement. Hearts underwent 2 hours each of unloaded and loaded ESHP perfusion.

RESULTS

Following 4 hours of ESHP perfusion, left ventricle developed pressure, dP/dt max, and fractional shortening were significantly decreased (P < .001) in DCD hearts receiving VEH compared with SHAM hearts. In contrast, DCD hearts receiving MITO exhibited significantly preserved left ventricle developed pressure, dP/dt max, and fractional shortening (P < .001 each vs VEH, not significant vs SHAM). Infarct size was significantly decreased in DCD hearts receiving MITO as compared with VEH (P < .001). Pediatric DCD hearts subjected to extended WIT demonstrated significantly preserved fractional shortening and significantly decreased infarct size with MITO (P < .01 each vs VEH).

CONCLUSIONS

Mitochondrial transplantation in neonatal and pediatric pig DCD heart donation significantly enhances the preservation of myocardial function and viability and mitigates against damage secondary to extended WIT.

Differential Effects of Reperfusion on Cardiac Mitochondrial Subpopulations in a Preclinical Porcine Model of Acute Myocardial Infarction

Acute myocardial infarction (AMI) leads to localized cardiac ischemia and can be fatal if untreated. Despite being treatable, the threat of ischemia-reperfusion (IR) injury remains high. Mitochondria are central to both propagation and mitigation of IR injury, and cardiac mitochondria are categorized into two major subtypes-subsarcolemmal and interfibrillar mitochondria (SSM and IFM, respectively). We hypothesized that, in our pre-clinical porcine model of AMI, SSM and IFM are differentially affected by reperfusion. AMI was induced in female pigs by balloon occlusion of the left anterior descending artery for 45 min, followed by 4 h of reperfusion. At the end of reperfusion, animals were euthanized. Cardiac SSM and IFM from the affected ischemic area and a nearby non-ischemic area were isolated to compare mitochondrial function using substrates targeting mitochondrial electron transport chain complexes I and II. Despite detecting overall significant differences in mitochondrial function including yield, mitochondrial S3 and S4 respirations, and calcium retention, consistent individual functional differences in the two mitochondrial subpopulations were not observed, both between the two mitochondrial subtypes, as well as between the ischemic and non-ischemic tissue. Nonetheless, this study describes the mitochondrial subtype response within the initial few hours of reperfusion in a clinically relevant model of AMI, which provides valuable information needed to develop novel mitochondrially targeted therapies for AMI.

Clocks, Rhythms, Sex, and Hearts: How Disrupted Circadian Rhythms, Time-of-Day, and Sex Influence Cardiovascular Health

Cardiovascular diseases are the top cause of mortality in the United States, and ischemic heart disease accounts for 16% of all deaths around the world. Modifiable risk factors such as diet and exercise have often been primary targets in addressing these conditions. However, mounting evidence suggests that environmental factors that disrupt physiological rhythms might contribute to the development of these diseases, as well as contribute to increasing other risk factors that are typically associated with cardiovascular disease. Exposure to light at night, transmeridian travel, and social jetlag disrupt endogenous circadian rhythms, which, in turn, alter carefully orchestrated bodily functioning, and elevate the risk of disease and injury. Research into how disrupted circadian rhythms affect physiology and behavior has begun to reveal the intricacies of how seemingly innocuous environmental and social factors have dramatic consequences on mammalian physiology and behavior. Despite the new focus on the importance of circadian rhythms, and how disrupted circadian rhythms contribute to cardiovascular diseases, many questions in this field remain unanswered. Further, neither time-of-day nor sex as a biological variable have been consistently and thoroughly taken into account in previous studies of circadian rhythm disruption and cardiovascular disease. In this review, we will first discuss biological rhythms and the master temporal regulator that controls these rhythms, focusing on the cardiovascular system, its rhythms, and the pathology associated with its disruption, while emphasizing the importance of the time-of-day as a variable that directly affects outcomes in controlled studies, and how temporal data will inform clinical practice and influence personalized medicine. Finally, we will discuss evidence supporting the existence of sex differences in cardiovascular function and outcomes following an injury, and highlight the need for consistent inclusion of both sexes in studies that aim to understand cardiovascular function and improve cardiovascular health.

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.

Phosphoproteomic analysis identifies phospho-Threonine-17 site of phospholamban important in low molecular weight isoform of fibroblast growth factor 2-induced protection against post-ischemic cardiac dysfunction

RATIONALE

Among its many biological roles, fibroblast growth factor 2 (FGF2) protects the heart from dysfunction and damage associated with an ischemic attack. Our laboratory demonstrated that its protection against myocardial dysfunction occurs by the low molecular weight (LMW) isoform of FGF2, while the high molecular weight (HMW) isoforms are associated with a worsening in post-ischemic recovery of cardiac function. LMW FGF2-mediated cardioprotection is facilitated by activation of multiple kinases, including PKCalpha, PKCepsilon, and ERK, and inhibition of p38 and JNK.

OBJECTIVE

Yet, the substrates of those kinases associated with LMW FGF2-induced cardioprotection against myocardial dysfunction remain to be elucidated.

METHODS AND RESULTS

To identify substrates in LMW FGF2 improvement of post-ischemic cardiac function, mouse hearts expressing only LMW FGF2 were subjected to ischemia-reperfusion (I/R) injury and analyzed by a mass spectrometry (MS)-based quantitative phosphoproteomic strategy. MS analysis identified 50 phosphorylation sites from 7 sarcoendoplasmic reticulum (SR) proteins that were significantly altered in I/R-treated hearts only expressing LMW FGF2 compared to those hearts lacking FGF2. One of those phosphorylated SR proteins identified was phospholamban (PLB), which exhibited rapid, increased phosphorylation at Threonine-17 (Thr17) after I/R in hearts expressing only LMW FGF2; this was further validated using Selected Reaction Monitoring-based MS workflow. To demonstrate a mechanistic role of phospho-Thr17 PLB in LMW FGF2-mediated cardioprotection, hearts only expressing LMW FGF2 and those expressing only LMW FGF2 with a mutant PLB lacking phosphorylatable Thr17 (Thr17Ala PLB) were subjected to I/R. Hearts only expressing LMW FGF2 showed significantly improved recovery of cardiac function following I/R (p < 0.05), and this functional improvement was significantly abrogated in hearts expressing LMW FGF2 and Thr17Ala PLB (p < 0.05).

CONCLUSION

The findings indicate that LMW FGF2 modulates intracellular calcium handling/cycling via regulatory changes in SR proteins essential for recovery from I/R injury, and thereby protects the heart from post-ischemic cardiac dysfunction.

E3-ubiquitin ligase TRIM6 aggravates myocardial ischemia/reperfusion injury via promoting STAT1-dependent cardiomyocyte apoptosis

Cardiomyocyte apoptosis is a major cause of myocardial ischemia/reperfusion (MI/R) injury, in which the activation of the signal transducer and activator of transcription 1 (STAT1) plays an important role. The E3-ubiquitin ligase TRIM6 has been implicated in regulating STAT1 activity, however, whether it is associated with MI/R injury and the underlying mechanism are not determined. In this study, by investigating a mouse MI/R injury model, we show that TRIM6 expression is induced in mouse heart following MI/R injury. Additionally, TRIM6 depletion reduces and its overexpression increases myocardial infarct size, serum creatine phosphokinase (CPK) level and cardiomyocyte apoptosis in mice subjected to MI/R injury, indicating that TRIM6 functions to aggravate MI/R injury. Mechanistically, TRIM6 promotes IKKε-dependent STAT1 activation, and the inhibition of IKKε or STAT1 with the specific inhibitor, CAY10576 or fludarabine, abolishes TRIM6 effects on cardiomyocyte apoptosis and MI/R injury. Similarly, TRIM6 mutant lacking the ability to ubiquitinate IKKε and induce IKKε/STAT1 activation also fails to promote cardiomyocyte apoptosis and MI/R injury. Thus, these results suggest that TRIM6 aggravates MI/R injury through promoting IKKε/STAT1 activation-dependent cardiomyocyte apoptosis, and that TRIM6 might represent a novel therapeutic target for alleviating MI/R injury.

Mitochondrial transplantation for myocardial protection in ex-situ‒perfused hearts donated after circulatory death

BACKGROUND

Donation after circulatory death (DCD) offers an additional source of cardiac allografts, potentially allowing expansion of the donor pool, but is limited owing to the effects of ischemia. In this study, we investigated the efficacy of mitochondrial transplantation to enhance myocardial function of DCD hearts.

