Inducible nitric oxide synthase augments injury elicited by oxidative stress in rat cardiac myocytes

Modeling Selenoprotein Se-Nitrosation: Synthesis of a Se-Nitrososelenocysteine with Persistent Stability

The Se-nitrosation in selenoproteins such as glutathione peroxidase and thioredoxin reductase to produce Se-nitrososelenocysteines (Sec-SeNOs) has been proposed to play crucial roles in signaling processes mediated by reactive nitrogen species and nitrosative-stress responses, although chemical evidence for the formation of Sec-SeNOs has been elusive not only in proteins but also in small-molecule systems. Herein, we report the first synthesis of a Sec-SeNO by employing a selenocysteine model system that bears a protective molecular cradle. The Sec-SeNO was characterized using ¹H and ⁷⁷Se nuclear magnetic resonance as well as ultraviolet/visible spectroscopy and found to have persistent stability at room temperature in solution. The reaction processes involving the Sec-SeNO provide experimental information that serves as a chemical basis for elucidating the reaction mechanisms involving the SeNO species in biological functions, as well as in selenol-catalyzed NO generation from S-nitrosothiols.

Molecular mechanisms of endothelial remodeling under doxorubicin treatment

Doxorubicin (DOX) is an effective antineoplastic agent used to treat various types of cancers. However, its use is limited by the development of cardiotoxicity, which may result in heart failure. The exact mechanisms underlying DOX-induced cardiotoxicity are not fully understood, but recent studies have shown that endothelial-mesenchymal transition (EndMT) and endothelial damage play a crucial role in this process. EndMT is a biological process in which endothelial cells lose their characteristics and transform into mesenchymal cells, which have a fibroblast-like phenotype. This process has been shown to contribute to tissue fibrosis and remodeling in various diseases, including cancer and cardiovascular diseases. DOX-induced cardiotoxicity has been demonstrated to increase the expression of EndMT markers, suggesting that EndMT may play a critical role in the development of this condition. Furthermore, DOX-induced cardiotoxicity has been shown to cause endothelial damage, leading to the disruption of the endothelial barrier function and increased vascular permeability. This can result in the leakage of plasma proteins, leading to tissue edema and inflammation. Moreover, DOX can impair the production of nitric oxide, endothelin-1, neuregulin, thrombomodulin, thromboxane B2 etc. by endothelial cells, leading to vasoconstriction, thrombosis and further impairing cardiac function. In this regard, this review is devoted to the generalization and structuring of information about the known molecular mechanisms of endothelial remodeling under the action of DOX.

Preparation and spectroscopic identification of methyl-Se-nitrososelenol

Herein, we report, for the first time, the preparation, matrix-isolation, and spectroscopic characterization of the methyl selenyl radical and methyl-Se-nitrososelenol in combination with DFT and CASSCF/NEVPT2 computations. The latter proved to be highly photolabile, and upon irradiation with light at λ = 465 nm it leads to methyl selenyl and nitric oxide radical pairs. Upon λ > 730 nm irradiation it rearranges back to methyl-Se-nitrososelenol.

The role of nitric oxide in Doxorubicin-induced cardiotoxicity: experimental study

Objective: We evaluated the myocardial damage in rats treated with doxorubicin (DOX) alone and in combination with nitric oxide synthase (NOS) inhibitors.

Materials and Methods: Twenty-four male Sprague Dawley rats (12 weeks old, weighing 262±18 g) were randomly assigned into 4 groups (n=6). Group I was the control group. In Group II, rats were treated with intraperitoneal (ip) injections of 3 mg/kg DOX once a week for 5 weeks. In Group III, rats received weekly ip injections of 30 mg/kg L-NAME (nonspecific NOS inhibitor) 30 min before DOX injections for 5 weeks. In Group IV, rats received weekly ip injections of 3 mg/kg L-NIL (inducible NOS inhibitor) 30 min before DOX injections for 5 weeks. Rats were weighed 2 times a week. At the end of 6 weeks, hearts were excised and then fixed for light and electron microscopy evaluation and tissue lipid peroxidation (malondialdehyde). Blood samples were also obtained for measuring plasma lipid peroxidation.

