To prevent, protect and save the ischemic heart: antioxidants revisited

Myocardial Ischemia-Reperfusion Injury: Unraveling Pathophysiology, Clinical Manifestations, and Emerging Prevention Strategies

Myocardial ischemia-reperfusion injury (MIRI) remains a challenge in the context of reperfusion procedures for myocardial infarction (MI). While early revascularization stands as the gold standard for mitigating myocardial injury, recent insights have illuminated the paradoxical role of reperfusion, giving rise to the phenomenon known as ischemia-reperfusion injury. This comprehensive review delves into the intricate pathophysiological pathways involved in MIRI, placing a particular focus on the pivotal role of endothelium. Beyond elucidating the molecular intricacies, we explore the diverse clinical manifestations associated with MIRI, underscoring its potential to contribute substantially to the final infarct size, up to 50%. We further navigate through current preventive approaches and highlight promising emerging strategies designed to counteract the devastating effects of the phenomenon. By synthesizing current knowledge and offering a perspective on evolving preventive interventions, this review serves as a valuable resource for clinicians and researchers engaged in the dynamic field of MIRI.

Protective role of nitric oxide donors on endothelium in ischemia-reperfusion injury: a meta-analysis of randomized controlled trials

BACKGROUND

Decreased bioavailability of nitric oxide (NO) under hypoxic conditions can lead to endothelial dysfunction. NO supplementation may protect endothelial function in ischemia-reperfusion (IR) injury. Therefore, a meta-analysis of randomized controlled trials (RCTs) was performed to verify the protective effect of NO donors on endothelium in IR injury.

METHODS

Medline, Embase, Cochrane Library, and Web of Science databases were searched from inception to April 1, 2023. The specific inclusion criteria were as follows: (1) RCTs; (2) trials comparing NO donors with placebo control groups; and (3) trials reporting the effects of these interventions on vascular endothelial functional outcomes in IR injury. Random-effects models were used to assess pooled effect sizes, which were expressed as standardized mean differences (SMD).

RESULTS

Seven studies satisfied the inclusion criteria and consisted of a total of 149 participants. NO donors were protective of endothelial function in IR injury (SMD: - 1.60; 95% confidence interval [CI]: - 2.33, - 0.88, P < 0.0001; heterogeneity [I² = 66%, P = 0.001]). Results of the subgroup analysis showed the following: absence of protective effect of NO donor use following ischemia on endothelial function in IR injury - 1.78 (95% CI: - 2.50, - 1.07) and loss of protective effect on endothelial function after prolonged NO donor use - 0.89 (95% CI: - 2.06, 0.28).

CONCLUSION

The short-period use of NO donors before the onset of ischemia can protect endothelial function in IR injury.

Melatonin ameliorates myocardial infarction in obese diabetic individuals: The possible involvement of macrophage apoptotic factors

In recent days, the hike in obesity-mediated epidemics across the globe and the prevalence of obesity-induced cardiovascular disease has become one of the chief grounds for morbidity and mortality. This epidemic-driven detrimental events in the cardiac tissues start with the altered distribution and metabolism pattern of high-density lipoprotein and low-density lipoprotein (LDL) leading to cholesterol (oxidized LDL) deposition on the arterial wall and atherosclerotic plaque generation, followed by vascular spasms and infarction. Subsequently, obesity-triggered metabolic malfunctions induce free radical generation which may further trigger pro-inflammatory signaling and nuclear factor kappa-light-chain-enhancer of activated B cells transcriptional factor, thus inducing interferon-gamma, tumor necrosis factor-alpha, and inducible nitric oxide synthase. This terrifying cardiomyopathy can be further aggravated in type 2 diabetes mellitus, thereby making obese diabetic patients prone toward the development of myocardial infarction (MI) or stroke in comparison to their nondiabetic counterparts. The accelerated oxidative stress and pro-inflammatory response induced cardiomyocyte hypertrophy, followed by apoptosis in obese diabetic individuals, causing progression of athero-thrombotic vascular disease. Being an efficient antioxidative and anti-inflammatory indolamine, melatonin effectively inhibits lipid peroxidation, pro-inflammatory reactions, thereby resolving free radical-induced myocardial damages along with maintaining antioxidant reservoir to preserve cardiovascular integrity. Prolonged melatonin treatment maintains balanced body weight and serum total cholesterol concentration by inhibiting cholesterol synthesis and promoting cholesterol catabolism. Additionally, melatonin promotes macrophage polarization toward the anti-inflammatory state, providing a proper shield during the recovery period. Therefore, the protective role of melatonin in maintaining the lipid metabolism homeostasis and blocking the atherosclerotic plaque rupture could be targeted as the possible therapeutic strategy for the management of obesity-induced acute MI. This review aimed at orchestrating the efficacy of melatonin in ameliorating irrevocable oxidative cardiovascular damage induced by the obesity-diabetes correlation.

Alternative autophagy: mechanisms and roles in different diseases

As an important mechanism to maintain cellular homeostasis, autophagy exerts critical functions via degrading misfolded proteins and damaged organelles. Recent years, alternative autophagy, a new type of autophagy has been revealed, which shares similar morphology with canonical autophagy but is independent of Atg5/Atg7. Investigations on different diseases showed the pivotal role of alternative autophagy during their physio-pathological processes, including heart diseases, neurodegenerative diseases, oncogenesis, inflammatory bowel disease (IBD), and bacterial infection. However, the studies are limited and the precise roles and mechanisms of alternative autophagy are far from clear. It is necessary to review current research on alternative autophagy and get some hint in order to provide new insight for further study. Video Abstract.