METHODS

Circulatory death was induced in Yorkshire pigs (40-50 kg, n = 29) by a cessation of mechanical ventilation. After 20 minutes of warm ischemia, cardioplegia was administered. The hearts were then reperfused on an ex-situ blood perfusion system. After 15 minutes of reperfusion, hearts received either vehicle alone (vehicle [VEH], 10 ml; n = 8) or vehicle containing autologous mitochondria (vehicle with mitochondria as a single injection [MT], 5 × 10⁹ in 10 ml, n = 8). Another group of hearts (serial injection of mitochondria [MT_S]; n = 6) received a second injection of mitochondria (5 × 10⁹ in 10 ml) after 2 hours of ex-situ heart perfusion and reperfused for an additional 2 hours. A Sham group (sham hearts; n = 6) did not undergo any warm ischemia.

RESULTS

At the end of 4 hours of reperfusion, MT and MT_S groups showed a significantly increased left ventricle/ventricular peak developed pressure (p = 0.002), maximal left ventricle/ventricular pressure rise (p < 0.001), fractional shortening (p < 0.001), and myocardial oxygen consumption (p = 0.004) compared with VEH. Infarct size was significantly decreased in MT and MT_S groups compared with VEH (p < 0.001). No differences were found in arterial lactate levels among or within groups throughout reperfusion.

CONCLUSIONS

Mitochondrial transplantation significantly preserves myocardial function and oxygen consumption in DCD hearts, thus providing a possible option for expanding the heart donor pool.

Expression of mitochondrial membrane-linked SAB determines severity of sex-dependent acute liver injury

SH3 domain-binding protein that preferentially associates with Btk (SAB) is an outer-membrane docking protein for JNK-mediated impairment of mitochondrial function. Deletion of Sab in hepatocytes inhibits sustained JNK activation and cell death. The current study demonstrates that an increase in SAB expression enhanced the severity of acetaminophen-induced (APAP-induced) liver injury. Female mice were resistant to liver injury and exhibited markedly decreased hepatic SAB protein expression compared with male mice. The mechanism of SAB repression involved a pathway from ERα to p53 expression that induced miR34a-5p. miR34a-5p targeted the Sab mRNA coding region, thereby repressing SAB expression. Fulvestrant or p53 knockdown decreased miR34a-5p and increased SAB expression in female mice, leading to increased injury from APAP and TNF/galactosamine. In contrast, an ERα agonist increased p53 and miR34a-5p, which decreased SAB expression and hepatotoxicity in male mice. Hepatocyte-specific deletion of miR34a also increased the severity of liver injury in female mice, which was prevented by GalNAc-ASO knockdown of Sab. Similar to mice, premenopausal women expressed elevated levels of hepatic p53 and low levels of SAB, whereas age-matched men expressed low levels of p53 and high levels of SAB, but there was no difference in SAB expression between the sexes in the postmenopausal stage. In conclusion, SAB expression levels determined the severity of JNK-dependent liver injury. Female mice expressed low levels of hepatic SAB protein because of the ERα/p53/miR34a pathway, which repressed SAB expression and accounted for the resistance to liver injury seen in these females.

del Nido cardioplegia in adult cardiac surgery: beyond single-valve surgery

OBJECTIVES

In recent years, the use of del Nido (DN) cardioplegia has been reported in single-valve surgery or isolated coronary artery bypass surgery with acceptable outcomes. The reports of its use in more complex adult cardiac procedures, however, have been scarce.

METHODS

We enrolled a total of 149 adult patients who underwent heart valve surgery with the use of DN cardioplegia between May 2014 and December 2016. For a benchmark comparison, 892 patients who underwent cardiac valve surgery with blood cardioplegia during the same period served as controls. To reduce selection bias, propensity score matching was used; the inverse probability of treatment weighting method was performed for further validations.

RESULTS

Overall, 57.7% of patients in the DN group underwent multiple or complex cardiac procedures. Early mortality rates were 0.7% and 2.4% in the DN and blood groups, respectively (P = 0.31). Propensity score matching yielded 111 pairs of patients who were well balanced for all 23 measured baseline covariates. In the matched cohort, the postoperative peak troponin I levels (P = 0.004) and the aortic clamping times (P < 0.001) were significantly lower and shorter compared with those in the blood group. There were no significant differences in early mortality rates (1.9% vs 0%, P > 0.99), low cardiac output (P = 0.57) and neurological events (P = 0.21). The quantities of postoperative transfusions (P = 0.008) and fluid supplements (P < 0.001) were significantly lower in the matched DN group compared with the blood group.

CONCLUSIONS

The use of DN in adult valve surgery including complex procedures may confer acceptable outcomes comparable to or even superior to those obtained with the use of blood cardioplegia.

Effects of Cardiovascular Risk Factors on Cardiac STAT3

Nuclear, mitochondrial and cytoplasmic signal transducer and activator of transcription 3 (STAT3) regulates many cellular processes, e.g., the transcription or opening of mitochondrial permeability transition pore, and its activity depends on the phosphorylation of Tyr705 and/or Ser727 sites. In the heterogeneous network of cardiac cells, STAT3 promotes cardiac muscle differentiation, vascular element formation and extracellular matrix homeostasis. Overwhelming evidence suggests that STAT3 is beneficial for the heart, plays a role in the prevention of age-related and postpartum heart failure, protects the heart against cardiotoxic doxorubicin or ischaemia/reperfusion injury, and is involved in many cardioprotective strategies (e.g., ischaemic preconditioning, perconditioning, postconditioning, remote or pharmacological conditioning). Ischaemic heart disease is still the leading cause of death worldwide, and many cardiovascular risk factors contribute to the development of the disease. This review focuses on the effects of various cardiovascular risk factors (diabetes, aging, obesity, smoking, alcohol, depression, gender, comedications) on cardiac STAT3 under non-ischaemic baseline conditions, and in settings of ischaemia/reperfusion injury with or without cardioprotective strategies.

Reprint of: Proteomics in cardiovascular diseases: Unveiling sex and gender differences in the era of precision medicine

Cardiovascular diseases (CVDs) represent the most important cause of mortality in women and in men. Contrary to the long-standing notion that the effects of the major risk factors on CVD outcomes are the same in both sexes, recent evidence recognizes new, potentially independent, sex/gender-related risk factors for CVDs, and sex/gender-differences in the clinical presentation of CVDs have been demonstrated. Furthermore, some therapeutic options may not be equally effective and safe in men and women. In this context, proteomics offers an extremely useful and versatile analytical platform for biomedical researches that expand from the screening of early diagnostic and prognostic biomarkers to the investigation of the molecular mechanisms underlying CDVs. In this review, we summarized the current applications of proteomics in the cardiovascular field, with emphasis on sex and gender-related differences in CVDs.

SIGNIFICANCE

Increasing evidence supports the profound effect of sex and gender on cardiovascular physio-pathology and the response to drugs. A clear understanding of the mechanisms underlying sexual dimorphisms in CVDs would not only improve our knowledge of the etiology of these diseases, but could also inform health policy makers and guideline committees in tailoring specific interventions for the prevention, treatment and management of CVDs in both men and women.

Mitochondrial transplantation: applications for pediatric patients with congenital heart disease

Mitochondrial transplantation refers to transplantation of respiratory competent mitochondria from healthy tissue into tissues injured by ischemia and reperfusion. This technique has been utilized for recovery of myocardial dysfunction in pediatric patients. The preclinical experience and initial patient experience with this technique are reviewed in this article. Initial experience is with pediatric patients undergoing extracorporeal membrane oxygenation support following myocardial ischemia and reperfusion. The initial pediatric experience suggests low side effect profile with favorable efficacy in a small group of patients.

The AMPK Activator Aicar Ameliorates Age-Dependent Myocardial Injury in Murine Hemorrhagic Shock

The development of myocardial dysfunction in patients with hemorrhagic shock is significantly impacted by the patient age. AMP-activated protein kinase (AMPK) is a pivotal orchestrator of energy homeostasis, which coordinates metabolic recovery after cellular stress. We investigated whether AMPK-regulated pathways are age-dependent in hemorrhage-induced myocardial injury and whether AMPK activation by 5-amino-4-imidazolecarboxamide riboside (AICAR) affords cardioprotective effects. Anesthetized C57/BL6 young (3-5 months old) and mature (9-12 months old) male mice were subjected to hemorrhagic shock by blood withdrawing followed by resuscitation with shed blood and Lactated Ringer's solution. Mice were sacrificed at 3 h after resuscitation, and plasma and hearts were harvested for biochemical assays. Vehicle-treated mature mice exhibited higher myocardial injury and higher levels of plasma biomarkers of cardiovascular injury (endocan and follistatin) when compared with young mice. Cardiac cell mitochondrial structure was also markedly impaired in vehicle-treated mature mice when compared with young mice. At molecular analysis, an increase of the phosphorylated catalytic subunit pAMPKα was associated with nuclear translocation of the peroxisome proliferator-activated receptor γ coactivator-α in young, but not mature mice. No changes in autophagy were observed as evaluated by the conversion of the light-chain (LC)3B-I protein to LC3B-II form. Treatment with AICAR ameliorated myocardial damage in both age groups. However, AICAR therapeutic effects were less effective in mature mice than young mice and involved distinct mechanisms of action. Thus, our data demonstrate that during hemorrhagic shock AMPK-dependent metabolic mechanisms are important for mitigating myocardial injury. However, these mechanisms are less competent with age.

