Peroxynitrite, the product of nitric oxide and superoxide, causes myocardial injury in the isolated perfused rat heart

An Analysis of Myocardial Efficiency in Patients with Severe Asymptomatic Mitral Regurgitation

BACKGROUND

It is difficult to determine left ventricular systolic performance in patients with severe mitral regurgitation (MR) since left ventricular ejection fraction (EF) could be preserved until the end stages of the disease. Myocardial efficiency (MEf) describes the amount of external work (EW) done by the left ventricle per unit of oxygen consumed (mVO₂). In the present study, we aimed to investigate MEf in patients with asymptomatic severe MR using a novel echocardiographic method.

METHODS

A total of 27 patients with severe asymptomatic MR and 26 healthy volunteers were included in this cross-sectional study. EW was measured using stroke volume and blood pressure, while mVO₂ was estimated using double product and left ventricular mass.

RESULTS

There were no differences between the groups with regards to EF (66% ± 5% vs. 69% ± 7%), while MEf was significantly reduced in patients with severe MR (25% ± 11% vs. 44% ± 12%, p < 0.001). This difference was maintained even after adjustment for age, gender and body surface area (adjusted x-: 0.44, 95% CI: 0.39–0.49 for controls and adjusted x-: 0.24, 95% CI: 0.19–0.29 for patients with severe MR). Further analysis showed that this reduction was due to an increase in total mVO₂ in the severe MR group. MEf of thepatients who were both on β-blockers and angiotensin converting enzyme inhibitors/angiotensin receptor blockers were higher than those who were not on any drugs, but this difference was not statistically significant (32% ± 15% vs. 23% ± 9%, p = 0.41).

CONCLUSIONS

MEf was significantly lower in patients with asymptomatic severe MR and preserved EF.

The influence of oxidative stress on cardiac remodeling in obese adolescents

Oxidative stress seems to be an important link between obesity and cardiovascular disease. The aim of our study was to assess oxidative stress in obese patients stratified according to ambulatory blood pressure status and to determine independent predictors of abnormal left ventricular geometry.A cross-sectional study was conducted. A total of 113 obese participants referred for 24-h ambulatory blood pressure monitoring (ABPM) aged 9-19 years, and 29 healthy controls were enrolled. In addition to anthropometric and biochemical measurements, such as fasting serum levels of glucose, insulin, lipid profile, and oxidative biomarkers, ABPM and echocardiography were performed.According to ABPM results, obese subjects were split in two groups: 57 hypertensive and 56 normotensive. Both hypertensive and normotensive obese participants had higher levels of oxidative stress parameters (pro-oxidative/antioxidative balance and total oxidant status) compared with control group. Levels of superoxide anion (O₂^-) and sulfhydryl groups were higher in obese hypertensive participants as compared to obese normotensive and control groups. Abnormal left ventricular geometry among obese participants was independently associated with O₂^- (p = .006) and body mass index z score (p = .020), with no significant impact of gender, while age and systolic blood pressure exhibited interaction term for the outcome.The independent effect of oxidative mechanisms on left ventricular geometry appears to start in childhood. Oxidative stress occurs in obese adolescents prior to the development of sustained hypertension.

Integrated molecular, biochemical, and physiological assessment unravels key extraction method mediated influences on rat neonatal cardiomyocytes

Neonatal cardiomyocytes are instrumental for disease modeling, but the effects of different cell extraction methods on basic cell biological processes remain poorly understood. We assessed the influence of two popular methods to extract rat neonatal cardiomyocytes, Pre-plating (PP), and Percoll (PC) on cell structure, metabolism, and function. Cardiomyocytes obtained from PP showed higher gene expression for troponins, titin, and potassium and sodium channels compared to PC. Also, PP cells displayed higher levels of troponin I protein. Cells obtained from PC displayed higher lactate dehydrogenase activity and lactate production than PP cells, indicating higher anaerobic metabolism after 8 days of culture. In contrast, reactive oxygen species levels were higher in PP cells as indicated by ethidium and hydroxyethidium production. Consistent with these data, protein nitration was higher in PP cells, as well as nitrite accumulation in cell medium. Moreover, PP cells showed higher global intracellular calcium under basal and 1 mM isoprenaline conditions. In a calcium-transient assessment under electrical stimulation (0.5 Hz), PP cells displayed higher calcium amplitude than cardiomyocytes obtained from PC and using a traction force microscope technique we observed that PP cardiomyocytes showed the highest relaxation. Collectively, we demonstrated that extraction methods influence parameters related to cell structure, metabolism, and function. Overall, PP derived cells are more active and mature than PC cells, displaying higher contractile function and generating more reactive oxygen species. On the other hand, PC derived cells display higher anaerobic metabolism, despite comparable high yields from both protocols.

Catalpol decreases peroxynitrite formation and consequently exerts cardioprotective effects against ischemia/reperfusion insult

CONTEXT

Peroxynitrite (ONOO(-)) formation triggers oxidative/nitrative stress and contributes to exacerbated myocardial ischemia/reperfusion (MI/R) injury. Catalpol, an iridoid glycoside, abundantly found in the roots of Rehmannia glutinosa L. that is included in the family Phrymaceae in the order Lamiales, endemic to China, was found to have neuroprotective effects. However, the effect of catalpol on MI/R injury has not been identified.

OBJECTIVE

This study investigated whether catalpol attenuates oxidative/nitrative stress in acute MI/R.

MATERIALS AND METHODS

Adult male rats were subjected to 30 min of myocardial ischemia and 3 h of reperfusion and were treated with saline, catalpol (5 mg/kg, i.p., 5 min before reperfusion) or catalpol plus wortmannin (15 µg/kg intraperitoneally injected 15 min before reperfusion).

