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

Reactive X (where X = O, N, S, C, Cl, Br, and I) species nanomedicine

Reactive oxygen, nitrogen, sulfur, carbonyl, chlorine, bromine, and iodine species (RXS, where X = O, N, S, C, Cl, Br, and I) have important roles in various normal physiological processes and act as essential regulators of cell metabolism; their inherent biological activities govern cell signaling, immune balance, and tissue homeostasis. However, an imbalance between RXS production and consumption will induce the occurrence and development of various diseases. Due to the considerable progress of nanomedicine, a variety of nanosystems that can regulate RXS has been rationally designed and engineered for restoring RXS balance to halt the pathological processes of different diseases. The invention of radical-regulating nanomaterials creates the possibility of intriguing projects for disease treatment and promotes advances in nanomedicine. In this comprehensive review, we summarize, discuss, and highlight very-recent advances in RXS-based nanomedicine for versatile disease treatments. This review particularly focuses on the types and pathological effects of these reactive species and explores the biological effects of RXS-based nanomaterials, accompanied by a discussion and the outlook of the challenges faced and future clinical translations of RXS nanomedicines.

Chemical Insights into Oxidative and Nitrative Modifications of DNA

This review focuses on DNA damage caused by a variety of oxidizing, alkylating, and nitrating species, and it may play an important role in the pathophysiology of inflammation, cancer, and degenerative diseases. Infection and chronic inflammation have been recognized as important factors in carcinogenesis. Under inflammatory conditions, reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from inflammatory and epithelial cells, and result in the formation of oxidative and nitrative DNA lesions, such as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-nitroguanine. Cellular DNA is continuously exposed to a very high level of genotoxic stress caused by physical, chemical, and biological agents, with an estimated 10,000 modifications occurring every hour in the genetic material of each of our cells. This review highlights recent developments in the chemical biology and toxicology of 2'-deoxyribose oxidation products in DNA.

Biological Relevance of Free Radicals and Nitroxides

Nitroxides are stable, kinetically-persistent free radicals which have been successfully used in the study and intervention of oxidative stress, a critical issue pertaining to cellular health which results from an imbalance in the levels of damaging free radicals and redox-active species in the cellular environment. This review gives an overview of some of the biological processes that produce radicals and other reactive oxygen species with relevance to oxidative stress, and then discusses interactions of nitroxides with these species in terms of the use of nitroxides as redox-sensitive probes and redox-active therapeutic agents.

Antisickling fetal hemoglobin reduces hypoxia-inducible factor-1α expression in normoxic sickle mice: microvascular implications

Chronic inflammation is a salient feature of sickle cell disease (SCD) and transgenic-knockout sickle (BERK) mice. Inflammation is implicated in the activation of hypoxia-inducible factor-1α (HIF-1α) under normoxic conditions. We hypothesize that, in SCD, inflammation coupled with nitric oxide (NO) depletion will induce expression of HIF-1α, a transcription factor with wide-ranging effects including activation of genes for vasoactive molecules. To this end, we have examined the expression of HIF-1α in normoxic BERK mice expressing exclusively human α- and β(S)- globins, and evaluated the effect of fetal hemoglobin (HbF) in BERK mice (i.e., <1.0%, 20%, and 40% HbF). HbF exerts antisickling and anti-inflammatory effects. Here, we show that HIF-1α is expressed in BERK mice under normoxic conditions, accompanied by increased expression of its vasoactive biomarkers such as VEGF, heme oxygenase-1 (HO-1), and serum ET-1 levels. In BERK mice expressing HbF, HIF-1α expression decreases concomitantly with increasing HbF, commensurately with increased NO bioavailability, and shows a strong inverse correlation with plasma NO metabolites (NOx) levels. Reduced HIF-1α expression is associated with decreased HO-1, VEGF, and ET-1. Notably, arteriolar dilation, enhanced volumetric blood flow, and low blood pressure in normoxic BERK mice all show a trend toward normalization with the introduction of HbF. Also, arginine treatment reduced HIF-1α, as well as VEGF expression in normoxic BERK mice, supporting a role of NO bioavailability in HIF-1α activation. Thus HIF-1α expression in normoxic sickle mice is likely a consequence of chronic inflammation, and HbF exerts an ameliorating effect by decreasing sickling, increasing NO bioavailability, and reducing inflammation.