Buckberg's blood cardioplegia for protection of adult and senile myocardium in a rat in vitro model of acute myocardial infarction

BACKGROUND

In patients undergoing surgical myocardial revascularization for acute myocardial infarction, excellent myocardial protection can be achieved by blood cardioplegia. We investigated the influence of age on cardiac function, metabolism, and infarct size using Buckberg's blood cardioplegia (BCP).

METHODS

The hearts of male Wistar rats ("adult", age 3 months, n = 8; "senile", age 24 months, n = 8) were excised and mounted on a blood-perfused isolated heart apparatus. An acute myocardial infarction was induced by coronary artery ligation for 30 min before aortic clamping and infusion of Buckberg's BCP. Throughout the experiment, functional parameters were recorded: coronary blood flow (normalized by heart weight), left ventricular peak developed pressure (LVpdP), and positive and negative derived left ventricular pressure over time (dLVPdt_max and dLVPdt_min). Oxygen consumption (MVO₂) and lactate production of the hearts were calculated. The infarct size after 90 min of reperfusion (in % of the area at risk) was measured with triphenyl tetrazolium chloride staining of the myocardium.

RESULTS

The baseline coronary flow normalized by heart weight was significantly lower in the senile hearts (1.6 ± 0.4 ml/(min ∗ g)) compared with the adult hearts (2.0 ± 0.3 ml/(min ∗ g); p = 0.04). After 90 min of aortic clamping, hemodynamic function of senile hearts recovered better than that of adult hearts: LVpdP (adult 57% of baseline [BL]; senile 88% BL; p = 0.044) and dLVPdt_max (adult 74% BL, senile 102% BL; p = 0.12). In contrast, myocardial infarct size was similar between the adult (26%) and senile (21%; p = 0.45) hearts, and coronary flow recovered to a similar extent (55% BL and 58% BL, respectively). During reperfusion, MVO₂ (80% BL and 81% BL) and lactate production (1.2 and 1.3 μmol/min) were similar in the two groups.

CONCLUSION

After acute myocardial infarction in a rat model, hearts recovered function after reperfusion with Buckberg's BCP solution. Hearts from aged animals recovered better than those from younger animals.

Alpha Lipoic Acid: A Therapeutic Strategy that Tend to Limit the Action of Free Radicals in Transplantation

Organ replacement is an option to mitigate irreversible organ damage. This procedure has achieved a considerable degree of acceptance. However, several factors significantly limit its effectiveness. Among them, the initial inflammatory graft reaction due to ischemia-reperfusion injury (IRI) has a fundamental influence on the short and long term organ function. The reactive oxygen species (ROS) produced during the IRI actively participates in these adverse events. Therapeutic strategies that tend to limit the action of free radicals could result in beneficial effects in transplantation outcome. Accordingly, the anti-oxidant α-lipoic acid (ALA) have been proved to be protective in several animal experimental models and humans. In a clinical trial, ALA was found to decrease hepatic IRI after hepatic occlusion and resection. Furthermore, the treatment of cadaveric donor and recipient with ALA had a protective effect in the short-term outcome in simultaneous kidney and pancreas transplanted patients. These studies support ALA as a drug to mitigate the damage caused by IRI and reinforce the knowledge about the deleterious consequences of ROS on graft injury in transplantation. The goal of this review is to overview the current knowledge about ROS in transplantation and the use of ALA to mitigate it.

Proteomics in cardiovascular diseases: Unveiling sex and gender differences in the era of precision medicine

Cardiovascular diseases (CVDs) represent the most important cause of mortality in women and in men. Contrary to the long-standing notion that the effects of the major risk factors on CVD outcomes are the same in both sexes, recent evidence recognizes new, potentially independent, sex/gender-related risk factors for CVDs, and sex/gender-differences in the clinical presentation of CVDs have been demonstrated. Furthermore, some therapeutic options may not be equally effective and safe in men and women. In this context, proteomics offers an extremely useful and versatile analytical platform for biomedical researches that expand from the screening of early diagnostic and prognostic biomarkers to the investigation of the molecular mechanisms underlying CDVs. In this review, we summarized the current applications of proteomics in the cardiovascular field, with emphasis on sex and gender-related differences in CVDs.

SIGNIFICANCE

Increasing evidence supports the profound effect of sex and gender on cardiovascular physio-pathology and the response to drugs. A clear understanding of the mechanisms underlying sexual dimorphisms in CVDs would not only improve our knowledge of the etiology of these diseases, but could also inform health policy makers and guideline committees in tailoring specific interventions for the prevention, treatment and management of CVDs in both men and women.

Novel cardioprotection strategies for the aged heart: evidence from pre-clinical studies

The incidence of cardiovascular disease is rising as the population ages. This has led to an increase in the need to perform cardiac surgery in older patients. However, aged hearts are particularly susceptible to reperfusion injury following periods of myocardial ischaemia that occur during cardiac surgery. Indeed, older adults experience myocardial dysfunction and reduced survival post-surgery compared to younger people and certain groups, including older women and frail older adults, are at particular risk. This highlights the need to design cardioprotective strategies specifically for the ageing heart. Cardioprotection during surgery is often accomplished by perfusing the heart with chemical arresting agents, known as cardioplegic solutions. New protective strategies have been developed and tested in animal models, where cardioplegic solutions have been modified by changing their temperature, chemical components and/or the frequency of delivery. In addition, drugs designed to activate cardioprotective mechanisms or to inhibit mechanisms involved in injury have been added to improve the efficacy of these solutions. However, most experimental studies have developed and optimized cardioplegic solutions in hearts from younger male animals. This review discusses pre-clinical models used to optimize cardioplegic solutions, with an emphasis on the few studies that have used hearts from older animals. Pharmacologic agents that have been shown to enhance the benefits of cardioplegia in younger hearts and could, in theory, protect vulnerable older hearts are also considered. We emphasize the need to conduct studies in frail older animals of both sexes to facilitate translation of laboratory-based observations to the clinic.

Attenuated recovery of contractile function in aging hearts following global ischemia/reperfusion: Role of extracellular HSP27 and TLR4

BACKGROUND

While cardiac functional recovery is attenuated in the elderly following cardiac surgery with obligatory global myocardial ischemia/reperfusion (I/R), the underlying mechanism remains incompletely understood. We observed previously that human and mouse myocardium releases heat shock protein (HSP) 27 during global I/R. Extracellular HSP27 induces myocardial inflammatory response and plays a role in post-ischemic cardiac dysfunction in adult mouse hearts.

OBJECTIVE

This study was to determine the role of extracellular HSP27 and Toll-like receptor 4 (TLR4) in the attenuated functional recovery in aging mouse hearts following global I/R.

METHODS AND RESULTS

Hearts isolated from aging (18-24 months) and adult (4-6 months) mice were subjected to ex vivo global I/R. Augmented release of HSP27 in aging hearts is associated with greater production of cytokines (TNF-α and IL-1β) and worse functional recovery. Anti-HSP27 suppressed the inflammatory response and markedly improved functional recovery in aging hearts. Perfusion of recombinant HSP27 to aging hearts resulted in greater cytokine production and more severe contractile depression in comparison to adult hearts. TLR4 deficiency abolished cytokine production and functional injury in aging hearts exposed to recombinant HSP27. Interestingly, aging hearts had higher TLR4 protein levels and displayed enhanced TLR4-mediated NF-κB activation following HSP27 stimulation or I/R.

CONCLUSION

Extracellular HSP27 and TLR4 jointly enhance the inflammatory response and hamper functional recovery following I/R in aging hearts. The enhanced inflammatory response to global I/R and attenuated post-ischemic functional recovery in aging hearts is due, at least in part, to augmented myocardial release of HSP27 and elevated myocardial TLR4 levels.