RESULTS

Pretreatment with catalpol significantly improved cardiac functions, reduced myocardial infarction, apoptosis and necrosis of cardiomyocytes after MI/R (all p < 0.05). Meanwhile, ONOO(-) formation was markedly reduced after catalpol treatment (3.01 ± 0.22 vs. 4.66 ± 0.53 pmol/mg protein in vehicle, p < 0.05). In addition, catalpol increased Akt and endothelial nitric oxide synthase phosphorylation, nitric oxide (NO) production, anti-oxidant capacity and reduced MI/R-induced inducible nitric oxide synthase expression and superoxide anion (·O(2)(-)) production in I/R hearts. PI3K inhibitor wortmannin not only blocked catalpol-induced Akt activation, but also attenuated all the beneficial effects of catalpol. Suppression of ONOO(-) formation by either catalpol or an ONOO(-) scavenger uric acid (5 mg/kg) reduced myocardial infarct size in MI/R rats.

DISCUSSION AND CONCLUSION

In conclusion, catalpol affords cardioprotection against MI/R insult by attenuating ONOO(-) formation, which is attributable to increased physiological NO and decreased ·O(2)(-) production.

Clofibrate PPARα activation reduces oxidative stress and improves ultrastructure and ventricular hemodynamics in no-flow myocardial ischemia

Peroxisome proliferator-activated receptors (PPAR) play a critical physiological role in energy homeostasis, in inflammation, and a protective role in cardiovascular function. We assessed the antioxidant effect of clofibrate-induced Peroxisome proliferator-activated receptor alpha (PPARα) stimulation on ischemic myocardium on myocardial morphology and hemodynamics. Male Wistar rats (300 g) were distributed into the following groups: (1) Sham, (2) myocardial ischemia vehicle treated (MI-V), and (3) myocardial ischemia clofibrate [100 mg/kg/ intraperitoneally) treated (MI-C). Reactive oxygen species (ROS) and lipid peroxidation increased in MI-V, whereas clofibrate prevented this effect. Superoxide dismutase (SOD)-1 and SOD-2 expression increased 4 times upon PPARα stimulation. SOD-1, SOD-2, and catalase activity also increased in response to clofibrate. eNOS mRNA and tetrahydrobiopterin increased in the MI-C group. Clofibrate was able to decrease Angiotensin II (AngII), AngII AT1-receptor, whereas Ang-(1-7) and AngII AT2-receptor expression increased. Assessment of myocardial morphology and cardiac function show that clofibrate improved histological features and hemodynamic parameters. Our results suggest that PPARα stimulation by clofibrate increases the antioxidant defense, leading to improved cardiac function.

Modulation of myocardial contraction by peroxynitrite

Peroxynitrite is a potent oxidant that is quickly emerging as a crucial modulator of myocardial function. This review will focus on the regulation of myocardial contraction by peroxynitrite during health and disease, with a specific emphasis on cardiomyocyte Ca²⁺ handling, proposed signaling pathways, and protein end-targets.

Quercetin reduces inflammatory responses in LPS-stimulated cardiomyoblasts

Flavonoids possess several biological and pharmacological activities. Quercetin (Q), a naturally occurring flavonoid, has been shown to downregulate inflammatory responses and provide cardioprotection. However, the mechanisms behind the anti-inflammatory properties of Q in cardiac cells are poorly understood. In inflammation, nitric oxide (NO) acts as a proinflammatory mediator and is synthesized by inducible nitric oxide synthase (iNOS) in response to pro-inflammatory agents such as lipopolysaccharide (LPS), a causative agent in myocardial depression during sepsis. In the present study, we evaluated the protective effect of Q on rat cardiac dysfunction during sepsis induced by LPS. Pretreatment of H9c2 cardiomyoblasts with Q inhibited LPS-induced iNOS expression and NO production and counteracted oxidative stress caused by the unregulated NO production that leads to the generation of peroxynitrite and other reactive nitrogen species. In addition, Q pretreatment significantly counteracted apoptosis cell death as measured by immunoblotting of the cleaved caspase 3 and caspase 3 activity. Q also inhibited the LPS-induced phosphorylation of the stress-activated protein kinases (JNK/SAPK) and p38 MAP kinase that are involved in the inhibition of cell growth as well as the induction of apoptosis. In conclusion, these results suggest that Q might serve as a valuable protective agent in cardiovascular inflammatory diseases.

Synergy of isoflurane preconditioning and propofol postconditioning reduces myocardial reperfusion injury in patients

Either isoflurane preconditioning or high-dose propofol treatment has been shown to attenuate myocardial IRI (ischaemia/reperfusion injury) in patients undergoing CABG (coronary artery bypass graft) surgery. It is unknown whether isoflurane and propofol may synergistically attenuate myocardial injury in patients. The present study investigated the efficacy of IsoPC (isoflurane preconditioning), propofol treatment (postconditioning) and their synergy in attenuating postischaemic myocardial injury in patients undergoing CABG surgery using CPB (cardiopulmonary bypass). Patients (n = 120) selected for CABG surgery were randomly assigned to one of four groups (n = 30 each). After induction, anaesthesia was maintained either with fentanyl and midazolam (control; group C); with propofol at 100 μg x kg(-1) of body weight x min(-1) before and during CPB followed by propofol at 60 μg x kg(-1) of body weight x min(-1) for 15 min after aortic declamping (group P); with isoflurane 1-1.5% end tidal throughout the surgery (group I) or with isoflurane 1-1.5% end tidal before CPB and switching to propofol at 100 μg x kg(-1) of body weight x min(-1) during CPB followed by propofol at 60 μg x kg(-1) of body weight x min(-1) for 15 min after aortic declamping (group IP, i.e. IsoPC plus propofol postconditioning). A joint isoflurane and propofol anaesthesia regimen synergistically reduced plasma levels of cTnI (cardiac troponin I) and CK-MB (creatine kinase MB) and f-FABP (heart-type fatty acid-binding protein) (all P < 0.05 compared with control, group P or group I) and facilitated postoperative myocardial functional recovery. During reperfusion, myocardial tissue eNOS (endothelial NO synthase) protein expression in group IP was significantly higher, whereas nitrotyrosine protein expression was lower than those in the control group. In conclusion, a joint isoflurane preconditioning and propofol anaesthesia regimen synergistically attenuated myocardial reperfusion injury in patients.