Implications of Oxidative and Nitrosative Post-Translational Modifications in Therapeutic Strategies against Reperfusion Damage

Post-translational modifications based on redox reactions "switch on-off" the biological activity of different downstream targets, modifying a myriad of processes and providing an efficient mechanism for signaling regulation in physiological and pathological conditions. Such modifications depend on the generation of redox components, such as reactive oxygen species and nitric oxide. Therefore, as the oxidative or nitrosative milieu prevailing in the reperfused heart is determinant for protective signaling, in this review we defined the impact of redox-based post-translational modifications resulting from either oxidative/nitrosative signaling or oxidative/nitrosative stress that occurs during reperfusion damage. The role that cardioprotective conditioning strategies have had to establish that such changes occur at different subcellular levels, particularly in mitochondria, is also presented. Another section is devoted to the possible mechanism of signal delivering of modified proteins. Finally, we discuss the possible efficacy of redox-based therapeutic strategies against reperfusion damage.

Barth syndrome cardiomyopathy: targeting the mitochondria with elamipretide

Barth syndrome (BTHS) is a rare, X-linked recessive, infantile-onset debilitating disorder characterized by early-onset cardiomyopathy, skeletal muscle myopathy, growth delay, and neutropenia, with a worldwide incidence of 1/300,000-400,000 live births. The high mortality rate throughout infancy in BTHS patients is related primarily to progressive cardiomyopathy and a weakened immune system. BTHS is caused by defects in the TAZ gene that encodes tafazzin, a transacylase responsible for the remodeling and maturation of the mitochondrial phospholipid cardiolipin (CL), which is critical to normal mitochondrial structure and function (i.e., ATP generation). A deficiency in tafazzin results in up to a 95% reduction in levels of structurally mature CL. Because the heart is the most metabolically active organ in the body, with the highest mitochondrial content of any tissue, mitochondrial dysfunction plays a key role in the development of heart failure in patients with BTHS. Changes in mitochondrial oxidative phosphorylation reduce the ability of mitochondria to meet the ATP demands of the human heart as well as skeletal muscle, namely ATP synthesis does not match the rate of ATP consumption. The presence of several cardiomyopathic phenotypes have been described in BTHS, including dilated cardiomyopathy, left ventricular noncompaction, either alone or in conjunction with other cardiomyopathic phenotypes, endocardial fibroelastosis, hypertrophic cardiomyopathy, and an apical form of hypertrophic cardiomyopathy, among others, all of which can be directly attributed to the lack of CL synthesis, remodeling, and maturation with subsequent mitochondrial dysfunction. Several mechanisms by which these cardiomyopathic phenotypes exist have been proposed, thereby identifying potential targets for treatment. Dysfunction of the sarcoplasmic reticulum Ca2+-ATPase pump and inflammation potentially triggered by circulating mitochondrial components have been identified. Currently, treatment modalities are aimed at addressing symptomatology of HF in BTHS, but do not address the underlying pathology. One novel therapeutic approach includes elamipretide, which crosses the mitochondrial outer membrane to localize to the inner membrane where it associates with cardiolipin to enhance ATP synthesis in several organs, including the heart. Encouraging clinical results of the use of elamipretide in treating patients with BTHS support the potential use of this drug for management of this rare disease.

The Cardiac Mineralocorticoid Receptor (MR): A Therapeutic Target Against Ventricular Arrhythmias

Mineralocorticoid antagonists have been shown to be useful in the treatment of severe heart failure and may even save lives in this context. However, the reason for the beneficial action of these drugs, as well as the physiological role played by the cardiac mineralocorticoid receptor (MR), are still poorly understood. While the proinflammatory action of aldosterone on the heart and the resulting fibrosis partly explain the improvement due to the anti-mineralocorticoid therapy, the reduction in sudden death is probably related to a lower occurrence of ventricular arrhythmias. In this review, the author explains the physiological mechanism linking the positive chronotropic response induced by aldosterone observed in vitro with isolated ventricular cardiomyocytes and the increased risk of ventricular arrhythmias reported in vivo in hyperaldosteronism. He describes the molecular steps involved between MR activation and acceleration of spontaneous myocyte contractions, including expression of a specific micro RNA (miR204), down-regulation of a silencing transcription factor (NRSF), and re-expression of a fetal gene encoding a low threshold voltage-gated calcium channel (CaV3.2). Finally, he provides evidence suggesting aldosterone-independent and redox-sensitive mechanisms of MR activation in cardiac myocytes. Taken together, this information suggests that the use of anti-mineralocorticoid therapy could benefit the heart by preventing ventricular arrhythmias, not only in established hyperaldosteronism, but also in various pathological situations such as Cushing's disease, oxidative stress, or even diabetes mellitus.