Results: Weight loss was observed in Group II, Group III, and Group IV. Weight loss was statistically significant in the DOX group. Findings of myocardial damage were significantly higher in animals treated with DOX only than in the control group. Histopathological findings of cardiotoxicity in rats treated with DOX in combination with L-NAME and L-NIL were not significantly different compared with the control group. The level of plasma malondialdehyde in the DOX group (9.3±3.4 µmol/L) was higher than those of all other groups.

Conclusion: Our results showed that DOX cardiotoxicity was significantly decreased when DOX was given with NO synthase inhibitors.

The theoretical comparison between two model NO carriers, MeSNO and MeSeNO

In this study, we apply a hybrid DFT functional, MPW1LYP, to make a comparison between MeSNO and MeSeNO. Due to the mesomeric effect and negative hyperconjugation, Se-nitrososelenols seem to be more unstable than S-nitrosothiols regarding unimolecular decomposition. Interestingly, however, the barrier of the transnitrosation reaction of MeSeNO is larger than that of MeSNO, disregarding nucleophiles in the gas phase. Using the polarizable continuum model to consider the water solvent effect, the transnitrosation reactions of MeXNO and YMe- (X = S, Se; Y = S, Se) are found to undergo concerted reactions, in sharp contrast to the two-step reaction pathways concluded in the gas phase. Moreover, the barriers of the transnitrosation reactions of MeSNO for nucleophiles SMe- and SeMe- from the gas phase to the aqueous solution are found to be decreased, while the transnitrosation reactions of MeSeNO are essentially barrierless in aqueous solution.

Selenium protects the immature rat heart against ischemia/reperfusion injury

The aim of the study was to find out whether administration of selenium (Se) will protect the immature heart against ischemia/reperfusion.The control pregnant rats were fed laboratory diet (0.237 mg Se/kg diet); experimental rats received 2 ppm Na(2)SeO(3) in the drinking water from the first day of pregnancy until day 10 post partum. The concentration of Se in the serum and heart tissue was determined by activation analysis, the serum concentration of NO by chemiluminescence, cardiac concentration of lipofuscin-like pigment by fluorescence analysis. The 10 day-old hearts were perfused (Langendorff); recovery of developed force (DF) was measured after 40 min of global ischemia. In acute experiments, 10 day-old hearts were perfused with selenium (75 nmol/l) before or after global ischemia. Sensitivity to isoproterenol (ISO, pD(50)) was assessed as a response of DF to increasing cumulative dose.Se supplementation elevated serum concentration of Se by 16%. Se increased ischemic tolerance (recovery of DF, 32.28 +/- 2.37 vs. 41.82 +/- 2.91%, P < 0.05). Similar results were obtained after acute administration of Se during post-ischemic reperfusion (32.28 +/- 2.37 vs. 49.73 +/- 4.40%, P < 0.01). The pre-ischemic treatment, however, attenuated the recovery (23.08 +/- 3.04 vs. 32.28 +/- 2.37%, P < 0.05). Moreover, Se supplementation increased the sensitivity to the inotropic effect of ISO, decreased cardiac concentration of lipofuscin-like pigment and serum concentration of NO. Our results suggest that Se protects the immature heart against ischemia/reperfusion injury. It seems therefore, that ROS may affect the function of the neonatal heart, similarly as in adults.

Ischaemia or reperfusion: which is a main trigger for changes in nitric oxide mRNA synthases expression?

OBJECTIVE

To investigate alterations in endothelial nitric oxide synthase and inducible nitric oxide synthase mRNA expressions and nitric oxide release in the myocardium during ischaemia/reperfusion and determine whether these changes are ischaemic and/or reperfusion dependent.

MATERIALS AND METHODS

Isolated rat hearts were perfused by a modified Langendorff system. Following 1 h of global cardioplegic ischaemia, left ventricle haemodynamic parameters were recorded at baseline and during 30 min of reperfusion. Levels of endothelial, inducible nitric oxide synthases mRNA expression and nitric oxide release were measured at baseline, after ischaemia and at 30 min of reperfusion.

