Iron dithiocarbamate as spin trap for nitric oxide detection: pitfalls and successes

What is the Mechanism of Nitric Oxide Conversion into Nitrosonium Ions Ensuring S-Nitrosating Processes in Living Organisms

Here, I present the data testifying that the conversion of free radical NO molecules to nitrosonium ions (NO⁺), which are necessary for the realization of one of NO biological effects (S-nitrosation), may occur in living organisms after binding NO molecules to loosely bound iron (Fe²⁺ ions) with the subsequent mutual one-electron oxidation-reduction of NO molecules (their disproportionation). Inclusion of thiol-containing substances as iron ligands into this process prevents hydrolysis of NO⁺ ions bound to iron thus providing the formation of stable dinitrosyl iron complexes (DNIC) with thiol ligands. Such complexes act in living organisms as donors of NO and NO⁺, providing stabilization and transfer of these agents via the autocrine and paracrine pathways. Without loosely bound iron (labile iron pool) and thiols participating in the DNIC formation, NO functioning as one of universal regulators of diverse metabolic processes would be impossible.

Role of nitric oxide in psychostimulant-induced neurotoxicity

In recent decades, consumption of psychostimulants has been significantly increased all over the world, while exact mechanisms of neurochemical effects of psychomotor stimulants remained unclear. It is assumed that the neuronal messenger nitric oxide (NO) may be involved in mechanisms of neurotoxicity evoked by psychomotor stimulants. However, possible participation of NO in various pathological states is supported mainly by indirect evidence because of its short half-life in tissues. Aim of this review is to describe the involvement of NO and the contribution of lipid peroxidation (LPO) and acetylcholine (ACH) release in neurotoxic effects of psychostimulant drugs. NO was directly determined in brain structures by electron paramagnetic resonance (EPR). Both NO generation and LPO products as well as release of ACH were increased in brain structures following four injections of amphetamine (AMPH). Pretreatment of rats with the non-selective inhibitor of NO-synthase (NOS) N-nitro-L-arginine or the neuronal NOS inhibitor 7-nitroindazole significantly reduced increase of NO generation as well as the rise of ACH release induced by AMPH. Both NOS inhibitors injected prior to AMPH had no effect on enhanced levels of LPO products. Administration of the noncompetitive NMDA receptor antagonist dizocilpine abolished increase of both NO content and concentration of LPO products induced by of the psychostimulant drug. Dizocilpine also eliminated the influence of AMPH on the ACH release. Moreover, the neurochemical and neurotoxic effects of the psychostimulant drug sydnocarb were compared with those of AMPH. Single injection of AMPH showed a more pronounced increase in NO and TBARS levels than after an equimolar concentration of sydnocarb. The findings demonstrate the crucial role of NO in the development of neurotoxicity elicited by psychostimulants and underline the key role of NOS in AMPH-induced neurotoxicity.

Molecular Bases of Brain Preconditioning

Preconditioning of the brain induces tolerance to the damaging effects of ischemia and prevents cell death in ischemic penumbra. The development of this phenomenon is mediated by mitochondrial adenosine triphosphate-sensitive potassium (KATP+) channels and nitric oxide signaling (NO). The aim of this study was to investigate the dynamics of molecular changes in mitochondria after ischemic preconditioning (IP) and the effect of pharmacological preconditioning (PhP) with the KATP+-channels opener diazoxide on NO levels after ischemic stroke in rats. Immunofluorescence-histochemistry and laser-confocal microscopy were applied to evaluate the cortical expression of electron transport chain enzymes, mitochondrial KATP+-channels, neuronal and inducible NO-synthases, as well as the dynamics of nitrosylation and nitration of proteins in rats during the early and delayed phases of IP. NO cerebral content was studied with electron paramagnetic resonance (EPR) spectroscopy using spin trapping. We found that 24 h after IP in rats, there is a two-fold decrease in expression of mitochondrial KATP+-channels (p = 0.012) in nervous tissue, a comparable increase in expression of cytochrome c oxidase (p = 0.008), and a decrease in intensity of protein S-nitrosylation and nitration (p = 0.0004 and p = 0.001, respectively). PhP led to a 56% reduction of free NO concentration 72 h after ischemic stroke simulation (p = 0.002). We attribute this result to the restructuring of tissue energy metabolism, namely the provision of increased catalytic sites to mitochondria and the increased elimination of NO, which prevents a decrease in cell sensitivity to oxygen during subsequent periods of severe ischemia.

