Nitric oxide, superoxide, and peroxynitrite in myocardial ischaemia-reperfusion injury and preconditioning

Differential effects of NADPH oxidase and xanthine oxidase inhibition on sympathetic reinnervation in postinfarct rat hearts

Superoxide has been shown to play a major role in ventricular remodeling and arrhythmias after myocardial infarction. However, the source of increased myocardial superoxide production and the role of superoxide in sympathetic innervation remain to be further characterized. Male Wistar rats, after coronary artery ligation, were randomized to vehicle, allopurinol, or apocynin for 4weeks. To determine the role of peroxynitrite in sympathetic reinnervation, we also used 3-morpholinosydnonimine (a peroxynitrite generator). The postinfarction period was associated with increased oxidative stress, as measured by myocardial superoxide, nitrotyrosine, xanthine oxidase activity, NADPH oxidase activity, and dihydroethidium fluorescent staining. Measurement of myocardial norepinephrine levels revealed a significant elevation in vehicle-treated infarcted rats compared with sham. Sympathetic hyperinnervation was blunted after administration of allopurinol. Arrhythmic scores in the allopurinol-treated infarcted rats were significantly lower than those in vehicle. For similar levels of ventricular remodeling, apocynin had no beneficial effects on oxidative stress, sympathetic hyperinnervation, or arrhythmia vulnerability. Allopurinol-treated hearts had significantly decreased nerve growth factor expression, which was substantially increased after coadministration of 3-morpholinosydnonimine. These results indicate that xanthine oxidase but not NADPH oxidase largely mediates superoxide production after myocardial infarction. Xanthine oxidase inhibition ameliorates sympathetic innervation and arrhythmias possibly via inhibition of the peroxynitrite-mediated nerve growth factor pathway.

Cannabidiol protects against hepatic ischemia/reperfusion injury by attenuating inflammatory signaling and response, oxidative/nitrative stress, and cell death

Ischemia/reperfusion (I/R) is a pivotal mechanism of liver damage after liver transplantation or hepatic surgery. We have investigated the effects of cannabidiol (CBD), the nonpsychotropic constituent of marijuana, in a mouse model of hepatic I/R injury. I/R triggered time-dependent increases/changes in markers of liver injury (serum transaminases), hepatic oxidative/nitrative stress (4-hydroxy-2-nonenal, nitrotyrosine content/staining, and gp91phox and inducible nitric oxide synthase mRNA), mitochondrial dysfunction (decreased complex I activity), inflammation (tumor necrosis factor α (TNF-α), cyclooxygenase 2, macrophage inflammatory protein-1α/2, intercellular adhesion molecule 1 mRNA levels; tissue neutrophil infiltration; nuclear factor κB (NF-κB) activation), stress signaling (p38MAPK and JNK), and cell death (DNA fragmentation, PARP activity, and TUNEL). CBD significantly reduced the extent of liver inflammation, oxidative/nitrative stress, and cell death and also attenuated the bacterial endotoxin-triggered NF-κB activation and TNF-α production in isolated Kupffer cells, likewise the adhesion molecule expression in primary human liver sinusoidal endothelial cells stimulated with TNF-α and attachment of human neutrophils to the activated endothelium. These protective effects were preserved in CB2 knockout mice and were not prevented by CB1/2 antagonists in vitro. Thus, CBD may represent a novel, protective strategy against I/R injury by attenuating key inflammatory pathways and oxidative/nitrative tissue injury, independent of classical CB1/2 receptors.

Post-ischemic early acidosis in cardiac postconditioning modifies the activity of antioxidant enzymes, reduces nitration, and favors protein S-nitrosylation

Postconditioning (PostC) modifies the early post-ischemic pH, redox environment, and activity of enzymes. We hypothesized that early acidosis in PostC may affect superoxide dismutase (SOD) and catalase (CAT) activities, may reduce 3-nitrotyrosine (3-NT) protein levels, and may increase S-nitrosylated (SNO) protein levels, thus deploying its protective effects. To verify this hypothesis, we studied the early (7(th) min) and late (120(th) min) phases of reperfusion (a) endogenous SOD and CAT activities and (b) 3-NT protein levels and SNO protein levels. Isolated rat hearts underwent 30-min ischemia/120-min reperfusion (I/R) or PostC (5 cycles of 10-s I/R at the beginning of 120-min reperfusion) either with or without exogenous CAT or SOD infused during the initial 3 min of reperfusion. The effects of early reperfusion with acid buffer (AB, pH 6.8) on endogenous antioxidant enzymes were also tested. Pressure, infarct size, and lactate dehydrogenase release were also measured. At the 7(th) min, PostC induced a significant decrease in SOD activity with no major change both in Mn and Cu/Zn SOD levels and in CAT activity and level. PostC also reduced 3-NT and increased SNO levels. Exogenous SOD, but not CAT, abolished PostC cardioprotection. In late reperfusion (120-min), I/R increased SOD activity but decreased CAT activity and Cu/Zn SOD levels; these effects were reversed by PostC; 3-NT was not affected, but SNO was increased by PostC. AB reproduced PostC effects on antioxidant enzymes. The conclusions are as follows: PostC downregulates endogenous SOD and preserves CAT activity, thus increasing SNO and reducing 3-NT levels. These effects are triggered by early post-ischemic acidosis. Yet acidosis-induced SOD downregulation may limit denitrosylation, thus contributing to PostC triggering. Hence, exogenous SOD, but not CAT, interferes with PostC triggering. Prolonged SOD downregulation and SNO increase may contribute to PostC and AB beneficial effects.

Post-ischemic early acidosis in cardiac postconditioning modifies the activity of antioxidant enzymes, reduces nitration, and favors protein S-nitrosylation

Postconditioning (PostC) modifies the early post-ischemic pH, redox environment, and activity of enzymes. We hypothesized that early acidosis in PostC may affect superoxide dismutase (SOD) and catalase (CAT) activities, may reduce 3-nitrotyrosine (3-NT) protein levels, and may increase S-nitrosylated (SNO) protein levels, thus deploying its protective effects. To verify this hypothesis, we studied the early (7(th) min) and late (120(th) min) phases of reperfusion (a) endogenous SOD and CAT activities and (b) 3-NT protein levels and SNO protein levels. Isolated rat hearts underwent 30-min ischemia/120-min reperfusion (I/R) or PostC (5 cycles of 10-s I/R at the beginning of 120-min reperfusion) either with or without exogenous CAT or SOD infused during the initial 3 min of reperfusion. The effects of early reperfusion with acid buffer (AB, pH 6.8) on endogenous antioxidant enzymes were also tested. Pressure, infarct size, and lactate dehydrogenase release were also measured. At the 7(th) min, PostC induced a significant decrease in SOD activity with no major change both in Mn and Cu/Zn SOD levels and in CAT activity and level. PostC also reduced 3-NT and increased SNO levels. Exogenous SOD, but not CAT, abolished PostC cardioprotection. In late reperfusion (120-min), I/R increased SOD activity but decreased CAT activity and Cu/Zn SOD levels; these effects were reversed by PostC; 3-NT was not affected, but SNO was increased by PostC. AB reproduced PostC effects on antioxidant enzymes. The conclusions are as follows: PostC downregulates endogenous SOD and preserves CAT activity, thus increasing SNO and reducing 3-NT levels. These effects are triggered by early post-ischemic acidosis. Yet acidosis-induced SOD downregulation may limit denitrosylation, thus contributing to PostC triggering. Hence, exogenous SOD, but not CAT, interferes with PostC triggering. Prolonged SOD downregulation and SNO increase may contribute to PostC and AB beneficial effects.

Emergent role of gasotransmitters in ischemia-reperfusion injury

Nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) are lipid-soluble, endogenously produced gaseous messenger molecules collectively known as gasotransmitters. Over the last several decades, gasotransmitters have emerged as potent cytoprotective mediators in various models of tissue and cellular injury. Specifically, when used at physiological levels, the exogenous and endogenous manipulation of these three gases has been shown to modulate ischemia/reperfusion injury by inducing a number of cytoprotective mechanisms including: induction of vasodilatation, inhibition of apoptosis, modulation of mitochondrial respiration, induction of antioxidants, and inhibition of inflammation. However, while the actions are similar, there are some differences in the mechanisms by which these gasotransmitters induce these effects and the regulatory actions of the enzyme systems can vary depending upon the gas being investigated. Furthermore, there does appear to be some crosstalk between the gases, which can provide synergistic effects and additional regulatory effects. This review article will discuss several models and mechanisms of gas-mediated cytoprotection, as well as provide a brief discussion on the complex interactions between the gasotransmitter systems.

