The mechanism of cardioprotection by S-nitrosoglutathione monoethyl ester in rat isolated heart during cardioplegic ischaemic arrest

Nitric oxide and the brain. Part 1: Mechanisms of regulation, transport and effects on the developing brain

Apart from its known actions as a pulmonary vasodilator, nitric oxide (NO) is a key signal mediator in the neonatal brain. Despite the extensive use of NO for pulmonary artery hypertension (PAH), its actions in the setting of brain hypoxia and ischemia, which co-exists with PAH in 20-30% of affected infants, are not well established. This review focuses on the mechanisms of actions of NO covering the basic, translational, and clinical evidence of its neuroprotective and neurotoxic properties. In this first part, we present the physiology of transport and delivery of NO to the brain and the regulation of cerebrovascular and systemic circulation by NO, as well the role of NO in the development of the immature brain. IMPACT: NO can be transferred from the site of production to the site of action rapidly and affects the central nervous system. Inhaled NO (iNO), a commonly used medication, can have significant effects on the neonatal brain. NO regulates the cerebrovascular and systemic circulation and plays a role in the development of the immature brain. This review describes the properties of NO under physiologic conditions and under stress. The impact of this review is that it describes the effects of NO, especially regarding the vulnerable neonatal brain, and helps understand the conditions that could contribute to neurotoxicity or neuroprotection.

Modulating the Bioactivity of Nitric Oxide as a Therapeutic Strategy in Cardiac Surgery

Cardiac surgery, including cardioplegic arrest and extracorporeal circulation, causes endothelial dysfunction, which can lead to no-reflow phenomenon and reduction of myocardial pump function. Nitric oxide (NO) deficiency is involved in this pathologic process, thereby providing a fundamental basis for the use of NO replacement therapy. Presently used drugs and additives to cardioplegic and heart preservation solutions are not able to reliably protect endothelial cells and cardiomyocytes from ischemia-reperfusion injury. This review discusses promising NO-releasing compounds of various chemical classes for cardioplegia and reperfusion, which effectively maintain NO homeostasis under experimental conditions, and presents the mechanisms of their action on the cardiovascular system. Incomplete preclinical studies and a lack of toxicity assessment, however, hinder translation of these drug candidates into the clinic. Perspectives for modulation of endothelial function using NO-mediated mechanisms are discussed. They are based on the cardioprotective potential of targeting vascular gap junctions and endothelial ion channels, intracoronary administration of progenitor cells, and endothelial-specific microRNAs. Some of these strategies may provide important therapeutic benefits for human cardiovascular interventions.

Protective effects of a modified apelin-12 and dinitrosyl iron complexes in experimental cardioplegic ischemia and reperfusion

The maintenance of nitric oxide (NO) bioavailability has been recognized as an important component of myocardial protection during cardiac surgery. This study was designed to evaluate the efficacy of using two NO-donating compounds in cardioplegia and reperfusion: (i) a modified peptide apelin-12 (MA12) that activates endothelial NO synthase (eNOS) and (ii) dinitrosyl iron complexes with reduced glutathione (DNIC-GS), a natural NO vehicle. Isolated perfused working rat hearts were subjected to normothermic global ischemia and reperfusion. St. Thomas' Hospital cardioplegic solution (STH) containing 140 μM MA12 or 100 μM DNIC-GS was used. In separate series, 140 μM MA12 or 100 μM DNIC-GS was administered at early reperfusion. Metabolic state of the hearts was evaluated by myocardial content of high-energy phosphates and lactate. Lactate dehydrogenase (LDH) activity in myocardial effluent was used as an index of cell membrane damage. Cardioplegia with MA12 or DNIC-GS improved recovery of coronary flow and cardiac function, and reduced LDH leakage in perfusate compared with STH without additives. Cardioplegic arrest with MA12 significantly enhanced preservation of high-energy phosphates and decreased accumulation of lactate in reperfused hearts. The overall protective effect of cardioplegia with MA12 was significantly greater than with DNIC-GS. The administration of MA12 or DNIC-GS at early reperfusion also increased metabolic and functional recovery of reperfused hearts. In this case, recovery of cardiac contractile and pump function indices was significantly higher if reperfusion was performed with DNIC-GS. The results show that MA12 and DNIC-GS are promising adjunct agents for protection of the heart during cardioplegic arrest and reperfusion.

Flunisolide attenuates nitric oxide-induced DNA damage in rat trachea epithelial cells

In asthma the bronchial epithelium is highly abnormal, with various structural changes. As a consequence, the epithelium becomes an important source of inflammatory mediators that contribute to the ongoing inflammation and remodeling responses occurring in asthma. Compared with normal individuals, the fraction of exhaled nitric oxide (NO) is elevated in patients with asthma, and these levels have been shown to vary with disease activity. Thus, in asthma, epithelial cells may be exposed to large amounts of NO. Increased NO production is associated with the formation of various nitrosating species capable of promoting DNA damage. In this study we investigated the effect of NO on DNA of rat trachea epithelial cells in the presence or absence of flunisolide. Rat airway epithelial cells were prepared and incubated with the NO donor S-nitroso-L-glutathione monoethyl ester (GSNO-MEE). DNA damage was evaluated using single cell gel electrophoresis 'comet assay.' The parameters used as an index of DNA damage were tail length, tail intensity, and tail moment. Results of our study demonstrated that NO induced significant DNA damage in rat airway epithelial cells. Flunisolide in amounts of 11-110 mumol/L significantly reduced all the considered parameters indicating DNA damage. These data indicate that flunisolide may protect epithelial cells from the NO-mediated DNA damage. NO overproduction could contribute to epithelial injury in asthma, and flunisolide seems to attenuate this damage.

S-nitrosoglutathione reduces oxidative injury and promotes mechanisms of neurorepair following traumatic brain injury in rats

BACKGROUND

Traumatic brain injury (TBI) induces primary and secondary damage in both the endothelium and the brain parenchyma, collectively termed the neurovascular unit. While neurons die quickly by necrosis, a vicious cycle of secondary injury in endothelial cells exacerbates the initial injury in the neurovascular unit following TBI. In activated endothelial cells, excessive superoxide reacts with nitric oxide (NO) to form peroxynitrite. Peroxynitrite has been implicated in blood brain barrier (BBB) leakage, altered metabolic function, and neurobehavioral impairment. S-nitrosoglutathione (GSNO), a nitrosylation-based signaling molecule, was reported not only to reduce brain levels of peroxynitrite and oxidative metabolites but also to improve neurological function in TBI, stroke, and spinal cord injury. Therefore, we investigated whether GSNO promotes the neurorepair process by reducing the levels of peroxynitrite and the degree of oxidative injury.

