Measurement of superoxide-derived free radicals in the reperfused heart. Evidence for a free radical mechanism of reperfusion injury

Oxidative Post-translational Protein Modifications upon Ischemia/Reperfusion Injury

While reperfusion, or restoration of coronary blood flow in acute myocardial infarction, is a requisite for myocardial salvage, it can paradoxically induce a specific damage known as ischemia/reperfusion (I/R) injury. Our understanding of the precise pathophysiological molecular alterations leading to I/R remains limited. In this study, we conducted a comprehensive and unbiased time-course analysis of post-translational modifications (PTMs) in the post-reperfused myocardium of two different animal models (pig and mouse) and evaluated the effect of two different cardioprotective therapies (ischemic preconditioning and neutrophil depletion). In pigs, a first wave of irreversible oxidative damage was observed at the earliest reperfusion time (20 min), impacting proteins essential for cardiac contraction. A second wave, characterized by irreversible oxidation on different residues and reversible Cys oxidation, occurred at late stages (6-12 h), affecting mitochondrial, sarcomere, and inflammation-related proteins. Ischemic preconditioning mitigated the I/R damage caused by the late oxidative wave. In the mouse model, the two-phase pattern of oxidative damage was replicated, and neutrophil depletion mitigated the late wave of I/R-related damage by preventing both Cys reversible oxidation and irreversible oxidation. Altogether, these data identify protein PTMs occurring late after reperfusion as an actionable therapeutic target to reduce the impact of I/R injury.

The Unfolded Protein Response: A Double-Edged Sword for Brain Health

Efficient brain function requires as much as 20% of the total oxygen intake to support normal neuronal cell function. This level of oxygen usage, however, leads to the generation of free radicals, and thus can lead to oxidative stress and potentially to age-related cognitive decay and even neurodegenerative diseases. The regulation of this system requires a complex monitoring network to maintain proper oxygen homeostasis. Furthermore, the high content of mitochondria in the brain has elevated glucose demands, and thus requires a normal redox balance. Maintaining this is mediated by adaptive stress response pathways that permit cells to survive oxidative stress and to minimize cellular damage. These stress pathways rely on the proper function of the endoplasmic reticulum (ER) and the activation of the unfolded protein response (UPR), a cellular pathway responsible for normal ER function and cell survival. Interestingly, the UPR has two opposing signaling pathways, one that promotes cell survival and one that induces apoptosis. In this narrative review, we discuss the opposing roles of the UPR signaling pathways and how a better understanding of these stress pathways could potentially allow for the development of effective strategies to prevent age-related cognitive decay as well as treat neurodegenerative diseases.

Do reactive oxygen species damage or protect the heart in ischemia and reperfusion? Analysis on experimental and clinical data

The role of reactive oxygen species (ROS) in ischemic and reperfusion (I/R) injury of the heart has been discussed for more than 40 years. It has been demonstrated that reperfusion triggers a multiple increase in free radical generation in the isolated heart. Antioxidants were found to have the ability to mitigate I/R injury of the heart. However, it is unclear whether their cardioprotective effect truly depends on the decrease of ROS levels in myocardial tissues. Since high doses and high concentrations of antioxidants were experimentally used, it is highly likely that the cardioprotective effect of antioxidants depends on their interaction not only with free radicals but also with other molecules. It has been demonstrated that the antioxidant N-2-mercaptopropionyl glycine or NDPH oxidase knockout abolished the cardioprotective effect of ischemic preconditioning. Consequently, there is evidence that ROS protect the heart against the I/R injury.

The Role of the Hypoxia-Related Unfolded Protein Response (UPR) in the Tumor Microenvironment

Despite our understanding of the unfolded protein response (UPR) pathways, the crosstalk between the UPR and the complex signaling networks that different cancers utilize for cell survival remains to be, in most cases, a difficult research barrier. A major problem is the constant variability of different cancer types and the different stages of cancer as well as the complexity of the tumor microenvironments (TME). This complexity often leads to apparently contradictory results. Furthermore, the majority of the studies that have been conducted have utilized two-dimensional in vitro cultures of cancer cells that were exposed to continuous hypoxia, and this approach may not mimic the dynamic and cyclic conditions that are found in solid tumors. Here, we discuss the role of intermittent hypoxia, one of inducers of the UPR in the cellular component of TME, and the way in which intermittent hypoxia induces high levels of reactive oxygen species, the activation of the UPR, and the way in which cancer cells modulate the UPR to aid in their survival. Although the past decade has resulted in defining the complex, novel non-coding RNA-based regulatory networks that modulate the means by which hypoxia influences the UPR, we are now just to beginning to understand some of the connections between hypoxia, the UPR, and the TME.

DJ-1 administration exerts cardioprotection in a mouse model of acute myocardial infarction

Cardiovascular diseases, and particularly acute myocardial infarction (MI), are the most common causes of death worldwide. Infarct size is the major predictor of clinical outcomes in MI. The Parkinson’s disease associated protein, DJ-1 (also known as PARK7), is a multifunctional protein with chaperone, redox sensing and mitochondrial homeostasis activities. Previously, we provided the evidence for a central role of endogenous DJ-1 in the cardioprotection of post-conditioning. In the present study, we tested the hypothesis that systemic administration of recombinant DJ-1 exerts cardioprotective effects in a mouse model of MI and also explored the associated transcriptional response. We report a significant treatment-induced reduction in infarct size, leukocyte infiltration, apoptosis and oxidative stress. Effects potentially mediated by G-protein-coupled receptor signaling and modulation of the immune response. Collectively, our results indicate a protective role for the exogenously administrated DJ-1 upon MI, and provide the first line of evidence for an extracellular activity of DJ-1 regulating cardiac injury in vivo.

The Effect of Resveratrol on Sphingosine-1 and Oxidative/ Nitrosative Stress in an Experimental Heart Ischemia Reperfusion Model

Objectives: Resveratrol (RSV) is a natural polyphenolic compound showing significant antioxidant effects. In this study, we aimed to investigate the effects of resveratrol on the sphingosine-1-phosphate (S1P) and oxidative stress biomarkers in hearth ischemia-reperfusion (I/R).

Materials and Methods: The biochemical and histopathological effects of RSV on cardiac ischemia-reperfusion injury were investigated through ELISA- and light microscope.

Results: We observed statistically significant differences between the treatment group and the control group in terms of malondialdehyde (MDA) level, catalase (CAT) and superoxide dismutase (SOD) activities (p<0.05). Histopathologically, we also observed decreased Polymorphonuclear Leucocyte (PMNL) infiltration, myocardial edema, miyositolysis in the treatment group compared to the I/R and sham groups.

Conclusion: Resveratrol may play an important role in cardiac I/R injury through its anti-inflammatory and antioxidant effects which were biochemically and histopathologically confirmed in the present study.

Prostaglandin E2 EP receptors in cardiovascular disease: An update

This review article provides an update for the role of prostaglandin E2 receptors (EP1, EP2, EP3 and EP4) in cardiovascular disease. Where possible we have reported citations from the last decade although this was not possible for all of the topics covered due to the paucity of publications. The authors have attempted to cover the subjects of ischemia-reperfusion injury, arrhythmias, hypertension, novel protein binding partners of the EP receptors and their pathophysiological significance, and cardiac regeneration. These latter two topics bring studies of the EP receptors into new and exciting areas of research that are just beginning to be explored. Where there is peer-reviewed literature, the authors have placed particular emphasis on clinical studies although these are limited in number.

