In vivo spin trapping of glyceryl trinitrate-derived nitric oxide in rabbit blood vessels and organs

Insulin inhibits lipopolysaccharide-induced nitric oxide synthase expression in rat primary astrocytes

Excessive production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) from reactive astrocytes and microglia may contribute to the development of many types of neurological diseases. Insulin has been shown to inhibit the expression of iNOS, in several organs and cell types. Although insulin and its receptors are present in the central nervous system, the effects of insulin on the iNOS pathway in the brain have not been determined. In this study, using lipopolysaccharide (LPS)-stimulated astrocytes as a model of reactive astrocytes, we investigated the effects of insulin on iNOS expression in activated astrocytes and the mechanism involved. The expression of iNOS was significantly upregulated by LPS in astrocytes. Insulin applied prior to LPS, dose-dependently inhibited LPS-induced iNOS gene expression and iNOS protein levels. In agreement with the suppressive effects of insulin on iNOS expression, insulin also inhibited LPS-induced iNOS activity and NO production. Moreover, insulin was found to significantly inhibit LPS-induced IκB-α phosphorylation and degradation, which led to a decrease in levels of the p65 subunit of NF-κB in the nuclear fraction. Therefore, insulin inhibited LPS-induced iNOS expression via suppressing NF-κB pathway in astrocytes. In addition, treatment with insulin had no effect on LPS-induced PKB phosphorylation. Based on our results, it is plausible to speculate that insulin in the brain may play a neuroprotective role in neurological disorders by controlling the release of NO via the regulation of iNOS expression in astrocytes.

Increased microparticle production and impaired microvascular endothelial function in aldosterone-salt-treated rats: protective effects of polyphenols

We aimed to characterize circulating microparticles in association with arterial stiffness, inflammation and endothelial dysfunction in aldosterone-salt-induced hypertension in rats and to investigate the preventive effects of red wine polyphenols. Uninephrectomized male Sprague-Dawley rats were treated with aldosterone-salt (1 µg.h⁻¹), with or without administration of either red wine polyphenols, Provinols™ (20 mg.kg⁻¹.day⁻¹), or spironolactone (30 mg.kg⁻¹.day⁻¹) for 4 weeks. Microparticles, arterial stiffness, nitric oxide (NO) spin trapping, and mesenteric arterial function were measured. Aldosterone-salt rats showed increased microparticle levels, including those originating from platelets, endothelium and erythrocytes. Hypertension resulted in enhanced aortic stiffness accompanied by increased circulating and aortic NO levels and an upregulation of aortic inducible NO-synthase, NFκB, superoxide anions and nitrotyrosine. Flow-induced dilatation was reduced in mesenteric arteries. These effects were prevented by spironolactone. Provinols™ did not reduce arterial stiffness or systolic hypertension but had effects similar to those of spironolactone on endothelial function assessed by flow-mediated vasodilatation, microparticle generation, aortic NO levels and oxidative stress and apoptosis in the vessel wall. Neither the contractile response nor endothelium-dependent relaxation in mesenteric arteries differed between groups. The in vivo effects of Provinols™ were not mediated by mineralocorticoid receptors or changes in shear stress. In conclusion, vascular remodelling and endothelial dysfunction in aldosterone-salt-mediated hypertension are associated with increased circulating microparticles. Polyphenols prevent the enhanced release of microparticles, macrovascular inflammation and oxidative stress, and microvascular endothelial dysfunction independently of blood pressure, shear stress and mineralocorticoid receptor activation in a model of hyperaldosteronism.

Pharmacological induction of vascular extracellular superoxide dismutase expression in vivo

Pentaerythritol tetranitrate (PETN) treatment reduces progression of atherosclerosis and endothelial dysfunction and decreases oxidation of low-density lipoprotein (LDL) in rabbits. These effects are associated with decreased vascular superoxide production, but the underlying molecular mechanisms remain unknown. Previous studies demonstrated that endogenous nitric oxide could regulate the expression of extracellular superoxide dismutase (ecSOD) in conductance vessels in vivo. We investigated the effect of PETN and overexpression of endothelial nitric oxide synthase (eNOS⁺⁺) on the expression and activity of ecSOD. C57BL/6 mice were randomized to receive placebo or increasing doses of PETN for 4 weeks and eNOS⁺⁺ mice with a several fold higher endothelial-specific eNOS expression were generated. The expression of ecSOD was determined in the lung and aortic tissue by real-time PCR and Western blot. The ecSOD activity was measured using inhibition of cytochrome C reduction. There was no effect of PETN treatment or eNOS overexpression on ecSOD mRNA in the lung tissue, whereas ecSOD protein expression increased from 2.5-fold to 3.6-fold (P < 0.05) by 6 mg PETN/kg body weight (BW)/day and 60 mg PETN/kg BW/day, respectively. A similar increase was found in aortic homogenates. eNOS⁺⁺ lung cytosols showed an increase of ecSOD protein level of 142 ± 10.5% as compared with transgene-negative littermates (P < 0.05), which was abolished by N^ω-nitro-L-arginine treatment. In each animal group, the increase of ecSOD expression was paralleled by an increase of ecSOD activity. Increased expression and activity of microvascular ecSOD are likely induced by increased bioavailability of vascular nitric oxide. Up-regulation of vascular ecSOD may contribute to the reported antioxidative and anti-atherosclerotic effects of PETN.

Effect of oral organic nitrates on expression and activity of vascular soluble guanylyl cyclase

BACKGROUND AND PURPOSE

The regulation of vascular soluble guanylyl cyclase (sGC) expression by nitric oxide (NO) is still under discussion. In vitro, NO has been shown to downregulate the expression of sGC but it is unclear if this mechanism is operative in vivo and occurs during nitrate treatment.

EXPERIMENTAL APPROACH

We investigated whether high dose isosorbide mononitrate (ISMN) or pentaerythrityl tetranitrate (PETN) treatment changes vascular sGC expression and activity in vivo. New Zealand White rabbits received a standard diet, 2 or 200 mg ISMN kg(-1) d(-1) for 16 weeks, and C57BL/6 mice received a standard diet, 6, 60 or 300 mg PETN kg(-1) d(-1) for four weeks. Absorption was checked by measuring the plasma levels of the drug/metabolite.

KEY RESULTS

Western blots of rabbit aortic rings showed similar protein levels of sGC alpha1- (P=0.2790) and beta1-subunits (P=0.6900) in all groups. Likewise, ANOVA showed that there was no difference in the expression of sGC in lungs of PETN-treated mice (P=0.0961 for alpha1 and P=0.3709 for beta1). The activities of isolated sGC in response to SNAP (1 microM-1 mM) were identical in aortae of ISMN-treated rabbits (P=0.0775) and lungs of PETN-treated mice (P=0.6348). The aortic relaxation response to SNAP slightly decreased at high ISMN but not at high PETN.

CONCLUSIONS AND IMPLICATIONS

These data refute the hypothesis that therapeutic treatment with long acting NO donors has a significant impact on the regulation of vascular sGC expression and activity in vivo.

Rosiglitazone, a peroxisome proliferator-activated receptor-gamma agonist, prevents microparticle-induced vascular hyporeactivity through the regulation of proinflammatory proteins

Microparticles are plasma membrane vesicles with procoagulant and proinflammatory properties. We recently demonstrated that microparticles induce vascular hyporeactivity and evoke up-regulation of proinflammatory protein expression. This study dissected the effect of either in vitro treatment or short-term oral administration of the peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist, rosiglitazone, on microparticle-induced vascular hyporeactivity of mouse vessels. Microparticles were produced from T cells by actinomycin D treatment. The effects of rosiglitazone on mouse aortic rings incubated with microparticles were investigated. Aortae treated in vitro with rosiglitazone or aortae taken from mice treated by oral administration of the same agonist completely prevented microparticle-induced vascular hyporeactivity in response to U46619 [9,11-dideoxy-11alpha, 9alpha-epoxymethanoprostaglandin F(2alpha)). These effects of rosiglitazone occurred independently of the presence of endothelium without modifications in blood parameters. The mechanisms involved abrogation of nitric oxide (NO) and prostacyclin overproduction linked to up-regulation of inducible NO-synthase and cyclooxygenase 2 elicited by microparticles. In addition, rosiglitazone treatment reduced the ability of microparticles to evoke increases in interleukin (IL)-6, IL-8, and nuclear factor (NF)-kappaB transcription, and NF-kappaB expression and activation. These results suggest that rosiglitazone, via PPARgamma activation, counteracts vascular dysfunction associated with increased release of proinflammatory proteins elicited by microparticles. They underscore therapeutic perspective for rosiglitazone in vascular diseases involving enhanced participation of microparticles.

