Nitric oxide donors: biochemical pharmacology and therapeutics

Photo-controlled and photo-calibrated nanoparticle enabled nitric oxide release for anti-bacterial and anti-biofilm applications

After numerous efforts to elucidate the biological role of nitric oxide (NO), NO treatments have become a hotspot at the forefront of medicine. NO-releasing substances are constantly needed, while the direct use of NO gas is unattainable in bio-systems. An ideal NO donor should possess controllable and visible NO-release capability. The reported NO donating nanoparticles, prepared via encapsulating a hydrophobic NO-releasing compound into DSPE-PEG₂₀₀₀, meet the criteria mentioned previously. The localization and flux of NO released from these nanoparticles could be manipulated by UV or blue light. Meanwhile, NOD-NPs emit a dose-dependent fluorescence intensity to calibrate the generation of NO. While the good biocompatibility of NOD-NPs has been validated, the NO from our nanoparticles demonstrates efficient anti-bacterial and anti-biofilm effects toward Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Therefore, the NOD-NPs developed in this work have potential application in evaluating the regulation of microbes by NO.

Fluorescent sensing for some nitric oxide donors in dosage forms and biological matrices

New fluorescent sensing of some nitric oxide donors, nitroglycerin and isosorbide dinitrate was developed in our laboratories. Two fluorescent reagents, 2-(2-hydroxyethylamino)-4,6-dimethylpyridine-3-carbonitrile, 3a and 2-(3-chloro-phenylamino)-4,6-dimethylpyridine-3-carbonitrile, 3b were synthesized in our laboratories and a comparative study was performed between them from the point of fluorescence intensity. The fluorophore, 3a, was selected for the analytical study as it exhibit higher quantum yield value. The interaction between the selected drugs and the fluorophore was noticed to be quenching. The mechanism of quenching was studied and it was supposed to be collisional quenching through photo induced electron transfer process. The proposed sensing method was applied successfully for the analysis of nitroglycerin and isosorbide dinitrate in dosage forms within concentration range of (0.05-0.5 µg/mL) with percentage recoveries of 99.9 ± 0.5 and 99.9 ± 0.7 respectively. The studied drugs, nitroglycerin and isosorbide dinitrate, were also probed in spiked biological matrices such as plasma samples with percentage recoveries of 99.1 ± 1.97 and 100.7 ± 1.96 and urine samples with percentage recoveries of 100.4 ± 1.8 and 100.3 ± 1.7 respectively. In vivo analysis of both drugs in real plasma was also investigated. The sensing method exhibit well intra-day and inter day precision with %RSD < 2%.

NO, CO and H2S based pharmaceuticals in the mission of vision (eye health): a comprehensive review

A set of well defined signaling molecules responsible for normal functioning of human physiology including nitric oxide along with carbon monoxide and hydrogen sulphide are referred as “gasotransmitters”. Due to their involvement in almost every system of a human body, the care of highly sensitive organs using these molecules as drugs represents highly fascinating area of research. In connection with these interesting aspects, the applied aspects of these gaseous molecules in maintaining healthy eye and vision have been targeted in this review. Several examples of eye-droppers including NORMs like latanoprost and nipradiol, CORMs like CORM-3 and CORM-A1, and Hydrogen sulfide releasing system like GYY4137 have been discussed in this context. Therefore the relation of these trio-gasotransmitters with the ophthalmic homeostasis on one hand, and de-infecting role on the other hand has been mainly highlighted. Some molecular systems capable of mimicking gasotransmitter action have also been introduced in connection with the titled theme.

Endothelial dysfunction and body mass index: is there a role for plasma peroxynitrite?

BACKGROUND

Endothelial function is dependent on the balance between vasoconstrictive and vasodilatory substances. The endothelium ability to produce nitric oxide is one of the most crucial mechanisms in regulating vascular tone. An increase in inducible nitric oxide synthase contributes to endothelial dysfunction in overweight persons, while in underweight persons, oxidative stress contributes to the conversion of nitric oxide to peroxynitrite (measured as nitrotyrosine in vivo). The objective of this study was to elucidate the interaction of body composition and oxidative stress on vascular function and peroxynitrite. This was done through an experimental design with three weight groups (underweight normal weight and overweight), with four treatment arms in each. Plasma nitrotyrosine levels were measured 15-20 hours post lipopolysaccharide (LPS) treatment, as were aortic ring tension changes. Acetylcholine (ACh) and sodium nitroprusside (SNP) challenges were used to observe endothelial dependent and independent vascular relaxation after pre-constriction of aortic rings with phenylephrine.