Percutaneous Coronary Intervention (PCI) Reprograms Circulating Extracellular Vesicles from ACS Patients Impairing Their Cardio-Protective Properties

Extracellular vesicles (EVs) are promising therapeutic tools in the treatment of cardiovascular disorders. We have recently shown that EVs from patients with Acute Coronary Syndrome (ACS) undergoing sham pre-conditioning, before percutaneous coronary intervention (PCI) were cardio-protective, while EVs from patients experiencing remote ischemic pre-conditioning (RIPC) failed to induce protection against ischemia/reperfusion Injury (IRI). No data on EVs from ACS patients recovered after PCI are currently available. Therefore, we herein investigated the cardio-protective properties of EVs, collected after PCI from the same patients. EVs recovered from 30 patients randomly assigned (1:1) to RIPC (EV-RIPC) or sham procedures (EV-naive) (NCT02195726) were characterized by TEM, FACS and Western blot analysis and evaluated for their mRNA content. The impact of EVs on hypoxia/reoxygenation damage and IRI, as well as the cardio-protective signaling pathways, were investigated in vitro (HMEC-1 + H9c2 co-culture) and ex vivo (isolated rat heart). Both EV-naive and EV-RIPC failed to drive cardio-protection both in vitro and ex vivo. Consistently, EV treatment failed to activate the canonical cardio-protective pathways. Specifically, PCI reduced the EV-naive Dusp6 mRNA content, found to be crucial for their cardio-protective action, and upregulated some stress- and cell-cycle-related genes in EV-RIPC. We provide the first evidence that in ACS patients, PCI reprograms the EV cargo, impairing EV-naive cardio-protective properties without improving EV-RIPC functional capability.

Controlling Reperfusion Injury With Controlled Reperfusion: Historical Perspectives and New Paradigms

Cardiac reperfusion injury is a well-established outcome following treatment of acute myocardial infarction and other types of ischemic heart conditions. Numerous cardioprotection protocols and therapies have been pursued with success in pre-clinical models. Unfortunately, there has been lack of successful large-scale clinical translation, perhaps in part due to the multiple pathways that reperfusion can contribute to cell death. The search continues for new cardioprotection protocols based on what has been learned from past results. One class of cardioprotection protocols that remain under active investigation is that of controlled reperfusion. This class consists of those approaches that modify, in a controlled manner, the content of the reperfusate or the mechanical properties of the reperfusate (e.g., pressure and flow). This review article first provides a basic overview of the primary pathways to cell death that have the potential to be addressed by various forms of controlled reperfusion, including no-reflow phenomenon, ion imbalances (particularly calcium overload), and oxidative stress. Descriptions of various controlled reperfusion approaches are described, along with summaries of both mechanistic and outcome-oriented studies at the pre-clinical and clinical phases. This review will constrain itself to approaches that modify endogenously-occurring blood components. These approaches include ischemic postconditioning, gentle reperfusion, controlled hypoxic reperfusion, controlled hyperoxic reperfusion, controlled acidotic reperfusion, and controlled ionic reperfusion. This review concludes with a discussion of the limitations of past approaches and how they point to potential directions of investigation for the future.

Reconditioning of circulatory death hearts by ex-vivo machine perfusion with a novel HTK-N preservation solution

BACKGROUND

Warm ischemia followed by blood reperfusion is associated with reduced myocardial contractility. Circulatory death (CD) hearts are maintained by machine perfusion (MP) with blood. However, the impact of MP with histidine-tryptophane-ketoglutarate (HTK) or novel HTK-N solution on reconditioning of CD-heart contractility is unknown.

METHODS

In a porcine model, native hearts were directly harvested (control), or CD was induced before harvesting, followed by left ventricular (LV) contractile assessment. In MP-groups, CD-hearts were maintained for 4 h by MP with blood (CD-B), cold oxygenated HTK (CD-HTK) or HTK-N (CD-HTK-N) before contractile evaluation (all groups n = 8). We performed immunohistochemistry of LV myocardial samples. We profiled myocardial expression of 84 oxidative stress-related genes and correlated the findings with myocardial contractility via a machine learning algorithm.

RESULTS

HTK-N improved end-systolic pressure (ESP=172±10 vs 132±5 mmHg, p = 0.02) and maximal slope of pressure increment (dp/dt_max=2161±214 vs 1240±167 mmHg/s, p = 0.005) compared to CD, whereas CD-B failed to improve contractility. Dp/dt_max (2161±214 vs 1177±156, p = 0.08) and maximal rate of pressure decrement (dp/dt_min=-1501±228 vs -637±79, p = 0.005) were also superior in CD-HTK-N compared to CD-B. In CD-HTK-N, myocardial 4-hydroxynonenal (marker for oxidative stress; p<0.001), nitrotyrosine (marker for nitrosative stress; p = 0.004), poly(adenosine diphosphate-ribose)polymerase (marker for necrosis; p = 0.028) immunoreactivity and cell swelling (p = 0.008) were decreased compared to CD-B. Strong correlation of gene expression with ESP was identified for oxidative stress defense genes in CD-HTK-N.

CONCLUSION

During harvesting procedure, MP with HTK-N reconditions CD-heart systolic and diastolic function by reducing oxidative and nitrosative stress and preventing cardiomyocytes from cell swelling and necrosis.

SUPPORT-1 (Subjects Undergoing PCI and Perioperative Reperfusion Treatment): A Prospective, Randomized Trial of CMX-2043 in Patients Undergoing Elective Percutaneous Coronary Intervention

OBJECTIVE

The natural molecule α-lipoic acid has been shown to be partially cytoprotective through antioxidant and antiapoptotic mechanisms. To obtain an initial assessment of the safety and potential efficacy of a synthetic derivative, CMX-2043, in preventing ischemic complications of percutaneous coronary intervention (PCI) we conducted the Subjects Undergoing PCI and Perioperative Reperfusion Treatment (SUPPORT-1) trial, the first patient experience with this agent.

METHODS AND RESULTS

SUPPORT-1 was a phase 2a, 6-center, international, placebo-controlled, randomized, double-blind trial. A total of 142 patients were randomized to receive a single intravenous bolus dose of drug or placebo administered 15-60 minutes before PCI. Cardiac biomarker assessments included serial measurements of creatine kinase myocardial band (CK-MB) at 6, 12, 18, and 24 hours after PCI and a single measurement of troponin T (TnT) at 24 hours. Peak concentrations of CK-MB and TnT were significantly reduced in the 2.4 mg/kg group compared with placebo (P = 0.05 and 0.03, respectively). No subject administered 2.4 mg/kg of CMX-2043 had an increase of CK-MB to ≥3X upper limit of normal versus 16% for placebo (P = 0.02); 16% of the 2.4-mg/kg dose group developed an elevation of TnT to ≥3X upper limit of normal versus 39% in the placebo group (P = 0.05). No drug-related serious adverse events were observed in any group.

CONCLUSION

These data suggest that CMX-2043 may reduce PCI periprocedural myonecrosis and support further clinical evaluation of this novel agent for its potential cytoprotective effects.

The Agonist of Inward Rectifier Potassium Channel (IK1) Attenuates Rat Reperfusion Arrhythmias Linked to CaMKII Signaling

Inward rectifier potassium channels (IK1, Kir) are known to play critical roles in arrhythmogenesis. Thus, how IK1 agonist affects reperfusion arrhythmias needs to be clarified, and its underlying mechanisms should be determined. Reperfusion arrhythmias were modeled by coronary ligation (ischemia, 15 minutes) and release (reperfusion, 15 minutes). Zacopride (1.5-50 μg/kg in vivo, or 0.1-10 μmol/Lex vivo) was applied in the settings of pretreatment (3 minutes before coronary ligation) and posttreatment (5 minutes after coronary ligation). Hypoxia (45 minutes) /reoxygenation (30 minutes) model was established in cultured H9c2 (2-1) cardiomyocytes. Zacopride or KN93 was applied before hypoxia (pretreatment). In the setting of pre- or posttreatment, zacopride at 15 μg/kg in vivo or 1 μmol/Lin vitro exhibited superlative protections on reperfusion arrhythmias or intracellular calcium overload. Western blot data from ex vivo hearts or H9c2 (2-1) cardiomyocytes showed that I/R (H/R) induced the inhibition of Kir2.1 (the dominant subunit of IK1 channel in ventricle), phosphorylation and oxidation of CaMKII, downregulation of SERCA2, phosphorylation of phospholamban (at Thr17), and activation of caspase-3. Zacopride treatment (1 μmol/L) was noted to strikingly restore the expression of Kir2.1 and SERCA2 and decrease the activity of CaMKII, phospholamban, and caspase-3. These effects were largely eliminated by co-application of IK1 blocker BaCl2. CaMKII inhibitor KN93 attenuated calcium overload and p-PLB (Thr17) in an IK1-independent manner. IK1-depedent inhibition of CaMKII activity is found to be a key cardiac salvage signaling under Ca2+ dyshomeostasis and reactive oxygen species (ROS) stress. IK1 might be a novel target for pharmacological conditioning of reperfusion arrhythmia, especially for the application after unpredictable ischemia.

