Increased exhaled nitric oxide in active pulmonary tuberculosis due to inducible NO synthase upregulation in alveolar macrophages

Nitric oxide in the nasal airway: a new dimension in otorhinolaryngology

The discovery that the gas nitric oxide (NO) is an important signaling molecule in the cardiovascular system earned its Nobel prize in 1998. NO has since been found to play important roles in a variety of physiologic and pathophysiologic processes in the body including vasoregulation, hemostasis, neurotransmission, immune defense, and respiration. The surprisingly high concentrations of NO in the nasal airway and paranasal sinuses has important implications for the field of otorhinolaryngology. NO provides a first-line defense against micro-organisms through its antiviral and antimicrobial activity and by its upregulation of ciliary motility. Nasal treatments such as polypectomy, sinus surgery, removal of hypertrophic adenoids and tonsils, and treatment of allergic rhinitis may alter NO output and, therefore, the microbial colonization of the upper airways. Nasal surgery aimed at relieving nasal obstruction may do the same but would also be expected to improve pulmonary function in patients with asthma and upper airway obstruction. NO output rises in a number of conditions associated with chronic airway inflammation, but not all of them. Concentrations are increased in asthma, allergic rhinitis, and viral respiratory infections, but reduced in sinusitis, cystic fibrosis, primary ciliary dysfunction, chronic cough, and after exposure to tobacco and alcohol. Therefore, NO, similar to several other inflammatory mediators, probably subserves different functions as local conditions dictate. At present, it seems that the measurement of NO in the upper airway may prove valuable as a simple, noninvasive diagnostic marker of airway pathologies. The objective of this review is to highlight some aspects of the origin, physiology, and functions of upper airway NO, and to discuss the particular methodological problems that result from the complex anatomy.

Influence of disease severity on nitrite and cytokine production by peripheral blood mononuclear cells (PBMC) from patients with pulmonary tuberculosis (TB)

Earlier studies in patients with pulmonary TB have revealed a higher production of Th1 cell type cytokines in moderate TB, with predominant Th2-like responses in advanced disease. Given the influence of IL-12 in T cell differentiation, as well as the roles of transforming growth factor-beta (TGF-beta), nitric oxide and tumour necrosis factor-alpha (TNF-alpha) in the immune response against intracellular pathogens, we decided to analyse the interferon-gamma (IFN-gamma), IL-4, IL-12, TGF-beta, TNF-alpha and nitrite concentrations in culture supernatants of PBMC from TB patients showing different degrees of lung involvement. The sample population comprised 18 untreated TB patients with either moderate (n = 9) or advanced (n = 9) disease and 12 age- and sex-matched healthy controls (total population (patients and controls) 12 women, 18 men, aged 37 +/- 13 years (mean +/- s.d.)). PBMC were stimulated with whole sonicate from Mycobacterium tuberculosis and the supernatants were collected on day 4 for measurement of cytokine and nitrite levels. Antigen-stimulated IFN-gamma, TGF-beta and TNF-alpha production was found to be significantly increased in TB patients, both moderate and advanced, compared with the controls. Levels of IFN-gamma were significantly higher in moderate disease than advanced cases, whereas advanced cases showed significantly higher IL-12, TGF-beta and TNF-alpha concentrations when compared with cases of moderate TB. Nitrite levels were also increased in TB patients and the increase was statistically significant when advanced cases were compared with controls. These findings may contribute to a clearer picture of the net effect of cytokine interactions in TB, essential for a better understanding of the immunopathological mechanisms underlying the distinct clinical forms of the disease.