RESULTS

Nitrotyrosine levels in saline-treated rats were similar among the weight-groups. There was a significant increase in nitrotyrosine levels between saline-treated rats and those treated with the highest lipopolysaccharide doses in each of the weight groups. In response to ACh challenge, Rmax (percentage reduction in aortic tension) was lowest in overweight rats (112%). In response to SNP, there was an insignificantly lower Rmax in the underweight (106%) compared to the normal weight (112%). Overweight rats had a significant decrease in Rmax (83%) in response to SNP, signifying involvement of a more chronic process in tension reduction changes. A lower Rmax accompanied an increase in peroxynitrite after acetylcholine challenge in all weight-groups.

CONCLUSIONS

Endothelial dysfunction, observed as an impairment in the ability to reduce tension, is associated with increased plasma peroxynitrite levels across the spectrum of body mass. In higher-BMI rats, an additional role is played by vascular smooth muscle in the causation of endothelial dysfunction.

A common humoral background of intraocular and arterial blood pressure dysregulation

BACKGROUND

It has been postulated that intraocular pressure, an important glaucoma risk factor, correlates positively with arterial blood pressure (blood pressure). However, results of experimental and clinical studies are often contradictory. It is hypothesized that, in some hypertensive patients, disturbances in intraocular pressure regulation may depend on biological effects of blood borne hormones underlying a particular type of hypertension, rather than on blood pressure level itself.

REVIEW

This review compares the effects of hormones on blood pressure and intraocular pressure, in order to identify a hormonal profile of hypertensive patients with an increased risk of intraocular pressure surge. The PUBMED database was searched to identify pre-clinical and clinical studies investigating the role of angiotensin II, vasopressin, adrenaline, noradrenaline, prostaglandins, and gaseous transmitters in the regulation of blood pressure and intraocular pressure.

RESULTS

Studies included in the review suggest that intraocular and blood pressures often follow a different pattern of response to the same hormone. For example, vasopressin increases blood pressure, but decreases intraocular pressure. In contrast, high level of nitric oxide decreases blood pressure, but increases intraocular pressure.

CONCLUSIONS

Arterial hypertension is associated with altered levels of blood borne hormones. Contradicting results of studies on the relationship between arterial hypertension and intraocular pressure might be partially explained by diverse effects of hormones on arterial and intraocular pressures. Further studies are needed to evaluate if hormonal profiling may help to identify glaucoma-prone patients.

Nitric oxide modulators: an emerging class of medicinal agents

Nitric oxide, a unique messenger in biological system, is ubiquitously present virtually in all tissues revealing its versatile nature of being involved in diverse physiological functions such as vascular tone, inhibition of platelet aggregation, cell adhesion, neurotransmission and enzyme and immune regulation. The tremendous advancements made in the past few decades in this area suggests that the nitric oxide modulation either by its exogenous release through nitric oxide donors or inhibition of its synthesis by nitric oxide synthase inhibitors in physiological milieu may provide newer clinical strategies for the treatment of some diseases. In this review, an attempt is made to document and understand the biological chemistry of different classes of nitric oxide modulators that would prove to be a fruitful area in the years to come.

Nitrates and nitrites in the treatment of ischemic cardiac disease

The organic nitrite, amyl of nitrite, was initially used as a therapeutic agent in the treatment of angina pectoris, but was replaced over a decade later by the organic nitrate, nitroglycerin (NTG), due to the ease of administration and longer duration of action. The administration of organic nitrate esters, such as NTG, continues to be used in the treatment of angina pectoris and heart failure since the birth of modern pharmacology. Their clinical effectiveness is due to vasodilator activity in large veins and arteries through an as yet unidentified method of delivering nitric oxide (NO), or a NO-like compound. The major drawback is the development of tolerance with NTG, and the duration and route of administration with amyl of nitrite. Although the nitrites are no longer used in the treatment of hypertension or ischemic heart disease, the nitrite anion has recently been discovered to possess novel pharmacologic actions, such as modulating hypoxic vasodilation, and providing cytoprotection in ischemia-reperfusion injury. Although the actions of these 2 similar chemical classes (nitrites and organic nitrates) have often been considered to be alike, we still do not understand their mechanism of action. Finally, the nitrite anion, either from sodium nitrite or an intermediate NTG form, may act as a storage form for NO and provide support for investigating the use of these agents in the treatment of ischemic cardiovascular states. We review what is presently known about the use of nitrates and nitrites including the historical, current, and potential uses of these agents, and their mechanisms of action.