Direct Observation of Enhanced Nitric Oxide in a Murine Model of Diabetic Nephropathy

Uncoupling of nitric oxide synthase (NOS) secondary to redox signaling is a central mechanism in endothelial and macrophage activation. To date studies on the production of nitric oxide (NO) during the development of diabetic complications show paradoxical results. We previously showed that recoupling eNOS by increasing the eNOS cofactor tetrahydrobiopterin (BH4) could restore endothelial function and prevent kidney injury in experimental kidney transplantation. Here, we employed a diabetic mouse model to investigate the effects of diabetes on renal tissue NO bioavailability. For this, we used in vivo NO trapping, followed by electron paramagnetic resonance spectroscopy. In addition, we investigated whether coupling of NOS by supplying the cofactor BH4 could restore glomerular endothelial barrier function. Our data show that overall NO availability at the tissue level is not reduced sixteen weeks after the induction of diabetes in apoE knockout mice, despite the presence of factors that cause endothelial dysfunction, and the presence of the endogenous NOS inhibitor ADMA. Targeting uncoupled NOS with the BH4 precursor sepiapterin further increases NO availability, but did not modify renal glomerular injury. Notably, glomerular heparanase activity as a driver for loss of glomerular barrier function was not reduced, pointing towards NOS-independent mechanisms. This was confirmed by unaltered increased glomerular presence of cathepsin L, the protease that activates heparanase.

Effects of NO Synthase Blocker L-NAME on Functional State of the Neuromotor System during Traumatic Disease of the Spinal Cord

Functional state of the neuromotor system after administration of a nonspecific NO synthase blocker L-NAME was studied on the model of experimental contusion of the spinal cord. Electron paramagnetic resonance measurements of NO production in the damaged segment of the spinal cord were performed for estimation of the dynamics of intensity of NO production during traumatic disease of the spinal cord and selection of optimal period for L-NAME administration. The status of the neuromotor system was evaluated by stimulation electromyography. Treatment with L-NAME during the acute period of traumatic injury to the spinal cord sharply reduced the intensity of evoked motor responses and more pronounced increase in excitability of peripheral motor structures. The results suggest that NO system is a factor of regulation of the stress-induced and adaptive responses of the body at the early stage of spinal cord injury.

Detection of Nitric Oxide by Electron Paramagnetic Resonance Spectroscopy: Spin-Trapping with Iron-Dithiocarbamates

Electron paramagnetic resonance (EPR) spectroscopy is the ideal methodology to identify radicals (detection and characterization of molecular structure) and to study their kinetics, in both simple and complex biological systems. The very low concentration and short life-time of NO and of many other radicals do not favor its direct detection and spin-traps are needed to produce a new and persistent radical that can be subsequently detected by EPR spectroscopy.In this chapter, we present the basic concepts of EPR spectroscopy and of some spin-trapping methodologies to study NO. The "strengths and weaknesses" of iron-dithiocarbamates utilization, the NO traps of choice for the authors, are thoroughly discussed and a detailed description of the method to quantify the NO formation by molybdoenzymes is provided.

Atrasentan Reduces Albuminuria by Restoring the Glomerular Endothelial Glycocalyx Barrier in Diabetic Nephropathy