Role of endothelial dysfunction in heart failure

Coronary artery disease is a major underlying etiology for heart failure. The role of coronary microvascular disease, and endothelial dysfunction, in the pathophysiology of heart failure is poorly appreciated. Endothelial dysfunction, induced by oxidative stress, contributes to the development of heart failure. Alterations of endothelial function and nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway are involved in the pathophysiology of heart failure with both reduced and preserved ejection fraction. Indeed, an altered endothelium dependent vasodilatation, causing repeated episodes of ischemia/reperfusion, can induce a chronic stunned myocardium with systolic dysfunction and an increased diastolic stiffness with diastolic dysfunction. Moreover, the altered NO-cGMP pathway directly affects myocardial homeostasis. Endothelial dysfunction is associated with worse prognosis and higher rate of cardiovascular events. Potential therapeutic strategies targeting the NO-cGMP pathway in patients with HF will be discussed in this review article. Although clinical data are still inconclusive, the NO-cGMP pathway represents a promising target for therapy.

Regulation of Nitric Oxide Metabolism and Vascular Tone by Cytoglobin

Significance: Cytoglobin (Cygb) was discovered as a new addition to the globin superfamily and subsequently identified to have potent nitric oxide (NO) dioxygenase function. Cygb plays a critical role in the oxygen-dependent regulation of NO levels and vascular tone. Recent Advances: In recent years, the mechanism of the Cygb-mediated NO dioxygenation has been studied in isolated protein, smooth muscle cell, isolated blood vessel, and in vivo animal model systems. Studies in Cygb^-/- mice have demonstrated that Cygb plays a critical role in regulating blood pressure and vascular tone. This review summarizes advances in the knowledge of NO dioxygenation/metabolism regulated by Cygb. Advances in measurement of NO diffusion dynamics across blood vessels and kinetic modeling of Cygb-mediated NO dioxygenation are summarized. The oxygen-dependent regulation of NO degradation by Cygb is also reviewed along with how Cygb paradoxically generates NO from nitrite under anaerobic conditions. The important role of Cygb in the regulation of vascular function and disease is reviewed. Critical Issues: Cygb is a more potent NO dioxygenase (NOD) than previously known globins with structural differences in heme coordination and environment, conferring it with a higher rate of reduction and more rapid process of NO dioxygenation with unique oxygen dependence. Various cellular reducing systems regenerate the catalytic oxyferrous Cygb species, supporting a high rate of NO dioxygenation. Future Directions: There remains a critical need to further characterize the factors and processes that modulate Cygb-mediated NOD function, and to develop pharmacological or other approaches to modulate Cygb function and expression.

Exosomal lncRNA AK139128 Derived from Hypoxic Cardiomyocytes Promotes Apoptosis and Inhibits Cell Proliferation in Cardiac Fibroblasts

Introduction

Myocardial infarction (MI) is the leading cause of congestive heart failure and mortality. Hypoxia is an important trigger in the cardiac remodeling of the myocardium in the development and progression of cardiac diseases.

Objective

Thus, we aimed to investigate the effect of hypoxia-induced exosomes on cardiac fibroblasts (CFs) and its related mechanisms.

Materials and Methods

In this study, we successfully isolated and identified the exosomes from hypoxic cardiomyocytes (CMs). Exosomes derived from hypoxic CMs promoted apoptosis and inhibited proliferation, migration, and invasion in CFs. RNA-Seq assay suggested that long noncoding RNA AK139128 (lncRNA AK139128) was found to overexpress in both hypoxic CMs and CMs-secreting exosomes. After coculturing with CFs, hypoxic exosomes increased the expression of AK139128 in recipient CFs. Moreover, exosomal AK139128 derived from hypoxic CMs stimulated CFs apoptosis and inhibited proliferation, migration, and invasion. Furthermore, the effect of exosomal AK139128 derived from hypoxic CMs could also exacerbate MI in the rat model.

Conclusion

Taken together, hypoxia upregulated the level of AK139128 in CMs and exosomes and exosomal AK139128 derived from hypoxic CMs modulated cellular activities of CFs in vitro and in vivo. This study provides a new understanding of the mechanism underlying hypoxia-related cardiac diseases and insight into developing new therapeutic strategies.

Unfolded protein response (UPR) integrated signaling networks determine cell fate during hypoxia

During hypoxic conditions, cells undergo critical adaptive responses that include the up-regulation of hypoxia-inducible proteins (HIFs) and the induction of the unfolded protein response (UPR). While their induced signaling pathways have many distinct targets, there are some important connections as well. Despite the extensive studies on both of these signaling pathways, the exact mechanisms involved that determine survival versus apoptosis remain largely unexplained and therefore beyond therapeutic control. Here we discuss the complex relationship between the HIF and UPR signaling pathways and the importance of understanding how these pathways differ between normal and cancer cell models.

Reperfusion injury as a target for diminishing infarct size

Therapies for preventing reperfusion injury (RI) have been widely studied. However, the attempts to transfer cardioprotective therapies for reducing RI from experiments into clinical practice have been so far unsuccessful. Pathophysiological mechanisms of RI are complicated and compose of many pathways e.g. hypercontracture-mediated sarcolemma rupture, mitochondrial permeability transition pore persistent opening, reactive oxygen species formation, inflammation and no-reflow phenomenon. Based on research, it cannot be determined which mechanism dominates, probably they cooperate with a domination of one or another in different clinical circumstances. Our hypothesis is, that only intervention that at the same time interferes with different (all?) pathways of RI may turn out to be effective in decreasing the final area of infarction.

Functional identification of apple MdMYB2 gene in phosphate-starvation response

Inorganic phosphate (Pi) starvation severely affects the normal growth and development of plants. Here, a Pi-responsive gene, named MdMYB2 (MDP0000823458), was cloned and functionally identified in apple. Overexpression of MdMYB2 regulated the expression of Pi starvation-induced (PSI) genes and then promoted phosphate assimilation and utilization. The ectopic expression of MdMYB2 in Arabidopsis influenced plant growth and flowering, which was partially rescued by application of exogenous gibberellin (GA). These results indicated that MdMYB2 may be an essential regulator in phosphate utilization and GA-regulated plant growth and development.

MiR-137-3p exacerbates the ischemia-reperfusion injured cardiomyocyte apoptosis by targeting KLF15

Ischemia-reperfusion (I/R) injury is a kind of the tissue damage caused by an abrupt re-supplying tissue with blood after a period of ischemia or hypoxia. It contributes to a wide range of pathological processes including kidney injury, circulatory arrest, and especially cardiovascular disease. However, the underlying pathological mechanism is not fully elucidated. Previously, extensive studies demonstrated that miRNAs participate in the pathogenesis of I/R injury, such as I/R-induced cardiomyocyte apoptosis. Here, we found that miR-137-3p, a mature form of miR-137, was up-regulated in I/R-injured cardiomyocytes of myocardial infarction patients. Deficiency of miR-137-3p partly alleviated the cardiomyocyte apoptosis and oxidative stress induced by hypoxia-reoxygenation (H/R) treatment in H9c2 cells. Also, we provided evidences that miR-137-3p directly targeted the 3' UTR of KLF15 mRNA to down-regulate its expression, and loss function of KLF15 significantly abolished the deleterious effects of ectopic miR-137-3p on cardiomyocytes both in vitro and in vivo. Collectively, these observations highlight a molecular perturbation in the pathogenesis of I/R injury in cardiomyocytes.