Adaptation of rat gastric tissue against indomethacin toxicity

Indomethacin is used in the treatment of inflammatory diseases. But the drug toxicity limits its usage. This study investigated whether adaptation occurred after various dosages of repeated (chronic) indomethacin in rats to the gastro-toxic effects of indomethacin. It also examined whether the adaptation was related to oxidant-antioxidant mechanisms and oxidative DNA damage in gastric tissue. To illuminate the adaptation mechanism in the gastric tissue of rats given various dosages of chronic indomethacin, the levels of oxidants and antioxidants (GSH, MDA, NO, SOD and MPO), activities of COX-1 and COX-2 enzymes and oxidative DNA damage (8-OHd Gua/10(5) Gua) were measured. Results were compared to 25-mg/kg single-dose indomethacin group, and the role of oxidant and antioxidant parameters and oxidative DNA damage in the adaptation mechanism was evaluated. The average ulcer areas of gastric tissue of the 0.5-, 1-, 2-, 3-, 4-, and 5-mg/kg dosages of chronic indomethacin given to rats were 19.5+/-3.7, 12.5+/-3.3, 10+/-5.2, 4.5+/-3.6, 8.6+/-2.4, and 9.5+/-2.1mm(2), respectively. This rate was measured as 21.3+/-2.6mm(2) in the single-dose indomethacin group. Consequently, after various dosages of repeated (chronic) indomethacin administration in rats, it was observed that a clear adaptation developed against gastric damage and that gastric damage was reduced. The best adaptation was observed in the gastric tissue of the 3-mg/kg chronic indomethacin group. In parallel with the damage reduction, the oxidant parameters (MDA and MPO) and oxidative DNA damage (8-OHd Gua/10(5) Gua) were reduced, and the antioxidant parameters (GSH, NO and SOD) were increased. There is no relation between COX enzymes and adaptation mechanism. This circumstance shows that not COX-1 and COX-2 enzymes, oxidant and antioxidant parameters may play a role in the adaptation mechanism.

Localized delivery of nitric oxide from hydrogels inhibits neointima formation in a rat carotid balloon injury model

Using novel nitric oxide (NO)-generating polymeric hydrogels that can be rapidly photopolymerized in situ, we can deliver NO locally at the site of vascular injury. Depending on material design, these poly(ethylene glycol) (PEG)-based hydrogels can generate NO for up to 50 d. This study demonstrates the ability of nitric oxide-generating hydrogels (PEG-Cys-NO) to influence key components of the restenosis cascade both in vitro and in vivo. PEG-Cys-NO hydrogels inhibited smooth muscle cell proliferation, increased endothelial cell proliferation, and inhibited platelet adhesion in vitro. Moreover, in vivo, PEG-Cys-NO hydrogels inhibited intimal thickening in a rat carotid balloon injury model. The perivascular application of NO-generating polymers post-injury reduced neointima formation at 14 d by approximately 80% compared to controls (intimal area/medial area (I/M): PEG-Cys-NO=0.20+/-0.17, control=0.84+/-0.19, p<0.00002; intimal thickness: PEG-Cys-NO=12+/-10 microm, control=60+/-18 microm, p<0.00002). Treatment with the PEG-Cys-NO hydrogels caused a significant decrease in the per cent of proliferating cell nuclear antigen positive medial cells (29+/-5%) at 4 d as compared to treatment with the control hydrogels (51+/-1%, p<0.02). Additionally, vessel re-endothelialization at 14 d was slightly enhanced in the presence of the NO-generating hydrogels. These data indicate that localized delivery of NO from these hydrogels can significantly inhibit neointima formation in a rat carotid balloon injury model and suggest that these materials may be useful in preventing restenosis.

Clinical pharmacokinetics and pharmacodynamics of glyceryl trinitrate and its metabolites

This review discusses the pharmacokinetics and pharmacodynamics of glyceryl trinitrate (nitroglycerin; GTN) pertinent to clinical medicine. The pharmacokinetics of GTN associated with various dose regimens are characterised by prominent intra- and inter-individual variability. It is, nevertheless, important to clearly understand the pharmacokinetics and characteristics of GTN to optimise its use in clinical practice and, in particular, to obviate the development of tolerance. Measurements of plasma concentrations of GTN and of 1,2-glyceryl dinitrate (1,2-GDN), 1,3-glyceryl dinitrate (1,3-GDN), 1-glyceryl mononitrate (1-GMN), and 2-glyceryl mononitrate (2-GMN), its four main metabolites, remain difficult and require meticulous techniques to obtain reliable results. Since GDNs have an effect on haemodynamic function, pharmacokinetic analyses that include the parent drug as well as the metabolites are important. Although the precise mechanisms of GTN metabolism have not been elucidated, two main pathways have been proposed for its biotransformation. The first is a mechanism-based biotransformation pathway that produces nitric oxide (NO) and contributes directly to vasodilation. The second is a clearance-based biotransformation or detoxification pathway that produces inorganic nitrite anions (NO(2) -). NO(2) - has no apparent cardiovascular effect and is not converted to NO in pharmacologically relevant concentrations in vivo. In addition, several non-enzymatic and enzymatic systems are capable of metabolising GTN. This complex metabolism complicates considerably the evaluation of the pharmacokinetics and pharmacodynamics of GTN. Regardless of the route of administration, concentrations of the metabolites exceed those of the parent compound by several orders of magnitude. During continuous steady-state delivery of GTN, for instance by a patch, concentrations of 1,2-GDN are consistently 2-7 times higher than those of 1,3-GDN, and concentrations of 2-GMN are 4-8 times higher than those of 1-GMN. Concentrations of GDNs are approximately 10 times higher, and of GMNs approximately 100 times higher, than those of GTN during sustained administration. The development of tolerance is closely related to the metabolism of GTN, and can be broadly categorised as haemodynamic tolerance versus vascular tolerance. Efforts are warranted to circumvent the development of tolerance and facilitate the use of GTN in clinical practice. Although this remains to be accomplished, it is likely that, in the near future, regimens will be developed based on a full understanding of the pharmacokinetics and pharmacodynamics of GTN and its metabolites.