The Crosstalk of Adipose-Derived Stem Cells (ADSC), Oxidative Stress, and Inflammation in Protective and Adaptive Responses

The potential use of stem cell-based therapies for the repair and regeneration of various tissues and organs is a major goal in repair medicine. Stem cells are classified by their potential to differentiate into functional cells. Compared with other sources, adipose-derived stem cells (ADSCs) have the advantage of being abundant and easy to obtain. ADSCs are considered to be tools for replacing, repairing, and regenerating dead or damaged cells. The capacity of ADSCs to maintain their properties depends on the balance of complex signals in their microenvironment. Their properties and the associated outcomes are in part regulated by reactive oxygen species, which mediate the oxidation-reduction state of cells as a secondary messenger. ADSC therapy has demonstrated beneficial effects, suggesting that secreted factors may provide protection. There is evidence that ADSCs secrete a number of cytokines, growth factors, and antioxidant factors into their microenvironment, thus regulating intracellular signaling pathways in neighboring cells. In this review, we introduce the roles of ADSCs in the protection of cells by modulating inflammation and immunity, and we develop their potential therapeutic properties.

Cardioprotective effect of thymol against adrenaline-induced myocardial injury in rats

Cardiovascular disease represents a vital global disease burden. This study aims to assess the possible cardioprotective effect of thymol against adrenaline-induced myocardial injury (MI) in rats. Furthermore the effect of thymol on cardiac function biomarkers, electrocardiogram (ECG) alterations, oxidative stress, inflammation, apoptosis and histopathological changes was assessed. MI was induced by adrenaline (2 mg/kg, s.c.) injected as a single dose for 2 consecutive days (24 h apart). Normal and control groups received the vehicle for 21 consecutive days. The other 3 groups were orally administered thymol (15, 30, 60 mg/kg) for 21 consecutive days and on day 22, adrenaline was injected as a single dose for 2 consecutive days. Then ECG examination, biochemical, histopathological, immunohistochemical analyses were carried out. Thymol reversed adrenaline-induced reduction of heart rate, prolongation of RR interval and elevation of ST interval. Thymol pretreatment significantly reduced serum aspartate dehydrogenase (AST), lactate dehydrogenase (LDH), and creatine kinase (CK) levels in MI rats. Oral pretreatment with thymol increased reduced glutathione (GSH), reduced malondialdehyde (MDA), nuclear factor-kappa B (NF-κB), and interleukin-1β (IL-1β) cardiac contents in MI rats. Additionally, thymol administration significantly decreased protein expression of caspase-3, increased Bcl-2 protein expression in cardiac tissue and ameliorated histopathological changes. This study reveals that thymol exerted cardioprotective effect against adrenaline-induced MI in rats evidenced by improving cardiac function, attenuating ECG and histopathological changes which may be partly mediated through its anti-oxidant, anti-inflammatory and anti-apoptotic effect.

Targeting the Mitochondria in Heart Failure: A Translational Perspective

The burden of heart failure (HF) in terms of health care expenditures, hospitalizations, and mortality is substantial and growing. The failing heart has been described as "energy-deprived" and mitochondrial dysfunction is a driving force associated with this energy supply-demand imbalance. Existing HF therapies provide symptomatic and longevity benefit by reducing cardiac workload through heart rate reduction and reduction of preload and afterload but do not address the underlying causes of abnormal myocardial energetic nor directly target mitochondrial abnormalities. Numerous studies in animal models of HF as well as myocardial tissue from explanted failed human hearts have shown that the failing heart manifests abnormalities of mitochondrial structure, dynamics, and function that lead to a marked increase in the formation of damaging reactive oxygen species and a marked reduction in on demand adenosine triphosphate synthesis. Correcting mitochondrial dysfunction therefore offers considerable potential as a new therapeutic approach to improve overall cardiac function, quality of life, and survival for patients with HF.

Nox2 and Nox4 Participate in ROS-Induced Neuronal Apoptosis and Brain Injury During Ischemia-Reperfusion in Rats

BACKGROUND

Previously studies have shown that Nox2 and Nox4, as members of nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase, Nox), participate in brain damage caused by ischemia-reperfusion (I/R). The aim of this study is to investigate the effects of specific chemical inhibitors of Nox2 and Nox4 on cerebral I/R-induced brain injury in rats.

METHODS

At 0.5 h before MCAO surgery, the rats were pretreated with vehicle, Nox2 inhibitor (gp91ds-tat), and Nox4 inhibitor (GKT137831), respectively. After reperfusion for 24 h, the infarct sizes of brain tissues in rats in various groups are determined. The penumbra (ischemic) tissues are collected to measure ROS levels, neuronal apoptosis, and degeneration, as well as the integrity of the blood-brain barrier (BBB) in brain tissues of rats.

RESULTS

gp91ds-tat and GKT137831 pretreatment significantly reduced the infarct sizes in brain tissues of rats, effectively suppressed I/R-induced increase in ROS levels, neuronal apoptosis and degeneration, and obviously alleviated BBB damage.

CONCLUSION

Under cerebral I/R conditions, Nox2 inhibitor (gp91ds-tat) and Nox4 inhibitor (GKT137831) can effectively play a protective role in the brain tissues of rats.

α-Tocopherol preserves cardiac function by reducing oxidative stress and inflammation in ischemia/reperfusion injury

OBJECTIVE

Myocardial infarction (MI) is a leading cause of mortality and morbidity worldwide and new treatment strategies are highly sought-after. Paradoxically, reperfusion of the ischemic myocardium, as achieved with early percutaneous intervention, results in substantial damage to the heart (ischemia/reperfusion injury) caused by cell death due to aggravated inflammatory and oxidative stress responses. Chronic therapy with vitamin E is not effective in reducing the cardiovascular event rate, presumably through failing to reduce atherosclerotic plaque instability. Notably, acute treatment with vitamin E in patients suffering a MI has not been systematically investigated.

