Effects of the nitric oxide-donor, GEA 3175, on guinea-pig airways

Physiology of nitric oxide in the respiratory system

Nitric oxide (NO) is an important endogenous neurotransmitter and mediator. It participates in regulation of physiological processes in different organ systems including airways. Therefore, it is important to clarify its role in the regulation of both airway and vascular smooth muscle, neurotransmission and neurotoxicity, mucus transport, lung development and in the. surfactant production. The bioactivity of NO is highly variable and depends on many factors: the presence and activity of NO-producing enzymes, activity of competitive enzymes (e.g. arginase), the amount of substrate for the NO production, the presence of reactive oxygen species and others. All of these can change NO primary physiological role into potentially harmful. The borderline between them is very fragile and in many cases not entirely clear. For this reason, the research focuses on a comprehensive understanding of NO synthesis and its metabolic pathways, genetic polymorphisms of NO synthesizing enzymes and related effects. Research is also motivated by frequent use of exhaled NO monitoring in the clinical manifestations of respiratory diseases. The review focuses on the latest knowledge about the production and function of this mediator and understanding the basic physiological processes in the airways.

Potential Protective Properties of a Stable, Slow-releasing Nitric Oxide Donor, GEA 3175, in the Lung

Nitric oxide (NO), is known to exert vasodilatory, bronchodilatory, and antiplatelet effects, and quantitative or functional NO deficiency has been implicated in various cardio-vascular and airway diseases. NO donors, which are drugs capable of releasing NO either spontaneously or tissue-dependently, represent a way of increasing NO. Here, we review our current understanding of the NO donor, GEA 3175, 1,2,3,4-oxatriazolium, 3-(3-chloro-2-methylphenyl)-5-[[(methylphenyl)sulphonyl]amino], hydroxide inner salt. GEA 3175 is a mesoionic 3-aryl substituted oxatriazole-5-imine derivative, which is a potent, stable, slow releasing NO donor with important actions in various organ systems. In isolated guinea pig trachea, rat bronchi and bovine and human small bronchioles, GEA 3175 induces potent, long-lasting relaxation. In vivo, in sensitized guinea pigs, GEA 3175 protects against antigen-induced bronchoconstriction. GEA 3175 also exerts potent vasodilatory properties. In isolated human pulmonary arteries, GEA 3175 induces relaxation which is long-lasting and more potent than in airways. In isolated systemic arteries, GEA 3175 is also a potent vasodilator. By intravenous infusion GEA 3175 reduces blood pressure similarly to nitroglycerin. Vascular and bronchiolar relaxations were shown to be mediated via NO dependent pathways. GEA 3175 is also a potent anti-inflammatory agent. Functions of polymorphnuclear cells (PMNs) such as leucotriene B(4) (LTB(4)) - synhesis, chemotaxis and superoxide (O(-) (2)) production are inhibited by GEA 3175. GEA3175 also inhibits upregulation of E-selectin in human umbilical vein endothelial cells (HUVECs) and hence adhesion of neutrophils. Another action of GEA 3175 on the endothelium is inhibition of prostacyclin release. Finally, GEA 3175 has been demonstrated to be an antiplatelet agent. Thrombin-induced platelet aggregation was inhibited by GEA 3175 in a cyclic GMP- and vasodilator-stimulated phosphoprotein (VASP)-phosphorylation-dependent manner. Thus, GEA 3175 has been demonstrated to exert bronchodilatory, pulmonary vasodilatory, antiplatelet as well as anti-inflammatory actions. Given these actions GEA 3175 may represent a potentially useful drug. The exact mechanism whereby GEA 3175 releases NO is, however, still unknown. In addition, most of the studies so far have been performed in isolated tissue preparations. Clearly, further in vivo studies involving animal models are required to clarify safety issues and whether GEA 3175 can be used in the treatment of pulmonary hypertension and/or airway diseases.

Dual actions of dephostatin on the nitric oxide/cGMP-signalling pathway in porcine iliac arteries