Atrasentan, a selective endothelin A receptor antagonist, has been shown to reduce albuminuria in type 2 diabetes. We previously showed that the structural integrity of a glomerular endothelial glycocalyx is required to prevent albuminuria. Therefore we tested the potential of atrasentan to stabilize the endothelial glycocalyx in diabetic apolipoprotein E (apoE)-deficient mice in relation to its antialbuminuric effects. Treatment with atrasentan (7.5 mg/kg/day) for 4 weeks reduced urinary albumin-to-creatinine ratios by 26.0 ± 6.5% (P < 0.01) in apoE knockout (KO) mice with streptozotocin-induced diabetes consuming an atherogenic diet, without changes in gross glomerular morphology, systemic blood pressure, and blood glucose concentration. Endothelial cationic ferritin surface coverage, investigated using large-scale digital transmission electron microscopy, revealed that atrasentan treatment increases glycocalyx coverage in diabetic apoE KO mice from 40.7 ± 3.2% to 81.0 ± 12.5% (P < 0.05). This restoration is accompanied by increased renal nitric oxide concentrations, reduced expression of glomerular heparanase, and a marked shift in the balance of M1 and M2 glomerular macrophages. In vitro experiments with endothelial cells exposed to laminar flow and cocultured with pericytes confirmed that atrasentan reduced endothelial heparanase expression and increased glycocalyx thickness in the presence of a diabetic milieu. Together these data point toward a role for the restoration of endothelial function and tissue homeostasis through the antialbuminuric effects of atrasentan, and they provide a mechanistic explanation for the clinical observations of reduced albuminuria with atrasentan in diabetic nephropathy.

L-arginine supplementation protects exercise performance and structural integrity of muscle fibers after a single bout of eccentric exercise in rats

Eccentric exercise is known to disrupt sarcolemmal integrity and induce damage of skeletal muscle fibers. We hypothesized that L-arginine (L-Arg; nitric oxide synthase (NOS) substrate) supplementation prior to a single bout of eccentric exercise would diminish exercise-induced damage. In addition, we used N-nitro-L-arginine methyl ester hydrochloride (L-NAME; NOS inhibitor) to clarify the role of native NOS activity in the development of exercise-induced muscle damage. Rats were divided into four groups: non-treated control (C), downhill running with (RA) or without (R) L-Arg supplementation and downhill running with L-NAME supplementation (RN). Twenty four hours following eccentric exercise seven rats in each group were sacrificed and soleus muscles were dissected and frozen for further analysis. The remaining seven rats in each group were subjected to the exercise performance test. Our experiments showed that L-Arg supplementation prior to a single bout of eccentric exercise improved subsequent exercise performance capacity tests in RA rats when compared with R, RN and C rats by 37%, 27% and 13%, respectively. This outcome is mediated by L-Arg protection against post-exercise damage of sarcolemma (2.26- and 0.87-fold less than R and RN groups, respectively), reduced numbers of damaged muscle fibers indicated by the reduced loss of desmin content in the muscle (15% and 25% less than R and RN groups, respectively), and diminished µ-calpain mRNA up-regulation (42% and 30% less than R and RN groups, respectively). In conclusion, our study indicates that L-Arg supplementation prior to a single bout of eccentric exercise alleviates muscle fiber damage and preserves exercise performance capacity.

Role of NO-synthase in regulation of protein metabolism of stretched rat m. soleus muscle during functional unloading

Gravitational unloading causes atrophy of muscle fibers and can lead to destruction of cytoskeletal and contractile proteins. Along with the atrophic changes, unloaded muscle frequently demonstrates significant shifts in the ratio of muscle fibers expressing fast and slow myosin heavy chain isoforms. Stretching of the m. soleus during hindlimb suspension prevents its atrophy. We supposed that neuronal NO-synthase (NOS) (which is attached to membrane dystrophin-sarcoglycan complex) can contribute to maintenance of protein metabolism in the muscle and prevent its atrophy when m. soleus is stretched. To test this hypothesis, we used Wistar rats (56 animals) in experiments with hindlimb suspension during 14 days. The group of hindlimb suspended rats with stretched m. soleus was injected with L-NAME to block NOS activity. We found that m. soleus mass and its protein content in hindlimb-suspended rats with stretched m. soleus were preserved due to prevention of protein degradation. NOS is involved in maintenance of expression of some muscle proteins. Proliferation of satellite cells in stretched m. soleus may be due to nNOS activity, but maintenance of muscle mass upon stretching is regulated not by NOS alone.