METHODS AND RESULTS

We applied alpha-tocopherol (α-TOH), the strongest anti-oxidant form of vitamin E, in murine cardiac ischemia/reperfusion injury induced by ligation of the left anterior descending coronary artery for 60 min. α-TOH significantly reduced infarct size, restored cardiac function as measured by ejection fraction, fractional shortening, cardiac output, and stroke volume, and prevented pathological changes as assessed by state-of-the-art strain and strain-rate analysis. Cardioprotective mechanisms identified, include a decreased infiltration of neutrophils into cardiac tissue and a systemic anti-inflammatory shift from Ly6Chigh to Ly6Clow monocytes. Furthermore, we found a reduction in myeloperoxidase expression and activity, as well as a decrease in reactive oxygen species and the lipid peroxidation markers phosphatidylcholine (PC) (16:0)-9-hydroxyoctadecadienoic acid (HODE) and PC(16:0)-13-HODE) within the infarcted tissue.

CONCLUSION

Overall, α-TOH inhibits ischemia/reperfusion injury-induced oxidative and inflammatory responses, and ultimately preserves cardiac function. Therefore, our study provides a strong incentive to test vitamin E as an acute therapy in patients suffering a MI.

ROS and redox signaling in myocardial ischemia-reperfusion injury and cardioprotection

Ischemia-reperfusion (IR) injury is central to the pathology of major cardiovascular diseases, such as stroke and myocardial infarction. IR injury is mediated by several factors including the elevated production of reactive oxygen species (ROS), which occurs particularly at reperfusion. The mitochondrial respiratory chain and NADPH oxidases of the NOX family are major sources of ROS in cardiomyocytes. The first part of this review discusses recent findings and controversies on the mechanisms of superoxide production by the mitochondrial electron transport chain during IR injury, as well as the contribution of the NOX isoforms expressed in cardiomyocytes, NOX1, NOX2 and NOX4, to this damage. It then focuses on the effects of ROS on the opening of the mitochondrial permeability transition pore (mPTP), an inner membrane non-selective pore that causes irreversible damage to the heart. The second part analyzes the redox mechanisms of cardiomyocyte mitochondrial protection; specifically, the activation of the hypoxia-inducible factor (HIF) pathway and the antioxidant transcription factor Nrf2, which are both regulated by the cellular redox state. Redox mechanisms involved in ischemic preconditioning, one of the most effective ways of protecting the heart against IR injury, are also reviewed. Interestingly, several of these protective pathways converge on the inhibition of mPTP opening during reperfusion. Finally, the clinical and translational implications of these cardioprotective mechanisms are discussed.

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS)

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.

Cardioprotective time-window of Penehyclidine hydrochloride postconditioning: A rat study

Pharmacological postconditioning offers a clinical perspective for all patients with ischemic heart disease. Penehyclidine hydrochloride (PHC) is a new type of anticholinergic drug. We previously reported that PHC preconditioning protects against I/R injury in rat hearts in vivo. Ischemic heart disease often occurs suddenly, so postconditioning is more significant than preconditioning. However, studies evaluating myocardial protective effects of PHC postconditioning are unavailable. We explored the effects and time-window of cardioprotection of PHC postconditioning in myocardial I/R injury. PHC was administered by intravenous at various times (t = -5, 0, 5, 10, 15, or 30min) after the onset of reperfusion in addition to I/R rat. We observed five different indicators including infarct size, inflammatory response, myocardial enzyme, oxidative stress, and Ca²⁺ overload to quantify the effect of cardioprotection. Evans blue and TTC staining were used to measure myocardial infarct size. The expression of NF-κ B and IκB-α was analyzed using Western blot. ELISA was conducted to detect inflammatory and anti-inflammatory mediators. The Ca²⁺ level was determined using assay kit. PHC postconditioning (from -5 to 10min after the onset of reperfusion) significantly reduced infarct size, downregulated NF-κ B expression, and decreased the release of inflammatory mediators, while significantly upregulating IκB-α expression and increasing the release of anti-inflammatory mediators. All PHC postconditioning groups significantly reduced Ca²⁺ level. PHC postconditioning is cardioprotective over a larger time-window (from -5 to 10min after the onset of reperfusion). The probable mechanism is inhibition of NF-кB regulated inflammatory response pathway.