A biphasic response to nitric oxide donation in an ex vivo model of donation after cardiac death renal transplantation

BACKGROUND

Donation after cardiac death (DCD) donors are vital to maximize the organ donor pool. Reperfusion injury (RI) is an important sequela in DCD organs due to warm and cold ischemia. RI manifests clinically as a high incidence of delayed graft function (DGF) and primary non-function (PNF) compared with donation after brain death organs. The importance of nitric oxide (NO) in the generation of reperfusion injury is pivotal.

METHODS

Using an ex vivo porcine model of kidney transplantation the effects of reperfusion with and without NO supplementation on initial renal blood flow and function were compared. Real-time hemodynamic measurements were recorded and biochemical samples taken at set time-points. Molecular markers of reperfusion injury were also measured. Sodium nitroprusside was chosen as the NO donor.

RESULTS

Results showed that NO donation initially improved renal blood flow significantly over controls; at the end of reperfusion this benefit was lost. In addition, there was an improvement in creatinine clearance, fractional excretion of sodium and renal oxygen consumption. There were observed to be higher levels of urinary nitrite/nitrate excretion, but no difference in isoprostane levels.

CONCLUSION

This study represents a good model for the initial reperfusion period in large animal renal transplantation. The improvement in renal blood flow observed in the NO supplemented groups represents NO mediated vasodilatation. Later in reperfusion, accumulation of nitrogenous free radicals impairs renal blood flow. Clinically, NO supplementation during initial reperfusion of DCD kidneys improves renal blood flow but should be considered with caution due to potential deleterious effects of nitrogenous compound accumulation.

Mitochondrial approaches to protect against cardiac ischemia and reperfusion injury

The mitochondrion is a vital component in cellular energy metabolism and intracellular signaling processes. Mitochondria are involved in a myriad of complex signaling cascades regulating cell death vs. survival. Importantly, mitochondrial dysfunction and the resulting oxidative and nitrosative stress are central in the pathogenesis of numerous human maladies including cardiovascular diseases, neurodegenerative diseases, diabetes, and retinal diseases, many of which are related. This review will examine the emerging understanding of the role of mitochondria in the etiology and progression of cardiovascular diseases and will explore potential therapeutic benefits of targeting the organelle in attenuating the disease process. Indeed, recent advances in mitochondrial biology have led to selective targeting of drugs designed to modulate or manipulate mitochondrial function, to the use of light therapy directed to the mitochondrial function, and to modification of the mitochondrial genome for potential therapeutic benefit. The approach to rationally treat mitochondrial dysfunction could lead to more effective interventions in cardiovascular diseases that to date have remained elusive. The central premise of this review is that if mitochondrial abnormalities contribute to the etiology of cardiovascular diseases (e.g., ischemic heart disease), alleviating the mitochondrial dysfunction will contribute to mitigating the severity or progression of the disease. To this end, this review will provide an overview of our current understanding of mitochondria function in cardiovascular diseases as well as the potential role for targeting mitochondria with potential drugs or other interventions that lead to protection against cell injury.

Glutamine contributes to ameliorate inflammation after renal ischemia/reperfusion injury in rats

The aim of this study was to investigate the effects of glutamine in an in vivo rat model of renal ischemia/reperfusion (I/R) injury. Male Wistar rats underwent bilateral renal pedicle clamping for 45 min followed by reperfusion for 6 h. Glutamine (1.5 mg/kg) was administered intraperitoneally (i.p.) 15 min prior to reperfusion. Plasma concentrations of urea, creatinine, γ-glutamyl transferase (γ-GT), and aspartate aminotransferase (AST) were measured for the assessment of renal function and reperfusion injury. Markers of oxidative stress, expression of the pro-inflammatory mediators inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), AT-1 expression, and changes in the oxidative stress-sensitive nuclear factor kappa B (NF-κB) signaling pathway were measured to investigate whether glutamine can reduce the renal dysfunction. Kidney myeloperoxidase (MPO) activity and malondialdehyde (MDA) levels were measured for assessment of polymorphonuclear (PMN) cell infiltration and lipid peroxidation, respectively. Renal sections were used for histologic grading of renal injury and for immunohistochemical localization of nitrotyrosine and poly(ADP-ribose) synthetase (PARS). In vivo, glutamine significantly reduced the increase in urea, creatinine, γ-GT, AST, produced by renal ischemia/reperfusion (I/R), suggesting an improvement in both renal function and injury. Glutamine significantly reduced iNOS and NF-κB, kidney MPO activity and MDA levels, indicating a reduction in PMN infiltration and lipid peroxidation, respectively. Glutamine reduced the histological evidence of renal damage associated with I/R and caused a substantial reduction in the staining for nitrotyrosine and PARS, suggesting reduced nitrosative and oxidative stress. Moreover, glutamine attenuated the reduction of COX-2 expression and prevented the increased AT-1 expression after I/R. Our results suggest that glutamine reduces the renal dysfunction and injury associated with I/R of the kidney.

Neonatal asphyxia induces the nitration of cardiac myosin light chain 2 that is associated with cardiac systolic dysfunction

Hypoxia followed by reoxygenation (H-R) observed during perinatal asphyxia is a serious complication with high mortality and morbidity rates that may cause adverse cardiovascular effects in neonates. Our aim was to determine if oxidative stress related to H-R induces peroxynitrite-dependent modifications of the cardiac contractile protein, myosin regulatory light chain 2 (MLC2), and whether this is associated with development of cardiac systolic dysfunction. Twelve newborn piglets were acutely instrumented for hemodynamic monitoring and randomized to a control group ventilated with only atmospheric air or to the H-R study group exposed to alveolar normocapnic hypoxia followed by reoxygenation. Afterward, animals were euthanized, and the hearts were harvested for biochemical analyses. Systolic function as well as cardiac MLC2 levels decreased in H-R animals, whereas nitrates and nitrotyrosine levels increased. Negative correlations between nitrates, nitrotyrosine, and MLC2 levels were observed. Moreover, H-R induced nitration of two tyrosine residues within the MLC2 protein. Similarly, in vitro exposure of MLC2 to peroxynitrite resulted in the nitration of tyrosine, which increased the susceptibility of MLC2 to subsequent degradation by matrix metalloproteinase 2. Substitution of this tyrosine with phenylalanine prevented the matrix metalloproteinase 2-dependent degradation of MLC2. In addition, a large decrease in MLC2 phosphorylation caused by H-R was observed. Oxidative stress related to asphyxia induces nitration of cardiac MLC2 protein and thus increases its degradation. This and a large decrease in MLC2 phosphorylation contribute to the development of systolic dysfunction. Inhibition of MLC2 nitration and/or direct inhibition of its degradation by MMP-2 could be potential therapeutic targets aiming at reduction of myocardial damage during resuscitation of asphyxiated newborns.

Effect of apelin-apelin receptor system in postischaemic myocardial protection: a pharmacological postconditioning tool?

In the heart, a great part of ischaemia and reperfusion injuries occurs mainly during the first minutes of reperfusion. The opening of the mitochondrial permeability transition pores is the end point of the cascade to myocardial damage. Also, oxidative stress contributes to cell death. Postconditioning is a protective maneuver that can be selectively timed at the beginning of reperfusion. It is hypothesized that it acts via the reperfusion injury salvage kinase pathway, which includes nitric oxide-dependent and nitric oxide-independent cascades. Apelin is an endogenous peptide that can protect the heart from reperfusion injury if given at the beginning of reperfusion but not before ischaemia. It is hypothesized that it may trigger the reperfusion injury salvage kinase pathway via a specific apelin receptor. Apelin can also limit the oxidative stress by the activation of superoxide dismutase. Apelin and apelin receptor expression increase early after ischaemia and at the beginning of an ischaemic heart failure. These observations suggest that the endogenous release of the peptide can limit the severity of an infarction and ameliorate myocardial contractility compromised by the appearance of the failure. Due to its protective activities, apelin could be a therapeutic tool if administered with the same catheter used for angioplasty or after the maneuvers aimed at bypassing a coronary occlusion.