Ischemia induced peroxynitrite dependent modifications of cardiomyocyte MLC1 increases its degradation by MMP-2 leading to contractile dysfunction

Damage to cardiac contractile proteins during ischemia followed by reperfusion is mediated by reactive oxygen species such as peroxynitrite (ONOO⁻), resulting in impairment of cardiac systolic function. However, the pathophysiology of systolic dysfunction during ischemia only, before reperfusion, remains unclear. We suggest that increased ONOO⁻ generation during ischemia leads to nitration/nitrosylation of myosin light chain 1 (MLC1) and its increased degradation by matrix metalloproteinase-2 (MMP-2), which leads to impairment of cardiomyocyte contractility. We also postulate that inhibition of ONOO⁻ action by use of a ONOO⁻ scavenger results in improved recovery from ischemic injury. Isolated rat cardiomyocytes were subjected to 15 and 60 min. of simulated ischemia. Intact MLC1 levels, measured by 2D gel electrophoresis and immunoblot, were shown to decrease with increasing duration of ischemia, which correlated with increasing levels of nitrotyrosine and nitrite/nitrate. In vitro degradation of human recombinant MLC1 by MMP-2 increased after ONOO⁻ exposure of MLC1 in a concentration-dependent manner. Mass spectrometry analysis of ischemic rat cardiomyocyte MLC1 showed nitration of tyrosines 78 and 190, as well as of corresponding tyrosines 73 and 185 within recombinant human cardiac MLC1 treated with ONOO⁻. Recombinant human cardiac MLC1 was additionally nitrosylated at cysteine 67 and 76 corresponding to cysteine 81 of rat MLC1. Here we show that increased ONOO⁻ production during ischemia induces MLC1 nitration/nitrosylation leading to its increased degradation by MMP-2. Inhibition of MLC1 nitration/nitrosylation during ischemia by the ONOO⁻ scavenger FeTPPS (5,10,15,20-tetrakis-[4-sulfonatophenyl]-porphyrinato-iron[III]), or inhition of MMP-2 activity with phenanthroline, provides an effective protection of cardiomyocyte contractility.

Insulin attenuates myocardial ischemia/reperfusion injury via reducing oxidative/nitrative stress

It is well known that insulin possesses a cardioprotective effect and that insulin resistance is closely related to cardiovascular diseases. Peroxynitrite (ONOO(-)) formation may trigger oxidative/nitrative stress and represent a major cytotoxic effect in heart diseases. This study was designed to investigate whether insulin attenuates ONOO(-) generation and oxidative/nitrative stress in acute myocardial ischemia/reperfusion (MI/R). Adult male rats were subjected to 30 min of myocardial ischemia and 3 h of reperfusion. Rats randomly received vehicle, insulin, or insulin plus wortmannin. Arterial blood pressure and left ventricular pressure were monitored throughout the experiment. Insulin significantly improved cardiac functions and reduced myocardial infarction, apoptotic cell death, and blood creatine kinase/lactate dehydrogenase levels following MI/R. Myocardial ONOO(-) formation was significantly attenuated after insulin treatment. Moreover, insulin resulted in a significant increase in Akt and endothelial nitric oxide (NO) synthase (eNOS) phosphorylation, NO production, and antioxidant capacity in ischemic/reperfused myocardial tissue. On the other hand, insulin markedly reduced MI/R-induced inducible NOS (iNOS) and gp91(phox) expression in cardiac tissue. Inhibition of insulin signaling with wortmannin not only blocked the cardioprotection of insulin but also markedly attenuated insulin-induced antioxidative/antinitrative effect. Furthermore, the suppression on ONOO(-) formation by either insulin or an ONOO(-) scavenger uric acid reduced myocardial infarct size in rats subjected to MI/R. We concluded that insulin exerts a cardioprotective effect against MI/R injury by blocking ONOO(-) formation. Increased physiological NO production (via eNOS phosphorylation) and superoxide anion reduction contribute to the antioxidative/antinitrative effect of insulin, which can be reversed by inhibiting phosphatidylinositol 3'-kinase. These results provide important novel information on the mechanisms of cardiovascular actions of insulin.

