The effects of modulating eNOS activity and coupling in ischemia/reperfusion (I/R)

Mixture of Doxycycline, ML-7 and L-NAME Restores the Pro- and Antioxidant Balance during Myocardial Infarction-In Vivo Pig Model Study

The restoration of blood flow to the ischemic myocardium inflicts ischemia/reperfusion (I/R) heart injury (IRI). The main contributors to IRI are increased oxidative stress and subsequent excessive production of ROS, increased expression of NOS and peroxinitate, activation of MMPs, and enhanced posttranslational modifications of contractile proteins, which make them more susceptible to proteolytic degradation. Since the pathophysiology of IRI is a complex issue, and thus, various therapeutic strategies are required to prevent or reduce IRI and microvascular dysfunction, in the current study we proposed an innovative multi-drug therapy using low concentrations of drugs applied intracoronary to reach microvessels in order to stabilize the pro- and antioxidant balance during a MI in an in vivo pig model. The ability of a mixture of doxycycline (1 μM), ML-7 (0.5 μM), and L-NAME (2 μM) to modulate the pro- and antioxidative balance was tested in the left ventricle tissue and blood samples. Data showed that infusion of a MIX reduced the total oxidative status (TOS), oxidative stress index (OSI), and malondialdehyde (MDA). It also increased the total antioxidant capacity, confirming its antioxidative properties. MIX administration also reduced the activity of MMP-2 and MMP-9, and then decreased the release of MLC1 and BNP-26 into plasma. This study demonstrated that intracoronary administration of low concentrations of doxycycline in combination with ML-7 and L-NAME is incredibly efficient in regulating pro- and antioxidant balance during MI.

The role of PI3K/AKT signaling pathway in myocardial ischemia-reperfusion injury

Myocardial ischemia has a high incidence and mortality rate, and reperfusion is currently the standard intervention. However, reperfusion may lead to further myocardial damage, known as myocardial ischemia/reperfusion injury (MIRI). There are currently no effective clinical treatments for MIRI. The PI3K/Akt signaling pathway is involved in cardiovascular health and disease and plays an important role in reducing myocardial infarct size and restoring cardiac function after MIRI. Activation of the PI3K/Akt pathway provides myocardial protection through synergistic upregulation of antioxidant, anti-inflammatory, and autophagy activities and inhibition of mitochondrial dysfunction and cardiomyocyte apoptosis. Many studies have shown that PI3K/Akt has a significant protective effect against MIRI. Here, we reviewed the molecular regulation of PI3K/Akt in MIRI and summarized the molecular mechanism by which PI3K/Akt affects MIRI, the effects of ischemic preconditioning and ischemic postconditioning, and the role of related drugs or activators targeting PI3K/Akt in MIRI, providing novel insights for the formulation of myocardial protection strategies. This review provides evidence of the role of PI3K/Akt activation in MIRI and supports its use as a therapeutic target.

The pharmacological effects and safety of the raw and prepared folium of Epimedium brevicornu Maxim. on improving kidney-yang deficiency syndrome and sexual dysfunction