Reactive oxygen and nitrogen intermediates in the relationship between mammalian hosts and microbial pathogens

This review summarizes recent evidence from knock-out mice on the role of reactive oxygen intermediates and reactive nitrogen intermediates (RNI) in mammalian immunity. Reflections on redundancy in immunity help explain an apparent paradox: the phagocyte oxidase and inducible nitric oxide synthase are each nonredundant, and yet also mutually redundant, in host defense. In combination, the contribution of these two enzymes appears to be greater than previously appreciated. The remainder of this review focuses on a relatively new field, the basis of microbial resistance to RNI. Experimental tuberculosis provides an important example of an extended, dynamic balance between host and pathogen in which RNI play a major role. In diseases such as tuberculosis, a molecular understanding of host-pathogen interactions requires characterization of the defenses used by microbes against RNI, analogous to our understanding of defenses against reactive oxygen intermediates. Genetic and biochemical approaches have identified candidates for RNI-resistance genes in Mycobacterium tuberculosis and other pathogens.

Exhaled nitric oxide in high-altitude pulmonary edema: role in the regulation of pulmonary vascular tone and evidence for a role against inflammation

High-altitude pulmonary edema (HAPE) is a life-threatening condition occurring in predisposed subjects at altitudes above 2,500 m. It is not clear whether, in addition to hemodynamic factors and defective alveolar fluid clearance, inflammation plays a pathogenic role in HAPE. We therefore made serial measurements of exhaled pulmonary nitric oxide (NO), a marker of airway inflammation, in 28 HAPE-prone and 24 control subjects during high-altitude exposure (4,559 m). To examine the relationship between pulmonary NO synthesis and pulmonary vascular tone, we also measured systolic pulmonary artery pressure (Ppa). In the 13 subjects who developed HAPE, exhaled NO did not show any tendency to increase during the development of lung edema. Throughout the entire sojourn at high altitude, pulmonary exhaled NO was roughly 30% lower in HAPE-prone than in control subjects, and there existed an inverse relationship between Ppa and exhaled NO (r = -0.51, p < 0.001). These findings suggest that HAPE is not preceded by airway inflammation. Reduced exhaled NO may be related to altered pulmonary NO synthesis and/or transport and clearance, and the data in our study could be consistent with the novel concept that in HAPE-prone subjects, a defect in pulmonary epithelial NO synthesis may contribute to exaggerated hypoxic pulmonary vasoconstriction and in turn to pulmonary edema.

Noninvasive measurement of airway inflammation using exhaled nitric oxide and induced sputum. Current status and future use

The recent use of IS and the analysis of exhaled mediators such as NO are important steps forward in our ability to noninvasively assess airway inflammation without the need to resort to bronchoscopy. Exhaled NO and IS are complementary techniques that provide different information (Table 1). Induced sputum can provide knowledge regarding the cells and mediators participating in the inflammatory response, but is time consuming and expensive. Exhaled NO measurement is performed simply and quickly, and is a nonspecific marker of an inflammatory process. The initial capital costs of equipment for NO analysis are high, however. Once the problems of standardized collection and oropharyngeal contamination have been dealt with, BC may also prove to be an additional tool for the assessment of airway inflammation. It is likely that the next 10 years will see the establishment of these noninvasive tools for the clinical assessment of airway inflammation and oxidative stress, and change the entire way we manage asthma.

Diminished inducible nitric oxide synthase expression in fulminant early-onset neonatal pneumonia

OBJECTIVE

Fulminant early-onset neonatal pneumonia is associated with ascending intrauterine infection (IUI), prematurity, persistent pulmonary hypertension (PPHN), and septicemia. Nitric oxide (NO) as an inflammatory mediator is included in antimicrobial defense and has a role in pathogenesis of septic shock. The aim was to study the role of inflammatory NO in neonatal pneumonia.

METHODS

Lungs from 36 autopsies were studied: 12 had fulminant early-onset neonatal pneumonia, 5 pneumonia of later onset, and 19 controls had similar gestational and postnatal age. In addition, airway specimens from 21 intubated newborns were analyzed: 7 with fulminant early-onset pneumonia, 7 apparently noninfected infants born prematurely attributable to IUI, and 7 premature infants of similar gestation. Specimens were analyzed for inducible NO synthase (NOS2) and nitrotyrosine, an indicator of NO toxicity. The degree of staining was analyzed.