Determination of in vivo nitric oxide levels in animal tissues using a novel spin trapping technology

It has been established that microdialysis ensured by the passage of aqueous solutions of Fe(3+) complexes with N-methyl-D: -glucamine dithiocarbamate (MGDMGD ) through fine dialysis fibers permeable for compounds with molecular weights below 5 kDa. These fibers can be implanted into heart, liver, and kidney tissues, enabling effective binding of Fe(3+)-MGD complexes to nitric oxide generated in interstitial fluids of narcotized rats in vivo. Subsequent treatment of dialyzate samples (60 μL) with sodium dithionite favors conversion of newly formed diamagnetic NO-Fe(3+)-MGD complexes into electron paramagnetic resonance-detectable NO-Fe(2+)-MGD complexes. The basal levels of NO determined from the concentrations of the complexes in the respective tissues are similar (1 μМ). The microdialysis data suggest that treatment of rats with a water-soluble analogue of nitroglycerine or a dinitrosyl iron complex with thiosulfate induces a long-lasting (>1 h) increase in the steady-state level of NO in animal tissues. This novel technology can be used for comparative analyses of production rates of NO and reactive oxygen species when using iron-dithiocarbamate complexes and spin traps for reactive oxygen species, respectively.

Direct EPR Detection of Nitric Oxide in Mice Infected with the Pathogenic Mycobacterium Mycobacterium tuberculosis

It has been shown that treatment of mice preinfected with Mycobacterium tuberculosis with spin NO traps (iron complexes with diethyldithiocarbamate) enables detection of large amounts of NO in internal organs 2 and 4 weeks after infection (up to 55-57 mumol/kg of wet lung tissue accumulated with spin NO traps during 30 min). The animals were infected with the drug-sensitive laboratory strain H37Rv and a clinical isolate nonrespondent to antituberculous drugs (the multidrug-resistant strain of M. tuberculosis) obtained from a patient with an active form of tuberculosis. Two weeks after infection with the multidrug-resistant strain, the NO level in the lungs, spleen, liver and kidney increased sharply concurrently with slight lesions of lung tissue. A reverse correlation, i.e., low level of NO in the lungs and other internal organs and extensive injury of lung tissue, was established for H37Rv-infected mice. Four weeks after infection, NO production in the lungs increased dramatically for both M. tuberculosis strains resulting in 80-84% damage of lung tissue. The lesion is suggested to be due to the development of defense mechanisms in M. tuberculosis counteracting NO effects.

The anti-inflammatory and antinociceptive effects of NF-kappaB inhibitory guanidine derivative ME10092

The guanidine compound ME10092 (1-(3,4-dimethoxy-2-chlorobenzylideneamino)-guanidine) is known to possess anti-radical and anti-ischemic activity but its molecular targets have not been identified. This study investigated whether ME10092 regulates the nuclear factor kappa B (NF-kappaB)-mediated signal transduction in vivo. The effect of ME10092 treatment (1-100 pmol/mouse) on nuclear translocation of NF-kappaB, activation of expression of inflammatory mediators and production of nitric oxide were measured in the lipopolysaccharide (LPS)-induced brain inflammation model in mice in vivo. The antinociceptive activity of ME10092 was tested in the formalin-induced paw licking test. ME10092 dose-dependently inhibited LPS-induced nuclear translocation of NF-kappaB, transcription of tumour necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Electron paramagnetic resonance measurements showed that ME10092 inhibited the LPS-induced increase in nitric oxide content in mouse brain tissue in a dose-dependent manner. In the formalin-induced paw licking test, ME10092 (at the dose of 3mg/kg, p.o. twice daily for eight days) significantly reduced nociceptive response. In conclusion, above results indicate that ME10092 inhibits NF-kappaB activation and suppresses the up-regulation of inflammatory mediators in experimental models in vivo.