MitoNEET Protects HL-1 Cardiomyocytes from Oxidative Stress Mediated Apoptosis in an In Vitro Model of Hypoxia and Reoxygenation

The iron-sulfur cluster containing protein mitoNEET is known to modulate the oxidative capacity of cardiac mitochondria but its function during myocardial reperfusion injury after transient ischemia is unknown. The purpose of this study was to analyze the impact of mitoNEET on oxidative stress induced cell death and its relation to the glutathione-redox system in cardiomyocytes in an in vitro model of hypoxia and reoxygenation (H/R). Our results show that siRNA knockdown (KD) of mitoNEET caused an 1.9-fold increase in H/R induced apoptosis compared to H/R control while overexpression of mitoNEET caused a 53% decrease in apoptosis. Necrosis was not affected. Apoptosis of both, mitoNEET-KD and control cells was diminished to comparable levels by using the antioxidants Tiron and glutathione compound glutathione reduced ethyl ester (GSH-MEE), indicating that mitoNEET-dependent apoptosis is mediated by oxidative stress. The interplay between mitoNEET and glutathione redox system was assessed by treating cardiomyocytes with 2-acetylamino-3-[4-(2-acetylamino-2-carboxyethylsulfanylthio-carbonylamino) phenylthiocarbamoylsulfanyl] propionic acid (2-AAPA), known to effectively inhibit glutathione reductase (GSR) and to decrease the GSH/GSSG ratio. Surprisingly, inhibition of GSR-activity to 20% by 2-AAPA decreased apoptosis of control and mitoNEET-KD cells to 23% and 25% respectively, while at the same time mitoNEET-protein was increased 4-fold. This effect on mitoNEET-protein was not accessible by mitoNEET-KD but was reversed by GSH-MEE. In conclusion we show that mitoNEET protects cardiomyocytes from oxidative stress-induced apoptosis during H/R. Inhibition of GSH-recycling, GSR-activity by 2-AAPA increased mitoNEET-protein, accompanied by reduced apoptosis. Addition of GSH reversed these effects suggesting that mitoNEET can in part compensate for imbalances in the antioxidative glutathione-system and therefore could serve as a potential therapeutic approach for the oxidatively stressed myocardium.

The Role of Mitochondrial Reactive Oxygen Species in Cardiovascular Injury and Protective Strategies

Ischaemia/reperfusion (I/R) injury of the heart represents a major health burden mainly associated with acute coronary syndromes. While timely coronary reperfusion has become the established routine therapy in patients with ST-elevation myocardial infarction, the restoration of blood flow into the previously ischaemic area is always accompanied by myocardial injury. The central mechanism involved in this phenomenon is represented by the excessive generation of reactive oxygen species (ROS). Besides their harmful role when highly generated during early reperfusion, minimal ROS formation during ischaemia and/or at reperfusion is critical for the redox signaling of cardioprotection. In the past decades, mitochondria have emerged as the major source of ROS as well as a critical target for cardioprotective strategies at reperfusion. Mitochondria dysfunction associated with I/R myocardial injury is further described and ultimately analyzed with respect to its role as source of both deleterious and beneficial ROS. Furthermore, the contribution of ROS in the highly investigated field of conditioning strategies is analyzed. In the end, the vascular sources of mitochondria-derived ROS are briefly reviewed.

Effects of Oxygen Concentrations on Postresuscitation Myocardial Oxidative Stress and Myocardial Function in a Rat Model of Cardiopulmonary Resuscitation

OBJECTIVE

Lipid peroxidation induced by free-radical species plays a prominent role in myocardial injury following ischemia and reperfusion. However, there is a lack of data in different oxygen concentrations on myocardial lipid peroxidation during the early phase of reperfusion. In this study, we investigated whether ventilation with medium or normal concentration of oxygen would decrease the severity of myocardial lipid peroxidation and postresuscitation myocardial dysfunction.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

University-affiliated animal research institution.

SUBJECTS

Sixty-three healthy male Sprague-Dawley rats.

INTERVENTIONS

Animals were randomized into three groups: 1) 100% group, 2) 50% group, and 3) 21% group. Ventricular fibrillation was induced and untreated for 8 minutes, and defibrillation was attempted after 8 minutes of cardiopulmonary resuscitation. Ventilation with 100%, 50%, or 21% oxygen was initiated in all groups during cardiopulmonary resuscitation and 1 hour following the return of spontaneous circulation. Normoxic ventilation was maintained thereafter.

MEASUREMENTS AND MAIN RESULTS

Myocardial function, including ejection fraction and myocardial performance index, were measured at baseline, 4, or 72 hours after resuscitation. Blood samples were drawn at baseline, 15 minutes, 1, 4, or 72 hours after resuscitation for the measurements of blood gas or biomarkers. Significantly better myocardial function and longer duration of survival were observed in the 50% group. Compared with the 21% and 100% groups, a mild hyperoxia and greater oxygen extraction with lower 8-iso-prostaglandin F2α were observed in the 50% group. Pearson correlation analysis confirmed that 8-iso-prostaglandin F2α was positively correlated with myocardial performance index at 4 hours postresuscitation.

CONCLUSIONS

In a rat model of cardiac arrest and resuscitation, ventilation with 50% inspired oxygen during early postischemic reperfusion phase contributed to a decreased lipid peroxidation and a better myocardial function and duration of survival.

