Nitric oxide, iNOS, and inflammation in cystic fibrosis

Nitric oxide (NO) is produced from three isoforms of nitric oxide synthase (NOS), neuronal (nNOS), endothelial (eNOS) and inducible (iNOS). Cystic fibrosis (CF) patients have an increased bacterial load in the airways which stimulates iNOS and therefore NO production. Upregulation of iNOS in normal epithelial cells protects the lung from damage, but in CF cells, iNOS is not upregulated and NO production is reduced. Reduced iNOS expression is associated with neutrophil sequestration in the lung, thus increasing the potential damage from neutrophil proteases and reactive oxygen species. In contrast, high concentrations of NO may augment the inflammatory process in acute lung injury from sepsis. Meng et al. have shown that cystic fibrosis epithelial cells, when stimulated by a cytokine mix and co-cultured with activated neutrophils, have reduced iNOS expression compared to normal epithelial cells. Although iNOS expression may not accurately reflect activity and NO production may arise from elsewhere, this study suggests that reduced iNOS expression may play a part in the pathophysiological processes in cystic fibrosis.     

Nitric oxide and interleukin-8 as inflammatory components of cystic fibrosis

We examined the production of reactive nitrogen intermediates in the tracheo-bronchial tree of patients with cystic fibrosis (CF). Examination of the soluble phase of sputa from 17 CF patients revealed the presence of high levels of NO ₂ ^– /NO ₃ ^– assayed by the Greiss reaction. We also examined the presence of the chemotactic cytokine interleukin-8 (IL-8) in these samples so as to assess another important inflammatory marker; high levels of IL-8 were present in the sputa of cystic fibrosis subjects. The elevated nitrite was not produced by the presence ofPseudomonas bacteria in the sputa, inasmuch as bacteria in culture released undetectable amounts of nitrite in culture media. Neutrophils from the sputa of CF patients with disease exacerbation released higher amounts of nitrite and IL-8. Neutrophils from the sputa were also shown to spontaneously release substantial amounts of nitrite in the supernatants, and this release was partly blocked by the antagonist N^G-monomethyl-L-arginine (L-NMMA). Blood neutrophils were shown to release nitrite only in response to challenge with CF-associated strains ofPseudomonas, and not exposure to cytokines. There was no significant differences in nitrite release between normal and CF blood polymorphonuclear leucocytes (PMNs). A study of upper airway epithelial cell lines showed that these cells released low amounts of nitrite after infection with CF-associated strains ofPseudomonas but not after cytokine exposure. Epithelial cell lines with CF or normal phenotypes were shown to release similar quantities of nitrite, upon stimulation withPseudomonas. These data demonstrate that elevated levels of reactive nitrogen intermediates and IL-8 are produced in the tracheo-bronchial tree of subjects with CF. Levels of IL-8 and nitrite were higher in the secretions of CF subjects with disease exacerbation. The involvement of nitric oxide and other reactive nitrogen intermediates produced by neutrophils and other cells in the tissue damaging processes in CF deserves further investigation.     

Nitric oxide production by polymorphonuclear leucocytes in infected cystic fibrosis sputum consumes oxygen

Chronic Pseudomonas aeruginosa lung infection in cystic fibrosis (CF) patients is characterized by persisting mucoid biofilms in hypoxic endobronchial mucus. These biofilms are surrounded by numerous polymorphonuclear leucocytes (PMNs), which consume a major part of present molecular oxygen (O₂) due to production of superoxide (O₂⁻). In this study, we show that the PMNs also consume O₂ for production of nitric oxide (NO) by the nitric oxide synthases (NOS) in the infected endobronchial mucus. Fresh expectorated sputum samples (n = 28) from chronically infected CF patients (n = 22) were analysed by quantifying and visualizing the NO production. NO production was detected by optode measurements combined with fluorescence microscopy, flow cytometry and spectrophotometry. Inhibition of nitric oxide synthases (NOS) with N^G-monomethyl-L-arginine (L-NMMA) resulted in reduced O₂ consumption (P < 0·0008, n = 8) and a lower fraction of cells with fluorescence from the NO-indicator 4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate (DAF-FM) (P < 0·002, n = 8). PMNs stained with DAF-FM and the superoxide indicator hydroethidine (HE) and host cells with inducible NOS (iNOS) were identified in the sputum. In addition, the production of the stable end-products of NO in CF sputum was correlated with the concentration of PMNs; NO₃⁻ (P < 0·04, r = 0·66, n = 10) and NO₂⁻ (P< 0·006, r = 0·78, n = 11). The present study suggests that besides consumption of O₂ for production of reactive oxygen species, the PMNs in CF sputum also consume O₂ for production of NO.     