Hype or hope: Vagus nerve stimulation against acute myocardial ischemia-reperfusion injury

Acute myocardial infarction (MI) is a major cause of death worldwide. Although timely and successful reperfusion could reduce myocardial ischemia injury, limit infarct size, and improve ventricular dysfunction and reduce acute mortality, restoring blood flow might also lead to unwanted myocardial ischemic-reperfusion (I/R) injury. Pre-clinical studies have demonstrated that multiple approaches are capable of attenuating the myocardial I/R injury. However, there is still no effective therapy for preventing myocardial I/R injury for the clinical setting. It is known that myocardial I/R injury could induce cardiac autonomic imbalance with over-activated sympathetic tone and reduced vagal activity, in turn, contributing to pathogenesis of myocardial I/R injury. Cumulative evidence shows that the enhancement of vagal activity, so called vagus nerve stimulation (VNS), is able to reduce injury and promote recovery of injured myocardium. Therefore, VNS might be a potentially novel strategy choice for preventing/attenuating myocardial I/R injury. In this review, we describe the protective role of VNS in myocardial I/R injury and related potential mechanisms. Then, we discuss the challenge and the opportunity of VNS in the treatment of acute myocardial I/R injury.

Significant reduction of ischemia-reperfusion cell death in mouse myocardial infarcts using the immediate-acting PrC-210 ROS-scavenger

Managing myocardial infarction (MI) to reduce cardiac cell death relies primarily on timely reperfusion of the affected coronary site, but reperfusion itself induces cell death through a toxic, ROS-mediated process. In this study, we determined whether the PrC-210 aminothiol ROS-scavenger could prevent ROS-induced damage in post-MI hearts. In a series of both in vitro and in vivo experiments, we show that: (a) in vitro, PrC-210 was the most potent and effective ROS-scavenger when functionally compared to eight of the most commonly studied antioxidants in the MI literature, (b) in vitro PrC-210 ROS-scavenging efficacy was both immediate (seconds) and long-lasting (hours), which would make it effective in both (1) real-time (seconds), as post-MI or cardiac surgery hearts are reperfused with PrC-210-containing blood, and (2) long-term (hours), as hearts are bathed with systemic PrC-210 after MI or surgery, (c) systemic PrC-210 caused a significant 36% reduction of mouse cardiac muscle death following a 45-minute cardiac IR insult; in a striking coincidence, the PrC-210 36% reduction in cardiac muscle death equals the 36% of the MI-induced cardiac cell death estimated 6 years ago by Ovize and colleagues to result from "reperfusion injury," (d) hearts in PrC-210-treated mice performed better than controls after heart attacks when functionally analyzed using echocardiography, and (e) the PrC-210 ROS-scavenging mechanism of action was corroborated by its ability to prevent >85% of the direct, H2O2-induced killing of neonate cardiomyocytes in cell culture. PrC-210 does not cause the nausea, emesis, nor hypotension that preclude clinical use of the WR-1065/amifostine aminothiol. PrC-210 is a highly effective ROS-scavenger that significantly reduces IR injury-associated cardiac cell death.

Therapeutic Potential of Salviae Miltiorrhizae Radix et Rhizoma against Human Diseases Based on Activation of Nrf2-Mediated Antioxidant Defense System: Bioactive Constituents and Mechanism of Action

Oxidative stress plays a central role in the pathogenesis of many human diseases. The nuclear factor erythroid 2-related factor 2 (Nrf2) is a key transcription factor regulating the intracellular antioxidant response and is an emerging target for the prevention and therapy of oxidative stress-related diseases. Salviae Miltiorrhizae Radix et Rhizoma (SMRR) is a traditional Chinese medicine (TCM) and is commonly used for the therapy of cardiac cerebral diseases. Cumulative evidences indicated that the extract of SMRR and its constituents, represented by lipophilic diterpenoid quinones and hydrophilic phenolic acids, were capable of activating Nrf2 and inhibiting oxidative stress. These bioactive constituents demonstrated a therapeutic potential against human diseases, exemplified by cardiovascular diseases, neurodegenerative diseases, diabetes, nephropathy, and inflammation, based on the induction of Nrf2-mediated antioxidant response and the inhibition of oxidative stress. In the present review, we introduced the SMRR and Nrf2 signaling pathway, summarized the constituents with an Nrf2-inducing effect isolated from SMRR, and discussed the molecular mechanism and pharmacological functions of the SMRR extract and its constituents.

Dissolved Oxygen Scavenging by Acoustic Droplet Vaporization using Intravascular Ultrasound

Modification of dissolved gas content by acoustic droplet vaporization (ADV) has been proposed for several therapeutic applications. Reducing dissolved oxygen (DO) during reperfusion of ischemic tissue during coronary interventions could inhibit reactive oxygen species production and rescue myocardium. The objective of this study was to determine whether intravascular ultrasound (IVUS) can trigger ADV and reduce DO. Perfluoropentane emulsions were created using high-speed shaking and microfluidic manufacturing. High-speed shaking resulted in a polydisperse droplet distribution ranging from less than 1 micron to greater than 16 microns in diameter. Microfluidic manufacturing produced a narrower size range of droplets with diameters between 8.0 microns and 9.6 microns. The DO content of the fluids was measured before and after ADV triggered by IVUS exposure. Duplex B-mode and passive cavitation imaging was performed to assess nucleation of ADV. An increase in echogenicity indicative of ADV was observed after exposure with a clinical IVUS system. In a flow phantom, a 20% decrease in DO was measured distal to the IVUS transducer when droplets, formed via high-speed shaking, were infused. In a static fluid system, the DO content was reduced by 11% when droplets manufactured with a microfluidic chip were exposed to IVUS. These results demonstrate that a reduction of DO by ADV is feasible using a clinical IVUS system. Future studies will assess the potential therapeutic efficacy of IVUS-nucleated ADV and methods to increase the magnitude of DO scavenging.

Genetic deletion of CD38 confers post-ischemic myocardial protection through preserved pyridine nucleotides

Following the onset of ischemia/reperfusion (I/R), CD38 activation occurs and is associated with depletion of NAD(P)(H) in the heart as well as myocardial injury and endothelial dysfunction. Studies with pharmacological inhibitors suggest that the NADP+-hydrolyzing ability of CD38 can deplete the NAD(P)(H) pools. However, there is a need for more specific studies on the importance of CD38 and its role in the process of endothelial dysfunction and myocardial injury in the post-ischemic heart. Therefore, experiments were performed in hearts of mice with global gene knockout of CD38. Isolated perfused CD38-/- and wild type (WT) mouse hearts were studied to determine the link between CD38 activation, the levels of NADP(H), endothelial dysfunction, and myocardial injury after I/R. Genetic deletion of CD38 preserves the myocardial and endothelial NADP(H) pools compared to WT. Whole heart BH4 levels in CD38-/- hearts were also preserved. Post-ischemic levels of cGMP were greatly depleted in WT hearts, but preserved to near baseline levels in CD38-/- hearts. The preservation of these metabolite pools in CD38-/- hearts was accompanied by near full recovery of NOS-dependent coronary flow, while in WT hearts, severe impairment of endothelial function and NOS uncoupling occurred with decreased NO and enhanced superoxide generation. CD38-/- hearts also exhibited marked protection against I/R with preserved glutathione levels, increased recovery of left ventricular contractile function, decreased myocyte enzyme release, and decreased infarct size. Thus, CD38 activation causes post-ischemic depletion of NADP(H) within the heart, with severe depletion from the endothelium, resulting in endothelial dysfunction and myocardial injury.