Multimodality imaging of nitric oxide and nitric oxide synthases

Nitric oxide (NO) and NO synthases (NOSs) are crucial factors in many pathophysiological processes such as inflammation, vascular/neurological function, and many types of cancer. Noninvasive imaging of NO or NOS can provide new insights in understanding these diseases and facilitate the development of novel therapeutic strategies. In this review, we will summarize the current state-of-the-art multimodality imaging in detecting NO and NOSs, including optical (fluorescence, chemiluminescence, and bioluminescence), electron paramagnetic resonance (EPR), magnetic resonance (MR), and positron emission tomography (PET). With continued effort over the last several years, these noninvasive imaging techniques can now reveal the biodistribution of NO or NOS in living subjects with high fidelity which will greatly facilitate scientists/clinicians in the development of new drugs and/or patient management. Lastly, we will also discuss future directions/applications of NO/NOS imaging. Successful development of novel NO/NOS imaging agents with optimal in vivo stability and desirable pharmacokinetics for clinical translation will enable the maximum benefit in patient management.

Nitrite as regulator of hypoxic signaling in mammalian physiology

In this review we consider the effects of endogenous and pharmacological levels of nitrite under conditions of hypoxia. In humans, the nitrite anion has long been considered as metastable intermediate in the oxidation of nitric oxide radicals to the stable metabolite nitrate. This oxidation cascade was thought to be irreversible under physiological conditions. However, a growing body of experimental observations attests that the presence of endogenous nitrite regulates a number of signaling events along the physiological and pathophysiological oxygen gradient. Hypoxic signaling events include vasodilation, modulation of mitochondrial respiration, and cytoprotection following ischemic insult. These phenomena are attributed to the reduction of nitrite anions to nitric oxide if local oxygen levels in tissues decrease. Recent research identified a growing list of enzymatic and nonenzymatic pathways for this endogenous reduction of nitrite. Additional direct signaling events not involving free nitric oxide are proposed. We here discuss the mechanisms and properties of these various pathways and the role played by the local concentration of free oxygen in the affected tissue.

Analytical chemistry of nitric oxide

Nitric oxide (NO) is the focus of intense research primarily because of its wide-ranging biological and physiological actions. To understand its origin, activity, and regulation, accurate and precise measurement techniques are needed. Unfortunately, analytical assays for monitoring NO are challenged by NO's unique chemical and physical properties, including its reactivity, rapid diffusion, and short half-life. Moreover, NO concentrations may span the picomolar-to-micromolar range in physiological milieus, requiring techniques with wide dynamic response ranges. Despite such challenges, many analytical techniques have emerged for the detection of NO. Herein, we review the most common spectroscopic and electrochemical methods, with a focus on the underlying mechanism of each technique and on approaches that have been coupled with modern analytical measurement tools to create novel NO sensors.

Electron paramagnetic resonance (EPR) spin trapping of biological nitric oxide

Nitric oxide (NO) is a free radical species with multiple physiological functions. Because of low concentrations and short half-life of NO, its direct measurement in living tissues remains a difficult task. Electron paramagnetic resonance (EPR) spin trapping is probably one of the best suitable platforms for development of new methods for quantification of biological NO. The most reliable EPR-based approaches developed so far are based on the reaction of NO with various iron complexes, both intrinsic and exogenously applied. This review is focused on the current state and perspectives of EPR spin trapping for experimental and clinical NO biology.

Reduction enhances yields of nitric oxide trapping by iron–diethyldithiocarbamate complex in biological systems

The mechanism of NO trapping by iron-diethylthiocarbamate complexes was investigated in cultured cells and animal and plant tissues. Contrary to common belief, the NO radicals are trapped by iron-diethylthiocarbamates not only in ferrous but in ferric state also in the biosystems. When DETC was excess over endogenous iron ligands like citrate, ferric DETC complexes were directly observed with EPR spectroscopy at g=4.3. This was the case when isolated spinach leaves, endothelial cultured cells were incubated in the medium with 2.5mM DETC or mouse liver was perfused with 100mM DETC solution. After trapping NO, the nitrosylated Fe-DETC adducts are mostly in diamagnetic ferric state, with only a minor fraction having been reduced to paramagnetic ferrous state by endogenous biological reductants. In actual in vivo trapping experiments with mice, the condition of excess DETC was not met. The substantial quantities of iron in animal tissues were bound to ligands other than DETC, in particular citrate. These non-DETC complexes appear as roughly equal mixtures of ferric and ferrous iron. The presence of NO favors the replacement of non-DETC ligands by DETC. In all biological systems considered here, the nitrosylated Fe-DETC adducts appear as mixture of diamagnetic and paramagnetic states. The diamagnetic ferric nitrosyl complexes may be reduced ex vivo to paramagnetic form by exogenous reductants like dithionite. The trapping yields are significantly enhanced upon exogenous reduction, as proven by NO trapping experiments in plants, cell cultures and mice.