Nitric oxide contributes to the augmented vasodilatation during hypoxic exercise

We tested the hypotheses that (1) nitric oxide (NO) contributes to augmented skeletal muscle vasodilatation during hypoxic exercise and (2) the combined inhibition of NO production and adenosine receptor activation would attenuate the augmented vasodilatation during hypoxic exercise more than NO inhibition alone. In separate protocols subjects performed forearm exercise (10% and 20% of maximum) during normoxia and normocapnic hypoxia (80% arterial O₂ saturation). In protocol 1 ( n = 12), subjects received intra-arterial administration of saline (control) and the NO synthase inhibitor N ^G-monomethyl- l -arginine ( l -NMMA). In protocol 2 ( n = 10), subjects received intra-arterial saline (control) and combined l -NMMA–aminophylline (adenosine receptor antagonist) administration. Forearm vascular conductance (FVC; ml min⁻¹ (100 mmHg)⁻¹) was calculated from forearm blood flow (ml min⁻¹) and blood pressure (mmHg). In protocol 1, the change in FVC (Δ from normoxic baseline) due to hypoxia under resting conditions and during hypoxic exercise was substantially lower with l -NMMA administration compared to saline (control; P < 0.01). In protocol 2, administration of combined l -NMMA–aminophylline reduced the ΔFVC due to hypoxic exercise compared to saline (control; P < 0.01). However, the relative reduction in ΔFVC compared to the respective control (saline) conditions was similar between l -NMMA only (protocol 1) and combined l -NMMA–aminophylline (protocol 2) at 10% (−17.5 ± 3.7 vs. −21.4 ± 5.2%; P = 0.28) and 20% (−13.4 ± 3.5 vs. −18.8 ± 4.5%; P = 0.18) hypoxic exercise. These findings suggest that NO contributes to the augmented vasodilatation observed during hypoxic exercise independent of adenosine.     

Nitric oxide has no beneficial effects on ion transport defects in cystic fibrosis human nasal epithelium

Nitric oxide (NO) has been reported to activate Cl- secretion via the cystic fibrosis transmembrane conductance regulator (CFTR) and inhibit epithelial Na+ absorption mediated by amiloride-sensitive epithelial Na+ channels (ENaC). These ion transport systems are defective in cystic fibrosis (CF): Cl- secretion by CFTR is impaired and Na+ absorption by ENaC is dramatically increased. By activating CFTR and depressing ENaC, NO is a potentially beneficial therapeutic agent for ion transport defects in human CF respiratory epithelia. To assess the effects of NO on human respiratory epithelial cells, the NO donors sodium nitroprusside (SNP) and spermine NONOate were applied to primary cultured nasal cells, surgically obtained from non-CF and CF patients. Measurements of transepithelial short-circuit current (ISC) showed that NO has no inhibitory potency against amiloride-sensitive nasal ENaC (nENaC) or amiloride-insensitive Na+-absorbing mechanisms in non-CF and CF epithelia. Furthermore, NO had no stimulatory effect on Cl- secretion by CFTR or any other Cl- conductance pathway in either tissue. Although NO elevated the intracellular Ca2+ concentration, we did not detect any activation of Ca2+-dependent Cl- channels. These results demonstrate that NO has no beneficial effect on CF epithelial cells of the upper airways.     

Serine proteases degrade airway mucins in cystic fibrosis

Airway mucins are the major molecular constituents of mucus. Mucus forms the first barrier to invading organisms in the airways and is an important defense mechanism of the lung. We confirm that mucin concentrations are significantly decreased in airway secretions of subjects with cystic fibrosis (CF) who have chronic Pseudomonas aeruginosa infection. In sputum from CF subjects without a history of P. aeruginosa, we found no significant difference in the mucin concentration compared to mucus from normal controls. We demonstrate that mucins can be degraded by synthetic human neutrophil elastase (HNE) and P. aeruginosa elastase B (pseudolysin) and that degradation was inhibited by serine proteases inhibitors (diisopropyl fluorophosphates [DFP], phenylmethylsulfonyl fluoride [PMSF], and 1-chloro-3-tosylamido-7-amino-2-heptanone HCl [TLCK]). The mucin concentration in airway secretions from CF subjects is similar to that for normal subjects until there is infection by P. aeruginosa, and after that, the mucin concentration decreases dramatically. This is most likely due to degradation by serine proteases. The loss of this mucin barrier may contribute to chronic airway infection in the CF airway.     