Cardioprotective pathways during reperfusion: focus on redox signaling and other modalities of cell signaling

Post-ischemic reperfusion may result in reactive oxygen species (ROS) generation, reduced availability of nitric oxide (NO•), Ca(2+)overload, prolonged opening of mitochondrial permeability transition pore, and other processes contributing to cell death, myocardial infarction, stunning, and arrhythmias. With the discovery of the preconditioning and postconditioning phenomena, reperfusion injury has been appreciated as a reality from which protection is feasible, especially with postconditioning, which is under the control of physicians. Potentially cooperative protective signaling cascades are recruited by both pre- and postconditioning. In these pathways, phosphorylative/dephosphorylative processes are widely represented. However, cardioprotective modalities of signal transduction also include redox signaling by ROS, S-nitrosylation by NO• and derivative, S-sulfhydration by hydrogen sulfide, and O-linked glycosylation with beta-N-acetylglucosamine. All these modalities can interact and regulate an entire pathway, thus influencing each other. For instance, enzymes can be phosphorylated and/or nitrosylated in specific and/or different site(s) with consequent increase or decrease of their specific activity. The cardioprotective signaling pathways are thought to converge on mitochondria, and various mitochondrial proteins have been identified as targets of these post-transitional modifications in both pre- and postconditioning.

Preemptive conditioning of the swine heart by H11 kinase/Hsp22 provides cardiac protection through inducible nitric oxide synthase

The second window of ischemic preconditioning (SWOP) provides maximal protection against ischemia through regulation of the inducible nitric oxide synthase (iNOS), yet its application is limited by the inconvenience of the preliminary ischemic stimulus required for prophylaxis. Overexpression of H11 kinase/Hsp22 (Hsp22) in a transgenic mouse model provides cardioprotection against ischemia that is equivalent to that conferred by SWOP. We hypothesized that short-term, prophylactic overexpression of Hsp22 would offer an alternative to SWOP in reducing ischemic damage through a nitric oxide (NO)-dependent mechanism. Adeno-mediated overexpression of Hsp22 was achieved in the area at risk of the left circumflex (Cx) coronary artery in chronically instrumented swine and compared with LacZ controls (n = 5/group). Hsp22-injected myocardium showed an average fourfold increase in Hsp22 protein expression compared with controls and a doubling in iNOS expression (both P < 0.05). Four days after ischemia-reperfusion, regional wall thickening was reduced by 58 ± 2% in the Hsp22 group vs. 82 ± 7% in the LacZ group, and Hsp22 reduced infarct size by 40% (both P < 0.05 vs. LacZ). Treatment with the NOS inhibitor N(G)-nitro-L-arginine (L-NNA) before ischemia suppressed the protection induced by Hsp22. In isolated cardiomyocytes, Hsp22 increased iNOS expression through the transcription factors NF-κB and STAT, the same effectors activated by SWOP, and reduced by 60% H(2)O(2)-mediated apoptosis, which was also abolished by NOS inhibitors. Therefore, short-term, prophylactic conditioning by Hsp22 provides NO-dependent cardioprotection that reproduces the signaling of SWOP, placing Hsp22 as a potential alternative for preemptive treatment of myocardial ischemia.

Impaired cardiac ischemic tolerance in spontaneously hypertensive rats is attenuated by adaptation to chronic and acute stress

Chronic hypertension may have a negative impact on the myocardial response to ischemia. On the other hand, intrinsic ischemic tolerance may persist even in the pathologically altered hearts of hypertensive animals, and may be modified by short- or long-term adaptation to different stressful conditions. The effects of long-term limitation of living space (ie, crowding stress [CS]) and brief ischemia-induced stress on cardiac response to ischemia/reperfusion (I/R) injury are not yet fully characterized in hypertensive subjects. The present study was designed to test the influence of chronic and acute stress on the myocardial response to I/R in spontaneously hypertensive rats (SHR) compared with their effects in normotensive counterparts. In both groups, chronic, eight-week CS was induced by caging five rats per cage in cages designed for two rats (200 cm(2)/rat), while controls (C) were housed four to a cage in cages designed for six animals (480 cm(2)/rat). Acute stress was evoked by one cycle of I/R (5 min each, ischemic preconditioning) before sustained I/R in isolated Langendorff-perfused hearts of normotensive and SHR rats. At baseline conditions, the effects of CS were manifested only as a further increase in blood pressure in SHR, and by marked limitation of coronary perfusion in normotensive animals, while no changes in heart mechanical function were observed in any of the groups. Postischemic recovery of contractile function, severity of ventricular arrhythmias and lethal injury (infarction size) were worsened in the hypertrophied hearts of C-SHR compared with normotensive C. However, myo-cardial stunning and reperfusion-induced ventricular arrhythmias were attenuated by CS in SHR, which was different from deterioration of I/R injury in the hearts of normotensive animals. In contrast, ischemic preconditioning conferred an effective protection against I/R in both groups, although the extent of anti-infarct and anti-arrhythmic effects was lower in SHR. Both forms of stress may improve the altered response to ischemia in hypertensive subjects. In contrast to short-term preconditioning stress, chronic psychosocial stress was associated with a higher risk of lethal arrhythmias and contractile failure in normotensive animals exposed to an acute ischemic challenge.

Hypothermia protects H9c2 cardiomyocytes from H2O2 induced apoptosis

The purpose of our study was to investigate underlying basic mechanisms of hypothermia-induced cardioprotection during oxidative stress in a cardiomyocyte cell culture model. For hypothermic treatment we cooled H9c2 cardiomyocytes to 20°C, maintained 20min at 20°C during which short-term oxidative damage was inflicted with 2mM H(2)O(2,) followed by rewarming to 37°C. Later on, we analyzed lactate dehydrogenase (LDH), caspase-3 cleavage, reactive oxygen species (ROS), mitochondrial activity, intracellular ATP production, cytoprotective signal molecules as well as DNA damage. Hypothermia decreased H(2)O(2) damage in cardiomyocytes as demonstrated in a lower LDH release, less caspase-3 cleavage and less M30 CytoDeath staining. After rewarming H(2)O(2) damaged cells demonstrated a significantly higher reduction rate of intracellular ROS compared to normothermic H(2)O(2) damaged cardiomyocytes(.) This was in line with a significantly greater mitochondrial dehydrogenase activity and higher intracellular ATP content in cooled and rewarmed cells. Moreover, hypothermia preserved cell viability by up-regulation of the anti-apoptotic protein Bcl-2 and a reduction of p53 phosphorylation. DNA damage, proven by PARP-1 cleavage and H2AX phosphorylation, was significantly reduced by hypothermia. In conclusion, we could demonstrate that hypothermia protects cardiomyocytes during oxidative stress by preventing apoptosis via inhibiting mitochondrial dysfunction and DNA damage.

Peroxynitrite induces HMGB1 release by cardiac cells in vitro and HMGB1 upregulation in the infarcted myocardium in vivo

AIMS

High-mobility group box 1 (HMGB1) is a nuclear protein actively secreted by immune cells and passively released by necrotic cells that initiates pro-inflammatory signalling through binding to the receptor for advance glycation end-products. HMGB1 has been established as a key inflammatory mediator during myocardial infarction, but the proximal mechanisms responsible for myocardial HMGB1 expression and release in this setting remain unclear. Here, we investigated the possible involvement of peroxynitrite, a potent cytotoxic oxidant formed during myocardial infarction, on these processes.