Microparticles from preeclamptic women induce vascular hyporeactivity in vessels from pregnant mice through an overproduction of NO

Preeclampsia is associated with an increase of circulating levels of microparticles (MPs), but their role in vascular dysfunction during the course of preeclampsia is not understood. Inasmuch as preeclampsia is a gestational disease, we tested the effect of MPs from preeclamptic women (PrMPs) and MPs from normal pregnant women (CMPs) on vessels from pregnant mice. We exposed aortic rings from pregnant mice to circulating levels of PrMPs or CMPs for 24 h and evaluated their response to serotonin (5-HT). PrMPs, but not CMPs, were able to induce hyporeactivity in response to 5-HT in aortas from pregnant mice. The nitric oxide (NO) synthase inhibitor NG-nitro-l-arginine strongly enhanced the response to 5-HT in PrMP-treated vessels but had no significant effect on CMP-treated vessels. The 5-HT-induced contraction in PrMP-treated vessels was completely abolished by the selective cyclooxygenase-2 (COX-2) inhibitor NS-398 but was only reduced in CMP-treated vessels, suggesting an increased participation of COX-2 vasoconstrictor products in the effect of PrMPs. Consistent with this hypothesis, PrMPs enhanced levels of 8-isoprostane and PGE2in vessels, despite reduction of thromboxane B2. These results strengthen the main concept that MPs in preeclampsia could act as vectors to stimulate intracellular cascades in vascular cells, leading to an enhanced NO production to counteract increased COX-2 vasoconstrictor metabolites by taking into account pregnancy.

Nitric oxide increases in the rat retina after continuous illumination

Continuous illumination (CI) of the retina induces an oxidative stress followed by the degeneration of photoreceptors. This phenomenon may be partially related to the excessive production of nitric oxide (NO). In order to confirm this hypothesis, the aims of this work are to determine NO levels during the illumination of the retina by electron paramagnetic resonance (EPR), and if an increase of NO is found, to characterize the NOS isoform responsible of the increment by using Western blot. Sprague-Dawley rats were continuously illuminated with white light (12,000 lux) for 2, 24, 48 h, 5 and 7 days while control rats were maintained at light/dark cycles of 12/12 h. Using EPR, an increase of NO signal was observed in the light exposed retinas peaking at 24 h of CI. Western blot analysis showed the expression of iNOS in the illuminated retinas with a peak after 24 h of CI, but did not show significant differences of nNOS among illuminated and control retinas. In summary, there is an increase of NO during CI. Further studies will reveal whether this mechanism is responsible for light induced photoreceptor degeneration.

Shed membrane particles from preeclamptic women generate vascular wall inflammation and blunt vascular contractility

We investigated the role of microparticles in vascular dysfunction of the multisystemic disorder of preeclampsia in women's omental arteries or mouse arteries. Preeclamptic women displayed increased circulating levels of leukocyte- and platelet-derived microparticles compared with healthy pregnant individuals. Microparticles from preeclamptic, but not healthy, pregnant women induced ex vivo vascular hyporeactivity to serotonin in human omental arteries and mouse aortas. Hyporeactivity was reversed by a nitric-oxide (NO) synthase inhibitor and associated with increased NO production. In the presence of a cyclooxygenase (COX)-2 inhibitor, serotonin-mediated contraction was partially reduced in arteries treated with healthy microparticles but was abolished after treatment with preeclamptic microparticles. This was associated with increased 8-isoprostane production. Preeclamptic microparticles induced up-regulation of inducible nitric-oxide synthase and COX-2 expression, evoked nuclear factor-kappaB activation, and enhanced oxidative and nitrosative stress. Interestingly, the microparticles originating most probably from leukocytes were responsible for the COX-2 vasoconstrictor component of preeclamptic microparticles, whereas those of platelet origin were mainly involved in NO release. Moreover, vascular hyporeactivity was observed in arteries taken from mice treated in vivo with preeclamptic microparticles. This study demonstrates pathophysiological relevance and provides a paradoxical effect of preeclamptic microparticles associated with proinflammatory properties on vessels, leading to enhanced NO and superoxide anion levels and counteraction of increased COX-2 metabolites.

Direct gas measurements indicate that the novel cyclooxygenase inhibitor AZD3582 is an effective nitric oxide donor in vivo

1. AZD3582 [4-(nitrooxy)butyl-(2S)-2-(6-methoxy-2-naphthyl)propanoate] is a COX-inhibiting nitric oxide donor that inhibits COX-1 and COX-2. It is as effective as naproxen in models of pain and inflammation, but causes less gastroduodenal damage. Nitric oxide (NO) is generated from AZD3582 in vitro, and this study sought to show that the drug donates NO in vivo. 2. In anaesthetised male New Zealand white rabbits, the endogenous NO concentration in exhaled air was reduced by N(G)-nitro-L-arginine methyl ester (L-NAME) (30 mg kg(- 1) i.v.) from 33.5+/-1.0 ppb (mean+/-s.e.m.; n=6 per group) to 3.0+/-1.0 ppb, while increasing blood pressure and reducing heart rate. AZD3582 (0.2, 0.6, 2.0 or 6.0 micromol kg(- 1) min(- 1)) given 30 min after L-NAME increased the concentration of NO in exhaled air (P<0.05), decreased blood pressure and increased heart rate in a dose-dependent manner versus L-NAME control values. The peak mean NO concentration obtained was 44+/-8.0 ppb. 3. In in situ-perfused rabbit lungs, L-NAME (185 micromol l(- 1)) reduced the NO concentration in exhaled air from 106+/-13 to 4.0+/-0.4 ppb (n=5). Addition of AZD3582 (6 micromol min(- 1)) to the perfusate produced an initial rapid increase in the NO concentration in exhaled air, followed by a sustained, but lower plateau. Infusion of L-NAME increased, and AZD3582 decreased, pulmonary arterial pressure. 4. In both anaesthetised rabbits and in the perfused lungs, brief periods of hypoxia increased NO concentrations generated by AZD3582. 5. We conclude that, in rabbits, AZD3582 donates NO in vivo with characteristics similar to those reported for nitroglycerin and isosorbide nitrates

A common pathway of nitric oxide release from AZD3582 and glyceryl trinitrate

4-(Nitrooxy)-butyl-(S)-2-(6-methoxy-2-naphthyl)-propanoate (AZD3582) is a cyclooxygenase (COX)-inhibiting nitric oxide donator (CINOD). It donates nitric oxide (NO) in biological systems through as yet unidentified mechanisms. cGMP, a marker of intracellularly generated NO, was increased up to 27-fold over basal levels by AZD3582 (1-30microM) in LLC-PK1 kidney epithelial cells. A 5h pretreatment with glyceryl tinitrate (GTN, 0.1-1microM) attenuated the cGMP response to a subsequent challenge with AZD3582 or GTN. Similarly, AZD3582 (10-30microM) pretreatment reduced the increase in cGMP on subsequent incubation with AZD3582 or GTN. In contrast, cGMP stimulation by SIN-1, which releases NO independently of enzymatic catalysis, remained unimpaired in cells pretreated with GTN or AZD3582. Our results demonstrate that AZD3582 decreases the sensitivity of the guanylyl cyclase/cGMP system to GTN and vice versa. This suggests that bioactivation pathways for organic nitrates, which involve enzymatic catalysis, may be responsible for NO donation from AZD3582.