Nitric oxide contributes to induction of innate immune responses to gram-negative bacteria in Drosophila

Studies in mammals uncovered important signaling roles of nitric oxide (NO), and contributions to innate immunity. Suggestions of conservation led us to explore the involvement of NO in Drosophila innate immunity. Inhibition of nitric oxide synthase (NOS) increased larval sensitivity to gram-negative bacterial infection, and abrogated induction of the antimicrobial peptide Diptericin. NOS was up-regulated after infection. Antimicrobial peptide reporters revealed that NO triggered an immune response in uninfected larvae. NO induction of Diptericin reporters in the fat body required immune deficiency (imd) and domino. These findings show that NOS activity is required for a robust innate immune response to gram-negative bacteria, NOS is induced by infection, and NO is sufficient to trigger response in the absence of infection. We propose that NO mediates an early step of the signal transduction pathway, inducing the innate immune response upon natural infection with gram-negative bacteria.     

Selenium deficiency contributes to the chronic myocarditis in coxsackievirus-infected mice

Both coxsackievirus B3 (CVB3) infection and selenium (Se) deficiency play a pivotal role in Keshan disease of the heart. The Se deficiency was known to contribute to the CVB3-induced myocarditis in acute and subacute phase of infection. However, its effect on the myocarditis in chronic phase of infection has not been examined yet. To address this question, we kept mice on a Se-replete or Se-deficient diet for 28 days, infected them intraperitoneally with CVB3 and maintaining previous diets, we examined them for next 90 days for several parameters indicative of the infection or disease. We found out that the mice on the Se-deficient diet exhibited a higher mortality, lower serum glutathione peroxidase (GPx) activity, evident histopathological changes indicative of myocarditis, and a higher level of viral RNA in the heart. Summing up, these data suggest that the Se-deficiency creates a chronic myocarditis-prone condition by fostering the active virus replication.     

Differential localization of the cystic fibrosis transmembrane conductance regulator in normal and cystic fibrosis airway epithelium.

Deletion of the amino acid residue Phe 508 of the cystic fibrosis transmembrane conductance regulator (CFTR) protein represents the most common mutation identified in cystic fibrosis (CF) patients. A monoclonal and a polyclonal antibody directed against different regions of CFTR were used to localize the CFTR protein in normal and CF airway epithelium derived from polyps of non-CF and CF subjects homozygous for the delta Phe 508 CFTR mutation. To identify the cellular and subcellular localization of CFTR, immunofluorescent light microscopy, confocal scanning microscopy, and immunogold transmission electron microscopy were performed on cryofixed tissue. A markedly different subcellular distribution was identified between normal and CF airway epithelial cells. In normal epithelium, labeling was restricted to the surface apical compartment of the ciliated cells. In contrast, in the epithelium from homozygous delta Phe 508 CF patients, CFTR markedly accumulated in the cytosol of all the epithelial cells. These findings are consistent with the concept that the CFTR delta Phe 508 mutation modifies the intracellular maturation and trafficking of the protein, leading to an altered subcellular distribution of the delta Phe 508 mutant CFTR.     

Defective lipoxin-mediated anti-inflammatory activity in the cystic fibrosis airway

In cystic fibrosis, dysregulated neutrophilic inflammation and chronic infection lead to progressive destruction of the airways. The underlying mechanisms have remained unclear. Lipoxins are anti-inflammatory lipid mediators that modulate neutrophilic inflammation. We report here that lipoxin concentrations in airway fluid were significantly suppressed in patients with cystic fibrosis compared to patients with other inflammatory lung conditions. We also show that administration of a metabolically stable lipoxin analog in a mouse model of the chronic airway inflammation and infection associated with cystic fibrosis suppressed neutrophilic inflammation, decreased pulmonary bacterial burden and attenuated disease severity. These findings suggest that there is a pathophysiologically important defect in lipoxin-mediated anti-inflammatory activity in the cystic fibrosis lung and that lipoxins have therapeutic potential in this lethal autosomal disease.     