Cardiovascular KATP channels and advanced aging

With advanced aging, there is a decline in innate cardiovascular function. This decline is not general in nature. Instead, specific changes occur that impact the basic cardiovascular function, which include alterations in biochemical pathways and ion channel function. This review focuses on a particular ion channel that couple the latter two processes, namely the K_ATP channel, which opening is promoted by alterations in intracellular energy metabolism. We show that the intrinsic properties of the K_ATP channel changes with advanced aging and argue that the channel can be further modulated by biochemical changes. The importance is widespread, given the ubiquitous nature of the K_ATP channel in the cardiovascular system where it can regulate processes as diverse as cardiac function, blood flow and protection mechanisms against superimposed stress, such as cardiac ischemia. We highlight questions that remain to be answered before the K_ATP channel can be considered as a viable target for therapeutic intervention.

Mitochondria in the middle: exercise preconditioning protection of striated muscle

Cellular and physiological adaptations to an atmosphere which became enriched in molecular oxygen spurred the development of a layered system of stress protection, including antioxidant and stress response proteins. At physiological levels reactive oxygen and nitrogen species regulate cell signalling as well as intracellular and intercellular communication. Exercise and physical activity confer a variety of stressors on skeletal muscle and the cardiovascular system: mechanical, metabolic, oxidative. Transient increases of stressors during acute bouts of exercise or exercise training stimulate enhancement of cellular stress protection against future insults of oxidative, metabolic and mechanical stressors that could induce injury or disease. This phenomenon has been termed both hormesis and exercise preconditioning (EPC). EPC stimulates transcription factors such as Nrf-1 and heat shock factor-1 and up-regulates gene expression of a cadre of cytosolic (e.g. glutathione peroxidase and heat shock proteins) and mitochondrial adaptive or stress proteins (e.g. manganese superoxide dismutase, mitochondrial KATP channels and peroxisome proliferator activated receptor γ coactivator-1 (PGC-1)). Stress response and antioxidant enzyme inducibility with exercise lead to protection against striated muscle damage, oxidative stress and injury. EPC may indeed provide significant clinical protection against ischaemia-reperfusion injury, Type II diabetes and ageing. New molecular mechanisms of protection, such as δ-opioid receptor regulation and mitophagy, reinforce the notion that mitochondrial adaptations (e.g. heat shock proteins, antioxidant enzymes and sirtuin-1/PGC-1 signalling) are central to the protective effects of exercise preconditioning.

Mitochondrial transplantation for therapeutic use

Mitochondria play a key role in the homeostasis of the vast majority of the body's cells. In the myocardium where mitochondria constitute 30 % of the total myocardial cell volume, temporary attenuation or obstruction of blood flow and as a result oxygen delivery to myocardial cells (ischemia) severely alters mitochondrial structure and function. These alterations in mitochondrial structure and function occur during ischemia and continue after blood flow and oxygen delivery to the myocardium is restored, and significantly decrease myocardial contractile function and myocardial cell survival. We hypothesized that the augmentation or replacement of mitochondria damaged by ischemia would provide a mechanism to enhance cellular function and cellular rescue following the restoration of blood flow. To test this hypothesis we have used a model of myocardial ischemia and reperfusion. Our studies demonstrate that the transplantation of autologous mitochondria, isolated from the patient's own body, and then directly injected into the myocardial during early reperfusion augment the function of native mitochondria damaged during ischemia and enhances myocardial post-ischemic functional recovery and cellular viability. The transplanted mitochondria act both extracellularly and intracellularly. Extracellularly, the transplanted mitochondria enhance high energy synthesis and cellular adenosine triphosphate stores and alter the myocardial proteome. Once internalized the transplanted mitochondria rescue cellular function and replace damaged mitochondrial DNA. There is no immune or auto-immune reaction and there is no pro-arrhythmia as a result of the transplanted mitochondria. Our studies and those of others demonstrate that mitochondrial transplantation can be effective in a number of cell types and diseases. These include cardiac and skeletal muscle, pulmonary and hepatic tissue and cells and in neuronal tissue. In this review we discuss the mechanisms leading to mitochondrial dysfunction and the effects on cellular function. We provide a methodology for the isolation of mitochondria to allow for clinical relevance and we discuss the methods we and others have used for the uptake and internalization of mitochondria. We foresee that mitochondrial transplantation will be a valued treatment in the armamentarium of all clinicians and surgeons for the treatment of varied ischemic disorders, mitochondrial diseases and related disorders.

Protecting the aged heart during cardiac surgery: single-dose del Nido cardioplegia is superior to multi-dose del Nido cardioplegia in isolated rat hearts

Background:

Aged hearts are particularly vulnerable to reperfusion injury. We recently showed that single-dose del Nido cardioplegia was superior to ‘standard’ multi-dose 4:1 blood cardioplegia in aged rat hearts. This study seeks to determine if multi-dose del Nido cardioplegia offers additional benefits over single-dose del Nido cardioplegia.

Methods:

Functional recovery after 60 min of cardioplegic arrest was assessed in isolated, working, senescent rat hearts. Single-dose del Nido cardioplegia (n=14) was compared to multi-dose del Nido cardioplegia (n=12) delivered every 20 min.

Results:

Troponin release during reperfusion was similar in the single (0.263±0.056 ng/ml) and multi-dose groups (0.261±0.055 ng/ml). Although functional recovery was similar early after reperfusion (stroke work 91±6 ml*mmHg*g−1 vs. 91±8 ml*mmHg*g−1 for single- vs. multi-dose), it declined over time in the multi-dose group (71±9 vs. 43±9 ml*mmHg*g−1 at 60 min, p=0.0175)

Conclusions:

In aged rat hearts, a single-dose del Nido cardioplegia strategy results in superior functional recovery compared to a multi-dose del Nido cardioplegia strategy.

Differences in ischemic damage between young and old hearts--Effects of blood cardioplegia

OBJECTIVE

Senescent patients exhibit an elevated perioperative risk for cardiac dysfunction, hemodynamic depression and subsequent cardiac death compared to young patients. Despite the fact that a growing proportion of cardiac surgery patients are octogenarians, cardioplegic regimes remain comparable across patients of all ages. We compared the hemodynamic performance, metabolic parameters and ultrastructural changes in adult and senescent rat hearts after application of Buckberg's blood cardioplegia (BCP) to evaluate differences between the age groups regarding postischemic myocardial function and cellular ultrastructure.

METHODS

Hearts of adult (young adult group, 3-4 months) and senescent (old group, 24 months) male Wistar rats were excised and inserted into a blood perfused isolated heart apparatus (Langendorff perfusion). After a stabilization period of 30 min, in 16 adult and 16 senescent hearts, Buckberg BCP was administered antegradely and repeated every 20 min. Six young adult and 3 senescent hearts served as ischemia control. After an aortic clamping time of 90 min an antegrade hot shot was administered. During reperfusion ex vivo cardiac functional parameters were recorded, including coronary blood flow, left ventricular developed pressure (LVDP) and velocity of myocardial contraction or relaxation (+/-dp/dt). Oxygen consumption and lactate production of the hearts were calculated. After perfusion fixation, the hearts of five rats in each BCP group and 3 rats in each ischemia group were investigated for cellular edema and mitochondrial damage by morphometry using transmission electron microscopy.

RESULTS

While recovery of cardiac function after 90 min of unprotected ischemia was significantly impaired in senescent hearts, functional recovery after ischemia protected by BCP was similar in adult and senescent hearts. Mitochondrial ultrastructure was severely damaged in both age groups after 90 min ischemia, but well preserved in both BCP groups. The qualitative analysis was confirmed by the morphometric cellular edema index and the volume-to-surface ratio of the mitochondria. Myocardial oxygen consumption was highest and lactate production was lowest in senescent hearts.

CONCLUSION

Senescent rat hearts were more susceptible to unprotected ischemia/reperfusion injury than young adult hearts. When protected by BCP, we found no difference in hemodynamic performance between adult and senescent hearts indicating preserved myocardial protection even in senescent individuals.

Effect of ATP-dependent channel modulators on ischemia-induced arrhythmia change depending on age and gender

The number of ATP-dependent potassium channels in myocardial cells has been previously shown to change depending on gender and age. Different effects of the ATP-dependent potassium channel blocker, glybenclamide and ATP-dependent potassium channel opener, pinacidil on ischemia or reperfusion-induced arrhythmia observed in various research might depend on different ages and genders of the animals used. The aim of this study is to research the effect of ATP-dependent potassium channel modulators on ischemia-induced arrhythmia in animals of different ages and genders. Sprague-Dawley rats of different ages and genders were used in this study. Ischemia was produced by the ligation of the left coronary artery for 30 min. Electrocardiogram (ECG), blood pressure, infarct area and blood glucose were determined during the 30 min of ischemia. An arrhythmia score from an ECG recorded during 30 min of ischemia was determined by examining the duration and type of arrhythmia. Different effects of glybenclamide and pinacidil on the arrhythmias were observed in male and female young and middle-age rats. Pinacidil decreased the infarct zone in younger female rats, but differences in the type and length of ischemia-induced arrhythmias between females and males disappeared in older age. The results of this study showed that the effect of ATP-dependent potassium channel modulators on ischemia-induced arrhythmia changed due to the age and gender of rats.