The heart-protective mechanism of nitronyl nitroxide radicals on murine viral myocarditis induced by CVB3

Our previous researches showed that nitronyl nitroxyl derivatives, NNP and NNVP were good anti-oxidants and provided radioprotective effects in C6 cells. The objective of the present study is to investigate the possible antiviral effects and underlying pharmacological of the two nitronyl nitroxide radicals against CVB3 in vitro and in vivo. The results showed that NNP and NNVP were some of the most potent compounds in terms of their antiviral effects by protecting myocardial cells against oxidative damage of free radicals. Treatment with NNP or NNVP could decrease the intracellular ROS level in vitro. They could lead to a significant decrease in activities of biochemical markers AST, CK and LDH in infected murine serum and could increase SOD and CAT activities and decreased MDA activities compared with infected control in vivo. NNP and NNVP could reduce NO production in infected mice by reacting with NO to produce the imino nitroxides which was confirmed by ESR spectrometry. In addition, NNP and NNVP could both decrease the mRNA expression of proinflammatory cytokines, TNF-α, IL-2 and IL-6. In conclusion, nitronyl nitroxide radicals NNP and NNVP were shown to have antiviral activities against CVB3 and they may represent potential therapeutic agents for viral myocarditis.

Caveolin-1-eNOS signaling promotes p190RhoGAP-A nitration and endothelial permeability

Caveolin-1–mediated inhibition of endothelial nitric oxide synthase signaling is essential for adherens junction integrity and endothelial permeability homeostasis.

Endothelial barrier function is regulated by adherens junctions (AJs) and caveolae-mediated transcellular pathways. The opening of AJs that is observed in caveolin-1^−/− (Cav-1^−/−) endothelium suggests that Cav-1 is necessary for AJ assembly or maintenance. Here, using endothelial cells isolated from Cav-1^−/− mice, we show that Cav-1 deficiency induced the activation of endothelial nitric oxide synthase (eNOS) and the generation of nitric oxide (NO) and peroxynitrite. We assessed S-nitrosylation and nitration of AJ-associated proteins to identify downstream NO redox signaling targets. We found that the GTPase-activating protein (GAP) p190RhoGAP-A was selectively nitrated at Tyr1105, resulting in impaired GAP activity and RhoA activation. Inhibition of eNOS or RhoA restored AJ integrity and diminished endothelial hyperpermeability in Cav-1^−/− mice. Thrombin, a mediator of increased endothelial permeability, also induced nitration of p120-catenin–associated p190RhoGAP-A. Thus, eNOS-dependent nitration of p190RhoGAP-A represents a crucial mechanism for AJ disassembly and resultant increased endothelial permeability.

Phospholipase C as a potential target for cardioprotection during oxidative stressThis review is one of a selection of papers published in a Special Issue on Oxidative Stress in Health and Disease

Cardiac dysfunction due to ischemia–reperfusion (I/R) is associated with marked changes in membrane function and subsequent Ca2+-handling abnormalities in cardiomyocytes. The membrane abnormalities in hearts subjected to I/R arise primarily from oxidative stress as a consequence of increased formation of reactive oxygen species and other oxidants, as well as reduced antioxidant defenses. Little is known, however, about the nature and mechanisms of the sarcolemmal membrane changes with respect to phospholipase C (PLC)-related signaling events. In addition, the mechanisms involved in protection of the postischemic myocardium and in ischemic preconditioning with respect to PLC function need to be established. Accordingly, this article reviews the historical and current information on PLC-mediated signal transduction mechanisms in I/R, as well as outlining future directions that should be addressed. Such information will extend our knowledge of ischemic heart disease and help improve its therapy.

The relationship between structure and antioxidative activity of piperidine nitroxides