Interaction between nitric oxide and subsets of human T lymphocytes with differences in glutathione metabolism

Nitric oxide (NO) modulates human T-lymphocyte responses through several mechanisms. In the current study we show that interactions between NO and glutathione (GSH) metabolism are related to the selective persistent inhibition of interferon-gamma (IFN-gamma) production by NO, which we previously identified. T cells were exposed to NO using the NO-donor compound Spermine-nonoate (Sper) and activated using anti-CD3 plus anti-CD28 monoclonal antibodies. Persistent inhibition of IFN-gamma by Sper was prevented by addition of the GSH precursor l-cysteine, which inhibits Sper induced GSH depletion. Subsets of cells were either susceptible (GSH(low)) or resistant (GSH(high)) to NO-induced GSH depletion. The GSH(low) subset was characterized by enhanced numbers of CD4+ cells, reduced numbers of activated cells as characterized by CD25 and CD69, and reduced numbers of memory (CD45RO+) cells relative to the GSH(high) population. Rather than directly affecting susceptibility to NO, these surface markers reflected different expression patterns. Particularly, the GSHlow subset was further characterized by decreased activity of the GSH synthesis related enzymes multi-drug resistance related protein (MRP)-1 and gamma-glutamyltranspeptidase (gamma-GT). Blocking gamma-GT, using acivicin was shown to exacerbate NO-induced GSH depletion and NO-induced apoptosis. Since NO induced apoptosis selectively affects IFN-gamma production these findings implicate GSH metabolism in the modulation and maintenance of the T helper (Th)1/Th2 balance.

Role of nitric oxide in histamine release from human basophils and rat peritoneal mast cells

The effects of a range of nitric oxide (NO)-related compounds on histamine release from human basophils and rat peritoneal mast cells were studied. Basal and immunologic histamine releases from human basophils were not affected by N(omega)-nitro-L-arginine, N(omega)-nitro-L-arginine methyl ester, aminoguanidine or methylene blue (all inhibitors of NO production), sodium nitroprusside (an NO donor), L-arginine (a substrate for NO synthase) or D-arginine (the inactive enantiomer of L-arginine). In rat peritoneal mast cells, NO donors such as sodium nitroprusside, sodium nitrite and sodium nitrate, and lipopolysaccharide (an inducer of NO synthase) had little effect on basal histamine release, while 3-morpholino-sydnonimine (SIN-1, an NO donor), L-arginine and D-arginine increased this release by up to threefold. None of the inhibitors of NO production had any striking effect on histamine release induced by anti-rat immunoglobulin E (IgE), compound 48/80, sodium fluoride, phospholipase C, 1,2-dioctanoyl-sn-glycerol or ionophore A23187. However, haemoglobin was found to inhibit histamine release by anti-rat IgE or A23187 by ca. 40%. Alone of the NO donors, low concentrations of L-arginine produced a mild inhibition of histamine release induced by anti-IgE, compound 48/80 and A23187, but not other ligands, while sodium nitroprusside dose-dependently inhibited (by a maximum of ca. 30%) histamine release by anti-rat IgE, sodium fluoride or A23187. Stimulation with a variety of secretagogues or treatment with L-arginine, D-arginine, lipopolysaccharide, SIN-1 or sodium nitroprusside had no effect on NO production. Similarly, L-arginine, D-arginine or sodium nitroprusside did not change intracellular cGMP levels. On the basis of these results, it is suggested that NO does not play a significant role in the modulation of histamine release from human basophils or rat peritoneal mast cells. The effects of L-arginine, D-arginine and sodium nitroprusside may involve mechanisms unrelated to NO.