Triarylmethyl-based biradical as a superoxide probe

Superoxide radical represents one of the most biologically relevant reactive oxygen species involved in numerous physiological and pathophysiological processes. Superoxide measurement through the decay of an electron paramagnetic resonance (EPR) signal of a triarylmethyl (TAM) radical possesses the advantage of a high selectivity and relatively high rate constant of TAM reaction with the superoxide. Hereby we report a straightforward synthesis and characterization of a TAM-TAM biradical showing a high reactivity with superoxide (second-order rate constant, (6.7 ± 0.2) × 103 M-1 s-1) enabling the measurement of superoxide radical by following the increase of a sharp EPR signal associated with the formation of a TAM-quinone-methide monoradical product.

New and revisited approaches to preserving the reperfused myocardium

Early coronary artery reperfusion improves outcomes for patients with ST-segment elevation myocardial infarction (STEMI), but morbidity and mortality after STEMI remain unacceptably high. The primary deficits seen in these patients include inadequate pump function, owing to rapid infarction of muscle in the first few hours of treatment, and adverse remodelling of the heart in the months that follow. Given that attempts to further reduce myocardial infarct size beyond early reperfusion in clinical trials have so far been disappointing, effective therapies are still needed to protect the reperfused myocardium. In this Review, we discuss several approaches to preserving the reperfused heart, such as therapies that target the mechanisms involved in mitochondrial bioenergetics, pyroptosis, and autophagy, as well as treatments that harness the cardioprotective properties of inhaled anaesthetic agents. We also discuss potential therapies focused on correcting the no-reflow phenomenon and its effect on healing and adverse left ventricular remodelling.

Protective effect of Ginkgo biloba leaves extract, EGb761, on myocardium injury in ischemia reperfusion rats via regulation of TLR-4/NF-κB signaling pathway

Beneficial actions of EGb 761 against ischemia/reperfusion (I/R) injury in lung, brain and renal ischemia have been described. However, the relationship between EGb 761 and signal molecules in myocardial ischemia reperfusion has not been well elucidated. In this study, we investigated the effects and mechanism of EGb 761 preconditioning on anti-myocardial I/R injuries in vivo. Meanwhile, their potential anti-oxidative stress and anti-inflammation effect were assessed. Hemodynamic parameters were monitored as left ventricular systolic pressure, LV end-diastolic pressure and maximal rate of increase and decrease of left ventricular pressure (dP/dtmax). The oxidative stress indicators and inflammatory factors were also evaluated. Western blot method was used for analysis of toll-like receptor 4 (TLR4), p-TLR4, nuclear factor-κB (NF-κB), p-NF-κB p65, Bax and Bcl-2 protein expressions. EGb 761 significantly improved cardiac function, decreased levels of creatine kinase, aspartate aminotransferase and lactate dehydrogenase. EGb 761 also restrained the oxidative stress related to myocardial ischemia injury as evidenced by decreased malondialdehyde, superoxide dismutase, catalase, glutathione-peroxidase, glutathione reductase activity. Meanwhile, the inflammatory cascade was inhibited as evidenced by decreased cytokines such as tumor necrosis factor-α, interleukin-6 and interleukin-1β. Our results still showed that EGb 761 pretreatment significantly decrease the level of cleaved Bax, and increase the level of Bcl-2 in rats subjected to I/R injury. Simultaneously, the expressions of myocardial TLR4 and NF-κB were significantly decreased. It can be concluded that EGb 761 pretreatment was protected against myocardium I/R injury by decreasing oxidative stress, repressing inflammatory cascade in vivo and inhibiting TLR4/NF-κB pathway.

MicroRNA-126a-5p enhances myocardial ischemia-reperfusion injury through suppressing Hspb8 expression

Previously, we found several genes are involved in myocardial ischemia-reperfusion (M-I/R) injury. In this report, we first developed a mouse model of M-I/R injury and demonstrated microRNA-126a-5p was associated with the M-I/R injury by using high-throughput microRNA expression analysis. We further investigated the expression and function of microRNA-126a-5p during mouse M-I/R injury. We observed high expression of microRNA-126a-5p in the M-I/R mice and increased levels of LDH and CK-MB (damage markers) in the serum. H₂O₂ and hypoxia/reoxygenation (H/R) treatment significantly increased the expression of microRNA-126a-5p in H9C2 cells in concentration- and time-dependent manners. Moreover, microRNA-126a-5p overexpression in H9C2 cells inhibited cell viability but increased LDH release and caspase 3 activity. Cardiac function analysis based on the measurements of hemodynamic parameters showed that microRNA-126a-5p expression ablation in M-I/R injured mice led to the reversal of the symptoms caused by M-I/R injury. Transesophageal echocardiography also revealed that the values of LVIDd and LVIDs were decreased while the values of LVFS% and LVEF% were increased in M-I/R injured mice after treatment with microRNA-126a-5p inhibitor, compared with the M-I/R injured mice treated with the control. Bioinformatic analysis demonstrated that Hspb8, a protective protein in myocardium, was the target of microRNA-126a-5p. Thus, these findings indicated that microRNA-126a-5p was up-regulated in mouse M-I/R model and promoted M-I/R injury in vivo through suppressing the expression of Hspb8, which may shed light on the development of potential therapeutic target for M-I/R injury.

Image-Guided Hydrogen Gas Delivery for Protection from Myocardial Ischemia-Reperfusion Injury via Microbubbles

Cardiomyocyte death induced by ischemia-reperfusion is a major cause of morbidity and mortality worldwide. Hydrogen (H₂), as an antioxidant, has been shown to have great potential in preventive and therapeutic applications against lethal injury that occurs from ischemia-reperfusion. However, H₂ is sparingly soluble in water, resulting in its poor bioavailability in blood and damaged tissues. Here, we have developed an ultrasound-visible H₂ delivery system by loading H₂ inside microbubbles (H₂-MBs) to prevent myocardial ischemia-reperfusion injury. Using this system, the concentration of H₂ in unit volume can be greatly improved under normal temperature and pressure conditions. H₂-MBs can be visually tracked with ultrasound imaging systems and can effectively release their therapeutic gas. In vivo systemic delivery of H₂-MBs in myocardial ischemic rats at the start of reperfusion resulted in a significant reduction of infarct size and pathological remodeling. Further analysis showed that this approach markedly inhibited cardiomyocyte apoptosis and reduced myocardial inflammation and oxidant damage in myocardial ischemia-reperfusion rats. These results indicate that H₂-MBs are a promising visual delivery system for H₂-based therapeutic applications.

Cardioprotective Effect of Aloe vera Biomacromolecules Conjugated with Selenium Trace Element on Myocardial Ischemia-Reperfusion Injury in Rats

The present study was undertaken to evaluate the cardioprotection potential and underlying molecular mechanism afforded by a selenium (Se) polysaccharide (Se-AVP) from Aloe vera in the ischemia-reperfusion (I/R) model of rats in vivo. Myocardial I/R injury was induced by occluding the left anterior descending coronary artery (LAD) for 30 min followed by 2-h continuous reperfusion. Pretreatment with Se-AVP (100, 200, and 400 mg/kg) attenuated myocardial damage, as evidenced by reduction of the infarct sizes, increase in serum and myocardial endogenous antioxidants (superoxide dismutase (SOD), glutathione peroxidase (GSH), and catalase (CAT)), and decrease in the malondialdehyde (MDA) level in the rats suffering I/R injury. This cardioprotective activity afforded by Se-AVP is further supported by the decreased levels of cardiac marker enzymes creatine kinase (CK) and lactate dehydrogenase (LDH), as well as the rise of myocardial Na⁺-K⁺-ATPase and Ca²⁺-Mg²⁺-ATPase activities in I/R rats. Additionally, cardiomyocytic apoptosis was measured by terminal-deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) staining and the result showed that the percent of TUNEL-positive cells in myocardium of Se-AVP-treated groups was lower than I/R rats. In conclusion, we clearly demonstrated that Se-AVP had a protective effect against myocardial I/R injury in rats by augmenting endogenous antioxidants and protecting rat hearts from oxidative stress-induced myocardial apoptosis.