We have investigated the relationship between structure and antioxidative activity of piperidine nitroxides which were substituted by different groups at the 4-position. All of the tested piperidine nitroxides inhibited malondialdehyde (MDA) generation caused either spontaneously or by a hydroxyl free radical generation system (Fe2+-ascorbic acid) in homogenates of liver, heart and kidney of rats, and antagonized H2O2-induced haemolysis from rat erythrocytes in a concentration-dependent manner. The same rank was followed: Bis-(4-amino-2,2,6,6-tetramethyl piperidinooxyl) (4-BIS-Tempo) and 4-azido-2,2,6,6-tetramethyl piperidinooxyl (4-N3-Tempo) &gt;4-isothiocyanate-2,2,6,6-tetramethyl piperidinooxyl (4-ISO-Tempo), 4-2′,4′-dinitrophenyl-hydrazone-2,2,6,6-tetramethyl piperidinooxyl (4-D-Tempo), 4-sulfonate-2,2,6,6-tetramethyl piperidinooxyl (4-S-Tempo) and 4-amino-2,2,6,6-tetramethyl piperidinooxyl (4-NH2-Tempo) &gt; 4-acetate ester-2,2,6,6-tetramethyl piperidinooxyl (4-A-Tempo) and 4-benzoate-2,2,6,6-tetra-methyl piperidinooxyl (4-B-Tempo). With the exception of 4-A-Tempo and 4-D-Tempo, the tested piperidine nitroxides inhibited superoxide anion (O2.-) release from neutrophils stimulated by zymosan. The concentration required for inhibiting O2.- release was higher than that of inhibiting MDA formation and haemolysis. However, 4-amino-2,2,6,6-tetramethyl piperidine (4-NH2-TempH) and other 4-position substitutes, such as NaN3 and isothiocyanate, had no effects on MDA formation, haemolysis or O2.- release. The results indicated that nitroxides have a wide range of scavenging reactive oxygen species (ROS) actions. The nitroxide moiety was the essential group while the 4-position substitutes could influence the activity of nitroxides on scavenging ROS.

Myocardial Hsp70 phosphorylation and PKC-mediated cardioprotection following exercise

Both protein kinase C (PKC) activation and Hsp70 expression have been shown to be key components for exercise-mediated myocardial protection during ischemia-reperfusion injury. Given that Hsp70 has been shown to undergo inducible phosphorylation in striated muscle and liver, we hypothesized that PKC may regulate myocardial Hsp70 function and subsequent exercise-conferred cardioprotection through this phosphorylation. Hence, acute exercise of male Sprague-Dawley rats (30 m/min for 60 min at 2% grade) was employed to assess the role of PKC and its selected isoforms in phosphorylation of Hsp70 and protection of the myocardium during ischemia-reperfusion injury. It was observed that administration of the PKC inhibitor chelerythrine chloride (5 mg/kg) suppressed the activation of three exercise-induced PKC isoforms (PKCalpha, PKCdelta, and PKCepsilon) and attenuated the exercise-mediated reduction of myocardial infarct size during ischemia-reperfusion injury. While this study also demonstrated that exercise led to an alteration in the phosphorylation status of Hsp70, this posttranslational modification appeared to be dissociated from PKC activation, as exercise-induced phosphorylation of Hsp70 was unchanged following inhibition of PKC. Taken together, these results indicate that selected isoforms of PKC play an important role in exercise-mediated protection of the myocardium during ischemia-reperfusion injury. However, exercise-induced phosphorylation of Hsp70 does not appear to be a mechanism by which PKC induces this cardioprotective effect.

INO-4885 [5,10,15,20-tetra[N-(benzyl-4'-carboxylate)-2-pyridinium]-21H,23H-porphine iron(III) chloride], a peroxynitrite decomposition catalyst, protects the heart against reperfusion injury in mice

Oxidative/nitrative stress caused by peroxynitrite, the reaction product of superoxide (O2(.-)) and nitric oxide (NO), is the primary cause of myocardial ischemia/reperfusion injury. The present study determined whether INO-4885 [5,10,15,20-tetra[N-(benzyl-4'-carboxylate)-2-pyridinium]-21H,23H-porphine iron(III) chloride], a new peroxynitrite decomposition catalyst, may provide cellular protection and protect heart from myocardial ischemia/reperfusion injury. Adult male mice were subjected to 30 min of ischemia and 3 or 24 h of reperfusion. Mice were randomized to receive vehicle, INO-4885 without catalytic moiety, or INO-4885 (3-300 microg/kg i.p.) 10 min before reperfusion. Infarct size, apoptosis, nitrotyrosine content, NO/O2(.-) production, and inducible nitric-oxide synthase (iNOS)/NADPH oxidase expression were determined. INO-4885 treatment reduced ischemia/reperfusion-induced protein nitration and caspase 3 activation in a dose-dependent fashion in the range of 3 to 100 microg/kg. However, doses exceeding 100 microg/kg produced nonspecific effects and attenuated its protective ability. At the optimal dose (30 microg/kg), INO-4885 significantly reduced infarct size (p < 0.01), decreased apoptosis (p < 0.01), and reduced tissue nitrotyrosine content (p < 0.01). As expected, INO-4885 had no effect on ischemia/reperfusion-induced iNOS expression and NO overproduction. To our surprise, this compound significantly reduced superoxide production and partially blocked NADPH oxidase overexpression in the ischemic/reperfused cardiac tissue. Additional experiments demonstrated that INO-4885 provided better cardioprotection than N-(3-(aminomethyl)benzyl)acetamidine (1400W, a selective iNOS inhibitor), apocynin (an NADPH oxidase inhibitor), or Tiron (a cell-permeable superoxide scavenger). Taken together, our data demonstrated that INO-4885 is a cardioprotective molecule that attenuates myocardial reperfusion injury by facilitating peroxynitrite decomposition and inhibiting NADPH oxidase-derived O2(.-) production.