Differential nitros(yl)ation of blood and tissue constituents during glyceryl trinitrate biotransformation in vivo

Nitric oxide (NO)-derived products may modify tissue constituents, forming S- and N-nitroso adducts and metal nitrosyls implicated in NO signaling. Nitrovasodilator drugs have been in widespread use for more than a century, yet their biotransformation pathways to NO and their effects as NO donors across tissues remain ill defined. By using a metabonomics approach (termed "NObonomics") for detailing the global NO-related metabolism of the cornerstone nitrovasodilator, glyceryl trinitrate (GTN; 0.1-100 mg/kg), in the rat in vivo, we find that GTN biotransformation elicits extensive tissue nitros(yl)ation throughout all major organ systems. The corresponding reaction products remained detectable hours after administration, and vascular tissue was not a major nitros(yl)ation site. Extensive heart and liver modifications involved both S- and N-nitrosation, and RBC S-nitrosothiol formation emerged as a sensitive indicator of organic nitrate metabolism. The dynamics of GTN-derived oxidative NO metabolites in blood did not reflect the nitros(yl)ation patterns in the circulation or in tissues, casting doubt on the usefulness of plasma nitrite/nitrate as an index of NO/NO-donor biodynamics. Target-tissue NO metabolites varied in amount and type with GTN dose, suggesting a dose-sensitive shift in the prevailing routes of GTN biotransformation ("metabolic shunting") from thiol nitrosation to heme nitrosylation. We further demonstrate that GTN-induced nitros(yl)ation is modulated by a complex, tissue-selective interplay of enzyme-catalyzed pathways. These findings provide insight into the global in vivo metabolism of GTN at pharmacologically relevant doses and offer an additional experimental paradigm for the NObonomic analysis of NO-donor metabolism and signaling.

Inhibition of vascular oxidative stress in hypercholesterolemia by eccentric isosorbide mononitrate

OBJECTIVES

We sought to determine if the nitric oxide (NO) donor isosorbide mononitrate (ISMN) (200 mg/kg body weight/day) decreases vascular bioavailability of superoxide in atherosclerosis.

BACKGROUND

Vascular oxidative stress limits the bioavailability of endothelial NO and promotes atherosclerosis, while NO itself exerts antioxidative effects. It is unknown if therapeutic NO impacts on vascular oxidative stress in atherosclerosis.

METHODS

New Zealand white rabbits (n = 10 each group) were fed either normal chow (control), cholesterol chow (CHOL) (0.75%), or cholesterol chow enriched with ISMN (CHOL-ISMN). Rabbits were fed twice daily. After 16 weeks we used aortic segments to measure vascular superoxide (5-microM lucigenin), intimal lesion formation, and vasoreactivity to acetylcholine (ACH) and ISMN.

RESULTS

Plasma cholesterol increased by 40-fold in CHOL and CHOL-ISMN. The plasma concentration of ISMN in CHOL-ISMN was 1,529 +/- 447 ng/ml. Superoxide formation (control: 228 +/- 20 counts/20 min/mg) was strongly enhanced in CHOL (345 +/- 46 counts/20 min/mg, p = 0.02) but not in CHOL-ISMN (229 +/- 23 counts/20 min/mg) demonstrating antioxidative effects of eccentric ISMN in vivo. In parallel, intima-media thickness of thoracic aorta (159 +/- 4 microm in control) was reduced from 645 +/- 41 microm (CHOL) to 440 +/- 51 microm (CHOL-ISMN, p < 0.05). Likewise, eccentric ISMN partially restored vascular responses to the NO donor S-nitroso-N-acetyl-D,L-penicillamine and improved endothelium-dependent vasorelaxation. The maximal ACH relaxation increased from 26.3 +/- 9.6% in CHOL to 49.7 +/- 8.1% in CHOL-ISMN; ISMN treatment induced a moderate nitrate tolerance as evidenced by diminished ISMN-induced vasodilation.

CONCLUSIONS

These data suggest that eccentric ISMN can completely inhibit the increase of vascular bioavailability of superoxide and partially prevent intimal lesion formation and endothelial dysfunction in hypercholesterolemia.

Direct demonstration of nitric oxide formation in organs of rabbits treated by transdermal glyceryl trinitrate using an in vivo spin trapping technique

Glyceryl trinitrate (GTN) is commonly delivered by a patch for the treatment of angina pectoris. The idea is now generally accepted that GTN requires a biotransformation process that activates the drug, in particular through nitric oxide (NO) generation. However, the pharmacokinetics of NO delivery from GTN still remains obscure. The objective of this study was to assess GTN-derived NO formation in vascular tissues and organs in rabbit given GTN patches. NO levels were evaluated in rabbits after 3 h of treatment with a 10 mg GTN patch (GTN group; n = 7) or a placebo patch (CTL; n = 7). Nitrosylhaemoglobin (HbNO) was evaluated by electron spin resonance (ESR) spectroscopy in red cell suspension. In vivo spin trapping technique using FeMGD as a spin trap, associated with ESR was used to quantify NO in tissues. The NO-spin trap complex, which is a relatively stable product, has been measured in several tissues. The ESR spectrum corresponding to HbNO was not found in red cell of GTN or CTL rabbits. The spectrum corresponding to the NO-spin trap complex was observed in all analysed tissues of CTL rabbits. The signal was significantly increased in liver, renal medulla, heart left ventricle and spleen of GTN-treated rabbits, and to a lesser extent in right ventricle and lung. No difference was shown between NO-spin trap levels measured in aorta or inferior vena cava from GTN or CTL rabbits. These data suggest that GTN patch treatment induced NO release, and that tissue-specific differences in transdermal GTN-derived NO exist. The GTN-NO pathway appears to be largely involved in organs such as the liver, kidney and heart.

Upregulated expression of neuronal nitric oxide synthase by insulin in both neurons and astrocytes

Both insulin and nitric oxide (NO) play important roles in the brain. However, there are no unequivocal evidences pointing to a direct effect of insulin on nitric oxide pathway in the brain. In the present study, the effects of insulin on the expression and activity of neuronal nitric oxide synthase (nNOS) were investigated in the cultured cerebellum cell line R2, cerebral cortical astrocytes, and neurons of rats by using flow cytometry, in situ hybridization, RT-PCR, and electron spin resonance (ESR) techniques. In astrocytes, the expression of nNOS was significantly stimulated by insulin in a concentration-dependent manner, with a maximal increase of about 47.6% compared with the control values (p<0.05, t test, n=5). Furthermore, in situ hybridization analysis showed that the expression of nNOS was also significantly increased by insulin (0.64 ng/ml, 6 h), reaching 134.2+/-9.6% of the control values (p<0.05, t test, n=3). In addition, by using nNOS specific primers, RT-PCR analysis also demonstrated the same effect of insulin (0.64 ng/ml, 6 h) on nNOS mRNA expression. Similarly, significant increase of the expression of nNOS protein and mRNA were also observed in both R2 cells and neurons of rats after incubation with insulin. In addition, significant increase of the activity of nNOS in R2 cells and astrocytes were also detected after incubation with insulin (0.64 ng/ml, 9 h) by using ESR technique. Overall, our results suggested that exogenous insulin could upregulate the expression and activity of nNOS in R2 cells, cerebral cortical astrocytes, and neurons of rats. The phenomena opened new insights for further investigation of the physical and pathological significances of insulin in the brain.

Evidence of nuclear localization of neuronal nitric oxide synthase in cultured astrocytes of rats

With immunocytochemistry, we have observed the nuclear localization of neuronal nitric oxide synthase (nNOS) in cultured cerebral cortical astrocytes of rats. During the early six days in the subcultures of these cells, nNOS-immunoreactivity was mainly distributed in the cytoplasm. However, nNOS-immunoreactivity was mainly distributed in the nucleus at day 7, and this nuclear localization lasted about ten hours. Meanwhile, inducible nitric oxide synthase expression was significantly inhibited in these cells. Thereafter, nNOS-immunoreactivity was mainly distributed in the cytoplasm again. By confocal microscopy and western blot analysis, the phenomenon of nNOS nuclear localization was further confirmed; and the activity of nNOS in nuclear protein extracts from astrocytes of day 7-subculture could be detected using electron spin resonance (ESR) technique. These results may represent a new pathway of nitric oxide/nNOS participating in inducible nitric oxide synthase gene transcription regulation.

Evidence for the extrapulmonary localization of inhaled nitric oxide

Inhaled nitric oxide (NO) has emerged as a promising pulmonary vasodilator to treat pulmonary hypertension associated with heart disease and ventilation/perfusion mismatching. However, the pharmacokinetics of inhaled NO still remains obscure and its cardiopulmonary selectivity appears to be increasingly under debate. In the present study measured NO content and levels of cyclic guanosine 3',5'monophosphate (cGMP), a mediator of NO-induced vasodilation, in a variety of organs from rats subjected to NO inhalation. Electron spin resonance spectroscopy associated to a spin trapping technique using N-methyl D-glucamine dithiocarbamate (FeMGD) was used to directly quantify NO levels in the lung, kidney, liver, aorta, and heart from anesthetized Wistar rats subjected to various doses (0, 20, 50, 100, or 200 ppm) and various times (0, 30, 45, or 75 minutes) of inhaled NO. Inhaled NO at a dose of 100 and 200 ppm significantly increased the NO-FeMGD complex in all organs studied. An increase of cGMP was detected in the lung and the aorta after inhaled NO for 45 minutes at the dose of 50 ppm. No changes in NO levels and its metabolites were shown between 30 and 75 minutes of inhaled NO. The results show that inhaled NO at a dose of 100 ppm or more increases NO levels in other organs beside the lung, strongly suggesting that inhaled NO would be more than a pulmonary vasodilator and its selectivity remains to be reconsidered when used for therapeutic purposes.