Sex and sex hormones in cardiac stress--mechanistic insights

Important sex differences in the onset and characteristics of cardiovascular disease are evident, yet the mechanistic details remain unresolved. Men are more susceptible to cardiovascular disease earlier in life, though younger women who have a cardiovascular event are more likely to experience adverse outcomes. Emerging evidence is prompting a re-examination of the conventional view that estrogen is protective and testosterone a liability. The heart expresses both androgen and estrogen receptors and is functionally responsive to circulating sex steroids. New evidence of cardiac aromatase expression indicates local estrogen production may also exert autocrine/paracrine actions in the heart. Cardiomyocyte contractility studies suggest testosterone and estrogen have contrasting inotropic actions, and modulate Ca(2+) handling and transient characteristics. Experimentally, sex differences are also evident in cardiac stress responses. Female hearts are generally less susceptible to acute ischemic damage and associated arrhythmias, and generally are more resistant to stress-induced hypertrophy and heart failure, attributed to the cardioprotective actions of estrogen. However, more recent data show that testosterone can also improve acute post-ischemic outcomes and facilitate myocardial function and survival in chronic post-infarction. The myocardial actions of sex steroids are complex and context dependent. A greater mechanistic understanding of the specific actions of systemic/local sex steroids in different cardiovascular disease states has potential to lead to the development of cardiac therapies targeted specifically for men and women.

Hyperkalemic cardioplegia for adult and pediatric surgery: end of an era?

Despite surgical proficiency and innovation driving low mortality rates in cardiac surgery, the disease severity, comorbidity rate, and operative procedural difficulty have increased. Today's cardiac surgery patient is older, has a "sicker" heart and often presents with multiple comorbidities; a scenario that was relatively rare 20 years ago. The global challenge has been to find new ways to make surgery safer for the patient and more predictable for the surgeon. A confounding factor that may influence clinical outcome is high K(+) cardioplegia. For over 40 years, potassium depolarization has been linked to transmembrane ionic imbalances, arrhythmias and conduction disturbances, vasoconstriction, coronary spasm, contractile stunning, and low output syndrome. Other than inducing rapid electrochemical arrest, high K(+) cardioplegia offers little or no inherent protection to adult or pediatric patients. This review provides a brief history of high K(+) cardioplegia, five areas of increasing concern with prolonged membrane K(+) depolarization, and the basic science and clinical data underpinning a new normokalemic, "polarizing" cardioplegia comprising adenosine and lidocaine (AL) with magnesium (Mg(2+)) (ALM™). We argue that improved cardioprotection, better outcomes, faster recoveries and lower healthcare costs are achievable and, despite the early predictions from the stent industry and cardiology, the "cath lab" may not be the place where the new wave of high-risk morbid patients are best served.

Chronic Tempol treatment restores pharmacological preconditioning in the senescent rat heart

Cardioprotective effects of anesthetic preconditioning and cyclosporine A (CsA) are lost with aging. To extend our previous work and address a possible mechanism underlying age-related differences, we investigated the role of oxidative stress in the aging heart by treating senescent animals with the oxygen free radical scavenger Tempol. Old male Fischer 344 rats (22–24 mo) were randomly assigned to control or Tempol treatment groups for 2 or 4 wk (T×2wk and T×4wk, respectively). Rats received isoflurane 30 min before ischemia-reperfusion injury or CsA just before reperfusion. Myocardial infarction sizes were significantly reduced by isoflurane or CsA in the aged rats treated with Tempol (T×4wk) compared with old control rats. In other experiments, young (4–6 mo) and old rats underwent either chronic Tempol or vehicle treatment, and the levels of myocardial protein oxidative damage, antioxidant enzymes, mitochondrial Ca2+ uptake, cyclophilin D protein, and mitochondrial permeability transition pore opening times were measured. T×4wk significantly increased MnSOD enzyme activity, GSH-to-GSSH ratios, MnSOD protein level, mitochondrial Ca2+ uptake capacity, reduced protein nitrotyrosine levels, and normalized cyclophilin D protein expression in the aged rat heart. T×4wk also significantly prolonged mitochondrial permeability transition pore opening times induced by reactive oxygen species in old cardiomyocytes. Our studies demonstrate that 4 wk of Tempol pretreatment restores anesthetic preconditioning and cardioprotection by CsA in the old rat and that this is associated with decreased oxidative stress and improved mitochondrial function. Our results point to a new protective strategy for the ischemic myocardium in the high-risk older population.

Age-associated differences in gene expression in response to delayed anesthetic preconditioning

Evidence suggests that the protective benefits of anesthetic preconditioning (APC) are significantly attenuated in the aged myocardium. In this study, we investigated the effect of aging on gene expression in delayed APC. Hearts from Fischer 344 rats, age 4 or 24 months, were divided into five groups: control; ischemia/reperfusion (I/R); and delayed APC at 6, 12, and 24 h. Whole-genome array was studied using Affymetrix Rat Genome 230 2.0 array. Data were analyzed for significant ≥2.0-fold changes in gene expression. Microarray results were confirmed by quantitative real-time reverse transcription-polymerase chain reaction. Of the 28,000 genes represented on the Affymetrix Rat Genome 230 2.0 Microarray chip, 24 transcripts in 6 h APC, 28 in 12 h APC, and 28 in 24 h APC group displayed significant up-regulation in mRNA levels, and 70 transcripts in 6 h APC, 101 in 12 h APC, and 82 in 24 h APC displayed significant down-regulation in young rat hearts. These altered genes fall into functional categories of cell defense/death, cell structure, gene expression/protein synthesis, inflammatory response/growth/remodeling, and signaling/communication. Although alterations for some genes were in common, the numbers of changed genes in old rats were markedly and consistently lower than the young rats. Twenty-four hour delayed APC also significantly reduced infarct size and improved myocardial left ventricular function in young hearts, effects that were not observed in old rat hearts. We concluded that delayed APC profoundly and differentially affected gene expression profiles of the cardiomyocyte in an age-associated pattern. The impaired genomic response to delayed APC could underlie the loss of the protective benefits of preconditioning in aged hearts.

Potassium-induced conversion of ventricular fibrillation after aortic declamping

OBJECTIVES

The anti-fibrillatory effect of potassium is well recognized from experimental models. There have, however, been very few clinical reports on the use of potassium to convert ventricular fibrillation (VF) after cardioplegic arrest.

METHODS

In total, 8465 adult patients undergoing cardiac operations on cardiopulmonary bypass (CPB) and with cold antegrade crystalloid cardioplegic arrest were consecutively enrolled in a database. Patients with VF after removal of the aortic clamp were given 20 mmol potassium, and if needed an extra 10 mmol, in the perfusion line and the conversion rate was registered. Preoperative and intraoperative factors possibly related to the occurrence of post-ischaemic VF were assessed.

RESULTS

Of these, 1721 (20%) patients had VF and 1366 of these (79%) were successfully treated with potassium infusion. Only 355 (21%) patients (4% of all operations) had direct-current countershock. The need for pacing was lower in the treatment group compared with the non-treatment group (P <0.001). Multivariate analysis revealed as the main findings that age, gender, amount of cardioplegia related to body mass index (BMI), and blood transfusion during the time of CPB had a highly significant (P <0.001) impact on reducing the rate of post-arrest VF. Somewhat contrary to expectation, left ventricular hypertrophy (LVH) was not a significant factor (P = 0.32) for post-arrest VF. No conversion by potassium was significant for age (P <0.001), gender (P <0.001) and LVH (P <0.001), but not for blood transfusion during CPB (P = 0.38) and for the ratio of cardioplegia-BMI (P = 0.26).

CONCLUSIONS

The results from this register study demonstrate that potassium infusion is an effective and convenient first-hand measure to convert post declamping VF on CPB.