The Protective Role of the TOPK/PBK Pathway in Myocardial Ischemia/Reperfusion and H₂O₂-Induced Injury in H9C2 Cardiomyocytes

T-LAK-cell-originated protein kinase (TOPK) is a PDZ-binding kinase (PBK) that was recently identified as a novel member of the mitogen-activated protein kinase (MAPK) family. It has been shown to play an important role in many cellular functions. However, its role in cardiac function remains unclear. Thus, we have herein explored the biological function of TOPK in myocardial ischemia/reperfusion (I/R) and oxidative stress injury in H9C2 cardiomyocytes. I/R and ischemic preconditioning (IPC) were induced in rats by 3-hour reperfusion after 30-min occlusion of the left anterior descending coronary artery and by 3 cycles of 5-min I/R. Hydrogen peroxide (H₂O₂) was used to induce oxidative stress in H9C2 cardiomyocytes. TOPK expression was analyzed by western blotting, RT-PCR, immunohistochemical staining, and immunofluorescence imaging studies. The effects of TOPK gene overexpression and its inhibition via its inhibitor HI-TOPK-032 on cell viability and Bcl-2, Bax, ERK1/2, and p-ERK1/2 protein expression were analyzed by MTS assay and western blotting, respectively. The results showed that IPC alleviated myocardial I/R injury and induced TOPK activation. Furthermore, H₂O₂ induced TOPK phosphorylation in a time-dependent manner. Interestingly, TOPK inhibition aggravated the H₂O₂-induced oxidative stress injury in myocardiocytes, whereas overexpression relieved it. In addition, the ERK pathway was positively regulated by TOPK signaling. In conclusion, our results indicate that TOPK might mediate a novel survival signal in myocardial I/R, and that its effect on anti-oxidative stress involves the ERK signaling pathway.

Redox Roles of Reactive Oxygen Species in Cardiovascular Diseases

Cardiovascular disease (CVD), a major cause of mortality in the world, has been extensively studied over the past decade. However, the exact mechanism underlying its pathogenesis has not been fully elucidated. Reactive oxygen species (ROS) play a pivotal role in the progression of CVD. Particularly, ROS are commonly engaged in developing typical characteristics of atherosclerosis, one of the dominant CVDs. This review will discuss the involvement of ROS in atherosclerosis, specifically their effect on inflammation, disturbed blood flow and arterial wall remodeling. Pharmacological interventions target ROS in order to alleviate oxidative stress and CVD symptoms, yet results are varied due to the paradoxical role of ROS in CVD. Lack of effectiveness in clinical trials suggests that understanding the exact role of ROS in the pathophysiology of CVD and developing novel treatments, such as antioxidant gene therapy and nanotechnology-related antioxidant delivery, could provide a therapeutic advance in treating CVDs. While genetic therapies focusing on specific antioxidant expression seem promising in CVD treatments, multiple technological challenges exist precluding its immediate clinical applications.

Apelin regulates FoxO3 translocation to mediate cardioprotective responses to myocardial injury and obesity

The increasing incidence of obesity accentuates the importance of identifying mechanisms and optimal therapeutic strategies for patients with heart failure (HF) in relation to obesity status. Here, we investigated the association between plasma level of apelin, an adipocyte-derived factor, and clinicopathological features of obese and non-obese patients with HF. We further explored potential regulatory mechanisms of cardiac cell fate responses in conditions combining myocardial injury and obesity. In a prospective, cross-sectional study involving patients with HF we show that obese patients (BMI ≥ 30 kg/m(2)) have higher left ventricular ejection fraction (LVEF) and greater levels of plasma apelin (p < 0.005) than non-obese patients (< 30 kg/m(2)), independently of ischemic etiology. In a mouse model combining ischemia-reperfusion (I/R) injury and high-fat diet (HFD)-induced obesity, we identify apelin as a novel regulator of FoxO3 trafficking in cardiomyocytes. Confocal microscopy analysis of cardiac cells revealed that apelin prevents nuclear translocation of FoxO3 in response to oxygen deprivation through a PI3K pathway. These findings uncover apelin as a novel regulator of FoxO3 nucleocytoplasmic trafficking in cardiac cells in response to stress and provide insight into its potential clinical relevance in obese patients with HF.

Mitochondrial reactive oxygen species: a double edged sword in ischemia/reperfusion vs preconditioning

Reductions in the blood supply produce considerable injury if the duration of ischemia is prolonged. Paradoxically, restoration of perfusion to ischemic organs can exacerbate tissue damage and extend the size of an evolving infarct. Being highly metabolic organs, the heart and brain are particularly vulnerable to the deleterious effects of ischemia/reperfusion (I/R). While the pathogenetic mechanisms contributing to I/R-induced tissue injury and infarction are multifactorial, the relative importance of each contributing factor remains unclear. However, an emerging body of evidence indicates that the generation of reactive oxygen species (ROS) by mitochondria plays a critical role in damaging cellular components and initiating cell death. In this review, we summarize our current understanding of the mechanisms whereby mitochondrial ROS generation occurs in I/R and contributes to myocardial infarction and stroke. In addition, mitochondrial ROS have been shown to participate in preconditioning by several pharmacologic agents that target potassium channels (e.g., ATP-sensitive potassium (mKATP) channels or large conductance, calcium-activated potassium (mBKCa) channels) to activate cell survival programs that render tissues and organs more resistant to the deleterious effects of I/R. Finally, we review novel therapeutic approaches that selectively target mROS production to reduce postischemic tissue injury, which may prove efficacious in limiting myocardial dysfunction and infarction and abrogating neurocognitive deficits and neuronal cell death in stroke.