Peroxynitrite Increases Protein Phosphatase Activity and Promotes the Interaction of Phospholamban with Protein Phosphatase 2a in the Myocardium

High levels of peroxynitrite have been shown to decrease cardiomyocyte contraction through a reduction in phospholamban (PLB) phosphorylation. However, previous reports did not examine the direct effect of peroxynitrite on protein phosphatase activity in the myocardium or the role of specific phosphatases. Here we test the effect of the peroxynitrite donor SIN-1 on protein phosphatase activity in whole heart homogenates, as well as the interaction of PLB with protein phosphatase 1 (PP1) and 2a (PP2a). SIN-1 (200 μmol/L) induced a significant increase in protein phosphatase activity, which was alleviated with the specific PP1/PP2a inhibitor okadaic acid. Conversely, lower concentrations of SIN-1 and the nitric oxide donor spermine NONOate (300 μmol/L) were both without effect on phosphatase activity. We next examined the effect of SIN-1 on the interaction of PLB with PP1 and PP2a using co-immunoprecipitation, since okadaic acid inhibited the effects of SIN-1 in our current and previous studies. SIN-1 significantly increased the interaction of PLB with PP2a, but had no effect on the interaction between PLB and PP1. Urate, a peroxynitrite scavenger, inhibited the effects of SIN-1 on phosphatase activity and the interaction of PLB with PP2a, thus implicating peroxynitrite as the causal species. The results of this study provide further insight into the mechanism through which high levels of peroxynitrite serve to decrease PLB phosphorylation and myocardial contraction. Therefore, peroxynitrite signaling could play a key role in the contractile dysfunction manifested in heart failure where peroxynitrite production and protein phosphatase activity are increased and PLB phosphorylation is decreased.

Biphasic effect of SIN-1 is reliant upon cardiomyocyte contractile state

Many studies have demonstrated a biphasic effect of peroxynitrite in the myocardium, but few studies have investigated this biphasic effect on beta-adrenergic responsiveness and its dependence on contractile state. We have previously shown that high 3-morpholinosydnonimine (SIN-1) (source of peroxynitrite, 200 micromol/L) produced significant anti-adrenergic effects during maximal beta-adrenergic stimulation in cardiomyocytes. In the current study, we hypothesize that the negative effects of high SIN-1 will be greatest during high contractile states, whereas the positive effects of low SIN-1 (10 micromol/L) will predominate during low contractility. Isolated murine cardiomyocytes were field stimulated at 1 Hz, and [Ca(2+)](i) transients and shortening were recorded. After submaximal isoproterenol (ISO) (beta-adrenergic agonist, 0.01 micromol/L) stimulation, 200 micromol/L SIN-1 induced two distinct phenomena. Cardiomyocytes undergoing a large response to ISO showed a significant reduction in contractility, whereas cardiomyocytes exhibiting a modest response to ISO showed a further increase in contractility. Additionally, 10 micromol/L SIN-1 always increased contractility during low ISO stimulation, but had no effect during maximal ISO (1 micromol/L) stimulation. SIN-1 at 10 micromol/L also increased basal contractility. Interestingly, SIN-1 produced a contractile effect under only one condition in phospholamban-knockout cardiomyocytes, providing a potential mechanism for the biphasic effect of peroxynitrite. These results provide clear evidence for a biphasic effect of peroxynitrite, with high peroxynitrite modulating high levels of beta-adrenergic responsiveness and low peroxynitrite regulating basal function and low levels of beta-adrenergic stimulation.

Targeting of phospholamban by peroxynitrite decreases beta-adrenergic stimulation in cardiomyocytes

AIMS

Peroxynitrite production increases during the pathogenesis of numerous cardiac disorders (e.g. heart failure). However, limited studies have investigated the mechanism through which peroxynitrite exerts anti-adrenergic effects. Thus, the purpose of this study is to investigate the contribution of phospholamban (PLB), a critical excitation-contraction coupling protein, to the peroxynitrite-induced dysfunction.

METHODS AND RESULTS

Isolated myocytes from wild-type (WT, CF-1) and PLB knockout (PLB(-/-)) mice were stimulated at 1 Hz, and myocyte shortening and Ca(2+) transients were simultaneously recorded. PLB phosphorylation was measured via western blot. Myocytes were superfused with isoproterenol, a beta-adrenergic agonist, and SIN-1, a peroxynitrite donor. SIN-1 superfusion dramatically decreased isoproterenol-stimulated Ca(2+) transients and myocyte shortening in WT myocytes. These effects were inhibited upon addition of the peroxynitrite decomposition catalyst, FeTPPS. Surprisingly, SIN-1 had no functional effect on beta-adrenergic-stimulated PLB(-/-) myocytes. Western blot analyses revealed that SIN-1 significantly decreased isoproterenol-stimulated PLB(Ser16) phosphorylation. Experiments with the protein phosphatase inhibitor, okadaic acid, alleviated the SIN-1-induced functional effects and the decrease in PLB phosphorylation.

CONCLUSIONS

The peroxynitrite donor SIN-1 decreases beta-adrenergic stimulation by reducing PLB(Ser16) phosphorylation via protein phosphatase activation. This peroxynitrite-induced decrease in PLB phosphorylation may be a key mechanism in the beta-adrenergic dysfunction observed in many cardiomyopathies.

Role of oxygen in postischemic myocardial injury

Myocardial function is dependent on a constant supply of oxygen from the coronary circulation. A reduction of oxygen supply due to coronary obstruction results in myocardial ischemia, which leads to cardiac dysfunction. Reperfusion of the ischemic myocardium is required for tissue survival. Thrombolytic therapy, coronary artery bypass surgery and coronary angioplasty are some of the treatments available for the restoration of blood flow to the ischemic myocardium. However, the restoration of blood flow may also lead to reperfusion injury, resulting in myocyte death. Thus, any imbalance between oxygen supply and metabolic demand leads to functional, metabolic, morphologic, and electrophysiologic alterations, causing cell death. Myocardial ischemia reperfusion (IR) injury is a multifactorial process that is mediated by oxygen free radicals, neutrophil activation and infiltration, calcium overload, and apoptosis. Controlled reperfusion of the ischemic myocardium has been advocated to prevent the IR injury. Studies have shown that reperfusion injury and postischemic cardiac function are related to the quantity and delivery of oxygen during reperfusion. Substantial evidence suggests that controlled reoxygenation may ameliorate postischemic organ dysfunction. In this review, we discuss the role of oxygenation during reperfusion and subsequent biochemical and pathologic alterations in reperfused myocardium and recovery of heart function.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Peroxynitrite and myocardial contractility: in vivo versus in vitro effects