RESULTS

Global cardioplegic ischaemia caused a significant depression of left ventricular function and a decrease of coronary flow. Postischaemic intensities of the endothelial nitric oxide synthase mRNA bands were significantly lower than at baseline (P < 0.01). There were no significant differences in endothelial nitric oxide synthase mRNA band intensities immediately after ischaemia compared to the end of reperfusion, nor between the intensities of inducible nitric oxide synthase mRNA bands at baseline, at end of ischaemia and at end of reperfusion. Nitric oxide in the myocardial effluent was below detectable levels at all measured points.

CONCLUSION

Ischaemic injury causes down-regulation of endothelial nitric oxide synthase mRNA expression, which is then associated with reduction of coronary flow during reperfusion, representing one possible mechanism of ischaemia/reperfusion injury. We did not find expected elevations of inducible nitric oxide synthase mRNA expression during ischaemia or reperfusion and we suggest that ischaemia/reperfusion injury is not associated with nitric oxide overproduction.

Delayed adenosine A1 receptor preconditioning in rat myocardium is MAPK dependent but iNOS independent

Adenosine A1 receptor delayed preconditioning (PC) against myocardial infarction has been well described; however, there have been limited investigations of the signaling mechanisms that mediate this phenomenon. In addition, there are multiple conflicting reports on the role of inducible nitric oxide synthase (iNOS) in mediating A1 late-phase PC. The purpose of this study was to determine the roles of the p38 and extracellular signal-regulated kinase (ERK) mitogen-activated protein kinases (MAPKs) in in vivo delayed A1 receptor PC and whether this protection at the myocyte level is due to upregulation of iNOS. Myocardial infarct size was measured in open-chest anesthetized rats 24 h after treatment with vehicle or the adenosine A1 agonist 2-chloro-N6-cyclopentyladenosine (CCPA; 100 microg/kg ip). Additional rats receiving CCPA were pretreated with the p38 inhibitor SB-203580 (1 mg/kg ip) or the MAPK/ERK kinase (MEK) inhibitor PD-098059 (0.5 mg/kg ip). At 24 h after CCPA administration, a group of animals was given the iNOS inhibitor 1400 W 10 min before ischemia. Treatment with CCPA reduced infarct size from 48 +/- 2 to 28 +/- 2% of the area at risk, an effect that was blocked by both SB-203580 and PD-098059 but not 1400 W. Ventricular myocytes isolated 24 h after CCPA injection exhibited significantly reduced oxidative stress during H2O2 exposure compared with myocytes from vehicle-injected animals, and this effect was not blocked by the iNOS inhibitor 1400 W. Western blot analysis of whole heart and cardiac myocyte protein samples revealed no expression of iNOS 6 or 24 h after CCPA treatment. These results indicate that adenosine A1 receptor delayed PC in rats is mediated by MAPK-dependent mechanisms, but this phenomenon is not associated with the early or late expression of iNOS.

Isolation of a Se-Nitrososelenol: A New Class of Reactive Nitrogen Species Relevant to Protein Se-Nitrosation

Nitric oxide (NO) is a messenger molecule implicated in a number of physiological processes. Nitrosation of selenoproteins has been suggested as playing an important role in NO-mediated cellular functions such as the inactivation of glutathione peroxidase (GPx), but no chemical information about Se-nitrosated species has been available to date. Here a stable Se-nitrososelenol (RSeNO), a new class of NO derivative, was synthesized and fully characterized by X-ray crystallography and spectroscopic methods. This Se-nitrososelenol can be formed by direct transnitrosation from an S-nitrosothiol to a selenol, as is the case in the proposed mechanism for the NO-mediated inactivation of GPx.

Inhibition of nuclear factor kappa B activation and inducible nitric oxide synthase transcription by prolonged exposure to high glucose in the human keratinocyte cell line HaCaT

BACKGROUND

In human skin, inducible nitric oxide synthase (iNOS) appears to be a key enzyme during wound healing and has roles in protection from infection. We speculated that diabetic skin complications such as delayed wound healing and skin infection were due to iNOS activity altered by high glucose in skin keratinocytes.