METHODS AND RESULTS

The ability of peroxynitrite to induce necrosis and HMGB1 release in vitro was evaluated in H9c2 cardiomyoblasts and in primary murine cardiac cells (myocytes and non-myocytes). In vivo, myocardial HMGB1 expression and nitrotyrosine content (a marker of peroxynitrite generation) were determined following myocardial ischaemia and reperfusion in rats, whereas peroxynitrite formation was inhibited by two different peroxynitrite decomposition catalysts: 5,10,15,20-tetrakis(4-sulphonatophenyl) porphyrinato iron (III) (FeTPPS) or Mn(III)-tetrakis(4-benzoic acid) porphyrin chloride (MnTBAP). In all types of cells studied, peroxynitrite (100 μM) elicited significant necrosis, the loss of intracellular HMGB1, and its passive release into the medium. In vivo, myocardial ischaemia-reperfusion induced significant myocardial necrosis, cardiac nitrotyrosine formation, and marked overexpression of myocardial HMGB1. FeTPPS reduced nitrotyrosine, decreased infarct size, and suppressed HMGB1 overexpression, an effect that was similarly obtained with MnTBAP.

CONCLUSION

These findings indicate that peroxynitrite represents a key mediator of HMGB1 overexpression and release by cardiac cells and provide a novel mechanism linking myocardial oxidative/nitrosative stress with post-infarction myocardial inflammation.

Ryanodine receptors: structure, expression, molecular details, and function in calcium release

Ryanodine receptors (RyRs) are located in the sarcoplasmic/endoplasmic reticulum membrane and are responsible for the release of Ca(2+) from intracellular stores during excitation-contraction coupling in both cardiac and skeletal muscle. RyRs are the largest known ion channels (> 2MDa) and exist as three mammalian isoforms (RyR 1-3), all of which are homotetrameric proteins that interact with and are regulated by phosphorylation, redox modifications, and a variety of small proteins and ions. Most RyR channel modulators interact with the large cytoplasmic domain whereas the carboxy-terminal portion of the protein forms the ion-conducting pore. Mutations in RyR2 are associated with human disorders such as catecholaminergic polymorphic ventricular tachycardia whereas mutations in RyR1 underlie diseases such as central core disease and malignant hyperthermia. This chapter examines the current concepts of the structure, function and regulation of RyRs and assesses the current state of understanding of their roles in associated disorders.

The potential for clinical use of cannabinoids in treatment of cardiovascular diseases

Cannabinoids, the constituents of the marijuana plant and their analogs, have not only neurobehavioral but also cardiovascular effects. Great advances in the last couple of decades have led to better understanding of the physiological effects of the cannabinoids and of their role in various cardiovascular pathologies. The potential therapeutic use of cannabinoids in various cardiac diseases, such as ischemic injury, heart failure, and cardiac arrhythmias, has been studied in animal models. The purpose of this article is to review the physiological cardiovascular properties of cannabinoids and to summarize the knowledge related to their potential therapeutic use.

CB1 cannabinoid receptors promote oxidative/nitrosative stress, inflammation and cell death in a murine nephropathy model

BACKGROUND AND PURPOSE

Accumulating recent evidence suggests that cannabinoid-1 (CB(1)) receptor activation may promote inflammation and cell death and its pharmacological inhibition is associated with anti-inflammatory and tissue-protective effects in various preclinical disease models, as well as in humans.

EXPERIMENTAL APPROACH

In this study, using molecular biology and biochemistry methods, we have investigated the effects of genetic deletion or pharmacological inhibition of CB(1) receptors on inflammation, oxidative/nitrosative stress and cell death pathways associated with a clinically relevant model of nephropathy, induced by an important chemotherapeutic drug cisplatin.

RESULTS

Cisplatin significantly increased endocannabinoid anandamide content, activation of p38 and JNK mitogen-activated protein kinases (MAPKs), apoptotic and poly (ADP-ribose)polymerase-dependent cell death, enhanced inflammation (leucocyte infiltration, tumour necrosis factor-alpha and interleukin-1beta) and promoted oxidative/nitrosative stress [increased expressions of superoxide-generating enzymes (NOX2(gp91phox), NOX4), inducible nitric oxide synthase and tissue 4-hydroxynonenal and nitrotyrosine levels] in the kidneys of mice, accompanied by marked histopathological damage and impaired renal function (elevated creatinine and serum blood urea nitrogen) 3 days following its administration. Both genetic deletion and pharmacological inhibition of CB(1) receptors with AM281 or SR141716 markedly attenuated the cisplatin-induced renal dysfunction and interrelated oxidative/nitrosative stress, p38 and JNK MAPK activation, cell death and inflammatory response in the kidney.

CONCLUSIONS AND IMPLICATIONS

The endocannabinoid system through CB(1) receptors promotes cisplatin-induced tissue injury by amplifying MAPK activation, cell death and interrelated inflammation and oxidative/nitrosative stress. These results also suggest that inhibition of CB(1) receptors may exert beneficial effects in renal (and most likely other) diseases associated with enhanced inflammation, oxidative/nitrosative stress and cell death.

The role of nitric oxide, superoxide and peroxynitrite in the anti-arrhythmic effects of preconditioning and peroxynitrite infusion in anaesthetized dogs

BACKGROUND AND PURPOSE

Both ischaemia preconditioning (PC) and the intracoronary infusion of peroxynitrite (PN) suppress ischaemia and reperfusion (I/R)-induced arrhythmias and the generation of nitrotyrosine (NT, a marker of PN). However, it is still unclear whether this latter effect is due to a reduction in nitric oxide (NO) or superoxide (O(2)(-)) production.

EXPERIMENTAL APPROACH

Dogs anaesthetized with chloralose and urethane were infused, twice for 5 min, with either saline (control) or 100 nM PN, or subjected to similar periods of occlusion (PC), 5 min prior to a 25 min occlusion and reperfusion of the left anterior descending coronary artery. Severities of ischaemia and ventricular arrhythmias, as well as changes in the coronary sinus nitrate/nitrite (NOx) levels were assessed throughout the experiment. The production of myocardial NOx, O(2)(-) and NT was determined following reperfusion.

KEY RESULTS

Both PC and PN markedly suppressed the I/R-induced ventricular arrhythmias, compared to the controls, and increased NOx levels during coronary artery occlusion. Reperfusion induced almost the same increases in NOx levels in all groups, but superoxide production and, consequently, the generation of NT were significantly less in PC- and PN-treated dogs than in controls.

CONCLUSIONS AND IMPLICATIONS

Since both PC and the administration of PN enhanced NOx levels during I/R, the attenuation of endogenous PN formation in these dogs is primarily due to a reduction in the amount of O(2) produced. Thus, the anti-arrhythmic effect of PC and PN can almost certainly be attributed to the preservation of NO availability during myocardial ischaemia.

Protease-activated receptor 2 deficiency reduces cardiac ischemia/reperfusion injury

OBJECTIVE

To investigate the effect of protease-activated receptor (PAR) 2 deficiency on ischemia/reperfusion (I/R) injury-induced infarct size, inflammation, heart remodeling, and cardiac function.

METHODS AND RESULTS

PAR-2 signaling enhances inflammation in different diseases. The effect of PAR-2 deficiency in cardiac I/R injury is unknown. PAR-2(-/-) mice and wild-type littermates were subjected to 30 minutes of ischemia and up to 4 weeks of reperfusion. Infarct size, oxidative/nitrative stress, phosphorylation of mitogen-activated protein kinases, and inflammatory gene expression were assessed 2 hours after reperfusion. Changes in heart size and function were measured by echocardiography up to 4 weeks after reperfusion. Infarct size was significantly reduced in hearts of PAR-2(-/-) mice compared with wild-type littermates. In addition, oxidative/nitrative stress, phosphorylation of mitogen-activated protein kinase, and expression of proinflammatory genes were significantly attenuated in injured hearts of PAR-2(-/-) mice. Finally, PAR-2(-/-) mice were protected from postinfarction remodeling and showed less impairment in heart function compared with wild-type littermates up to 4 weeks after I/R injury.

CONCLUSIONS

PAR-2 deficiency reduces myocardial infarction and heart remodeling after I/R injury.