METHODS

TBI was induced by controlled cortical impact (CCI) in adult male rats. GSNO or 3-Morpholino-sydnonimine (SIN-1) (50 μg/kg body weight) was administered orally two hours following CCI. The same dose was repeated daily until endpoints. GSNO-treated (GSNO group) or SIN-1-treated (SIN-1 group) injured animals were compared with vehicle-treated injured animals (TBI group) and vehicle-treated sham-operated animals (Sham group) in terms of peroxynitrite, NO, glutathione (GSH), lipid peroxidation, blood brain barrier (BBB) leakage, edema, inflammation, tissue structure, axon/myelin integrity, and neurotrophic factors.

RESULTS

SIN-1 treatment of TBI increased whereas GSNO treatment decreased peroxynitrite, lipid peroxides/aldehydes, BBB leakage, inflammation and edema in a short-term treatment (4-48 hours). GSNO also reduced brain infarctions and enhanced the levels of NO and GSH. In a long-term treatment (14 days), GSNO protected axonal integrity, maintained myelin levels, promoted synaptic plasticity, and enhanced the expression of neurotrophic factors.

CONCLUSION

Our findings indicate the participation of peroxynitrite in the pathobiology of TBI. GSNO treatment of TBI not only reduces peroxynitrite but also protects the integrity of the neurovascular unit, indicating that GSNO blunts the deleterious effects of peroxynitrite. A long-term treatment of TBI with the same low dose of GSNO promotes synaptic plasticity and enhances the expression of neurotrophic factors. These results support that GSNO reduces the levels of oxidative metabolites, protects the neurovascular unit, and promotes neurorepair mechanisms in TBI.

Regulation of mitochondrial processes by protein S-nitrosylation

BACKGROUND

Nitric oxide (NO) exerts powerful physiological effects through guanylate cyclase (GC), a non-mitochondrial enzyme, and through the generation of protein cysteinyl-NO (SNO) adducts-a post-translational modification relevant to mitochondrial biology. A small number of SNO proteins, generated by various mechanisms, are characteristically found in mammalian mitochondria and influence the regulation of oxidative phosphorylation and other aspects of mitochondrial function.

SCOPE OF REVIEW

The principles by which mitochondrial SNO proteins are formed and their actions, independently or collectively with NO binding to heme, iron-sulfur centers, or to glutathione (GSH) are reviewed on a molecular background of SNO-based signal transduction.

MAJOR CONCLUSIONS

Mitochondrial SNO-proteins have been demonstrated to inhibit Complex I of the electron transport chain, to modulate mitochondrial reactive oxygen species (ROS) production, influence calcium-dependent opening of the mitochondrial permeability transition pore (MPTP), promote selective importation of mitochondrial protein, and stimulate mitochondrial fission. The ease of reversibility and the affirmation of regulated S-nitros(yl)ating and denitros(yl)ating enzymatic reactions support hypotheses that SNO regulates the mitochondrion through redox mechanisms. SNO modification of mitochondrial proteins, whether homeostatic or adaptive (physiological), or pathogenic, is an area of active investigation.

GENERAL SIGNIFICANCE

Mitochondrial SNO proteins are associated with mainly protective, bur some pathological effects; the former mainly in inflammatory and ischemia/reperfusion syndromes and the latter in neurodegenerative diseases. Experimentally, mitochondrial SNO delivery is also emerging as a potential new area of therapeutics. This article is part of a Special Issue entitled: Regulation of cellular processes by S-nitrosylation.

Nitric oxide plays a key role in myelination in the developing brain

Inhaled nitric oxide (iNO) is one of the most promising therapies used in neonates, but there is little information available about its effect on the developing brain. We explored the effects of both iNO and endogenous NO on developing white matter in rodents. Rat or mouse pups and their mothers were placed in a chamber containing 5 to 20 ppm of NO for 7 days after birth. Neonatal exposure to iNO was associated with a transient increase in central nervous system myelination in rats and C57BL/6 mice without any deleterious effects at low doses (5 ppm) or behavioral consequences in adulthood. Exposure to iNO was associated with a proliferative effect on immature oligodendrocytes and a subsequent promaturational effect. The role of endogenous NO in myelination was investigated in animals treated with the nitric oxides synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) in the neonatal period; this led to protracted myelination defects and subsequent behavioral deficits in adulthood. These effects were reversed by rescuing L-NAME-treated animals with iNO. Thus, we demonstrate considerable effect of both exogenous and endogenous NO on myelination in rodents. These data point to potential new avenues for neuroprotection in human perinatal brain damage.

S-nitrosylation in cardiovascular signaling

Well over 2 decades have passed since the endothelium-derived relaxation factor was reported to be the gaseous molecule nitric oxide (NO). Although soluble guanylyl cyclase (which generates cyclic guanosine monophosphate, cGMP) was the first identified receptor for NO, it has become increasingly clear that NO exerts a ubiquitous influence in a cGMP-independent manner. In particular, many, if not most, effects of NO are mediated by S-nitrosylation, the covalent modification of a protein cysteine thiol by an NO group to generate an S-nitrosothiol (SNO). Moreover, within the current framework of NO biology, endothelium-derived relaxation factor activity (ie, G protein-coupled receptor-mediated, or shear-induced endothelium-derived NO bioactivity) is understood to involve a central role for SNOs, acting both as second messengers and signal effectors. Furthermore, essential roles for S-nitrosylation have been implicated in virtually all major functions of NO in the cardiovascular system. Here, we review the basic biochemistry of S-nitrosylation (and denitrosylation), discuss the role of S-nitrosylation in the vascular and cardiac functions of NO, and identify current and potential clinical applications.

Nitric oxide homeostasis as a target for drug additives to cardioplegia

The vascular endothelium of the coronary arteries has been identified as the important organ that locally regulates coronary perfusion and cardiac function by paracrine secretion of nitric oxide (NO) and vasoactive peptides. NO is constitutively produced in endothelial cells by endothelial nitric oxide synthase (eNOS). NO derived from this enzyme exerts important biological functions including vasodilatation, scavenging of superoxide and inhibition of platelet aggregation. Routine cardiac surgery or cardiologic interventions lead to a serious temporary or persistent disturbance in NO homeostasis. The clinical consequences are "endothelial dysfunction", leading to "myocardial dysfunction": no- or low-reflow phenomenon and temporary reduction of myocardial pump function. Uncoupling of eNOS (one electron transfer to molecular oxygen, the second substrate of eNOS) during ischemia-reperfusion due to diminished availability of L-arginine and/or tetrahydrobiopterin is even discussed as one major source of superoxide formation. Therefore maintenance of normal NO homeostasis seems to be an important factor protecting from ischemia/reperfusion (I/R) injury. Both, the clinical situations of cardioplegic arrest as well as hypothermic cardioplegic storage are followed by reperfusion. However, the presently used cardioplegic solutions to arrest and/or store the heart, thereby reducing myocardial oxygen consumption and metabolism, are designed to preserve myocytes mainly and not endothelial cells. This review will focus on possible drug additives to cardioplegia, which may help to maintain normal NO homeostasis after I/R.