OBJECTIVES

The purpose of this study was to see how high levels of glucose affect iNOS activity in the human keratinocyte cell line (HaCaT).

METHODS

HaCaT cells were exposed to high glucose for 1 day or 10 days. We measured nitric oxide (NO) end product nitrite in the culture medium using the Griess reagent, and intracellular tetrahydrobiopterin (BH(4), a cofactor of NOS) content by using high-performance liquid chromatography, analysed the expression level of iNOS mRNA by the reverse transcriptase-polymerase chain reaction method and evaluated the DNA binding activity of nuclear factor kappa B (NF-kappaB) by enzyme-immunoassay.

RESULTS

Short-term exposure (1 day) to a high level of glucose increased BH(4) and iNOS activity at the post-translational level. However, long-term exposure (10 days) to high glucose downregulates NF-kappaB binding activity and inhibits iNOS transcription and its activity.

CONCLUSIONS

Pretreatment with high glucose for 10 days down-regulated NF-kappaB activity and inhibited iNOS transcription and NO production, implying the involvement of a deficiency in NO synthesis in both skin infection and impaired wound healing in diabetic patients.

Oxidative stress caused by inactivation of glutathione peroxidase and adaptive responses

Reactive oxygen species (ROS) are generated as by-products of cellular metabolism, primarily in the mitochondria. When the cellular production of ROS exceeds the cell's antioxidant capacity, cellular macromolecules such as lipids, proteins and DNA can be damaged. Because of this, 'oxidative stress' is thought to contribute to aging and pathogenesis of a variety of human diseases. However, in the last 10-15 years, a considerable body of evidence has accumulated that ROS serve as subcellular messengers, and play a role in gene regulation and signal transduction pathways, which may be involved in defensive mechanisms against oxidative stress. This review focuses on oxidative stress caused by the inactivation of glutathione peroxidase (GPx), a major peroxide scavenging enzyme. GPx is inactivated by a variety of physiological substances, including nitric oxide and carbonyl compounds in vitro and in cell culture. Decreased GPx activity has also been reported in tissues where oxidative stress occurs in several pathological animal models. The accumulation of increased levels of peroxide resulting from inactivation of GPx may act as a second messenger and regulate expression of anti-apoptotic genes and the GPx itself to protect against cell damage. These findings suggest that GPx undergoes inactivation under various conditions such as nitroxidative stress and glycoxidative stress, and that these changes are a common feature of various types of oxidative stress which may be associated with the modification of redox regulation and cellular function.

Down-regulation of acyl-CoA oxidase gene expression and increased NF-kappaB activity in etomoxir-induced cardiac hypertrophy

Activation of nuclear factor-kappaB (NF-kappaB) is required for hypertrophic growth of cardiomyocytes. Etomoxir is an irreversible inhibitor of carnitine palmitoyltransferase I (CPT-I) that activates peroxisome proliferator-activated receptor alpha (PPARalpha) and induces cardiac hypertrophy through an unknown mechanism. We studied the mRNA expression of genes involved in fatty acid oxidation in the heart of mice treated for 1 or 10 days with etomoxir (100 mg/kg/day). Etomoxir administration for 1 day significantly increased (4.4-fold induction) the mRNA expression of acyl-CoA oxidase (ACO), which catalyzes the rate-limiting step in peroxisomal beta-oxidation. In contrast, etomoxir treatment for 10 days dramatically decreased ACO mRNA levels by 96%. The reduction in ACO expression in the hearts of 10-day etomoxir-treated mice was accompanied by an increase in the mRNA expression of the antioxidant enzyme glutathione peroxidase and the cardiac marker of oxidative stress bax. Moreover, the activity of the redox-regulated transcription factor NF-kappaB was increased in heart after 10 days of etomoxir treatment. Overall, the findings here presented show that etomoxir treatment may induce cardiac hypertrophy via increased cellular oxidative stress and NF-kappaB activation.