RESULTS

In fulminant pneumonia, alveolar macrophages (AM) showed significantly less NOS2 immunoactivity than the controls. In the airway specimens, the infants with fulminant pneumonia 0 to 2 days after birth had significantly lower intracellular NOS2 and nitrotyrosine and significantly lower interleukin-1beta and surfactant protein-A than apparently noninfected IUI infants. NOS2 and the other indices increased significantly during the recovery.

CONCLUSIONS

For the first time, we report NOS2 expression by macrophages from human neonates. In fulminant early-onset neonatal pneumonia, delayed production rather than excess of pulmonary inflammatory NO is associated with severe symptoms.

A commercial preparation of catalase inhibits nitric oxide production by activated murine macrophages: role of arginase

Catalase is widely used as a pharmacological probe to evaluate the role of hydrogen peroxide in antimicrobial activities of phagocytic cells. This report demonstrates that the ability of a commercial preparation of catalase to inhibit concomitantly macrophage antimycobacterial activity and production of reactive nitrogen intermediates can be attributed, at least in part, to the depletion of L-arginine by contaminating arginase. In experimental systems that employ pharmacological probes, the existence of nonspecific effects should be considered in data interpretation.

Reactive nitrogen intermediates and the pathogenesis of Salmonella and mycobacteria

Over the past decade, reactive nitrogen intermediates joined reactive oxygen intermediates as a biochemically parallel and functionally non-redundant pathway for mammalian host resistance to many microbial pathogens. The past year has brought a new appreciation that these two pathways are partially redundant, such that each can compensate in part for the absence of the other. In combination, their importance to defense of the murine host is greater than previously appreciated. In addition to direct microbicidal actions, reactive nitrogen intermediates have immunoregulatory effects relevant to the control of infection. Genes have been characterized in Mycobacterium tuberculosis and Salmonella typhimurium that may regulate the ability of pathogens to resist reactive nitrogen and oxygen intermediates produced by activated macrophages.

Nitric oxide modulates interleukin-1beta and tumor necrosis factor-alpha synthesis by alveolar macrophages in pulmonary tuberculosis

Interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha released from alveolar macrophages (AM) in pulmonary tuberculosis (TB) are important in host defense against mycobacterial infection. Nitric oxide (NO) production is enhanced in AM of TB patients. We examined whether NO was implicated in (IL)-1beta and TNF-alpha synthesis by AM of TB patients. Purified AM were retrieved by bronchoalveolar lavage from 11 TB patients and 10 normal subjects, and were cultured with or without the NO inhibitor N(G)-monomethyl-L-arginine (L-NMMA). The release of IL-1beta and TNF-alpha, and expression of their messenger RNAs (mRNAs), were determined by enzyme-linked immunosorbent assay and Northern blot analysis. The release of IL-1beta and TNF-alpha was greater from AM of TB patients than from AM of normal subjects. L-NMMA inhibited nitrite, IL-1beta, and TNF-alpha production in TB patients. The mRNA expression for IL-1beta and TNF-alpha was upregulated in TB patients and was depressed by L-NMMA. Immunocytochemistry done with a monoclonal antibody against the p65 subunit of nuclear factor (NF)-kappaB showed that NF-kappaB was highly expressed and translocated to the nuclei of AM from TB patients, and was inhibited by L-NMMA. Inhibition of NF-kappaB by pyrrolidine dithiocarbamate attenuated IL-1beta and TNF-alpha synthesis. In conclusion, enhanced NO generation by AM of TB patients plays an autoregulatory role in amplifying the synthesis of proinflammatory cytokines, probably through NF-kappaB activation.