Developmental expression and activity variation of nitric oxide synthase in the brain of golden hamster

Nitric oxide (NO) is the downstream effector after the activation of N-methyl-D-aspartate (NMDA) receptors. It is involved in various physiological processes, such as synapse reconstruction and plasticity, neurotoxity and neuronal death. It also participates in the development and maturation of cortical neurons. The expression of nitric oxide synthase (NOS) during the postnatal development of the visual cortex was investigated by both electron spin resonance (ESR) and Western blot methods. A typical spectrum of (DETC)(2)-Fe(II)-NO complex was found in the visual cortex of different age golden hamsters by ESR method. The signal intensity increased after birth, peaked at postnatal day 14 (PD14) and then gradually decreased. An analysis of variance (ANOVA) implied that the NO synthase expression significantly correlated with the developmental processes (p < 0.05). Results of Western blot further confirmed (one-way ANOVA, p < 0.05) the developmental relating expression pattern of NO synthase shown by ESR technique.

Increased synthesis of nitric oxide in rat brain cortex due to halogenated volatile anesthetics confirmed by EPR spectroscopy

BACKGROUND

Halogenated volatile anesthetics (HVAs) are considered to be inhibitors of nitric oxide synthase (NOS). On other hand, NO mediates the vasodilation produced by HVAs. Thus, both increase and decrease of NO concentration in brain tissues are possible during anesthesia. Previously, we have observed an increase of NO content in rat brain cortex under halothane anesthesia. The goal of this study was to determine whether the observed phenomenon was general for this anesthetic group, if it was specific for brain cortex, and if the NO increase was due changes in NOS activity.

METHODS

NO scavengers were injected to adult rats 30 min prior to anesthesia. Rats were anesthetized by inhalation of an O2 mixture with volatile anesthetics (1.5% for halothane; 1% for isoflurane, 2% for sevoflurane). After 30 min of anesthesia, rats were decapitated and brain cortex, cerebellum, liver, heart, kidneys and testes were dissected, frozen in liquid nitrogen and subjected to EPR spectroscopy. Nitric oxide content was determined quantitatively based on the intensity of the NO-Fe-DETC complex spectrum and its comparison with the calibration curve.

RESULTS

In rats anesthetized with HVAs, we observed a greater than twofold increase of NO content in brain cortex as compared to the nonanesthetized animals. No significant changes were detected in other organs. The NOS inhibitor N(omega)-nitro-L-arginine abolished the increase of NO content in brain produced by volatile anesthetics.

CONCLUSION

The action of volatile anesthetics is coupled with an increase of NO content in the cortex dependent on NOS activity.

Beneficial effect of pentaerythrityl tetranitrate on functional and morphological changes in the rat thoracic aorta evoked by long-term nitric oxide synthase inhibition

The present study examined whether pentaerythrityl tetranitrate (PETN), a tolerance-devoid exogenous donor of nitric oxide (NO), could attenuate functional and morphological changes in the rat thoracic aorta evoked by 6-week NO synthase inhibition by NG-nitro-L-arginine methyl ester (L-NAME). Systolic blood pressure in L-NAME + PETN-treated rats (163 +/- 1 mm Hg) was significantly lower than in L-NAME-treated rats (172 +/- 2 mm Hg) but was still higher than in age-matched controls (126 +/- 2 mm Hg). Six weeks of treatment of rats with L-NAME significantly inhibited endothelium-dependent relaxation of the isolated thoracic aorta induced by acetylcholine. The inhibitory effect of L-NAME was entirely reversed by the simultaneous treatment with PETN. The enhancing effect of L-NAME on noradrenaline-induced contraction was antagonised by long-term treatment with PETN. Wall thickness, cross-sectional area and wall/diameter ratio of the thoracic aorta in L-NAME-treated rats were markedly increased. In the L-NAME + PETN-treated rats, the increment of these parameters was significantly lower. The results suggest that PETN administered to rats during development of NO-deficient hypertension prevented functional impairment and at the same time reduced structural changes in the thoracic aorta induced by long-term inhibition of NO synthase.

Effect of selenolipoic acid on peroxynitrite-dependent inactivation of NADPH-cytochrome P450 reductase

Seleno-organic compounds are known as efficient "scavengers" of peroxynitrite (PN). Here we studied the protective effect of selenolipoic acid (SeLA), the seleno-containing analogue of lipoic acid, on peroxynitrite-dependent inactivation of NADPH-cytochrome P450 reductase. 3-Morpholinosydnonimine hydrochloride (SIN-1) was used as a source of peroxynitrite. The reductase was irreversibly inactivated by PN generated from SIN-1. The inactivation occurred with the rate constant of about 3 x 10(4) M-1 s-1. The presence of SeLA at low concentration (0.5 microM) led to synergistic increase of the reductase inactivation by PN. Our results suggest the formation of a reactive derivative of SeLA in the reaction of SeLA with PN, probably selenolseleninate, that mediates the aggravation of reductase inactivation. In the presence of SeLA, the inactivation was reversible under the action of thiols, allowing us to conclude that the observed action of SeLA may be considered as protective.

A common pathway for nitric oxide release from NO-aspirin and glyceryl trinitrate

NO-Aspirin (NCX-4016) releases nitric oxide (NO) in biological systems through as yet unidentified mechanisms. In LLC-PK1 kidney epithelial cells, a 5-h pretreatment with glyceryl trinitrate (GTN, 0.1-1 microM) significantly attenuated the cyclic GMP response to a subsequent challenge with both NO-aspirin or GTN. Similarly, NO-aspirin (10-100 microM) was found to induce tolerance to its own cyclic GMP stimulatory action and to that of GTN. In contrast, cyclic GMP stimulation by the spontaneous NO donor SIN-1, which releases NO independently of enzymatic catalysis, remained unimpaired in cells pretreated with GTN or NO-aspirin. The observed cross-tolerance between NO-aspirin and GTN cells indicates that bioactivation pathways of organic nitrates, which have been shown to involve cytochrome P450, may also be responsible for NO release from NO-aspirin. Prolonged treatment with NO-aspirin causes down-regulation of the cellular cyclic GMP response, suggesting that tolerance may occur during therapy with NO-aspirin.

Nitric oxide-forming reaction between the iron-N-methyl-D-glucamine dithiocarbamate complex and nitrite

The objective of this study was to elucidate the origin of the nitric oxide-forming reactions from nitrite in the presence of the iron-N-methyl-D-glucamine dithiocarbamate complex ((MGD)(2)Fe(2+)). The (MGD)(2)Fe(2+) complex is commonly used in electron paramagnetic resonance (EPR) spectroscopic detection of NO both in vivo and in vitro. Although it is widely believed that only NO can react with (MGD)(2)Fe(2+) complex to form the (MGD)(2)Fe(2+).NO complex, a recent article reported that the (MGD)(2)Fe(2+) complex can react not only with NO, but also with nitrite to produce the characteristic triplet EPR signal of (MGD)(2)Fe(2+).NO (Hiramoto, K., Tomiyama, S., and Kikugawa, K. (1997) Free Radical Res. 27, 505-509). However, no detailed reaction mechanisms were given. Alternatively, nitrite is considered to be a spontaneous NO donor, especially at acidic pH values (Samouilov, A., Kuppusamy, P., and Zweier, J. L. (1998) Arch Biochem. Biophys. 357, 1-7). However, its production of nitric oxide at physiological pH is unclear. In this report, we demonstrate that the (MGD)(2)Fe(2+) complex and nitrite reacted to form NO as follows: 1) (MGD)(2)Fe(2).NO complex was produced at pH 7.4; 2) concomitantly, the (MGD)(3)Fe(3+) complex, which is the oxidized form of (MGD)(2)Fe(2+), was formed; 3) the rate of formation of the (MGD)(2)Fe(2+).NO complex was a function of the concentration of [Fe(2+)](2), [MGD], [H(+)] and [nitrite].