Lutein, zeaxanthin and astaxanthin protect against DNA damage in SK-N-SH human neuroblastoma cells induced by reactive nitrogen species

The purpose of this study was to evaluate the ability of the predominant carotenoids (lutein and zeaxanthin) of the macular pigment of the human retina, to protect SK-N-SH human neuroblastoma cells against DNA damage induced by different RNOS donors. Although astaxanthin has never been isolated from the human eye, it was included in this study because its structure is very close to that of lutein and zeaxanthin and because it affords protection from UV-light. DNA damage was induced by GSNO-MEE, a nitric oxide donor, by Na(2)N(2)O(3), a nitroxyl anion donor and by SIN-1, a peroxynitrite-generating agent. DNA damage was assessed using the comet assay, a rapid and sensitive single cell gel electrophoresis technique able to detect primary DNA damage in individual cells. The tail moment parameter was used as an index of DNA damage. The values of tail moment increased in all the samples incubated with the RNOS donors, indicating DNA impairment. Data obtained show that the ability of zeaxanthin, lutein, and astaxanthin to reduce the DNA damage depends on the type of RNOS donor and the carotenoid concentration used. All the carotenoids studied were capable of protecting against DNA damage in neuroblastoma cells when the cells were exposed to GSNO-MEE. However, a different behaviour was present when the other two RNOS donors were used. The presence of a carotenoid alone (without an RNOS donor) did not cause DNA damage. Spectrophotometric studies showed that the order with which tested carotenoids reacted with RNOS was not always in agreement with the DNA protection results. The data from this study provides additional information on the activities of the macular pigment carotenoids of the human retina.

Cardioprotection and mitochondrial S-nitrosation: effects of S-nitroso-2-mercaptopropionyl glycine (SNO-MPG) in cardiac ischemia-reperfusion injury

Mitochondrial dysfunction is a key pathologic event in cardiac ischemia-reperfusion (IR) injury, and protection of mitochondrial function is a potential mechanism underlying ischemic preconditioning (IPC). Acknowledging the role of nitric oxide (NO()) in IPC, it was hypothesized that mitochondrial protein S-nitrosation may be a cardioprotective mechanism. The reagent S-nitroso-2-mercaptopropionyl-glycine (SNO-MPG) was therefore developed to enhance mitochondrial S-nitrosation and elicit cardioprotection. Within cardiomyocytes, mitochondrial proteins were effectively S-nitrosated by SNO-MPG. Consistent with the recent discovery of mitochondrial complex I as an S-nitrosation target, SNO-MPG inhibited complex I activity and cardiomyocyte respiration. The latter effect was insensitive to the NO() scavenger c-PTIO, indicating no role for NO()-mediated complex IV inhibition. A cardioprotective role for reversible complex I inhibition has been proposed, and consistent with this SNO-MPG protected cardiomyocytes from simulated IR injury. Further supporting a cardioprotective role for endogenous mitochondrial S-nitrosothiols, patterns of protein S-nitrosation were similar in mitochondria isolated from Langendorff perfused hearts subjected to IPC, and mitochondria or cells treated with SNO-MPG. The functional recovery of perfused hearts from IR injury was also improved under conditions which stabilized endogenous S-nitrosothiols (i.e. dark), or by pre-ischemic administration of SNO-MPG. Mitochondria isolated from SNO-MPG-treated hearts at the end of ischemia exhibited improved Ca(2+) handling and lower ROS generation. Overall these data suggest that mitochondrial S-nitrosation and complex I inhibition constitute a protective signaling pathway that is amenable to pharmacologic augmentation.

S-Nitrosylation of human variant albumin Liprizzi (R410C) confers potent antibacterial and cytoprotective properties

The S-nitrosylated forms of certain proteins such as albumin have been thought to be circulating endogenous reservoirs of nitric oxide (NO) and may have potential as NO donors in therapeutic applications. In this study, we investigated the characteristics of R410C, a genetic variant of human serum albumin with two free thiols at positions 34 (Cys-34) and 410 (Cys-410), as a NO carrier via S-nitroso formation. A biotin switch assay revealed that Cys-410 was more rapidly and efficiently nitrosylated than was Cys-34. Nitrosylation of Cys-410 introduced only small conformational changes in the protein, which were detected by far-UV circular dichroism but not by near-UV circular dichroism. In addition, both native R410C and S-nitrosylated R410C did not induce molecular heterogeneity through oligomerization. S-Nitrosylated R410C exhibited strong antibacterial activity against Salmonella typhimurium in vitro and suppressed apoptosis of U937 human promonocytic cells induced by Fas ligand. In a rat ischemia-reperfusion liver injury model, S-nitrosylated R410C treatment significantly reduced liver damage, as indicated by markedly decreased release of liver enzymes (aspartate aminotransferase and alanine aminotransferase). Pharmacokinetic analyses indicated retention of the S-nitroso moiety of S-nitrosylated R410C in circulation after i.v. injection, with an approximate half-life of 20.4 min in the mouse. These data suggest that R410C can be a useful NO carrier and can be regarded as a new class of S-nitrosylated proteins possessing antibacterial and cytoprotective properties with a circulation time sufficient for in vivo biological activity.

Oxidative stress in myocardial ischaemia reperfusion injury: a renewed focus on a long-standing area of heart research

Advances in the treatment of coronary artery disease have seen a significant drop in mortality and morbidity particularly amongst patients with acute myocardial infarction (MI). In particular, percutaneous trans-luminal balloon angioplasty (PTCA) with stenting to re-open atherosclerotic coronary arteries has yielded marked improvement in clinical outcome for patients with acute MI. Furthermore, with the advent of drug-eluting stents occurrence rates for coronary artery restenosis, one common clinical problem associated with angioplasty and stent deployment, have declined markedly. However, coronary restenosis in diabetic patients remains an on-going problem. The success of drug-eluting stents has seen a renewed focus on myocardial ischaemia reperfusion (IR) injury as this represents one area of research where many questions remain unanswered. In particular, the relationship between myocardial IR injury and decreased myocardial micro-vasculature re-flow post PTCA (that ultimately leads to poor clinical outcome and myocardial damage/dysfunction) is one area of research with the potential to decrease current complication rates further in patients suffering myocardial IR injury sustained during MI. This review discusses the role for oxidative stress, oxidant source(s) and both gene regulation and stem-cell therapy as potential strategic targets in the ischaemic myocardium, with the ultimate aim of providing significant cardioprotection in the setting of acute MI.