New aspects of p66Shc in ischaemia reperfusion injury and other cardiovascular diseases

Although reactive oxygen species (ROS) act as crucial factors in the onset and progression of a wide array of diseases, they are also involved in numerous signalling pathways related to cell metabolism, growth and survival. ROS are produced at various cellular sites, and it is generally agreed that mitochondria generate the largest amount, especially those in cardiomyocytes. However, the identification of the most relevant sites within mitochondria, the interaction among the various sources, and the events responsible for the increase in ROS formation under pathological conditions are still highly debated, and far from being clarified. Here, we review the information linking the adaptor protein p66Shc with cardiac injury induced by ischaemia and reperfusion (I/R), including the contribution of risk factors, such as metabolic syndrome and ageing. In response to several stimuli, p66Shc migrates into mitochondria where it catalyses electron transfer from cytochrome c to oxygen resulting in hydrogen peroxide formation. Deletion of p66Shc has been shown to reduce I/R injury as well as vascular abnormalities associated with diabetes and ageing. However, p66Shc-induced ROS formation is also involved in insulin signalling and might contribute to self-endogenous defenses against mild I/R injury. In addition to its role in physiological and pathological conditions, we discuss compounds and conditions that can modulate the expression and activity of p66Shc.

LINKED ARTICLES

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

Parathyroid Hormone-Related Peptide: A Novel Endocrine Cardioprotective "Conditioning Mimetic"

An as-yet limited body of evidence suggests that calcium-regulating endocrine hormones-in particular, parathyroid hormone-related peptide (PTHrP)-may have unappreciated cardioprotective effects. The current review focuses on the concept that PTHrP may, via modulation of classic cardioprotective signaling pathways, provide a novel strategy to attenuate myocardial ischemia-reperfusion injury.

Preventive and therapeutic application of molecular hydrogen in situations with excessive production of free radicals

Excessive production of oxygen free radicals has been regarded as a causative common denominator of many pathological processes in the animal kingdom. Hydroxyl and nitrosyl radicals represent the major cause of the destruction of biomolecules either by a direct reaction or by triggering a chain reaction of free radicals. Scavenging of free radicals may act preventively or therapeutically. A number of substances that preferentially react with free radicals can serve as scavengers, thus increasing the internal capacity/activity of endogenous antioxidants and protecting cells and tissues against oxidative damage. Molecular hydrogen (H(2)) reacts with strong oxidants, such as hydroxyl and nitrosyl radicals, in the cells, that enables utilization of its potential for preventive and therapeutic applications. H(2) rapidly diffuses into tissues and cells without affecting metabolic redox reactions and signaling reactive species. H(2) reduces oxidative stress also by regulating gene expression, and functions as an anti-inflammatory and anti-apoptotic agent. There is a growing body of evidence based on the results of animal experiments and clinical observations that H(2) may represent an effective antioxidant for the prevention of oxidative stress-related diseases. Application of molecular hydrogen in situations with excessive production of free radicals, in particular, hydroxyl and nitrosyl radicals is relatively simple and effective, therefore, it deserves special attention.

The Nrf2/Keap1/ARE Pathway and Oxidative Stress as a Therapeutic Target in Type II Diabetes Mellitus

Despite improvements in awareness and treatment of type II diabetes mellitus (TIIDM), this disease remains a major source of morbidity and mortality worldwide, and prevalence continues to rise. Oxidative damage caused by free radicals has long been known to contribute to the pathogenesis and progression of TIIDM and its complications. Only recently, however, has the role of the Nrf2/Keap1/ARE master antioxidant pathway in diabetic dysfunction begun to be elucidated. There is accumulating evidence that this pathway is implicated in diabetic damage to the pancreas, heart, and skin, among other cell types and tissues. Animal studies and clinical trials have shown promising results suggesting that activation of this pathway can delay or reverse some of these impairments in TIIDM. In this review, we outline the role of oxidative damage and the Nrf2/Keap1/ARE pathway in TIIDM, focusing on current and future efforts to utilize this relationship as a therapeutic target for prevention, prognosis, and treatment of TIID.

Measurement of Reactive Oxygen Species, Reactive Nitrogen Species, and Redox-Dependent Signaling in the Cardiovascular System: A Scientific Statement From the American Heart Association

Reactive oxygen species and reactive nitrogen species are biological molecules that play important roles in cardiovascular physiology and contribute to disease initiation, progression, and severity. Because of their ephemeral nature and rapid reactivity, these species are difficult to measure directly with high accuracy and precision. In this statement, we review current methods for measuring these species and the secondary products they generate and suggest approaches for measuring redox status, oxidative stress, and the production of individual reactive oxygen and nitrogen species. We discuss the strengths and limitations of different methods and the relative specificity and suitability of these methods for measuring the concentrations of reactive oxygen and reactive nitrogen species in cells, tissues, and biological fluids. We provide specific guidelines, through expert opinion, for choosing reliable and reproducible assays for different experimental and clinical situations. These guidelines are intended to help investigators and clinical researchers avoid experimental error and ensure high-quality measurements of these important biological species.

Intravenous delivery of adeno-associated virus 9-encoded IGF-1Ea propeptide improves post-infarct cardiac remodelling

The insulin-like growth factor Ea propeptide (IGF-1Ea) is a powerful enhancer of cardiac muscle growth and regeneration, also blocking age-related atrophy and beneficial in multiple skeletal muscle diseases. The therapeutic potential of IGF-1Ea compared with mature IGF-1 derives from its local action in the area of synthesis. We have developed an adeno-associated virus (AAV) vector for IGF-1Ea delivery to the heart to treat mice after myocardial infarction and examine the reparative effects of local IGF-1Ea production on left ventricular remodelling. A cardiotropic AAV9 vector carrying a cardiomyocyte-specific IGF-1Ea-luciferase bi-cistronic gene expression cassette (AAV9.IGF-1Ea) was administered intravenously to infarcted mice, 5 h after ischemia followed by reperfusion (I/R), as a model of myocardial infarction. Virally encoded IGF-1Ea in the heart improved global left ventricular function and remodelling, as measured by wall motion and thickness, 28 days after delivery, with higher viral titers yielding better improvement. The present study demonstrates that single intravenous AAV9-mediated IGF-1Ea Gene Therapy represents a tissue-targeted therapeutic approach to prevent the adverse remodelling after myocardial infarct.

Sulfite Oxidase Activity of Cytochrome c: Role of Hydrogen Peroxide

In humans, sulfite is generated endogenously by the metabolism of sulfur containing amino acids such as methionine and cysteine. Sulfite is also formed from exposure to sulfur dioxide, one of the major environmental pollutants. Sulfite is used as an antioxidant and preservative in dried fruits, vegetables, and beverages such as wine. Sulfite is also used as a stabilizer in many drugs. Sulfite toxicity has been associated with allergic reactions characterized by sulfite sensitivity, asthma, and anaphylactic shock. Sulfite is also toxic to neurons and cardiovascular cells. Recent studies suggest that the cytotoxicity of sulfite is mediated by free radicals; however, molecular mechanisms involved in sulfite toxicity are not fully understood. Cytochrome c (cyt c) is known to participate in mitochondrial respiration and has antioxidant and peroxidase activities. Studies were performed to understand the related mechanism of oxidation of sulfite and radical generation by ferric cytochrome c (Fe³⁺cyt c) in the absence and presence of H₂O₂. Electron paramagnetic resonance (EPR) spin trapping studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were performed with sulfite, Fe³⁺cyt c, and H₂O₂. An EPR spectrum corresponding to the sulfite radical adducts of DMPO (DMPO-SO₃^-) was obtained. The amount of DMPO-SO3- formed from the oxidation of sulfite by the Fe³⁺cyt c increased with sulfite concentration. In addition, the amount of DMPO-SO3- formed by the peroxidase activity of Fe³⁺cyt c also increased with sulfite and H₂O₂ concentration. From these results, we propose a mechanism in which the Fe³⁺cyt c and its peroxidase activity oxidizes sulfite to sulfite radical. Our results suggest that Fe³⁺cyt c could have a novel role in the deleterious effects of sulfite in biological systems due to increased production of sulfite radical. It also shows that the increased production of sulfite radical may be responsible for neurotoxicity and some of the injuries which occur to humans born with molybdenum cofactor and sulfite oxidase deficiencies.

