Nitric Oxide Story

James Watt, of Steam Engine Fame, Offered Inhaled Carbon Monoxide for Putative Therapeutic Action

James Watt (1736-1819) is remembered as a steam engine innovator and industrial magnate. A polymath, he was also a hands-on contributor to the Medical Pneumatic Institution of Thomas Beddoes. Watt recruited Humphry Davy, who there discovered analgesic action of inhaled nitrous oxide in 1799. Watt also built pneumatic equipment, and he introduced a gas mixture, dubbed hydro-carbonate, as a medical tonic. The bioactive component was carbon monoxide, a readily-lethal inhibitor of the transport and utilization of respiratory oxygen. Despite appreciable toxicity, carbon monoxide is an endogenous product of heme catabolism, and low doses of the gas are under laboratory investigation for therapeutic purposes. However, Watt's hydro-carbonate constituted a setback in the development of pharmacologically useful gases.

Mechanistic analysis of the photolytic decomposition of solid-state S-nitroso-N-acetylpenicillamine

S-Nitroso-N-acetylpenicillamine (SNAP) is among the most common nitric oxide (NO)-donor molecules and its solid-state photolytic decomposition has potential for inhaled nitric oxide (iNO) therapy. The photochemical NO release kinetics and mechanism were investigated by exposing solid-state SNAP to a narrow-band LED as a function of nominal wavelength and intensity of incident light. The photolytic efficiency, decomposition products, and the photolytic pathways of the SNAP were examined. The maximum light penetration depth through the solid layer of SNAP was determined by an optical microscope and found to be within 100-200 μm, depending on the wavelength of light. The photolysis of solid-state SNAP to generate NO along with the stable thiyl (RS·) radical was confirmed using Electron Spin Resonance (ESR) spectroscopy. The fate of the RS· radical in the solid phase was studied both in the presence and absence of O2 using NMR, IR, ESR, and UPLC-MS. The changes in the morphology of SNAP due to its photolysis were examined using PXRD and SEM. The stable thiyl radical formed from the photolysis of solid SNAP was found to be reactive with another adjacent thiyl radical to form a disulfide (RSSR) or with oxygen to form various sulfonyl and sulfonyl peroxyl radicals {RS(O)xO·, x = 0 to 7}. However, the thiyl radical did not recombine with NO to reform the SNAP. From the PXRD data, it was found that the SNAP loses its crystallinity by generating the NO after photolysis. The initial release of NO during photolysis was increased with increased intensity of light, whereas the maximum light penetration depth was unaffected by light intensity. The knowledge gained about the photochemical reactions of SNAP may provide important insight in designing portable photoinduced NO-releasing devices for iNO therapy.

Inhaled Nitric Oxide Promotes Angiogenesis in the Rodent Developing Brain

Inhaled nitric oxide (iNO) is a therapy used in neonates with pulmonary hypertension. Some evidence of its neuroprotective properties has been reported in both mature and immature brains subjected to injury. NO is a key mediator of the VEGF pathway, and angiogenesis may be involved in the reduced vulnerability to injury of white matter and the cortex conferred by iNO. Here, we report the effect of iNO on angiogenesis in the developing brain and its potential effectors. We found that iNO promotes angiogenesis in the developing white matter and cortex during a critical window in P14 rat pups. This shift in the developmental program of brain angiogenesis was not related to a regulation of NO synthases by exogenous NO exposure, nor the VEGF pathway or other angiogenic factors. The effects of iNO on brain angiogenesis were found to be mimicked by circulating nitrate/nitrite, suggesting that these carriers may play a role in transporting NO to the brain. Finally, our data show that the soluble guanylate cyclase/cGMP signaling pathway is likely to be involved in the pro-angiogenetic effect of iNO through thrombospondin-1, a glycoprotein of the extracellular matrix, inhibiting soluble guanylate cyclase through CD42 and CD36. In conclusion, this study provides new insights into the biological basis of the effect of iNO in the developing brain.

Photodissociation of nitric oxide from designed ruthenium nitrosyl complex: Studies on wound healing and antibacterial activity

A photoactivable NO releasing complex [Ru(L^1-2)(PPh₃)(NO)Cl₂](PF₆)(1a) have been synthesized by complex [RuL^1-2(PPh₃)₂Cl₂](1). Newly designed bidentate ligands, i.e., 4-methoxy-N'-phenyl-N'-(pyridin-2-ylmethyl)benzohydrazide(L¹) and 4-nitro-N'-phenyl-N'-(pyridin-2-ylmethyl)benzohydrazide (L²) were utilized to synthesize complex (1). Complex (1) was characterized by ESI-MS, and the solid structure of the complex [1a](PF₆) was acquired by X-ray crystallography. Different spectroscopic techniques were employed for the identification of ligands (L¹ and L²) and complexes (1 and [1a](PF₆)). Calculations employing DFT and TD-DFT were made better to understand the electronic properties of the complex [1a](PF₆). The photo liberation experiments were screened in the presence of visible light lamp. Griess assay experiment was used to quantify the photo released amount to NO. The photo liberated NO was successfully transferred to reduced myoglobin (Mb). The complex [1a](PF₆) at 50 μg/mL concentration was used for wound healing and antimicrobial activity on B16F1 mouse skin cells and Escherichia coli bacteria, respectively. In results, we observed a considerable wound healing activity of [1a](PF₆) complex after 36 h of incubation in the light-treated cells compared to the control medium, and also it shows more than 99% inhibition of bacterial cells after 1.5 h of treatment in the presence of light. These study suggested that this complex 1a](PF₆) could be utilized for topical delivery of NO for combating several dermatological infections.