Detection of reactive oxygen species and nitric oxide in vascular cells and tissues: comparison of sensitivity and specificity

Reactive oxygen and nitrogen species are thought to contribute to pathogenesis of many cardiovascular diseases including hypertension, atherosclerosis, restenosis, heart failure, and diabetic vascular complications. Some of these reactive oxygen species also play an important role in vascular signaling. In this chapter, we describe various techniques that we have successfully employed to reliably measure superoxide and hydrogen peroxide. Because reactive oxygen species are capable of rapidly inactivating nitric oxide and because endothelial function characterized by nitric oxide bioavailability is an important indicator of vascular health, we have also included novel techniques capable of directly measuring nitric oxide radical from vascular cells and tissues.

Why iron–dithiocarbamates ensure detection of nitric oxide in cells and tissues

The in vivo mechanism of NO trapping by iron-dithiocarbamate complexes is considered. Contrary to common belief, we find that in biological systems the NO radicals are predominantly trapped by ferric iron-dithiocarbamates. Therefore, the trapping leads to ferric mononitrosyl complexes which are diamagnetic and cannot be directly detected with Electron Paramagnetic Resonance spectroscopy. The ferric mononitrosyl complexes are far easily reduced to ferrous state with L-cysteine, glutathione, ascorbate or dithiocarbamate ligands than their non-nitrosyl counterpart. When trapping NO in oxygenated biological systems, the majority of trapped nitric oxide is found in diamagnetic ferric mononitrosyl iron complexes. Only a minority fraction of NO is trapped in the form of paramagnetic ferrous mononitrosyl iron complexes with dithiocarbamate ligands. Subsequent ex vivo reduction of biological samples sharply increases the total yield of the paramagnetic mononitrosyl iron complexes. Reduction also eliminates the overlapping EPR spectrum from Cu(2+)-dithiocarbamate complexes. This facilitates the quantification of yields from NO trapping.

Specific detection of gaseous NO and 15NO in the headspace from liquid-phase reactions involving NO-generating organic, inorganic, and biochemical samples using a mid-infrared laser

Nitric oxide (NO) is an important biological signaling agent. The specific detection of NO represents a continuing challenge in the field of NO research. Many methods are currently employed for the detection of NO. Here, we report a qualitative but specific detection method for gaseous NO liberated in and from solution taking advantage of its low solubility. Importantly, our mid-infrared laser absorption method does not depend on any chemical derivatization of NO, and is applicable over a wide range of concentrations for both protein work and in organic-inorganic modeling work. We also apply this method to the specific detection of 15NO.

The MC3 receptor binding affinity of melanocortins correlates with the nitric oxide production inhibition in mice brain inflammation model

Melanocortins possess strong anti-inflammatory effects acting in the central nervous system via inhibition of the production of nitric oxide (NO) during brain inflammation. To shed more light into the role of melanocortin (MC) receptor subtypes involved we synthesized and evaluated some novel peptides, modified in the melanocyte-stimulating hormone (MSH) core structure, natural MCs and known MC receptor selective peptides - MS05, MS06. Since the study included both selective, high affinity binders and the novel peptides, it was possible to do the correlation analysis of binding activities and the NO induction-related anti-inflammatory effect of the peptides. beta-MSH, gamma1-MSH, gamma2-MSH, alpha-MSH, MS05, Ac-MS06 and Ac-[Ser12]MS06 caused dose dependent inhibition of the lipopolysaccharide (LPS)-induced increase of NO overproduction in the mice forebrain whereas MSH core modified peptides Ac-[Asp9,Ser12]MS06, [Asp9]alpha-MSH and [Asp16]beta-MSH were devoid of this effect in doses up to 10 nmol per mouse. When the minimal effective dose required for inhibition of NO production was correlated with the in vitro binding activity to MC receptor subtypes a strong and significant correlation was found for the MC3 receptor (r = 0.90; p = 0.0008), whereas weak correlation was present for the other receptors. Our results suggest that the MC3 receptor is the major player in mediating the anti-inflammatory activity of MCs in the central nervous system.