NADPH oxidase 1 and its derived reactive oxygen species mediated tissue injury and repair

Reactive oxygen species are mostly viewed to cause oxidative damage to various cells and induce organ dysfunction after ischemia-reperfusion injury. However, they are also considered as crucial molecules for cellular signal transduction in biology. NADPH oxidase, whose only function is reactive oxygen species production, has been extensively investigated in many cell types especially phagocytes. The deficiency of NADPH oxidase extends the process of inflammation and delays tissue repair, which causes chronic granulomatous disease in patients. NADPH oxidase 1, one member of the NADPH oxidase family, is not only constitutively expressed in a variety of tissues, but also induced to increase expression in both mRNA and protein levels under many circumstances. NADPH oxidase 1 and its derived reactive oxygen species are suggested to be able to regulate inflammation reaction, cell proliferation and migration, and extracellular matrix synthesis, which contribute to the processes of tissue injury and repair.

Normobaric, intermittent hypoxia conditioning is cardio- and vasoprotective in rats

Favorable versus detrimental cardiovascular responses to intermittent hypoxia conditioning (IHC) are heavily dependent on experimental or pathological conditions, including the duration, frequency and intensity of the hypoxia exposures. Recently, we demonstrated that a program of moderate, normobaric IHC (FIO2 9.5-10% for 5-10 min/cycle, with intervening 4 min normoxia, 5-8 cycles/day for 20 days) in dogs afforded robust cardioprotection against infarction and arrhythmias induced by coronary artery occlusion-reperfusion, but this protection has not been verified in other species. Accordingly, in this investigation cardio- as well as vasoprotection were examined in male Wistar rats completing the normobaric IHC program or a sham program in which the rats continuously breathed atmospheric air. Myocardial ischemia and reperfusion (IR) was imposed by occlusion and reperfusion of the left anterior descending coronary artery in in situ experiments and by subjecting isolated, perfused hearts to global ischemia-reperfusion. Cardiac arrhythmias and myocardial infarct size were quantified in in situ experiments. Endothelial function was evaluated from the relaxation to acetylcholine of norepinephrine-precontracted aortic rings taken from in situ IR experiments, and from the increase in coronary flow produced by acetylcholine in isolated hearts. IHC sharply reduced cardiac arrhythmias during ischemia and decreased infarct size by 43% following IR. Endothelial dysfunction in aorta was marked after IR in sham rats, but not significant in IHC rats. Similar findings were found for the coronary circulations of isolated hearts. These findings support the hypothesis that moderate, normobaric IHC is cardio- and vasoprotective in a rat model of IR.

Cyclic nucleotide phosphodiesterase 3A1 protects the heart against ischemia-reperfusion injury

Phosphodiesterase 3A (PDE3A) is a major regulator of cAMP in cardiomyocytes. PDE3 inhibitors are used for acute treatment of congestive heart failure, but are associated with increased incidence of arrhythmias and sudden death with long-term use. We previously reported that chronic PDE3A downregulation or inhibition induced myocyte apoptosis in vitro. However, the cardiac protective effect of PDE3A has not been demonstrated in vivo in disease models. In this study, we examined the role of PDE3A in regulating myocardial function and survival in vivo using genetically engineered transgenic mice with myocardial overexpression of the PDE3A1 isozyme (TG). TG mice have reduced cardiac function characterized by reduced heart rate and ejection fraction (52.5±7.8% vs. 83.9±4.7%) as well as compensatory expansion of left ventricular diameter (4.19±0.19mm vs. 3.10±0.18mm). However, there was no maladaptive increase of fibrosis and apoptosis in TG hearts compared to wild type (WT) hearts, and the survival rates also remained the same. The diminution of cardiac contractile function is very likely attributed to a decrease in beta-adrenergic receptor (β-AR) response in TG mice. Importantly, the myocardial infarct size (4.0±1.8% vs. 24.6±3.8%) and apoptotic cell number (1.3±1.0% vs. 5.6±1.5%) induced by ischemia/reperfusion (I/R) injury were significantly attenuated in TG mice. This was associated with decreased expression of inducible cAMP early repressor (ICER) and increased expression of anti-apoptotic protein BCL-2. To further verify the anti-apoptotic effects of PDE3A1, we performed in vitro apoptosis study in isolated adult TG and WT cardiomyocytes. We found that the apoptotic rates stimulated by hypoxia/reoxygenation or H2O2 were indeed significantly reduced in TG myocytes, and the differences between TG and WT myocytes were completely reversed in the presence of the PDE3 inhibitor milrinone. These together indicate that PDE3A1 negatively regulates β-AR signaling and protects against I/R injury by inhibiting cardiomyocyte apoptosis.

Licorice treatment prevents oxidative stress, restores cardiac function, and salvages myocardium in rat model of myocardial injury

The present study examined the effects of licorice on antioxidant defense, functional impairment, histopathology, and ultrastructural alterations in isoproterenol (ISP)-induced myocardial injury in rats. Myocardial necrosis was induced by two subcutaneous injection of ISP (85 mg/kg) at an interval of 24 h. Licorice was administered orally for 30 days in the doses of 100, 200, 400, or 800 mg/kg. ISP-treated rats showed impaired hemodynamics, left ventricular dysfunction, and caused depletion of antioxidants and marker enzymes along with lipid peroxidation from myocardium. ISP also induced histopathological and ultrastructural alterations in myocardium. Pretreatment with licorice prevented the depletion of endogenous antioxidants and myocyte injury marker enzymes, inhibited lipid peroxidation, and showed recovery of hemodynamic and ventricular functions. Licorice treatment also reduced myonecrosis, edema, and infiltration of inflammatory cells and showed preservation of subcellular and ultrastructural components. Our results demonstrate that licorice exerts cardioprotection by reducing oxidative stress, augmenting endogenous antioxidants, and restoring functional parameters as well as maintaining structural integrity.