Protective role of endothelial nitric oxide synthase

Nitric oxide is a versatile molecule, with its actions ranging from haemodynamic regulation to anti-proliferative effects on vascular smooth muscle cells. Nitric oxide is produced by the nitric oxide synthases, endothelial NOS (eNOS), neural NOS (nNOS), and inducible NOS (iNOS). Constitutively expressed eNOS produces low concentrations of NO, which is necessary for a good endothelial function and integrity. Endothelial derived NO is often seen as a protective agent in a variety of diseases. This review will focus on the potential protective role of eNOS. We will discuss recent data derived from studies in eNOS knockout mice and other experimental models. Furthermore, the role of eNOS in human diseases is described and possible therapeutic intervention strategies will be discussed.

Myocardial contractile effects of nitric oxide

Recent experimental and clinical research solved some of the controversies surrounding the myocardial contractile effects of NO. These controversies were: (1) does NO exert a contractile effect at baseline? (2) is NO a positive or a negative inotrope? (3) Are the contractile effects of NO similar when NO is derived from NO-donors or from the different isoforms of NO synthases (NOS)? (4) Does NO exert the same effects in hypertrophied, failing or ischemic myocardium? Transgenic mice with cardioselective overexpression of NOS revealed NO to produce a small reduction in basal developed LV pressure and a LV relaxation-hastening effect mainly through myofilamentary desensitization. Similar findings had previously been reported during intracoronary infusions of NO-donors in isolated rodent hearts and in humans. The LV relaxation hastening effect was accompanied by increased diastolic LV distensibility, which augmented LV preload reserve especially in heart failure patients. This beneficial effect on diastolic LV function always overrode the small NO-induced attenuation in LV developed pressure in terms of overall LV performance. In most experimental and clinical conditions, contractile effects of NO were similar when NO was derived from NO-donors or produced by the different isoforms of NOS. Because expression of inducible NOS (NOS2) is frequently accompanied by elevated oxidative stress, NO produced by NOS2 can lead to peroxynitrite-induced contractile impairment as observed in ischemic or septic myocardium. Finally, shifts in isoforms or in concentrations of myofilaments can affect NO-mediated myofilamentary desensitization and alter the myocardial contractile effects of NO in hypertrophied or failing myocardium.

Mixed tocopherol preparation is superior to alpha-tocopherol alone against hypoxia-reoxygenation injury

Hypoxia-reoxygenation (H-R) is associated with alterations in oxidant-antioxidant balance and L-arginine-nitric oxide system. Tocopherols decrease the activity of reactive oxygen species (ROS) and yet are not beneficial in clinical trials. It has been proposed that mixed tocopherols as found in nature may be more tissue protective than alpha-tocopherol alone found in commercial preparations. We compared the effect of a mixed tocopherol preparation with that of alpha-tocopherol alone on superoxide dismutase (SOD) activity and iNOS expression in cultured myocytes exposed to H-R. Myocytes from Sprague-Dawley rat hearts were subjected to hypoxia for 24 h followed by reoxygenation for 3 h H-R. Parallel groups of myocytes were pretreated with alpha-tocopherol alone or a mixed-tocopherol preparation (containing alpha-, gamma-, and delta-tocopherols) (50 microM) for 30 min. H-R resulted in myocyte injury (determined by LDH release), a decrease in SOD activity and an upregulation of iNOS expression/activity. Both tocopherol preparations attenuated cell injury and markedly decreased the effects of H-R on SOD activity and iNOS expression/activity (all P < 0.05 vs H-R group, n = 5). However, mixed-tocopherol preparation was much superior to alpha-tocopherol in terms of myocyte protection from the adverse effect of H-R (P < 0.05). Lack of efficacy of commercial tocopherol preparations in clinical trials may reflect absence of gamma- and delta-tocopherols.

Nitric oxide synthase expression and function in embryonic and adult cardiomyocytes

Nitric oxide (NO) is an important signalling molecule that plays a relevant role in different cell systems, among them the adult heart. The effects of NO are primarily mediated through modulation of Ca(2+) homeostasis, myofibrillar contractility, and metabolic regulation in cardiomyocytes. Recent evidence also suggests an important role of NO for cardiomyogenesis by modulating proliferation and differentiation and regulating cardiac function. In the embryonic, but also the healthy and diseased, adult mammalian heart, the inducible (iNOS) and the endothelial (eNOS) nitric oxide synthases (NOS) are detected. However, the expression pattern of NO and its function differ during development. Furthermore, under pathophysiological conditions NOS expression can also change and cause impairment of cardiac performance and cytotoxic effects. The present review focuses on the role and function of NO during cardiomyogenesis, the mechanisms responsible for eNOS availability, and the paracrine effects of NO generated by cardiomyocytes.