Matrix metalloproteinase inhibitors: a critical appraisal of design principles and proposed therapeutic utility

Matrix metalloproteinases (MMPs) play an important role in tissue remodelling associated with various physiological and pathological processes, such as morphogenesis, angiogenesis, tissue repair, arthritis, chronic heart failure, chronic obstructive pulmonary disease, chronic inflammation and cancer metastasis. As a result, MMPs are considered to be viable drug targets in the therapy of these diseases. Despite the high therapeutic potential of MMP inhibitors (MMPIs), all clinical trials have failed to date, except for doxycycline for periodontal disease. This can be attributed to (i) poor selectivity of the MMPIs, (ii) poor target validation for the targeted therapy and (iii) poorly defined predictive preclinical animal models for safety and efficacy. Lessons from previous failures, such as recent discoveries of oxidative/nitrosative activation and phosphorylation of MMPs, as well as novel non-matrix related intra- and extracellular targets of MMP, give new hope for MMPI development for both chronic and acute diseases. In this article we critically review the major structural determinants of the selectivity and the milestones of past design efforts of MMPIs where 2-/3-dimensional structure-based methods were intensively applied. We also analyse the in vitro screening and preclinical/clinical pharmacology approaches, with particular emphasis on drawing conclusions on how to overcome efficacy and safety problems through better target validation and design of preclinical studies.

Potential therapeutic benefits of strategies directed to mitochondria

The mitochondrion is the most important organelle in determining continued cell survival and cell death. Mitochondrial dysfunction leads to many human maladies, including cardiovascular diseases, neurodegenerative disease, and cancer. These mitochondria-related pathologies range from early infancy to senescence. The central premise of this review is that if mitochondrial abnormalities contribute to the pathological state, alleviating the mitochondrial dysfunction would contribute to attenuating the severity or progression of the disease. Therefore, this review will examine the role of mitochondria in the etiology and progression of several diseases and explore potential therapeutic benefits of targeting mitochondria in mitigating the disease processes. Indeed, recent advances in mitochondrial biology have led to selective targeting of drugs designed to modulate and manipulate mitochondrial function and genomics for therapeutic benefit. These approaches to treat mitochondrial dysfunction rationally could lead to selective protection of cells in different tissues and various disease states. However, most of these approaches are in their infancy.

Role of iNOS and peroxynitrite–matrix metalloproteinase-2 signaling in myocardial late preconditioning in rats

We have previously shown that the inhibition of myocardial nitric oxide (NO) and peroxynitrite-matrix metalloproteinase (MMP) signaling by early preconditioning (PC) is involved in its cardioprotective effect. Therefore, in the present study, we investigated the role of NO and peroxynitrite-MMP signaling in the development of late PC. PC was performed by five consecutive cycles of 4-min coronary occlusion and 4-min reperfusion in anesthetized rats in vivo. Twenty-four hours later, hearts were subjected to a 30-min coronary occlusion followed by 180-min reperfusion to measure infarct size. In separate experiments, heart tissue was sampled to measure biochemical parameters before and 3, 6, 12, or 24 h after the PC protocol, respectively. Late PC decreased infarct size, increased cardiac inducible NO synthase (iNOS) activity and gene expression, and decreased SOD activity at 24 h significantly compared with sham-operated controls. Late PC increased cardiac superoxide levels significantly at 24 h; however, it did not change cardiac NO levels. Cardiac peroxynitrite levels were significantly decreased. Downstream cellular targets of peroxynitrite, MMP-2 and MMP-9 activities were decreased in the late PC group at 24 h compared with the sham-operated group. To verify if PC-induced inhibition of MMPs had a causative role in the reduction of infarct size, in separate experiments, we measured infarct size after the pharmacological inhibition of MMPs by ilomastat and found a significant reduction of infarct size compared with the vehicle-treated group. In conclusion, this is the first demonstration that the inhibition of cardiac peroxynitrite-MMP signaling contributes to cardioprotection by late PC and that pharmacological inhibition of MMPs is able to reduce infarct size in vivo. Furthermore, increased expression of iNOS may play a role in the development of late PC; however, increased iNOS activity does not lead to increased NO production in late PC.

Dietary red palm oil supplementation reduces myocardial infarct size in an isolated perfused rat heart model

Background and Aims

Recent studies have shown that dietary red palm oil (RPO) supplementation improves functional recovery following ischaemia/reperfusion in isolated hearts. The main aim of this study was to investigate the effects of dietary RPO supplementation on myocardial infarct size after ischaemia/reperfusion injury. The effects of dietary RPO supplementation on matrix metalloproteinase-2 (MMP2) activation and PKB/Akt phosphorylation were also investigated.

Materials and methods

Male Wistar rats were divided into three groups and fed a standard rat chow diet (SRC), a SRC supplemented with RPO, or a SRC supplemented with sunflower oil (SFO), for a five week period, respectively. After the feeding period, hearts were excised and perfused on a Langendorff perfusion apparatus. Hearts were subjected to thirty minutes of normothermic global ischaemia and two hours of reperfusion. Infarct size was determined by triphenyltetrazolium chloride staining. Coronary effluent was collected for the first ten minutes of reperfusion in order to measure MMP2 activity by gelatin zymography.

Results

Dietary RPO-supplementation decreased myocardial infarct size significantly when compared to the SRC-group and the SFO-supplemented group (9.1 ± 1.0% versus 30.2 ± 3.9% and 27.1 ± 2.4% respectively). Both dietary RPO- and SFO-supplementation were able to decrease MMP2 activity when compared to the SRC fed group. PKB/Akt phosphorylation (Thr 308) was found to be significantly higher in the dietary RPO supplemented group when compared to the SFO supplemented group at 10 minutes into reperfusion. There was, however, no significant changes observed in ERK phosphorylation.

Conclusions

Dietary RPO-supplementation was found to be more effective than SFO-supplementation in reducing myocardial infarct size after ischaemia/reperfusion injury. Both dietary RPO and SFO were able to reduce MMP2 activity, which suggests that MMP2 activity does not play a major role in protection offered by RPO. PKB/Akt phosphorylation may, however, be involved in RPO mediated protection.

Increased inducible nitric oxide synthase and arginase II expression in heart failure: no net nitrite/nitrate production and protein S-nitrosylation

Our objective was to address the balance of inducible nitric oxide (NO) synthase (iNOS) and arginase and their contribution to contractile dysfunction in heart failure (HF). Excessive NO formation is thought to contribute to contractile dysfunction; in macrophages, increased iNOS expression is associated with increased arginase expression, which competes with iNOS for arginine. With substrate limitation, iNOS may become uncoupled and produce reactive oxygen species (ROS). In rabbits, HF was induced by left ventricular (LV) pacing (400 beats/min) for 3 wk. iNOS mRNA [quantitative real-time PCR (qRT-PCR)] and protein expression (confocal microscopy) were detected, and arginase II expression was quantified with Western blot; serum arginine and myocardial nitrite and nitrate concentrations were determined by chemiluminescence, and protein S-nitrosylation with Western blot. Superoxide anions were quantified with dihydroethidine staining. HF rabbits had increased LV end-diastolic diameter [20.0 + or - 0.5 (SE) vs. 17.2 + or - 0.3 mm in sham] and decreased systolic fractional shortening (11.1 + or - 1.4 vs. 30.6 + or - 0.7% in sham; both P < 0.05). Myocardial iNOS mRNA and protein expression were increased, however, not associated with increased myocardial nitrite or nitrate concentrations or protein S-nitrosylation. The serum arginine concentration was decreased (124.3 + or - 5.6 vs. 155.4 + or - 12.0 micromol/l in sham; P < 0.05) at a time when cardiac arginase II expression was increased (0.06 + or - 0.01 vs. 0.02 + or - 0.01 arbitrary units in sham; P < 0.05). Inhibition of iNOS with 1400W attenuated superoxide anion formation and contractile dysfunction in failing hearts. Concomitant increases in iNOS and arginase expression result in unchanged NO species and protein S-nitrosylation; with substrate limitation, uncoupled iNOS produces superoxide anions and contributes to contractile dysfunction.

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.