Beta-MSH inhibits brain inflammation via MC(3)/(4) receptors and impaired NF-kappaB signaling

The anti-inflammatory effects of melanocortin peptides have been demonstrated in different inflammation models. This is the first report describing the molecular mechanisms for the beta-MSH-induced suppression of bacterial lipopolisaccharide (LPS)-caused brain inflammation. We found that beta-MSH suppresses LPS-induced nuclear translocation of the transcription factor NF-kappaB, and inhibits the expression of inducible nitric oxide synthase, and the following nitric oxide overproduction in the brain, in vivo. Moreover, administering the preferentially MC(4) receptor selective antagonist HS014 blocked completely these effects, suggesting a tentative MC(4) receptor mediated mechanism of action for the beta-MSH. However, as HS014 shows quite low selectivity vis-à-vis the MC(3) receptor, a role for the MC(3) receptor cannot be excluded. In conclusion, our results show that beta-MSH is capable of inhibiting brain inflammation via activation of melanocortin receptors, of the subtypes 4 and/or 3.

Nitrite as the major source of nitric oxide production byArabidopsis thalianain response toPseudomonas syringae

The origin of nitric oxide (*NO) in plants is unclear and an *NO synthase (NOS)-like enzyme and nitrate reductase (NR) are claimed as potential sources. Here we used wild-type and NR-defective double mutant plants to investigate *NO production in Arabidopsis thaliana in response to Pseudomonas syringae pv maculicola. NOS activity increased substantially in leaves inoculated with P. syringae. However, electron paramagnetic resonance experiments showed a much higher *NO formation that was dependent on nitrite and mitochondrial electron transport rather than on arginine or nitrate. Overall, these results indicate that NOS, NR and a mitochondrial-dependent nitrite-reducing activity cooperate to produce *NO during A. thaliana-P. syringae interaction.

Discrimination of nitroxyl and nitric oxide by water-soluble Mn(III) porphyrins

The water-soluble manganese(III) meso-tetrakis (N-ethylpyridinium-2-yl) porphyrin (Mn(III)TEPyP) and manganese(III) meso-(tetrakis(4-sulfonato-phenyl)) porphyrinate (Mn(III)TPPS) are able to chemically distinguish between HNO and NO donors, reacting with the former in a fast, efficient, and selective manner with concomitant formation of the {MnNO}(7) complex (k(on(HNO)) approximately equal to 10(5) M(-1) s(-1)), while they are inert or react very slowly with NO donors. DFT calculations and kinetic data suggest that HNO trapping is operative at least in the case of Mn(III)TPPS, while catalytic decomposition of the HNO donors (sodium trioxodinitrate and toluene sulfohydroxamic acid) seems to be the main pathway for Mn(III)TEPyP. In the presence of oxygen, the product Mn(II)TEPyP(NO) oxidizes back to Mn(III)TEPyP, making it possible to process large ratios of nitroxyl donor with small amounts of porphyrin.

New methods to evaluate endothelial function: Evaluation of endothelial function by hemoglobin-nitric oxide complex using electron paramagnetic resonance spectroscopy

This minireview describes the practical use of assay systems to detect nitric oxide (NO) by electron paramagnetic resonance (EPR) spectroscopy for evaluation of endothelial functions. The iron(II)-dithiocarbamate complexes, such as iron(II)-(N-methyl-D-glucamine dithiocarbamate), are commonly used in EPR detection of NO both in vivo and in vitro. However, due to their redox activity, these complexes have some drawbacks that limit their usefulness for the detection of NO. On the other hand, the measurement of hemoglobin-NO adduct (HbNO) in whole blood by the EPR method seems relevant for the assessment of systemic NO levels. However, ceruloplasmin and an unknown radical species overlapping the same magnetic field as that of HbNO, which makes it physically impossible to measure small amounts of HbNO. Thus, to reveal the EPR spectrum of HbNO, we developed the EPR signal subtraction method, which is based on the computer-assisted subtraction of the digitized EPR spectrum of HbNO-depleted blood from that of the sample blood using software. Using this technique, we succeeded in measuring the steady blood HbNO level as an index of NO by the EPR HbNO signal subtraction method. We also demonstrated that temocapril reduces abnormalities of NO dynamics in the L-NAME (N(omega)-nitro-L-arginine-methylester)-induced endothelial dysfunction of rats using the EPR HbNO signal subtraction method.