High Doses of Inhaled Nitric Oxide as an Innovative Antimicrobial Strategy for Lung Infections

Since the designation of nitric oxide as “Molecule of the Year” in 1992, the scientific and clinical discoveries concerning this biomolecule have been greatly expanding. Currently, therapies enhancing the release of endogenous nitric oxide or the direct delivery of the exogenous compound are recognized as valuable pharmacological treatments in several disorders. In particular, the administration of inhaled nitric oxide is routinely used to treat patients with pulmonary hypertension or refractory hypoxemia. More recently, inhaled nitric oxide has been studied as a promising antimicrobial treatment strategy against a range of pathogens, including resistant bacterial and fungal infections of the respiratory system. Pre-clinical and clinical findings have demonstrated that, at doses greater than 160 ppm, nitric oxide has antimicrobial properties and can be used to kill a broad range of infectious microorganisms. This review focused on the mechanism of action and current evidence from in vitro studies, animal models and human clinical trials of inhaled high-dose nitric oxide as an innovative antimicrobial therapy for lung infections.

Relation between endothelial nitric oxide synthase genetic polymorphisms and pulmonary arterial hypertension in newborns with congenital heart disease

OBJECTIVE

To investigate whether endothelial nitric oxide synthase (eNOS) rs1799983, rs2070744, and rs61722009 gene polymorphisms are associated with pulmonary arterial hypertension (PAH) in South Fujian newborns with congenital heart disease (CHD).

METHODS

Genotyping for the eNOS rs1799983, rs2070744, and rs61722009 polymorphisms was performed using Sanger sequencing in 50 newborns with PAH secondary to CHD [CHD PAH (+)], 52 newborns with CHD without PAH [CHD PAH (-)], and 60 healthy controls.

RESULTS

The genotype and allele frequency distributions of eNOS rs1799983, rs2070744, and rs61722009 were similar between CHD and healthy controls (P > .05). The frequencies of the eNOS rs1799983 G/T allele were 85% and 15% in the CHD PAH (+) group and 96.15% and 3.85% in the CHD PAH (-) group, the frequency of the T allele was higher in the CHD PAH (+) group than in the CHD PAH (-) group(P< .05), and patients with the GT/TT genotypes of eNOS rs1799983 may present higher PAH (OR = 4.412, 95%CI:1.411-13.797, P= .011). Newborns with the GT/TT genotypes had decreased plasma NO production compared to newborns with the GG genotype (P< .01), and NO levels in the CHD PAH (+) group were significantly lower than those in the CHD PAH (-) group (P < .05).

CONCLUSION

The T allele could be a risk factor for PAH in newborns with CHD in South Fujian through decreased levels of nitric oxide production by the endothelium.

Roles of single gene in plant hypoxia and pathogen responses

Hypoxia stress can be caused by submergence or pathogen infection. These two stresses often occur sequentially or at the same time in nature. Therefore, plants have evolved economical and efficient strategies to deal with them, such as "single-gene multi-functions", that is, one gene could play roles in hypoxia or pathogen responses at the corresponding stress. This review mainly introduces the ERF-VII (ethylene response factor VII) and WRKYs (WRKY transcription factors) that can play roles in these two stresses. Meanwhile, the relationship between hypoxia and pathology has certain similarities in animals and plants, so we can learn from their related studies and develop new ideas for disease therapy and breeding.

Antimicrobial effects of nitric oxide in murine models of Klebsiella pneumonia

RATIONALE

Inhalation of nitric oxide (NO) exerts selective pulmonary vasodilation. Nitric oxide also has an antimicrobial effect on a broad spectrum of pathogenic viruses, bacteria and fungi.

OBJECTIVES

The aim of this study was to investigate the effect of inhaled NO on bacterial burden and disease outcome in a murine model of Klebsiella pneumonia.

METHODS

Mice were infected with Klebsiella pneumoniae and inhaled either air alone, air mixed with constant levels of NO (at 80, 160, or 200 parts per million (ppm)) or air intermittently mixed with high dose NO (300 ppm). Forty-eight hours after airway inoculation, the number of viable bacteria in lung, spleen and blood was determined. The extent of infiltration of the lungs by inflammatory cells and the level of myeloperoxidase activity in the lungs were measured. Atomic force microscopy was used to investigate a possible mechanism by which nitric oxide exerts a bactericidal effect.

MEASUREMENTS AND MAIN RESULTS

Compared to control animals infected with K. pneumoniae and breathed air alone, intermittent breathing of NO (300 ppm) reduced viable bacterial counts in lung and spleen tissue. Inhaled NO reduced infection-induced lung inflammation and improved overall survival of mice. NO destroyed the cell wall of K. pneumoniae and killed multiple-drug resistant K. pneumoniae in-vitro.

CONCLUSIONS

Intermittent administration of high dose NO may be an effective approach to the treatment of pneumonia caused by K. pneumoniae.