Generation of peroxynitrite (ONOO-) as a result of altered redox balance has been shown to affect cardiac function; however, inconsistencies in the data exist, particularly for myocardial contractility. The hypothesis that the cardiac impact of ONOO- formation depends on its site of generation, intravascular or intramyocardial, was examined. Cardiac contractility was assessed by pressure-volume analysis to delineate vascular versus cardiac changes on direct infusion of ONOO- into the right atria of conscious dogs both with normal cardiac function and in heart failure. Additionally, ONOO- was administered to isolated murine cardiomyocytes to mimic in situ cardiac generation. When infused in vivo, ONOO- had little impact on inotropy but led to systemic arterial dilation, likely as a result of rapid decomposition to NO2- and NO3-. In contrast, infused ONOO- was long lived enough to abolish beta-adrenergic (dobutamine)-stimulated contractility/relaxation, most likely through catecholamine oxidation to aminochrome. When administered to isolated murine cardiomyocytes, ONOO- induced a rapid reduction in sarcomere shortening and whole cell calcium transients, although neither decomposed ONOO- or NaNO2 had any effect. Thus, systemic generation of ONOO- is unlikely to have primary cardiac effects, but may modulate cardiac contractile reserve, via blunted beta-adrenergic stimulation, and vascular tone, as a result of generation of NO2- and NO3-. However, myocyte generation of ONOO- may impair contractile function by directly altering Ca2+ handling. These data demonstrate that the site of generation within the cardiovascular system largely dictates the ability of ONOO- to directly or indirectly modulate cardiac pump function.

Renal damage in rats induced by myocardial ischemia/reperfusion: Role of nitric oxide

BACKGROUND

It has been demonstrated that myocardial ischemia/reperfusion (MI/R) causes renal damage. However, the mechanism underlying this damage in kidneys during revascularization of myocardium is unclear. Direct renal ischemia/reperfusion has been implicated in the induction of inducible nitric oxide synthase (iNOS) that leads to increase production of nitric oxide (NO). Recently, excessive production of NO has been found to be involved in causing renal injury by formatting peroxinitrite (ONOO(-)). The aim of this study was to investigate whether NO has a role in this damage, using aminoguanidine (AMG), a known iNOS inhibitor and an antioxidant, in rats undergoing MI/R.

METHODS

Male Wistar rats were used for the experiments (n = 7 each group). In the MI/R group, the left coronary artery was occluded for 30 min and then reperfused for 120 min; the same procedure was used for the AMG group, with the additional step of AMG (200 mg/kg) administered 10 min prior to ischemia. A control group underwent sham operation. At the end of the reperfusion period, all rats were killed and their kidneys removed for biochemical determination and histopathological analysis.

RESULTS

Myocardial ischemia/reperfusion in the rat kidney was accompanied by a significant increase in malondialdehyde and NO production, and a decrease in glutathione content. Administration of AMG reduced malondialdehyde and NO production and prevented depletion of glutathione content. These beneficial changes in the biochemical parameters were also associated with parallel changes in histopathological appearance.

CONCLUSION

These findings suggest that MI/R plays a causal role in kidney injury and AMG exerts renal-protective effects, probably by inhibiting NO production and antioxidant activities.

Effect of aminoguanidine on ischemia-reperfusion induced myocardial injury in rats

Myocardial ischemia-reperfusion (MI/R) has been implicated in the induction of inducible nitric oxide synthase (iNOS) that leads to increase production of nitric oxide (NO). Recently, excessive production of NO has been involved in causing myocardial injury. In our in vivo model, we examined the effects of aminoguanidine (AMG), a known iNOS inhibitor, on percentage infarct size in anaesthetized rats. A total of 14 rats were equally divided into two groups (n = 7 in each group). To produce myocardial necrosis, the left main coronary artery was occluded for 30 min, followed by 120 min of reperfusion, in anesthetized rats. AMG (200 mg kg(-1)) was given intravenously 10 min before occlusion. The volume of infarct size and the risk zone were determined by planimentry of each tracing and multiplying by the slice thickness. Infarct size was normalized by expressing it as a percentage of the area at risk. Hemodynamic parameters were measured via the left carotid artery. Compared to MI/R group, whereas AMG administration elevated mean arterial blood pressure, statistically reduced the myocardial infarct size (21+/- 1 and 14+/- 4%, respectively) and infract size/risk zone (53+/- 3 and 37+/- 5%, respectively) in rat model of ischemia-reperfusion. In conclusion, this study indicates that iNOS inhibitor, AMG, show reduction in NO's side effect in I/R injury.