Microarray and proteomic analysis of the cardioprotective effects of cold blood cardioplegia in the mature and aged male and female

Recently we have shown that the cardioprotection afforded by cardioplegia is modulated by age and gender and is significantly decreased in the aged female. In this report we use microarray and proteomic analyses to identify transcriptomic and proteomic alterations affecting cardioprotection using cold blood cardioplegia in the mature and aged male and female heart. Mature and aged male and female New Zealand White rabbits were used for in situ blood perfused cardiopulmonary bypass. Control hearts received 30 min sham ischemia and 120 min sham reperfusion. Global ischemia (GI) hearts received 30 min of GI achieved by cross-clamping of the aorta. Cardioplegia (CP) hearts received cold blood cardioplegia prior to GI. Following 30 min of GI the hearts were reperfused for 120 min and then used for RNA and protein isolation. Microarray and proteomic analyses were performed. Functional enrichment analysis showed that mitochondrial dysfunction, oxidative phosphorylation and calcium signaling pathways were significantly enriched in all experimental groups. Glycolysis/gluconeogenesis and the pentose phosphate pathway were significantly changed in the aged male only (P < 0.05), while glyoxylate/dicarboxylate metabolism was significant in the aged female only (P < 0.05). Our data show that specific pathways associated with the mitochondrion modulate cardioprotection with CP in the aged and specifically in the aged female. The alteration of these pathways significantly contributes to decreased myocardial functional recovery and myonecrosis following ischemia and may be modulated to allow for enhanced cardioprotection in the aged and specifically in the aged female.

Isoflurane-induced post-conditioning in senescent hearts is attenuated by failure to activate reperfusion injury salvage kinase pathway

BACKGROUND

We investigated the cardioprotective effects of isoflurane administered at the onset of reperfusion in senescent rat in vivo, and the activation of the reperfusion injury salvage kinase (RISK) pathway to address a possible mechanism underlying age-related differences.

METHODS

Male Wistar rats were assigned to age groups (young, 3-5 months; old, 20-24 months), and randomly selected to receive isoflurane (1 minimum alveolar concentration) or not for 3 min before and 2 min after reperfusion (ISO postC). Rats were subjected to coronary occlusion for 30 min followed by 2 h of reperfusion. Western blot analysis was used to assess the phosphorylation of extracellular signal-regulated kinase (ERK1/2), Akt, and GSK3β 15 min after reperfusion.

RESULTS

Brief administration of isoflurane 3 min before and 2 min after the initiation of early reperfusion reduced infarct size (56 ± 8% of left ventricular area at risk, mean ± standard deviation) compared with controls (68 ± 4%) in young rats, but had no effect in old rats (56 ± 8% in ISO postC and 56 ± 10% in control, respectively). Phosphorylation of ERK1/2, Akt, and GSK3β were increased in the young ISO postC group but not in the old ISO postC group compared with control groups of the respective ages.

CONCLUSIONS

We demonstrated that isoflurane post-conditions the heart in young but not in senescent rats. Failure to activate RISK pathway may contribute to attenuation of isoflurane-induced post-conditioning effect in senescent rats.

Age and ovariectomy abolish beneficial effects of female sex on rat ventricular myocytes exposed to simulated ischemia and reperfusion

Sex differences in responses to myocardial ischemia have been described, but whether cardiomyocyte function is influenced by sex in the setting of ischemia and reperfusion has not been elucidated. This study compared contractions and intracellular Ca²⁺ in isolated ventricular myocytes exposed to ischemia and reperfusion. Cells were isolated from anesthetized 3-month-old male and female Fischer 344 rats, paced at 4 Hz (37°C), exposed to simulated ischemia (20 mins) and reperfused. Cell shortening (edge detector) and intracellular Ca²⁺ (fura-2) were measured simultaneously. Cell viability was assessed with Trypan blue. Ischemia reduced peak contractions and increased Ca²⁺ levels equally in myocytes from both sexes. However, contraction amplitudes were reduced in reperfusion in male myocytes, while contractions recovered to exceed control levels in females (62.6±5.1 vs. 140.1±15.8%; p<0.05). Only 60% of male myocytes excluded trypan blue dye after ischemia and reperfusion, while all female cardiomyocytes excluded the dye (p<0.05). Parallel experiments were conducted in myocytes from ∼24-month-old female rats or 5–6-month-old rats that had an ovariectomy at 3–4 weeks of age. Beneficial effects of female sex on myocyte viability and contractile dysfunction in reperfusion were abolished in cells from 24-month-old females. Aged female myocytes also exhibited elevated intracellular Ca²⁺ and alternans in ischemia. Cells from ovariectomized rats displayed increased Ca²⁺ transients and spontaneous activity in ischemia compared to sham-operated controls. None of the myocytes from ovariectomized rats were viable after 15 minutes of ischemia, while 75% of sham cells remained viable at end of reperfusion (p<0.05). These findings demonstrate that cardiomyocytes from young adult females are more resistant to ischemia and reperfusion injury than cells from males. Age and OVX abolish these beneficial effects and induce Ca²⁺ dysregulation at the level of the cardiomyocyte. Thus, beneficial effects of estrogen in ischemia and reperfusion are mediated, in part, by effects on cardiomyocytes.

Calcium-mediated cell death during myocardial reperfusion

Reperfusion may induce additional cell death in patients with acute myocardial infarction receiving primary angioplasty or thrombolysis. Altered intracellular Ca(2+) handling was initially considered an essential mechanism of reperfusion-induced cardiomyocyte death. However, more recent studies have demonstrated the importance of Ca(2+)-independent mechanisms that converge on mitochondrial permeability transition (MPT) and are shared by cardiomyocytes and other cell types. This article analyses the importance of Ca(2+)-dependent cell death in light of these new observations. Altered Ca(2+) handling includes increased cytosolic Ca(2+) levels, leading to activation of calpain-mediated proteolysis and sarcoplasmic reticulum-driven oscillations; this can induce hypercontracture, but also MPT due to the privileged Ca(2+) transfer between sarcoplasmic reticulum and mitochondria through cytosolic Ca(2+) microdomains. In the opposite direction, permeability transition can worsen altered Ca(2+) handling and favour hypercontracture. Ca(2+) appears to play an important role in cell death during the initial minutes of reperfusion, particularly after brief periods of ischaemia. Developing effective and safe treatments to prevent Ca(2+)-mediated cardiomyocyte death in patients with transient ischaemia, by targeting Ca(2+) influx, intracellular Ca(2+) handling, or Ca(2+)-induced cell death effectors, is an unmet challenge with important therapeutic implications and large potential clinical impact.

Cardiac ischaemic stress: cardiomyocyte Ca²⁺, sex and sex steroids

1. Important sex differences exist in ischaemic heart disease. Oestrogen has been conventionally regarded as providing a cardioprotective benefit and testosterone frequently perceived to exert a deleterious effect. However, there is accumulating evidence that argues against this simple dichotomy, suggesting that the influence of oestrogen and testosterone conferring benefit or detriment may be context specific. 2. Cardiomyocyte calcium (Ca(2+)) loading is recognized to be a major factor in acute ischaemia-reperfusion pathology, promoting cell death, contractile dysfunction and arrhythmogenic activity. Ca(2+)/calmodulin-dependent kinase II (CaMKII) is a mediator of many of the cardiomyocyte Ca(2+)-related pathologies in ischaemia-reperfusion. Cardiomyocyte Ca(2+)-handling processes have been shown to be modulated by the actions of oestrogen and testosterone. A role for these sex steroids in influencing CaMKII activation is argued. 3. Although many experimental studies of oestrogen manipulation can identify a cardioprotective role for this sex steroid, there are also numerous reports that fail to demonstrate sex differences in postischaemic recovery. Experimental studies report that testosterone can be protective in ischaemia-reperfusion in males and females in some settings. 4. Further studies of sex steroid influence in the ischaemic heart will allow the development of therapeutic interventions that are specifically targeted for male and female hearts.