Therapeutic potential of endothelin receptor antagonists and nitric oxide donors in pulmonary hypertension

Pulmonary hypertension can occur idiopathically as a primary disorder of the pulmonary circulation or more commonly, it can exist as a haemodynamic manifestation of a wide variety of pulmonary and cardiovascular diseases, including acute lung injury, chronic obstructive lung disease, congenital heart disease, mitral stenosis, chronic left-sided congestive heart failure and connective tissue diseases such as scleroderma. Pulmonary hypertension is associated with changes in vascular tone as well as vascular structure, with the relative contribution of each dependent upon the aetiology of the increased pulmonary vascular resistance. Most currently available treatments utilise anticoagulants as well as vasodilator drugs that only attenuate the vasoconstrictive component of the disease. The latter category includes oral calcium channel blockers, iv. and aerosolised prostacyclin analogues and inhaled nitric oxide but all three classes of vasodilators have disadvantages and limitations. Treatment with vasodilators is often ineffective in patients with longstanding pulmonary hypertension in which structural changes contribute significantly to the pulmonary hypertension, blood flow obstruction and right heart failure. In view of the immense clinical need, new therapies are being developed by pharmaceutical companies to treat pulmonary hypertension. This update will focus on the current development status of endothelin receptor antagonists and nitric oxide donors for the treatment of pulmonary hypertension.

O-Alkylation of cupferron: aiming at the design and synthesis of controlled nitric oxide releasing agents

O-Alkylation of N-nitroso-N-phenylhydroxylamine ammonium salt (cupferron) was studied for the synthesis of novel nitric oxide (NO) releasing agents. The alkylation occurred regioselectively at the terminal oxygen, leading to a single product N-(alkyloxy)-N'-phenyldiimide N'-oxide as indicated by NMR and X-ray analysis. The O-alkyl derivatives exhibited significantly improved stability compared to their parent compound, cupferron. It was demonstrated that the cupferron O-alkyl derivatives could function as photoreleasing NO donor compounds. N-(N"-acetylphenylalanylmethylenyloxy)-N'-phenyldiimide N'-oxide), which linked the cupferron portion with an amino acid via an acetal moiety, was synthesized as an model NO prodrug where controlled NO release would occur either by increasing pH or by a protease-catalyzed hydrolysis.

Calcitonin gene-related peptide-dependent vascular relaxation of rat aorta. An additional mechanism for nitroglycerin

We investigated the involvement of calcitonin gene-related peptide (CGRP) in the vasodilatory mechanism of action of nitric oxide (NO) donors. The functional role of CGRP in NO donor-induced vasodilation of isolated rat aortic rings was determined by incubating these drugs with and without CGRP(8-37), a selective CGRP receptor antagonist. CGRP(8-37) (0.63 microM) induced rightward shifts in the vasodilatory concentration-response curves for nitroglycerin (NTG), Piloty's acid (PA), and SIN-1 (linsidomine). The EC(50) values for NTG, PA, and SIN-1 were increased by 8.3-, 5.2-, and 2.3-fold, respectively (P < 0.05). The release of CGRP from rat aorta in response to NTG and PA was measured specifically by radioimmunoassay. Thirty-minute incubations of NTG or PA with rat aorta induced 189.5 and 214.6% increases, respectively, in CGRP release when compared with the control (P < 0.05). The concentration-response curves of sodium nitroprusside (SNP), S-nitroso-acetylpenicillamine (SNAP), tetranitromethane (TNM), diethylamine NO complex (DEA-NO), and diethylenetriamine/nitric oxide adduct (DETA NONOate) were not inhibited significantly by CGRP(8-37) co-incubation (P 0.05). NO donors also were incubated with aortic strips, and NTG and PA alone induced significant formation of hydroxylamine, a NO(-) metabolite (232.4 and 364.9%, respectively, P < 0.05). These results indicate that only NTG and PA, and to a lesser extent SIN-1, stimulate the release of CGRP from the rat aorta, which subsequently contributes to the vasodilatory activity of these agents. The hydroxylamine formation suggests a possible link between NO(-) generation and CGRP release from the vascular wall.