L-cysteine stimulates hydrogen sulfide synthesis in myocardium associated with attenuation of ischemia-reperfusion injury

Hydrogen sulfide (H( 2)S) is a biological mediator produced by enzyme-regulated pathways from L-cysteine, which is a substrate for cystathionine-gamma-lyase (CSE). In myocardium, endogenously and exogenously administered H(2)S has been shown to protect against ischemia-reperfusion injury. We hypothesized that L-cysteine exerts its protective action through stimulation of H(2)S production. Rat isolated hearts were Langendorff-perfused and underwent 35-minute regional ischemia and 120-minute reperfusion. L-cysteine perfusion from 10 minutes before ischemia until 10 minutes after reperfusion limited infarct size in a concentration-dependent manner, maximal at 1 mmol/L (control 36.4% +/- 2.4% vs L-cysteine 24.3% +/- 3.4%, P < .05). This protective action was attenuated by the CSE inhibitor, DL-propargylglycine (PAG) 1 mmol/L (31.4 +/- 5.9%, not significant vs control) but administration of the CSE cofactor pyridoxal-5'-phosphate (PLP) 50 mumol/L did not enhance the effect of L-cysteine. Ten minutes normoxic perfusion with L-cysteine 1 mmol/L caused a 3-fold increase in myocardial H(2)S concentration (0.64 +/- 0.16 vs 2.01 +/- 0.07 mumol/g protein, P < .01), an effect that was significantly attenuated by PAG (1.17 +/- 0.15 mumol/g protein). These data provide evidence that exogenous L-cysteine administration limits ischemia-reperfusion injury through a mechanism that appears to be at least partially dependent on H(2)S synthesis.

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.

Role of cGMP-PKG signaling in the protection of neonatal rat cardiac myocytes subjected to simulated ischemia/reoxygenation

Nitric oxide (NO) and B-type natriuretic peptide (BNP) are protective against ischemia-reperfusion injury as they increase intracellular cGMP level via activation of soluble (sGC) or particulate guanylate cyclases (pGC), respectively. The aim of the present study was to examine if the cGMP-elevating mediators, NO and BNP, share a common downstream signaling pathway via cGMP-dependent protein kinase (PKG) in cardiac cytoprotection. Neonatal rat cardiac myocytes in vitro were subjected to 2.5 h simulated ischemia (SI) followed by 2 h reoxygenation. Cell viability was tested by trypan blue exclusion assay. PKG activity of cardiac myocytes was assessed by phospholamban (PLB) phosphorylation determined by western blot. Cell death was 34 +/- 2% after SI/reoxygenation injury in the control group. cGMP-inducing agents significantly decreased irreversible cell injury: the cGMP analog 8-bromo-cGMP (8-Br-cGMP, 10 nM) decreased it to 13 +/- 1% (p < 0.001), the direct NO-donor S-nitroso-N-acetylpenicillamine (SNAP, 1 microM) to 18 +/- 6% (p < 0.05) and BNP (10 nM) to 12 +/- 2% (p < 0.001), respectively. This protective effect was abolished by the selective PKG inhibitor KT-5823 (600 nM) in each case. As PLB is not a unique reporter for PKG activity since it is also phosphorylated by protein kinase A (PKA), we examined PLB phosphorylation in the presence of the PKA inhibitor KT-5720 (1 microM). The ratio of pPLB/PLB significantly increased after administration of both BNP and 8-Br-cGMP under ischemic conditions, which was abolished by the PKG inhibitor. This is the first demonstration that elevated cGMP produced either by the sGC activator SNAP or the pGC activator BNP exerts cytoprotective effects via a common downstream signaling pathway involving PKG activation.

Effect of L-arginine oral supplementation on response to myocardial infarction in hypercholesterolemic and hypertensive rats

The well known metabolic functions of L-arginine have been recently increased with the discovery of its role as the substrate for the synthesis of nitric oxide (NO), which has emerged as an endogenous signaling molecule with potential therapeutic implications for cardiovascular disease. Steady-state levels of NO are derived in part from dietary sources. It has been reported that supplementation of L-arginine reduces atherosclerosis in rabbits and reduces the arterial pressure in hypertensive rats. Therefore, we investigated the effect of L-arginine supplementation using a group of induced hypercholesterolemic rats and a group of spontaneously hypertensive rats; the infarcted area in cardiac tissue of both groups was measured during the response to myocardial infarction in the ischemia-reperfusion model. Hypercholesterolemic rats supplemented with 170 mg kg(-1) of L-arginine showed a significant (P <or= 0.05) reduction in total cholesterol (25.2%) and LDL (27.8%). Spontaneously hypertensive rats supplemented with L-arginine presented a significant reduction (20.3%) in mean blood pressure (P <or= 0.05). The index infarcted area/total heart area, in both: hypercholesterolemic and hypertensive rats supplemented with L-arginine, showed a significant 36% and 29% of cardio protection (P <or= 0.05) effect, respectively. Dietary supplementation with L-arginine may represent a potentially novel nutritional strategy for the treatment of cardiovascular disease.

3-Nitropropionic acid as a tool to study the mechanisms involved in Huntington's disease: past, present and future

Huntington's disease (HD) is an inheritable autosomal-dominant disorder whose causal mechanisms remain unknown. Experimental models have begun to uncover these pathways, thus helping to understand the mechanisms implicated and allowing for the characterization of potential targets for new therapeutic strategies. 3-Nitropropionic acid is known to produce in animals behavioural, biochemical and morphologic changes similar to those occurring in HD. For this reason, this phenotypic model is gaining attention as a valuable tool to mimick this disorder and further developing new therapies. In this review, we will focus on the past and present research of this molecule, to finally bring a perspective on what will be next in this promising field of study.

Protein S-nitrosylation and cardioprotection

Nitric oxide (NO) plays an important role in the regulation of cardiovascular function. In addition to the classic NO activation of the cGMP-dependent pathway, NO can also regulate cell function through protein S-nitrosylation, a redox dependent, thiol-based, reversible posttranslational protein modification that involves attachment of an NO moiety to a nucleophilic protein sulfhydryl group. There are emerging data suggesting that S-nitrosylation of proteins plays an important role in cardioprotection. Protein S-nitrosylation not only leads to changes in protein structure and function but also prevents these thiol(s) from further irreversible oxidative/nitrosative modification. A better understanding of the mechanism regulating protein S-nitrosylation and its role in cardioprotection will provide us new therapeutic opportunities and targets for interventions in cardiovascular diseases.

Evaluation of the role of nitric oxide in acid sensing ion channel mediated cell death

Acid sensing ion channels (ASICs) are widely expressed in central and peripheral nervous system. They are involved in a variety of physiological and pathophysiological processes: synaptic transmission, learning and memory, pain perception, ischemia, etc. During ischemia, metabolic acidosis causes the drop of extracellular pH (pHe) which in turn activates ASICs. Activation of calcium permeable ASIC1a has been implicated in neuronal death. ASICs are modulated by several redox reagents, divalent cations and nitric oxide (NO). Although NO potentiates ASIC mediated currents, the physiological significance of such modulation has not been studied in detail. We have evaluated the role of endogenous NO in cell death at different pH, mediated by the activation of ASICs. At pH 6.1, death rates of ASIC1 expressing Neuro2A (N2A) cells are significantly higher in comparison to the cells that do not express ASICs. Amiloride, a blocker of ASICs protects the cell from acid-injury. Sodium nitroprusside, a potent NO donor not only increases the ASIC mediated currents but also increases cell death at low pH. L-Arg, the precursor of NO also potentiates ASICs in a pH dependent manner. L-Arg-induced NO production and potentiation of ASICs were observed at pHs 7.4, 7.2, 7.0 and 6.8. Lowering the pH below 6.8 did not result in significant production of NO or potentiation of ASICs upon L-Arg stimulation. Our results suggest that potentiation of ASICs by NO and subsequent cell death in vivo depends on the severity of acidosis. During mild and moderate acidosis, NO promotes cell death by potentiating ASICs, whereas this potentiation subsides in severe acidosis due to inhibition of NO synthase.