Opposing effects of age and calorie restriction on molecular determinants of myocardial ischemic tolerance

We test the hypothesis that moderate calorie restriction (CR) reverses negative influences of age on molecular determinants of myocardial stress resistance. Postischemic contractile dysfunction, cellular damage, and expression of regulators of autophagy/apoptosis and of prosurvival and prodeath kinases were assessed in myocardium from young adult (YA; 2- to 4-month-old) and middle-aged (MA; 12-month-old) mice, and MA mice subjected to 14 weeks of 40% CR (MA-CR). Ventricular dysfunction after 25%±2%), as was cell death indicated by troponin I (TnI) efflux (1,701±214 ng vs. 785±102 ng in YA). MA hearts exhibited 30% and 65% reductions in postischemic Beclin1 and Parkin, respectively, yet 50% lower proapoptotic Bax and 85% higher antiapoptotic Bcl2, increasing the Bcl2/Bax ratio. Age did not influence Akt or p38-mitogen-activated protein kinase (MAPK) expression; reduced expression of increasingly phosphorylated ribosomal protein S6 kinase (p70S6K), increased expression of dephosphorylated glycogen synthase kinase 3β (GSK3β) and enhanced postischemic p38-MAPK phosphorylation. CR countered the age-related decline in ischemic tolerance, improving contractile recovery (60%±4%) and reducing cell death (123±22 ng of TnI). Protection was not associated with changes in Parkin or Bax, whereas CR partially limited the age-related decline in Beclin1 and further increased Bcl2. CR counteracted age-related changes in p70S6K, increased Akt levels, and reduced p38-MAPK (albeit increasing preischemic phosphorylation), and paradoxically reduced postischemic GSK3β phosphorylation. In summary, moderate age worsens cardiac ischemic tolerance; this is associated with reduced expression of autophagy regulators, dysregulation of p70S6K and GSK3β, and postischemic p38-MAPK activation. CR counters age effects on postischemic dysfunction/cell death; this is associated with reversal of age effects on p70S6K, augmentation of Akt and Bcl2 levels, and preischemic p38-MAPK activation. Age and CR thus impact on distinct determinants of ischemic tolerance, although p70S6K signaling presents a point of convergence.

Aromatase deficiency confers paradoxical postischemic cardioprotection

The conventional view is that estrogen confers female cardioprotection. Estrogen synthesis depends on androgen availability, with aromatase regulating conversion of testosterone to estradiol. Extragonadal aromatase expression mediates estrogen production in some tissues, but a role for local steroid conversion has not yet been demonstrated in the heart. This study's goal was to investigate how aromatase deficiency influences myocardial function and ischemic resilience. RT-PCR analysis of C57Bl/6 mouse hearts confirmed cardiac-specific aromatase expression in adult females. Functional performance of isolated hearts from female aromatase knockout (ArKO) and aromatase wild-type mice were compared. Left ventricular developed pressures were similar in aerobic perfusion, but the maximal rate of rise of ventricular pressure was modestly reduced in ArKO hearts (3725 ± 144 vs. 4272 ± 154 mm Hg/sec, P < 0.05). After 25 min of ischemia, the recovery of left ventricular developed pressure was substantially improved in ArKO (percentage of basal at 60 min of reperfusion, 62 ± 8 vs. 30 ± 6%; P < 0.05). Hypercontracture was attenuated (end diastolic pressure, 25 ± 5 vs. 51 ± 1 mm Hg; P < 0.05), and lactate dehydrogenase content of coronary effluent was reduced throughout reperfusion in ArKO hearts. This was associated with a hyperphosphorylation of phospholamban and a reduction in phosphorylated Akt. Immediately after reperfusion, ArKO hearts exhibited increased incidence of ventricular premature beats (194 ± 70 vs. 46 ± 6, P < 0.05). These observations indicate more robust functional recovery, reduced cellular injury, and modified cardiomyocyte Ca(2+) handling in aromatase-deficient hearts. Our findings indicate that androgen-to-estrogen conversion may be of pathophysiologic importance to the heart and challenge the notion that estrogen deficiency is deleterious. These studies suggest the possibility that aromatase suppression may offer inotropic benefit in the acute ischemia/reperfusion setting with appropriate arrhythmia management.

Histidine-tryptophan-ketoglutarate or celsior: which is more suitable for cold preservation for cardiac grafts from older donors?

BACKGROUND

The growing number of patients awaiting heart transplantation, coupled with the worldwide donor shortage, has led to increased use of marginal organs, specifically hearts from older donors. This study compared the protective effects of two widely used preservation solutions, histidine-tryptophan-ketoglutarate (HTK) and Celsior (CEL; Sangstat Medical, Menlo Park, CA), for ischemia-reperfusion injury using a rat heterotopic heart transplantation model with older donors.

METHODS

The hearts were excised from 16- and 80-week-old Lewis donor rats, stored in HTK, CEL, or saline for 6 hours and heterotopically transplanted into syngenic young Lewis recipients. Serum troponin I and creatine phosphokinase, graft infiltrating cells, graft apoptosis, graft proinflammatory messenger ribonucleic acid levels, and adenosine monophosphate-activated protein kinase phosphorylation were analyzed 3, 6, and 12 hours after reperfusion as markers of graft injury. Tissue adenosine triphosphate levels were measured after cold storage for 0, 6, 12, and 18 hours.

RESULTS

The HTK and CEL reduced injury comparably in grafts from young donors. The recipients of grafts from older donors and stored in HTK for 6 hours had lower levels of serum troponin I and creatine phosphokinase, less upregulation of the messenger ribonucleic acid for interleukin-6, intercellular adhesion molecule-1, and tumor necrosis factor-α, fewer infiltrating cells, less apoptosis, and less phosphorylated adenosine monophosphate-activated protein kinase than recipients of grafts stored in CEL. Adenosine triphosphate levels in the hearts stored in HTK were significantly higher than those stored in CEL or saline.

CONCLUSIONS

Cold storage in HTK exhibited superior protective effects against ischemia-reperfusion injury of hearts from older donors in this rat transplantation model.

Long-term effects of intrauterine growth restriction on cardiac metabolism and susceptibility to ischaemia/reperfusion

AIMS

Adult offspring who are born intrauterine growth restricted (IUGR) are at risk of developing cardiovascular diseases during adulthood. Additionally, several cardiac diseases are associated with changes in myocardial energy metabolism. However, the potential long-term effects of being born IUGR on cardiac energetics are unknown. The aim of this study was to assess the long-term effect of IUGR on cardiac performance and energy metabolism under aerobic conditions and after ischaemia/reperfusion (IR) injury.

METHODS AND RESULTS

To induce IUGR, pregnant Sprague-Dawley rats were randomly assigned to hypoxic (11.5% O(2)) or control (21% O(2)) environments from day 15 to 21 of pregnancy. Cardiac susceptibility to IR was evaluated in male and female offspring at 4 (young-adult) or 12 (ageing) months of age using isolated working hearts. Cardiac production of energy was evaluated using radiolabelled substrates. Both male and female IUGR offspring exhibited an increased susceptibility to IR injury compared with controls (P< 0.05) as well as an increased post-ischaemic production of protons (P< 0.001) secondary to a mismatch between myocardial glycolysis and glucose oxidation rates. Moreover, offspring born IUGR exhibited an increased myocardial production of acetyl-CoA during reperfusion. The mismatch between energy production and cardiac performance indicates that in IUGR offspring, cardiac efficiency during reperfusion was decreased relative to controls.

CONCLUSION

Our results suggest that hypoxia-induced IUGR has long-term effects on cardiac susceptibility to IR injury that are independent of sex and age. Moreover, we identified a mismatch in glucose metabolism, leading to proton accumulation in the post-ischaemic myocardium of offspring born IUGR as a potential mechanism involved.

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.

Diazoxide protects myocardial mitochondria, metabolism, and function during cardiac surgery: a double-blind randomized feasibility study of diazoxide-supplemented cardioplegia

OBJECTIVES

The study was designed to assess whether diazoxide-mediated cardioprotection might be used in human subjects during cardiac surgery.

METHODS

Forty patients undergoing coronary artery bypass grafting were randomized to receive intermittent warm blood antegrade cardioplegia supplemented with either diazoxide (100 micromol/L) or placebo (n = 20 in each group). Mitochondria were assessed before and after ischemia and reperfusion in myocardial biopsy specimens. Myocardial oxygen and glucose and lactic acid extraction ratios were measured before ischemia and in the first 20 minutes of reperfusion. Hemodynamic data were collected, and troponin I, creatine kinase-MB, and N-terminal prohormone brain natriuretic peptide levels were measured. All outcomes were analyzed by using mixed-effects modeling for repeated measures.

RESULTS

No deaths, strokes, or infarcts were observed. Patients received, on average, 36.2 +/- 1.2 mg of diazoxide and 37.3 +/- 1.9 mg of placebo (P = .6). Diazoxide added to cardioplegia prevented mitochondrial swelling (8899 +/- 474 vs 9273 +/- 688 pixels before and after the procedure, respectively; P = .6) compared with that seen in the placebo group (8474 +/- 163 vs 11,357 +/- 759 pixels, P = .004). No oxygen debt was observed in the diazoxide group. Glucose consumption and lactic acid production returned to preischemic values faster in the diazoxide group. The following hemodynamic parameters differed between the diazoxide and placebo groups, respectively, in the postoperative period: cardiac index, 3.0 +/- 0.09 versus 2.6 +/- 0.09 L . min(-1) . m(-2) (P = .002); left cardiac work index, 2.81 +/- 0.07 versus 2.31 +/- 0.07 kg/m(2) (P < .001); oxygen delivery index, 420 +/- 14 versus 377 +/- 13 mL . min(-1) . m(-2) (P = .03); and oxygen extraction ratio, 29.3% +/- 1.1% versus 32.6% +/- 1.1% (P = .02). Postoperative myocardial enzyme levels did not differ, but N-terminal prohormone brain natriuretic peptide levels were lower in the diazoxide group (120 +/- 27 vs 192 +/- 29 pg/mL, P = .04).

