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

NO donors and NO delivery methods for controlling biofilms in chronic lung infections

Nitric oxide (NO), the highly reactive radical gas, provides an attractive strategy in the control of microbial infections. NO not only exhibits bactericidal effect at high concentrations but also prevents bacterial attachment and disperses biofilms at low, nontoxic concentrations, rendering bacteria less tolerant to antibiotic treatment. The endogenously generated NO by airway epithelium in healthy populations significantly contributes to the eradication of invading pathogens. However, this pathway is often compromised in patients suffering from chronic lung infections where biofilms dominate. Thus, exogenous supplementation of NO is suggested to improve the therapeutic outcomes of these infectious diseases. Compared to previous reviews focusing on the mechanism of NO-mediated biofilm inhibition, this review explores the applications of NO for inhibiting biofilms in chronic lung infections. It discusses how abnormal levels of NO in the airways contribute to chronic infections in cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), and primary ciliary dyskinesia (PCD) patients and why exogenous NO can be a promising antibiofilm strategy in clinical settings, as well as current and potential in vivo NO delivery methods. KEY POINTS : • The relationship between abnormal NO levels and biofilm development in lungs • The antibiofilm property of NO and current applications in lungs • Potential NO delivery methods and research directions in the future.

Genetic deficit of KCa 3.1 channels protects against pulmonary circulatory collapse induced by TRPV4 channel activation

BACKGROUND AND PURPOSE

The intermediate conductance calcium/calmodulin-regulated K⁺ channel K_Ca 3.1 produces hyperpolarizing K⁺ currents that counteract depolarizing currents carried by transient receptor potential (TRP) channels, and provide the electrochemical driving force for Cl^- and fluid movements. We investigated whether a deficiency in K_Ca 3.1 (K_Ca 3.1^-/- ) protects against fatal pulmonary circulatory collapse in mice after pharmacological activation of the calcium-permeable TRP subfamily vanilloid type 4 (TRPV4) channels.

EXPERIMENTAL APPROACH

An opener of TRPV4 channels, GSK1016790A, was infused in wild-type (wt) and K_Ca 3.1^-/- mice; haemodynamic parameters, histology and pulmonary vascular reactivity were measured; and patch clamp was performed on pulmonary arterial endothelial cells (PAEC).

KEY RESULTS

In wt mice, GSK1016790A decreased right ventricular and systemic pressure leading to a fatal circulatory collapse that was accompanied by increased protein permeability, lung haemorrhage and fluid extravasation. In contrast, K_Ca 3.1^-/- mice exhibited a significantly smaller drop in pressure to GSK1016790A infusion, no haemorrhage and fluid water extravasation, and the mice survived. Moreover, the GSK1016790A-induced relaxation of pulmonary arteries of K_Ca 3.1^-/- mice was significantly less than that of wt mice. GSK1016790A induced TRPV4 currents in PAEC from wt and K_Ca 3.1^-/- mice, which co-activated K_Ca 3.1 and disrupted membrane resistance in wt PAEC, but not in K_Ca 3.1^-/- PAEC.

CONCLUSIONS AND IMPLICATIONS

Our findings show that a genetic deficiency of K_Ca 3.1 channels prevented fatal pulmonary circulatory collapse and reduced lung damage caused by pharmacological activation of calcium-permeable TRPV4 channels. Therefore, inhibition of K_Ca 3.1channels may have therapeutic potential in conditions characterized by abnormal high endothelial calcium signalling, barrier disruption, lung oedema and pulmonary circulatory collapse.