Induction of Thioredoxin and Mitochondrial Survival Proteins Mediates Preconditioning-Induced Cardioprotection and Neuroprotection

Delayed cardio- and neuroprotection are observed following a preconditioning procedure evoked by a brief and nontoxic oxidative stress due to deprivation of oxygen, glucose, serum, trophic factors, and/or antioxidative enzymes. Preconditioning protection can be observed in vivo and is under clinical trials for preservation of cell viability following organ transplants of liver. Previous studies indicated that ischemic preconditioning increases the expression of heat-shock proteins (HSPs) and nitric oxide synthase (NOS). Our pilot studies indicate that the treatment of neuronal NOS inhibitor (7-nitroindazole) and 6Br-cGMP blocks and mimics, respectively, preconditioning protection in human neuroblastoma SH-SY5Y cells. This minireview focuses on nitric oxide-mediated cellular adaptation and the related cGMP/PKG signaling pathway in a compensatory mechanism underlying preconditioning-induced hormesis. Both preconditioning and 6Br-cGMP increase the induction of human thioredoxin (Trx) mRNA and protein for cytoprotection, which is largely prevented by transfection of cells with Trx antisense but not sense oligonucleotides. Cytosolic Trx1 and mitochondrial Trx2 suppress free radical formation, lipid peroxidation, oxidative stress, and mitochondria-dependent apoptosis; knock out/down of either Trx1 or Trx2 is detrimental to cell survival. Other recent findings indicate that a transgenic increase of Trx in mice increases tolerance against oxidative nigral injury caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Trx1 can be translocated into nucleus and phosphoactivated CREB for a delayed induction of mitochondrial anti-apoptotic Bcl-2 and antioxidative MnSOD that is known to increase vitality and survival of cells in the brain and the heart. In conclusion, preconditioning adaptation or a brief oxidative stress induces a delayed nitric oxide-mediated compensatory mechanism for cell survival and vitality in the central nervous system and the cardiovascular system. Preconditioning-induced adaptive tolerance may be signaling through a cGMP-dependent induction of cytosolic redox protein Trx1 and subsequently mitochondrial proteins such as Bcl-2, MnSOD, and perhaps Trx2 or HSP70.

S-nitroso human serum albumin attenuates ischemia/reperfusion injury after cardioplegic arrest in isolated rabbit hearts

BACKGROUND

Depletion of nitric oxide (NO) is associated with ischemia/reperfusion injury. The novel NO donor, S-nitroso human serum albumin (S-NO-HSA), could bridge NO depletion during reperfusion in cardiac transplantation and minimize ischemia/reperfusion injury.

METHODS

In an isolated erythrocyte-perfused working heart model, rabbit hearts were randomly assigned after assessment of hemodynamic baseline values to receive S-NO-HSA (0.2 micromol/100 ml, n = 8), L-arginine (10 mmol/100 ml, n = 8) or albumin (control) (0.2 micromol/100 ml, n = 8). After 20 minutes of infusion, the hearts were arrested and stored in Celsior (4 degrees C) enriched with respective drugs for 6 hours, followed by 75 minutes of reperfusion. Hemodynamic values were assessed and biopsy specimens were taken to determine calcium-ionophore stimulated release of NO and superoxide.

RESULTS

During early reperfusion, recovery of cardiac output (75% +/- 6% vs 49% +/- 5%, p < 0.05) and coronary flow (99% +/- 8% vs 70% +/- 5%, p < 0.05) were higher, and myocardial oxygen consumption was reduced in the S-NO-HSA Group compared with Control (4.08 +/- 0.46 ml/min/0.1 kg vs 6.78 +/- 0.38 ml/min/0.1 kg, p < 0.01). At the end of the experiment cardiac output (53% +/- 5% vs 27% +/- 5%, p < 0.01) was higher and left atrial pressure (115% +/- 9% vs 150% +/- 8%, p < 0.05) was lower in the S-NO-HSA Group compared with Control. NO release was increased (1,040 +/- 50 nmol/liter and 1,070 +/- 60 nmol/liter vs 860 +/- 10 nmol/liter, p < 0.01) and superoxide release diminished (31 +/- 5 nmol/liter and 38 +/- 5 nmol/liter vs 64 +/- 5 nmol/liter, p < .01) in the S-NO-HSA and L-arginine Groups compared with Control.

CONCLUSION

S-NO-HSA improved hemodynamic functions after prolonged hypothermic cardiac arrest by supplementing NO and thereby decreasing ischemia/reperfusion injury.

The effects of exogenous nitric oxide donor on motor functional recovery of reperfused peripheral nerve

PURPOSE

To investigate the effects of the nitric oxide donor S-nitroso-N-acetylcysteine (SNAC) on motor functional recovery of reperfused rat sciatic nerve.

METHODS

Seventy-eight rats were divided into groups treated with SNAC (100 nmol/100 g/min), methylprednisolone 30 mg/kg/h for 15 minutes, 45-minute pause, 5.4 mg/kg/h for 1.5 h), and phosphate-buffered saline 0.2 mL/100 g/h). A 1-cm segment of sciatic nerve had 2 hours of ischemia and the results were evaluated after various reperfusion periods using a walking track test, muscle contractile testing, muscle weight, and histology.

RESULTS

During reperfusion there was a significant overall improvement in sciatic functional index measurement and isometric titanic contractile force for the SNAC-treated group compared with the methylprednisolone- and phosphate-buffered saline- treated groups. The SNAC group had significantly earlier improvement in the sciatic functional index measurement between days 7 and 28. Restoration of the contractile force and muscle weight of the extensor digitorum longus muscle began earlier in the SNAC group--after day 11--whereas the other 2 groups showed progressive atrophy until day 21, with a significant difference between the SNAC group and the other 2 groups. Histologic examination showed that SNAC-treated rats had less severe degeneration and earlier regeneration of axons than the others. Although methylprednisolone-treated rats showed earlier recovery than phosphate-buffered saline-treated rats in all parameters there were no significant differences between these 2 groups.

CONCLUSIONS

Supplementation of nitric oxide is effective in promoting motor functional recovery of the reperfused peripheral nerve and has potential to replace or augment steroids as therapeutic agents in treatment of nervous system ischemia/reperfusion injury.

Synthesis, characterization and antioxidant activity of new copper(i) complexes of scorpionate and water soluble phosphane ligands

New copper(I) complexes have been synthesised from the reaction of CuCl with potassium hydrotris(4-bromo-1H-pyrazol-1-yl)borate, KTp4Br or lithium bis(3,5-dimethylpyrazol-1-yl)acetate, Li[L2CO2] ligands and 4- or 2-(diphenylphosphane)benzoic acid or tris(m-sulfonatophenyl)posphine trisodium salt (TPPTS) coligands. The complexes obtained have been characterized by elemental analyses and FT-IR in the solid state, and by NMR (1H and 31P[1H]) and electrospray mass spectrometry (ESI-MS) in solution. Single crystal structural characterisation was undertaken for the [Cu[PPh2(4-C6H4COOH)](Tp4Br)] derivative, an interesting dimeric supramolecular assembly. A chemiluminescence study has demonstrated the superoxide scavenging activity of these new copper complexes. The Comet assay was used to evaluate the impairment of DNA in rat epithelial cells exposed to different reactive nitrogen species. In addition, the same complexes were included in this study to determine their efficacy as antioxidants in mitigating oxidative DNA damage. The parameter tail moment, used as an index of DNA damage, showed that the complex [Cu[PPh2(4-C6H4COOH)](Tp4Br)] remarkably inhibited DNA strand breaks induced by the different nitrogen oxide species. The other copper complexes under study showed a different ability to reduce tail moment values depending on the type of RNOS donor used.