Anandamide uptake by human endothelial cells and its regulation by nitric oxide

Anandamide (AEA) has vasodilator activity, which can be terminated by cellular re-uptake and degradation. Here we investigated the presence and regulation of the AEA transporter in human umbelical vein endothelial cells (HUVECs). HUVECs take up AEA by facilitated transport (apparent K(m) = 190 +/- 10 nm and V(max) = 45 +/- 3 pmol. min(-1).mg(-1) protein), which is inhibited by alpha-linolenoyl-vanillyl-amide and N-(4-hydroxyphenyl)-arachidonoylamide, and stimulated up to 2.2-fold by nitric oxide (NO) donors. The NO scavenger hydroxocobalamin abolishes the latter effect, which is instead enhanced by superoxide anions but inhibited by superoxide dismutase and N-acetylcysteine, a precursor of glutathione synthesis. Peroxynitrite (ONOO(-)) causes a 4-fold activation of AEA transport into cells. The HUVEC AEA transporter contributes to the termination of a typical type 1 cannabinoid receptor (CB(1)) -mediated action of AEA, i.e. the inhibition of forskolin-stimulated adenylyl cyclase, because NO/ONOO(-) donors and alpha-linolenoyl-vanillyl-amide/N-(4-hydroxyphenyl)-arachidonoylamide were found to attenuate and enhance, respectively, this effect of AEA. Consistently, activation of CB(1) cannabinoid receptors by either AEA or the cannabinoid HU-210 caused a stimulation of HUVEC inducible NO synthase activity and expression up to 2.9- and 2. 6-fold, respectively. Also these effects are regulated by the AEA transporter. HU-210 enhanced AEA uptake by HUVECs in a fashion sensitive to the NO synthase inhibitor Nomega-nitro-l-arginine methyl ester. These findings suggest a NO-mediated regulatory loop between CB(1) cannabinoid receptors and AEA transporter.

Oxidative stress and S-nitrosylation of proteins in cells

The effect of prolonged exposure to nitric oxide on enzymes involved in cell metabolism was investigated in T lymphocyte-derived Jurkat and L929 fibroblast human cell lines using a constant concentration of nitric oxide (1.5 microM) released by the nitric oxide donor DETA-NO (0.5 mM). Nitric oxide inhibited immediately the respiration of the cells acting reversibly at complex IV. With time, the inhibition became progressively persistent, i.e. not reversed by trapping of nitric oxide with oxyhaemoglobin, and was preceded by a decrease in the concentration of the intracellular reduced glutathione. This persistent effect of nitric oxide on respiration was due to inhibition of complex I activity which could be reversed by addition of reduced glutathione or by cold light, suggesting that it was due to S-nitrosylation of thiols necessary for the activity of the enzyme. The activity of other enzymes also known to be susceptible to inhibition by S-nitrosylation, i.e. glyceraldehyde-3-phosphate dehydrogenase and glutathione reductase, was progressively decreased by exposure to nitric oxide with a similar time course to that observed for the inhibition of complex I. Furthermore, inhibition of these enzymes only occurred when the concentrations of reduced glutathione had previously fallen and could be prevented by increasing the intracellular concentrations of reduced glutathione. Our results suggest that S-nitrosylation of different enzymes by nitric oxide may occur only if the reducing potential of the cells is impaired.

para-Substituted N-nitroso-N-oxybenzenamine ammonium salts: a new class of redox-sensitive nitric oxide releasing compounds

N-Nitroso-N-oxybenzenamine ammonium salts with -OMe, -Me, -H, -F, -Cl, -CF3, and -SO2Me substituents at the para position of the phenyl ring constitute a new class of-redox sensitive nitric oxide (NO) releasing compounds. These compounds yield nitric oxide and the corresponding nitrosobenzene derivatives by a spontaneous dissociation mechanism after undergoing a one electron oxidation. Oxidation of these compounds can be achieved through chemical, electrochemical and enzymatic methods. It was observed electrochemically that the amount of NO generated was dependent on the substituent effect and the applied oxidation potential. Electron-withdrawing substituents increase the oxidation potential of the compound. A linear correlation was observed when the peak potentials for the oxidation were graphed versus the Hammett substituent constant. Density functional theory calculations were also performed on this series of compounds. The theoretical oxidation energies of the corresponding anions show a strong linear correlation with the experimental potentials. Furthermore, enzymatic oxidation using horseradish peroxidase showed a similar substituent effect. These results indicate that substitution at the para position of the phenyl ring has a profound effect on the stability, oxidation potential and enzymatic kinetic properties of the compounds. Thus para-substituted N-nitroso-N-oxybenzenamine salts comprise a new class of redox-sensitive nitric oxide releasing agents.