Reactive oxygen species mediate abnormal contractile response to sympathetic nerve stimulation and noradrenaline in the vas deferens of chronically diabetic rats: effects of in vivo treatment with antioxidants

Previous studies suggest that a link exists between increased oxidative stress and diabetic neuropathy. Moreover, antioxidants may protect neurones from the degenerative effects of reactive oxygen species. In our study, we used streptozotocin (STZ)-diabetic rats in a 8-month chronic diabetes model to study the effects of in vivo treatment with stobadine (ST), a pyridoindole antioxidant, and vitamin E. STZ-diabetic rats were treated with ST (24.7 mg/kg/day), vitamin E (D,L-alpha-tocopheryl acetate, 400-500 IU/kg/day) or ST plus vitamin E through an intra-oral catheter for a 8-month period beginning 10 days after STZ injection. Blood glucose and HbA1c levels were increased in diabetic rats by about 400 and 100%, respectively. Antioxidant treatment significantly decreased haemoglobin glycosylation (P < 0.05). We also determined the effects of chronic diabetes on sympathetic neurotransmission by measuring the contractility of isolated vas deferens. Furthermore, we investigated contractions elicited by electrical field stimulation (EFS) (1-64 Hz) which were significantly decreased in diabetic rats when compared with control rats. Treatment with ST or vitamin E alone partly enhanced the amplitude of the contractions induced by EFS, but a combination of ST and vitamin E treatment showed no additional effects. Contractile response of the vas deferens to exogenous noradrenaline, was increased in diabetic rats when compared with control rats. While the addition of vitamin E alone had no effect, ST completely returned noradrenaline-induced contractions to basal levels. The tension induced by 120 mm KCl was not statistically different among the experimental groups. In normal rats, EFS-induced contractions were significantly inhibited by pyrogallol (10(-4) m), a free-radical generator. Percentage inhibition of pyrogallol on EFS (32 Hz)-induced contractions in ring sections was 48 +/- 5.8 in control, 75 +/- 5.5 in untreated-diabetic, 54 +/- 2.7 in ST-treated diabetic, and 58 +/- 4.7 in vitamin E-treated diabetic rats. Combining both ST and vitamin E treatment had the same effects as each antioxidant alone with a percent inhibition of 48 +/- 6.8. These results are consistent with the degenerative changes seen in sympathetic nerves and the abnormal function observed in chronically diabetic rats, leading to a decrease in EFS response and an increase in response to adrenergic agonists in the vas deferens. Furthermore, we demonstrated that reactive oxygen species are responsible for impaired sympathetic neurotransmission and abnormal function of diabetic vas deferens, and that a combination of antioxidants may be better for the therapy of reproductive system disabilities in male diabetics.

Role of nitric oxide in the pathophysiology of heart failure

Nitric oxide (NO) plays critical roles in the regulation of integrated cardiac and vascular function and homeostasis. An understanding of the physiologic role and relative contribution of the three NO synthase isoforms (neuronal--NOS1, inducible--NOS2, and endothelial--NOS3) is imperative to comprehend derangements of the NO signaling pathway in the failing cardiovascular system. Several theories of NO and its regulation have developed as explanations for the divergent observations from studies in health and disease states. Here we review the physiologic and pathophysiologic influence of NO on cardiac function, in a framework that considers several theories of altered NO signaling in heart failure. We discuss the notion of spatial compartmentalization of NO signaling within the myocyte in an effort to reconcile many controversies about derangements in the influences of NO in the heart and vasculature.

Effect of deferoxamine and L-arginine treatment on lipid peroxidation in an intestinal ischaemia-reperfusion model in rats

This study investigated lipid peroxidation (LPO) changes during intestinal ischaemia-reperfusion with and without deferoxamine or L-arginine treatment. White Wistar rats were allotted into four groups as follows: sham-operated (Group SOP), ischaemia-reperfusion only (Group I/R), I/R with deferoxamine (Group D) or L-arginine (Group A) treatment. Concentration of thiobarbituric acid reactive substances (TBARS), overall concentration of malondialdehyde and 4-hydroxy-alkenals (LPO586), activities of superoxide dismutase (SOD) and glutathione peroxidase (GPX) of the jejunal homogenates were determined. The same analytes except LPO586 were assayed in RBC haemolysates. Measurements of ferric reducing ability (FRAP), total antioxidant status (TAS) and nitric oxide (NO) concentrations of plasma samples were also completed. The only significant change observed in the SOP group was an increased SOD activity after the ischaemic period. In the I/R group significant increase of intestinal LPO586 concentration was observed during hypoxia that was followed by similar changes in intestinal and RBC TBARS and plasma FRAP values upon reperfusion. In Group D the intestinal TBARS and LPO586 concentrations were significantly lower while FRAP and NO concentrations were significantly higher compared to the I/R group. At the same time RBC TBARS concentration and GPX activity significantly decreased within Group D. In Group A the intestinal LPO586 concentration was significantly lower than in the I/R group whilst RBC TBARS concentration showed a similar pattern. Plasma FRAP and NO concentration showed similar changes to those seen in Group D. It is concluded that I/R increased the LPO in the intestinal tissue and altered some parameters of plasma and RBCs, too. Deferoxamine treatment prevented these effects, while the usefulness of L-arginine remained doubtful.

Implications of nitric oxide synthase isoforms in the pathophysiology of Peyronie's disease

Peyronie's disease is an idiopathic, localized connective tissue disorder of the penis which involves the tunica albuginea of the corpus cavernosum and the adjacent areolar space. Peyronie's disease is characterized by local changes in the collagen and elastic fiber composition of the tunica albuginea. The formation of fibrotic plaques alters penile anatomy and can cause different degrees of bending and narrowing, as well as penile pain and erectile dysfunction. Though long recognized as an important clinical entity of the male genitalia, the etiology of this disease has remained poorly understood. Until recently there have been no studies to examine the role nitric oxide (NO) and nitric oxide synthase (NOS) isoforms may play in the onset and progression of Peyronie's disease. NO is a potent biological mediator with diverse physiological and pathophysiological roles. The purpose of this review is to describe each of the NOS isoforms and their potential roles in the pathophysiology of Peyronie's disease, with particular emphasis on the regulation of endothelial and inducible NOS isoforms.