Detection and imaging of endogenously produced nitric oxide with electron paramagnetic resonance spectroscopy

Nitric oxide (NO) represents a new paradigm for second messengers in regulation. Despite the numerous physiological and pathophysiological functions of NO, its importance as an endogenous second messenger and a cytostatic and/or cytotoxic agent was unknown until 1987. Recent developments in detection methods for endogenous NO produced directly or indirectly from NO synthases (NOSs) have enabled major advances in our understanding of the role of NO in biological systems. The spin-trapping technique combined with electron paramagnetic resonance (EPR) spectroscopy is a method for analyzing NO production directly both in vivo and in vitro. Iron complexes with dithiocarbamate derivatives are noteworthy among the spin-trapping reagents for NO because NO has a high affinity for iron complexes. The resultant stable nitrosyl iron complexes exhibit an intense three-line signal at room temperature and an axial signal at low temperature. Besides the facility and wide applicability of this method, its outstanding feature is that noninvasive in vivo measurements are available by using a low-frequency EPR spectrometer. In this article, we review on previous and recent developments of in vitro, in vivo, and ex vivo EPR detection and imaging of endogenously produced NO.

Effects of superoxide anion generators and thiol modulators on nitrergic transmission and relaxation to exogenous nitric oxide in the sheep urethra

The effects of superoxide anion generators, the nitric oxide (NO) scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoine-1-oxyl 3-oxide (carboxy-PTIO), the specific guanylate cyclase inhibitor 1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one (ODQ), and thiol modulating agents were investigated on relaxations induced by nitrergic stimulation and exogenous NO addition in the sheep urethra. Methylene blue (MB, 10 microM), pyrogallol (0.1 mM) and xanthine (X, 0.1 mM)/xanthine oxidase (XO, 0.1 u ml(-1)) inhibited NO-mediated relaxations, without affecting those induced by nitrergic stimulation. This resistance was not diminished following inhibition of endogenous Cu/Zn superoxide dismutase (Cu/Zn SOD) with diethyldithiocarbamic acid (DETCA, 3 mM), which almost abolished tissue SOD activity. Carboxy-PTIO (0.1 - 0.5 mM) inhibited NO-mediated relaxations but had no effect on responses to nitrergic stimulation, which were not changed by treatment with ascorbate oxidase (2 u ml(-1)). Relaxations to NO were reduced, but not abolished, by ODQ (10 microM), while nitrergic responses were completely blocked. The thiol modulators, ethacrynic acid (0.1 mM), diamide (1.5 mM), or 5,5'-dithio-bis (2-nitrobenzoic acid) (DTNB, 0. 5 mM), and subsequent treatment with dithiothreitol (DTT, 2 mM) had no effect on responses to nitrergic stimulation or NO. In contrast, N-ethylmaleimide (NEM, 0.2 mM) markedly inhibited both relaxations. L-cysteine (L-cys, 0.1 mM) had no effect on responses to NO, while it inhibited those to nitrergic stimulation, in a Cu/Zn SOD-independent manner. Our results do not support the view that the urethral nitrergic transmitter is free NO, and the possibility that another compound is acting as mediator still remains open. British Journal of Pharmacology (2000) 129, 53 - 62

A case of hemolytic uremic syndrome improved with nitric oxide

Hemolytic uremic syndrome (HUS) after transplantation is difficult to treat, and there is no consensus regarding optimal mode of treatment. We attached transdermal isosorbide tape as a nitric oxide (NO) donor to patients with HUS after bone marrow transplantation (BMT). This was very effective in ameliorating the hemolysis and increasing platelet numbers. We report here the successful use of an isosorbide in a patient with HUS after transplantation. Bone Marrow Transplantation (2000) 25, 109-110.

Drastic increase in nitric oxide content in rat brain under halothane anesthesia revealed by EPR method

A drastic increase in nitric oxide (NO) content was revealed by the EPR method in rat brain cortex and cerebellum under halothane anesthesia. The NO scavenger diethyldithiocarbamate sodium salt (DETC) and ferrous citrate were injected into adult rats 30-60 min before anesthesia. Rats were anesthetized by inhalation of a halothane-oxygen mixture (1%, 1.5%, 2%, or 4%). After different times of anesthesia, rats were decapitated, and brain cortex and cerebellum were dissected, frozen in liquid nitrogen, and subjected to EPR spectroscopy. The concentration of NO was determined from the NO-Fe-DETC radical spectrum. In control animals, NO content in the cerebellum was only 68% of that in the cortex. We observed a time-dependent increase in NO content in the cortex and cerebellum of rats anesthetized with 1.5% halothane. In brain cortex, the NO level increased to six times that of waking animals after 30 min and remained at this level up to 60 min of anesthesia. In cerebellum the changes were less drastic, the NO level showing only a 2-fold increase. The same effect was produced by 1% and 2% halothane. Ketamine, chloral hydrate, and pentobarbital were used as reference drugs. None of these anesthetics produced effects similar to those of halothane. In ketamine-anesthetized rat brain, the NO content slightly decreased. Pentobarbital and chloral hydrate produced an insignificant increase in NO. Data are discussed in the context of possible interference of halothane in the regulation of nitric oxide synthase activity.

Nitric oxide generation, tachyphylaxis and cross-tachyphylaxis from nitrovasodilators in vivo

Nitric oxide (NO) increments in exhaled air and changes in mean arterial pressure of anaesthetised rabbits were measured in order to study the NO generation from NO donors and tachyphylaxis in NO formation from nitroglycerin. Continuous infusions of isosorbide dinitrate, isosorbide-5-mononitrate and 3-morpholino-sydnonimine (SIN-1) evoked dose-dependent increases in exhaled NO, paralleled by decrements in mean arterial pressure. Repeated infusions of nitroglycerin resulted in attenuation (P<0.01) of the NO increase from a given dose. Concurrent infusions of isosorbide dinitrate, isosorbide-5-mononitrate or nitroglycerin reduced the amount of NO emanating from the bioconversion of a given dose nitroglycerin as measured in the expired air (P<0.01 for all drugs), indicating cross-tachyphylaxis. SIN-1 did not exhibit such cross-tachyphylaxis. In conclusion, measurements of exhaled NO can be a useful tool for exploration of nitrovasodilator tachyphylaxis. Cross-tachyphylaxis is only shared between some nitrovasodilators and is possibly not due to feedback from the generated NO.

Triggering role of nitric oxide in the delayed protective effect of monophosphoryl lipid A in rat heart

1. The main objective of the present study was to further evaluate the role of nitric oxide (NO) in delayed cardiac protection against ischaemia-reperfusion injury induced by monophosphoryl lipid A (MLA). 2. For this purpose, rats were administered with either 0.5 or 2.5 mg kg(-1) MLA (i.p.). Eight or 24 h later, in vivo NO production in the heart was analysed by electron paramagnetic resonance (EPR) spin trapping technique. In parallel experiments, hearts were removed and perfused according to Langendorff. Functional ventricular parameters and incidence of ventricular fibrillation (VF) were determined after 30 min global ischaemic insult (37 degrees C) followed by 30 min reperfusion. Vascular reactivity of aortic rings was also assessed. 3. Hearts from rats pretreated with 2.5 mg kg(-1) MLA for 24 h (but not those from rats treated with 0.5 mg kg(-1) MLA for 8 and 24 h, or with 2.5 mg kg(-1) MLA for 8 h) exhibited preservation of ventricular function (LVDP, +/-dP/dtmax) and a reduced incidence of VF (25% vs 87.5% in vehicle control) during reperfusion. At the cardioprotective dose of 2.5 mg kg(-1) (for 8 or 24 h), MLA did not produce alterations of the contractile response of aortic rings to noradrenaline. 4. An increased formation of NO was detected in hearts removed from rats pretreated with 2.5 mg kg(-1) MLA for 8 h, but not in those from rats treated for 24 h (or with 0.5 mg kg(-1) MLA). 5. Pretreatment of the animals with the inhibitors of inducible NO-synthase, aminoguanidine (2x300 mg kg(-1)) or L-N6-(1-Iminoethyl)-lysine (L-NIL, 10 mg kg(-1)) abolished both MLA (2. 5 mg kg(-1))-induced rise of NO production (observed 8 h after MLA) and cardioprotection (observed 24 h after MLA). However MLA-induced cardioprotection was not attenuated when the hearts were perfused with aminoguanidine (150 microM) for 30 min before the ischaemic insult. 6. Altogether, the present data suggest that NO acts as a trigger rather then a direct mediator of the delayed cardioprotective effect of MLA in rat heart.