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Cytochrome c oxidizes sulfite to sulfite radical.

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In the presence of H₂O₂, sulfite radical generation from cyt c increases.

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The formation of sulfite radical is sulfite concentration dependent.

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This mechanism of sulfite radical formation may be important in sulfite toxicity.

The potential of the novel leukocyte removal filter in cardiopulmonary bypass

Cardiopulmonary bypass (CPB) is indispensable for cardiac surgery but leads to systemic inflammatory responses and leukocyte activation, possibly due to blood contact with the surface of the CPB unit, surgical, ischemic reperfusion injury, etc. Systemic inflammatory responses during CPB result in increased morbidity and mortality. Activation of leukocytes is an important part of this process and directly contributes to coagulopathy and hemorrhage. This inflammatory response may contribute to the development of postoperative complications, including myocardial dysfunction, respiratory failure, renal and neurologic dysfunction, altered liver function and ultimately, multiple organ failure. Various pharmacologic and mechanical strategies have been developed to minimize the systemic inflammatory response during CPB. For example, leukocyte removal filters were developed in the 1990s for incorporation into the CPB circuit. However, studies of this approach have yielded conflicting findings. The purpose of this was to review the studies of a novel leukocyte removal filter in patients undergoing CPB.

Mitochondrial translocator protein (TSPO): From physiology to cardioprotection

The mitochondrial translocator protein (TSPO) is a high affinity cholesterol binding protein which is primarily located in the outer mitochondrial membrane where it has been shown to interact with proteins implicated in mitochondrial permeability transition pore (mPTP) formation. TSPO is found in different species and is expressed at high levels in tissues that synthesize steroids but is also present in other peripheral tissues especially in the heart. TSPO has been involved in the import of cholesterol into mitochondria, a key step in steroidogenesis. This constitutes the main established function of the protein which was recently challenged by genetic studies. TSPO has also been associated directly or indirectly with a wide range of cellular functions such as apoptosis, cell proliferation, differentiation, regulation of mitochondrial function or porphyrin transport. In the heart the role of TSPO remains undefined but a growing body of evidence suggests that TSPO plays a critical role in regulating physiological cardiac function and that TSPO ligands may represent interesting drugs to protect the heart under pathological conditions. This article briefly reviews current knowledge regarding TSPO and discusses its role in the cardiovascular system under physiological and pathologic conditions. More particularly, it provides evidence that TSPO can represent an alternative strategy to develop new pharmacological agents to protect the myocardium against ischemia-reperfusion injury.

Parathyroid hormone-related peptide protects cardiomyocytes from oxidative stress-induced cell death: First evidence of a novel endocrine-cardiovascular interaction

Although there is a growing interest in the molecular cross-talk between the endocrine and cardiovascular systems, the cardiac effects of calcium-regulating hormones (i.e., parathyroid hormone-related peptide (PTHrP)) have not been explored. In this study, we examined the effect of PTHrP on the viability of isolated adult mouse cardiomyocytes subjected to oxidative stress. Myocytes from 19 to 22 week old male 129J/C57BL6 mice were exposed to oxidative insult in the form of H2O2 which led to more than 70% loss of cell viability. Herein we demonstrate, for the first time, that pretreatment with 100 nM PTHrP prior to 100 μM H2O2 incubation prevents H2O2 -induced cell death by more than 50%. Immunoblot analysis revealed H2O2 induction of MKP-1 protein expression while PTHrP decreased MKP-1 expression. Moreover, myocytes derived from MKP1 KO mice were resistant to oxidative injury. No added benefit of PTHrP treatment was noted in MKP-1 null cardiomyocytes. Using specific pharmacological inhibitors we demonstrated that P-p38, P-ERK and P-AKT mediated PTHrP's cardioprotective action. These data provide novel evidence that: i) down-regulation of MKP1 affords profound protection against oxidative stress; and ii) PTHrP is cardioprotective, possibly via down-regulation of MKP-1 and activation of MAPK and PI3K/AKT signaling.

Reactive oxygen species-activated nanomaterials as theranostic agents

Reactive oxygen species (ROS) are generated from the endogenous oxidative metabolism or from exogenous pro-oxidant exposure. Oxidative stress occurs when there is excessive production of ROS, outweighing the antioxidant defense mechanisms which may lead to disease states. Hydrogen peroxide (H2O2) is one of the most abundant and stable forms of ROS, implicated in inflammation, cellular dysfunction and apoptosis, which ultimately lead to tissue and organ damage. This review is an overview of the role of ROS in different diseases. We will also examine ROS-activated nanomaterials with emphasis on hydrogen peroxide, and their potential medical implications. Further development of the biocompatible, stimuli-activated agent responding to disease causing oxidative stress, may lead to a promising clinical use.

Liposomal tetrahydrobiopterin preserves eNOS coupling in the post-ischemic heart conferring in vivo cardioprotection

Tetrahydrobiopterin (BH4) is an essential cofactor of nitric oxide synthase (NOS), and reduced BH4 availability leads to endothelial NOS (eNOS) uncoupling and increased reactive oxygen species (ROS) generation. Questions remain regarding the functional state of eNOS and role of BH4 availability in the process of in vivo myocardial ischemia-reperfusion (I/R) injury. Rats were subjected to 60min of in vivo left coronary artery occlusion and varying periods of reperfusion with or without pre-ischemic liposomal BH4 supplementation (1mg/kg, iv). Myocardial infarction was correlated with cardiac BH4 content, eNOS protein level, NOS enzyme activity, and ROS generation. In the vehicle group, 60-min ischemia drastically reduced myocardial BH4 content in the area at risk (AAR) compared to non-ischemic (NI) area and the level remained lower during early reperfusion followed by recovery after 24-h reperfusion. Total eNOS, activated eNOS protein level (eNOS Ser1177 phosphorylation) and NOS activity were also significantly reduced during ischemia and/or early reperfusion, but recovered after 24-h reperfusion. With liposomal BH4 treatment, BH4 levels were identical in the AAR and NI area during ischemia and/or early reperfusion, and were significantly higher than with vehicle. BH4 pre-treatment preserved eNOS Ser1177 phosphorylation and NOS activity in the AAR, and significantly reduced myocardial ROS generation and infarction compared to vehicle. These findings provide direct evidence that in vivo I/R induces eNOS dysfunction secondary to BH4 depletion, and that pre-ischemic liposomal BH4 administration preserves eNOS function conferring cardioprotection with reduced oxidative stress.