Effect of nitric oxide and nitroxide SOD-mimic on the recovery of isolated rat heart following ischemia and reperfusion

Nitric oxide synthesized from L-arginine in cells has important salutary physiological roles, but can also exert deleterious effects. Nitric oxide (NO) can ameliorate post-ischemic reperfusion myocardial injury, yet formation from NO and O(2)z*(-) of peroxynitrite and its downstream toxic products, such as *OH, *NO(2) and CO(3)*(-), can ultimately exacerbate reperfusion damage. Nitroxide stable radicals, such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TPL), unlike SOD, readily penetrate cells and catalytically remove intracellular O(2)*(-). Hence, nitroxides by virtue of catalytic removal of O(2)*(-) would be expected to diminish the adverse effect of NO and lower post-ischemic reperfusion cardiac damage. We show that post-ischemic recovery of hemodynamic functions of isolated perfused rat hearts treated with L-arginine or TPL alone did not differ from that of the control hearts. However, the recovery of hearts treated with the combined regimen of L-arginine and TPL was significantly improved, e.g. the Work Index=(left ventricular developed pressure x heart rate) recovered to 92+/-1.6% (L-arginine and TPL) vs. 59.4+/-5.4% (Control), 60+/-2.9% (L-arginine) and 53.3+/-4.3% (TPL) of the pre-ischemic value; mean+/-SEM, N=10, P<0.001. The enhanced recovery of hemodynamic function of hearts treated with L-arginine and TPL was accompanied by an increased recovery of oxygen consumption during the reperfusion. The combined regimen of L-arginine and TPL reduces the negative effects of NO by either inhibiting the production of ONOO(-) or through reaction with CO(3)z.rad;(-) and *NO(2) radicals formed during the decomposition of peroxynitrite in the presence of bicarbonate, thus promoting cardioprotection following post-ischemic reperfusion.

Nitroxide radicals protect against DNA damage in rat epithelial cells induced by nitric oxide, nitroxyl anion and peroxynitrite

In order to gain more knowledge on the antioxidant role of nitroxide radicals, in this study we investigate their possible protective action against DNA damage induced by nitric oxide (NO) and reactive nitrogen oxide species deriving from it, namely nitroxyl anion (NO(-)) and peroxynitrite (ONOO(-)). Rat trachea epithelial cells were exposed under aerobic conditions to (1) NO generated by 150 microM S-nitrosoglutathione monoethyl ester (GSNO-MEE), (2) NO(-) generated by 200 microM Angeli's salt (Na(2)N(2)O(3)) (3) ONOO(-) generated by 1mM SIN-1 (3-morpholino-sydnonimine) and (4) 100 microM synthesized ONOO(-), in the absence and presence of 5 microM of two indolinonic nitroxides synthesized by us and the piperidine nitroxide TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl). DNA damage was assessed using the comet assay-a rapid and sensitive, single-cell gel electrophoresis technique used to detect primary DNA damage in individual cells. The parameter tail moment, used as an index of DNA damage, showed that in all cases the nitroxides remarkably inhibited DNA strand breaks induced by the different nitrogen oxide species. All three nitroxides protect to the same extent, except in the case of synthesized peroxynitrite where the aromatic nitroxides 1 and 2 are more efficient than TEMPO. These findings are consistent with the antioxidant character of nitroxide compounds and give additional information on the potential implications for their use as therapeutic agents.

Preconditioning-mediated neuroprotection: role of nitric oxide, cGMP, and new protein expression

Preconditioning adaptation induced by transient ischemia can increase brain tolerance to oxidative stress, but the underlying neuroprotective mechanisms are not fully understood. Recently, we developed a human brain-derived cell model to investigate preconditioning mechanism in SH-SY5Y neuroblastoma cells.(1) Our results demonstrate that a non-lethal serum deprivation-stress for 2 h (preconditioning stress) enhanced the tolerance to a subsequent lethal oxidative stress (24 h serum deprivation) and also to 1-methyl-4-phenyl-pyridinium (MPP(+)).(2) Two-hour non-lethal preconditioning stress increased the expression of neuronal nitric oxide (NOS1/nNOS) mRNA, Fos, Ref-1, NOS protein, and then nitric oxide (*NO) production. As well as MnSOD expression, the *NO-cGMP-PKG pathway mediated the preconditioning-induced upregulation of antiapoptotic protein Bcl-2 and the downregulation of adaptor protein p66(shc). We also propose that cGMP-mediated preconditioning-induced adaptation against oxidative stress may be due to the synthesis of a new protein, such as thioredoxin (Trx) since the protective effect can be blocked by Trx reductase inhibitor.(3) The antioxidative potency of Trx was approximately 100 and 1,000 times greater than GSNO and GSH, respectively. These results suggest that *NO-cGMP-PKG signaling pathway plays an important role in the preconditioning-induced neuroprotection, and perhaps cardioprotection, against oxidative stress.

Metabolism of S-nitrosoglutathione by endothelial cells

S-nitrosoglutathione (GSNO) is an inhibitor of platelet aggregation and has also been shown to protect the ischemic heart from reperfusion-mediated injury. Although GSNO is often used in cell culture as a source of nitric oxide, the mechanisms of GSNO metabolism are not well established. We show here that GSNO decomposition by bovine aortic endothelial cells has an absolute dependence on the presence of cystine in the cell culture medium. In addition, GSNO decay is inhibited by diethyl maleate, an intracellular glutathione scavenger, but not by buthionine sulfoximine, a glutathione synthesis inhibitor. This indicates that thiols in general, rather than specifically glutathione, are the major factors that influence GSNO decay. Only 40% of the nitroso group of GSNO could be recovered as nitrite/nitrate, suggesting that the primary route of GSNO decay is reductive and that nitric oxide is only a minor product of GSNO decay. We conclude that the intracellular thiol pool causes the reduction of extracellular disulfides to thiols, which then directly reduce GSNO.

Preparation and properties of S-nitroso-L-cysteine ethyl ester, an intracellular nitrosating agent

In this report, a protocol for the preparation of the hydrochloride of S-nitroso-L-cysteine ethyl ester (SNCEE.HCl; 2) is presented. The synthesis of 2 has been targeted because S-nitroso-L-cysteine (SNC; 2b), which is extensively used for trans-S-nitrosation of thiol-containing proteins, has a limited ability of crossing cellular membranes. The nitrosothiol 2 was prepared via direct S-nitrosation of the hydrochloride of L-cysteine ethyl ester (CEE.HCl; 1a) with ethyl nitrite. 2 is relatively stable in crystal form and when neutralized to SNCEE (2a) in aqueous solutions treated with chelators of metal ions. Traces of metal ions, however, triggered the decomposition of 2a to nitric oxide and a S-centered radical, which were detected by ESR spectrometry. In contrast to 2b, 2a is a lipophilic compound that was taken up by human neutrophils. The latter process was paralleled by inhibition of the NADPH oxidase-dependent generation of superoxide anion radicals, presumably via reaction(s) of intracellular trans-S-nitrosation. Intracellular accumulation of S-nitrosothiols was observed with 2a but not with 2b. It is expected that the use of 2a will be advantageous when intracellular reactions of trans-S-nitrosation are to be studied.