Comparison of glyceryl trinitrate-induced with pentaerythrityl tetranitrate-induced in vivo formation of superoxide radicals: effect of vitamin C

Glyceryl trinitrate (GTN) and pentaerythrityl tetranitrate (PETN) are among the most known organic nitrates that are used in cardiovascular therapy as vasodilators. However, anti-ischemic therapy with organic nitrates is complicated by the induction of nitrate tolerance. When nitrates are metabolized to release nitric oxide (NO), there is considerable coproduction of superoxide radicals in vessels leading to inactivation of NO. However, nitrate-induced increase of superoxide radical formation in vivo has not been reported. In this work, the authors studied the in vivo formation of superoxide radicals induced by treatment with PETN or GTN and determined the antioxidant effect of vitamin C. The formation of superoxide radicals was determined by the oxidation of 1-hydroxy-3-carboxy-pyrrolidine (CP-H) to paramagnetic 3-carboxy-proxyl (CP) using electron spin resonance spectroscopy. CP-H (9 mg/kg intravenous bolus and 0.225 mg/kg per minute continuous intravenous GTN or PETN 130 microg/kg) were infused into anesthetized rabbits. Every 5 min, blood samples were obtained from Arteria carotis to measure the CP formation. Both PETN and GTN showed similar vasodilator effects. Formation of CP in blood after infusions of GTN and PETN were 2.0+/-0.4 microM and 0.98+/-0.23 microM, respectively. Pretreatment with 30 mg/kg vitamin C led to a significant decrease in CP formation: 0.27+/-0.14 microM (vitamin C plus GTN) and 0.34+/-0.15 microM (vitamin C plus PETN). Pretreatment of animals with superoxide dismutase (15,000 units/kg) significantly inhibited nitrate-induced nitroxide formation. Therefore, in vivo infusion of GTN or PETN in rabbits increased the formation of superoxide radicals in the vasculature. PETN provoked a minimal stimulation of superoxide radical formation without simultaneous development of nitrate tolerance. The data suggest that the formation of superoxide radicals induced by organic nitrate correlates with the development of nitrate tolerance. The effect of vitamin C on CP formation leads to the conclusion that vitamin C can be used as an effective antioxidant for protection against nitrate-induced superoxide radical formation in vivo.

Nitric oxide inhibits caspase-3 by S-nitrosation in vivo

In cultured human endothelial cells, physiological levels of NO prevent apoptosis and interfere with the activation of the caspase cascade. In vitro data have demonstrated that NO inhibits the activity of caspase-3 by S-nitrosation of the enzyme. Here we present evidence for the in vivo occurrence and functional relevance of this novel antiapoptotic mechanism. To demonstrate that the cysteine residue Cys-163 of caspase-3 is S-nitrosated, cells were transfected with the Myc-tagged p17 subunit of caspase-3. After incubation of the transfected cells with different NO donors, Myc-tagged p17 was immunoprecipitated with anti-Myc antibody. S-Nitrosothiol was detected in the immunoprecipitate by electron spin resonance spectroscopy after liberation and spin trapping of NO by N-methyl-D-glucamine-dithiocarbamate-iron complex. Transfection of cells with a p17 mutant, where the essential Cys-163 was mutated into alanine, completely prevented S-nitrosation of the enzyme. As a functional correlate, in human umbilical vein endothelial cells the NO donors sodium nitroprusside or PAPA NONOate (50 microM) significantly reduced the increase in caspase-3-like activity induced by overexpressing caspase-3 by 75 and 70%, respectively. When human umbilical vein endothelial cells were cotransfected with beta-galactosidase, morphological analysis of stained cells revealed that cell death induction by overexpression of caspase-3 was completely suppressed in the presence of sodium nitroprusside, PAPA NONOate, or S-nitroso-L-cysteine (50 microM). Thus, NO supplied by exogenous NO donors serves in vivo as an antiapoptotic regulator of caspase activity via S-nitrosation of the Cys-163 residue of caspase-3.

Alterations of the vascular and the myocardial guanylate cyclase/cGMP-system induced by long-term hypertension in rats

NO as produced by NO-synthases (NOS) contributes to the regulation of cardiovascular functions. In hypertension, there is a reduced production and/or activity of endogenous NO in the vasculature. We investigated if hypertension alters the NO-sensitivity of soluble guanylate cyclase (sGC) in blood vessels and heart muscle isolated from 15 month old spontaneously hypertensive rats (SHR15) and normal Wistar rats (WIS). Inhibition of NOS by 1 mM N omega-nitro-L-arginine decreased dP/dtmax in WIS (-27.6 +/- 3.4%) and SHR15 (-26.0 +/- 4.4%), while stimulation of NOS with 1 mM L-arginine increased dP/dtmax in WIS (9.9 +/- 0.7%) and SHR15 (8.9 +/- 2.3%). The positive inotropic response to 0.1 microM glyceryl trinitrate (GTN) was comparable in WIS (dP/dtmax: 4.5 +/- 1.7%) and SHR15 (dP/dtmax: 3.75 +/- 0.7%) as was the positive inotropic response to the NO-donor sodium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolat (DEA/NO, 1 microM) in WIS (dP/dtmax: 10.7 +/- 2.9%) and SHR15 (dP/dtmax: 5.1 +/- 1.5%, P = 0.1873). In aortas of SHR15 we found an increased superoxide production of 19.4 +/- 1.7 nM/mg/min (WIS: 6.1 +/- 0.6 nM/mg/min) in the smooth muscle and the endothelial layer. Endothelium-dependent relaxation by acetylcholine was markedly impaired in SHR15 as was the vasorelaxant activity of S-nitroso-N-acetyl-D,L-penicillamine (SNAP), pentaerythritol tetranitrate and GTN. Maximal cGMP-production by sGC isolated from the lung and stimulated with SNAP (0.5 mM) was much lower in SHR15 (115 +/- 14 pmol/mg/min) than in WIS (348 +/- 36 pmol/mg/min). We suggest that hypertension is associated with a reduced activity of the sGC/cGMP-system in the vasculature but not in the heart muscle. Our results provide the first evidence that excess superoxide production in hypertension may trigger a desensitization of vascular sGC.

Effects of EGb 761 on nitric oxide and oxygen free radicals, myocardial damage and arrhythmia in ischemia-reperfusion injury in vivo

The cardioprotective effects of EGb 761 on the release of nitric oxide (NO), the concentration of serum thiobarbituric acid reaction substance (TBARS), the activity of creatine kinase (CK) and the incidence of ventricular arrhythmias were investigated in myocardial ischemia-reperfusion injury in vivo. Using sodium nitrite (NaNO2) as standard source of nitric oxide (NO), we compared the correlation coefficients of the three measuring methods used currently in the determination of NOFe2+(DETC)2 complex with that of the measuring method suggested in this study. The result showed that measuring the whole height of three splitting signals is the best linear correlation to the concentration of NO comparing with other methods in this system. Using this method, we observed the effects of EGb 761 on NOFe2+(DETC)2 complex in myocardial ischemia-reperfusion injury in vivo. The hearts of the Wistar rats were subjected to 30 min of ischemia and 10 min of reperfusion in vivo. Different doses of EGb 761 (25, 50, 100, 200 mg/kg i.p.), superoxide dismutase (SOD, 10(4) U/kg), l-arginine (50 mg/kg i.p.) and nitric oxide synthase (NOS) inhibitor NG-nitro-l-arginine (NNA, 50 mg/kg i.p.) were administered to the ischemia-reperfusion rats. EGb 761 under the dose of 100 mg/kg increased the signal intensity of NOFe2+(DETC)2 complex, while EGb 761 at 200 mg/kg showed an effect of decreasing the signal intensity of NOFe2+(DETC)2 complex. EGb 761 inhibited the formation of TBARS, the release of CK, and mitigated the incidence of ventricular arrhythmias in a dose dependent way. Both l-arginine and SOD increased the signal intensity of NOFe2+(DETC)2 complex and inhibited the formation of TBARS, the leakage of CK and the incidence of ventricular arrhythmia. NNA not only had no protective effects on myocardial injury, but also increased the incidence of reperfusion-induced arrhythmia. In conclusion, EGb 761 has cardiovascular protective effects by means of adjusting the level of NO and inhibiting oxygen free radicals induced lipid peroxidation in myocardial ischemia-reperfusion injury in vivo.