Endothelial dysfunction and peroxynitrite formation are early events in angiotensin-induced cardiovascular disorders

Angiotensin II (ANG II) is a well-established participant in many cardiovascular disorders, but the mechanisms involved are not clear. Vascular cell experiments suggest that ANG II is a potent stimulator of free radicals such as superoxide anion, an agent known to inactivate nitric oxide and promote the formation of peroxynitrite. Here we hypothesized that ANG II reduces the efficacy of NO-mediated vascular relaxation and promotes vascular peroxynitrite formation in vivo. ANG II was infused in rats at sub-pressor doses for 3 days. Systolic blood pressure and heart rate were unchanged on day 3 despite significant reductions in plasma renin activity. Thoracic aorta was isolated for functional and immunohistochemical evaluations. No difference in isolated vascular contractile responses to KCI (125 mM), phenylephrine, or ANG II was observed between groups. In contrast, relaxant response to acetylcholine (ACh) was decreased sixfold without a change in relaxant response to sodium nitroprusside. Extensive prevalence of 3-nitrotyrosine (3-NT, a stable biomarker of tissue peroxynitrite formation) immunoreactivity was observed in ANG II-treated vascular tissues and was specifically confined to the endothelium. Digital image analysis demonstrated a significant inverse correlation between ACh relaxant response and 3-NT immunoreactivity. These data demonstrate that ANG II selectively modifies vascular NO control at sub-pressor exposures in vivo. Thus, endothelial dysfunction apparently precedes other established ANG II-induced vascular pathologies, and this may be mediated by peroxynitrite formation in vivo. Wattanapitayakul, S., Weinstein, D. M., Holycross, B. J., Bauer, J. A. Endothelial dysfunction and peroxynitrite formation are early events in angiotensin-induced cardiovascular disorders.

Nitric oxide controls src kinase activity through a sulfhydryl group modification-mediated Tyr-527-independent and Tyr-416-linked mechanism

c-Src kinase was activated when either murine NIH3T3 fibroblast cells or immunoprecipitated c-Src proteins were treated with nitric oxide generator, S-nitroso-N-acetyl penicillamine (SNAP) or sodium nitroprusside. Nitric oxide (NO) scavenger hemoglobin and N(2)O(3) scavenger homocysteine abolished the SNAP-mediated c-Src kinase activation. Phosphoamino acid analysis and peptide mapping of in vitro labeled phospho-c-Src proteins revealed that SNAP promoted the autophosphorylation at tyrosine, which preferentially took place at Tyr-416. Peptide mapping of in vivo labeled c-Src kinase excluded the involvement of phospho-Tyr-527 dephosphorylation in the SNAP-mediated activation mechanism. Correspondingly, protein-tyrosine phosphatase inhibitor Na(3)VO(4) did not abolish the SNAP-mediated activation of Src kinase, and the constitutively activated v-Src kinase was also further up-regulated in activity by SNAP. SNAP, however, failed to up-regulate the kinase activity of Phe-416 mutant v-Src. 2-Mercaptoethanol or dithiothreitol, which should disrupt N(2)O(3)-mediated S-nitrosylation and subsequent formation of the S-S bond, abolished the up-regulated catalytic activity, and the activity was regained after re-exposing the enzyme to SNAP. Exposure of Src kinase to SNAP promoted both autophosphorylation and S-S bond-mediated aggregation of the kinase molecules, demonstrating a linkage between the two events. These results suggest that the NO/N(2)O(3)-provoked S-nitrosylation/S-S bond formation destabilizes the Src structure for Tyr-416 autophosphorylation-associated activation bypassing the Tyr-527-linked regulation.

In vitro comparison of two NONOates (novel nitric oxide donors) on rat pulmonary arteries

The pulmonary vasorelaxant properties of two NONOates (diazeniumdiolates) were examined because this novel group of nitric oxide (NO) donors may be useful in pulmonary hypertension. MAHMA NONOate ((Z)-1-¿N-Methyl-N-[6-(N-methylammoniohexyl)amino]¿ diazen-1-ium-1,2-diolate) and spermine NONOate ((Z)- 1-¿N-[3-aminopropyl]-N-[4-(3-aminopropylammonio)butyl]-amino¿di azen-1-ium-1,2-diolate) decomposed at different rates (half-lives 1.3 min and 73 min, respectively; 37 degrees C, pH 7.3) but generated the same total amount of NO. They fully relaxed submaximally contracted ring preparations of main and intralobar pulmonary arteries from rats. Responses were inhibited by the guanylate cyclase inhibitor, ODQ (1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one). Potency was not affected by choice of contractile spasmogen (phenylephrine, endothelin-1, thromboxane-mimetic) or endothelium removal, and tolerance did not develop; thus the drugs had properties important for use in pulmonary hypertension. MAHMA NONOate was 10-40-fold more potent than spermine NONOate but responses to spermine NONOate were more sustained (spermine NONOate > 60 min; MAHMA NONOate < 7 min). It is concluded that the differences in potency and time-course reflect the different rates of NO generation by these NONOates.