Background: Kidney-Yang deficiency syndrome (KDS) is a group of diseases related to hypothalamic-pituitary-adrenal (HPA) axis and sexual dysfunction. The folium of Epimedium brevicornu Maxim. (FEB) includes raw and prepared slices, named RFEB and PFEB, respectively. PFEB is traditionally believed to be good for tonifying kidney-Yang and improving sexual dysfunction. However, there are few studies comparing the pharmacological effects of RFEB and PFEB, and their underlying mechanisms. In this study, we aimed to compare the effects and safety of RFEB and PFEB on the HPA axis and sexual function. Additionally, the mechanisms of their roles in relation to the neuroendocrine-immune (NEI) network in the KDS model mice were explored. Methods: Male adult C57BL/6 mice were treated with corticosterone to establish a KDS mouse model, and RFEB and PFEB were administered intragastrically. Corticotropin releasing hormone (CRH), adrenocorticotropic hormone (ACTH), cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), testosterone levels and oxidative damage indexes were measured. The mRNA and protein levels of CRH and ACTH in hypothalamus and pituitary, endothelial nitric oxide synthase (eNOS) and phosphodiesterase 5 (PDE5) in corpus cavernosum were examined. TNFα, IL-6, NF-κB, eNOS and PDE5 were investigated in mouse corpus cavernosum. Results: Our results showed that PFEB was more effective than RFEB in increasing corticosterone-suppressed ACTH levels, enhancing CRH levels and cAMP/cGMP ratio, and reducing oxidative damage. In vivo, PFEB significantly increased eNOS and inhibited PDE5 expression in corpus cavernosum. PFEB showed stronger protective effect on normal spleen lymphocytes from apoptosis both in vitro and in vivo. Additionally, it noticeably inhibited the levels of inflammatory cytokines in corpus cavernosum. Both RFEB and PFEB were safe and did not cause any clinical signs of toxicity in mice at the dosage of 20 times dosages of that in the Chinese Pharmacopeia. Conclusion: We demonstrated that PFEB was better than RFEB at tonifying the kidney-Yang by comparing their effects on improving the NEI network, which includes the HPA axis, immune system and corpus cavernosum. This study revealed that PFEB could significantly improve the sexual function of KDS mice by regulating the HPA axis and activating the immune system through the NEI network.

Endothelial cell-specific roles for tetrahydrobiopterin in myocardial function, cardiac hypertrophy, and response to myocardial ischemia-reperfusion injury

The cofactor tetrahydrobiopterin (BH4) is a critical regulator of nitric oxide synthase (NOS) function and redox signaling, with reduced BH4 implicated in multiple cardiovascular disease states. In the myocardium, augmentation of BH4 levels can impact on cardiomyocyte function, preventing hypertrophy and heart failure. However, the specific role of endothelial cell BH4 biosynthesis in the coronary circulation and its role in cardiac function and the response to ischemia has yet to be elucidated. Endothelial cell-specific Gch1 knockout mice were generated by crossing Gch1fl/fl with Tie2cre mice, generating Gch1fl/flTie2cre mice and littermate controls. GTP cyclohydrolase protein and BH4 levels were reduced in heart tissues from Gch1fl/flTie2cre mice, localized to endothelial cells, with normal cardiomyocyte BH4. Deficiency in coronary endothelial cell BH4 led to NOS uncoupling, decreased NO bioactivity, and increased superoxide and hydrogen peroxide productions in the hearts of Gch1fl/flTie2cre mice. Under physiological conditions, loss of endothelial cell-specific BH4 led to mild cardiac hypertrophy in Gch1fl/flTie2cre hearts. Endothelial cell BH4 loss was also associated with increased neuronal NOS protein, loss of endothelial NOS protein, and increased phospholamban phosphorylation at serine-17 in cardiomyocytes. Loss of cardiac endothelial cell BH4 led to coronary vascular dysfunction, reduced functional recovery, and increased myocardial infarct size following ischemia-reperfusion injury. Taken together, these studies reveal a specific role for endothelial cell Gch1/BH4 biosynthesis in cardiac function and the response to cardiac ischemia-reperfusion injury. Targeting endothelial cell Gch1 and BH4 biosynthesis may provide a novel therapeutic target for the prevention and treatment of cardiac dysfunction and ischemia-reperfusion injury.NEW & NOTEWORTHY We demonstrate a critical role for endothelial cell Gch1/BH4 biosynthesis in coronary vascular function and cardiac function. Loss of cardiac endothelial cell BH4 leads to coronary vascular dysfunction, reduced functional recovery, and increased myocardial infarct size following ischemia/reperfusion injury. Targeting endothelial cell Gch1 and BH4 biosynthesis may provide a novel therapeutic target for the prevention and treatment of cardiac dysfunction, ischemia injury, and heart failure.