Electron paramagnetic resonance oximetry and redoximetry

Reactive oxygen/nitrogen species (ROS/RNS) have been increasingly recognized as important mediators and play a number of critical roles in cell injury, metabolism, disease pathology, diagnosis, and clinical treatment. Electron paramagnetic resonance (EPR) spectroscopy enables the spectral information at certain spatial position, and, from the observed line-width and signal intensity, the localized tissue oxygenation, and tissue redox status can be determined. We applied in vivo EPR oximetry and redoximetry technique and implemented its physiological/pathophysiological applications, along with the use of biocompatible lithium pthalocyanine (liPc) and nitroxide redox sensitive probes, on in vivo tissue oxygenation and redox profile of the ischemic and reperfused heart in living animals. We have observed that the hypoxia during myocardial ischemia limited mitochondrial respiration and caused a shift of tissue redox status to a more reduced state. ROS/RNS generated at the beginning of reperfusion not only caused a shift of redox status to a more oxidized state which may contribute to the postischemic myocardial injury, but also a marked suppression of in vivo tissue O(2) consumption in the postischemic heart through modulation of mitochondrial respiration based on alterations in enzyme activity and mRNA expression of NADH dehydrogenase (NADH-DH) and cytochrome c oxidase (CcO). In addition, ischemic preconditioning was found to be able to markedly attenuate postischemic myocardial hyperoxygenation with less ROS/RNS generation and preservation of mitochondrial O(2) metabolism, due to conserved NADH-DH and CcO activities. These studies have demonstrated that EPR oximetry and redoximetry techniques have advanced to a stage that enables in-depth insight in the process of ischemia reperfusion injury.

CB1 cannabinoid receptors promote oxidative stress and cell death in murine models of doxorubicin-induced cardiomyopathy and in human cardiomyocytes

AIMS

Here we investigated the mechanisms by which cardiovascular CB1 cannabinoid receptors may modulate the cardiac dysfunction, oxidative stress, and interrelated cell death pathways associated with acute/chronic cardiomyopathy induced by the widely used anti-tumour compound doxorubicin (DOX).

METHODS AND RESULTS

Both load-dependent and -independent indices of left-ventricular function were measured by the Millar pressure-volume conductance system. Mitogen-activated protein kinase (MAPK) activation, cell-death markers, and oxidative/nitrosative stress were measured by molecular biology/biochemical methods and flow cytometry. DOX induced left-ventricular dysfunction, oxidative/nitrosative stress coupled with impaired antioxidant defense, activation of MAPK (p38 and JNK), and cell death and/or fibrosis in hearts of wide-type mice (CB1(+/+)), and these effects were markedly attenuated in CB1 knockouts (CB1(-/-)). In human primary cardiomyocytes expressing CB1 receptors (demonstrated by RT-PCR, western immunoblot, and flow cytometry) DOX, likewise the CB1 receptor agonist HU210 and the endocannabinoid anandamide (AEA), induced MAPK activation and cell death. The DOX-induced MAPK activation and cell death were significantly enhanced when DOX was co-administered with CB1 agonists AEA or HU210. Remarkably, cell death and MAPK activation induced by AEA, HU210, and DOX +/- AEA/HU210 were largely attenuated by either CB1 antagonists (rimonabant and AM281) or by inhibitors of p38 and JNK MAPKs. Furthermore, AEA or HU210 in primary human cardiomyocytes triggered increased reactive oxygen species generation.

CONCLUSION

CB1 activation in cardiomyocytes may amplify the reactive oxygen/nitrogen species-MAPK activation-cell death pathway in pathological conditions when the endocannabinoid synthetic or metabolic pathways are dysregulated by excessive inflammation and/or oxidative/nitrosative stress, which may contribute to the pathophysiology of various cardiovascular diseases.

Cholesterol diet-induced hyperlipidemia impairs the cardioprotective effect of postconditioning: role of peroxynitrite

The aim of the present study was to investigate if hyperlipidemia interferes with the infarct size-limiting effect of postconditioning and to study the involvement of peroxynitrite in this phenomenon. Rats were fed a 2% cholesterol-enriched or normal diet for 12 wk. Infarct size by triphenyltetrazolium chloride staining was measured in hearts isolated from both groups and subjected to 30 min coronary occlusion followed by 120 min reperfusion with or without the postconditioning protocol induced by six cycles of 10 s coronary occlusion and 10 s reperfusion at the onset of the reperfusion. Postconditioning significantly decreased infarct size in the normolipidemic but not in the hyperlipidemic group. Postconditioning increased cardiac 3-nitrotyrosine concentration (a marker for peroxynitrite formation) in the normal but not in the cholesterol-fed group when measured at the 5th min of reperfusion. Next, we tested if the postconditioning-induced acute increase in peroxynitrite is involved in the cardioprotection in normolipidemic animals in separate experiments. Postconditioning failed to decrease infarct size in the presence of the peroxynitrite decomposition catalyst 5,10,15,20-tetrakis-[4-sulfonatophenyl]-porphyrinato-iron [III] (20 mg/l) in normolipidemic animals. We conclude that an early increase in peroxynitrite after postconditioning plays a role in cardioprotection. Furthermore, hyperlipidemia blocks the cardioprotective effect of postconditioning at least in part via deterioration of the postconditioning-induced early increase in peroxynitrite formation.

Hyperlipidaemia induced by a high-cholesterol diet leads to the deterioration of guanosine-3',5'-cyclic monophosphate/protein kinase G-dependent cardioprotection in rats

BACKGROUND AND PURPOSE

Hyperlipidaemia interferes with cardioprotective mechanisms, but the cause of this phenomenon is largely unknown, although hyperlipidaemia impairs the cardioprotective NO-cGMP system. However, it is not known if natriuretic peptide-cGMP-protein kinase G (PKG) signalling is affected by hyperlipidaemia. Therefore, we investigated the cardioprotective efficacy of cGMP-elevating agents in hearts from normal and hyperlipidaemic rats.

EXPERIMENTAL APPROACH

Male Wistar rats were rendered hyperlipidaemic by feeding with 2% cholesterol-enriched chow for 12 weeks. Hearts isolated from normal and hyperlipidaemic rats were perfused (Langendorff mode) and subjected to 30 min occlusion of the left main coronary artery, followed by 120 min reperfusion. 8-Br-cGMP (CG, 10 nM), B-type natriuretic peptide-32 (BNP, 10 nM), S-nitroso-N-acetyl-penicillamine (SNAP, 1 microM) were perfused from 10 min prior to coronary occlusion until the 15th min of reperfusion. Infarct size (% of ischaemic risk zone) was determined by triphenyltetrazolium staining.

KEY RESULTS

Treatment with CG, SNAP or BNP decreased infarct size significantly in normal hearts from its control value of 41.6 +/- 2.9% to 15.5 +/- 2.4%, 23.3 +/- 3.0% and 25.3 +/- 4.6%, respectively (P < 0.05). Protection by BNP was abolished by co-perfusion of PKG inhibitors KT5823 (600 nM) or Rp-8pCPT-PET-cGMPs (1 microM), confirming its PKG dependence. In hearts from hyperlipidaemic rats, CG, SNAP or BNP failed to decrease infarct size. Hyperlipidaemia did not alter basal myocardial PKG content, but decreased its activity as assessed by phosphorylation of cardiac troponin I.

CONCLUSIONS AND IMPLICATIONS

This is the first demonstration that defects in the cardioprotective cGMP-PKG system could be a critical biochemical anomaly in hyperlipidaemia.

The in vitro effects of superoxide, some commercially available antioxidants and red palm oil on sperm motility

In this study, two commercially available superoxide scavengers, tetrakis (1-methyl-4-pyridyl) porphyrin (Mn[III]TMPyP) and superoxide dismutase (SOD), as well as red palm oil (RPO), a natural vegetable oil, had been used to investigate their possible in vitro effects against the toxic effects of superoxide (O(2).) on human sperm motility. Semen samples were obtained from 12 normozoospermic healthy volunteer donors aged between 19 and 23 years. The O(2). donor 2,3-dimetoxyl-1,4-naphthoquinone (DMNQ) (2.5 micromol L(-1)-100 micromol L(-1)) was added to normozoospermic post-swim-up sperm in the presence or absence of Mn(III)TMPyP (50 micromol L(-1)), SOD (50 IU) or RPO (0.1% or 0.5%). Computer-assisted semen analysis was used to analyze various motility parameters. The parameters of interest were percentage of motile cells, progressive motility, rapid cells and static cells. Concentrations of higher than 25 micromol L(-1) DMNQ were detrimental to sperm motility. Mn(III)TMPyP was able to attenuate the effect of O(2). on the motility parameters. In vitro addition of SOD and RPO showed harmful effects on sperm motility.