Nitric oxide inhibits vascular bioactivation of glyceryl trinitrate: a novel mechanism to explain preferential venodilation of organic nitrates

Organic nitrates undergo enzymatic metabolization in the vasculature to release the active compound nitric oxide (NO). The resulting preferential venodilation has been suggested to be related to the vascular bioactivation process of organic nitrates because sodium nitroprusside, which is bioactivated differently, is not venoselective. We sought to determine whether NO has an influence on vascular bioconversion of organic nitrates because endogenous endothelial production of NO is smaller in veins than in arteries. Rings of porcine coronary arteries were subjected to radioactive glyceryl trinitrate (GTN) after preincubation with defined amounts of NO. The vascular content of GTN and the dinitrates (GDNs) 1,2-GDN and 1,3-GDN then was quantified. NO (3 microM, 30 min) significantly impaired bioactivation of GTN as indicated by a 30-50% reduction in the accumulation of 1,2-GDN and 1,3-GDN, whereas unchanged GTN was increased. Incubation with NO also reduced the stimulated specific activity of soluble guanylate cyclase isolated from human platelets. Its specific activity was reduced from 2.6 +/- 0.2 to 2.1 +/- 0.13 nmol of cGMP/mg/min. Relaxation studies with rings of porcine coronary arteries showed that NO-induced inhibition of vascular GTN metabolism and cGMP accumulation decreased the vasodilator potency of GTN by 10-fold. Further experiments showed that the duration of NO treatment is more important for this effect than the concentration of NO. We suggest that NO can inhibit vascular bioactivation of organic nitrates and might slightly desensitize soluble guanylate cyclase. The preferential venodilation induced by organic nitrates might be the result of the comparably low production of endogenous NO in veins.

Formation of Reactive Oxygen Species in Various Vascular Cells During Glyceryltrinitrate Metabolism

BACKGROUND: Anti-ischemic therapy with organic nitrates as nitric oxide (NO) donors is complicated by the induction of tolerance. When nitrates are metabolized to release NO, there is a considerable coproduction of reactive oxygen species (superoxide radical and peroxynitrite) in vessels leading to inactivation of NO, to diminished cyclic quanosine monophosphate production in smooth muscle cells (SMC), to impaired vasomotor responses to the endothelium-derived relaxation factor (EDRF), and to formation of nitrotyrosine as a marker of glyceryltrinitrate (GTN)-induced formation of peroxynitrite. The aim of the study was to analyze in vitro the formation of superoxide radicals and of peroxynitrite in GTN-treated endothelial and smooth muscle cells and in washed ex vivo platelets using electron spin resonance and spin-trapping techniques. METHODS AND RESULTS: Using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap, it was shown that in platelets, smooth muscle, and endothelial cells incubated acutely for 15 minutes with 0.5 mM GTN, the rate of generation of reactive oxygen species (ROS) was twice as high as under control conditions. Using the new spin-trap 2H-imidazole-1-oxide (TMIO), a GTN-induced peroxynitrite formation was detected in SMC and in platelets incubated with 0.5 mM GTN for 15 minutes. Spin-trap 1-hydroxy-3-carboxy-pyrrolidine (CP-H) was used to estimate the rate of ROS formation in platelets incubated for 15 minutes with 0.5 mM GTN; the rate amounted to 14.6 +/- 1.1 nM/min/mg protein compared with 4.0 +/- 0.4 nM/min/mg protein in controls. The rate of ROS formation in SMCs was substantially increased (240 +/- 16%) after initiation of GTN tolerance by treatment of the cells in culture with 100 µM GTN for 24 hours. CONCLUSIONS: GTN increases the formation of superoxide radicals in endothelial cells, SMCs, and platelets. Peroxynitrite is formed during GTN metabolism in vascular cells and may contribute to the development of tolerance. A decrease in the nitrate-induced inhibition of platelet aggregation during GTN tolerance is associated with oxidative actions of ROS formed in platelets during GTN metabolism.

Positive inotropic effect of exogenous and endogenous NO in hypertrophic rat hearts

1. Recent evidence suggests that nitric oxide (NO) modulates the contractile force of isolated cardiomyocytes in a biphasic manner. We sought to examine whether myocardial hypertrophy induced by long-term hypertension changes the effects of NO on myocardial contractility. 2. We used constant flow perfused non-paced Langendorff preparations of hearts of 3 months old Wistar rats (WIS, n = 23) and of stroke-prone spontaneously hypertensive rats (SHR) at the age of 10 months (SHR10, n = 16) and 15 months (SHR15, n = 8). Changes of left ventricular peak pressure (LVP), +dP/dt(max), -dP/dt(max), coronary perfusion pressure (CPP) and heart rate (HR) were recorded after infusion of noradrenaline (NA, 0.1 micromol l(-1)), glyceryl trinitrate (GTN, 1-100 micromol l(-1)), S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 1-10 micromol l(-1)) and N(omega)-nitro-L-arginine (L-NOARG, 0.1-1 mmol l(-1)). 3. Long-term hypertension induced myocardial hypertrophy and an abnormal response to NA. The relative heart weight (in mg kg(-1)) increased from 2.95 +/- 0.04 (WIS) to 6.67 +/- 0.34 (SHR15), while the increase in +dP/dt(max) induced by NA was absent in SHR15. Hearts of SHR10 showed an intermediate response. 4. Both SNAP and GTN significantly increased LVP, +dP/dt(max) and -dP/dt(max) in hearts of WIS and of SHR. In WIS but not in SHR10, SNAP also increased HR. In SHR10 the lowest concentration of SNAP (1 micromol l(-1)) showed no effect on contractility but a significantly diminished reduction of CPP suggesting inactivation of extracellularly released NO in the coronary circulation of SHR. 5. L-NOARG significantly reduced contractility in hearts of WIS and of SHR to a similar extent. At a concentration of 1 mmol l(-1) L-NOARG also reduced HR. 6. These results suggests that positive inotropic effects of exogenous and endogenous NO are not changed in hypertension induced myocardial hypertrophy.

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.

Induction of nitric oxide production by polyosides from the cell walls of Streptococcus mutans OMZ 175, a gram-positive bacterium, in the rat aorta

The cardiovascular dysfunctions associated with septic shock induced by gram-negative or gram-positive bacteria (gram-positive or gram-negative septic shock) are comparable. In gram-negative septic shock, lipopolysaccharide (LPS) induces nitric oxide (NO) synthase, which contributes to the vascular hypotension and hyporeactivity to vasoconstrictors. The role of NO in gram-positive septic shock and the nature of the bacterial wall components responsible for the vascular effects of gram-positive bacteria are not well known. This study investigated the vascular effects of cell wall serotype polyosides, rhamnose glucose polymers (RGPs), from Streptococcus mutans, in comparison with lipoteichoic acid (LTA) from Staphylococcus aureus, on the induction of NO synthase activity in the rat aorta. We show that 10 microg of both RGPs and LTA per ml induced hyporeactivity to noradrenaline, L-arginine-induced relaxation, increases of 2.2- and 7.8-fold, respectively, of cyclic GMP production, and increases of 7- and 12-fold in nitrite release. All of these effects appeared after several hours of incubation and were inhibited by N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase. Electron paramagnetic resonance spin trapping experiments demonstrated directly that RGPs and LTA induced NO overproduction (four- to eightfold, respectively) in rat aortic rings; this production was inhibited by L-NAME and prevented by dexamethasone. These results demonstrate directly the induction of NO production in vascular tissue by LTA and show that another, chemically different component of gram-positive bacteria can also have these properties. This result suggests that different components of the gram-positive bacterial wall could be implicated in the genesis of cardiovascular dysfunctions observed in gram-positive septic shock.

Urinary NItrotyrosine Content as a Marker of Peroxynitrite-induced Tolerance to Organic NItrates

BACKGROUND: Anti-ischemic therapy with nitrovaasodilators as NO-donors is complicated by the induction of tolerance. When nitrovasodilators are metabolized to release NO there is a considerable coproduction of oxygen-derived radicals leading to a diminished cyclic GMP production and to impaired vasomotory responses. We analyzed in vivo the glyceroltrinitrate-induced generation of strong oxidative/nitrating compounds contributing to development of tolerance. METHODS AND RESULTS: In 16 patients we studied the urinary nitrotyrosine excretion during either (1) placebo control conditions, (2) 2-day nonintermittent transdermal nitroglycerin administration (0.4 mg/h), (3) 2-day nonintermittent glyceroltrinitrate administration (0.4 mg/h) along with a continuous infusion of vitamin C (55 µg/kg/min) as an antioxidant, or (4) with vitamin C but without glyceroltrinitrate (diminished urinary nitrotyrosine content of 34 +/- 18 µg/day observed). Glyceroltrinitrate administration augmented urinary nitrotyrosine from 56 +/- 24 (basal) to 186 +/- 32 µg/day (glyceroltrinitrate tolerance). Coadministration of vitamin C caused complete elimination of tolerance and a decrease in urinary nitrotyrosine to 130 +/- 28 µg/day. Glyceroltrinitrate-induced formation of oxidants was confirmed in vitro comparing glyceroltrinitrate-induced and peroxynitrite-induced tachyphylaxis in isolated perfused rabbit hearts and analyzing tolerance-induced inactivation of solbule guanylyl cyclase in cultured aortic smooth muscle cells. CONCLUSIONS: Augmented urinary nitrotyrosine excretion during glyceroltrinitrate administration reflects enhanced formation of peroxynitrite and of nitrotyrosine. Glyceroltrinitrate-induced tolerance is the result of oxidative stress and can be suppressed by additional antioxidant therapy aimed to prevent glyceroltrinitrate-induced formation and/or actions of peroxynitrite.

Supersensitive dilator response to nitroglycerin but not to atrial natriuretic peptide in spastic coronary arteries in coronary spastic angina

It has been shown that there is the supersensitivity of the dilator effect of nitrovasodilators in the coronary arteries of patients with coronary spastic angina. This study was aimed to elucidate its mechanism(s) by examination of dilator response of spastic coronary arteries to atrial natriuretic peptide (ANP), which is known to dilate arteries by the same final common pathway through cyclic guanosine monophosphate (cGMP) as nitrovasodilators. Effects of infusion of nitroglycerin and ANP on epicardial coronary diameter of left coronary arteries were thus examined by quantitative coronary angiography in 20 patients with coronary spastic angina, who had spasm in left coronary arteries, and in 27 control subjects. Dilator response of coronary diameter to intracoronary infusion of ANP (0.5 microgram/kg) was found to be comparable between spastic coronary arteries and control arteries, whereas dilator response to nitroglycerin (250 micrograms) was enhanced in the spastic arteries compared with control arteries. The results indicate that spastic coronary arteries exhibit supersensitive dilator response to nitroglycerin but not to ANP. There is a possibility that dilator response to cGMP may be comparable between spastic and control coronary arteries and that soluble guanylate cyclase activity and/or conversion of nitric oxide bio-activity from nitroglycerin may be enhanced in spastic coronary arteries.

Nitric oxide production and endothelium-dependent vasorelaxation induced by wine polyphenols in rat aorta

1. The aim of this work was to investigate the mechanism of vasorelaxation induced by red wine polyphenolic compounds (RWPC) and two defined polyphenols contained in wine, leucocyanidol and catechin. The role of the endothelium, especially endothelium-derived nitric oxide (NO), was also investigated. 2. Relaxation produced by polyphenols was studied in rat aortic rings with and without functional endothelium, pre-contracted to the same extent with noradrenaline (0.3 and 0.1 microM, respectively). RWPC and leucocyanidol, but not catechin, produced complete relaxation of vessels with and without endothelium. However, 1000 fold higher concentrations were needed to relax endothelium-denuded rings compared to those with functional endothelium. 3. High concentrations of catechin (in the range of 10(-1) gl-1) only produced partial relaxation (maximum 30%) and had the same potency in rings with and without endothelium. 4. The NO synthase inhibitor, N omega-nitro-L-arginine-methyl-ester (L-NAME, 300 microM) completely abolished the endothelium-dependent but not the endothelium-independent relaxations produced by all of the polyphenolic compounds. 5. In contrast to superoxide dismutase (SOD, 100 u ml-1), neither RWPC nor leucocyanidol affected the concentration-response curve for the NO donor, SIN-1 (3-morpholino-sydnonimine) which also produces superoxide anion (O2-). 6. In aortic rings with endothelium, RWPC (10(-2) gl-1) produced, a 7 fold increase in the basal production of guanosine 3':5'-cyclic monophosphate (cyclic GMP) which was prevented by L-NAME (300 microM). 7. Electron paramagnetic resonance (e.p.r.) spectroscopy studies with Fe(2+)-diethyldithiocarbamate as an NO spin trap demonstrated that RWPC and leucocyanidol increased NO levels in rat thoracic aorta about 2 fold. This NO production was entirely dependent on the presence of the endothelium and was abolished by L-NAME (300 microM). 8. These results show that RWPC and leucocyanidol, but not the structurally closely related polyphenol catechin, induced endothelium-dependent relaxation in the rat aorta. They indicate that this effect results from enhanced synthesis of NO rather than enhanced biological activity of NO or protection against breakdown by O2. It is concluded that some polyphenols, with specific structure, contained in wine possess potent endothelium-dependent vasorelaxing activity.

Effect of YC-1, an NO-independent, superoxide-sensitive stimulator of soluble guanylyl cyclase, on smooth muscle responsiveness to nitrovasodilators

1. We studied the effects of 3-(5'-hydroxymethyl-2'furyl)-1-benzyl indazole (YC-1) on the activity of purified soluble guanylyl cyclase (sGC), the formation of guanosine-3':5' cyclic monophosphate (cyclic GMP) in vascular smooth muscle cells (VSMC), and on the tone of rabbit isolated aortic rings preconstricted by phenylephrine (PE). In addition, we assessed the combined effect of YC-1, and either NO donors, or superoxide anions on these parameters. 2. YC-1 elicited a direct concentration-dependent activation of sGC (EC50 18.6 +/- 2.0 microM), which was rapid in onset and quickly reversible upon dilution. YC-1 altered the enzyme kinetics with respect to GTP by decreasing KM and increasing Vmax. Activation of sGC by a combination of sodium nitroprusside (SNP) and YC-1 was superadditive at low and less than additive at high concentrations, indicating a synergistic activation of the enzyme by both agents. A specific inhibitor of sGC, 1H-(1,2,4)-oxdiazolo-(4,3-a)-6-bromo-quinoxazin-1-one (NS 2028), abolished activation of the enzyme by either compound. 3. YC-1 induced a concentration-dependent increase in intracellular cyclic GMP levels in rat cultured aortic VSMC, which was completely inhibited by NS 2028. YC-1 applied at the same concentration as SNP elicited 2.5 fold higher cyclic GMP formation. Cyclic GMP-increases in response to SNP and YC-1 were additive. 4. YC-1 relaxed preconstricted endothelium-denuded rabbit aortic rings in a concentration-dependent manner (50% at 20 microM) and markedly increased cyclic GMP levels. Relaxations were inhibited by NS 2028. A concentration of YC-1 (3 microM), which elicited only minor effects on relaxation and cyclic GMP, increased the vasodilator potency of SNP and nitroglycerin (NTG) by 10 fold and markedly enhanced SNP- and NTG-induced cyclic GMP formation. 5. Basal and YC-1-stimulated sGC activity was sensitive to inhibition by superoxide (O-2) generated by xanthine/xanthine oxidase, and was protected from this inhibition by superoxide dismutase (SOD). YC-1-stimulated sGC was also sensitive to inhibition by endogenously generated (O-2 in rat preconstricted endothelium-denuded aortic rings. Relaxation to YC-1 was significantly attenuated in aortae from spontaneously hypertensive rats (SHR), which generated O-2 at a higher rate than aortae from normotensive Wistar Kyoto rats (WKY). SOD restored the vasodilator responsiveness of SHR rings to YC-1. 6. In conclusion, these results indicate that YC-1 is an NO-independent, O-2-sensitive, direct activator of sGC in VSMC and exerts vasorelaxation by increasing intracellular cyclic GMP levels. The additive or even synergistic responses to NO-donors and YC-1 in cultured VSMC and isolated aortic rings apparently reflect the direct synergistic action of YC-1 and NO on the sGC. The synergism revealed in this in vitro study suggests that low doses of YC-1 may be of therapeutic value by permitting the reduction of nitrovasodilator dosage.