The roles of PKC-δ and PKC-ε in myocardial ischemia/reperfusion injury

Ischemia and reperfusion (I/R) cause a reduction in arterial blood supply to tissues, followed by the restoration of perfusion and consequent reoxygenation. The reestablishment of blood flow triggers further damage to ischemic tissue through reactive oxygen species (ROS) accumulation, interference with cellular ion homeostasis, opening of mitochondrial permeability transition pores (mPTPs) and promotion of cell death (apoptosis or necrosis). PKC-δ and PKC-ε, belonging to a family of serine/threonine kinases, have been demonstrated to play important roles during I/R injury in cardiovascular diseases. However, the cardioprotective mechanisms of PKC-δ and PKC-ε in I/R injury have not been elaborated until now. This article discusses the roles of PKC-δ and PKC-ε during myocardial I/R in redox regulation (redox signaling and oxidative stress), cell death (apoptosis and necrosis), Ca²⁺ overload, and mitochondrial dysfunction.

Role of Oxidative Stress in Reperfusion following Myocardial Ischemia and Its Treatments

Myocardial ischemia is a disease with high morbidity and mortality, for which reperfusion is currently the standard intervention. However, the reperfusion may lead to further myocardial damage, known as myocardial ischemia/reperfusion injury (MI/RI). Oxidative stress is one of the most important pathological mechanisms in reperfusion injury, which causes apoptosis, autophagy, inflammation, and some other damage in cardiomyocytes through multiple pathways, thus causing irreversible cardiomyocyte damage and cardiac dysfunction. This article reviews the pathological mechanisms of oxidative stress involved in reperfusion injury and the interventions for different pathways and targets, so as to form systematic treatments for oxidative stress-induced myocardial reperfusion injury and make up for the lack of monotherapy.

Mixture of MMP-2, MLC, and NOS Inhibitors Affects NO Metabolism and Protects Heart from Cardiac I/R Injury

Objectives

Coronary reperfusion procedure leads to ischemia/reperfusion injury of the heart (IRI). IRI arises from increased degradation of myosin light chains and increased activity of matrix metalloproteinase 2 (MMP-2). Increased production of toxic peroxynitrite (ONOO^-) during oxidative stress is a source of increased nitration/nitrosylation of contractile proteins, which enhance their degradation through MMP-2. Hence, an imbalance in nitric oxide (NO) metabolism along with oxidative stress is an important factor contributing to pathophysiology of cardiovascular disorders, including myocardial infarction. The aim of the current study was to provide an important insight into understanding the interaction of iNOS, eNOS, and ADMA during oxidative stress and to propose the beneficial therapy to modulate this interaction. Material and Methods. Pathogen-free Wistar rats were used in this study as a surrogate heart model ex vivo. Rat hearts perfused using the Langendorff method were subjected to global no-flow ischemia with or without administration of DOXY (1 µM), ML-7 (0.5 µM), and L-NAME (2 µM) mixture. Haemodynamic parameters of heart function, markers of I/R injury, tissue expression of iNOS, eNOS, and phospho-eNOS, asymmetric dimethylarginine, and NO production as well as MMP-2 activity were measured.

Results

Mechanical heart function and coronary flow (CF) were decreased in the hearts subjected to I/R. Treatment of the hearts with the tested mixture resulted in a recovery of mechanical function due to decreased activity of MMP-2. An infusion of Doxy, ML-7, and L-NAME mixture into I/R hearts decreased the expression of iNOS, eNOS, and phospho-eNOS and in consequence reduced ADMA expression. Decreased ADMA production led to enhanced NO synthesis and improvement of cardiac function at 85% of aerobic control.

Conclusions

Synergistic effect of the multidrug therapy with the subthreshold doses allows addressing a few pathways of I/R injury simultaneously to achieve protection of cardiac function during I/R.

Nitroglycerine limits infarct size through S-nitrosation of cyclophilin D: a novel mechanism for an old drug

AIMS

Nitroglycerine (NTG) given prior to an ischaemic insult exerts cardioprotective effects. However, whether administration of an acute low dose of NTG in a clinically relevant manner following an ischaemic episode limits infarct size, has not yet been explored.