Reaction of S-nitrosoglutathione with the heme group of deoxyhemoglobin

The mechanism of interaction between S-nitrosoglutathione (GSNO) and hemoglobin is a crucial component of hypotheses concerning the role played by S-nitrosohemoglobin in vivo. We previously demonstrated (Patel, R. P., Hogg, N., Spencer, N. Y., Kalyanaraman, B., Matalon, S., and Darley-Usmar, V. M. (1999) J. Biol. Chem. 274, 15487-15492) that transnitrosation between oxygenated hemoglobin and GSNO is a slow, reversible process, and that the reaction between GSNO and deoxygenated hemoglobin (deoxyHb) did not conform to second order reversible kinetics. In this study we have reinvestigated this reaction and show that GSNO reacts with deoxyHb to form glutathione, nitric oxide, and ferric hemoglobin. Nitric oxide formed from this reaction is immediately autocaptured to form nitrosylated hemoglobin. GSNO reduction by deoxyHb is essentially irreversible. The kinetics of this reaction depended upon the conformation of the protein, with more rapid kinetics occurring in the high oxygen affinity state (i.e. modification of the Cysbeta-93) than in the low oxygen affinity state (i.e. treatment with inositol hexaphosphate). A more rapid reaction occurred when deoxymyoglobin was used, further supporting the observation that the kinetics of reduction are directly proportional to oxygen affinity. This observation provides a mechanism for how deoxygenation of hemoglobin/myoglobin could facilitate nitric oxide release from S-nitrosothiols and represents a potential physiological mechanism of S-nitrosothiol metabolism.

Doxorubicin-induced apoptosis in endothelial cells and cardiomyocytes is ameliorated by nitrone spin traps and ebselen. Role of reactive oxygen and nitrogen species

Doxorubicin (DOX) is a broad spectrum anthracycline antibiotic used to treat a variety of cancers. Redox activation of DOX to form reactive oxygen species has been implicated in DOX-induced cardiotoxicity. In this work we investigated DOX-induced apoptosis in cultured bovine aortic endothelial cells and cardiomyocytes isolated from adult rat heart. Exposure of bovine aortic endothelial cells or myocytes to submicromolar levels of DOX induced significant apoptosis as measured by DNA fragmentation and terminal deoxynucleotidyltransferase-mediated nick-end labeling assays. Pretreatment of cells with 100 microm nitrone spin traps, N-tert-butyl-alpha-phenylnitrone (PBN) or alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) dramatically inhibited DOX-induced apoptosis. Ebselen (20-50 microm), a glutathione peroxidase mimetic, also significantly inhibited apoptosis. DOX (0.5-1 microm) inactivated mitochondrial complex I by a superoxide-dependent mechanism. PBN (100 microm), POBN (100 microm), and ebselen (50 microm) restored complex I activity. These compounds also inhibited DOX-induced caspase-3 activation and cytochrome c release. PBN and ebselen also restored glutathione levels in DOX-treated cells. We conclude that nitrone spin traps and ebselen inhibit the DOX-induced apoptotic signaling mechanism and that this antiapoptotic mechanism may be linked in part to the inhibition in formation or scavenging of hydrogen peroxide. Therapeutic strategies to mitigate DOX cardiotoxicity should be reexamined in light of these emerging antiapoptotic mechanisms of antioxidants.

Chronic myocardial hypoxia increases nitric oxide synthase and decreases caveolin-3

Nitric oxide synthase (NOS) is believed to play an important role in protecting the myocardium against ischemia. Chronic hypoxia from birth increases NOS activity in the myocardium resulting in enhanced nitric oxide production and increased resistance to ischemia. We examined the effects of chronic hypoxia on NOS gene and protein expression and on NOS protein association with caveolin-3. Rabbits were raised from birth in a normoxic (F(I)O(2) = 0.21) or a hypoxic (F(I)O(2) = 0.12) environment for 9 d, and then the hearts were isolated. Ribonuclease protection assays revealed that chronic hypoxia did not alter NOS transcript levels for NOS1, NOS2, or NOS3. The most abundant transcript was NOS3. Western analysis revealed NOS3 was the only isoform detected. Immunoblots of NOS3 immunoprecipitates showed that chronic hypoxia increases NOS3 protein by 2.0 +/- 0.4-fold and decreases the amount of caveolin-3 that can be coprecipitated with NOS3 by 5.5 +/- 0.9-fold. Immunoblots of normoxic and hypoxic hearts showed that chronic hypoxia decreases the amount of caveolin-3 in heart homogenates by 2. 2 +/- 0.5-fold. These data suggest that a decrease in caveolin-3 plays a role in the mechanisms by which chronic hypoxia increases NOS3 activity in the myocardium.

Biological chemistry and clinical potential of S-nitrosothiols

S-Nitrosothiols are endogenous metabolites of nitric oxide that have been detected in extra- and intracellular spaces. Many biological functions of S-nitrosothiols have been described that can be categorized as being due to one or more of the following: (i) nitric oxide release, (ii) transnitrosation, (iii) S-thiolation, and (iv) direct action. This emphasizes the fact that S-nitrosothiols are more than simply nitric oxide donors. Many of the biological functions that have been described for S-nitrosothiols have clinical correlates. This review describes the biological chemistry, biological actions, and clinical potential of these compounds.

Neuroprotective properties of nitric oxide

The discoveries of physiological roles of nitric oxide (.NO) as the mediator of endothelium-derived relaxing factor (EDRF) action and the activator of guanylyl cyclase to increase cyclic guanosine monophosphate (cGMP), which lead to vasorelaxation in the cardiovascular system, have been awarded with the 1998 Nobel Prize of Medicine. The present review discusses putative beneficial effects of .NO in the central nervous system (CNS). In addition to its prominent roles of the regulation of cerebral blood flow and the modulation of cell to cell communication in the brain, recent in vitro and in vivo results indicated that .NO is a potent antioxidative agent. .NO terminates oxidant stress in the brain by (i) suppressing iron-induced generation of hydroxyl radicals (.OH) via the Fenton reaction, (ii) interrupting the chain reaction of lipid peroxidation, (iii) augmenting the antioxidative potency of reduced glutathione (GSH) and (iv) inhibiting cysteine proteases. It is apparent that .NO--a relative long half-life nitrogen-centered weak radical--scavenges those short-lived, highly reactive free radicals such as superoxide anion (O2.-), .OH, peroxyl lipid radicals (LOO.) and thiyl radicals (i.e., GS.), yielding reactive nitrogen species including nitrites, nitrates, S-nitrosoglutathione (GSNO) and peroxynitrite (ONOO-). GSNO is 100-fold more potent than GSH; it completely inhibits the weak peroxidative effect of ONOO-. Moreover, CO2 and .NO neutralize prooxidative effects of ONOO-. CO2 prevents protein oxidation but not 3-nitrotyrosine formation caused by ONOO-. Finally, neuroprotective effects of GSNO and .NO have been demonstrated in brain preparations in vivo. These novel neuroprotective properties of .NO and GSNO may have their physiological significance, since oxidative stress depletes GSH while increasing GS. and .NO formation in astroglial and endothelial cells, resulting in the generation of a more potent antioxidant GSNO and providing additional neuro-protection at microM concentrations. This putative GSNO pathway (GSH-->GS.-->GSNO-->.NO + GSSG-->GSH) may be an important part of endogenous antioxidative defense system, which could protect neurons and other brain cells against oxidative stress caused by oxidants, iron complexes, proteases and cytokines. In conclusion, .NO is a potent antioxidant against oxidative damage caused by reactive oxygen species, which are generated by Fenton reaction or other mechanisms in the brain via redox cycling of iron complexes.