Arginine therapy of transgenic-knockout sickle mice improves microvascular function by reducing non-nitric oxide vasodilators, hemolysis, and oxidative stress

In sickle cell disease, nitric oxide (NO) depletion by cell-free plasma hemoglobin and/or oxygen radicals is associated with arginine deficiency, impaired NO bioavailability, and chronic oxidative stress. In transgenic-knockout sickle (BERK) mice that express exclusively human alpha- and beta(S)-globins, reduced NO bioavailability is associated with induction of non-NO vasodilator enzyme, cyclooxygenase (COX)-2, and impaired NO-mediated vascular reactivity. We hypothesized that enhanced NO bioavailability in sickle mice will abate activity of non-NO vasodilators, improve vascular reactivity, decrease hemolysis, and reduce oxidative stress. Arginine treatment of BERK mice (5% arginine in mouse chow for 15 days) significantly reduced expression of non-NO vasodilators COX-2 and heme oxygenase-1. The decreased COX-2 expression resulted in reduced prostaglandin E(2) (PGE(2)) levels. The reduced expression of non-NO vasodilators was associated with significantly decreased arteriolar dilation and markedly improved NO-mediated vascular reactivity. Arginine markedly decreased hemolysis and oxidative stress and enhanced NO bioavailability. Importantly, arteriolar diameter response to a NO donor (sodium nitroprusside) was strongly correlated with hemolytic rate (and nitrotyrosine formation), suggesting that the improved microvascular function was a response to reduced hemolysis. These results provide a strong rationale for therapeutic use of arginine in sickle cell disease and other hemolytic diseases.

Protective effect of arginine on oxidative stress in transgenic sickle mouse models

Sickle cell disease (SCD) is characterized by reperfusion injury and chronic oxidative stress. Oxidative stress and hemolysis in SCD result in inactivation of nitric oxide (NO) and depleted arginine levels. We hypothesized that augmenting NO production by arginine supplementation will reduce oxidative stress in SCD. To this end, we measured the effect of arginine (5% in mouse chow) on NO metabolites (NOx), lipid peroxidation (LPO), and selected antioxidants in transgenic sickle mouse models. Untreated transgenic sickle (NY1DD) mice (expressing approximately 75% beta(S)-globin of all beta-globins; mild pathology) and knockout sickle (BERK) mice (expressing exclusively hemoglobin S; severe pathology) showed reduced NOx levels and significant increases in the liver LPO compared with C57BL mice, with BERK mice showing maximal LPO increase in accordance with the disease severity. This was accompanied by reduced activity of antioxidants (glutathione, total superoxide dismutase, catalase, and glutathione peroxidase). However, GSH levels in BERK were higher than in NY1DD mice, indicating a protective response to greater oxidative stress. Importantly, dietary arginine significantly increased NOx levels, reduced LPO, and increased antioxidants in both sickle mouse models. In contrast, nitro-L-arginine methylester, a potent nonselective NOS inhibitor, worsened the oxidative stress in NY1DD mice. Thus, the attenuating effect of arginine on oxidative stress in SCD mice suggests its potential application in the management of this disease.