METHODS AND RESULTS

Adult mice were subjected to acute myocardial infarction in vivo and then treated with vehicle or low-dose NTG prior to reperfusion. This treatment regimen minimized myocardial infarct size without affecting haemodynamic parameters but the protective effect was absent in mice rendered tolerant to the drug. Mechanistically, NTG was shown to nitrosate and inhibit cyclophilin D (CypD), and NTG administration failed to limit infarct size in CypD knockout mice. Additional experiments revealed lack of the NTG protective effect following genetic (knockout mice) or pharmacological inhibition (L-NAME treatment) of the endothelial nitric oxide synthase (eNOS). The protective effect of NTG was attributed to preservation of the eNOS dimer. Moreover, NTG retained its cardioprotective effects in a model of endothelial dysfunction (ApoE knockout) by preserving CypD nitrosation. Human ischaemic heart biopsies revealed reduced eNOS activity and exhibited reduced CypD nitrosation.

CONCLUSION

Low-dose NTG given prior to reperfusion reduces myocardial infarct size by preserving eNOS function, and the subsequent eNOS-dependent S-nitrosation of CypD, inhibiting cardiomyocyte necrosis. This novel pharmacological action of NTG warrants confirmation in clinical studies, although our data in human biopsies provide promising preliminary results.

Say NO to ROS: Their Roles in Embryonic Heart Development and Pathogenesis of Congenital Heart Defects in Maternal Diabetes

Congenital heart defects (CHDs) are the most prevalent and serious birth defect, occurring in 1% of all live births. Pregestational maternal diabetes is a known risk factor for the development of CHDs, elevating the risk in the child by more than four-fold. As the prevalence of diabetes rapidly rises among women of childbearing age, there is a need to investigate the mechanisms and potential preventative strategies for these defects. In experimental animal models of pregestational diabetes induced-CHDs, upwards of 50% of offspring display congenital malformations of the heart, including septal, valvular, and outflow tract defects. Specifically, the imbalance of nitric oxide (NO) and reactive oxygen species (ROS) signaling is a major driver of the development of CHDs in offspring of mice with pregestational diabetes. NO from endothelial nitric oxide synthase (eNOS) is crucial to cardiogenesis, regulating various cellular and molecular processes. In fact, deficiency in eNOS results in CHDs and coronary artery malformation. Embryonic hearts from diabetic dams exhibit eNOS uncoupling and oxidative stress. Maternal treatment with sapropterin, a cofactor of eNOS, and antioxidants such as N-acetylcysteine, vitamin E, and glutathione as well as maternal exercise have been shown to improve eNOS function, reduce oxidative stress, and lower the incidence CHDs in the offspring of mice with pregestational diabetes. This review summarizes recent data on pregestational diabetes-induced CHDs, and offers insights into the important roles of NO and ROS in embryonic heart development and pathogenesis of CHDs in maternal diabetes.

Succinate metabolism: a new therapeutic target for myocardial reperfusion injury

Myocardial ischaemia/reperfusion (IR) injury is a major cause of death worldwide and remains a disease for which current clinical therapies are strikingly deficient. While the production of mitochondrial reactive oxygen species (ROS) is a critical driver of tissue damage upon reperfusion, the precise mechanisms underlying ROS production have remained elusive. More recently, it has been demonstrated that a specific metabolic mechanism occurs during ischaemia that underlies elevated ROS at reperfusion, suggesting a unifying model as to why so many different compounds have been found to be cardioprotective against IR injury. This review will discuss the role of the citric acid cycle intermediate succinate in IR pathology focusing on the mechanism by which this metabolite accumulates during ischaemia and how it can drive ROS production at Complex I via reverse electron transport. We will then examine the potential for manipulating succinate accumulation and metabolism during IR injury in order to protect the heart against IR damage and discuss targets for novel therapeutics designed to reduce reperfusion injury in patients.