Nitric oxide in the cardiovascular system: a simple molecule with complex actions

Since it was identified as the elusive endothelium-derived relaxing factor (EDRF) in the 1980s, nitric oxide (NO) has rapidly gained status as one of the most important signalling molecules in the cardiovascular system. Now, 20 years later, NO is regarded by most to be a ubiquitous mediator of cardioprotection. However, due to various complex underlying cellular mechanisms, the actions of NO often seem to be contradictory. This article sheds light on some of the mechanisms that may influence the variable actions of NO in the heart. Its role in conditions of oxygen deprivation (ischaemia and hypoxia) in particular is relevant to basic scientists and clinicians alike, since the prevalence of ischaemic heart disease is on the rise (in both the developed and the developing worlds) and novel therapeutic options are in constant demand. NO is a promising candidate molecule that could find therapeutic application. For this to be achieved, a sound understanding of this simple molecule and its complex actions is required.

Emerging role of nitrite in myocardial protection

Nitrite has long been considered an inert oxidative metabolite of nitric oxide (NO). However, recent experimental findings strongly suggest that nitrite is a critical storage form of NO that is converted back into NO during ischemic or hypoxic events as well as under physiological conditions. Thus, the conversion of nitrite into NO during cellular stress may be an evolutionarily conserved and redundant means for NO generation at a time when endothelial nitric oxide synthase is non-functional. As a result of the recent revelation that the nitrite anion serves an important biological function a large number of studies have been performed to characterize both the physiological actions and therapeutic potential of nitrite under diverse conditions. While the earliest experiments characterized the vasodilatory effects of nitrite in both animal models and humans, more recent research efforts have focused on the potential benefits of nitrite in a number of pathological states. Nitrite therapy has now been studied in numerous animal models and has proven to be an effective means to ameliorate myocardial ischemia-reperfusion (I/R) injury. This review will focus on recent experimental findings related to the cytoprotective actions of nitrite therapy in the setting of myocardial I/R injury.

Mitochondria and reactive oxygen species

Mitochondria are a quantitatively relevant source of reactive oxygen species (ROS) in the majority of cell types. Here we review the sources and metabolism of ROS in this organelle, including the conditions that regulate the production of these species, such as mild uncoupling, oxygen tension, respiratory inhibition, Ca2+ and K+ transport, and mitochondrial content and morphology. We discuss substrate-, tissue-, and organism-specific characteristics of mitochondrial oxidant generation. Several aspects of the physiological and pathological roles of mitochondrial ROS production are also addressed.

The comparison of the effects of anesthetic doses of ketamine, propofol, and etomidate on ischemia-reperfusion injury in skeletal muscle

The fact that a considerable amount of clinical conditions suffering from ischemia-reperfusion injury (IRI) occur under general anesthesia has triggered researchers to focus on the effects of anesthetic drugs on IRI. Hence, the aim of this study was to compare the use of different anesthetic drugs in a skeletal IRI model. Tourniquet IRI method was performed and two experimental groups were established as sham-control and IRI group. Rats in each group were anesthetized either with thiopental, ketamine, propofol or etomidate. Malondialdehyde, superoxide dismutase, catalase, and glutathione peroxidase were measured in skeletal muscle via a spectrophotometer. Zinc, iron, copper, and selenium were evaluated by atomic absorption spectrophotometer. In rats anesthetized with thiopental (40 mg/kg, i.p.), malondialdehyde values in IRI group were higher and glutathion peroxidase levels were lower compared to sham-control group. However, superoxide dismutase and catalase activities were identical. On the other hand, while the level of zinc in IRI group attenuated, no differences in iron and copper values were determined. Rats anesthetized with ketamine (60 mg/kg), propofol (100 mg/kg), or etomidate (20 mg/kg) did not show increased malondialdehyde levels in comparison with control levels. While the drugs did not cause a distinction in the levels of superoxide dismutase, catalase, glutathion peroxidase, iron, and copper, zinc was in a lower level in IRI group compared to sham-control. In conclusion, ketamine, propofol, and etomidate, with anesthetic doses, denoted efficacious effects on IRI; hence the drugs might be preferred in certain operations with the risk of IRI.

The role of nitric oxide in myocardial repair and remodeling

Nitric oxide (NO) plays a crucial role in many aspects of the pathophysiology of heart failure. NO is a double-edged sword; NO inhibits ischemia/reperfusion (I/R) injury, represses inflammation, and prevents left ventricular (LV) remodeling, whereas excess NO and co-existence of reactive oxygen species (ROS) with NO are injurious. The failing heart is exposed to not only oxidative stress by a plethora of humoral factors and inflammatory cells but also nitrosative stress. Activation of nitric oxide synthase (NOS) of any isoforms, [i.e., endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS)], concomitant with oxidative stress results in NOS uncoupling, leading to further oxidative/nitrosative stress. Indiscriminate removal of oxidative stress is not an effective means to prevent this detrimental process, because oxidative stress is necessary for an adaptive mechanism for cell survival against noxious stimuli. Therefore, removal of ROS in a site-specific manner or inhibition of the source of injurious ROS without affecting redox-sensitive survival signal transduction pathways represents a promising approach to elicit the beneficial effect of NO. Recent emerging pharmacological tools and regular exercise inhibit ROS generation in the proximity of NOSs, thereby increasing bioavailable NO and exerting cardioprotection against I/R injury and LV remodeling.

The opposite roles of nNOS in cardiac ischemia-reperfusion-induced injury and in ischemia preconditioning-induced cardioprotection in mice

The role of neuronal nitric oxide synthase (nNOS) in cardiac ischemia-reperfusion (IR) and ischemia preconditioning (IP) is still controversial. Here, we focused on the possible roles of nNOS in cardiac IR and IP. Wild type C57BL/6 (WT) mice were subjected to coronary artery occlusion for 30 min followed by 24-h reperfusion (IR). Cardiac injury (infarct size and apoptotic cell number) was increased, associated with elevation of oxidative stress (lipid peroxidation) and nitrative stress (nitrotyrosine formation). A potent nNOS inhibitor, L-VNIO, and a superoxide dismutase mimetic and peroxynitrite scavenger, MnTBAP, significantly reduced IR-induced increases of oxidative/nitrative stress and cardiac injury. IR-induced cardiac injury in nNOS(-/-) (KO) mice was significantly lower than that in WT mice. MnTBAP markedly reduced IR-induced cardiac injury by suppression of oxidative/nitrative stress in KO mice. Cardiac IP was performed by three cycles of 5-min IR before 30-min ischemia followed by 24-h reperfusion. IP attenuated IR-induced cardiac injury in WT mice associated with reductions of oxidative/nitrative stress. IP-induced reduction of cardiac injury and oxidative/nitrative stress were eliminated by pretreatment with L-VNIO. In contrast with WT mice, IP had no protective effects in nNOS KO mice. In conclusion, nNOS played a dual role during cardiac IR and IP; nNOS exacerbated IR-induced injury by increasing oxidative/nitrative stress and contributed to IP-induced protection by inhibition of oxidative/nitrative stress.

Coronary vasodilator activity of vulgarenol, a sesquiterpene isolated from Magnolia grandiflora, and its possible mechanism

The aim of this study was to investigate the biodynamic effects of vulgarenol, a sesquiterpene isolated from Magnolia grandiflora flower petals and its possible mechanism on the Langendorff isolated and perfused heart model. Vulgarenol (5 microm) caused a statistically significant decrease in coronary vascular resistance (15.21 +/- 6.00 dyn s cm(-5) vs 36.80 +/- 5.01 dyn s cm(-5), control group), increased nitric oxide release (223.01 +/- 8.76 pmol/mL vs 61.00 +/- 12.00 pmol/mL, control group) and cyclic guanosine monophosphate accumulation in left ventricular tissue samples (142.17 +/- 8.41 pmol/mg of tissue vs 43.94 +/- 5.00 pmol/mg of tissue, control group). Pre-treatment with 3 microm gadolinium chloride hexahydrate, 100 microm N(omega)-nitro-L-arginine methyl ester hydrochloride, and 10 microm 1H-[1,2,4]oxadiazolo[4,2-a]quinoxalin-1-one significantly abolished the vulgarenol-induced coronary vascular resistance decrease, nitric oxide increased release and cGMP accumulation in left ventricular tissue samples. The results support the fact that nitric oxide and cyclic guanosine monophosphate are likely involved in the endothelium-dependent coronary vasodilation.