Prevention of Postischemic Myocardial Reperfusion Injury by the Combined Treatment of NCX-4016 and Tempol

Nitric oxide (NO) plays a protective role in myocardial ischemia-reperfusion (I/R) injury. However, the concomitant production of superoxide and other reactive oxygen species (ROS) during I/R may diminish the bioavailability of NO and hence compromise the beneficial effects. The objective of this study was to investigate the protective effect of the coadministration of NCX-4016 [2-(acetyloxy)benzoic acid 3-(nitrooxymethyl)phenyl ester] (an NO donor) with antioxidants Tempol, superoxide dismutase (SOD), or urate on I/R injury. Isolated rat hearts, perfused with Krebs-Henseleit buffer, were subjected to 30 minutes of global ischemia, followed by 45 minutes of reperfusion. Before the induction of ischemia, the hearts were infused for 1 minute with NCX-4016 (100 microM) either alone or in combination with Tempol (100 microM), SOD (200 U/mL), or urate (100 microM). Hearts pretreated with NCX-4016 showed a significantly enhanced recovery of function and decreased infarct size and LDH/CK release compared with the controls. However, treatment of hearts with NCX-4016 + Tempol, SOD, or urate showed a significantly enhanced recovery of heart function compared with NCX-4016 alone. The treatment of hearts with NCX-4016 + Tempol showed significantly enhanced NO generation and decreased ROS and dityrosine (a marker of peroxynitrite) formation. In conclusion, NCX-4016 in combination with Tempol demonstrated significant cardioprotection and, thus, may offer a novel therapeutic strategy to prevent I/R-mediated myocardial injury.

Structure−Activity Relationship of Cyclic Nitroxides as SOD Mimics and Scavengers of Nitrogen Dioxide and Carbonate Radicals

Synthetic nitroxide antioxidants attenuate oxidative damage in various experimental models. Their protective effect reportedly depends on ring size and ring substituents and is greater for nitroxides having lower oxidation potential. The present study focuses on the kinetics and mechanisms of the reactions of piperidine, pyrrolidine and oxazolidine nitroxides with HO2*/O2*-, *NO2 and CO3*- radicals, which are key intermediates in many inflammatory and degenerative diseases. It is demonstrated that nitroxides are the most efficient scavengers of *NO2 at physiological pH (k = (3-9) x 10(8) M(-1) s(-1)) and among the most effective metal-independent scavengers of CO3*- radicals (k = (2 - 6) x 10(8) M(-1) s(-1)). Their reactivity toward HO2*, though not toward *NO2 and CO3*-, depends on the nature of the ring side-chain and particularly on the ring-size. All nitroxide derivatives react slowly with O2*- and are relatively inefficient SOD mimics at physiological pH. Even piperidine nitroxides, having the highest SOD-like activity, demonstrate a catalytic activity of about 1000-fold lower than that of native SOD at pH 7.4. The present results do not indicate any correlation between the kinetics of HO2*/O2*-, *NO2 and CO3*- removal by nitroxides and their protective activity against biological oxidative stress and emphasize the importance of target-oriented nitroxides, i.e., interaction between the biological target and specific nitroxides.

Catalytic superoxide scavenging by metal complexes of the calcium chelator EGTA and contrast agent EHPG

Metal ion chelators widely used in experimental protocols and clinical diagnosis are generally assumed to be inert. We previously reported that the ubiquitous chelator EDTA has high levels of superoxide suppressing activity. Here, we report that the common chelators calcium chelator EGTA and contrast agent EHPG have significant activities in suppressing superoxide levels depending on the nature of metal ion chelated. The most active species is Mn(II)-EGTA which exhibited an IC50 value of 0.19 microM for superoxide destruction. In addition, IC50 values for Mn(II)-EHPG and 2Cu(II)-EGTA were 0.69 and 0.60 microM, respectively. In conclusion, Mn(II) and Cu(II) complexes of the common chelators EGTA and EHPG exhibit considerable superoxide scavenging activities. Caution should be employed in their use in biological systems where superoxide has a key role and they may be useful for the development of catalytic anti-oxidants.

Oxygen therapeutics: can we tame haemoglobin?

Chemically modified or genetically engineered haemoglobins (Hbs) developed as oxygen therapeutics (often termed 'blood substitutes') are designed to correct oxygen deficit due to ischaemia in a variety of clinical settings. These modifications are intended to stabilize Hb outside its natural environment--red blood cells--in a functional tetrameric and/or polymeric form. Uncontrolled haem-mediated oxidative reactions of cell-free Hb and its reactions with various oxidant/antioxidant and cell signalling systems have emerged as an important pathway of toxicity. Current protective strategies designed to produce safe Hb-based products are focused on controlling or suppressing the 'radical' nature of Hb while retaining its oxygen-carrying function.