Nitric oxide contributes to resistance of the Brown Norway rat to experimental autoimmune encephalomyelitis

The Brown Norway (BN) rat is reported to be resistant to the induction of experimental autoimmune encephalomyelitis (EAE) and a number of mechanisms have been suggested to explain this resistance. In work reported here we provide evidence that such resistance in the BN rat can be accounted for, at least in part, by their ability to produce higher levels of nitric oxide (NO) than susceptible strains of rats. Spleen cells from the BN rat make significantly more NO following in vitro stimulation than do cells from the Lewis or PVG rat and following in vivo immunization using complete Freund's adjuvant (CFA) the BN rat makes substantially more NO than either susceptible strain. If carbonyl iron is used as adjuvant in vivo there is no increase in NO levels in the BN rat and they are rendered highly susceptible to EAE. Immunizing with CFA simultaneously with neuroantigen and carbonyl iron drives up NO levels and the resistance is restored. EAE produced using carbonyl iron is characterized by extensive macrophage/microglia presence in the central nervous system lesions of the BN rat yet the cytokine profile in the lymph nodes does not differ from that in the EAE Lewis rats.     

Nitric oxide and redox signaling in allergic airway inflammation

A number of diseases of the respiratory tract, as exemplified in this review by asthma, are associated with increased amounts of nitric oxide (NO) in the expired breath. Asthma is furthermore characterized by increased production of reactive oxygen species that scavenge NO to form more reactive nitrogen species as demonstrated by the enhanced presence of nitrated proteins in the lungs of these patients. This increased oxidative metabolism leaves less bioavailable NO and coincides with lower amounts of S-nitrosothiols. In this review, we speculate on mechanisms responsible for the increased amounts of NO in inflammatory airway disease and discuss the apparent paradox of higher levels of NO as opposed to decreased amounts of S-nitrosothiols. We will furthermore give an overview of the regulation of NO production and biochemical events by which NO transduces signals into cellular responses, with a particular focus on modulation of inflammation by NO. Lastly, difficulties in studying NO signaling and possible therapeutic uses for NO will be highlighted.     

Altered NaCl concentration of airway surface liquid in cystic fibrosis

A novel isotopic technique suggests that the [Na] and [Cl] of airway surface liquid are both normally approximately 50 mM. In cystic fibrosis, lack of the functional cystic fibrosis transmembrane conductance regulator (CFTR) causes failure of transcellular Cl absorption, resulting in an elevation of [Na] and [Cl] of airway surface liquid to approximately 100 mM.     

Reduced expression of psoriasin in human airway cystic fibrosis epithelia

Psoriasin is a low molecular weight Ca(2+)-binding protein with known antimicrobial activity. Since human airway epithelial cells produce a number of powerful antimicrobial agents as part of their host defence, we investigated whether psoriasin was expressed in human bronchial epithelial cell lines. Expression was investigated in 16HBE14o- cells, derived from a normal individual, and compared to CFBE41o- cells, derived from a cystic fibrosis patient. We also examined psoriasin expression following treatment with factors pertinent to the CF lung-oxidant stress and exposure to pro-inflammatory cytokines. CFBE41o- cells demonstrated much reduced psoriasin levels compared to the 16HBE14o- cells. Increased psoriasin expression was seen following treatment with IL-22 and a cytomix of the pro-inflammatory cytokines IL-1β, TNF-α and IFN-γ; however, the oxidant stressor tert-butyl hydroperoxide had no apparent effect. Over-expression of human psoriasin into both cell lines resulted in increased internalization of Pseudomonas aeruginosa. In conclusion, expression of psoriasin - which has known anti-microbial activity in other systems - appears to be reduced in CFBE410- compared to 16HBE14o- cells, and its expression modified by exposure to pro-inflammatory cytokines.     

Microbiology of airway disease in patients with cystic fibrosis.