Spin trapping of nitric oxide with the iron-dithiocarbamate complex: chemistry and biology

This brief review describes chemical and biological aspects concerning spin trapping of nitric oxide (NO) with the iron-dithiocarbamate (Fe-DTC) complex as a spin trap. Knowledge on basic properties of the Fe-DTC complex would help in understanding the applicability and limitation of the Fe-DTC-based NO spin-trapping method when it is employed in viable biological systems.

Detection of reactive oxygen and nitrogen species by EPR spin trapping

Electron paramagnetic resonance spin trapping has become an indispensable tool for the specific detection of reactive oxygen free radicals in biological systems. In this review we describe some of the advantages as well as some experimental considerations of this technique and how it can be applied to biological systems to measure oxidative stress.

Endogenous superoxide production and the nitrite/nitrate ratio control the concentration of bioavailable free nitric oxide in leaves

We have quantitatively measured nitric oxide production in the leaves of Arabidopsis thaliana and Vicia faba by adapting ferrous dithiocarbamate spin tapping methods previously used in animal systems. Hydrophobic diethyldithiocarbamate complexes were used to measure NO interacting with membranes, and hydrophilic N-methyl-d-glucamine dithiocarbamate was used to measure NO released into the external solution. Both complexes were able to trap levels of NO, readily detectable by EPR spectroscopy. Basal rates of NO production (in the order of 1 nmol g(-) (1) h(-1)) agreed with previous studies. However, use of methodologies that corrected for the removal of free NO by endogenously produced superoxide resulted in a significant increase in trapped NO (up to 18 nmol g(-) (1) h(-1)). Basal NO production in leaves is therefore much higher than previously thought, but this is masked by significant superoxide production. The effects of nitrite (increased rate) and nitrate (decreased rate) are consistent with a role for nitrate reductase as the source of this basal NO production. However, rates under physiologically achievable nitrite concentrations never approach that reported following pathogen induction of plant nitric-oxide synthase. In Hibiscus rosa sinensis, the addition of exogenous nitrite generated sufficient NO such that EPR could be used to detect its production using endogenous spin traps (forming paramagnetic dinitrosyl iron complexes). Indeed the levels of this nitrosylated iron pool are sufficiently high that they may represent a method of maintaining bioavailable iron levels under conditions of iron starvation, thus explaining the previously observed role of NO in preventing chlorosis under these conditions.

β- and γ-melanocortins inhibit lipopolysaccharide induced nitric oxide production in mice brain

The pro-opiomelanocortin-derived peptide alpha-melanocyte stimulating hormone (alpha-MSH) mediates many diverse physiological actions, including anti-inflammatory and immunomodulatory effects. However, little is known about the physiological roles of the other melanocortins, beta- and gamma-MSH. Here, we investigated the effects of melanocortin peptides in an in vivo neuroinflammation model. Six hours following intracisternal (i.c.) administration of 10 microg lipopolysaccharide (LPS) to mice a five-fold increase in the nitric oxide (NO) level was seen in the animals' brains, when detected by electron paramagnetic resonance (EPR). All tested melanocortins, alpha-, beta-, gamma1- and gamma2-MSH (0.001-10 nmol/mouse i.c.), dose dependently reduced the LPS induced increases in brain NO, with an order of effectiveness: beta-MSH > or = gamma1-MSH=gamma2-MSH>alpha-MSH. Our results suggest specialized functions of beta- and gamma-MSH melanocortins in inflammatory signal modulation in the brain.