Induction of glutathione peroxidase in response to inactivation by nitric oxide

To determine effect of nitric oxide (NO) on cellular glutathione peroxidase (GPX) level in living cells, we measured the activity, protein and mRNA of GPX in rat kidney (KNRK) cells under a high NO condition. Combined treatment of lipopolysaccharide (LPS, 1 microgram/ml) and tumor necrosis factor-alpha (TNF-alpha, 50 ng/ml) synergistically enhanced (23-folds) nitrite production from KNRK cells. This was suppressed by an inducible NO synthase (iNOS) inhibitor (aminoguanidine, N-nitro-L-arginine methylester hydrochloride) and arginase. iNOS expression was detected by RT-PCR in the treated cells. GPX was inactivated irreversibly when the cells had been homogenized before exposure to a NO donor, S-nitroso-N-acetylpenicillamine (SNAP). In living KNRK cells, SNAP and LPS + TNF-alpha exerted a transient effect on the GPX activity. The treatment with SNAP (200 microM) or sodium nitroprusside (200 microM) enhanced GPX gene expression, which was blocked by a NO scavenger, 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide. GPX mRNA was markedly increased by the treatment with LPS + TNF-alpha, and aminoguanidine blocked the effect. In cells metabolically labeled with 75Se, LPS + TNF-alpha accelerated the incorporation of radioactivity into GPX molecule by 2.1-fold. These results suggest that inactivation of GPX by NO triggers a signal for inducing GPX gene expression in KNRK cells, thereby restoring the intracellular level of this indispensable enzyme.

UV light synergistically enhances the cardiotoxic effects of interleukin 1beta through peroxynitrite formation

BACKGROUND

Proinflammatory cytokines play an important role in chronic cardiac diseases.

METHODS AND RESULTS

Neonatal rat cardiomyocytes were exposed to interleukin (IL)-1beta (2 ng/mL) for 4 days. We assessed contractility through videomicroscopy and calcium transients with the Ca(2+)-sensitive dye fura-2. In IL-1beta-treated cells, the UV excitation (380 nm) necessary to induce dye fluorescence effected a rapid cessation of Ca(2+) transients and contraction, accompanied by calcium overload originating from an intracellular compartment. This occurred in the absence of fura-2 but required UV illumination. Incubation with 10 mmol/L N-acetylcysteine prevented this response, suggesting a free radical-mediated event. However, exposure to IL-1beta either increased or did not change the activity of the free radical scavengers superoxide dismutase, catalase, and glutathione peroxidase. In contrast, lipid peroxidation increased by 600% (P < or =.0001) in the IL-1beta plus UV-treated cells, an effect eliminated by L-NMMA. L-NMMA also completely abolished the UV-mediated cytotoxicity. We used immunohistochemistry to localize nitrotyrosine accumulation in the myocytes cotreated with IL-1beta and UV, an effect that was also blocked by L-NMMA.

CONCLUSIONS

We hypothesize that the toxic radical peroxynitrite, arising from nitric oxide and superoxide anion, may be responsible for tetany and acute cardiomyocyte death. These results demonstrate the potential role of peroxynitrite in cardiotoxicity, which may be important in cardiac diseases associated with proinflammatory cytokines.