Sodium nitroprusside enhances contractions of the guinea-pig isolated vas deferens

The effects of sodium nitroprusside on the electrical and mechanical properties of the smooth muscle of the guinea-pig vas deferens, and its responses to transmitter substances, have been investigated by use of the sucrose-gap technique. Isolated longitudinal segments of guinea-pig vas deferens contracted in response to electrical field stimulation (100 V, 0.04-0.1 ms, 1-5 Hz, 10 s train every 60 s) and application of ATP (1 mM) or noradrenaline (10 microM). Sodium nitroprusside (0.1 mM) did not affect resting tension but did enhance contractions evoked by electric-field stimulation but not by ATP or noradrenaline. The sodium nitroprusside-induced enhancement was unaffected by the nitric oxide synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME) (0.1 mM). Conversely, electrically evoked contractions were unaffected by the nitric oxide precursor L-arginine (1 mM) or the nitric oxide donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) (0.1 mM). The amplitudes of electrically evoked excitatory junction potentials (EJPs) were not affected by application of sodium nitroprusside, although it caused a small depolarization of 0.7+/-0.3 mV. Similarly, the depolarization caused by exogenous application of ATP or noradrenaline was unaffected by the presence of sodium nitroprusside. L-NAME, L-arginine and SNAP did not affect EJP amplitude or baseline membrane potential. It is concluded that sodium nitroprusside enhances electrically evoked contractions of the guinea-pig vas deferens by reducing the threshold voltage for action potential firing in smooth-muscle cells.

In vivo production of nitric oxide in rats after administration of hydroxyurea

The metabolism of nitrovasodilators such as glyceryl trinitrate and nitroprusside provides the active moiety of these drugs (that is, nitric oxide). This process is not limited to the known nitrovasodilators, but also occurs with nitroaromatic antimicrobials. Here we report that the administration of hydroxyurea, an antitumor drug, to rats at pharmacological doses formed detectable nitrosyl hemoglobin, which increased with dose. At higher doses, nitrosyl hemoprotein complexes could also be detected in liver tissue. [15N]hydroxyurea was synthesized and compared with [14N]hydroxyurea. These observations verified that nitric oxide detected as nitrosyl hemoglobin or nitrosyl hemoprotein complexes in rats was the result of the metabolism of hydroxyurea. The time course and dose-dependence of nitric oxide generation were also investigated. Hydroxyurea's antineoplastic activity is caused by its direct action on ribonucleotide reductase, the rate-limiting enzyme in DNA synthesis. Because nitric oxide also inhibits ribonucleotide reductase, this metabolite may supplement this action of hydroxyurea. In addition, the known ability of hydroxyurea to ease the pain of sickle cell anemia patients may be the result of vasodilation by the drug-derived nitric oxide.

Modulation of bradykinin receptor ligand binding affinity and its coupled G-proteins by nitric oxide

To determine whether nitric oxide (NO) can modulate bradykinin (BK) signaling pathways, we treated endothelial cells with an NO donor, S-nitrosoglutathione (GSNO), to determine its effect(s) on G-proteins (Gi and Gq) that are coupled to the type II kinin (BK2) receptor. Radioligand binding assays and Western analyses showed that GSNO (10-500 microM, 0-72 h) did not alter the expression of BK2 receptor, Gi, or Gq. However, GSNO caused a 6-fold increase in basal cGMP production and decreased high affinity BK bindings sites and GTPase activity by 74 and 85%, respectively. The cGMP analogue, dibutyryl-cGMP, also inhibited BK-stimulated GTPase activity by 74% suggesting that some of the effects of NO may be mediated through activation of guanylyl cyclase. The NO synthase inhibitor, Nomega-monomethyl-L-arginine, inhibited endogenous NO synthase activity and cGMP production by 91 and 76%, respectively, but increased BK-stimulated GTPase activity by 61%. To determine which G-proteins are affected by NO, we performed GTP binding assays with [35S]GTPgammaS followed by immunoprecipitation with specific G-protein antisera. Both GSNO and dibutyryl-cGMP increased basal G-protein GTP binding activities by 18-26%. However, GSNO decreased BK-stimulated Galphai2, Galphai3, and Galphaq/11 GTP binding activity by 93, 61, and 90%, respectively, whereas epinephrine-stimulated Galphas GTP binding activity was unaffected. These results suggest that NO can modulate BK signaling pathways by selectively inhibiting G-proteins of the Gi and Gq family.

Role of vascular nitric oxide in physiological and pathological conditions

This review describes the ability of certain diseases, such as essential hypertension, atherosclerosis, angina, and vasospasm, to reduce vascular nitric oxide (NO) formation or to increase its metabolism. In contrast, others, such as hypotension, sepsis, stroke, myocardial depression, and inflammatory responses, increase NO synthesis. The mechanism implicated in the changes in the formation and metabolism of NO are described. To prevent or treat these pathological processes, in which a deficiency in vascular NO formation plays a causative role, NO may be provided through methods such as direct NO administration or indirect NO supply through either NO donors or L-arginine, which facilitates NO formation.