A new nitrosyl ruthenium complex nitric oxide donor presents higher efficacy than sodium nitroprusside on relaxation of airway smooth muscle

Nitric oxide (NO) has been demonstrated to be the primary agent in relaxing airways in humans and animals. We investigated the mechanisms involved in the relaxation induced by NO-donors, ruthenium complex [Ru(terpy)(bdq)NO(+)](3+) (TERPY) and sodium nitroprusside (SNP) in isolated trachea of rats contracted with carbachol in an isolated organs chamber. For instance, we verified the contribution of K(+) channels, the importance of sGC/cGMP pathway, the influence of the extra and intracellular Ca(2+) sources and the contribution of the epithelium on the relaxing response. Additionally, we have used confocal microscopy in order to analyze the action of the NO-donors on cytosolic Ca(2+) concentration. The results demonstrated that both compounds led to the relaxation of trachea in a dependent-concentration way. However, the maximum effect (E(max)) of TERPY is higher than the SNP. The relaxation induced by SNP (but not TERPY) was significantly reduced by pretreatment with ODQ (sGC inhibitor). Only TERPY-induced relaxation was reduced by tetraethylammonium (K(+) channels blocker) and by pre-contraction with 75mM KCl (membrane depolarization). The response to both NO-donors was not altered by the presence of thapsigargin (sarcoplasmic reticulum Ca(2+)-ATPase inhibitor). The epithelium removal has reduced the relaxation only to SNP, and it has no effect on TERPY. The both NO-donors reduced the contraction evoked by Ca(2+) influx, while TERPY have shown a higher inhibitory effect on contraction. Moreover, the TERPY was more effective than SNP in reducing the cytosolic Ca(2+) concentration measured by confocal microscopy. In conclusion, these results show that TERPY induces airway smooth muscle relaxation by cGMP-independent mechanisms, it involves the fluxes of Ca(2+) and K(+) across the membrane, it is more effective in reducing cytosolic Ca(2+) concentration and inducing relaxation in the rat trachea than the standard drug, SNP.

Mechanisms underlying epithelium-dependent relaxation in rat bronchioles: analogy to EDHF-type relaxation in rat pulmonary arteries

This study investigated the mechanisms underlying epithelium-derived hyperpolarizing factor (EpDHF)-type relaxation in rat bronchioles. Immunohistochemistry was performed, and rat bronchioles and pulmonary arteries were mounted in microvascular myographs for functional studies. An opener of small (SKCa) and intermediate (IKCa)-conductance calcium-activated potassium channels, NS309 (6,7-dichloro-1H-indole-2,3-dione 3-oxime) was used to induce EpDHF-type relaxation. IKCa and SKCa3 positive immunoreactions were observed mainly in the epithelium and endothelium of bronchioles and arteries, respectively. In 5-hydroxytryptamine (1 μM)-contracted bronchioles (828 ± 20 μm, n = 84) and U46619 (0.03 μM)-contracted arteries (720 ± 24 μm, n = 68), NS309 (0.001–10 μM) induced concentration-dependent relaxations that were reduced by epithelium/endothelium removal and by blocking IKCa channels with charybdotoxin and in bronchioles also by blocking SKCa channels with apamin. Inhibition of cyclooxygenase, nitric oxide synthase, and cytochrome 2C isoenzymes, or blockade of large (BKCa)-conductance calcium-activated potassium channels with iberiotoxin, failed to reduce NS309 relaxation. In contrast to the pulmonary arteries, relaxations to a β2-adrenoceptor agonist, salbutamol, were reduced in bronchioles by removing the epithelium or blocking IKCa and/or SKCa channels. Extracellular K+ (2–20 mM) induced relaxation in both bronchioles and arteries. An inhibitor of Na+-K+-ATPase, ouabain, abolished relaxations to NS309, salbutamol, and K+. These results suggest that IKCa and SKCa3 channels are located in the epithelium of bronchioles and endothelium of pulmonary arteries. Analog to the endothelium-derived hyperpolarizing factor (EDHF)-type relaxation in pulmonary arteries, these channels may be involved in EpDHF-type relaxation of bronchioles caused by epithelial K+ efflux followed by activation of Na+-K+-ATPase in the underlying smooth muscle layer.

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.