Modulation of myocardial SOD and iNOS during ischemia-reperfusion by antisense directed at ACE mRNA

Renin-angiotensin system (RAS) is involved in the regulation of superoxide dismutase (SOD) and nitric oxide (NO) equilibrium, and its modulation protects hearts from ischemic dysfunction. We examined the effect of a new antisense-oligodeoxynucleotides (AS-ODNs) directed at ACE mRNA on SOD and iNOS expression during myocardial ischemia. Sprague-Dawley rats were treated with saline, AS-ODNs, or inverted-ODNs (IN-ODNs), given with liposome DOTAP/DOPE. Hearts were excised and subjected to 25 min of ischemia followed by 30 min of reperfusion. Ischemia-reperfusion in saline-treated hearts resulted in a decrease in the expression of SOD and an increase in the expression of inducible NOS (iNOS) genes concurrently with myocardial dysfunction. AS-ODNs, but not IN-ODNs, protected hearts against functional deterioration, and upregulated SOD expression and inhibited the expression of iNOS. ACE protein expression was decreased in the rat hearts of the AS-ODNs-treated group, but not in the IN-ODNs group. Thus manipulation of RAS with AS-ODNs directed at ACE mRNA can ameliorate cardiac dysfunction and modulate expression of SOD and iNOS at genomic level.

Attenuation of myocardial ischemia/reperfusion injury by superinduction of inducible nitric oxide synthase

BACKGROUND

Nitric oxide (NO) has been implicated as a mediator in myocardial ischemia/reperfusion (I/R) injury, but its functional properties have been conflicting. We investigated whether NO has a protective role against I/R injury.

METHODS AND RESULTS

Using endothelial NO synthase knockout (eNOS KO) mice, inducible NOS KO mice, the NO donor S-nitroso-N-acetylpenicillamine (SNAP), and the NOS inhibitor N-iminoethyl-L-ornithine (L-NIO), we performed studies of isolated perfused hearts subjected to 30 minutes of global ischemia followed by reperfusion. After 60 minutes of reperfusion, nitrite levels in the coronary effluent in the SNAP and eNOS KO groups were significantly elevated compared with other groups. Immunoblot and immunohistochemistry showed that iNOS was markedly induced in the eNOS KO hearts. Under spontaneous beating conditions during reperfusion, increased NO activity was correlated with a prevention of the hyperdynamic contractile response and enhanced myocardial protection, as evidenced by a reduction in myocardial injury and infarct size. During prolonged reperfusion, SNAP-treated hearts were able to preserve contractile functions for 180 minutes, whereas L-NIO-treated hearts showed a sustained deterioration in contractility.

CONCLUSIONS

NO protects against I/R injury by preventing the hyperdynamic response of isolated perfused hearts during early reperfusion. In the eNOS KO hearts, a paradoxical increase in NO production was seen, accompanied by a superinduction of iNOS, possibly due to an adaptive mechanism.

T-0162, a novel free radical scavenger, reduces myocardial infarct size in rabbits

1. We investigated the effects of 1-(3-tert-butyl-2-hydroxy-5-methoxyphenyl)-3-(3-pyridylmethyl)urea hydrochloride (T-0162), a novel low-molecular weight free radical scavenger, on the generation of superoxide anions and hydroxyl radicals in vitro and in vivo and on myocardial infarct (MI) size in an in vivo model of MI in rabbits. 2. It was found that T-0162 scavenged both superoxide anions and hydroxyl radicals in a concentration-dependent manner in vitro. 3. In an in vivo rabbit model with 30 min coronary occlusion and 30min reperfusion, T-0162 scavenged hydroxyl radicals generated in the myocardium during reperfusion. 4. Anaesthetized open-chest Japanese white male rabbits were subjected to 30 min coronary occlusion and 48 h reperfusion. The control group (n = 10) was infused with 10% lecithin solution for 220 min from 10 min before occlusion to 180 min after reperfusion. The pretreatment group (n = 10) was infused with T-0162 dissolved in 10% lecithin solution for 220 min from 10 min before occlusion to 180 min after reperfusion at a rate of 400 microg/kg per min. The post-treatment group (n = 10) was injected with an i.v. bolus of 10 mg/kg T-0162 and was then infused with 400 microg/kg per min T-0162 for 190 min from 10 min before reperfusion to 180 min after reperfusion. After 48 h reperfusion, infarct size was measured histologically and expressed as a percentage of area at risk (AAR). 5. There was no significant difference in haemodynamic parameters among the three groups throughout the experimental period. The per cent infarct size of the AAR in the T-0162 groups (24.8+/-4.3 and 30.5+/-3.9% for pre- and posttreatment groups, respectively) was significantly reduced compared with control (44.7+/-4.1%; P<0.05). There was no significant difference in the AAR among the three groups. 6. In conclusion, T-0162 reduces MI size through the inhibition of reperfusion injury.