Neuroprotective strategies in Parkinson's disease: protection against progressive nigral damage induced by free radicals

Brain undergoes neurodegeneration when excess free radicals overwhelm antioxidative defense systems during senescence, head trauma and/or neurotoxic insults. A site-specific accumulation of ferrous citrate-iron complexes in the substantia nigra dopaminergic neurons could lead to exaggerated dopamine turnover, dopamine auto-oxidation, free radical generation, and oxidant stress. Eventually, this iron-catalyzed dopamine auto-oxidation results in the accumulation of neuromelanin, a progressive loss of nigral neurons, and the development of Parkinson's disease when brain dopamine depletion is greater than 80%. Emerging evidence indicates that free radicals such as hydroxyl radicals ((.-)OH) and nitric oxide ((.-)NO) may play opposite role in cell and animal models of parkinsonism. (.-)OH is a cytotoxic oxidant whereas oNO is an atypical neuroprotective antioxidant. (.-)NO and S-nitrosoglutathione (GSNO) protect nigral neurons against oxidative stress caused by 1-methyl-4-phenylpyridinium (MPP(+)), dopamine, ferrous citrate, hemoglobin, sodium nitroprusside and peroxynitrite. MPP(+), the toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), increases the nigral uptake of iron complexes and dopamine overflow leading to the generation of (.-)OH, protein oxidation, lipid peroxidation, and associated retrograde degeneration. In addition to GSNO, MPP(+)-induced oxidative neurotoxicity can be prevented by antioxidants including selegiline, 7-nitroindazole, 17beta-estradiol, melatonin, alpha-phenyl-tert-butylnitrone and U78517F. Similar to selegiline, 7-nitroindazole is a MAO-B inhibitor, which blocks the bio-activation of MPTP and oxidative stress. Freshly prepared but not light exposed, (.-)NO-exhausted GSNO is about 100 times more potent than the classic antioxidant glutathione. Via S-nitrosylation, GSNO also inhibits proteolysis and cytotoxicity caused by caspases and HIV-1 protease. Furthermore, in addition to protection against serum deprivation stress, the induction of neuronal NOS1 in human cells increases tolerance to MPP(+)-induced neuro-toxicity since newly synthesized (.-)NO prevents apoptosis possibly through up-regulation of bcl-2 and down regulation of p66(shc). In conclusion, reactive oxygen species are unavoidable by-products of iron-catalyzed dopamine auto-oxidation, which can initiate lipid peroxidation, protein oxidation, DNA damage, and nigral loss, all of which can be prevented by endogenous and exogenous (.-)NO. Natural and man-made antioxidants can be employed as part of preventative or neuroprotective treatments in Parkinson's disease and perhaps dementia complexes as well. For achieving neuroprotection and neuro-rescue in early clinical parkinsonian stages, a cocktail therapy of multiple neuroprotective agents may be more effective than the current treatment with extremely high doses of a single antioxidative agent.

The redox pathway of S-nitrosoglutathione, glutathione and nitric oxide in cell to neuron communications

Recent results demonstrated that S-nitrosoglutathione (GSNO) and nitric oxide (*NO) protect brain dopamine neurons from hydroxyl radical (*OH)-induced oxidative stress in vivo because they are potent antioxidants. GSNO and *NO terminate oxidant stress in the brain by (i) inhibiting iron-stimulated hydroxyl radicals formation or the Fenton reaction, (ii) terminating lipid peroxidation, (iii) augmenting the antioxidative potency of glutathione (GSH), (iv) mediating neuroprotective action of brain-derived neurotrophin (BDNF), and (v) inhibiting cysteinyl proteases. In fact, GSNO--S-nitrosylated GSH--is approximately 100 times more potent than the classical antioxidant GSH. In addition, S-nitrosylation of cysteine residues by GSNO inactivates caspase-3 and HIV-1 protease, and prevents apoptosis and neurotoxicity. GSNO-induced antiplatelet aggregation is also mediated by S-nitrosylation of clotting factor XIII. Thus the elucidation of chemical reactions involved in this GSNO pathway (GSH GS* + *NO-->[GSNO]-->GSSG + *NO-->GSH) is necessary for understanding the biology of *NO, especially its beneficial antioxidative and neuroprotective effects in the CNS. GSNO is most likely generated in the endothelial and astroglial cells during oxidative stress because these cells contain mM GSH and nitric oxide synthase. Furthermore, the transfer of GSH and *NO to neurons via this GSNO pathway may facilitate cell to neuron communications, including not only the activation of guanylyl cyclase, but also the nitrosylation of iron complexes, iron containing enzymes, and cysteinyl proteases. GSNO annihilates free radicals and promotes neuroprotection via its c-GMP-independent nitrosylation actions. This putative pathway of GSNO/GSH/*NO may provide new molecular insights for the redox cycling of GSH and GSSG in the CNS.

Nitric oxide-forming reactions of the water-soluble nitric oxide spin-trapping agent, MGD

The objective of this study was to elucidate the nitric oxide-forming reactions of the iron-N-methyl-D-glucamine dithiocarbamate (Fe-MGD) complex from the nitrogen-containing compound hydroxyurea. The Fe2+(MGD)2 complex is commonly used in electron paramagnetic resonance (EPR) spectroscopic detection of NO both in vivo and in vitro. The reaction of Fe2+(MGD)2 with NO yields the resultant NO-Fe2+(DETC)2 complex, which has a characteristic triplet EPR signal. It is widely believed that only NO reacts with Fe2+(MGD)2 to form the NO-Fe2+(MGD)2 complex. In this report, the mechanism leading to the formation of NO-Fe2+(MGD)2 was investigated using oxygen-uptake studies in conjunction with the EPR spin-trapping technique. We found that the air oxidation of Fe2+(MGD)2 complex results in the formation of the Fe3+(MGD)3 complex, presumably concomitantly with superoxide (O3*-). Dismutation of superoxide forms hydrogen peroxide, which can subsequently reduce Fe3+(MGD)3 back to Fe2+(MGD)2. The addition of NO to the Fe3+(MGD)3 complex resulted in the formation of the NO-Fe2+(MGD)2 complex. Hydroxyurea is not considered to be a spontaneous NO donor, but has to be oxidized in order to form NO. We present data showing that in the presence of oxygen, Fe2+(MGD)2 can oxidize hydroxyurea to yield the stable NO-Fe2+(MGD)2 complex. These results imply that hydroxyurea can be oxidized by reactive oxygen species that are formed from the air oxidation of the Fe2+(MGD)2 complex. Formation of the NO-Fe2+(MGD)2 complex in this case could erroneously be interpreted as spontaneous formation of NO from hydroxyurea. The chemistry of the Fe2+(MGD)2 complexes in aerobic conditions must be taken into account in order to avoid erroneous conclusions. In addition, the use of these complexes may contribute to the overall oxidative stress of the system under investigation.