We examined the effects of the nitrosoamine dephostatin on the nitric oxide (NO)/cyclic guanosine 3',5'-monophosphate (cGMP)-signalling in porcine iliac arteries. Dephostatin has been characterised as a tyrosine phosphatase inhibitor, but Western blot analyses showed that dephostatin did not augment tyrosine phosphorylation of arterial proteins. However, dephostatin relaxed pre-contracted arteries, and this effect was antagonised by the soluble guanylyl cyclase inhibitor 1H[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). Furthermore, dephostatin increased the cGMP content and the serine phosphorylation of vasodilator-stimulated phosphoprotein. Dephostatin also inhibited the relaxation induced by acetylcholine and the NO-donor S-nitroso-N-acetyl-penicillamine (SNAP). In contrast, dephostatin did not affect the NO-dependent actions of 1,2,3,4-Oxatriazolium, 3-(3-chloro-2-metylphenyl)-5-[[(4methylphenyl)sulfonyl]amino]-hydroxide inner salt (GEA 3175). Measurement of NO revealed that dephostatin accelerated the consumption of NO. In conclusion, dephostatin exerts dual effects on the NO/cGMP-signalling pathway in iliac arteries. The drug actions included scavenging of NO, but also stimulation of cGMP production. These effects were not related to inhibition of tyrosine phosphatases.

Cross-talk between adenosine and the oxatriazole derivative GEA 3175 in platelets

We examined the interplay between adenosine and the nitric oxide (NO)-containing oxatriazole derivative GEA 3175 in human platelets. The importance of cyclic guanosine 3'5'-monophosphate (cGMP)-inhibited phosphodiesterases (PDEs) was elucidated by treating the platelets with adenosine combined with either GEA 3175 or the PDE3-inhibitor milrinone. The drug combinations provoked similar cyclic adenosine 3'5'-monophosphate (cAMP) responses. On the contrary, cGMP levels were increased only in GEA 3175-treated platelets. Both drug combinations reduced P-selectin exposure, platelet adhesion and fibrinogen-binding. However, adenosine together with GEA 3175 was more effective in inhibiting platelet aggregation and ATP release. Thrombin-induced rises in cytosolic Ca2+ were suppressed by the two drug combinations. Adenosine administered with GEA 3175 was, however, more effective in reducing Ca2+ influx. In conclusion, the interaction between adenosine and GEA 3175 involves cGMP-mediated inhibition of PDE3. The results also imply that inhibition of Ca2+ influx represent another cGMP-specific mechanism that enhances the effect of adenosine.

Dual impact of a nitric oxide donor, GEA 3175, in human pulmonary smooth muscle

Nitric oxide (NO) donors could constitute an alternative to inhaled NO as treatment in some patients with pulmonary hypertension. Therefore, the present study investigated the relaxation mechanisms of a novel NO donor, 3-(3-chloro-2-methylphenyl)-5-[[4-methylphenyl)sulphonyl]amino]-)hydroxide (GEA 3175) in segments of human pulmonary arteries and bronchioles, which were mounted in microvascular myographs. GEA 3175 induced concentration-dependent relaxations and was more potent in pulmonary arteries than in bronchioles. A blocker of soluble guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), and iberiotoxin, a blocker of large-conductance calcium-activated K channels, both reduced relaxations induced by GEA 3175 in pulmonary arteries and bronchioles. Combining of ODQ and iberiotoxin did not produce additional inhibition. GEA 3175 relaxation is mediated through guanylyl cyclase-dependent mechanisms followed by activation of large-conductance calcium-activated K(+) channels. The dilatation of both pulmonary small arteries and airways by GEA 3175 seems advantageous, if it is considered administered as inhalation therapy for pulmonary hypertension.

Characterisation of GEA 3175 on human platelets; comparison with S-nitroso-N-acetyl-D,L-penicillamine

By comparing the effect of two nitric oxide (NO)-containing compounds, we found that S-nitroso-N-acetyl-D,L-penicillamine (SNAP), but not GEA 3175 (1,2,3,4-Oxatriazolium,3-(3-chloro-2-metylphenyl)-5-[[(4-methylphenyl)sulfonyl]amino]-, hydroxide inner salt), released NO. Despite this, both drugs elevated cyclic guanosine 3',5'-monophosphate (cGMP) levels in human platelets. However, SNAP was more effective after short exposure times (5 and 20 s). The compounds also inhibited thrombin-induced rises in cytosolic Ca2+. Time studies revealed that the action of SNAP rapidly declined by increasing the length of incubation (from 5 s to 30 min). This desensibilisation phenomenon mainly involved the release of Ca2+ from intracellular stores. In comparison, GEA 3175-induced inhibition of cytosolic Ca2+ signalling was much more long-lasting. The soluble guanylyl cyclase (sGC) inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) reversed the effect of GEA 3175 on cytosolic Ca2+. Consequently, this inhibition depends solely on the increase in cGMP. In summary, differences between GEA 3175 and SNAP were observed in NO releasing, cGMP elevating and Ca2+ suppressive properties.