Superoxide dismutase 1 and glutathione peroxidase 1 are involved in the protective effect of sulodexide on vascular endothelial cells exposed to oxygen-glucose deprivation

Sulodexide (SDX) is widely used in the treatment of both arterial and venous thrombotic disorders. In addition to its recognized antithrombotic action, SDX has endothelial protective potential, which is independent of the coagulation/fibrinolysis system. However, the detailed molecular mechanisms of the endothelioprotective action of the drug are still unresolved. The aim of the present study was to determine whether treatment with SDX at concentrations of 0.125-0.5 lipase releasing unit (LRU)/ml have on the expression and activity of antioxidant enzymes in ischemic endothelial cells and how these effects might be related to the antiapoptotic properties of SDX. In the present study, human umbilical vein endothelial cells (HUVECs) were subjected to ischemia-simulating conditions (combined oxygen and glucose deprivation, OGD) for 6h to determine the protective effects of SDX. SDX (0.25 and 0.5LRU/ml) in OGD significantly increased the cell viability and prevented mitochondrial depolarization in the HUVECs. Moreover, SDX protected the HUVECs against OGD-induced apoptosis. At concentrations of 0.25 and 0.5LRU/ml, the drug increased both superoxide dismutase 1 (SOD1) and glutathione peroxidase 1 (GPx1) mRNA/protein expression together with a significant attenuation of oxidative stress in ischemic HUVECs. Our findings also demonstrate that an increase in both SOD and GPx activity is involved in the protective effect of SDX on ischemic endothelial cells. Altogether, these results suggest that SDX has a positive effect on ischemia-induced endothelial damage because of its antioxidant and antiapoptotic properties.

Reperfusion injury and reactive oxygen species: The evolution of a concept

Reperfusion injury, the paradoxical tissue response that is manifested by blood flow-deprived and oxygen-starved organs following the restoration of blood flow and tissue oxygenation, has been a focus of basic and clinical research for over 4-decades. While a variety of molecular mechanisms have been proposed to explain this phenomenon, excess production of reactive oxygen species (ROS) continues to receive much attention as a critical factor in the genesis of reperfusion injury. As a consequence, considerable effort has been devoted to identifying the dominant cellular and enzymatic sources of excess ROS production following ischemia-reperfusion (I/R). Of the potential ROS sources described to date, xanthine oxidase, NADPH oxidase (Nox), mitochondria, and uncoupled nitric oxide synthase have gained a status as the most likely contributors to reperfusion-induced oxidative stress and represent priority targets for therapeutic intervention against reperfusion-induced organ dysfunction and tissue damage. Although all four enzymatic sources are present in most tissues and are likely to play some role in reperfusion injury, priority and emphasis has been given to specific ROS sources that are enriched in certain tissues, such as xanthine oxidase in the gastrointestinal tract and mitochondria in the metabolically active heart and brain. The possibility that multiple ROS sources contribute to reperfusion injury in most tissues is supported by evidence demonstrating that redox-signaling enables ROS produced by one enzymatic source (e.g., Nox) to activate and enhance ROS production by a second source (e.g., mitochondria). This review provides a synopsis of the evidence implicating ROS in reperfusion injury, the clinical implications of this phenomenon, and summarizes current understanding of the four most frequently invoked enzymatic sources of ROS production in post-ischemic tissue.

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Reperfusion injury is implicated in a variety of human diseases and disorders.

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Evidence implicating ROS in reperfusion injury continues to grow.

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Several enzymes are candidate sources of ROS in post-ischemic tissue.

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Inter-enzymatic ROS-dependent signaling enhances the oxidative stress caused by I/R.

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Oxidized LDL and NO synthesis--Biomarkers of endothelial dysfunction and ageing

Oxidized LDL (oxLDL) and nitric oxide (NO) exert contradictory actions within the vascular endothelium microenvironment influencing key events in atherogenesis. OxLDL and NO are so far regarded as representative parameters of oxidative stress and endothelial dysfunction, new targets in prevention, diagnosis and therapy of cardiovascular diseases, and also as candidate biomarkers in evaluating the human biological age. The aim of this review is to explore recent literature on molecular mechanisms and pathophysiological relationships between LDL oxidation, NO synthesis and vascular endothelium function/dysfunction in ageing, focusing on the following aspects: (1) the impact of metabolic status on both LDL oxidation and NO synthesis in relation with oxidative stress, (2) the use of oxidized LDL and NO activity as biomarkers in human studies reporting on cardiovascular outcomes, and (3) evidences supporting the importance of oxidized LDL and NO activity as relevant biomarkers in vascular ageing and age-related diseases.