Adaptation to chronic hypoxia confers tolerance to subsequent myocardial ischemia by increased nitric oxide production

Chronic exposure to hypoxia from birth increased the tolerance of the rabbit heart to subsequent ischemia compared with age-matched normoxic controls. The nitric oxide donor GSNO increased recovery of post-ischemic function in normoxic hearts to values not different from hypoxic controls, but had no effect on hypoxic hearts. The nitric oxide synthase inhibitors L-NAME and L-NMA abolished the cardioprotective effect of hypoxia. Message and catalytic activity for constitutive nitric oxide synthase as well as nitrite, nitrate, and cGMP levels were elevated in hypoxic hearts. Inducible nitric oxide synthase was not detected in normoxic or chronically hypoxic hearts. Increased tolerance to ischemia in rabbit hearts adapted to chronic hypoxia is associated with increased expression of constitutive nitric oxide synthase.

Nitrosation of uric acid by peroxynitrite. Formation of a vasoactive nitric oxide donor

Peroxynitrite (ONOO-), formed by the reaction between nitric oxide (. NO) and superoxide, has been implicated in the etiology of numerous disease processes. Low molecular weight antioxidants, including uric acid, may minimize ONOO---mediated damage to tissues. The tissue-sparing effects of uric acid are typically attributed to oxidant scavenging; however, little attention has been paid to the biology of the reaction products. In this study, a previously unidentified uric acid derivative was detected in ONOO--treated human plasma. The product of the uric acid/ONOO- reaction resulted in endothelium-independent vasorelaxation of rat thoracic aorta, with an EC50 value in the range of 0.03-0.3 microM. Oxyhemoglobin, a .NO scavenger, completely attenuated detectable .NO release and vascular relaxation. Uric acid plus decomposed ONOO- neither released .NO nor altered vascular reactivity. Electrochemical quantification of .NO confirmed that the uric acid/ONOO- reaction resulted in spontaneous (thiol-independent) and protracted (t1/2 approximately 125 min) release of .NO. Mass spectroscopic analysis indicated that the product was a nitrated uric acid derivative. The uric acid nitration/nitrosation product may play a pivotal role in human pathophysiology by releasing .NO, which could decrease vascular tone, increase tissue blood flow, and thereby constitute a role for uric acid not previously described.

Enzyme inactivation through sulfhydryl oxidation by physiologic NO-carriers

Nitric oxide (NO) is a pluripotent regulatory molecule, yet the molecular mechanisms by which it exerts its effects are largely unknown. Few physiologic target molecules of NO have been identified, and even for these, the modifications caused by NO remain uncharacterized. Human glutathione reductase (hGR), a central enzyme of cellular antioxidant defense, is inhibited by S-nitrosoglutathione (GSNO) and by diglutathionyl-dinitroso-iron (DNIC-[GSH]2), two in vivo transport forms of NO. Here, crystal structures of hGR inactivated by GSNO and DNIC-[GSH]2 at 1.7 A resolution provide the first picture of enzyme inactivation by NO-carriers: in GSNO-modified hGR, the active site residue Cys 63 is oxidized to an unusually stable cysteine sulfenic acid (R-SOH), whereas modification with DNIC-[GSH]2 oxidizes Cys 63 to a cysteine sulfinic acid (R-SO2H). Our results illustrate that various forms of NO can mediate distinct chemistry, and that sulfhydryl oxidation must be considered as a major mechanism of NO action.

Nitric oxide protects cardiomyocytes against tert-butyl hydroperoxide-induced formation of alkoxyl and peroxyl radicals and peroxidation of phosphatidylserine

We studied protective effects of nitric oxide against tert-butyl hydroperoxide-induced oxidative damage to cardiac myocytes. Two distinct free radicals species--alkoxyl radicals associated with non-heme iron catalytic sites and myoglobin protein-centered peroxyl radicals--were found in low-temperature EPR spectra of cardiac myocytes exposed to t-BuOOH. The t-BuOOH-induced radical formation was accompanied by site-specific oxidative stress in membrane phospholipids (peroxidation of phosphatidylserine) assayed by fluorescence HPLC after metabolic labeling of cell phospholipids with oxidation-sensitive cis-parinaric acid. An NO-donor, (Z)-1-[N-(3-ammonio-propyl)-N-(n-propyl) amino]-diazen-1-ium-1,2-diolate], protected cardiac myocytes against tert-butyl hydroperoxide-induced: (i) formation of non-protein- and protein-centered free radical species and (ii) concomitant peroxidation of phosphatidylserine. Thus nitric oxide can act as an effective antioxidant in live cardiomyocytes.

EPR detection of endogenous nitric oxide in postischemic heart using lipid and aqueous-soluble dithiocarbamate-iron complexes

Spin-trapping techniques combined with electron paramagnetic resonance (EPR) spectroscopy to measure nitric oxide (NO) production were compared in the ischemic-reperfused myocardium for the first time, using both aqueous-soluble and lipophilic complexes of reduced iron (Fe) with dithiocarbamate derivatives. The aqueous-soluble complex of Fe and N-methyl-D-glucamine dithiocarbamate (MGD) formed MGD2-Fe-NO complex with a characteristic triplet EPR signal (aN 12.5 G and giso = 2.04) at room temperature, in native isolated rat hearts following 40 min global ischemia and 15 min reperfusion. Diethyldithiocarbamate (DETC) and Fe formed in ischemic-reperfused myocardium the lipophilic DETC2-Fe-NO complex exhibiting an EPR signal (g perpendicular = 2.04 and g parallel = 2.02 at 77 K) with a triplet hyperfine structure at g perpendicular. Dithiocarbamate-Fe-NO complexes detected by both trapping agents were abolished by the .NO synthase inhibitor, NG-nitro-L-arginine methyl ester. Quantitatively, both trapping procedures provided similar values for tissue .NO production, which were observed primarily during ischemia. Postischemic hemodynamic recovery of the heart was not affected by the trapping procedure.