Nitric oxide in respiratory diseases

The formation and modulation of nitric oxide (NO) in the lungs is reviewed. Its beneficial and deleterious roles in airways diseases, including asthma, chronic obstructive pulmonary disease, and cystic fibrosis, and in animal models is discussed. The pharmacological effects of agents that modulate NO production or act as NO donors are described. The clinical pharmacology of these agents is described and the therapeutic potential for their use in airways disease is considered.

Glutathione and other low-molecular-weight thiols relax guinea pig trachea ex vivo: interactions with nitric oxide?

The aim of this study was to determine the effects of glutathione (GSH) on trachea smooth muscle tension in view of previously reported interactions between GSH and nitric oxide (NO) (Gaston B. Biochim Biophys Acta 1411: 323-333, 1999; Kelm M. Biochim Biophys Acta 1411: 273-289, 1999; and Kharitonov VG, Sundquist AR, and Sharma VS. J Biol Chem 270: 28158-28164, 1995) and the high (millimolar) concentrations of GSH in trachea epithelium (Rahman I, Li XY, Donaldson K, Harrison DJ, and MacNee W. Am J Physiol Lung Cell Mol Physiol 269: L285-L292, 1995). GSH and other thiols (1.0-10 mM) dose dependently decreased the tension in isolated guinea pig tracheas. Relaxations by GSH were paralleled with sevenfold increased nitrite levels (P < 0.05) in the tracheal effluent, suggesting an interaction between GSH and NO. However, preincubation with a NO scavenger did not reduce the relaxations by GSH or its NO adduct, S-nitrosoglutathione (GSNO). Inhibition of guanylyl cyclase inhibited the relaxations induced by GSNO, but not by GSH. Blocking potassium channels, however, completely abolished the relaxing effects of GSH (P < 0.05). Preincubation of tracheas with GSH significantly (P < 0.05) suppressed hyperreactivity to histamine as caused by removal of tracheal epithelium. These data indicate that GSH plays a role in maintaining tracheal tone. The mechanism is probably an antioxidative action of GSH itself rather than an action of NO or GSNO.

Nitric oxide in the lung: therapeutic and cellular mechanisms of action

Nitric oxide is produced by many cell types in the lung and plays an important physiologic role in the regulation of pulmonary vasomotor tone by several known mechanisms. Nitric oxide stimulates soluble guanylyl cyclase, resulting in increased levels of cyclic GMP in lung smooth muscle cells. The gating of K+ and Ca2+ channels by cyclic GMP binding is thought to play a role in nitric oxide-mediated vasodilation. Nitric oxide may also regulate pulmonary vasodilation by direct activation of K+ channels or by modulating the expression and activity of angiotensin II receptors. Administration of nitric oxide by inhalation has been shown to acutely improve hypoxemia associated with pulmonary hypertension in humans and animals. This is presumably due to its ability to induce pulmonary vasodilation. Inhaled nitric oxide improves oxygenation and reduces the need for extracorporeal membrane oxygenation in term and near-term infants with persistent pulmonary hypertension. However, long-term benefits to these infants have been difficult to demonstrate. In other pathologic conditions, such as prematurity and acute respiratory distress syndrome, short-term benefits have not been shown conclusively to outweigh potential toxicities. For example, high-dose inhaled nitric oxide decreases surfactant function in the lung. Inhaled nitric oxide also acts as a pulmonary irritant, causing priming of lung macrophages and oxidative damage to lung epithelial cells. Conversely, protective effects of nitric oxide have been described in a number of pathological states, including hyperoxic and ischemia/reperfusion injury. Nitric oxide has also been reported to protect against oxidative damage induced by other reactive intermediates, including superoxide anion and hydroxyl radical. The dose and timing of nitric oxide administration needs to be ascertained in clinical trials before recommendations can be made regarding its optimal use in patients.

Interactions between beta2-adrenoreceptor agonist and NO donors in the relaxation of guinea pig trachea in vitro

The effects of interaction between the beta2-adrenoreceptor agonist, salbutamol, and the nitric oxide donors, sodium nitroprusside and 3-morpholinosydnonimine (SIN-1), on guinea pig trachea contraction were studied. Cumulatively increased concentrations (0.1-10 nM) of salbutamol together with a single concentration of SNP (0.33 microM) or with SIN-1 (1 microM) showed significant (p < 0.001) synergy for the inhibition of 1 microM metacholine-induced contraction. Significant synergy (p < 0.05) was also found for the inhibition of this contraction by cumulatively increased concentrations (0.1-33 microM) of SNP and a single concentration (1 nM) of salbutamol. No synergistic effect was found on the 40 mM KC1-induced contraction. We suggest that the combination of NO donors with salbutamol has a synergistic effect on metacholine contraction.