Individuals with cystic fibrosis have abbreviated life spans primarily due to chronic airway infection. A limited number of types of organisms are responsible for these infections, with Staphylococcus aureus and Pseudomonas aeruginosa being of primary importance. In the pre-antibiotic era, greater than 90% of deaths due to infection were caused by S. aureus and death usually occurred in the first 2 years of life. With the advent of effective antistaphylococcal therapy, life spans increased and P. aeruginosa became the pathogen of primary importance. P. aeruginosa isolates recovered from patients with cystic fibrosis have a unique phenotypic characteristic referred to as "mucoid." The mucoid phenotype is due to the production of a mucoid exopolysaccharide. A mucoid exopolysaccharide is believed to play a central role in the establishment of chronic pseudomonal lung infection in these patients. A third organism, Pseudomonas cepacia, has recently been detected in the airways of older patients with cystic fibrosis and is associated with increased mortality. The virulence of P. cepacia is not understood, but the organism is extremely refractory to antimicrobial therapy. Other bacteria, including Haemophilus influenzae and members of the family Enterobacteriaceae, appear to play a secondary role in airway infection. Aspergillus fumigatus is the most important fungal agent causing allergic bronchopulmonary disease. The role of viruses has only recently been examined. At least in some patients with cystic fibrosis, respiratory syncytial virus may be important in predisposing to subsequent bacterial infections.     

Fenretinide corrects newly found ceramide deficiency in cystic fibrosis

Chronic and persistent lung infections cause the majority of morbidity and mortality in patients with cystic fibrosis (CF). Galactosyl ceramide has been previously shown to be involved in Pseudomonas internalization. Therefore, we assessed ceramide levels in the plasma of patients with CF and compared them to healthy volunteers using high-performance liquid chromatography followed by mass spectrometry. Our results demonstrate that patients with CF display significantly lower levels of several ceramide sphingolipid species, specifically C14:0, C20:1, C22:0, C22:1, and C24:0 ceramides, and dihydroxy ceramide (DHC16:0). We report that Cftr-knockout mice display diminished ceramide levels in CF-related organs (lung, pancreas, ileum, and plasma) compared with their littermate controls. Since it has been previously reported that in vitro treatment with fenretinide induced ceramide in neuroblastoma cell lines, we decided to test this drug in vivo using our Cftr-knockout mice in an attempt to correct this newly identified defect in ceramide levels. We demonstrate that treatment with fenretinide is able to increase ceramide concentrations in CF-related organs. We further assessed the biological effect of fenretinide on the ability of Cftr-knockout mice to combat lung infection with P. aeruginosa. Our data show dramatic improvement in the ability of Cftr-knockout mice to control P. aeruginosa infection. Overall, these findings not only document a novel deficiency in several ceramide species in patients with CF, but also demonstrate a pharmacologic means to correct this defect in Cftr-knockout mice. Our data provide a strong rationale for clinical intervention that may benefit patients with CF suffering from CF lung disease.     

Co-ordinate regulation of the cystic fibrosis and multidrug resistance genes in cystic fibrosis knockout mice

The cystic fibrosis (Cftr and multidrug resistance (Mdr1) genes encode structurally similar proteins which are members of the ABC transporter superfamily. These genes exhibit complementary patterns of expression in vivo, suggesting that the regulation of their expression may be co- ordinated. We have tested this hypothesis in vivo by examining Cftr and Mdr1 expression in cystic fibrosis knockout transgenic mice (Cftr(tm1CAM)). Cftr mRNA expression in Cftr(tm1CAM)/Cftr(tm1CAM) mice was 4-fold reduced in the intestine, as compared with littermate wild- type mice. All other Cftr(tm1CAM)/Cftr(tm1CAM) mouse tissues examined showed similar reductions in Cftr expression. In contrast, we observed a 4-fold increase in Mdr1 mRNA expression in the intestines of neonatal and 3- to 4-week-old Cftr(tm1CAM)/Cftr(tm1CAM) mice, as compared with age-matched +/+ mice, and an intermediate level of Mdr1 mRNA in heterozygous Cftr(tm1CAM) mice. In 10-week-old, Cftr(tm1CAM)/Cftr(tm1CAM) mice and in contrast to the younger mice, Mdr1 mRNA expression was reduced, by 3-fold. The expression of two control genes, Pgk-1 and Mdr2, was similar in all genotypes, suggesting that the changes in Mdr1 mRNA levels observed in the Cftr(tm1CAM)/Cftr(tm1CAM) mice are specific to the loss of Cftr expression and/or function. These data provide further evidence supporting the hypothesis that the regulation Cftr and Mdr1 expression is co-ordinated in vivo, and that this co-ordinate regulation is influenced by temporal factors.