CONCLUSIONS

Supplementing blood cardioplegia with diazoxide is safe and improves myocardial protection during cardiac surgery, possibly through its influence on the mitochondria.

Injection of isolated mitochondria during early reperfusion for cardioprotection

Previously, we demonstrated that ischemia induces mitochondrial damage and dysfunction that persist throughout reperfusion and impact negatively on postischemic functional recovery and cellular viability. We hypothesized that viable respiration-competent mitochondria, isolated from tissue unaffected by ischemia and then injected into the ischemic zone just before reperfusion, would enhance postischemic functional recovery and limit infarct size. New Zealand White rabbits (n = 52) were subjected to 30 min of equilibrium and 30 min of regional ischemia (RI) induced by snaring the left anterior descending coronary artery. At 29 min of RI, the RI zone was injected with vehicle (sham control and RI vehicle) or vehicle containing mitochondria (7.7 x 10(6) +/- 1.5 x 10(6)/ml) isolated from donor rabbit left ventricular tissue (RI-Mito). The snare was released at 30 min of RI, and the hearts were reperfused for 120 min. Our results show that left ventricular peak developed pressure and systolic shortening in RI-Mito hearts were significantly enhanced (P < 0.05 vs. RI-vehicle) to 75% and 83% of equilibrium value, respectively, at 120 min of reperfusion compared with 57% and 62%, respectively, in RI-vehicle hearts. Creatine kinase-MB, cardiac troponin I, and infarct size relative to area at risk were significantly decreased in RI-Mito compared with RI-vehicle hearts (P < 0.05). Confocal microscopy showed that injected mitochondria were present and viable after 120 min of reperfusion and were distributed from the epicardium to the subendocardium. These results demonstrate that viable respiration-competent mitochondria, isolated from tissue unaffected by ischemia and then injected into the ischemic zone just before reperfusion, significantly enhance postischemic functional recovery and cellular viability.

Estrogen, NFkappaB, and the heat shock response

Estrogen has pleiotropic actions, among which are its anti-apoptotic, anti-inflammatory, and vasodilatory effects. Recently, an interaction between 17beta-estradiol (E2) and the transcription factor nuclear factor kappaB (NFkappaB) has been identified. NFkappaB has a central role in the control of genes involved in inflammation, proliferation, and apoptosis. Prolonged activation of NFkappaB is associated with numerous inflammatory pathological conditions. An important facet of E2 is its ability to modulate activity of NFkappaB via both genomic and nongenomic actions. E2 can activate NFkappaB rapidly via nongenomic pathways, increase cellular resistance to injury, and induce expression of the protective class of proteins, heat shock proteins (HSPs). HSPs can bind to many of the pro-apoptotic and pro-inflammatory targets of NFkappaB and, thus, indirectly inhibit many of its deleterious effects. In addition, HSPs can block NFkappaB activation and binding directly. Similarly, genomic E2 signaling can inhibit NFkappaB, but does so through alternative mechanisms. This review focuses on the molecular mechanisms of cross-talk between E2, NFkappaB, and HSPs, and the biological relevance of this cross-talk.

Simulated ischemia-induced preconditioning of isolated ventricular myocytes from young adult and aged Fischer-344 rat hearts

The impact of ischemic preconditioning (IPC) on contraction, Ca(2+) homeostasis, and cell survival was compared in isolated ventricular myocytes from young adult ( approximately 3 mo) and aged ( approximately 24 mo) male Fischer-344 rats. Myocytes were field stimulated at 4 Hz (37 degrees C). Contraction (edge detector) and intracellular Ca(2+) (fura-2) were measured simultaneously. Viability was assessed with trypan blue. All cells were exposed to 30 min of simulated ischemia followed by reperfusion. Some cells were preconditioned by exposure to 5 min of simulated ischemia before prolonged ischemia. Pretreatment with IPC abolished postischemic contractile depression, inhibited diastolic contracture, and increased Ca(2+) transient amplitudes in reperfusion in young adult and aged cells. IPC did not affect the modest rise in diastolic Ca(2+) in ischemia in young adult myocytes. However, IPC abolished the marked rise in diastolic Ca(2+) observed in ischemia and early reperfusion in aged myocytes. IPC also suppressed mechanical alternans in ischemia in aged cells, but younger myocytes showed little evidence of mechanical alternans whether or not cells were preconditioned. IPC markedly improved cell viability in reperfusion in young adult but not aged cells. These results suggest that IPC augments the recovery of contractile function in reperfusion by increasing Ca(2+) transient amplitudes in ventricular myocytes from young adult and aged rats. IPC reduced diastolic Ca(2+) accumulation in ischemia in aged myocytes, which may diminish the severity of mechanical alternans in aged cells. Nonetheless, the efficacy of IPC is compromised in aging, as IPC did not improve survival of aged myocytes exposed to ischemia and reperfusion.

Effects of ischemia and reperfusion on isolated ventricular myocytes from young adult and aged Fischer 344 rat hearts

This study examined the impact of age on contractile function, Ca2+homeostasis, and cell viability in isolated myocytes exposed to simulated ischemia and reperfusion. Ventricular myocytes were isolated from anesthetized young adult (3 mo) and aged (24 mo) male Fischer 344 rats. Cells were field-stimulated at 4 Hz (37°C), exposed to simulated ischemia, and reperfused with Tyrode solution. Cell shortening and intracellular Ca2+were measured simultaneously with an edge detector and fura-2. Cell viability was assessed by Trypan blue exclusion. Ischemia (20–45 min) depressed amplitudes of contraction equally in isolated myocytes from young adult and aged animals. The degree of postischemic contractile depression (stunning) was comparable in both groups. Ca2+transient amplitudes were depressed in early reperfusion in young adult and aged cells and then recovered to preischemic levels in both groups. Cell viability also declined equally in reperfusion in both groups. In short, some cellular responses to simulated ischemia and reperfusion were similar in both groups. Even so, aged myocytes exhibited a much greater and more prolonged accumulation of diastolic Ca2+in ischemia and in early reperfusion compared with myocytes from younger animals. In addition, the degree of mechanical alternans in ischemia increased significantly with age. The observation that there is an age-related increase in accumulation of diastolic Ca2+in ischemia and early reperfusion may account for the increased sensitivity to ischemia and reperfusion injury in the aging heart. The occurrence of mechanical alternans in ischemia may contribute to contractile dysfunction in ischemia in the aging heart.

Age-related attenuation of isoflurane preconditioning in human atrial cardiomyocytes: roles for mitochondrial respiration and sarcolemmal adenosine triphosphate-sensitive potassium channel activity

BACKGROUND

Clinical trials suggest that anesthetic-induced preconditioning (APC) produces cardioprotection in humans, but the mechanisms of APC and significance of aging for APC in humans are not well understood. Here, the impact of age on the role of two major effectors of APC, mitochondria and sarcolemmal adenosine triphosphate-sensitive potassium (sarcKATP) channels, in preconditioning of the human atrial myocardium were investigated.

METHODS

Right atrial appendages were obtained from adult patients undergoing cardiac surgery and assigned to mid-aged (MA) and old-aged (OA) groups. APC was induced by isoflurane in isolated myocardium and isolated cardiomyocytes. Mitochondrial oxygen consumption measurements, myocyte survival testing, and patch clamp techniques were used to investigate mitochondrial respiratory function and sarcKATP channel activity.

RESULTS

After in vitro APC with isoflurane, the respiratory function of isolated mitochondria was better preserved after hypoxia-reoxygenation stress in MA than in OA. In isolated intact myocytes, APC significantly decreased oxidative stress-induced cell death in MA but not in OA, and isoflurane protection from cell death was attenuated by the sarcKATP channel inhibitor HMR-1098. Further, the properties of single sarcKATP channels were similar in MA and OA, and isoflurane sensitivity of pinacidil-activated whole cell KATP current was no different between MA and OA myocytes.

CONCLUSION

Anesthetic-induced preconditioning with isoflurane decreases stress-induced cell death and preserves mitochondrial respiratory function to a greater degree in MA than in OA myocytes; however, sarcKATP channel activity is not differentially affected by isoflurane. Therefore, effectiveness of APC in humans may decrease with advancing age partly because of altered mitochondrial function of myocardial cells.