NADPH oxidases as a source of oxidative stress and molecular target in ischemia/reperfusion injury

Ischemia/reperfusion injury (IRI) is crucial in the pathology of major cardiovascular diseases, such as stroke and myocardial infarction. Paradoxically, both the lack of oxygen during ischemia and the replenishment of oxygen during reperfusion can cause tissue injury. Clinical outcome is also determined by a third, post-reperfusion phase characterized by tissue remodeling and adaptation. Increased levels of reactive oxygen species (ROS) have been suggested to be key players in all three phases. As a second paradox, ROS seem to play a double-edged role in IRI, with both detrimental and beneficial effects. These Janus-faced effects of ROS may be linked to the different sources of ROS or to the different types of ROS that exist and may also depend on the phase of IRI. With respect to therapeutic implications, an untargeted application of antioxidants may not differentiate between detrimental and beneficial ROS, which might explain why this approach is clinically ineffective in lowering cardiovascular mortality. Under some conditions, antioxidants even appear to be harmful. In this review, we discuss recent breakthroughs regarding a more targeted and promising approach to therapeutically modulate ROS in IRI. We will focus on NADPH oxidases and their catalytic subunits, NOX, as they represent the only known enzyme family with the sole function to produce ROS. Similar to ROS, NADPH oxidases may play a dual role as different NOX isoforms may mediate detrimental or protective processes. Unraveling the precise sequence of events, i.e., determining which role the individual NOX isoforms play in the various phases of IRI, may provide the crucial molecular and mechanistic understanding to finally effectively target oxidative stress.

Methanol Extract of Cassia mimosoides var. nomame Attenuates Myocardial Injury by Inhibition of Apoptosis in a Rat Model of Ischemia-Reperfusion

Interruption of blood flow through coronary arteries and its subsequent restoration triggers the generation of a burst of reactive oxygen species (ROS), leading to myocardial cell death. In this study, we determined whether a methanol extract of Cassia mimosoides var. nomame Makino could prevent myocardial ischemia-reperfusion injury. When radical scavenging activity of the extract was measured in vitro using its α,α-diphenyl-β-picrylhydrazyl (DPPH) radical quenching ability, the extract showed an activity slightly lower than that of ascorbic acid. Three days after oral administration of the extract (400 mg/kg/day) to rats, myocardial ischemia/reperfusion injury was generated by 30 min of ligation of the left anterior descending coronary artery (LAD), followed by 3 hr reperfusion. Compared with the vehicle-treated group, administration of the extract significantly reduced infarct size (IS) (ratio of infarct area to area at risk) in the extract-treated group by 28.3%. Reduction in the cellular injury was mediated by attenuation of Bax/Bcl-2 ratio by 33.3%, inhibition of caspase-3 activation from procas-pase-3 by 40%, and subsequent reduction in the number of apoptotic cells by 66.3%. These results suggest that the extract attenuates myocardial injury in a rat model of ischemia-reperfusion by scavenging ROS, including free radicals, and consequently blocking apoptotic cascades. Therefore, intake of Cassia mimosoides var. nomame Makino might be beneficial for preventing ischemic myocardial injury.

Oxidative stress increases SNAT1 expression and stimulates cysteine uptake in freshly isolated rat cardiomyocytes

Intracellular cysteine availability is an important rate-limiting factor governing glutathione synthesis in the heart. This is also dependent on the magnitude and rate of cysteine uptake into cardiomyocytes, which has been little studied. This study investigated the hypothesis that changes to cysteine transporter expression and activity during oxidative stress influence cardiomyocyte glutathione levels. The uptake of 0-3 mM L-[(35)S]cysteine into ventricular cardiomyocytes isolated from adult male Wistar rats was measured using oil filtration. Cysteine transporter expression was investigated by conventional and real-time quantitative reverse-transcription polymerase chain reaction and Western blotting. Glutathione levels were measured enzymatically. Oxidative stress was induced via 0-6 h incubation with 0.05 mM H(2)O(2). Cysteine uptake was greatest in sodium-containing media and was inhibited by glutamine, 2-(methylamino)-isobutyric acid (αMeAIB), serine or alanine. The K(m) and V(max) of the αMeAIB insensitive and sensitive portions were 0.133 ± 0.01 mM and 468.11 ± 9.04 pmol/μl cell vol/min, and 0.557 ± 0.096 mM and 279.87 ± 16.06 pmol/μl cell vol/min, respectively. Cardiomyocytes expressed ASCT2, SNAT1 and SNAT2 but not ASCT1. Oxidative stress significantly enhanced cysteine uptake, which was attenuated by αMeAIB. This was accompanied by significantly enhanced SNAT1 expression, whilst SNAT2 and ASCT2 were unaffected. Incubation with cysteine significantly reduced the oxidative-stress-induced decline in cardiomyocyte glutathione as compared to cells incubated without cysteine or cells incubated with cysteine and αMeAIB. In conclusion, under control conditions SNAT transporters aid in the delivery of cysteine for cardiomyocyte GSH synthesis, whilst oxidative stress increases cardiomyocyte cysteine uptake and stimulates cardiomyocyte SNAT1 expression.