Advances in pulmonary laboratory testing

This review examines emerging technologies that are of potential use in the routine clinical pulmonary laboratory. These technologies include the following: the measurement of exercise tidal flow-volume (FV) loops plotted within the maximal FV envelope for assessment of ventilatory constraint during exercise; the use of negative expiratory pressures to asses expiratory flow limitation in various populations and under various conditions; the potential use of expired nitric oxide for assessing airway inflammation; and the use of forced oscillation for assessment of airway resistance. These methodologies have been used extensively in the research setting and are gaining increasing popularity and clinical application due to the availability of commercially available, simplified, and automated systems. An overview of each technique, its potential advantages and limitations will be discussed, along with suggestions for further investigation that is considered necessary prior to extensive clinical use.

Increased progenitor cell proliferation in the peripheral blood of patients with bronchial asthma: the role of nitric oxide

BACKGROUND

Asthma exacerbation is associated with increased numbers of circulating CD34(+) progenitor cells, which may migrate to airways and develop into mature cells under the effects of cytokines and hematopoietic factors. Nitric oxide (NO) generation is enhanced in asthma and is known to suppress human hematopoiesis.

OBJECTIVES

We studied circulating progenitor cells in the blood of patients with varying severity of asthma and examined the contribution of NO to their proliferation into eosinophil-forming colonies ex vivo.

METHODS

With use of multiparameter flow cytometric analyses, the cell numbers and intracellular inducible NO synthase (iNOS) immunoreactivity of circulating CD34(+) cells in peripheral blood was measured. The serum level of GM-CSF or IL-5 was also determined. The colonies grown from progenitor cells were cultured in methylcellulose either in the presence or absence of growth factors, including GM-CSF, stem cell factor, and IL-3.

RESULTS

A significantly greater number of circulating CD34(+) cells increased together with higher intracellular iNOS immunoreactivity in moderate asthmatics compared with mild intermittent asthmatics and healthy subjects. There was no significant difference in iNOS immunoreactivities or CD34(+) progenitor cell numbers between healthy subjects and those with mild intermittent asthma. Serum levels of GM-CSF or IL-5 were significantly higher in all asthmatics compared with healthy subjects and correlated with circulating CD34(+) cells. A greater number of colonies was grown either in the presence or absence of growth factors with a higher percentage of cells of eosinophil lineage in asthmatics than in health subjects. N(G)-nitro-L-arginine methyl ester potentiated and sodium nitroprusside inhibited the colony growth in both asthmatic and healthy subjects without a significant change in the percentage of eosinophil lineage.

CONCLUSIONS

The production of NO from progenitor cells or other circulating cells may act in an autocrine or paracrine fashion to regulate progenitor cell growth and colony formation. However, this is not sufficient to control the increased proliferation of progenitor cells observed in asthma.

noxR3, a novel gene from Mycobacterium tuberculosis, protects Salmonella typhimurium from nitrosative and oxidative stress

Reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI) produced by activated macrophages participate in host defense against the facultative intracellular pathogens Mycobacterium tuberculosis and Salmonella typhimurium. To survive within macrophages, such pathogens may have evolved ROI and RNI resistance mechanisms. ROI resistance pathways have been intensively studied. Much less is known about the mechanisms of resistance to RNI. To identify possible RNI resistance genes in M. tuberculosis, a mycobacterial library was expressed in S. typhimurium and subjected to selection by exposure to the NO donor S-nitrosoglutathione (GSNO) in concentrations sufficient to kill the vast majority of nontransformed salmonellae. Among the rare surviving recombinants was a clone expressing noxR3, a novel and previously anonymous M. tuberculosis gene predicted to encode a small, basic protein. Expression of noxR3 protected S. typhimurium not only from GSNO and acidified nitrite but also from H2O2. noxR3 is the third gene cloned from M. tuberculosis that has been shown to protect heterologous cells from both RNI and ROI. This suggests diversity in the repertoire of mechanisms that help pathogens resist the oxidative and nitrosative defenses of the host.

Nitric oxide production and nitric oxide synthase type 2 expression by human mononuclear phagocytes: a review

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