Relation of functional capacity with the oxidative stress and antioxidants in chronic heart failure

Chronic heart failure is a common, disabling disorder with high mortality. Oxidative stress may have both functional and structural effects on the myocardium, leading to myocardial decompensation. In this study, the authors examined the relationship of oxidative stress and functional capacity in patients with varying degrees of heart failure. Fifty-one patients with chronic heart failure and 31 control subjects were studied. The functional capacity of patients was determined. Plasma malondialdehyde, vitamin E, and beta-carotene levels were measured. The malondialdehyde levels were significantly different between control subjects and heart failure patients (p=0.03). There was a positive correlation between patients' malondialdehyde levels and New York Heart Association functional class (r=0.59; p<0.0001). There was a negative correlation between the functional class and vitamin E and beta-carotene levels (r=20.43; p<0.0001 and r=20.25; p<0.01, respectively). These data demonstrate that oxidative stress is increased systemically in patients with chronic heart failure. It seems that this increase correlates with functional class. (c)2001 CHF, Inc.

Protein kinase C activation and cardioprotective effect of preconditioning with oxidative stress in isolated rat heart

The present study is designed to investigate the effect of myocardial preconditioning with oxidative stress induced by pyrogallol or H2O2, on ischaemia-reperfusion induced myocardial injury. Isolated perfused rat heart was subjected to global ischaemia for 30 min followed by reperfusion for 120 min. Coronary effluent was analysed for LDH and CK release to assess the degree of cardiac injury. Myocardial infarct size was estimated macroscopically using TTC staining. Four episodes of preconditioning induced by pyrogallol or hydrogen peroxide (H2O) or ischaemia markedly reduced LDH and CK release in coronary effluent and decreased myocardial infarct size. Administration of polymyxin B, a protein kinase C (PKC) inhibitor, during pyrogallol, H2O2 or ischaemic preconditioning markedly attenuated the cardioprotective effect of preconditioning produced with oxidative stress or ischaemia. These results suggest that preconditioning with oxidative stress may provide cardioprotection similar to ischaemic preconditioning, against ischaemia-reperfusion injury and this cardioprotective effect may be mediated through activation of PKC.

Nitroxyl anion exerts redox-sensitive positive cardiac inotropy in vivo by calcitonin gene-related peptide signaling

Nitroxyl anion (NO(-)) is the one-electron reduction product of nitric oxide (NO( small middle dot)) and is enzymatically generated by NO synthase in vitro. The physiologic activity and mechanism of action of NO(-) in vivo remains unknown. The NO(-) generator Angeli's salt (AS, Na(2)N(2)O(3)) was administered to conscious chronically instrumented dogs, and pressure-dimension analysis was used to discriminate contractile from peripheral vascular responses. AS rapidly enhanced left ventricular contractility and concomitantly lowered cardiac preload volume and diastolic pressure (venodilation) without a change in arterial resistance. There were no associated changes in arterial or venous plasma cGMP. The inotropic response was similar despite reflex blockade with hexamethonium or volume reexpansion, indicating its independence from baroreflex stimulation. However, reflex activation did play a major role in the selective venodilation observed under basal conditions. These data contrasted with the pure NO donor diethylamine/NO, which induced a negligible inotropic response and a more balanced veno/arterial dilation. AS-induced positive inotropy, but not systemic vasodilatation, was highly redox-sensitive, being virtually inhibited by coinfusion of N-acetyl-l-cysteine. Cardiac inotropic signaling by NO(-) was mediated by calcitonin gene-related peptide (CGRP), as treatment with the selective CGRP-receptor antagonist CGRP(8-37) prevented this effect but not systemic vasodilation. Thus, NO(-) is a redox-sensitive positive inotrope with selective venodilator action, whose cardiac effects are mediated by CGRP-receptor stimulation. This fact is evidence linking NO(-) to redox-sensitive cardiac contractile modulation by nonadrenergic/noncholinergic peptide signaling. Given its cardiac and vascular properties, NO(-) may prove useful for the treatment of cardiovascular diseases characterized by cardiac depression and elevated venous filling pressures.

The cytotoxic effects of diesel exhaust particles on human pulmonary artery endothelial cells in vitro: role of active oxygen species

Diesel exhaust particles (DEP) have been proved to induce serious pulmonary injury, among which lethal pulmonary edema has been assumed to be mediated by vascular endothelial cell damage. In the present study, we investigated the cytotoxic mechanism of DEP on human pulmonary artery endothelial cells focusing on the role of active oxygen species. Endothelial cell viability was assessed by WST-8, a novel tetrazolium salt. Nitric oxide (NO) production was measured by using a new fluorescence indicator, diaminofluorescein-2 (DAF-2). Organic compounds in DEP were extracted by dichloromethane and methanol. DEP-extracts damaged endothelial cells under both subconfluent and confluent conditions. The DEP-extract-induced cytotoxicity was markedly reduced by treatment with SOD, catalase, N-(2-mercaptopropionyl)-glycine (MPG), or ebselen (a selenium-containing compound with glutathione peroxidase-like activity). Thus superoxide, hydrogen peroxide, and other oxygen-derived free radicals are likely to be implicated in DEP-extract-induced endothelial cell damage. Moreover, L-NAME and L-NMA, inhibitors of NO synthase, also attenuated DEP-extract-induced cytotoxicity, while sepiapterin, the precursor of tetrahydrobiopterin (BH(4), a NO synthase cofactor) interestingly enhanced DEP-extract-induced cell damage. These findings suggest that NO is also involved in DEP-extract-mediated cytotoxicity, which was confirmed by direct measurement of NO production. These active oxygen species, including peroxynitrite, may explain the mechanism of endothelial cell damage upon DEP exposure during the early stage.