Targeted intracellular accumulation of macrophage migration inhibitory factor in the reperfused heart mediates cardioprotection

S-nitrosation of macrophage migration inhibitory factor (MIF) has been shown to be cytoprotective in myocardial ischaemia/reperfusion (I/R) injury. Since the exact mechanism of action is unknown, we here characterise the cardioprotective effects of targeted intracellular accumulation of MIF in myocardial I/R injury. We used different in vivo, ex vivo and in vitro models of myocardial I/R and hypoxia/reoxygenation (H/R) injury to determine MIF levels by immunoblots and ELISA in different phases of reperfusion and reoxygenation, respectively. We discovered a rapid decrease of cardiac MIF that was specific to the early phase of reperfusion. Posttranslational modification of MIF via S-nitrosation--proofed by a modified version of the Biotin Switch Assay--prevented this rapid decrease, leading to a targeted intracellular accumulation of MIF in the early phase of reperfusion. Intracellular MIF accumulation preserved the intracellular ability of MIF to reduce oxidative stress as shown by hydrogen peroxide and aconitase activity measurements. Infarct size measurements by TTC staining showed an overall enhanced cardioprotective effect of this protein by reduction of reperfusion injury. In summary, we have unravelled a novel mechanism of MIF-mediated cardioprotection. Targeted intracellular accumulation of MIF by S-nitrosation may offer a novel therapeutic approach in the treatment of myocardial I/R-injury.

Mitochondrial dynamics in diabetic cardiomyopathy

SIGNIFICANCE

Cardiac function is energetically demanding, reliant on efficient well-coupled mitochondria to generate adenosine triphosphate and fulfill the cardiac demand. Predictably then, mitochondrial dysfunction is associated with cardiac pathologies, often related to metabolic disease, most commonly diabetes. Diabetic cardiomyopathy (DCM), characterized by decreased left ventricular function, arises independently of coronary artery disease and atherosclerosis. Dysregulation of Ca(2+) handling, metabolic changes, and oxidative stress are observed in DCM, abnormalities reflected in alterations in mitochondrial energetics. Cardiac tissue from DCM patients also presents with altered mitochondrial morphology, suggesting a possible role of mitochondrial dynamics in its pathological progression.

RECENT ADVANCES

Abnormal mitochondrial morphology is associated with pathologies across diverse tissues, suggesting that this highly regulated process is essential for proper cell maintenance and physiological homeostasis. Highly structured cardiac myofibers were hypothesized to limit alterations in mitochondrial morphology; however, recent work has identified morphological changes in cardiac tissue, specifically in DCM.

CRITICAL ISSUES

Mitochondrial dysfunction has been reported independently from observations of altered mitochondrial morphology in DCM. The temporal relationship and causative nature between functional and morphological changes of mitochondria in the establishment/progression of DCM is unclear.

FUTURE DIRECTIONS

Altered mitochondrial energetics and morphology are not only causal for but also consequential to reactive oxygen species production, hence exacerbating oxidative damage through reciprocal amplification, which is integral to the progression of DCM. Therefore, targeting mitochondria for DCM will require better mechanistic characterization of morphological distortion and bioenergetic dysfunction.

Interaction between neuronal nitric oxide synthase signaling and temperature influences sarcoplasmic reticulum calcium leak: role of nitroso-redox balance

RATIONALE

Although nitric oxide (NO) signaling modulates cardiac function and excitation-contraction coupling, opposing results because of inconsistent experimental conditions, particularly with respect to temperature, confound the ability to elucidate NO signaling pathways. Here, we show that temperature significantly modulates NO effects.

OBJECTIVE

To test the hypothesis that temperature profoundly affects nitroso-redox equilibrium, thereby affecting sarcoplasmic reticulum (SR) calcium (Ca(2+)) leak.

METHODS AND RESULTS

We measured SR Ca(2+) leak in cardiomyocytes from wild-type (WT), NO/redox imbalance (neuronal nitric oxide synthase-deficient mice-1 [NOS1(-/-)]), and hyper S-nitrosoglutathione reductase-deficient (GSNOR(-/-)) mice. In WT cardiomyocytes, SR Ca(2+) leak increased because temperature decreased from 37°C to 23°C, whereas in NOS1(-/-) cells, the leak suddenly increased when the temperature surpassed 30°C. GSNOR(-/-) cardiomyocytes exhibited low leak throughout the temperature range. Exogenously added NO had a biphasic effect on NOS1(-/-) cardiomyocytes; reducing leak at 37°C but increasing it at subphysiological temperatures. Oxypurinol and Tempol diminished the leak in NOS1(-/-) cardiomyocytes. Cooling from 37°C to 23°C increased reactive oxygen species generation in WT but decreased it in NOS1(-/-) cardiomyocytes. Oxypurinol further reduced reactive oxygen species generation. At 23°C in WT cells, leak was decreased by tetrahydrobiopterin, an essential NOS cofactor. Cooling significantly increased SR Ca(2+) content in NOS1(-/-) cells but had no effect in WT or GSNOR(-/-).

CONCLUSIONS

Ca(2+) leak and temperature are normally inversely proportional, whereas NOS1 deficiency reverses this effect, increasing leak and elevating reactive oxygen species production because temperature increases. Reduced denitrosylation (GSNOR deficiency) eliminates the temperature dependence of leak. Thus, temperature regulates the balance between NO and reactive oxygen species which in turn has a major effect on SR Ca(2+).

Mitochondrial DNA damage and repair during ischemia-reperfusion injury of the heart

Ischemia-reperfusion (IR) injury of the heart generates reactive oxygen species that oxidize macromolecules including mitochondrial DNA (mtDNA). The 8-oxoguanine DNA glycosylase (OGG1) works synergistically with MutY DNA glycosylase (MYH) to maintain mtDNA integrity. Our objective was to study the functional outcome of lacking the repair enzymes OGG1 and MYH after myocardial IR and we hypothesized that OGG1 and MYH are important enzymes to preserve mtDNA and heart function after IR. Ex vivo global ischemia for 30min followed by 10min of reperfusion induced mtDNA damage that was removed within 60min of reperfusion in wild-type mice. After 60min of reperfusion the ogg1(-/-) mice demonstrated increased mtDNA copy number and decreased mtDNA damage removal suggesting that OGG1 is responsible for removal of IR-induced mtDNA damage and copy number regulation. mtDNA damage was not detected in the ogg1(-/-)/myh(-/-), inferring that adenine opposite 8-oxoguanine is an abundant mtDNA lesion upon IR. The level and integrity of mtDNA were restored in all genotypes after 35min of regional ischemia and six week reperfusion with no change in cardiac function. No consistent upregulation of other mitochondrial base excision repair enzymes in any of our knockout models was found. Thus repair of mtDNA oxidative base lesions may not be important for maintenance of cardiac function during IR injury in vivo. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease."

Measurement and characterization of superoxide generation from xanthine dehydrogenase: a redox-regulated pathway of radical generation in ischemic tissues

The enzyme xanthine oxidoreductase (XOR) is an important source of oxygen free radicals and related postischemic injury. Xanthine dehydrogenase (XDH), the major form of XOR in tissues, can be converted to xanthine oxidase (XO) by oxidation of sulfhydryl residues or by proteolysis. The conversion of XDH to XO has been assumed to be required for radical generation and tissue injury. It is also possible that XDH could generate significant quantities of superoxide, ^•O₂^–, for cellular signaling or injury; however, this possibility and its potential ramifications have not been previously considered. To unambiguously determine if XDH can be a significant source of ^•O₂^–, experiments were performed to measure and characterize ^•O₂^– generation using XDH from chicken liver that is locked in the dehydrogenase conformation. Electron paramagnetic resonance spin trapping experiments with 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide demonstrated that XDH in the presence of xanthine produces significant amounts of ^•O₂^–. NAD⁺ and NADH inhibited the generation of ^•O₂^– from XDH in a dose-dependent manner, with NAD⁺ exhibiting stronger inhibition than NADH at low physiological concentrations. Decreased amounts of NAD⁺ and NADH, which occur during and following tissue ischemia, enhanced the generation of ^•O₂^– from XDH in the presence of xanthine. It was observed that XDH-mediated oxygen radical generation markedly depressed Ca²⁺-ATPase activity of isolated sarcoplasmic reticulum vesicles from cardiac muscle, and this was modulated by NAD⁺ and NADH. Thus, XDH can be an important redox-regulated source of ^•O₂^– generation in ischemic tissue, and conversion to XO is not required to activate radical formation and subsequent tissue injury.