Inhibitory effect of Ginkgo biloba extract on the expression of inducible nitric oxide synthase in endothelial cells

Excessive production of nitric oxide (NO) may have cytotoxic effects through the formation of peroxynitrite with superoxide. The extract of Ginkgo biloba leaves (EGb) has been demonstrated to be a potent scavenger of free radicals. Although EGb has been shown recently to inhibit NO production in macrophages, its effect on NO production in endothelial cells is largely unknown. The objective of this study was to elucidate the mechanism by which EGb affects NO production in a human endothelial cell line (ECV304). After cells were incubated with EGb (10-100 microg/mL) for 2 or 4 hr, the amounts of NO metabolites released by the cells were quantitated, and cellular NOS activities were determined following the conversion of [3H]arginine to [3H]citrulline. NOS protein expression was determined by western immunoblotting analysis. mRNA levels were examined by reverse transcription-polymerase chain reaction (RT-PCR) analysis. EGb (50 microg/mL) caused a 30% reduction of NO metabolites released by endothelial cells. Following EGb treatment, cellular inducible NO synthase (iNOS) activity was reduced by 28% with a concomitant reduction in the levels of iNOS protein mass and mRNA. There was no change in the activity or protein mass of constitutive NO synthase in these cells. EGb inhibited NO production by attenuating the level of iNOS mRNA in ECV304 cells. Selective inhibition of iNOS by EGb may be therapeutically relevant in modulating NO production in endothelial cells.

Acute right ventricular restrictive physiology after repair of tetralogy of Fallot: association with myocardial injury and oxidative stress

BACKGROUND

Acute right ventricular (RV) restrictive physiology after tetralogy of Fallot repair results in low cardiac output and a prolonged stay in the intensive care unit (ICU). However, its mechanism remains uncertain.

METHODS AND RESULTS

In the first 24 hours after tetralogy of Fallot repair (n=11 patients), serial prospective measurements were performed of cardiac troponin T, indexes of NO production (NO(2)(-) and NO(3)(-) combined as NOx), and iron metabolism and antioxidants. RV diastolic function was assessed by transthoracic Doppler echocardiography. Patients who had a long stay in the ICU were characterized by restrictive RV physiology (nonrestrictive group [n=7]: 3.0+/-0.6 days [mean+/-SD]; restrictive group [n=4]: 10.7+/-3.1 days). Troponin T peak concentration and the area under its concentration-time curve (AUC) were higher in the restrictive RV group (peak: restrictive group 17. 0+/-2.8 microg/L, nonrestrictive group 10.4+/-4.6 microg/L, P<0.03; AUC: restrictive group 268.8+/-73.6 microg. h(-1). L(-1), nonrestrictive group 136.2+/-48.3 microg. h(-1). L(-1), P<0.03). Plasma NOx/creatinine concentrations were higher in the restrictive group than the nonrestrictive group at 2 hours after bypass (restrictive group 1.3+/-0.4, nonrestrictive group 0.8+/-0.2; P=0. 04) but were similar by 24 hours. Iron loading peaked 2 to 10 hours after bypass and was more severe in the restrictive group (peak transferrin saturation: restrictive group 83.9+/-13.0%, nonrestrictive group 58.3+/-16.2%, P=0.05; minimum total iron-binding capacity: restrictive group 0.59+/-0.21%, nonrestrictive group 0.76+/-0.06%, P=0.04; minimum iron-binding antioxidant activity to oxyorganic radicals: restrictive group 9. 5+/-22.4%, nonrestrictive group 50.6+/-11.4%, P=0.01).

CONCLUSIONS

After tetralogy of Fallot repair, acute restrictive RV physiology is associated with greater intraoperative myocardial injury and postoperative oxidative stress with severe iron loading of transferrin.