Dual role of endothelial nitric oxide synthase in oxidized LDL-induced, p66Shc-mediated oxidative stress in cultured human endothelial cells

BACKGROUND

The aging gene p66Shc, is an important mediator of oxidative stress-induced vascular dysfunction and disease. In cultured human aortic endothelial cells (HAEC), p66Shc deletion increases endothelial nitric oxide synthase (eNOS) expression and nitric oxide (NO) bioavailability via protein kinase B. However, the putative role of the NO pathway on p66Shc activation remains unclear. This study was designed to elucidate the regulatory role of the eNOS/NO pathway on p66Shc activation.

METHODS AND RESULTS

Incubation of HAEC with oxidized low density lipoprotein (oxLDL) led to phosphorylation of p66Shc at Ser-36, resulting in an enhanced production of superoxide anion (O2-). In the absence of oxLDL, inhibition of eNOS by small interfering RNA or L-NAME, induced p66Shc phosphorylation, suggesting that basal NO production inhibits O2- production. oxLDL-induced, p66Shc-mediated O2- was prevented by eNOS inhibition, suggesting that when cells are stimulated with oxLDL eNOS is a source of reactive oxygen species. Endogenous or exogenous NO donors, prevented p66Shc activation and reduced O2- production. Treatment with tetrahydrobiopterin, an eNOS cofactor, restored eNOS uncoupling, prevented p66Shc activation, and reduced O2- generation. However, late treatment with tetrahydropterin did not yield the same result suggesting that eNOS uncoupling is the primary source of reactive oxygen species.

CONCLUSIONS

The present study reports that in primary cultured HAEC treated with oxLDL, p66Shc-mediated oxidative stress is derived from eNOS uncoupling. This finding contributes novel information on the mechanisms of p66Shc activation and its dual interaction with eNOS underscoring the importance eNOS uncoupling as a putative antioxidant therapeutical target in endothelial dysfunction as observed in cardiovascular disease.

Netrin-1 abrogates ischemia/reperfusion-induced cardiac mitochondrial dysfunction via nitric oxide-dependent attenuation of NOX4 activation and recoupling of NOS

Despite an established role of mitochondrial dysfunction in cardiac ischemia/reperfusion (I/R) injury, the upstream activators have remained incompletely defined. We have recently identified an innovative role of exogenously applied netrin-1 in cardioprotection, which is mediated by increased nitric oxide (NO) bioavailability. Here, we tested the hypothesis that this "pharmacological" treatment of netrin-1 preserves mitochondrial function via novel mechanisms that are NO dependent. Freshly isolated C57BL6 mouse hearts were perfused using a Langendorff system, and subjected to a 20min global ischemia/60min reperfusion, in the presence or absence of netrin-1. I/R induced marked increases in infarct size, total superoxide and hydrogen peroxide production, activity and protein abundance of NADPH oxidase (NOX) isoform 4 (NOX4), as well as impaired mitochondrial integrity and function, all of which were attenuated by netrin-1. This protective effect of netrin-1 is attributed to cGMP, a downstream effector of NO. The protein levels of NOX1 and NOX2 were however unaffected, and infarct size from NOX1 and NOX2 knockouts was not different from wild type animals. Scavenging of NO with PTIO reversed inhibitory effects of netrin-1 on NOX4, while NO donor attenuated NOX4 protein abundance. In vivo NOX4 RNAi, or sepiapterin perfusion, resulted in recoupling of NOS, decreased infarct size, and blockade of dysfunctional mitochondrial swelling and mitochondrial superoxide production. These data demonstrate that netrin-1 induces cardioprotection through inhibition of NOX4 activity, which leads to recoupling of NOS, augmented NO bioavailability, reduction in oxidative stress, and ultimately preservation of mitochondrial function. The NO-dependent NOX4 inhibition connects with our previously established pathway of DCC/ERK1/2/eNOS/NO/DCC feed-forward mechanism, to maintain NOS in the coupling state to attenuate oxidative stress to preserve mitochondrial function. These findings may promote development of novel therapeutics for cardiac I/R injury. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease".