Oxidation, nitrosation, and nitration of serotonin by nitric oxide-derived nitrogen oxides: biological implications in the rat vascular system

The evolution of radiobiology through the work of women scientists: the work of Christiane Ferradini

PURPOSE

Pay tribute to Christiane Ferradini and highlight the importance of her work as a scientist.

CONCLUSIONS

Christiane Ferradini was born in 1924 in the south of France. She graduated from the Paul Sabatier University in Toulouse, France. In 1947, she joined the Curie Laboratory of the Radium Institute (which was then under the leadership of Madame Irène Joliot-Curie) to pursue her doctoral research. After her defence in 1955, she commenced her journey dedicated to the advancement of science. She became an exceptional teacher. She led a research group that contributed, through many fruitful collaborations, to the opening of a new chapter in radiation biology and medicine. Together they shed light on free radical formation and their reactions with biomolecules. Christiane published a total of 190 scientific articles and 9 books. She died in 2002.

Top-Down and Bottom-Up Proteomics of Circulating S100A8/S100A9 in Plasma of Septic Shock Patients

Well-characterized prognostic biomarkers and reliable quantitative methods are key in sepsis management. Among damage-associated molecular patterns, S100A8/S100A9 complexes are reported to be markers for injured cells and to improve the prediction of death in septic shock patients. In view of the structural diversity observed for the intracellular forms, insight into circulating complexes and proteoforms is required to establish prognostic biomarkers. Here, we developed top-down and bottom-up proteomics to characterize the association of S100A8 and S100A9 in complexes and major circulating proteoforms. An antibody-free method was developed for absolute quantification of S100A8/S100A9 in a cohort of 49 patients to evaluate the prognostic value on the first day after admission for septic shock. The predominant circulating forms identified by top-down proteomics were S100A8, mono-oxidized S100A8, truncated acetylated S100A9, and S-nitrosylated S100A9. S100A8, truncated acetylated S100A9, and mono-oxidized S100A8 discriminated between survivors and nonsurvivors, along with total S100A8/S100A9 measured by the antibody-free bottom-up method. Overall, new insights into circulating S100A8/S100A9 and confirmation of its prognostic value in septic shock are crucial in qualification of this biomarker. Also, the simple antibody-free assay would support the harmonization of S100A8/S100A9 measurements.

Inhaled nitric oxide and the risk of renal dysfunction in patients with acute respiratory distress syndrome: a propensity-matched cohort study

Background

Inhaled nitric oxide (iNO) is a rescue therapy for severe hypoxemia in patients with acute respiratory distress syndrome (ARDS). Pooled data from clinical trials have signaled a renal safety warning for iNO therapy, but the significance of these findings in daily clinical practice is unclear. We used primary data to evaluate the risk of iNO-associated renal dysfunction in patients with ARDS.

Methods

We conducted a cohort study using data from a tertiary teaching hospital to evaluate the risk of incident renal replacement therapy (RRT) in iNO users compared with that of non-users. Propensity score matching and competing-risks regression were used for data analysis. Residual confounding was assessed by means of a rule-out approach. We also evaluated effect modification by pre-specified factors using stratified analysis.

Results

We identified 547 patients with ARDS, including 216 iNO users and 331 non-users. At study entry, 313 (57.2%) patients had moderate ARDS and 234 (42.8%) had severe ARDS. The mean patient age was 63 ± 17 years. The crude hazard ratio of the need for RRT in iNO users compared with non-users was 2.23 (95% CI, 1.61–3.09, p < 0.001). After propensity score matching, there were 151 iNO users matched to 151 non-users. The adjusted hazard ratio was 1.59 (95% CI, 1.08–2.34, p = 0.02). In the stratified analysis, we found that older aged patients (≥65 years) were more susceptible to iNO-associated kidney injury than younger patients (p = 0.05).

Conclusions

This study showed that iNO substantially increased the risk of renal dysfunction in patients with ARDS. Older aged patients were especially susceptible to this adverse event.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1566-0) contains supplementary material, which is available to authorized users.

Inhaled nitric oxide therapy and risk of renal dysfunction: a systematic review and meta-analysis of randomized trials

INTRODUCTION

Inhaled nitric oxide (iNO) is an important therapy for acute respiratory distress syndrome (ARDS), pulmonary hypertension and pediatric hypoxemic respiratory failure. Safety concerns regarding iNO and renal dysfunction have been reported; however, there are currently no systematic reviews on this issue. Our objective was to evaluate published randomized controlled trials (RCTs) to ascertain the risk of renal dysfunction associated with iNO therapy in patients with and without ARDS.

METHODS

A systematic review of databases was performed to identify RCTs which compared iNO with controls up to September 2014. Effect estimates for risk ratio (RR) of acute kidney injury (AKI) were pooled using a random-effects model.

RESULTS

Ten RCTs involving 1363 participants were included. Inhaled nitric oxide significantly increased the risk of AKI compared with controls (RR, 1.4, 95%CI, 1.06 to 1.83, p = 0.02). In the stratified analysis, a high cumulative-dose of iNO significantly increased the risk of AKI (RR, 1.52, 95%CI, 1.14 to 2.02, p = 0.004), whereas medium and low cumulative-doses did not (RR, 0.64, 95%CI, 0.23 to 1.81 and RR, 0.56, 95%CI, 0.11 to 2.86 respectively). In subgroup analysis by study population, an increased risk of AKI was observed in patients with ARDS (RR, 1.55, 95%CI, 1.15 to 2.09, p = 0.005) but not in those without (RR, 0.90, 95%CI, 0.49 to 1.67, p = 0.75).

CONCLUSIONS

The available data show that iNO therapy may increase the risk of renal dysfunction, especially with prolonged use and in patients with ARDS. The risk in pediatric population is unknown owing to limited data. We suggest monitoring renal function during iNO therapy, and that future trials of iNO should evaluate renal safety.

Oxidation of tryptamine and 5-hydroxytryptamine: a pulse radiolysis and quantum chemical study

The reactions of oxidizing radicals (*)OH, N(3)(*), Br(2)(*-), and NO(2)(*) with tryptamine (Tpe) and 5-hydroxytryptamine (HTpe) were studied by pulse radiolysis and analyzed by quantum chemical calculations. Barring NO(2)(*) radical, the rate constants for their reaction with Tpe and HTpe were found to be diffusion controlled and the rates in the NO(2)(*) radical reaction with HTpe are lower by 2 orders of magnitude with k approximately 1 x 10(7) dm(3) mol(-1) s(-1). The transient spectra formed on oxidation of Tpe and HTpe exhibited peaks at 330 and 530 nm (indolyl radical) and 420 nm (indoloxyl radical), respectively, and the latter is in reasonable agreement with the calculated value (407 nm). Both radicals decay through direct recombination, but only the indoloxyl radical was observed to react with the parent molecule to give a (HTpe-Ind)(*) radical adduct for [HTpe] > or = 50 x 10(-6) mol dm(-3). The calculated optimized geometries in water revealed the formation of two distinct types of radical adducts, one through the H-O bond and the other by C-C linkage. The H-O bonded radical adduct was found to be exothermic with a reaction enthalpy of -4 kcal mol(-1) and bond length 0.1819 nm and the C-C bonded radical adducts are endothermic and rate determining but are finally driven by exothermic processes involving intermolecular H transfer followed by intramolecular reorganization through H shift resulting in stable C4-C4' and C2-C4' dimers with reaction enthalpies of -39 and -44 kcal mol(-1), respectively, and this process was found to be thermodynamically as efficient as direct recombination of indoloxyl radicals. The formation of the two dimer products was also seen in steady-state radiolysis. The lack of adduct formation in the case of indolyl radical with Tpe is due to the positive free energy change (DeltaG = 10 kcal mol(-1)). The energetics for the (*)OH addition have shown dependence on the site of activation with (HTpe-OH)(*) adducts at C2 and C4 and the (Tpe-OH)(*) adduct at C2 being more thermodynamically stable and the water elimination to give the indoloxyl radical proceeds fast from (HTpe-OH)(*) adduct at C4 due to favorable geometry.

Theoretical investigation of nitration and nitrosation of dimethylamine by N2O4

Reactive nitrogen oxygen species (RNOS) contribute to the deleterious effects attributed to reacting with biomolecules. The mechanisms of the nitration and nitrosation of dimethylamine (DMA), which is the simplest secondary amine by N2O4, a member of RNOS, have been investigated at the CBS-QB3 level of theory. The nitration and nitrosation proceed via different pathways. The nitration of DMA follows three pathways. The first is the abstraction of the hydrogen atom of the amino group of DMA by the NO2 radical followed by a recombination reaction of the resulting aminyl radical with another NO2 radical. The second is DMA directly reacting with symmetrical O2NNO2 leading to dimethylnitramine via a concerted and a stepwise mechanism. The third is the reaction of DMA with asymmetrical ONONO2. By computation, the main pathway for the formation of dimethylnitramine in the gas phase is by DMA directly reacting with asymmetrical ONONO2. As to the nitrosation, a concerted mechanism for the reaction of DMA with asymmetrical ONONO2 plays a major role in nitrosodimethylamine (NDMA) formation. In addition, the solvent effect on these nitration and nitrosation reactions has been also studied by using the implicit polarizable continuum model. Two major pathways of the formation of dimethylnitramine in water were found, and they are the radical process involving NO2 and the concerted mechanism starting from symmetrical O2NNO2. The result of the nitrosation of DMA in water is consistent with that in the gas phase. Comparison of the energy barriers of each mechanism leads to the conclusion that the nitrosation is more favorable than the nitration in the reaction of DMA with N2O4. This conclusion is in good agreement with the experimental results. The results obtained here will help elucidate the mechanism of the lesions of biomolecules by RNOS.

N-nitroso-melatonin releases nitric oxide in the presence of serotonin and its derivatives

A novel reaction was observed between 5-hydroxytryptophan derivatives like serotonin and N-nitroso-melatonin (NOMela). This reaction decreased the concentration of serotonin by about 50% and generated initially as detectable products nitric oxide and melatonin with stoichiometrical yields. The other expected product, a serotonin-derived radical, could not be detected by electron spin resonance (ESR) spectrometry, probably because the self-decay of phenoxyl type radicals proceed at the diffusion-controlled limit. From the facts that the decay rate of NOMela corresponded very well with the nitric oxide releasing rate and that nitrite was the only thermodynamically stable nitrogen oxide-containing product, it is concluded that the NOMela-serotonin reaction proceeded quantitatively. The observed reaction might be a possibility to counteract a pharmacologically abnormal high serotonin concentration in various diseases.

The endogenous neurotransmitter, serotonin, modifies neuronal nitric oxide synthase activities

Serotonin, an important neurotransmitter, is colocalized with neuronal nitric oxide synthase (nNOS), a homodimeric enzyme which catalyzes the production of nitric oxide (NO(.-)) and/or oxygen species. As many interactions have been reported between the nitrergic and serotoninergic systems, we studied the effect of serotonin on nNOS activities. Our results reveal that nNOS is activated by serotonin as both NADPH consumption and oxyhemoglobin (OxyHb) oxidation were enhanced. The generation of L-citrulline from L-arginine (L-Arg) was not affected by serotonin in the range of 0-200 microM, suggesting an additional production of oxygen-derived species. But 5-hydroxytryptamine (5HT) induced the formation of both O and H(2)O(2) by nNOS, as evidenced by electron paramagnetic resonance (EPR) and by using specific spin traps. Overall, these results demonstrate that serotonin is able to activate nNOS, leading to the generation of reactive oxygen species (ROS) in addition to the NO(.-) production. Such a property must be considered in vivo as various nNOS-derived products mediate different signaling pathways.

3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), a food-born carcinogenic heterocyclic amine, promotes nitric oxide production in murine macrophages

A heterocyclic amine, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) is one of the potent food-born dietary carcinogens derived mainly from burnt meat products. In the present study, we investigated the inductive effect of Trp-P-1 on nitric oxide (NO) production in murine macrophages since NO and its oxidized derivatives are directly involved in triggering mutagenesis and carcinogenesis. Our results show that Trp-P-1 induced mRNA expression of inducible NO synthase (iNOS) and NO production without co-stimulation in murine peritoneal macrophages and RAW 264.7 cells. Trp-P-1 further enhanced both iNOS mRNA expression and NO production, which were primarily induced by lipopolysaccharide (LPS). Electrophoretic mobility shift assay demonstrated that Trp-P-1, alone or in the presence of LPS, facilitated the DNA binding activity of the transcription factor NF-kappaB, and the trans-acting activity of the NF-kappaB was confirmative as determined by in vitro transfection and a luciferase reporter gene assay. Moreover, Trp-P-1 induced increasing intracellular reactive oxygen species (ROS), which play an important role in NF-kappaB activation. These results suggest that Trp-P-1 induces NO production mediated by an increased intracellular ROS, NF-kappaB activation, and subsequent iNOS gene expression.

A novel mutagen, 2-(5-hydroxy-4,6-dinitroindolyl) ethanol, formed in the reaction between 5-hydroxytryptamine and nitrite under acid conditions, especially in the presence of l-cysteine

We examined the mutagenic activity of each of 29 amino acids mixed under acidic conditions with 5-hydroxytryptamine (5-HT) and nitrite using Salmonella typhimurium strain TA 100 with or without a metabolic activation system (S9 mix). The reaction mixture containing L-cysteine was strongly mutagenic without S9 mix. We subjected an ethyl acetate extract of the reaction mixture to HPLC, isolated a mutagenic component, and investigated its chemical structure by LC-mass spectrometry (MS), high-resolution fast atom bombardment (HRFAB)-MS, and 1H and 13C NMR. We identified the mutagen as 2-(5-hydroxy-4,6-dinitro-3-indolyl) ethanol (2HDIE). We injected 8 mg/kg 2HDIE i.p. into male ICR mice and found that the compound increased the frequency of micronuclei in peripheral reticulocytes. Our results suggest that 2HDIE might be formed in vivo by consumption of 5-HT, nitrite and L-cysteine in foods, and might act as a mutagen.

Pindolol is a potent scavenger of reactive nitrogen species

Pindolol is an indolic drug that has been shown to enhance and/or accelerate selective serotonin specific reuptake inhibitors (SSRI)-induced antidepressant (AD) effect, even though the respective mechanism is still unclear. It has been demonstrated that inhibition of nitric oxide (*NO) synthesis in CNS produces anxiolytic and AD-like behavioural effects in a variety of animal paradigms. On the other hand, sustained high levels of *NO may be deleterious to CNS, predominantly due to the formation of peroxynitrite anion (ONOO-), which is generated via reaction of *NO with superoxide radical (O2*-). Therefore, the purpose of the present study was to characterize the putative pindolol scavenging effect on *NO, ONOO-, and O2*-, using in vitro non-cellular systems. The obtained results clearly show that pindolol is a potent scavenger of *NO (IC50 of 449+/-33 microM) and ONOO- (IC50 of 131+/-24 microM). Additionally, the scavenging effect of pindolol increased almost 8 times in the presence of 25 mM NaHCO3 (IC50 of 17+/-3 microM), which indicates that pindolol efficiently scavenges reactive species that are produced from the ONOO-/CO2 reaction such as the nitrogen dioxide radical (*NO2) and the carbonate radical anion (CO3*-). These effects may contribute for the reduction of SSRI antidepressant latency that has been attributed to pindolol and may also constitute an additional value for this drug when depression is associated with pro-oxidant neurodegenerative diseases.

Nitric oxide synthase inhibitors and nitric oxide donors modulate the biosynthesis of thaxtomin A, a nitrated phytotoxin produced by Streptomyces spp

Evidence for the involvement of a bacterial nitric oxide synthase (NOS) in the biosynthesis of a phytotoxin is presented. Several species of Streptomyces bacteria produce secondary metabolites with unusual nitrogen groups, such as thaxtomin A (ThxA), which contains a nitroindole moiety. ThxA is a phytotoxin made by three pathogenic Streptomyces species that cause common scab of potato. All three species possess a gene homologous to the oxygenase domain of murine inducible NOS, and this gene, nos, is essential for normal levels of ThxA production. We grew Streptomyces turgidiscabies in the presence of several known NOS inhibitors and a nitric oxide (NO) scavenger to determine their effect on ThxA production. The NO scavenger (CPTIO) and four NOS inhibitors (NAME, NMMA, AG, and 7-NI) reduced ThxA production without affecting bacterial growth. A strain of S. turgidiscabies from which the nos gene had been deleted was grown in the presence of three NO donors (DEANO, SIN, and SNAP), and all three partially restored ThxA production. Our data suggest that bacterial nitric oxide synthases may, at least in part, produce NO for biosynthetic purposes, rather than for cellular signaling, as they do in mammals.

6-Nitrotryptophan: A Specific Reaction Product Of Tryptophan Residue In Human Cu, Zn-Sod Treated With Peroxynitrite

Human Cu,Zn-superoxide dismutase (SOD) was treated with peroxynitrite. The modified enzyme was digested by trypsin. Decrease of one peptide and appearance of three new peptides (A, B, C) with increase molecular weights of 16, 16, and 45 compared to that of the decreased peptide, respectively, were observed by LC/MS analysis. These increased molecular weights correspond to the addition of one oxygen and nitro group, respectively. Among these new peptides, the peptide C showed thesame visible absorption spectrum as that of 6-nitrotryptophan. We conclude 6-nitrotryptophan is one of the reaction products between tryptophan residue in Cu, Zn-SOD and peroxynitrite.

Pulmonary vasoconstriction by serotonin is inhibited by S-nitrosoglutathione

Nitric oxide (NO) functions as an endothelium-derived relaxing factor by activating guanylate cyclase to increase cGMP levels. However, NO and related species may also regulate vascular tone by cGMP-independent mechanisms. We hypothesized that naturally occurring NO donors could decrease the pulmonary vascular response to serotonin (5-HT) in the intact lung through chemical interactions with 5-HT(2) receptors. In isolated rabbit lung preparations and isolated pulmonary artery (PA) rings, 50-250 microM S-nitrosoglutathione (GSNO) inhibited the response to 0.01-10 microM 5-HT. The vasoconstrictor response to 5-HT was mediated by 5-HT(2) receptors in the lung, since it could be blocked completely by the selective inhibitor ketanserin (10 microM). GSNO inhibited the response to 5-HT by 77% in intact lung and 82% in PA rings. In PA rings, inhibition by GSNO could be reversed by treatment with the thiol reductant dithiothreitol (10 mM). 3-Morpholinosydnonimine (100-500 microM), which releases NO and O simultaneously, also blocked the response to 5-HT. Its chemical effects, however, were distinct from those of GSNO, because 5-HT-mediated vasoconstriction was not restored in isolated rings by dithiothreitol. In the intact lung, neither NO donor altered the vascular response to endothelin, which activates the same second-messenger vasoconstrictor system as 5-HT. These findings, which did not depend on guanylate cyclase, are consistent with chemical modification by NO of the 5-HT(2) G protein-coupled receptor system to inhibit vasoconstriction, possibly by S-nitrosylation of the receptor or a related protein. This study demonstrates that GSNO can regulate vascular tone in the intact lung by a reversible mechanism involving inhibition of the response to 5-HT.

Microglial derived nitric oxide decreases serotonin content in rat basophilic leukemia (RBL-2H3) cells

Nitric oxide (NO) and serotonin (5-hydroxytryptamine; 5-HT) are important neuromodulators that are involved in a myriad of biochemical reactions. In this work, we describe a novel model co-culture system to study the interactions between NO and 5-HT. NO derived from cytokine stimulated Bv2 microglial cells depleted 5-HT from RBL-2H3 cells. Reduction of 5-HT content by NO derived from the NO donor S-nitroso-N-acetylpenicillamine (SNAP) was concentration-dependent, independent of intracellular Ca(2+) and inhibited by reduced glutathione (GSH). Collectively, these data indicate that this cell co-culture system is a viable model to study the mechanisms of interaction between nitrergic and serotonergic pathways.

Serotonin-induced nitric oxide production in the ventral nerve cord of the earthworm, Eisenia fetida

Effect of serotonin on nitric oxide (NO) production in the ventral nerve cord (VNC) of the earthworm Eisenia fetida was investigated by a bio-imaging and an electrochemical technique. In the bio-imaging, the spatial pattern of NO production in VNC was visualized using an NO-specific fluorescent dye, diaminofluorescein-2 diacethyl (DAF-2 DA). Application of serotonin (100 microM) increased NO production in VNC by about 65% (P<0.05), compared with basal NO production. The increase was mainly from the nitergic neurons in the ventral side of VNC. In the electrochemical technique, real-time basal and serotonin-induced NO production was estimated with an NO-specific electrode. On the ventral surface of VNC, the estimated basal NO production was stable at 200+/-52 nM, and was transiently augmented to 840+/-193 nM by the addition of 10 microM serotonin. In conclusion, the estimated basal NO production in the earthworm VNC is relatively high compared with other nervous systems earlier reported, and transiently augmented by serotonin. Our results suggest that NO signaling in VNC is involved in neuromodulation by serotonin.

Visualization of nitric oxide production in the earthworm ventral nerve cord

Distribution of nitric oxide (NO)-producible neurons in the ventral nerve cord (VNC) of the earthworm was investigated by nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry. Some neurons (20-30 microm in diameter) were intensely stained and were localized in areas between the 1st and 2nd lateral nerves in the ventral side of VNC. In contrast, no neurons including giant fibers were stained in the dorsal side. Endogenous NO production from VNC was visualized using a fluorescent dye, diaminofluorescein-2 diacethyl (DAF-2 DA). When VNC was incubated in a saline, a relative high level of NO was produced from the ventral side, especially from NADPH-d-positive neurons. Under high-K+ stimulation, NO was also detected in the giant fibers in the dorsal side of VNC. Our results suggest that the earthworm VNC constantly and relative highly produces NO as a neuromodulator, and that NO produced from the ventral side sometimes reaches and affects the giant fibers. In conclusion, we successfully visualized NO in the earthworm VNC by clarifying both the distribution of NO-producible neurons and the endogenous NO production.

Rapid recovery and identification of anthrax bacteria from the environment

Bacillus anthracis has been recognized as a highly likely biological warfare or terrorist agent. We have designed culture techniques to rapidly isolate and identify "live" anthrax from suspected environmental release. A special medium (3AT medium) allows for discrimination between closely related bacilli and non-pathogenic strains. Nitrate was found to be a primary factor influencing spore formation in Bacillus anthracis. Nitrate reduction in anthrax is not an adaptation to saprophytic environmental existence, but it is a signal to enhance environmental survival upon the death of the anthrax host, which can be mimicked in culture.

Chemical evaluation of compounds as nitric oxide or peroxynitrite donors using the reactions with serotonin

The aim of this work was to assess the capacities of some .NO-donors to release .NO, and consequently NOx in aerobic medium, or to give peroxynitrite. The method was based on the differential reactivity of serotonin (5-HT) with either NO(x) or peroxynitrite, leading in phosphate-buffered solutions to 4-nitroso- and 4-nitro-5-HT formation, respectively. Yields and formation rates of 5-HT derivatives with .NO-donor were compared to those obtained with authentic .NO or peroxynitrite in similar conditions. Aside from the capacity of diazenium diolates (SPER/NO and DEA/NO) to release .NO spontaneously, converting 5-HT exclusively to 4-nitroso-5-HT, all other .NO donors must undergo redox reactions to produce .NO. S-nitrosoglutathione (GSNO) and sodium nitroprusside (SNP) modified 5-HT only in the presence of Cu2+, GSNO yielding 6 times more 4-nitroso-5-HT than SNP. Furthermore, in the presence of Cu+, the yield of .NO-release from GSNO was 45%. The molsidomine metabolite (SIN-1), which was presumed to release both .NO and O2(7-) at pH 7.4, reacted with 5-HT differently, depending on the presence of reductant or oxidant. Under aerobic conditions, SIN-1 acted predominantly as a 5-HT oxidant and also as a poor .NO and peroxynitrite donor (15% yield of .NO-release and 14 % yield of peroxynitrite formation). The strong oxidant Cu2+, even in the presence of air oxygen, accelerated oxidation and increased .NO release from SIN-1 up to 86%. Only a small part of SIN-1 gave simultaneously .NO and O2(7-) able to link together to give peroxynitrite, but other oxidants could enhance .NO release from SIN-1.

Intervention du monoxyde d'azote, NO, et de ses dérivés oxydés, particulièrement chez les mammifères

Nitric oxide (NO) is a natural and stable free radical produced in soil and water by the bacteriological reduction of nitrites and nitrates and in animals by the enzyme oxidation of L-arginine. NO is biosynthesised by finely regulated enzymatic systems called NO-synthases and readily diffuses through tissues. It reacts rapidly with hemoproteins and iron-sulphur centers to form nitrosylated compounds. It oxidises more slowly to form nitrogen oxides that nitrosate thiols into thionitrite. NO is transported in these various forms and released spontaneously or through yet unclear mechanisms into most cells; it also regulates oxygen consumption at the mitochondrial respiratory chain level through interaction with cytochrome oxidase. In the cardiovascular system, NO lowers blood pressure by activating a hemoprotein, the guanylate cyclase present in muscle cells; through such interaction it acts also as a neuromediator and neuromodulator in the nervous system. However, many of NO's roles result from rapid coupling to other radicals; for example, it reacts with the superoxide anion (O–2) to form oxoperoxinitrate (ONOO–, also known as peroxynitrite). This strong oxidant of metallic centers, thiols, and antioxidants is also able to convert tyrosine to 3-nitrotyrosine and to act upon tyrosine residues contained in proteins. The biological aspects of the roles of NO are presented with particular respect to the rapid interactions of NO with hemoproteins' iron and other radicals. Concurrently, NO oxidation enables nitrosation reactions primarily of thiols but ultimately of nucleic bases. The thionitrite function (R-S-NO) thus formed and the dimerisation and nitration of tyrosine residues are protein post-translational modifications that are being investigated in animals.Key words: nitric oxide, peroxynitrite, nitration, nitrosation, nitrosylation. [Translated by the editors.]

Inhaled nitric oxide and acute lung injury

The nitric oxide (NO) field has been one of the most exciting scientific ventures over the past 10 years. Among the researches developed, the use of inhalation of NO gas allowed us to propose this therapy in lung diseases with promising results. Because of its property as a "selective" pulmonary vasodilator and because of its apparent clinical safety, inhaled NO has been proposed in acute lung injury (ALI) to improve severe hypoxemia. In this situation, the abnormal ventilation-perfusion ratio is improved by inhaled NO, limiting arterial hypoxia. The major clinical trials performed in adults, however, have failed to show any benefit on mortality and on mechanical ventilation requirements. Inhaled NO has been shown as an efficient therapy in pediatric ALI, probably because of a lower comorbidity. Because of the inhaled NO uptake by the lung, the extra vascular lung effects might be in the future the most important development in relation with platelet anti-agregant and anti-inflammatory properties.

Nitric oxide transforms serotonin into an inactive form and this affects neuromodulation

Nitric oxide is a highly reactive molecule, diffusible and therefore ubiquitous in the central nervous system. Consequently, nitric oxide or nitric oxide-derived nitrogen oxides must enter into contact with neuromodulators and they can modify these molecules, especially monoamines, and thus change their regulatory action on synaptic transmission. We tested this possibility on a well-known, identified cholinergic synapse of Aplysia buccal ganglion, in which we have found that evoked acetylcholine release was decreased by extracellularly applied serotonin. We show that this modulatory effect of serotonin was largely reduced not only in the presence of 3-morpholinosydnonimine, a nitric oxide donor, but also when endogenous nitric oxide synthase was activated. We have shown that this decrease in the serotonin effect is due to the formation of chemical derivatives of serotonin, mainly a symmetric serotonin dimer, 4-nitroso-serotonin and 4-nitro-serotonin, which are ineffective in reproducing the modulatory effect of serotonin. Serotonin is involved in the regulation of several central functions, such as sleep-wake activity or mood. The consequences of chemical modifications of serotonin by nitric oxide must be taken into account in physiological as well as pathological situations. In addition, our results highlight the importance of the physiological implications of interactions between free radicals and neuromediators in the nervous system.

Nitration modifying function of proteins, hormones and neurotransmitters

Several lines of evidence have been accumulated for occurrence of nitration in vivo. In this brief review, we summarized nitration studies on functional changes of proteins, hormones and neurotransmitters, before as well as after the discovery of peroxynitrite. Most of nitrated molecules exhibit less active properties than the parental compounds. It is still unknown whether nitration is merely a footprint of oxidative stress, an important pathway of nitric oxide metabolisms or a part of integral processes for maintaining cellular homeostasis.