Glutathione Reverses Endothelial Damage From Peroxynitrite, the Byproduct of Nitric Oxide Degradation, in Crystalloid Cardioplegia

Background —NO has been advocated as an adjunct to cardioplegia solutions. However, NO undergoes a rapid biradical reaction with superoxide anions to produce peroxynitrite (ONOO − ). ONOO − in crystalloid cardioplegia solution induces injury to coronary endothelium and to systolic function after cardioplegia and reperfusion. However, ONOO − may be degraded to less lethal or cardioprotective intermediates with glutathione (GSH) in reactions separate from its well known antioxidant effects. We hypothesized that GSH detoxifies ONOO − and reverses defects in endothelial function and systolic function when present in crystalloid cardioplegia.

Methods and Results —In anesthetized dogs on cardiopulmonary bypass, a 45-minute period of global normothermic ischemia was followed by 60 minutes of intermittent cold crystalloid cardioplegia (Plegisol) and 2 hours of reperfusion. The cardioplegia solution contained 5 μmol/L authentic ONOO − ; catalase was included to attenuate the potential antioxidant effects of GSH and to unmask the effects on ONOO − . In 1 group (CP+GSH, n=5), the cardioplegia contained 500 μmol/L GSH, whereas 1 group received crystalloid cardioplegia without GSH (CCP, n=6). There were no group differences in postcardioplegia left ventricular systolic function (end-systolic pressure-volume relation, impedance catheter: CCP 10.0±2.4 versus CP+GSH 10.6±1.3 mm Hg/mL) or diastolic chamber stiffness (β-coefficient: CCP 0.35±0.2 versus CP+GSH 0.31±0.18). Myocardial neutrophil accumulation (myeloperoxidase activity) was attenuated in CP+GSH versus CCP (2.2±0.7 versus 5.4±1.2, P <0.05). In postexperimental coronary arteries, maximal endothelium-dependent relaxation was greater in CP+GSH than in CCP (118±6% versus 92±5%, P <0.05), with a smaller EC 50 value (−7.10±0.05 versus −6.98±0.03, respectively, P <0.05). Smooth muscle relaxation was complete in both groups. The adherence of neutrophils to postexperimental coronary arteries as a measure of endothelial function was less in CP+GSH than in CCP (98±18 versus 234±36 neutrophils/mm 2 , P <0.05). Nitrosoglutathione, a byproduct of the reaction between ONOO − and GSH, was greater in CP+GSH than in CCP (4.1±2.3 versus 0.4±0.2 μg/mL, P <0.05).

Conclusions —GSH in crystalloid cardioplegia detoxifies ONOO − and forms cardioprotective nitrosoglutathione, resulting in attenuated neutrophil adherence and selective endothelial protection through the inhibition of neutrophil-mediated damage.

Mechanism of decreased adenosine protection in reperfusion injury of aging rats

The purpose of this study was to determine whether the protective effects of adenosine on myocardial ischemia-reperfusion injury are altered with age, and if so, to clarify the mechanisms that underlie this change related to nitric oxide (NO) derived from the vascular endothelium. Isolated perfused rat hearts were exposed to 30 min of ischemia and 60 min of reperfusion. In the adult hearts, administration of adenosine (5 micromol/l) stimulated NO release (1. 06 +/- 0.19 nmol. min(-1). g(-1), P < 0.01 vs. vehicle), increased coronary flow, improved cardiac functional recovery (left ventricular developed pressure 79 +/- 3.8 vs. 57 +/- 3.1 mmHg in vehicle, P < 0.001; maximal rate of left ventricular pressure development 2,385 +/- 103 vs. 1,780 +/- 96 in vehicle, P < 0.001), and reduced myocardial creatine kinase loss (95 +/- 3.9 vs. 159 +/- 4.6 U/100 mg protein, P < 0.01). In aged hearts, adenosine-stimulated NO release was markedly reduced (+0.42 +/- 0.12 nmol. min(-1). g(-1) vs. vehicle), and the cardioprotective effects of adenosine were also attenuated. Inhibition of NO production in the adult hearts significantly decreased the cardioprotective effects of adenosine, whereas supplementation of NO in the aged hearts significantly enhanced the cardioprotective effects of adenosine. The results show that the protective effects of adenosine on myocardial ischemia-reperfusion injury are markedly diminished in aged animals, and that the loss in NO release in response to adenosine may be at least partially responsible for this age-related alteration.

Peroxynitrite irreversibly decreases diastolic and systolic function in cardiac muscle

Much of the damaging action of nitric oxide in heart may be due to its diffusion-limited reaction with superoxide to form peroxynitrite. Direct infusion of peroxynitrite into isolated perfused hearts fails to model the effects of in situ formation because the bulk of peroxynitrite decomposes before reaching the myocytes. To examine the direct effects of peroxynitrite on the contractile apparatus of the heart, we exposed intact and skinned rat papillary muscles to a steady state concentration of 4-microM peroxynitrite for 5 min, followed by a 30-min recovery period to monitor irreversible effects. In intact muscles developed force fell immediately to 26% of initial force, recovering to 43% by 30 min. Resting tension increased by 600% immediately, and was still elevated 500% by 30 min. Nitrotyrosine immunochemistry showed that peroxynitrite can induce tyrosine nitration at low concentrations and is capable of penetrating 200-380 microm into the papillary muscle after a 5-min infusion. Decomposed peroxynitrite had no effect on either intact or skinned muscle developed force or resting tension. Our results show that peroxynitrite directly damages both developed force and resting tension of isolated heart muscle, which can be extrapolated to systolic and diastolic injury in intact hearts.